JP2006018120A - Optical waveguide device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide device in which miniaturization of the optical circuit is contrived. <P>SOLUTION: The optical waveguide device is composed of a waveguide having a clad layer formed on a substrate and a core embedded in the clad layer. The device further comprises one or more inputting optical waveguides 301, an optical branching circuit 302 connected to the inputting optical waveguide(s), an optical waveguide array 304 which is connected to the optical branching circuit 302 with each optical waveguide containing a phase adjusting means 303, and an optical multiplexing circuit 305 which is connected to the optical waveguide array 304 and which has a core composed of a pixel shaped part defined by a plurality of scattering points having a lower refractive index than the waveguides. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical waveguide device, and more particularly to an optical waveguide device to which a holographic wave transmission medium that transmits waves holographically by multiple scattering according to a two-dimensional refractive index distribution is applied.

  In the optical communication field, integrated optical components using an optical waveguide structure have been developed as an optical circuit that can easily realize branching and interference of light. Integrated optical components that utilize the properties of light waves make it easy to manufacture optical interferometers by adjusting the optical waveguide length, and to easily integrate optical components by applying circuit processing technology in the semiconductor field. Become.

Such an optical waveguide structure is an “optical confinement structure” that realizes spatial light confinement of light propagating through the optical waveguide by utilizing a spatial distribution of refractive index. As shown in FIG. 1, a typical optical waveguide has a two-stage refractive index distribution comprising a refractive index N ₀ cladding layer 103 and a core portion 102 having a refractive index N ₁ on a substrate 101. In addition, an optical waveguide having a three-stage refractive index distribution including a lower cladding layer having a refractive index N ₀ , a core portion having a refractive index N ₁ , and an upper cladding layer having a refractive index N ₂ is widely used. The advantage of the conventional optical waveguide is that the optical waveguide can be manufactured from two to three kinds of materials, and the manufacturing process is simple.

  A waveguide type optical switch is known as a typical integrated optical component. The waveguide type optical switch includes (1) one using a deflector that deflects light in an analog manner and selects an output port, (2) one that deflects by a diffraction grating and selects an output port, (3) A multi-stage connection of 2-input 2-output optical switching elements is known. FIG. 2 is a diagram illustrating an example of a conventional multistage optical switch (see, for example, Non-Patent Document 1). An 8 × 8 optical switch is configured by cascading 8 stages of 2-input / 2-output optical switching elements 121. As the optical switching element 121, for example, elements such as a directional coupler type, a Mach-Zehnder type, and an asymmetric X type are known.

T. Goh, et al., “Low loss and high extinction ratio strictly nonblocking 16 × 16 thermooptic matrix switch on 6-in wafer using silica-based planar lightware circuit technology”, Lightwave Tech., J. of, vol.19, Issue 3, March 2001, pp.371-379

  However, the 8 × 8 optical switch configured by the conventional multistage connection optical switch has to connect 64 optical switching elements, and has a problem that the circuit becomes large. In order to reduce the size of the optical circuit, it is necessary to strongly confine light in the waveguide. Therefore, the optical waveguide needs to have a very large refractive index difference. For example, in a conventional step index type optical waveguide, the optical waveguide is designed so as to have a spatial distribution of the refractive index so that the relative refractive index difference becomes a value larger than 0.1%. When optical confinement is performed using such a large refractive index difference, there is a problem that the degree of freedom of circuit configuration is limited.

  Furthermore, even if the refractive index difference in the optical waveguide is to be realized by local ultraviolet irradiation, the thermo-optic effect, the electro-optic effect, or the like, the obtained refractive index variation is at most about 0.1%. When changing the propagation direction of light, the direction must be gradually changed along the optical path of the optical waveguide, and the optical circuit length is inevitably extremely long. As a result, miniaturization of the optical circuit is reduced. It becomes difficult.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical waveguide device that can be applied to a holographic wave transmission medium and can reduce the size of an optical circuit. is there.

  In order to achieve such an object, the present invention includes a waveguide comprising a clad layer formed on a substrate and a core portion embedded in the clad layer. In the optical waveguide device, the core portion includes a pixel shape portion defined by a plurality of scattering points having a refractive index lower than that of the waveguide, and a constant width portion including a phase adjusting unit.

  According to a second aspect of the present invention, there is provided an optical waveguide device including a waveguide including a clad layer formed on a substrate and a core portion embedded in the clad layer, wherein A is an integer of 1 or more, B And C are integers of 2 or more, A input optical waveguides, A input B output optical branching means connected to the input optical waveguides, and each optical waveguide connected to the optical branching means B input C comprising B optical waveguide arrays including phase adjusting means, and a pixel-shaped portion connected to the optical waveguide array, wherein the core portion is defined by a plurality of scattering points having a refractive index lower than that of the waveguide. Output optical multiplexing means.

  According to a third aspect of the present invention, the optical branching unit according to the second aspect is characterized in that the core portion includes a pixel shape portion defined by a plurality of scattering points having a refractive index lower than that of the waveguide. To do.

  According to a fourth aspect of the present invention, in the waveguide type optical device according to the third aspect, A, B and C are equal to each other.

  The invention according to claim 5 is the optical waveguide device according to any one of claims 1 to 4, wherein the substrate is either a silicon substrate or a quartz substrate, and the optical waveguide is a silica-based optical waveguide. The phase adjusting means is a thin film heater formed on a clad layer.

  As described above, according to the present invention, it is possible to reduce the size of the optical circuit by applying the holographic wave transmission medium and combining it with the phase adjusting means.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The optical waveguide device of this embodiment controls the optical path of guided light by a holographic wave transmission medium. The holographic wave transmission medium is defined by a plurality of scattering points having a refractive index lower than that of the waveguide, and transmits a wave to the holographic by multiple scattering according to a two-dimensional refractive index distribution.

  First, the basic concept of the wave transmission medium used in the present invention will be described. Here, since it is applied to an optical circuit, the “wave” propagating in the wave transmission medium is “light”. The theory relating to the wave transmission medium specifies the characteristics of the medium based on a general wave equation, and can also hold in principle in general waves. In order to input a coherent light pattern and output a desired light pattern, the wave transmission medium has a phase difference between forward propagation light and back propagation light propagating in the wave transmission medium. The refractive index distribution is determined so as to be small even at the location. A desired light pattern is output by repeatedly repeating holographic control at a local level according to the refractive index distribution.

With reference to FIG. 3, the basic structure of the wave transmission medium according to the present embodiment will be described. As shown in FIG. 3A, an optical circuit design area 1-1 constituted by a wave transmission medium exists in the optical circuit board 1. One end surface of the optical circuit is an incident surface 2-1 on which the input light 3-1 is incident. The input light 3-1 propagates through the optical circuit having a spatial refractive index distribution constituted by the wave transmission medium while being subjected to multiple scattering, and is output as the output light 3-2 from the exit surface 2-2 which is the other end face. Is output. Coordinate z in FIG. 3 (a), the coordinates (z = 0 is the incident surface, z = z _e is output surface) of the propagation direction of the light is, the coordinate x is at a transverse coordinates for the light propagation direction is there. In this embodiment, it is assumed that the wave transmission medium is made of a dielectric, and the spatial refractive index distribution is based on the theory described below for the local refractive index of the dielectric constituting the wave transmission medium. This is realized by setting based on this.

  The “field” (input field) formed by the input light 3-1 is modulated according to the spatial distribution of the refractive index of the wave transmission medium constituting the optical circuit, and the “field” formed by the output light 3-2. "(Output field). In other words, the wave transmission medium of the present invention is (electromagnetic) field conversion means for correlating the input field and the output field according to the spatial refractive index distribution. For these input field and output field, the light field in the cross section (cross section along the x axis in the figure) perpendicular to the propagation direction (z axis direction in the figure) in the optical circuit is represented by its location (x, This is called a (forward) propagation image (propagation field or propagation light) in z) (see FIG. 3B).

  Here, “field” generally means an electromagnetic field (electromagnetic field) or a vector potential field of an electromagnetic field. The control of the electromagnetic field in this embodiment corresponds to changing the spatial refractive index distribution provided in the optical circuit, that is, the dielectric constant distribution. Although the dielectric constant is given as a tensor, since the transition between the polarization states is usually not so large, it is an approximation that may be a scalar wave approximation for only one component of the electromagnetic field. Therefore, in this specification, the electromagnetic field is treated as a complex scalar wave. Since the “state” of light includes an energy state (wavelength) and a polarization state, when the “field” is used to express the state of light, the light wavelength and polarization state are also included. Will get.

  In general, in an optical circuit that does not cause amplification or attenuation of propagating light, when the spatial distribution of the refractive index is determined, an image (input field) of the input light 3-1 other than the focal point is an image of the output light 3-2. (Output field) is determined uniquely. Such a field of light traveling from the exit surface 2-2 side to the entrance surface 2-1 side is referred to as a back propagation image (a back propagation field or a back propagation light) (see FIG. 3C). Such a back propagation image can be defined for each place in the optical circuit. That is, when a light field at an arbitrary place in the optical circuit is considered, if the place is considered as an emission point of a virtual “input light”, the image of the output light 3-2 can be obtained in the same manner as described above. The back-propagation image at that location can be considered. In this way, a back propagation image can be defined for each location in the optical circuit.

  In particular, in a single optical circuit, when the outgoing field is a propagation field of the incident field, the propagation field and the reverse propagation field coincide with each other at any point of the optical circuit. The field is generally a function over the entire target space, but the term “incident field” or “exit field” means a cross section of the field on the entrance surface or exit surface. In addition, even in the case of “field distribution”, when a discussion is made regarding a specific cross section, it means a cross section of the field with respect to that cross section.

  In order to explain the method of determining the refractive index distribution, it is better to use symbols, so the following symbols are used to represent each quantity. Note that the target light (field) is not limited to light in a single state. Therefore, an index j is assigned to light in each state so that light in which a plurality of states are superimposed can be targeted. In general.

Ψ ^j (x): j-th incident field (complex vector value function, defined by intensity distribution and phase distribution set on the incident surface, and wavelength and polarization)
Φ ^j (x): j-th outgoing field (complex vector value function, defined by intensity distribution and phase distribution, wavelength and polarization set on the outgoing face)
Note that ψ ^j (x) and φ ^j (x) have the same total light intensity (or a negligible loss) unless intensity amplification, wavelength conversion, and polarization conversion are performed in the circuit. Their wavelength and polarization are the same.
{Ψ ^j (x), φ ^j (x)}: Input / output pair (a set of input / output fields)
{Ψ ^j (x), φ ^j (x)} is defined by the intensity distribution and the phase distribution, the wavelength and the polarization at the entrance surface and the exit surface.
{N _q }: Refractive index distribution (a set of values for the entire optical circuit design area)
Since one field of light is determined when one refractive index distribution is given to a given incident field and outgoing field, it is necessary to consider a field for the entire refractive index distribution given by the qth iterative operation. Therefore, the entire refractive index distribution may be expressed as n _q (x, z) with (x, z) as an indefinite variable, but the refractive index value n _q (x, z) at the location (x, z) For distinction, {n _q } is used for the entire refractive index distribution.
N _core : A symbol indicating a high refractive index value with respect to the surrounding refractive index, such as a core portion in an optical waveguide.
N _clad : a symbol indicating a low refractive index value with respect to n _core , such as a clad portion in an optical waveguide.
Ψ ^j (z, x, {n _q }): field at location (x, z) when the ^jth incident field ψ ^j (x) is propagated through the refractive index profile {n _q } to z The value of the.
Φ ^j (z, x, {n _q }): at the location (x, z) when the j-th outgoing field φ ^j (x) is propagated back to z in the refractive index profile {n _q } The field value.

In the present embodiment, the refractive index distribution, all j for _{^{ψ j (z e, x,}} {n q}) is given = φ ^j (x), or the so close state {n _q}.

  “Input port” and “output port” are “areas” where the fields at the entrance end face and the exit end face are concentrated. For example, by connecting an optical fiber to the part, the optical intensity can be propagated to the fiber. It is an area. Here, since the field intensity distribution and phase distribution can be designed to be different for the j-th and k-th ones, a plurality of ports can be provided on the entrance end face and the exit end face. Furthermore, when considering a pair of an incident field and an outgoing field, the phase generated by the propagation between them differs depending on the frequency of light. Therefore, for light having different frequencies (that is, light having different wavelengths), the field shape including the phase is included. Regardless of whether they are the same or orthogonal, they can be configured as different ports.

Here, the electromagnetic field is a field of a real vector value, and has a wavelength and a polarization state as parameters, but the value of the component is displayed as a complex number that can be easily handled in a general mathematical manner, and represents the solution of the electromagnetic wave. In the following calculation, it is assumed that the strength of the entire field is normalized to 1. As shown in FIGS. 3B and 3C, with respect to the jth incident field ψ ^j (x) and the output field φ ^j (x), the propagation field and the back propagation field are set at the respective locations. As complex vector value functions, they are expressed as ψ ^j (z, x, {n}) and φ ^j (z, x, {n}). Since the values of these functions vary depending on the refractive index distribution {n}, the refractive index distribution {n} is a parameter. According to the definition of the symbols, ψ ^j (x) = ψ ^j (0, x, {n}) and φ ^j (x) = φ ^j (z _e , x, {n}). The values of these functions can be easily calculated by a known method such as a beam propagation method, given an incident field ψ ^j (x), an outgoing field φ ^j (x), and a refractive index distribution {n}. it can.

In the following, a general algorithm for determining the spatial refractive index distribution will be described. FIG. 4 shows a calculation procedure for determining the spatial refractive index distribution of the wave transmission medium. Since this calculation is repeatedly executed, the number of repetitions is represented by q, and the state of the qth calculation when the calculation is executed up to the (q−1) th is shown. Based on the refractive index distribution {n _q-1 } obtained by the (q-1) th calculation, the propagation field and the ^jth incident field ψ ^j (x) and the outgoing field φ ^j (x) The back propagation field is obtained by numerical calculation, and the results are expressed as ψ ^j (z, x, {n _q-1 }) and φ ^j (z, x, {n _q-1 }), respectively (step S220). ).

Based on these results, the refractive index n _q (z, x) at each location (z, x) is obtained by the following equation (step S240).
n _q (z, x) = n _q-1 (z, x) −αΣ _j Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })] (1)
Here, the symbol “·” in the second term on the right side means an inner product operation, and Im [] means an imaginary number component of the field inner product operation result in []. The symbol “*” is a complex conjugate. The coefficient α is a value obtained by dividing a value equal to or less than a fraction of n _q (z, x) by the number of field pairs, and is a small positive value. Σ _j means that the sum is taken for the index j.

Step S220 and S240 and repeats the value in the exit plane of the propagation field _{^{ψ j (z e, x,}} {n}) the absolute value of the difference between the exit field φ ^j (x) is than desired error d _j When it becomes smaller (step S230: YES), the calculation ends.

In the above calculation, the initial value {n ₀ } of the refractive index distribution may be set appropriately. However, if this initial value {n ₀ } is close to the expected refractive index distribution, the calculation converges faster accordingly ( Step S200). When calculating φ ^j (z, x, {n _q-1 }) and ψ ^j (z, x, {n _q-1 }) for each j, , J (that is, φ ^j (z, x, {n _q-1 }) and ψ ^j (z, x, {n _q-1 })). Thus, calculation efficiency can be improved (step S220). If the computer is configured with a relatively small memory, an appropriate j is selected for each q in the sum of the index j in equation (1), and φ ^j (z, x, { It is also possible to calculate only n _q-1 }) and ψ ^j (z, x, {n _q-1 }) and repeat the subsequent calculations (step S220).

In the above ^{operation, φ j (z, x,} {n q-1}) in the case of values and ^{ψ j (z, x, {} n q-1}) and the value of the near, the formula (1) Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })] is a value corresponding to the phase difference, and by reducing this value, It is possible to obtain a desired output.

The determination of the refractive index distribution can be rephrased as defining a virtual mesh in the wave transmission medium and determining the refractive index of a minute region (pixel) defined by the mesh for each pixel. In principle, such a local refractive index can be an arbitrary (desired) value for each location. The simplest system is a system consisting only of pixels having a low refractive index (n _L ) and pixels having a high refractive index (n _H ), and the overall refractive index distribution due to the spatial distribution of these two types of pixels. Is determined. In this case, the place where the low refractive index pixel exists in the medium is considered as a gap of the high refractive index pixel, and conversely, the place where the high refractive index pixel exists is considered as the gap of the low refractive index pixel. Can do. That is, the wave transmission medium of the present invention can be expressed as a desired place (pixel) in a medium having a uniform refractive index replaced with a pixel having a different refractive index.

  The calculation contents for determining the refractive index distribution described above are summarized as follows. An input port and an output port are provided in a medium capable of transmitting a wave in a holographic manner (dielectric in the case of light). Field distribution 1 (forward propagation light) of propagating light incident from the input port and from the input port A field distribution 2 (reverse propagation light) of phase conjugate light in which an output field expected when an incident optical signal is output from the output port is propagated backward from the output port side is obtained by numerical calculation. In the field distribution 1 and the field distribution 2, a spatial refractive index distribution in the medium is obtained so as to eliminate the phase difference at each point (x, z) of the propagating light and the counter propagating light. If the steepest descent method is adopted as a method for obtaining such a refractive index distribution, the refractive index is calculated by changing the refractive index in the direction obtained by the steepest descent method using the refractive index of each point as a variable. By changing as in (1), the difference between the two fields can be reduced. If such a wave transmission medium is applied to an optical component that emits light incident from an input port to a desired output port, an effective optical path length is reduced due to interference phenomenon caused by multiple scattering of propagation waves generated in the medium. An optical circuit having a sufficiently high optical signal controllability can be configured even with a long and gentle refractive index change (distribution).

  FIG. 5 shows an optical switch using a deflector according to an embodiment of the present invention. The optical signal input from the input optical waveguide 301 is output to the waveguide array 304 including a plurality of optical waveguides for each wavelength by the optical branch circuit 302. Each waveguide array 304 is provided with a light modulation means 303. The light modulation means 303 changes the phase of the transmitted optical signal by changing the refractive index in the waveguide by the electro-optic effect, the thermo-optic effect, or the like. The signal output from the waveguide array 304 is composed of a wave transmission medium, is input to an optical multiplexing circuit 305 that functions as a deflector, and is output from a predetermined output waveguide 306.

  The optical multiplexing circuit 305 is a pixel shape portion defined by a plurality of scattering points having a low refractive index, and is a holographic wave transmission medium in which a refractive index distribution is calculated by applying the above-described algorithm. By repeating about 200 times, an optical multiplexing circuit having the refractive index distribution shown in FIG. 6 is obtained. Here, the black part in the optical circuit design region 1-1 in the figure is a high refractive index part (dielectric multiple scattering part) 1-11 corresponding to the core, and the part other than the black part corresponds to the clad. The low refractive index portion 1-12 is a scattering point having a refractive index lower than that of the waveguide. The refractive index of the clad assumes the refractive index of quartz glass, and the refractive index of the core has a value that is higher by 0.75% than the relative refractive index of quartz glass. The size of the optical circuit is 200 μm long and 500 m wide.

  Note that the minimum dimension of the mesh is assumed to be a sufficiently small value as the shape in which light scattering occurs with respect to the wavelength of the optical signal of 1.55 μm, and the minimum dimension is set to 0 in order to suppress the consumption of computer memory in the actual design. .2 μm.

  The wave transmission medium is designed to output an optical signal input from each input port connected to the waveguide array 304 from a predetermined output waveguide 306 according to a combination of phases of the optical modulation means 303. ing. By using the algorithm described above, it is possible to realize light beams having different directions, that is, combinations of outputs, according to combinations of phases, that is, combinations of inputs. Further, by using the above-described algorithm, the optical coupling between the optical multiplexing circuit 305 and the output waveguide 306 can be optimized so that the light beam can be efficiently incident on the output waveguide 306. In this way, the optical signal transmitted through the waveguide array 304 can be selectively output to a predetermined output waveguide 306 by changing the phase by the respective optical modulation means 303.

  FIG. 7 shows an optical switch using an optical coupling / branching circuit according to an embodiment of the present invention. The optical signal input from the input optical waveguide 401 is output to the waveguide array 404 including a plurality of optical waveguides by the optical coupling / branching circuit 402. Each waveguide array 404 is provided with a light modulation means 403. The light modulation unit 403 changes the phase of the transmitted optical signal by changing the refractive index in the waveguide by the electro-optic effect, the thermo-optic effect, or the like. The signal output from the waveguide array 404 is composed of a wave transmission medium, is input to the optical coupling / branching circuit 405, and is output from a predetermined output waveguide 406.

  The optical coupling / branching circuit 402 and the optical coupling / branching circuit 405 are pixel shapes defined by a plurality of scattering points having a low refractive index, and are holographic wave transmission media in which the refractive index distribution is calculated by applying the above-described algorithm. is there. FIG. 8 shows the refractive index distribution of the wave transmission medium applied to the optical coupling / branching circuit. Here, the black part in the optical circuit design region 1-1 in the figure is a high refractive index part (dielectric multiple scattering part) 1-11 corresponding to the core, and the part other than the black part corresponds to the clad. The low refractive index portion 1-12 is a scattering point having a refractive index lower than that of the waveguide. The refractive index of the clad assumes the refractive index of quartz glass, and the refractive index of the core has a value that is higher by 0.75% than the relative refractive index of quartz glass. The size of the optical circuit is 200 μm in length and 500 m in width.

  The wave transmission medium that is the optical coupling / branching circuit 402 is designed to output the optical signal input from the input optical waveguide 401 to the waveguide array 404. The wave transmission medium serving as the optical coupling / branching circuit 405 is designed to output an optical signal input to the waveguide array 404 from a predetermined output waveguide 406 according to the phase. The optical coupling / branching circuit 402 and the optical coupling / branching circuit 405 can realize a small and low-loss optical switch by using the above-described algorithm. On the other hand, the optical modulation means 403 changes the refractive index in the waveguide by the electro-optic effect, the thermo-optic effect, etc., and changes the phase of the transmitted optical signal. The conventional waveguide that performs modulation can be modulated more efficiently in a lumped constant than the wave transmission medium required by the algorithm described above. Therefore, it is possible to realize an optical switch with a small size and low loss as a whole as compared with the prior art.

It is sectional drawing which shows an example of the conventional optical waveguide structure. It is a figure which shows an example of the conventional multistage connection optical switch. It is a figure for demonstrating the basic structure of a wave transmission medium. It is a flowchart which shows the calculation procedure for determining the spatial refractive index distribution of a wave transmission medium. It is a figure which shows the optical switch using the deflector concerning one Embodiment of this invention. It is a figure which shows the refractive index distribution of the wave transmission medium applied to an optical multiplexing circuit. It is a figure which shows the optical switch using the optical coupling / branching circuit concerning one Embodiment of this invention. It is a figure which shows the refractive index distribution of the wave transmission medium applied to an optical coupling / branching circuit.

Explanation of symbols

1-1 Optical Circuit Design Area 1-2 Substrate 1-11 High Refractive Index Section 1-12 Low Refractive Index Section 2-1 Incident Surface 2-2, 2-3 Emitting Surface 301, 401 Input Optical Waveguide 302 Optical Branch Circuit 303, 403 Optical modulation means 304, 404 Waveguide array 305 Optical multiplexing circuit 306, 406 Output waveguide 402, 405 Optical multiplexing / branching circuit

Claims (5)

In an optical waveguide device configured by a waveguide including a clad layer formed on a substrate and a core portion embedded in the clad layer, the core portion includes:
A pixel shape defined by a plurality of scattering points having a lower refractive index than the waveguide;
An optical waveguide device comprising: an equal width portion including a phase adjusting means. In an optical waveguide device constituted by a waveguide composed of a clad layer formed on a substrate and a core portion embedded in the clad layer, A is an integer of 1 or more, and B and C are integers of 2 or more. ,
A input optical waveguides;
A input B output optical branching means connected to the input optical waveguide;
B optical waveguide arrays connected to the optical branching means, each optical waveguide including phase adjusting means;
B input C output optical multiplexing means comprising a pixel-shaped portion connected to the optical waveguide array, the core portion being defined by a plurality of scattering points having a refractive index lower than that of the waveguide. Optical waveguide device.   The optical waveguide device according to claim 2, wherein the light branching unit includes a pixel-shaped portion in which the core portion is defined by a plurality of scattering points having a refractive index lower than that of the waveguide.   4. A waveguide type optical device according to claim 3, wherein A, B and C are equal to each other. The substrate is either a silicon substrate or a quartz substrate,
The optical waveguide is a silica-based optical waveguide,
5. The optical waveguide device according to claim 1, wherein the phase adjusting means is a thin film heater formed on a clad layer.

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