JP2009088015A - Diffraction grating device, semiconductor laser, and variable wavelength filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction grating device whose reflection factor peak has small wavelength dependence. <P>SOLUTION: An optical waveguide core 3 of the diffraction grating device 1 has first and second regions 3a and 3b arranged alternately in the direction of a predetermined axis Ax, and those regions 3a and 3b are adjacent to each other. A diffraction grating structure 5 includes diffraction grating portions 5a to 5n disposed in order in the direction of the axis Ax. The diffraction grating portions 5a to 5n are optically coupled to the first region 3a of the optical waveguide core 3. The diffraction grating portions 5a to 5n are periodically arranged. The period of the repetitive arrangement is a value Λs. The diffraction grating portions 5a and 5n are arranged apart from one another. The period of the diffraction grating structure is predetermined by a function f(x) providing the period of chirp diffraction gratings monotonously changing with coordinates on an (x) axis set for the predetermined axis Ax. The chirped period of the respective diffraction grating portions 5a to 5n is predefined by the function f(x). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a diffraction grating device, a semiconductor laser, and a wavelength tunable filter.

Non-Patent Document 1 describes a wavelength tunable laser having a pair of nonuniform diffraction gratings having a plurality of reflection spectrum peaks. A gain region (active layer) is provided between the pair of non-uniform diffraction gratings. In this wavelength tunable laser, the laser oscillation wavelength is greatly changed with a small injection current to each non-uniform diffraction grating using the vernier effect. As the structure of the non-uniform diffraction grating, a sampled diffraction grating (Sampled Grating) and a superstructure diffraction grating (Super Structure Grating) are described.
Optical Integrated Device, Isao Kobayashi, Kyoritsu Shuppan, 1999, p. 116

  When the non-uniform diffraction grating of the wavelength tunable laser described in Non-Patent Document 1 is a sampled diffraction grating, the reflection spectrum of the sampled diffraction grating has maximum values at a plurality of peak wavelengths, and these maximum reflectances. The wavelength dependence of is large. Due to this large wavelength dependence, the laser light output value of the wavelength tunable laser varies greatly with respect to the laser oscillation wavelength. Therefore, in the wavelength tunable laser of Non-Patent Document 1, the optical output of the wavelength tunable laser shows a large wavelength dependency.

  When the non-uniform diffraction grating of the wavelength tunable laser described in Non-Patent Document 1 is a superstructure diffraction grating, the reflection spectrum of the superstructure diffraction grating tries to obtain a uniform reflectance at a plurality of peak wavelengths. The structure becomes complicated. In addition, the reflectance varies due to the influence of manufacturing errors.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a diffraction grating device in which the wavelength dependency of the reflectance peak is small, and a semiconductor laser and a wavelength tunable filter using the diffraction grating device. The purpose is to provide.

  According to one aspect of the present invention, a diffraction grating device includes: (a) an optical waveguide core including first and second regions alternately arranged in a predetermined axis direction; and (b) a predetermined axis direction. A diffraction grating structure including first to nth diffraction grating portions arranged in order, and the first to nth diffraction grating portions are periodically arranged, and the first to nth diffraction gratings The grating portions are optically coupled to the first regions of the optical waveguide core, respectively, and the first to nth diffraction grating portions are arranged apart from each other, and the diffraction grating structure The period is defined by a function that provides a period of the chirped diffraction grating that changes monotonically with respect to coordinates on the coordinate axis taken as the predetermined axis, and the period in each of the first to nth diffraction grating portions is , Defined by the function.

  According to this diffraction grating device, the first to nth diffraction grating portions are periodically arranged, and the period in each of the first to nth diffraction grating portions is determined by a function that provides the period of the chirped diffraction grating. As defined, the optical spectrum of the diffraction grating structure has a plurality of reflectance peaks, and the wavelength dependence of these reflectance peaks is small.

  In the diffraction grating device according to the present invention, it is preferable that a length of the first to nth diffraction grating portions is shorter than an interval between the first to nth diffraction grating portions that are separated from each other. According to this diffraction grating device, the interval between the plurality of reflectance peaks is defined by the sum of the lengths of the first to nth diffraction grating portions and the interval therebetween. Further, when the length of the first to nth diffraction grating portions is shorter than the above-described interval, the full width at half maximum of the spectrum at each reflectance peak can be narrowed.

  The diffraction grating device according to the present invention includes (c) a first cladding region provided on the first to nth diffraction grating portions and the second region of the optical waveguide core, and (d) a second. The optical waveguide core is provided between the first cladding region and the second cladding region, and the first cladding region is disposed apart from each other. Further, the first to nth diffraction grating portions are provided.

  According to this diffraction grating device, the first cladding region is provided between the first to nth diffraction grating portions that are spaced apart from each other, whereby each structure of the first to nth diffraction grating portions is provided. And a coupling coefficient of the diffraction grating having a certain value determined by optical coupling between the diffraction grating and the first region of the optical waveguide core can be periodically generated.

  In the diffraction grating device according to the present invention, the optical waveguide core includes a third region provided adjacent to the first region, and a period in the first to nth diffraction grating portions of the diffraction grating structure. The structure is provided on the surface shape of the third region. In this diffraction grating device, the diffraction grating structure is provided in the form of an optical waveguide core.

  In the diffraction grating device according to the present invention, each of the optical waveguide core, the first cladding region, and the second cladding region may be composed of first to third III-V compound semiconductors. This diffraction grating device is manufactured by applying a semiconductor element manufacturing process. Also, a semiconductor integrated optical element can be provided by integrating the diffraction grating device with another semiconductor element. Alternatively, in the diffraction grating device according to the present invention, the optical waveguide core, the first cladding region, and the second cladding region may be formed of first to third silicon oxides. This diffraction grating device is manufactured by applying a planar waveguide manufacturing process. Also, an integrated optical element can be provided by integrating the diffraction grating device with the waveguide element.

  The diffraction grating device according to the present invention may further include an electrode provided on the diffraction grating structure. According to this diffraction grating device, the refractive index in the diffraction grating structure can be changed by using the electrode.

  A semiconductor laser according to another aspect of the present invention includes (a) a first optical reflector for a laser resonator, (b) a second optical reflector for the laser resonator, and (c). An optical gain region provided in the laser resonator on the substrate and having an optical gain in response to carrier injection, the laser resonator provided on the substrate, and the first light reflection The vessel includes any of the above diffraction grating devices.

  According to this semiconductor laser, the wavelength dependence of the reflectance peak is small in the optical spectrum of the diffraction grating device. For this reason, the wavelength dependence of the optical output of the semiconductor laser is small.

  In the semiconductor laser according to the present invention, the second light reflector may include any one of the diffraction grating devices described above. According to this semiconductor laser, the optical gain region is located between the two diffraction grating devices. For this reason, the laser oscillation wavelength can be changed by the vernier effect using the first and second light reflectors. In this change, the wavelength dependence of the optical output of the wavelength tunable semiconductor laser is small.

  The semiconductor laser according to the present invention includes (d) a third optical reflector for the laser resonator, and (e) optically coupling the first and third optical reflectors with the optical gain region. And an optical coupler. The second light reflector includes an end face of the semiconductor laser, and the third light reflector includes any one of the diffraction grating devices described above.

  According to this semiconductor laser, each of the first and third light reflectors is coupled to the optical gain region by the optical coupler. For this reason, the laser oscillation wavelength can be changed by the vernier effect using the first and third light reflectors. In this change, the wavelength dependence of the optical output of the wavelength tunable semiconductor laser is small.

  In the semiconductor laser according to the present invention, the second optical reflector includes an end face of the semiconductor laser, and the semiconductor laser further includes a ring resonator located in the laser resonator and positioned on the substrate. Can be provided. The ring resonator and the optical gain region constitute a semiconductor light source. In the semiconductor light source, the ring resonator is optically coupled in series with the optical gain region.

  According to this semiconductor laser, the ring resonator has a Fabry-Perot transmission spectrum, and the wavelength dependence of the reflectance peak is small in the optical spectrum of the diffraction grating device. For this reason, the laser oscillation wavelength can be changed by the vernier effect using the diffraction grating device and the ring resonator. In this change, the wavelength dependence of the optical output of the wavelength tunable semiconductor laser is small.

  The semiconductor laser according to the present invention may further include a phase adjuster including an electrode for applying a signal for adjusting the phase of the optical waveguide provided in the laser resonator. The optical waveguide is provided on the substrate. According to this semiconductor laser, the phase matching at the time of wavelength variable becomes easy using the phase adjuster.

  A wavelength tunable filter according to still another aspect of the present invention includes: (a) any one of the diffraction grating devices described above; and (b) a signal for wavelength tuning provided on the diffraction grating structure of the diffraction grating device. A receiving electrode.

  According to this wavelength tunable filter, in addition to the optical spectrum of the diffraction grating device having a plurality of reflectance peaks, the wavelength dependence of these reflectance peaks is small. For this reason, the wavelength dependence of the reflectance of the wavelength tunable filter can be reduced.

  The wavelength tunable filter according to the present invention may further include (c) an optical element optically coupled in series with the diffraction grating device. The optical element is one of the ring resonator and the Fabry-Perot etalon.

  According to this tunable filter, it is possible to provide a tunable filter having a small wavelength-dependent reflectivity by utilizing the vernier effect by a combination of a ring resonator or Fabry-Perot etalon and a diffraction grating device.

  The diffraction grating device, the semiconductor laser, and the wavelength tunable filter described above can be manufactured on a semiconductor substrate, for example. Alternatively, these devices can be fabricated in, for example, an optical waveguide on a quartz substrate. These devices can also be optically coupled with a semiconductor device having a gain waveguide. When the vernier effect is used, the reflection spectrum can be controlled by the refractive index due to temperature change.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, a diffraction grating device having a wavelength dependency of a reflectance peak is provided. In addition, according to the present invention, a semiconductor laser and a wavelength tunable filter using this diffraction grating device are provided.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the diffraction grating device, the semiconductor laser, and the wavelength tunable filter according to the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1 is a drawing schematically showing the structure of a diffraction grating device according to the present embodiment. FIG. 2A is a drawing showing a structure in the vicinity of the waveguide of the diffraction grating device shown in FIG. The diffraction grating device 1 includes an optical waveguide core 3 and a diffraction grating structure 5. The optical waveguide core 3 includes a plurality of first regions 3a and a plurality of second regions 3b, and the first and second regions 3a, 3b are alternately arranged in the direction of a predetermined axis Ax. The first and second regions 3a and 3b are adjacent to each other in the direction of the predetermined axis Ax. The diffraction grating structure 5 includes first to nth diffraction grating portions 5a, 5b, and 5n arranged in order in the direction of a predetermined axis Ax. The first to nth diffraction grating portions 5 a to 5 n are optically coupled to the first region 3 a of the optical waveguide core 3, respectively. The first to nth diffraction grating portions 5a to 5n are periodically arranged. For this reason, the 1st field 3a is arranged periodically and the 2nd field 3b is arranged periodically. The period of these repeated arrangements is the value Λs. The first to nth diffraction grating portions 5a to 5n are spaced apart from each other, and the interval is a length Λsa. Each of the first to nth diffraction grating portions 5a to 5n has a length Λsb. There is a relationship of Λs = Λsa + Λsb between them.

  Apart from this, the period of the diffraction grating structure is a function f () that provides the period of the chirped diffraction grating that changes monotonically with respect to the coordinates on the coordinate axis (the x axis of the coordinate form S) taken on the predetermined axis Ax. x). The chirped period in each of the first to nth diffraction grating portions 5a to 5n is defined by the function f (x).

  FIG. 2B is a diagram for explaining the chirped period in the first to nth diffraction grating portions 5a to 5n. As shown in FIG. 2A, the first to nth diffraction grating portions 5a to 5n are spaced apart from each other, but in FIG. 2B, the first to nth diffraction grating portions are arranged. In order to show the relationship between the chirped periods in each of 5a to 5n, a virtual diffraction grating portion is also indicated by a broken line on the second region 3b.

Throughout the diffraction grating structure 5, the chirped period is defined by the function f (x). As shown in FIG. 2B, in the section (x _{0 to} x ₁ ) on the x-axis, the chirped period of the diffraction grating portion 5a is defined by the function f (x). In the section (x _{2 to} x ₃ ), the chirped period of the diffraction grating portion 5b is defined by the function f (x). In the section (x _{2n to} x _{2n + 1} ), the chirped period of the diffraction grating portion 5n is defined by the function f (x). The function f (x) changes monotonically with the independent variable x, and preferably decreases monotonically with the independent variable x. As the function f (x), for example, a linear function of the coordinate x can be used. For two adjacent diffraction grating portions, the maximum period in one diffraction grating portion is smaller than the minimum period in the other diffraction grating portion.

  The diffraction grating device 1 exhibits an optical spectrum shown in FIG. FIG. 3A shows an optical spectrum provided by simulation. According to this diffraction grating device 1, the first to nth diffraction grating portions 5a to 5n are arranged with a period Λs, and the chirped period in each of the first to nth diffraction grating portions 5a to 5n is Since it is defined by the function f (x), the optical spectrum of the diffraction grating structure 5 has a plurality of reflectance peaks shown in FIG. 3A, and the wavelength dependence of these reflectance peaks is small.

In the simulation model for FIG. 3A, the period Λs is 50 μm, the length Λsb is 8 μm, and the diffraction grating structure has first to tenth diffraction grating parts, that is, diffraction grating parts for 10 periods. including. The chirped period varies in the range of 0.2047 μm to 0.2224 μm. In each diffraction grating portion, a forward wave and a backward wave are optically coupled with a coupling coefficient κ, and κ = 200 cm ⁻¹ was used in this case. Referring to FIG. 3 (a), a reflection spectrum in the 1.55 μm wavelength band is shown. In this reflection spectrum, the wavelength dependence of many reflectance peaks is small.

  The period Λs defines the interval between the plurality of reflectance peaks, and the ratio of the length Λsb to the length Λsa is related to the spectral width of each reflectance peak. In order to narrow the spectrum width, it is preferable that Λsb <Λsa.

  Referring again to FIG. 1 and FIG. 2 (a), the diffraction grating device 1 may further include a first cladding region 7 and a second cladding region 9. The optical waveguide core 3 is provided between the first cladding region 7 and the second cladding region 9. The average refractive index of the optical waveguide core 3 is larger than the refractive indexes of the first cladding region 7 and the second cladding region 9, and light propagating through the optical waveguide is confined in the optical waveguide core 3. The periodic shape in each of the diffraction grating portions 5 a to 5 n is provided by the region 11, and the refractive index of the region 11 is different from the refractive index of the first cladding region 7.

  The first cladding region 7 is provided on the diffraction grating portions 5 a to 5 n and the second region 3 b of the optical waveguide core 3. The first cladding region 7 is provided between the diffraction grating portions 5a to 5n that are arranged apart from each other.

  According to this diffraction grating device 1, the first cladding region 7 is provided between the diffraction grating portions 5 a to 5 n that are spaced apart from each other, so that each of the diffraction grating portions 5 a to 5 n and the optical waveguide core 3 are connected. A diffraction grating with a certain coupling coefficient determined by optical coupling with the first region 3a is provided periodically. In the drawing, the diffraction grating portions 5 a to 5 n are formed immediately above the optical waveguide core 3, but may not be directly above the optical waveguide core 3. For example, the cladding region 7 may form a layer between the diffraction grating portions 5 a to 5 n and the optical waveguide core 3.

  In a preferred embodiment of the diffraction grating device, when the optical waveguide core 3, the first cladding region 7 and the second cladding region 9 are made of first to third III-V compound semiconductors, respectively, this implementation is performed. The example diffraction grating device 1 is manufactured by applying a semiconductor element manufacturing process. The diffraction grating device 1 can be integrated with other semiconductor elements to provide a semiconductor integrated optical element. For example, the optical waveguide core 3 can be made of GaInAsP, the first cladding region 7 and the second cladding region 9 can be made of InP, and the region 11 for the diffraction grating structure 5 can be made of GaInAsP. The GaInAsP hand gap of the optical waveguide core 3 is preferably equal to or less than the GaInAsP band gap of the region 11. The optical waveguide core 3, the first cladding region 7, and the second cladding region 9 are formed from a conductive semiconductor layer deposited on a support 12 such as a conductive InP substrate. If necessary, the support 12 can include a cladding region 9.

In another preferred embodiment of the diffraction grating device, when the optical waveguide core 3, the first cladding region 7 and the second cladding region 9 are made of the first to third silicon oxides, the diffraction of this embodiment is performed. The grating device 1 is manufactured by applying a planar waveguide manufacturing process. Also, an integrated optical element can be provided by integrating the diffraction grating device 1 with a waveguide element. Optical waveguide core 3 is made of SiO ₂ of Ge addition, the first cladding region 7 and the second cladding region 9 is made of SiO ₂ of undoped region 11 may be made of SiO ₂ of Ge added. The Ge concentration of the optical waveguide core 3 is preferably equal to or higher than the Ge concentration of the region 11. The optical waveguide core 3, the first cladding region 7 and the second cladding region 9 are formed from a silicon compound layer deposited on a support 12 such as a Si substrate.

  For example, the material of the optical waveguide core 3 can be the same as the material of the region 11. This structure includes a third region in which the optical waveguide core 3 is provided in the direction of the axis adjacent to the first region 3a and perpendicular to the predetermined axis Ax, and the third region is located at the region 11. To do. The periodic structure in the diffraction grating portions 5a to 5n of the diffraction grating structure 5 is provided by the surface shape of the third region. The diffraction grating structure 5 is provided as the shape of the optical waveguide core 3. This structure has an advantage that the coupling coefficient κ of the diffraction grating can be increased.

  The diffraction grating device 1 can further include an electrode 13 provided on the diffraction grating structure 5. The refractive index of the diffraction grating structure 5 can be adjusted using this electrode 13.

  When the diffraction grating device 1 is formed in a semiconductor element, conductivity can be imparted to the semiconductor. By flowing current from the electrode 13 to the electrode 15, carriers can be injected into the diffraction grating structure 5 to change the refractive index of the diffraction grating structure 5. The refractive index decreases due to the current injection. Alternatively, the refractive index can be changed using the electric field applied by the electrode 13.

  When the diffraction grating device 1 is formed as a planar waveguide element, heat generated by application of an electrical signal to the electrode 13 is used. That is, the electrode 13 is provided for the heater.

FIG. 3B is a diagram showing an example of optical spectrum adjustment using electrodes. The characteristic line A ₁ is a reflection spectrum when a current of 5 mA is injected from the electrode 13, and the characteristic line A ₀ is a reflection spectrum when there is no electrical signal from the electrode 13. Each peak wavelength position of the optical spectrum can be adjusted by applying an electronic signal.

  As described above, the diffraction grating structure 5 includes the diffraction grating parts 5a to 5n, and the period of the diffraction grating parts 5a to 5n is defined by the function f (x) over the entire diffraction grating structure 5. The optical spectrum of 5 (for example, FIG. 3A) is different from the optical spectra of the sampled diffraction grating and the superstructure diffraction grating. FIG. 4 shows an example of the reflection spectrum of the sampled diffraction grating. By comparison between the two, it is understood that the reflection spectrum of the diffraction grating device 1 has an optical spectrum in which the wavelength dependency of the reflectance peak is small.

  Next, a semiconductor laser and a wavelength tunable filter using this diffraction grating device will be described.

  FIG. 5 is a drawing showing the structure of the semiconductor laser according to the present embodiment. The semiconductor laser 21 includes a first light reflector 23a, a second light reflector 23b, and an optical gain region 27. The first and second light reflectors 23 a and 23 b are provided so as to constitute a laser resonator, and the laser resonator is provided on the substrate 31. The optical gain region 27 is provided in the laser resonator on the substrate 31 and has an optical gain in response to carrier injection from the electrode 33. For this optical gain, the optical gain region 27 includes a gain waveguide 35. The first light reflector 23 a includes a structure equivalent to that of the diffraction grating device 1.

  According to the semiconductor laser 21, the wavelength dependency of the reflectance peak is small due to the characteristics of the comb-shaped optical spectrum of the diffraction grating device 1. For this reason, the wavelength dependence of the optical output of the semiconductor laser 21 is small.

  The second light reflector 23 b can include, for example, a diffraction grating (for example, a sampled diffraction grating or a superstructure diffraction grating) that injects a comb-shaped optical spectrum, and can be an end face of the semiconductor laser 21. The first light reflector 23a includes an electrode 37a and an optical waveguide 39a. The optical waveguide 37a includes an optical waveguide core 3 and a diffraction grating structure 5 as shown in FIG. For this reason, the wavelength dependence of the reflectance peak of the reflection spectrum of the first light reflector 23a is small. The wavelength can be changed by the vernier effect using the electrode 37a.

  Alternatively, the second light reflector 23 b can include a structure equivalent to that of the diffraction grating device 1. The second light reflector 23b includes an electrode 37b and an optical waveguide 39b. The optical waveguide 39b includes an optical waveguide core 3 and a diffraction grating structure 5 as shown in FIG. For this reason, also with respect to the second light reflector 23b, the wavelength dependence of the reflectance peak of the reflection spectrum is small.

  In this semiconductor laser 21, the two light reflectors 23a and 23b include the diffraction grating device 1, and the optical gain region is located between the light reflectors 23a and 23b. For this reason, the laser oscillation wavelength can be changed by the vernier effect using the light reflectors 23a and 23b. In this tunable wavelength, the wavelength dependence of the optical output of the tunable semiconductor laser 21 is small.

  The semiconductor laser 21 can further include a phase adjuster 41 provided in the laser resonator. The phase adjuster 41 includes an optical waveguide 43 provided on the substrate 31 and an electrode 45 for applying a signal for phase adjustment of the optical waveguide 43. Use of the phase adjuster 41 facilitates phase matching when changing the wavelength.

  In the semiconductor laser 21, the light reflectors 23 a and 23 b, the optical gain region 27, and the phase adjuster 41 are formed on a single substrate 31. The components of the semiconductor laser 21 (for example, semiconductor stack, optical waveguide, electrode, etc.) are produced by a combination of processes (crystal growth, etching, electrode formation, etc.) for producing a semiconductor element, for example.

  FIG. 5B is a drawing schematically showing a longitudinal section of the semiconductor laser taken along the line I-I shown in FIG. The optical gain region 27 includes an n-type cladding layer 61, a light guide layer 63, an active layer 65a having a quantum well structure, a light guide layer 67a, a p-type cladding layer 69, and a contact layer 71a formed in this order on the substrate 31. And generates light in response to carrier injection. In the optical gain region 27, the electrode 33 is provided on the contact layer 71a. The light reflector 23a includes an n-type cladding layer 61, a light guide layer 63, an optical waveguide core 65b, a diffraction grating structure 68a, a p-type cladding layer 69, and a contact layer 71b, which are sequentially formed on the substrate 31. In the light reflector 23a, an electrode 37a is provided on the contact layer 71b. The diffraction grating structure 68a is composed of a periodic structure provided on the surface of the light guide layer 67b. The phase adjuster 41 includes an n-type cladding layer 61, an optical guide layer 63, an optical waveguide core 65c, an optical guide layer 67c, a p-type cladding layer 69, and a contact layer 71c that are sequentially formed on the substrate 31. In the phase adjuster 41, an electrode 45 is provided on the contact layer 71c. The light reflector 23b includes an n-type cladding layer 61, a light guide layer 63, an optical waveguide core 65d, a diffraction grating structure 68b, a p-type cladding layer 69, and a contact layer 71d that are sequentially formed on the substrate 31. In the light reflector 23b, an electrode 37b is provided on the contact layer 71d. The diffraction grating structure 68b is composed of a periodic structure provided on the surface of the light guide layer 67d. A shared electrode 73 is provided on the back surface of the substrate 31.

The coupling coefficient κ _68b in the diffraction grating structure _68b is different from the coupling coefficient κ _68a in the diffraction grating structure 68a. The period of the diffraction grating part in the diffraction grating structure 68b is different from the period of the diffraction grating part in the diffraction grating structure 68a. Thereby, for example, at the same environmental temperature, the FSR by the diffraction grating structure 68b is different from the FSR of the diffraction grating structure 68a. The reflectance in the diffraction grating structure 68b is different from the reflectance in the diffraction grating structure 68a. In order to obtain the laser beam L _OUT , the reflectance of the diffraction grating structure 68b is smaller than the reflectance of the diffraction grating structure 68a.

The optical confinement in the vertical direction is performed by the cladding layers 61 and 69. Also, lateral light confinement is provided by a striped waveguide structure and a buried layer that embeds this waveguide structure. For example, the active layer in the gain region may have a GaInAsP / GaInAsP quantum well structure having a gain in the 1.25 μm to 1.65 μm band. The optical waveguide layer can be made of a GaInAsP semiconductor having a wavelength shorter than the band gap wavelength of the quantum well structure, and the n-type and p-type cladding layers can be made of InP semiconductor. The contact layer can comprise a highly doped GaInAs layer. The buried layer can be made of semi-insulating InP. Due to the vernier effect using the light reflectors 23a and 23b, the wavelength can be changed over a wide wavelength range with a small injection current. The laser end face is, for example, non-reflective coated, and a laser beam L _OUT is output.

  FIG. 6 is a drawing showing the structure of the semiconductor laser according to the present embodiment. The semiconductor laser 21a includes a first light reflector 23c, a second light reflector 23d, a third light reflector 24a, an optical gain region 27, and an optical coupler 47. Each of the first light reflector 23c and the second light reflector 23d includes the diffraction grating device 1 shown in the present embodiment, in which the period of the diffraction grating portion is different. For example, the first light reflector 23 c and the second light reflector 23 d can each include a semiconductor layer structure similar to the light reflectors 23 a and 23 d in the semiconductor laser 21. The first to third light reflectors 23c, 23d, and 24a are provided on the substrate for the laser resonator. The third light reflector 24a includes an end face of the semiconductor laser 21a, and this laser end face has a reflecting film. A dielectric multilayer film is formed on the end face so as to provide a desired reflectance in a range of 1% to 30%, for example. The optical coupler 47 optically couples the first and second optical reflectors 23 c and 23 d with the optical gain region 27. The optical resonator is formed on the substrate 31. The optical coupler 47 is, for example, an MMI (Multi Mode Interferometer) coupler.

According to this semiconductor laser 21a, each of the first and second light reflectors 23c and 23d is coupled to the optical gain region 27 by the optical coupler 47, and therefore, due to the vernier effect using the light reflectors 23c and 23d. The laser oscillation wavelength can be changed. In this change, the wavelength dependence of the optical output of the wavelength tunable semiconductor laser is small. The optical reflector 23c is optically coupled to the port 47a of the optical coupler 47 through the optical waveguide 49a, and the optical reflector 23d is optically coupled to the port 47b of the optical coupler 47 through the optical waveguide 49b. The optical gain region 27 is optically coupled to the port 47c of the optical coupler 47 through the phase adjuster 41 and the optical waveguide 49c. The light in the optical resonator reciprocates along a path between the light reflector 23c and the light reflector 24 and a path between the light reflector 23d and the light reflector 24a. From the light reflector (laser end face) 24a, laser light L _OUT having a wavelength selected by the vernier effect is provided.

  FIG. 7 is a drawing showing the structure of the semiconductor laser according to the present embodiment. The semiconductor laser 21b includes a light reflector 23e, another light reflector 24b, an optical gain region 27, and a ring resonator 51a. The light reflector 23e includes the diffraction grating device 1 shown in the present embodiment. This diffraction grating device 1 has a period of a reflection peak wavelength different from the FSR (free spectral range) of the ring resonator 51a. For example, the light reflector 23 e can include a semiconductor layer structure similar to the light reflector 23 a in the semiconductor laser 21. The light reflectors 23e and 24b are provided for the laser resonator. The light reflector 24b includes an end face of the semiconductor laser 21a, and a reflection film for the light reflector 24b, for example, a dielectric multilayer film is formed on the laser end face. The semiconductor laser 21b is formed on the substrate 31.

  The ring resonator 51 a is provided in the laser resonator and is located on the substrate 31. The ring resonator 51a includes a closed optical waveguide 53a and an electrode 55a provided on the optical waveguide 53a. The ring resonator 51a and the optical gain region 27 constitute a semiconductor light source 57. In the semiconductor light source 57, the ring resonator 51a is optically coupled in series with the optical gain region 27. The FSR of the ring resonator is, for example, about 25 GHz to 800 GHz.

  According to this semiconductor laser 21b, the ring resonator 51a has a Fabry-Perot transmission spectrum, and the wavelength dependence of the reflectance peak is small in the optical spectrum of the diffraction grating device 1. For this reason, the laser oscillation wavelength can be changed by the vernier effect using the diffraction grating device 1 and the ring resonator 51a. In this change, the wavelength dependence of the optical output of the wavelength tunable semiconductor laser 21b is small. By combining the comb-shaped transmission spectrum of the ring resonator 51 with the comb-shaped reflection spectrum of the light reflector 23e, there is an advantage that the wavelength dependence of the laser light output can be reduced when the wavelength is variable.

  The optical waveguide 53a of the ring resonator 51a is coupled to the optical gain region 27 via the optical coupler 58a and the optical waveguide 59a. The optical waveguide 53a of the ring resonator 51a is coupled to the optical reflector 23e via the optical coupler 58b and the optical waveguide 59b. The optical couplers 58a and 58b are, for example, MMI couplers.

  FIGS. 8A and 8B are diagrams showing the structure of the wavelength tunable filter according to the present embodiment. The wavelength tunable filter 22a includes the diffraction grating device 1 according to the present embodiment, and an electrode 13 provided on the diffraction grating structure 5 of the diffraction grating device 1 and receiving a signal for variable wavelength. The diffraction grating device 1 is provided on a substrate 31. According to the wavelength tunable filter 22a, the optical spectrum of the diffraction grating device 1 has a plurality of reflectance peaks, and the wavelength dependence of these reflectance peaks is small. For this reason, the wavelength dependence of the reflectance of the wavelength tunable filter 22a can be reduced.

  The wavelength tunable filters 22b and 22c are optically coupled in series with the diffraction grating device 1 and have an optical element having a Fabry-Perot comb-shaped transmission spectrum (for example, a ring resonator 51c or a Fabry-Perot etalon 51b). ). According to the wavelength tunable filters 22b and 22c, a tunable filter having a small wavelength-dependent reflectivity is provided by using the vernier effect by the combination of the ring resonator 51c or Fabry-Perot etalon 51b and the diffraction grating device 1. it can. The diffraction grating device 1 has a period of a reflection peak wavelength different from the FSR of the ring resonator 51c and the Fabry-Perot etalon 51b.

The wavelength tunable filter 22b includes a lens 60 provided between the Fabry-Perot etalon 51b and the end face 26a of the wavelength tunable filter 22b. End face 26 a is optically coupled to diffraction grating device 1. In the wavelength tunable filter 22c, the optical waveguide 53c of the ring resonator 51c is coupled to the diffraction grating device 1 via the optical coupler 58c and the optical waveguide 59c. The optical waveguide 53c of the ring resonator 51c is coupled to the end face 26b of the wavelength tunable filter 22c through the optical coupler 58d and the optical waveguide 59d. The end face 26b, the filter light L _F is input and output. The optical couplers 58c and 58d are, for example, MMI couplers. The end faces 26a and 26b are provided with a non-reflective coating. The wavelength tunable filters 22a, 22b, and 22c are manufactured using, for example, a semiconductor manufacturing process.

The incident light L _IN comprising a plurality of wavelength components is incident, out of the wavelength components of the incident light, filtered light L _F of one particular wavelength selected by the diffraction grating device and the ring resonator is outputted. An optical component having a desired wavelength is selected by the vernier effect of the comb-shaped transmission spectrum peak wavelength of the ring resonator filter and the comb-shaped reflection spectrum peak wavelength of the diffraction grating.

  The wavelength tunable filters 22a, 22b, and 22c are not limited to the fabrication on the semiconductor substrate, but can be fabricated using, for example, an optical waveguide on a quartz substrate or a silicon substrate. Optical coupling with a semiconductor device having a waveguide is also possible. The reflection spectrum for utilizing the vernier effect can be controlled by changing the refractive index according to the temperature change.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 is a drawing schematically showing the structure of a diffraction grating device according to the present embodiment. FIG. 2A is a drawing showing the structure in the vicinity of the waveguide of the diffraction grating device shown in FIG. FIG. 2B is a diagram for explaining the chirped period in the first to nth diffraction grating portions 5a to 5n. FIG. 3A shows an optical spectrum provided by the diffraction grating device 1. FIG. 3B is a diagram showing an example of optical spectrum adjustment using electrodes. FIG. 4 shows an example of the reflection spectrum of the sampled diffraction grating. FIG. 5 is a drawing showing the structure of the semiconductor laser according to the present embodiment. FIG. 6 is a drawing showing another structure of the semiconductor laser according to the present embodiment. FIG. 7 is a drawing showing still another structure of the semiconductor laser according to the present embodiment. FIGS. 8A and 8B are diagrams showing the structure of the wavelength tunable filter according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Diffraction grating device, 3 ... Optical waveguide core, 3a, 3b ... Optical waveguide core area, 5 ... Diffraction grating structure, 5a, 5b, 5n ... Diffraction grating part, Ax ... Predetermined axis, Λs ... Period, Λsa ... Length of diffraction grating part, Λ sb ... spacing of diffraction grating part, 7, 9 ... cladding region, 11 ... region, 12 ... support, 13 ... electrode, κ ... coupling coefficient, 21, 21a, 21b ... semiconductor laser, 22a , 22b, 22c ... wavelength tunable filter, 23a, 23b, 23c, 23d, 23e ... optical reflector, 24a, 24b ... another optical reflector, 26a, 26b ... end face, 27 ... optical gain region, 35 ... gain waveguide 37a, 37b ... electrodes, 39a, 39b ... optical waveguide, 41 ... phase adjuster, 43 ... optical waveguide, 45 ... electrode, 47 ... optical coupler, 51a ... ring resonator, 51b ... Fabry-Perot etalon, 51c Ring resonators, 53a ... closed waveguide, 53a ... optical waveguide, 53c ... optical waveguide, 55a, 55c ... electrode, 60 ... lens

Claims (14)

An optical waveguide core including a plurality of first and second regions alternately arranged in a direction of a predetermined axis;
A diffraction grating structure including first to n-th diffraction grating portions arranged in order in the direction of the predetermined axis,
The first to nth diffraction grating portions are optically coupled to the first region of the optical waveguide core, respectively.
The first to nth diffraction grating portions are periodically arranged;
The first to n-th diffraction grating portions are spaced apart from each other;
The period of the grating structure is defined by a function that provides a period of the chirped grating that varies monotonically with respect to coordinates on a coordinate axis taken in the direction of the predetermined axis;
A period in each of the first to nth diffraction grating portions is defined by the function.   2. The diffraction grating device according to claim 1, wherein a length of the first to n-th diffraction grating portions is shorter than a distance between the first to n-th diffraction grating portions spaced apart from each other. The optical waveguide core includes a third region provided adjacent to the first region,
3. The diffraction according to claim 1, wherein the periodic structure in the first to n-th diffraction grating portions of the diffraction grating structure is provided on a surface of the third region. 4. Lattice device. A first cladding region provided on the first to nth diffraction grating portions and the second region of the optical waveguide core;
A second cladding region,
The optical waveguide core is provided between the first cladding region and the second cladding region,
4. The first clad region is provided between the first to nth diffraction grating portions arranged to be spaced apart from each other. 5. The diffraction grating device described in 1.   5. The diffraction grating according to claim 4, wherein the optical waveguide core, the first cladding region, and the second cladding region are each composed of first to third III-V compound semiconductors. 6. device.   The diffraction grating device according to claim 4, wherein the optical waveguide core, the first cladding region, and the second cladding region are made of first to third silicon oxides.   The diffraction grating device according to claim 1, further comprising an electrode provided on the diffraction grating structure. A first light reflector for the laser resonator;
A second light reflector for the laser resonator;
An optical gain region provided in the laser resonator on the substrate and having an optical gain in response to carrier injection;
The laser resonator is provided on the substrate;
The semiconductor laser according to claim 1, wherein the first light reflector includes the diffraction grating device according to claim 1.   9. The semiconductor laser according to claim 8, wherein the second light reflector includes the diffraction grating device according to any one of claims 1 to 5. A third light reflector for the laser resonator;
An optical coupler that optically couples the first and third optical reflectors with the optical gain region;
The second light reflector includes an end face of the semiconductor laser;
9. The semiconductor laser according to claim 8, wherein the second light reflector includes the diffraction grating device according to any one of claims 1 to 5. The second light reflector includes an end face of the semiconductor laser;
The semiconductor laser further includes a ring resonator provided in the laser resonator and positioned on the substrate,
The ring resonator and the optical gain region constitute a semiconductor light source,
9. The semiconductor laser according to claim 8, wherein in the semiconductor light source, the ring resonator is optically coupled in series with the optical gain region. A phase adjuster including an electrode for applying a signal for adjusting the phase of the optical waveguide provided in the laser resonator;
The semiconductor laser according to claim 8, wherein the optical waveguide is provided on the substrate. A tunable filter,
The diffraction grating device according to any one of claims 1 to 7,
A wavelength tunable filter comprising: an electrode provided on the diffraction grating structure of the diffraction grating device and receiving a signal for variable wavelength. An optical element optically coupled in series with the diffraction grating device;
The tunable filter according to claim 13, wherein the optical element is one of the ring resonator and the Fabry-Perot etalon.

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