JP2007232786A - Optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide which has small optical loss while acquiring stable signal quality. <P>SOLUTION: The optical waveguide comprises a plate-like phase grating 1 comprising a first area 1a formed so that the refractive index becomes larger toward the central part in the direction of thickness X, and a 2nd area 1b which has a smaller refractive index than the first area and is formed on both main surfaces of the first area 1a with the side faces of the first area 1a exposed, and transmits the light made incident from one side face 1c of the first area 1a in the plane direction of the first area 1a, and makes the light exit from the other side face 1d of the first area 1a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical waveguide for optical interconnection used for connection to an optical communication device, an optical sensing system device, an inside of a module, or an outside.

  In optical communication equipment, a multi-core optical fiber transmission method using an optical fiber is used as a large-capacity transmission method for connecting various devices or circuit boards. At that time, for example, when the memory bus connecting the microprocessor and the memory is formed as an optical wiring, multi-channel transmission is required for the bus-type wiring. In such bus-type wiring, a technique of transmitting optical signals in parallel using a flat optical waveguide is used in order to realize a one-core-to-multi-core connection structure (see, for example, Patent Document 1).

  And as an optical component provided with such a transmission means, the optical multi-branch using the optical sheet bus | bath 8 equivalent to a flat optical waveguide is proposed (for example, refer patent document 2). As the material of the optical sheet bus 8, an optical resin material such as amorphous polyfillene having a core layer thickness of 1 mm and a refractive index of 1.49, polymethyl methacrylate (PMMA), etc. is used to cover the core layer. For the cladding layer, a fluorine-based resin having a refractive index of 1.34 is used. Such an optical multi-branch is configured by connecting a plastic optical fiber 3 (hereinafter referred to as POF) having a core diameter of about 1 mm to the light incident / exit end of the optical sheet bus 8. In this optical multi-branch device, since the core layer of the optical sheet bus 8 and the core diameter of the POF are equal, positioning accuracy is easy and mounting cost is low.

Such an optical multi-demultiplexer has, for example, a 1 × 4 type using a laminated optical sheet bus 8 composed of four layers and a POF. One POF is mounted on one side of each layer, and four on the output side. In this case, the incident light 9 is branched into the four optical fibers on the output side when light having a wavelength of 680 to 850 nm is incident from one optical fiber 3 of the POF on the incident side. be able to.
IEICE technical report OCS2001-1 Optical communication by optical sheet bus JP 2004-93600 A

  However, the laminated flat optical waveguide described above is mainly composed of a resin material, and the transmission optical fiber 3 is composed of POF. For this reason, the transmission speed is about 500 Mbps at the maximum due to the influence of distortion of signal light due to crosstalk or dispersion of the resin material. If a transmission speed higher than that is obtained, it is difficult to obtain stable signal quality. Further, in order to maintain uniform output, it is necessary to enlarge the optical multi-branch itself such that the optical waveguide length is about 20 mm and the outer diameter of the POF is about 1 mm or more. In such an optical multi-branch, it was necessary to make the storage space for the POF as small as possible in order to reduce the size of the parts. However, if the POF is wound in a relatively small circular shape and stored, the POF is bent. A large loss occurs in the propagating light.

  An optical waveguide according to the present invention includes a first region formed so that a refractive index increases toward a central portion in a thickness direction, a refractive index smaller than the first region, and both side surfaces of the first region. An optical waveguide comprising a planar phase grating that is exposed and formed on a peripheral surface of the first region, and that receives light incident from one side of the first region. It transmits in the plane direction of a 1st area | region, and radiate | emits from the other side of the said 1st area | region.

  Further, the present invention is characterized in that a reflecting portion is provided on a side surface of the phase grating where light is not incident / exited.

In the present invention, the phase grating is made of quartz glass containing at least one of GeO ₅ , TiO ₂ , and Al ₂ O ₃ .

  Further, the present invention is characterized in that different numbers of input / output optical fibers are joined to one side surface and the other end surface of the first region.

  Further, in the present invention, the input / output optical fiber is fusion bonded to one side surface and the other side surface of the first region.

  Furthermore, in the present invention, the input / output optical fiber is joined to one side surface and the other side surface of the first region via a gradient index lens.

  The present invention provides the first region formed so that the refractive index increases toward the center in the thickness direction, the refractive index is smaller than the first region, and the side surface of the first region is exposed. An optical waveguide is configured by a flat phase grating including second regions formed on both main surfaces of the first region. Therefore, according to the optical waveguide of the present invention, light can be transmitted in the planar direction of the first region due to the difference in refractive index between the first region and the second region. As a result, the optical waveguide of the present invention can realize light transmission using the phase grating by making light incident on the first region of the phase grating.

  The optical waveguide of the present invention has a refractive index distribution type lens function because the first region has a refractive index distributed from the center to the outside. As a result, the optical waveguide of the present invention can input and output light so as to be focused on, for example, the core portion of the optical fiber connected to both side surfaces of the first region. The coupling efficiency is improved.

  Further, in the present invention, if a reflection part is provided on the side surface of the phase grating where light is not incident / exited, the light is emitted by the reflection part even if light is emitted from the first region due to fluctuation of the incident angle of light, for example. Can re-enter the first region, so that loss of light can be suppressed.

Furthermore, in the present invention, if the phase grating is made of quartz glass containing at least one of GeO ₅ , TiO ₂ , and Al ₂ O ₃ , the function of changing the refractive index according to the irradiated light is changed to quartz. Since the glass can be provided, the first region and the second region having a desired refractive index profile can be easily formed. Furthermore, if it is an optical waveguide which consists of a phase grating comprised with such a material, compared with the optical waveguide comprised with a resin material, heat resistance and moisture resistance can be improved.

  Further, in the present invention, if a different number of input / output optical fibers are bonded to one side surface and the other side surface of the first region, the optical branching function can be provided, so that the present invention is applied to an optical multi-branch device. Can do. The input / output optical fiber is fusion bonded to one side surface and the other side surface of the first region, so that there is no intervening factor for changing the refractive index such as an optical adhesive. As a result, according to such a configuration, it is possible to reduce the loss of light generated at the interface between the input / output optical fiber and the first region.

  Furthermore, in the present invention, if the input / output optical fiber is joined to one side surface and the other side surface of the first region via a gradient index lens, the refractive index of the gradient index lens and the phase grating is determined. Since the distribution can be matched, the loss of light that occurs during optical transmission can be further reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the optical waveguide 100 of the present invention includes a first region 1a having a refractive index distribution, a phase grating 1 having a second region 1b having a refractive index smaller than the first region 1a, and a first region 1a. The optical fiber 2 and the optical fiber 3 are respectively connected to both side surfaces. FIG. 2 shows a laminated optical waveguide in which a plurality of optical waveguides 100 are laminated.

  The phase grating 1 has a function of transmitting light using a refractive index distribution in the medium, and the shape thereof is a flat plate. This phase grating 1 has both a first region 1a set so that the refractive index gradually increases toward the center Y of the phase grating 1 with respect to the thickness direction X of the phase grating 1, and both of the first region 1a. The second region 1b is disposed on the main surface and has a smaller refractive index than the first region 1b.

  In the case of the laminated optical waveguide 100 ′, the phase grating 1 has an interval between the central portions of the adjacent first regions 1a (hereinafter referred to as a grating interval Λ) and a refractive index distribution n (x) in FIG. The relationship is as shown. As shown in FIG. 3, the phase grating 1 has a distribution that fluctuates in a sine wave shape such that the refractive index at the center of the first region 1a is the largest and gradually decreases toward the second region 1b. In addition, the refractive index is minimized in the second region 1b. Since the first region 1a and the second region 2b do not have a clear boundary surface, the boundary is shown in the drawing for convenience.

  The light incident from the optical fiber 2a is reflected in the first region 1a while being reflected at the boundary surface between the first region 1a and the second region 1b, as indicated by the arrow in FIG. Light is transmitted in the plane direction of the region 1a and is incident on the optical fiber 2b.

The refractive index distribution n (x) is expressed by the following formula. The refractive index n1 indicates a refractive index of a substance (hereinafter referred to as a base 1 ′) in a state before the first region 1a and the second region 1b formed in the phase grating 1 are formed. The rate n0 is an intermediate value between the highest refractive index and the refractive index n1 of the first region 1a. Further, the refractive index modulation degree δ is the difference between the maximum value and the minimum value in the refractive index distribution in the phase grating 1.

As the material of the base 1 'of the phase grating 1, for example, a substrate mainly made of quartz glass to which a photothermal reactive material for increasing the refractive index is added can be used. If GeO ₅ , TiO ₂ , or Al ₂ O ₃ is used as the photothermal reactive material, a portion having a refractive index larger than that of quartz glass can be formed by UV irradiation. Therefore, the first region 1a and The refractive index fluctuation of the second region 1b can be increased (for example, a range of δ = 0.001 to 0.1). As a result, in the phase grating 1, light can be more reliably reflected at the boundary surface between the first region 1a and the second region 1b, so that light loss can be reduced. Further, the material of the substrate 1 ′ is not limited to the above-described materials, and may be constituted by, for example, PTR (Photo-Thermo-Refractive) glass in which Ge and Ag are added to fluorescent silica glass.

  The optical fiber (optical fiber 2 to optical fiber 6) is composed of a core portion (core portion 2a to core portion 6b) having a high refractive index and a cladding portion (cladding portions 2b to 6b) covering the outer periphery of the core portion. Light is transmitted in the core portion by utilizing reflection due to a difference in refractive index between the portion and the cladding portion, and is made of, for example, cylindrical quartz.

  As shown in FIG. 4, one optical fiber is connected to one side surface 1c of the first region 1a, and three optical fibers are connected to the other side surface 1d. Therefore, different numbers of optical fibers are connected to the one phase grating 1 on both side surfaces of the first region 1a. In this way, if the number of optical fibers connected to the phase grating 1 is varied, for example, the light incident on one optical fiber 2a is branched into a plurality of optical fibers connected to the other side surface and light is transmitted to the outside. It is possible to produce an optical component having an optical multi-branching function that emits light.

For connection between the optical fiber and the phase grating 1, for example, there are a method of bonding using a translucent UV curing adhesive and a method of connecting by fusion. In particular, bonding by fusion is preferable in terms of suppressing light loss because it can be connected to the interface between the optical fiber and the phase grating 1 without interposing substances having different refractive indexes. This fusion bonding includes, for example, heat fusion by high frequency discharge or heat fusion by CO ₂ laser irradiation.

  Further, in this optical fiber, it is preferable that at least a part of the portion connected to the phase grating 1 is a gradient index lens. This gradient index lens is a fiber having a nearly square refractive index distribution in its axial symmetry, and has a function of condensing or collimating light incident on the phase grating 1. This refractive index distribution type lens is made of, for example, cylindrical quartz or the like, and has an outer diameter of the cladding portion of about 125 μm and a diameter of the core portion of about 50 μm, and has the above-described refractive index distribution in the core portion. In other words, if the refractive index distribution of the core portion is set to a value similar to the refractive index distribution of the phase grating 1, the matching between the gradient index lens and the phase grating 1 is improved, so that the connection loss of light is further suppressed. be able to.

  Further, in the optical waveguide 100 of the present invention, as shown in FIG. 4, it is preferable to provide a light reflecting portion 12 on the side surface of the phase grating 1 where light does not enter and exit. Note that the side surface on which light does not enter and exit refers to a side surface other than the side surfaces 1c and 1d to which the optical fiber is connected. The light reflecting portion 12 is obtained, for example, by mirror polishing the side surface of the phase grating 1. The light reflecting portion 12 may be provided with a metal film or a dielectric film containing titanium or chromium by a method such as vapor deposition. And this light reflection part 12 is radiate | emitted outside the medium (for example, optical fiber) other than the medium (for example, optical fiber) for transmitting light from the 1st area | region 1a by the fluctuation | variation of the incident angle of the light which injects into an optical fiber, for example. Therefore, the loss of light transmitted through the phase grating 1 can be prevented.

  Further, in the case of the laminated optical waveguide 100 ′, as shown in FIG. 5, optical fibers may be connected at a distance 2Λ with respect to the lamination direction of the optical waveguide 100 ′. That is, in this configuration, optical fibers are connected to every other phase grating 1 that is laminated. As described above, since the phase gratings 1 are alternately used in the stacking direction, it is possible to prevent deterioration of a transmission signal due to crosstalk of signal light between different phase gratings 1.

  Hereinafter, a method for manufacturing the optical waveguide 100 ′ of the present invention will be described in detail.

  The phase grating 1 constituting the optical waveguide 100 ′ is a first region having a refractive index distribution by utilizing the fact that the substrate 1 ′ is mainly irradiated with UV light and the refractive index is increased at the portion irradiated with the UV light. 1a and second region 1b are formed.

  The grating interval Λ of the phase grating is expressed by Λ = λm / (2 × sin Θ2). Here, λm = λuv / n1, and λuv is the wavelength of the UV light irradiated onto the substrate 1 '. Θ2 is the incident angle of the UV light to the substrate 1 '. As represented by the above equation, the phase grating interval Λ can be set by adjusting the incident angle Θ2 of the UV light.

FIG. 6 is a schematic diagram showing an optical system of an optical interference method used when the phase grating 1 is manufactured. In this optical system, first, coherent parallel UV light having a phase of intensity P is made incident on a partial reflection mirror 13 having reflectance R1 and transmittance T1 at an incident angle Θ1. Therefore, a part of the light is reflected with the intensity P0 and transmitted with the intensity P1. The UV parallel light transmitted at the intensity P1 is incident on the total reflection mirror 14 having the reflectivity R2 inclined by Θ2 with respect to the partial reflection mirror 13, and is incident at the intensity P2. Thereafter, the reflected light is incident again on the partial reflection mirror 13 at an incident angle {Θ1-2Θ2}, and a part thereof is transmitted in the state of parallel UV light having an intensity P3. Then, the parallel UV light having the intensity P3 and the parallel UV light having the intensity P0 intersect at an angle 2Θ2, and the light enters the base 1 ′ in a state of interference. That is, by placing the base 1 ′ at an angle {Θ1-Θ2} with respect to the partial reflection mirror 13 at the intersecting location, two parallel exposure UV lights can be incident on the base 1 ′ at an incident angle Θ2. it can. The adjustment of the incident angle Θ <b> 2 to the base body 1 ′ can be obtained by adjusting the angle of the total reflection mirror 14. Further, if the UV light exposure intensities P0 and P3 are made equal, the refractive index distribution in the cross section of the phase grating 1 can be formed symmetrically about the central portion of the first region 1a. In this case, the reflectance R1 of the partial reflection mirror 13 can be expressed by R1 = {2K + 1− (4K + 1) ^1/2 } / 2K. Here, K = R ² T 1 ² , R 2 represents the reflectance of the total reflection mirror 14, and T 1 represents the transmittance of the partial reflection mirror 13.

FIG. 7 is a schematic diagram showing exposure recording conditions when the substrate 1 ′ is inclined with respect to the partial reflection mirror 13 at an angle {Θ1−Θ2} and UV parallel light is incident on the substrate 1 ′ at an incident angle Θ2 ′. It is. When this substrate 1 ′ is exposed, the substrate 1 ′ is exposed in a matching oil substantially equal to the refractive index n1 (refractive index of the substrate 1 ′). When UV light is incident from the air into the matching oil having the refractive index n1, the incident angle Θ2 ′ changes depending on the refractive index difference, so that Θ2 ′ = sin− ¹ (n1sinΘ2) needs to be considered. Then, since the first region 1a and the second region 1b are formed in a stripe shape through such an exposure step, the phase grating 1 having a desired refractive index distribution, that is, the optical waveguide 100 ′ is manufactured. FIG. 8 is a graph showing the relationship between the lattice spacing Λ exposed and recorded using the UV light having a wavelength of 325 nm and the incident angle Θ2 ′ of the parallel UV light. The incident angle Θ2 ′ of the parallel UV light is changed. By doing so, an optical waveguide 100 ′ (phase grating 1) having a desired grating interval Λ can be obtained.

  In this example, evaluation was performed using a laminated optical waveguide. The laminated optical waveguide is a 1 × 4 optical waveguide as shown in FIG. 4, that is, one input optical fiber and four output optical fibers are connected to one phase grating 1. Therefore, the optical waveguide is actually a 4 × 16 type optical waveguide.

First, the phase grating 1 was manufactured using the optical system based on optical interference shown in FIG. The substrate 1 ′ was made of PTR glass having a refractive index n = 1.487, a 10 mm square and a thickness T = 3 mm. And this base | substrate 1 'is installed and fixed on the jig | tool which can carry out fine adjustment of an inclination angle, and it immerses in the matching oil of about 10 mm in depth which has the refractive index 1.49 similar to the phase grating 1, It adjusted and fixed to the predetermined | prescribed angle ((theta) 1- (theta) 2) with respect to the horizontal surface. As the exposure recording light source, a He—Cd laser having a wavelength of 325 nm and a coherent length of 30 cm and an output of 50 mW was used. The exposure optical system used a condensing lens with a pinhole for the laser emitted light, and expanded the collimator lens into parallel light having a diameter of 20 mm with an output intensity of 1 / e ² and installed in the separation parallel optical system. The partial reflection mirror 13 and the total reflection mirror 14 to be used are both formed by depositing a dielectric multilayer film. The transmittance T1 of the partial reflection mirror 13 is 60%, the reflectance R1 is 33%, and the total reflection mirror 7 The reflectance R2 is 90%. And it arrange | positioned so that the space | interval of the partial reflection mirror 13 and the total reflection mirror 14 might be set to L = 20mm. By applying such an optical system, the intensities of the light P0 from the partial reflection mirror 13 and the transmitted light P3 from the partial reflection mirror 13 become substantially equal, and symmetrical with respect to the exposure recording on the substrate 1 ′ at the interval Λ. A refractive index distribution can be obtained. The graph of FIG. 8 shows the incident angle Θ2 to the substrate 5 and the phase grating 1 when the laser light source having a wavelength of 325 nm is used for the recording UV light by the optical system with respect to the base 1 ′ having the refractive index n1 = 1.487. The relationship of the lattice spacing Λ is shown. When the lattice spacing Λ = 40 μm, the incident angle Θ2 ′ in the substrate 5 is 0.1 degrees. However, when converted into air having a refractive index of 1, Θ2 = 0.15 degrees. Accordingly, the angle of the optical total reflection mirror 7 is set to Θ2 = 0.15 degrees. Further, Θ1 = 30 degrees and Θ1−Θ2 = 29.85 degrees.

  Using such an optical system, the substrate 1 ′ is exposed and recorded for 15 minutes in a dark room environment with UV laser light, and then the exposed substrate 1 ′ is heat-treated at 450 to 500 ° C. to be 10 × 10 × 3 mm. A base body 1 ′ having a refractive index distribution of 1 was produced.

  Next, the substrate 1 ′ is cut by a dicing machine with a width W = 350 μm, a height H = 500 μm, and a thickness T = 3000 μm, and four end faces of H = 500 μm are polished to remove the incident / exit surface. A reflective material 12 was formed by applying a translucent material with a translucent UV adhesive having a refractive index of 1.47 to the side surface of the substrate. The optical fiber used for input / output is an optical fiber having a core diameter of 50 μm, a cladding diameter of 80 μm, and a relative refractive index difference Δ = 1.9% (α = 16.9 degrees). In the phase grating, one line on one side and four lines on the other side are aligned and connected to form four stages, so that the four optical fibers 3 on the incident side have four end faces in four rows. The length of a structure in which four aligned optical fibers 3 having a length of 10 mm are fixed by using a ferrule having a minute hole that can be closely arranged and juxtaposed, and four 4 × 4 optical fibers on the emission side can be stacked in close contact with each other. A 10 mm solid fiber array is used for fixing and polishing each end face. At this time, the interval between the optical axes of the optical fibers used is 80 μm. Such an optical fiber is bonded to the light incident / exit surface of the phase grating 1 by a UV adhesive made of a translucent member on a four-stage laminated phase grating 1 having a size of W = 350 μm, H = 500 μm, and T = 3000 μm. And it was configured as a four-stage 1 × 4 type optical multi-branch.

Laser light having a wavelength of 850 nm and an output power of 5 mW was incident on four incident-side optical fibers, and light was emitted from the 16 output-side optical fibers. In this optical waveguide, the insertion loss was evaluated using a first-stage phase grating as shown in FIG. Specifically, light is incident from the input optical fiber 2 connected to the first-stage phase grating 1 with the above-described output, and is emitted from the four output optical fibers 8, 9, 10, and 11. Measure the output loss of each output optical fiber, calculate the insertion loss of each output optical fiber, measure the insertion loss of each output side optical fiber (four) arranged in the first stage, and calculate the average value It is shown in Table 1. Note that T = 3000 μm> 1.5 × 350 / tan (16.9 °) = 1728 μm, and the insertion loss of each optical fiber is represented by −10 Log ₁₀ (In / I0) (n = 1 to 4). The

  In addition, as a reliability test, 11 prototype samples were prepared, and a constant temperature and humidity test and a temperature cycle test with contents conforming to Telcodia 1221 were performed, and it was confirmed that there was no problem in reliability.

As described above, by using the phase grating type optical waveguide according to the present invention, even if a module structure is used as compared with a conventional optical multi-branch unit using a resinous optical sheet bus, In contrast to a length of 60 mm, a height of 8 mm, and a width of 12 mm, the one according to the present invention is small and integrated with a length of about 25 mm, a height of 3 mm, and a width of about 3 mm. The average of the total insertion loss (= −10 Log ₁₀ {the sum of the outputs of the output optical fibers / the output of the optical fibers on the incident side}) is about 1.9 dB, which is about the same as that of the conventional resin optical sheet bus. It was possible to reduce significantly to 4 dB.

It is a side view which shows the optical waveguide of this invention. It is a side view which shows the optical waveguide which laminated | stacked multiple optical waveguides of this invention. It is a graph which shows the refractive index fluctuation | variation of the phase grating used for the optical waveguide of this invention. It is a top view which shows other embodiment of the optical waveguide of this invention. It is a side view which shows other embodiment of the optical waveguide which laminated | stacked multiple optical waveguides of this invention. It is a schematic diagram which shows the optical system of the optical interference method used when manufacturing the phase grating used for the optical waveguide of this invention. It is a schematic diagram which shows the process of exposing and recording the base | substrate which is a precursor of the phase grating used for the optical waveguide of this invention using an optical interference method. It is the graph which showed the relationship between UV light incident angle (theta) 2 and the grating | lattice space | interval (LAMBDA) in an optical interference method.

Explanation of symbols

100, 100 ': Optical waveguide 1: Phase grating 1': Base 1a: First region 1b: Second region 2-11: Optical fiber 12: Reflector 13: Partial reflection mirror 14: Total reflection mirror

Claims (6)

A first region formed such that the refractive index increases toward the center in the thickness direction, and the refractive index is smaller than that of the first region and the side surface of the first region is exposed to expose the first region; An optical waveguide comprising a planar phase grating comprising: second regions formed on both main surfaces;
An optical waveguide, wherein light incident from one side surface of the first region is transmitted in a planar direction of the first region and emitted from the other side surface of the first region. The optical waveguide according to claim 1, wherein a reflection portion is provided on a side surface of the phase grating where light is not incident / exited. The optical waveguide according to claim 1, wherein the phase grating is made of quartz glass containing at least one of GeO ₅ , TiO ₂ , and Al ₂ O ₃ .   4. The optical waveguide according to claim 1, wherein different numbers of input / output optical fibers are bonded to one side surface and the other side surface of the first region.   The optical waveguide according to claim 4, wherein the input / output optical fiber is fusion bonded to one side surface and the other side surface of the first region.   6. The optical waveguide according to claim 4, wherein the input / output optical fiber is joined to one side surface and the other side surface of the first region via a gradient index lens.

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