JPH0818145A - Wavelength stabilizer - Google Patents

Abstract

PURPOSE:To provide a wavelength stabilizer which can stabilize the oscillation wavelength and emitting power of LD with high precision using a simplified structure. CONSTITUTION:An LD 24, a temperature detector 26 for detecting temperature in the vicinity of LD 24, a heating/cooling means 32 for heating or cooling LD 24, an LD temperature controller 28 for controlling the heating/cooling means 32 to set an output of the temperature 26 to the preset temperature and a wavelength discriminating means 38 for transmitting or reflecting the light beam emitted from LD 24 are comprised. Moreover, a photodetector PD 40 for detecting amount of the output light beam transmitted or reflected by the wavelength discriminating means 38 and a current controller 42 for controlling injected current of LD 24 so that an output of LD40 is maintained at the predetermined condition are also comprised. Moreover, provided is a preset temperature changing means 30 for changing the preset temperature, when the injected current goes out of the predetermined current range, on the basis of the direction of such deviated current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength stabilizing device used for a light source such as a laser length measuring machine.

[0002]

2. Description of the Related Art Conventionally, there is known a laser length measuring machine which measures a moving displacement of an object with an oscillation wavelength of a semiconductor laser (hereinafter referred to as an LD) as a length measuring reference. L like this
In D, as shown in FIG. 7A, the oscillation wavelength (λ) depends on the injection current (i) and the temperature (T) of the LD. Therefore, in order to stabilize the oscillation wavelength (λ) which is the length measurement reference, the injection current (i) and the temperature (T) may be controlled.

FIG. 9 schematically shows the structure of a conventional wavelength stabilizing device. That is, in the LD holding body 2, L
D4 and an LD temperature sensor 6 for detecting the temperature near the LD4 are provided, and the output of the LD temperature sensor 6 is input to the LD temperature control unit 8. Then, the LD temperature control unit 8 controls the drive current of the Peltier element 10 so that the output of the LD temperature sensor 6 is maintained at a predetermined set temperature. A fin 12 for heat dissipation is attached to the Peltier element 10.

The emitted light from the LD 4 is split by a beam splitter 14, one of the emitted lights is used as a length measuring light, and the other emitted light is transmitted through an etalon 16 serving as a wavelength reference and then the The transmitted light is detected by a photodiode (hereinafter referred to as PD) 18, and its output is input to the current control unit 20. This current control unit 2
0 controls the injection current of the LD 4 so that the output of the PD 18 is maintained at a predetermined output.

Further, as shown in FIG.
Has a characteristic of transmitting a periodic wavelength. For example, in order to stabilize the oscillation wavelength of LD4 to λ1, PD
The injection current may be controlled so that the output of 18 always has the peak value (the value at point c in the figure). At this time, the temperature of the LD 4 is stabilized so that the injection current sweep range is in the vicinity of the symbol λ1 in the figure. As a result, the oscillation wavelength of the LD 4 can be stabilized at a predetermined wavelength.

[0006]

However, since the LD temperature sensor 6 only detects the temperature in the vicinity of the LD 4, if the ambient temperature changes even if normal temperature control is performed, The temperature of LD4 also fluctuates.
At this time as well, since the injection current is controlled with the etalon 16 as the wavelength reference, the oscillation wavelength of the LD 4 is stabilized,
The injection current fluctuates greatly as the temperature of LD4 changes, and L
The output power of D4 changes.

That is, as shown in FIG.
In order to stabilize the oscillation wavelength (λ) of
When the temperature (T) of 4 changes from T1 to T2, the injection current (i) must be controlled from i1 to i2. However, since the emission power (P) of the LD4 varies depending on the temperature (T) of the LD4 and the injection current (i) as shown in FIG. 7B, when the injection current (i) changes from i1 to i2. The output power (P) also greatly changes from P1 to P2.

It is known that the characteristics of the LD 4 shown in FIGS. 7A and 7B change with time. For this reason, even if the environmental temperature is always constant, the emission power (P) thereof changes with time.

When the emission power (P) of the LD 4 changes in this way, the output signal of the PD 18 also changes. In particular, when the emission power (P) becomes small, S of the output signal of the PD 18
The N ratio deteriorates, which affects the wavelength stability.

Further, as shown in FIGS. 8 and 9, the control to the above-mentioned peak value (value at the point in FIG. 8c) originally does not improve the detection accuracy because the detection signal hardly changes. Therefore, consider the case where the stabilization control is performed at the wavelength λ3 at which the detection signal ½ of the peak value (the detection signal corresponding to the point in FIG. 8d) is obtained. At this time, the current control unit 20 determines that PD1
Injection current (i) so that the detection signal of 8 is always Vd
However, if the emission power (P) of the LD 4 fluctuates, there is a problem that the oscillation wavelength of the LD 4 fluctuates even if the detection signal of the PD 18 is always constant at Vd.

Further, when the wavelength stabilizing device as described above is used as a light source of, for example, a laser length measuring machine, a detection circuit (not shown) for detecting interference light is required in order to sufficiently allow the power fluctuation of the light source. It becomes complicated and the circuit scale becomes large. Therefore, a counter circuit (not shown)
Then, the power fluctuation affects the counting error.

The present invention has been made to solve such a problem, and its purpose is to provide an L
An object of the present invention is to provide a wavelength stabilization device capable of stabilizing the oscillation wavelength and the emission power of D with high accuracy.

[0013]

In order to achieve such an object, the invention according to claim 1 is directed to a semiconductor laser and a temperature detector which is arranged near the semiconductor laser and detects the temperature near the semiconductor laser. Unit, heating / cooling means for heating or cooling the semiconductor laser, a temperature control section for controlling the heating / cooling means so that the output of the temperature detector reaches a set temperature, and the emitted light of the semiconductor laser is transmitted. Alternatively, a wavelength discriminating means for reflecting, a photodetector for detecting the amount of the emitted light transmitted or reflected by the wavelength discriminating means, and an output of the photodetector are maintained in a predetermined state, the semiconductor laser In a wavelength stabilization device having a current control unit for controlling an injection current, when the injection current is out of a predetermined current range, the set temperature is changed based on the outlying current direction. Comprises a set temperature changing means that.

The invention according to claim 2 is a semiconductor laser,
A temperature detector that is arranged near the semiconductor laser, detects a temperature near the semiconductor laser, a heating / cooling unit that heats or cools the semiconductor laser, and an output of the temperature detector reaches a set temperature. A temperature controller for controlling heating / cooling means, a wavelength discriminating means for transmitting or reflecting the emitted light of the semiconductor laser, a photodetector for detecting the amount of the emitted light transmitted or reflected by the wavelength discriminating means, and In a wavelength stabilizer having a current control unit for controlling the injection current of the semiconductor laser so that the output of the photodetector is maintained in a predetermined state, after the output of the photodetector is controlled in a predetermined state And a set temperature changing means for changing the set temperature so that the output of the photodetector is kept constant.

In the invention according to claim 3, the set temperature changing means changes the set temperature only after the output of the photodetector is controlled to a predetermined state. According to a fourth aspect of the present invention, a semiconductor laser, a temperature detector arranged near the semiconductor laser to detect the temperature in the vicinity of the semiconductor laser, a heating / cooling unit for heating or cooling the semiconductor laser, and the temperature detection. In a wavelength stabilization device having a temperature control unit for controlling the heating / cooling means and a wavelength discriminating means for transmitting or reflecting the emitted light of the semiconductor laser, the output of the device is set to a preset temperature, A plurality of photodetectors capable of detecting at least two light amounts among the light amount of emitted light, the light amount of transmitted light from the wavelength discriminating means, and the light amount of reflected light from the wavelength discriminating means, and a plurality of photodetectors from these photodetectors. A wavelength control unit for stabilizing the oscillation wavelength of the semiconductor laser in a predetermined mode of the wavelength discriminating means on the basis of a signal; and on the basis of a signal from the photodetector, ; And a power control unit for stabilizing the output power of the conductor laser to a predetermined level.

In the invention according to claim 5, the wavelength control unit of the semiconductor laser is so arranged that the output of the photodetector for detecting the amount of transmitted light from the wavelength discriminating means is maintained in a predetermined state. The power control unit includes a current control unit that controls an injection current, and the power control unit is configured such that the photodetector that detects a light amount of emitted light of the semiconductor laser is built in the semiconductor laser, and A preset temperature changing means is provided for changing the preset temperature so that the output of the photodetector that detects the amount of light emitted from the laser is kept constant.

In the invention according to claim 6, the wavelength control unit of the semiconductor laser is configured so that the output of the photodetector for detecting the amount of transmitted light from the wavelength discriminating means is maintained in a predetermined state. Based on the output of the photodetector that detects the amount of transmitted light from the wavelength discriminating means, a current control portion that controls the injection current, and a wavelength control means that drives and controls the current control portion. The power control unit includes set temperature changing means for changing the set temperature so that the output of the photodetector for detecting the light amount of the emitted light of the semiconductor laser is kept constant, and the emitted light of the semiconductor laser. Power control means for driving and controlling the set temperature changing means based on the output of the photodetector for detecting the amount of light.

In the invention according to claim 7, the wavelength control unit detects the output signal of the photodetector for detecting the amount of transmitted light from the wavelength discriminating means and the amount of reflected light from the wavelength discriminating means. And a controller for performing a predetermined calculation on the output signal of the photodetector, and controlling the injection current of the semiconductor laser so as to stabilize the oscillation wavelength of the semiconductor laser in a predetermined mode of the wavelength discriminating means. The power control unit includes a current control unit and a wavelength control unit that drives and controls the current control unit based on the calculation result of the arithmetic unit, and the power control unit detects the light amount of the reflected light from the wavelength discriminating unit. The output of the photodetector for detecting the light amount of the reflected light from the wavelength discriminating means and the set temperature changing means for changing the set temperature so that the output of the photodetector is maintained constant. Based on, and a power control means for driving and controlling the set temperature changing means.

[0019]

In the wavelength stabilizing device according to the first aspect, the temperature control unit controls the heating / cooling means so that the temperature near the semiconductor laser detected by the temperature detector becomes the set temperature.
The emitted light of the semiconductor laser is transmitted or reflected by the wavelength discriminating means, and the amount of the transmitted or reflected light is detected by the photodetector. The current control unit controls the injection current of the semiconductor laser so that the output of the photodetector is maintained in a predetermined state. Here, when the injected current is out of the predetermined current range, the set temperature changing means determines the change direction of the set temperature based on the deviated current direction, and gradually changes the set temperature.

In the wavelength stabilizing device according to claim 2,
The temperature control unit controls the heating / cooling unit so that the temperature in the vicinity of the semiconductor laser detected by the temperature detector reaches the set temperature. The emitted light of the semiconductor laser is transmitted or reflected by the wavelength discriminating means, and the amount of the transmitted or reflected light is detected by the photodetector. The current control unit controls the injection current of the semiconductor laser so that the output of the photodetector is maintained in a predetermined state. Then, after the output of the photodetector is maintained in a predetermined state, the set temperature changing means changes the set temperature so that the output of the photodetector is maintained constant.

In the wavelength stabilizing device according to claim 3,
The temperature control unit controls the heating / cooling unit so that the temperature in the vicinity of the semiconductor laser detected by the temperature detector reaches the set temperature. The emitted light of the semiconductor laser is transmitted or reflected by the wavelength discriminating means, and the amount of the transmitted or reflected light is detected by the photodetector. The current control unit controls the injection current of the semiconductor laser so that the output of the photodetector is maintained in a predetermined state. Then, the set temperature changing means changes the set temperature only after the output of the photodetector is controlled to a predetermined state.

In the wavelength stabilizer according to claim 4,
The temperature control unit controls the heating / cooling unit so that the temperature in the vicinity of the semiconductor laser detected by the temperature detector reaches the set temperature. At this time, at least two light amounts of the light amount of the emitted light of the semiconductor laser, the light amount of the transmitted light from the wavelength discriminating means, and the light amount of the reflected light from the wavelength discriminating means are detected by the plurality of photodetectors. Then, based on the signals from these photodetectors, the wavelength control unit stabilizes the oscillation wavelength of the semiconductor laser in a predetermined mode of the wavelength discriminating means, and the power control unit sets the emission power of the semiconductor laser to a predetermined level. Stabilize.

In the wavelength stabilization device according to claim 5,
The wavelength control unit includes a current control unit, and by controlling the injection current of the semiconductor laser by this current control unit, the output of the photodetector for detecting the light amount of the transmitted light from the wavelength discriminating means is brought into a predetermined state. Maintained. The power control unit is configured such that the semiconductor laser has a built-in photodetector that detects the amount of light emitted from the semiconductor laser, and also has a set temperature changing means. Is changed, the output of the photodetector that detects the light amount of the emitted light of the semiconductor laser is maintained constant.

In the wavelength stabilizing device according to claim 6,
The wavelength control unit includes a current control unit and a wavelength control unit, and the wavelength control unit drives and controls the current control unit based on the output of the photodetector that detects the amount of transmitted light from the wavelength discrimination unit. . At this time, the current control unit controls the injection current of the semiconductor laser, so that the output of the photodetector that detects the amount of transmitted light from the wavelength discriminating unit is maintained in a predetermined state. Further, the power control unit includes a set temperature changing unit and a power control unit, and the power control unit determines the set temperature changing unit based on the output of the photodetector that detects the light amount of the emitted light of the semiconductor laser. Drive control. At this time, the set temperature changing means changes the set temperature, so that the output of the photodetector that detects the amount of light emitted from the semiconductor laser is maintained constant.

In the wavelength stabilizer according to claim 7,
The wavelength control unit includes an arithmetic unit, a current control unit, and a wavelength control unit, and the arithmetic unit detects the output signal of the photodetector that detects the amount of transmitted light from the wavelength discriminating unit and the reflection from the wavelength discriminating unit. A predetermined calculation is performed on the output signal of the photodetector that detects the amount of light. The wavelength controller drives and controls the current controller based on the calculation result of the calculator. At this time, the current controller controls the injection current of the semiconductor laser to stabilize the oscillation wavelength of the semiconductor laser in the predetermined mode of the wavelength discriminating means. Further, the power control unit includes a set temperature changing unit and a power control unit, and the power control unit drives the set temperature changing unit based on the output of the photodetector that detects the light amount of the emitted light of the semiconductor laser. Control. At this time, the set temperature changing means changes the set temperature, so that the output of the photodetector that detects the amount of light emitted from the semiconductor laser is maintained constant.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A wavelength stabilizing device according to a first embodiment of the present invention will be described below with reference to FIG. In each of the following embodiments, the semiconductor laser is called LD.
As shown in FIG. 1A, in the wavelength stabilizer of the present embodiment, in order to stabilize the temperature of the LD 24 provided in the LD holder 22, the temperature near the LD 24 is set near the LD 24. A temperature detector 26 for detecting the temperature is provided.
The temperature detector 26 is electrically connected to the LD temperature control unit 28, and the temperature detection signal output from the temperature detector 26 is input to the LD temperature control unit 28.

A set temperature changing means 30 for changing the set temperature is electrically connected to the LD temperature control section 28,
The LD temperature control unit 28 controls the drive current of the heating / cooling means 32 based on the temperature detection signal and the set temperature so that the temperature of the LD 24 becomes equal to the set temperature, and the LD 2
4. Stabilize temperature. The heating / cooling means 32 includes
The fins 34 for heat dissipation are attached.

The light emitted from the LD 24 is branched by the optical element 36.
Is split into two by one, one of the emitted lights is used as a length measuring light, and the other emitted light is the wavelength discriminating means 3
It is incident on 8.

The wavelength discriminating means 38 has a function of transmitting or reflecting the incident light, but the wavelength discriminating means 38 applied to the present embodiment is constructed to transmit the incident light.
As a result, the other emitted light branched by the branching optical element 36 passes through the wavelength discriminating means 38, and the amount of transmitted light is detected by a photodetector (hereinafter referred to as PD) 40.

The light amount detection signal output from the PD 40 is
The current is input to the current controller 42, and the current controller 42 controls the injection current of the LD 24 so that the light amount detection signal is maintained in a predetermined state (for example, peak value).

At this time, if the injection current exceeds the preset current range, the set temperature changing means 30 changes the set temperature. The LD temperature control unit 28 controls the drive current of the heating / cooling means 32 based on the changed set temperature,
Perform temperature stabilization control.

The temperature detector 26 is, for example, a thermistor most suitable for miniaturization, the heating / cooling means 32 is, for example, a Peltier element, the branching optical element 36 is, for example, a beam splitter or a branching prism, and For example, a solid etalon or the like is applied to the wavelength discriminating means 38, and in the following description, an example in which these specific configurations are used will be described.

As a characteristic of the LD 24, it is generally known that the amount by which the LD temperature contributes to the emission power is smaller than the amount by which the injection current contributes to the emission power for the same wavelength variation. The results of an experiment conducted by the applicant using, for example, ML774A2F manufactured by Mitsubishi Electric Corporation are shown below.

[0034]

[Equation 1]

Equation (1) shows the amount that the LD temperature contributes to the oscillation wavelength, equation (2) shows the amount that the injection current contributes to the oscillation wavelength, and equation (3) shows that the LD temperature changes the emission power. The amount of contribution of the injection current to the emission power is expressed by the equation (4). The equations (1) and (2) are
It is an experimental value when the environmental temperature is around 20 ° C.
Equation (4) is the calculated value (20
-25 ° C).

In this way, LDs that bring about the same wavelength change
The temperature and the injection current cause a power change of about 10 times. Therefore, it is preferable to use an injection current with good controllability for short-term wavelength stabilization, and to use an LD temperature that has little influence on the wavelength for power stabilization.

FIG. 1 (b) shows an operation flow of the wavelength stabilizer of this embodiment. The operation flow will be described for the case where the oscillation wavelength of the LD 24 is stabilized to a predetermined mode (wavelength λ1 in FIGS. 7 and 8) of the solid etalon 38. Further, in the following operation flow, FIG. 7 and FIG. 8 are referred to.

After the power is turned on, first, the LD temperature control unit 28 controls the Peltier element 32 to stabilize the temperature of the LD 24 at a preset initial setting temperature (S1). L
The injection current (i) is swept by the current controller 42 when the temperature of D24 stabilizes near the initial set temperature or after a sufficient time has passed for stabilization. After this,
The LD temperature control unit 28 continues the temperature control for the set temperature. Since the mode of wavelength λ1 is included in the current sweep range determined by the temperature control step of S1, when the injection current (i) is swept, the output of PD40 becomes
It peaks at a certain current i1 (S2).

Next, the current controller 42 supplies the peak current i1 to the LD 24 (S3), and thereafter changes only a minute current so as to always lock at the apex (wavelength λ1) of the mountain. (S4).

If the environmental temperature is always constant, the injection current (i) may be approximately i1 and the set temperature may be the initial value. However, in the thermistor 26, L
Since the temperature of D24 cannot be detected, if the temperature of LD24 changes due to a change in the environmental temperature, as shown in FIG.
As shown in (a), when trying to oscillate at wavelength λ1,
The injection current (i) changes, and as a result, the emission power (P) changes as shown in FIG. 7B.

Therefore, the set temperature changing means 30 determines whether the injection current (i) is in the vicinity of i1 (that is, whether the injection current (i) is out of the predetermined current width) (S5). ).

At this time, when the injection current (i) greatly deviates from i1, the temperature direction for suppressing the fluctuation of the emission power (P) is set, and the set temperature is output to the LD temperature control section 28. The LD temperature control unit 28 controls the Peltier element 32 to stabilize the LD 24 at the set temperature. That is, if the injection current (i) is smaller than i1, the set temperature is raised, and if it is larger, the set temperature is lowered (S6).

As described above, according to this embodiment, it is possible to suppress the variation of the emission power (P) caused by the environmental temperature change and the like, so that the SN ratio of the output signal of the PD 40 becomes stable and the LD 24 has a stable output signal. It is possible to stabilize the oscillation wavelength (λ) and the emission power (P) with high accuracy. Furthermore, if the environmental temperature is limited to some extent, it is possible to perform stabilization control of the emission power (P) before the current sweep, that is, before the mode lock.

Next, a wavelength stabilizing device according to a second embodiment of the present invention will be described with reference to FIG. As shown in FIG. 2, the wavelength stabilizer of the present embodiment is characterized in that the light amount detection signal output from the PD 40 is directly input to the set temperature changing unit 30a. Since the other configurations are the same as those of the first embodiment (see FIG. 1A), the same reference numerals are given and the description thereof is omitted. In the description of this embodiment, FIGS. 4 and 5 will be referred to.

As in the first embodiment, the LD temperature control unit 2
8 continues the temperature control for the set temperature, and the current control unit 4
2 controls the injection current (i) so that the output of the PD 40 is locked in a predetermined mode of the wavelength discriminating means, for example, the solid etalon 38. Here, the oscillation wavelength (λ) of the LD 24
In order to stabilize the solid etalon 38 in a predetermined mode (wavelength λ1), the current controller 42 performs hill climbing control near the injection current (i) i1.

At this time, the output of the PD 40 is input to the current controller 42 and the set temperature changing means 30a. The set temperature changing means 30a lowers the set temperature if the output of the PD 40 is smaller than a predetermined value (for example, the output of the PD 40 when the temperature (T) of the LD 24 is T = T1), and outputs the signal to the LD temperature control unit. To 28. LD
The temperature control unit 28 controls the drive current of the heating / cooling means, that is, the Peltier element 32, based on the input signal. On the other hand, if the output of the PD 40 is larger than the predetermined value, the set temperature is raised and the signal is output to the LD temperature control unit 28. The LD temperature control unit 28, based on the input signal,
The drive current of the Peltier element 32 is controlled. As a result, L
The oscillation wavelength (λ) and emission power (P) of D24 can be stabilized.

As described above, according to this embodiment, since the output of the PD 40 is directly input to the set temperature converting means 30a, the SN ratio of the output signal of the PD 40 is further stabilized and the LD24 characteristic is improved. The oscillation wavelength (λ) and the emission power (P) of the LD 24 even when it changes with time.
Can be stabilized with high precision.

Next, a wavelength stabilizer according to a third embodiment of the present invention will be described with reference to FIG. As shown in FIG. 3, in the wavelength stabilizer of this embodiment, the LD 24a having a built-in monitor photodetector (not shown) for monitoring the emitted light and the output of the monitor photodetector are kept constant. Temperature changing means 30b for changing the temperature setting so that
It is characterized in that and are provided, and other configurations are the same as those in the first and second embodiments (see FIGS. 1A and 2).
Therefore, the same reference numerals are given and the description thereof will be omitted. Further, in the description of this embodiment, FIGS. 7 and 8 will be referred to. The monitor photodetector will be referred to as a monitor PD hereinafter.
Called.

Similar to the first and second embodiments, the LD temperature control unit 28 continues the temperature control with respect to the set temperature, and the current control unit 42 outputs the PD 40 to the wavelength discriminating means, for example, the predetermined mode of the solid etalon 38. The injection current (i) is controlled so as to lock at (wavelength λ 1). Where LD
When the oscillation wavelength (λ) of 24a is locked in the predetermined mode of the solid etalon 38, that is, the current control unit 4
When 2 is performing hill climbing control near i1 of the injection current (i), the output of the photodetector for monitoring built in the LD 24a is input to the set temperature changing means 30b.

At this time, the oscillation wavelength (λ) of the LD 24a
Is locked in the predetermined mode of the solid etalon 38, the injection current (i) of the LD 24a is maintained substantially constant unless the environmental temperature changes. However, even if the environmental temperature changes, the solid etalon 3
Since the injection current (i) is controlled with 8 as the wavelength reference, the oscillation wavelength (λ) of the LD 24a is stabilized, but
Since the injection current (i) greatly changes with the temperature change of 24a, the emission power (P) of the LD 24a changes.

Therefore, if the output of the monitor PD is smaller than a predetermined value (for example, the output of the monitor PD when the temperature (T) of the LD 24a is T = T1), the set temperature is lowered.
The signal is output to the LD temperature control unit 28. The LD temperature control unit 28 controls the drive current of the heating / cooling means, that is, the Peltier element 32, based on the input signal. On the other hand, PD
If the output of 40 is larger than the predetermined value, the set temperature is raised and the signal is output to the LD temperature control unit 28. LD
The temperature control unit 28 controls the drive current of the Peltier element 32 based on the input signal. As a result, the LD 24a
It is possible to stabilize the oscillation wavelength (λ) and the emission power (P) of the.

As described above, according to this embodiment, it is possible to suppress the variation of the emission power (P) of the LD 24a caused by the environmental temperature change and the like.
The ratio becomes stable, and even when the characteristics of the LD 24a change with time, the oscillation wavelength (λ) and the emission power (P) of the LD 24a can be stabilized with high accuracy. Furthermore, in this embodiment, since the monitor light output corresponding to the emission power (P) of the LD 24a is used, any value other than the peak value (value at point c in FIG. 8) (for example, d in FIG. 8) is used. It is especially effective for mode lock to (point value).

Next, a wavelength stabilizer according to a fourth embodiment of the present invention will be described with reference to FIG. As shown in FIG. 4, the wavelength stabilizer of the present embodiment relates to the improvement of the third embodiment (see FIG. 3), and outputs the light emitted from the LD 24 to 2
A branching optical element 44 (for example, a beam splitter or a branching prism) that branches in a direction, and the branching optical element 4
A power control PD 46 that receives one of the outgoing lights branched by 4 and outputs a signal corresponding to the received light amount.
And a power control means 48 for driving and controlling the set temperature changing means 30b based on the output signal from the power control PD 46, and a wavelength control means 50 for driving and controlling the current control section 42 based on the output signal of the PD 40. It has and. Since the other structure is the same as that of the third embodiment, the same reference numerals are given and the description thereof is omitted. Further, in the description of this embodiment, FIGS. 7 and 8 will be referred to.

In this embodiment, the wavelength control means 50 is
The current controller 42 is driven and controlled so that the output of the PD 40 is locked in a predetermined mode (wavelength λ1) of the wavelength discriminating means, for example, the solid etalon 38. Here, when the oscillation wavelength (λ) of the LD 24 is locked in the predetermined mode of the solid etalon 38, that is, when the current control unit 42 performs hill climbing control in the vicinity of i1 of the injection current (i), The output of the control PD 46 is input to the set temperature changing means 30b.

Since the oscillation wavelength (λ) of the LD 24 is locked in the predetermined mode of the solid etalon 38, the LD
The injection current (i) of 24 is as long as there is no change in ambient temperature.
It remains almost constant. However, even when the ambient temperature changes, the injection current (i) is controlled with the solid etalon 38 as the wavelength reference, so that the oscillation wavelength (λ) of the LD 24 is stabilized, but the LD 24 changes in temperature. As a result, the injection current (i) fluctuates greatly and the emission power (P) of the LD 24 also fluctuates.

Therefore, the output of the power control PD 46 (for example, the output when the temperature (T) of the LD 24 is T = T1)
If is smaller than the predetermined value, the set temperature is lowered and the signal is output to the LD temperature control unit 28. LD temperature control unit 28
Controls the driving current of the heating / cooling means, that is, the Peltier element 32, based on the input signal. On the other hand, if the output of the power control PD 46 is larger than the predetermined value, the set temperature is raised and the signal is output to the LD temperature control unit 28.
The LD temperature control unit 28 controls the drive current of the Peltier element 32 based on the input signal. As a result, LD2
The oscillation wavelength (λ) and the emission power (P) of No. 4 can be stabilized.

As described above, according to this embodiment, it is possible to suppress the variation of the emission power (P) of the LD 24 caused by the environmental temperature change and the like, so that the SN ratio of the output signal of the PD 40 is stable and the LD 24 is stable. Even if the characteristics change with time, the oscillation wavelength (λ) and the emission power (P) of the LD 24 can be stabilized with high accuracy.

In this embodiment, the wavelength is stabilized by hill-climbing control, but other than this, as a method for realizing the wavelength stabilization, for example, the light amount level to be mode-locked is set to the peak value ( It is also effective to set it at the midpoint of the mountain (for example, the value of point d in FIG. 8) other than the value of point c in FIG. In this case, it is possible to realize wavelength stabilization with higher accuracy than the hill climbing control.

Next, a wavelength stabilizer according to a fifth embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 5, the wavelength stabilizer of the present embodiment relates to the improvement of the fourth embodiment, and the wavelength discriminating means, for example, the solid etalon 38, applied to this wavelength stabilizer transmits the incident light. And configured to reflect.

In this case, one of the emitted lights branched by the branching optical element 36 is used as a length measuring light,
Others pass through the solid etalon 38 and then PD
The amount of transmitted light is detected by 40.

On the other hand, the reflected light reflected from the solid etalon 38 is irradiated again on the branching optical element 36,
A power control PD reflected from the branching optical element 36
46 is irradiated.

At this time, the signal output from the power control PD 46 is input to the power control means 48, as in the fourth embodiment. Further, the wavelength stabilizing device of the present embodiment is provided with a subtractor 52 that performs a subtraction process on the output signal of the PD 40 and the output signal of the power control PD 46, and the wavelength control means 50 uses this subtracter. It is configured to drive and control the current control unit 42 based on the output of 52.

Since the other structure is the same as that of the fourth embodiment, the same reference numerals are given and the description thereof is omitted. Further, in the description of this embodiment, FIGS. 7 and 8 will be referred to. In this embodiment, the LD temperature control unit 28 continues the temperature control for the set temperature. At this time, the wavelength control unit 50 drives and controls the current control unit 42 so that the output of the subtractor 50 becomes zero, and the injection current (i) to the LD 24.
Control.

Specifically, as shown in FIG. 6A, the PD 4 that receives the transmitted light that has passed through the solid etalon 38.
The output signal of 0 has the characteristic as shown by the solid line in the figure, while the output signal of the power control PD 46 which receives the reflected light reflected from the solid etalon 38 has the characteristic as shown by the dotted line in the figure. Have.

These PD 40 and power control PD 46
After being input to the subtracter 50, the output signal of is converted into an output signal as shown in FIG. 6B.

At this time, the wavelength control means 50 uses the subtractor 5
The current controller 42 is drive-controlled so that the output of 0 becomes zero, and the injection current (i) to the LD 24 is controlled. In this case, as shown in FIG. 6B, the output of the subtractor 50 becomes zero at the wavelength λ1.

Therefore, the wavelength control means 50 includes the subtractor 50.
In order to lock the output of the solid etalon 38 in a predetermined mode (that is, the wavelength λ1), the current controller 42 is drive-controlled to control the injection current (i) to the LD 24.

Here, when the oscillation wavelength (λ) of the LD 24 is locked in the predetermined mode (that is, the wavelength λ1) of the solid etalon 38, that is, the current controller 42 causes the injection current (i) to be around i1. When the power control unit 48 is controlled to, the output signal of the power control PD 46 (the output signal shown by the dotted line in FIG. 6A) is input to the power control unit 48.

At this time, the oscillation wavelength (λ) of the LD 24 is
Since the solid etalon 38 is locked in the predetermined mode, the injection current (i) to the LD 24 is maintained substantially constant unless the environmental temperature changes. However, even when the environmental temperature changes, the injection current (i) is controlled with the solid etalon 38 as the wavelength reference, so the LD
Although the oscillation wavelength (λ) of the laser diode 24 is stabilized, the injection current (i) changes greatly with the temperature change of the LD 24, so
The output power (P) of D24 changes.

Therefore, when the output of the power control PD 46 is smaller than the predetermined value (the output Vf (<peak value Ve) in FIG. 6A), the power control means 48 outputs a large power control PD 46. And outputs a command to change the set temperature to the set temperature changing unit 30b. The set temperature changing means 30b operates the LD temperature control unit 28 according to the command.
A new set temperature signal is output to. At this time, the LD temperature control unit 28 controls the drive current of the heating / cooling means, that is, the Peltier element 32, based on the new set temperature signal so that the LD 24 reaches the new set temperature.

On the other hand, when the output of the power control PD 46 is larger than the predetermined value, the power control means 48 issues a command to change the set temperature so that the output of the power control PD 46 becomes small. Output to.
The set temperature changing means 30b outputs a new set temperature signal to the LD temperature control unit 28 in accordance with the above command. At this time, the LD temperature control unit 28 controls the drive current of the Peltier element 32 based on the new set temperature signal so that the LD 24 reaches the new set temperature.

By executing such control, it becomes possible to stabilize the oscillation wavelength (λ) and the emission power (P) of the LD 24. As described above, according to the present embodiment, it is possible to suppress the variation of the emission power (P) of the LD 24 due to the environmental temperature change, etc.
The SN ratio of the output signal of the LD is stable, and even when the LD24 characteristic changes with time, the oscillation wavelength (λ) of the LD24
Also, the output power (P) can be stabilized with high accuracy. Further, in this embodiment, the solid etalon 38 is used.
Since both the amount of transmitted light and the amount of reflected light are detected, it is possible to perform a quick lock process to the predetermined mode. Further, the output of the subtractor 50 is zero (that is, (amount of transmitted light)-(amount of reflected light) = 0) by the subtractor 52 and the wavelength control means 50.
Since the arithmetic processing control is performed so that
It is possible to improve the control accuracy as compared with a method of stabilizing the wavelength based on one of the output signals of 0 and 46 (for example, a hill climbing control method). As a result, it becomes possible to realize highly accurate wavelength stabilization processing. In this embodiment, the output power of the LD 24 is stabilized by using the reflected light from the solid etalon 38.
For example, the output power of the LD 24 can be stabilized by using transmitted light that passes through the solid etalon 38.

In each of the above-described embodiments, the case where the solid etalon is used as the wavelength discriminating means has been described, but the same operational effect can be obtained even if an absorption cell or the like is applied. Further, in each of the above-described embodiments, it is assumed that the LD characteristics change with time due to a change in the set temperature from the initial value, and therefore, for example, an alarm is used to notify the worker of the LD replacement time. Is also preferable. Furthermore, since the output power of the LD is always stable,
It is also possible to estimate the life of the LD in advance.

If the wavelength stabilizing device of each of the above-mentioned embodiments is used as a light source of a laser length measuring machine, for example, the circuit on the detection side can be simplified and fluctuations in the Lissajous length can be reduced. It is also possible to suppress the above.

[0075]

According to the present invention, since the set temperature changing means for changing the set temperature is provided so that the output of the photodetector becomes constant, the oscillation wavelength and the emission power of the semiconductor laser can be accurately adjusted. It is possible to provide a wavelength stabilization device that can be stabilized.

[Brief description of drawings]

FIG. 1A is a diagram schematically showing a configuration of a wavelength stabilizing device according to a first embodiment of the present invention, and FIG. 1B is a flowchart showing an operation of the wavelength stabilizing device.

FIG. 2 is a diagram schematically showing a configuration of a wavelength stabilizing device according to a second embodiment of the present invention.

FIG. 3 is a diagram schematically showing a configuration of a wavelength stabilizing device according to a third embodiment of the present invention.

FIG. 4 is a diagram schematically showing a configuration of a wavelength stabilizing device according to a fourth embodiment of the present invention.

FIG. 5 is a diagram schematically showing the configuration of a wavelength stabilizing device according to a fifth embodiment of the present invention.

FIG. 6A is a diagram showing the relationship between the output signal characteristics of a PD that receives transmitted light that has passed through a solid etalon and the output signal characteristics of a power control PD that receives reflected light that has been reflected from a solid etalon. , (B) are diagrams showing output signal characteristics of the subtractor.

7A is a diagram showing a relationship between an injection current and an oscillation wavelength with respect to an LD temperature, and FIG. 7B is a diagram showing a relationship between an injection current and an emission power with respect to an LD temperature.

FIG. 8 is a diagram showing characteristics of an etalon that transmits a periodic wavelength.

FIG. 9 is a diagram schematically showing a configuration of a conventional wavelength stabilization device.

[Explanation of symbols]

24 ... LD, 26 ... Temperature detector, 28 ... LD temperature control section, 30 ... Set temperature changing means, 32 ... Heating / cooling means, 3
8 ... Wavelength discrimination means, 40 ... PD, 42 ... Current control section.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Yukawa 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Hirohisa Fujimoto 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd.

Claims (7)

[Claims] 1. A semiconductor laser, a temperature detector arranged near the semiconductor laser for detecting a temperature near the semiconductor laser, a heating / cooling unit for heating or cooling the semiconductor laser, and an output of the temperature detector. To a set temperature, a temperature control unit that controls the heating / cooling unit, a wavelength discriminating unit that transmits or reflects the emitted light of the semiconductor laser, and a light amount of the emitted light that is transmitted or reflected by the wavelength discriminating unit. In a wavelength stabilizer having a photodetector for detecting, and a current controller for controlling the injection current of the semiconductor laser, so that the output of the photodetector is maintained in a predetermined state, the injection current is If the current is out of the specified current range,
A wavelength stabilizing device comprising a set temperature changing means for changing the set temperature based on a deviated current direction. 2. A semiconductor laser, a temperature detector arranged near the semiconductor laser for detecting a temperature near the semiconductor laser, a heating / cooling unit for heating or cooling the semiconductor laser, and an output of the temperature detector. To a set temperature, a temperature control unit that controls the heating / cooling unit, a wavelength discriminating unit that transmits or reflects the emitted light of the semiconductor laser, and a light amount of the emitted light that is transmitted or reflected by the wavelength discriminating unit. In a wavelength stabilizing device having a photodetector for detecting, and a current controller for controlling the injection current of the semiconductor laser so that the output of the photodetector is maintained in a predetermined state, After the output is controlled to a predetermined state, a set temperature changing means for changing the set temperature is provided so that the output of the photodetector is kept constant. Apparatus. 3. The wavelength stabilizing device according to claim 1, wherein the set temperature changing unit changes the set temperature only after the output of the photodetector is controlled to a predetermined state. 4. A semiconductor laser, a temperature detector arranged near the semiconductor laser for detecting a temperature near the semiconductor laser, a heating / cooling unit for heating or cooling the semiconductor laser, and an output of the temperature detector. Is a set temperature, in the wavelength stabilizing device having a temperature control unit for controlling the heating and cooling means, and a wavelength discriminating means for transmitting or reflecting the emitted light of the semiconductor laser, of the emitted light of the semiconductor laser, A plurality of photodetectors capable of detecting at least two of the light intensity, the light intensity of the transmitted light from the wavelength discriminating device, and the light intensity of the reflected light from the wavelength discriminating device, and a signal from these photodetectors. A wavelength control unit for stabilizing the oscillation wavelength of the semiconductor laser to a predetermined mode of the wavelength discriminating means, and the semiconductor laser based on a signal from the photodetector. Wavelength stabilizing apparatus characterized by comprising a power control unit for stabilizing the output power of the laser to a predetermined level. 5. A current for controlling an injection current of the semiconductor laser, wherein the wavelength control unit controls an injection current of the semiconductor laser so that an output of the photodetector for detecting a light amount of transmitted light from the wavelength discriminating means is maintained in a predetermined state. The power control unit, the power control unit, the light detector for detecting the light amount of the emitted light of the semiconductor laser is built in the semiconductor laser, and the light amount of the emitted light of the semiconductor laser. 5. The wavelength stabilizing device according to claim 4, further comprising a set temperature changing means for changing the set temperature so that the output of the photodetector for detecting is kept constant. 6. A current for controlling an injection current of the semiconductor laser, wherein the wavelength control unit controls an injection current of the semiconductor laser so that an output of the photodetector for detecting a light amount of transmitted light from the wavelength discriminating means is maintained in a predetermined state. Based on the output of the photodetector that detects the light amount of the transmitted light from the control unit and the wavelength discriminating unit, a wavelength control unit that drives and controls the current control unit, and the power control unit, Set temperature changing means for changing the set temperature so that the output of the photodetector for detecting the light amount of the emitted light of the semiconductor laser is kept constant, and the light amount of the emitted light of the semiconductor laser is detected. The wavelength stabilizing device according to claim 1, further comprising a power control unit that drives and controls the set temperature changing unit based on the output of the photodetector. 7. The wavelength control unit of the photodetector for detecting the output signal of the photodetector for detecting the light amount of the transmitted light from the wavelength discriminating means and the photodetector for detecting the light amount of the reflected light from the wavelength discriminating means. A calculator for performing a predetermined calculation on the output signal; a current controller for controlling the injection current of the semiconductor laser so as to stabilize the oscillation wavelength of the semiconductor laser in a predetermined mode of the wavelength discriminating means; Based on the calculation result of the arithmetic unit, the wavelength control means for driving and controlling the current control unit, and the power control unit, the photodetector of the photodetector for detecting the light amount of the reflected light from the wavelength discrimination means. Based on the output of the set temperature changing means for changing the set temperature and the photodetector for detecting the light quantity of the reflected light from the wavelength discriminating means so that the output is maintained constant, the set temperature change means Wavelength stabilization device of claim 1, characterized in that it comprises a power control means for driving and controlling means.