JP2016142995A - Optical waveguide circuit and method for manufacturing optical waveguide circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide circuit that can reduce power consumption, and has a high reliability characteristics.SOLUTION: An optical waveguide circuit 1 includes a substrate 3, a lower cladding layer 5a, an upper cladding layer 5b, a core 7, a heater 9, an insulation film 13 and the like. On the substrate 3, the lower cladding layer 5a is formed. On the lower cladding layer 5a, the core 7 is formed. Further, the upper cladding layer 5b is formed on the lower cladding layer 5a so as to cover the core 7. On the upper cladding layer 5b, the heater 9 is formed. An upper surface 15 and the heater 9 of a cladding layer 5 are covered with the insulation film 13. In addition, a side surface 17 of the cladding layer 5 exposed to a heat insulating groove 11 is also covered with the insulation film 13.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical waveguide circuit in an optical switch and a manufacturing method thereof.

  In order to realize CDC (Colorless, Directionless and Contentionless) -ROADM (Reconfigurable Optical Add / Drop Multiplexer), a multicast switch combining an optical splitter and an optical switch is used. As the multicast switch, a dual type in which an ADD / DROP function is mounted in one housing is the mainstream, and for example, an 8 × 8 multicast switch is used. In the future, a further increase in the number of wavelengths is predicted, and miniaturization of the multicast switch is required.

  The optical switch includes, for example, two optical waveguide circuits sandwiched between couplers, and has a plurality of MZIs (Mach-Zehnder interferometers) provided with heaters as heating means on the optical waveguide circuits. The path through which the optical signal passes can be changed by turning on / off the heater of each MZI.

  On the other hand, when the multicast switch is miniaturized, the ratio of the heater to the chip area becomes very large. For this reason, reduction of the power consumption with respect to one heater is calculated | required strongly.

  As described above, as a method for reducing the low power consumption of the heater on the optical waveguide circuit, for example, there is a method of constructing heat insulation grooves on both sides of the optical waveguide circuit (Patent Document 1).

JP 2007-65645 A

  As in Patent Document 1, by providing heat insulating grooves on both sides of an optical waveguide circuit provided with a heater, heat from the heater can be efficiently transmitted to the waveguide. For this reason, the power consumption of a heater can be reduced. Such an effect is more effective as the ridge width of the optical waveguide circuit is reduced.

  However, when the ridge width is reduced, the reliability characteristics of the optical switch may be deteriorated. On the other hand, increasing the ridge width is contrary to the above-described reduction in power consumption.

  The present invention has been made in view of such problems, and an object thereof is to provide an optical waveguide circuit that can reduce power consumption and has high reliability characteristics.

  In order to achieve the above-described object, the first invention provides a substrate, a cladding layer formed on the substrate, a core formed inside the cladding layer, and one of the cladding layers along the core. And a heater disposed on the upper surface of the cladding layer, and the upper surface of the cladding layer and the side surface of the cladding layer exposed to the heat insulating groove are insulating films. An optical waveguide circuit characterized by being coated.

  The clad layer desirably has a width that increases from the upper surface toward the substrate.

  According to the first invention, the intrusion of moisture into the cladding layer can be prevented by forming the insulating film not only on the upper surface of the cladding layer but also on the side surface of the cladding layer exposed in the heat insulating groove. For this reason, even if the ridge width is reduced to reduce power consumption, high reliability characteristics can be obtained.

  In particular, the thickness of the insulating layer on the side surface of the cladding layer exposed to the heat insulating groove can be increased by forming the cladding layer so that the width increases from the upper surface to the substrate side. Therefore, even if the ridge width is further reduced to reduce power consumption, high reliability characteristics can be obtained.

  The second invention includes a step of forming a clad layer and a core layer on a substrate, a step of forming a core and covering the core with a clad layer, and a heat insulating groove in the clad layer on both sides of the core. And a step of covering the upper surface of the clad layer and the side surface of the clad layer exposed to the heat insulation groove with an insulating film.

  The insulating film is coated by a plasma CVD method, and the substrate is inclined to cover the insulating film when the upper surface of the cladding layer and the side surface of the cladding layer exposed to the heat insulating groove are covered with the insulating film. May be.

  According to the second invention, since the cladding layer is covered with the insulating film after the heat insulating groove is formed, the insulating film can also be formed on the side surface of the cladding layer exposed to the heat insulating groove.

  Further, when the insulating film is formed by the plasma CVD method, the insulating film is formed by tilting the substrate, whereby the insulating film can be easily formed also on the side surface of the cladding layer exposed to the heat insulating groove.

  According to the present invention, it is possible to provide an optical waveguide circuit or the like that can reduce power consumption and has high reliability characteristics.

The figure which shows the optical waveguide circuit 1. FIG. (A)-(c) is a figure which shows the process of manufacturing the optical waveguide circuit 1. FIG. (A)-(c) is a figure which shows the process of manufacturing the optical waveguide circuit 1. FIG. The figure which shows the optical waveguide circuit 1a. The figure which shows the change of PDL in a high temperature, high humidity test.

(Embodiment 1)
The optical waveguide circuit 1 according to the first embodiment of the present invention will be described below. FIG. 1 is a schematic cross-sectional view showing the optical waveguide circuit 1. The optical waveguide circuit 1 includes a substrate 3, a lower clad layer 5a, an upper clad layer 5b, a core 7, a heater 9, an insulating film 13, and the like. The arrangement and the number of columns of the optical waveguide circuit 1 are not limited to the illustrated example.

  The optical waveguide circuit 1 constitutes a thermo-optic phase shifter. The substrate 3 is a silicon substrate, for example. On the substrate 3, a lower clad layer 5a is formed. A core 7 is formed on the lower clad layer 5a. Further, an upper clad layer 5b is formed on the lower clad layer 5a so as to cover the core 7. In the following description, the lower cladding layer 5a and the upper cladding layer 5b are collectively referred to as the cladding layer 5.

A heater 9 is formed on the upper cladding layer 5b. In addition, wiring is connected to the heater 9, and it connects to the electrode part on the board | substrate 3 which abbreviate | omitted illustration. A plurality of clad layers 5 formed in this way are provided along with the heat insulating grooves 11. That is, a plurality of cladding layers 5 are formed separately from each other in a direction perpendicular to the light transmission direction. As the material of the cladding layer 5, a material obtained by adding phosphorus, boron or the like to SiO ₂ can be applied in consideration of workability and the like.

  The upper surface 15 of the cladding layer 5 and the heater 9 are covered with an insulating film 13. The side surface 17 of the clad layer 5 exposed to the heat insulating groove 11 is also covered with the insulating film 13. That is, the outer peripheral surfaces of both the upper surface 15 and the side surface 17 of the cladding layer 5 are covered with the insulating film 13. The insulating film 13 is preferably an insulating film having high heat insulation and high hardness.

  In the following description, the entire width of the cladding layer 5 in a cross section perpendicular to the light transmission direction is referred to as a ridge width. In the example shown in FIG. 1, the ridge width is substantially constant with respect to the height direction of the cladding layer 5.

  If the ridge width is reduced, the reliability characteristics of the optical switch may be deteriorated. More specifically, when the ridge width is reduced, the change in the polarization dependence characteristic (PDL) in the high temperature and high humidity test (85 ° C./85%/2000 h) may increase.

  The inventors have found that the deterioration of the reliability characteristics is caused by the entry of moisture into the optical waveguide circuit from the outside. That is, it has been found that the moisture state is mixed into the cladding layer of the optical waveguide circuit exposed in the heat insulating groove, thereby changing the stress state of the optical waveguide circuit, thereby deteriorating the reliability characteristics.

As a countermeasure, there is a method of increasing the ridge width to reduce the influence of moisture mixing. However, increasing the ridge width is contrary to the aforementioned reduction in power consumption. In addition, the method of increasing the ridge width cannot completely suppress the influence of moisture.
Therefore, infiltration of moisture can be suppressed by covering the outer peripheral surfaces of both the upper surface 15 and the side surface 17 of the cladding layer 5 with the insulating film 13 in this way. For example, SiO ₂ can be used as the insulating film 13, but other materials may be used as long as the above-described characteristics are satisfied and moisture can be prevented from entering.

Since phosphorus and boron are added to SiO ₂ in the clad layer 5, water easily enters compared to high-purity SiO ₂ . As described above, when water enters the clad layer 5 from the heat insulating groove 11 side, the stress state of the optical waveguide circuit changes, and the reliability characteristics deteriorate. In particular, when the ridge width is narrowed, this effect is significant. However, in this embodiment, the side surface 17 of the cladding layer 5 is also covered with the insulating film 13, thereby preventing water from entering. As a result, the ridge width can be narrowed and the power consumption of the heater 9 can be suppressed. According to this embodiment, even when the ridge width is, for example, 15 μm or less and the distance from the side surface of the cladding layer 5 to the core is 6 μm or less, it is possible to suppress deterioration of the reliability characteristics.

  Next, a method for manufacturing the optical waveguide circuit 1 will be described. First, as shown in FIG. 2A, the lower clad layer 5 a is formed on the substrate 3. The lower cladding layer 5a can be formed by, for example, an FHD (Frame Hydrolysis Deposition) method.

  Next, as shown in FIG. 2B, the core layer 7a is formed on the lower cladding layer 5a by the FHD method or the like.

  Next, as shown in FIG. 2C, the core 7 is formed by photolithography, reactive ion etching, or the like. In the figure, an example in which three rows of cores 7 are formed is shown.

  Thereafter, as shown in FIG. 3A, the upper cladding layer 5b is formed on the lower cladding layer 5a by the FHD method or the like so that the core 7 is embedded. The lower clad layer 5a, the core 7, and the upper clad layer 5b are each subjected to heat treatment as necessary.

  Next, a metal film is formed on the upper clad layer 5b by sputtering or vapor deposition, and the heater 9 is formed by photolithography, reactive ion etching, or the like. Further, a part of the clad layer 5 is removed by the same method to form the heat insulating groove 11.

  Next, the cladding layer 5 and the heater 9 are covered with the insulating film 13 by plasma CVD or the like. At this time, the insulating film 13 can be efficiently formed also on the side surface 17 of the cladding layer 5 by forming the film while tilting the substrate 3 by a predetermined angle with the light transmission direction as the rotation axis.

  As described above, according to the present embodiment, the side surface 17 of the cladding layer 5 exposed to the heat insulating groove 11 is covered with the insulating film 13. That is, the cladding layer 5 is not directly exposed to the heat insulating groove 11 and is protected by the insulating film 13. Accordingly, it is possible to prevent water from entering the cladding layer 5. For this reason, the ridge width of the cladding layer 5 can be narrowed, and the power consumption of the heater can be suppressed.

(Embodiment 2)
Next, a second embodiment will be described. FIG. 4 is a schematic cross-sectional view showing an optical waveguide circuit 1a according to the second embodiment. In the following description, components having the same functions as those of the optical waveguide circuit 1 are denoted by the same reference numerals as those in FIG.

  The optical waveguide circuit 1a has substantially the same structure as the optical waveguide circuit 1, but the shape of the cladding layer 5 is different. In the cross section perpendicular to the light transmission direction, the cladding layer 5 of the optical waveguide circuit 1a is formed so that the ridge width gradually increases from the upper surface 15 side toward the substrate 3 side. In the illustrated example, the cross-sectional shape of the cladding layer 5 is a substantially trapezoid.

  In order to increase the ridge width toward the substrate 3, process parameters such as the mask shape and gas flow rate may be adjusted in the etching for forming the heat insulating grooves 11.

  According to the second embodiment, an effect similar to that of the first embodiment can be obtained. Further, since the ridge width of the cladding layer 5 becomes wider toward the substrate side, the insulating film 13 can be efficiently formed on the side surface 17 of the cladding layer 5. Therefore, the film thickness of the insulating film 13 on the side surface 17 of the cladding layer 5 can be increased. For this reason, infiltration of water can be prevented more reliably.

  Moreover, since the ridge width of the upper clad layer 5b on the upper surface side where the heater 9 is disposed can be reduced, the power consumption of the heater 9 can be further suppressed. Even when the cross-sectional shape of the cladding layer 5 is trapezoidal, the insulating film 13 may be formed while the substrate 3 is tilted as necessary.

The reliability characteristics of the optical waveguide circuit were evaluated. First, as shown in FIG. 1, the clad layer 5 and the heat insulating groove 11 having a rectangular cross section (ridge width is substantially constant) were formed by the method described above. The ridge width was 30 μm. After the formation of the heat insulating groove 11, an insulating film 13 made of SiO ₂ was formed on the obtained cladding layer 5. The thickness of the insulating film 13 was 5 μm on the upper surface 15 and 0.5 μm on the side surface 17 (Sample A).

Further, as shown in FIG. 4, the trapezoidal clad layer 5 and the heat insulating groove 11 were formed by the above-described method. The ridge width of the upper surface 15 was 15 μm, and the angle between the upper surface 15 and the side surface 17 was 100 °. After the formation of the heat insulating groove 11, an insulating film 13 made of SiO ₂ was formed on the obtained cladding layer 5. The thickness of the insulating film 13 was 5 μm on the upper surface 15 and 2 μm on the side surface 17 (Sample B).

  For comparison, a sample having no insulating film on the side surface 17 of the clad layer 5 was prepared for the sample A (sample C). Specifically, the clad layer 5 is formed under the same conditions and shape as the sample A, but the heat insulating groove 11 is formed after the insulating film 13 is formed.

  Each sample was placed in a high-temperature and high-humidity environment (85 ° C./85%), and analyzed by secondary ion mass spectrometry after 500 hours. As a result, in any of Samples A to C, moisture was not confirmed from the upper surface 15 on which the insulating film 13 was formed, but in Sample C, moisture from the side surface 17 was confirmed.

  Next, each sample was placed in a high-temperature and high-humidity environment (85 ° C./85%), and the change in polarization-dependent characteristics until 2000 hours elapsed was evaluated. FIG. 5 is a diagram illustrating the relationship between time and the amount of change (dB) in the polarization-dependent characteristics. Black triangles in the figure indicate the results of sample A, black circles indicate the results of sample B, and x indicates the results of sample C.

  In Sample C that does not have the insulating film 13 on the side surface 17, the polarization dependence characteristic changed by about 1 dB after 2000 hours, whereas in Sample A in which the insulating film 13 was provided on the side surface 17, 0.15 dB even after 2000 hours. There was little change with the following. In addition, the power consumption of the heater 9 at that time was 150 mW / π shift, and a sufficiently small power consumption was realized.

  Further, Sample B was able to obtain sufficient reliability characteristics even though the ridge width of the upper surface 15 was narrower than that of Sample A. In addition, the power consumption of the heater 9 at that time was 100 mW / π shift, and a smaller power consumption was realized.

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, the technical scope of this invention is not influenced by embodiment mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

  For example, the shape of the cladding layer 5 is not limited to the illustrated example. For example, the angle between the upper surface 15 and the side surface 17 in the trapezoid does not need to be 100 °. Further, even if it is not a perfect trapezoid, it is sufficient that the ridge width widens on the substrate side and the side surface 17 is not shaded during film formation from the upper surface side.

DESCRIPTION OF SYMBOLS 1, 1a ... Optical waveguide circuit 3 ... Substrate 5 ... Cladding layer 5a ... Lower clad layer 5b ... Upper clad layer 7 ... Core 7a ... Core layer 9 ... Heater 11 .... Insulating groove 13 ... ... Insulating film 15 ... ... Top 17 ... ... Side

Claims (4)

A substrate,
A clad layer formed on the substrate;
A core formed inside the cladding layer;
A heat insulating groove formed by removing a portion of the cladding layer along the core;
A heater disposed on an upper surface of the cladding layer;
Comprising
An optical waveguide circuit, wherein an upper surface of the cladding layer and a side surface of the cladding layer exposed to the heat insulating groove are covered with an insulating film.   The optical waveguide circuit according to claim 1, wherein the cladding layer has a width that increases from the upper surface toward the substrate. Forming a clad layer and a core layer on a substrate;
Forming a core, and further covering the core with a cladding layer;
Forming a heat insulating groove in the clad layer on both sides of the core;
Coating the upper surface of the cladding layer and the side surface of the cladding layer exposed in the heat insulating groove with an insulating film;
A method of manufacturing an optical waveguide circuit, comprising: The insulating film is coated by a plasma CVD method,
The light guide according to claim 3, wherein when the upper surface of the cladding layer and the side surface of the cladding layer exposed to the heat insulating groove are coated with the insulating film, the substrate is inclined to cover the insulating film. Wave circuit manufacturing method.

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