JP2007163835A - Wavelength selecting element and optical resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To flexibly change a ratio of a wavelength variation of a selected wavelength to a variation of an optical path length. <P>SOLUTION: A reflective diffraction grating 16 which includes a channel waveguide 14 for coupling input light I<SB>1</SB>to a plane waveguide 12 and a grating face 16a inclined at a tilt angle Θ<SB>g</SB>and is disposed in opposition to the channel waveguide with the plane waveguide between and diffracts coupled light I<SB>2</SB>, a reflecting mirror 18 which has a reflecting face 18a extended with an inclination of a tilt angle Θ<SB>m</SB>and having a normal 18N intersecting the grating face and is disposed in opposition to the reflective diffraction grating with the plane waveguide between and reflects diffracted light I<SB>3</SB>toward the reflective diffraction grating, and a light deflecting part 20 which changes an angle Θ of incidence on the grating face of the coupled light are integrated on a common substrate 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wavelength selection element that selects light of a specific wavelength from light including a plurality of wavelengths, and an optical resonator using the wavelength selection element.

  In recent years, with the development of a wavelength division multiplexing (WDM) system, the importance of wavelength selection elements that select light of a specific wavelength from wavelength multiplexed light has increased. The wavelength selection element is used, for example, as a component of a wavelength tunable laser (see, for example, Non-Patent Document 1).

  The wavelength tunable laser disclosed in Non-Patent Document 1 includes a laser light source, an optical deflector, a reflection mirror, a lens, and a reflection type diffraction grating arranged in series along the light propagation direction. Here, the wavelength selection element includes an optical deflector, a lens, and a reflective diffraction grating.

  In this wavelength tunable laser, the emission angle of the light generated from the laser light source is adjusted by the optical deflector. The light whose emission angle is adjusted is emitted toward a lens provided outside the laser light source. At this time, the light propagation path (optical path length) from the optical deflector to the reflective diffraction grating changes according to the light emission angle.

The light is refracted when passing through the lens, and enters the reflective diffraction grating at a predetermined incident angle. Of the light incident on the reflective diffraction grating, the light reflected at a diffraction angle equal to the incident angle is monochromatized according to the diffraction angle. The monochromatized light returns to the reflecting mirror through a path (reflection type diffraction grating → lens) opposite to that upon incidence. The light returned to the reflection mirror is reflected again and reciprocates several times within the optical resonator (between the reflection type diffraction grating and the reflection mirror). As a result, laser light with a predetermined wavelength oscillates.
Oh Kee Kwon et al. “Proposal of Electrically Tunable External-Cavity Laser Diode”, IEEE PHOTOTONICS TECHNOLOGY LETTERS, VOL. 16, NO. 8, AUGUST 2004, pp. 1804-1806

  This tunable laser is designed so that mode hopping does not occur. That is, the wavelength selection element constituting the wavelength tunable laser is designed so that the optical path length increases as the selection wavelength of the laser light increases. That is, in this wavelength selection element, the ratio between the wavelength change rate of the selected wavelength and the change rate of the optical path length (hereinafter also referred to as “wavelength-optical path length ratio”) is fixed to positive (> 0).

  Thus, this wavelength selection element is designed so that the optical path length, that is, the delay time becomes longer as the selected wavelength becomes longer. Therefore, this wavelength selection element can also be regarded as an optical delay line that changes the delay time according to the length of the selected wavelength.

  However, since this wavelength selection element has a fixed wavelength-optical path length ratio, it has only been able to “make the delay time longer as the selected wavelength becomes longer”. This hinders flexible application to optical delay lines.

  The present invention has been made in view of the above problems.

  Accordingly, a first object of the present invention is to provide a wavelength selection element capable of flexibly changing the wavelength-optical path length ratio.

  A second object of the present invention is to provide an optical resonator using the above-described wavelength selection element, in which mode hopping is suppressed by adjusting the wavelength-optical path length ratio. .

  In order to solve the above-described problem, a wavelength selection element according to the first aspect of the present invention includes a planar waveguide, a channel-type waveguide, a reflection-type diffraction grating, a reflection mirror, and an optical deflection unit. Yes.

  The channel-type waveguide couples input light into a planar waveguide via one surface of the channel-type waveguide along the light propagation direction.

  The reflective diffraction grating has a grating surface extending at a first inclination angle with respect to the above-described light propagation direction, and is disposed to face the channel-type waveguide with the planar waveguide interposed therebetween. . The reflective diffraction grating diffracts the light coupled to the planar waveguide.

  The reflecting mirror includes a reflecting surface that extends with an inclination of the second inclination angle with respect to the light propagation direction and has a normal line that intersects the lattice plane. And it arrange | positions facing a reflection type diffraction grating on both sides of a planar waveguide. The reflecting mirror reflects the light diffracted on the grating surface toward the reflection type diffraction grating.

  The light deflector changes the incident angle of the light coupled to the planar waveguide with respect to the lattice plane.

  According to this wavelength selection element, the light input to the channel type waveguide is coupled to the planar waveguide. Then, this light is incident on the reflection type diffraction grating after the incident angle is adjusted by the light deflector. The light incident on the reflective diffraction grating is selected in wavelength by being diffracted in different directions for each wavelength.

  Of the diffracted light, only light having a wavelength propagating in a direction perpendicular to the reflecting mirror is reflected by the reflecting mirror and returned to the reflective diffraction grating. The returned light is diffracted by the reflection type diffraction grating, the wavelength is selected again, the propagation path is reversed, and the wavelength-selected output light is output from the channel waveguide.

  Here, the wavelength of the output light can be changed by changing the incident angle of the light with respect to the reflective diffraction grating by using the light deflecting unit. More specifically, the smaller the incident angle, the longer the wavelength of the output light.

  Further, by adjusting the first tilt angle and the second tilt angle, the ratio of the change rate of the optical path length to the change rate of the wavelength of the output light (wavelength-optical path length ratio) can be set to a desired value. .

  In practicing the present invention, preferably, the optical deflecting unit is provided in the channel type waveguide, and the incident angle may be adjusted by changing the refractive index of the channel type waveguide.

  Thus, by changing the refractive index of the channel-type waveguide, the propagation direction of light coupled from the channel-type waveguide to the planar waveguide can be changed. Thereby, the incident angle of the light with respect to a reflection type diffraction grating can be adjusted.

  According to another preferred embodiment of the present invention, preferably, the light deflector is provided in a part or all of the area of the planar waveguide, and the incident angle is adjusted by changing the refractive index of this area. It may be configured to.

  Thus, the propagation direction of light propagating in the planar waveguide can also be changed by changing the refractive index of a part or all of the region of the planar waveguide. Thereby, the incident angle of the light with respect to a reflection type diffraction grating can be adjusted.

  According to still another preferred embodiment of the present invention, preferably, the optical deflection section is provided in the first optical deflection section provided in the channel-type waveguide and in a part or all of the planar waveguide. The second optical deflecting unit, the first optical deflecting unit is incident by changing the refractive index of the channel waveguide, and the second optical deflecting unit is incident by changing the refractive index of the planar waveguide region. The structure which adjusts a corner | angular may be sufficient.

  According to still another preferred embodiment of the present invention, when the light deflection unit is a partial region of the planar waveguide, the light deflection unit has a planar shape whose width becomes narrower toward the reflective diffraction grating. It is preferable that

  In carrying out the present invention, a gap is provided between one surface of the channel-type waveguide and the surface of the planar waveguide facing the one surface, and the width of this gap is directed to the reflective diffraction grating. It is preferable that the channel-type waveguide and the planar waveguide are arranged so as to become smaller with time.

  By doing so, the intensity distribution of the light coupled from the channel-type waveguide to the planar waveguide can be a Gaussian distribution.

  In this wavelength selection element, it is preferable that the planar waveguide, the channel type waveguide, the reflection type diffraction grating, the reflecting mirror, and the light deflection unit are integrated on a common substrate.

  A first optical resonator according to a second aspect of the present invention includes the above-described wavelength selection element as a constituent element, and includes a reflection mirror on the light input / output end face of the channel waveguide.

  A second optical resonator according to a third aspect of the present invention includes the above-described wavelength selection element as a component, and a reflection mirror is provided facing the light input / output end face of the channel waveguide with a space therebetween. I have.

  The first optical resonator and the second optical resonator include the above-described wavelength selection element. Therefore, the wavelength-optical path length ratio can be set to a desired value by adjusting the first tilt angle (reflection diffraction grating) and the second tilt angle (reflecting mirror). Therefore, by setting the wavelength-optical path length ratio so that the optical path length becomes longer as the output light becomes longer, the first optical resonator and the second optical resonator cause mode hopping. Therefore, the wavelength of the laser beam can be selected.

  The wavelength selection element of the present invention can flexibly change the wavelength-optical path length ratio as compared with the prior art. Therefore, by using this wavelength selection element, not only “the longer the selected wavelength, the longer the delay time” but also “the longer the selected wavelength, the shorter the delay time” can be obtained. it can.

  In addition, in an optical resonator including a wavelength selection element with an appropriately set wavelength-optical path length ratio, mode hopping does not occur in the process of changing the selection wavelength.

  Embodiments of the present invention will be described below with reference to the drawings. The embodiment described below is divided into (Embodiment 1) and (Embodiment 2). In (Embodiment 1), a wavelength selection element will be described. In (Embodiment 2), an optical resonator using this wavelength selection element will be described.

  Each drawing merely schematically shows the shape, size, and arrangement relationship of each component to the extent that the present invention can be understood. Moreover, although the preferable structural example of this invention is demonstrated below, the material of each component, a numerical condition, etc. are only a suitable example. Therefore, the present invention is not limited to the following embodiment.

(Embodiment 1: Wavelength selection element)
The wavelength selection element will be described with reference to FIGS. FIG. 1 is an enlarged perspective view showing a schematic configuration of the wavelength selection element. FIG. 2 is a view showing a cross-section cut along the line II in FIG. FIG. 3 is an enlarged schematic view of the structure near the optical coupling portion in the wavelength selection element. FIG. 4 is a diagram for explaining the conversion of the combined light into a Gaussian beam. FIG. 5 is a schematic diagram for explaining the design conditions of the wavelength selection element. FIGS. 6A to 6C and FIG. 7 are schematic views for explaining a modification of the light deflection unit.

  The planar structure of the wavelength selection element 10 will be described mainly with reference to FIG.

  First, a coordinate system used in the following description is defined. As shown in FIG. 1, the traveling direction of light propagating in the channel waveguide 14 is referred to as the X direction. A direction perpendicular to the X direction in the plane in which the planar waveguide 12 extends is referred to as a Y direction. A direction orthogonal to the X direction and the Y direction is referred to as a Z direction.

  The wavelength selection element 10 includes a planar waveguide 12, a channel type waveguide 14, a reflection type diffraction grating 16, a reflection mirror 18, and an optical deflection unit 20. These components 12, 14, 16, 18 and 20 are integrated on a common substrate 22.

  The substrate 22 is a plate having a rectangular planar shape, and includes a first main surface 22a and a second main surface 22b that extend in parallel to each other. Here, the X direction and the Y direction are in a plane parallel to the first main surface 22a. The Z direction is in the plane perpendicular to the first main surface 22a.

  The planar waveguide 12 is a planar waveguide disposed on the first major surface 22a. The planar waveguide 12 is smaller in area than the substrate 22 and has a substantially rectangular planar shape. The long side of the planar waveguide 12 (extending in the X direction) and the long side of the substrate 22 extend in parallel. Two portions are cut out near the end of the planar waveguide 12 on the reflective diffraction grating 16 side. Due to this notch, notches 12 a and 12 b are formed in the planar waveguide 12. A p-type cladding layer 13 is laminated on the planar waveguide 12 (described later: FIG. 2). The p-type cladding layer 13 has the same planar shape as that of the planar waveguide 12.

  Around the planar waveguide 12, a channel type waveguide 14, a reflection type diffraction grating 16, and a reflection mirror 18 are arranged.

  The channel type waveguide 14 is disposed along the X direction on the first main surface 22a. The channel-type waveguide 14 is a long rectangular column having a rectangular cross section. One end face of the channel waveguide 14 is an optical input / output end face 14a. The light input / output end face 14 a is connected to the side face of the substrate 22 without any step.

  Further, one surface along the X direction of the channel waveguide 14, that is, the side surface 14 b and the side surface 12 c of the planar waveguide 12 are opposed to each other with an interval E (described later: FIG. 3). The optical coupling portion 28 is configured by the side surface 14b, the side surface 12c, and the interval E. The optical coupling unit 28 will be described later. A p-type cladding layer 15 is laminated on the channel-type waveguide 14 (described later: FIG. 2). The p-type cladding layer 15 has the same planar shape as the channel waveguide 14.

  The reflective diffraction grating 16 is formed on the side surface 12 d facing the notch 12 a of the planar waveguide 12. The reflective diffraction grating 16 is disposed to face the channel type waveguide 14 with the planar waveguide 12 interposed therebetween.

The reflective diffraction grating 16 extends with an inclination with respect to the X direction. More specifically, the grating surface 16 a of the reflective diffraction grating 16 forms a first inclination angle Θ _g (hereinafter also referred to as an inclination angle Θ _g ) with respect to the light propagation direction of the channel waveguide 14. It is extended.

  The reflective diffraction grating 16 is a blazed grating. The lattice grooves formed on the lattice surface 16a extend in the Z direction.

A reflective film (not shown) is formed on the side surface 12d (grating surface 16a) of the planar waveguide 12 in which the reflective diffraction grating 16 is formed. The reflection film is, for example, a so-called dielectric multilayer film in which SiO ₂ films and SiN films having different refractive indexes are alternately stacked.

  The reflecting mirror 18 is formed on the side surface 12 e facing the notch 12 b of the planar waveguide 12. The reflecting mirror 18 is disposed to face the reflective diffraction grating 16 with the planar waveguide 12 interposed therebetween.

The reflecting mirror 18 extends while being inclined with respect to the X direction. More specifically, the reflecting surface 18 a of the reflecting mirror 18 extends at a second inclination angle Θ _m (hereinafter also referred to as an inclination angle Θ _m ) with respect to the light propagation direction of the channel-type waveguide 14. is doing.

  The reflecting surface 18 a of the reflecting mirror 18 faces the reflective diffraction grating 16. The reflecting mirror 18 is arranged so that the normal line 18N of the reflecting surface 18a intersects the grating surface 16a of the reflective diffraction grating 16.

A reflective film (not shown) is formed on the reflective surface 18a (side surface 12e). The reflection film is, for example, a so-called dielectric multilayer film in which SiO ₂ films and SiN films having different refractive indexes are alternately stacked.

  The optical deflection unit 20 includes electrodes 20a and 20b and a waveguide portion 14d which is a channel-type waveguide 14 sandwiched between the electrodes 20a and 20b. The electrode 20a is provided on the surface of a p-type cladding layer 15 (described later: FIG. 2) laminated on the waveguide portion 14d. More specifically, in a region where the channel-type waveguide 14 and the planar waveguide 12 face each other with the interval E therebetween, the electrode 20a has a planar shape equal to the waveguide portion 14d. Further, the electrode 20 b is provided on the entire surface of the second main surface 22 b of the substrate 22.

  The insulating layer 26 is provided on the first main surface 22a so as to surround the planar waveguide 12 and the channel-type waveguide 14 except for the notches 12a and 12b. Therefore, the insulating layer 26 is also filled in the gap E between the side surface 14b of the channel waveguide 14 and the side surface 12c of the planar waveguide 12.

  Next, a cross-sectional structure of the wavelength selection element 10 will be described mainly with reference to FIG.

  On the first main surface 22a of the substrate 22, a structure S1 in which the planar waveguide 12 and the p-type cladding layer 13 are laminated in this order is formed. Similarly, on the first main surface 22a, a structure S2 in which the channel type waveguide 14 and the p-type cladding layer 15 are stacked in this order is formed. The structures S1 and S2 are arranged to face each other with an interval E therebetween. An electrode 20 a is provided on the upper surface of the p-type cladding layer 15. An electrode 20 b is provided on the second main surface 22 b of the substrate 22.

  Next, with reference to FIG. 1 and FIG. 2, the dimensions and materials of the components constituting the wavelength selection element 10 will be described.

  For example, the substrate 22 preferably has a length in the X direction of about 600 μm, a length in the Y direction of about 50 μm, and a length (thickness) in the Z direction of about 300 μm. As the substrate 22, for example, n-type InP is preferably used.

The planar waveguide 12 preferably has a length in the X direction of about 500 μm, a length in the Y direction of about 40 μm, and a length (thickness) in the Z direction of about 0.4 μm, for example. As the planar waveguide 12, for example, InGaAsP is preferably used. As a result, the equivalent refractive index n _p of the planar waveguide 12 is about 3.4, for example.

For example, the channel waveguide 14 preferably has a length in the X direction of about 350 μm, a length in the Y direction of about 2 μm, and a length (thickness) in the Z direction of about 0.4 μm. As the channel waveguide 14, for example, InGaAsP is preferably used. As a result, the equivalent refractive index _{n c} of the channel waveguide 14, for example, is about 3.4. In order to satisfy the later-described (1), the equivalent refractive index n _p of the equivalent refractive index n _c and a planar waveguide 12 of the channel waveguide 14 is the magnitude relation between n _c> n _p .

  In addition, the length along the X direction of the portion of the channel-type waveguide 14 facing the planar waveguide 12 (the waveguide portion 14d) is preferably about 300 μm, for example.

  The p-type cladding layers 13 and 15 preferably have a length (thickness) in the Z direction of about 2 μm, for example. As the p-type cladding layers 13 and 15, InP whose conductivity type is p-type is used.

  As the insulating layer 26, insulating (non-doped) InP is used. The insulating layer 26 has a thickness (about 2 μm) equal to the structures S1 and S2. The equivalent refractive index of the insulating layer 26 is, for example, about 3.17.

  As the electrodes 20a and 20b, for example, a structure in which a Ti film, a Pt film, and an Au film are stacked in this order and then heat-treated is used. The length (thickness) in the Z direction of the electrodes 20a and 20b is preferably about 0.5 μm, for example.

  The grating constant d of the reflective diffraction grating 16 is preferably about 0.4 μm, for example.

  Next, the optical coupling unit 28 will be described with reference to FIG.

  The side surface 14b of the channel-type waveguide 14 and the side surface 12c of the planar waveguide 12 are smooth planes. Moreover, the side surface 14b and the side surface 12c are arrange | positioned non-parallel. Therefore, the distance E between the side surfaces 12c and 14b is such that the length (width) H in the Y direction gradually decreases from the light input / output end surface 14a of the channel-type waveguide 14 toward the opposite end surface 14c. It is formed. In other words, the channel-type waveguide 14 and the planar waveguide 12 are arranged such that the width H of the interval E becomes smaller toward the reflective diffraction grating 16.

  Specifically, the width of the interval E is about 1.5 μm at the end of the waveguide portion 14d on the light input / output end face 14a side. Further, the width of the interval E is about 0.5 μm at the end face 14c of the waveguide portion 14d.

  Next, the operation of the wavelength selection element 10 will be described with reference to FIG.

A light I ₁ to be wavelength-selected (hereinafter also referred to as input light I ₁ ) is input from the light input / output end face 14 a of the channel waveguide 14. Input light I ₁ along the channel waveguide 14 in the X direction propagates toward the end face 14c.

The input light I ₁ is coupled to the planar waveguide 12 by the optical coupling unit 28 in the process of propagating through the channel waveguide 14. More specifically, the input light I ₁ is as evanescent wave, oozes from the side 14b to the interval E, is coupled to the planar waveguide 12 through the side surface 12c.

By appropriately selecting the width H of the interval E and the length of the optical coupling portion 28 in the X direction, the input light I ₁ is coupled to the planar waveguide 12 with a coupling efficiency of substantially 100%. The “coupling efficiency” refers to the intensity ratio of light that has been transferred from the channel-type waveguide 14 to the planar waveguide 12 via the optical coupling unit 28.

The light I ₂ coupled to the planar waveguide 12 (hereinafter also referred to as coupled light I ₂ ) becomes a Gaussian beam and propagates through the planar waveguide 12 toward the reflective diffraction grating 16 at a changeable exit angle Θ. To do.

The mechanism by which the coupled light I ₂ is converted into a Gaussian beam by the optical coupling unit 28 will be described later. A mechanism by which the emission angle Θ of the combined light I ₂ is changed by the light deflecting unit 20 will also be described later.

The coupled light I ₂ is incident on the point P on the grating surface 16a at an incident angle θ. Here, the incident angle θ is the angle between the normal 16N lattice plane 16a, the propagation direction of the coupled light I _2. As is clear from the figure, there is a relationship between the outgoing angle Θ and the incident angle θ that decreases as Θ increases.

As a result, the coupled light I ₂ is diffracted at different diffraction angles depending on the wavelength length. That is, the coupled light I ₂ is wavelength-separated by being diffracted by the reflective diffraction grating 16.

Of the wavelength separated light, the light of the diffraction angle beta (hereinafter, also referred to as the diffracted light I _3.) Propagates the planar waveguide 12 in the direction corresponding to the normal 18N of the reflective surface 18a. Then, the diffracted light _{I 3} is incident perpendicularly to the reflecting surface 18a, is reflected by the reflecting surface 18a. That is, only the diffracted light I ₃ having a wavelength (λ ± Δλ ₁ ) corresponding to the diffraction angle β can be reflected by the reflecting surface 18a and returned to the point P on the grating surface 16a.

Here, Δλ ₁ is a variable representing the width of the wavelength distribution curve (center wavelength = λ) of the diffracted light I ₃ . Further, the diffraction angle β is an angle formed between the normal 16N and the propagation direction of the diffracted light I ₃ .

The diffracted light I ₃ is reflected by the reflecting surface 18a, and travels back to the reflecting surface 18a and enters the point P on the grating surface 16a again. Here refers to light propagating the route to the grating surface 16a from the reflecting surface 18a and the reflected light I _4.

The reflected light I ₄ is diffracted again by the grating surface 16a. Of the diffracted reflected light I ₄ , only light having a diffraction angle equal to the above incident angle θ (hereinafter also referred to as wavelength selection light I ₅ ) can be fed back to the channel-type waveguide 14.

Incidentally, the combined light I ₂ (described above) and the reflected light I ₄ are diffracted under the same diffraction conditions. Therefore, the reflected light I ₄ is subjected to the second wavelength selection by the reflective diffraction grating 16 under the condition that the wavelength λ is selected. As a result of the wavelength selection twice, the wavelength distribution of the wavelength selective light I ₅ becomes sharper than the wavelength distribution of the diffracted light I ₃ . That is, the wavelength of the wavelength selection light I ₅ is λ ± Δλ ₂ (where Δλ ₁ ≧ Δλ ₂ ).

The wavelength selection light I ₅ follows the propagation path of the coupled light I _{2 in} the reverse direction and is coupled to the channel-type waveguide 14 via the optical coupling unit 28.

The wavelength-selected light I ₅ coupled to the channel-type waveguide 14 follows a propagation path opposite to that of the input light I ₁ and is output from the light input / output end face 14a as the wavelength-selected output light I ₆ .

Here, with reference to FIG. 4, the mechanism by which the coupled light I ₂ is converted into a Gaussian beam by the optical coupling unit 28 will be described.

  The Gaussian beam refers to light whose intensity distribution in a plane perpendicular to the propagation direction follows the Gaussian distribution.

FIG. 4 shows the distance along the X direction of the channel waveguide 14 on the horizontal axis. The vertical axis (left) indicates the coupling efficiency (arbitrary unit) in the optical coupling unit 28. The vertical axis (right) is the intensity (arbitrary unit) of the input light I ₁ in the channel waveguide 14.

  A curve i schematically represents a change in coupling efficiency in the optical coupling unit 28. It is known that the coupling efficiency depends on the width H of the interval E. That is, the wider the width H, the smaller the coupling efficiency, and the narrower the width H, the greater the coupling efficiency. As a result, the coupling efficiency of the optical coupling portion 28 gradually increases from the input / output end face 14a to the end face 14c of the channel waveguide 14.

A curve ii schematically represents a change in intensity of the input light I _{1 in} the channel waveguide 14. The input light I ₁ is coupled to the planar waveguide 12 along with propagation and is removed from the channel-type waveguide 14. As a result, the intensity of the input light I channel waveguide 14 of ₁ gradually decreases toward the end face 14c from the light output end face 14a.

Curve iii represents an intensity distribution in the side surface 12c of the channel waveguide 14 is coupled to the planar waveguide 12 from the combined light I ₂ schematically.

The shape of the curve iii is determined by a balance between an increase in coupling efficiency along the X direction (curve i) and a decrease in intensity of the input light I ₁ (curve ii). That is, as shown by the curve i, the coupling efficiency gradually increases along the X direction, so that the curve iii gradually increases. Incidentally, since the intensity of the input light I ₁ gradually decreases as shown by the curve ii, the curve iii eventually takes a peak and then gradually decreases. As a result, the intensity distribution (curve iii) of the coupled light I ₂ coupled from the channel-type waveguide 14 to the planar waveguide 12 is substantially Gaussian.

That is, by reducing the width H of the interval E along the X direction, the coupled light I ₂ coupled to the planar waveguide 12 becomes a Gaussian beam.

Next, a mechanism by which the emission angle Θ of the combined light I ₂ is changed by the light deflecting unit 20 will be described.

It is known that the emission angle Θ varies depending on the refractive indexes of the channel waveguide 14 (more specifically, the waveguide portion 14d) and the planar waveguide 12. Here, the equivalent refractive index of the channel waveguide 14 and n _c, the equivalent refractive index of the planar waveguide 12 and n _p. At this time, it is known that the relationship of the following formula (1) is established between the emission angle Θ and the equivalent refractive indexes n _c and n _p .

cos Θ = n _p / n _c (1)
By the way, when a reverse bias voltage is applied between the electrodes 20a and 20b in the optical deflection unit 20, an electric field is generated in the waveguide portion 14d. Electro-optical effect caused by the electric field, the equivalent refractive index n _c of the waveguide portion 14d is changed. Therefore, based on the equation (1), the emission angle Θ of the coupled light I ₂ and, therefore, the incident angle θ to the reflective diffraction grating 16 changes.

More specifically, by increasing the equivalent refractive index n _c of the waveguide portion 14d, the emission angle Θ increases. Therefore, the incident angle θ of the coupled light I _{2 on} the grating surface 16a is reduced. As a result, the selection wavelength λ of the wavelength selection light I ₅ becomes longer for the reason described later.

Conversely, by reducing the equivalent refractive index n _c of the waveguide portion 14d, the emission angle Θ is reduced. Therefore, the incident angle θ of the coupled light I _{2 on} the grating surface 16a is increased. As a result, the selection wavelength λ of the wavelength selection light I ₅ is shortened for reasons described later.

From the above description, the ratio of the rate of change .DELTA..theta output angle with respect to the change rate [Delta] n _c of the equivalent refractive index n _{c (channel} waveguide ₁₄₎ (ΔΘ / Δn c) is found to be positive (> 0).

Next, with reference to FIG. 5, the following two items will be described regarding the design conditions of the wavelength selection element 10.
(A) Relationship between emission angle Θ and selected wavelength λ.
(B) Relationship between the inclination angles Θ _g and Θ _m and the optical path length.

  In FIG. 5, the components of the wavelength selection element 10 are shown in a simplified manner, and the components that are not necessary for the description are omitted.

  Prior to the description of (A) and (B), the arrangement of each component of the wavelength selection element 10 in FIG. 5 will be outlined.

The reflective diffraction grating 16 is simply shown as a grating surface 16a. Lattice plane 16a extends inclined at an inclination angle theta _g with respect to the X direction. That is, acute side of the angle between the light propagation direction of the grating surface 16a and the channel waveguide 14 is theta _g.

The reflecting mirror 18 is simply shown as a reflecting surface 18a. Reflecting surface 18a extends inclined at an inclination angle theta _m with respect to the X direction. That is, acute side of the angle between the light propagation direction of the reflection surface 18a and the channel waveguide 14 is theta _m.

  The light deflecting unit 20 and the optical coupling unit 28 provided in the channel-type waveguide 14 are collectively referred to as a light incident / exiting unit 30 and are simply shown as a rectangle.

Further, it is assumed that the combined light I ₂ and the wavelength selection light I ₅ enter and exit the center point O in the X direction of the light incident / exit section 30.

(A) Relationship between Output Angle Θ and Selected Wavelength λ Consider the coupled light I ₂ a emitted from the light incident / exit section 30 at an exit angle Θ of 0 °.

The coupled light I ₂ a propagates through the planar waveguide 12 (not shown) and enters the point P1 on the grating surface 16a at an incident angle α. Here, the distance between the center point O and the point P1 is L _g . Further, the distance from the point P1 to the reflecting surface 18a and _{L m.}

At this time, the incident angle α of the coupled light I ₂ a to the grating surface 16a is geometrically given by the following equation (2).

α = π / 2−Θ _g (2)
Further, the diffraction angle β of the diffracted light I ₃ a is geometrically given by the following equation (3).

β = Θ _g −Θ _m (3)
Incidentally, the condition that the light of wavelength λ incident on the grating surface 16a at the incident angle α is diffracted at the diffraction angle β is given by the following equation (4) as is well known.

mλ = d (sin (α + Θ) + sinβ) (4)
Here, m is the diffraction order. D is the grating constant of the reflective diffraction grating 16.

  Here, by taking the variation of both sides of the equation (4) and substituting the equations (2) and (3), the following equation (5) is obtained.

Δλ / λ = Θcosα / (sinα + sinβ) = ΘsinΘ g / (cosΘ g + sin (Θ g -Θ m)) ··· (5)
From the equation (5), it can be seen that as the incident angle Θ increases, the selected wavelength λ of the selected wavelength light I ₅ a becomes longer.

(B) Consider per coupling light I _{2 b} emitted by the emission angle theta from the light incidence and emission portions 30 the relationship between the inclination angle theta _g and theta _m and the optical path length (≠ 0 °).

The coupled light I ₂ b propagates through the planar waveguide 12 (not shown) and enters the point P2 on the grating surface 16a. Here, the distance between the center point O and the point P2 and L _1. Further, the distance from the point P2 to the reflecting surface 18a and _{L 2.} Furthermore, the distance between the point P2 and the point P1 described above and _{L ong.}

At this time, the optical path length L _tot of the coupled light I ₂ b from the center point O to the reflecting surface 18a is given by the following equation (6).

L _tot = L ₁ + L ₂ (6)
Therefore, if each of L ₁ and L ₂ can be expressed by Θ _m and Θ _g , the relationship between the arrangement of the grating surface 16a and the reflecting surface 18a and the optical path length L _tot becomes clear.

For the L _1, geometrically following equation (7) holds.

L ₁ sin Θ = tan Θ _g (L ₁ cos Θ−L _g ) (7)
Thus, _{L 1} is given by the following equation (8) obtained by modifying equation (7).

_{L 1 = L g / (cosΘ} -sinΘ / tanΘ g) = L g sinΘ g / sin (Θ g -Θ) ··· (8)
As for the _{L 2,} geometrically below equation (9) is satisfied.

_{L 2 = L m -L ong sin} (Θ g -Θ m) ··· (9)
Regarding _Long , the following equation (10) holds geometrically.

_{L ong sin (Θ g -Θ)} = L g sinΘ ··· (10)
Thus, _{L 2} is given by the following equation (11) erasing the _{L ong} from (9) and (10).

_{L 2 = L m -L g sinΘsin} (Θ g -Θ m) / sin (Θ g -Θ) ··· (11)
By substituting the equations (7) and (11) into the equation (6), the optical path length L _tot is given by the following equation (12).

_{L tot = L m + (L} g / sin (Θ g -Θ) (sinΘ g -sinΘsin (Θ g -Θ m)) ··· (12)
When the equation (12) is rearranged using the equations (2) and (3), the following equation (13) is obtained.

L _tot = L _m + (L _g / cos (α + Θ) (cos α−sin Θ sin β)) (13)
By taking the variation of both sides of the equation (13), the change in the optical path length L _{tot with} respect to the emission angle Θ is given by the following equation (14).

ΔL _tot = L _g (tan α−sin β / cos α) Θ (14)
Expression (14) indicates that the rate of change ΔL _tot of the optical path length L _tot with respect to the rate of change ΔΘ of the emission angle Θ can be changed by adjusting the values of α and β.

More specifically, the value of ΔL _tot / ΔΘ can be changed to plus (> 0) or minus (<0) by adjusting α and β (and hence Θ _g and Θ _m ).

  Next, the effect produced by the wavelength selection element 10 will be described.

In this wavelength selection element 10, it is possible to freely change the change rate ΔL _tot of the optical path length L _{tot with} respect to the change rate ΔΘ of the emission angle Θ of the coupled light I ₂ (Equation (14)). Incidentally, changing the emission angle Θ is synonymous with changing the selection wavelength λ of the wavelength selection light I ₅ . Therefore, in the wavelength selection element 10, the change rate ΔL of the optical path length L _{tot with} respect to the change rate Δλ of the selected wavelength λ is adjusted by adjusting the inclination angle Θ _g of the grating surface 16a and the inclination angle Θ _m of the reflection surface 18a. _tot (wavelength-optical path length ratio) can be freely changed.

  Thereby, the relationship between the wavelength and the optical path length can be changed more flexibly than the wavelength selection element of the prior art. Therefore, the wavelength selecting element 10 can be applied to an optical delay line such as “the longer the selected wavelength, the shorter the delay time”.

Further, in the wavelength selecting element 10, the input light I ₁ is diffracted by the reflection type diffraction grating 16 for two times until output from the light output end face 14a as output light I ₅ which is wavelength selective. As a result, the width (Δλ ₂ ) of the wavelength distribution curve of the selection wavelength λ of the output light I ₅ can be made narrower than that of a Littrow type wavelength selection element. That is, the wavelength selectivity can be improved over the Littrow wavelength selectivity.

Further, in the prior art wavelength selection element, a lens must be used to obtain a Gaussian beam. However, the wavelength selecting element 10, without using a lens, the optical coupling portion 28 is coupled light I ₂ as a Gaussian beam. By the way, the intensity distribution (horizontal axis: wavelength and vertical axis: intensity) related to the wavelength of the wavelength selection light I ₅ is Fourier transform of the intensity distribution (horizontal axis: position and vertical axis: intensity) related to the position of the coupled light I _2. Given in. Therefore, the intensity distribution regarding the wavelength of the wavelength selection light I ₅ can be a Gaussian distribution by setting the intensity distribution regarding the position of the coupled light I ₂ to be a Gaussian distribution.

  In addition, since the wavelength selection element of the prior art uses a lens, the optical axis between the components must be precisely adjusted. However, since the wavelength selection element 10 does not use a lens, there is no need to align the optical axes of the components (planar waveguide 12, channel waveguide 14, reflection diffraction grating 16, and reflection mirror 18).

  In addition, the wavelength selection element 10 has all the components (planar waveguide 12, channel type waveguide 14, reflection type diffraction grating 16, and reflection mirror 18) monolithically integrated on the substrate 22. Smaller than a wavelength selective element.

  Next, changes and modifications of the design conditions allowed for the wavelength conversion element 10 will be described.

  First, a modified example of the light deflection unit 20 will be described.

  The optical deflecting unit need not be provided in the channel-type waveguide 14. For example, as shown in FIG. 6A, the entire region of the planar waveguide 12 may be used as the light deflection unit 32.

That is, the electrode 34 is provided on the entire surface of the p-type cladding layer 13 disposed on the planar waveguide 12. Then, the emission index Θ of the coupled light I ₂ may be adjusted by changing the equivalent refractive index n _p of the planar waveguide 12 by the applied voltage between the electrodes 34 and 20b.

As apparent from the equation (1), when the equivalent refractive index n _p of the planar waveguide 12 is increased in the light deflecting unit 32, the emission angle Θ decreases. Conversely, when the equivalent refractive index n _p of the planar waveguide 12 is reduced, the emission angle Θ is increased. That is, the ratio (ΔΘ / Δn _p ) of the exit angle change rate ΔΘ to the change rate Δn _p of the equivalent refractive index n _p of the planar waveguide 12 is negative (<0).

  Further, as shown in FIGS. 6B and 6C, the light deflection unit 36 may be provided in a partial region of the planar waveguide 12. In this case, the light deflection unit 36 has a planar shape whose width becomes narrower toward the reflective diffraction grating 16.

More precisely, the light deflection unit 36 is provided in a region including the propagation paths of the combined light I ₂ and the wavelength selection light I ₅ . The light deflection unit 36 is formed so that the length (width) in the Y direction decreases as it goes in the lattice surface 16a direction along the X direction.

  The cross-sectional structure of the light deflection unit 36 is the same as that of the light deflection unit 32 described above. That is, the planar electrode 38 congruent with the light deflection section 36 is provided on the p-type cladding layer 13.

  In the light deflection section 36 shown in FIG. 6B, a side 36a facing the grating surface 16a extends with an inclination with respect to the X direction. 6C, both the side 36a facing the grating surface 16a and the side 36b facing the channel waveguide 14 are inclined with respect to the X direction. ing.

Even these optical deflecting unit 36, the voltage applied between the electrodes 38 and 20b to change the equivalent refractive index n _p of the planar waveguide 12, it is possible to adjust the exit angle Θ of the coupled light I _2.

  In addition, as shown in FIG. 7, the channel-type waveguide 14 is provided with a first optical deflection unit 40a, and the planar waveguide 12 is provided with a second optical deflection unit 40b, and the first and second optical deflection units 40a and 40 The light deflection unit 40 may be configured by 40b. In this case, any of the light deflection units 32 and 36 described with reference to FIGS. 6A to 6C can be used as the second light deflection unit 40b.

  As described above, by providing the first and second light deflection units 40a and 40b in the channel waveguide 14 and the planar waveguide 12, the light deflection unit 40 has the following effects.

That is, (ΔΘ / Δn _c ) in the first optical deflection section 40 a provided in the channel-type waveguide 14 is positive (> 0) as described above (see the description of the expression (1)). In addition, (ΔΘ / Δn _p ) in the second optical deflection unit 40 b provided in the planar waveguide 12 is negative (<0).

Therefore, in this case, the change width (ΔΘ) of the emission angle Θ can be approximately double that when the optical deflector is provided in only one of the channel-type waveguide 14 and the planar waveguide 12. More specifically, by changing the equivalent refractive indexes n _c and n _p as (Δn _c > 0 and Δn _p <0) or (Δn _c <0 and Δn _p > 0), the emission angle Θ The change width (ΔΘ) can be increased.

Further, in this embodiment, the width H of the interval E between the optical coupling portions 28 is gradually narrowed. However, when the coupled light I ₂ does not have to be a Gaussian beam, the width H of the interval E may be constant regardless of the location. That is, the side surface 14b of the channel-type waveguide 14 and the side surface 12c of the planar waveguide 12 may be arranged in parallel. This also allows the input light I ₁ to be coupled from the channel waveguide 14 to the planar waveguide 12 with a coupling efficiency of substantially 100%.

  In this embodiment, a blazed grating is used as the reflective diffraction grating 16. However, as the reflective diffraction grating 16, a relief type in which the cross-sectional shape of the grating grooves has a shape other than a sawtooth shape or a refractive index modulation type may be used.

  In this embodiment, the refractive index of the channel-type waveguide 14 is changed using the electro-optic effect. However, the refractive index control of the channel-type waveguide 14 is not limited to the electro-optic effect, and uses, for example, any of the free carrier plasma effect, the acousto-optic effect, the magneto-optic effect, the thermo-optic effect, and the nonlinear optical effect. May be changed. In particular, when the free carrier plasma effect is used, the change width of the refractive index of the channel-type waveguide 14 can be made larger than when the electro-optic effect is used. As a result, wavelength selection can be performed in a wider range.

  Further, in this embodiment, the electrode 20b is provided on the entire surface of the second main surface 22b of the substrate 22. However, the electrode 20b only needs to be provided to face the electrode 20a, and does not need to be provided on the entire surface of the second main surface 22b.

  Some of the components of the wavelength selection element 10 (planar waveguide 12, channel waveguide 14, reflection diffraction grating 16, and reflection mirror 18) may be separated from the substrate 22. For example, the reflective diffraction grating 16 and the reflecting mirror 18 may be arranged outside the substrate 22 as separate components from the substrate 22.

(Embodiment 2: Optical resonator)
The optical resonator of the present invention will be described with reference to FIG. FIG. 8 is a perspective view showing a schematic configuration of the optical resonator. FIGS. 9A and 9B are schematic views showing a modification of the optical resonator.

  The optical resonator 50 has the same structure as that of the wavelength selection element 10 except that the optical resonator 50 includes the reflection mirror 52. Therefore, in FIG. 8, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted as appropriate.

The optical resonator 50 includes a wavelength selection element 10 and a reflection mirror 52. The reflection mirror 52 covers the light input / output end face 14 a of the channel type waveguide 14. The reflection mirror 52 has a reflectance of less than 100%, and is made of, for example, a so-called dielectric multilayer film in which SiO ₂ films and SiN films having different refractive indexes are alternately stacked.

In the optical resonator 50, the tilt angle Θ _g of the reflective diffraction grating 16 and the tilt angle Θ _m of the reflecting mirror 18 are adjusted so that mode hopping does not occur. The conditions for suppressing mode hopping will be described later.

  Although not shown, a laser light source (not shown) is provided outside the optical resonator 50. The light emission port of the laser light source is disposed to face the reflection mirror 52.

  Next, the operation of the optical resonator 50 will be described mainly with reference to FIG.

Light emitted from the laser light source is input to the channel-type waveguide 14 as input light I ₁ from the light input / output end face 14 a via the reflection mirror 52. The input light I ₁ is coupled to the planar waveguide 12 by the optical coupling portion 28 in the process of propagating through the channel waveguide 14 in the direction of the end face 14 c. Then, it propagates in the planar waveguide 12 toward the reflective diffraction grating 16 as the coupled light I ₂ whose emission angle is adjusted to Θ by the light deflecting unit 20.

The coupled light I ₂ propagating through the planar waveguide 12 enters the point P on the grating surface 16a at an incident angle θ. The coupled light I ₂ incident on the reflective diffraction grating 16 is diffracted at different diffraction angles depending on the length of the wavelength. That is, the coupled light I ₂ is wavelength-separated by being diffracted by the reflective diffraction grating 16.

Of the diffracted coupled light I ₂ , the diffracted light I ₃ having a diffraction angle β is reflected by the reflecting surface 18 a of the reflecting mirror 18. The reflected light I ₄ reflected by the reflecting surface 18 a returns to the point P on the grating surface 16 a and is diffracted by the reflecting diffraction grating 16 again.

Of the reflected light I ₄ that has been subjected to the second wavelength selection by being diffracted, the wavelength selective light I ₅ whose diffraction angle is θ follows the propagation path of the coupled light I _{2 in} the reverse direction, and the channel-type waveguide 14. Return to Then, the light is reflected by the reflecting mirror 52 provided on the light input / output end face 14a and reciprocates several times in the same path as the above-described path.

  The light intensity increases with each round-trip, and is eventually emitted from the reflection mirror 52 as laser light having a wavelength λ.

In the optical resonator 50, the selection wavelength λ of the laser beam can be changed by changing the emission angle Θ of the coupled light I ₂ by the optical deflecting unit 20. In addition, as described above, the inclination angle theta _g and theta _m is adjusted, there is no mode hopping when changing the selected wavelength lambda.

  Next, conditions for suppressing mode hopping in the optical resonator 50 will be described.

  Here, the mode hopping indicates a phenomenon in which the selection wavelength λ changes discontinuously as the selection wavelength λ of the laser light is changed. Mode hopping occurs due to the fact that the selected wavelength (longitudinal mode wavelength) of the laser light takes a discrete value determined by the optical path length of the optical resonator.

  Therefore, in order to suppress mode hopping, it is necessary to lengthen (shorten) the selected wavelength λ and lengthen (shorten) the optical path length of the optical resonator 50. The conditions will be described below.

  The resonance condition in the optical resonator 50 is given by the following equation (15), where T is the optical path length of the optical resonator 50.

kT = qπ (15)
Here, k represents the wave number (= 2π / λ) of light of wavelength λ. Further, q represents a positive integer (vertical mode order + 1).

  Here, the optical path length T is given by the following equation (16).

T = n _p L _tot + n _c L _c + n _o L _o (16)
Here, L _c indicates the geometric length of the light propagation path in the waveguide portion 14 d corresponding to the light deflection unit 20. L _o represents a geometric length obtained by subtracting (L _tot + L _c ) from the geometric total length of the light propagation path in the optical resonator 50. That is, L _o is the geometric length of the light propagation path (hereinafter also referred to as other path) in the optical resonator 50 other than the planar waveguide 12 and the waveguide portion 14d. Further, n _o represents an equivalent refractive index in the other path.

From the equations (15) and (16), the resonance condition is given by the following equation (17).
k (n _p L _tot + n _c L _c + n _o L _o ) = qπ (17)
Here, with respect to the minute change Δk of the wave number k caused by changing the emission angle Θ, the equation (17) which is the resonance condition is modified as the following equation (18).

Δk (n _p L _tot + n _c L _c + n _o L _o ) + k (n _p ΔL _tot + Δn _c L _c ) = Δqπ (18)
Here, Δq = 0 must be satisfied so that mode hopping does not occur even if the wave number k (wavelength λ) changes. Thus, the following equation (19) is obtained.

Δk (n _p L _tot + n _c L _c + n _o L _o ) + k (n _p ΔL _tot + Δn _c L _c ) = 0 (19)
Further, by substituting Δk = −k ² / 2π × Δλ obtained by differentiating both sides of k = 2π / λ and the equation (14) into the equation (19), the following equation (20) is obtained.

−qπcos α (sin α + sin β) + kn _p L _g (sin α-sin β) / cos α = −Δn _c L _c / Θ (20)
By determining α and β, and thus Θ _g and Θ _m so as to satisfy the equation (20), it is possible to continuously change the selection wavelength λ while suppressing mode hopping.

  Next, the effect produced by the optical resonator 50 will be described.

The optical resonator 50 uses the wavelength selection element 10. Accordingly, wavelength by appropriate selection of theta _g and theta _m - can be arbitrarily set the optical path length ratio.

In particular, by determining Θ _g and Θ _m so as to satisfy the equation (20), it is possible to perform wavelength selection of laser light without causing mode hopping.

  Next, design condition changes and modifications allowed in the optical resonator 50 will be described.

  In the optical resonator 50, the reflection mirror 52 is provided on the light input / output end face 14a of the channel type waveguide 14. However, the arrangement of the reflection mirror 52 is not limited to this. For example, as shown in FIG. 9A, the reflection mirror 54 may be disposed separately from the wavelength selection element 10 and opposed to the light input / output end face 14a with a gap.

  Further, as shown in FIG. 9B, the light input / output end face 14a and the reflection mirror 54 may be arranged to face each other with an interval, and a laser light source 56 may be provided at this interval.

  Further, the optical resonator 50 of this embodiment can be modified in the same manner as the wavelength selection element 10.

It is a perspective view which shows schematic structure of a wavelength selection element. It is a figure which shows the cross section cut along the II line | wire of FIG. It is the schematic diagram which expanded the structure of the optical coupling part vicinity in a wavelength selection element. It is the figure which showed the graph with which it uses for description of gauss beam-izing of combined light. It is a schematic diagram with which it uses for description of the design conditions of a wavelength selection element. (A)-(C) is a schematic diagram with which it uses for description of the modification of an optical deflection | deviation part. It is a schematic diagram with which it uses for description of the modification of an optical deflection | deviation part. It is a perspective view which shows schematic structure of an optical resonator. (A) And (B) is a schematic diagram which shows the modification of an optical resonator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Wavelength selection element 12 Planar waveguide 12a Notch part 12b Notch part 12c Side face 12d Side face 12e Side face 13 P-type clad layer 14 Channel type waveguide 14a Optical input / output end face 14b Side face 14c End face 14d Waveguide part 15 P-type clad layer 16 Reflection Type diffraction grating 16N normal line 16a grating surface 18 reflecting mirror 18a reflecting surface 18N normal line 20 light deflection unit 20a electrode 20b electrode 22 substrate 22a first main surface 22b second main surface 26 insulating layer 28 optical coupling unit 30 light incident / exiting unit 32 Optical deflection unit 34 Electrode 36 Optical deflection unit 36a Side 36b Side 38 Electrode 40 Optical deflection unit 40a First optical deflection unit 40b Second optical deflection unit 50 Optical resonator 52 Reflective mirror 54 Reflective mirror 56 Laser light source

Claims (9)

The channel-type waveguide that couples input light to a planar waveguide through one surface of the channel-type waveguide along the light propagation direction;
The lattice plane extending at a first inclination angle with respect to the light propagation direction and extending opposite to the channel-type waveguide with the planar waveguide interposed therebetween are coupled to each other. A reflective diffraction grating that diffracts light;
A reflecting mirror having a reflecting surface extending at a second inclination angle with respect to the light propagation direction and having a normal intersecting the grating surface, the reflecting type sandwiching the planar waveguide A reflecting mirror disposed opposite to the diffraction grating and reflecting the diffracted light toward the reflective diffraction grating;
A wavelength selection element comprising: an optical deflecting unit that changes an incident angle of the combined light with respect to the grating surface. The optical deflection unit is provided in the channel-type waveguide,
The wavelength selection element according to claim 1, wherein the incident angle is adjusted by changing a refractive index of the channel-type waveguide. The light deflection unit is provided in a part or all of the planar waveguide,
The wavelength selection element according to claim 1, wherein the incident angle is adjusted by changing a refractive index of the region. The optical deflection unit includes a first optical deflection unit provided in the channel-type waveguide, and a second optical deflection unit provided in a part or all of the planar waveguide,
The first light deflection unit adjusts the incident angle by changing the refractive index of the channel-type waveguide, and the second light deflection unit adjusts the refractive index of the region of the planar waveguide. The wavelength selective element according to claim 1.   5. The wavelength selective element according to claim 3, wherein the partial region has a planar shape whose width becomes narrower toward the reflective diffraction grating. The one surface of the channel-type waveguide and the surface of the planar waveguide facing the one surface are provided with a gap therebetween,
6. The channel-type waveguide and the planar waveguide are arranged so that the width of the gap becomes smaller toward the reflective diffraction grating. The wavelength selection element according to 1.   7. The planar waveguide, the channel-type waveguide, the reflective diffraction grating, the reflecting mirror, and the light deflecting unit are integrated on a common substrate. The wavelength selection element according to 1. An optical resonator comprising the wavelength selection element according to any one of claims 1 to 7,
An optical resonator comprising a reflection mirror on an optical input / output end face of the channel waveguide. An optical resonator comprising the wavelength selection element according to any one of claims 1 to 7,
An optical resonator comprising a reflection mirror facing and spaced from the light input / output end face of the channel waveguide.

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