JP2014165377A - Integrated semiconductor laser element and semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an integrated semiconductor laser element which improves a low-noise property over wide bands, and a semiconductor laser device.SOLUTION: The integrated semiconductor laser element is formed by integrating a semiconductor light output part outputting laser light of two or more wavelengths different from each other, and a semiconductor light amplification part which includes an electrode for applying a current to a semiconductor active layer and amplifies output laser light from the semiconductor light output part while guiding it in a length direction. In the semiconductor light amplification part, two or more semiconductor light amplifiers with peak wavelength of amplification gains being different from each other are arrayed in the length direction, and the electrode is formed separately for each semiconductor light amplifier.

Description

  The present invention relates to an integrated semiconductor laser element and a semiconductor laser device.

  For example, as a wavelength variable light source for DWDM (Density Wavelength Division Multiplexing) optical communication, an integrated semiconductor laser element in which a plurality of semiconductor lasers having different laser oscillation wavelengths are integrated is disclosed (for example, see Patent Document 1). This type of integrated semiconductor laser device functions as a wavelength tunable laser by switching the semiconductor laser to be operated and changing the wavelength of the laser beam to be output. An optical combiner and a semiconductor optical amplifier (SOA) are sequentially connected to the plurality of semiconductor lasers. The laser light from the semiconductor laser to be operated passes through the optical combiner, is optically amplified by the SOA, and is output from the output terminal of the element.

  The integrated semiconductor laser device as described above is used by being incorporated in a laser module with a pigtail fiber, for example. Such a laser module is used as a signal light source in combination with an external modulator for long-distance optical transmission in, for example, a DWDM optical communication network system.

JP 2005-317695 A

  Here, the SOA amplifies light by stimulated emission in the active layer of the semiconductor. Therefore, the active layer of the semiconductor needs to be in an inversion distribution state by applying a voltage. At this time, spontaneous emission (ASE) light due to spontaneous emission is also generated in parallel with stimulated emission.

  Examination of the relationship between the wavelength of the integrated semiconductor laser element and the output light intensity reveals that when the integrated semiconductor laser element oscillates at each wavelength, there is an output light component at a wavelength other than the oscillation wavelength. This is ASE light by spontaneous emission, and it can be seen that the peak light intensity of the ASE light is strong particularly on both the short wavelength side and the long wavelength side where the wavelength of the laser light is away from the peak wavelength of the amplification gain of the SOA. In optical communication, this ASE light becomes noise and degrades communication quality. Therefore, there is a demand for a wavelength tunable light source that reduces the generation of ASE light.

  The present invention has been made in view of the above, and an object of the present invention is to provide an integrated semiconductor laser element and a semiconductor laser device which are excellent in low noise over a wide band.

  In order to solve the above-described problems and achieve the object, an integrated semiconductor laser device according to the present invention includes a semiconductor optical output unit that outputs laser beams having two or more different wavelengths, and a current to the semiconductor active layer. And a semiconductor optical amplifier that amplifies the laser light output from the semiconductor optical output unit while guiding the output laser light in the longitudinal direction. The semiconductor optical amplification unit amplifies in the longitudinal direction. Two or more semiconductor optical amplifiers having different gain peak wavelengths are arranged, and the electrodes are formed so as to be spaced apart from each other.

  In the integrated semiconductor laser device according to the present invention as set forth in the invention described above, the semiconductor optical amplifier section is different in the thickness of the active layer or the composition of the active layer in the longitudinal direction.

  The integrated semiconductor laser device according to the present invention is the integrated semiconductor laser device according to the above invention, wherein the semiconductor optical output section is a plurality of distributed feedback semiconductor lasers that oscillate in a single mode at different oscillation wavelengths. Output laser light from each of the semiconductor lasers, and an optical converging unit capable of combining and outputting the output laser light, and the semiconductor optical amplifier outputs the semiconductor optical output via the optical converging unit The output laser light from the unit is amplified while being guided in the longitudinal direction.

  In the integrated semiconductor laser device according to the present invention, the wavelength of the laser light output from the semiconductor optical output unit is the saturation wavelength of the amplification gain of at least one of the semiconductor optical amplifiers. It is included in the belt.

  In the integrated semiconductor laser device according to the present invention as set forth in the invention described above, the wavelength of the laser light output from the semiconductor light output unit is any one of 1520 nm and 1610 nm.

  The integrated semiconductor laser element according to the present invention is the laser that is finally output from the integrated semiconductor laser element in any of the above-mentioned inventions, for any wavelength of laser light output from the semiconductor optical output unit. The ratio of signal light to spontaneous emission of light is 40 dB / nm or more.

  The integrated semiconductor laser device according to the present invention is the integrated semiconductor laser device according to the above invention, wherein the semiconductor optical amplifier has a peak wavelength of amplification gain on the long wavelength side, and the semiconductor optical amplifier is located at a position close to the semiconductor optical output unit. The semiconductor optical amplifier disposed and having a peak wavelength of amplification gain on the short wavelength side is disposed at a position far from the semiconductor optical output section.

  According to another aspect of the present invention, there is provided a semiconductor laser device comprising: the integrated semiconductor laser element according to the invention described above; and a current application unit that applies a current to the semiconductor optical amplification unit, wherein the current application unit includes the semiconductor optical device. Among the amplifiers, the largest amount of current is applied to the semiconductor optical amplifier having a peak wavelength of amplification gain close to the wavelength of the output laser light from the semiconductor optical output unit.

  Further, in the semiconductor laser device according to the present invention, in the above invention, the wavelength of the output laser light from the semiconductor optical output unit is a saturation wavelength band of the amplification gain of any one of the semiconductor optical amplifiers. Is applied to the semiconductor optical amplifier so that the laser light intensity finally output from the integrated semiconductor laser element is constant regardless of the wavelength, and the current application unit further includes the semiconductor optical amplifier. A current is applied to the semiconductor optical amplifier other than the amplifier so that the light intensity output from the semiconductor optical amplifier is equal to or lower than the light intensity input to the semiconductor optical amplifier.

  According to the present invention, it is possible to realize an integrated semiconductor laser element and a semiconductor laser device that are excellent in low noise over a wide band.

FIG. 1 is a schematic plan view of a semiconductor laser device using an integrated semiconductor laser element according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing a part of a section taken along line II-II of the integrated semiconductor laser device shown in FIG. 3 is a cross-sectional view of the integrated semiconductor laser element shown in FIG. 1 taken along the line III-III. 4 is a view showing a part of a cross section taken along line IV-IV of the integrated semiconductor laser device shown in FIG. FIG. 5 is a longitudinal sectional view of the semiconductor optical amplifier in the integrated semiconductor laser device shown in FIG. FIG. 6 is a diagram for explaining an example of the manufacturing method of the integrated semiconductor laser device according to the first embodiment. FIG. 7 is a diagram showing the relationship between the peak wavelength at which the amplification gain of the semiconductor optical amplifier is maximized and the active layer thickness ratio. FIG. 8 is a diagram illustrating the relationship between the wavelength of each semiconductor optical amplifier in the integrated semiconductor laser device according to the example and the ratio of the signal light to the spontaneous emission light ratio of the laser light finally output from the integrated semiconductor laser device. is there. FIG. 9 shows the relationship between the wavelength of the integrated semiconductor laser element according to the example and the integrated semiconductor laser element according to the comparative example and the ratio of the signal light to the spontaneous emission light ratio of the laser light finally output from the integrated semiconductor laser element. It is a figure showing a relationship. FIG. 10 is a longitudinal sectional view of the semiconductor optical amplifier in the integrated semiconductor laser device according to the second embodiment of the present invention. FIG. 11 is a diagram for explaining an example of a manufacturing method of the integrated semiconductor laser device according to the second embodiment of the present invention. FIG. 12 is a diagram for explaining an example of a manufacturing method of the integrated semiconductor laser device according to the second embodiment of the present invention. FIG. 13 is a diagram for explaining an example of a manufacturing method of the integrated semiconductor laser device according to the second embodiment of the present invention. FIG. 14 is a diagram for explaining an example of the method of manufacturing the integrated semiconductor laser device according to the second embodiment of the present invention. FIG. 15 is a diagram for explaining an example of the manufacturing method of the integrated semiconductor laser device according to the second embodiment of the present invention. FIG. 16 is a diagram for explaining an example of the manufacturing method of the integrated semiconductor laser device according to the second embodiment of the present invention. FIG. 17 is a cross-sectional view in the longitudinal direction of the semiconductor optical amplifier in the integrated semiconductor laser device according to the third embodiment of the present invention. FIG. 18 is a diagram for explaining an example of the manufacturing method of the integrated semiconductor laser device according to the third embodiment of the present invention. FIG. 19 is a longitudinal sectional view of the semiconductor optical amplifier in the integrated semiconductor laser device according to the fourth embodiment of the present invention. FIG. 20 is a cross-sectional view in the longitudinal direction of the semiconductor optical amplifier in the integrated semiconductor laser device according to the fifth embodiment of the present invention.

  Hereinafter, embodiments of an integrated semiconductor laser device and a semiconductor laser device according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments. In the description of the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. Further, the drawings are schematic, and it should be noted that the relationship between the thickness and width of each layer, the ratio of each layer, and the like may differ from the actual situation. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included.

(Embodiment 1)
FIG. 1 is a schematic plan view of a semiconductor laser device using an integrated semiconductor laser element according to Embodiment 1 of the present invention. As shown in FIG. 1, the semiconductor laser device 100 has a configuration in which a power supply device 17 that is a current application unit is further connected to the integrated semiconductor laser element 1 according to the first embodiment. The power supply device 17 applies current to the DFB lasers 11-1 to 11 -N (N is an integer of 2 or more) and the SOAs 14-1, 14-2, and 14-3 of the integrated semiconductor laser element 1.

  The integrated semiconductor laser device 1 includes N DFB lasers 11-1 to 11-N, which are semiconductor optical output units, each having a mesa structure, N optical waveguides 12-1 to 12-N, It has a structure in which the optical combiner 13 that is a converging part and the three SOAs 14-1, 14-2, and 14-3 that are semiconductor optical amplifying parts are integrated on one semiconductor substrate and embedded in the embedding part 15. In the buried portion 15 between the DFB lasers 11-1 to 11-N, trench grooves 16-1 to 16-M (M = N-1) are provided.

  The DFB lasers 11-1 to 11 -N are edge-emitting lasers each having a stripe-shaped embedded structure with a width of 1.5 μm to 3 μm, and at one end of the integrated semiconductor laser element 1 at a pitch of, for example, 25 μm. Is formed. In the DFB lasers 11-1 to 11-N, the output light becomes single-mode oscillation laser light by making the intervals of diffraction gratings provided in the respective DFB lasers different from each other, and the laser oscillation wavelength is, for example, 1530 nm to They are configured to be different from each other in the range of 1570 nm. The oscillation wavelengths of the DFB lasers 11-1 to 11-N can be finely adjusted by changing the set temperature of the integrated semiconductor laser element 1. That is, the integrated semiconductor laser device 1 realizes a wide wavelength tunable range by switching the driving DFB laser and controlling the temperature.

  The range of fine adjustment of the laser oscillation wavelengths of the DFB lasers 11-1 to 11-N by temperature adjustment is preferably about 3 nm or less. Therefore, in order to cover the wavelength range of about 1530 nm to 1570 nm, the number of DFB lasers 11-1 to 11 -N is preferably 12 or more, for example, 16. However, the value of N is not particularly limited. The range of the oscillation wavelength of the DFB lasers 11-1 to 11-N may be, for example, 1570 nm to 1610 nm.

  FIG. 2 is a diagram showing a part of a section taken along line II-II of the integrated semiconductor laser device shown in FIG. As shown in FIG. 2, for example, the DFB laser 11-2 includes an n-type InP buffer layer 22 also serving as a lower cladding, which is sequentially stacked on an n-type InP substrate 21, and a lower InGaAsP-SCH whose composition is continuously changed. A layer (separate configuration heterostructure) layer 23, an active layer 24 having an MQW (Multi-Quantum Well) structure, an upper InGaAsP-SCH layer 25, an InP spacer layer 26, a grating layer 27 made of InGaAsP or AlGaInAs, and a p-type InP layer 28 I have. A diffraction grating is formed on the grating layer 27.

  The layers from the p-type InP layer 28 to a part of the n-type InP buffer layer 22 have a striped mesa structure. This mesa structure is buried with a p-type InP buried layer 32 and an n-type InP current blocking layer 33. A p-type InP cladding layer 34 and an InGaAs contact layer 35 are sequentially stacked on the p-type InP layer 28 and the n-type InP current blocking layer 33. Further, the outer surface of each semiconductor layer is protected by the SiN protective film 38. Further, a part of the SiN protective film 38 is opened on the InGaAs contact layer 35. A p-side electrode 39 is formed in the opening. An n-side electrode 40 is formed on the bottom surface on the n-type InP substrate 21.

  The active layer 24 has a plurality of well layers and barrier layers that are alternately stacked. The well layer and the barrier layer are made of a GaInAsP-based semiconductor material or an AlGaInAs-based semiconductor material. The composition of the active layer 24-1 is set to have a gain peak wavelength in the band corresponding to the oscillation wavelength of the DFB lasers 11-1 to 11-N, for example, near the center of 1530 nm to 1570 nm, that is, near 1550 nm. ing. The wavelength of the gain peak of the semiconductor laser according to the setting of the composition is from 10 ° C. to 50 ° C., which is the operating temperature of the integrated semiconductor laser device 1. Further, the width of the active layer 24 is, for example, 1.4 μm to 1.7 μm. The other DFB lasers 11-1, 11-3 to 11-N have substantially the same structure as the DFB laser 11-2, including the composition and thickness of the active layer.

  The optical combiner 13 is an MMI (Multi-Mode Interferometer) type optical coupler having N input ports and one output port. 3 is a cross-sectional view of the integrated semiconductor laser element shown in FIG. 1 taken along the line III-III. As shown in FIG. 3, the optical combiner 13 has a buried mesa structure similar to that of the DFB lasers 11-1 to 11 -N, but has a stacked structure from the lower InGaAsP-SCH layer 23 to the p-type InP layer 28. It has a structure replaced with a laminated structure of an InGaAsP core layer 30 and an i-type InP layer 31. The optical combiner 13 has a mesa width wider than that of the DFB lasers 11-1 to 11-N. In the optical combiner 13, the opening of the SiN protective film 38 and the p-side electrode 39 are not formed.

  The optical combiner 13 is not limited to the MMI type optical coupler, and may be another N × 1 optical coupler such as a Fresnel coupler.

  The optical waveguides 12-1 to 12-N are formed between the DFB lasers 11-1 to 11-N and the optical combiner 13, and have the same embedded mesa structure as the optical combiner 13. The DFB lasers 11-1 to 11-N and the N input ports of the optical combiner 13 are optically connected.

  The SOA 14-1 is connected to one output port 13 a of the optical combiner 13. 4 is a view showing a part of a cross section taken along line IV-IV of the integrated semiconductor laser device shown in FIG. As shown in FIG. 4, the SOA 14-1 has a buried mesa structure similar to the DFB lasers 11-1 to 11-N. The SOA 14-1 may have a lower InGaAsP-SCH layer and an upper InGaAsP-SCH layer formed in the same manner as the DFB lasers 11-1 to 11-N. In the first embodiment, the n-type InP layer 41 is used. It is assumed that a p-type InP layer 28 is formed. However, the SOA 14-1 does not have the grating layer 27 unlike the DFB lasers 11-1 to 11-N, and a p-type InP layer 28 is formed instead. The composition of the active layer 24-1 of the SOA 14-1 may be the same as that of the active layer 24 of the DFB laser, but a different composition or a different material may be selected as appropriate.

  FIG. 5 is a longitudinal sectional view of the semiconductor optical amplifier in the integrated semiconductor laser device shown in FIG. As shown in FIG. 5, the active layer of the semiconductor optical amplifying unit includes three active layers 24-1, active layers 24-2, and active layers 24-3 having different thicknesses. Further, the p-side electrode 39 formed on the upper portion is formed to be separated by the trench groove 50-1 and the trench groove 50-2. As a result, different intensity currents can be applied to the active layer 24-1, the active layer 24-2, and the active layer 24-3, and the semiconductor optical amplifier is connected in series in three longitudinal directions. Functions as the SOA 14-1, SOA 14-2, and SOA 14-3. The three SOAs function as three SOAs having different amplification gains for each wavelength due to the different thicknesses of the active layers. The widths of the active layers 24-1, 24-2, and 24-3 are, for example, 1.4 μm to 1.7 μm, and the laser beams output from the DFB lasers 11-1 to 11-N are guided in a single mode. The width is not particularly limited as long as it can be made.

  Here, a method for manufacturing an SOA in which the thickness of the active layer is changed will be described. FIG. 6 is a diagram for explaining an example of the manufacturing method of the integrated semiconductor laser device according to the first embodiment. After sequentially stacking the n-type InP buffer layer 22 to the n-type InP layer 41 on the n-type InP substrate 21, a mask M having a shape as shown in FIG. 6 is formed on the outermost surface. Here, when the active layer is grown in the gap of the mask M under a uniform condition, the active layer is formed thick on the left side of the paper with the large width of the mask M, and the active layer is formed on the right side of the paper with the small width of the mask M. Thinly formed. Further, by forming the p-side electrode 39 on the three active layers 24-1, active layer 24-2, and active layer 24-3 having different thicknesses, the three active layers are respectively separated. Different currents can be applied, and three SOAs 14-1, SOA 14-2, and SOA 14-3 can be formed.

  Next, the operation of the integrated semiconductor laser device 1 will be described. First, one DFB laser selected from the DFB lasers 11-1 to 11-N is driven to output a single mode laser beam having a desired wavelength. The output laser light may be modulated signal light obtained by applying a modulated voltage by the power supply device 17, and may be CW light having a constant intensity to which a constant voltage is applied from the power supply device 17. There may be. Since the trench grooves 16-1 to 16-M electrically separate the DFB lasers 11-1 to 11-N, the isolation resistance between the DFB lasers is increased, and 1 of the DFB lasers 11-1 to 11-N One can be selected and driven easily.

  Next, among the plurality of optical waveguides 12-1 to 12-N, the optical waveguide optically connected to the driving DFB laser guides the laser light from the driving DFB laser in a single mode. The optical combiner 13 passes the laser light guided through the optical waveguide and outputs it from the output port 13a. The SOAs 14-1, 14-2, and 14-3 amplify the laser beam output from the output port 13a and output the amplified laser beam from the output end 14a to the outside of the integrated semiconductor laser device 1. The SOAs 14-1, 14-2, and 14-3 are used to compensate for the loss of light by the optical combiner 13 of the laser light from the driving DFB laser and to obtain a light output with a desired intensity from the output end 14a. . When the optical combiner 13 has N input ports and one output port, the intensity of the laser light from the driving DFB laser is attenuated to about 1 / N by the optical combiner 13.

  Here, the integrated semiconductor laser device 1 includes an SOA 14-1 in which laser light of one wavelength selected from the DFB lasers 11-1 to 11-N is connected in series to three series having different amplification gain wavelength characteristics. 14-2 and 14-3. At this time, among the three laser beams SOA 14-1, 14-2, and 14-3 with respect to the wavelength of the laser beam oscillated by the DFB laser, the peak wavelength of the amplification gain is close, and optical amplification is performed with the smallest ASE light. Select a possible SOA. Further, a current is applied to the selected SOA so that the output light intensity from the integrated semiconductor laser element 1 is constant. On the other hand, a current is applied to the other two SOAs so that the light intensity output from the SOA is equal to or lower than the light intensity input to the SOA. Further, when the wavelength of the laser beam output from the semiconductor light output unit is changed, another SOA suitable for the wavelength is selected.

  On the other hand, when amplification is performed with a single SOA, ASE light increases on both sides of the short wavelength side and the long wavelength side where the wavelength of the laser light is away from the peak wavelength of the amplification gain. However, the integrated semiconductor laser element 1 according to the first embodiment is close to the wavelength of the output laser light from the DFB laser that is the semiconductor light output unit among the three SOAs from the power supply device 17 that is the current application unit. The most current is applied to the SOA having the peak wavelength of the amplification gain. Thus, the selected SOA can amplify the output laser light from the DFB laser in the vicinity of the peak wavelength of the amplification gain of the SOA. Therefore, even when the wavelength of the laser light is close to both ends of the short wavelength side and the long wavelength side, an increase in ASE light can be suppressed. As described above, the integrated semiconductor laser device 1 according to the first embodiment can optically amplify with a small amount of ASE light over a wide range, compared with the case where amplification is performed with a single SOA. If generation of ASE light accompanying optical amplification can be reduced, noise of signal light can be reduced. Therefore, the integrated semiconductor laser element 1 according to the first embodiment is an integrated semiconductor laser element that is excellent in low noise over a wide band.

(Example)
Next, examples of the present invention will be described. As an example, the integrated semiconductor laser device according to the first embodiment was actually manufactured and its performance was evaluated. First, it is necessary to determine the thickness of the active layer so that the amplification gains for the wavelengths of the three SOAs have an optimum relationship. Therefore, the relationship between the peak wavelength at which the amplification gain is maximized and the active layer thickness ratio was determined. FIG. 7 is a diagram showing the relationship between the peak wavelength at which the amplification gain of the semiconductor optical amplifier is maximized and the active layer thickness ratio. As shown in FIG. 7, when the thickness of the active layer is changed, the peak wavelength at which the amplification gain is maximized changes. At this time, when the ratio of the thicknesses is SOA14-1, 14-2, and 14-3 and is 1: 0.65: 0.46, the peak wavelengths are 1588 nm, 1564 nm, and 1540 nm, respectively. It falls within the range of 20 nm to 25 nm.

  Next, FIG. 8 shows the relationship between the wavelength of each semiconductor optical amplifier in the integrated semiconductor laser device according to the embodiment and the ratio of the signal light to the spontaneous emission light ratio of the laser light finally output from the integrated semiconductor laser device. FIG. In FIG. 8, the ratio of the thicknesses of the SOAs was set to 1: 0.65: 0.46 as determined in FIG. As shown in FIG. 8, the signal light to spontaneous emission ratio (SSER) of the laser light finally output from the integrated semiconductor laser device 1 is approximately near the peak wavelength of each SOA. It can be seen that there is a saturation wavelength band that is constant. Here, since SSER is the ratio of the signal light in the final output light of the integrated semiconductor laser device 1 to the peak value of the ASE light intensity per 1 nm, the integrated semiconductor laser device has a constant output signal light intensity. When 1 is used, it is equivalent that SSER is large and ASE light is small. Further, the saturation wavelength band is defined as a wavelength band in which the SSER is 3 dB / nm lower than the peak wavelength SSER at which the amplification gain is maximum. Therefore, it can be seen from FIG. 8 that the SSER is 40 dB / nm or more in the saturation wavelength band of each SOA.

  Furthermore, as can be seen from FIG. 8, the saturation wavelength band has a width of about 25 nm to 30 nm with respect to the wavelength. Therefore, from FIG. 7, when the thickness of the active layer is selected so that the peak wavelength of each SOA differs by about 25 nm, the saturation wavelength band of each SOA is connected without any gap, and for any wavelength in the series of wavelength bands. At least one SOA may be a semiconductor optical amplifier having a saturation wavelength band. 8, in the integrated semiconductor laser device 1 according to the first embodiment, the saturation wavelength band A of the SOA 14-1 covers 1577 nm to 1610 nm, and the saturation wavelength band B of the SOA 14-2 ranges from 1553 nm to 1577 nm. The saturation wavelength band C of the SOA 14-3 covers 1520 nm to 1553 nm. At this time, the light can be amplified with a small amount of ASE light by performing optical amplification using an SOA having a saturation wavelength band corresponding to the wavelength of the output light of the DFB laser. Therefore, the integrated semiconductor laser element 1 can output signal light with less ASE light in the wavelength band of 1520 nm or more and 1620 nm or less.

  Further, when the integrated semiconductor laser element is used for communication, it is desirable that the output of the light source be constant. Therefore, as an ideal use condition of the integrated semiconductor laser device, a current that does not absorb light is applied to an SOA whose saturation wavelength band is out of the output light oscillated by the DFB laser, or no current is applied at all. A current having such a strength that the final output light intensity from the integrated semiconductor laser element is constant regardless of the wavelength is applied to the SOA having a saturation wavelength band in the output light oscillated by the DFB laser without being applied. It is desirable. Therefore, it is preferable that the power supply device 17 in the semiconductor laser device 100 has a function of controlling such an applied current.

  Here, it is generally known that a semiconductor absorbs light having energy larger than band gap energy, that is, light having a wavelength shorter than the peak wavelength of amplification gain. Therefore, for example, when no current is applied and no inversion distribution is formed, in the present integrated semiconductor laser device 1, the SOA 14-1 emits light having a wavelength of 1520 nm to 1577 nm, which is shorter than its saturation wavelength band. Although it absorbs, SOA 14-3 hardly absorbs light having a wavelength of 1553 nm to 1610 nm, which is longer than its saturation wavelength band. At this time, if the SOA 14-3 having a saturation wavelength band on the short wavelength side is disposed at a position close to the semiconductor light output portion in the longitudinal direction, the SOA 14-1 absorbs the light amplified by the SOA 14-3, and the output is lowered. Therefore, it is not preferable. Therefore, it is conceivable to apply a minimum amount of power to the SOA 14-1 so that the SOA 14-1 does not absorb light. However, if power is applied to the SOA 14-1, ASE light is generated, which is not preferable. On the other hand, when the SOA 14-1 having a saturation wavelength band on the long wavelength side is disposed at a position close to the semiconductor light output portion in the longitudinal direction, the light amplified by the SOA 14-1 is hardly absorbed by the SOA 14-3. Therefore, almost no current needs to be applied to the SOA 14-3, and almost no ASE light is generated. Thus, in order to reduce ASE light and further to reduce power consumption, the SOA 14-1 having a saturated wavelength band on the long wavelength side is arranged at a position close to the semiconductor optical output unit, and the short wavelength side It is preferable that the SOA 14-3 having a saturated wavelength band is disposed at a position far from the semiconductor optical output unit.

  FIG. 9 shows the relationship between the wavelength of the integrated semiconductor laser element according to the example and the integrated semiconductor laser element according to the comparative example and the ratio of the signal light to the spontaneous emission light ratio of the laser light finally output from the integrated semiconductor laser element. It is a figure showing a relationship. The integrated semiconductor laser device according to the comparative example in FIG. 9 has a configuration in which the semiconductor optical amplification unit is composed of a single SOA, and the other configuration is the same as that of the integrated semiconductor laser device according to the example. The peak wavelength of the amplification gain of the SOA of this comparative example was 1564 nm, the same as that of the SOA 14-2 of the example. Further, in the integrated semiconductor laser device according to this example, the wavelength band of 1577 nm to 1610 nm is SOA 14-1, the wavelength band of 1553 nm to 1577 nm is SOA 14-2, the wavelength band of 1520 nm to 1553 nm is SOA 14-3, Each will be used for amplification. As shown in FIG. 9, in the comparative example, the SSER is remarkably reduced particularly in the wavelength regions at both the low and high ends, whereas in this example, a high SSER of 40 dB / nm or more is maintained in the entire wavelength band. I understand that. Therefore, it can be seen that the integrated semiconductor laser device according to this example is an integrated semiconductor laser device having excellent low noise over a wide band.

  In this way, by integrating SOAs having different amplification gains for each of a plurality of wavelengths and optimizing the current applied to each SOA, it is possible to realize an integrated semiconductor laser element that is excellent in low noise over a wide band. it can.

(Embodiment 2)
Next, an integrated semiconductor laser element according to the second embodiment of the present invention will be described. FIG. 10 is a longitudinal sectional view of the semiconductor optical amplifier in the integrated semiconductor laser device according to the second embodiment of the present invention. As shown in FIG. 10, the semiconductor optical amplifier of the integrated semiconductor laser device according to the second embodiment includes SOAs 14-1, 14 having active layers 24-1, 24-2, 24-3 having different compositions. -2 and 14-3. The configuration other than the active layer and the configuration other than the semiconductor optical amplifier are the same as those of the integrated semiconductor laser device 1 according to the first embodiment. For example, in a GaInAsP-based material, when the proportion of P is increased and the proportion of As is decreased, the peak wavelength at which the amplification gain is maximized is shortened. Similarly, when the proportion of Ga is increased and the proportion of In is decreased, The peak wavelength at which the amplification gain is maximized is shortened. As a result, as in the integrated semiconductor laser device 1 according to the first embodiment, SOAs having different peak wavelengths that maximize the amplification gain can be manufactured. Therefore, the ASE light can be reduced by optimizing the composition so that the saturation wavelength bands of the three SOAs cover the oscillation wavelength band of the DFB laser. Thus, by changing not only the thickness of the active layer but also the composition of the active layer, it is possible to realize an integrated semiconductor laser device that is excellent in low noise over a wide band.

  Next, an example of a manufacturing method of the integrated semiconductor laser device according to the second embodiment will be described. FIGS. 11 to 16 are views for explaining an example of a manufacturing method of the integrated semiconductor laser device according to the second embodiment of the present invention. First, as shown in FIG. 11, an n-type InP buffer layer 22 to an n-type InP layer 41 are sequentially laminated on an n-type InP substrate 21, and an active layer 24-1 and a p-type InP layer 28 are further laminated. To do. Then, as shown in FIG. 12, a mask M is formed on the outermost surface of the region to be the SOA 14-1, and the active layer 24-1 and the p-type InP layer 28 in the region where the mask M is not formed are removed by etching. To do. Next, as shown in FIG. 13, an active layer 24-2 and a p-type InP layer 28 are selectively stacked in a region where the mask M is not formed. Further, as shown in FIG. 14, a mask M is formed not only on the region to be the SOA 14-1 but also on the outermost surface of the region to be the SOA 14-2. Then, as shown in FIG. 15, the active layer 24-2 and the p-type InP layer 28 in the region where the mask M is not formed are removed by etching. Finally, as shown in FIG. 16, the active layer 24-3 and the p-type InP layer 28 are selectively grown in a region where the mask M is not formed and is to be the SOA 14-3. As a result, SOAs 14-1, 14-2, and 14-3 are formed. When the p-type InP cladding layer 34 to the p-side electrode 39 are formed for each SOA, the integrated semiconductor laser device according to the second embodiment can be manufactured.

  A plurality of SOAs having different active layer thicknesses as in the first embodiment may be formed by a method of repeatedly performing such selective growth and etching.

(Embodiment 3)
Next, an integrated semiconductor laser element according to the third embodiment of the present invention will be described. FIG. 17 is a cross-sectional view in the longitudinal direction of the semiconductor optical amplifier in the integrated semiconductor laser device according to the third embodiment of the present invention. As shown in FIG. 17, the thickness of the semiconductor optical amplifier of the integrated semiconductor laser device according to the third embodiment is continuously changed so that the left side of the paper is thick and the right side of the paper is thin. Other configurations are the same as those of the integrated semiconductor laser device 1 according to the first embodiment. Here, by forming the electrodes apart from each other corresponding to the area to be the SOA, the peak wavelength at which the amplification gain is maximized is different as in the integrated semiconductor laser element 1 according to the first embodiment. An SOA can be manufactured. Therefore, the ASE light can be reduced by optimizing the thickness of the active layer so that the saturation wavelength bands of the three SOAs cover the oscillation wavelength band of the DFB laser. As described above, even when the thickness of the active layer continuously changes, an integrated semiconductor laser element excellent in low noise over a wide band can be realized by forming the electrodes apart from each other.

  Next, an example of a manufacturing method of the integrated semiconductor laser device according to the second embodiment will be described. FIG. 18 is a diagram for explaining an example of the manufacturing method of the integrated semiconductor laser device according to the third embodiment of the present invention. After the n-type InP buffer layer 22 to the n-type InP layer 41 are sequentially laminated on the n-type InP substrate 21, a mask M formed on the outermost surface when the active layer 24 is laminated is shown in FIG. By making the shape, the thickness of the active layer can be continuously changed. Further, by forming the p-side electrode 39 apart from the active layer, currents of different strengths can be applied to the three active layers, respectively, and the three SOAs 14-1, SOA 14-2, SOA 14-3 can be formed. Thus, the integrated semiconductor laser element according to the third embodiment can be realized.

(Embodiment 4)
Next, an integrated semiconductor laser element according to Embodiment 4 of the present invention will be described. FIG. 19 is a longitudinal sectional view of the semiconductor optical amplifier in the integrated semiconductor laser device according to the fourth embodiment of the present invention. As shown in FIG. 19, the semiconductor optical amplifier of the integrated semiconductor laser device according to the fourth embodiment corresponds to the trench grooves 50-1 and 50-2 of the integrated semiconductor laser device 1 according to the first embodiment. The i-type InP current blocking layers 51-1 and 51-2 are formed in the region to be formed. Thus, the electrodes of each SOA may be electrically separated by an insulating layer such as an i-type InP current blocking layer instead of the trench groove.

(Embodiment 5)
Next, an integrated semiconductor laser element according to Embodiment 5 of the present invention will be described. FIG. 20 is a cross-sectional view in the longitudinal direction of the semiconductor optical amplifier in the integrated semiconductor laser device according to the fifth embodiment of the present invention. As shown in FIG. 20, the semiconductor optical amplifier of the integrated semiconductor laser device according to the fifth embodiment corresponds to the trench grooves 50-1 and 50-2 of the integrated semiconductor laser device 1 according to the first embodiment. The resin layer 52-1 and the resin layer 52-2 are formed in the region from the p-type InP layer 28 to the n-type InP buffer layer 22 below it. The resin layer 52-1 and the resin layer 52-2 are insulating materials for electrically separating the electrodes of each SOA, and further, InP and refractive index are set so that no light loss occurs between the SOAs. A close material is preferred. Thus, the electrodes between the SOAs may be electrically separated by an insulating material such as a resin layer, and the insulating layer may be formed below the active layer.

  As described above, according to the above embodiment, an integrated semiconductor laser device excellent in low noise over a wide band can be provided. Furthermore, by connecting the power supply device to the above embodiment, a semiconductor laser device having excellent low noise performance over a wide band can be provided.

  In the above embodiment, the light source that makes the output light incident on the SOA is a DFB laser. However, the present invention is not limited to this, and any light source that outputs light having two or more different wavelengths may be used. At this time, signal light with reduced ASE light is obtained by using, for amplification, an SOA having a saturation wavelength band corresponding to the wavelength of light output from the light source among a plurality of formed SOAs having different saturation wavelength bands. Can do. As a result, an integrated semiconductor laser device excellent in low noise over a wide band can be provided even if a light source other than a DFB laser is used.

  In the above embodiment, the number of SOAs is three, but may be three or more or two. The saturated wavelength band of each SOA is preferably formed continuously with no gap with respect to the wavelength. However, it is not necessarily continuous, and the saturated wavelength band of each SOA causes the output light to enter the SOA. Although it is preferable to cover the output wavelength band of the light source, it is not always necessary to cover the entire output wavelength band.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

DESCRIPTION OF SYMBOLS 1 Integrated semiconductor laser element 11-1 to 11-N DFB laser 12-1 to 12-N Optical waveguide 13 Optical combiner 13a Output port 14-1, 14-2, 14-3 SOA
14a Output end 15 Embedded portion 16-1 to 16-M, 50-1, 50-2 Trench groove 17 Power supply device 21 n-type InP substrate 22 n-type InP buffer layer 23 Lower InGaAsP-SCH layer 24, 24-1, 24 -2, 24-3 Active layer 25 Upper InGaAsP-SCH layer 26 InP spacer layer 27 Grating layer 28 p-type InP layer 30 InGaAsP core layer 31 i-type InP layer 32 p-type InP buried layer 33 n-type InP current blocking layer 34 p Type InP cladding layer 35 InGaAs contact layer 38 SiN protective film 39 p-side electrode 40 n-side electrode 41 n-type InP layer 51-1 and 51-2 i-type InP current blocking layer 52-1 and 52-2 Resin layer 100 Semiconductor laser Equipment A, B, C Saturation wavelength band M Mask

Claims (9)

A semiconductor light output unit that outputs laser beams having two or more wavelengths different from each other;
A semiconductor optical amplifying unit comprising an electrode for applying a current to the semiconductor active layer, and amplifying the laser light output from the semiconductor optical output unit while guiding the laser beam in the longitudinal direction;
Are integrated, and the semiconductor optical amplifier section includes two or more semiconductor optical amplifiers having different peak wavelengths of amplification gain in the longitudinal direction.
The integrated semiconductor laser device, wherein the electrodes are formed separately for each of the semiconductor optical amplifiers.   2. The integrated semiconductor laser device according to claim 1, wherein the semiconductor optical amplifying unit is different in thickness of the active layer or composition of the active layer in the longitudinal direction. The semiconductor optical output unit is a plurality of distributed feedback semiconductor lasers that oscillate in a single mode at different oscillation wavelengths,
Furthermore, an output laser beam from each of the plurality of semiconductor lasers is input, and an optical confluence unit that can output the combined laser beams is output.
3. The integrated type according to claim 1, wherein the semiconductor optical amplifier amplifies an output laser beam from the semiconductor optical output unit while being guided in the longitudinal direction via the optical converging unit. Semiconductor laser element.   The wavelength of the laser beam output from the semiconductor optical output unit is included in a saturation wavelength band of amplification gain of at least one semiconductor optical amplifier among the semiconductor optical amplifiers. The integrated semiconductor laser device according to one.   5. The integrated semiconductor laser device according to claim 1, wherein the wavelength of the laser light output from the semiconductor light output unit is any one of 1520 nm to 1610 nm. .   The ratio of the signal light to the spontaneous emission light of the laser light finally output from the integrated semiconductor laser element is 40 dB / nm or more with respect to the laser light of any wavelength output from the semiconductor light output unit. The integrated semiconductor laser device according to claim 1, wherein the integrated semiconductor laser device is a semiconductor laser device.   In the semiconductor optical amplifier, the semiconductor optical amplifier having an amplification gain peak wavelength on the long wavelength side is disposed at a position close to the semiconductor optical output unit, and the semiconductor optical amplifier has an amplification gain peak wavelength on the short wavelength side. The integrated semiconductor laser device according to claim 1, wherein an amplifier is disposed at a position far from the semiconductor optical output unit. An integrated semiconductor laser device according to claim 1, and a current application unit that applies a current to the semiconductor optical amplification unit,
The current application unit applies the largest amount of current to the semiconductor optical amplifier having a peak wavelength of an amplification gain close to the wavelength of the laser beam output from the semiconductor optical output unit among the semiconductor optical amplifiers. Semiconductor laser device.   When the wavelength of the output laser light from the semiconductor optical output unit is a saturation wavelength band of the amplification gain of any one of the semiconductor optical amplifiers, the integrated semiconductor laser element is included in the semiconductor optical amplifier. Current is applied so that the laser light intensity finally output from the semiconductor optical amplifier is constant regardless of the wavelength, and the current application unit outputs the semiconductor optical amplifier other than the semiconductor optical amplifier from the semiconductor optical amplifier. 9. The semiconductor laser device according to claim 8, wherein a current is applied to the semiconductor optical amplifier so that a light intensity to be applied is equal to or lower than a light intensity input to the semiconductor optical amplifier.

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