JP2003283043A - Oscillation mode monitor device and semiconductor laser device - Google Patents

Abstract

(57) [Problem] To provide an oscillation mode monitor device capable of detecting an oscillation mode state of oscillation light with high accuracy with a simple and inexpensive configuration. SOLUTION: A photodetector 9 which receives a monitor light of a semiconductor laser and converts it into an electric signal, and an oscillation which outputs a ratio of a signal intensity of a DC component to a signal intensity of an AC component of an output signal of the photodetector 9 A mode signal generation circuit 10. The oscillation mode signal generation circuit 10 includes, for example, a branch circuit 1 that branches an output signal of the photodetector 9 into a DC component signal and an AC component signal.
2 and the ratio of the AC component signal to the DC component signal
A divider 1 that outputs this ratio as an oscillation mode monitor signal
3 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation mode monitor device for detecting an oscillation mode of a semiconductor laser used as a light source of an optical communication device applied to wavelength division multiplex transmission (WDM), and the semiconductor laser device. The present invention relates to a semiconductor laser drive device that is drive-controlled, and further to a semiconductor laser device in which the semiconductor laser drive device is mounted.

[0002]

2. Description of the Related Art In an optical communication system using optical fibers, DWDM (Dense Wave Division Multiplexing) is used.
The length division multiplexing method has come into use. The DWDM method is a method of multiplexing a plurality of different wavelengths in one optical fiber and transmitting the same, and it is necessary to stabilize the wavelength of light with high accuracy.

A light source used in the DWDM system is generally a distributed feedback type (DFB).
k) A laser is used. With this DFB laser,
A diffraction grating that selectively reflects only one wavelength is formed in the optical amplification region. Therefore, when the DFB laser is used, the oscillation mode is stable and a single wavelength semiconductor laser can be realized. Normally, one light source is used for each channel (wavelength) in an optical device used in a WDM system. However, since a DFB laser has a small wavelength tunable region, one light source for each channel is also used as a backup light source for troubleshooting. Since the DFB laser is required, there is a problem that the system becomes expensive.

In order to overcome the above problems, it is necessary to use a laser having a large wavelength variable region as a light source. D
In a BR (Distributed Bragg Reflector) semiconductor laser, diffraction gratings having wavelength dependence are arranged on both sides of an optical amplification region, and only a specific wavelength is selectively reflected and amplified in the optical amplification region, so that one It is for generating oscillation light having a peak wavelength. At that time, the oscillation wavelength can be changed by several tens of nm by changing the injection current to the diffraction grating portions on both sides. However, in a semiconductor laser having a DBR structure in which the reflection peak interval is relatively narrow, due to mode hopping in which the wavelengths at which the reflection peaks of the diffraction gratings on both sides match coincide with each other, or competition between adjacent oscillation longitudinal modes, There is a problem that the oscillation mode tends to be unstable.

As described above, the DBR semiconductor laser has a plurality of reflection peaks within the gain band, and therefore, multimode oscillation is easy. Therefore, in this type of semiconductor laser, there is a demand for an oscillation mode monitor capable of detecting the oscillation mode state of the oscillation light with a simple configuration and high performance.

FIG. 18 is a configuration diagram of a semiconductor laser light source device disclosed in Japanese Patent Laid-Open No. 5-28294. The output light of the semiconductor laser 101 is converted into parallel light by the collimator lens 102 and is incident on the hologram 103. The hologram 103 has a function of outputting a part of the incident light at an angle depending on the wavelength due to the diffraction effect. Hologram 1
At 03, a part of the input light is diffracted and an image is formed on the light receiving surface of the CCD array 104 as the oscillation mode detecting laser light. The emission angle of the oscillation mode detecting laser beam output from the hologram 103 has wavelength dependency due to the diffraction effect.
Therefore, the position where an image is formed on the CCD array 104 differs depending on the wavelength, and the oscillation wavelength can be detected by finding the position of the CCD element on the array that takes the peak value by the peak detector 105. When a plurality of peaks are detected on the CCD array 104, it indicates that the semiconductor laser 101 is oscillating in a plurality of modes. Therefore, the peak detector 105 monitors the number of peaks to keep the oscillation mode. Can be detected.

The comparator circuit 106 compares the monitor signal with a predetermined criterion, calculates the wavelength deviation from the criterion or the change in the oscillation mode state, and inputs it to the driver circuit 107. Using this data, the drive current supplied to the semiconductor laser 101 by the driver circuit 107 is changed.

[0008]

In the above conventional technique, the hologram 103 and the CCD array 104 are used as the functional elements for discriminating the oscillation wavelength and the oscillation mode. Generally, in order to discriminate the wavelength and the oscillation mode with high resolution by utilizing the diffraction effect like the hologram 103, it is necessary to narrow the interval of the diffraction grating.
This is because the wavelength dependence of the emission angle is increased by narrowing the lattice spacing. However, hologram elements are generally expensive, and there is a limit even if the lattice spacing is narrowed,
Wavelength accuracy required for DWDM systems (several pm
Below) is difficult to achieve.

As another method of increasing the wavelength resolution for discrimination, the distance between the hologram 103 and the CCD array 104 is increased, and the CCD array 10 is used.
It is conceivable to arrange the CCD elements of No. 4 small and densely. However, the hologram 103 and the CCD array 10
Increasing the distance from 4 increases the size of the device. In addition, CCD arrays are generally expensive, and the finer elements make them more expensive.

The present invention has been made in view of the above,
An object of the present invention is to obtain an oscillation mode monitor device capable of detecting the oscillation mode state of oscillation light with high accuracy with a simple and inexpensive structure.

Another object of the present invention is to obtain a semiconductor laser device capable of controlling the oscillation state of oscillation light with high accuracy and stability with a simple and inexpensive structure.

[0012]

SUMMARY OF THE INVENTION An oscillation mode monitor according to the present invention includes a photodetector for receiving output light of a semiconductor laser and converting it into an electric signal, and a signal of a DC component of the output signal of the photodetector. And an oscillation mode signal generation circuit for outputting the ratio of the intensity and the signal intensity of the AC component.

Further, the oscillation mode signal generation circuit obtains a ratio of the AC component signal to the DC component signal and a branch circuit for branching the output signal of the photodetector into a DC component signal and an AC component signal. May be provided as an oscillation mode monitor signal.

Further, the oscillation mode signal generation circuit is preset with a branch circuit for branching the output signal of the photodetector into a DC component signal and an AC component signal, and an AC component output from the branch circuit. A bandpass filter for extracting only a predetermined frequency component and a divider for obtaining a ratio of the output of the bandpass filter with respect to the DC component signal and outputting this ratio as an oscillation mode monitor signal may be provided.

A semiconductor laser device according to the present invention determines the oscillation mode based on the oscillation mode monitor device of the above invention and an oscillation mode monitor signal from the oscillation mode monitor device, and the semiconductor laser device according to the result of the determination. And a laser control circuit for controlling the oscillation mode.

A semiconductor laser driving device according to the present invention is the above-mentioned oscillation mode monitor device of the invention, and a wavelength monitor having a characteristic that an output signal of the semiconductor laser is input and an output signal changes in accordance with the wavelength of the laser light. A circuit and a laser control circuit that stabilizes the oscillation mode of the semiconductor laser based on the oscillation mode monitor signal from the oscillation mode monitor device and controls the oscillation wavelength of the semiconductor laser based on the output of the wavelength monitor circuit. It is a thing.

The wavelength monitor circuit includes a wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a wavelength monitor photodetector which receives the light transmitted through the wavelength filter and converts it into an electric signal. Further, it may be provided with a divider for obtaining a ratio between the wavelength monitor photodetector and the DC component signal from the oscillation mode signal generating circuit and outputting the obtained ratio as a wavelength monitor signal.

Further, the wavelength monitor circuit has a narrow band wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a first band which receives the transmitted light of the narrow band wavelength filter.
Photodetector, a broadband wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, a second photodetector that receives the transmitted light of the broadband wavelength filter, and the first photodetector. The ratio of the DC component signal from the detector and the oscillation mode signal generation circuit to the ratio of the DC component signal from the second photodetector and the oscillation mode signal generation circuit, and the calculated two ratios. May be provided as the first and second wavelength monitor signals.

A semiconductor laser device according to the present invention includes an oscillation mode photodetector for receiving output light of a semiconductor laser and converting it into an electric signal, and an output signal of the oscillation mode photodetector for a direct current component signal and an alternating current signal. A branch circuit for branching into a component signal and a direct current component signal from the branch circuit are used to control the light intensity of the semiconductor laser to be constant, and an alternating current component signal from the branch circuit is used to oscillate the semiconductor laser. And a laser control circuit for stabilizing the mode.

Further, the semiconductor laser further comprises a wavelength monitor circuit having a characteristic that the output light of the semiconductor laser is input and the output signal changes in accordance with the wavelength of the laser light, and the laser control circuit outputs the output signal of the wavelength monitor circuit. May be used to control the oscillation wavelength of the semiconductor laser.

A semiconductor laser device according to the present invention receives an output light of a semiconductor laser and converts it into an electric signal, and an oscillation mode photodetector, and an AC component of an output signal of the oscillation mode photodetector. A high pass filter to
An intensity control photodetector that receives the output light of the semiconductor laser and converts it into an electrical signal, and controls the light intensity of the semiconductor laser to be constant using the output signal of the intensity control photodetector. A laser control circuit for stabilizing the oscillation mode of the semiconductor laser by using the AC component signal from the high pass filter.

Further, a wavelength monitor circuit having a characteristic that the monitor light is input and the output signal changes according to the wavelength of the laser light is further provided, and the laser control circuit uses the output signal of the wavelength monitor circuit. The oscillation wavelength of the semiconductor laser may be controlled.

Further, the wavelength monitor circuit includes a wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a wavelength monitor photodetector which receives the transmitted light of the wavelength filter and converts it into an electric signal. , May be provided.

The wavelength monitor circuit has a narrow band wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a first filter which receives the transmitted light of the narrow band wavelength filter and converts it into an electric signal. 1 a photodetector, a wideband wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a second photodetector which receives the transmitted light of this wideband wavelength filter and converts it into an electrical signal. May be provided.

Further, the wavelength discrimination area of the narrow band wavelength filter may correspond to the ITU grid, and the wavelength discrimination area of the wide band wavelength filter may be larger than the wavelength variable range of the semiconductor laser.

The wavelength filter may be any of a Fabry-Perot etalon, a birefringent filter having a birefringent crystal and a polarizer, a multilayer film filter, and a fiber grating.

Further, the laser control circuit compares the oscillation mode monitor signal with a preset threshold value, determines that the oscillation is unstable when the oscillation mode monitor signal is larger than the threshold value, and outputs the oscillation mode monitor signal. It may be determined that the oscillation is stable when it is smaller than the threshold value, and the injection current to the semiconductor laser may be controlled based on the determination result.

Further, one to a plurality of optical branching devices for branching the laser light may be further provided on the optical axis of the front light output of the semiconductor laser.

The output light of the semiconductor laser may be a part or all of the back light of the semiconductor laser.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of an oscillation mode monitor device and a semiconductor laser device according to the present invention will be described in detail below with reference to the accompanying drawings.

Embodiment 1. 1 is a configuration diagram showing a semiconductor laser device including an oscillation mode monitor device according to a first embodiment of the present invention.

As shown in FIG. 1, this wavelength tunable semiconductor laser device is arranged adjacent to the DBR semiconductor laser 1 and the chip of the semiconductor laser 1 in order to temperature-compensate the chip of the semiconductor laser 1 to a constant temperature. A heat sink 2 and a Peltier element 3, a beam splitter 4 as a light splitting means, and a semiconductor laser driving device 5.
In each block diagram of the following embodiments, the heat sink 2 and the Peltier element 3 are provided in the same manner as in FIG. 1, although they are not shown.

The semiconductor laser driving device 5 inputs an oscillation mode monitor circuit 7 for monitoring the oscillation mode based on the output light of the semiconductor laser 1 split by the beam splitter 4, and an oscillation mode monitor signal from the oscillation mode monitor circuit 7. The laser control circuit 8 adjusts the drive current or temperature of the semiconductor laser 1 which is the light source according to the signal.

The oscillation mode monitor circuit 7 receives the output light from the semiconductor laser 1 and converts it into an electric signal, and a photodetector 9 and an electric signal from the photodetector 9 are input, and an oscillation mode monitor signal is output. And an oscillation mode signal generation circuit 10 that operates.

The oscillation mode signal generating circuit 10 includes a branching circuit 12 (for example, bias tee BI) that branches and outputs a DC component and an AC component of the electric signal input from the photodetector 9.
AS TEE) and a divider 13 for calculating and outputting the ratio of two input signals.

First, the semiconductor laser 1 as a light source will be described. In this case, as the semiconductor laser 1, for example, a superstructure grating DBR semiconductor laser (hereinafter referred to as SS
Super Structure Grating DB, abbreviated as GDBR-LD
R Laser Diode) is used. Fig. 2 shows SSG DBR-L
A typical structure of D is shown.

In FIG. 2, in the front SSG DBR region 31 as one optical reflector forming the resonator, non-uniform diffraction gratings (non-uniform gratings) having varying grating intervals are arranged in multiple stages in the optical axis direction. It has a different structure, and a reflection spectrum having a plurality of reflection peaks can be realized. The rear SSG DBR region 34 as the other light reflector has a structure in which diffraction gratings having different periodic intervals from the front SSG DBR region 31 are arranged in multiple stages.
It is possible to realize a reflection spectrum having a plurality of reflection peaks having different periods of reflection peaks from the SG DBR region 31. That is, in the DBR regions 31 and 34, a group of diffraction gratings (chirped grating) whose grating intervals (periods) are continuously changed is set as one unit, and the diffraction grating groups are arranged at the same intervals an integer number of times. And basically, the front SSG DBR area 31 and the rear SSG DBR
By changing the arrangement period of the chirped gratings in the R region 34, the periods of the reflection peaks are made different in the front SSG DBR region 31 and the rear SSG DBR region 34. Note that changing the arrangement period of the chirped grating is equivalent to changing the length of the chirped grating alone. In order to keep the reflection characteristics of the chirped grating alone, the chirped grating (one unit) The cycle changes may be changed accordingly.

Front SSG DBR area 31 and rear S
An active layer region 32 that is a gain region and a phase control region 33 that does not have a gain effect are arranged between the SG DBR region 34 and the SG DBR region 34. A current can be independently injected into each of these regions 31 to 34. The injection current into the active layer region 32 is Ia, the injection current into the phase control region 33 is Ip, and the front SSG DBR region 3
1 is the injection current into the rear SSG DBR region 3
The injection current to 4 is Ir.

The operation of the semiconductor laser 1 will be described. When the drive current Ia in the active layer region 32 that is equal to or higher than the threshold value is injected, the front SSG DBR region 31 and the rear SS
Light that resonates with the G DBR region 34 is amplified in the active layer region 32, and emitted light is extracted from the front SSG DBR region 31.

The oscillation wavelength at this time is determined by the gain characteristic and the loss characteristic as shown in FIG. FIG. 3 shows the gain characteristic 40 and the front SSG DBR region 31.
Reflection characteristics (thick line) 41 and rear SSG DBR region 3
4 reflection characteristics (dotted line) 42 and front SSG DBR
A resonant longitudinal mode 43 (thin line) determined by the resonator length between the region 31 and the rear SSG DBR region 34 is shown. The reflectance is maximized at the peak in each reflection characteristic and the resonance longitudinal mode. Front SSG DBR area 31
Of the reflection peak 41 of the rear SSG DBR region 3
As described above, the period 42 (wavelength interval) of the reflection peak of No. 4 is slightly different.

Within the gain band 40, the front SSG DB
Reflection peak of R region 31 and rear SSG DBR region 34
The wavelength at which the reflection peak of is matched is called the SSG mode in particular, and oscillation occurs at the wavelength at which this SSG mode and the resonance longitudinal mode match. In the case of FIG. 3, at the wavelength λ0 near the center, S
The SG mode and the resonance longitudinal mode match, and this wavelength λ
It oscillates at 0.

Currents Ia, If, Ir injected into each of them
The gain band and the SSG mode are adjusted by changing the element temperature Tld of the semiconductor laser 1, and the wavelength is adjusted by changing the resonant longitudinal mode by changing the injection current Ip to the phase control region 33.

FIG. 4 shows the injection current Ia into the active layer region 32.
Shows the distribution of the oscillation wavelength when If and Ir are changed under a constant condition. FIG. 5 shows the wavelength boundaries of the wavelength distribution in FIG. 4 with solid lines and broken lines, because FIG. 4 has wavelengths classified by color and it is difficult to visually recognize in a monochrome state for the sake of explanation. is there. In FIG. 5, the wavelength boundary in the direction extending from the upper left to the lower right, which is particularly difficult to visually recognize in FIG. 4, is indicated by a broken line.

FIG. 4 shows that the oscillation wavelength becomes longer as the color becomes darker. Further, in FIG. 4, although it is difficult to visually recognize, in each of a plurality of regions surrounded by a solid line extending from the lower left to the upper right on the paper surface shown in FIG. 5, the oscillation wavelength is continuously short from the lower left to the upper right. It changes to the wavelength side. The boundary of this continuous change corresponds to the broken line shown in FIG.

On the other hand, if either If or Ir is made constant,
When the other is continuously changed, there is a point where the wavelength changes abruptly (shown as a small rectangular block K in FIG. 4). This is the front SS shown in FIG.
This is because the reflection characteristics of the G DBR region 31 and the rear SSG DBR region 34 change with respect to the wavelength. That is, this is the front SSG DBR area 31 and the rear S
When only one of the reflection characteristics 41 and 42 of the SG DBR region 34 is changed, the SSG mode shifts to the adjacent reflection peak due to the vernier effect, which is caused by mode hopping in which the wavelength jumps greatly.

FIG. 6A shows, as an example, a current condition in which the wavelength changes rapidly (point A in FIGS. 4 and 5: If = 13.
8 shows the oscillation spectrum measured at 8 mA and Ir = 17 mA). In addition, in FIG. 6B, other current conditions (see FIG.
And point B in 5: If = 18 mA, Ir = 17 mA). It should be noted that the point B is selected in the vicinity of the center of one scaly region surrounded by a solid line and a broken line in FIG.

As shown in FIG. 6 (a), oscillation occurs at two different wavelengths at point A, resulting in multimode oscillation.
Note that the two wavelengths do not always oscillate, but one of them oscillates irregularly on the time axis. This is due to the competition between the adjacent SSG modes described above, and therefore the oscillation becomes unstable. On the other hand, at point B, which selects the vicinity of the center of the scaly region, single longitudinal mode oscillation is obtained as shown in FIG. 6B.

On the other hand, unstable oscillation may occur in addition to SSG mode competition. That is, in FIGS. 4 and 5, the wavelength jumps a little even when If and Ir are continuously changed from the lower left to the upper right. This indicates that the oscillation longitudinal mode has shifted to the adjacent mode, and the oscillation becomes unstable in this case as well.

Summarizing these two types of mode jumps, the central portion of the plurality of scale-like regions described above becomes a region in which a single longitudinal mode is oscillating stably, and the boundary portion (solid line and broken line in FIG. 5). It can be seen that the oscillation becomes unstable in the vicinity region of.

In a laser having such oscillation characteristics, the present applicant has devised a method for distinguishing between single longitudinal mode oscillation and unstable oscillation state by observing the intensity noise component of oscillation light.

FIG. 7A shows the intensity spectrum after converting the laser light into an electric signal in the unstable oscillation state at point A in FIGS. 4 and 5. FIG. 7B shows an intensity spectrum after converting the laser light into an electric signal in the stable oscillation state at point B in FIGS. 4 and 5. 7 (a) and 7 (b), the levels on the vertical axis (intensity) are on the same scale. Comparing these, it can be clearly seen that when the oscillation is unstable, the high-frequency component is increased as compared with the single longitudinal mode oscillation.

FIG. 8 shows If-Ir when the frequency is 1 MHz.
The characteristic (intensity distribution corresponding to If and Ir) is shown. In this case, for convenience, points where the signal strength is higher than a certain threshold level are shown as black points. As can be seen by comparing FIG. 8 and FIG. 4, the signal intensity becomes large at the boundary portion of the scale-like region where oscillation is unstable (= region where oscillation is unstable), and the signal intensity becomes larger than the threshold level. In the central part of the scale-like region where stable oscillation is performed, the signal intensity becomes low and is smaller than the threshold level. That is, the signal intensity is higher than the threshold level at the boundary portion (unstable oscillation portion) of the scale-like region shown by the solid line and the dotted line in FIG.
Therefore, the oscillation mode can be monitored by measuring the level of the high frequency component from the intensity spectrum after converting the laser light into the electric signal, and by determining the signal intensity of the AC component of the electric signal, It is possible to detect the occurrence of a stable oscillation state.

Next, the operation of the semiconductor laser device of FIG. 1 will be described. A laser beam emitted from the semiconductor laser 1 is split into two by a beam splitter 4, one of which is output to the outside of the device as a signal output, and the other is input to an oscillation mode monitor circuit 7. In the oscillation mode monitor circuit 7, the input laser light is received by the photodetector 9. The photodetector 9 converts the laser light into an electric signal. The photodetector 9 has a characteristic capable of sensing a DC component and an AC component (for example, several MH).
z has a frequency characteristic that can be sensed). The electric signal output from the photodetector 9 is input to the oscillation mode signal generation circuit 10. Branch circuit 1 of oscillation mode signal generation circuit 10
Reference numeral 2 branches the electric signal from the photodetector 9 into an AC component including a DC component and a high frequency component. The AC component is the sum of all high frequency components detected by the photodetector 9.

On the other hand, the DC component has a dependency that it increases when the output light intensity of the semiconductor laser 1 increases and decreases when it decreases. Therefore, it is possible to detect the laser light intensity change by detecting the DC component.

The divider 13 divides the AC component / DC component and outputs the calculation result as an oscillation mode monitor signal. As described above, since the DC component depends on the output change of the semiconductor laser 1, the AC component is divided by the DC component to obtain an oscillation mode monitor signal that does not depend on the laser light output intensity change. be able to. This oscillation mode monitor signal is input to the laser control circuit 8.

In the laser control circuit 8, a threshold value for determining whether or not the single longitudinal mode oscillation is performed with respect to the intensity of the oscillation mode monitor signal is set. That is, the laser control circuit 8 determines multimode oscillation when the oscillation mode monitor signal from the divider 13 is equal to or higher than the threshold value, and determines that the oscillation mode monitor signal is single longitudinal mode oscillation when the oscillation mode monitor signal is lower than the threshold value. judge. When the laser control circuit 8 determines that the oscillation is multimode, the currents If and I to be injected into the semiconductor laser 1 are increased.
The r, Ip or the element temperature Tld is changed to adjust to the single longitudinal mode oscillation region. As an adjustment method, for example,
By continuously changing each applied current, a point where the oscillation mode monitor signal becomes equal to or less than the threshold value is found. Also, I
f and Ir may be fixed and Ip may be continuously changed.
This also applies to the embodiments described below.

In the above description, the AC component is
Although the intensity components of all frequencies other than the DC component are extracted, the intensity information of only a specific frequency may be used as the monitor signal. That is, a bandpass filter (not shown) for extracting only a predetermined frequency component set in advance from the AC component output from the branch circuit 12 is provided, and the divider 13 controls the DC component signal from the branch circuit 12 by the divider 13. Obtaining the output ratio of the bandpass filter,
The laser control circuit 8 uses this ratio as an oscillation mode monitor signal.
Should be output to. Also in this case, the oscillation mode monitor signal can be obtained in the same manner.

As described above, according to the first embodiment, the laser output light is branched into the AC component and the DC component, the ratio of the AC component to the DC component is obtained using the branched AC component and the DC component, and this ratio is calculated. Is output as the oscillation mode monitor signal, it is possible to obtain the oscillation mode monitor signal with high accuracy from only the laser light. Further, by comparing the oscillation mode monitor signal with the threshold value, the oscillation mode is discriminated, and each current If, Ir, Ip or element temperature Tld injected into the semiconductor laser 1 is changed based on the discrimination result. The oscillation mode of the laser light output from the semiconductor laser 1 can be easily stabilized to a single longitudinal mode with high accuracy.

Further, the oscillation mode monitor signal is supplied to the divider 1
3 is standardized by using the DC component of the intensity, the oscillation mode monitor signal is not affected by the change in the output intensity of the semiconductor laser 1.

Further, since the oscillation mode monitor circuit 7 is composed of one photodetector 9, the branch circuit 12 and the divider 13, a highly accurate oscillation mode monitor circuit can be realized with an extremely simple and inexpensive structure. . Therefore, the oscillation mode monitor circuit can be miniaturized so that it can be housed in a butterfly type module package that is usually used in semiconductor laser devices. Moreover, since the configuration is simplified, the reliability as an oscillation mode monitor can be improved.

Embodiment 2. Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 9 shows the configuration of the semiconductor laser device according to the second embodiment. In the second embodiment, the output signal of the branch circuit 12 is directly input to the laser control circuit 28 without passing through the divider 13 shown in FIG.

The laser control circuit 28 uses the DC component signal from the branch circuit 12 to adjust the injection current Ia to the active layer region 32 so that the output intensity of the semiconductor laser 1 becomes constant. That is, as described above, it is possible to detect the intensity change of the laser light by detecting the DC component signal.

In this case, since the output intensity of the semiconductor laser 1 is controlled to be constant based on the DC component signal, the output light intensity of the semiconductor laser 1 is always constant and the branch circuit 12
The AC component signal output from the device is always obtained under the condition that the laser light intensity is constant. Therefore, it is possible to detect the oscillation mode monitor signal with high accuracy using only the AC component signal without normalizing with the DC component signal as in the first embodiment.

The laser control circuit 28 determines that the multi-mode oscillation is generated when the AC component is equal to or more than the threshold value, and determines the single longitudinal mode oscillation when the AC component is smaller than the threshold value. When the laser control circuit 28 determines that multi-mode oscillation is generated, the currents If, Ir, I injected into the semiconductor laser 1 are determined.
The oscillation mode is stabilized by adjusting p or the element temperature Tld.

As described above, according to the second embodiment, the laser control circuit 28 uses the DC component signal from the branch circuit 12 to inject the current into the active layer region 32 so that the output intensity of the semiconductor laser 1 becomes constant. Since Ia is adjusted, the output light intensity of the semiconductor laser 1 can always be controlled to be constant. Further, the AC component signal directly input from the branch circuit 12 to the laser control circuit 28 can also be detected under the condition that the laser light intensity is always constant, so that a highly accurate oscillation mode monitor signal can be obtained only with the AC component signal. Further, the currents If and I injected into the semiconductor laser 1 based on the oscillation mode state determined based on the oscillation mode monitor signal.
Since r, Ip or element temperature Tld is adjusted,
The oscillation mode of the laser light output from the semiconductor laser 1 can be stabilized to a single longitudinal mode.

Moreover, since the divider 13 is not used, the structure of the semiconductor laser device can be further simplified, and the miniaturization can be realized so that it can be accommodated in a commonly used butterfly type module package with a margin. . Further, since the structure is simplified, the reliability as the oscillation mode monitor can be improved.

Embodiment 3. Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 10 shows the configuration of the semiconductor laser device according to the third embodiment.

As shown in FIG. 10, in the third embodiment, the beam splitter 14 is arranged on the optical axis between the beam splitter 4 and the photodetector 9. The beam splitter 14 is arranged so that a part of the laser light is incident on the photodetector 9 and the other is incident on the photodetector 15. Further, a high-pass filter 16 that cuts the DC component of the output signal of the photodetector 9 is provided.

The AC component of the output electric signal from the photodetector 9 is extracted by the high-pass filter 16 and the extracted AC component is input to the laser control circuit 38. Photo detector 1
The output signal of No. 5 is directly input to the laser control circuit 38. The output signal of the photodetector 15 has a dependency that it increases when the output light of the semiconductor laser 1 increases and decreases when it decreases. Therefore, the output intensity of the semiconductor laser 1 is kept constant by adjusting the injection current Ia to the active layer region 32 by the laser control circuit 38 so that the signal intensity of the output signal of the photodiode 15 becomes constant.

As described above, since the output light intensity of the semiconductor laser 1 is kept constant, the AC component output from the high-pass filter 16 depends only on the oscillation mode. Therefore, oscillation is performed using this AC component. The mode can be detected.

That is, the laser control circuit 38 determines that the mode is multi-mode oscillation when the AC component is equal to or larger than the threshold value, and determines the single longitudinal mode oscillation when the AC component is smaller than the threshold value. When the laser control circuit 38 determines that multi-mode oscillation is generated, each current I to be injected into the semiconductor laser 1
The oscillation mode is stabilized by adjusting f, Ir, Ip or the element temperature Tld.

As described above, according to the third embodiment, the beam splitter 14 is provided on the optical axis between the beam splitter 4 and the photodetector 9, and one output light of the branched light of the beam splitter 14 is received. As described above, the photodetector 15 is provided, and the laser control circuit 38 adjusts the injection current Ia to the active layer region 32 using the detection signal of the photodetector 15 so that the output intensity of the semiconductor laser 1 becomes constant. Because
The output light intensity of the semiconductor laser 1 can always be controlled to be constant. Further, the AC component signal input from the high-pass filter 16 to the laser control circuit 38 can always be detected under the condition that the laser light intensity is constant, so that it is possible to obtain a highly accurate oscillation mode monitor signal only with the AC component signal.
Further, each current If injected into the semiconductor laser 1 based on the oscillation mode state determined based on the oscillation mode monitor signal,
Since the Ir, Ip or the element temperature Tld is adjusted, the oscillation mode of the laser light output from the semiconductor laser 1 can be stabilized to the single longitudinal mode.

Fourth Embodiment Next, FIG. 11 and FIG.
Embodiment 4 of the present invention will be described with reference to FIG.
FIG. 11 shows the structure of the semiconductor laser device according to the fourth embodiment. In the fourth embodiment, a wavelength monitor for monitoring the oscillation wavelength of the semiconductor laser 1 is added to the oscillation mode monitor circuit to stabilize the oscillation laser light with higher accuracy.

In FIG. 11, a wavelength filter 17 is arranged between the beam splitter 14 and the photodetector 15. The wavelength filter 17 has a characteristic that the transmittance changes depending on the wavelength of incident light, and in the present embodiment, a birefringent filter including a birefringent crystal and a polarizer is used.
A Fabry-Perot etalon, a thin film filter, a fiber grating, or the like is used as the other wavelength filter.

The wavelength filter 17 and the photodetector 15 constitute a wavelength monitor. That is, the wavelength filter 17 converts the wavelength information into the intensity information by utilizing the characteristic of changing the transmittance according to the wavelength of the input light of the wavelength filter 17. Then, by converting the optical signal from the wavelength filter 17 into an electric signal by the photodetector 15, an electric signal having an intensity corresponding to the wavelength can be obtained.

Further, a divider 18 is provided, and the divider 18
The ratio of the output signal of the photodetector 15 to the DC component signal from the branch circuit 12 is obtained by this, and this ratio is input to the laser control circuit 48.

Next, the operation will be described. The laser beam output from the semiconductor laser 1 is split into two by the beam splitter 4. One of the split lights is the beam splitter 14
It is branched into two more. Of the branched laser beams, for example, the laser beam traveling in the L1 direction, which is the direction that passes through the beam splitter 14, is converted into an electric signal by the photodetector 9 as in the first embodiment, and is branched by the branch circuit 12 and the split circuit. Calculator 1
After passing through 3, the laser control circuit 48 is inputted as an oscillation mode monitor signal.

On the other hand, for example, laser light reflected by the beam splitter 14 and traveling in the L2 direction, which is a direction bent 90 degrees from the incident light, passes through the wavelength filter 17, enters the photodetector 15, and is converted into an electrical signal. To be converted.

FIG. 12 shows the wavelength characteristic of the output signal of the photodetector 15. Now, the target wavelength to be stabilized is λ0. λ
In the vicinity of 0, the output signal of the photodetector 15 decreases as the wavelength becomes longer, and increases as the wavelength becomes shorter. Therefore, when the wavelength λ0 is used as the reference wavelength, the intensity change of the output signal of the photodetector 15 indicates the change of the laser light wavelength from the reference wavelength λ0. Therefore, the oscillation wavelength can be monitored by determining the intensity level of the output signal of the photodetector 15. The output signal of the photodetector 15 is input to the divider 18. The direct current component signal of the laser light intensity, which is the output from the branch circuit 12, is also input to the divider 18 at the same time,
The divider 18 outputs the ratio of both (the output signal of the photodetector 15 / the DC component signal from the branch circuit 12).

That is, the wavelength change can be monitored by the output signal of the photodetector 15, but this signal also includes the laser light intensity change. Therefore, in the divider 18, the branch circuit 1
By standardizing the output signal of the photodiode 15 with the DC component of the laser light from 2, the wavelength monitor signal that is not affected by the intensity change of the output light of the semiconductor laser 1 can be obtained.

The laser control circuit 48 uses the standardized oscillation mode monitor signal from the divider 13 and the standardized wavelength monitor signal from the divider 18 to inject currents Ia and If into the semiconductor laser 1. , Ir, Ip, or all, or the Peltier element 3 is driven and controlled to adjust the element temperature Tld to control the wavelength and oscillation mode of the semiconductor laser 1.

As described above, according to the fourth embodiment, the beam splitter 14 is provided on the optical axis between the beam splitter 4 and the photodetector 9, and the branched light of this beam splitter 14 is changed according to the wavelength of the input light. Is received by the photodetector 15 through the wavelength filter 17 having the characteristic of changing the transmittance, and the wavelength monitor signal is obtained by normalizing the received signal of the photodetector 15 with the DC component of the laser light. Therefore, the wavelength monitor signal that depends only on the wavelength of the laser light can be detected. Further, since the currents Ia, If, Ir, Ip or the element temperature Tld to be injected into the semiconductor laser 1 are adjusted based on the oscillation wavelength determined based on the wavelength monitor signal, the wavelength of the laser light output from the semiconductor laser 1 is adjusted. Can be stabilized.

In addition, the two beam splitters 4 and 14
And an oscillation mode monitor having a simple configuration including the photodetector 9, the branch circuit 12 and the divider 13, and a wavelength having a simple configuration including the wavelength filter 17, the photodetector 15 and the divider 18. Since the monitor is provided, the structure of the semiconductor laser device can be simplified and the size can be reduced so that the semiconductor laser device can be housed in a commonly used butterfly type module package. Further, since the structure is simplified, the reliability as the oscillation mode monitor and the wavelength monitor can be improved.

Further, the AC component and the DC component of the laser output light are respectively extracted, the ratio of the AC component to the DC component is obtained using the extracted AC component and DC component, and this ratio is output as an oscillation mode monitor signal. Since this is done, it is possible to obtain a highly accurate oscillation mode monitor signal that depends only on the oscillation mode of the laser light. Also, by comparing the oscillation mode monitor signal with the threshold value, the oscillation mode is determined,
Since the currents If, Ir, Ip or the element temperature Tld injected into the semiconductor laser 1 are changed based on the determination result, the oscillation mode of the laser light output from the semiconductor laser 1 can be easily changed to the single longitudinal mode. It can be stabilized with high accuracy.

Further, the oscillation mode monitor signal is supplied to the divider 1
3 is standardized by using the DC component of the intensity, the oscillation mode monitor signal is not affected by the change in the output intensity of the semiconductor laser 1.

In the fourth embodiment, the beam splitter 14 splits the output light of the semiconductor laser 1 into two directions of L1 and L2. However, the beam splitter 14 is not used, and the photodetector 15 is provided next to the photodetector 9. Aligned with the wavelength filter 17
Is installed between the beam splitter 4 and the photodetector 15,
You may make it input into both photodetectors only by the light which advances to a L1 direction.

Embodiment 5. Next, a fifth embodiment of the invention will be described with reference to FIG. FIG. 13 shows the structure of the semiconductor laser device according to the fifth embodiment.
In the fifth embodiment, the outputs of the branch circuit 12 and the photodetector 15 are not input to the laser control circuit 48 via the dividers 13 and 18 as in the fourth embodiment shown in FIG. The outputs of the branch circuit 12 and the photodetector 15 are directly input to the laser control circuit 58.

The laser control circuit 58 uses the DC component signal from the branch circuit 12 to adjust the injection current Ia into the active layer region 32 of the semiconductor laser 1 so that the output intensity of the semiconductor laser 1 becomes constant. That is, as mentioned above,
By detecting the DC component signal, it is possible to detect the intensity change of the laser light.

In this case, since the output intensity of the semiconductor laser 1 is controlled to be constant based on the DC component signal, the output light intensity of the semiconductor laser 1 is always constant, and the AC component signal output from the branch circuit 12 is always constant. Laser intensity can be obtained under constant conditions. Therefore, it is possible to detect the oscillation mode monitor signal with high accuracy using only the AC component signal without normalizing the DC component signal using the divider 13.

The laser control circuit 58 determines that the multimode oscillation is generated when the AC component is equal to or more than the threshold value, and determines the single longitudinal mode oscillation when the AC component is smaller than the threshold value. Then, when the laser control circuit 58 determines that the oscillation is multimode oscillation, the currents If, Ir, I injected into the semiconductor laser 1 are determined.
The oscillation mode is stabilized by adjusting p or the element temperature Tld.

Also, the output signal of the photodetector 15 is directly input to the laser control circuit 58 without passing through the divider 18 as in the fourth embodiment. At that time, the semiconductor laser 1
As described above, since the output intensity constant control based on the DC component signal is performed, the output signal of the photodetector 15 is detected to obtain a highly accurate wavelength monitor signal that depends only on the wavelength. You can

The laser control circuit 58 adjusts any or all of the injection currents Ia, If, Ir, Ip to the semiconductor laser 1 or the element temperature Tld by using the wavelength monitor signal from the photodetector 15. The wavelength of the semiconductor laser 1 is controlled.

As described above, according to the fifth embodiment, the output signal of the branch circuit 12 is input to the laser control circuit 58 without passing through the divider 18, and the laser control circuit 58 causes the direct current from the branch circuit 12 to flow. Since the component signal is used to adjust Ia so that the output intensity of the semiconductor laser 1 becomes constant, the output light intensity of the semiconductor laser can always be controlled to be constant. Further, since the AC component signal output from the branch circuit 12 is always obtained under the condition that the laser light intensity is constant, it is possible to obtain a highly accurate oscillation mode monitor signal only with the AC component signal. Further, the oscillation mode is determined based on the detected oscillation mode monitor signal, and each current If injected into the semiconductor laser 1 based on the determination result,
Since the Ir, Ip or the element temperature Tld is adjusted, the oscillation mode of the laser light output from the semiconductor laser 1 can be easily stabilized to the single longitudinal mode with high accuracy.

Since the output signal of the photodiode 15 is always obtained under the condition that the laser light intensity is constant, a highly accurate wavelength monitor signal can be obtained only by this signal. Further, since the currents If, Ir, Ip or the element temperature Tld to be injected into the semiconductor laser 1 are adjusted based on the detected wavelength monitor signal, the laser light wavelength output from the semiconductor laser 1 can be stabilized.

Since the dividers 13 and 18 are not used,
The configuration of the semiconductor laser device can be further simplified, and a compact size that can be accommodated in a butterfly type module package that is normally used can be realized. Further, since the structure is simplified, the reliability as the oscillation mode monitor can be improved.

In the fifth embodiment, the beam splitter 14 splits the output light of the semiconductor laser 1 into two directions of L1 and L2. However, the beam splitter 14 is not used, and the photodetector 15 is provided next to the photodetector 9. Aligned with the wavelength filter 17
Is installed between the beam splitter 4 and the photodetector 15,
You may make it input into both photodetectors only by the light which advances to a L1 direction.

Sixth Embodiment Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 14 shows the structure of the semiconductor laser device according to the sixth embodiment.
In the sixth embodiment, the beam splitter 1 is placed on the optical axis between the beam splitter 4 and the beam splitter 14.
9 is further arranged. The beam splitter 19 is arranged so that a part of the light is incident on the beam splitter 14 and the rest is incident on the photodetector 20.

The output signal of the photodiode 20 is directly input to the laser control circuit 68. The output signal of the photodetector 20 has a dependency that it increases when the output light of the semiconductor laser 1 increases and decreases when it decreases. Therefore, the laser control circuit 68 controls the output intensity of the semiconductor laser 1 to be kept constant by adjusting Ia so that the signal intensity of the output signal of the photodetector 20 becomes constant.

The photodetector 9 and the high pass filter 16 constitute an oscillation mode monitor. The high-pass filter 16 extracts only the AC component of the output signal of the photodetector 9 and inputs it to the laser control circuit 68. Since the output light intensity of the semiconductor laser 1 is kept constant by the output light constant control based on the output of the photodetector 20, the high-pass filter 16
The AC component output from the output depends on only the oscillation mode, and an unstable oscillation state can be detected. The laser control circuit 68 controls the oscillation mode by adjusting If, Ir, and Ip based on the AC component output from the high-pass filter 16 to obtain single longitudinal mode oscillation.

The wavelength filter 17 and the photodetector 15 constitute a wavelength monitor. Photodiode 15
The output signal of is directly input to the laser control circuit 68.
At that time, since the output intensity of the semiconductor laser 1 is kept constant as described above, a highly accurate wavelength monitor signal depending only on the wavelength can be obtained by detecting the output signal of the photodiode 15. In the laser control circuit 68, the currents If, Ir, I of the semiconductor laser 1 are based on this wavelength monitor signal.
By adjusting p or the element temperature Tld, the wavelength of the laser light output from the semiconductor laser 1 is stabilized.

Although the beam splitter 19 is arranged on the optical axis between the beam splitter 4 and the beam splitter 14 in FIG. 14, the beam splitter 19 is arranged on the optical axis between the beam splitter 14 and the photodiode 9. You may make it arrange | position above and may make the photodiode 20 receive the branched light. Also in this case, the same operation as described above is performed and the same effect is obtained.

As described above, according to the sixth embodiment, the beam splitter 19 is arranged on the optical axis between the beam splitter 4 and the photodetector 9, and one output light of the beam splitter 19 is received. As described above, the photodetector 20 is provided and the output current of the photodetector 20 is used to adjust the injection current Ia to the active layer region 32 so that the output intensity of the semiconductor laser 1 becomes constant. The output light intensity of the laser 1 can always be controlled to be constant. Further, the AC component signal input from the high-pass filter 16 to the laser control circuit 68 can be detected under the condition that the laser light intensity is always constant, so that it is possible to obtain a highly accurate oscillation mode monitor signal only with the AC component signal. Further, since the currents If, Ir, Ip or the element temperature Tld injected into the semiconductor laser 1 are adjusted based on the oscillation mode state determined based on the oscillation mode monitor signal, the oscillation of the laser light output from the semiconductor laser 1 is adjusted. The mode can be stabilized to a single longitudinal mode.

Further, since the output signal of the photodetector 15 is always obtained under the condition that the laser light intensity is constant, a highly accurate wavelength monitor signal can be obtained only by this signal. Further, each current If, Ir, Ip or element temperature Tld injected into the semiconductor laser 1 based on the detected wavelength monitor signal.
Is adjusted, the wavelength of the laser beam output from the semiconductor laser 1 can be stabilized.

Since the dividers 13 and 18 are not used,
The configuration of the semiconductor laser device can be further simplified, and a compact size that can be accommodated in a butterfly type module package that is normally used can be realized. Further, since the structure is simplified, the reliability as the oscillation mode monitor can be improved.

In the sixth embodiment, the beam splitter 14 splits the output light of the semiconductor laser 1 into two directions of L1 and L2. However, the beam splitter 14 is not used, and the photodetector 15 is provided next to the photodetector 9. Aligned with the wavelength filter 17
Is installed between the beam splitter 4 and the photodetector 15,
You may make it input into both photodetectors only by the light which advances to a L1 direction.

Seventh Embodiment Next, another configuration example of the wavelength monitor which is a component of the semiconductor laser device of FIGS. 11, 13 and 14 will be described with reference to FIGS. The wavelength monitor shown in FIG. 15 includes a narrow band wavelength filter 50 whose transmittance changes according to the wavelength of input oscillation light (monitor light), and a photodetector 51 which receives the transmitted light of the narrow band wavelength filter 50. A wideband wavelength filter 52 having a transmittance that changes according to the wavelength of the input oscillation light, and a photodetector 53 that receives the transmitted light of the wideband wavelength filter 52 are provided.

That is, in each wavelength filter 50, 52,
The wavelength information is converted into intensity information, and each photodetector 51, 53 is converted.
Then, by converting the optical signals from the wavelength filters 50 and 52 into electric signals, it is possible to obtain electric signals having an intensity corresponding to the wavelength.

FIG. 16 shows the wavelength characteristic of the narrow band wavelength filter 50 and the wavelength characteristic of the wide band wavelength filter 52. Δλld is the wavelength variable region of the semiconductor laser,
Δλf1 is a wavelength discrimination region of the wideband wavelength filter 52, and Δλf2 is a wavelength discrimination region of the narrowband wavelength filter 50. In addition, the wavelength (channel) interval of the ITU grid is twice the wavelength discrimination region of the narrow band wavelength filter 50 (2
× λf2). ITU grid is
International Telecommunication Union
Union) specified wavelength range, eg 1550
It is a set of closely spaced wavelengths in a window of nm, for example, in the case of 100 GHZ spacing, it corresponds to a wavelength spacing of about 0.8 nm.

In this type of SSG DBR-LD, the wavelength tunable region (Δλld) is larger than that of a normal semiconductor laser.
It is as wide as 30 nm to 40 nm. Narrow band wavelength filter 50
Has the advantage that the signal intensity changes greatly with respect to the wavelength change and that the wavelength can be detected with high accuracy.
Since the wavelength discrimination region (Δλf2) of 0 is narrow, the narrow band wavelength filter 50 alone cannot cover the entire wavelength tunable region (Δλld) of the semiconductor laser, and the absolute wavelength cannot be detected. Therefore, the entire wavelength tunable region (Δλld) of the semiconductor laser has a wideband wavelength filter 52 having a wavelength discrimination region (Δλf1) wider than Δλld.
By covering with, the grid is located, that is, the absolute wavelength of the oscillation wavelength is detected.

When only one slope characteristic of the narrow band wavelength filter is used, each wavelength filter 50, 52 is set so that the relationship of ITU grid wavelength interval = 2 × Δλf2 2 × Δλf2 <Δλld <Δλf1 is established. Set the wavelength characteristics of.

When the characteristics of both slopes of the narrow band wavelength filter are utilized, the wavelength filters 50 and 52 are set so that the relationship of ITU grid wavelength interval = Δλf2 2 × Δλf2 <Δλld <Δλf1 is established. Set the wavelength characteristics.

A wavelength control operation using the wavelength monitor of FIG. 15 will be described with reference to FIG. First, the laser control circuit 8
Acquires the output of the photodetector 53 on the side of the broadband wavelength filter 52 (step 300), and determines whether or not the target wavelength λc is reached based on this output (step 31).
0). The accuracy of reaching the target wavelength by the wideband wavelength filter may be equal to or less than the wavelength discrimination region Δλ2 of the narrowband wavelength filter. If the target wavelength λc has not been reached, the Peltier element 3 is driven to adjust the element temperature Tld while monitoring the temperature in the vicinity of the semiconductor laser with a temperature detector (not shown) to stabilize the target wavelength λc (step 320).

Further, the target wavelength λ is determined by the determination in step 310.
When it is detected that the wavelength c has reached c, the laser control circuit 8 acquires the output of the photodetector 51 on the narrow band wavelength filter 50 side (step 330) and stabilizes at the target wavelength λc based on this output. It is determined whether or not (Step 3
40). When the amount of wavelength shift is larger than the predetermined specification value (oscillation wavelength accuracy), the laser control circuit 8 drives the Peltier device 3 while monitoring the temperature to drive the device temperature T.
Stabilize the target wavelength λc by adjusting ld (step 350).

As described above, in the wavelength monitor shown in FIG. 15, the oscillation wavelength is roughly adjusted based on the output from the wide band wavelength filter 52, and then the narrow band wavelength filter 5 is used.
By finely adjusting the oscillation wavelength based on the output on the 0 side,
Even if the wavelength tunable region of the semiconductor laser is large, highly accurate wavelength control can be performed.

When a standardized wavelength monitor signal is required as in the embodiment shown in FIG. 1 or FIG. 11, each output of the photodetectors 51 and 53 is connected to the DC component signal from the branch circuit 12. The photodetector 51 is divided by
It suffices to find the ratio between the output of each of 53 and 53 and the DC component signal.

Although the SSG DBR-LD is used for the semiconductor laser 1 in each of the above-described embodiments, other SG-DBR LDs (Sampled Gratings) are used.
The present invention can be applied to an LD having a rating DBR) structure. In this case, the same effect as above can be obtained. This SG-DBR LD has a region with a diffraction grating of the same period and a region without a diffraction grating as one unit and is arranged an integer number of times. The rows are arranged at the same intervals. Also in the case of the SG-DBR LD, basically, the front SSG DBR area is changed by changing the arrangement period between the front SSG DBR area and the rear SSG DBR area.
The periods of the reflection peaks of the region and the rear SSG DBR region are made different. In the case of this SG-DBR LD, SS
Unlike the G-DBR, the difference in the period of the reflection peak can be achieved by changing the distance of the region without the grating, so that the period of the grating alone does not have to be changed. The difference in the cycle of the reflection peak may be realized by changing the cycle of the grating alone.

Further, in each of the above embodiments, a part of the front output light from the semiconductor laser 1 is taken out as the monitor light. However, a part or the whole of a small amount of oscillation light output from the back surface of the semiconductor laser 1 is extracted. It may be used as monitor light. In that case, it can be used as an external output signal without reducing the front light output. Further, the beam splitter 4 is unnecessary, and the configuration is simplified.

[0118]

As described above, the oscillation mode monitor device according to the present invention includes a photodetector for receiving the output light from the semiconductor laser and an output signal of the photodetector.
Obtain the ratio of the signal strength of the DC component and the signal strength of the AC component,
Since this ratio is output as the oscillation mode monitor signal, a highly accurate oscillation mode monitor signal that depends only on the oscillation mode of the laser light without being affected by changes in the laser output intensity is extremely simple and inexpensive. Can be obtained by.

Further, the ratio of the intensity of the DC component signal to the intensity of the AC component signal of the output light from the semiconductor laser is obtained, the oscillation mode is determined based on this ratio, and the oscillation of the semiconductor laser is determined according to the determination result. Since the modes are controlled, the oscillation mode of the laser light output from the semiconductor laser can be easily stabilized to a single longitudinal mode with high accuracy.

In the semiconductor laser device according to the present invention, the direct current component signal of the monitor light is used to control the light intensity of the semiconductor laser to be constant, and the oscillation mode is controlled using the alternating current component signal of the monitor light. Judgment is made and the oscillation mode of the semiconductor laser is controlled according to the result of this discrimination, so that a highly accurate oscillation mode monitor signal that depends only on the oscillation mode of the laser light without being affected by changes in the laser output intensity It can be obtained with a simple and inexpensive structure, and the oscillation mode of the laser beam can be easily stabilized to a single longitudinal mode with high accuracy.

The semiconductor laser device according to the present invention controls the light intensity of the semiconductor laser to be constant by using the output signal of the photodetector, and extracts the AC component of the monitor light by the high-pass filter, The oscillation mode is determined using this AC component signal, and a highly accurate oscillation mode monitor signal that is dependent only on the oscillation mode of the laser light and is not affected by changes in the laser output intensity according to the determination result is extremely simple and It can be obtained with an inexpensive structure, and the oscillation mode of the laser light can be easily stabilized to a single longitudinal mode with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a semiconductor laser device including an oscillation mode monitor circuit according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the structure of an SSG DBR LD.

FIG. 3 is a diagram showing wavelength characteristics of gain or loss in each region of the SSG DBR LD.

FIG. 4 I of oscillation wavelength in SSG DBR LD
It is a figure which shows f and Ir characteristic.

5 is a diagram clarifying the wavelength boundary region of the If and Ir characteristics of the oscillation wavelength of FIG.

FIG. 6 is a diagram showing wavelength spectra of single longitudinal mode and unstable mode oscillation in the SSG DBR LD.

FIG. 7 is a graph showing an intensity spectrum of a single longitudinal mode oscillation and an unstable oscillation state in the SSG DBR LD.

FIG. 8 is a diagram showing If and Ir characteristics of a light intensity high frequency component in the SSG DBR LD.

FIG. 9 is a block diagram showing a configuration of a semiconductor laser device including an oscillation mode monitor circuit according to a second embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a semiconductor laser device including an oscillation mode monitor circuit according to a third embodiment of the present invention.

FIG. 11 is a block diagram showing a configuration of a semiconductor laser device including an oscillation mode monitor circuit and a wavelength monitor circuit according to a fourth embodiment of the present invention.

FIG. 12 is a diagram illustrating wavelength characteristics of transmission intensity in a birefringent filter.

FIG. 13 is a block diagram showing a configuration of a semiconductor laser device including an oscillation mode monitor circuit and a wavelength monitor circuit according to a fifth embodiment of the present invention.

FIG. 14 is a block diagram showing a configuration of a semiconductor laser device including an oscillation mode monitor circuit and a wavelength monitor circuit according to a sixth embodiment of the present invention.

FIG. 15 shows Embodiment 7 of the present invention and is a block diagram showing another embodiment of the wavelength monitor circuit.

16 is a diagram showing wavelength characteristics of a wideband wavelength filter and a narrowband wavelength filter used in the wavelength monitor of FIG.

17 is a flowchart showing a procedure of wavelength control using the wavelength monitor of FIG.

FIG. 18 is a block diagram showing a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 semiconductor laser, 2 heat sink, 3 Peltier device, 4, 14, 19 beam splitter, 5 semiconductor laser driving device, 7 oscillation mode monitor circuit, 8, 28, 3
8, 48, 58, 68 Laser control circuit, 9, 15, 2
0 photodetector (photodiode), 10 oscillation mode signal generation circuit, 12 branch circuit, 13, 18 divider,
16 high-pass filter, 17 wavelength filter, 31
Front SSG DBR region, 32 Active layer region, 33
Phase control area, 34 Rear SSG DBR area, 50
Narrow band wavelength filter, 51, 53 (photodiode) Photodetector, 52 Wide band wavelength filter.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akihiro Adachi             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Yoshihito Hirano             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Tetsuya Nishimura             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Mitsunobu Gotoda             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Tetsuo Obama             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Akira Takemoto             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Takashi Nishimura             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Junichiro Yamashita             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 5F073 AA65 AA89 AB21 AB25 AB27                       EA03 GA12 GA13 GA21 GA38

Claims (18)

[Claims] 1. A photodetector for receiving the output light of a semiconductor laser and converting it into an electric signal, and an oscillation mode for outputting the ratio of the signal strength of the DC component and the signal strength of the AC component of the output signal of the photodetector. An oscillation mode monitoring device comprising: a signal generation circuit. 2. The oscillation mode signal generation circuit obtains a ratio of the AC component signal to the DC component signal, and a branch circuit that branches the output signal of the photodetector into a DC component signal and an AC component signal, The oscillator mode monitor device according to claim 1, further comprising: a divider that outputs the oscillator mode monitor signal. 3. The oscillation mode signal generation circuit, wherein a branch circuit for branching the output signal of the photodetector into a DC component signal and an AC component signal, and an AC component output from the branch circuit are set in advance. A bandpass filter for extracting only a predetermined frequency component, and a divider for obtaining a ratio of the output of the bandpass filter with respect to the direct current component signal and outputting this ratio as an oscillation mode monitor signal, The oscillation mode monitor device according to claim 1. 4. The oscillation mode monitoring device according to claim 1, an oscillation mode is determined based on an oscillation mode monitor signal from the oscillation mode monitoring device, and the semiconductor is determined according to the determination result. A semiconductor laser device comprising: a laser control circuit for controlling a laser oscillation mode. 5. The oscillation mode monitor according to claim 1, wherein the output light of the semiconductor laser is input, and the wavelength has a characteristic that an output signal changes according to the wavelength of the laser light. A monitor circuit, a laser control circuit that stabilizes the oscillation mode of the semiconductor laser based on an oscillation mode monitor signal from an oscillation mode monitor device, and controls the oscillation wavelength of the semiconductor laser based on the output of the wavelength monitor circuit, A semiconductor laser device comprising: 6. The wavelength monitor circuit comprises: a wavelength filter whose transmittance changes according to the wavelength of the input oscillation light; and a wavelength monitor photodetector which receives the transmitted light of the wavelength filter and converts it into an electric signal. And a divider for obtaining a ratio between the wavelength monitor photodetector and the DC component signal from the oscillation mode signal generation circuit, and outputting the obtained ratio as a wavelength monitor signal. Item 6. The semiconductor laser device according to item 5. 7. The wavelength monitor circuit includes a narrow band wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a first photodetector for receiving the transmitted light of the narrow band wavelength filter. A broadband wavelength filter whose transmittance changes according to the wavelength of the input oscillation light; a second photodetector for receiving the transmitted light of the broadband wavelength filter; the first photodetector and the oscillation mode; The ratio between the direct current component signal from the signal generating circuit and the direct current component signal from the second photodetector and the oscillation mode signal generating circuit is obtained, and the two obtained ratios are calculated as the first and second ratios. The semiconductor laser device according to claim 5, further comprising: a divider that outputs a wavelength monitor signal of 2. 8. An oscillation mode photodetector for receiving the output light of a semiconductor laser and converting it into an electric signal, and a branch circuit for branching the output signal of the oscillation mode photodetector into a DC component signal and an AC component signal. And laser control for controlling the light intensity of the semiconductor laser to be constant using the DC component signal from the branch circuit and stabilizing the oscillation mode of the semiconductor laser using the AC component signal from the branch circuit. A semiconductor laser device comprising: a circuit. 9. The output light of the semiconductor laser is input,
A wavelength monitor circuit having a characteristic that an output signal changes according to the wavelength of the laser light, wherein the laser control circuit controls the oscillation wavelength of the semiconductor laser using the output signal of the wavelength monitor circuit. The semiconductor laser device according to claim 8. 10. An oscillation mode photodetector that receives output light of a semiconductor laser and converts it into an electric signal, a high-pass filter that passes an AC component of the output signal of the oscillation mode photodetector, and the semiconductor An intensity control photodetector for receiving the output light of the laser and converting it into an electric signal, and controlling the light intensity of the semiconductor laser to be constant using the output signal of the intensity control photodetector, and A semiconductor laser device comprising: a laser control circuit that stabilizes the oscillation mode of the semiconductor laser using an AC component signal from a high-pass filter. 11. The apparatus further comprises a wavelength monitor circuit having a characteristic that the monitor light is input and an output signal changes in accordance with the wavelength of the laser light, wherein the laser control circuit uses the output signal of the wavelength monitor circuit. 11. The semiconductor laser device according to claim 10, wherein the oscillation wavelength of the semiconductor laser is controlled. 12. The wavelength monitor circuit comprises: a wavelength filter whose transmittance changes according to the wavelength of input oscillation light; and a wavelength monitor photodetector which receives the transmitted light of the wavelength filter and converts it into an electrical signal. The semiconductor laser device according to claim 9, further comprising: 13. The wavelength monitor circuit includes a narrow band wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a first narrow band wavelength filter which receives the transmitted light of the narrow band wavelength filter and converts it into an electric signal. 1. a photodetector, a broadband wavelength filter whose transmittance changes according to the wavelength of the input oscillation light, and a second photodetector which receives the transmitted light of this broadband wavelength filter and converts it into an electrical signal. The semiconductor laser device according to claim 9, further comprising: 14. The wavelength discrimination region of the narrow band wavelength filter corresponds to the ITU grid, and the wavelength discrimination region of the wide band wavelength filter is larger than the wavelength variable range of the semiconductor laser. 13. The semiconductor laser device according to item 13. 15. The wavelength filter is any one of a Fabry-Perot etalon, a birefringent filter having a birefringent crystal and a polarizer, a multi-layer film filter, and a fiber grating. 13,
15. The semiconductor laser device according to any one of 14 and 14. 16. The laser control circuit compares the oscillation mode monitor signal with a preset threshold value, determines that the oscillation is unstable when the oscillation mode monitor signal is larger than the threshold value, and outputs the oscillation mode monitor signal. The semiconductor laser device according to any one of claims 4 to 14, wherein the oscillation is determined to be stable when it is smaller than a threshold value, and the injection current to the semiconductor laser is controlled based on the determination result. . 17. The semiconductor device according to claim 4, further comprising 1 to a plurality of optical branching devices for branching laser light on an optical axis of a front light output of the semiconductor laser. Semiconductor laser device. 18. The semiconductor laser device according to claim 4, wherein the output light of the semiconductor laser is a part or all of the back light of the semiconductor laser.