Patent Publication Number: US-10320150-B2

Title: Optical semiconductor apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of International Application No. PCT/JP2016/074065, filed on Aug. 18, 2016 which claims the benefit of priority of the prior Japanese Patent Application No. 2015-160846, filed on Aug. 18, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to an optical semiconductor apparatus. 
     For example, an optical semiconductor apparatus where semiconductor laser devices having different emission wavelengths are integrated is known as a wavelength-tunable light source used for DWDM (Dense Wavelength Division Multiplexing) optical communication and the like. In such an optical semiconductor apparatus where semiconductor laser devices are integrated, generally, an optical coupling unit and the semiconductor laser devices are integrated on the same substrate. The optical coupling unit combines laser light beams output from the semiconductor laser devices. The combined laser light is output from the optical semiconductor apparatus. 
     At this point in time, suppose that the optical coupling unit integrated in the optical semiconductor apparatus is one without wavelength selectivity such as a multimode interferometer (MMI: Multi Mode Interferometer) optical coupler, the output optical power of the optical semiconductor apparatus with respect to the output optical power of the semiconductor laser devices is equal to or less than a factor of the number of the integrated semiconductor laser devices. Therefore, a loss is high. 
     Hence, in order to reduce the loss and increase the output efficiency of the device, an optical semiconductor apparatus using an arrayed waveguide grating (AWG: Arrayed Waveguide Grating) as the optical coupling unit is known (see, for example, Japanese Laid-open Patent Publication No. 2008-282937). The AWG includes an input slab waveguide, a waveguide array, and an output slab waveguide. The AWG uses the diffraction phenomenon caused by an optical path difference of the waveguide array to have a similar effect to the diffraction grating. 
     However, if an AWG and semiconductor laser devices having different wavelengths are combined for use, the loss characteristics of the AWG and the gain characteristics of the semiconductor laser device are multiplied. Accordingly, there is a problem that it is difficult to increase the optical power of laser light at a band edge. 
     The AWG has a characteristic that the loss (coupling loss) is the lowest at the central wavelength and the loss increases farther away from the central wavelength. On the other hand, the semiconductor laser device is generally designed such that the gain of the active layer is the largest around the central wavelength. Accordingly, the gain decreases farther away from the central wavelength. As a result, there arises a situation where although the gain of the active layer of the semiconductor laser device at the band edge is low, the loss of laser light at the band edge is also high in the AWG. As a result, if an attempt is made to increase the power of the optical semiconductor apparatus, a power limit at the band edge where the disadvantageous conditions result in being linked restricts power over the entire band by the method of the known technology. 
     SUMMARY 
     It is an object of the present disclosure to at least partially solve the problems in the conventional technology. 
     An optical semiconductor apparatus according to one aspect of the present disclosure includes: semiconductor laser devices having different emission wavelengths and grouped into at least a first group and a second group; and an arrayed waveguide grating connected to the semiconductor laser devices of the first and second groups and configured to combine laser light beams radiating from the semiconductor laser devices into a same point. The arrayed waveguide grating is configured to combine laser light beams from the semiconductor laser devices belonging to the first group into the same point by diffraction in a first diffraction order in the arrayed waveguide grating, and combine laser light beams from the semiconductor laser devices belonging to the second group into the same point by diffraction in a second diffraction order different from the first diffraction order, in the arrayed waveguide grating. 
     An optical semiconductor apparatus according to another aspect of the present disclosure includes: semiconductor laser devices having different emission wavelengths; an arrayed waveguide grating configured to combine laser light beams radiating from the semiconductor laser devices into a same point; and input waveguides configured to guide each of the laser light beams from the semiconductor laser devices to an input facet of an input slab waveguide of the arrayed waveguide grating. There is at least one point where an arrangement order of the input waveguides in a width direction on the input facet is inverted with respect to an order of magnitudes of wavelengths of the laser light beams guided respectively by the input waveguides. 
     The above and other objects, features, advantages and technical and industrial significance of this disclosure will be better understood by reading the following detailed description of presently preferred embodiments of the disclosure, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an optical semiconductor apparatus according to a first embodiment; 
         FIG. 2  is an enlarged view of an interface between a waveguide array and an input slab waveguide; 
         FIG. 3  is an enlarged view of an interface between input waveguides and the input slab waveguide; 
         FIG. 4  is a diagram illustrating the arrangement order of the input waveguides that guide laser light from DFB laser devices to the input slab waveguide; 
         FIG. 5  is a diagram illustrating a graph of the wavelength dependence of an AWG alone; 
         FIG. 6  is a diagram illustrating a graph of results obtained by compensating the wavelength dependence in an integrated device; 
         FIG. 7  is a diagram illustrating a graph of the wavelength dependence of the AWG of a modification of the embodiment; 
         FIG. 8  is a diagram illustrating an optical semiconductor apparatus according to a second embodiment; 
         FIG. 9  is a diagram illustrating an optical semiconductor apparatus according to a third embodiment; 
         FIG. 10  is a diagram illustrating an optical semiconductor apparatus according to a fourth embodiment; 
         FIG. 11  is a diagram illustrating a first modification of a semiconductor optical integrated device; and 
         FIG. 12  is a diagram illustrating a second modification of the semiconductor optical integrated device. 
     
    
    
     DETAILED DESCRIPTION 
     An optical semiconductor apparatus according to embodiments of the present disclosure is described in detail hereinafter with reference to the accompanying drawings. The present disclosure is not limited by the embodiments described below. Moreover, it should be noted that the drawings are schematic, and the dimensional relationship of each component, the ratio of each component, and the like may be different in reality. Portions whose mutual dimensional relationships and ratios are different between the drawings may also be included. 
     First Embodiment 
       FIG. 1  is a diagram illustrating an optical semiconductor apparatus  100  according to a first embodiment. Only a part corresponding to a semiconductor optical integrated device is extracted to describe main portions of the optical semiconductor apparatus  100  illustrated in  FIG. 1 . Therefore, even if an optical system such as a lens to adjust a ray of light output from the semiconductor optical integrated device, a Peltier device and a thermistor to control the temperature of the semiconductor optical integrated device, and the like are not described in  FIG. 1 , they may be included in part of the configuration of the optical semiconductor apparatus  100 . 
     As illustrated in  FIG. 1 , the optical semiconductor apparatus  100  includes a buried waveguide structure region  110  where waveguides are formed by buried waveguides, slab waveguide structure regions  120   a  and  120   b  where a waveguide is formed by a slab waveguide, and a high-mesa waveguide structure region  130  where waveguides are formed by high-mesa waveguides. 
     The buried waveguide structure region  110  includes distributed feed-back (DFB: Distributed Feed-Back) laser devices  111   1  to  111   12  having different emission wavelengths, and input waveguides  113 . The slab waveguide structure region  120   a  includes an input slab waveguide  141 . The slab waveguide structure region  120   b  includes an output slab waveguide  142 . The high-mesa waveguide structure region  130  includes a waveguide array  143 . The input slab waveguide  141 , the output slab waveguide  142 , and the waveguide array  143  form an AWG  140  as one unit. The embodiment is described using the optical semiconductor apparatus  100  with the 12 DFB laser devices  111   1  to  111   12  having different emission wavelengths. However, the embodiment is not limited by the number of the DFB laser devices. 
     The DFB laser devices  111   1  to  111   12  are one mode of the semiconductor laser device. For example, the DFB laser devices  111   1  to  111   12  are designed such that their emission wavelengths are different by 3.5 nm in a 1.55 μm wavelength bandwidth. The DFB laser devices  111   1  to  111   12  have a characteristic that a change in temperature brings a change in emission wavelength. In the optical semiconductor apparatus  100 , one of the DFB laser devices  111   1  to  111   12  is selected to make coarse adjustments to the output wavelength, and the temperature is changed to make fine adjustments to the output wavelength. As a result, the optical semiconductor apparatus  100  as a whole operates as a wavelength-tunable light source that emits laser light within a continuous wavelength range. 
     Moreover, as illustrated in  FIG. 1 , the DFB laser devices  111   1  to  111   12  are grouped into a group G 1  and a group G 2 . In terms of the grouping, they are grouped according to the differences in the emission wavelengths of the DFB laser devices  111   1  to  111   12  as described in detail below. The adjacent DFB laser devices  111   1  to  111   6  and the adjacent DFB laser devices  111   7  to  111   12  are arranged in the same groups such that the emission wavelengths are continuous. However, the emission wavelengths of the DFB laser devices  111   6  and  111   12  that are adjacent to each other are largely different between the groups G 1  and G 2 . In the embodiment, the configuration where the number of groups is two is illustrated by example. However, also if the number of groups is three or more, adjacent DFB laser devices are similarly arranged in the same groups such that the emission wavelengths are continuous. 
     Laser light radiating from the DFB laser devices  111   1  to  111   12  is guided to the input slab waveguide  141  via the input waveguides  113 . The input slab waveguide  141  is a waveguide that does not confine light with respect to a direction parallel to a substrate. The input slab waveguide  141  guides the laser light input from the input waveguides  113  to the waveguide array  143  while being diffracted in the direction parallel to the substrate. 
     The waveguide array  143  includes waveguides formed by bending channels, and is provided with an optical path difference that is dependent on a wavelength. Therefore, if the input position of laser light into the input slab waveguide  141  is changed according to the optical path difference that is dependent on a wavelength, all the wavelengths of the laser light are coupled at the same position at an output end of the output slab waveguide  142 . 
     In the embodiment, laser light radiates directly from an output end  142   a  of the output slab waveguide  142 . The output end  142   a  also serves as an output end of the optical semiconductor apparatus  100 . 
     Here, a specific configuration example of the AWG  140  according to the embodiment is disclosed. 
     A group refractive index n g  of the high-mesa waveguide included in the waveguide array  143  is 3.54, and an effective refractive index n eff  is 3.19. Moreover, an optical path difference ΔL between adjacent waveguides among the waveguides forming the waveguide array  143  is 16.3 μm. A focal length L f  of the AWG  140  is 480 μm. 
     A waveguide spacing d 1  of the waveguide array  143  on an input facet  141   b  of the input slab waveguide  141  is 3.5 μm (see  FIG. 2 ). Moreover, a waveguide spacing d 2  between the input waveguides  113  on an input facet  141   a  of the input slab waveguide  141  is 5 μm (see  FIG. 3 ).  FIGS. 2 and 3  are enlarged views of the input facets  141   b  and  141   a  between the waveguide array  143  and the input waveguides  113 , and the input slab waveguide  141 . As illustrated in  FIGS. 2 and 3 , each of the waveguide array  143  and the input waveguides  113  is tapered in the waveguide width at connection portions of the input facets  141   b  and  141   a  of the input slab waveguide  141 . The waveguide array  143  and the input waveguide  113  are designed to have a large opening for the input facets  141   b  and  141   a  of the input slab waveguide  141 . 
       FIG. 4  is a diagram illustrating the order of arrangement of the input waveguides  113  that guide laser light from the DFB laser devices  111   1  to  111   12  to the input slab waveguide  141 . As illustrated in  FIG. 4 , in this configuration example, the number of the input waveguides  113  that guide laser light to the input slab waveguide  141  is 12 from ch 1  to ch 12 . The channel numbers, ch 1  to ch 12 , of the input waveguides  113  are assigned in order of arrangement with respect to the width direction (the wavelength resolution direction of the AWG  140 ) of the input facet  141   a  of the input slab waveguide  141 . Moreover, the input waveguides  113  of ch 1  to ch 6  are connected to the DFB laser devices  111   7  to  111   12  that belong to the group G 2 . The input waveguides  113  of ch 7  to ch 12  are connected to the DFB laser devices  111   1  to  111   6  that belong to the group G 1 . 
     As illustrated in  FIG. 4 , the input waveguides  113  of ch 1  to ch 6  are connected respectively to the DFB laser devices  111   7  to  111   12  whose emission wavelengths are λ 7  to λ 12 . Moreover, the input waveguides  113  of ch 7  to ch 12  are connected respectively to the DFB laser devices  111   1  to  111   6  whose emission wavelengths are λ 1  to λ 6 . To put it another way, the DFB laser devices  111   1  to  111   6  whose emission wavelengths are λ 1  to λ 6  belong to the group G 1 . The DFB laser devices  111   7  to  111   12  whose emission wavelengths are λ 7  to λ 12  belong to the group G 2 . 
     Here, the emission wavelengths λ 1  to λ 12  are arranged in order of wavelengths from long to short. In other words, the emission wavelengths λ 1  to λ 12  satisfy the following relationship:
 
λ 1 λ 3 λ 4 λ 5 λ 7 λ 8 λ 9 λ 10 λ 11  
 
A wavelength interval Δλ between the emission wavelengths is substantially equal to 3.5 nm. Specifically, λ i-1 −λ i ≈3.5 nm (i=2, . . . , 12). However, as described above, the DFB laser devices  111   1  to  111   12  have the characteristic that a change in the temperature of the device causes the emission wavelength to change. Accordingly, the wavelength interval between the emission wavelengths here is assumed to indicate the wavelength interval at the same temperature. As described above, when the wavelength interval Δλ is set to be substantially equal to 3.5 nm, and a wavelength bandwidth with a central wavelength of 1.55 μm is configured by the 12 DFB laser devices  111   1  to  111   12 , it results in a tunable wavelength bandwidth of 1.53 μm to 1.57 μm.
 
     As illustrated in  FIG. 4 , in the input waveguides of ch 7  to ch 12  assigned to the emission wavelengths λ 1  to λ 6  that belong to the group G 1 , the order of arrangement with respect to the width direction of the input facet  141   a  agrees with the order of arrangement of the emission wavelengths of the connected DFB laser devices  111   1  to  111   6 . Similarly, in the input waveguides of ch 1  to ch 6  assigned to the emission wavelengths λ 7  to λ 12  that belong to the group G 2 , the order of arrangement with respect to the width direction of the input facet  141   a  agrees with the order of arrangement of the emission wavelengths of the connected DFB laser devices  111   7  to  111   12 . 
     On the other hand, as illustrated in  FIG. 4 , the input waveguide of ch 7  assigned to the longest wavelength λ 1  is adjacent to the input waveguide of ch 6  assigned to the shortest wavelength λ 12  between the groups G 1  and G 2 . In other words, the physical arrangement order and the order of arrangement of emission wavelengths change their places between the input waveguide of ch 7  and the input waveguide of ch 6 . To put it another way, there is at least one point where the order of arrangement of input waveguides in the width direction of the input facet is inverted with respect to the order of magnitudes of wavelengths of laser light guided by the input waveguides. In JP-A-2008-282937, the physical arrangement order agrees with the order of arrangement of emission wavelengths in the input waveguides over the entire wavelength bandwidth in the AWG. Accordingly, the arrangement order for the AWG  140  of this configuration is characteristic. 
     As described above, the reason why the AWG  140  has the point where the physical arrangement order of input waveguides and the order of arrangement of emission wavelengths assigned to the input waveguides change their places is that the AWG  140  uses diffraction phenomena of different orders. Specifically, in the AWG  140 , the input waveguides of ch 7  to ch 12  that belong to the group G 1  combine the emission wavelengths λ 1  to λ 6  of laser light, using a diffraction phenomenon where an diffraction order m is 33. The input waveguides of ch 1  to ch 6  that belong to the group G 2  combine the emission wavelengths λ 7  to λ 12  of laser light, using a diffraction phenomenon where the diffraction order m is 34. The emission wavelength bandwidth of laser light corresponding to the group G 1  is substantially equal to half the FSR for the diffraction order m=33. The emission wavelength bandwidth of laser light corresponding to the group G 2  is substantially equal to half the FSR for the diffraction order m=34. Here, the free spectral range (FSR: Free Spectral Range) of the AWG is the largest wavelength bandwidth for a given order that does not overlap the same range in an adjacent order. 
     The reason why the input waveguide of ch 7  assigned to the longest wavelength λ 1  is adjacent to the input waveguide of ch 6  assigned to the shortest wavelength λ 12  is that the input waveguide of ch 7  is the longest wave end in the diffraction order m=33, and the input waveguide of ch 6  is the shortest wave end in the diffraction order m=34. To put it another way, there is a boundary between the diffraction order m=33 and the diffraction order m=34, between the input waveguide of ch 7  assigned to the longest wavelength λ 1  and the input waveguide of ch 6  assigned to the shortest wavelength λ 12 . 
     As in the above description, the FSR of the AWG  140  is substantially equal to a tunable wavelength bandwidth configured by the 12 DFB laser devices  111   1  to  111   12 . The FSR of the AWG  140  is not necessarily required to completely agree with the bandwidth configured by the DFB laser devices  111   1  to  111   12 . The difference between the FSR of the AWG  140  and the bandwidth configured by the DFB laser devices  111   1  to  111   12  may be adjusted by the waveguide spacing between the input waveguide of ch 6  and the input waveguide of ch 7 . In other words, as described above, the waveguide spacing d 2  between input waveguides of channels is 5 μm. However, the waveguide spacing between the input waveguide of ch 6  and the input waveguide of ch 7  is changed from 5 μm to enable absorption of the difference between the FSR of the AWG  140  and the bandwidth configured by the DFB laser devices  111   1  to  111   12 . 
     Here, a description is given of a design guideline of the AWG to achieve the above configuration. 
     A central wavelength λ c  of the AWG  140  is determined according to the arrangement of the emission wavelengths of the DFB laser devices  111   1  to  111   12 . The central wavelength λ c  typically selects the shortest or longest wavelength in the bandwidth configured by the DFB laser devices  111   1  to  111   12 . As described above, this is because the gains of the active layers of DFB laser devices  111   1  to  111   12  are often designed to be the largest around the central wavelength in the bandwidth; therefore, the gain decreases farther away from the central wavelength. In order to suppress the wavelength dependence of the DFB laser devices  111   1  to  111   12  by cancelling out the wavelength characteristic of the gain of the active layer and wavelength characteristic of the AWG  140 , it is preferable to set the central wavelength λ c  of the AWG  140  at the shortest or longest wavelength in the bandwidth configured by the DFB laser devices  111   1  to  111   12 . 
     The central wavelength λ c  of the AWG  140  is not limited to the above example, but may also be set at one other than the shortest or longest wavelength in the bandwidth configured by the DFB laser devices  111   1  to  111   12 . From the viewpoint of improving a minimum value of the optical power among the DFB semiconductor laser devices  111   1  to  111   12 , it is preferable to set the central wavelength λ c  of the AWG  140  at the emission wavelength of a DFB semiconductor laser device  111   1  (i=1 to 12) having the minimum value. Moreover, also if an attempt is made to improve not the minimum value but the average, there may arise a case where a setting at one other than the shortest or longest wavelength in the bandwidth configured by the DFB laser devices  111   1  to  111   12  is optimum. Accordingly, the central wavelength λ c  of the AWG  140  is a parameter that is required to be altered by design as appropriate. 
     Next, the diffraction order m in which the FSR of the AWG  140  is substantially equal to the bandwidth configured by the DFB laser devices  111   1  to  111   12  is selected using the following equation (1). In other words, the diffraction order m in which substantially the same wavelength range as a bandwidth FSR that is determined by required specifications and should be configured by the DFB laser devices  111   1  to  111   12  is calculated by the following equation (1). 
     
       
         
           
             
               
                 
                   
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     Next, the diffraction order m required by the equation (1), and the central wavelength λ c  are used to determine the optical path difference ΔL between adjacent waveguides in the AWG  140  with the following equation (2). 
     
       
         
           
             
               
                 
                   
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     Furthermore, the focal length L f  of the AWG  140  is determined with the following equation (3) such that the waveguide spacing d 2  on the input facet  141   a  of the input slab waveguide  141  is waveguide resolution that matches the wavelength interval Δλ. n s  in the following equation (3) is the effective refractive index of the input slab waveguide. 
     
       
         
           
             
               
                 
                   
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     Here, a description is given of an effect of the compensation of the optical power of when the AWG  140  and the DFB laser devices  111   1  to  111   12  of the embodiment are integrated.  FIG. 5  is a diagram illustrating a graph of wavelength dependence of transmittance of the AWG alone.  FIG. 6  is a diagram illustrating a graph of results where the wavelength dependence is compensated within the integrated device. 
     Both of  FIGS. 5 and 6  describe comparisons between the embodiment, a first comparative example, and a second comparative example. In  FIGS. 5 and 6 , the embodiment is an example where the above-described AWG  140  is used. The first comparative example is an example where a known AWG of the diffraction order m=30 is used. The second comparative example is an example where a known AWG of the diffraction order m=15. The horizontal axes of  FIGS. 5 and 6  describe the wavelength in the 1.55 μm wavelength bandwidth. The vertical axis of  FIG. 5  represents the coupling efficiency of the AWG alone. The vertical axis of  FIG. 6  is an arbitrary unit (a.u.) representing the output optical power. 
     As in the graph illustrated in  FIG. 5 , the wavelength characteristic of the AWGs of the comparative examples is upward convex. The loss at the central wavelength (1.55 μm) in the tunable wavelength bandwidth is the lowest. The loss increases farther away from the central wavelength. Moreover, as in the comparison between the first and second comparative examples, as the diffraction order increases, the tendency is more noticeable. 
     On the other hand, the focal length L f  of the AWG  140  obtained from the equation (3) is inversely proportional to the diffraction order m. Accordingly, the size of the AWG  140  of the second comparative example is increased as compared to the first comparative example. Hence, it is preferable that the diffraction order be high in the viewpoint of the performance of mass production, a reduction in the size of the optical semiconductor apparatus, and an increase in packing density. 
     On the other hand, in terms of the AWG  140  of the embodiment, the wavelength characteristic is downward convex. The loss at the central wavelength (1.55 μm) in the tunable wavelength bandwidth is the largest. The loss decreases farther away from the central wavelength. As described above, this is because in the AWG  140  of the embodiment, the shortest and longest wavelengths in the 1.55 μm wavelength bandwidth are the central wavelength of the AWG  140 . Moreover, the central wavelength (1.55 μm) in the tunable wavelength bandwidth is located at both ends of the input facet  141   a  in order of arrangement with respect to the width direction of the input facet  141   a  of the input slab waveguide  141  even at the center on the wavelength axis of the graph. 
       FIG. 6  illustrates results of the combinations of the wavelength characteristic of the AWGs illustrated in  FIG. 5  and another wavelength dependence within the integrated device. Here, the wavelength dependence of the gain of the active layer of the DFB laser device is assumed. However, the results illustrated in  FIG. 6  are examples. The wavelength dependence varies largely depending on the design of the DFB laser device. Moreover, the results illustrated in  FIG. 6  are wavelength dependence of the gain of the active layer of the DFB laser device. However, also if a semiconductor optical amplifier (SOA: Semiconductor Optical Amplifier) described below is integrated together with the AWG, similar effects may be obtained. 
     As illustrated in  FIG. 6 , in the first and second comparative examples, the wavelength characteristic of the AWG and the wavelength dependence of the gain of the active layer are multiplied. The wavelength dependence of the integrated device as a whole is increased. Specifically, the magnitude of the optical power is large around the central wavelength, but the optical power decreases farther away from the central wavelength. This indicates that if an attempt is made to increase the optical power as the optical integrated device, optical power around 1.53 μm and 1.57 μm restricts the performance as a product. 
     On the other hand, in the AWG  140  of the embodiment, the loss of the wavelength dependence of the AWG  140  alone at the central wavelength is the largest, and the loss decreases farther away from the central wavelength. Accordingly, the wavelength dependence of the AWG  140  alone and the wavelength dependence of the gain of the active layer of the DFB laser device cancel each other out. The difference between the minimum value and the maximum value of the optical power is reduced. As a result, if an attempt is made to increase the optical power as the semiconductor optical integrated device, a high optical power as the product is obtained by the amount of the improvement of the minimum value. This may also be considered as the achievement of a reduction in power consumption by the amount of the improvement of the minimum value. 
       FIG. 7  is a diagram illustrating a graph of the wavelength dependence of the AWG of a modification of the embodiment. The horizontal axis of  FIG. 7  describes the wavelength in the 1.55 μm wavelength bandwidth μm. The vertical axis of  FIG. 7  represents the coupling efficiency of the AWG. As already described, the central wavelength λ c  of the AWG may also be set at one other than the shortest or longest wavelength in the bandwidth configured by the DFB laser devices. This is because, from the viewpoint of improving the minimum value of the gain of the active layer in the DFB laser devices  111   1  to  111   12 , the emission wavelength of the DFB laser device  111   i  (i=1 to 12) having the minimum value is preferable to be set for the central wavelength λ c  of the AWG. The example of the wavelength dependence of the AWG illustrated in  FIG. 7  is an example where the central wavelength λ c  of the AWG is set around a wavelength of 1.543 μm, and a wavelength λ b  at both ends of the arrangement of the input waveguides on the slab waveguide facet is placed around a wavelength of 1.564 μm. If the AWG of the wavelength dependence illustrated in  FIG. 7  is combined with the DFB laser device array whose minimum value of the gain of the active layer is around the wavelength of 1.543 μm, the wavelength dependence is cancelled out to improve the minimum value of the optical power. 
     In this manner, when the AWG  140  of the embodiment is applied to an actual semiconductor optical integrated device, the position of the central wavelength λ c  of the AWG is selected such that the wavelength dependence decreases, according to the wavelength dependence obtained by design of a laser device and an SOA. 
     As described above, the optical semiconductor apparatus  100  according to the first embodiment is configured such that: the semiconductor laser devices  111   1  to  111   12  are grouped into the first group G 1  and the second group G 2 ; Laser light beams from the semiconductor laser devices  111   1  to  111   6  that belong to the first group G 1  are combined into the same point by diffraction in a first diffraction order in the AWG  140 ; and Laser light beams from the semiconductor laser devices  111   7  to  111   12  that belong to the second group G 2  are combined into the same point by diffraction in a second diffraction order different from the first diffraction order, in the AWG  140 . Accordingly, the wavelength dependence of the AWG  140  and the wavelength dependence of the active layers of the DFB laser devices  111   1  to  111   12  may cancel each other out. The wavelength dependence of the optical power of the optical semiconductor apparatus  100  may be reduced. 
     Second Embodiment 
       FIG. 8  is a diagram illustrating an optical semiconductor apparatus  200  according to a second embodiment. Only a part corresponding to a semiconductor optical integrated device is extracted to describe main portions of the optical semiconductor apparatus  200  illustrated in  FIG. 8  as in the optical semiconductor apparatus  100  of the first embodiment. Moreover, the optical semiconductor apparatus  200  according to the second embodiment has a similar configuration to that of the optical semiconductor apparatus  100  of the first embodiment. Therefore, a description of the details is assumed to be omitted as appropriate. 
     As illustrated in  FIG. 8 , the optical semiconductor apparatus  200  includes a buried waveguide structure region  210  where waveguides are formed by buried waveguides, slab waveguide structure regions  220   a  and  220   b  where a waveguide is formed by a slab waveguide, a high-mesa waveguide structure region  230  where waveguides are formed by high-mesa waveguides, and a window structure region  250  without a waveguide structure. 
     The buried waveguide structure region  210  includes DFB laser devices  211   1  to  211   12  having different emission wavelengths, and input waveguides  213 . The slab waveguide structure region  220   a  includes an input slab waveguide  241 . The slab waveguide structure region  220   b  includes an output slab waveguide  242 . The high-mesa waveguide structure region  230  includes a waveguide array  243 . The input slab waveguide  241 , the output slab waveguide  242 , and the waveguide array  243  form an AWG  240  as one unit. The window structure region  250  is formed between the output slab waveguide  242  and an emission end. Laser light radiates from the output slab waveguide  242  via the window structure region  250 . Accordingly, it is possible to suppress return light due to edge reflection and also reduce the astigmatic difference of the laser light that radiates. The embodiment is described here using the optical semiconductor apparatus  200  with the 12 DFB laser devices  211   1  to  211   12  having different emission wavelengths. However, the embodiment is not limited by the number of the DFB laser devices. 
     The DFB laser devices  211   1  to  211   12  are configured to be able to function as a wavelength-tunable light source in a wavelength bandwidth having a central wavelength of, for example, 1.55 μm as in the first embodiment. Moreover, as in the first embodiment, the DFB laser devices  211   1  to  211   12  are grouped into a group G 1  and a group G 2 . In terms of the grouping, as in the first embodiment, the adjacent DFB laser devices  211   1  to  211   6  and the adjacent DFB laser devices  211   7  to  211   12  are arranged in the same groups such that the emission wavelengths are continuous. However, among the emission wavelengths of the DFB laser devices  211   1  to  211   12 , the DFB laser device  211   1  of the shortest wavelength and the DFB laser device  211   12  of the longest wavelength are adjacent across the groups G 1  and G 2 . 
     Laser light radiating from the DFB laser devices  211   1  to  211   12  is guided to the AWG  240  via the input waveguides  213 . A specific configuration of the AWG  240  may be made similar to, for example, that of the AWG  140  of the first embodiment. 
     The optical semiconductor apparatus  200  with the above configuration according to the second embodiment is also configured such that: the semiconductor laser devices  211   1  to  211   12  are grouped into the first group G 1  and the second group G 2 ; Laser light beams from the semiconductor laser devices  211   1  to  211   6  that belong to the first group G 1  are combined into the same point by diffraction in a first diffraction order in the AWG  240 ; and Laser light beams from the semiconductor laser devices  211   7  to  211   12  that belong to the second group G 2  are combined into the same point by diffraction in a second diffraction order different from the first diffraction order, in the AWG  240 . Accordingly, the wavelength dependence of the AWG  240  and the wavelength dependence of the active layers of the DFB laser devices  211   1  to  211   12  may cancel each other out. The wavelength dependence of the optical power of the optical semiconductor apparatus  200  may be reduced. 
     Third Embodiment 
       FIG. 9  is a diagram illustrating an optical semiconductor apparatus  300  according to a third embodiment. Only a part corresponding to a semiconductor optical integrated device is extracted to describe main portions of the optical semiconductor apparatus  300  illustrated in  FIG. 9  as in the optical semiconductor apparatus  100  of the first embodiment. Moreover, the optical semiconductor apparatus  300  according to the third embodiment has a similar configuration to that of the optical semiconductor apparatus  100  of the first embodiment. Therefore, a description of the details is assumed to be omitted as appropriate. 
     As illustrated in  FIG. 9 , the optical semiconductor apparatus  300  includes buried waveguide structure regions  310  and  360  where waveguides are formed by buried waveguides, slab waveguide structure regions  320   a  and  320   b  where a waveguide is formed by a slab waveguide, and a high-mesa waveguide structure region  330  where waveguides are formed by high-mesa waveguides. 
     The buried waveguide structure region  310  includes DFB laser devices  311   1  to  311   12  having different emission wavelengths, and input waveguides  313 . The slab waveguide structure region  320   a  includes an input slab waveguide  341 . The slab waveguide structure region  320   b  includes an output slab waveguide  342 . The high-mesa waveguide structure region  330  includes a waveguide array  343 . The input slab waveguide  341 , the output slab waveguide  342 , and the waveguide array  343  form an AWG  340  as one unit. The buried waveguide structure region  360  includes an SOA  361  and output waveguides  362  and  363 . The embodiment is described using the optical semiconductor apparatus  300  with the 12 DFB laser devices  311   1  to  311   12  having different emission wavelengths. However, the embodiment is not limited by the number of the DFB laser devices. 
     The DFB laser devices  311   1  to  311   12  are configured to be able to function as a wavelength-tunable light source in a wavelength bandwidth having a central wavelength of, for example, 1.55 μm as in the first embodiment. Moreover, as in the first embodiment, the DFB laser devices  311   1  to  311   12  are grouped into a group G 1  and a group G 2 . In terms of the grouping, as in the first embodiment, the adjacent DFB laser devices  311   1  to  311   6  and the adjacent DFB laser devices  311   7  to  311   12  are arranged in the same groups such that the emission wavelengths are continuous. However, among the emission wavelengths of the DFB laser devices  311   1  to  311   12 , the DFB laser device  311   1  of the shortest wavelength and the DFB laser device  311   12  of the longest wavelength are adjacent across the groups G 1  and G 2 . 
     Laser light radiating from the DFB laser devices  311   1  to  311   12  is guided to the AWG  340  via the input waveguides  313 . A specific configuration of the AWG  340  may be made similar to, for example, that of the AWG  140  of the first embodiment. 
     Laser light output from the output slab waveguide  342  of the AWG  340  is guided to the SOA  361  by the output waveguide  362 . The SOA  361  amplifies laser light input from the output waveguide  362 . The output waveguide  363  is a waveguide for guiding the laser light amplified by the SOA  361  to the outside of the optical semiconductor apparatus  300 . 
     As illustrated in  FIG. 9 , the optical semiconductor apparatus  300  according to the third embodiment is configured such that the DFB laser devices  311   1  to  311   12  and the SOA  361  are on the same semiconductor optical integrated device. In such a case, from the viewpoint of manufacture, the active layers of the DFB laser devices  311   1  to  311   12  are often of the same kind as the active layer of the SOA  361 . Therefore, the wavelength dependence of the active layers of the DFB laser devices  311   1  to  311   12  and the wavelength dependence of the active layer of the SOA  361  result in being of the same kind. In other words, a wavelength providing a minimum value of gain in the DFB laser devices  311   1  to  311   12  results in agreeing with a wavelength providing a minimum value of gain of the SOA  361 . Accordingly, a synergistic effect of wavelength dependence works strongly. 
     In the optical semiconductor apparatus  300  according to the third embodiment, the wavelength dependence of the AWG  340  and the wavelength dependence of the active layers of the DFB laser devices  311   1  to  311   12  and the SOA  361  may cancel each other out. Accordingly, even if the synergistic effect of the wavelength dependence works strongly due to the DFB laser devices  311   1  to  311   12  and the SOA  361 , the wavelength dependence of the optical semiconductor apparatus  300  as a whole may be suppressed. If the kinds of the active layers of the DFB laser devices  311   1  to  311   12  and the active layer of the SOA  361  are made the same, the degree of flexibility in design is reduced. However, in the optical semiconductor apparatus  300  according to the third embodiment, flexibility in design is produced in the wavelength dependence of the AWG  340 . Accordingly, flexibility in the suppression of the wavelength dependence may be ensured as the optical semiconductor apparatus  300  as a whole. 
     Moreover, generally, the wavelength dependence of the SOA  361  is larger than the wavelength dependence of the DFB laser devices  311   1  to  311   12 . Hence, it is efficient for design to set the central wavelength of the AWG  340  at a wavelength providing a minimum value of the gain of the SOA. 
     Fourth Embodiment 
       FIG. 10  is a diagram illustrating an optical semiconductor apparatus  400  according to a fourth embodiment. The optical semiconductor apparatus  400  according to the fourth embodiment has a configuration including an SOA, but has a configuration including an SOA being a separate body from a semiconductor optical integrated device unlike the optical semiconductor apparatus  300  according to the third embodiment. 
     As illustrated in  FIG. 10 , the optical semiconductor apparatus  400  according to the fourth embodiment includes a semiconductor optical integrated device  410 , a first optical system  420 , an SOA  430 , a second optical system  440 , and an optical fiber  450 . 
     The semiconductor optical integrated device  410  may have substantially the same configuration as that of the optical semiconductor apparatus  200  according to the second embodiment. Therefore, DFB laser devices included in the semiconductor optical integrated device  410  are grouped into a group G 1  and a group G 2 . In terms of the grouping, adjacent DFB laser devices are arranged in the same groups such that the emission wavelengths are continuous. However, among the emission wavelengths of the DFB laser devices, the DFB laser device of the shortest wavelength and the DFB laser device of the longest wavelength are adjacent across the groups G 1  and G 2 . In addition, the semiconductor optical integrated device  410  also includes an AWG, but has substantially the same configuration as that of the second embodiment. Therefore, its description is omitted here. 
     The first optical system  420  is an optical system for coupling laser light radiating from the semiconductor optical integrated device  410  in space to the SOA  430 . The first optical system  420  includes, for example, two collimator lenses, and collimates the laser light radiating from the semiconductor optical integrated device  410  at a predetermined NA (numerical aperture). The predetermined NA of the collimated light is converted into NA appropriate for the SOA  430 . The laser light is caused to enter the SOA  430 . In the fourth embodiment, when the laser light radiating from the semiconductor optical integrated device  410  is coupled to the SOA  430 , the optical system for spatial coupling is used. However, butt coupling of the semiconductor optical integrated device  410  and the SOA  430  may be used, or waveguides for coupling of a PLC, a Si waveguide, or the like may be used. 
     The SOA  430  is a semiconductor optical amplifying device for amplifying the input laser light. The SOA  430  is a semiconductor optical amplifying device that is independent of the semiconductor optical integrated device  410 . Accordingly, its degree of flexibility in selection is high. If the wavelength bandwidth of the laser light radiating from the semiconductor optical integrated device  410  may be amplified, any semiconductor optical amplifying device may be adopted as the SOA  430  of the embodiment. 
     The second optical system  440  is an optical system for coupling laser light radiating from the SOA  430  in space to the optical fiber  450 . The second optical system  440  includes, for example, two collimator lenses, and collimates the laser light radiating from the SOA  430  at a predetermined NA. The predetermined NA of the collimated light is converted into NA appropriate for the optical fiber  450 . The laser light is caused to enter the optical fiber. 
     The optical semiconductor apparatus  400  with the above configuration may select the SOA  430  separately from the DFB laser devices integrated in the semiconductor optical integrated device  410 . In other words, the degree of flexibility in design for cancelling the wavelength dependence is high. Therefore, not only the cancellation of the wavelength dependence of the active layers of the DFB laser devices and the wavelength dependence of the AWG but also the cancellation effect of the wavelength dependence may be improved by the design of the SOA  430 . As a result, the optical semiconductor apparatus  400  according to the fourth embodiment may not only, for example, improve the minimum value, but also make more advanced adjustments by, for example, a reduction in wavelength dependence over the entire wavelength bandwidth. 
     Moreover, also in the embodiment, as in the third embodiment, efficient design is to set the central wavelength of the AWG at a wavelength providing a minimum value of gain of the SOA  430 . 
     MODIFICATIONS 
     Modifications of the semiconductor optical integrated device are described here. The modifications of the semiconductor optical integrated device, described below, may also be applied to the first to fourth embodiments of the optical semiconductor apparatus after being altered, as appropriate. However, modifications of the first embodiment of the semiconductor optical integrated device are described here as a representative. 
       FIG. 11  is a diagram illustrating a first modification of the semiconductor optical integrated device. Only a part corresponding to a semiconductor optical integrated device  500  illustrated in  FIG. 11  is extracted to describe main portions of an optical semiconductor apparatus. Moreover, a description of the already described details of the semiconductor optical integrated device  500  is assumed to be omitted as appropriate. 
     As illustrated in  FIG. 11 , the semiconductor optical integrated device  500  includes a DFB laser region  510 , an input waveguide region  510   a , slab waveguide structure regions  520   a  and  520   b  where a waveguide is formed by a slab waveguide, and a waveguide array region  530 . 
     However, in the semiconductor optical integrated device  500 , part of the input waveguide region  510   a , the slab waveguide structure regions  520   a  and  520   b , and the waveguide array region  530  include what is called silicon wire waveguides. Parts of the DFB laser region  510  and the input waveguide region  510   a  include waveguides made of an InP-based semiconductor material. In other words, the semiconductor optical integrated device  500  according to the first modification is a hybrid semiconductor optical integrated device including a region R 2  having silicon wire waveguides and a region R 1  having waveguides made of another material. 
     Here, the silicon wire waveguide indicates an optical waveguide configured to include a core made of silicon (Si) and clads with a lower refractive index than that of the core, confine light in the core, and guide the light. 
     The DFB laser region  510  is made of the InP-based semiconductor material, and includes DFB laser devices  511   1  to  511   12  having different emission wavelengths. The DFB laser devices  511   1  to  511   12  are configured to be able to function as a wavelength-tunable light source in a wavelength bandwidth having a central wavelength of, for example, 1.55 μm as in the first embodiment. Moreover, as in the first embodiment, the DFB laser devices  511   1  to  511   12  are grouped into a group G 1  and a group G 2 . In terms of the grouping, as in the first embodiment, the adjacent DFB laser devices  511   1  to  511   6  and the adjacent DFB laser devices  511   7  to  511   12  are arranged in the same groups such that the emission wavelengths are continuous. However, among the emission wavelengths of the DFB laser devices  511   1  to  511   12 , the DFB laser device  511   1  of the shortest wavelength and the DFB laser device  511   12  of the longest wavelength are adjacent across the groups G 1  and G 2 . 
     On the other hand, the slab waveguide structure regions  520   a  and  520   b , and the waveguide array region  530  are made of the silicon-based semiconductor material. The slab waveguide structure regions  520   a  and  520   b , and the waveguide array region  530  include an input slab waveguide  541 , an output slab waveguide  542 , and an AWG  540 , respectively. The functions of these configurations are similar to those of the first embodiment. 
     Input waveguides  513  are formed on both of the InP- and silicon-based regions. The input waveguide  513  including a silicon wire waveguide is optically connected to the input waveguide  513  made of the InP material across the regions R 1  and R 2 . 
     The semiconductor optical integrated device  500  with the above configuration may also cause the wavelength dependence of the AWG  540  and the wavelength dependence of the active layers of the DFB laser devices  511   1  to  511   12  to cancel each other out, and may reduce the wavelength dependence of optical power of the semiconductor optical integrated device  500 . 
       FIG. 12  is a diagram illustrating a second modification of the semiconductor optical integrated device. Only a part corresponding to a semiconductor optical integrated device  600  illustrated in  FIG. 12  is extracted to describe main portions of an optical semiconductor apparatus. Moreover, a description of the already described details of the semiconductor optical integrated device  600  is assumed to be omitted as appropriate. 
     As illustrated in  FIG. 12 , the semiconductor optical integrated device  600  includes a DFB laser region  610 , slab waveguide structure regions  620   aa ,  620   ab , and  620   b  where a waveguide is formed by a slab waveguide, and a waveguide array region  630 . 
     However, in the semiconductor optical integrated device  600 , the slab waveguide structure region  620   ab  and  620   b , and the waveguide array region  630  include what is called silicon wire waveguides. The DFB laser region  610  and the slab waveguide structure region  620   aa  include waveguides made of an InP-based semiconductor material. In other words, the semiconductor optical integrated device  600  according to the second modification is also a hybrid semiconductor optical integrated device including a region R 2  having the silicon wire waveguides and a region R 1  having the waveguides made of another material, as in the first modification. 
     The DFB laser region  610  is formed of the InP-based semiconductor material, and includes DFB laser devices  611   1  to  611   12  having different emission wavelengths, and input waveguides  613 . The DFB laser devices  611   1  to  611   12  are configured to be able to function as a wavelength-tunable light source in a wavelength bandwidth having a central wavelength of, for example, 1.55 μm as in the first embodiment. Moreover, as in the first embodiment, the DFB laser devices  611   1  to  611   1 , are grouped into a group G 1  and a group G 2 . In terms of the grouping, as in the first embodiment, the adjacent DFB laser devices  611   1  to  611   6  and the adjacent DFB laser devices  611   7  to  611   12  are arranged in the same groups such that the emission wavelengths are continuous. However, among the emission wavelengths of the DFB laser devices  611   1  to  611   12 , the DFB laser device  611   1  of the shortest wavelength and the DFB laser device  611   12  of the longest wavelength are adjacent across the groups G 1  and G 2 . Moreover, the slab waveguide structure region  620   aa  is also made of an InP-based semiconductor material, and includes part of an input slab waveguide  641 . 
     On the other hand, the slab waveguide structure regions  620   ab  and  620   b  and the waveguide array region  630  are made of the silicon-based semiconductor material. The slab waveguide structure regions  620   ab  and  620   b  and the waveguide array region  630  include part of an input slab waveguide  641 , an output slab waveguide  642 , and an AWG  640 , respectively. The functions of these configurations are similar to those of the first embodiment. 
     The semiconductor optical integrated device  600  with the above configuration may also cause the wavelength dependence of the AWG  640  and the wavelength dependence of the active layers of the DFB laser devices  611   1  to  611   12  to cancel each other out, and may reduce the wavelength dependence of the optical power of the semiconductor optical integrated device  600 . 
     The optical semiconductor apparatus according to the present disclosure has an effect that the wavelength dependence of optical power may be suppressed. 
     Although the disclosure has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.