JP2000277845A - Light emitting module - Google Patents

Abstract

(57) Abstract: Provided is a light-emitting module which is capable of adjusting an oscillation wavelength in an operating state, is downsized, and is suitable for a WDM communication system. A light emitting module includes a semiconductor laser 16, a control circuit 22, a waveguide type diffraction grating (AWG) 18, a photoelectric conversion element 20,
And a package 12 for accommodating them. The semiconductor laser 16 oscillates with a predetermined oscillation spectrum,
This light can be extracted from the first end face 16a. The AWG 18 has an input optically coupled to the second end face 16b of the semiconductor laser 16, splits light within a predetermined oscillation spectrum, and outputs the light to output ports at spatially different positions. Photoelectric conversion element 20
Is optically coupled to the output of the AWG 18, and outputs an electrical signal corresponding to each of a plurality of lights having different wavelengths among the light from the AWG 18. The control circuit 22 adjusts the temperature of the semiconductor laser 16 based on the photoelectrically converted electric signal so that the oscillation wavelength of the semiconductor laser 16 becomes constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting module, and more particularly to a light emitting module suitable for a wavelength division multiplexing (WDM) system.

[0002]

2. Description of the Related Art In a 1.55-μm band WDM system, the wavelength interval between adjacent channels is specified to be 0.8 nm. This requires that the absolute accuracy of the channel wavelength be controlled by more than four digits. Suitable semiconductor lasers for this purpose include DFB semiconductor lasers and DBs.
An R-type semiconductor laser can be used. In these semiconductor lasers, a sharp oscillation spectrum is obtained, but the oscillation wavelength is determined by a diffraction grating formed in a laser chip in a laser manufacturing stage. Obtaining a desired oscillation wavelength stably and accurately has not been easy because of the influence of process factors.

[0003]

In order to achieve this, it is necessary to make various adjustments after the semiconductor laser chip is assembled as a light emitting module, or to add an additional device to the outside.

[0004] However, wavelength division multiplexing (WDM) systems use 16 or 32 channels using multiple wavelengths.
Since the channels are transmitted in parallel, a light emitting module practically applicable to a WDM system is required to be approximately the same size as a light emitting module used in a conventional communication system.

Accordingly, an object of the present invention is to provide a light emitting module which can adjust the oscillation wavelength in an operating state and which is downsized.

[0006]

The inventor has made various studies to realize such a light emitting module. In order to adjust the oscillation wavelength in the operating state, it is necessary to extract the oscillation light and monitor this wavelength. However, coupling an optical splitter such as an optical coupler with the output of the light emitting module causes an increase in the size of the device. Further, as is conventionally done, a change in the oscillation power can be detected only by monitoring the total power of the oscillation light, but a change in the oscillation wavelength cannot be grasped. That is, it is necessary to monitor the optical power at a plurality of wavelengths.

[0007] Based on such studies, it has been found that there are the following technical problems. (1) An optical coupling means is required to monitor the light of the semiconductor laser. (2) Spectral means for separating the light obtained from the coupling means is required. (3) In order to realize the coupling means and the spectroscopic means, it is necessary to have a configuration capable of miniaturization.
In view of such a problem, the present invention has the following configuration.

[0008] A light emitting module according to the present invention includes a semiconductor laser, adjusting means, an optical circuit, and photoelectric conversion means. The semiconductor laser includes a first end face and a second end face, and an optical resonator for laser oscillation. In this semiconductor laser, light oscillated by a predetermined oscillation spectrum can be extracted from the first end face. The optical circuit has an input optically coupled to the second end face of the semiconductor laser, and can split and output light within a predetermined oscillation spectrum. The optical circuit can guide the split light to spatially different positions. The photoelectric conversion unit is optically coupled to an output of the optical circuit, and can output an electric signal corresponding to each of a plurality of lights having different wavelengths among the lights separated in the optical circuit. The adjusting unit adjusts the temperature of the semiconductor laser based on the electric signal from the photoelectric conversion unit. Thereby, the wavelength of the laser oscillation light of the semiconductor laser is adjusted.

The light extracted from the second end face of the semiconductor laser is split using an optical circuit, and the split light is photoelectrically converted to generate an electric signal. These electric signals indicate the intensity of the photoelectrically converted light. By changing the temperature of the semiconductor laser based on electric signals corresponding to the light intensities of a plurality of wavelengths, it is possible to adjust the wavelength of light to be generated by the semiconductor laser.

Further, the light extracted from the second end face of the semiconductor laser is converted into an electric signal corresponding to a plurality of light wavelengths through an optical circuit and a photoelectric conversion means, so that the flow of the optical signal is simple. Has been The plurality of electric signals obtained by processing the optical signal reflect the oscillation state (oscillation wavelength and light intensity) of the semiconductor laser. For this reason,
If the temperature of the semiconductor laser is adjusted based on a plurality of electric signals, the oscillation wavelength of the semiconductor laser is adjusted. There is no need for optical monitoring means for optically coupling with laser light extracted outside the semiconductor laser.

Therefore, in the light emitting module of the present invention,
The semiconductor laser, the wavelength adjusting means, the optical circuit, and the photoelectric conversion means can be housed in the housing.

In the light emitting module of the present invention, it is preferable that a plurality of wavelengths are selected so as to sandwich the wavelength of light to be generated by the semiconductor laser. The laser oscillation light can be adjusted based on a difference between a plurality of electric signals corresponding to the light having the selected wavelength on both sides of the center wavelength of the light to be oscillated.

[0013] In the light emitting module of the present invention, the adjusting means can include a control circuit and a temperature changing means. The control circuit can generate a control signal for adjusting the wavelength of the laser oscillation light of the semiconductor laser based on the electric signal from the photoelectric conversion unit. The temperature changing means can adjust the temperature of the semiconductor laser based on the control signal.

The following modes can be applied to the light emitting module of the present invention. The optical circuit can output a first wavelength within a predetermined oscillation spectrum and a second wavelength different from the first wavelength. The photoelectric conversion unit can output first and second electric signals corresponding to the light of the first wavelength and the light of the second wavelength. The adjusting unit can adjust the temperature of the semiconductor laser based on a difference signal generated from the first electric signal and the second electric signal from the photoelectric conversion unit. The adjusting means can adjust the drive signal of the semiconductor laser based on the sum signal generated from the first electric signal and the second electric signal from the photoelectric conversion means. It is preferable that the center of the wavelength of the light generated by the semiconductor laser is included between the first wavelength and the second wavelength.

According to the present invention, the optical circuit includes an input section for receiving input light, a plurality of waveguides, and a waveguide diffraction grating including a slab waveguide region. Each of the plurality of waveguides is optically coupled to the input section such that the input light is substantially equally distributed to each waveguide. The plurality of waveguides have a difference by a predetermined length and have different lengths. The plurality of waveguides reach and terminate in the slab waveguide region. The light is split from the slab waveguide region to the output.

A light emitting module according to the present invention includes a semiconductor laser, a demultiplexing unit, a photoelectric conversion unit, a control circuit, and a temperature controller. The semiconductor laser oscillates with an oscillation spectrum centered on a predetermined wavelength. The demultiplexing means
It has a function of splitting laser oscillation light received from a semiconductor laser into light in a wavelength region centered on a plurality of different wavelengths in the oscillation spectrum. The photoelectric conversion unit has a function of converting light in a wavelength region around a plurality of wavelengths into a plurality of electric signals. The control circuit can output a difference signal of at least two electric signals of the plurality of electric signals from the photoelectric conversion unit, and can output a sum signal. The temperature controller changes the temperature of the semiconductor laser based on the difference signal of the control circuit.

In such a light emitting module, the laser oscillation light is split into a plurality of lights having different wavelengths, and a difference signal between two electric signals among the electric signals corresponding to the respective split lights is generated. The temperature of the semiconductor laser is changed so that the value of the difference signal maintains a predetermined value. Each of the wavelength regions centered on the plurality of wavelengths can have a portion that overlaps with an adjacent wavelength region.

[0018]

Embodiments of the present invention will be described with reference to the drawings.

A light emitting module according to an embodiment of the present invention will be described with reference to FIGS. This light emitting module has a configuration of a semiconductor laser module. FIG. 1 is a perspective view of a semiconductor laser module, which is partially cut away so as to clarify the inside thereof. FIG. 2 shows a main part of the semiconductor laser module, and FIG.
FIG. 2 is a cross-sectional view taken along line II of FIG.

Referring to FIGS. 1 and 2, a semiconductor laser module 1 includes a main part 10 of a semiconductor laser module.
And a housing 12.

The housing 12 is a butterfly-type package in the embodiment shown in FIG. Package 12
The semiconductor laser module main part 10 is arranged on the bottom surface inside. The semiconductor laser module main part 10 is sealed in the package 12 in a state where an inert gas, for example, nitrogen gas is sealed. The housing 12 includes a main body 12 a that houses the semiconductor laser module 10 and a cylindrical portion 1 that guides the optical fiber 14 to the main portion 10.
2b, and a plurality of lead pins 12c.

The main part 10 of the semiconductor laser module includes mounting members 24, 26, 28, 30 and a lens (32 in FIG. 2).
a) holding a lens holding member.

The mounting members 24, 26, 28, 30 mount the semiconductor optical elements 16, 20a, 20b, the optical circuit 18, and the signal processing element section 22. In the semiconductor laser module main part 10, the mounting member 24 is arranged on a thermoelectric cooler (thermoelectric cooler) 34. Thermionic cooler 34 can control the temperature by extracting thermal energy according to the received current,
For example, it has been put to practical use as a temperature control element using the Peltier effect. The semiconductor laser 1 is mounted on the mounting member 24.
6, the thermoelectric cooler 34 functions as a temperature changing unit for controlling the temperature of the semiconductor laser. For this reason, the material of the mounting member 24 is preferably a good thermal conductor such as aluminum nitride (AlN) used for a chip carrier.

On the inner wall of the package body 12a, an optical window sealed with hermetic glass 36 is formed at a portion communicating with the cylindrical portion 12b. Package 12
Has a through hole communicating with the main body 12a. The light propagating from the semiconductor laser 16 toward the end (not shown) of the optical fiber 14 passes through this through hole. A lens (38 in FIG. 2) is provided at the tip of the cylindrical portion 12b.
A lens holding member 38 for holding a) is provided.
An optical isolator 40 can be provided between the lens holding member 38 and the cylindrical portion 12b. Optical isolator 4
0 blocks light in the opposite direction from the optical fiber 14.

An optical fiber 14 is introduced from the tip of the cylindrical portion 12b. The optical fiber 14 has a ferrule 42
The tip is covered and protected by. The lens holding section 38 holds the sleeve 44. Ferrule 4
2 is optically positioned with respect to package 12 when inserted into sleeve 44. That is, the optical fiber 1
4. The lens of the lens holding member 40 and the main part 10 of the semiconductor laser module are aligned.

Referring to FIG. 2, in the main part 10 of the semiconductor laser module, the mounting member 24 includes an element mounting portion 24a.
And a lens support 24b. Lens holder 24a
Is provided on one main surface of the element mounting portion 24b. The lens support 24a has a guide hole for receiving the lens holding member 32. The lens holding member 3 is provided in the guide hole.
2 is inserted, and the lens holding member 32 is attached to the element mounting portion 24b.
Holds a lens 32a for condensing light from the semiconductor laser 16 mounted on the camera. By moving the position of the lens holding member 32 in the guide hole, the distance between the semiconductor laser 16 and the lens 32a can be adjusted.

The semiconductor laser 16 is mounted on a mounting member 26. The semiconductor laser 16 includes a light emitting surface 16a and a light reflecting surface 16b that can form an optical resonator. The light reflectance of the light exit surface 16a is
Lower than the light reflectance. Therefore, laser oscillation light can be extracted from the light emitting surface 16a. Light emitting surface 16a
Is optically coupled to the optical fiber 14 via the lenses 32a and 38a.

As the semiconductor laser 16, for example, a distributed feedback (DFB) semiconductor laser can be used. D
The present invention is not limited to the FB laser, but can be similarly applied to a Fabry-Perot semiconductor laser. FIG. 3A is a schematic view of a distributed feedback (DFB) semiconductor laser 16,
FIG. 4 shows a partially cutaway view along the optical axis direction of emitted laser light.

Referring to FIG. 3A, the semiconductor substrate 50
The embedded portion 61 and the second
, A contact layer 64, and a stripe electrode 66 on the first conductive side, and a second conductive side electrode 68 is provided on the entire back surface facing the main surface of the substrate 50. The buried portion 61 includes a buffer layer 52, a first cladding layer 54, a first guide layer 56,
An active layer 58 and a second guide layer 60 are provided in a rectangular area extending from one end face 16a of the semiconductor laser 16 to the other end face 16b facing the end face.

The buried portion 61 extends along the optical axis direction (z-axis) of the emitted laser light. The embedding unit 61
The two side surfaces are sandwiched by a first block layer 72 formed on the substrate 50 and a second block layer 74 formed on the current block layer 72. n-I
When the nP substrate is used, the first block layer 72
Is a p-InP semiconductor layer, and the second block layer 74 is n-
It is formed of an InP semiconductor layer. The substrate 50 and the second cladding layer 62 are electrically separated by a pn junction.

The stripe electrode 66 is electrically connected to the contact layer 64 at an opening provided in the insulating film 70. The opening provided in the insulating film 70 is provided along the buried portion 61 and has a rectangular shape. Therefore, carriers can be efficiently supplied to the buried portion 61.
As a result, the narrowing of carriers and the confinement of light due to the narrowing are efficiently realized.

In the buried portion 61, the buffer layer 52 and the first clad layer 5
4. A mesa-shaped portion including the first guide layer 56, the active layer 58, and the second guide layer 60 is formed. The two opposing side surfaces of the mesa-shaped portion are sandwiched between the block layers 72 and 74 from both sides.

The diffraction grating comprises a cladding layer 54 and a guide layer 5.
6, and at least one of the boundary between the cladding layer 62 and the guide layer 60. The diffraction grating is formed along the direction in which the optical axis of the laser light extends. For example, there are periodically concave portions or convex portions formed at the boundary. The light generated in the active layer 58 is optically coupled to the diffraction grating, and a predetermined wavelength is selected.

The active layer 58 confines electrons and holes that contribute to light emission by recombination. Therefore, the active layer 5
8 is sandwiched between the first guide layer 56 and the second guide layer 60. The active layer 58 and the guide layers 56 and 60 sandwiching the active layer 58 form a photoactive layer region. The photoactive layer region is sandwiched between the guide layers 56 and 60 by the first clad layer 54 and the second clad layer 62. The photoactive layer regions 56, 58, 60
Since it has a refractive index higher than 4, 62, the laser light generated in the active layer is efficiently confined in the active layer region.

The laser oscillation in the active layer is caused by the first conductive side stripe electrode 66 and the second conductive side back electrode 6.
8 is caused by connecting a power supply and injecting current. The active layer 58 includes an InGaAsP semiconductor. For example, an MQW structure in which InGaAsP semiconductor layers having different compositions are multiplexed can be employed. As the cladding layer, it is preferable to use an InP semiconductor whose proper conductivity type is selected. As the contact layer, an InGaAs semiconductor can be adopted.

It is preferable that a low-reflection coating film for lowering the reflectance is applied to the light emitting surface 16a of the semiconductor laser chip, and a light reflection coating film for increasing the light reflectance is applied to the light reflecting surface 16b. . By adjusting the thickness of the multilayer film such as SiN or a-Si, a low reflection coating film and a light reflection coating film can be obtained.

Referring again to FIG. 2, the optical circuit 18 is mounted on a mounting member 26. The input of the optical circuit 18 is
It is optically coupled to the light reflecting surface 16b of the semiconductor laser 16. Therefore, the first input surface 18a of the optical circuit 18
It faces the light reflecting surface 16b of the semiconductor laser 16. The output of the optical circuit 18 faces the photoelectric conversion means 12 and is optically coupled.

An example of such an optical circuit 18 is an array waveguide diffraction grating (AWG). FIG. 3 (b)
FIG. 2 shows a schematic view of an arrayed waveguide diffraction grating. The arrayed waveguide grating 18 has n input ports 82a, 82a.
b, 82c and n output ports 84a, 84b, 84
c and the input and output slab waveguide regions 86, 8
8 and n optical waveguides 90a, 90b, 90c that optically connect the slab waveguide regions 86, 88. The n optical waveguides 90a, 90b, 90c are different from each other in optical waveguide length by ΔL. n input ports 82a,
One of 82b and 82c, for example, only 82b, is optically coupled to the light reflecting surface 16b of the semiconductor laser 16. Also, the n output ports 84a, 84b, 84c
Are coupled to the photoelectric conversion means 12, respectively. Such a configuration can be obtained by providing a quartz waveguide of a predetermined shape on a Si substrate.

Light from the semiconductor laser 16 is input to one input port 82b of the arrayed waveguide diffraction grating 18. This light is introduced into the slab waveguide region 86 on the input side.
The introduced light is divided into n optical waveguides 90a, 90b, 90
In c, it is divided substantially equally. Each optical waveguide 90
Light propagating in a, 90b, 90c meets again in slab waveguide region 88. At this time, each optical waveguide 90
Since the lights from a, 90b, and 90c each have an optical path difference of a length ΔL, diffraction occurs in the slab waveguide region 88. As a result of this diffraction, output ports 84a, 84b, 84 provided at positions corresponding to the diffraction angles of the respective lights
Light centering on a specific wavelength is selectively output to c. Therefore, the light input from the single input port 82b is split into light in a predetermined wavelength region centered on n different wavelengths. Further, by extending the optical waveguide of each output port from the slab waveguide region 88, the light emitting ends of each of the output ports 84a, 84b, 84c can be provided at desired positions. It will be easier.

In the embodiment shown in FIGS. 1 and 2, the photoelectric conversion means 20 includes a plurality of photoelectric conversion elements 20a,
20b. As the photoelectric conversion elements 20a and 20b, for example, photodiodes can be employed. The output of the optical circuit 18 is provided as many as the number of photoelectric conversion elements.

Referring to FIG. 2, a plurality of photoelectric conversion elements 2
0 (20a, 20b) is mounted on the mounting member 28. Each photoelectric conversion element 20 (20a, 20b) is arranged so as to be optically coupled to the output of the optical circuit 18. For this reason, the light receiving surface of the photoelectric conversion element 20 (20a, 20b) faces the output surface 18b of the optical circuit 18.

The signal processing element section 22 is mounted on the mounting member 30. The signal processing element unit 22 includes a temperature adjustment unit for driving the thermoelectric cooler 34 and a power adjustment unit for driving the semiconductor laser 16. The temperature adjustment unit receives the electric signal from the photoelectric conversion element 20 (20a, 20b), adjusts the electric signal to the thermoelectric cooler 34 based on the electric signal, and controls the oscillation wavelength of the semiconductor laser 16. The power adjustment unit receives an electric signal from the photoelectric conversion element 20 (20a, 20b), adjusts a drive current to the semiconductor laser 16 based on the electric signal, and controls the oscillation power of the semiconductor laser 16.

The mounting member 26 and the mounting member 28 are composed of the semiconductor laser 16, the optical circuit 18, the photoelectric conversion elements 20a, 20
b is arranged on the mounting member 24 so as to be optically coupled. The mounting member 30 includes the photoelectric conversion elements 20a, 20
b is arranged on the mounting member 24 so as to receive an electric signal from the mounting member 24. That is, the main functions of the semiconductor laser module are concentrated on the mounting member 24. Therefore, it is not necessary to exchange electrical and optical signals with the outside of the package 12 to control the oscillation wavelength and oscillation power of the semiconductor laser 16. A semiconductor laser module whose oscillation wavelength can be adjusted with high accuracy is housed in a package similar to the conventional one.

Referring to FIG. 1 and FIG. 2, in such a semiconductor laser module 1, the optical fiber 14, the lenses 32a and 38a, the semiconductor laser 16, the optical circuit 18, and the photoelectric conversion means 20 (20a and 20b) are provided in predetermined positions. Are arranged along the axis 46. This ensures their optical coupling.

The semiconductor laser module 1 extracts output light from the back of the semiconductor laser 16. The output light is split using the optical circuit 18 to obtain optical signals in at least two wavelength regions having a predetermined wavelength interval in the wavelength spectrum of the semiconductor laser 16. The temperature of the semiconductor laser 16 is adjusted based on the difference information of the light intensity of these light signals. Thereby, the laser oscillation wavelength can be adjusted to a desired value. Further, the driving current of the semiconductor laser 16 is adjusted based on the sum information of the light intensities of these optical signals. Thereby, the laser oscillation power can be adjusted to a desired value.

The flow of light in the semiconductor laser module 1 will be described. FIG. 4A is a schematic diagram illustrating the flow of light in the semiconductor laser module 1. Referring to FIG. 4A, along a predetermined axis 46, the optical fiber 14, the lens 38a, the lens 32a, the semiconductor laser 16, the optical circuit 1
8, photoelectric conversion elements 20a and 20b are arranged in order. The light A extracted from the light emitting slope 16a of the semiconductor laser 16 is condensed toward the lens 38a via the lens 32a to become light B. Further, the light is condensed by the lens 38a so as to be incident on the end face of the optical fiber 14, and becomes light C. On the other hand, the light D extracted from the light reflecting surface 16b of the semiconductor laser 16 is input to the input surface 18a of the optical circuit 18. The spectrum of light D is shown in FIG. This spectrum reflects the oscillation characteristics of the semiconductor laser 16. The optical circuit 18 splits the incident light and guides the split light to spatially different positions. A plurality of outputs of the optical circuit 18 are provided at positions where the split light is guided. Each output of the optical circuit 18 outputs split light E and F. The solid line shown in FIG. 4C represents the spectrum of light E and F, and the broken line represents the spectrum of light D. This spectrum reflects the spectral characteristics of the optical circuit 18. These lights E and F are input to the light receiving surfaces of the photoelectric conversion elements 12a and 12b. The light input to the photoelectric conversion elements 20a and 20b is converted into an electric signal.

The semiconductor laser 16 thus obtained
An algorithm for adjusting the oscillation spectrum based on the information on the light intensity at two wavelengths in the oscillation spectrum will be described. FIGS. 5A to 5C are schematic diagrams showing the oscillation spectrum of the semiconductor laser. The horizontal axis shows the wavelength of light,
The vertical axis indicates the spectrum intensity (power). The center wavelength of the laser light to be oscillated is λ ₀ . This center wavelength λ ₀
, At least two wavelengths (wavelength regions) λ ₁ and λ ₂ are selected in the laser oscillation spectrum. The optical circuit 18 shown in FIG. 3 (b) selects light of wavelengths λ ₁ and λ ₂ , and provides the split light from the corresponding output port to the photoelectric conversion element.

FIG. 5A shows a spectrum when the semiconductor laser 16 oscillates at the center wavelength λ _{0 at} which oscillation is to be performed. At this time, the signal intensities obtained by photoelectrically converting the lights λ ₁ and λ ₂ split by the optical circuit 18 are equal. Therefore, the difference signal V (R1) -V (R2) becomes a predetermined value, in this case, zero.

FIG. 5B shows a spectrum when the semiconductor laser 16 oscillates at a wavelength shorter than the central wavelength λ _{0 at} which oscillation should occur. At this time, the difference signal V (R1) -V (R2) becomes larger than a predetermined value. This difference signal indicates that the oscillation wavelength of the semiconductor laser 16 needs to be shifted to the longer wavelength side. Based on this signal, the semiconductor laser 16 is
Change the temperature of the. In this case, since the temperature of the semiconductor laser 16 needs to be increased, the current to the Peltier element 34 is reduced.

FIG. 5C shows a spectrum when the semiconductor laser 16 oscillates at a wavelength longer than the wavelength λ ₀ to be oscillated. At this time, these difference signals V
(R1) -V (R2) becomes smaller than a predetermined value. This difference signal indicates that it is necessary to shift the oscillation wavelength of the semiconductor laser 16 to the shorter wavelength side. Based on this signal, the temperature of the semiconductor laser 16 is changed by the Peltier device 34. In this case, since the temperature of the semiconductor laser 16 needs to be lowered, the current to the Peltier element 34 is increased.

As described above, when the light intensities at two wavelengths in the oscillation spectrum are monitored and the negative feedback control is performed based on the difference information of the light intensities at the two wavelengths, the oscillation spectrum can be adjusted. In the above example, two wavelengths are selected so as to sandwich the center wavelength λ _{0 at} which laser oscillation is to be performed, but the control algorithm is not limited to this. Even when a monitoring wavelength is selected on the shorter wavelength side than the center wavelength λ ₀ , the oscillation spectrum can be similarly adjusted by controlling the difference signal V (R 1) −V (R 2) to a predetermined value. it can. Note that the coefficient of the temperature change of the oscillation wavelength of the semiconductor laser 16 is exemplarily 0.1 n
m / ° C.

Further, automatic control of the oscillation power of the semiconductor laser 16 based on the sum signal of the plurality of monitoring wavelengths (APC
Control) can be performed. That is, the drive current of the semiconductor laser 16 can be controlled so that the value of the sum signal becomes constant.

In the above example, the case where the number of photoelectric conversion elements 12 for monitoring the oscillation spectrum is two has been described. However, three or more photoelectric conversion elements can be provided. In this case, if the electric signals from these photoelectric conversion elements are controlled using a microcomputer (CPU), information on the shape of the oscillation spectrum can also be obtained. Also at this time, the oscillation power of the semiconductor laser 16 can be estimated based on the sum of the signals of three or more photoelectric conversion elements.

FIG. 6 is a circuit exemplarily showing a circuit capable of realizing the above algorithm. Such a circuit
The signal processing unit 22 is housed in a package as the semiconductor laser module of the present invention.

Referring to FIG. 6, the photoelectric conversion element 20a,
The current signal from each of the current-to-voltage converters 10b
₁ , 102 convert the signals into voltage signals V ₁ and V ₂ . The voltage signals V ₁ and V ₂ are supplied to the preamplifiers 103 a and 103
b, 103c and 103d to generate voltage signals V ₃ , V ₄ , V ₅ and V ₆ respectively. The voltage signal V ₃ ,
V ₄ is input to the difference signal generation circuit 104 and is converted into a current signal to drive the Peltier device 34. The voltage signals V ₅ and V ₆ are input to the sum signal generation circuit 105 and are converted into current signals for driving the semiconductor laser 16.

The difference signal generating circuit 104 receives the input voltage signal V ₃ at one end of the resistor R ₁ . The other end of the resistor R ₁ is,
It is connected to the negative input and one end of a resistor R ₂ of the operational amplifier (OpAmp1). The other end of the resistor R ₂ is connected to the output of the operational amplifier (OpAmp1). Difference signal generating circuit 104 receives the voltage signal V ₄ which is input to one end of a resistor R _3. The other end of the resistor R ₃ is an operational amplifier (OPam
It is connected to the positive input and one end of the resistor R ₄ in p1). The other end of the resistor R ₄ is connected to a reference potential (ground). The output of the operational amplifier (OpAmp1)
When the resistances of R ₁ , R ₂ , R ₃ and R ₄ are equal, the input signal V
_3, the voltage appears indicative of a difference V _4. This difference signal is input to the Peltier element drive circuit 106 to drive the Peltier element 34. The output of the operational amplifier (OpAmp1) is added to the positive input of the operational amplifier (OpAmp2), and
The output of mp2) can be applied to the input of the Peltier element driving circuit 106. If a voltage source V _OFF1 for offset adjustment is connected to the negative input of the operational amplifier (OpAmp2), the Peltier element 34 can be driven appropriately.

[0057] sum signal generating circuit 105 receives the voltage signal V ₅ that is input to one end of a resistor R _5. The other end of the resistor R ₅ is,
It is connected to the negative input and one end of a resistor R ₆ of the operational amplifier (OpAmp3). The other end of the resistor R ₆ is connected to the output of the operational amplifier (OpAmp3). Sum signal generating circuit 105 receives the voltage signal V6 inputted to one end of a resistor R _7. The other end of the resistor R ₇ includes an operational amplifier (OPam
It is connected to the negative input and one end of the resistor R _5, R ₆ of p3). The positive input of the operational amplifier (OpAmp3) is connected to a reference potential (ground). Operational amplifier (OpA
At the output of mp3), when the resistances of R ₅ , R ₆ , and R ₇ are equal, a voltage that indicates the sum of the input signals V ₅ and V ₆ appears. This sum signal is input to the drive circuit 107 of the semiconductor laser 16,
The semiconductor laser 16 is driven. Operational amplifier (OpAmp
The output of 3) can be applied to the positive input of the operational amplifier (OpAmp4), and the output of the operational amplifier (OpAmp4) can be applied to the input of the drive circuit 107 of the semiconductor laser 16. If a voltage source V _OFF2 for offset adjustment is connected to the negative input of the operational amplifier (OpAmp4), the semiconductor laser 16 can be driven appropriately.

The signal processing unit 22 shown in FIG. 6 is realized in a small size using an integrated circuit and passive elements such as resistors and capacitors. Therefore, these components are housed in the same housing.

[0059]

As described in detail above, according to the light emitting module of the present invention, the light extracted from one end face of the semiconductor laser is split using an optical circuit. Each of a plurality of separated lights from the output of the optical circuit was photoelectrically converted to generate an electric signal. Since this electric signal indicates the intensity of the photoelectrically converted light, the wavelength of the light to be generated by the semiconductor laser can be adjusted based on these signals.

The light extracted from one end face of the semiconductor laser is converted into an electric signal corresponding to a plurality of light wavelengths via an optical circuit and photoelectric conversion means. Therefore, the flow of the optical signal is simplified. The electric signal obtained by processing the optical signal reflects the oscillation state of the semiconductor laser. If the temperature of the semiconductor laser is adjusted based on these electric signals, the oscillation wavelength is adjusted.

Therefore, there is provided a light emitting module which can adjust the oscillation wavelength in the operating state and can be downsized.

[Brief description of the drawings]

FIG. 1 is a perspective view of a semiconductor laser module, which is partially cut away so as to clarify an internal state thereof.

FIG. 2 is a cross-sectional view taken along the line II of FIG. 1 showing a main part of the semiconductor laser module.

FIG. 3A is a schematic view of a distributed feedback (DFB) semiconductor laser, showing a partly broken laser beam emitted along the optical axis direction. FIG. 3B is a schematic diagram of an arrayed waveguide diffraction grating (AWG).

FIG. 4A is a schematic diagram showing a flow of light in a semiconductor laser module. FIG. 4B is a characteristic diagram of an oscillation spectrum of light emitted from the semiconductor laser,
FIG. 4B is a characteristic diagram of the spectrum of the light emitted from the optical circuit.

FIGS. 5A to 5C are schematic diagrams showing oscillation spectra of a semiconductor laser.

FIG. 6 is a circuit diagram exemplarily showing a circuit capable of realizing an algorithm for wavelength adjustment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser module, 10 ... Main part of semiconductor laser module, 12 ... Housing, 14 ... Optical fiber,
16, 20a, 20b semiconductor optical element, 18 optical circuit, 22 signal processing element section, 24, 26, 28, 30 ...
Mounting member, 32: lens holding member, 34: thermoelectric cooler, 38: lens holding portion, 40: optical isolator, 42
... ferrule, 44 ... sleeve, 50 ... semiconductor substrate, 5
2 ... buffer layer, 54 ... first cladding layer, 56 ... first
Guide layer, 58 ... active layer, 60 ... second guide layer, 6
1 embedded portion, 62 second cladding layer, 64 contact layer, 66 electrode, 82a, 82b, 82c input port, 84a, 84b, 84c output port, 86,
88: slab waveguide region, 90a, 90b, 90c: optical waveguide

Claims (8)

[Claims] A semiconductor laser including a first end face and a second end face, capable of extracting light oscillated with a predetermined oscillation spectrum from the first end face; and the second laser of the semiconductor laser. An optical circuit having an input optically coupled to the end face, for dispersing light within the predetermined oscillation spectrum, and receiving a plurality of lights having different wavelengths among the lights from the optical circuit corresponding to the respective wavelengths A light emitting module comprising: a photoelectric conversion unit for outputting an electric signal; and an adjusting unit for adjusting a temperature of the semiconductor laser based on the electric signal from the photoelectric conversion unit. 2. An optical circuit, comprising: a first wavelength in the predetermined oscillation spectrum; and a second wavelength different from the first wavelength.
And the photoelectric conversion unit outputs first and second electric signals corresponding to the light of the first wavelength and the light of the second wavelength, and the adjusting unit outputs the first electric signal. The light emitting module according to claim 1, wherein the temperature of the semiconductor laser is adjusted based on a difference signal generated from a signal and the second electric signal. 3. An optical circuit, comprising: a first wavelength in the predetermined oscillation spectrum; and a second wavelength different from the first wavelength.
And the photoelectric conversion unit outputs first and second electric signals corresponding to the light of the first wavelength and the light of the second wavelength, and the adjusting unit outputs the first and second electric signals from the photoelectric conversion unit. 3. The light emitting module according to claim 1, wherein a driving signal of the semiconductor laser is adjusted based on a sum signal generated from the first electric signal and the second electric signal. 4. 4. An optical circuit comprising: an input, a plurality of waveguides optically coupled to the input, having a predetermined length difference and different lengths, and a slab terminating the plurality of waveguides. The light emitting module according to claim 1, further comprising a waveguide diffraction grating including a waveguide region. 5. A control circuit for generating a control signal for adjusting a wavelength of laser oscillation light of the semiconductor laser based on the electric signal from the photoelectric conversion means, and a control circuit based on the control signal. The light emitting module according to claim 1, further comprising: a temperature changing unit configured to adjust a temperature of the semiconductor laser. 6. The light emitting module according to claim 2, wherein the semiconductor laser oscillates around a wavelength included between the first wavelength and the second wavelength. 7. The semiconductor laser, the temperature changing unit, the optical circuit, the optical circuit, the photoelectric conversion unit,
The light emitting module according to claim 5, further comprising a housing that houses the control circuit. 8. A semiconductor laser that oscillates with an oscillation spectrum centered on a predetermined wavelength, and a laser oscillation light received from the semiconductor laser is applied to a laser beam of a predetermined wavelength region centered on a plurality of wavelengths in the oscillation spectrum. A demultiplexing unit for demultiplexing the light into light; a photoelectric conversion unit that converts light in a predetermined wavelength region around the plurality of wavelengths into a plurality of electric signals; and the plurality of electricity from the photoelectric conversion unit. A control circuit that outputs a difference signal between two electric signals selected from the signals; and a temperature controller that changes a temperature of the semiconductor laser based on the difference signal of the control circuit; A light emitting module having a wavelength region centered on each of which has a portion overlapping an adjacent wavelength region.