JP2008276074A - Filter for optical communication, and module for optical communication using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter for optical communication which can be made compact and has excellent demultiplexing characteristics and productivity and to provide a module for optical communication using the same. <P>SOLUTION: The filter 100 for optical communication includes a substrate 101 on the principal surface of which a periodical projecting and recessed shapes having prescribed pitches are formed in directions x and y when the principal surface is a plane xy and a multilayer film formed on the principal surface and formed by alternately layering low refractive index layers 107 and high refractive index layers 106. The periodical projecting and recessed shapes are formed on the substrate 101 to be divided into a plurality of regions 102, 103 and 104 for every pitch. The high refractive index film 106 has a refractive index of 2.5 or more and the refractive index ratio of the refractive index of the high refractive index film 106 to the refractive index of the low refractive index film 107 is 1.6 or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical communication filter and an optical communication module using the same, and more particularly to an optical communication filter and an optical communication module using a photonic crystal.

  In recent years, introduction of wavelength division multiplexing (WDM) has been promoted in the communication field. In optical communication, a combination of three-terminal modules in a cascade enables multiplexing / demultiplexing of band light of a plurality of wavelengths. However, at least one three-terminal module less than the number of multiplexing / demultiplexing is required, and there is a limit to downsizing.

  On the other hand, Patent Document 1 discloses a module in which a plurality of band-pass filters and edge filters are incorporated in a single module to multiplex / demultiplex a plurality of wavelengths. Conventionally, since it has been difficult to form optical communication filters of different wavelengths on the same substrate, optical communication filters of each wavelength have been prepared separately and attached on a single substrate. For this reason, there is a problem inferior in productivity.

  Under such circumstances, in order to separate light of different wavelengths, an optical communication filter in which a photonic crystal formed of a dielectric multilayer film having different refractive indexes is formed on a substrate has attracted attention (for example, Patent Documents 2 to 5). reference).

As disclosed in Patent Documents 2 to 5, when a photonic crystal is laminated on a substrate surface on which a periodic concavo-convex structure is formed under predetermined conditions, the cross-sectional shape corresponding to the concavo-convex structure is a triangular wave type. A photonic crystal having a periodic structure is formed. By changing the pitch of the concavo-convex structure, the center wavelength of the transmission band can be changed while the film thickness remains constant. Accordingly, a concavo-convex structure with different pitches is formed by dividing into a plurality of regions on a single substrate, and a plurality of transmission bands are formed on a single substrate by laminating a photonic crystal thereon by sputtering or the like. A multi-wavelength filter can be easily formed.
JP-A-8-82711 JP 2003-255161 A JP 2004-325902 A JP 2004-325903 A JP 2004-341506 A

  By the way, if the substrate surface on which the concavo-convex structure is formed is an xy plane, polarization dependency can be eliminated by making the pitch of the concavo-convex structure in the x direction and the pitch of the concavo-convex structure in the y direction the same. On the other hand, if the pitch of the concavo-convex structure in the x direction is the same as the pitch of the concavo-convex structure in the y direction, the shift amount of the center wavelength of the transmission band with respect to the pitch change amount becomes small, and there is a problem inferior in the demultiplexing characteristics.

  The present invention has been made to solve such problems, and provides an optical communication filter that can be miniaturized and has excellent demultiplexing characteristics and productivity, and an optical communication module using the same. For the purpose.

  The optical communication filter according to the present invention has a main surface as an xy plane, a periodic uneven shape having a predetermined pitch in the x direction and the y direction, formed on the main surface, and the main surface. An optical communication comprising a multilayer film in which a low refractive index film and a high refractive index film are alternately laminated, wherein the periodic uneven shape is divided into a plurality of regions for each pitch and formed on the substrate. The high-refractive-index film has a refractive index of 2.5 or more, and a refractive-index ratio between the high-refractive-index film and the low-refractive-index film is 1.6 or more. .

Further, lamination period a is 300～850Nm, and the ratio _p x / a and _p y / a between the pitch _{p x} and y direction of the pitch _{p y} and the lamination period a in the x direction of the periodic irregularities There is a 0.75 to 1.25 both, it is preferable that _{0.5 ≦ p x / p y ≦} 2. Furthermore, it is preferable that the low refractive index film is made of SiO ₂ or MgF ₂ , and the high refractive index film is made of any one of Si, Ge, CdSe, CdTe, ZnSe, and SiGe. And it is preferable that the lamination | stacking number of the said multilayer film is 30 or more sets.

  In addition, an optical communication module according to the present invention includes the optical communication filter and a reflection portion disposed to face the incident surface of the filter.

  ADVANTAGE OF THE INVENTION According to this invention, the filter for optical communication which can be reduced in size and is excellent in a demultiplexing characteristic and productivity, and an optical communication module using the same can be provided.

  Embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiment. Further, in order to clarify the explanation, the following description and drawings are appropriately omitted and simplified.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an optical communication filter according to the present invention will be described with reference to FIGS. FIG. 1 is a plan view showing an optical communication filter according to the present invention. As shown in FIG. 1, the optical communication filter 100 is formed with three transmission regions of a substrate 101, a first wavelength transmission region 102, a second wavelength transmission region 103, and a third wavelength transmission region 104. . That is, the optical communication filter 100 includes three transmission bands on a single substrate. Thus, the optical communication filter according to the present invention is a multi-wavelength filter in which a plurality of wavelength transmission regions are formed on a single substrate, and is suitable for miniaturization. Here, the first wavelength transmission region 102, the second wavelength transmission region 103, and the third wavelength transmission region 104 need to be larger than the beam diameter of the used wavelength. Is desirable. The shape of the filter forming portion may be circular, square, or hexagonal.

  FIG. 2 is an enlarged plan view of the first wavelength transmission region 102 in FIG. 1 and shows a periodic concavo-convex structure formed on the surface of the substrate 101. As shown in FIG. 2, a large number of square-shaped concave portions 105 are formed on the surface of the main surface of the substrate 101 when viewed from the normal direction of the main surface of the substrate 101. In other words, a periodic uneven shape is formed in the first wavelength transmission region 102.

  Here, as the substrate 101, a transparent substrate in a wavelength band (1200 to 1600 nm) used in optical communication, an oxide such as SiO2, Al2O3, Si, Ge, GaAs, GaP, ZnS, ZnSe, CdTe, CdSe, etc. A semiconductor, glass, or the like may be used. Further, as will be described in detail later, the recess 105 can be formed by forming a resist pattern on a flat substrate 101 and then etching the substrate 101. The depth of the recess 105 is about λ / 4 as the wavelength λ used.

Further, as shown in FIG. 2, the concave portions 105 are formed at substantially the same pitch in the x direction and the y direction with the main surface of the substrate 101 as the xy plane. That is, the pitch _{p y} of pitch _{p x} and y direction of the x direction shown in FIG. 2 Ryakutoku a _{p x} ≒ _{p y} ≒ p. The shape of the recess 105 is not limited to a square, and may be an isotropic shape such as a circle, a regular triangle, or a regular hexagon.

  FIG. 3 is a sectional view taken along line XX in FIG. That is, it is a cross-sectional view of the first wavelength transmission region 102 of the optical communication filter 100. As shown in FIG. 3, a photonic crystal in which a large number of high refractive index films 106 and low refractive index films 107 are alternately stacked is formed on one main surface of a substrate 101 on which concave portions 105 are periodically formed. ing.

  Here, the film thicknesses of the high refractive index film 106 and the low refractive index film 107 are λ / (4 · n) or λ / (2 · n) (where n is the refractive index of each film) where λ is the wavelength used. ). The number of stacked high refractive index films 106 and low refractive index films 107 is preferably 30 periods, that is, 30 sets or more. If 30 sets or more are formed, the transmittance in the reflection region of the filter becomes sufficiently small, and crosstalk in which unnecessary band light leaks can be suppressed. A cavity layer may be provided in the middle of the lamination. In order to suppress ripples, the film thicknesses of the high refractive index film 106 and the low refractive index film 107 are determined from λ / (4 · n) or λ / (2 · n) (where n is the refractive index of each film). It may be shifted by about ± 20%.

  As described above, since the periodic concavo-convex structure is formed on the surface of the substrate 101, a photonic crystal having a periodic structure having a triangular wave cross section corresponding to the concavo-convex structure is formed. With such a configuration, a specific wavelength can be transmitted.

Further, since the pitch _{p y} of pitch _{p x} and y direction of the x-direction is substantially equal _{p x} ≒ _{p y,} there is no polarization dependency. Here, it is desirable that 0.5 ≦ p _x / _py ≦ 2. Further, as shown in FIG. 3, when the sum of the film thicknesses of the high refractive index film and the low refractive index film is a, the lamination period of the laminated film is a = 300 to 850 nm, and the periodic uneven shape is it is preferred ratios _p x / a and _p y / a between the pitch _{p x} and y direction of the pitch _{p y} a lamination period a in the x direction is 0.75 to 1.25 both. Since the film thickness of each layer is λ / (4 · n) or λ / (2 · n) (where n is the refractive index of each film), the stacking period a is the wavelength λ used. It becomes 850 nm. When it is less than 300 nm and exceeds 850 nm, the transmission band is out of the range of 1200 to 1600 nm, which is often used in optical communication. That is, the stacking period a is determined by the wavelength used. In terms of design, it is advantageous to set the average wavelength in the wavelength band to be used. The wavelength band normally used in optical communication is 1200 to 1600 nm, and the average wavelength is 1400 nm. Therefore, if the ratios p _x / a and p _y / a, which are the ratios of the uneven pitches p _x and p _y of the substrate of each filter to the film stacking period a, are in the range of 0.75 to 1.25, each filter Can be designed to fall within the range of 1200-1600 nm.

  The refractive index of the high refractive index film is 2.5 or more, and the refractive index ratio between the high refractive index film and the low refractive index film is 1.6 or more. Conventionally, when the configuration has no polarization dependency, there is a problem that the shift amount of the center wavelength of the transmission band with respect to the pitch change amount becomes small, and the demultiplexing characteristic is deteriorated. According to the present invention, it is possible to improve the demultiplexing characteristics while maintaining the polarization-independent configuration.

Specifically, the high refractive index film 106 is preferably made of any one of Si, Ge, CdSe, CdTe, ZnSe, and SiGe. On the other hand, the low refractive index film 107 is preferably made of SiO ₂ or MgF ₂ . Thereby, the said conditions are satisfy | filled and a demultiplexing characteristic can be improved.

  Further, the center wavelength of the transmission band can be changed by changing the pitch of the periodic uneven structure. Specifically, in the first wavelength transmission region 102, the second wavelength transmission region 103, and the third wavelength transmission region 104, the pitch of the concavo-convex structure is different from each other. In other words, the periodic uneven shape is formed on the substrate 101 by being divided into a plurality of regions 102, 103, 104 for each pitch. Therefore, a different wavelength can be transmitted for each transmission region.

  On the other hand, in any wavelength transmission region, the thickness of the multilayer film composed of the high refractive index film 106 and the low refractive index film 107 is constant. Therefore, the filter for optical communication according to the present invention can form a plurality of wavelength transmission regions on a single substrate by a film forming method such as sputtering or vacuum evaporation, and is excellent in productivity. Conventionally, the optical communication filter for each wavelength was separately prepared and stuck on a single substrate, so that the productivity was inferior. Further, since the optical communication filter of each wavelength that has been affixed is a multilayer film, warping is likely to occur, and there is a limit to downsizing itself.

  Next, a method for manufacturing an optical communication filter according to the present invention will be described. First, a resist pattern is formed on one main surface of the glass substrate 101 so as to expose the concave portion 105 formation portion. The resist pattern can be formed by photolithography or nanoimprint that is usually used in the production of LSI or MEMS devices.

  Thereafter, a recess 105 is formed in the substrate 101 by wet etching or dry etching. As a result, recesses 105 having a desired pitch can be collectively formed in each of the first wavelength transmission region 102, the second wavelength transmission region 103, and the third wavelength transmission region 104. That is, the optical communication filter according to the present invention is excellent in productivity and can be downsized.

  Next, a large number of high-refractive index films 106 and low-refractive index films 107 are alternately stacked on the main surface of the substrate 101 in which the concave portion 105 is formed on one main surface by sputtering, vacuum deposition, or the like. As described above, RF sputtering, ion beam sputtering, ion-assisted vapor deposition, and RF bias vapor deposition are used as a film forming method in order to form a periodic structure having a triangular wave cross section corresponding to the concavo-convex structure on the substrate 105. Is preferred. A desired periodic structure can be formed by known film forming conditions described in Patent Documents 2 to 5 and the like.

  As described above, when the uneven structure having different pitches is formed on a single substrate 101 by dividing it into a plurality of regions, and then a photonic crystal is laminated on the single substrate 101 by sputtering or the like, a plurality of the uneven structures are formed on the single substrate 101. The multi-wavelength filter 100 for optical communication having a transmission band can be easily formed collectively.

  Next, an example of an optical communication module using the optical communication filter according to the present embodiment will be described with reference to FIG. FIG. 4 is a sectional view showing an optical communication module 200 according to the present invention. As illustrated in FIG. 4, the optical communication module 200 includes an optical communication filter 100 having a first wavelength transmission region 102, a second wavelength transmission region 103, and a third wavelength transmission region 104, and optical fibers 211 and 212. 213, 214, lenses 221, 222, 223, 224, and a reflector 230.

  The reflecting surface of the reflecting plate 230 is disposed opposite to the incident surface of the optical communication filter 100. The lens 221 is optically connected to one end of the optical fiber 211 and is disposed on the incident surface side of the optical communication filter 100. On the other hand, the optical fibers 212, 213, and 214 and the lenses 222, 223, and 224 are disposed on the emission surface side of the optical communication filter 100.

  More specifically, the lens 222 is optically connected to one end of the optical fiber 212 and is disposed so that transmitted light that has passed through the first wavelength transmission region 102 of the optical communication filter 100 is incident thereon. Similarly, the lens 223 is optically connected to one end of the optical fiber 213 and is disposed so that the transmitted light that has passed through the second wavelength transmission region 103 of the optical communication filter 100 is incident thereon. The lens 224 is optically connected to one end of the optical fiber 214 and is disposed so that transmitted light that has passed through the third wavelength transmission region 104 of the optical communication filter 100 is incident thereon.

Signal light including the first wavelength λ ₁ , the second wavelength λ ₂ , and the third wavelength λ ₃ is emitted from the lens 221 through the optical fiber 211. The emitted light is incident on the first wavelength transmission region 102 of the optical communication filter 100. Here, only the first wavelength λ ₁ passes through the optical communication filter 100, enters the lens 222, and propagates through the optical fiber 212. On the other hand, light having a wavelength other than the _first wavelength λ ₁ is reflected by the optical communication filter 100.

The reflected light is further reflected by the reflector 230 and enters the second wavelength transmission region 104 of the optical communication filter 100. Here, only the second wavelength λ ₂ passes through the optical communication filter 100, enters the lens 223, and propagates through the optical fiber 213. On the other hand, light having a wavelength other than the _second wavelength λ ₂ is reflected by the optical communication filter 100.

The reflected light is further reflected by the reflecting plate 230 and enters the third wavelength transmission region 104 of the optical communication filter 100. Here, the third wavelength λ ₃ passes through the optical communication filter 100, enters the lens 224, and propagates through the optical fiber 214.

As described above, by using the optical communication module according to the present embodiment, the signal light including the first wavelength λ ₁ , the second wavelength λ ₂ , and the third wavelength λ ₃ is demultiplexed into each wavelength. be able to.

It is a top view which shows the filter for optical communications which concerns on this invention. FIG. 2 is an enlarged plan view of a first wavelength transmission region in FIG. 1. It is XX sectional drawing of FIG. It is sectional drawing which shows the module for optical communication which concerns on this invention.

Explanation of symbols

100 Optical communication filter 101 Substrate 102 First wavelength transmission region 103 Second wavelength transmission region 104 Third wavelength transmission region 105 Recess 106 High refractive index film 107 Low refractive index film 200 Optical communication modules 211, 212, 213 , 214 Optical fibers 221, 222, 223, 223 Lens 230 Reflector

Claims (6)

A substrate in which a periodic concavo-convex shape having a predetermined pitch in the x direction and the y direction is formed on the main surface with the main surface as an xy plane;
A multilayer film formed on the main surface and alternately laminated with a low refractive index film and a high refractive index film;
The periodic uneven shape is an optical communication filter formed on the substrate by dividing into a plurality of regions for each pitch,
An optical communication filter, wherein a refractive index of the high refractive index film is 2.5 or more, and a refractive index ratio between the high refractive index film and the low refractive index film is 1.6 or more. Lamination period a is 300～850Nm, both the ratio _p x / a and _p y / a between the pitch _{p y} and the lamination period a pitch _{p x} and y direction of the x-direction of the periodic irregularities 0 a .75～1.25, optical communication filter according to claim 1, characterized in that a _{0.5 ≦ p x / p y ≦} 2. The optical communication filter according to claim 1, wherein the low refractive index film is made of SiO ₂ or MgF ₂ .   The optical communication filter according to claim 1, wherein the high refractive index film is made of any one of Si, Ge, CdSe, CdTe, ZnSe, and SiGe.   The optical communication filter according to any one of claims 1 to 4, wherein the number of laminated multilayer films is 30 or more.   6. An optical communication module comprising: the optical communication filter according to claim 1; and a reflection portion disposed so as to face the incident surface of the filter.

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