JP2017135252A - Light-emitting module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting module capable of aligning an optical component by detecting TM polarized light.SOLUTION: The light-emitting module relating to one embodiment includes: a wavelength variable LD 10; a polarizing optical system 7 for rotating a polarization plane of output light L2 exiting from an end face 10B of the wavelength variable LD 10 by 90° and returning the light to the wavelength variable LD 10; a PBS (polarization beam splitter) 4 for separating output light L1 output from an end face 10A of the wavelength variable LD 10 into light P1 having a polarization plane perpendicular to an active layer of the wavelength variable LD 10 and light P2 having a polarization plane parallel to the active layer; and a monitor PD 6a for detecting the light P1 separated by the PBS 4 and having a polarization plane perpendicular to the active layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light emitting module.

  Patent Document 1 discloses a method and system for synthesizing an optical signal having high frequency stability. In this system, it is required to narrow the line width of the output light of the semiconductor laser. In the semiconductor laser equipped with a whispering gallery mode (WGM) resonator, the line width is reduced by increasing the Q value. I am letting. As another method for narrowing the line width, a light source constituted by a semiconductor laser and an optical filter that functions as a frequency discriminator is known. In this light source, the laser light reflected by the optical filter is negatively fed back to the semiconductor laser to perform frequency modulation, thereby stabilizing the frequency of the oscillation light and narrowing the line width.

U.S. Pat. No. 8,981,273

  Also known is a method in which output light of a semiconductor laser is incident on a mirror via a polarization rotation optical system, and return light reflected by the mirror is fed back to the semiconductor laser via a polarization rotation optical system. FIG. 8 schematically shows an optical system for realizing the method. The optical system shown in FIG. 8 includes a semiconductor laser 101, a wave plate 102 that is a polarization rotation optical system, and a mirror 103. The light having TE polarization output from the semiconductor laser 101 enters the wave plate 102, and the wave plate 102 rotates its polarization plane by 45 °. The light transmitted through the wave plate 102 enters the mirror 103. Part of the light incident on the mirror 103 is reflected and incident on the wave plate 102 again. The wave plate 102 further rotates the polarization plane of the light incident from the mirror 103 by 45 °. As a result, the light transmitted through the wavelength plate 102 toward the semiconductor laser 101 is converted into TM polarized light whose polarization plane is rotated by 90 ° with respect to the TE polarized light that the output light of the semiconductor laser 101 has, and enters the semiconductor laser 101. . Here, the TE polarization indicates a polarization parallel to the active layer of the semiconductor laser 101, and the TM polarization indicates a polarization perpendicular to the active layer of the semiconductor laser 101.

  In general, the above-described optical components such as the mirror 103 and the wave plate 102 have processing tolerances, and further, mounting tolerance due to misalignment or the like occurs when these optical components are mounted. Since such a tolerance is generated, it is necessary to align the wavelength plate 102 and the mirror 103 in order to ensure that the TM polarized light is incident on the semiconductor laser 101 as described above. However, since the current light emitting module does not have a means for detecting the TM polarization component incident on the semiconductor laser 101, it is required to detect the TM polarization component.

  An object of the present invention is to provide a light emitting module capable of aligning optical components by detecting TM polarized light.

  A light emitting module according to an aspect of the present invention includes a semiconductor laser, a polarization optical system that rotates the polarization plane of output light output from one light emitting surface of the semiconductor laser, and returns the semiconductor laser to the semiconductor laser, and a semiconductor laser A polarization separation element that separates output light output from the other light emitting surface into light having a polarization perpendicular to the active layer of the semiconductor laser and light having a polarization parallel to the active layer; and a polarization separation element And a first photodetecting element that detects light having a polarization perpendicular to the active layer separated by.

  In one embodiment of the present invention, alignment of optical components can be performed by detecting TM polarized light.

FIG. 1 is a diagram illustrating an internal configuration of the light emitting module according to the first embodiment. FIG. 2 is a diagram schematically showing a cross section of the semiconductor laser. FIG. 3 is a block diagram showing an optical system of the light emitting module of FIG. FIG. 4 is a perspective view showing each component of the polarization optical system. FIG. 5A is a diagram conceptually showing a path of TE polarized light output from the semiconductor laser. FIG. 5B is a diagram conceptually showing a path of TM polarized light output from the semiconductor laser. FIG. 6A shows an optical system according to the second embodiment. FIG. 6B shows an optical system according to the third embodiment. FIG. 6C is a diagram illustrating an optical system according to the fourth embodiment. FIG. 7 is a block diagram showing an optical system according to the fifth embodiment. FIG. 8 is a diagram showing a conventional polarization optical system.

  Specific examples of the light emitting module according to the embodiment of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and is intended that all the changes within the meaning and range equivalent to the claim are included. In the following description, the same or corresponding elements are denoted by the same reference numerals in the description of the drawings, and redundant description is omitted.

(First embodiment)
FIG. 1 is a diagram illustrating components inside the light emitting module 1 according to the first embodiment. The light emitting module 1 includes a housing 2 including a front wall 2a, a rear wall 2b, and two side walls 2c and 2d connecting the front wall 2a and the rear wall 2b. In the light emitting module 1, each component is mounted inside the housing 2, and then the inside of the housing 2 is hermetically sealed by a lid. The light emitting module 1 includes a wavelength tunable laser diode (LD) 10 that is a semiconductor laser. The wavelength tunable LD 10 outputs output light L2 from an end face 10B that is one light emitting surface, and the other light emitting surface. The output light L1 is output from the end face 10A. The output lights L1 and L2 include only TE polarized light that is substantially polarized in parallel with the active layer of the wavelength tunable LD 10, and even if the output lights L1 and L2 include the TM polarized component, the ratio is TE polarized light. Very small compared to the ingredients.

  A collimating lens 3a, a polarization beam splitter (PBS) 4, and a reflection filter 5 are provided on the optical path of the output light L1. The PBS 4 is a flat plate-shaped polarization separation element, and has a light incident surface that is optically coupled to the collimating lens 3a. The PBS 4 receives the output light L1 from the wavelength tunable LD 10 via the collimator lens 3a and separates it into light P1 having a TM polarization component and light P2 having a TE polarization component. The light P2 having TE polarization passes through the PBS 4. The light P1 having TM polarization is reflected by the PBS 4 and travels in a direction orthogonal to the traveling direction of the light P2 having TE polarization. A monitoring photodiode (monitor PD, first light detection element) 6a is provided on the optical path of the light P1 having TM polarization. The monitor PD 6a receives the light P1 having TM polarization reflected by the PBS 4, and outputs an electrical signal corresponding to the intensity of the received light P1 having TM polarization.

  The reflection filter 5 is optically coupled to the back surface of the PBS 4 and receives the light P2 having TE polarization transmitted through the PBS 4. The light P <b> 2 having TE polarization enters the front surface of the reflection filter 5 and is branched by the reflection filter 5. The reflectance of the reflection filter 5 is, for example, 5%, but can be changed as appropriate. The optical axis of the reflected light (monitor light P21) of the reflective filter 5 and the optical axis of the transmitted light P22 of the reflective filter 5 are substantially perpendicular. A monitor PD 6b is provided on the optical path of the monitor light P21. The monitor PD 6b receives the monitor light P21 reflected by the reflection filter 5, and outputs an electrical signal corresponding to the intensity of the received monitor light P21.

  The collimating lens 3a, the PBS 4, the reflection filter 5, and the monitor PDs 6a and 6b are mounted on the base B1. The transmitted light P22 that has passed through the reflection filter 5 is output to the outside of the housing 2. The transmitted light P <b> 22 taken out of the housing 2 is optically coupled to a component incorporating a single mode fiber by a condensing lens provided outside the housing 2. Parts outside the housing 2 and the housing 2 are optically aligned and joined by YAG welding.

  A collimating lens 3b, a polarization optical system 7, a half mirror 8, and an etalon filter 9 are provided on the optical path of the output light L2. The polarization optical system 7 includes a 0.5-stage optical isolator 7A that rotates the polarization plane (polarization plane) of the output light L2 and transmits only light having a specific polarization direction, and a mirror 7B. The detailed configuration of the polarization optical system 7 will be described later. The half mirror 8 receives the light L3 transmitted through the polarization optical system 7 on the front surface and splits it into two lights L4 and L5. One of the branched lights L4 passes through the half mirror 8 and enters the etalon filter 9. The other branched light L5 is reflected by the half mirror 8 and enters the monitor PD 6c. The monitor PD 6c outputs an electrical signal corresponding to the intensity of the light L5. The light L4 incident on the etalon filter 9 passes through the etalon filter 9 and enters the monitor PD 6d. The monitor PDs 6c and 6d, the polarization optical system 7, the half mirror 8, and the etalon filter 9 are mounted on the base B2.

  Incidentally, the light L5 detected by the monitor PD 6c does not pass through any optical element having a specific transmission spectrum. That is, it can be considered that the output of the monitor PD 6c directly reflects the optical output of the wavelength variable LD 10. Therefore, the value obtained by dividing the output of the monitor PD 6d by the output of the monitor PD 6c exactly indicates the transmittance of the etalon filter 9. Since the transmittance of the etalon filter 9 depends on the wavelength, the wavelength of the light currently output from the wavelength variable LD 10 can be specified by the outputs of the two monitors PD6c and 6d. Thus, the etalon filter 9 and the monitor PDs 6c and 6d function as a wavelength detection unit. The ratio of the outputs of the two monitor PDs 6c and 6d is fed back to the bias signal that determines the wavelength of the wavelength variable LD 10, thereby determining the wavelength of the output light of the wavelength variable LD 10 as a target wavelength and maintaining this. Is possible.

  FIG. 2 is a schematic cross-sectional view showing the configuration of the wavelength tunable LD 10 in the present embodiment. As shown in FIG. 2, the wavelength tunable LD 10 includes an SG-DFB (Sampled Grating Distributed Feedback) 10b, a CSG-DBR (Chirped Sampled Grating Distributed Bragg Reflector) 10c, an SOA (Semiconductor Optical Amplifier) 10a, and an SOA / VOA 10d. And have a monolithically integrated structure. The SG-DFB 10b and the CSG-DBR 10c function as a wavelength selection element of the wavelength variable LD 10.

  In the wavelength tunable LD 10, the SOA 10a, SG-DFB 10b, CSG-DBR 10c, and SOA / VOA 10d are arranged in this order. The SG-DFB 10b has a sampled grating. The CSG-DBR 10c has a sampled grating. The SOA 10a functions as a semiconductor optical amplification region (second semiconductor optical amplification region), and the SOA / VOA 10d functions as a semiconductor optical amplification region (first semiconductor optical amplification region) and a semiconductor optical attenuation region.

  The SG-DFB 10 b has a structure in which a lower cladding layer 13 including a sampled grading, an optical waveguide layer 14, and an upper cladding layer 15 are stacked on a substrate 12. The CSG-DBR 10 c has a structure in which a lower cladding layer 13 including a sampled grating, an optical waveguide layer 24, an upper cladding layer 15, an insulating film 16, and a plurality of heaters 17 are stacked on a substrate 12. Each heater 17 is provided with a power supply electrode 18 and a ground electrode 19. The SOA 10a has a structure in which a lower cladding layer 13, an active layer 25, an upper cladding layer 15, a contact layer 20, and an electrode 21 are stacked on a substrate 12. The SOA / VOA 10 d has a structure in which a lower cladding layer 13, an active layer 26, an upper cladding layer 15, a contact layer 22, and an electrode 23 are stacked on a substrate 12.

  In the SOA 10a, the SG-DFB 10b, the CSG-DBR 10c, and the SOA / VOA 10d, the substrate 12, the lower cladding layer 13, and the upper cladding layer 15 are integrally formed. The optical waveguide layers 14 and 24 and the active layers 25 and 26 are formed on the same plane. The optical waveguide layer 14 has a structure in which active layers 14a and waveguide layers 14b are alternately arranged along the light propagation direction. The upper cladding layer 15 located above the waveguide layer 14b is provided with a heater 28 via an insulating film 16, and the heater 28 is provided with a power supply electrode 29 and a ground electrode 30.

  In the SG-DFB 10b and the CSG-DBR 10c, a sampled grating (SG) 27, which is a sampling diffraction grating discretely formed in the lower cladding layer 13 with a predetermined interval, is formed. The SG-DFB 10b has a gain region A1 and a modulation region A2. In the gain region A1, carriers are injected into the active layer 14a from the electrode 31 disposed thereon. Therefore, it has an optical gain. On the other hand, the modulation region A2 has a heater 28 in the upper part thereof, and changes the temperature of the waveguide layer 14b by supplying electric power to the heater 28. SG27 is composed of a region having a diffraction grating and a region having no diffraction grating between them, and shows an optical gain spectrum in which a plurality of peaks appear at equal intervals as the entire gain region A1 and modulation region A2. Then, by changing the power applied to the heater 28 to change the refractive index of the waveguide layer 14b, the wavelength of each peak and the interval between them can be changed.

  The CSG-DBR 10c has three segments A3, A4, and A5. Each segment A3, A4, A5 has the heater 17 and SG27 which drive independently, respectively. Unlike the SG-DFB 10b, the CSG-DBR 10c does not have a gain region. Therefore, CSG-DBR 10c exhibits a reflection spectrum in which a plurality of peaks appear discretely due to the action of SG27. Then, the refractive index of the optical waveguide layer 24 is changed by the electric power applied to the heater 17, and the peak wavelength and its interval can be changed as described above. Here, at least one of the three segments A3, A4, and A5 has physical characteristics different from those of the other segments. At least one segment differs from the other segments in the interval of the region where the diffraction grating is formed. This is called a chirped diffraction grating (CSG). The reason why the three segments A3, A4, and A5 are provided is that the wavelength region in which discrete reflection peaks appear is expanded by locally changing the temperature independently for each of the segments A3, A4, and A5.

  The wavelength of one gain peak derived from the SG-DFB 10b and the wavelength of one reflection peak derived from the CSG-DBR 10c can be matched by adjusting the power applied to the heaters 17 and 28. The SG-DFB 10b and the CSG-DBR 10c constitute a resonator, and the wavelength tunable LD 10 performs laser oscillation at the same wavelength. This matching wavelength can be adjusted by adjusting the power applied to the heater 28 of the SG-DFB 10b and the power applied to the heater 17 of the CSG-DBR 10c. That is, the laser oscillation wavelength of the wavelength tunable LD 10 can be changed.

  The SOA 10a amplifies light having a wavelength determined by coupling between the SG-DFB 10b and the CSG-DBR 10c. The optical amplification degree of the SOA 10a, that is, the intensity of the output light L1 can be adjusted by the amount of carriers injected from the electrode 21 into the active layer 25. Like the SOA 10a, the SOA / VOA 10d has a function of amplifying light having a determined wavelength, and also has a function of attenuating the light. The function of the SOA / VOA 10d as an optical amplifier and the function as an optical attenuator can be changed by a forward bias and a reverse bias to the SOA / VOA 10d.

  FIG. 3 is a block diagram schematically showing an optical arrangement of each component included in the light emitting module 1. In FIG. 3, the solid line indicates an optical signal, and the broken line indicates an electrical signal. As shown in FIG. 3, the light emitting module 1 further includes a bias supply unit 41 that supplies a bias signal to the wavelength tunable LD 10 and an automatic light output control unit that receives an electrical signal from the monitor PD 6b (third light detection element). Auto Power Control (APC) 42 and an APC 43 that receives an electrical signal from the monitor PD 6c (second light detection element).

  The bias supply unit 41 supplies current corresponding to the designated oscillation wavelength to the electrodes 18, 29, and 31 of the wavelength tunable LD 10 in order to cause the wavelength tunable LD 10 to oscillate at the designated wavelength. The APC 42 (second control element) receives the electrical signal from the monitor PD 6b and determines the intensity of the monitor light P21. Here, since the reflectance of the reflection filter 5 has neither wavelength dependency nor polarization dependency, the APC 42 can determine the intensity of the light P2 having TE polarization from the intensity of the monitor light P21. Then, the APC 42 controls the optical gain of the SOA 10a to adjust the optical amplification factor, and maintains the intensity of the light P2 having TE polarization at a desired value. The APC 43 (first control element) adjusts the optical amplification factor and optical attenuation factor of the SOA / VOA 10dSOA / VOA 10d, and maintains the light intensity output by the SOA / VOA 10d at a desired value.

  The light L2 having the TE polarized light P3 output from the end face 10B on the SOA / VOA 10d side is incident on the polarization optical system 7. FIG. 4 is a perspective view showing a 0.5-stage optical isolator 7A of the polarization optical system 7. FIG. 5A and FIG. 5B are schematic diagrams showing the optical path of light incident on the polarization optical system 7. The 0.5-stage optical isolator 7A includes a rotator 7a and a polarizer 7b, and the rotator 7a and the polarizer 7b are integrated. The rotator 7a rotates the polarization plane of the light L2 having the incident TE-polarized light P3 by 45 °. The polarizer 7b transmits only the polarization component rotated by 45 ° with respect to the TE polarized light P3.

  The mirror 7B is disposed on the output side of the polarizer 7b. The mirror 7B receives the light having the polarized light P4 transmitted through the polarizer 7b. The light having the polarization P4 is branched by the mirror 7B. The reflectance of the mirror 7B is, for example, 5%, but can be changed as appropriate. The traveling direction of the light L5 reflected by the mirror 7B differs from the traveling direction of the light L4 transmitted through the mirror 7B by 180 °.

  As shown in FIG. 5A, the light reflected by the mirror 7B is incident on the polarizer 7b again. Here, since there is no rotation of the polarization plane due to reflection by the mirror 7B, the polarization plane of the reflected light P5 and the polarization plane of the incident light P4 are the same, and the reflected light having the polarization P5 is transmitted through the polarizer 7b. To do. The light transmitted through the polarizer 7b reenters the rotator 7a, and the rotator 7a rotates its polarization plane again by 45 °. The light whose polarization plane is further rotated by 45 ° by the rotator 7a is re-applied to the end face 10B of the wavelength tunable LD 10 as light having a polarization plane (TM polarization P7) rotated by 90 ° with respect to the polarization plane of the light having the TE polarization P3. Incident.

  Next, the function and effect of the light emitting module 1 according to this embodiment will be described. In the light emitting module 1, when the light having the TM polarization P7 is incident on the end face 10B of the wavelength tunable LD10, the light is transmitted through the LD10 without interfering with the light having the TE polarization, and the light having the TM polarization P1 is transmitted as the wavelength. Output from the end face 10A of the variable LD 10. Since the light emitting module 1 includes the PBS 4 that separates the light having the TM polarization P1 from the output light L1 and the monitor PD 6a that receives the light having the TM polarization P1, the monitor PD 6a detects the light P1 having the TM polarization. Thus, the intensity of the light having the TM polarized light P7 incident on the end face 10B of the wavelength tunable LD 10 can be detected. Therefore, alignment of the 0.5-stage optical isolator 7A and the mirror 7B constituting the polarization optical system 7 can be performed. During this alignment, the direction parallel to the optical axes of the 0.5-stage optical isolator 7A and the mirror 7B and the angle of the mirror 7B are adjusted so as to maximize the electrical signal output from the monitor PD 6a.

  In the light emitting module 1, the light having the TM polarization P <b> 7 enters the end face 10 </ b> B of the wavelength tunable LD 10. Since the TM polarization component is not substantially absorbed in the wavelength tunable LD 10, the light having the TM polarization component P7 incident from the end face 10B is output from the end face 10A, reaches the monitor PD 6a, is reflected by the monitor PD 6a, and is reflected from the end face 10A. After entering again, the possibility of being output from the end face 10B remains. Alternatively, it is assumed that light having the polarization P5 incident on the end face 10B is reflected by the end face 10B and reaches the 0.5-stage optical isolator 7A again. When light having TM polarization is incident on the wavelength tunable LD 10 after the plane of polarization is rotated by 90 ° by the polarization optical system 7, the characteristics such as the coherent property, line width, etc. of the wavelength tunable LD 10 are extremely deteriorated. End up. However, in the polarizing optical system 7 according to the present invention, the polarization plane of the light having the TM polarized light P8 incident on the 0.5 stage isolator is rotated by 45 ° by the rotator 7a. Here, since the polarizer 7b transmits only light having a polarization plane rotated by 45 ° with respect to the polarization plane of the TE polarization P3, the light having the TM polarization P8 is blocked by the polarizer 7b. The polarization plane of the transmitted light that has passed through the rotator 7a is rotated 135 ° (−45 °) with respect to the polarization plane of the TE polarized light P3. Therefore, it is possible to avoid a situation in which the polarization direction of the light based on the light having the TM polarization P8 is changed to the TE polarization by the polarization optical system 7 and the TE polarization enters the wavelength variable LD 10.

  In the polarization optical system 7, since the rotator 7a and the polarizer 7b are integrated, the polarization optical system 7 can be reduced in size. The light emitting module 1 also includes a monitor PD 6b that receives the monitor light P21 reflected by the reflection filter 5 and converts the monitor light P21 into an electrical signal, and an APC 42 that receives the electrical signal from the monitor PD 6b and controls the optical gain of the SOA 10a. Prepare. Further, the light emitting module 1 receives the light P6 transmitted through the polarization optical system 7 and converts the light P6 into an electrical signal, and the APC 43 that controls the intensity of the output light L2 based on the electrical signal from the monitor PD 6c. Is provided. Accordingly, the APC 42 controls the SOA 10a so that the intensity of the output light L1 becomes a desired value, and the APC 43 controls the SOA / VOA 10d to maintain the intensity of the output light L2 having the TE polarized light P3 at a predetermined value. The frequency noise in the output lights L1 and L2 from the wavelength variable LD 10 can be reduced.

  In addition, the light emitting module 1 may include an optical attenuator for attenuating light input to and output from the mirror 7B in the polarization optical system. Specifically, an optical attenuator (VOA) is disposed between the wavelength tunable LD 10 and the 0.5-stage optical isolator 7A, or between the 0.5-stage optical isolator 7A and the mirror 7B. May be. Thereby, the intensity | strength of the light which has the TM polarized light P7 input into the end surface 10B can be attenuated.

(Second Embodiment)
FIG. 6A shows a beam splitter (BS) 54, a polarization separation filter 55, and monitor PDs 56a and 56b mounted on the light emitting module according to the second embodiment. The BS 54, the polarization separation filter 55, and the monitor PDs 56a and 56b are provided in place of the PBS 4 and the monitor PD 6a of the first embodiment. Below, the detailed description is abbreviate | omitted about the content which overlaps with 1st Embodiment.

  The BS 54 separates the output light L1 output from the wavelength tunable LD 10 through the collimator lens 3a into output light L12 and output light L11. The output light L11 passes through the BS 54. The output light L12 is reflected by the BS 54 and travels in a direction orthogonal to the traveling direction of the output light L11. The reflectance of the BS 54 is 5%, for example. The monitor PD 56a receives the output light L12 and outputs an electrical signal corresponding to the intensity of the received output light L12.

  The polarization separation filter 55 receives the output light L11 optically coupled to the BS 54 and transmitted through the BS 54. The polarization separation filter 55 includes a PBS 55a and a mirror 55b as a unit. The output light L11 is incident on the PBS 55a, and the PBS 55a separates the output light L11 into light P1 having TM polarization and light P2 having TE polarization. The light P2 passes through the PBS 55a.

  The light P1 having TM polarization is reflected by the PBS 55a, further reflected by the mirror 55b, and travels in a direction parallel to the traveling direction of the light P2 having TE polarization. The monitor PD 56b receives the light P1 having TM polarization and outputs an electrical signal corresponding to the intensity of the received light. As described above, since the light emitting module according to the second embodiment can detect the light P1 having TM polarization by the monitor PD 56b, the same effect as that of the first embodiment can be obtained.

(Third embodiment)
FIG. 6B shows an optical arrangement of the polarization separation filter 64 and the monitor PDs 66a and 66b of the light emitting module according to the third embodiment. The polarization separation filter 64 and the monitor PDs 66a and 66b are provided in place of the PBS 4 and the monitor PD 6a of the first embodiment. The polarization separation filter 64 integrally includes a BS 64a and a PBS 64b. The output light L1 enters the BS 64a, and is branched into two output lights L13 and L14 by the BS 64a. The reflectance of BS 64a is 5%, for example. The output light L14 is light transmitted through the BS 64a.

  The branched light L13 enters the PBS 64b, and the PBS 64b separates the branched light L13 into light P1 having TM polarization and light P2 having TE polarization. The light P1 having TM polarization is reflected by the PBS 64b, and the light P2 having TE polarization is transmitted through the PBS 64b. Since the monitor PD 66a detects the light P2 having TE polarization and the monitor PD 66b detects the light P1 having TM polarization, the same effect as in the first and second embodiments can be obtained. Furthermore, in the third embodiment, the number of parts can be reduced as compared with the second embodiment.

(Fourth embodiment)
FIG. 6C shows an arrangement relationship of the polarization separation filter 74, the monitor PDs 76a and 76b, and the shielding member 77 of the light emitting module according to the fourth embodiment. The polarization separation filter 74 and the monitor PDs 76a and 76b have the same configuration as the polarization separation filter 64 and the monitor PDs 66a and 66b of the third embodiment. The shielding member 77 is made of a material that does not substantially transmit light, such as ceramic or metal. The shielding member 77 extends in the propagation direction of the output light L14 from the intermediate portion from the BS 64a to the PBS 64b in the polarization separation filter 74. Therefore, the light P1 having TM polarization and the output light L14 can be isolated.

(Fifth embodiment)
FIG. 7 is a block diagram showing components of the light emitting module according to the fifth embodiment. The fifth embodiment is different from the first embodiment in that a polarizing optical system 87 having a wave plate 87A is provided. The wave plate 87A rotates the polarization plane of the light P3 having TE polarization by 45 °. The light P34 that has passed through the wave plate 87A is reflected by 180 ° by the mirror 7B and is incident on the wave plate 87A again as reflected light P35. The wave plate 87A further rotates the polarization plane of the reflected light P35 by 45 °, so that the light output from the wave plate 87A toward the wavelength variable LD 10 is rotated by 90 ° with respect to the polarization plane of the light P3 having TE polarization. The light P37 having polarization is incident on the end face 10B of the wavelength tunable LD10. Even if the configuration of the polarization optical system is changed as in the fifth embodiment, the light P37 having TM polarization can be detected by the monitor PD 6a as in the first embodiment, and thus the same effect as in the first embodiment can be obtained. can get.

  As mentioned above, although embodiment which concerns on this invention was described, this invention is not limited to embodiment mentioned above. That is, it is easily recognized by those skilled in the art that various modifications and changes can be made within the scope of the present invention described in the claims. For example, in the above-described embodiment, the 0.5-stage optical isolator 7A in which the rotor 7a and the polarizer 7b are integrated has been described. However, the rotor 7a and the polarizer 7b may not be integrated.

DESCRIPTION OF SYMBOLS 1 ... Light emitting module, 2 ... Housing, 2a ... Front wall, 2b ... Rear wall, 2c, 2d ... Side wall, 3a, 3b ... Collimating lens, 4 ... PBS, 5 ... Reflection filter, 6a ... Monitor PD (1st light detection Element), 6b ... monitor PD (third light detection element), 6c ... monitor PD (second light detection element), 6d, 56a, 56b, 66a, 66b, 76a, 76b ... monitor PD, 7 ... polarization optical system, 7A ... 0.5-stage optical isolator, 7B ... Mirror, 7a ... Rotor, 7b ... Polarizer, 8 ... Half mirror, 9 ... Etalon filter, 10 ... Wavelength tunable LD (semiconductor laser), 10A, 10B ... End face, 10a ... SOA (second semiconductor optical amplification region), 10b ... SG-DFB, 10c ... CSG-DBR, 10d ... SOA / VOA (first semiconductor optical amplification region), 12 ... substrate, 13 ... lower cladding layer, 4 ... Optical waveguide layer, 14a ... Active layer, 14b ... Waveguide layer, 15 ... Upper cladding layer, 16 ... Insulating film, 17, 28 ... Heater, 18, 29 ... Power supply electrode, 19, 30 ... Ground electrode, 20, 22 ... contact layer, 21, 23, 31 ... electrode, 24 ... optical waveguide layer, 25, 26 ... active layer, 27 ... SG, 41 ... bias supply unit, 42 ... APC (second control element), 43 ... APC ( First control element), 54, 55a, 64b ... PBS, 55, 64, 74 ... polarization separation filter, 55b ... mirror, 64a ... BS, 77 ... shielding member, A1 ... gain region, A2 ... modulation region, A3 A4, A5 ... segment, B1, B2 ... base, L1, L2 ... output light, L3, L4, L5 ... light.

Claims (8)

A semiconductor laser comprising an active layer;
A polarization optical system that returns the output light to the semiconductor laser after rotating the polarization plane of the output light output from one light exit surface of the semiconductor laser by 90 °;
A polarization separation element that separates output light output from the other light emitting surface of the semiconductor laser into light having a polarization plane perpendicular to the active layer and light having a polarization plane parallel to the active layer; ,
A first light detecting element for detecting light having a polarization plane perpendicular to the active layer separated by the polarization separating element;
A light emitting module comprising: The semiconductor laser has a first semiconductor optical amplification region on the one light emitting surface side,
The light emitting module according to claim 1. A second light detecting element that converts light transmitted through the polarizing optical system into an electrical signal;
A first control element that receives the electrical signal and controls an optical gain of the first semiconductor optical amplification region;
A light emitting module according to claim 2. The semiconductor laser has a second semiconductor optical amplification region on the other light emission surface side,
The light emitting module according to claim 1 or 2. A third photodetector that receives light having a polarization plane parallel to the active layer separated by the polarization separation element, and converts the light having the polarization plane into an electrical signal;
A second control element that receives the electrical signal and controls an optical gain of the second semiconductor optical amplification region;
The light-emitting module according to claim 4. A wavelength detection unit for detecting the wavelength of light transmitted through the polarization optical system;
The light emitting module as described in any one of Claims 1-5. The polarization optical system includes a rotator that rotates a plane of polarization of output light of the semiconductor laser by 45 °, a polarizer that receives light transmitted through the rotator, and directs light transmitted through the polarizer toward the polarizer. And a reflective mirror
A light emitting module according to any one of claims 1 to 6. The polarizing optical system includes a wave plate that receives the output light of the semiconductor laser, a mirror that reflects light transmitted through the wave plate toward the wave plate,
A light emitting module according to any one of claims 1 to 6.

Images