JP2001156359A - Wavelength monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a smaller wavelength monitor, with less parts required for a device. SOLUTION: An optical element is provided which comprises both a beam parallelizing function with a conventional collimator lens and a beam splitting function with a wedge plate. Here, using a GRIN rod lens 10 where a part of the end surface is diagonally polished, a beam 2a is emitted from a surface 11a, which is that part while a beam 2b is emitted from a surface 11b which is the other part of that end surface, so that the incident beam is split and parallelized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength monitor for monitoring a wavelength of an optical signal transmitted to an optical fiber and detecting a deviation from a set wavelength.

[0002]

2. Description of the Related Art Information trunk systems previously realized by metal cables are being replaced by optical fibers capable of high-speed communication in large quantities, and FTTH (Fiber).
The multimedia concept typified by ToThe Home) is also approaching reality. In particular, in recent years, long-distance trunk lines have been constructed with silica-based single mode optical fibers, and have been used in homes and premises LANs (Local Area).
a Network) can be constructed with plastic optical fibers.

[0003] In such an optical fiber transmission system,
An optical signal propagating in an optical fiber generally requires a repeater because the intensity of the optical signal decreases as the transmission distance increases and the waveform spreads. As the repeater, an electrical optical amplifier is generally used, which converts an input optical signal into an electrical signal once, amplifies it, converts it into an optical signal again, and guides it to an optical fiber. In recent years, as another repeater, in recent years, an optical fiber amplifier, which includes an optical waveguide and a pumping laser and is capable of taking out an optical signal as light, has attracted attention.

On the other hand, in optical transmission using such an optical fiber, in order to increase the transmission capacity, optical signals of a plurality of different wavelengths are simultaneously transmitted to one optical fiber, and the transmission band is increased by the number of wavelengths used. There is a trend to adopt an expanded wavelength division multiplexing (WDM) transmission scheme. However, this W
In order to introduce the above-described optical fiber amplifier into an optical fiber transmission system employing the DM transmission method, it is necessary to prepare pump light corresponding to each wavelength of the multiplexed optical signal, which is not practical.

Further, since the above-mentioned electrical optical amplifier has a finite response characteristic to the transmission band,
Even if it is introduced into an optical fiber transmission system that employs a transmission method, multiplexing is necessarily limited. Therefore, a high-density WDM transmission system in which the wavelength interval of each optical signal is narrowed has attracted attention. In this method, since optical signals are multiplexed at narrow wavelength intervals, it is essential that a laser serving as a light source oscillates stably at a set wavelength.

Also, when light propagates through a medium, the velocity (properly, phase velocity) of the propagating light varies depending on the wavelength due to the refractive index of the medium depending on the wavelength. It has been known. This phenomenon is called dispersion, and becomes a problem particularly when an optical signal is transmitted using an optical fiber or the like. For this reason, in an optical fiber transmission system adopting the WDM transmission system, dispersion compensation is usually performed by introducing a dispersion compensation fiber or the like. Therefore, also from this aspect, stable oscillation of the laser at the set wavelength is required.

Therefore, in an optical fiber transmission system, a wavelength monitor for monitoring a wavelength of an optical signal transmitted from a laser into an optical fiber and detecting a deviation from a set wavelength is introduced. As this wavelength monitor, for example, one disclosed in Japanese Patent Application Laid-Open No. H11-122176 is known.

FIG. 13 is a diagram showing the configuration of a conventional wavelength monitor. In particular, FIG.
No. 3, pp. 1 to 3 which are based on “Devices for wavelength monitoring and wavelength control”. In FIG. 13, a conventional wavelength monitor 50 includes an optical fiber 51 and an optical fiber 5.
An input port is constituted by the ferrule 54 whose end is inserted and fixed so that the end face of the optical fiber 61 is exposed, and the optical fiber 61 and the end thereof are inserted and fixed so that the end face of the optical fiber 61 is exposed. The ferrule 62 forms an output port.

On the other hand, the optical fiber 51 is optically connected to a laser diode as a light source, and guides an optical signal to the wavelength monitor 50 as a beam. The wavelength monitor 50 is provided with a collimator lens 54 facing the ferrule 52, and the beam emitted from the optical fiber 51 is converted into a parallel beam 59.

At the position where the parallel beam 59 is emitted, a wedge plate 55 made of a material substantially transparent to the parallel beam 59 is provided. The parallel beam 59 is incident on the wedge plate 55. A beam 59a reflected by the first surface 55a, a beam 59b transmitted through the first surface 55a, reflected by the second surface 55b, and transmitted again through the first surface 55a,
It is divided into a beam 59c transmitted through the first surface 15a and the second surface 55b.

In the wavelength monitor 50, a lens 64 is provided on the ferrule 62 side so as to face the ferrule 62, and the beam 59c transmitted through the wedge plate 55 is
The light is converged by the lens 64 and input to the optical fiber 61 from its end face.

On the other hand, the split beam 59a and the beam 5
9b passes through an optical filter 56 having different wavelength transmission characteristics depending on the incident angle, is further condensed by a condenser lens 57, and reaches photodetectors 58a and 58b, respectively. The optical filter 56 is installed at a position such that when the beams 59a and 59b have a predetermined wavelength, the same transmittance is shown with respect to the incident angle of each beam. In this case, the photodetectors 58a and 58b have the same transmittance. Indicates the received light power.

Therefore, when the beam 59a and the beam 59b deviate from the predetermined wavelength, the transmittance of the optical filter 56 with respect to the incident angle of each beam differs, and a difference occurs in the light receiving power between the photodetectors 58b and 58b. The difference is detected as a wavelength shift.

[0014]

However, according to the above-mentioned conventional wavelength monitor, the collimator lens 54 and the wedge plate 55 are used to split the beam to be monitored and to filter the split beam with high accuracy. Since one optical element is used, there is a problem that the number of parts increases and the device configuration becomes complicated.

Further, an optical axis through which the beam emitted from the optical fiber propagates to the wedge plate 55, and the split beam pass through the optical filter 56, and pass through the photodetectors 58a and 58a.
Since there are two optical axes until reaching the position 8b, there is also a problem that miniaturization of the apparatus is hindered.

The present invention has been made in order to solve the above problems, and has a function of collimating a beam by a conventional collimator lens and a function of splitting a beam by a wedge plate.
An object of the present invention is to realize a wavelength monitor that is realized by two optical elements, reduces the number of components required for the apparatus, and reduces the number of parts required for monitoring the wavelength.

[0017]

Means for Solving the Problems To solve the above-mentioned problems,
In order to achieve the object, in the wavelength monitor according to the present invention, the first surface on which the light beam is incident and the second surface for emitting the first and second transmitted light beams traveling in different directions from each other are provided. An optical element that splits the light beam into the first and second transmitted light beams, and an optical wavelength filter that exhibits different wavelength transmission characteristics according to an incident angle and passes the first and second transmitted light beams And first and second light receiving elements that respectively receive the first and second transmitted light beams that have passed through the optical wavelength filter.

According to the present invention, the light beam can be split into two transmitted light beams as transmitted light instead of reflected light by the above-described optical element, and the above-mentioned light beam is shifted from a predetermined wavelength. In this case, when the first and second transmitted light beams split by the optical element pass through the above-described optical wavelength filter, a difference can be caused between the transmitted light powers of the first and second transmitted light beams. Can be detected by the first and second light receiving elements.

In the wavelength monitor according to the next invention, in the invention according to the first aspect, the optical element emits the first and second transmitted light beams as parallel beams.

According to the present invention, the branched first and second transmitted light beams can be made to enter the above-mentioned optical wavelength filter as a parallel beam, so that the incident angle dependence of the optical wavelength filter becomes more remarkable. The difference between the transmitted light powers of the first and second transmitted light beams transmitted through the optical wavelength filter can be processed as a large signal.

In the wavelength monitor according to the next invention, in the invention according to the first or second aspect, the optical wavelength filter is arranged so that the first transmitted light beam is incident on a predetermined wavelength. The second transmission light beam exhibits a wavelength transmission characteristic in which the transmittance decreases as the wavelength of the first transmission light beam increases, and the second transmission light beam for the predetermined wavelength with respect to the incidence of the second transmission light beam. It is characterized by exhibiting a wavelength transmission characteristic in which the transmittance increases as the wavelength of the light beam increases.

According to the present invention, the wavelength transmission characteristics different according to the incident angle of the optical wavelength filter increase and decrease in the first and second transmitted light beams in directions opposite to each other with respect to the direction of deviation from the predetermined wavelength. Since the transmittance is shown, when the light beam deviates from a predetermined wavelength, a difference in transmitted light power can be obtained as a large signal.

In a wavelength monitor according to the next invention, the invention according to any one of claims 1, 2 and 3 further comprises a differential amplifier for comparing outputs of the first and second light receiving elements. Features.

According to the present invention, when the transmitted light powers of the first and second transmitted light beams that have passed through the optical wavelength filter are received by the first and second light receiving elements, respectively, the received light power Can be detected by the differential amplifier.

[0025] In a wavelength monitor according to the next invention, the first and second light receiving elements are formed on a common semiconductor substrate. It is housed in a body-shaped package.

According to the present invention, the first and second light receiving elements are formed on a common semiconductor substrate or are housed in an integrated package. Output changes caused by dark current and differences in element characteristics at the time of manufacturing can be offset.

In the wavelength monitor according to the next invention, in the invention according to any one of the first to fifth aspects, the optical wavelength filter is not perpendicular to the first and second transmitted light beams. It is characterized by being arranged at a position.

According to the present invention, since the optical wavelength filter is arranged at a position that is not perpendicular to the first and second transmitted light beams, the first or second transmitted light beam is reflected. Thus, the return light of the light beam to the light source side caused by this can be reduced.

In the wavelength monitor according to the next invention, in the invention according to any one of the first to sixth aspects, the optical wavelength filter is a Fabry-Perot etalon constituted by two reflecting surfaces. Features.

According to the present invention, a Fabry-Perot etalon can be used as an optical wavelength filter exhibiting different wavelength transmission characteristics according to the incident angle.

In the wavelength monitor according to the next invention, in the invention according to any one of the first to seventh aspects, an optical signal introduced into an optical fiber transmission system and propagated in an optical fiber is used as the optical beam. It is characterized by being incident.

According to the present invention, since it can be introduced into an optical fiber transmission system, wavelength monitoring is possible even for an optical signal propagating in an optical fiber.

[0033] A wavelength monitor according to the next invention is characterized in that, in any one of the first to seventh inventions, the wavelength monitor is provided in a laser module for oscillating the light beam.

According to the present invention, since the laser module can be provided in the laser module, a laser module capable of monitoring the oscillation state of the laser can be obtained.

In the wavelength monitor according to the next invention, the laser for oscillating the light beam according to the output of the first and second light receiving elements is provided. Characterized in that the oscillation wavelength is controlled.

According to the present invention, the oscillation wavelength of the laser that oscillates the light beam can be adjusted, for example, by controlling the Peltier element provided in the laser, according to the outputs of the first and second light receiving elements. As a result, the oscillation wavelength can be always stabilized.

[0037] In a wavelength monitor according to the next invention, in the invention according to any one of the first to tenth aspects, the optical element is a GRIN rod lens in which a part of the second surface is obliquely polished. The part is defined as a first emission surface, and the other part is defined as a second emission surface, the first transmitted light beam is emitted from the first emission surface, and the second transmitted light beam is emitted from the second emission surface. The light is emitted.

According to the present invention, a GRIN rod lens in which a part of the second surface is polished obliquely can be used as an optical element for branching or collimating a light beam.

In a wavelength monitor according to the next invention, the optical element according to any one of claims 1 to 10, wherein the optical element is a GRIN rod lens in which a part of the first surface is obliquely polished. A light beam incident on the portion and emitted from the second surface is defined as the first transmitted light beam, and a light beam incident on another portion and emitted from the second surface is defined as the second transmitted light beam. It is characterized by doing.

According to the present invention, a GRIN rod lens in which a part of the first surface is polished obliquely can be used as an optical element for branching or collimating a light beam.

A wavelength monitor according to the next invention is characterized in that, in the invention according to any one of the first to tenth aspects, the optical element comprises at least two light-collecting elements.

According to the present invention, a light beam can be branched or collimated by an optical element constituted by at least two light-collecting elements.

In the wavelength monitor according to the next invention, in the twelfth aspect of the invention, the light-collecting element is a part of the Fresnel lens obtained by cutting a Fresnel lens, and the optical element is It is characterized in that a part of the cut surfaces is bonded to each other.

According to the present invention, a light beam can be branched or collimated by an optical element in which a part of the Fresnel lens obtained by cutting the Fresnel lens is combined as a condensing element.

In the wavelength monitor according to the next invention, in the invention according to the twelfth aspect, the light-collecting element is a microlens, and the optical element forms the first surface by the microlens. It is characterized by.

According to the present invention, a light beam can be branched or parallelized by an optical element in which a microlens is combined as a condensing element.

[0047]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the wavelength monitor according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited by the embodiment.

Embodiment 1 First, the wavelength monitor according to the first embodiment will be described. The wavelength monitor according to the first embodiment is an optical element having both a function of collimating a beam by a conventional collimator lens and a function of branching a beam by a wedge plate, and a GRIN (g
characterized by using a rod lens (raded refractive index).

FIG. 1 is a diagram showing a main part of the wavelength monitor according to the first embodiment. In the wavelength monitor shown in FIG.
A beam emitted from an optical fiber fixed by a ferrule or the like is incident on one end face of the IN rod lens 10, and is split into two beams 2a and 2b having different angles at the other end face. The split beams 2a and 2b pass through the band-pass filter 3 and are received by the light receiving elements 4a and 4b.

FIG. 2 shows the GRIN rod lens 1 described above.
FIG. 9 is a view showing the other end face of the zero. As shown in FIG.
GRI used in wavelength monitor according to the first embodiment
In a state where the N rod lens 10 has a circular end face obtained by being cut perpendicularly to the long axis direction of the rod ((a) in the figure), the semicircular portion is given a predetermined angle with respect to the end face described above. By performing the polishing process obliquely according to the angle (FIG. 13B), the rod has a surface 11b perpendicular to the long axis direction of the rod and a surface 11a processed obliquely.

FIG. 3 is an explanatory diagram showing how light propagates in the GRIN rod lens 10. As shown in FIG. First, the optical signal to be monitored emitted from the optical fiber is
The light is incident so that its optical axis is aligned with the central axis of the GRIN rod lens 10. As shown in FIG. 3, the GRIN rod lens 10 is a lens having a characteristic that the refractive index decreases as the distance from the center increases, so that light incident on the GRIN rod lens 10 propagates in a sine wave shape.

The light that has propagated inside the GRIN rod lens 10 is applied to a surface 1 perpendicular to the longitudinal direction of the rod.
1b, a beam 2b is emitted perpendicularly to the surface 11b and is polished obliquely.
Is emitted obliquely to the surface 11a as a beam 2a.

In particular, as shown in FIG. 3, the surface 11a is polished so that its surface coincides with the peak of the sine wave indicated by the propagating light, so that a parallel beam can be emitted. With this parallel beam, it becomes possible to improve the filtering accuracy of the band-pass filter 3 provided at the subsequent stage.

As shown in FIG. 2, a semicircular portion of the end surface of the GRIN rod lens 10 is polished to
1b, and a GRIN is formed on the boundary between these two surfaces.
Since the optical axis of the light propagating inside the rod lens 10 is located, the beams 2a and 2b branched by the surfaces 11a and 11b have almost half the light intensity of the beam incident on the GRIN rod lens 10, and The light is emitted at different angles.

Therefore, by using the GRIN rod lens 10 shown in FIG.
an angle inclined toward the surface 11b with respect to a vertical line of the beam 2a, that is, a beam 2a emitted upward in the drawing;
and 2b emitted along the vertical line of b can be branched into parallel beams. That is,
The GRIN rod lens 10 functions as an optical element having both a beam collimating function and a beam splitting function.

The beam 2a split in this way
As shown in FIG. 1, after spatially propagating, the light passes through the band-pass filter 3 and reaches the light receiving element 4a, where the beam 2b
Also passes through the band-pass filter 3 and
To reach.

FIG. 4 is a diagram showing the transmission characteristics of the band-pass filter 3 with respect to the wavelength. In particular, it is shown that the characteristics are different depending on the angle of the beam incident on the band-pass filter 3. That is, the bandpass filter 3 has a feature that the transmission center wavelength shifts depending on the incident angle.

More specifically, as shown in FIG. 4, the bandpass filter 3
The wavelength at which the transmitted light power peaks, that is, based on the transmission center wavelength, has a characteristic that the transmitted light power decreases as the wavelength becomes longer and shorter, and further has such a characteristic for each incident angle. I have.

As a filter having this feature, for example, there is a Fabry-Perot etalon. The Fabry-Perot etalon is one in which two glass plates each having a reflecting surface on both sides are fixed at fixed intervals by invar or quartz.

In particular, in the band-pass filter 3,
As described above, the branched beams 2a and 2a are provided by the beam collimating function of the GRIN rod lens 10.
Since b is incident as a parallel beam, the wavelength transmission characteristics are improved. FIG. 5 is an explanatory diagram for describing incidence of a parallel beam and a beam that is not parallel to the bandpass filter.

Since the beam has a certain width,
As shown in FIG. 5A, in the case of a non-parallel beam, that is, a beam having a spread in the traveling direction, angles incident on the band-pass filter 3 at both ends that determine the width of the beam are different (θ). ₁ ≠ θ ₂ ). For this reason, the bandpass filter 3 having different wavelength transmission characteristics depending on the incident angle functions as a filter in which such a beam has a wider transmission band and loses the sharpness of the cutoff characteristics.

On the other hand, as shown in FIG. 5B, in the case of a parallel beam, the angles of incidence on the band-pass filter 3 at both ends of the beam are equal (θ ₁ = θ ₂ ).
The band-pass filter 3 functions as a filter showing a steep cutoff characteristic without widening the transmission band.

The beams 2a and 2b split by the GRIN rod lens 10 are, as described above, only split into almost half the light intensity, so that the spectral intensities of the respective spectral components are also equal. FIG. 6 is an explanatory diagram for explaining detection of a wavelength shift by the bandpass filter 3. In FIG. 6, the wavelength of the optical signal to be transmitted, that is, the wavelength of the optical signal to be monitored is λ, the band-pass filter 3 functions as a filter 9a showing a wavelength transmission characteristic with respect to the incident angle of the beam 2a, and The transmission light power-wavelength characteristic when functioning as the filter 9b showing the wavelength transmission characteristic with respect to the incident angle of the beam 2b is shown.

In particular, the above-mentioned λ corresponds to these filters 9a
In the wavelength transmission characteristics shown by 9 and 9b, it is necessary to select as the only wavelengths whose transmitted light powers match each other. In other words, the incident angles of the two beams 2a and 2b to the bandpass filter 3 are adjusted such that the intersection of the two wavelength transmission characteristic graphs as shown in FIG. 6 is located on the wavelength λ. This means adjusting the installation position of the bandpass filter 3 or adjusting the inclination angle of the surface 11a of the GRIN rod lens 10 to be polished.

Therefore, in the state where λ is maintained without changing the wavelength to be monitored, as shown in FIG.
The transmitted light powers of the two beams 2a and 2b passing through the bandpass filter 3 are both equal to _Pst . Therefore, the light receiving element 4 for receiving these beams 2a and 2b
There is no difference in the received light power between a and 4b.

On the other hand, in a state where a diode laser or the like, which is a light source of a signal to be monitored, is oscillated at a wavelength λ ′ deviated from the wavelength λ due to the influence of temperature or the like, as shown in FIG. 9a is transmitted through the bandpass filter 3 with a transmission light power P _b on the wavelength transmission characteristic graph of the beam 2b is transmitted through the bandpass filter 3 with a transmission light power P _a of the wavelength transmission characteristic graph of the filter 9b. Therefore, the light receiving elements 4a and 4b that receive these beams 2a and 2b have different light receiving powers.

The difference in light receiving power between the light receiving elements 4a and 4b is detected by a wavelength monitoring circuit. FIG. 7 is a diagram illustrating a wavelength monitoring circuit used in the wavelength monitor according to the first embodiment.
The wavelength monitoring circuit shown in FIG. 7 includes a differential amplifier 13 and has a positive-phase input terminal and a negative-phase input terminal, each of which operates with a reverse bias voltage.
2a and 12b are connected.

The photodiodes 12a and 12b
Correspond to the light receiving elements 4a and 4b, respectively. The beam 2a passing through the bandpass filter 3 is received by the photodiode 12a, and the beam 2b is received by the photodiode 12b.

In FIG. 7, when each of the photodiodes 12a and 12b receives the above-described beam, a current flows to change the potential of the anode. Then, the potentials of the two photodiodes are input to the differential amplifier 13, and when the wavelength of each of the beams fluctuates, the amount of deviation from the predetermined wavelength λ at that wavelength is determined by the input potential difference, that is, the differential amplifier 13 Can be obtained as output.

The two photodiodes 12a and 12b used in the above-described wavelength monitoring circuit are preferably formed on a common semiconductor substrate or housed in an integrated package. As a result, the influence of disturbance such as a temperature change becomes the same, and there is no variation in characteristics between elements, and the accuracy of wavelength monitoring can be improved.

Next, installation of the bandpass filter 3 shown in FIG. 1 in the wavelength monitor according to the first embodiment will be described. FIG. 8 is an explanatory diagram for explaining the installation of the bandpass filter 3. The light splitting element 15 in the figure corresponds to the GRIN rod lens 10. As described above, the transmission characteristics of the band-pass filter 3 change depending on the incident angle. Therefore, the two beams 2a and 2b split by the light splitting element 15 enter the band-pass filter 3 at different angles. Is required.

FIG. 8 shows a state in which the band-pass filter 3 is arranged so that the angles of incidence of the two beams 2a and 2b are not perpendicular. This is because, when the beam is made perpendicular to the band-pass filter 3, the reflected light re-enters the light splitting element 15 and returns to the laser diode or the like as the light source, causing malfunction of the light source and monitoring. This is because accuracy is reduced. Therefore, as shown in FIG. 8, the monitoring accuracy can be improved by arranging the bandpass filter 3 so that the angle of the incident beam does not become vertical.

As shown in FIG. 1, the wavelength monitor according to the first embodiment uses a GRIN rod lens 10, which is one optical element, to split and collimate a beam. The wavelength monitor can be incorporated in a laser module that is a light source unit.

In this case, the output of the differential amplifier 13 constituting the wavelength monitoring circuit is fed back as a laser control signal, whereby the wavelength of the light to be monitored can be stabilized. For example, since the oscillation wavelength of a laser diode as a light source depends on temperature, a temperature control circuit including a Peltier element is provided in a laser module, and the output of the wavelength monitoring circuit is input to the temperature control circuit. This makes it possible to correct the oscillation wavelength of the laser diode to the wavelength to be oscillated based on the wavelength shift detected by the wavelength monitoring circuit.

As described above, according to the wavelength monitor according to the first embodiment, the GRIN rod lens 10 in which a part of the end face is polished obliquely, the wavelength transmission characteristic that differs depending on the incident angle, and the GRIN rod lens 1
A band-pass filter 3 for inputting two beams 2a and 2b branched by 0, and a band-pass filter 3
And two light receiving elements 4a and 4b for respectively receiving the two beams 2a and 2b that have passed through the lens, so that a collimator lens for collimating the beams and a wedge plate for splitting are conventionally provided. A single optical element can be realized by the GRIN rod lens 10, and reflection is used to split a beam as in the case of using a conventional wedge plate, and a space in a direction perpendicular to the beam direction to be monitored is secured. It is not necessary to perform the operation, and the device configuration can be simplified and reduced in size.

The bandpass filter 3 having different wavelength transmission characteristics depending on the angle of incidence is provided with two beams 2a and 2b split by the GRIN rod lens 10.
Are installed at positions where they are incident at different angles other than perpendicular, it is possible to prevent malfunction of the light source due to reflected light generated when the light is incident perpendicularly, and it is possible to further improve monitoring accuracy.

Further, there is provided a differential amplifier 13 for inputting respective light receiving powers of two light receiving elements 4a and 4b for respectively receiving the two beams 2a and 2b transmitted through the band pass filter 3, and the output of the differential amplifier 13 is provided. Is detected as a deviation from the wavelength to be oscillated by a light source such as a laser diode, and a signal indicating this deviation is fed back as a signal for controlling the oscillation wavelength of the laser diode, thereby correcting the wavelength of the optical signal. Becomes possible.

The GRIN rod lens 10 shown in the first embodiment is obtained by processing a part of the laser beam emission surface obliquely. By processing diagonally,
Beam splitting and collimation can be realized at the exit surface.

Embodiment 2 Next, a wavelength monitor according to the second embodiment will be described. The wavelength monitor according to the second embodiment is different from the wavelength monitor according to the first embodiment in that a Fresnel lens created by special processing is used instead of the GRIN rod lens 10 described in the first embodiment. Are the same, and the description thereof is omitted here.

FIG. 9 is a diagram showing a main part of a wavelength monitor according to the second embodiment. The wavelength monitor shown in FIG. 9 is different from the GRIN rod lens 10 used in the first embodiment in that
An integrated Fresnel lens 20 having two light-collecting regions with one lens is used. That is, the beam emitted from the optical fiber or the like enters the integrated Fresnel lens 20, and is split into two parallel beams by the integrated Fresnel lens 20.

As described in the first embodiment, the two split beams are input to bandpass filter 3 having different wavelength transmission characteristics depending on the incident angle, and received by light receiving elements 4a and 4b, respectively.

FIG. 10 is a plan view for explaining an integrated Fresnel lens used in the wavelength monitor according to the second embodiment. The integrated Fresnel lens 20 described above
Is formed by cutting out a part of surfaces 21a and 21b surrounded by a dotted line of a normal Fresnel lens shown in FIG. 10 (a), and bonding the cut surfaces to each other as shown in FIG. 10 (b). At this time, the shape of the laminated lens is elliptical.

As shown in FIG. 9, the beam emitted from the optical fiber is incident on the integrated Fresnel lens 20 as a beam spread radially. Here, in the normal Fresnel lens shown in FIG. 10A, the beam incident on the surface 21a is directed toward the central axis of the lens (to the right in the drawing) and the surface 21a.
b is also designed to travel toward the center of the lens (to the left in the drawing) and efficiently converge the transmitted beam with an extremely short focal length.

Therefore, in the ordinary Fresnel lens designed as described above, the outer portions (surfaces 21a and 21a)
Extracting only 1b) means extracting the beam refraction function in the direction determined by each lens surface, and in particular, the refraction angle is due to the lens surface located outside in FIG. From steep.

FIG. 11 is a sectional view for explaining the function of the integrated Fresnel lens 20 used for the wavelength monitor according to the second embodiment. As described above, the integrated Fresnel lens 20 formed by bonding two lenses having a steep refraction angle functions as a lens having two focal points with one lens. This means that the integrated Fresnel lens 20 functions as a lens that splits the incident beam.

Therefore, as shown in FIG. 11, when the beam is incident on the integrated Fresnel lens 20 such that the center thereof coincides with the center of the lens, the beam incident on the surface 21a moves rightward in the drawing. , The beam incident on the surface 21b advances to the lower right in the drawing, and is split into two beams.

The two beams 2a and 2b branched by the integrated Fresnel lens 20 are incident on the band-pass filter 3, and the wavelength shift is detected as in the first embodiment.

As described above, according to the wavelength monitor according to the second embodiment, the GRIN shown in the first embodiment is used.
Since the integrated Fresnel lens 20 processed so as to have two focal points is used instead of the rod lens 10, beam collimation and branching can be realized by one optical element as in the first embodiment. Therefore, it is possible to simplify the component configuration and reduce the size of the device.

Embodiment 3 Next, a wavelength monitor according to the third embodiment will be described. The wavelength monitor according to the third embodiment differs from the wavelength monitor according to the first embodiment in that an integrated microlens in which two or more microlenses are incorporated in one package is used instead of the GRIN rod lens 10 described in the first embodiment. The other components and their functional operations are the same, and a description thereof will be omitted here.

FIG. 12 is a diagram showing a main part of a wavelength monitor according to the third embodiment. The wavelength monitor shown in FIG. 12 uses an integrated microlens 30 in which two microlenses 31a and 31b are incorporated in one package, instead of the GRIN rod lens 10 used in the first embodiment. That is, the beam emitted from the optical fiber or the like enters the integrated microlens 30 and is split into two parallel beams by the integrated microlens 30.

The integrated microlens 30 has a size equal to or smaller than the spread width of the incident beam. As shown in FIG. 12, the beam entering the lens 31a and the beam entering the lens 31b exit at different exit angles. Further, the beam that has spread radially is incident on these lenses, so that the transmitted beam is collimated.

The two beams 2a and 2b branched by the integrated microlens 30 are incident on the band-pass filter 3, and the wavelength shift is detected as in the first embodiment.

As described above, according to the wavelength monitor according to the third embodiment, GRIN shown in the first embodiment is used.
Instead of the rod lens 10, two micro lenses 31
Since the integrated microlens 30 in which a and 31b are incorporated in one package is used, parallelization and splitting of the beam can be realized by one optical element as in the first embodiment. And the size of the device can be reduced.

In the wavelength monitors described in the first to third embodiments, the band-pass filter 3 is used as the filter having the incident angle dependency. Instead, the band-pass filter 3 has the same wavelength transmission characteristic. Other optical wavelength filters may be used.

[0095]

As described above, according to the present invention, a light beam can be split into two transmitted light beams as transmitted light instead of reflected light by the above-described optical element. Deviates from the predetermined wavelength, the first and second optical elements are branched by the optical element.
When the transmitted light beams pass through the above-described band-pass filter, the transmitted light power can be different from each other, and the transmitted light power can be changed to the first and second transmitted light beams.
It is necessary to use reflection to split a beam as in the conventional wavelength monitor and to secure a space in a direction perpendicular to the beam direction to be monitored, as in a conventional wavelength monitor. This has the effect of simplifying and reducing the size of the device.

According to the next invention, the first and second split transmitted light beams can be made to enter the above-mentioned bandpass filter as parallel beams, so that the incident angle dependency of the bandpass filter can be reduced. The difference between the transmitted light powers of the first and second transmitted light beams transmitted through the band-pass filter can be processed as a large signal, and highly reliable wavelength monitoring can be performed. It has the effect of becoming.

According to the next invention, the wavelength transmission characteristics that differ according to the incident angle of the band-pass filter increase and decrease in the first and second transmitted light beams in directions opposite to each other with respect to the direction of deviation from the predetermined wavelength. When the light beam deviates from a predetermined wavelength,
The difference in transmitted light power can be obtained as a large signal, and there is an effect that highly reliable wavelength monitoring becomes possible.

According to the next invention, the wavelength transmission characteristics different according to the incident angle of the band-pass filter increase and decrease in the first and second transmitted light beams in directions opposite to each other with respect to the direction of deviation from the predetermined wavelength. When the light beam deviates from a predetermined wavelength,
The difference in transmitted light power can be obtained as a large signal, and there is an effect that highly reliable wavelength monitoring becomes possible.

According to the next invention, since the first and second light receiving elements are formed on a common semiconductor substrate or are housed in an integrated package, these first and second light receiving elements are provided. In this case, it is possible to cancel the output change caused by the dark current and the difference in the element characteristics at the time of manufacture, and it is possible to perform the wavelength monitoring with high reliability.

According to the next invention, since the band-pass filter is arranged at a position not perpendicular to the first and second transmitted light beams, the first or second transmitted light beam is reflected. Thus, the return light of the light beam to the light source side generated by the above operation can be reduced, and the monitoring accuracy can be further improved.

According to the next invention, there is an effect that a Fabry-Perot etalon can be used as a band-pass filter having different wavelength transmission characteristics according to the incident angle.

According to the next invention, since it can be introduced into an optical fiber transmission system, it is possible to monitor the wavelength of an optical signal propagating in an optical fiber.

According to the next invention, since the size is reduced as described above, it is possible to obtain a small laser module capable of monitoring the oscillation state of the laser.

According to the next invention, the oscillation wavelength of the laser that oscillates the light beam is adjusted according to the output of the first and second light receiving elements, for example, by controlling a Peltier element provided in the laser. Therefore, there is an effect that the oscillation wavelength can be always stabilized.

According to the next invention, as the optical element for branching or collimating the light beam, a GRIN rod lens in which a part of the second surface is polished obliquely is used, thereby branching or collimating the light beam. Is achieved.

According to the next invention, a GRIN rod lens in which a part of the first surface is polished obliquely is used as an optical element for branching or collimating a light beam, thereby branching or collimating the light beam. Is achieved.

According to the next invention, there is an effect that a light beam can be branched or parallelized by an optical element composed of at least two light-collecting elements.

According to the next invention, an optical element in which a part of the Fresnel lens obtained by cutting the Fresnel lens is combined as a condensing element can branch or collimate the light beam. Play.

According to the next invention, there is an effect that a light beam can be branched or parallelized by an optical element in which a microlens is combined as a condensing element.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of a wavelength monitor according to a first embodiment.

FIG. 2 shows a GR used for the wavelength monitor according to the first embodiment.
FIG. 3 is a diagram showing an end surface of an IN rod lens.

FIG. 3 is a diagram illustrating a wavelength monitor according to the first embodiment;
FIG. 4 is an explanatory diagram showing a state of light propagation in a RIN rod lens.

FIG. 4 is a diagram showing transmission characteristics with respect to wavelength of a band-pass filter in the wavelength monitor according to the first embodiment.

FIG. 5 is an explanatory diagram for describing incidence of a parallel beam and a beam that is not parallel to a bandpass filter.

FIG. 6 is an explanatory diagram for explaining detection of wavelength shift by a bandpass filter in the wavelength monitor according to the first embodiment.

FIG. 7 is a diagram illustrating a wavelength monitoring circuit used for the wavelength monitor according to the first embodiment;

FIG. 8 is an explanatory diagram for explaining installation of a bandpass filter 3 used for the wavelength monitor according to the first embodiment.

FIG. 9 is a diagram showing a main part of a wavelength monitor according to a second embodiment.

FIG. 10 is a plan view illustrating an integrated Fresnel lens used for a wavelength monitor according to a second embodiment.

FIG. 11 is a cross-sectional view for explaining a function of an integrated Fresnel lens used for the wavelength monitor according to the second embodiment.

FIG. 12 is a diagram showing a main part of a wavelength monitor according to a third embodiment.

FIG. 13 is a diagram showing a configuration of a conventional wavelength monitor.

[Explanation of symbols]

2a, 2b beams, 3 bandpass filters, 4a,
4b light receiving element, 10GRIN rod lens, 12a,
12b photodiode, 13 differential amplifier, 15
Light splitting element, 20 integrated Fresnel lens, 30 integrated micro lens, 31a, 31b micro lens

Continued on front page F term (reference) 2G020 BA20 CA12 CB06 CB23 CC23 CC26 CD03 CD13 CD24 5F072 AB13 JJ05 KK30 TT05 TT22 TT27 YY15 5K002 BA05 BA13 CA05 DA02 FA01

Claims (15)

[Claims] A first surface on which a light beam is incident; and a second surface for emitting first and second transmitted light beams traveling in different directions from each other. An optical element for splitting into two transmitted light beams, and having different wavelength transmission characteristics according to an incident angle;
And a light wavelength filter that passes the second transmitted light beam, and first and second light receiving elements that respectively receive the first and second transmitted light beams that have passed through the light wavelength filter. A wavelength monitor characterized by the following. 2. The wavelength monitor according to claim 1, wherein the optical element emits the first and second transmitted light beams as parallel beams. 3. The optical wavelength filter according to claim 1, wherein, for the incidence of the first transmitted light beam, a wavelength whose transmittance decreases as the wavelength of the first transmitted light beam becomes longer than a predetermined wavelength. Exhibiting transmission characteristics, and exhibiting a wavelength transmission characteristic in which, for the incidence of the second transmitted light beam, the transmittance increases as the wavelength of the second transmitted light beam increases with respect to the predetermined wavelength. 3. The method according to claim 1, wherein
The wavelength monitor according to 1. 4. The wavelength monitor according to claim 1, further comprising a differential amplifier for comparing outputs of said first and second light receiving elements. 5. The light receiving device according to claim 1, wherein the first and second light receiving elements are formed on a common semiconductor substrate or are housed in an integrated package. The wavelength monitor according to 1. 6. The apparatus according to claim 1, wherein the optical wavelength filter is arranged at a position that is not perpendicular to the first and second transmitted light beams. Wavelength monitor. 7. The wavelength monitor according to claim 1, wherein said optical wavelength filter is a Fabry-Perot etalon constituted by two reflection surfaces. 8. The wavelength monitor according to claim 1, wherein an optical signal introduced into an optical fiber transmission system and propagated through the optical fiber is incident as the light beam. 9. The wavelength monitor according to claim 1, wherein the wavelength monitor is provided in a laser module for oscillating the light beam. 10. The apparatus according to claim 1, wherein an oscillation wavelength of a laser that oscillates the light beam is controlled according to outputs of the first and second light receiving elements. Wavelength monitor. 11. The optical element according to claim 1, wherein a part of the second surface is obliquely polished to a GRIN (graded ref).
a first exit surface, and the other portion as a second exit surface, the first transmitted light beam exits from the first exit surface, and the second transmitted light beam. The wavelength monitor according to any one of claims 1 to 10, wherein the wavelength is emitted from the second emission surface. 12. The optical element is a GRIN rod lens in which a part of the first surface is obliquely polished, and a light beam incident on the part and emitted from the second surface is transmitted by the first transmitted light. The wavelength monitor according to any one of claims 1 to 10, wherein the light beam is a beam, and a light beam that is incident on another portion and emitted from the second surface is the second transmitted light beam. 13. The optical element according to claim 1, wherein the optical element comprises at least two light-collecting elements.
The wavelength monitor according to any one of the above. 14. The light-collecting element is a part of the Fresnel lens obtained by cutting a Fresnel lens, and the optical element is formed by laminating cut surfaces of the part. The wavelength monitor according to claim 13. 15. The light-collecting element is a micro lens, and the optical element is the first lens by the micro lens.
14. The wavelength monitor according to claim 13, wherein a surface is formed.