JP2006259104A - Optical circuit and optical variable attenuator with waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waveguide type optical variable attenuator whose operation speed is fast. <P>SOLUTION: The waveguide type optical variable attenuator has a Mach-Zehnder type optical waveguide 22, having a couple of channel waveguides 28 and 29 between an input waveguide 24 and an output waveguide 25, formed on a quartz substrate 21, is provided with a thin-film heater 31 on the surface of the channel waveguide 28, and supplies electric power to the thin-film heater 31 to attenuate signal light. The one channel waveguide 28 or both the channel waveguides are raised from the substrate, a heater 31 is provided on one flank 33a of the channel waveguide, and a film 32 for heat conduction is provided on the other flank 34a. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical circuit in which a heating means is provided in an optical waveguide, and more particularly to a waveguide type optical variable attenuator in which a heater is provided in a Mach-Zehnder type waveguide.

An optical variable attenuator is one of optical circuits including a core-embedded optical waveguide and heating means such as a heater. An optical variable attenuator used in optical communication has a function of attenuating light having a certain intensity P _in to an arbitrary intensity P _out (P _in > P _out ).

  FIG. 6 shows a conventional general waveguide type optical variable attenuator. As shown in FIG. 6, the waveguide type optical variable attenuator 80 includes an input waveguide 82 formed on a substrate, an output waveguide 83, and light connected to the input waveguide 82 and the output waveguide 83, respectively. A symmetric Mach-Zehnder optical waveguide 88 including a coupler section 84 and 85 and a pair of channel waveguides 86 and 87 connected between the optical coupler sections 84 and 85 is provided. A metal film heater 89 is provided on the clad surface above one of the channel waveguides 86, and a power supply 90 is connected to the heater 89.

  The input-side optical coupler unit 84 demultiplexes the light transmitted through the input waveguide 82 and transmits the demultiplexed light to the channel waveguides 86 and 87, respectively. The output-side optical coupler unit 85 multiplexes the light transmitted through the channel waveguides 86 and 87, and outputs the combined light to the output waveguide 83.

  The heater 89 generates high heat as the power supplied from the power supply 90 increases, and the channel waveguide 86 is warmed by the heat to change the refractive index of the channel waveguide 86.

  According to such a configuration, one of the channel waveguides 86 is heated to change the refractive index of the channel waveguide 86, so that it is branched by the input-side optical coupler unit 84 and propagates through both channel waveguides 86 and 87. The signal light to be phased has a phase difference, and the signal light is attenuated and output by the interference in the optical coupler unit 85 on the output side. If the temperature of the channel waveguide 86 is controlled by a heater, the refractive index of the channel waveguide 86, that is, the phase of the signal light can be controlled, and the attenuation amount of the light emitted from the output waveguide 83 can be controlled.

  Another example of a conventional waveguide-type optical variable attenuator is one in which two waveguide-type optical variable attenuators are connected.

  As shown in FIG. 7, a waveguide-type variable optical attenuator 91 includes a front-stage waveguide-type variable optical attenuator 92 and a rear-stage waveguide-type variable optical attenuator 93 connected via a half-wave plate 94. Configured.

  Each of the waveguide-type variable optical attenuators 92 and 93 includes a pair of optical couplers 95 and 96 and a pair of channel waveguides 97 and 98 connected between the optical couplers 95 and 96. A waveguide 99 is provided, and heaters 100 and 101 are formed on the channel waveguides 97 and 98, respectively.

  The signal light emitted from the preceding attenuator 92 and incident on the subsequent attenuator 93 is converted by the half-wave plate 94 into horizontal polarization of the signal light, and the vertical polarization becomes horizontal polarization. Converted. Therefore, the polarization dependent loss (PDL) generated in the front-stage waveguide type optical variable attenuator 92 is canceled out by the rear-stage waveguide type optical variable attenuator 93, and the waveguide-type optical variable attenuator 91 reduces PDL. There is an advantage that it can be performed (see Patent Document 1).

JP 11-133364 A

As shown in FIG. 8, the above-described waveguide type optical variable attenuator 80 is formed by laminating a substrate 102, an underclad 103, a core 86, an upper clad 81, and a heater 89 in this order, as a material for forming the core and the clad. SiO ₂ glass is used. That is, the heater 89 is provided on the upper surface of the channel waveguide 86, and the heat conductivity of the SiO ₂ glass is low, so that the heat of the heater 89 is not easily transmitted to the core 86 and the operation speed is low.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and provide an optical circuit with a fast core temperature change speed and a waveguide type optical variable attenuator with a high operating speed.

  In order to achieve the above object, the invention of claim 1 is an optical circuit in which an optical waveguide comprising a core and a clad covering the periphery of the core is formed on a quartz substrate, and heating means is provided on the surface of the optical waveguide. The optical waveguide is formed by raising a substrate or a lower clad layer formed on the substrate, a heating means is provided on one side of the optical waveguide, and a heat conducting film is provided on the other side. Circuit.

  The invention according to claim 2 is the optical circuit according to claim 1, wherein one side surface or both side surfaces of the optical waveguide are inclined.

  A third aspect of the invention is the optical circuit according to the first or second aspect, wherein the heat conducting film is formed of any one of gold, silver, copper, aluminum, silicon, and nickel.

  According to a fourth aspect of the present invention, a Mach-Zehnder type optical waveguide having a pair of channel waveguides is formed between an input waveguide and an output waveguide on a quartz substrate, and a thin film heater is provided above one of the channel waveguides. In a waveguide-type variable optical attenuator that attenuates signal light by energizing a heater, one or both channel waveguides are formed so as to protrude from the substrate, and a heater is provided on one side of the channel waveguide. This is a waveguide type optical variable attenuator provided with a heat conducting film on the side surface.

  The invention according to claim 5 is the waveguide type optical variable attenuator according to claim 4, wherein one side surface or both side surfaces of the channel waveguide are inclined.

  The invention according to claim 6 is the waveguide type optical variable attenuator according to claim 4 or 5, wherein the heat conducting film is formed of gold, silver, copper, aluminum, silicon, or nickel.

The present inventor conducted various experiments and formed a material that requires higher power consumption, that is, higher heat generation, at a different position from the heater in order to raise the temperature of the optical waveguide to a certain target value. As a result, it has been found that a faster response can be realized, and the present invention has been achieved. That is, a high-speed response can be realized by forming a film with a material having a higher thermal conductivity than that of SiO ₂ glass and increasing the heat radiation amount.

  According to the present invention, an excellent effect that the operation speed can be increased is exhibited.

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

  FIG. 1 is a sectional view showing a preferred embodiment of an optical circuit according to the present invention.

  As shown in FIG. 1, the optical circuit 10 includes a substrate 11 and an optical waveguide 12 provided on the substrate 11. The optical waveguide 12 includes a core 13 having a rectangular cross section and a clad 14 covering the core 13, and is formed so as to protrude from the substrate 11 so that the side surfaces 15 and 16 of the optical waveguide 12 are formed. Yes. The substrate 11 and the clad 14 are made of pure quartz, and the core 13 is made of a quartz-based material obtained by adding an additive to quartz.

  In the optical circuit 10 of the present embodiment, both side surfaces 15 and 16 of the optical waveguide 12 are inclined, and the optical waveguide 12 is formed in a so-called mesa shape. Both inclined surfaces 15 and 16 are inclined symmetrically with respect to the core 13, a heating means 17 is provided on one side surface 15 of the optical waveguide 12, and a heat conducting film 18 is provided on the other side surface 16. . The side surfaces 15 and 16 of the optical waveguide 12 may be formed perpendicular to the substrate 11. Examples of the heating means 17 include a metal thin film heater connected to a power source. The heat conduction film 18 is formed of a material having good heat conductivity, and the material may be any material having a heat conductivity higher than that of the clad, and is preferably a metal. More preferably, it is made of gold, silver, copper, aluminum, silicon, or nickel.

  The operation of the optical circuit of the present embodiment will be described.

  As shown in FIG. 5, when the heating means 17 generates heat, the heat conducting film 18 is provided in the vicinity of the heating means 17, and the heat conductivity of the heat conducting film 18 is greater than the heat conductivity of the cladding. Since it is high, most of the generated heat is conducted to the heat conducting film 18. At this time, since the core 13 is provided between the heating means 17 and the heat conducting film 18 via the clad 14, the heat conducted from the heating means 17 to the heat conducting film 18 heats the core. Thus, the core can be efficiently heated.

  Further, since the heat conducting film 18 radiates heat to the outside air more easily than the clad 14, the heat conducting film 18 is provided in the vicinity of the core 13, so that when the heating means 17 is stopped or reduced in heat, Heat is mainly conducted to the heat conducting film 18 and easily radiated.

  That is, in the conventional optical circuit, the heat flow (see FIG. 8) of the thin film heater → the core → the substrate, the optical circuit 10 of the present embodiment provides the optical waveguide by providing the heat conducting film 18 in the vicinity of the core 13. 12 has a structure that heats and cools easily, and heat generated from the thin film heater 17 flows in the direction parallel to the substrate 11 in the direction of the thin film heater → the core → the heat conducting film, thereby increasing the speed of heating and heat dissipation of the core 13. It is.

  Furthermore, by increasing the thickness of the heat conducting film 18 and increasing its heat capacity, greater heat generation is promoted (the power consumption of the thin film heater is increased), and the heating and heat dissipation speed of the core 13 is increased. Can be faster.

  As described above, in the optical circuit 10 of the present embodiment, the temperature of the core 13 can be adjusted at high speed, so that a high-speed response of the refractive index control of the core 13 by the thermo-optic effect can be realized.

  The optical circuit 10 of the present embodiment can be applied to an optical element including an optical circuit that uses the thermo-optic effect by controlling the temperature of the core 13.

  Next, the waveguide type optical variable attenuator will be described.

  FIG. 2 is a plan view showing a preferred embodiment of a waveguide type optical variable attenuator according to the present invention, and FIG. 3 is a sectional view taken along line 3A-3A in FIG.

  2 and 3, the waveguide type optical variable attenuator 20 includes a substrate 21, an optical waveguide 22 provided on the substrate 21, a thin film heater 31 and a heat conducting film 32 provided on the surface thereof. Have The optical waveguide 22 is composed of a core having a rectangular cross section and a clad covering the core. For example, in FIG. 3, channel waveguides 28 and 29 are composed of cores 28a and 29a and clads 28b and 29b, respectively. The optical waveguide 22 constitutes a Mach-Zehnder type optical waveguide comprising an input waveguide 24, an output waveguide 25, and a pair of channel waveguides 28 and 29 connected therebetween via optical coupler portions 26 and 27. ing.

  The substrate 11 and the clad 14 are made of pure quartz, and the core 13 is made of a quartz-based material obtained by adding an additive to quartz.

  In this embodiment, Y branch waveguides are formed as the optical coupler units 26 and 27, but a directional coupler type 3 dB coupler or a multimode interference type 3 dB coupler may be formed.

  The waveguide type optical variable attenuator 20 is characterized in that the phase control unit 23 that controls the phase of the signal light propagating through the channel waveguide 28 is configured by the optical circuit 10 described above. That is, as the phase control unit 23, at least one channel waveguide 28 is formed so as to protrude from the substrate 21, and a thin film heater 31 as a heating unit is provided on one side surface 33a of the channel waveguide 28, and the other side surface. A heat conducting film 32 is provided on 34a.

  Specifically, grooves 33, 34, and 35 are formed on both sides of the pair of channel waveguides 28 and 29, respectively, and the channel waveguides 28 and 29 are raised from the bottom surface of the grooves. . The reason why grooves are formed on both sides of both channel waveguides 28 and 29 is to make the structures of both channel waveguides 28 and 29 equal to eliminate the difference in characteristics due to the waveguide structure.

  The lengths of the grooves 33, 34, and 35 (longitudinal direction of the channel waveguide) are all the same length, and the inclination angles of the side walls of the grooves are also equal. The thin film heater 31 and the heat conducting film 32 are formed in the same shape and are arranged symmetrically with respect to the channel waveguide 28.

  The thin film heater 31 and the heat conducting film 32 are respectively applied to a part of the upper surface of the channel waveguide 28 and a part of the bottom surface of the grooves 33 and 34 in addition to the side surfaces (side walls of the grooves) 33a and 34a of the channel waveguide 28. Is provided. However, in a part of the upper surface of the channel waveguide 28, the thin film heater 31 and the heat conducting film 32 are disposed so as to avoid the surface of the channel waveguide 28 above the core 28a.

  A power supply (not shown) for energizing is connected to the thin film heater 31. The distance between the channel waveguide 28 and the thin film heater 31 may be approximately the same as the distance between the heater and the core in the conventional waveguide type optical variable attenuator. In the present embodiment, the thickness of the heat conducting film 32 is set to about 3 μm.

The heat conducting film 32 may be a film formed of a material having a higher thermal conductivity than SiO ₂ which is a material for forming the cladding, and is preferably a metal film. Furthermore, the heat dissipation film 22 is more preferably a film formed of any one of gold, silver, copper, aluminum, nickel, and Si.

  Next, a manufacturing method of the waveguide type optical variable attenuator 20 will be described.

  As shown in FIG. 4A, first, a core is formed on the quartz substrate 21, clads 28b and 29b covering the cores 28a and 29a are formed, and the optical waveguides 28 and 29 having a rectangular core embedded type are formed. Form. The optical waveguides 28 and 29 are formed by a conventional optical waveguide manufacturing method. The pattern of the optical waveguide formed at this time is the Mach-Zehnder type optical waveguide 22 shown in FIG.

  As shown in FIG. 4B, an etching mask 41 is provided on the cladding surface above the cores of the channel waveguides 28 and 29. After the etching mask 41 is provided, the clads on both sides of the channel waveguides 28 and 29 are etched to form grooves 33, 34 and 35. At this time, by controlling the substrate temperature to 10 ° C. or less in the etching apparatus, the side walls of the grooves 33, 34, and 35 are not vertical, but are inclined as shown by broken lines in the figure. In the present embodiment, the inclined angles of the side surfaces 33a and 34a of the channel waveguides 28 and 29 formed to be raised are set to 70 to 75 °.

As shown in FIG. 4C, the thin film heater 31 is formed on one side surface 33 a of one channel waveguide 28. Here, the material of the thin film heater 31 was Ta ₂ N, which has a small resistance change with time and excellent long-term reliability.

  As shown in FIG. 4D, the thin film heater 31 and the heat conducting film 32 are arranged symmetrically with respect to the channel waveguide 28 on the other side surface 34 a of one channel waveguide 28. The film type optical attenuator 20 is obtained by forming the film 32.

  Next, the operation of the present embodiment will be described.

  According to the waveguide type optical variable attenuator 20, the temperature of the thin film heater 31 is changed by changing the voltage applied to the thin film heater 31, and the refractive index (optical path length) of the channel waveguide 28 is changed by the thermo-optic effect. The attenuation of the signal light can be freely controlled by adjusting the heater temperature, that is, the applied voltage.

  In the waveguide type optical variable attenuator 20 of the present embodiment, the above-described optical circuit 10 is configured as the phase control unit 23, so that the heating and heat dissipation rates of the core can be increased. As a result, the refractive index change rate due to the temperature change of the core is increased, and the operation speed for controlling the attenuation amount of the signal light can be increased.

  By the way, in order to increase the operation speed of the waveguide type optical variable attenuator, a waveguide type optical variable attenuator in which a heater is provided in the clad above the core and a heat conducting film is provided below the core is conceivable.

  However, when forming a heat conduction film below the core, it is a process of forming each layer in the order of the heat conduction film, underclad, core, upper clad, and heater on the substrate. Manufactured. Therefore, the manufacturing cost is increased.

  Further, when a Si film is formed as a heat conducting film between the substrate and the under cladding layer, the warpage of the substrate increases due to the sputtering of the Si film. Even if this warpage is controlled, the warp may occur due to the formation of an undercladding layer or annealing of the formed layer.

  Further, the underclad requires a film thickness of 20 to 80 μm. In order to form such a thick film, it is necessary to repeat the film forming and annealing steps several times. Therefore, each time these steps are repeated, the warpage of the substrate increases and the flatness of the surface becomes worse.

  In short, the waveguide-type variable optical attenuator in which the Si layer is formed below the core cannot obtain excellent characteristics and the manufacturing process becomes complicated.

On the other hand, the waveguide-type variable optical attenuator 20 of the present embodiment is manufactured by a slightly improved method of manufacturing the conventional waveguide-type variable optical attenuator as described in the manufacturing method. Therefore, it can be easily manufactured at low cost. In addition, since the optical variable attenuator 20 is formed using the SiO ₂ glass (quartz) substrate 21, it is not necessary to form a thick under clad, so that there is almost no warpage caused by the formation of the under clad and the device surface. A waveguide type optical variable attenuator with good flatness can be produced. Therefore, an optical variable attenuator having good characteristics can be obtained.

In addition, since the substrate 21 is a quartz substrate and the optical waveguide 22 on the substrate 21 is formed using SiO ₂ glass, the substrate 21 and the optical waveguide 22 have the same thermal expansion coefficient because they are the same material. Therefore, the internal stress of the attenuator due to thermal drive can be reduced, and the polarization dependent loss due to the stress can be reduced.

  Further, the heat conducting film 32 is formed in the same shape as the thin film heater 31 and provided symmetrically with respect to the channel waveguide 28, whereby an optical waveguide formed by forming a metal film of the thin film heater 31 and the heat conducting film 32. Residual stress is reduced. Therefore, the polarization dependent loss of the signal light can be reduced.

  The embodiment of the present invention is not limited to the above-described embodiment.

  In the present embodiment, the side walls are inclined to form the grooves 33 and 34, and the inclined surfaces 33a and 34a are provided with the heater 31 and the heat conducting film 32. However, the side walls are perpendicular to the substrate. A heater and a heat conducting film may be provided along the side wall. In this case, the thin film heater and the heat conducting film are provided substantially in parallel with the channel waveguide interposed therebetween.

  In the present embodiment, as shown in FIG. 3, the side walls 33a and 34a of the grooves are inclined surfaces, thereby facilitating the formation and patterning of the thin film as compared with the case where the side walls of the grooves are vertical surfaces. The uniformity of the sputtered film 31 and the heat conducting film 32 is improved, and the patterning is stabilized by photolithography.

  Further, in the waveguide type optical variable attenuator 20 of the present embodiment, the core 13 is formed on the quartz substrate 21, but the lower cladding layer is formed on the upper layer of the quartz substrate 21, and the core 13 is formed on the upper layer of the lower cladding layer. May be formed.

1 is a cross-sectional view of an optical circuit according to a preferred embodiment of the present invention. 1 is a plan view of a waveguide type optical variable attenuator according to a preferred embodiment of the present invention. It is the 3A-3A sectional view taken on the line of FIG. 4A to 4D are cross-sectional views illustrating a method for manufacturing the waveguide type optical variable attenuator shown in FIG. It is sectional drawing explaining the heat conduction of the waveguide type optical variable attenuator of FIG. It is a top view which shows the conventional waveguide type optical variable attenuator. It is a top view which shows the other example of the conventional waveguide type optical variable attenuator. It is the 8A-8A sectional view taken on the line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical circuit 11 Board | substrate 12 Optical waveguide 13 Core 14 Clad 17 Heating means 18 Thermal conduction film | membrane 20 Waveguide-type variable optical attenuator 22 Mach-Zehnder type optical waveguide 23 Phase control part 24 Input waveguide 25 Output waveguide 26, 27 Optical coupler Portion 28, 29 Channel waveguide 31 Thin film heater 32 Heat conduction film 33, 34, 35 Groove

Claims (6)

In an optical circuit in which an optical waveguide composed of a core and a clad covering the periphery of the core is formed on a quartz substrate, and a heating means is provided on the surface of the optical waveguide.
The optical waveguide is formed to protrude from a substrate or a lower clad layer formed on the substrate, a heating means is provided on one side of the optical waveguide, and a heat conducting film is provided on the other side. An optical circuit.   The optical circuit according to claim 1, wherein one side surface or both side surfaces of the optical waveguide are inclined.   3. The optical circuit according to claim 1, wherein the heat conducting film is formed of any one of gold, silver, copper, aluminum, silicon, and nickel. On the quartz substrate, a Mach-Zehnder type optical waveguide having a pair of channel waveguides is formed between the input waveguide and the output waveguide. In a waveguide type optical variable attenuator that attenuates
One or both channel waveguides are formed so as to protrude from the substrate, a heater is provided on one side of the channel waveguide, and a heat conducting film is provided on the other side. Attenuator.   5. The waveguide type optical variable attenuator according to claim 4, wherein one side surface or both side surfaces of the channel waveguide are inclined. 6. The waveguide type optical variable attenuator according to claim 4, wherein the heat conducting film is formed of gold, silver, copper, aluminum, silicon, or nickel.

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