JP2006350115A - Optical circuit and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized and high performance optical circuit that materializes a desired optical function with a single optical circuit element without combining a plurality of optical circuit elements. <P>SOLUTION: The optical circuit is provided with at least one input optical waveguide and at least one output optical waveguide formed on a substrate. The optical circuit is also provided, between the input and output optical waveguides, with an optical waveguide array comprising a plurality of optical waveguides arrayed in a light propagation direction, and with a plurality of comb-shaped slab optical waveguides arrayed substantially orthogonally to the optical waveguide array. In addition, the width of each optical waveguide of the optical waveguide array and the width of the slab optical waveguides are modulated along the longitudinal direction of the waveguides. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes an optical waveguide including a core and a clad formed on a substrate, and condenses incident light from an input port to a desired output port to produce desired output light, and an optical circuit of the optical circuit It relates to a manufacturing method.

  With the expansion of the application area of optical communication systems, further increases in capacity and speed, the importance of optical circuits that branch and switch signal light and optical circuits that combine and demultiplex multiple signal lights with different wavelengths has increased. Yes. Such an optical circuit is required to be small and have high performance.

  FIG. 8 shows a configuration example of a conventional arrayed waveguide grating filter as an example of such an optical circuit. The arrayed waveguide grating filter is an optical circuit for multiplexing and demultiplexing a plurality of signal lights having different wavelengths (see, for example, Non-Patent Document 1). The arrayed waveguide grating filter shown in FIG. 8 is provided between one slab optical waveguide 82 connected to a plurality of input optical waveguides 81 and one slab optical waveguide 84 connected to a plurality of output optical waveguides 85. Are connected by a plurality of arrayed waveguides 83. Each waveguide of the arrayed waveguide 83 is set so that the optical length of the adjacent waveguide sequentially increases by a predetermined equal size from the inside toward the outside.

  The optical path of the signal light input to the input optical waveguide 81 is expanded by the slab optical waveguide 82 and guided to each waveguide of the arrayed waveguide 83. Due to the optical path length difference of the arrayed waveguide 83, the wavefront of the signal light synthesized by the slab optical waveguide 84 has an inclination according to the wavelength. As a result, the signal light is output to different waveguides of the output optical waveguide 85 according to the wavelength, and a wavelength demultiplexer is realized.

Katsunari Okamoto, “Fundamentals of Optical Waveguides” 2000 Academic Press (Figure 9.8)

  However, since the conventional optical circuit as described above is configured by combining individual optical circuit elements such as a slab optical waveguide and an array optical waveguide, there is a problem that miniaturization is difficult. In addition, when a large-scale optical circuit system is configured by combining optical circuit elements in a complex manner, it is necessary to perform a detailed layout design in accordance with the characteristics of the optical circuit elements. There was a problem of becoming.

  The present invention has been made in view of the above points, and an object thereof is to realize a desired optical function with a single optical circuit element without combining a plurality of optical circuit elements. Another object of the present invention is to provide a small and high-performance optical circuit.

  In order to achieve the above object, an optical circuit according to claim 1 of the present invention includes at least one input optical waveguide formed on a substrate and at least one output optical waveguide, and the input circuit An optical waveguide array comprising a plurality of optical waveguides arranged in the light propagation direction between the optical waveguide and the output optical waveguide, and a plurality of comb-shaped slab optical waveguides arranged substantially orthogonal to the optical waveguide array And the width of each optical waveguide of the optical waveguide array and the width of the slab optical waveguide are modulated along the longitudinal direction of the waveguide. With such a configuration, the present invention can realize a desired optical function with a single optical circuit element, and can provide a small and high-performance optical circuit.

  According to a second aspect of the present invention, in the configuration of the first aspect, the amount of change in the width of each optical waveguide of the optical waveguide array and the width of the slab optical waveguide is a unit length (1 μm) in the light propagation direction. It is characterized by being within a range of ± 8.0 μm per hit.

  According to a third aspect of the present invention, there is provided an optical circuit according to the first or second aspect, wherein the interval between adjacent slab optical waveguides is 1 in the plurality of slab optical waveguides arranged substantially orthogonal to the optical waveguide array of the first or second configuration. 0.0 μm or more. With such a configuration, the present invention can be manufactured by an existing optical circuit manufacturing process, and can provide a small and high-performance optical circuit configured by a single optical circuit element. .

  An optical circuit according to a fourth aspect of the present invention is characterized in that, in the configuration of the first to third aspects, each optical waveguide of the optical waveguide array includes a portion where the optical waveguide partially disappears. With such a configuration, the present invention can realize a desired optical function with a single optical circuit element, and can provide a small and high-performance optical circuit.

  An optical circuit according to a fifth aspect of the present invention is characterized in that, in the configuration of the first to fourth aspects, the substrate is a silicon substrate, and the optical waveguide is a silica glass optical waveguide. By setting it as such a structure, this invention can provide the optical circuit which was stable and excellent in workability.

  According to a sixth aspect of the present invention, there is provided an optical circuit according to any one of the first to fifth aspects, wherein the optical circuit condenses incident light from an input port to a desired output port to obtain desired output light. It is one of a waver, an optical tap circuit, and an optical splitter.

  According to a seventh aspect of the present invention, there is provided an optical circuit manufacturing method including an optical waveguide including a core and a clad formed on a substrate, and condensing incident light from an input port to a desired output port. An optical circuit manufacturing method for emitting light, wherein a first step of forming a lower clad layer on a substrate and a second step of forming a core layer having a higher refractive index than the clad layer on the lower clad layer And a third step of forming a patterned core portion from the core layer, and a fourth step of forming an upper clad layer on the lower clad layer and the core portion, in the third step The patterned core portion constitutes at least one input optical waveguide formed on the substrate and at least one output optical waveguide, and is between the input optical waveguide and the output optical waveguide. Light propagation direction An optical waveguide array comprising a plurality of optical waveguides arranged, and a plurality of comb-shaped slab optical waveguides arranged substantially orthogonal to the optical waveguide array, the width of each optical waveguide of the optical waveguide array The width of the slab optical waveguide is modulated along the longitudinal direction of the waveguide.

  According to an eighth aspect of the present invention, there is provided an optical circuit manufacturing method further comprising the step of predesigning the patterned core portion in the configuration of the seventh aspect, wherein the design step comprises initial refraction constituting the optical circuit. A first step of obtaining a field distribution 1 of the incident light and a field distribution 2 of light in which the emitted light is virtually back-propagated from the output port in an optical circuit medium assuming a rate distribution; A second step of changing a width of each optical waveguide of the optical waveguide array and a width of the slab optical waveguide so that a phase difference between the field distribution 1 and the field distribution 2 becomes small at each point in the circuit medium; The first step and the second step are repeated until the field distribution 1 and the field distribution 2 are equal to or less than a desired error at the output port position. It is characterized in that it comprises a third step of sequentially determines the width of the width and the slab optical waveguide of the optical waveguide of the optical waveguide array Te.

  With the above configuration, according to the present invention, a desired optical function can be realized with a single optical circuit element, and a small and high-performance optical circuit can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each embodiment of the present invention, parts having the same function are denoted by the same reference numerals, and redundant description thereof is omitted. In the following embodiments of the present invention, the optical circuit is a silica-based glass optical waveguide formed on a silicon substrate. This is because an optical circuit which is stable and excellent in processability can be provided by using such a combination. However, the present invention is not limited to this combination, and a quartz substrate, a sapphire substrate, a polymer substrate, or the like is used as a substrate, and a material such as a semiconductor, a dielectric, or a polymer is used as a core and a clad formed on the substrate. Of course. In the following embodiments of the present invention, an example in which the core is embedded in the clad is shown, but even the ridge-shaped core can sufficiently obtain the effects of the present invention.

(First embodiment)
FIG. 1 is a plan view of an optical circuit according to a first embodiment of the present invention viewed from above in a direction perpendicular to a substrate. The z axis in this figure indicates the propagation direction of the signal light. Here, the first embodiment is a wavelength demultiplexer, but this is an optical circuit in which the optical circuit according to the present invention must be configured by a combination of a plurality of optical circuit elements such as a wavelength demultiplexer. This is because it is excellent to realize this with a single optical circuit element. However, the optical circuit according to the present invention is not limited to this embodiment, and can also be configured as an optical circuit having other functions such as a spot size converter.

  As shown in FIG. 1, the optical circuit according to the first embodiment includes, on a substrate 10, one input optical waveguide 11 and an optical waveguide array 12 including a plurality of optical waveguides arranged in the light propagation direction. Two output optical waveguides 14a and 14b are optically connected in this order, and a plurality of comb-shaped slab optical waveguides 13 arranged substantially orthogonal to the optical waveguide array 12 are arranged.

  Hereinafter, the design of each optical waveguide of the optical waveguide array 12 and the slab optical waveguide 13 shown in FIG. 1 will be described. The width of each optical waveguide of the optical waveguide array 12 and the width of each slab optical waveguide 13 are determined by applying the basic concept of the wave transmission medium. 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 for general waves.

In order to describe the design of each optical waveguide and each slab optical waveguide 13 of the optical waveguide array 12, 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. In the following description, the propagation direction of the coordinate axes of the optical z axis (z = 0 is the incident surface, z = z _e is emitting surface), the x-axis coordinate in the lateral direction (perpendicular direction) relative to the light propagation direction.
Ψ ^j (x): j-th incident field (a complex vector value function, which is defined by the intensity distribution and phase distribution set on the incident plane, and the wavelength and polarization)
Φ ^j (x): j-th outgoing field (a complex vector value function, which is defined by the intensity distribution and phase distribution set on the outgoing face, and the wavelength and polarization)

Here, “field” generally means a potential field (electromagnetic field) or a vector potential field of an electromagnetic field. 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 optical circuit. The 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 phase distribution, wavelength, and polarization at the entrance and exit surfaces.
{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 given by the qth iteration. Therefore, the entire refractive index distribution may be represented as n _q (z, x) with (z, x) as an indefinite variable, but the refractive index value n _q (z, x) at the location (z, x) In order to distinguish, {n _q } is used for the entire refractive index distribution.
Ψ ^j (z, x, {n _q }): field at location (z, x) when the j-th 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 (z, x) when the j-th outgoing field Φ ^j (x) is propagated back to z in the refractive index distribution {n _q }. The field value.

In this embodiment, the width and the width of the slab optical waveguide 13 of the optical waveguide of the optical waveguide array 12, for all _{^{j Ψ j (z e, x}} , {n q}) = Φ j (x), or in {N _q } is given so as to be in a close state.

  “Input port” and “output port” are “regions” 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 the 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. Can be configured as different ports regardless of whether they are the same or orthogonal.

Here, the electromagnetic field is a field of a real vector value, and has a wavelength and a polarization state as parameters. The value of the component is displayed as a complex number that can be easily handled in general mathematical terms, and the electromagnetic wave solution is expressed. . In the following calculation, it is assumed that the strength of the entire field is normalized to 1. For the jth incident field Ψ ^j (x) and the outgoing field Φ ^j (x), Ψ ^j (z, x, {n}) with the propagation field and the back propagation field as complex vector value functions at the respective locations. 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. The definitions of the ^{symbols, Ψ j (x) = Ψ} j (0, x, {n}) and ^{Φ j (x) = Φ j} (z e, x, {n}) becomes. 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 propagation medium. Since this calculation is repeatedly executed, the number of repetitions is represented by q, and the state of the qth calculation when the calculations up to the (q-1) th are executed is shown in FIG. Based on the refractive index distribution {n _q-1 } obtained by the (q-1) th calculation, a propagation field (field in the propagation direction) for the initial value Ψ ^j (x) of each jth incident field And the value of the back propagation field (field in the back propagation direction) for the outgoing field Φ ^j (x) are obtained by numerical calculation, and the results are respectively obtained as Ψ ^j (z, x, {n _q−1 } ) And Φ ^j (z, x, {n _q-1 }) (step S2).

Based on these results, the refractive index n _q (z, x) at each location (z, x) is obtained by the following equation (1). Then, at the boundary between the core and the clad in the refractive index profile {n _q−1 }, Im [φ ^j (z, x, {n _q−1 }) ^* · Ψ ^j (z, x, The width of the optical waveguide written in the optical waveguide array and the width of the optical waveguide are enlarged or reduced so that the absolute value of {n _q-1 })] is reduced. (Step S4).

Here, the symbol “·” in the second term on the right side means an inner product operation, and Im [] means an imaginary part 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 less than a fraction of n _q (z, x) by the number of field pairs. Σ _j means that the sum is taken for the index j.

Steps S2 and S4 are repeated, and the absolute value of the difference between the value Ψ ^j (z _e , x, {n}) on the exit surface of the propagation field and the initial value Φ ^j (x) of the exit field is the desired error d. _When it becomes smaller than _j (step S3: YES), the calculation is completed.

In the above calculation, the initial value {n ₀ } of the refractive index distribution may be set appropriately, but if this initial value {n ₀ } is close to the expected refractive index distribution, the convergence of the calculation is accelerated accordingly ( Step S0). In calculating Φ ^j (z, x, {n _q-1 }) and Ψ ^j (z, x, {n _q-1 }) for each j, in the case of a computer that can calculate in parallel, , J (that is, Φ ^j (z, x, {n _q-1 }) and Ψ ^j (z, x, {n _q-1 })), the cluster system. Etc. can be used to improve calculation efficiency (step S2).

When a computer is configured with a relatively small memory, an appropriate j is selected for each q in the sum of the index j in the above equation (1), and Φ ^j (z, x , {N _q-1 }) and Ψ ^j (z, x, {n _q-1 }), and the subsequent calculation can be repeated (step S2).

In the above calculation, when Φ ^j (z, x, {n _q-1 }) is close to the value of Ψ ^j (z, x, {n _q-1 }), the above 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 between the propagation field and the back propagation field, It is possible to obtain a desired output by reducing the value of this phase difference. That is, when determining the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13, Im [φ ^{j at} the boundary surface between the core and the clad in the refractive index distribution of the (q-1) th calculation result. The core width may be enlarged or reduced so that the value of (z, x, {n _q-1 }) ^* · Ψ ^j (z, x, {n _q-1 })] is reduced (step S4). .

The calculation contents based on the wave equation in the wave transmission medium described above are used to determine the width of each optical waveguide of the optical waveguide array 12 modulated in the optical waveguide longitudinal direction and the width of the slab optical waveguide 13 in the optical circuit according to the present invention. The following is a summary from the viewpoint of: The field of signal light input from the input port of the input optical waveguide 11 in FIG. 1 is propagated from the input optical waveguide 11 side to the output optical waveguide 14 side (forward-propagating light) Ψ, and the desired output optical waveguide 14 A field (reversely propagated light) in which a field in which the phase of the field of the desired signal light output from the output port is inverted is propagated from the output optical waveguide 14 side to the input optical waveguide 11 side is denoted by Φ ^* .

Here, a case is considered where the number of output ports of the optical circuit to be designed is N (N is an integer of 1 or more). An optical circuit can be designed by superimposing a desired output field at each output port N times in consideration of the output port position, and setting the overlapped field as a desired field at the output end face. At this time, if a refractive index distribution that minimizes the phase difference between the forward propagating light Ψ and the counter propagating light Φ ^* is given at each position on the z-axis shown in FIG. 1, the input signal light is converted into a desired output signal light. An optimal optical circuit for converting to can be configured.

Specifically, the phase difference (Ψ−Φ ^* ) between the forward propagation light and the back propagation light at the interface between the core and the clad is calculated at each position on the z axis shown in FIG. When the phase difference between the forward propagation light and the back propagation light at the boundary surface between the core and the clad is positive (Ψ−Φ ^* > 0), the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13 are set as follows. By enlarging, it is possible to minimize the phase difference between Ψ and Φ ^* . When the phase difference between the forward propagation light and the back propagation light at the interface between the core and the clad is negative (Ψ−Φ ^* <0), the width of each optical waveguide of the optical waveguide array 12 and the slab optical waveguide 13 By reducing the width, it is possible to minimize the phase difference between ψ and Φ ^* .

  As described above, by changing only the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13, it is possible to design an optical circuit that suppresses wave scattering and has a small signal light propagation loss. it can.

Here, in the plurality of comb-shaped slab optical waveguides 13 arranged orthogonal to the optical waveguide array 12, when the interval between the adjacent slab optical waveguides 13 is very narrow, it becomes difficult to manufacture an optical circuit. The problem arises. Therefore, when the minimum value of the interval between the adjacent slab optical waveguides 13 is d _min , it is desirable to satisfy d _min ≧ 1.0 μm in consideration of using an existing optical circuit manufacturing process.

  Further, in each optical waveguide and slab optical waveguide 13 of the optical waveguide array 12 modulated in the longitudinal direction of the optical waveguide, the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13 with respect to the signal light propagation direction. When the change is steep, there arises a problem that it becomes difficult to manufacture an optical circuit. Therefore, it is desirable that the change of the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13 is continuous and smooth. Further, in consideration of the wavelength of the signal light as described below, it is desirable to be within a range of ± 8.0 μm per unit length (1 μm) in the signal light propagation direction.

  That is, generally, the wavelength of signal light used for optical communication is in the range of 1.2 to 1.7 μm. Here, when the amount of change in the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13 is extremely larger than the wavelength of the signal light, the direction of the signal light is perpendicular to the substrate 10. Will be scattered. For this reason, the propagation loss of signal light increases. Therefore, in order to suppress the scattering of the signal light, the amount of change in the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13 is set to about several times the wavelength, specifically within ± 8.0 μm. It is effective to make it. As will be described later, a sufficient effect can be obtained even when the amount of change in the width of each optical waveguide of the optical waveguide array 12 and the width of the slab optical waveguide 13 is limited to within ± 4.0 μm.

The optical circuit shown in FIG. 1 was manufactured by the following procedure. First, a SiO ₂ lower cladding layer is deposited on a silicon substrate by a flame deposition method or the like, and then a SiO ₂ glass layer doped with GeO ₂ as a dopant on the lower cladding layer has a higher refractive index than the lower cladding layer. Deposited as a layer. Next, the core layer was etched using a pattern as shown in FIG. 1 based on the above-described design to form a core portion (optical waveguide). Finally, a SiO ₂ upper cladding layer was deposited on the lower cladding and the core.

The optical circuit shown in FIG. 1 changes in the width of each optical waveguide of the optical waveguide array 12 modulated in the longitudinal direction of the optical waveguide and the width of the slab optical waveguide 13 in consideration of using a conventional optical circuit manufacturing process. The upper limit of the quantity is designed to be ± 4.0 μm per unit length (1 μm) in the signal light propagation direction, and each adjacent slab optical waveguide in the plurality of slab optical waveguides 13 arranged orthogonal to the optical waveguide array 12 The minimum value of the 13 intervals is designed as d _min = 3.0 μm. The number of slab optical waveguides 13 arranged orthogonal to the optical waveguide array 12 is 32. The core width of the input optical waveguide 11 and the core widths of the two output optical waveguides 14a and 14b are 7 μm, and the distance between the centers of the two output optical waveguides 14a and 14b is 15 μm. The thickness of the core of the optical waveguide in the optical circuit is 6 μm. The refractive index of the core was 1.45523, and the refractive index of the clad was 1.44428. The length of the optical circuit is 500 μm.

  In addition, when the width of each optical waveguide of the optical waveguide array 12 is changed, the optical waveguide may include a portion where the optical waveguide partially disappears with the change in the width of the core. That is, the optical circuit according to the present embodiment may be configured by an optical waveguide in which the core width is partially zero in each optical waveguide of the optical waveguide array 12, and even with such a configuration, The effect explained can be obtained.

  FIG. 3 shows the transmittance of the optical circuit according to the first embodiment of the present invention. The signal light obtained by combining the light having the wavelength of 1.31 μm and the wavelength of 1.55 μm is input from the input optical waveguide 11 to the optical waveguide array 12 including a plurality of optical waveguides arranged in the light propagation direction. It can be seen that signal light having a wavelength of 1.31 μm is output from the output optical waveguide 14b and signal light having a wavelength of 1.55 μm is output from the output optical waveguide 14a, thus functioning as a wavelength demultiplexer.

Thus, the upper limit of the change amount of the width of each optical waveguide of the optical waveguide array 12 modulated in the longitudinal direction of the optical waveguide and the width of the slab optical waveguide 13 is set to ± 4 per unit length (1 μm) in the signal light propagation direction. Even if the minimum value of the interval between adjacent slab optical waveguides 13 in the plurality of slab optical waveguides 13 arranged orthogonally to the optical waveguide array 12 is limited to d _min = 3.0 μm It is possible to realize an optical circuit that functions sufficiently as a wavelength demultiplexer that selects a wavelength and outputs it from an arbitrary output optical waveguide.

(Second Embodiment)
FIG. 4 is a plan view of an optical circuit according to the second embodiment of the present invention viewed from above in a direction perpendicular to the substrate. The z axis indicates the propagation direction of the signal light. Here, although the optical circuit of FIG. 4 is an optical tap circuit, the optical circuit according to the present invention is not limited to this embodiment. The optical circuit shown in FIG. 4 was designed and manufactured by the same procedure as the optical circuit shown in the first embodiment. In the optical circuit shown in FIG. 4, the width of each optical waveguide of the optical waveguide array 12 modulated in the longitudinal direction of the optical waveguide and a plurality of comb-shaped slab optical waveguides 13 are considered in consideration of using a conventional optical circuit manufacturing process. The upper limit of the amount of change in the width of each slab optical waveguide 13 in the plurality of slab optical waveguides 13 designed to be ± 4.0 μm per unit length (1 μm) in the signal light propagation direction and arranged orthogonal to the optical waveguide array 12 The minimum value of the interval between the slab optical waveguides 13 is designed with d _min = 3.0 μm.

  The number of slab optical waveguides 13 arranged orthogonal to the optical waveguide array 12 is eighteen. The width of the core of one input optical waveguide 11 and the width of the cores of the two output optical waveguides 14a and 14b are 7 μm, and the distance between the centers of the two output optical waveguides 14a and 14b is 10 μm. The thickness of the core of the optical waveguide in the optical circuit is 6 μm. The refractive index of the core was 1.45523, and the refractive index of the clad was 1.44428. The length of the optical circuit is 250 μm.

  In addition, when the width of each optical waveguide of the optical waveguide array 12 is changed, there may be a portion where the optical waveguide partially disappears with the change in the core width. In other words, the optical circuit according to the present embodiment may be configured by optical waveguides in which the core width is partially zero in each optical waveguide of the optical waveguide array 12. The effect explained can be obtained.

  FIG. 5 shows the transmittance of the optical tap circuit according to the second embodiment of the present invention. Of the signal light input to the input optical waveguide 11, 90% is output from the output optical waveguide 14a and 10% is output from the output optical waveguide 14b, and functions as an optical tap circuit that extracts part of the signal light. You can see that The ratio of extracting the signal light, that is, the tap amount of the optical tap circuit can be adjusted by setting a desired output field according to the tap amount in the design of the optical tap circuit.

Thus, the upper limit of the change amount of the width of each optical waveguide of the optical waveguide array 12 modulated in the longitudinal direction of the optical waveguide and the width of the slab optical waveguide 13 is set to ± 4 per unit length (1 μm) in the signal light propagation direction. Even if the minimum value of the interval between adjacent slab optical waveguides 13 in the plurality of slab optical waveguides 13 arranged orthogonally to the optical waveguide array 12 is limited to d _min = 3.0 μm An optical circuit sufficiently functioning as an optical tap circuit that outputs signal light at an arbitrary output ratio to the output optical waveguide can be realized.

  Further, if the optical circuit of the second embodiment is used, not only an optical circuit having a wavelength dependency in transmittance but also an optical circuit having a small wavelength dependency can be provided.

(Third embodiment)
FIG. 6 is a plan view of an optical circuit according to the third embodiment of the present invention viewed from above in a direction perpendicular to the substrate. The z axis indicates the propagation direction of the signal light. Here, the optical circuit of FIG. 6 is a 1 × 4 optical splitter, but the optical circuit according to the present invention is not limited to this embodiment. The 1 × 4 optical splitter shown in FIG. 6 was designed and manufactured by the same procedure as the optical circuit shown in the first embodiment.

The optical circuit shown in FIG. 6 changes the width of each optical waveguide of the optical waveguide array 12 modulated in the longitudinal direction of the optical waveguide and the width of the slab optical waveguide 13 in consideration of using the conventional optical circuit manufacturing process. The upper limit of the amount is ± 8.0 μm per unit length (1 μm) in the signal light propagation direction, and the interval between adjacent slab optical waveguides 13 in the plurality of slab optical waveguides 13 arranged orthogonal to the optical waveguide array 12 The minimum value is designed with d _min = 5.0 μm.

  The number of comb-shaped slab optical waveguides 13 arranged orthogonal to the optical waveguide array 12 is 23. The width of the input optical waveguide 11 and the width of the core of the output optical waveguide 14 are 7 μm, and the intervals between the four output optical waveguides 14a, 14b, 14c, and 14d are 10 μm. The thickness of the core of the optical waveguide in the optical circuit is 6 μm. The refractive index of the core was 1.45523, and the refractive index of the clad was 1.44428. The length of the optical circuit is 500 μm.

  In addition, when the width of each optical waveguide of the optical waveguide array 12 is changed, there may be a portion where the optical waveguide partially disappears with the change in the core width. In other words, the optical circuit according to the present embodiment may be configured by an optical waveguide in which the core width is partially zero in each optical waveguide of the optical waveguide array 12, and even with such a configuration, FIG. The effects described below can be obtained with reference to FIG.

  FIG. 7 shows the transmittance of the four output optical waveguides of the 1 × 4 optical splitter according to the third embodiment of the present invention. As shown in FIG. 7, the signal light input to one input optical waveguide 11 is output from the four output optical waveguides 14a, 14b, 14c, and 14d as 25% output light, respectively. It can be seen that the circuit functions as an optical splitter circuit that branches the signal light. The output ratio of the signal light in each output optical waveguide can be adjusted by setting a desired output field according to the output ratio in the design of the 1 × 4 optical splitter.

Thus, the upper limit of the amount of change in the width of each optical waveguide of the optical waveguide array 12 modulated in the longitudinal direction of the optical waveguide and the width of the slab optical waveguide 13 is set to ± 8 per unit length (1 μm) in the signal light propagation direction. Even if the minimum value of the interval between adjacent slab optical waveguides 13 in the plurality of slab optical waveguides 13 arranged orthogonally to the optical waveguide array 12 is limited to d _min = 5.0 μm An optical circuit that sufficiently functions as a 1 × 4 optical splitter that outputs signal light to the output optical waveguide at an arbitrary output ratio can be realized.

(Other embodiments)
In the above, the preferred embodiment of the present invention has been described by way of example. However, the embodiment of the present invention is not limited to the above-described example, and the constituent members thereof are within the scope of the claims. Various modifications such as replacement, change, addition, increase / decrease in number, change in shape design, etc. are all included in the embodiments of the present invention.

It is a top view which shows the structure of the optical circuit of the 1st Embodiment of this invention. It is a flowchart which shows the calculation procedure for determining refractive index distribution. It is a characteristic view which shows the transmittance | permeability of the optical circuit of the 1st Embodiment of this invention. It is a top view which shows the structure of the optical circuit of the 2nd Embodiment of this invention. It is a characteristic view which shows the transmittance | permeability of the optical circuit of the 2nd Embodiment of this invention. It is a top view which shows the structure of the optical circuit of the 3rd Embodiment of this invention. It is a characteristic view which shows the transmittance | permeability of the optical circuit of the 3rd Embodiment of this invention. It is a perspective view which shows the structure of the conventional array waveguide grating filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,80 Board | substrate 11,81 Input optical waveguide 12 Optical waveguide array which consists of several optical waveguide arranged in the light propagation direction 13 Slab optical waveguide 14a, 14b, 14c, 14d, 85 output arranged orthogonally to optical waveguide array Optical waveguide 82, 84 Slab optical waveguide 83 Array waveguide

Claims (8)

Having at least one input optical waveguide formed on the substrate and at least one output optical waveguide;
An optical waveguide array comprising a plurality of optical waveguides arranged in the light propagation direction between the input optical waveguide and the output optical waveguide, and a plurality of comb-like slabs arranged substantially orthogonal to the optical waveguide array An optical waveguide,
An optical circuit, wherein the width of each optical waveguide of the optical waveguide array and the width of the slab optical waveguide are modulated along the longitudinal direction of the waveguide.   The width of each optical waveguide of the optical waveguide array and the amount of change in the width of the slab optical waveguide are within a range of ± 8.0 μm per unit length (1 μm) in the light propagation direction. An optical circuit according to 1.   3. The light according to claim 1, wherein, in the plurality of slab optical waveguides arranged substantially orthogonal to the optical waveguide array, an interval between adjacent slab optical waveguides is 1.0 μm or more. circuit.   4. The optical circuit according to claim 1, wherein each optical waveguide of the optical waveguide array includes a portion where the optical waveguide partially disappears. 5.   5. The optical circuit according to claim 1, wherein the substrate is a silicon substrate, and the optical waveguide is a silica glass optical waveguide.   The optical circuit is any one of a wavelength demultiplexer, an optical tap circuit, or an optical splitter that collects incident light from an input port to a desired output port to produce desired output light. The optical circuit according to claim 1. An optical circuit manufacturing method including an optical waveguide composed of a core and a clad formed on a substrate, and condensing incident light from an input port to a desired output port to obtain desired output light,
A first step of forming a lower cladding layer on the substrate;
A second step of forming a core layer having a higher refractive index than the cladding layer on the lower cladding layer;
A third step of forming a patterned core portion from the core layer;
A fourth step of forming an upper cladding layer on the lower cladding layer and the core part,
In the third step, the patterned core portion constitutes at least one input optical waveguide formed on the substrate and at least one output optical waveguide, and the input optical waveguide and the output optical waveguide An optical waveguide array comprising a plurality of optical waveguides arranged in the light propagation direction between the waveguides, and a plurality of comb-shaped slab optical waveguides arranged substantially orthogonal to the optical waveguide array, A method of manufacturing an optical circuit, wherein the width of each optical waveguide of the optical waveguide array and the width of the slab optical waveguide are modulated along the longitudinal direction of the waveguide. The method further includes a step of pre-designing the patterned core portion,
In an optical circuit medium that assumes an initial refractive index distribution constituting the optical circuit, a field distribution 1 of the incident light and a field distribution 2 of light in which the emitted light is virtually propagated backward from the output port are obtained. A first step;
A second width of each optical waveguide of the optical waveguide array and a width of the slab optical waveguide are changed so that a phase difference between the field distribution 1 and the field distribution 2 becomes small at each point in the optical circuit medium. Steps,
At the output port position, the first step and the second step are repeated until the field distribution 1 and the field distribution 2 are equal to or less than a desired error, and the width of each optical waveguide of the optical waveguide array and The method for manufacturing an optical circuit according to claim 7, further comprising a third step of sequentially obtaining a width of the slab optical waveguide.

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