JP2006030733A - Optical waveguide and method for manufacturing optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical waveguide which generates SC (super continuum) light near visible light. <P>SOLUTION: A light guide portion 12a of a quartz glass film 12 laid on a silicon substrate 11 functions to guide light. Holes 13 are formed in a position along the both sides of the light guide portion 12a. A vacancy 14 is formed in a part of the silicon substrate 11 opposing the bottom of the light guide portion 12a, and the vacancy 14 is connected to the holes 13. Consequently, the entire upper surface of the light guide portion 12a is surrounded by air, the entire lower surface is surrounded by air in the vacancy 14, and most of both side faces are surrounded by air in the holes 13. The light guide portion 12a thereby functions as a core while air functions as a clad to produce an optical waveguide having an extremely large specific refractive-index difference, which generates SC light near visible light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical waveguide and a method for manufacturing the optical waveguide.

  With the progress of optical sensing technology, there is an increasing demand for a light source that can output a wide wavelength range near visible light.

  Conventionally, as a light source capable of outputting such a wide wavelength range, a light source using supercontinuum light (hereinafter abbreviated as SC light) using optical nonlinearity in an optical fiber is known. SC light in the visible region can be generated by an optical fiber processed to have a small diameter, an optical fiber having a gap in the cross section, or the like.

  FIG. 1 shows the structure of a conventional small-diameter processed optical fiber for use as an SC light source. When a normal optical fiber is partially stretched so that light is not confined in the core, both the core glass 101 and the clad glass 102 act as a core, and the air 103 acts as a clad. The waveguide has a very high refractive index difference. In this way, the region where the chromatic dispersion is zero is also shifted to the vicinity of visible light, and at the same time, the optical confinement becomes extremely strong, so that the SC light near the visible light can be realized with a short optical fiber length. Such a technique is also described in Non-Patent Document 1.

`` Supercontinuum generation in tapered fibers '' T.A.Birks, W.J.Wadsworth, and P.St.J.Russell, OPTICS LETTERS Vol. 25, No 19, p.1415-1417, 2000

  However, the conventional optical fiber having a small diameter has the following problems. First, in the conventional optical fiber processed with a small diameter, there is a problem that it is difficult to adjust the diameter of the thin processed part with good reproducibility. Secondly, in the conventional optical fiber processed with a small diameter, there is a problem that a portion processed with a small diameter is fragile and difficult to handle.

  Further, the conventional optical fiber having a gap has a problem that the manufacturing process is complicated and the price is high.

  An optical waveguide of the present invention for solving the above-mentioned problems is an optical waveguide comprising a substrate and a glass film formed on the substrate, and the glass film has both sides of a light guide portion for guiding light. A plurality of holes penetrating in the direction perpendicular to the substrate are provided in a row along the substrate, and the substrate is provided with voids connected to the plurality of holes in a portion facing the lower surface of the light guide portion. It is characterized by having.

  By adopting such a structure, it is possible to provide an optical waveguide that can generate SC light in the visible region, which is inexpensive and excellent in controllability and handling.

  Further, if the glass film above the hole has a rib-type structure in which the glass film is convexly thick, it is possible to provide an optical waveguide with excellent optical confinement and low loss.

  Further, if the width of the rib-type structure is smoothly reduced or increased in the longitudinal direction, it becomes possible to control the wavelength dispersion in the longitudinal direction and generate flat SC light.

  Further, if the film thickness of the glass film is gradually increased toward the end portion at the input / output end of the optical waveguide, an optical waveguide excellent in connectivity with a normal optical fiber can be provided.

  Further, if the substrate is a silicon substrate and the glass film is a quartz glass film, an optical waveguide that is stable and excellent in workability can be provided.

  The optical waveguide as described above includes a glass film forming step of forming a glass film on the substrate, and a plurality of the glass films penetrating in a direction perpendicular to the substrate at positions along both sides of the light guide portion for guiding light. A method of manufacturing an optical waveguide, comprising: a hole forming step of forming holes in a row; and a void forming step of providing a void in a portion of the substrate facing the lower surface of the light guide portion through the plurality of holes. be able to.

  Moreover, the said rib type structure can be formed by including the process of processing the said glass film into a rib type structure between the said glass film formation process and the said hole formation process.

  In addition, between the glass film forming step and the hole forming step, by including a step of gradually increasing or decreasing the film pressure of the glass film toward the end portion, the film thickness of the glass film becomes the end portion. It is possible to realize a structure that gradually becomes thicker toward the surface.

  By using the optical waveguide and the method for manufacturing the optical waveguide of the present invention, it is possible to provide an optical waveguide that can generate SC light in the visible region at low cost and excellent in controllability and handling.

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

  Further, in the following embodiments, the substrate is a silicon substrate, and the glass film is a quartz glass film. This is because such a combination can provide an optical waveguide that is stable and excellent in workability. However, the present invention is not limited to this combination. Of course, other substrates and glass films may be used.

[First Embodiment]
FIG. 2 is a diagram showing the structure of the optical waveguide according to the first embodiment of the present invention. A quartz glass film 12 is provided on the silicon substrate 11, and holes 13 are provided on the left and right of a region (light guide portion 12 a) in which the light of the quartz glass film 12 is guided. Further, a gap 14 is provided in the silicon substrate 11 below the light guide region (light guide portion 12 a), and the gap 14 is connected to the hole 13 described above. In FIG. 2, the shape of the hole 13 is rectangular, but the shape of the hole may be elliptical or circular.

  More specifically, the quartz glass film 12 functions as a portion where the light guide portion 12a guides light. The quartz glass film 12 is provided with holes 13 in rows at positions along the light guide portion 12a with the light guide portion 12a interposed therebetween. In other words, the light guide portion 13a is sandwiched between the row of the right holes 13 provided at regular intervals and the row of the left holes 13 provided at regular intervals. Each hole 13 passes through the quartz glass film 12 along the vertical direction of the silicon substrate 11 (the thickness direction of the quartz glass film 12). As a result, most of the right side surface and the left side surface of the light guide portion 12 a come into contact with the hole 13, that is, the air in the hole 13. The entire upper surface of the light guide portion 12a (the surface opposite to the silicon substrate 11) is in contact with air.

  The silicon substrate 11 is provided with a gap 14 extending in a direction along the light guide portion 12a. That is, a gap 14 is formed in a portion of the silicon substrate 11 that faces the lower surface of the light guide portion 12 a, and the gap 14 is connected to each hole 13. As a result, the lower surface of the light guide portion 12 a comes into contact with the air gap 14, that is, the air in the air gap 14.

Because of this structure, the entire upper and lower surfaces of the light guide portion 12a are in contact with air, and most of the right and left sides of the light guide portion 12a are in contact with air.
As described above, since the periphery of the ultrafine light guide portion 12a is almost surrounded by air, the light guide portion 12a acts as a core, and the surrounding air acts as a clad, resulting in a relative refractive index. The difference is an extremely large optical waveguide. When a waveguide with a large relative refractive index difference and a small cross section is made in this way, the wavelength at which chromatic dispersion (speed difference due to the wavelength of light) becomes zero shifts to the visible light region, and the light confinement is very strong. Therefore (because the cross-sectional area of the region through which light passes is small), the optical nonlinear phenomenon is strongly generated in the visible light region, and supercontinuum light can be generated.

  FIG. 3 is a diagram showing a method for manufacturing an optical waveguide according to an embodiment of the present invention. A glass film forming step 21 for depositing a quartz glass film 12 on the silicon substrate 11, a hole forming step 22 (including steps 22a and 22b) for forming a hole 13 penetrating the quartz glass film 12, a quartz system It comprises a gap forming step 23 (including steps 23a and 23b) in which a gap 14 is provided in the silicon substrate 11 through a hole 13 penetrating the glass 12.

  Here, as the step 21, flame deposition, physical vapor deposition, chemical vapor deposition, or the like can be used.

  Further, as the step 22, for example, a step 22a in which a resist 15 is applied to the quartz glass film 12 and then partially removed using a photomask or the like, and a portion where the resist 15 is removed is processed by plasma etching or the like. It can be realized from step 22b. However, the present invention is not limited to this example, and it goes without saying that the holes 14 penetrating the quartz glass film 12 may be processed by another means.

  Further, the step 23 can be realized by, for example, a step 23a for etching the silicon substrate by performing plasma etching with a different gas type following the step 22b, and a step 23b for removing the resist. However, the present invention is not limited to this example, and it goes without saying that the air gap 14 may be provided in the silicon substrate 11 through the hole 13 penetrating the quartz glass film 12 by another means.

Through the above-described steps, a hole 13 is made in a very thin quartz glass film 12, and the lower side of the glass film 12 (the part facing the light guide portion 12a in the silicon substrate 11) is cut through the hole 13. Thus, it is possible to realize a structure in which the periphery of the light guide portion 12a is surrounded by “almost” air.
In this sense, the hole 13 is a window (etchant passage) for etching the lower side of the glass film 12, and the portion of the glass film 12 remaining between the adjacent holes 13 supports the light guide portion 12a. It has become a pillar to do.

  FIG. 4 shows an optical field distribution of the optical waveguide according to the first embodiment of the present invention manufactured by the process of FIG. Here, the height of the quartz glass film 12 was 1 micron, and the width of the glass film 12 sandwiched by the holes 14 was 1 micron. However, the present invention is not limited to this value, and other values may of course be used. From FIG. 4, it can be seen that the light is almost confined in a 1 micron square region.

  FIG. 5 shows the chromatic dispersion characteristics of the optical waveguide according to the first embodiment of the present invention produced by the process of FIG. As shown in the figure, the wavelength at which chromatic dispersion is 0 is 0.7 microns. Therefore, the strongly confined light satisfies the phase matching condition in the vicinity of visible light, and can generate SC light in the visible light region.

[Second Embodiment]
FIG. 6 is a view showing the structure of an optical waveguide according to the second embodiment of the present invention. A quartz glass film 12 is provided on the silicon substrate 11, and the quartz glass film 12 is provided with a rib type structure 16 for guiding light. A gap 14 is provided in the lower part of the rib type structure 16 provided in the quartz glass film 12, and a hole 13 that penetrates the quartz glass film 12 and reaches the gap 14 is provided in the vicinity of the rib type structure 16. Is provided. Although the hole 13 is rectangular in FIG. 6, the present invention is not limited to this example, and the shape may be oval or circular. In the second embodiment, a portion of the rib-type structure 16 in the quartz glass film 12 is a light guide portion.

  FIG. 7 is a diagram showing a method for manufacturing an optical waveguide according to an embodiment of the present invention. A step 21 for depositing the quartz-based glass film 12 on the silicon substrate 11, a step 24 (including the steps 24a and 24b) for processing the quartz-based glass film 12 into a rib-type structure, and a portion 16 processed into a rib-type structure. Step 22 (including Step 22a and Step 22b) for producing a hole 13 penetrating the quartz glass film 12 in the vicinity of the substrate, and Step 23 for providing a void 14 in the silicon substrate 11 through the hole 13 penetrating the quartz glass film 12 (Including step 23a and step 23b).

  Here, as the step 21, flame deposition, physical vapor deposition, chemical vapor deposition, or the like can be used.

  Further, as the step 22, for example, a step 22a in which a resist 15 is applied to the quartz glass film 12 and then partially removed using a photomask or the like, and a portion from which the resist 15 has been removed is processed by plasma etching or the like. It can be realized from step 22b. However, the present invention is not limited to this example, and it goes without saying that the holes 13 penetrating the quartz glass film 12 may be processed by another means.

  Further, the step 23 can be realized by, for example, a step 23a for etching the silicon substrate by performing plasma etching with a different gas type following the step 22b, and a step 23b for removing the resist. However, the present invention is not limited to this example, and it goes without saying that the air gap 14 may be provided in the silicon substrate 11 through the hole 13 penetrating the quartz glass film 12 by another means.

  Further, as the step 24, for example, a step 24a in which the resist 17 is applied to the quartz glass film 12 and then the resist 17 is partially removed using a photomask, and a portion of the quartz glass from which the resist 17 has been removed. This can be realized by the step 24b of removing the film 12 by etching or the like. However, the present invention is not limited to this example, and it goes without saying that the quartz glass film 12 may be processed into a rib-type structure by another means such as direct processing using a laser.

  FIG. 8 shows an optical field distribution of the optical waveguide of the second embodiment of the present invention manufactured by the process of FIG. Here, the height and width of the rib-type structure 16 were 0.7 microns and 1 micron, respectively, and the thickness of the quartz-based glass film 12 at a place other than the rib-type structure 16 was 0.3 microns. However, the present invention is not limited to this example, and the height and width of the rib-type structure 16 and the thickness of the quartz glass film 12 at a place other than the rib-type structure 16 may of course be different values. I do not care. From FIG. 8, it can be seen that the light is almost confined in a 1 micron square region.

  In the optical waveguide according to the first embodiment of the present invention, since light is guided by the hole 13, the light is easily scattered due to a portion where the hole 13 does not exist or wall surface fluctuation of the hole 13 generated in the manufacturing process. However, in the optical waveguide according to the second embodiment of the present invention, light is guided by the rib-type structure 16 in the lateral direction, so that there is an advantage that an optical waveguide with less scattering can be provided.

  FIG. 9 is a diagram showing the structure of an optical waveguide according to a modification of the second embodiment of the present invention. In addition to the structure of the optical waveguide shown in FIG. 6, a part of the rib type structure 16 is provided with a lateral taper portion 18 that smoothly changes the width of the rib type structure 16. That is, the width of the rib structure 16 is smoothly reduced or increased along the longitudinal direction (light propagation direction). In this way, the wavelength at which chromatic dispersion becomes 0 in the longitudinal direction can be changed smoothly, so that SC light can be generated in a wide range.

  FIG. 10 shows an optical waveguide according to a second modification of the second embodiment of the present invention. In addition to the structure of the optical waveguide shown in FIG. 6, a thick film portion 19 in which the thickness of the quartz glass film 12 is increased at the end of the optical waveguide is provided. If it does in this way, the optical waveguide excellent in connectivity with normal optical parts, such as an optical fiber, can be provided.

  FIG. 11 shows a manufacturing process of the optical waveguide according to the second modification of the second embodiment of the present invention. The quartz glass film 12 deposited on the silicon substrate 11 is further subjected to additional deposition using a shadow deposition jig 20 so that only the left and right ends of the optical waveguide are thickened. A system glass film can be obtained. The optical waveguide structure shown in FIG. 7 can be obtained by inserting the step 25 shown in FIG. 11 between the step 21 and the step 24 of the optical waveguide manufacturing step shown in FIG.

  FIG. 12 shows an output light field at the end of the optical waveguide according to the second modification of the second embodiment of the present invention. As is clear from comparison with FIG. 8, an optical field having a large spot size can be obtained by using the structure 19 in which the quartz glass film is thick at the end, and for example, connectivity with an optical fiber is improved. It can be greatly improved.

It is a perspective view showing the structure of the thin optical fiber for the conventional visible region SC light generation. It is a perspective view showing the structure of the optical waveguide of 1st Embodiment of this invention. It is explanatory drawing showing the preparation methods of the optical waveguide of 1st Embodiment of this invention. It is a characteristic view showing the optical field distribution in the optical waveguide of 1st Embodiment of this invention. It is a characteristic view showing the wavelength dispersion characteristic of the optical waveguide of 1st Embodiment of this invention. It is a perspective view showing the structure of the optical waveguide of 2nd Embodiment of this invention. It is explanatory drawing showing the preparation methods of the optical waveguide of 2nd Embodiment of this invention. It is a characteristic view showing the optical field distribution in the optical waveguide of 2nd Embodiment of this invention. It is a perspective view showing the structure of the optical waveguide of the deformation | transformation of 2nd Embodiment of this invention. It is a perspective view showing the structure of the optical waveguide of the 2nd modification of 2nd Embodiment of this invention. It is explanatory drawing showing the preparation methods of the optical waveguide of the 2nd modification of 2nd Embodiment of this invention. It is a characteristic view showing the optical field distribution in the optical waveguide of the 2nd modification of a 2nd embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Core glass 102 Clad glass 103 Air 11 Silicon substrate 12 Quartz-type glass film 12a Light guide part 13 Hole 14 Space | gap 15 Resist 16 Rib type structure 17 Resist 18 Lateral taper part 19 Thick film part 20 Shadow deposition jig

Claims (9)

An optical waveguide comprising a substrate and a glass film formed on the substrate,
The glass film is provided with a plurality of holes penetrating in the direction perpendicular to the substrate at positions along both sides of the light guide portion for guiding light,
The optical waveguide according to claim 1, wherein air gaps connected to the plurality of holes are provided in a portion facing the lower surface of the light guide portion. The optical waveguide according to claim 1,
An optical waveguide characterized in that the light guide portion of the glass film has a convex rib-shaped structure. The optical waveguide according to claim 2, wherein
An optical waveguide characterized in that the width of the light guide portion having a rib type structure is smoothly reduced or increased along the longitudinal direction. In the optical waveguide according to any one of claims 1 to 3,
An optical waveguide, wherein the glass film has a thickness gradually increasing toward an end at an input / output end of the optical waveguide. In the optical waveguide according to any one of claims 1 to 4,
An optical waveguide, wherein the substrate is a silicon substrate and the glass film is a quartz glass film. An optical waveguide manufacturing method for manufacturing an optical waveguide comprising a substrate and a glass film formed on the substrate,
A glass film forming step of forming a glass film on the substrate;
A hole forming step of forming a plurality of holes penetrating in a direction perpendicular to the substrate at positions along both sides of the light guide portion that guides light in the glass film, and
A method of manufacturing an optical waveguide, comprising: a gap forming step of providing a gap in a portion of the substrate facing a lower surface of the light guide portion through the plurality of holes. In the manufacturing method of the optical waveguide according to claim 6,
A method of manufacturing an optical waveguide, comprising a step of processing the glass film into a rib-type structure between the glass film forming step and the hole forming step. In the manufacturing method of the optical waveguide according to any one of claims 6 to 7,
A method of manufacturing an optical waveguide, comprising a step of gradually increasing or decreasing a film pressure of a glass film toward an end portion between the glass film forming step and the hole forming step. In the manufacturing method of the optical waveguide according to any one of claims 6 to 8,
The method of manufacturing an optical waveguide, wherein the substrate is a silicon substrate, and the glass film is a quartz glass film.

Images