JP2006047508A - Optical functional circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fabricate an optical functional circuit which conducts a plurality of functions on a substrate. <P>SOLUTION: The optical functional circuit is provided with an undulation propagation medium in which a spatial distribution of refractive indexes, determined so as to make an optical signal incident from an input port be branched with multiple scattering corresponding to refractive indexes possessed by respective virtual pixels delimited with a virtual mesh and be emitted from an output port, is formed, wherein each pixel has a high refractive index part corresponding to a core and a low refractive index part composed of a void and realizes the function by making an arbitrary material be injected in the void. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical functional circuit, and more particularly to an optical functional circuit using a holographic wave transmission medium that transmits waves holographically by multiple scattering according to a two-dimensional refractive index distribution.

  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. In order to configure an optical circuit, each component is connected in a cascade using an optical wiring or the like. For this reason, the optical path length of the optical waveguide circuit must be longer than the optical path length required for causing an interference phenomenon in the optical circuit, and as a result, the optical circuit itself becomes extremely large. There was a problem.

For example, taking a typical arrayed waveguide grating as an example, light of multiple wavelengths (λ _j ) input from the input port is repeatedly demultiplexed and combined by a star coupler having a slab waveguide. The output light is output from the output port, but the optical path length required for demultiplexing the light with a resolution of about one thousandth of the wavelength is several tens of thousands of the wavelength of the light propagating through the waveguide. Moreover, it is necessary to perform processing for providing a wave plate for correcting circuit characteristics depending on the polarization state, including waveguide patterning of an optical circuit. (For example, refer nonpatent literature 1).

  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, the degree of freedom in circuit configuration is limited. In particular, even if the refractive index difference in the optical waveguide is to be realized by local ultraviolet irradiation, the thermo-optic effect, or the electro-optic effect, 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.

Y. Hibino, “Passive optical devices for photonic networks”, IEIC Trans. Commun., Vol.E83-B No. 10, (2000).

  Therefore, a wave transmission medium that is smaller than a conventional optical circuit using an optical waveguide circuit or a holographic circuit and has a gentle refractive index distribution, that is, sufficiently high-efficiency optical signal control even with a small refractive index difference is used. As a result, a highly efficient and compact optical circuit is realized. However, in order to realize an optical functional circuit that executes a plurality of functions, it is necessary to connect a plurality of optical circuits having one function, and there is a limit to downsizing the entire optical functional circuit.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical functional circuit that performs a plurality of functions that is small and easy to manufacture.

  In order to achieve such an object, the present invention provides the invention according to claim 1, wherein light incident from an input port is generated by a refractive index of each virtual pixel defined by a virtual mesh. The signal includes a wave transmission medium in which a spatial refractive index distribution determined so as to be branched while being scattered and emitted from an output port, and the pixel includes a high refractive index portion corresponding to a core; And having a low refractive index portion composed of a gap, and a function is realized by injecting an arbitrary material into the gap.

  According to a second aspect of the present invention, a material having a temperature dependency of refractive index is injected into the gap according to the first aspect, and the refractive index of the low refractive index portion is changed by changing the temperature of the wave transmission medium. And a plurality of functions are realized.

  According to a third aspect of the present invention, a material having an electro-optic effect is injected into the gap according to the first aspect, and a voltage or an electric current is applied to the wave transmission medium to inject the low refractive index portion. A plurality of functions are realized by controlling the refractive index.

  According to a fourth aspect of the present invention, a material having a light-induced refractive index change effect is injected into the gap according to the first aspect, and the wave transmission medium is irradiated with light so that the low refractive index portion It is characterized by controlling the refractive index and realizing a plurality of functions.

  According to a fifth aspect of the present invention, in the optical functional circuit according to the first aspect of the present invention, the gap is filled with air or a state in which a liquid having an arbitrary refractive index is injected into the gap. It is characterized by realizing two functions.

  As described above, according to the present invention, an optical functional circuit capable of executing a plurality of functions can be manufactured on one substrate, and the circuit can be shortened and the circuit can be miniaturized. It becomes possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The optical functional circuit according to the present embodiment is a holographic wave transmission medium defined by a plurality of scattering points, and transmits waves holographically by multiple scattering according to a two-dimensional refractive index distribution. The holographic wave transmission medium is a system composed of pixels having a low refractive index and pixels having a high refractive index, and the overall refractive index distribution is determined by the spatial distribution of these two types of pixels. At this time, an optical functional circuit that performs a plurality of functions is realized by making the low refractive index pixels in the medium variable.

  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. 1, the basic structure of the wave transmission medium according to the present embodiment will be described. As shown in FIG. 1A, 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. 1 (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. 1B).

  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. Uniquely defined for (output field). 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 back propagation light) (see FIG. 1C). 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 a virtual “input light” emission point, the image of the output light 3-2 is similar to the 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 the 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 FIG. 1 (b) and FIG. 1 (c), the propagation field and the back propagation field for the ^jth incident field ψ ^j (x) and output field φ ^j (x) 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. 2 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. 3 shows an optical multiplexing / demultiplexing circuit according to an embodiment of the present invention. According to the algorithm described above, a 1 × 2 optical multiplexing / demultiplexing circuit having the refractive index distribution shown in FIG. 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 1.5% than the quartz glass. The size of the optical circuit is 300 μm in length and 140 μm in width. The mesh used for the calculation when obtaining the refractive index distribution is 300 × 140.

  FIG. 3B shows a transmission spectrum of the optical multiplexing / demultiplexing circuit. It can be seen that an optical signal of 1.31 μm is output from the output port a, and an optical signal of 1.55 μm is output from the output port b, thereby forming an optical multiplexer / demultiplexer according to wavelength.

FIG. 4 shows a method for creating a waveguide including a wave transmission medium. A lower clad glass soot 402 mainly composed of SiO ₂ is deposited on the Si substrate 401 by a flame deposition method. Next, a core glass soot 403 obtained by adding GeO ₂ to SiO ₂ is deposited (FIG. 4A). Then, glass transparency is performed at a high temperature of 1000 ° C. or higher. At this time, the glass is deposited so that the lower clad glass 404 is 30 microns thick and the core glass 405 is 7 microns thick (FIG. 4B).

Subsequently, an etching mask 406 is formed on the core glass 405 using a photolithography technique (FIG. 4C), and the core glass 405 is patterned by reactive ion etching (FIG. 4D). That is, among the virtual pixels defined by the virtual mesh, a high refractive index portion corresponding to the core is formed. After removing the etching mask 406, the upper clad glass 407 is bonded (FIG. 4E). The upper cladding glass 407 is SiO _{2 to} which a dopant such as B ₂ O ₃ or P ₂ O ₅ is added.

  The high refractive index portion (dielectric multiple scattering portion) 1-11 shown in FIG. 3 corresponds to the core 405, and the low refractive index portion 1-12, which is a scattering point having a refractive index lower than that of the waveguide, is the lower clad glass. This corresponds to a gap sandwiched between 404 and the upper clad glass 407. In this embodiment, as will be described later, various materials are injected into this portion. (FIG. 4 (f)).

  In order to inject the material into the gap of the wave transmission medium, as shown in FIG. 5A, a gap through which the material passes is provided between the high refractive index portion corresponding to the core and the upper cladding glass 407. . In the etching of FIGS. 4C and 4D, two steps of etching are performed to provide a high step 408 in the periphery of the wave transmission medium. Further, as shown in FIG. 5B, a part of the step is removed so that the material inlet 411 and the outlet 412 can be connected.

By injecting an appropriate material such as air, polymer, semiconductor, or liquid into the gap of the wave transmission medium, the low refractive index portion 1-12 can be set to an arbitrary refractive index, and a plurality of functions can be performed on one substrate. An optical functional circuit that can be implemented can be realized. In particular,
1) A liquid, such as a polymer, a semiconductor, or silicon oil, is injected into the gap, and a predetermined function is realized by the temperature dependence of the refractive index.
2) A material having an electro-optic effect, such as a liquid crystal or a ferroelectric material, is injected into the gap, and a voltage is applied to change the refractive index to perform a plurality of functions.
3) A material having an electro-optic effect, such as a semiconductor or a polymer, is injected into the gap, a current is injected to change the refractive index, and a plurality of functions are executed.
4) A material having a light-induced refractive index change effect, such as a polymer, is injected into the gap, irradiated with light to change the refractive index, and perform a plurality of functions. Examples of the light-induced refractive index change effect include a light Kerr effect, a thermal lens effect due to light absorption, a refractive index change due to a phase transition, and a refractive index change due to a light-absorbing carrier.
5) Two functions are executed as a binary state of a state in which the gap is filled with air and a state in which liquid is injected into the gap.
Such a method is conceivable.

When the refractive index of the liquid injected into the gap is n, if n = n _clad , the wave transmission medium has a refractive index distribution as calculated, and a given function is realized. If n = n _core , the wave transmission medium functions as a slab waveguide. If n _clad <n <n _core is satisfied, for example, in the optical multiplexing / demultiplexing circuit shown in FIG. 3, the wavelength output to each port can be shifted. Furthermore, if n> n _core , it functions as an attenuation circuit.

  FIG. 6 shows an optical functional circuit according to Example 1 of the present invention. Wave transmission media 502 and 503 are formed on the substrate 501. An input waveguide 504 is connected to the wave transmission medium 502, and an injection port 506 for injecting a liquid into a gap that is a low refractive index portion and an exhaust port 507 are connected. An output waveguide 505 is connected to the wave transmission medium 503.

When a liquid having n = n _core is injected into the gap of the wave transmission medium 502, a slab waveguide is formed, and the wave transmission medium 502 functions as a lens. That is, the optical signal from the input waveguide 504 is branched and output to the wave transmission medium 503. The wave transmission medium 503 guides the branched optical signals to the output waveguides 505, respectively.

When a liquid _satisfying n = n _clad is injected into the gap of the wave transmission medium 502, it functions as a wave transmission medium and functions as a wavelength demultiplexing element. That is, the optical signal from the input waveguide 504 is output to the wave transmission medium 503 by changing the optical path according to the wavelength. The wave transmission medium 503 guides the demultiplexed optical signals to the output waveguides 505, respectively. In this way, the two functions of the branch circuit and the branch circuit can be realized on one substrate.

FIG. 7 shows an optical functional circuit according to Example 2 of the present invention. Wave transmission media 602 a and 602 b are formed on the substrate 601 with the waveguide 604 interposed therebetween. An output waveguide 605 is connected to the wave transmission medium 602, and an injection port 606 for injecting a liquid into a gap that is a low refractive index portion and an exhaust port 607 are connected. FIG. 8 is a cross-sectional view of the optical functional circuit according to the second embodiment. The coupling portion 608 is glass made of n _core > n ≧ n _clad . A communication groove 609 is formed on the upper portion of the coupling portion 608 so that the liquid flows.

When air is injected into the gap of the wave transmission medium 602, the light is confined in the core portion of the waveguide 604. Accordingly, the optical signal input to the waveguide 604 is propagated through the waveguide 604 and output as it is. On the other hand, when a liquid _satisfying n ≧ n _clad is injected into the gap of the wave transmission medium 602, the waveguide 604 and the wave transmission medium 602 are optically coupled. Accordingly, the optical signals input to the waveguide 604 are output from the output waveguides 605a and 605b via the wave transmission medium 602, respectively. That is, it functions as a branch circuit.

Note that the scattering loss of light in the film thickness direction can be reduced when n> n _clad than when n = n _clad . In this embodiment, silicon oil is used as the liquid, but a refractive index change can also be obtained by light irradiation or temperature change using a polymer-containing solvent. In addition, when the liquid crystal is filled, the refractive index can be changed by applying an electric field in the film thickness direction.

  Furthermore, it is possible to change the characteristics by filling the gap with a non-fluid medium such as a semiconductor and changing the refractive index of the wave transmission medium by applying voltage or carrier injection. In this way, two functions of a straight waveguide and a branch circuit can be realized on one substrate.

  FIG. 9 shows an optical functional circuit according to Example 3 of the present invention. A wave transmission medium 702 is formed on a substrate 701 in which quartz is deposited on Si. An input waveguide 704 is connected to the wave transmission medium 502, and an output waveguide 705 is optically coupled to an output port of the wave transmission medium 703. The output waveguide 705 may be an optical fiber. The wave transmission medium 702 is formed of a Ge-doped quartz glass core, and the gap is filled with a polymer. The refractive index of the polymer matches that of a Ge-doped quartz glass core at room temperature.

  At normal temperature, the wave transmission medium 702 functions as a simple slab waveguide, and an output having a very wide spot in the lateral direction can be obtained. When the substrate 701 is heated by a heater, the spot size is gradually reduced. This is because the refractive index of the filled polymer has decreased with the temperature change due to the heating of the heater. When an optical fiber is used as the output waveguide 705, it functions as a variable attenuator.

  In this embodiment, the refractive index of the polymer at room temperature is matched with the doped quartz glass core, but there is a wide degree of freedom in selecting the polymer and its refractive index. Therefore, the operating temperature at which the loss is low can be varied by adjusting the refractive index at room temperature. For example, if the refractive index is slightly lowered, the operating temperature can be lowered. In addition, when the refractive index change due to temperature change is used as the operating principle, the operating speed is about several milliseconds to seconds. However, if a medium whose refractive index is changed by light irradiation is used as the polymer, it is several times by the control light. High-speed operation of μs or less can be performed.

  FIG. 10 shows an optical functional circuit according to Example 4 of the present invention. The fourth embodiment is an optical functional circuit that realizes a more complicated function by further connecting a wave transmission medium to the optical functional circuit of the second embodiment. Wave transmission media 802 a and 802 b are formed on the substrate 801 with the waveguide 804 interposed therebetween. To the wave transmission medium 802, wave transmission media 803a and 803b are further connected via a waveguide. The wave transmission medium 802 is connected to an inlet 806 for injecting a liquid into a gap that is a low refractive index portion and an outlet 807. The refractive index can be changed by injecting liquid into the gap of the wave transmission medium 803 through an inlet and an outlet (not shown).

When air is injected into the gap of the wave transmission medium 802, the light is confined in the core portion of the waveguide 804. Accordingly, the optical signal input to the waveguide 804 is propagated through the waveguide 804 and output as it is. On the other hand, when a liquid _satisfying n ≧ n _clad is injected into the gap of the wave transmission medium 802, the waveguide 804 and the wave transmission medium 802 are optically coupled. Accordingly, the optical signal input to the waveguide 804 is input to the wave transmission media 803a and 803b via the wave transmission medium 802.

  The wave transmission medium 803a can switch the optical path to one of the output waveguides 805a and 805b depending on whether or not liquid is injected into the gap, and the wave transmission medium 803b is one of the output waveguides 805c and 805d. The optical path can be switched. In this way, an optical functional circuit in which a switch circuit is added to the two functions of a straight waveguide and a branch circuit can be realized on one substrate.

  In this embodiment, the configuration mainly composed of quartz glass has been described. However, as described above, a semiconductor, a polymer, a liquid crystal, or the like can be used. A method for manufacturing an optical functional circuit using these materials will be described below.

  In the case of a semiconductor, a normal semiconductor optical waveguide device process such as a laser is used. First, a low refractive index film (for example, InP) and a high refractive index film (for example, InGaAsP) are formed on a conductive substrate by crystal growth. Pattern processing of at least a portion of the film having a high refractive index is performed by a photo process and a dry etching process. A low refractive index film (InP or InGaAsP having a lower refractive index than the core film) is formed by crystal growth. Similarly, a conductive cladding layer is formed as a cladding layer by crystal growth. Next, an electrode metal is formed on the top of the wave transmission medium and the back surface of the substrate for current application / voltage application. The optical functional circuit is completed by cleaving and forming an antireflection film on the end face.

  In the case of a polymer, in the method shown in FIG. 4, when the patterning of FIG. 4D is performed, the polymer is applied and the solvent is evaporated to be cured. If necessary, planarization is performed by a polishing process or the like. Finally, if necessary, a heating electrode is formed on the surface.

  In the case of liquid crystal, the manufacturing method is mainly the same as that of quartz glass, and electrodes for voltage application are formed on the upper and lower surfaces of the wave transmission medium for voltage application.

In the manufacturing method using LiNbO ₃ as a material, a waveguide and a wave transmission medium are formed on a LiNbO ₃ substrate by dopant diffusion. Furthermore, after forming the protective film, an electrode is formed on the upper surface of the wave transmission medium for voltage application.

  Thus, in Examples 1 to 4 described above, not only quartz glass but also semiconductors, polymers, liquid crystals, and the like can be used.

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 multiplexing / demultiplexing circuit concerning one Embodiment of this invention. It is a figure which shows the production method of the waveguide containing a wave transmission medium. It is a figure which shows the method of inject | pouring material into the space | gap of a wave transmission medium. It is a figure which shows the optical function circuit concerning Example 1 of this invention. It is a figure which shows the optical function circuit concerning Example 2 of this invention. 6 is a cross-sectional view of an optical functional circuit according to Example 2. FIG. It is a figure which shows the optical function circuit concerning Example 3 of this invention. FIG. 6 is a diagram illustrating an optical functional circuit according to a fourth embodiment of the present invention.

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 Emission Surface 3-1 Input Port 3-2 Output Port

Claims (5)

Due to the refractive index of each of the virtual pixels defined by the virtual mesh, a spatial signal determined so that the optical signal incident from the input port branches while being scattered multiple times and is output from the output port. A wave transmission medium having a refractive index distribution formed;
The pixel has a high refractive index portion corresponding to a core and a low refractive index portion consisting of a gap,
An optical functional circuit that realizes a function by injecting an arbitrary material into the gap.   A material having a temperature dependency of a refractive index is injected into the gap, and the temperature of the wave transmission medium is changed to control the refractive index of the low refractive index portion, thereby realizing a plurality of functions. The optical functional circuit according to claim 1.   A material having an electro-optic effect is injected into the gap, and a plurality of functions are realized by controlling a refractive index of the low refractive index portion by applying a voltage or injecting a current into the wave transmission medium. The optical functional circuit according to claim 1, wherein   A material having a light-induced refractive index change effect is injected into the gap, and a plurality of functions are realized by controlling the refractive index of the low refractive index portion by irradiating the wave transmission medium with light. The optical functional circuit according to claim 1. 2. The optical function according to claim 1, wherein two functions are realized by one of a state where the gap is filled with air and a state where a liquid having an arbitrary refractive index is injected into the gap. circuit.

Images