JP2006330245A - Optical waveguide device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide device which has fundamental optical circuits connected each other on the same substrate without spoiling their characteristics, and a manufacturing method thereof. <P>SOLUTION: In the optical waveguide device which has an input waveguide 12 and output waveguides 13 optically connected through an optical multiplexing/demultiplexing part 14, a cross section of a core of the input waveguide 12 is formed into a rectangle, side walls 18 on sides facing each other of cores of the output waveguides 13 are tapered by providing elevation angles, and side walls 19 on the other core are formed perpendicularly. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a planar optical waveguide element used for optical communication and a method for manufacturing the same.

  A planar optical waveguide device used in optical communication includes a basic circuit such as an optical wavelength multiplexer / demultiplexer, an optical variable attenuator, a Y-branch waveguide, a directional coupler, and a plurality of optical waveguides that connect these basic circuits. With. In order to optimize the characteristics of the circuit itself of each basic circuit, the shape of the core of the channel type optical waveguide included in each basic circuit is classified into two types with respect to the inclination angle of the side wall of the core.

  One is to form both side walls of the core in a tapered shape, and the other is to form both side walls of the core perpendicular to the substrate. Each tapered core side wall is formed in order to reduce loss at the arrayed waveguide in the arrayed waveguide type optical wavelength multiplexer / demultiplexer and the branching portion of the Y-branched waveguide. Each of the vertical core side walls is formed in order to reduce a loss in an interference optical circuit such as a directional coupler, an MMI coupler, and a Mach-Zehnder type optical waveguide. The cross section of the optical waveguide connecting the basic optical circuits or the core of the input / output waveguide of the basic optical circuit is formed in a rectangular shape.

JP 2004-77859 A

  However, there is a desirable shape for each basic optical circuit in the shape of the core side wall. However, when many types of basic optical circuits are monolithically integrated on the same substrate, a tapered core or a rectangular core is used. Either one must be selected. When forming a planar optical waveguide device that contains a basic optical circuit with a tapered core and a basic optical circuit with a rectangular core, the characteristics of all the basic optical circuits that make up the planar optical waveguide device are not impaired. It was difficult to connect.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide an optical waveguide element in which each basic optical circuit is connected on the same substrate without impairing its characteristics, and a method for manufacturing the same.

  In order to achieve the above object, a first aspect of the present invention is an optical waveguide device in which an input waveguide and an output waveguide are optically connected via an optical multiplexing / demultiplexing section, and a cross section of a core of the input waveguide. Are formed in a rectangular shape, and the opposite side walls of the output waveguide core in the vicinity of the optical multiplexing / demultiplexing portion are formed in a tapered shape with an elevation angle, and the side wall of the other core is provided with a vertical or elevation angle. This is an optical waveguide element formed in a tapered shape.

  A second aspect of the present invention is the optical waveguide device according to the first aspect, wherein the opposing side walls of the core in the vicinity of the optical multiplexing / demultiplexing portion of the output waveguide are tapered.

  According to a third aspect of the present invention, there is provided the optical waveguide device according to the first or second aspect, wherein the taper portion of the side wall formed in a tapered shape has an elevation angle of 75 ± 10 degrees.

  According to a fourth aspect of the present invention, there is provided the optical waveguide device according to the third aspect, wherein the taper portions immediately adjacent to the optical multiplexing / demultiplexing portion of the output waveguide are overlapped with each other while maintaining the elevation angle.

  According to a fifth aspect of the present invention, a dummy waveguide is formed at a boundary between a rectangular output waveguide having a rectangular core section of the output waveguide and a tapered output waveguide in which the core is formed in a tapered shape. 5. The optical waveguide according to claim 1, wherein the side wall of the core on the input waveguide side of the dummy waveguide is formed in a tapered shape, and the side wall of the core on the opposite side is formed in a vertical or tapered shape. It is an element.

  The invention according to claim 6 is the optical waveguide device according to claim 5, wherein the average core width of the output waveguide and the core width of the rectangular output waveguide are formed to be substantially equal.

  According to a seventh aspect of the present invention, in the method of manufacturing an optical waveguide device in which an input waveguide and an output waveguide are optically connected via an optical multiplexing / demultiplexing unit, a core film for forming a core is formed on a substrate. And providing a first mask on the core film, etching the non-masked portion of the core film provided with the mask, and taper the side walls of the output waveguide core facing each other with an elevation angle. In addition, a second mask is provided on the core film, and a non-mask portion of the core film provided with the mask is etched so as to etch the side wall on the other side of the core of the output waveguide and the input guide. This is a method of manufacturing an optical waveguide device in which both side walls of the core of the waveguide are formed vertically.

  According to the present invention, it is possible to reduce the loss of an optical waveguide connecting a plurality of basic optical circuits.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a plan view showing a preferred embodiment of an optical waveguide device according to the present invention.

  As shown in FIGS. 1 and 2A to 2E, the optical waveguide element 10 includes a substrate 11, a core formed on the substrate 11, and a clad covering the core. The substrate 11, the core, and the clad are made of quartz glass, and the core has a higher refractive index than the clad and the substrate.

  In the optical waveguide device, an input waveguide and an output waveguide are optically connected via an optical multiplexing / demultiplexing unit. In the optical waveguide device 10 of the present embodiment, an input waveguide 12 and its input are connected. A Y branch waveguide is formed by two output waveguides 13 and 13 connected to one end of the waveguide 12 and an optical multiplexing / demultiplexing unit 14 formed by branching the output waveguides 13 and 13 to the input waveguide 12. An element is formed.

  The input waveguide 12 is an optical waveguide that causes an optical signal transmitted from the outside to enter the optical multiplexing / demultiplexing unit 14 or transmits the optical signal combined by the optical multiplexing / demultiplexing unit 14 to the outside. , 17 are perpendicular to the substrate 11, that is, the cross section of the core is formed in a rectangular shape.

  The output waveguide 13 includes a tapered output waveguide 15 and a rectangular output waveguide 16. In the tapered output waveguide 15, in the vicinity of the optical multiplexing / demultiplexing unit 14, one side wall 19 of the core is formed perpendicular to the substrate 11, and the other side wall 18 is formed in a tapered shape with an elevation angle. It is a waveguide. The rectangular output waveguide 16 is an optical waveguide having a rectangular cross section in which both side walls 20 and 20 of the core are formed perpendicular to the substrate, and is connected to the input waveguide 12 via the tapered output waveguide 15. .

  Specifically, the side walls 18 and 18 of the cores on the opposite sides of the tapered output waveguides 15 and 15 are respectively formed in a tapered shape, and the opposite side walls 19 and 19 are formed vertically. The core below the side wall 18 formed in a tapered shape is a tapered portion 21. The elevation angle of the taper portion 21 is preferably 75 ± 10 degrees. This is because if the elevation angle of the taper portion 21 exceeds 85 degrees, it is difficult to reduce the loss at the optical multiplexing / demultiplexing portion 14. The reason why the lower limit of the elevation angle of the taper portion 21 is set to 65 degrees is that it is difficult to form the elevation angle of the taper portion 21 below 65 degrees even if various process conditions for taper etching are currently studied. .

  In the tapered output waveguide 15 closest to the optical multiplexing / demultiplexing portion 14, the tapered portions 21, 21 of both tapered output waveguides 15, 15 are formed so as to overlap each other while maintaining their elevation angle. That is, as the tapered output waveguides 15 and 15 are separated from each other, the portions that gradually contact each other from the center of the upper surface of the core are gradually reduced, and the tapered portions 21 and 21 are separated from each other. In other words, both taper portions 21, 21, with a line (valley line) 24 connecting the intersection of the lower edges 22, 22 of both taper portions 21, 21 and the intersection of the upper edges 23, 23 of both taper portions 21, 21 21 is bonded. Here, the immediate vicinity of the optical multiplexing / demultiplexing unit 14 means that the core width gradually increases as the output waveguide 13 continuously formed in the optical multiplexing / demultiplexing unit 14 advances in the light propagation direction (right side in FIG. 1). It represents up to near the core width of the waveguide 12.

In the output waveguide 13, the average core width of the tapered output waveguide 15 and the core width of the rectangular output waveguide 16 are substantially equal, and the outer core side walls 19 and 20 that are formed vertically are straight lines. Are touching. Here, the average core width of the tapered output waveguide 15 indicates a length represented by (the width of the core upper surface l ₁ + the width of the core lower surface l ₂ ) / 2 (FIG. 2C). reference).

  Furthermore, a dummy waveguide 26 directed toward the other boundary 25 is formed at each boundary 25 between the tapered output waveguide 15 and the rectangular output waveguide 16. In the dummy waveguide 26, the side wall 27 of the core on the input waveguide 12 side is formed in a tapered shape, and the side wall 28 on the opposite side is formed perpendicular to the substrate 11. The dummy waveguide 26 does not affect the characteristics of the optical signal propagating through the tapered output waveguide 15 and the rectangular output waveguide 16 with respect to the tapered output waveguide 15 and the rectangular output waveguide 16. It is formed by connecting at an angle close to 90 ° (substantially at a right angle). By connecting the dummy waveguides 26 at substantially right angles, an optical signal propagating from the tapered output waveguide 15 or an optical signal propagating from the rectangular output waveguide 16 does not propagate to the dummy waveguide 26. In this embodiment, one boundary 25 and the other boundary 25 are connected and connected by a single dummy waveguide 26. However, the one boundary 25 and the other boundary 25 are not necessarily connected. Good.

  In FIG. 1, the vertical scale and the horizontal scale are significantly different and are displayed compressed in the light propagation direction (horizontal direction in the figure), but the branch angle in this embodiment is very small. For example, it is formed below 1 °.

  Next, a method for manufacturing the optical waveguide element 10 of FIG. 1 will be described with reference to FIGS. 3A to 3G, taking the 2C-2C cross section as an example.

  As shown in FIG. 3A, first, a core film 31 having a uniform film thickness is provided on a substrate 11 by using a conventional film forming method. Next, a mask material 32 for forming an etching mask is provided on the core film 31. In the present embodiment, the mask material 32 is formed of WSi.

  As shown in FIG. 3B, the mask material 32 is subjected to photolithography and etching to form a first mask 33 having an optical waveguide pattern. The pattern of the first mask 33 is a pattern for forming the core side wall 18 described in FIG. Thereafter, the non-mask portion 38 of the core film 31 is etched (first etching). At this time, by appropriately selecting the etching conditions, for example, the substrate heating temperature, the type of the etchant gas, the mixing ratio of the gas, the gas pressure of the etchant gas, the high-frequency power for plasma generation, etc. Etching can be performed at an angle, and as shown in FIG. 3C, a tapered core side wall 18 is formed. In this embodiment mode, etching is performed with the etching conditions set so that the inclination angle is 75 degrees.

  After the first etching, the first mask 33 on the core film 34 is peeled off.

  As shown in FIG. 3D, a mask material 35 is provided on the core film 34 and the substrate 11 on which the core side wall 18 is formed. The mask material 35 was formed of WSi like the mask material 32. Here, it is preferable that the thickness of the mask material 35 be equal to or greater than the film thickness of the core film 34 × 0.05 in order to withstand side etching by the second etching performed later.

  As shown in FIG. 3E, the mask material 35 is subjected to photolithography and etching to form a second mask 36 having an optical waveguide pattern. The pattern of the second mask 36 is a pattern for forming the core side wall 19 shown in FIG. Thereafter, the non-masked portion 39 of the core film 34 is etched (second etching). In the second etching, the etching conditions are changed from those in the first etching, and etching is performed in a direction perpendicular to the substrate 11 to form the core side wall 19. As shown in FIG. The core of the waveguide 15 is obtained.

  After the second etching, the mask 36 is peeled off.

  As shown in FIG. 3G, the optical waveguide device 10 is obtained by forming the clad 37 on the substrate 11 on which the core of the tapered output waveguide 15 is formed so as to cover the core.

  3A to 3G, the sectional view of the tapered output waveguide 15 is shown and described. However, when the core film 31 is etched in a tapered shape, the core side wall 27 of the dummy waveguide 26 is removed. When the core film 34 is formed at the same time and etched vertically, both the core side walls 17 of the input waveguide 12, both the core side walls 20 of the rectangular output waveguide 16, and the core side wall 28 opposite to the dummy waveguide 26 are simultaneously formed. Thus, the optical waveguide device 10 is obtained.

  In the optical waveguide device 10 of the present embodiment, in the input waveguide 12 and the rectangular output waveguide 16, the core is formed in a rectangular shape to reduce transmission loss of an optical signal transmitted over a long distance. Since the tapered output waveguides 15 and 15 having the tapered portions 21 and 21 are formed inside each other and the core is gradually branched at the optical multiplexing / demultiplexing portion 14, the optical signal is branched or coupled. The resulting radiation loss is reduced.

  That is, since the optical signal is transmitted through the core with the lowest loss in each optical waveguide, the optical waveguide device 10 including these optical waveguides can reduce the loss of the optical signal.

  Further, in the optical waveguide in which the tapered portion 21 and the vertical core side wall 20 are in contact with each other without providing the dummy waveguide 26 at the boundary 25 between the tapered output waveguide 15 and the rectangular output waveguide 16, Since the etching is performed twice when forming the core connected to the vertical core side wall 20, both the taper etching and the vertical etching are performed at the boundary 25 due to manufacturing errors, and the tapered portion 21 and the rectangular output are formed. There is a high possibility that a groove or the like is formed between the waveguide 16 and the core. As a result, the propagating optical signal is emitted and reflected at the boundary 25.

  Therefore, by providing a dummy waveguide 26 that separates the tapered portion 21 and the vertical core side wall 20 by a predetermined distance at the boundary 25, one core of the core side wall 20 of the rectangular output waveguide 16 and the dummy waveguide 26 is provided. Since the side wall 28 is in contact with the core side wall 18 of the tapered output waveguide 15 and the other core side wall 27 of the dummy waveguide 26 is in contact with each other, the taper portion 21 and the vertical core side wall 20 are not in direct contact with each other. Therefore, the output waveguide 13 to which the cores having different sidewall shapes are connected can be formed without being etched twice at the boundary 25, and the loss at the boundary 25 can be reduced.

  Here, the loss of the optical waveguide device of the present embodiment will be described.

  As an example, an optical circuit (referred to as a rectangular branched optical circuit) in which five stages of optical waveguide elements having a Y-branch structure in which the core cross section is formed of only a rectangular optical waveguide, and the optical waveguide element 10 in FIG. The loss was measured when an optical signal having a wavelength band of 1.3 μm was transmitted to each of optical circuits (referred to as tapered branched optical circuits) cascaded in five stages. As a result, the loss of the tapered branch optical circuit was 15.75 dB, and the loss of the rectangular branch optical circuit was 16.18 dB. The additional loss per stage of the optical multiplexing / demultiplexing part excluding the propagation loss from these losses is 0.15 dB for the tapered branch optical circuit and 0.24 dB for the rectangular branch optical circuit.

  Accordingly, the tapered branch optical circuit can reduce the additional loss per stage of the optical multiplexing / demultiplexing unit by about 0.1 dB compared to the rectangular branch optical circuit.

  In the manufacturing method of the present embodiment, a resist film formed by applying a liquid resist on the taper-etched core film in the step of FIG. 3D is used as a photosensitive film during photolithography. Used.

  When the second mask 36 is formed by patterning the mask material 35, since the irregularities are formed in the core film 34 by the first etching, the mask material 35 is formed on the surface where the irregularities are formed. Therefore, when the resist solution is applied onto the mask material 35, uneven coating occurs on the resist. In particular, the difference in height of the mask material 35 is large near the boundary between the etched portion and the unetched portion, and the resist thickness is difficult to be constant. When the resist film having such uneven coating is exposed, the accuracy of the pattern formed after development is deteriorated, and hence the accuracy of the pattern of the core formed by etching is deteriorated.

  Therefore, the optical waveguide device 10 is manufactured by designing the mask pattern so that the dummy waveguide 26 is provided in the pattern formed by the first etching and the pattern formed by the second etching, thereby causing the resist coating unevenness. Etching unevenness appears on the side wall of the dummy waveguide 26. Since the dummy waveguide 26 is provided so that the optical signal does not propagate, it does not affect the optical signal near the boundary.

  As described above, the structure in which the dummy waveguide 26 is provided in the connection portion 25 between the tapered output waveguide 15 and the rectangular output waveguide 16 makes it possible to connect the core having two different core side walls on the substrate. The waveguide element 10 can be formed with high accuracy. Thereby, the loss resulting from the waveguide structure when the optical signal propagates through the boundary 25 can be reduced.

  Considering manufacturing errors due to photolithography and etching, the width of the dummy waveguide 26 is preferably 1 μm or more. Further, the upper limit of the width of the dummy waveguide 26 may be an appropriate width that does not affect the optical specifications that require optical transmission loss.

  In the present embodiment, the tapered core side wall 18 is first formed by the first etching, and then the vertical core side wall 19 is formed by the second etching later to produce the optical waveguide device 10. After the vertical core side wall 19 is formed first as the first etching, the tapered core side wall 18 may be formed later as the second etching. At this time, the thickness of the second mask is preferably set to a core film thickness × 0.07 or more and a core film thickness × 0.2 or less. The reason why the thickness of the second mask is equal to or larger than the core film thickness × 0.07 is to sufficiently protect the previously formed vertical core side wall 19 from the second etching. The reason for setting the thickness of the second mask to be equal to or less than the core film thickness × 0.2 is to reduce the amount of mask thickness reduction by etching. If the reduction is large, the difference from the thickness of the design mask becomes large, and it becomes difficult to produce a desired optical waveguide.

  Further, in the optical waveguide device 10, one side wall 18 of the core of the tapered output waveguide 15 is formed in a taper shape and the other side wall 19 is formed in a vertical shape. However, both side walls 18 and 19 of the core are formed in a taper shape. It may be formed.

  Next, another preferred embodiment of the optical waveguide according to the present invention will be described with reference to FIG.

  As shown in FIG. 4, the optical waveguide 40 of the present embodiment is a Mach-Zehnder type optical waveguide provided by connecting two optical waveguide elements 10 of FIG. 1 on one substrate. Specifically, the optical waveguide 40 includes both rectangular output waveguides 16 and 16 of one optical waveguide element 10 and both rectangular output waveguides 16 and 16 of the other optical waveguide. The input waveguides 12 and 12 are formed as input / output optical waveguides. Here, a portion surrounded by the tapered output waveguide 15 and the dummy waveguide 26 is a region 45, and a portion surrounded by the rectangular output waveguide 16 and the dummy waveguide 26 is a region 46.

  Next, the manufacturing method of the optical waveguide of this Embodiment is demonstrated based on Fig.5 (a) and FIG.5 (b).

  Since the optical waveguide 40 of the present embodiment uses two optical waveguide elements 10 of FIG. 1, the basic manufacturing method is the same as the manufacturing method of the optical waveguide element 10 of FIG. 1 described above. The difference is that the waveguide pattern of the mask to be formed is different and the order of vertical etching and taper etching is reversed.

  As shown in FIG. 5A, the first mask 41 is a mask 33 formed in the step of FIG.

  The first mask 41 is a pattern for forming the side wall of the core vertically. The pattern includes an input waveguide forming portion 42, an output waveguide forming portion 43, a dummy waveguide forming portion 44, and the vicinity of the optical multiplexing / demultiplexing portion surrounded by the output waveguide forming portion 43 and the dummy waveguide forming portion 44. The region 45 is formed on the core film 31.

  After the mask 41 is formed, the core film 31 in the non-mask portion is etched vertically so that the core of the input waveguide 12, the core of the rectangular output waveguide 16, the core sidewall 19 outside the tapered output waveguide 15, and A core side wall 28 on the non-input waveguide side (region 46 side in FIG. 5) of the dummy waveguide 26 is formed.

  As shown in FIG. 5B, the second mask 47 is the mask 36 formed in the step of FIG. The second mask 47 covers a portion excluding the region 45 shown in FIG.

  A second mask 47 is formed on the core film 34, and the core film in the region 45 is taper-etched so that the core side wall 17 inside the tapered output waveguide 15 and the core on the input waveguide 12 side of the dummy waveguide 26. Side walls 27 are formed.

  The optical waveguide 40 of the present embodiment also has the same function and effect as the optical waveguide of FIG.

In the present embodiment, the two optical waveguide elements 10 are connected by the output waveguides 13 and 13 to form the Mach-Zehnder type optical waveguide element. However, another optical waveguide element is added to the output waveguide 13 of a certain optical waveguide element 10. 10 input waveguides 12 may be connected to form an input / output 1 × 2 ⁿ coupler optical waveguide device in which a plurality of optical waveguide devices 10 are connected in multiple stages.

1 is a plan view of an optical waveguide device according to a preferred embodiment of the present invention. 2A is a sectional view taken along line 2A-2A in FIG. 1, FIG. 2B is a sectional view taken along line 2B-2B in FIG. 1, and FIG. 2C is a sectional view taken along line 2C-2C in FIG. 2 (d) is a cross-sectional view taken along line 2D-2D of FIG. 1, and FIG. 2 (e) is a cross-sectional view taken along line 2E-2E of FIG. 3A to 3G are cross-sectional views illustrating a method for manufacturing the optical waveguide device of FIG. It is a top view of the optical waveguide device of other suitable embodiments. 5A is a plan view showing a first mask for forming the optical waveguide device of FIG. 4, and FIG. 5B is a second view for forming the optical waveguide device of FIG. It is a top view which shows a mask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical waveguide element 12 Input waveguide 13 Output waveguide 14 Optical multiplexing / demultiplexing part 15 Tapered output waveguide 16 Rectangular output waveguide 21 Tapered part 26 Dummy waveguide

Claims (7)

  In an optical waveguide element in which an input waveguide and an output waveguide are optically connected via an optical multiplexing / demultiplexing unit, a cross section of the core of the input waveguide is formed in a rectangular shape, and an output in the vicinity of the optical multiplexing / demultiplexing unit An optical waveguide device characterized in that the opposite side walls of the waveguide core are tapered with an elevation angle, and the sidewall of the other core is tapered with a vertical or elevation angle.   2. The optical waveguide device according to claim 1, wherein the side walls of the core in the vicinity of the optical multiplexing / demultiplexing portion of the output waveguide facing each other are tapered.   The optical waveguide device according to claim 1 or 2, wherein an elevation angle of the tapered portion of the side wall formed in a tapered shape is 75 ± 10 degrees.   4. The optical waveguide device according to claim 3, wherein each taper portion nearest to the optical multiplexing / demultiplexing portion of the output waveguide is overlapped with the elevation angle maintained.   A dummy waveguide is formed at the boundary between the rectangular output waveguide having a rectangular core cross section of the output waveguide and the tapered output waveguide in which the core is formed in a tapered shape, and the input waveguide of the dummy waveguide is input. 5. The optical waveguide device according to claim 1, wherein the side wall of the core on the waveguide side is formed in a tapered shape, and the side wall of the core on the opposite side is formed in a vertical or tapered shape.   6. The optical waveguide device according to claim 5, wherein an average core width of the output waveguide and a core width of the rectangular output waveguide are formed to be substantially equal. In a method for manufacturing an optical waveguide device in which an input waveguide and an output waveguide are optically connected via an optical multiplexing / demultiplexing unit, a core film for forming a core is provided on a substrate, and the core film is provided on the core film. A first mask is provided, a non-mask portion of the core film provided with the mask is etched, and the side walls of the core of the output waveguide opposite to each other are provided with an elevation angle and tapered. A second mask is provided on the core film, and the non-masked portion of the core film provided with the mask is etched so that the other side wall of the core of the output waveguide and both side walls of the core of the input waveguide are formed. A method for manufacturing an optical waveguide device, wherein the optical waveguide device is formed vertically.

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