JP2012014029A - Optical resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical resonator whose structure and manufacturing process are simple and which easily obtains strong resonance by using grating and total reflection.SOLUTION: An optical resonator comprises: a total reflection unit; and a waveguide. The total reflection unit has a first main surface and a second main surface as two main surfaces parallel to each other, and the first main surface and the second main surface are optically mirror surfaces. The waveguide is formed on the second main surface of the total reflection unit and has a grating unit. The grating unit diffracts light transmitted in the waveguide and sends it to the total reflection unit, and diffracts light entering from the total reflection unit and transmits it in the waveguide. Also, the light sent to total reflection unit is totally reflected on the first main surface of the total reflection unit toward the waveguide.

Description

  The present invention relates to an optical resonator that can be used as, for example, a wavelength separation element or a delay element.

  In order to perform large-capacity optical communication, a technique for multiplexing and transmitting light of many wavelengths is important. For this reason, a wavelength separation element that separates light of different wavelengths is required.

  In recent years, optical resonators that can extract only light of a specific wavelength have been studied as wavelength separation elements. The optical resonator can also be used as a delay element by circulating light in the optical resonator.

  As an optical resonator, many ring resonators in which a ring-shaped waveguide is disposed on a substrate have been studied. However, the ring-shaped waveguide has a curved shape that is not good for EB (Electron Beam) drawing. For this reason, light scattering occurs due to minute disturbances in the waveguide, and it is difficult to obtain strong resonance.

  On the other hand, as an optical resonator that does not use a ring-shaped waveguide, an optical resonator in which a waveguide resonant grating and a multilayer reflective mirror are combined has recently been proposed (for example, see Non-Patent Document 1).

  There has also been proposed a technique for realizing an optical resonator using a directional coupler having two upper and lower waveguides (see, for example, Non-Patent Document 2).

  In addition, there is a technique in which an oblique reflection surface is used to resonate by total reflection on each surface (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-303497

Optics Express vol. 16, no. 22, p. 17282, October 27, 2008 Optics Express vol. 17, no. 6, p. 4348, March 16, 2009

  However, the above-described optical resonator disclosed in Non-Patent Document 1 resonates with a dielectric multilayer film as a multilayer film reflection mirror and a waveguide resonance grating. Since the production of the body multilayer film is also necessary, the manufacturing process becomes complicated.

  Further, since the optical resonator disclosed in Non-Patent Document 2 described above uses a directional coupler having two upper and lower waveguides, the thickness of the waveguide and the interval between the two waveguides are set. It cannot be made larger and the scope of application is limited.

  In addition, the optical resonator disclosed in Patent Document 1 described above is difficult to manufacture because a special process is required for manufacturing the oblique reflection surface.

  The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to use a grating and total reflection to simplify the structure and manufacturing process and easily obtain strong resonance. It is to provide a simple optical resonator.

  In order to achieve the above-described object, an optical resonator according to the present invention includes a total reflection resonator and a waveguide.

  The total reflection resonance part has a first main surface and a second main surface as two main surfaces parallel to each other, and the first main surface and the second main surface are optically mirror surfaces. is there. The waveguide is formed on the second main surface of the total reflection resonance part and has a grating part.

  The grating unit diffracts the light propagating through the waveguide and sends it to the total reflection resonance unit, and diffracts the light incident from the total reflection resonance unit to propagate through the waveguide. The light transmitted to the total reflection resonance part is totally reflected toward the waveguide on the first main surface of the total reflection resonance part.

Here, light diffracted by the grating portion, in order to totally reflected by the total reflection resonator portion, the refractive index n ₀ of the surrounding of the optical resonator with respect to the equivalent refractive index n _e of the waveguide light propagates wavelength λ Therefore, the grating period Λ may be set so as to satisfy the following expression (1).

Λ <λ / (n ₀ + _ne ) (1)
Further, it may be configured such that light propagating through the waveguide does not contribute to resonance. In this case, the grating period Λ may satisfy the following expression (2) with respect to the refractive index n ₀ around the optical resonator.

Λ <λ / 2 · n ₀ (2)

  According to the optical resonator of the present invention, since the curved portion is not included in the optical resonator, the resonance characteristics are not deteriorated due to the boundary roughness that tends to occur in the curved portion.

It is the schematic for demonstrating the optical resonator of 1st Embodiment. It is a figure which shows the result of the simulation using the two-dimensional FDTD method. It is the schematic for demonstrating an optical resonator provided with an input-output waveguide. It is a schematic diagram of the optical resonator in which the input part and the output part were provided in the waveguide. It is a figure for demonstrating the optical resonator of 2nd Embodiment. It is a figure for demonstrating the optical resonator of 3rd Embodiment. It is a figure which shows the result of the simulation using the two-dimensional FDTD method. It is a figure which shows the result of the simulation about the temperature dependence of a resonant wavelength.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(First embodiment)
With reference to FIGS. 1A and 1B, the optical resonator of the first embodiment will be described. 1A and 1B are schematic views for explaining the optical resonator of the first embodiment, and show a cut end surface of a main part.

  The optical resonator 10 includes a total reflection resonance unit 20 and a waveguide 30. The total reflection resonance part 20 has a first main surface 20a and a second main surface 20b as two main surfaces parallel to each other. The waveguide 30 is provided on the second main surface 20 b of the total reflection resonance part, and has a grating part 32.

  A light path in the optical resonator 10 will be described with reference to FIG.

  Light 101 (hereinafter also referred to as propagating light) 101 propagating through the waveguide 30 is diffracted by the grating section 32. The diffracted light (hereinafter sometimes referred to as diffracted light) 103 travels toward the first main surface 20 a of the total reflection resonance portion 20.

  The diffracted light 103 incident on the total reflection resonator 20 is totally reflected by the first main surface 20a. The totally reflected light (hereinafter sometimes referred to as reflected light) 105 travels toward the waveguide 30.

  The reflected light 105 is diffracted by the grating portion 32 of the waveguide 30, that is, is coupled and becomes the propagation light 101 that propagates through the waveguide 30. Resonance is realized by this round path.

  In order to cause the light having the resonance wavelength λ to stay in the optical resonator 10, that is, to resonate, the optical resonator 10 is configured as follows.

  In order to efficiently reflect the diffracted light 103, the first main surface 20a is configured as an optical mirror surface. Further, in order to suppress scattering between the total reflection resonator 20 and the waveguide 30, the second main surface 20b is also configured as an optical mirror surface. The surface of the total reflection resonance part 20 other than the first main surface 20a and the second main surface 20b may not be an optical mirror surface.

  The grating portion 32 of the waveguide 30 periodically digs a groove from the upper surface 30b of the waveguide 30 to the lower surface 30a in contact with the second main surface 20b of the total reflection resonator 20 in order to increase diffraction efficiency. Is formed.

  In order to realize resonance, the length of the grating portion 32 in the propagation direction is the length required for the propagation light 101 to be diffracted and converted into the diffracted light 103, and the diffracted light 103 is reflected to become the reflected light 105. It must be longer than the horizontal distance to return to the grating section 32.

The grating period Λ of the grating portion 32 is set so that the incident angle θ of the diffracted light 103 to the first main surface 20a is larger than the critical angle θ _c at which the first main surface 20a is totally reflected. . The surrounding refractive index n ₀ and the wavelength λ of the equivalent refractive index n _e of the waveguide 30 through which light propagates in the optical resonator 10, so as to satisfy the following equation (1), by setting the grating period Λ good.

Λ <λ / (n ₀ + _ne ) (1)
This expression (1) is derived as follows.

As is well known, the equivalent refractive index n _e of the waveguide 30, the refractive index n of the total reflection resonator portion 20, the wavelength (resonance wavelength) lambda and grating period Λ that resonate, when satisfying the following equation (3), the waveguide The propagating light 101 propagating 30 is diffracted so that the incident angle on the first main surface 20a becomes θ.

_{Λ = λ / (n e +} n · sinθ) (3)
Here, the equivalent refractive index _ne of the waveguide 30 is obtained from the material of the waveguide 30 and the wavelength (resonance wavelength λ here).

In addition, in order for the diffracted light 103 to be totally reflected on the first main surface 20a of the total reflection resonator 20, the refractive index n ₀ around the optical resonator 10, the refractive index n of the total reflection resonator 20, and the first The incident angle θ of one main surface 20a needs to satisfy the following expression (4).

sin θ> sin θ _c = n ₀ / n (4)
From the above equations (3) and (4), equation (1) is obtained.

  Here, the propagating light 101 is diffracted by the grating section 32 to become diffracted light 103, and this diffracted light 103 is totally reflected by the first main surface 20a to become reflected light 105, and the reflected light 105 becomes propagating light 101 again. Although an example of making a round has been described, the route is not limited to this. The reflected light incident on the waveguide 30 may be converted to diffracted light directed toward the first main surface 20a of the total reflection resonance unit 20 again without propagating through the waveguide 30 by the grating unit 32.

  The light path in this case will be described with reference to FIG.

  The first diffracted light 111 diffracted by the grating part 32 is totally reflected by the first main surface 20a. The totally reflected first reflected light 113 travels toward the waveguide 32. The first reflected light 113 is diffracted by the grating portion 32 of the waveguide 30 and becomes the second diffracted light 115 directed toward the first main surface 20a. The second diffracted light 115 is totally reflected by the first main surface 20 a, and the second reflected light 117 totally reflected is directed to the waveguide 30. The second reflected light 117 is diffracted by the grating section 32 and becomes the first diffracted light 111.

  Resonance is realized by this round path. In this case, propagating light propagating through the waveguide 30 does not contribute to resonance.

The grating period Λ of the grating portion 32 is a critical angle at which the incident angle θ of the first diffracted light 111 and the second diffracted light 115 with respect to the first main surface 20a is totally reflected by the first main surface 20a. It is set to be larger than θ _c . The grating period Λ may be set so as to satisfy the following expression (2) with respect to the refractive index n ₀ around the optical resonator 10.

Λ <λ / 2 · n ₀ (2)
This expression (2) is derived as follows.

  As is well known, when the refractive index n, resonance wavelength λ, and grating period Λ of the total reflection resonator 20 satisfy the following expression (5), the first reflected light 113 and the second reflected light 117 are the first Is diffracted so that the incident angle to the main surface 20a becomes θ.

Λ = λ / (2 · n · sin θ) (5)
In addition, in order for the first diffracted light 111 and the second diffracted light 115 to be totally reflected at the first main surface 20 a, the refractive index n ₀ around the optical resonator 10 and the refraction of the total reflection resonator 20. The rate n and the incident angle θ of the first main surface 20a need to satisfy the above formula (4).

  Therefore, equation (2) is obtained from equations (4) and (5).

  Next, simulation using a two-dimensional time domain difference (FDTD) method will be described. FIG. 2 is a diagram showing a result of simulation using the two-dimensional FDTD method.

  2A and 2B show simulation results when the length of the grating portion 32 is finite and about 24 nm. At this time, the wavelength λ is 1378 nm.

  2C and 2D show the simulation results when the length of the grating portion 32 is infinite. At this time, the wavelength λ is set to 1379.5 nm.

  2A and 2C, the first main surface 20a generates continuous light having a resonance wavelength λ toward the waveguide 30, and the normalized time (standardized time) cT is 1000 (μm). It shows the distribution of the electric field strength when 2B and 2D show temporal changes in light intensity on the first main surface 20a of the total reflection resonance portion 20. FIG. 2B and 2D, the horizontal axis indicates the normalized time cT (μm), and the vertical axis indicates the light intensity (arbitrary unit).

  Here, the material of the total reflection resonator 20 is quartz, and the refractive index n is 1.46. Further, the thickness from the first main surface 20a of the total reflection resonator 20 to the upper surface 30b of the waveguide 30 is set to 3 μm.

  The waveguide 30 is made of silicon (Si) and has a refractive index of 3.5. The thickness of the waveguide 30 is 300 nm, and the grating period Λ of the grating portion 32 is 641.52 nm.

Further, the entire periphery of the optical resonator 10 is air, and its refractive index n ₀ is 1.0.

  According to FIGS. 2A and 2C, a strong electric field and a weak electric field repeatedly appear in the total reflection resonance part 20 in directions perpendicular to the direction parallel to the first main surface 20a. ing. 2B and 2D show that the light intensity on the first main surface 20a of the total reflection resonance portion 20 increases as the normalized time cT (μm) elapses.

(Input / output means)
Next, light input / output means for the optical resonator 10 will be described. Input / output of light to / from the optical resonator 10 can be performed using any suitable means.

  As a first example, there is a technique for creating a structural disorder in the grating section 32, such as providing regions in the grating section 32 with different grating periods Λ. In this way, when structural disturbance is created in the grating section 32, scattering occurs in the area where the disturbance is present, and light can be extracted.

  As a second example, there is a technique of providing an input / output optical waveguide (input / output waveguide). With reference to FIGS. 3A and 3B, an optical resonator including this input / output waveguide will be described. FIG. 3A is a schematic configuration diagram of an optical resonator including an input / output waveguide, and shows a cut end surface of a main part. FIG. 3B is a diagram showing a result of simulation using the two-dimensional FDTD method. In FIG. 3B, the horizontal axis indicates the wavelength (μm) and the vertical axis indicates the light intensity (arbitrary unit) of the output light.

  The optical resonator 11 includes an input / output waveguide 40 that is disposed close to the first main surface 20a of the total reflection resonator 20. The input / output waveguide 40 includes an input unit 42, a coupling unit 44, and an output unit 46 in this order. Light (input light) 121 input to the input / output waveguide 40 is propagated in the order of the input unit 42, the coupling unit 44, and the output unit 46. The input light 121 generates evanescent light 123 at the coupling part 44 on the total reflection resonance part 20 side. The evanescent light 123 is diffracted by the grating portion 32 of the waveguide 30 and resonates in the optical resonator 11 as described with reference to FIG. 1A or 1B.

  In addition, the light (diffracted light) 125 resonating in the optical resonator 11 generates evanescent light on the input / output waveguide 40 side in the vicinity of the first main surface 20a of the total reflection resonator 20. The evanescent light is output as output light 127 from the input / output waveguide 40 via the output unit 46.

  Next, a simulation result using the two-dimensional FDTD method will be described with reference to FIG.

  Here, the material of the total reflection resonator 20 is quartz, and the refractive index n is 1.46. Further, the thickness from the first main surface 20a of the total reflection resonator 20 to the upper surface 30b of the waveguide 30 is set to 3 μm.

The waveguide 30 is made of silicon (Si) and has a refractive index of 3.5. The thickness of the waveguide 30 is 450 nm. The grating section 32 has a grating period Λ of 430 nm and a length of the grating section 32 of about 27 μm. The width of the input / output waveguide 40 is 600 nm, and the distance d between the coupling portion 44 of the input / output waveguide 40 and the first main surface 20a of the total reflection resonator 20 is 500 nm. The length of the coupling portion 44 is 10 μm. Further, the entire periphery of the optical resonator 10 is air, and its refractive index n ₀ is 1.0.

  As shown in FIG. 3B, since the light having the resonance wavelength λ (= 1.588 μm) stays in the optical resonator 11, the light intensity of the output light near 1.588 μm is other than It decreases compared to the light intensity of the wavelength.

  As a third example, there is a technique in which a waveguide having a grating part is provided with an input part and an output part. With reference to FIG. 4, an optical resonator in which an input portion and an output portion are provided in a waveguide will be described. FIG. 4 is a schematic diagram of an optical resonator in which an input unit and an output unit are provided in a waveguide.

  When the optical waveguide is a single mode waveguide, the size of the waveguide is approximately 300 nm in width and 300 nm in height. If a grating part is formed in this waveguide, resonance is difficult to be established due to diffusion of diffracted light in the grating part. Accordingly, it is desirable that the width of the grating portion is at least five times the wavelength.

  Therefore, in this optical resonator 12, the waveguide 50 includes an input unit 54, a grating unit 52, and an output unit 56 in this order. Further, the waveguide 50 has tapered portions 58 between the input portion 54 and the grating portion 52 and between the grating portion 54 and the output portion 56, respectively.

  The widths of the input unit 54 and the output unit 56 are set to a width that functions as a single mode waveguide, for example, about 300 nm. On the other hand, the width of the grating portion 52 is set to 5 times or more the resonance wavelength λ. The taper portion 58 gradually becomes wider from the input portion 54 and the output portion 56 toward the grating portion 52.

  4 includes a substrate 90 on the first main surface 20a side of the total reflection resonator 20. This substrate is configured as a silicon substrate, for example. In addition, an opening 92 is formed in the substrate 90 to expose a partial region of the first main surface 20a by wet etching using potassium hydroxide (KOH) as an etchant.

  With this configuration, if a means for amplifying light is provided in the total reflection resonator 20 or the waveguide 50, the optical resonator 12 can function as a laser light source. As a means for amplifying light, the total reflection resonator 20 can be made of quartz into which erbium (Er) is introduced and pumped with pump light incident from the side. Further, by configuring the waveguide 50 with a compound semiconductor, the waveguide 50 can be used as an optical amplification medium.

(Second Embodiment)
The optical resonator of the second embodiment will be described with reference to FIG. FIG. 5 is a diagram for explaining the optical resonator of the second embodiment, and FIG. 5A is a schematic configuration diagram of the optical resonator including an input / output waveguide. 5B and 5C are diagrams showing the results of simulation using the two-dimensional FDTD method. FIG. 5B shows the electric field intensity distribution when the continuous light having the resonance wavelength λ toward the waveguide 30 is generated on the first main surface 20a and the normalized time cT becomes 1000 (μm). Show. FIG. 5C shows how the light intensity on the first main surface 20a of the total reflection resonator 20 changes with time. FIG. 5C shows the normalized time cT (μm) on the horizontal axis and the light intensity (arbitrary unit) on the vertical axis.

  The optical resonator 13 of this embodiment includes two grating portions 62a and 62b in the waveguide 60, and a region 61 where no grating is formed exists between the grating portions 62a and 62b. 1 is different from the optical resonator described with reference to FIG. Since the other configuration is the same as that of the optical resonator described with reference to FIG.

  The light path in this case will be described.

  The propagating light 141 propagating through the waveguide 60 is diffracted by one grating portion 62b. The diffracted diffracted light 143 travels toward the first main surface 20a of the total reflection resonator 20. The diffracted light 143 incident on the total reflection resonator 20 is totally reflected by the first main surface 20a. The totally reflected light 145 travels toward the waveguide 60.

  The reflected light 145 is diffracted by the other grating portion 62 a of the waveguide 60, that is, coupled to be propagated light 141 that propagates through the waveguide 60. The propagating light 141 is sent to the grating part 62b through the region 61 between the grating parts 62a and 62b. Resonance is realized by this round path.

  Next, simulation results using the two-dimensional FDTD method will be described.

  Here, the material of the total reflection resonator 20 is quartz, and the refractive index n is 1.46. Further, the thickness from the first main surface 20a of the total reflection resonator 20 to the upper surface 60b of the waveguide 60 is set to 7 μm.

The material of the waveguide 60 is silicon (Si) and the refractive index is 3.5. The thickness of the waveguide 60 is 450 nm. The grating parts 62a and 62b have a grating period Λ of 470 nm and the lengths of the grating parts 62a and 62b are about 8.5 μm, respectively. The interval between the grating portions 62a and 62b, that is, the length of the region 61 is 10 μm. Further, the entire periphery of the optical resonator 13 is air, and its refractive index n ₀ is 1.0.

  In FIG. 5C, the light intensity at the first main surface 20a is indicated by a curve I, and the light intensity propagated to the outside is indicated by a curve II. As shown in FIG. 5C, when the standardized time cT is 500 (μm), the light intensity exceeds 1, and according to the configuration of FIG. 5A, refer to FIG. Compared to the optical resonator of the first embodiment described above, stronger resonance can be achieved more quickly.

(Third embodiment)
The optical resonator of the third embodiment will be described with reference to FIG. FIG. 6 is a diagram for explaining the optical resonator of the third embodiment, and FIG. 6A is a schematic configuration diagram of the optical resonator including an input / output waveguide. 6B and 6C are diagrams showing the results of simulation using the two-dimensional FDTD method. FIG. 6B shows the electric field intensity distribution when the continuous light having the resonance wavelength λ toward the waveguide 30 is generated on the first main surface 20a and the normalized time cT becomes 1000 (μm). Show. FIG. 6C shows how the light intensity on the first main surface 20a of the total reflection resonator 20 changes with time. FIG. 6C shows the normalized time cT (μm) on the horizontal axis and the light intensity (arbitrary unit) of the output light on the vertical axis.

  The optical resonator 14 of this embodiment is different from the optical resonator described with reference to FIG. 1 in that a block 70 is provided on the waveguide 30. Since the other configuration is the same as that of the optical resonator described with reference to FIG.

  The block 70 may be formed of the same material as that of the waveguide 30 or may be formed of the same material as that of the total reflection resonance unit 20. In addition, the surface (lower surface) 70a in contact with the waveguide 30 of the block 70 and the upper surface 70b of the block 70 are optically mirror surfaces.

  The first diffracted light 151 diffracted by the grating part 32 is totally reflected by the first main surface 20a. The totally reflected first reflected light 153 travels toward the waveguide 30.

  The first reflected light 153 is diffracted by the grating portion 32 of the waveguide 30 and becomes second diffracted light 155 directed toward the upper surface 70 b of the block 70.

  The second diffracted light 155 is totally reflected by the upper surface 70 b of the block 70, and the second reflected light 157 that has been totally reflected is directed to the waveguide 30.

  The second reflected light 157 is diffracted by the grating unit 32 and becomes the first diffracted light 151. Resonance is realized by this round path.

  Next, simulation results using the two-dimensional FDTD method will be described with reference to FIGS.

  Here, the material of the total reflection resonator 20 is quartz, and the refractive index n is 1.46. In addition, the thickness from the first main surface 20a of the total reflection resonator 20 to the upper surface 30b of the waveguide 30 is set to 2 μm.

  The waveguide 30 is made of silicon (Si) and has a refractive index of 3.5. The thickness of the waveguide 30 is 450 nm. The grating section 32 has a grating period Λ of 470 nm and the length of the grating section 32 is infinite. The wavelength is 1586 nm.

The block 70 is made of the same material as that of the waveguide 30, that is, silicon, and its refractive index is 3.5. Further, the thickness of the block 70 is set to 500 nm. Further, the entire periphery of the optical resonator 14 is air, and its refractive index n ₀ is 1.0.

  As shown in FIG. 6 (C), according to the configuration of FIG. 6 (A), when the standardized time cT is 700 (μm), the light intensity exceeds 1, see FIG. 1 (A). Compared to the optical resonator of the first embodiment described above, stronger resonance can be achieved more quickly.

  Next, a simulation result using the two-dimensional FDTD method when the material of the block 70 is changed will be described with reference to FIGS. FIGS. 7A and 7B are diagrams showing the results of simulation using the two-dimensional FDTD method. FIG. 7A shows the distribution of the electric field intensity when the continuous light having the resonance wavelength λ toward the waveguide 30 is generated on the first main surface 20a and the normalized time cT becomes 1000 (μm). Show. FIG. 7B shows how the light intensity on the first main surface 20a of the total reflection resonator 20 changes with time. FIG. 7B shows the normalized time cT (μm) on the horizontal axis and the light intensity (arbitrary unit) of the output light on the vertical axis.

  Here, the material of the block 70 is quartz like the total reflection resonator 20, the refractive index is 1.46, and the wavelength is 1384 nm. The simulation conditions of FIGS. It is different and other conditions are the same.

  As shown in FIG. 7B, even when the material of the block 70 is the same as that of the total reflection resonator 20, the light intensity exceeds 1 when the normalized time cT is 1000 (μm). Thus, stronger resonance can be achieved more quickly than the optical resonator of the first embodiment described with reference to FIG.

(Temperature dependence)
Resonance condition in the structure shown in FIG. 1 (A), the propagation length Lg in the grating portion, the equivalent refractive index ng, the propagation length L _b in the total reflection resonator unit, and the refractive index n _b, to an integer m M = ( _ng · L _g + n _b · L _b ) / λ. Here, when the evanescent light to the upper surface 30b of the waveguide 30 is used, the refractive index change can be estimated from the shift of the resonance wavelength.

The resonance wavelength change due to temperature change is expressed by the following equation (6).
m · dλ / dT = (dn _g / dT) · L _g + (dn _b / dT) · L _b
+ _Ng · (dL _g / dT) + n _b · (dL _b / dT) (6)
Given in.

For example, when the waveguide 30 is made of silicon, dn _g /dT=1.8×10 ⁻⁴ . Further, when the total reflection resonance part 20 is a polymer, dn _b / dT = −1 × 10 ⁻⁴ to −3 × 10 ⁻⁴ . In this way, when materials having opposite refractive index changes due to temperature changes are used for the waveguide 30 and the total reflection resonance unit 20, a resonance wavelength shift due to temperature changes can be prevented.

When the change in propagation length can be ignored, L _b / L _g = − (dn _g / dT) / (dn _b /dT)=0.6 to 1.8. Geometrically, the resonance path is not established unless L _b / L _g > 1. If the incident angle is 45 °, L _b / L _g = 1.414, and if the incident angle is 60 °, L _b / L _g = 1.155 is required.

  Further, if the portion (slot portion) in which the groove of the grating portion 32 is dug is filled with another material, for example, a polymer, the temperature dependency of the grating portion 32 becomes small. In this case, a material having a small temperature dependency of the refractive index, such as glass, can be used as the total reflection resonance unit 20.

  Note that the total reflection resonance unit 20 may not be formed of a single material. The total reflection resonator 20 may be configured to include a plurality of layers, and the material of each layer may be different. Moreover, the total reflection resonance part 20 may be formed by mixing a plurality of materials.

  FIG. 8 shows a simulation result of the temperature dependence of the resonance wavelength when the total reflection resonator 20 is made of polymer or glass. In FIG. 8, the horizontal axis indicates the wavelength (μm), and the vertical axis indicates the light intensity (arbitrary unit) on the first main surface 20 a of the total reflection resonator 20. Curve I shows the wavelength dependence at room temperature. Curve II shows the wavelength dependence at 50 ° C. when the total reflection resonator 20 is a polymer. Curve III shows the wavelength dependence at 50 ° C. when the total reflection resonator 20 is made of glass.

  Here, the thickness of the total reflection resonance part 20 is 3 μm.

  The waveguide 30 is made of silicon (Si) and has a refractive index of 3.5. The thickness of the waveguide 30 is 450 nm. The grating period Λ of the grating portion 32 is 470 nm.

The entire periphery of the optical resonator 10 is air, and its refractive index n ₀ is 1.0.

Here, the refractive index of the total reflection resonator 20 is set to 1.6 regardless of the material, and the temperature dependency in each case where the material is polymer and quartz is taken into consideration. The temperature dependence of the refractive index of quartz is dn / dT = 10 ^−5, and the temperature dependence of the refractive index of the polymer is dn / dT = −1 × 10 ⁻⁴ .

  When the total reflection resonance part 20 is glass, when the temperature rises from room temperature to 50 ° C., the resonance wavelength changes from 1.578 nm to 1.580 nm (III). On the other hand, when the total reflection resonance part is a polymer, even if the temperature rises from room temperature to 50 ° C., the resonance wavelength does not change (II).

10, 11, 12, 13, 14 Optical resonator 20 Total reflection resonator 20a First main surface 20b Second main surface 30, 50, 60 Waveguide 30a, 70a Lower surface 30b, 60b, 70b Upper surface 32, 52, 62a, 62b Grating part 40 Input / output waveguide 42, 54 Input part 44 Coupling part 46, 56 Output part 58 Tapered part 61 Area 70 Block 90 Substrate 92 Opening 101, 141 Propagating light 103, 125, 143 Diffracted light 105, 145 Reflected light 111, 151 First diffracted light 113, 153 First reflected light 115, 155 Second diffracted light 117, 157 Second reflected light 121 Input light 123 Evanescent light 127 Output light

Claims (11)

A total reflection resonance part having a first main surface and a second main surface as two mutually parallel main surfaces, wherein the first main surface and the second main surface are optically mirror surfaces When,
A waveguide having a grating portion formed on the second main surface of the total reflection resonance portion;
The grating part diffracts light propagating through the waveguide and sends it to the total reflection resonance part, and diffracts light incident from the total reflection resonance part to propagate through the waveguide,
The light transmitted to the total reflection resonance part is totally reflected toward the waveguide on the first main surface. A total reflection resonance part having a first main surface and a second main surface as two mutually parallel main surfaces, wherein the first main surface and the second main surface are optically mirror surfaces When,
A waveguide having a grating portion formed on the second main surface of the total reflection resonance portion;
Refractive index n ₀ of the surrounding of the optical resonator, the waveguide of the equivalent refractive index n _e, and grating period Λ of the grating portion, of light that resonates in the optical resonator to the wavelength lambda, the following An optical resonator characterized by satisfying Expression (1).
Λ <λ / (n ₀ + _ne ) (1) Refractive index n ₀ of the surrounding of the optical resonator, the waveguide of the equivalent refractive index n _e, and grating period Λ of the grating portion, of light that resonates in the optical resonator to the wavelength lambda, the following The optical resonator according to claim 1, wherein the expression (1) is satisfied.
Λ <λ / (n ₀ + n _e ) (1) A total reflection resonance part having a first main surface and a second main surface as two mutually parallel main surfaces, wherein the first main surface and the second main surface are optically mirror surfaces When,
A waveguide having a grating portion formed on the second main surface of the total reflection resonance portion;
The grating section diffracts the light incident from the total reflection resonance section and sends the light to the total reflection resonance section. The light transmitted to the total reflection resonance section is the first main surface, and the waveguide An optical resonator characterized by being totally reflected toward. A total reflection resonance part having a first main surface and a second main surface as two mutually parallel main surfaces, wherein the first main surface and the second main surface are optically mirror surfaces When,
A waveguide having a grating portion formed on the second main surface of the total reflection resonance portion;
The refractive index n ₀ around the optical resonator and the grating period Λ of the grating section satisfy the following expression (2) with respect to the wavelength λ of light resonating in the optical resonator. Optical resonator.
Λ <λ / 2 · n ₀ (2) The refractive index n ₀ around the optical resonator and the grating period Λ of the grating section satisfy the following expression (2) with respect to the wavelength λ of light resonating in the optical resonator. The optical resonator according to claim 4.
Λ <λ / 2 · n ₀ (2) 7. The waveguide according to claim 1, further comprising a block having a lower surface and an upper surface as two parallel main surfaces on the waveguide, wherein the lower surface and the upper surface are optically mirror surfaces. The optical resonator as described in any one of Claims. The optical resonator according to claim 7, wherein the block is made of the same material as the waveguide or the total reflection resonator. The optical resonator according to any one of claims 1 to 8, wherein the refractive index change with respect to temperature of the material of the total reflection resonance part and the material of the waveguide has an opposite sign. 9. The optical resonance according to claim 1, wherein the refractive index change with respect to temperature of the material filled in the slot portion of the grating portion and the material of the waveguide has an opposite sign. vessel. The optical resonator according to claim 1, wherein the waveguide includes a plurality of grating portions.