JP2008166577A - Laser module with wavelength monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser module with a wavelength monitor having a compact wavelength monitor that can be housed in an LD module of a coaxial package (CAN package). <P>SOLUTION: The laser module with the wavelength monitor includes a laser diode, and a light receiving element for detecting the light emitted by the laser diode by means of a light output according to the wavelength of the light, wherein a light transmission plate is disposed that is provided with a reflection lattice on a light receiving side of the light receiving element. The light transmission plate is configured to guide the light reflected from the reflection lattice to focus onto the light receiving element, while causing the light reflected from the reflection lattice to reflect off at least one of the upper and lower surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor laser module used for an optical transmitter, and more particularly, to a laser module including a wavelength monitor for a transmitter / receiver used in a wavelength division multiplexing (WDM) optical communication network system.

In the WDM system, the optical transmission unit in the optical transceiver needs to control the emission wavelength to a predetermined constant value. The control is roughly divided into
(1) A method of investigating temperature / current dependency of the wavelength of an LD (laser diode) in advance and performing temperature / current control so as to obtain a required wavelength;
(2) A method of measuring the emission wavelength of the LD and applying feedback to the temperature and current of the LD, or applying feedback to the wavelength control terminal if the LD has a wavelength control terminal.
There are two methods. The present invention relates to the latter.

There are various prior arts of the control method as described above. Typical examples are as follows.
For example, the output light of the LD is extracted by an optical branching device provided on the optical fiber cable, the output light wavelength of the extracted LD is detected by a wavelength monitor, the detected wavelength is compared with a reference value, and the comparison result is compared with the temperature of the LD. There is a control method that feeds back for control. Note that the specific configuration of the wavelength monitor used here is not specified (see Patent Document 1).

Further, the carrier beam from the LD is branched by a device having an optical coupler function, and a monitoring beam is output, and the wavelength of this beam is fed back for temperature control of the LD via a wavelength monitor using a wedge etalon. There is a control method. The wavelength monitor used here operates by the difference in intensity between two lights passing through different paths of a wedge-shaped etalon (see Patent Document 2).
Furthermore, the back light output of the light emitting element is bifurcated by a rear half mirror through a parallel lens, one is a path via an etalon, the other is a direct path, and the wavelength is detected and detected by the path difference There is a control method for controlling the temperature of the light emitting element based on the wavelength. At this time, the temperature of the LD and the wavelength monitor is individually controlled (see Patent Document 3).
JP 2000-164977 A JP-A-11-122176 JP 2002-043686 A

  Both of these methods divide the output light of the LD by reflection or branching, pass it through a device whose transmission or direction of transmitted light depends on the wavelength (eg etalon), and then change the optical power at the PD (photodiode) It is something to monitor. In principle, the wavelength can be monitored with high accuracy, but the number of parts is large and the connection work is difficult, so that there is a drawback that it is difficult to reduce the cost and size.

That is, the above-mentioned prior patent documents 1 to 3
(1) A type that monitors the wavelength of light output from a laser diode (LD) module outside the LD module;
(2) A type that stores a laser module and wavelength monitor in a package,
However, all of them have a large number of parts, making it difficult to reduce the cost and size.
Furthermore, although it can be made smaller than the former, it cannot be made as small as an LD module using a coaxial package (CAN package) that has become mainstream in non-WDM communication.

  In view of the above problems, an object of the present invention is to provide a laser module with a wavelength monitor including a small wavelength monitor that can be accommodated in an LD module of a coaxial package (CAN package).

  A laser module with a wavelength monitor according to the present invention is a laser module with a wavelength monitor including a laser diode and a light receiving element that detects light emitted from the laser diode with an optical output corresponding to the wavelength of the light. A light transmission plate provided with a reflection grating is arranged on the light receiving side, and the light transmission plate guides the light reflected by the reflection grating to be condensed on the light receiving element while reflecting at least one of the upper surface and the lower surface. It is configured as follows.

  Further, the reflection grating is provided on the surface of the light transmission plate main body layer having a wavy groove portion on the surface, and on the wavy groove portion with a uniform film thickness made of a transparent member having a refractive index different from that of the light transmission plate main body. The intermediate layer includes an intermediate layer and an upper surface layer having substantially the same refractive index as that of the light transmission plate body. Further, the light transmission plate body is configured as a photoconductive element, the element is bias-driven, and a current flowing through the element is output to the monitoring terminal. Further, the intermediate layer is configured such that the thickness of the intermediate layer is changed in a gradient shape so that the direction of the reflected light changes depending on the wavelength. Further, the periphery of the light transmission plate is joined to the submount so that the central portion is separated from the submount.

According to the laser module with a wavelength monitor of the present invention, optically the light reflected by the reflection grating is totally reflected by the light transmission plate body a plurality of times and transmitted, so that the intermediate layer of the etalon and the output detection PD Can be made substantially longer, and the effect of changing the direction of light depending on the wavelength using the etalon intermediate layer can be made more effective.
In addition, physically, since the light transmission plate body totally reflects the light a plurality of times, the distance can be shortened as compared with the case where the light transmission plate body extends straight. As a result, a laser module with a wavelength monitor having a small wavelength monitor that can be housed in an LD module of a coaxial package (CAN package) can be configured.

(Example 1)
FIG. 1 is a diagram for explaining the outline of Embodiment 1 of the present invention.
As shown in FIG. 1, a laser module with a wavelength monitor 1 of the present invention includes a stem base 3 and a submount 4 constituting a stem 2 serving as a base portion, and a plurality of inserted and held by the stem base 3 and the submount 4. Lead pin 5 and a monitor circuit connected to the lead pin 5. The stem base 3 has a large-diameter flange portion 3a and a small-diameter pedestal portion 3b that are continuously provided.

  The submount 4 is formed such that its end surface does not protrude from the end surface of the pedestal portion 3b, and includes a wall portion 4a that forms an axial surface, an upper end portion 4b that is formed perpendicular to the axial direction, and an upper end portion 4b. And an inclined portion 4c provided at the other end. A heat sink 7 on which a laser diode (LD) 6 is mounted is provided on the wall 4a. A wavelength monitor 8 serving as the center of the monitor circuit is provided on the upper end 4b. A light receiving element for power monitoring (for example, a photodiode, hereinafter referred to as mPD) is provided on the inclined portion 4c. A light receiving element for wavelength monitoring (for example, a photodiode, λPD) is provided on the back surface (not shown) of the wavelength monitor.

The wavelength monitor 8 is attached to the upper end 4b of the submount 4 so that only the surrounding U-shaped portion is fixed as will be described later. The heat sink 7 mounts the LD 6 and is fixed to the wall 4 a of the submount 4, and aligns the substantially central portions of the mPD 9 and the wavelength monitor 8 on the optical axis of the LD 6.
With the LD 6, mPD 9 and wavelength monitor 8 aligned on the submount 4, the submount 4 is mounted on the stem base 3.

  Further, since the inclined portion 4c of the submount 4 is formed so as to rise from the surface of the wall portion 4a, the structure is opposed to the wavelength monitor 8 provided in a state of being raised substantially perpendicular to the wall portion 4a. Thus, it becomes easy to form the optical axis. The stem base 3 includes a large-diameter flange portion 3a and a base portion 3b having a smaller diameter than the flange portion 3a. The submount 4 has an end surface having a smaller area than the end surface of the pedestal portion 3b, and is configured such that an optical axis is formed on the inclined portion 4c projecting on the wall portion 4a side, and the heat sink 7 is provided on the wall portion 4a. The configuration is such that the optical axis of the wavelength monitor 8 can be formed on the upper end 4b.

  As shown in FIG. 1, the wavelength monitor 8 is mounted on the upper end 4 b of the submount 4. All the output light from the LD 6 is guided through the wavelength monitor 8 in the direction of a lens system / fiber (not shown). The wavelength monitor 8 taps a part of the transmitted light and measures the wavelength. In FIG. 1, all the front output light of the LD 6 is transmitted through the wavelength monitor 8. However, if the output light wavelength of the LD 6 can be measured by the output of the wavelength monitor 8, an arbitrary amount of light, for example, about half of the output light is transmitted. You may do it.

The lead pin 5 is provided in a region portion that does not contact the submount 4 of the pedestal 3b, and is wired to the LD 6, the wavelength monitor 8, and the mPD 9 provided on the wall 4a side of the submount 4.
On the flange portion 3a of the stem base 3, a cap (not shown) provided with a lens so as to accommodate the submount 4 provided with the wavelength monitor 8 and the like is attached in a sealed state.

FIG. 2 is a diagram for explaining an LD wavelength monitor circuit according to the present invention.
The wavelength monitor circuit 10 in FIG. 2 is incorporated in the laser module with wavelength monitor 1 in FIG. 1, and the terminals 10a to 10e of the wavelength monitor circuit 10 become the lead pin 5 and the stem (GND). The LD6 cathode is connected to the LD6 cathode terminal 10a of the wavelength monitor circuit 10, the LD6 wavelength control terminal is similarly connected to the wavelength control terminal 10b, and the LD6 anode is connected to the stem (GND) terminal 10c and the reversely connected mPD9. To the power monitor terminal 10d.

The mPD 9 detects the light of the LD 6 and outputs it to the power monitor terminal 10d. The anode terminal of the LD 6 outputs to the wavelength monitor terminal 10e via λPD11. The light from the LD 6 is input to the λPD 11 through the light transmission plate 12.
Here, the LD 6 is a DBR-LD (Distributed Bragg Reflector laser diode) having a terminal for controlling optical power (LD cathode) and a terminal for controlling wavelength. The mPD 9 measures the output power of the LD 6, and the wavelength monitor 8 is constituted by the light transmission plate 12 and λPD 11 to measure the wavelength.

  Since the optical power incident on λPD11 has wavelength dependence, the wavelength can be determined from the ratio of the wavelength monitor output to the mPD output. If the wavelength and optical power thus obtained are fed back to the two terminals (LD cathode 10a and wavelength control terminal 10b) of the LD 6, the optical wavelength of the LD module is stabilized. Feedback control is performed by a control circuit (not shown) connected to each terminal of the wavelength monitor circuit 10.

FIG. 3 is a diagram showing a mounted state of the wavelength monitor of the present invention. 3A is a cross-sectional view taken along the line AA in FIG. 3B, FIG. 3B is a front view of the state where the light transmission plate is attached to the submount, and FIG. 3C is B in FIG. It is -B sectional drawing.
As shown in FIG. 3, a part of the submount 4 has a recess 4d, and the light transmission plate 12 is die-bonded in a U-shape so as to cover the recess 4d. The die bonding method may be an adhesive or AuSn solder.

  The light transmission plate 12 is thus slightly lifted from the submount 4 via the recess 4d, thereby enabling wave guide by total reflection described later. Thus, since the light transmission plate 12 is die-bonded to the submount 4 so as to cover the recess 4d, the light reflected by the reflection grating can be totally reflected to the λPD 11 and transmitted, and the captured light is lost. It can be used effectively without any problems.

  FIG. 4 is a diagram showing an example of the wavelength monitor of the present invention. As shown in FIG. 4, the light transmission plate 12 has a configuration in which a reflection grating 13 is formed in part, and λPD 11 is mounted at a place where the reflected light from the reflection grating 13 is focused. The “+” mark in the figure represents the optical axis of the LD. Any number of reflection gratings 13 can be formed. In FIG. 4, five reflection gratings 13 are provided so that light necessary for measurement enters λPD as a whole. As shown in FIG. 4, the reflection grating 13 has a substantially arcuate curved shape as seen in a plan view, but may be, for example, a combination of straight lines that approximate the curve.

  FIG. 5 is a view for explaining an example of the light transmission plate of the present invention. As shown in FIG. 5, a reflection grating is formed on one surface of a light transmission plate main body serving as a total reflection type parallel planar light guide in a region where incident light is transmitted. The reflection grating 13 includes a light transmission plate body 12a having a wavy groove 12b formed on the surface thereof, and a glass formed on the surface of the wavy groove 12b with a uniform film thickness having a different refractive index than the light transmission plate body 12a. A thin film layer (intermediate layer) 12c and a surface film layer (upper surface layer) 12d having a refractive index substantially the same (or the same) as that of the light transmitting plate body 12a are provided on the glass thin film layer 12c.

  The laminated structure of the light transmission plate main body 12a in which these wave-like grooves 12b are formed, the glass thin film layer 12c provided in the wave-like grooves 12b, and the surface film layer 12d provided on the glass thin film layer 12c has a built-in reflection grating. 13 constitutes a part of the light transmission plate 12. The glass thin film layer 12c may be formed of a multilayer film. Finally, since the surface of the surface film layer 12d and the back surface of the light transmission plate body 12a are parallel, the trajectory of the light beam emitted from the LD is hardly affected by the light transmission plate.

About several to 20% of light from the LD 6 is reflected by the glass thin film 12c layer depending on the wavelength. The reflected light is guided through the light transmission plate 12a body to λPD11 by total reflection by the surface 12e of the light transmission plate body 12a.
The inclination of the glass thin film layer 12c in the reflection grating 13 with respect to the incident optical axis of the LD 6 is the total reflection on the surface 12e of the light transmission plate body 12a after the light of the wavelength to be monitored is reflected by the reflection grating 13. Are formed so as to propagate through the light transmission plate body 12a and enter the λPD11. The inclination of the glass thin film layer 12c forming the plurality of reflection gratings 13 takes a value that increases from the side closer to λPD11 toward the side farther. The number and interval of the grooves are determined according to the output of λPD.

  In this way, the light transmission plate can be formed by a simple configuration and procedure in which a wavy groove is formed on the surface, a uniform intermediate layer thin film is formed on the groove, and an upper layer is provided thereon. . Since the upper layer can be formed of the same material as the light transmission plate layer, internal strain due to different materials can be reduced. Moreover, since the same material is used, manufacture becomes easy.

  The light transmission plate main body 12 a fixes a substantially U-shaped region other than the recess 4 d in the region facing the upper end portion 4 b of the submount 4 so as to be separated from the upper end portion 4 b of the submount 4 by a minute interval. By separating them by a minute distance in this way, it is possible to prevent the reflected light totally reflected in the light transmitting plate main body 12a from leaking into the submount 4 and passing therethrough. The arc shape of the reflection grating 13 in FIG. 4 is formed so that each reflected light is incident on the λPD 11. The light incident on the light transmission plate is reflected by the reflection grating 13 at different reflection angles depending on the wavelength. Of the reflected light, the light entering λPD11 changes periodically as shown in FIG. 6 according to the wavelength.

  FIG. 6 is a wavelength-PD output characteristic diagram of the light transmission plate of the present invention. If the emitted light of the monitored LD is light of a predetermined wavelength, the PD output having the characteristics shown in FIG. 6 can be detected. However, if the wavelength varies for some reason, the output of λPD 11 also varies accordingly. Therefore, if the output of λPD11 is detected, it is possible to measure how much the wavelength is deviated from the expected wavelength. If measurement is possible, control is performed by a method in which the measured deviation amount is fed back to the wavelength control terminal of the LD. Feedback control is performed by a control circuit (not shown).

Rather than having the maximum (or minimum) output at a predetermined wavelength, it is desirable that the predetermined wavelength comes where the output change is greatest. At this time, since the light from the LD is not parallel light, the inclination of the wavy groove on the surface of the light transmission plate main body is changed so as to be focused on λPD11. The wavy groove is partially provided on one side surface of the light transmission plate body, and the remaining portion has a total reflection parallel light guide structure.
The light transmission plate body is basically formed of an organic material such as InP, Si, glass, or plastic. When the light transmission plate body is formed of a semiconductor material, the groove may be formed by etching. If not, the groove may be formed by machining (in this case, the groove is linear). If the light transmission plate body is formed of glass or an organic material, the grooves may be formed by machining or pressing.

  FIG. 7 is a diagram for explaining the reflection grating of the present invention. The shape of each part of the reflection grating 13 is, for example, as shown in FIG. 7, when the light transmission plate body 12a has a thickness of 0.5 mm, the two sides of the wavy groove 12b of the reflection grating are from the corner of the groove. The side of the angle 20 ° from the horizontal in the counterclockwise direction, and the other side is formed by the side of the angle 60 ° from the horizontal in the clockwise direction from the corner of the groove. The 20 ° side has a length in the horizontal direction of 0.5 mm, and an interval between adjacent grooves is 0.05 mm.

  When the reflection grating 13 is set to the angle shown in FIG. 7, the incident light reflected by the waved groove 12 b of the light transmission plate body out of the light vertically incident on the light transmission plate body 12 a from below is reflected on the light transmission plate body. Hit the bottom at 50 ° from the horizontal. In this case, a material having a critical angle of 50 ° or more is required as the material of the light transmission plate body. As described with reference to FIG. 5, an intermediate layer of a glass thin film is formed on the wavy groove 12b of the light transmitting plate body 12a, and an upper layer of a surface film made of the same material as the light transmitting plate body is formed thereon. The upper surface of the upper layer is formed flush with the surface of the light transmitting plate main body not provided with the reflection grating (continuous surface).

In principle, the intermediate layer can be formed of a vapor-deposited film of a transparent material having a refractive index different from that of the lower layer of the light transmitting plate body, but attention must be paid to compatibility with the light transmitting plate body.
For the upper layer of the surface film, there is a method of applying a melted transparent member if the light transmission plate body or the glass thin film layer is heat resistant, and there is also a method of applying a transparent resin if it is not heat resistant. If it is simply performed, the lower layer of the light transmission plate body is formed of polyimide, the intermediate layer of the glass thin film is fluorinated polyimide, and the upper layer of the surface film is also polyimide. The size of the intermediate layer is about 10 μm.

  The reflective grating is not intended to cause interference. The intermediate layer is not an etalon, but a uniform layer and serves as a filter. For example, as long as the light receiving power of λPD is sufficient, the number of grooves may be one (for example, it may not be a grating). Basically, self-interference is caused in the plane of one groove. However, when the light receiving power to λPD is not sufficient, a plurality of grooves are cut into a lattice shape. Also in this case, it is not necessary to cut a groove for the entire output light beam of the LD, and only a part of the light receiving power to λPD is sufficient.

When the mounting accuracy of λPD is sufficiently high, in this case, the groove pitch is made narrower than the thickness of the light transmission plate, and the light reflected by each groove is designed to enter λPD. The reason for cutting a large number of grooves is to increase the light receiving power of λPD. The angle of the slope varies depending on the groove. The film pressure control of the light transmission plate main body and the glass thin film layer is required to have high accuracy so that the effect of interference does not disappear due to the reflected light from different grooves.
When the mounting accuracy of λPD is low, in this case, the light reflected by each groove is designed to enter a different location. Even if λPD is appropriately mounted, light from any of the grooves enters. The angle of the slope is constant for each groove. In either case, it is necessary to design so that the interference effect is not lost by the reflected light from different grooves.

  The laser module with a wavelength monitor of the present invention optically transmits the light reflected by the reflection grating by being totally reflected a plurality of times by the light transmission plate body, so that the intermediate layer of the etalon and the output detection λPD The optical path length between them can be made substantially longer, and the effect of changing the direction of light depending on the wavelength using the etalon intermediate layer can be made more effective.

  In addition, since the light transmission plate is totally reflected a plurality of times, the physical distance between the first reflection point and λPD for output detection can be shortened compared to the optical path length necessary to obtain high wavelength resolution. As a result, a laser module with a wavelength monitor having a small wavelength monitor that can be housed in an LD module of a coaxial package (CAN package) can be configured.

(Example 2)
In Example 2 of the present invention, the thickness of the glass thin film layer (the thickness in the optical axis direction of the LD) is changed in a gradient shape toward the length direction of the light transmission plate (the direction toward λPD) ( The direction of the reflected light changes depending on the wavelength by gradually increasing or decreasing the thickness). Other configurations are the same as those of the first embodiment (FIG. 5). The problem when using an etalon is the distance between λPD and the etalon (glass thin film layer).

  Since the etalon changes the direction of light depending on the wavelength, the characteristic shown in FIG. 7 cannot be obtained unless the distance between the λPD and the etalon (glass thin film layer) is taken to some extent (the difference between the maximum and minimum becomes small). ) However, in general, the size becomes a problem in order to put a wavelength monitor in a small TOSA (transmission optical device). In the second embodiment, an etalon is used, and the total reflection method of the light transmission plate of FIG. 5 is used instead of the waveguide. Since the reflected light is transmitted to λPD while being reflected by total reflection, the distance between λPD and the etalon (glass thin film) can be substantially increased.

  If the thickness of the intermediate layer is uniform, the intermediate layer functions as an etalon to change the direction of light depending on the wavelength, and therefore the distance between the intermediate layer and the output λPD must be increased to some extent. However, since the intermediate layer has a thickness that changes in a gradient state, the direction of reflected light changes depending on the wavelength in the glass thin film. For this reason, the distance between the intermediate layer and the output λPD can be shortened as compared with the case where the film thickness of the intermediate layer is uniform.

(Example 3)
In the third embodiment of the present invention, the output monitor of the LD is not performed by the mPD behind the LD (mounted on the inclined portion of the submount) but by the wavelength monitor. In this case, for example, if the light transmission plate body is made of InP for a long wavelength and a bias of about 0.2 V is applied to the light transmission plate body itself, the amount of light can be monitored by monitoring the current. In this case, InP is used as a photo-conductive element. In this case, it is possible to integrate the λPD in the light transmission plate body rather than mounting it on the light transmission plate body. In this example as well, in order to avoid reflected light from the rear, the submount inclined portion 4c, which is the location where the mPD is mounted in the first embodiment described in FIG.

  In Examples 1 and 2, the wavelength is monitored by a light transmission plate. In addition to this, an mPD that monitors the amount of light is also necessary, but in Example 3, the amount of light is also monitored by a light transmission plate. Note that λPD can be a PN type, but since it receives light from the back side, an MSM type can also be used. In this method, the mPD of FIG. 1 is not necessary, but in order to prevent the reflected light from the back of the LD, the inclined portion 4c on which the λPD 11 is mounted needs to be cut obliquely as described above. This is the meaning of “oblique cut” formation of the inclined portion 4 c of the submount 4.

  In addition, although the method of applying feedback to the wavelength control terminal of the LD after monitoring the wavelength has been described, for example, if the LD does not have a terminal for controlling the wavelength, such as a DFB-LD, a thermoelectric element is incorporated into the LD. Feedback may be applied to the temperature and current. The wavelength control terminal of the LD shown in FIG. 1 is a DBR-LD wavelength control terminal. Recently, the wavelength of the LD can be changed by changing the position of a mirror or applying a stress to a part of the micro electro mechanical systems (MEMS). This corresponds to the wavelength control terminal.

FIG. 8 is a diagram showing another LD monitor circuit of the present invention. This circuit is configured by providing a temperature measurement terminal 10 f connected to the thermistor 14 in the circuit of FIG. 1 and incorporating an electroabsorption element (EA: Electro absorption) 15 in the LD 6.
As described above, the EA terminal 10g for the EA 15 for modulation may be provided, and the temperature measurement terminal 10f is prepared in case the wavelength measurement is performed with higher accuracy or the temperature dependency of the light transmission plate is large. May be provided. In this case, the thermistor 14 is mounted on the light transmission plate 12.
In the above description, the LD 6 is an example of a one-chip LD having the anode terminal 10h, the cathode terminal (10c), and the wavelength control terminal 10b. However, these may be discrete LDs having a plurality of chips. For example, a combination of a light emitting chip that oscillates a laser and a waveguide element whose refractive index changes depending on an applied voltage may be used. In this case, the terminal of the voltage applied to the waveguide element becomes the wavelength control terminal.

It is a figure explaining the outline of the present invention. It is a figure explaining the monitor circuit of LD of this invention. It is a figure which shows the mounting state of the wavelength monitor of this invention. It is a figure which shows an example of the wavelength monitor of this invention. It is a figure explaining an example of the light-transmitting plate of this invention. It is a wavelength-PD output characteristic figure of the light-transmitting plate of this invention. It is a figure explaining an example of the reflective grating of this invention. It is a figure explaining the monitor circuit of other LD of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser module with wavelength monitor, 2 ... Stem, 3 ... Stem base, 3a ... Flange part, 3b ... Base part, 4 ... Submount, 4a ... Wall part, 4b ... Upper end part, 4c ... Inclined part, 4d ... Indentation DESCRIPTION OF SYMBOLS 5 ... Lead pin, 6 ... LD (laser diode), 7 ... Heat sink, 8 ... Wavelength monitor, 9 ... mPD, 10 ... Wavelength monitor circuit, 10a ... LD cathode terminal, 10b ... Wavelength control terminal, 10c ... Stem (GND) Terminal 10d Power monitor terminal 10e Wavelength monitor terminal 10f Temperature measuring terminal 10g EA terminal 11 λPD 12 Light transmission plate 12a Light transmission plate body 12b Wave-shaped groove 12c Glass thin film (Intermediate layer), 12d ... surface layer (upper surface layer), 12e ... surface, 13 ... reflection grating, 14 ... thermistor, 15 ... EA.

Claims (5)

A laser module with a wavelength monitor comprising a laser diode and a light receiving element that detects light emitted from the laser diode with an optical output corresponding to the wavelength of the light,
A light transmission plate provided with a reflection grating is disposed on the light receiving side of the light receiving element, and the light transmission plate condenses the light reflected by the reflection grating onto the light receiving element while reflecting at least one of an upper surface and a lower surface. A laser module with a wavelength monitor, characterized by being guided as follows.   The reflection grating includes a light transmission plate body provided with a wavy groove on a surface, an intermediate layer having a uniform film thickness on the wavy groove formed of a transparent member having a refractive index different from that of the light transmission plate body, 2. The laser module with a wavelength monitor according to claim 1, comprising a top layer having a refractive index substantially equal to a refractive index of the light transmitting plate body provided on the intermediate layer.   3. The laser module with a wavelength monitor according to claim 1, wherein the intermediate layer is configured such that the thickness of the intermediate layer is changed in a gradient shape so that the direction of reflected light changes depending on the wavelength.   The laser module with a wavelength monitor according to any one of claims 1 to 3, wherein the light transmission plate body is configured as a photoconductive element, the element is bias-driven, and a current flowing through the element is monitored. .   5. The laser module with a wavelength monitor according to claim 1, wherein a periphery of the light transmission plate is joined to the submount so that a central portion is separated from the submount.

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