JP2011123272A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device the collected light intensity of which is increased to improve an SNR (signal-noise ratio), and to achieve a high-speed response and in which crosstalk between channels can be reduced when optical wiring work is performed in parallel. <P>SOLUTION: Each of a first multilayer film 11 and a second multilayer film 12 has a structure including: a cyclic structure formed by repeatedly layering specific pattern layers P each of which comprises a high refractive index layer 15 and a low refractive index layer 16 on each other in such a cycle that the wavelength of incident light has photonic band characteristics near the edge of a low refractive index band; and an auxiliary low refractive index layer 17 layered further at the edge side of the low refractive index layer 16 of the cyclic structure. A metallic film 13 has a plurality of openings 14 arranged in a regular pattern satisfying a super-oscillation condition and is inserted between the auxiliary low refractive index layer 17 of the first multilayer film 11 and the auxiliary low refractive index layer 17 of the second multilayer film 12 at such a position that the light quantity distributed to the optical axis direction of the incident light does not become the maximum. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical device capable of condensing to a spot diameter equal to or smaller than the light wavelength through an air gap, and more specifically, a nano-order necessary for high-speed response in a photoelectric conversion part of a parallel optical wiring of an optical integrated circuit. The present invention relates to an optical device that can reduce crosstalk between channels while using a focused beam diameter.

  With the development of high-speed information communication infrastructure in recent years, digital-related devices that calculate, store, and display a large amount of data are rapidly developing. In order to handle this large amount of data, it is required to increase the speed of signal transmission and the density of signal wiring in information transmission over a relatively short distance such as between boards in an electronic device or between chips on a board. However, wiring using electrical signals has problems such as signal delay and noise generation due to wiring time constants, and there is a limit to increasing the transmission speed and increasing the wiring density.

  In order to solve such problems, attention has been paid to optical wiring using optical signals. The optical wiring is an optical transmission path used for transmitting an optical signal, and is typically an optical waveguide. For example, when a signal is transmitted over a short distance from a first chip mounted on a substrate to a second chip, an optical wiring is formed by an optical waveguide between the first chip and the second chip. The electrical signal output from the first chip is modulated into laser light and propagates through the optical waveguide, and then demodulated again into an electrical signal and output to the second chip.

  The optical wiring is required to be fine and integrated, and the line width of the optical wiring, the distance between the lines, and the distance between the waveguide and the light receiving element are approximately several hundred nm to several tens of μm. For this reason, a butt joint that joins an optical waveguide and a light receiving element without using a refractive lens has become the mainstream because it is expensive to manufacture and mount an adaptable microlens.

  However, in the butt joint, since the light incident on the light receiving element from the optical waveguide becomes diffused light, the beam diameter at the light receiving part is increased and the response speed of the light receiving element is decreased. Also, in parallel optical wiring in which a plurality of optical wirings (channels) are arranged in parallel, diffused light from the optical waveguide of one channel is received by the light receiving element of another channel, which causes a problem of crosstalk between channels. It has become.

In order to make the light receiving element respond at a high speed at 10 Gbps or more, it is necessary to make the light receiving diameter nano-order less than the wavelength. In order to realize this, various optical configurations exceeding the diffraction limit have been proposed. As one of them, it is arranged near the opening of the metal film using near-field light that oozes from the opening when light is incident on the metal film having an opening sufficiently smaller than the wavelength λ of the light. A configuration has been proposed in which a spot diameter of a wavelength not exceeding the diffraction limit is formed in the light receiving portion of the light receiving element.
However, this configuration has a problem that since the aperture is very small, the amount of light received by the light receiving portion is small and the signal-to-noise ratio (SNR) is poor.

Therefore, by providing a surface periodic structure around the opening on the metal film and resonating incident light on the metal film and plasmon through this periodic structure, an evanescent wave with a spot diameter of less than the wavelength from the opening is generated. There is a technique for resolving the shortage of light quantity by increasing the intensity (see, for example, Patent Document 1).
However, since the near-field light has a property of rapidly decaying as the distance from the opening increases, the distance between the opening and the light-receiving portion is about λ / 4 or less, no matter how much the intensity of the near-field light is increased. It will be limited to. On the other hand, since a butt joint of several μm or more is formed between the optical waveguide and the metal film-like opening, in the case of multi-channel parallel optical wiring, diffused light from the optical waveguide of other channels is on the metal film. Cross talk is inevitable because it reaches the opening.

As a method of solving the problem of crosstalk at the time of multi-channel in the light receiving system using this near-field light, using wavelength multiplexed light, a plurality of openings corresponding to each wavelength provided on the surface of the metal film, There is a technique of having a periodic structure with a different period corresponding to each wavelength concentrically around each opening, and converting each wavelength into a surface plasmon and receiving light by an electrically separated light receiving unit (for example, , See Patent Document 2).
However, in order to make the wavelength multiplexed light transmitted through the same waveguide and irradiated at the same position on the metal film efficiently enter the plurality of openings, it is necessary to make the interval between the plurality of openings very small. is there. For this reason, the periodic structure corresponding to each wavelength concentrically around each opening intersects with the periodic structure of other wavelengths in a complex manner. Due to the increase in complex crossing of the concentric periodic structures corresponding to plasmons, plasmons excited at different wavelengths are combined to cause crosstalk.

  On the other hand, many methods for obtaining a nano-order focused spot diameter below the wavelength without using near-field light have been reported.

First, in 2000, a perfect lens effect capable of condensing a point light source to a complete point light source without being subjected to the conventional diffraction limit due to the amplification action of the evanescent wave was theoretically proved (Non-Patent Document 1). reference). Therefore, if the negative refraction material having the perfect lens effect is used as a lens, not only the incident light from the optical waveguide can be condensed to a nano-order light receiving diameter of a wavelength or less, but also a multi-channel parallel optical wiring. Incident light from each channel waveguide can be condensed on the light receiving element of each channel without crosstalk.
However, at present, there is no technology capable of industrially producing a negative refraction material having a perfect lens effect, so that it is difficult to realize.

Conventionally, the use of evanescent light was considered to be indispensable for obtaining a resolution below the wavelength as described above. However, in 2006, if super oscillation is used, the propagating light can be used without using evanescent light. It was theoretically proved that a resolution of a wavelength or less can be obtained by using only (see Non-Patent Document 2). Based on this result, a nanohole pattern (Penrose pattern) that satisfies the super oscillation condition is provided on the metal film, and the self-imaging position of the Talbot effect due to interference of diffracted light (Talbot Distance = 2a ² / λ (a: minimum between nanoholes There is a report that realizes condensing light with a spot diameter equal to or smaller than the wavelength (distance, λ: wavelength) (see Non-Patent Document 3). This optical super-oscillation is composed of propagating light with a spatial frequency smaller than the frequency of the light source, so in principle it is larger than when evanescent light is used between the aperture and the light receiving part. An air gap can be realized.

International Publication No. 2005/029164 Pamphlet (Fig. 1) JP 2009-8724 A (FIG. 1) Japanese Patent Laid-Open No. 60-10585 (FIG. 1) Japanese Patent Laid-Open No. 2001-110635 (FIG. 2)

JBPendry, “Negative Refraction Makes a Perfect Lens”, Physical Review Letters, Vol. 85, No. 18, 2000, 3966-3969 MVBerry and S. Popescu, “Evolution of Quantum Super Oscillations and Optical Super Resolution and Without Evanescent Waves” quantum superoscillations and optical superresolution without evanescent waves), Journal of Physics A: Mathematical and General, Vol. 39, 2006, 6965-6777. Fu.Min.Huang, Tsun.Sheng.Kao, Vassili.A.Fedotov, Yifang.Chen, and Nikolay I. Zheludev, “Nanohole Array as a Lens”, Nano Letters, Vol. 8, No. 8, 2008 2469-2472, FIG.

  The technique described in Non-Patent Document 3 has an effect of reducing crosstalk while realizing a nano-order condensing diameter equal to or less than the wavelength as in a perfect lens. However, unlike the perfect lens, focusing by self-imaging of the Talbot effect has a large transmission loss in the metal film and diffusion in free space, so that the optical characteristics change with the distance from the central axis (optical axis). Compared with the collection of propagating light by the bulk type lens, the energy efficiency is poor. For example, in Non-Patent Document 3, it is reported that light is condensed to a beam diameter below a wavelength at a position of about 11 μm from the metal film at a = 1200 nm and λ = 660 nm. There is a problem that the SNR deteriorates and the high-speed response cannot be made.

  Therefore, as a technique different from the method for enhancing the surface plasmon of the metal described in Patent Documents 1 and 2, a layered light-emitting source semiconductor or a dielectric of a Faraday element has a refractive index period of about a half wavelength in the optical axis direction. There is a method in which a resonator is formed by sandwiching a multilayer film having a structure to enhance the interaction between electrons and photons inside a semiconductor layer or a dielectric layer (see, for example, Patent Documents 3 and 4).

  In this method, as shown in FIG. 8, the first multilayer film 110 in which the high refractive index layer 15 and the low refractive index layer 16 are repeatedly laminated, and the high refractive index layer 15 and the low refractive index layer 16 are similarly formed. A structure in which the semiconductor layer / dielectric layer 200 is sandwiched between the second multilayer film 120 repeatedly stacked is used. 9 is used to resonate inside the semiconductor layer / dielectric layer 200 using the photonic band gap portion of the photonic band characteristics (dispersion characteristics) of the multilayer film having the refractive index periodic structure shown in FIG. The maximum portion of the large amount of light is formed, and an output having a large Q value and a large Faraday rotation angle are obtained in the optical axis direction z.

  It is conceivable to combine the resonance structures described in Patent Documents 3 and 4 with the technique described in Non-Patent Document 3. However, even if these are combined to form a maximum amount of light at the position of the metal film, the metal cannot transmit (reflect) light frequencies above the plasma frequency. For this reason, even if the amount of light is maximized at the position of the metal film, only the transmission loss (reflection amount) increases, which is counterproductive.

  Therefore, it is an object of the present invention to improve the SNR by increasing the concentration of light and to realize a high-speed response in a light receiving system of an optical wiring that uses light of a wavelength or less by propagating light that satisfies the super oscillation condition. Is to provide a device. It is another object of the present invention to provide an optical device that can reduce crosstalk between channels during parallel optical wiring.

  The present invention is directed to an optical device that collects incident light. In order to achieve the above object, an optical device of the present invention includes a first periodic structure whose refractive index periodically changes in the optical axis direction of incident light, the same refractive index as the first periodic structure, and A second periodic structure whose refractive index changes periodically in the optical axis direction of the incident light, and a transparent portion that is provided between the first periodic structure and the second periodic structure and transmits light; And having a film. The first periodic structure body and the second periodic structure body have a refractive index that changes with a period having a photonic band characteristic near the edge of the low refractive index band with respect to the wavelength of the incident light. The film is disposed at a position where the light quantity does not become maximum with respect to the change in the light quantity distribution in the optical axis direction that appears between the first periodic structure and the second periodic structure.

  The first and second periodic structures are multilayer films in which a high refractive index layer and a low refractive index layer are repeatedly stacked. The film is provided between the low-refractive index layer at the end of the first periodic structure and the low-refractive index layer at the end of the second periodic structure, and is disposed at a position where the light amount is minimized with respect to the light amount distribution change. Is preferred. In addition, the second refractive index layer has a refractive index equal to or lower than that of the low refractive index layer between the low refractive index layer and the film at the end of the first periodic structure and between the low refractive index layer and the film at the end of the second periodic structure. The first and second auxiliary low refractive index layers may be further provided.

  Typically, the total film of the low refractive index layer at the end of the first periodic structure, the first auxiliary low refractive index layer, the film, the second auxiliary low refractive index layer, and the low refractive index layer at the end of the second periodic structure The thickness is designed to be 1.2 to 2.4 times the period in which the refractive indexes of the first and second periodic structures change. In addition, it is desirable that the film thickness of the first auxiliary low refractive index layer is equal to the film thickness of the second auxiliary low refractive index layer. Moreover, the period in which the refractive index of the first and second periodic structures changes is designed to be 0.4 to 0.8 times the wavelength of the incident light.

  The film is a metal film having a film thickness equal to or less than the wavelength of incident light, and the transparent portion is an opening that penetrates the metal film. If a plurality of openings are provided on the metal film in a regular pattern that satisfies the super-oscillation condition, the optical device can be positioned at the self-imaging position of the Talbot effect due to interference of diffracted light output from the metal film. It has a light quantity distribution with which a condensed diameter equal to or smaller than the wavelength of incident light can be obtained. Here, examples of the shape of the plurality of openings provided on the metal film include a rotationally symmetric shape having no periodicity around the optical axis of incident light, such as a Penrose pattern shape.

  Furthermore, the optical device of the present invention may further include an optical waveguide that outputs incident light to the first periodic structure, and a photoelectric conversion element that includes a light receiving unit that receives light output from the second periodic structure. it can. The light receiving unit is desirably provided at the first self-imaging position. In addition, when outputting a plurality of incident light from a plurality of cores provided with optical waveguides in parallel, a plurality of light receiving units provided in parallel corresponding to the plurality of incident lights are provided in the photoelectric conversion element, The corresponding light output from the second periodic structure may be received. Note that the first periodic structure, the film, and the second periodic structure may have a single configuration.

  According to the present invention, since the light collection intensity can be increased, the SNR of the light receiving element in the optical wiring can be improved and a high-speed response can be realized. Further, according to the present invention, crosstalk between channels can be reduced during parallel optical wiring.

The figure explaining the structure of the optical device 1 which concerns on the 1st Embodiment of this invention. Cross-sectional view of optical device 1 and light quantity distribution by controlling photonic band characteristics Outline diagram of simulation results in the vicinity of the metal film position of the optical device 1 Outline diagram of simulation results in the vicinity of the metal film position of the optical device 1 Outline diagram of simulation results in the vicinity of the condensing position of the optical device 1 The figure explaining the structure of the optical device 2 which concerns on the 2nd Embodiment of this invention. The figure explaining the structure of the optical device 3 which concerns on the 3rd Embodiment of this invention. Cross-sectional view of structure of conventional optical device 1 and light amount distribution by photonic band characteristic control The figure explaining the photonic band characteristic of the multilayer film which has the periodic structure of refractive index

Embodiments of the present invention will be specifically described below with reference to the drawings.
<First Embodiment>
FIG. 1 is a view for explaining the structure of an optical device 1 according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view of the optical device 1 shown in FIG. 1 viewed from the A direction on a plane including the optical axis 32 of the light emitted from the light source 31, and the light quantity distribution by photonic band characteristic control. FIG.

First, the detailed structure of the optical device 1 according to the first embodiment will be described.
The optical device 1 of the present invention has a structure in which a metal film 13 is sandwiched between a first multilayer film 11 and a second multilayer film 12. The first multilayer film 11 includes a periodic structure in which a specific pattern layer P composed of a high refractive index layer 15 and a low refractive index layer 16 is repeatedly laminated twice or more (that is, the refractive index changes periodically) The periodic structure has a structure including an auxiliary low refractive index layer 17 further laminated on the end side of the low refractive index layer 16. Similarly, the second multilayer film 12 is a cycle in which the specific pattern layer P composed of the high refractive index layer 15 and the low refractive index layer 16 is repeatedly laminated twice or more (that is, the refractive index changes periodically). The structure includes a structure and an auxiliary low refractive index layer 17 further laminated on the end side of the low refractive index layer 16 of the periodic structure. The refractive index of the auxiliary low refractive index layer 17 should just be the low refractive index layer 16 or less. The metal film 13 has a plurality of openings 14 (outlined portions in FIG. 2) that are regularly distributed. The metal film 13 is sandwiched between the auxiliary low refractive index layer 17 of the first multilayer film 11 and the auxiliary low refractive index layer 17 of the second multilayer film 12.

  The specific pattern layer P of the first multilayer film 11 and the second multilayer film 12 is typically set to a thickness of 0.4 to 0.8 times the wavelength of incident light. The metal film 13 is made of a metal material such as aluminum (Al), gold (Au), silver (Ag), or copper (Cu), and the thickness of the metal film 13 is preferably less than the wavelength of incident light. . Further, the distribution used for the plurality of openings 14 of the metal film 13 has regularity (rotationally symmetric) but no periodicity, such as the Penrose pattern shown in FIG. . Further, in the first multilayer film 11, the film thickness of the output-end low refractive index layer 18, which is the combination of the auxiliary low refractive index layer 17 and the low refractive index layer 16 adjacent thereto, and the auxiliary multilayer low refractive index in the second multilayer film 12. The film thickness of the input-end low-refractive-index layer 19 including the layer 17 and the adjacent low-refractive-index layer 16 is equal, and the output-end low-refractive-index layer 18, the input-end low-refractive-index layer 19, and the metal film 13 It is desirable that the film thickness of the optical path length L consisting of is 1.2 to 2.4 times that of the specific pattern layer P.

  Next, in the optical device 1 having the above structure, the amount of each diffracted light output from the plurality of openings 14 distributed in the Penrose pattern of the metal film 13 is increased, and the amount of light collected by interference is increased. The mechanism will be described with reference to FIGS. 3 to 5 and FIG. 9. The case where the optical axis 32 of the light emitted from the light source 31 intersects the high refractive index layer 15 of the first multilayer film 11 of the optical device 1 perpendicularly will be described.

  First, the light quantity distribution in the optical axis direction z by a multilayer film (one-dimensional photonic crystal) in which a high refractive index layer and a low refractive index layer are periodically stacked in the optical axis direction z will be described. FIG. 9 is a diagram for explaining the outline of the light amount distribution by the photonic band control as described in the background art.

  In general, as shown in FIG. 9, the photonic band characteristics of the traveling wave of the multilayer film in which the refractive index layer periodically changes are in a region where the period a is less than a half wavelength (0 ≦ ka / 2π ≦ 0.5). ), As the wave number k (horizontal axis) increases in the optical axis direction z, the frequency ω (vertical axis) increases monotonously from the origin, and becomes a high refractive index band 23 saturated at ka / 2π = 0.5. Further, in the region where the period a is a half wavelength or more (ka / 2π ≧ 0.5), the frequency discontinuity region at ka / 2π = 0.5 (in accordance with the increase of the wave number k (horizontal axis) in the optical axis direction z ( From the discontinuous point that has passed through the photonic band gap 22, the frequency ω (vertical axis) monotonously increases and becomes a low refractive index band 24 that is saturated again with ka / 2π = 1. However, since FIG. 9 uses a representation in which the photonic band characteristics are reduced to the first Brillouin zone (−0.5 ≦ ka / 2π ≦ 0.5), a region having a half wavelength or more (ka / 2π ≧ 0). .5) is expressed by a parallel translation of the wave number k by −2π (ka / 2π is −1).

  This photonic band characteristic shows that the localization of light is remarkable at the band edge where the period a of the multilayer film is near the half wavelength, and the light is highly refracted at the high refractive index band edge 25 where the period a is slightly smaller than the half wavelength. In contrast to the locality on the refractive index layer side (maximum in the high refractive index layer and minimum in the low refractive index layer), light is refracted at the low refractive index band edge 26 where the period a is slightly larger than a half wavelength. It is known that it is localized on the refractive index side (minimum in the high refractive index layer and maximum in the low refractive index layer).

  By using such a photonic band, the specific pattern layer P of the first multilayer film 11 and the second multilayer film 12 is set to 0.4 to 0.8 times the light wavelength as shown in FIG. The photonic band characteristic of the low refractive index band edge 26 is given, the light is localized in the low refractive index layer 16 of the first multilayer film 11 and the second multilayer film 12, and the low refractive index at the output edge of the first multilayer film 11 is obtained. The amount of light is maximized by the layer 18 and the input end low refractive index layer 19 of the second multilayer film 12. As a result, at least one light amount minimum portion is formed between the light amount maximum portion of the output end low refractive index layer 18 and the light amount maximum portion of the input end low refractive index layer 19. In particular, the film thickness of the low refractive index layer 18 at the output end and the low refractive index layer 19 at the input end are equal, and the film thickness of the optical path length L is 1.2 to 2.4 times that of the specific pattern layer P of the first multilayer film 11. In this case, there is only one minimum amount of light at the position of the metal film 13. In addition, when there are a plurality of light intensity minimum portions, the metal film 13 may be disposed at any light intensity minimum position.

  Next, the relationship between the multilayer film structure and the light amount distribution will be described. As shown in the simulation results of FIG. 3 (near metal film position: with metal film), FIG. 4 (near metal film position: without metal film), and FIG. If it is arranged on 32, the localization of light by the multilayer film and the intensity at the condensing position can be evaluated by the light quantity distribution on the optical axis 32. 3 and 4, the periodic structure of the high refractive index layer 15 and the low refractive index layer 16 in the first multilayer film 11 and the second multilayer film 12 is shown.

First, the light quantity distribution in the structure in which the metal film 13 is arranged at the position where the light quantity is minimal as in this embodiment will be described. The constants used for the simulation are as follows: the wavelength of the point light source that is incident light is 660 nm, the thickness of the specific pattern layer P of the first multilayer film 11 and the second multilayer film 12 is 330 nm (0.5 times the light wavelength), The repetition of the pattern layer P is 3 periods, the refractive index of the high refractive index layer 15 is 1.5, the refractive index of the low refractive index layer 16 is 1.0, the film thickness of the aluminum metal film 13 is 100 nm, and the output end low refractive index. The film thickness of the refractive index layer 18 and the input end low refractive index layer 19 is 247.5 nm (the film thickness of the optical path length L is about 1.8 times that of the specific pattern layer P).
The light intensity distribution in the vicinity of the metal film 13 (thick solid line in FIG. 3 and FIG. 4) and the light intensity distribution in the vicinity of the condensing position (thick solid line in FIG. 5), although the absolute intensity changes before and after the metal film 13, The maximum / minimum position does not change with or without the metal film 13. For this reason, the intensity of radiated light from the opening 14 immediately after the metal film 13 is made stronger than the conventional one (only the metal film, thin solid line in FIG. 5), and is about 2.0 times that of the conventional one at the far-field condensing position. It turns out that strong condensing intensity is obtained.

On the other hand, the light quantity distribution in the structure in which the metal film 13 is arranged at the position where the light quantity is maximum as in the prior art will be described. The constant used for the simulation is that the film thickness of the output end low refractive index layer 18 and the input end low refractive index layer 19 is 82.5 nm (the film thickness of the optical path length L is about 0.8 times that of the specific pattern layer P). The others are as described above.
The light quantity distribution in the vicinity of the metal film 13 (dotted line in FIGS. 3 and 4) and the light quantity distribution in the vicinity of the condensing position (dotted line in FIG. 5) are mostly obtained by the metal film 13 disposed at the light quantity maximum position. Since the light is reflected, the position of the metal film 13 is minimized. For this reason, it can be seen that the intensity of radiated light from the opening 14 immediately after the metal film 13 is weaker than before, and the intensity is reduced to a level at which far-field condensing can no longer be confirmed.

  In this way, most of the incident light is reflected on the metal film 13 and the amount of light suddenly decreases. Therefore, if the light amount is not maximized at the position of the metal film 13 and is distributed so that the light amount is maximized before and after the metal film 13, the opening 14 of the metal film 13 that is a source of light collection due to the interference of diffracted light is used. The output, that is, the output immediately after the metal film 13 can be enhanced.

  In FIG. 3, the change in the light amount distribution in the vicinity of the metal film 13 in the first multilayer film 11 is shifted from the period of the high / low refractive index layer. This is because the spherical wave (concentric phase change) emitted from the point light source is changed to a plane wave in the optical axis direction z (phase change in the optical axis direction z) by the first multilayer film 11.

  As described above, according to the optical device 1 according to the first embodiment of the present invention, the refractive index changes at a period that gives the photonic band characteristics near the low refractive index band edge 26 with respect to the wavelength of the incident light. The metal film 13 is disposed between the first multilayer film 11 and the second multilayer film 12 to be aligned so that the minimum position of the light amount distribution is aligned on the metal film 13. As a result, the light collection intensity by the metal film 13 can be increased, so that the SNR of the light receiving element in the optical wiring can be improved and a high-speed response can be realized.

<Second Embodiment>
FIG. 6 is a diagram illustrating the structure of the optical device 2 according to the second embodiment of the present invention. The optical device 2 according to the second embodiment shows a specific optical device structure using the optical device 1 according to the first embodiment. FIG. 6 is a cross-sectional view of the horizontal cross section of the plane including the optical axis 32 of the incident light viewed from the A direction, as in FIG.

  The optical device 2 includes an optical waveguide 43, the optical device 1, and a photoelectric conversion element 58. The optical waveguide 43 includes a core 41 and a clad 42, and outputs the light propagating through the core 41 to the optical device 1 as incident light from the light source 31. The photoelectric conversion element 58 is a PN connection type semiconductor composed of an insulating light shielding layer 52, an anode 53 made of a conductive transparent electrode, a P layer 54 that is a light receiving portion, a depletion layer 55, an N layer 56, and a cathode 57. . The central axis of the photoelectric conversion element 58 coincides with the optical axis 32 of the optical waveguide 43. The distance between the optical device 1 and the photoelectric conversion element 58 is set so that the P layer 54 is disposed at a position where the light output from the optical device 1 first forms self-imaging. The optical device 1 and the photoelectric conversion element 58 are covered with a light shielding portion 51 and block outside light other than light passing through the metal film 13.

  As described above, according to the optical device 2 according to the second embodiment of the present invention, in addition to the effects described in the first embodiment, incident light is effectively collected in the P layer 54 that is a light receiving portion. Can be lighted.

  The configuration for making light incident on the optical device 1 is not limited to the optical waveguide 43 described above, and may be an optical fiber or the like. If the light emitting end of the optical waveguide 43 is replaced with an object and the P layer 54 is replaced with an imaging unit such as a CCD, and reflected light from the object is received by the imaging unit using external light such as illumination, the wavelength or less is obtained. The subject image can be taken with a resolution of. Further, when the light quantity from the optical waveguide 43 is increased and the P layer 54 is replaced with an object, the object can be processed with an accuracy less than the wavelength due to a light collection effect less than the wavelength. Further, the P layer 54 is replaced with an optical memory unit such as an optical disk for recording optical information, and the incident light from the light source 31 such as the optical waveguide 43 is guided to the metal film 13 and the reflected light from the optical memory unit other than the light source 31 is used. An optical pickup capable of recording / reading optical information with a spot diameter less than a wavelength on an optical disk is realized by providing a light separating part such as a hologram that guides light to the light source and a light receiving part that receives reflected light guided to other than the light source 31. it can.

<Third Embodiment>
FIG. 7 is a diagram illustrating the structure of the optical device 3 according to the third embodiment of the present invention. The optical device 3 according to the third embodiment shows an optical device structure in which a plurality of optical devices 2 according to the second embodiment are arranged. FIG. 7 is also a diagram showing a cross-sectional view of the horizontal cross section in the plane including the optical axis 32 of the incident light as seen from the A direction, similarly to FIG.

  The optical device 3 includes a parallel optical waveguide 44, the optical device 1, and a parallel photoelectric conversion element 59. The parallel optical waveguide 44 includes a plurality of cores 41 and a plurality of clads 42, and outputs a plurality of lights propagating through the plurality of cores 41 to the optical device 1 as incident light from the plurality of light sources 31. The optical device 1 has an area capable of simultaneously receiving incident light from the plurality of cores 41. The parallel photoelectric conversion element 59 includes a plurality of insulating light shielding layers 52, a plurality of anodes 53, a plurality of P layers 54, a plurality of depletion layers 55, a plurality of N layers 56, a plurality of cathodes 57, and a plurality of block layers 60. PN connection type parallel semiconductor. The central axis of each P layer 54 of the parallel photoelectric conversion element 59 coincides with each optical axis 32 of the parallel optical waveguide 44. The distance between the optical device 1 and the parallel photoelectric conversion element 59 is set such that a plurality of P layers 54 are respectively arranged at positions where a plurality of lights output from the optical device 1 first form self-imaging. The optical device 1 and the parallel photoelectric conversion element 59 are covered with a light shielding portion 51 to block outside light other than light passing through the metal film 13. The plurality of block layers 60 are inserted in order to prevent leakage current between the plurality of N layers 56.

  In the optical device 3 configured as described above, a mechanism capable of reducing crosstalk between the parallel optical waveguide 44 and the plurality of P layers 54 is a parallel optical wiring in which the intervals between the plurality of cores 41 (a plurality of channels) are several tens of μm or less. Will be described as an example.

  First, as described in the first embodiment, the light intensity of the plurality of lights incident from the plurality of cores 41 is enhanced for each channel. Between different channels of parallel optical wiring with a channel interval of several tens of μm or less, incident light of all channels is diffused on the metal film 13 by diffraction between the parallel optical waveguide 44 and the metal film 13. Since each incident light is condensed on each channel by the openings 14 regularly distributed on the top, the incident light of other channels is not condensed.

  As described above, according to the optical device 3 according to the third embodiment of the present invention, a plurality of incident lights can be effectively condensed on the plurality of P layers 54 that are light receiving portions. Therefore, in addition to the effects described in the first embodiment, crosstalk between channels can be reduced during parallel optical wiring.

  The optical device of the present invention can be used for a light receiving system of an optical wiring that uses a light having a wavelength shorter than that of propagating light that satisfies the super oscillation condition, and is particularly necessary for a high-speed response in a photoelectric conversion unit of a parallel optical wiring. This is useful for reducing crosstalk between channels while using a nano-order focused beam diameter.

1, 2, 3 Optical device 11, 12, 110, 120 Multilayer film 13 Metal film 14 Opening 15 High refractive index layers 16, 17, 18, 19 Low refractive index layer 22 Photonic band gap 23 High refractive index band 24 Low Refractive index band 25 High refractive index band edge 26 Low refractive index band edge 31 Light source 32 Optical axis 41 Core 42 Clad 43, 44 Optical waveguide 51 Light shielding part 52 Insulating light shielding layer 53 Anode 54 P layer 55 Depletion layer 56 N layer 57 Cathode 58 59 Photoelectric conversion element 60 Block layer 200 Semiconductor layer / dielectric layer

Claims (15)

An optical device that collects incident light,
A first periodic structure whose refractive index periodically changes in the optical axis direction of the incident light;
A second periodic structure whose refractive index periodically changes in the optical axis direction of the incident light with the same refractive index and period as the first periodic structure;
A film having a transparent portion that is provided between the first periodic structure and the second periodic structure and transmits light;
The first periodic structure and the second periodic structure have a refractive index that changes with a period having a photonic band characteristic near a low refractive index band edge with respect to the wavelength of the incident light,
The optical device is an optical device in which the amount of light is not maximized with respect to a change in light amount distribution in the optical axis direction that appears between the first periodic structure and the second periodic structure.   The optical device according to claim 1, wherein the film is disposed at a position where a light amount is minimized with respect to the light amount distribution change. The first and second periodic structures are multilayer films in which a high refractive index layer and a low refractive index layer are repeatedly laminated,
2. The optical device according to claim 1, wherein the film is provided between a low refractive index layer at an end of the first periodic structure body and a low refractive index layer at an end of the second periodic structure body. A first auxiliary low-refractive index layer having a refractive index equal to or lower than that of the low-refractive index layer between the low-refractive index layer at the end of the first periodic structure and the film,
The second auxiliary low refractive index layer having a refractive index equal to or lower than that of the low refractive index layer is further provided between the low refractive index layer at the end of the second periodic structure and the film. Optical devices.   The total film of the low refractive index layer at the end of the first periodic structure, the first auxiliary low refractive index layer, the film, the second auxiliary low refractive index layer, and the low refractive index layer at the end of the second periodic structure The optical device according to claim 4, wherein the thickness is 1.2 to 2.4 times a period in which a refractive index of the first and second periodic structures changes.   The optical device according to claim 4, wherein a film thickness of the first auxiliary low refractive index layer is equal to a film thickness of the second auxiliary low refractive index layer.   The optical device according to claim 1, wherein a period in which a refractive index of the first and second periodic structures changes is 0.4 to 0.8 times a wavelength of the incident light.   The optical device according to claim 1, wherein the film is a metal film having a film thickness equal to or less than a wavelength of the incident light, and the transparent portion is an opening that penetrates the metal film. A plurality of the openings are provided on the metal film in a regular pattern that satisfies super oscillation conditions.
9. The optical device according to claim 8, wherein the optical device has a light amount distribution that provides a condensing diameter equal to or less than the wavelength of the incident light at a self-imaging position of the Talbot effect due to interference of diffracted light output from the metal film. .   The optical device according to claim 9, wherein the plurality of openings are provided on the metal film in a rotationally symmetric shape about the optical axis of the incident light.   The optical device according to claim 10, wherein the plurality of openings are provided on the metal film in a Penrose pattern shape. An optical waveguide for outputting the incident light to the first periodic structure;
The optical device according to claim 1, further comprising: a photoelectric conversion element including a light receiving unit that receives light output from the second periodic structure.   The optical device according to claim 12, wherein the light receiving unit is provided at an initial self-imaging position. The optical waveguide has a plurality of cores provided in parallel, outputs a plurality of incident light from the plurality of cores,
The photoelectric conversion element includes a plurality of light receiving portions provided in parallel corresponding to the plurality of incident lights, and receives the corresponding lights output from the second periodic structure, respectively. The optical device described.   The optical device according to claim 14, wherein the first periodic structure, the film, and the second periodic structure have a single configuration.

Images