JP2012078512A - Wavelength splitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength splitter using a WGM resonator in which lowering of characteristics of an element is suppressed while the scale of the element is reduced.SOLUTION: A wavelength splitter includes a plurality of waveguides and a plurality of resonators by way of Whispering Gallery Mode. Each of part of the plurality of the resonators among the plurality of the resonators satisfies a resonance condition of first light, which is in a propagation mode of either TE or TM and has a first wavelength. The part of the plurality of the resonators are subjected to resonant coupling of the first light with the waveguide and are arranged from the waveguide in order to form one coupling resonator type optical waveguide. Each of part of the plurality of the resonators among the plurality of the resonators satisfies a resonance condition of second light, which is in a propagation mode of either TE or TM and has a second wavelength. The part of the plurality of the resonators are subjected to resonant coupling of the second light with the waveguide and are arranged from the waveguide in order to form one coupling resonator type optical waveguide.

Description

  The present invention relates to a wavelength splitter using a resonator in a whispering gallery mode.

  Whispering Gallery Mode (hereinafter referred to as WGM) is a resonance phenomenon that occurs inside a resonator such as a disk or a ring. The boundary with the outside of the resonator (WGM resonator) by WGM is generally circular. The WGM in geometric optics is a resonance phenomenon in which light is totally reflected inside the boundary and propagates inside the boundary. If the radius of the circular boundary is r, the wavelength of light is λ, and the relative refractive index to the outside of the WGM resonator is n, the resonance condition is that the circumference is an integral multiple of the wavelength, that is, 2πr = m (λ / n ).

  Here, m is an integer that is the number of resonance modes. With WGM in geometric optics, m takes a sufficiently large value. For example, Patent Document 1 describes a wavelength filter using a geometrical optical WGM resonator.

JP-T 2006-515081

  When the value of m is large, the light resonating inside the WGM resonator is reflected adjacent to the tangent of the circular boundary, so that the geometrical optical approximation, which is regarded as total reflection of light, becomes When the value of m is reduced, the scale of the element of the WGM resonator can be reduced, but the light scattering effect is increased and the geometrical optical approximation is not established.

  A region where the value of m is 1 or more and the geometrical optical approximation is no longer valid is equal to or less than the value of m is defined as a Mie region by Mie scattering with a wavelength similar to the particle diameter. The resonance condition of WGM in the Mie region is derived from Mie theory as will be described later. In other words, the region where the resonance condition derived from the Mie theory is satisfied may be the Mie region.

  In the WGM resonator in the Mie region, an evanescent wave (evanescent wave) is generated in which light oozes out to the wavelength, and as the value of m becomes smaller, the evanescent wave increases. Since evanescent waves are also generated in light that is in a non-resonant state, light of a wavelength other than the resonating light can easily enter and be emitted in one WGM resonator. When a wavelength splitter is configured, the extinction ratio is lowered and the characteristics as an element are lowered as compared with a WGM resonator in which geometrical optical approximation is established.

  In view of such a problem, the present invention is to provide a wavelength splitter using a WGM resonator in which a reduction in element characteristics is suppressed while reducing an element scale.

  (1) In order to solve the above-described problem, a wavelength splitter according to the invention includes a waveguide that propagates light input from the outside, and a whispering gallery mode that is disposed on the side of the waveguide and spaced apart from each other. A plurality of resonators, wherein a plurality of the resonators, each of which is a propagation mode of either the TE mode or the TM mode, has a first wavelength. A plurality of resonators that resonantly couple the waveguide with the first light and that are arranged in order from the waveguide, A coupled resonator type optical waveguide is formed, and among the plurality of resonators, each of some of the resonators is a propagation mode of either a TE mode or a TM mode and has a second wavelength. ,in front The first light satisfies the resonance condition of the second light, which is different in wavelength or propagation mode, or both, and the some of the plurality of resonators include the waveguide and the second light. And another one coupled resonator type optical waveguide is formed in order from the waveguide.

  (2) The wavelength splitter according to (1), wherein the one coupled resonator type optical waveguide and the other one coupled resonator type optical waveguide are arranged in order from the waveguide. Both resonators may be included.

  (3) The wavelength splitter according to (1), wherein the one or more of the plurality of resonators forming the one coupled resonator type optical waveguide and the other one coupled resonator type The some of the plurality of resonators forming the optical waveguide may be different from each other.

  (4) In the wavelength splitter according to (1) above, the first light and the second light may have the same wavelength and different propagation modes.

ＴＭモードにあっては、下記数式２を満たしていてもよい。

ただし、波数ｋは、ｋ＝２π／λで定義され、Ｊ_ｍは第１種ベッセル関数であり、Ｈ_ｍ ^（１）は第１種ハンケル関数である。 (5) The wavelength splitter according to (1), wherein each of the resonators has a cross section in which a relative refractive index with respect to the outside is n and a boundary with the outside is a circular shape having a radius r. And the resonance condition satisfies the following formula 1 when the resonance condition is in the TE mode.

In the TM mode, the following formula 2 may be satisfied.

However, the wave number k is defined by k = 2π / λ, J _m is a first kind Bessel function, and H _m ⁽¹⁾ is a first kind Hankel function.

(6) The wavelength splitter according to (5), wherein the one coupled resonator type optical waveguide and the other one coupled resonator type optical waveguide are arranged in order from the waveguide, Among the plurality of resonators that include a plurality of resonators and are arranged in order, in the branch resonator located on the opposite side to the waveguide side, the number of resonance modes for the first light is m ₁ , The number of resonance modes for the light of m is m ₂ , and in the one coupled resonator type optical waveguide, the center of the branch resonator and the resonator immediately before the branch resonator are counted from the waveguide. An angle formed by a straight line connecting the center and a straight line connecting the center of the branch resonator and the center of the next resonator of the branch resonator is an integral multiple of π / m ₁ , In the one coupled resonator type optical waveguide, the branch resonance is counted from the waveguide. And a straight line connecting the center of the branch resonator and the center of the resonator immediately preceding the branch resonator, and a straight line connecting the center of the branch resonator and the center of the next resonator of the branch resonator. The angle may be an integer multiple of π / m ₂ .

  (7) In the wavelength splitter according to (1), the resonating unit may have a circular column shape having a circular cross section.

  (8) In the wavelength splitter according to (1), the resonating unit may have a spherical shape having a circular cross section on the equator plane.

  (9) In the wavelength splitter according to (1), the resonating unit may have a toroidal shape having a circular cross section.

  According to the present invention, there is provided a wavelength splitter using a WGM resonator in which a reduction in element characteristics is suppressed while reducing an element scale.

1 is an overall perspective view of a wavelength splitter according to an embodiment of the present invention. It is the schematic which shows the structure inside the wavelength splitter which concerns on the 1st Embodiment of this invention. It is a top view of the wavelength splitter principal part which concerns on the 1st Embodiment of this invention. It is a figure which shows the wavelength spectrum obtained from the simulation with respect to the wavelength splitter which concerns on the 1st Embodiment of this invention. It is a top view of the wavelength splitter main part which concerns on the 2nd Embodiment of this invention. It is a figure which shows the wavelength spectrum obtained from the simulation with respect to the wavelength splitter which concerns on the 2nd Embodiment of this invention. It is the schematic showing the shape of the resonator which concerns on the 4th Embodiment of this invention. It is a top view of the wavelength splitter principal part which concerns on the 5th Embodiment of this invention.

[First Embodiment]
The wavelength splitter 1 according to the first embodiment of the present invention will be described in detail below.

  FIG. 1 is an overall perspective view of the wavelength splitter 1 according to this embodiment. As shown in FIG. 1, the wavelength splitter 1 includes an input terminal 3, an output terminal 4 a, and an output terminal 4 b (not shown) on the side surface of the housing 2. An optical fiber or the like is connected to the input terminal 3 and the output terminals 4a and 4b, and is optically connected to the input waveguide 11 provided inside the housing 2 and the output waveguides 13a and 13b via the input terminal 3. The

  FIG. 2 is a schematic diagram showing the internal structure of the wavelength splitter 1 according to this embodiment. 2A is a part of a cross-sectional view of the wavelength splitter 1 shown in FIG. 1, and FIG. 2B is a perspective view of a part of the main part of the wavelength splitter 1.

As shown in FIG. 2A, the input waveguide 11 and the disk resonator 12 are formed in the high refractive index layer 7. The high refractive index layer 7 is formed between the base layer 6 and the low refractive index layer 8. The high refractive index layer 7 is made of a material having a higher refractive index than that of the low refractive index layer 8, and is silicon (Si) here, but may be SiN or the like. The low refractive index layer 8 is made of a material having a refractive index lower than that of the high refractive index layer 7 and is made of silica (SiO ₂ ) here, but may be a gas such as air, for example. The underlying layer 6 is composed of SiO _2. The underlayer 6 is formed on a substrate 5 such as Si.

  As shown in FIG. 2B, the input waveguide 11 has a rectangular cross section and extends in a straight line. The disk resonator 12 is provided on one side of the input waveguide 11 and has a disk shape. In other words, the cross section is circular, and is a cylindrical shape having a thickness comparable to the thickness of the input waveguide 11. The disk resonator 12 is a WGM resonator in the Mie region.

  FIG. 3 is a top view of the main part of the wavelength splitter 1 according to this embodiment. An input waveguide 11 that is optically connected to the input terminal 3, output waveguides 13a and 13b that are optically connected to the output terminals 4a and 4b, and an input waveguide 11 and output waveguides 13a and 13b, respectively. Six disk resonators 12 disposed therebetween are formed on the underlayer 6. As described above, each disk resonator 12 is a WGM resonator, and light is propagated by resonance coupling between the disk resonator 12 and the disk resonator 12, thereby a plurality of disks. The resonator 12 forms a coupled resonator type optical waveguide (hereinafter referred to as CROW).

  As shown in FIG. 3, the input waveguide 11 extends in the lateral direction in the figure on the lower side in the figure. The left side of the input waveguide 11 in the drawing is optically connected to the input terminal 3, and input light enters from the left side of the input waveguide 11 in the drawing and is input from the outside through the input waveguide 11. Is transmitted in the right direction in the figure, and is emitted to the outside from the right end of the input waveguide 11 in the figure. On the upper side in the figure, two output waveguides 13 extend in the lateral direction in the figure. The left side of the output waveguide 13a in the drawing is optically connected to the output terminal 4a, and the output light is emitted to the upper side of the output waveguide 13a in the drawing. Similarly, the right side of the output waveguide 13b in the drawing is optically connected to the output terminal 4b (not shown), and the output light is emitted to the right side of the output waveguide 13b in the drawing. The input light and the output light are respectively represented by arrows in FIG.

  The disk resonator 12 is a WGM resonator as described above. In the WGM resonator, the radius r of the resonator satisfies a predetermined condition derived from Mie theory with respect to the wavelength λ of light.

A predetermined condition derived from the Mie theory will be described. The resonator has a resonator section having a cross section in which the relative refractive index to the outside is n and the boundary with the outside is a circular shape with a radius r, and the number of resonance modes is m for light of wavelength λ. In the TE mode in which the electric field is perpendicular to the boundary surface, the resonance condition of WGM satisfies the following formula 1.

However, the wave number k is defined by k = 2π / λ, J _m is a first kind Bessel function, and H _m ⁽¹⁾ is a first kind Hankel function.

  In the TM mode in which the electric field is parallel to the boundary surface, the WGM resonance condition satisfies the following formula 2.

Light including the first light and the second light is input from the outside via the input terminal 3 and propagates through the input waveguide 11. The first light, be any propagation mode of the TE mode or the TM mode, and has a first wavelength lambda _A. Similarly, the second light, be any propagation mode of the TE mode or the TM mode, and has a second wavelength lambda _B. Note that the first light and the second light have different wavelengths or propagation modes, or both. That is, the first light and the second light have the same wavelength (λ _A = λ _B ) and the propagation modes are not the same. Note that, for example, and the light of the wavelength lambda _A, the intensity of the spectrum of the light is strong wavelength wavelength lambda _A, the difference between the half-value width wavelength lambda _A and the wavelength lambda _B | against _| λ _{B -λ A} Refers to sufficiently narrow light.

FIG. 3 shows six disk resonators 12 that are spaced apart from each other on the side of the input waveguide 11. Drawing the two disc resonator 12 arranged in the upper left, the resonance conditions of the first light satisfies but does not satisfy the resonance condition of the second light, hereinafter referred to as lambda _A disc resonator 12a. Drawing the two disc resonator 12 arranged in the upper right, the resonance condition of the second light meet, but does not satisfy the resonance condition of the first light, hereinafter referred to as lambda _B disc resonator 12b. The two disk resonators 12 arranged in the middle of the figure satisfy both the first light resonance condition and the second light resonance condition, and are hereinafter referred to as a λ _C disk resonator 12c.

The four disk resonators 12 of the two λ _C disk resonators 12 c and the two λ _A disk resonators 12 a all satisfy the resonance condition of the first light, and are sequentially from the input waveguide 11. One coupled resonator type optical waveguide (CROW) is formed. The one CROW is defined as a first CROW 21. The first CROW 21 includes four disk resonators 12 arranged in order from the input waveguide 11, and sequentially includes a first λ _C disk resonator 12c, a second λ _C disk resonator 12c, and a first λ _A. disk resonator 12a, the second lambda _a disc resonator 12a.

Since the first λ _C disk resonator 12c is disposed in the vicinity of the input waveguide 11, and the input waveguide 11 and the first λ _C disk resonator 12c perform resonance coupling of the first light, The first light propagating through the input waveguide 11 propagates to the first λ _C disk resonator 12c, and resonance coupling of the first light also occurs between adjacent disk resonators constituting the first CROW 21. Therefore, the first light propagates through the first CROW 21 in order from the input waveguide 11. That is, when viewed from the input waveguide 11, the first light propagates upward in the figure, and from the second λ _C disk resonator 12c, two λ _A disk resonators 12a in the upper left direction in the figure. Are propagated in order.

The second λ _A disk resonator 12a is disposed in the vicinity of the output waveguide 13a, and the second λ _A disk resonator 12a and the output waveguide 13a perform resonance coupling of the first light. The first light propagating through the first CROW 21 propagates to the output waveguide 13a, propagates upward through the output waveguide 13a, and is output to the outside via the output terminal 4a.

The four disk resonators 12 of the two λ _C disk resonators 12 c and the two λ _B disk resonators 12 b all satisfy the second light resonance condition, and are sequentially from the input waveguide 11. One other coupled resonator type optical waveguide (CROW) is formed. The other one CROW is defined as a second CROW 22. Similar to the first CROW 21, the second CROW 22 includes four disk resonators 12 arranged in order from the input waveguide 11, and in order, the first λ _C disk resonator 12 c and the second λ _C disk resonance. The two λ _B disk resonators 12b are arranged as a first λ _B disk resonator 12b and a second λ _B disk resonator 12b.

Similar to the first CROW21, in the second CROW22, the second light propagates in order from the input waveguide 11 to the output waveguide 13b. That is, when viewed from the input waveguide 11, the second light propagates upward in the figure, and from the second λ _C disk resonator 12 c, two λ _B disk resonators 12 b in the upper right direction in the figure. Are sequentially propagated to the output waveguide 13b, propagated in the right direction in the figure, and output to the outside via the output terminal 4b.

The feature of the wavelength splitter 1 according to this embodiment is that the first CROW 21 and the second CROW 22 both include two λ _C disk resonators 12 c arranged in order from the input waveguide 11. . That is, since the λ _C disk resonator 12c satisfies both the first and second light resonance conditions, both the first light and the second light are transmitted from the input waveguide 11 to the second light wave. To the λ _C disk resonator 12c. Only the first light propagates from the second λ _C disk resonator 12c to the first λ _A disk resonator 12a. Similarly, only the second light propagates from the second λ _C disk resonator 12c to the first λ _B disk resonator 12b. Earlier than the second lambda _C disk resonator 12c, since the first light and second light is demultiplexed (split) to each, the second lambda _C disk resonator 12c is also referred to as a branch resonator Good.

Here, it has been described that only the first light propagates from the second λ _C disk resonator 12c to the first λ _A disk resonator 12a. However, since the above-described evanescent wave is actually generated, Part of the light of 2 also propagates. That is, the demultiplexing is insufficient in the resonance coupling from the second λ _C disk resonator 12c to the first λ _A disk resonator 12a alone. However, even if the second light propagates to the first λ _A disk resonator 12a, it does not satisfy the resonance condition. Therefore, the second light is attenuated in the first λ _A disk resonator 12a, and further the second λ _A disk resonator 12a _{In the} propagation to the _A disk resonator 12a, the second light is further attenuated by further attenuation.

  A feature of the wavelength splitter 1 according to the present invention is that the input light is input and the first light is propagated from the propagating input waveguide 11 to the output side, and the second light is transmitted similarly to the first CROW 21. Propagate the second CROW 22 to propagate. For example, since the first CROW 21 satisfies the resonance condition of the first light, the first light propagates through the first CROW 21 to the output side. On the other hand, light that does not satisfy the resonance condition attenuates rapidly as it propagates through the first CROW 21.

  Furthermore, in the wavelength splitter 1 according to this embodiment, the first CROW 21 and the second CROW 22 include a plurality of resonators in order from the input waveguide 11, so that the plurality of resonators are The first light 21 and the second light propagate together, but following the plurality of resonance paths, the first CROW 21 satisfies the first light resonance condition but satisfies the second light resonance condition. The second light is attenuated in the resonator because it contains no resonator. The same applies to the second CROW22.

  In the wavelength splitter 1 according to the present invention, light propagates from the input waveguide to the CROW. That is, if a plane parallel to the plane of the substrate 5 is an xy plane, the light propagation direction is one of the directions parallel to the xy plane and propagates from the side surface of the waveguide to the side surface of the resonator. In this case, the space between the side surface of the waveguide and the side surface of the resonator and the space between the side surface of the resonator and the side surface of the resonator are filled with a material having a refractive index lower than that of the resonator or the waveguide. It is good to be. Therefore, the low refractive index layer 8 is disposed between the waveguide and the resonator, and between the resonator and the resonator.

  In order for light to propagate in the direction of the xy plane, it is desirable that the light is confined in a direction perpendicular to the xy plane (for example, the vertical direction in FIG. 2A). Therefore, the underlayer 6 is also preferably made of a material having a refractive index lower than that of the resonator or the waveguide.

Furthermore, WGM has a mode that rotates counterclockwise and a mode that rotates clockwise. The light input to the input waveguide 11 is propagating rightward in FIG. 3, and the first first λ _C disk resonator 12c resonates with the input waveguide 11 due to resonance coupling. In the first λ _C disk resonator 12c, a mode that rotates counterclockwise is dominant. Thereafter, in turn, by a resonant coupling between the disc resonator 12, since the light propagates through the CROW, for example, in the first CROW21, in the second lambda _C disk resonator 12c, clockwise, a first lambda _A in disk resonator 12a, counterclockwise, in the second lambda _a disc resonator 12a, clockwise, a mode for rotating each dominant. Since the second λ _A disk resonator 12a mainly resonates by rotating clockwise, the output waveguide 13a is arranged to extend upward. Also, external and intensity distribution of light of the second lambda _A disc resonator 12a, and the like the strength of the resonant coupling between the output waveguides 13b, may determine the arrangement of the output waveguide 13a. The same applies to the other output waveguides 13.

Next, a method for manufacturing the wavelength splitter 1 according to the embodiment will be described. On the substrate 5 made of Si, SiO ₂ is laminated by the CVD (Chemical Vapor Deposition) method, and the base layer 6 is formed. Further, Si is laminated to a predetermined thickness on the base layer 6 by the CVD method, and the high refractive index layer 7 is formed. By processing the high refractive index layer 7 into the shape shown in FIG. 3 by a known lithography process and etching process, the input waveguide 11, the disk resonator 12, and the output waveguide 13 are formed in the high refractive index layer 7. . Furthermore, SiO ₂ is laminated by the CVD method to form the low refractive index layer 8.

  As described above, the main part of the wavelength splitter 1 is manufactured and housed in the housing 2 and optically connected to the input terminal 3 and the output terminal 4 to complete the wavelength splitter 1.

  Next, the high-precision simulation result performed by the inventors will be described. Although the propagation of light in the Mie region is very complicated, high-precision simulation is possible using the Nonstandard Finite Difference Time Domain (hereinafter referred to as NS-FDTD) algorithm.

The wavelengths of the first and second light are λ _A = 1300 nm and λ _B = 1550 nm, respectively, and the radii of the three types of λ _A disk resonator 12a, λ _B disk resonator 12b, and λ _C disk resonator 12c, respectively. Approximately satisfies Equation (2), which is the resonance condition for TE mode light, and in order, r _A = 1310.52 nm, r _B = 1562.54 nm, and r _C = 1214.08 nm. The radius r _A of the λ _A disk resonator 12a has a resonance mode number m of 12 for the wavelength λ _A and does not satisfy the resonance condition for the wavelength λ _B. The radius r _B of the λ _B disk resonator 12b has a resonance mode number m of 12 for the wavelength λ _B and does not satisfy the resonance condition for the wavelength λ _A. The radius r _C of the λ _C disk resonator 12c has a resonance mode number m of 11 for the wavelength λ _A , which is m _1, and a resonance mode number m of 9 for the wavelength λ _{B. 2} .

  Here, the interval between the disk resonators is the same, but the interval between the disk resonators having the same radius is 0.2 times the radius, and the radius between the disk resonators having different radii is two disk resonators. 0.2 times the average of the radii.

The angles θ _A and θ _B shown in FIG. 3 are θ _A = 3π / 11 and θ _B = 3π / 9. Here, the light propagating through the first CROW 21 first propagates upward in the drawing of FIG. 3 from the input waveguide 11 to the second λ _C disk resonator 12c, and then turns counterclockwise. , Θ _A and propagates to the second λ _A disk resonator 12a in the upper left direction in FIG. That is, the angle θ _A is defined by a straight line connecting the centers of the first and second λ _C disk resonators 12c, a center of the second λ _C disk resonator 12c, and a center of the first λ _A disk resonator 12a. This is the angle formed by the connecting line. Here, in the first CROW21, Counting from the input waveguide 11 in this order, the first lambda _C disk resonator 12c is preceding resonators of the second lambda _C disk resonator 12c is a branch resonator The first λ _A disk resonator 12a is a resonator one ahead of the second λ _C disk resonator 12c which is a branch resonator.

For the angle theta _B, it is similar, the angle theta _B is a straight line connecting the centers of the first and second lambda _C disk resonator 12c, center and the first lambda second lambda _C disk resonator 12c _This is an angle formed by a straight line connecting the centers of the _B disk resonators 12b.

In the simulation, the light source 31 was set inside the first λ _C disk resonator 12c that propagates first from the input waveguide 11 as shown in FIG. For the output terminal 4a side, the observation point is located outside the second disk resonator 12a adjacent to the output waveguide 13a and has a strong light intensity. For the output terminal 4b side, the observation point is the output waveguide 13b. Is located outside the second disk resonator 12b adjacent to the position where the light intensity is high. The relative refractive index n is the absolute refractive index (3.5) of Si of the high refractive index layer 7 with respect to the absolute refractive index (1.45) of SiO ₂ of the low refractive index layer 8, that is, 3.5 / 1. .45. The simulation grid space in the simulation was in the range of 14 μm × 12 μm every 5 nm and the time step was 2 ²⁰ (approximately 2400 in wavelength period).

FIG. 4 is a diagram showing a wavelength spectrum obtained by simulation for the wavelength splitter 1 according to the embodiment. 4A shows a wavelength spectrum at an observation point provided outside the second λ _A disk resonator 12a, and FIG. 4B shows an observation provided outside the second λ _B disk resonator 12b. Each wavelength spectrum at a point is shown.

In the wavelength spectrum shown in FIG. 4A, the amplitude of the wavelength λ _B (= 1550 nm) is sufficiently smaller than the amplitude of the wavelength λ _A (= 1300 nm) to an extinction ratio of 26.3 dB. ), The amplitude of the wavelength λ _A is sufficiently smaller than the amplitude of the wavelength λ _B to an extinction ratio of 29.1 dB, indicating that it functions as a wavelength splitter. These satisfy the extinction ratio standard required for a general wavelength splitter.

Here, the angles θ _A and θ _B are set to θ _A = 3π / 11 and θ _B = 3π / 9, but this is based on the intensity distribution of light outside the second λ _C disk resonator 12c. ing. That is, in consideration of the direction in which the light intensity distribution is strong, θ _A is π with respect to the resonance mode numbers m ₁ and m ₂ of the first light and the second light in the second λ _C disk resonator 12c. It is desirable that / m ₁ is an integer multiple and θ _B is an integer multiple of π / m ₂ .

  Further, the interval between the WGM resonators will be described. As described above, an evanescent wave is generated in the WGM resonator in the Mie region, and light having a wavelength other than the resonating light easily invades and is easily emitted from the WGM resonator. Therefore, when the resonator and the resonator are brought into contact with each other or sufficiently close to each other, the resonance coupling of the desired light is increased, but coupling of light other than the desired light is also generated. On the other hand, when the space between the resonators is widened, the coupling of light other than the desired light rapidly decreases, but the resonance coupling of the desired light also decreases.

  Therefore, the interval between the resonators is preferably 10% or more and 30 or less of the radius of the resonator, and more preferably 20% of the radius of the resonator.

  Hereinafter, a manufacturing error of the resonator in a manufacturing process for manufacturing the resonator will be described. For both TE mode and TM mode propagation modes, the production error Δr of the radius r, the production error Δn of the relative refractive index n, and the error Δλ of the wavelength λ of the resonating light are expressed by the following Equation 3. There is a relationship.

  According to Equation 3, the manufacturing error Δr in the recent lithography process is about Δr≈5 nm, and when Δn = 0, the error Δλ of the light wavelength λ is about Δλ≈7 nm. As the value of Δn increases, the error Δλ of the wavelength λ increases accordingly. By using Expression 3, it is possible to estimate the manufacturing error of the resonator in the CROW manufacturing process.

[Second Embodiment]
The basic configuration of the wavelength splitter 1 according to the second embodiment of the present invention is the same as that of the wavelength splitter 1 according to the first embodiment. The main difference from the wavelength splitter 1 according to the first embodiment is the arrangement of the CROW.

FIG. 5 is a top view of the main part of the wavelength splitter 1 according to this embodiment. Similar to the wavelength splitter 1 according to the first embodiment, light including the first light and the second light is input to the input terminal 3 from the outside. Lambda _A disc resonator 12a shown in FIG. 5, like the lambda _A disc resonator 12a shown in FIG. 3, the resonance conditions of the first light satisfies but does not satisfy the resonance condition of the second light, lambda _B disc resonator 12b shown in FIG. 5, like, the resonance condition of the second light meet, but resonant conditions of the first light does not meet.

Three lambda _A disc resonator 12a are all satisfy the resonance condition of the first light, arranged in order from the input waveguide 11 to form a single coupled resonator type optical waveguide (CROW). The one CROW is defined as a first CROW 21. Three lambda _B disc resonator 12b are all satisfy the resonance condition of the second light, arranged in order from the input waveguide 11, by forming the other one coupled resonator type optical waveguide (CROW) Yes. The other one CROW is defined as a second CROW 22. In the first CROW21, the first light propagates in order from the input waveguide 11 to the output waveguide 13a, and in the second CROW22, the second light in order from the input waveguide 11 to the output waveguide 13b. Is propagated. Here, in the first CROW 21 along the light propagation direction from the input waveguide 11, the first λ _A disk resonator 12a, the second λ _A disk resonator 12a, and the third λ _A disk are sequentially arranged. Resonator 12a, and in the second CROW 22, in order, a first λ _B disk resonator 12b, a second λ _B disk resonator 12b, and a third λ _B disk resonator 12b.

Light including the first light and the second light is input from the outside via the input terminal 3 and propagates through the input waveguide 11. Only the first light propagates through the first CROW 21 from the input waveguide 11 to the output waveguide 13a. Strictly speaking, although it propagates the second light also partially attenuated in the lambda _A disk resonator 12a, further, further attenuated between. Similarly, only the second light propagates through the second CROW 22 from the input waveguide 11 to the output waveguide 13b. Then, the first light propagates in the left direction in the drawing through the output waveguide 13a and is output to the outside via the output terminal 4a, and the first light propagates in the right direction in the drawing through the output waveguide 13b. And output to the outside via the output terminal 4a.

In the wavelength splitter 1 according to this embodiment, the three λ _A disk resonators 12a that form the first CROW 21 and the three λ _B disk resonators 12b that form the second CROW 22 are different from each other. . That is, the three disk resonators 12 forming the first CROW 21 all satisfy the resonance condition of the first light, but do not satisfy the resonance condition of the second light, and the second CROW 22 The three disk resonators 12 to be formed all satisfy the resonance condition of the second light, but do not satisfy the resonance condition of the first light.

  Therefore, even if a part of the second light propagates to the first CROW 21, the second light attenuates rapidly, and similarly, a part of the first light propagates to the second CROW 22. However, the first light is rapidly attenuated, the extinction ratio is improved, and the characteristics as a wavelength splitter are improved.

  Next, similarly to the first embodiment, a high-precision simulation result performed by the inventors will be described.

The wavelengths of the first and second lights are λ _A = 1400 nm and λ _B = 1550 nm, respectively, and the radii of the two types of λ _A disk resonator 12a and λ _B disk resonator 12b are the same as those for TE mode light. Equation (2), which is the resonance condition, is approximately satisfied, and in order, r _A = 1307.43 nm and r _B = 1447.51 nm. The radius r _A of the λ _A disk resonator 12a has a resonance mode number m of 11 for the wavelength λ _A and does not satisfy the resonance condition for the wavelength λ _B. The radius r _B of the λ _B disk resonator 12b has a resonance mode number m of 11 for the wavelength λ _B and does not satisfy the resonance condition for the wavelength λ _A.

  Here, the distance between the disk resonators is 0.2 times the radius, and the distance between the input waveguide 11 and the disk resonator is also 0.2 times the radius.

In the simulation, the light source 31 was set on the left side of the input waveguide 11 in the drawing as shown in FIG. Also, the observation point, the output terminal 4a side, be external to the third lambda _A disc resonator 12a adjacent to the output waveguide 13a, and a strong position in intensity of light, the output terminal 4b side, It is external to the third lambda _B disc resonator 12b adjacent to the output waveguide 13b, and a strong position in intensity of light. As in the first embodiment, the relative refractive index n is 3.5 / 1.45, the calculation grid space in the simulation is in the range of 12 μm × 12 μm every 5 nm, and the time step is 2 ²⁰ (wavelength The simulation was performed with a period of approximately 2400).

FIG. 6 is a diagram showing a wavelength spectrum obtained by simulation for the wavelength splitter 1 according to this embodiment. 6A shows a wavelength spectrum at an observation point provided outside the third λ _A disk resonator 12a, and FIG. 6B shows an observation provided outside the third λ _B disk resonator 12b. Each wavelength spectrum at a point is shown. In the simulation, the time step is set to 2 ²⁰ (approximately 2400 in wavelength period).

In the wavelength spectrum shown in FIG. 6A, the amplitude of the wavelength λ _B (= 1550 nm) is sufficiently smaller than the amplitude of the wavelength λ _A (= 1400 nm) to an extinction ratio of 21.5 dB. ), The amplitude of the wavelength λ _A is sufficiently smaller than the amplitude of the wavelength λ _B , ie, an extinction ratio of 24.5 dB, indicating that it functions as a wavelength splitter. These satisfy the extinction ratio standard required for a general wavelength splitter.

[Third Embodiment]
The basic configuration of the wavelength splitter 1 according to the third embodiment of the present invention is the same as that of the wavelength splitter 1 according to the first or second embodiment. The main difference from the wavelength splitter 1 according to the first or second embodiment is the resonance condition of CROW.

In the wavelength splitter 1 according to this embodiment, the first light and the second light have the same wavelength and different propagation modes. That is, the wavelength λ _A of the first light and the wavelength λ _{B of} the second light
Are equal (λ _A = λ _B ), and if the propagation mode of the first light is the TE mode, the propagation mode of the second light is the TM mode.

  In WGM in geometric optics, in the case of light of the same wavelength λ, there was no difference in resonance conditions between the TE mode and the TM mode, whereas in the wavelength splitter 1 according to the embodiment, the same wavelength and the propagation mode By demultiplexing the first light and the second light that are different from each other, two types of information corresponding to the TE mode and the TM mode can be included in one wavelength.

[Fourth Embodiment]
The basic configuration of the wavelength splitter 1 according to the fourth embodiment of the present invention is the same as that of the wavelength splitter 1 according to any one of the first to third embodiments. The main difference from the wavelength splitter 1 according to any one of the first to third embodiments is the structure of the resonator constituting the CROW.

  The resonator according to the first to third embodiments is a disk resonator 12 formed on the underlayer 6, and the disk resonator 12 has a circular cross section and a thickness of the input waveguide 11. It is a cylindrical shape with the same thickness as that. On the other hand, the resonator 18 according to the embodiment has another shape.

  FIG. 7 is a schematic diagram showing the shape of the resonator 18 according to this embodiment. The resonator 18 shown in FIG. 7A has a shape in which a thin disk resonator serves as a resonance part and the resonance part is arranged on a post having a truncated cone shape. That is, the resonance part has a circular cross section, and the resonance part has a cylindrical shape.

  The resonator 18 shown in FIG. 7B has a spherical shape, and a cross section at the equator plane of the sphere is a resonance part. The resonance part being in the resonance state means a case where predetermined light satisfies the resonance condition in the cross section. As shown in the figure, the resonator 18 can be resonantly coupled with a waveguide 17 extending in the vicinity of the equator plane, and a plurality of spherical resonators 18 are arranged to resonate between the resonance portions on the equator plane. It can also be combined.

  In the resonator 18 shown in FIG. 7C, the resonance part has a toroid shape, and the resonance part is disposed on the post. When the toroidal shape of the resonance part is cut by a cross section where the outer edge is the largest, it becomes a circular shape. The resonance part being in the resonance state means a case where predetermined light satisfies the resonance condition in the cross section. As shown in the figure, the resonator 18 can be resonantly coupled with a waveguide 17 extending in the vicinity of the cross section, or a plurality of resonators 18 having toroid-shaped resonance portions are arranged between the cross sections of the resonance portions. It can also be resonantly coupled.

  The resonator 18 shown in FIG. 7A is a resonator having a very high Q value and a high Q value, and can reduce the propagation loss of light that occurs when propagating through the CROW. The resonator 18 shown in FIGS. 7B and 7C is a resonator having an even higher Q value and an extremely high Q value, and can further reduce the propagation loss.

[Fifth Embodiment]
The basic configuration of the wavelength splitter 1 according to the fifth embodiment of the present invention is the same as that of the wavelength splitter 1 according to any one of the first to fourth embodiments. In the first to fourth embodiments, the wavelength splitter 1 that demultiplexes the first light and the second light has been described. However, the present invention is not limited to two types of light demultiplexing.

FIG. 8 is a top view of the main part of the wavelength splitter 1 according to this embodiment. The wavelength splitter 1 shown in FIG. 5 includes the first CROW 21 that propagates the first light and the second CROW 22 that propagates the second light, whereas the wavelength splitter shown in FIG. 1 further includes a third CROW 23 for propagating the third light and a fourth CROW 24 for propagating the fourth light. Here, the third light and the fourth light are propagation modes of either the TE mode or the TM mode, and have third and fourth wavelengths λ _D and λ _E , respectively. Also, it is assumed that none of the first to fourth lights has the same wavelength and propagation mode.

  Further, for example, in the first light propagating through the first CROW 21 and the second light propagating through the second CROW 22, the wavelength λ is equal, one of the propagation modes is the TE mode, and the other propagation mode is In the TM mode, the first CROW 21 can demultiplex the TE mode light, and the second CROW 22 can demultiplex the TM mode light, and synthesize them under a predetermined condition. It can also be returned to polarization independence.

  The present invention has been described in detail above. The WGM resonator in the Mie region can reduce the scale of the element compared to the WGM resonator in geometric optics, but the extinction ratio decreases. By forming the CROW, the light in the resonance state can be obtained. Can demultiplex. Furthermore, since CROW can be shaped with a high degree of freedom in the propagation direction, using CROW itself as a circuit waveguide enables flexible element design and layout.

1 wavelength splitter, 2 housing, 3 input terminal, 4 output terminal, 5 substrate, 6 underlayer, 7 high refractive index layer, 8 low refractive index layer, 11 input waveguide, 12 disk resonator, 12a λ _A disk resonator , 12b λ _B disk resonator, 12c λ _C disk resonator, 13 output waveguide, 17 waveguide, 18 resonator, 21 first CROW, 22 second CROW, 23 third CROW, 24 fourth CROW, 31 light source.

Claims (9)

A waveguide for propagating light input from outside,
A wavelength splitter comprising a plurality of resonators according to whispering gallery modes, which are arranged apart from each other on the side of the waveguide,
Among the plurality of resonators, each of some of the resonators satisfies a resonance condition of a first light having a first wavelength in a propagation mode of a TE mode or a TM mode, Some of the plurality of resonators resonantly couple the waveguide and the first light, and are arranged in order from the waveguide to form one coupled resonator-type optical waveguide.
Among the plurality of resonators, each of some of the plurality of resonators is a propagation mode of either a TE mode or a TM mode and has a second wavelength, and the first light is a wavelength or The resonance condition of the second light, which is different in one or both of the propagation modes, is satisfied, and the some of the plurality of resonators resonately couple the waveguide and the second light, and Arranged in order from the waveguide to form another coupled resonator type optical waveguide,
A wavelength splitter. The wavelength splitter according to claim 1,
The one coupled resonator type optical waveguide and the other one coupled resonator type optical waveguide both include a plurality of resonators arranged in order from the waveguide.
A wavelength splitter. The wavelength splitter according to claim 1,
A part of the plurality of resonators forming the one coupled resonator type optical waveguide;
The some of the plurality of resonators forming the other one coupled resonator type optical waveguide are different from each other,
A wavelength splitter. The wavelength splitter according to claim 1,
The first light and the second light have the same wavelength and different propagation modes.
A wavelength splitter. The wavelength splitter according to claim 1,
Each of the resonators has a resonance part having a cross section in which the relative refractive index with respect to the outside is n and the boundary with the outside is a circular shape with a radius r,
For light of wavelength λ, as the resonance mode number m, the resonance condition satisfies the following formula 1 in the TE mode,

In TM mode, the following formula 2 is satisfied,

A wavelength splitter.
However, the wave number k is defined by k = 2π / λ, J _m is a first kind Bessel function, and H _m ⁽¹⁾ is a first kind Hankel function. The wavelength splitter according to claim 5, wherein
The one coupled resonator type optical waveguide and the other one coupled resonator type optical waveguide are arranged in order from the waveguide and include a plurality of resonators.
Among the plurality of resonators arranged in order, in the branch resonator located on the side opposite to the waveguide side, the number of resonance modes for the first light is m ₁ and the number of resonance modes for the second light is m _2. And
In the one coupled resonator type optical waveguide, a straight line connecting the center of the branch resonator and the center of the resonator immediately before the branch resonator, counting from the waveguide, and the branch resonator The angle formed by the straight line connecting the center and the center of the next resonator of the branch resonator is an integer multiple of π / m ₁ ,
In the other coupled resonator type optical waveguide, a straight line connecting the center of the branch resonator and the center of the resonator immediately before the branch resonator, counting from the waveguide, and the branch resonance The angle formed by the straight line connecting the center of the resonator and the center of the next resonator of the branch resonator is an integer multiple of π / m ₂ .
A wavelength splitter. The wavelength splitter according to claim 1,
The resonating portion has a cylindrical shape having a cross section that is circular.
A wavelength splitter. The wavelength splitter according to claim 1,
The resonating part is a sphere having a circular cross section on the equator plane,
A wavelength splitter. The wavelength splitter according to claim 1,
The resonating portion is a toroid shape having a cross section that is the circular shape,
A wavelength splitter.

Images