JP4091944B2 - Optical circuit - Google Patents

Description

  The present invention relates to an optical circuit, and more particularly to a small and high-performance optical circuit formed on a substrate.

  With the rapid spread of optical communication systems, the importance of optical circuits for branching optical signals and switching optical paths and optical circuits for multiplexing and demultiplexing optical signals of different wavelengths has increased. Such an optical circuit is required to be small and have high performance. Against this background, integrated optical components using an optical waveguide structure have been developed. 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.

  FIG. 1 shows the configuration of a conventional arrayed waveguide grating filter. The arrayed waveguide grating filter is an optical circuit for multiplexing / demultiplexing a plurality of optical signals having different wavelengths (see, for example, Non-Patent Document 1). An array waveguide 103 connects the slab optical waveguide 102 connected to the input optical waveguide 101 and the slab optical waveguide 104 connected to the output optical waveguide 105. Each waveguide of the arrayed waveguide 103 is set so that the optical length of the adjacent waveguide increases by an equal amount from the inside toward the outside.

  The optical signal input to the input optical waveguide 101 is guided to the respective arrayed waveguides 103 by expanding the optical path by the slab optical waveguide 102. Due to the optical path length difference of the arrayed waveguide 103, the wavefront of the optical signal synthesized by the slab optical waveguide 104 has an inclination according to the wavelength. As a result, output to the different output optical waveguides 104 depending on the wavelength is achieved, and a wavelength demultiplexer is realized.

K. Okamoto, “Fundamentals of optical waveguides,” Academic Press, 2000

  However, since the conventional optical circuit is configured by combining individual optical circuit elements such as a slab optical waveguide and an arrayed 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 combination, it is necessary to perform a detailed layout design according to the characteristics of the optical circuit elements, which increases the design man-hours. There was also.

  The present invention has been made in view of such problems, and an object of the present invention is to realize different functions with a single optical circuit element without combining a plurality of optical circuit configurations, and to be small in size. The object is to provide a high-performance optical circuit.

In order to achieve such an object, the present invention is characterized in that at least one input optical waveguide formed on a substrate and at least one output formed on the substrate. Two or more optical waveguides are arranged in parallel along the propagation direction of the optical signal between the optical waveguide, the input optical waveguide, and the output optical waveguide, and optically between adjacent optical waveguides. And the number of optical waveguides constituting the arrayed waveguide is greater than both the number of the input optical waveguides and the number of the output optical waveguides, and the optical waveguides constituting the arrayed waveguides. In at least one of the waveguides, the width of the optical waveguide changes along the light propagation direction, and the order of the input field from the input end of the arrayed waveguide at any point in the arrayed waveguide. Propagation field And the surface, so that the wave front of the back propagation is allowed fields of the output fields from the output end of the arrayed waveguide matches, characterized in that the width of the optical waveguide fluctuates.

According to a second aspect of the present invention, the optical waveguide constituting the arrayed waveguide according to the first aspect is configured to demultiplex a plurality of optical signals having different wavelengths input from the input optical waveguide according to the wavelength. Then, the width of the optical waveguide is changed so that the optical signals output from the different output optical waveguides are combined and the optical signals input from the different output optical waveguides are combined and output from the input optical waveguide. It is characterized by that.

According to a third aspect of the present invention, in the optical waveguide constituting the arrayed waveguide according to the first or second aspect , the minimum value of the optical waveguide width is 1 μm, and the interval between the adjacent optical waveguides is 1 μm or more. It is characterized by being.

The invention according to claim 5 is characterized in that the substrate according to claim 1 is either a silicon substrate or a quartz substrate, and the optical waveguide is an embedded optical waveguide made of quartz glass.

  As described above, according to the present invention, different functions can be realized with a single optical circuit element by aperiodically modulating the width of the optical waveguide constituting the arrayed waveguide according to the application. It is possible to realize a small and high-performance optical circuit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, parts having the same function are denoted by the same reference numerals, and redundant description thereof is omitted.

  In the present embodiment, the optical circuit is a silica-based optical waveguide formed on a silicon substrate or a quartz substrate. This is because such a combination can provide an optical circuit with excellent reliability. However, the present invention is not limited to such a combination. Of course, a substrate material such as a polymer or other waveguide material such as a dielectric or a semiconductor may be used.

  FIG. 2 shows the configuration of the optical circuit according to the first embodiment of the present invention. On the substrate 10, the input optical waveguide 11, the arrayed waveguide 12, and the output optical waveguide 13 are optically connected in this order. The arrayed waveguide 12 is composed of 21 optical waveguides, and the width of each optical waveguide is aperiodically modulated. That is, the width of the optical waveguide changes aperiodically along the light guiding direction. The aperiodic modulation of the width of each optical waveguide can be designed by wavefront matching methods or genetic algorithms.

  For example, when designing by the wavefront matching method, the input field is input from the input end of the arrayed waveguide 12 to which the input optical waveguide 11 is connected, and is propagated forward. On the other hand, a desired output field is input from the output end of the arrayed waveguide 12 to which the output optical waveguide 13 is connected, and propagates backward. The width of each optical waveguide of the arrayed waveguide 12 is changed so that the wavefronts of the two fields input from the input end and the output end coincide at an arbitrary point in the arrayed waveguide 12.

  On the other hand, when designing with a genetic algorithm, first, an arrayed waveguide 12 that is an initial value is provided. Next, a first generation array waveguide in which at least a part of the refractive index distribution of the array waveguide 12 is minutely changed is created. A second generation array waveguide is created by selecting and mixing array waveguides with excellent characteristics from the first generation array waveguides. Similarly, the compounding is repeated for several generations to create an arrayed waveguide that provides a given characteristic from input to output.

  By modulating the width of each optical waveguide of the arrayed waveguide 12 non-periodically, adjacent optical waveguides are sufficiently coupled and have a large wavelength dependency. Therefore, when a plurality of optical signals having different wavelengths are input from the input optical waveguide 11, the optical signals having the respective wavelengths propagate through the arrayed waveguide 12 and are output from the different output optical waveguides 13.

  Here, the non-periodic modulation of the optical waveguide width of the arrayed optical waveguide 12 is a direction perpendicular to the light propagation direction (paper surface) with respect to 1 μm of the light propagation direction (lateral direction toward the paper surface in FIG. 2). The change width in the vertical direction) is ± 0.1 μm at the maximum. This is because by prohibiting the rapid modulation of the optical waveguide width, the wavelength dependency becomes smooth, and an optical circuit with excellent reproducibility can be provided. However, the present invention is not limited to this example, and it is of course possible that there are more steep fluctuations in the optical waveguide width.

  The optical waveguide width of the arrayed waveguide 12 is a minimum of 1 μm. This is because an optical circuit that can be easily manufactured can be realized under such conditions. However, the present invention is not limited to this example, and the minimum value of the optical waveguide width may of course be 0.1 μm. The maximum value of the optical waveguide width of the arrayed waveguide 12 is 3 μm. However, this value may of course be 20 μm.

  The interval between adjacent optical waveguides of the arrayed waveguide 12 is 1 μm at the minimum. This is because an optical circuit that can be easily manufactured can be realized under such conditions. However, the present invention is not limited to this example, and the adjacent optical waveguides may of course be at least 0.5 μm. On the other hand, the distance between adjacent optical waveguides of the arrayed waveguide 12 is 3 μm at the maximum. However, the present invention is not limited to this example, and of course, a maximum of 20 μm may be used. However, in order to sufficiently combine adjacent optical waveguides and realize a large wavelength dependence, it is desirable that the maximum is about 10 μm.

  The optical circuit of the first embodiment is manufactured by a quartz optical waveguide formed on a silicon substrate. However, the present invention is not limited to this example, and it may be formed on a quartz substrate, and may of course be a dielectric optical waveguide or a polymer optical waveguide instead of a silica-based optical waveguide.

  FIG. 3 is a sectional view of an optical circuit according to the first embodiment of the present invention. A lower clad 21 is deposited on the substrate 10 by a flame deposition method, and a core layer is deposited on the lower clad 21 by a flame deposition method to make it transparent. A mask is formed on the core layer so as to be the array optical waveguide 12 shown in FIG. 2, and the core layer is patterned by reactive ion etching to form the core 22. Finally, the upper clad 23 is deposited by a flame deposition method so as to cover the lower clad 21 and the core 22 and is made transparent. The refractive index of the lower cladding 21 and the upper cladding 23 is 1.4443, and the refractive index of the core 22 is 1.4552.

  The substrate 10 is a silicon substrate, and the lower clad 21, the core 22, and the upper clad 23 are configured as a silica-based optical waveguide. The quartz optical waveguide can provide an optical circuit with excellent reliability. Note that the present invention is not limited to this example, and other materials such as a dielectric and a semiconductor may be used as a matter of course, or a ridge type optical waveguide structure without an upper clad may be used.

  FIG. 4 shows the transmittance of the optical circuit according to the first embodiment of the present invention. An optical signal in which four different wavelengths included in the 1.55 μm band are combined is input from the input optical waveguide 11 to the arrayed waveguide 12. An optical signal having a wavelength of 1.52 μm is output from the output optical waveguide 13a, an optical signal having a wavelength of 1.54 μm is output from the output optical waveguide 13b, and an optical signal having a wavelength of 1.56 μm is output from the output optical waveguide 13c. It can be seen that an optical signal of .58 μm is output from the output optical waveguide 13d. Thus, if the optical circuit according to the first embodiment is used, an arbitrary wavelength can be selected and output from an arbitrary output optical waveguide.

  FIG. 5 shows a modification of the optical circuit according to the first embodiment of the present invention. The arrayed waveguide 12 shown in FIG. 3 is rectangular, but may be an arrayed waveguide 14 having a polygonal shape as shown in FIG. Moreover, even if it is a rectangle, an optical circuit can also be comprised by different length and width.

  FIG. 6 shows a configuration of an optical circuit according to the second embodiment of the present invention. On the substrate 10, the input optical waveguide 11, the arrayed waveguide 15, and the output optical waveguide 13 are optically connected in this order. The arrayed waveguide 15 is composed of nine optical waveguides, and the width of each optical waveguide is aperiodically modulated. The non-periodic modulation of the width of each optical waveguide can be designed by a wavefront matching method or a genetic algorithm as in the first embodiment.

  The optical circuit of the second embodiment is manufactured by a silica-based optical waveguide formed on a quartz substrate. However, the present invention is not limited to this example, and may be formed on a silicon substrate, and may of course be a dielectric optical waveguide or a polymer optical waveguide instead of a silica-based optical waveguide. .

  FIG. 7 shows the transmittance of the optical circuit according to the second embodiment of the present invention. It can be seen that 90% of the optical signal input to the input optical waveguide 11 is output from the output optical waveguide 13b and 10% is output from the output optical waveguide 13a to constitute a branch circuit. As described above, when the optical circuit of the second embodiment is used, not only an optical circuit having wavelength dependency but also an optical circuit having small wavelength dependency can be provided. That is, as in the first embodiment, optical circuits having various functions can be converted into a single optical circuit element by aperiodically modulating the width of the optical waveguides constituting the arrayed waveguide according to the application. Can be realized.

  FIG. 8 shows a first modification of the optical circuit according to the second embodiment of the present invention. In the optical circuit of the first modification of the second embodiment, the arrayed waveguide 16 is composed of seven optical waveguides, and the waveguide width of one of the waveguides 16a is not modulated. Even in such a configuration, the waveguide 16a and the adjacent optical waveguide can be coupled to each other because the width of the optical waveguide adjacent to the waveguide 16a is aperiodically modulated. Therefore, similarly to the optical circuit shown in FIG. 6, it is possible to configure a branch circuit having a small wavelength dependency.

  FIG. 9 shows a second modification of the optical circuit according to the second embodiment of the present invention. In the optical circuit of the second modification, the arrayed waveguide 18 is composed of three optical waveguides, and only one of the waveguides 18a is aperiodically modulated. Even in such a configuration, the waveguide 18a and the adjacent optical waveguide can be coupled by asymmetrically modulating the width of the waveguide 18a. Therefore, similarly to the optical circuit shown in FIG. 6, it is possible to configure a branch circuit having a small wavelength dependency.

  FIG. 10 shows a configuration of an optical circuit according to the third embodiment of the present invention. On the substrate 10, two input optical waveguides 11, an arrayed waveguide 17, and two output optical waveguides 13 are optically connected in this order. The arrayed waveguide 17 is composed of 17 optical waveguides, and the width of each optical waveguide is aperiodically modulated. Such a configuration is also within the scope of the present invention and has the same effect. The non-periodic modulation of the width of each optical waveguide can be designed by a wavefront matching method or a genetic algorithm as in the first embodiment.

  FIG. 11 is a cross-sectional view of an optical circuit according to the third embodiment of the present invention. A lower clad 21 is deposited on the substrate 10 by a flame deposition method, and a core layer is deposited on the lower clad 21 by a flame deposition method to make it transparent. A mask is formed on the core layer so as to be the array optical waveguide 17 shown in FIG. 10, and the core layer is patterned by reactive ion etching to form the core 22. Next, the second core 24 is deposited to the same height as the core 22 to make it transparent. Finally, the upper clad 23 is deposited by a flame deposition method so as to cover the core 22 and the second core 24 to be transparent.

  The refractive index of the lower cladding 21 and the upper cladding 23 is 1.4443, the refractive index of the core 22 is 1.4552, and the refractive index of the second core 24 is 1.4491. By providing the second core 24, scattered light can be reduced and deterioration of transmission loss of the optical circuit can be prevented. However, the present invention is not limited to this example, and a configuration excluding the second core 24 may of course be used.

  FIG. 12 shows the transmittance of the optical circuit according to the third embodiment of the present invention. Of the optical signals input to one of the input optical waveguides 11, optical signals having a wavelength of 1.52 μm and a wavelength of 1.58 μm are output from the output optical waveguide 13 a, and have a wavelength of 1.54 μm and a wavelength of 1.56 μm. It can be seen that the optical signal is output from the output optical waveguide 13b. As described above, when the optical circuit according to the third embodiment is used, an arbitrary plurality of wavelengths can be selected and output from an arbitrary output optical waveguide.

  A small and high-performance optical circuit having various characteristics can be configured. In particular, the present invention can be applied to an optical filter for multiplexing / demultiplexing optical signals having a plurality of wavelengths and a branch circuit having no wavelength dependence.

It is a perspective view which shows the structure of the conventional array waveguide grating filter. It is a top view which shows the structure of the optical circuit concerning the 1st Embodiment of this invention. It is sectional drawing which shows the optical circuit concerning the 1st Embodiment of this invention. It is a figure which shows the transmittance | permeability of the optical circuit concerning the 1st Embodiment of this invention. It is a top view which shows the modification of the optical circuit concerning the 1st Embodiment of this invention. It is a top view which shows the structure of the optical circuit concerning the 2nd Embodiment of this invention. It is a figure which shows the transmittance | permeability of the optical circuit concerning the 2nd Embodiment of this invention. It is a top view which shows the 1st modification of the optical circuit concerning the 2nd Embodiment of this invention. It is a top view which shows the 2nd modification of the optical circuit concerning the 2nd Embodiment of this invention. It is a top view which shows the structure of the optical circuit concerning the 3rd Embodiment of this invention. It is sectional drawing which shows the optical circuit concerning the 3rd Embodiment of this invention. It is a figure which shows the transmittance | permeability of the optical circuit concerning the 3rd Embodiment of this invention.

Explanation of symbols

100, 10 Substrate 101, 11 Input optical waveguide 102, 104 Slab optical waveguide 103, 12-18 Array waveguide 105, 13 Output optical waveguide

Claims (4)

At least one input optical waveguide formed on the substrate;
At least one output optical waveguide formed on the substrate;
An array in which two or more optical waveguides are arranged in parallel along the optical signal propagation direction between the input optical waveguide and the output optical waveguide, and are optically coupled between adjacent optical waveguides. A waveguide,
The number of optical waveguides constituting the arrayed waveguide is greater than both the number of input optical waveguides and the number of output optical waveguides,
In at least one of the optical waveguides constituting the arrayed waveguide, the width of the optical waveguide changes along the light propagation direction, and at any point in the arrayed waveguide, The width of the optical waveguide varies so that the wavefront of the forward propagation field of the input field from the input end coincides with the wavefront of the backpropagated field of the output field from the output end of the arrayed waveguide. An optical circuit characterized by that.   The optical waveguides that constitute the arrayed waveguides are demultiplexed according to the wavelength and output from different output optical waveguides depending on the wavelength, and differ according to the wavelength. 2. The optical circuit according to claim 1, wherein the width of the optical waveguide is changed so that optical signals input from the output optical waveguide are combined and output from the input optical waveguide.   3. The optical circuit according to claim 1, wherein the optical waveguide constituting the arrayed waveguide has a minimum optical waveguide width of 1 μm, and an interval between adjacent optical waveguides is 1 μm or more.   2. The optical circuit according to claim 1, wherein the substrate is one of a silicon substrate and a quartz substrate, and the optical waveguide is a buried optical waveguide made of quartz glass.

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