JP2017161765A - Optical element and light generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a downsized optical element.SOLUTION: An optical element comprises: an optical waveguide 12a; a plurality of diffraction gratings DBR1 to DBR11 that are arranged along the optical waveguide 12a, the plurality of diffraction gratings DBR1 to DBR11 reflecting part of light propagating through the optical waveguide 12a in a direction intersecting with a direction in which the optical waveguide 12a extends, where the wavelengths of the maximum values of reflection light spectra of the rays of light reflected by the diffraction gratings DBR1 to DBR11 are different from each other.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an optical element and a light generation apparatus.

  Conventionally, a light generation apparatus having a semiconductor laser or the like is used in communication. Corresponding to the increase in the amount of communication accompanying the spread of the Internet and the like, an increase in communication speed and an increase in communication capacity in optical communication or optical transmission using a light generation device have been attempted.

  For example, the development of a wavelength tunable laser device with a variable wavelength in a wide wavelength range and a spectral width of 100 kHz or less to support digital coherent communication whose market scale is expanding as a long-distance large-capacity optical transmission system Has been done energetically.

  As an example of the wavelength tunable laser device, there is a wavelength tunable laser device including a silicon platform having a wavelength filter function formed of a silicon-based material and a gain element (for example, a semiconductor optical amplification element: SOA) formed of a compound semiconductor. .

  In order to oscillate light at an oscillation wavelength (grid wavelength) defined at a predetermined interval, the tunable laser device detects the wavelength of the oscillated light and controls the wavelength of the light so that it becomes a target wavelength. .

  FIG. 1 is a diagram showing a conventional tunable laser device.

  The wavelength tunable laser device 101 includes an optical element 110 that outputs the generated laser toward the optical fiber 140, a collimator lens 132, a beam splitter 135, a condenser lens 134, an etalon 136, and a light receiving unit 118a.

  Part of the light generated by the optical element 110 is branched by the beam splitter 135 and received by the light receiving unit 118 a via the etalon 136. Further, the light transmitted through the beam splitter 135 is condensed on the optical fiber 140 by the condenser lens 134.

  In addition, a part of the laser generated by the wavelength tunable laser device 101 is output to the side opposite to the optical fiber 140 and is received by the light receiving unit 118b via the collimator lens 132. The intensity of the light received by the light receiving unit 118b is used for controlling the laser output in the optical element 110.

  As shown in FIG. 2, the light transmittance of the etalon 136 changes periodically with respect to the wavelength. Therefore, the intensity of the light transmitted through the etalon 136 varies depending on the oscillation wavelength of the light generated by the optical element 110. The light intensity is detected by the light receiving unit 118a, and the oscillation wavelength of the laser oscillating from the optical element 110 is detected.

  Normally, the target wavelength (grid wavelength) is set at a wavelength position where the transmittance change rate with respect to the wavelength of the etalon 136 is large (the slope of the slope is large).

  When the oscillation wavelength of the optical element 110 shifts to a longer wavelength side than the target wavelength, the transmittance of the light etalon 136 increases and the intensity of the light detected by the light receiving unit 118a increases. The oscillation wavelength is controlled to be shortened to the short wavelength side.

  On the other hand, when the oscillation wavelength of the optical element 110 shifts to a shorter wavelength side than the target wavelength, the transmittance of the light etalon 136 decreases and the intensity of light detected by the light receiving unit 118a decreases. The oscillation wavelength of the element 110 is controlled to be longer on the longer wavelength side.

  In this way, the oscillation wavelength of the laser oscillated by the wavelength tunable laser device 101 is detected, and the laser is dynamically controlled so that the laser is output at a wavelength that matches the grid wavelength.

  In the example shown in FIG. 1, an optical element for detecting an oscillation wavelength using an etalon is arranged in parallel along the optical path direction of the optical element 110. Further, the optical element for detecting the oscillation wavelength may be arranged at a position (position on the light receiving unit 118b side) in series with the optical path direction of the optical element 110.

JP 2006-245346 A JP 2013-89961 A JP 2014-7435 A

  As shown in FIG. 1, detecting the oscillation wavelength of an optical element using an etalon arranges optical elements such as a beam splitter or an etalon in parallel or in series in the optical path direction. It becomes an increase factor.

  On the other hand, in recent years, it has been required to reduce the size (form factor) of an optical module such as a wavelength tunable laser device. For this reason, in the wavelength tunable laser device, the size of the device is reduced so as to correspond to CFP2 or CFP4, and it has become difficult to arrange the optical elements in parallel or in series in the optical path as described above. .

  It has also been proposed to integrate a semiconductor device such as a ring resonator or an asymmetric Mach-Zehnder interference filter having a periodic transmission characteristic with respect to the wavelength of the input light on a silicon platform to realize the same function as an etalon. ing. However, these semiconductor elements have a larger wavelength dispersion of the refractive index than an optical element using a dielectric material such as quartz forming an etalon. For this reason, even if a ring resonator or the like having a periodic light transmission characteristic similar to that of an etalon is formed, the peak interval (Free Spectral Range: FSR) of the light transmission characteristic becomes unequal. Therefore, using these semiconductor elements makes it difficult to control the oscillation wavelength because an equally spaced grid wavelength (actually a frequency grid) cannot be obtained.

  An object of the present invention is to downsize an optical element.

  Another object of the present invention is to reduce the size of the light generation device.

  In one aspect, the optical element is an optical waveguide and a plurality of diffraction gratings arranged along the optical waveguide, and each of the diffraction gratings transmits a part of light propagating through the optical waveguide to the optical waveguide. A plurality of diffraction gratings that are reflected in a direction intersecting with the extending direction of the waveguide and that have different maximum wavelengths of reflected light spectra of light reflected by the diffraction gratings.

  In one aspect, the light generation device includes an optical waveguide and a plurality of diffraction gratings arranged along the optical waveguide, wherein each of the diffraction gratings transmits a part of light propagating through the optical waveguide. An optical element having a plurality of diffraction gratings that are reflected in a direction intersecting with an extending direction of the optical waveguide and that have different maximum wavelengths of reflected light spectra of light reflected by the diffraction gratings. A light generation unit that propagates light to the optical waveguide, a wavelength selection unit that selects a wavelength of light that oscillates in the optical waveguide, and a light having a wavelength that is selected by the wavelength selection unit in the optical waveguide An oscillating unit to be provided.

  As one aspect, the optical element can be reduced in size.

  Further, as one aspect, a light generation device that generates light of different wavelengths can be downsized.

  The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the appended claims.

  Both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

It is a figure which shows the wavelength variable laser apparatus of a prior art example. It is a figure explaining controlling an oscillation wavelength using an etalon. It is a figure which shows the wavelength tunable laser apparatus of 1st Embodiment disclosed in this specification. It is a figure which shows the optical element which is the principal part of the wavelength variable laser apparatus of 1st Embodiment. It is the X1-X1 line expanded sectional view of FIG. It is the X2-X2 line expanded sectional view of FIG. It is a figure explaining a several diffraction grating. It is a figure which shows the reflected light spectrum of a several diffraction grating. It is a figure explaining controlling the oscillation wavelength of an optical element. It is a figure which shows the optical element of the modification 1 of 1st Embodiment. It is a figure which shows the optical element of the modification 2 of 1st Embodiment. It is a figure which shows the principal part of FIG. It is a figure which shows the wavelength tunable laser apparatus of 2nd Embodiment disclosed in this specification. It is a figure which shows the optical element which is the principal part of the wavelength variable laser apparatus of 2nd Embodiment. It is the Y1-Y1 line expanded sectional view of FIG. It is the Y2-Y2 line expanded sectional view of FIG. It is a figure explaining a several diffraction grating. It is a figure which shows the reflected light spectrum of the diffraction grating of a 1st group and a 2nd group. It is a figure which shows the optical element of the modification 1 of 2nd Embodiment. It is a figure which shows the optical element of the modification 2 of 2nd Embodiment. It is a figure which shows the principal part of FIG.

  Hereinafter, a preferred first embodiment of a wavelength tunable laser device disclosed in this specification will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 3 is a diagram illustrating the wavelength tunable laser device according to the first embodiment disclosed in this specification. FIG. 4 is a diagram illustrating an optical element that is a main part of the wavelength tunable laser device according to the first embodiment. FIG. 5 is an enlarged sectional view taken along line X1-X1 of FIG. 6 is an enlarged sectional view taken along line X2-X2 of FIG.

  The wavelength tunable laser device 1 according to the present embodiment (hereinafter also simply referred to as the device 1) generates a laser by changing the wavelength of the oscillating laser. For this reason, the apparatus 1 detects the wavelength of the oscillating laser, and if it does not match the target wavelength, the apparatus 1 controls the oscillation wavelength so as to match the target wavelength.

  The apparatus 1 includes an optical element 10 that oscillates and outputs a laser at a predetermined wavelength, a temperature adjustment unit 31 that controls the temperature of the optical element 10, and a control unit 30 that controls operations of the optical element 10 and the temperature adjustment unit 31. Is provided.

  The apparatus 1 also includes a collimating lens 32 that converts light output from the optical element 10 into parallel light, a condensing lens 34 that condenses the parallel light onto the optical fiber 40, and return light is incident on the optical element 10. An isolator 33 is provided to prevent this. The light output from the condenser lens 34 propagates through the optical fiber 40 and is output to the outside. Optical elements such as the optical element 10, the temperature adjustment unit 31, the control unit 30, and the isolator 33 are arranged on the substrate 2.

  As illustrated in FIG. 4, the optical element 10 includes three optical waveguides 12 a to 12 c, two ring resonators 13 a and 13 b, a light generation unit 20, and optical elements such as a loop mirror 14. The three optical waveguides 12a to 12c extend in a straight line and are arranged side by side at intervals. Each optical element is integrated on a single silicon substrate 11a using the silicon platform technology except for the light generation unit 20. As the three optical waveguides 12a to 12c and the two ring resonators 13a and 13b, for example, silicon fine wire optical waveguides can be used.

  The ring resonator 13a is disposed between the optical waveguide 12a and the optical waveguide 12b. The optical waveguide 12a and the optical waveguide 12b are optically coupled to the ring resonator 13a. The ring resonator 13b is disposed between the optical waveguide 12b and the optical waveguide 12c. The optical waveguide 12b and the optical waveguide 12c are optically coupled to the ring resonator 13b.

  In the ring resonator 13a, the transmittance of light transmitted through the ring resonator 13a periodically changes with the wavelength. Similarly, also in the ring resonator 13b, the transmittance of light transmitted through the ring resonator 13b periodically changes with the wavelength. The transmission characteristics of light transmitted through the ring resonator 13a and the ring resonator 13b are determined based on the radius of curvature, the refractive index, and the like. The radius of curvature of the ring resonator 13a is preferably different from that of the ring resonator 13b from the viewpoint of accurately controlling the oscillation wavelength using the vernier effect. For example, the radius of curvature of the ring resonator 13a can be 700 μm, and the radius of curvature of the ring resonator 13b can be 650 μm. The radius of curvature of the loop mirror 14 can be 300 μm.

  A heater 16a that changes the light transmission characteristics by changing the refractive index by changing the temperature of the ring resonator 13a is disposed on the ring resonator 13a. Similarly, a heater 16b that controls the light transmission characteristics by changing the refractive index by changing the temperature of the ring resonator 13b is also disposed on the ring resonator 13b.

  A heater 16c that controls the phase of propagating light by changing the refractive index by changing the temperature of the optical waveguide 12c is disposed on the portion of the optical waveguide 12c on the side of the loop mirror 14 in the longitudinal direction. .

  The heaters 16a to 16c can be formed using a metal layer that generates heat when a current such as aluminum or titanium flows. The operations of the heaters 16a to 16c are controlled by the control unit 30.

  As shown in FIG. 6, in the optical element 10, a clad layer 11b is disposed on a silicon substrate 11a, and the three optical waveguides 12a to 12c and the two ring resonators 13a and 13b are embedded in the clad layer 11b. ing. An upper cladding layer 11c is disposed on the cladding layer 11b. The clad layer 11b and the upper clad layer 11c can be formed using, for example, silicon oxide.

  The thickness of the three optical waveguides 12a to 12c and the two ring resonators 13a and 13b can be set to 250 nm, for example, and the width can be set to 500 nm, for example. The distance between the optical waveguide 12a and the ring resonator 13a can be set to 180 nm, for example.

  The light generation unit 20 generates light and propagates the generated light to the optical waveguide 12a. The light generation unit 20 includes an optical waveguide 21 having a gain unit that generates a photon when current is injected. As the light generation unit 20, for example, a semiconductor optical amplification element having a compound semiconductor can be used. As the gain section, a quantum well active layer, a quantum dot active layer, a bulk type active layer, or the like can be used. The optical waveguide 21 is optically coupled to the optical waveguide 12 a on the second end face 20 b side of the light generation unit 20. The optical waveguide 21 extends with a predetermined angle (for example, 7 degrees) from the normal line with respect to the second end face 20b. The optical waveguide 12a also extends at a predetermined angle (for example, 15 degrees) from the normal line with respect to the second end face 20b.

  The path of light propagating through the optical element 10 is formed by the optical waveguide 21 of the light generation unit 20, the optical waveguides 12a to 12c, and the ring resonators 13a and 13b. The light propagating in the light path is reflected between the first end face 20a of the light generation unit 20 and the loop mirror 14 optically coupled to one end of the optical waveguide 12c. . That is, the device 1 includes the first end face 20a of the light generation unit 20 and the loop mirror 14 as an oscillation unit (resonance unit). The first end surface 20a of the light generation unit 20 reflects a part of the light propagating through the optical waveguide 21 toward the first end surface 20a toward the second end surface 20b. Further, the first end face 20a of the light generation unit 20 transmits the other part of the light propagating through the optical waveguide 21 toward the first end face 20a to the outside and outputs it as a laser. As the first end surface 20a of the light generation unit 20, for example, a cleavage plane can be used. The loop mirror 14 reflects the light propagating through the optical waveguide 12c toward the loop mirror 14 toward the opposite side.

  The optical path length including the optical waveguides 12a to 12c and the optical waveguide 21 can be appropriately determined according to the spectral width required for the oscillating laser. In general, as the optical path length increases, a narrow spectral width can be obtained.

  Next, a mechanism for detecting the oscillation wavelength in the optical element 10 will be described below.

  The optical element 10 has a plurality of diffraction gratings DBR1 to DBR11 arranged along the optical waveguide 12a. In the present embodiment, the optical element 10 has 11 diffraction gratings DBR1 to DBR11. Each diffraction grating reflects a part of the light propagating through the optical waveguide 12a in a direction crossing the extending direction of the optical waveguide 12a. In the present embodiment, each of the diffraction gratings DBR1 to DBR11 reflects part of the light propagating through the optical waveguide 12a in the same direction (upward in FIG. 4) orthogonal to the direction in which the optical waveguide 12a extends.

  As shown in FIG. 5, the plurality of diffraction gratings DBR1 to DBR11 are arranged in series along the optical waveguide 12a. The plurality of diffraction gratings DBR1 to DBR11 can be formed by processing the cladding layer 11b from above. The reflectivity and reflected light peak width (bandwidth) of the diffraction grating with respect to the light propagating through the optical waveguide 12a can be determined based on the coupling constant of the diffraction grating. The coupling constant of the diffraction grating can be determined based on the depth of the groove and the distance from the optical waveguide 12a. On the cladding layer 11b on which the plurality of diffraction gratings DBR1 to DBR11 are formed, the upper cladding layer 11c is disposed so as to fill the grooves of the diffraction grating. The plurality of diffraction gratings DBR1 to DBR11 can be arranged on a silicon substrate together with other optical elements by using silicon platform technology.

  A heater 15 is disposed on the upper cladding layer 11c. The heater 15 is disposed above the diffraction gratings DBR1 to DBR11. Although the peak wavelength of the reflected light of each of the diffraction gratings DBR1 to DBR11 is determined based on the period of the grooves of the diffraction grating, an error may occur in the dimensions of the diffraction grating due to the influence of the manufacturing process or the like. The shift of the peak wavelength of the reflected light based on the error in the size of the diffraction grating is adjusted by changing the refractive index of the portion including each diffraction grating using heating by the heater 15. The operation of the heater 15 is controlled by the control unit 30.

  As shown in FIG. 7, each of the diffraction gratings DBR1 to DBR11 has a plurality of periodically formed grooves extending in a direction intersecting with the extending direction of the optical waveguide 12a.

  Specifically, each of the diffraction gratings DBR1 to DBR11 is formed with a plurality of grooves having a direction inclined by 45 degrees with respect to the optical axis direction in which the light of the optical waveguide 12a propagates. Each of the diffraction gratings DBR1 to DBR11 reflects a part of the light propagating through the optical waveguide 12a in a direction orthogonal to the optical axis direction and guides it to the optical waveguide 17. The light propagating through the optical waveguide 17 is received by the light receiving unit 18. The light receiving unit 18 converts the intensity of the received light into an electric signal and outputs it to the control unit 30. The eleven light receiving portions 18 arranged in correspondence with the diffraction gratings DBR1 to DBR11 form an array 18A of light receiving portions. The light receiving unit 18 is formed using, for example, Ge or SiGe.

  Each set of the optical waveguide 17 and the light receiving unit 18 is arranged for each of the diffraction gratings DBR1 to DBR11. The reflected light reflected by each diffraction grating propagates through the optical waveguide 17 connected to each diffraction grating and is received by each light receiving unit 18. The reflected light reflected by the adjacent diffraction grating is received by different light receiving portions 18 arranged adjacent to each other.

  The length of the diffraction gratings DBR1 to DBR11 can be set to, for example, 50 μm. The distance between adjacent diffraction gratings can be set to 5 μm, for example. The width of the optical waveguide 17 that connects the diffraction gratings DBR1 to DBR11 and the light receiving unit 18 can be set to, for example, 50 μm, which is the same as the length of the diffraction grating.

  FIG. 8 is a diagram showing reflected light spectra of a plurality of diffraction gratings.

  Each of the diffraction gratings DBR1 to DBR11 has grooves with different periods, and the maximum wavelength of the reflected light spectrum of the reflected light is different. That is, the groove period of one diffraction grating and the maximum wavelength of the reflected light spectrum are different from those of other diffraction gratings.

  The maximum value of the reflected light spectrum can be determined based on the coupling constant of the diffraction grating. As the coupling constant of the diffraction grating increases, the maximum value of the reflected light spectrum also increases. When the maximum value of the reflected light spectrum increases, the amount of light received by the light receiving unit 18 increases, so that the detection accuracy of the oscillation wavelength can be improved.

  On the other hand, the maximum value of the reflected light spectrum increases and the amount of light propagating through the optical waveguide 12a decreases, so that the intensity of the laser output from the optical element 10 decreases. If the coupling constant of the diffraction grating is increased, the amount of light propagating through the optical waveguide is reduced, and if the coupling constant is reduced, the amount of reflected light is reduced, which may affect the detection accuracy of the oscillation wavelength.

Therefore, the coupling constant of the diffraction grating can be appropriately determined in consideration of the above-described viewpoint. For example, the ratio of peaks and valleys in the grooves of the diffraction grating may be 1: 1, the coupling coefficient may be 150 cm ⁻¹ , and the maximum value of the reflected light spectrum may be 40%.

  Envelopes R1 to R11 of the reflected light spectrum of one diffraction grating are positions of wavelengths having spectral components having a magnitude of 1/10 or more, preferably 3/10 or more of the maximum value of the reflected light spectrum. It intersects with the envelope of the reflected light spectrum of the diffraction grating.

  Specifically, the envelope R1 of the reflected light spectrum of one diffraction grating DBR1 is a wavelength position having a spectral component having a magnitude of 1/10 or more, preferably 3/10 or more of the maximum value of the reflected light spectrum. And intersects with the envelope R2 of the reflected light spectrum of another adjacent diffraction grating DBR2. This description also applies to other adjacent diffraction gratings. In the present embodiment, the position where the envelopes R1 to R11 of the reflected light spectrum of adjacent diffraction gratings intersect is set to the position of the wavelength having a spectral component that is 1/2 the maximum value of the reflected light spectrum. The

  Further, the positions of the wavelengths at which the envelopes R1 to R11 of the reflected light spectrum of one diffraction grating intersect with the envelopes of the reflected light spectrum of other diffraction gratings adjacent to the one diffraction grating are equally spaced. In the present embodiment, the position where the envelopes R1 to R11 of the reflected light spectrum of adjacent diffraction gratings intersect at a wavelength having a spectral component of 1/10 or more of the maximum value of the reflected light spectrum is 4.5 nm (frequency 50 GHz).

  In addition, the envelope of the reflected light spectrum of one diffraction grating DBR1 and the envelope of the reflected light spectrum intersect at a wavelength position having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The diffraction grating may not be an adjacent diffraction grating. The positions of the wavelengths at which the envelopes R1 to R11 of the reflected light spectrum of one diffraction grating intersect the envelopes of the reflected light spectrum of other diffraction gratings adjacent to the one diffraction grating are unequal intervals. Also good.

  As shown in FIG. 8, the positions of the wavelengths where the envelopes R1 to R11 of the reflected light spectra of these adjacent diffraction gratings intersect with each other are the target wavelengths (grid wavelengths) λ1 to λ10 of the laser oscillated by the apparatus 1. Can be determined to match.

  Next, examples of dimensions of the eleven diffraction gratings DBR1 to DBR11 of the present embodiment will be described below.

  The diffraction gratings DBR1 to DBR11 have a diffraction grating period in the range of 410.060 nm to 420.923 nm. The center wavelength of the reflected light spectrum reflected by these diffraction gratings DBR1 to DBR11 is in the range of 1528.084 nm to 1568.563 nm at an interval of 4.5 nm.

  The position of the wavelength of the intersection of the envelopes R1 and R2 of the reflected light spectrum of the diffraction grating DBR1 and the adjacent diffraction grating DBR2 is 1530.334 nm (frequency 195.9 THz), which is the grid wavelength λ1. Similarly, the position of the wavelength at the intersection of the envelopes R2 and R3 of the reflected light spectrum of the diffraction grating DBR2 and the adjacent diffraction grating DBR3 is the grid wavelength λ2. Similarly, the position of the wavelength of the intersection of the envelopes R10 and R11 of the reflected light spectrum of the diffraction grating DBR10 and the adjacent diffraction grating DBR11 is the grid wavelength λ10.

  For example, when the optical element 10 is oscillating at the grid wavelength λ1, the wavelength of the light propagating through the optical waveguide 12a is the intersection of the reflected light spectrum envelopes R1 and R2 of the diffraction grating DBR1 and the adjacent diffraction grating DBR2. Located near the wavelength. Therefore, a part of the light propagating through the optical waveguide 12a is reflected by the two adjacent diffraction gratings DBR1 and DBR2, and each of the reflected lights is received by the two adjacent light receiving portions 18 via the optical waveguide 17. The

  In this case, since the wavelength of the grid wavelength λ1 does not substantially overlap with the wavelengths of the envelopes R3 to R11 of the reflected light spectrum of the diffraction gratings DBR3 to DBR11 (see FIG. 8), the diffraction gratings DBR3 to DBR11 are optical waveguides. The light propagating through 12a is not reflected. Accordingly, the diffraction gratings DBR3 to DBR11 are substantially transparent with respect to light in the vicinity of the grid wavelength λ1 propagating through the optical waveguide 12a.

  In this specification, the fact that the wavelength of light propagating through the optical waveguide 12a does not substantially overlap with the wavelength of the envelope of the reflected light spectrum of the diffraction grating means that the wavelength of light propagating through the optical waveguide 12a is reflected light. This means that they do not overlap in the wavelength region of 1/10 or more of the maximum value of the spectrum.

  The envelopes R1 and R2 of the reflected light spectrum of one diffraction grating DBR1 and DBR2 are wavelength regions having a spectral component having a magnitude of 1/10 or more, preferably 1/30 of the maximum value of the reflected light spectrum. Then, it does not intersect with the envelope of the reflected light spectrum of the other diffraction gratings DBR3 to DBR11 that are not adjacent to one diffraction grating DBR1 and DBR2. The above description is also applied as appropriate to other adjacent diffraction gratings.

  When the light having the grid wavelength λ1 is oscillated, the light is reflected between the first end face 20a of the light generation unit 20 and the loop mirror 14, but is reflected by the diffraction gratings DBR1 and DBR2. Is reflected toward the optical waveguide 17. Therefore, it is considered that the light reflected by the diffraction gratings DBR1 and DBR2 has substantially no influence on the oscillation of the optical path including the optical waveguide 12a.

  Each of the diffraction gratings DBR1 to DBR11 has a function of reflecting the light of the grid wavelengths λ1 to λ10 corresponding to the positions where the envelopes R1 to R11 of the reflected light spectrum intersect toward the light receiving unit 18, but the grid wavelengths λ1 to λ10. It does not substantially affect the oscillation of light.

  Next, control for oscillating light of grid wavelengths λ1 to λ11 will be described below.

  First, consider a case where light is oscillated with the grid wavelength λ1 as a target.

  The control unit 30 controls the heaters 16a to 16c so that the refractive indexes of the ring resonators 13a and 13b and the optical waveguide 12c become preset values in order to oscillate light having the grid wavelength λ1. . As a result, light having a wavelength λr close to the grid wavelength λ1 is generated in the optical waveguide 12a.

  Since the wavelength λr overlaps with the wavelength region of the reflected light spectrum of the diffraction gratings DBR1 and DBR2, the diffraction grating DBR1 and the diffraction grating DBR2 reflect a part of the light propagating through the optical waveguide 12a. The reflected light is received by two adjacent light receiving portions 18 via the optical waveguide 17. Each light receiving unit 18 converts the received light intensity into an electric signal and outputs it to the control unit 30.

  As shown in FIG. 9A, when the wavelength λr of the light propagating through the optical waveguide 12a matches the grid wavelength λ1, the intensity S1 of the reflected light reflected by the diffraction grating DBR1 and the diffraction grating DBR2 The intensity S2 of the reflected light reflected is equal. In order for the wavelength λr to coincide with the grid wavelength λ1, an allowable error may be provided for the intensity of light received by the light receiving unit 18.

  Next, as shown in FIG. 9B, when the wavelength λr of the light propagating through the optical waveguide 12a is larger than the grid wavelength λ1, the intensity S1 of the reflected light reflected by the diffraction grating DBR1 is diffracted. It becomes smaller than the intensity S2 of the reflected light reflected by the grating DBR2.

  In this case, the control unit 30 controls the heaters 16a to 16c, adjusts the refractive index of the ring resonators 13a and 13b or the optical waveguide 12c, and the intensity S1 of the reflected light reflected by the diffraction grating DBR1, The intensity S2 of the reflected light reflected by the diffraction grating DBR2 is matched.

  As shown in FIG. 9C, when the wavelength λr of the light propagating through the optical waveguide 12a is smaller than the grid wavelength λ1, the intensity S1 of the reflected light reflected by the diffraction grating DBR1 is It becomes larger than the intensity S2 of the reflected light reflected by the DBR2.

  In this case, the control unit 30 controls the heaters 16a to 16c, adjusts the refractive index of the ring resonators 13a and 13b or the optical waveguide 12c, and the intensity S1 of the reflected light reflected by the diffraction grating DBR1, The intensity S2 of the reflected light reflected by the diffraction grating DBR2 is matched.

  In this way, the wavelength λr of the light propagating through the optical waveguide 12a is detected, and the wavelength λr is controlled so as to coincide with the grid wavelengths λ1 to λ10. Further, when the intensity of the oscillated light changes as a result of controlling the wavelength λr, the current injected into the light generation unit 20 can also be controlled.

  From the viewpoint of increasing the sensitivity for detecting the wavelength λr of light propagating through the optical waveguide 12a, it is preferable that the envelopes of adjacent reflected light spectra intersect at a position where the slope of the envelope of the reflected light spectrum is large.

  Similarly, the wavelengths of light oscillated at other grid wavelengths λ2 to λ10 are controlled.

  According to the apparatus 1 of the present embodiment described above, the wavelengths of light oscillating at different wavelengths are detected using a plurality of diffraction gratings. Since the plurality of diffraction gratings can be arranged on a silicon substrate together with other optical elements by using silicon platform technology, the optical element can be miniaturized. Therefore, a miniaturized wavelength tunable laser device can be realized.

  In the above-described embodiment, the position of the wavelength where the envelopes R1 to R11 of the reflected light spectrum of one diffraction grating intersect the envelope of the reflected light spectrum of another diffraction grating adjacent to the one diffraction grating is It was equally spaced. In the apparatus 1, the position of the wavelength at which the envelopes of the reflected light spectra of adjacent diffraction gratings intersect can be changed by designing the groove period of the diffraction grating, and can also be set at unequal intervals. As described above, even if the grid wavelengths are unequal, the oscillation wavelength can be easily controlled by making the light intensities received by the two light receiving portions coincide.

  Next, Modification 1 and Modification 2 of the above-described wavelength tunable laser device according to the first embodiment will be described with reference to the drawings.

  FIG. 10 is a diagram illustrating an optical element according to Modification 1 of the first embodiment.

  In the optical element 10 of this modified example, the optical waveguide 17 and the light receiving unit 18 are disposed on both sides of the optical waveguide 12a with respect to each of the diffraction gratings DBR1 to DBR11, and an array of light receiving units on both sides of the optical waveguide 12a. 18A and an array 18B of light receiving parts are arranged.

  In the first embodiment described above, as shown in FIG. 7, each of the diffraction gratings DBR <b> 1 to DBR <b> 11 reflects light propagating through the optical waveguide 12 a from the left side to the right side, and the reflected light is received by the light receiving unit 18. Received light. On the other hand, the light propagating from the right side to the left side of the optical waveguide 12a is reflected by each of the diffraction gratings DBR1 to DBR11. However, since the optical waveguide and the light receiving unit are not arranged, the reflected light is not detected. .

  Therefore, in the optical element 10 of this modified example, the light propagating from the right side to the left side of the optical waveguide 12a is also reflected downward, received, and detected, so that the detection accuracy of the oscillating wavelength can be improved. It is made like that.

  FIG. 11 is a diagram illustrating an optical element according to Modification 2 of the first embodiment. FIG. 12 is a diagram showing a main part of FIG.

  The optical element 10 of the present modification is different from the above-described modification 1 in that no optical waveguide is disposed between the diffraction gratings DBR1 to DBR11 and the light receiving unit 18.

  As shown in FIG. 12, the light receiving portions 18 are arranged on both sides with a space from the region of the optical waveguide 12a where the diffraction gratings DBR1 to DBR11 are arranged. The light receiving unit 18 is embedded in the cladding layer 11b. The viewpoint that setting the distance between the optical waveguide 12a and the light receiving unit 18 to a distance at which the envelope of light propagating through the optical waveguide 12a is sufficiently reduced does not excessively reduce the intensity of light propagating through the optical waveguide 12a. To preferred.

  According to this modified example, since the optical waveguide is not disposed between the diffraction gratings DBR1 to DBR11 and the light receiving unit 18, the size of the optical element 10 is reduced and the intensity of the reflected light received by the light receiving unit 18 is reduced. Can be increased.

  Next, a second embodiment of the light generation apparatus described above will be described below with reference to FIGS. For points that are not particularly described in the second embodiment, the description in detail regarding the first embodiment is applied as appropriate. Moreover, the same code | symbol is attached | subjected to the same component.

  FIG. 13 is a diagram illustrating a wavelength tunable laser device according to a second embodiment disclosed in this specification. FIG. 14 is a diagram illustrating an optical element that is a main part of the wavelength tunable laser device according to the second embodiment. FIG. 15 is an enlarged sectional view taken along line Y1-Y1 of FIG. 16 is an enlarged sectional view taken along line Y2-Y2 of FIG.

  The optical element 10 of the present embodiment is different from the first embodiment described above in the arrangement of a plurality of diffraction gratings, the optical waveguide that propagates the reflected light of the diffraction grating to the light receiving unit, and the configuration of the light receiving unit.

  As shown in FIGS. 15 and 17, the optical element 10 has a first group G1 having a predetermined number of diffraction gratings DBR1 to DBR4 arranged in series along the optical waveguide 12a. The optical element 10 includes a second group G2 that is arranged along the optical waveguide 12a and includes the same predetermined number of diffraction gratings DBR5 to DBR8 as the first group G1. The first group G1 and the second group G2 are arranged in series along the optical element 12a. In the present embodiment, the first group G1 and the second group G2 have four diffraction gratings.

  As shown in FIG. 17, the diffraction gratings DBR1 to DBR4 of the first group G1 and the diffraction gratings DBR5 to DBR8 of the second group G1 extend in a direction intersecting with the extending direction of the optical waveguide 12a and are formed in a plurality of periods. It has a groove. In each group G1, G2, each diffraction grating is arrange | positioned without spacing.

  Each of the diffraction gratings DBR1 to DBR8 has grooves with different periods, and the maximum wavelength of the reflected light spectrum of the reflected light is different. That is, the groove period of one diffraction grating and the maximum wavelength of the reflected light spectrum are different from the groove period of the other diffraction grating.

  As shown in FIGS. 14 and 15, a heater 15a is arranged above the diffraction gratings DBR1 to DBR4 of the first group G1. Similarly, a heater 15b is disposed above the diffraction gratings DBR5 to DBR8 of the second group G2. The shift of the peak wavelength of the reflected light based on the error in the size of the diffraction grating is adjusted by changing the refractive index of the diffraction grating portion of each group using heating by the heaters 15a and 15b. The operations of the heaters 15a and 15b are controlled by the control unit 30.

  Each of the diffraction gratings DBR1 to DBR4 of the first group G1 reflects a part of light propagating through the optical waveguide 12a in a direction orthogonal to or intersecting with the extending direction of the optical waveguide 12a and guides it to the optical waveguide 19a. The light propagating through the optical waveguide 19a is received by the light receiving unit 18a. The light receiving unit 18 a converts the intensity of the received reflected light into an electric signal and outputs the electric signal to the control unit 30.

  Similarly, each of the diffraction gratings DBR5 to DBR8 of the second group G2 reflects a part of the light propagating through the optical waveguide 12a in a direction orthogonal to or intersecting the optical axis direction and guides it to the optical waveguide 19b. The light propagating through the optical waveguide 19b is received by the light receiving unit 18b. The light receiving unit 18 b converts the intensity of the received reflected light into an electric signal and outputs the electric signal to the control unit 30.

  In the optical waveguide 19a, the width of the portion connected to the diffraction gratings DBR1 to DBR4 of the first group G1 is wide, the width of the portion connected to the light receiving portion 18a is narrow, and has a tapered shape as a whole. The optical waveguide 19b has the same shape as the optical waveguide 19a.

  The length of each diffraction grating of each group G1, G2 can be set to 80 μm, for example. The distance between the first group G1 and the second group G2 can be set to 5 μm, for example.

For example, the ratio of peaks and valleys in the grooves of the diffraction gratings DBR1 to DBR8 may be 1: 1, the coupling coefficient may be 180 cm ⁻¹ , and the maximum value of the reflected light spectrum may be 80%.

  FIG. 18 is a diagram illustrating reflected light spectra of the diffraction gratings of the first group and the second group.

  The diffraction grating DBR1 of the first group G1 is paired with the diffraction grating DBR5 of the second group G2. Similarly, the diffraction grating DBR2 of the first group G1 is the diffraction grating DBR6 of the second group G2, the diffraction grating DBR3 of the first group G1 is the diffraction grating DBR7 of the second group G2, and the diffraction grating DBR4 of the first group G1 is It is paired with the diffraction grating DBR8 of the second group G2.

  The envelope R1 of the reflected light spectrum of the diffraction grating DBR1 of the first group G1 is a position of a wavelength having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. This crosses the envelope R2 of the reflected light spectrum of the diffraction grating DBR5. The envelopes of the reflected light spectra of other pairs of diffraction gratings have the same relationship.

  Specifically, the envelope R1 of the reflected light spectrum of the diffraction grating DBR1 of the first group G1 has a spectral component having a magnitude of 1/10 or more, preferably 3/10 or more of the maximum value of the reflected light spectrum. At the position of the wavelength, it intersects with the envelope R5 of the reflected light spectrum of the diffraction grating DBR5 of the second group G2 as a pair. This explanation also applies to the envelope of the reflected light spectrum of another pair of diffraction gratings. In the present embodiment, the position where the envelopes of the reflected light spectrum of the diffraction gratings that are paired with each other is set to the position of the wavelength having a spectral component that is 1/2 the maximum value of the reflected light spectrum.

  The envelopes R1 to R4 of the reflected light spectra of the first diffraction gratings DBR1 to DBR4 of the first group G1 intersect the envelopes R5 to R8 of the reflected light spectra of the diffraction gratings DBR5 to DBR8 of the second group G2. The positions of the wavelengths are equally spaced. In the present embodiment, the interval between the wavelengths at which the envelopes of the reflected light spectrum forming a pair intersect is about 20 nm.

  The envelope R1 of the reflected light spectrum of the diffraction grating DBR1 of the first group G1 is 1/10 or more, preferably 1/30 or more of the maximum value of the reflected light spectrum. What are the envelopes R2 to R4 and R6 to R8 of the reflected light spectra of the other diffraction gratings DBR2 to DBR4 and DBR6 to DBR8 of the first group G1 and the second group G2 other than the diffraction grating DBR5 of the second group G2 to be paired? Do not cross. This explanation also applies to other diffraction gratings.

  As shown in FIG. 18, the position of the wavelength where the envelopes of the reflected light spectra of the diffraction gratings of the first group G1 and the second group G2 that form a pair intersect each other is the target wavelength of the laser oscillated by the apparatus 1 ( (Grid wavelength) can be determined to coincide with λ1 to λ4.

  Next, examples of dimensions of the diffraction gratings DBR1 to DBR4 of the first group G1 and the diffraction gratings DBR5 to DBR8 of the second group G2 according to this embodiment will be described below.

  The diffraction gratings DBR1 to DBR4 of the first group G1 have a diffraction grating period in the range of 410.06 nm to 431.33 nm. The center wavelength of the reflected light spectrum reflected by the diffraction grating DBR1 is 1528.084 nm, and the center wavelength of the reflected light spectrum reflected by the diffraction gratings DBR2 to DBR4 increases by about 20 nm.

  The diffraction gratings DBR5 to DBR8 of the second group G2 have a diffraction grating period in the range of 411.83 nm to 433.10 nm. The center wavelength of the reflected light spectrum reflected by each of the diffraction gratings DBR5 to DBR8 of the second group G2 is about 6 than the center wavelength of the reflected light spectrum reflected by the paired diffraction gratings DBR1 to DBR4 of the first group G1. .5 nm larger.

  The position of the wavelength of the intersection point of the envelopes R1, R5 of the reflected light spectrum of the diffraction grating DBR1 of the first group G1 and the diffraction grating DBR5 of the second group G2 to be paired is about 1530 nm, which is the grid wavelength λ1. Similarly, the position of the wavelength at the intersection of the envelopes R2 and R6 of the reflected light spectrum of the diffraction grating DBR2 and the paired diffraction grating DBR6 is the grid wavelength λ2. Similarly, the position of the wavelength at the intersection of the envelopes R3 and R7 of the reflected light spectrum of the diffraction grating DBR3 and the paired diffraction grating DBR7 is the grid wavelength λ3, and the reflection of the diffraction grating DBR4 and the paired diffraction grating DBR8. The position of the wavelength at the intersection of the envelopes R4 and R8 of the optical spectrum is the grid wavelength λ4. The grid wavelengths λ1 to λ4 have different wavelengths by about 20 nm, and correspond to the frequency intervals of the CWDM division wavelengths.

  Next, control for oscillating light of grid wavelengths λ1 to λ4 will be described below.

  First, consider a case where light is oscillated with the grid wavelength λ1 as a target.

  The control unit 30 controls the heaters 16a to 16c so that the refractive indexes of the ring resonators 13a and 13b and the optical waveguide 12c become preset values in order to oscillate light having the grid wavelength λ1. . As a result, light having a wavelength λr close to the grid wavelength λ1 is generated in the optical waveguide 12a. The wavelength λr overlaps with the wavelength region of the reflected light spectrum of the diffraction gratings DBR1 and DBR2.

  The diffraction grating DBR1 of the first group G1 reflects a part of the light propagating through the optical waveguide 12a, and the reflected light is received by the light receiving unit 18a through the optical waveguide 19a. The pair of diffraction gratings DBR5 of the second group G2 reflects part of the light propagating through the optical waveguide 12a, and the reflected light is received by the light receiving unit 18a via the optical waveguide 19b. Each of the light receiving units 18 a and 18 b converts the received light intensity into an electric signal and outputs the electric signal to the control unit 30.

  When the light receiving intensity of the light receiving unit 18a matches the light receiving intensity of the light receiving unit 18b, the light is oscillated at the target wavelength.

  On the other hand, when the light receiving intensity of the light receiving unit 18a does not match the light receiving intensity of the light receiving unit 18b, the control unit 30 controls the heaters 16a to 16c to change the refractive index of the ring resonators 13a, 13b or the optical waveguide 12c. Is adjusted so that the light receiving intensity of the light receiving unit 18a and the light receiving intensity of the light receiving unit 18b are matched.

  According to the above-described embodiment, the configuration of the optical waveguide and the light receiving element that propagates the reflected light reflected by the diffraction grating is simplified as compared with the first embodiment, so that the manufacture is facilitated. Moreover, the same effect as 1st Embodiment mentioned above is show | played.

  Next, Modification 1 and Modification 2 of the above-described wavelength tunable laser device according to the second embodiment will be described with reference to the drawings.

  FIG. 19 is a diagram illustrating an optical element according to Modification 1 of the first embodiment.

  In the optical element 10 of this modification, the optical waveguides 19a to 19c and the light receiving portions 18a to 18d are arranged at positions on both sides of the optical waveguide 12a with respect to the diffraction gratings DBR1 to DBR8 of the first group G1 and the second group G2. Is done.

  In the second embodiment described above, as shown in FIG. 17, each of the diffraction gratings DBR1 to DBR8 reflects light propagating through the optical waveguide 12a from the left side to the right side, and the reflected light is received by the light receiving unit 18a, Light is received at 18b. On the other hand, the light propagating from the right side to the left side in the optical waveguide 12a is reflected by each of the diffraction gratings DBR1 to DBR8. However, since the optical waveguide and the light receiving unit are not arranged, the reflected light is not detected. .

  Therefore, in the optical element 10 of this modified example, the light propagating from the right side to the left side of the optical waveguide 12a is also reflected downward, received, and detected, so that the detection accuracy of the oscillating wavelength can be improved. I am doing so.

  FIG. 20 is a diagram illustrating an optical element according to Modification 2 of the first embodiment. FIG. 21 is a diagram showing a main part of FIG.

  The optical element 10 of the present modification is different from the first modification described above in that no optical waveguide is disposed between the diffraction gratings DBR1 to DBR8 and the light receiving portions 18a to 18d of the first group G1 and the second group G2. ing.

  As shown in FIG. 21, the light receiving portions 18a and 18c are arranged on both sides with a space from the region of the optical waveguide 12a where the diffraction gratings DBR1 to DBR4 of the first group G1 are arranged. Similarly, the light receiving portions 18b and 18d are arranged on both sides with a space from the region of the optical waveguide 12a where the diffraction gratings DBR5 to DBR8 of the second group G2 are arranged.

  According to this modification, the optical waveguide 10 is not disposed between the diffraction gratings DBR1 to DBR8 and the light receiving portions 18a to 18d of the first group G1 and the second group G2, thereby reducing the size of the optical element 10 and The intensity of the reflected light received by the light receiving units 18a to 18d can be increased.

  In the present invention, the optical element and the light generation apparatus of the above-described embodiments can be appropriately changed without departing from the gist of the present invention. In addition, the configuration requirements of one embodiment can be applied to other embodiments as appropriate.

  For example, in each of the above-described embodiments, the oscillating unit is formed using the first end face 20a of the light generating unit 20, but the distributed reflecting mirror is disposed in the optical waveguide 21 of the light generating unit 20 to oscillate the unit. May be formed.

  In each of the above-described embodiments, the coupling coefficient (groove depth) of each diffraction grating is the same. However, in order to correct the reflectance variation due to the coupling coefficient variation caused by wavelength dispersion, the diffraction grating is used. The coupling coefficient may be different for each lattice.

  In each of the above-described embodiments, the optical element is formed using the silicon platform technology. However, the optical element may be a silica-based PLC waveguide technology, a III-V group compound semiconductor technology such as a GaInAsP system, or the like. It may be formed using polymer-based waveguide technology.

  In each of the above-described embodiments, the light receiving unit is formed using Ge or SiGe. However, when the optical element is formed using a III-V group compound semiconductor technology such as a GaInAsP system, You may form using the same compound semiconductor. Further, the reflected light of the diffraction grating may be propagated to the side edge of the silicon substrate using an optical waveguide, and the reflected light may be received using a light receiving element separate from the substrate.

  Further, in each of the above-described embodiments, the wavelength of the oscillating light is set to the 1.55 μm band.

  Moreover, in each embodiment mentioned above, although the grid wavelength was provided in the space | interval of 50 GHz or 20 nm, a grid wavelength is not limited to this.

  In each of the above-described embodiments, the heater is disposed above the diffraction grating. However, when fine adjustment of the grid wavelength is not performed, the heater may not be disposed.

  Further, the number of the plurality of diffraction gratings is not limited to the example of the embodiment described above. The number can be appropriately increased or decreased according to the number of grid wavelengths to be oscillated.

  Furthermore, the reflected light spectrum of the reflected light reflected by the diffraction grating or the envelope of the reflected light spectrum can be appropriately changed in design.

  All examples and conditional words mentioned herein are intended for educational purposes to help the reader deepen and understand the inventions and concepts contributed by the inventor. All examples and conditional words mentioned herein are to be construed without limitation to such specifically stated examples and conditions. Also, such exemplary mechanisms in the specification are not related to showing the superiority and inferiority of the present invention. While embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions or modifications can be made without departing from the spirit and scope of the invention.

  Regarding the above-described embodiments, the following additional notes are disclosed.

(Appendix 1)
An optical waveguide;
A plurality of diffraction gratings arranged along the optical waveguide, wherein each of the diffraction gratings reflects a part of light propagating through the optical waveguide in a direction intersecting with an extending direction of the optical waveguide; A plurality of diffraction gratings having different maximum wavelengths of reflected light spectrum of light reflected by the diffraction grating; and
An optical element comprising:

(Appendix 2)
The envelope of the reflected light spectrum of one of the diffraction gratings is an envelope of the reflected light spectrum of the other diffraction grating at the position of the wavelength having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element according to appendix 1, which intersects the line.

(Appendix 3)
The optical element according to appendix 1 or 2, wherein each of the diffraction gratings has a plurality of periodically formed grooves extending in a direction intersecting with an extending direction of the optical waveguide.

(Appendix 4)
The plurality of diffraction gratings are arranged side by side along the optical waveguide,
The envelope of the reflected light spectrum of one of the diffraction gratings is a reflected light spectrum of another adjacent diffraction grating at a wavelength position having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element according to any one of appendices 1 to 3, which intersects the envelope of

(Appendix 5)
The wavelength positions at which the envelope of the reflected light spectrum of one diffraction grating intersects the envelope of the reflected light spectrum of another diffraction grating adjacent to the one diffraction grating are equally spaced. Optical element.

(Appendix 6)
The envelope of the reflected light spectrum of one of the diffraction gratings is not adjacent to the one of the diffraction gratings in a wavelength region having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element according to appendix 5, which does not intersect with the envelope of the reflected light spectrum of the diffraction grating.

(Appendix 7)
A first light receiving unit that receives reflected light reflected by one diffraction grating, converts the received light intensity into an electrical signal, and outputs the reflected light, and reflected light reflected by another diffraction grating adjacent to the one diffraction grating The optical element according to any one of appendices 4 to 6, further comprising: a second light receiving unit that receives the light and converts the received light intensity into an electric signal and outputs the electric signal.

(Appendix 8)
A first group having a predetermined number of the diffraction gratings arranged side by side along the optical waveguide;
A second group having the predetermined number of the diffraction gratings arranged side by side along the optical waveguide;
Have
The diffraction gratings of the first group are paired with the other diffraction gratings of the second group;
The envelope of the reflected light spectrum of the diffraction grating in the first group has a wavelength position having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element according to any one of appendices 1 to 3, which intersects an envelope of a reflected light spectrum of another diffraction grating of the group.

(Appendix 9)
The positions of the wavelengths at which the envelopes of the reflected light spectra of the diffraction gratings of the first group intersect the envelopes of the reflected light spectra of the other diffraction gratings of the second group as a pair are equally spaced. The optical element according to appendix 8.

(Appendix 10)
The envelope of the reflected light spectrum of the diffraction grating of the first group has the second pair in the wavelength region having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element according to appendix 9, which does not intersect with envelopes of reflected light spectra of the other diffraction gratings of the first group and the second group other than the diffraction gratings of the group.

(Appendix 11)
A first light-receiving unit that receives reflected light reflected by one of the diffraction gratings of the first group, converts the received light intensity into an electrical signal, and outputs the first light-receiving unit; and the other diffraction gratings of the second group that form a pair The optical element according to appendix 9 or 10, further comprising: a second light receiving unit that receives the reflected light reflected by the light, converts the received light intensity into an electric signal, and outputs the electric signal.

(Appendix 12)
An optical waveguide;
A plurality of diffraction gratings arranged along the optical waveguide, wherein each of the diffraction gratings reflects a part of light propagating through the optical waveguide in a direction intersecting with an extending direction of the optical waveguide; A plurality of diffraction gratings having different maximum wavelengths of reflected light spectrum of light reflected by the diffraction grating; and
An optical element having
A light generation unit that propagates the generated light to the optical waveguide;
A wavelength selection unit for selecting a wavelength of light oscillated in the optical waveguide;
An oscillation unit that oscillates light of a wavelength selected by the wavelength selection unit in the optical waveguide;
A light generation apparatus comprising:

(Appendix 13)
The envelope of the reflected light spectrum of one of the diffraction gratings is an envelope of the reflected light spectrum of the other diffraction grating at the position of the wavelength having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. Intersects the line,
Receiving the reflected light reflected by one of the diffraction gratings, receiving the reflected light reflected by the other diffraction gratings, and receiving the reflected light reflected by the first light receiving unit that converts the received light intensity into an electrical signal and outputs it; A second light receiving unit that converts the electric signal into an electric signal and outputs the electric signal;
The electric signal output from the first light receiving unit and the electric signal output from the second light receiving unit are input to match the light receiving intensity of the first light receiving unit with the light receiving intensity of the second light receiving unit. As described above, the light generation device according to attachment 12, further comprising a control unit that controls the wavelength selection unit.

(Appendix 14)
The oscillating unit is disposed at a first end of an optical path including the optical waveguide, and includes a first mirror unit that reflects light propagating toward the first end, and a second end of the optical path. The light generation device according to appendix 12 or 13, further comprising: a second mirror unit that is disposed and reflects light propagating toward the second end.

1 Tunable laser device (light generator)
2 substrate 10 optical element 11a substrate 11b cladding layer 11c upper cladding layer 12a, 12b, 12c optical waveguide 13a, 13b ring resonator 14 loop mirror 15, 15a, 15b heater 16a, 16b, 16c heater 17 optical waveguide 18, 18a, 18b , 18c, 18d Light receiving unit 18A, 18B Light receiving unit array 19a, 19b Optical waveguide DBR1-DBR11 Diffraction grating R1-R11 Reflected light spectrum envelope 20 Light generating unit 20a First end surface 20b Second end surface 21 Optical waveguide 30 Control Unit 31 Temperature adjustment unit 32 Collimating lens 33 Isolator 34 Condensing lens 40 Optical fiber 101 Tunable laser device 110 Optical element 118a, 118b Light receiving unit 132 Collimating lens 133 Isolator 134 Condensing lens 135 Bi Beam splitter 136 etalon 140 an optical fiber

Claims (6)

An optical waveguide;
A plurality of diffraction gratings arranged along the optical waveguide, wherein each of the diffraction gratings reflects a part of light propagating through the optical waveguide in a direction intersecting with an extending direction of the optical waveguide; A plurality of diffraction gratings having different maximum wavelengths of reflected light spectrum of light reflected by the diffraction grating; and
An optical element comprising:   The envelope of the reflected light spectrum of one of the diffraction gratings is an envelope of the reflected light spectrum of the other diffraction grating at the position of the wavelength having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element according to claim 1, which intersects the line.   3. The optical element according to claim 1, wherein each of the diffraction gratings has a plurality of periodically formed grooves extending in a direction intersecting with an extending direction of the optical waveguide. The plurality of diffraction gratings are arranged side by side along the optical waveguide,
The envelope of the reflected light spectrum of one of the diffraction gratings is a reflected light spectrum of another adjacent diffraction grating at a wavelength position having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element as described in any one of Claims 1-3 which cross | intersects. A first group having a predetermined number of the diffraction gratings arranged side by side along the optical waveguide;
A second group having the predetermined number of the diffraction gratings arranged side by side along the optical waveguide;
Have
The diffraction gratings of the first group are paired with the other diffraction gratings of the second group;
The envelope of the reflected light spectrum of the diffraction grating in the first group has a wavelength position having a spectral component having a magnitude of 1/10 or more of the maximum value of the reflected light spectrum. The optical element as described in any one of Claims 1-3 which cross | intersects the envelope of the reflected light spectrum of the said other diffraction grating of a group. An optical waveguide;
A plurality of diffraction gratings arranged along the optical waveguide, wherein each of the diffraction gratings reflects a part of light propagating through the optical waveguide in a direction intersecting with an extending direction of the optical waveguide; A plurality of diffraction gratings having different maximum wavelengths of reflected light spectrum of light reflected by the diffraction grating; and
An optical element having
A light generation unit for propagating the generated light to the optical waveguide;
A wavelength selection unit for selecting a wavelength of light oscillated in the optical waveguide;
An oscillation unit that oscillates light of a wavelength selected by the wavelength selection unit in the optical waveguide;
A light generation apparatus comprising:

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