JP2009162933A - Waveguide-type optical circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waveguide-type optical circuit which has excellent optical characteristics, by suppressing unnecessary TE/TM polarized light coupling caused by stress due to an electric wiring pattern. <P>SOLUTION: The waveguide-type optical circuit has electric wiring nearby a waveguide and is such that the electric wiring nearby the waveguide has a symmetric wiring pattern with respect to the waveguide. Consequently, a main-axis direction of stress close to a waveguide core is made horizontal, and a main axis of birefringence is not made to incline in a projection plane (XY projection plane), perpendicular to the waveguide, and unnecessary TE/TM polarized light coupling can be restrained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a waveguide type optical circuit, and more particularly to a waveguide type optical circuit provided with an electric circuit.

  The current communication network includes optical switches such as optical switches for flexible switching of routes according to communication failures and demand, and multiplexers / demultiplexers for wavelength multiplexing / demultiplexing of multiple channels on a single optical fiber. Many parts are used. There are various methods for realizing these optical components, but an optical circuit using a waveguide can be integrated in a small size, has no movable part, is structurally stable, and has excellent reliability. Since it has many features such as excellent mass productivity by lithography technology, it is used in many optical components.

  In an optical circuit using a waveguide, an electric circuit is often provided in order to realize a dynamic operation. For example, in a silica-based waveguide, a minute heater is provided in the vicinity of the waveguide core in order to realize a variable phase shifter. Since the refractive index of the quartz-based waveguide changes due to the thermo-optic effect, the amount of phase shift is controlled by locally heating the waveguide temperature by energizing the heater. FIG. 1 shows a configuration example of the phase shifter 100 in the quartz-based waveguide 101. A thin film heater 102 as a thermo-optic phase shift heater is formed on the surface of the clad 106 immediately above the embedded waveguide core 107 manufactured on the silicon substrate 105. In addition, an electrical wiring 103 including a power supply pad 104 for supplying power to the thin film heater 102 is also formed on the surface of the clad 106 (see, for example, Patent Document 1).

  The phase shifter 100 can produce various application circuits by being incorporated in the interferometer circuit. FIG. 2 shows an optical switch 200 realized by incorporating a phase shifter in a Mach-Zehnder interferometer (MZI). The MZI is composed of two 50% directional couplers 202 and two arm waveguides connecting the two 50% directional couplers 202. The lengths of the two arm waveguides are usually equal or half the wavelength of the operating wavelength. Designed with either optical path length difference. Here, a half-wavelength optical path length difference is provided with the short arm on the upper side and the long arm on the lower side. At least one arm waveguide of the MZI is equipped with the phase shifter 100 shown in FIG. 1 (see, for example, Patent Document 2).

  The signal light incident on the input 1 is guided to the output 1 when the phase shifter 100 is not operating (when OFF) according to a known interference principle. When the phase shift amount π corresponding to the half wavelength is generated in the phase shifter to cancel the optical path length difference corresponding to the half wavelength (On), the signal light is guided to the output 2. When the phase shift amount generated by the phase shifter 100 takes an intermediate value between On and Off, the output (that is, the transmittance) of each path changes in an analog manner according to the phase shift amount.

  As an optical circuit manufacturing method using such a silica-based waveguide, for example, a combination of glass film deposition technology such as flame deposition (FHD) method and microfabrication technology such as reactive ion etching (RIE) is used. ing. Specifically, a glass film to be the lower cladding layer 204 is deposited / transparent on the silicon substrate 203, and subsequently, a core layer having a refractive index slightly higher than that of the cladding layer 204 is deposited / transparent. Then, the core pattern 205 to be an optical waveguide circuit is patterned by a fine processing technique, and a glass film to be the upper clad layer 204 is deposited / transparent to obtain an embedded optical waveguide. Finally, a metal that becomes the thin film heater 206 and the electric wiring 207 is deposited on the surface of the upper clad by a vacuum evaporation method or the like, and this is patterned by a fine processing technique to form a thermo-optic phase shifter.

Japanese Patent No. 3770313 (FIG. 13) Japanese Patent No. 3555842 (FIG. 1)

  However, in a waveguide type optical circuit equipped with such an electrical circuit, a stress caused by the electrical wiring pattern is generated, and this stress causes a change in refractive index and the surroundings through the photoelastic effect. It caused a change in birefringence. In particular, when the birefringent principal axis sensed by light propagating in the waveguide is tilted with respect to the substrate in the projection plane perpendicular to the waveguide, unintentional coupling occurs between the TE polarized light and the TM polarized light. In some cases, desired optical characteristics cannot be obtained.

  For example, as an extreme event, in the optical switch 200 shown in FIG. 2, when the birefringent principal axis direction 208 is tilted, the input TE-polarized light is polarized and the polarization plane of the upper arm waveguide is half-clockwise. It is assumed that the polarization plane of the lower arm waveguide rotates 45 degrees clockwise. Then, since the respective polarization planes are orthogonal to each other, no interference occurs in the directional coupler 202 on the output side. That is, even if the phase shifter 100 is operated, the switching operation cannot be performed.

  The above example is a very extreme example, but when an analog operation is performed, that is, when it is operated as a variable attenuator, there is often a problem that the amount of attenuation is dependent on polarization.

  The present invention has been made in view of such problems, and its object is to suppress unnecessary coupling between TE / TM polarized light due to stress caused by an electric wiring pattern and to have good optical characteristics. A waveguide type optical circuit is provided.

  In order to achieve such an object, according to the first aspect of the present invention, in the waveguide type optical circuit having an electrical wiring near the waveguide, the electrical wiring near the waveguide is symmetrical with respect to the waveguide. It is a wiring pattern.

  The invention according to claim 2 is characterized in that the waveguide type optical circuit is an optical interferometer comprising a plurality of waveguides, and the waveguide is a waveguide in the optical interferometer.

  According to a third aspect of the present invention, the waveguide includes a phase shifter, and the electrical wiring is connected to the phase shifter.

  According to a fourth aspect of the present invention, there is provided a phase shifter of one of the plurality of waveguides and the electric wiring connected to the phase shifter, and a non-driven dummy shifter is disposed on the other of the plurality of waveguides. One or both of a phaser and a dummy electric wiring are provided.

  The invention according to claim 5 includes one phase shifter of the plurality of waveguides and the electric wiring connected to the phase shifter, and the electric wiring is connected to the other of the plurality of waveguides. Are also arranged in a pattern.

  According to a sixth aspect of the present invention, in the waveguide type optical circuit, a clad groove is disposed around the phase shifter, and the dummy phase shifter has a disconnection gap in a region where the clad groove is present. It is characterized by that.

  The invention according to claim 7 is characterized in that the electric wiring in a direction along the waveguide of the waveguide type optical circuit is a pattern covering the plurality of waveguides.

  According to an eighth aspect of the present invention, the waveguide optical circuit is an optical interferometer including two couplers on an input side and an output side, and the electric wiring is a pattern that covers the two couplers. It is characterized by.

  The invention described in claim 9 is characterized in that a range for securing the symmetry of the electric wiring is 25 μm or more.

  According to the present invention, since the electrical wiring is a symmetrical pattern with respect to the waveguide in the vicinity of the waveguide, the principal axis of stress on the waveguide generated from the electrical wiring pattern is not inclined in a plane orthogonal to the waveguide. The birefringent main axis is always perpendicular or horizontal to the substrate in the projection plane perpendicular to the waveguide. Therefore, unnecessary TE / TM interpolar polarization coupling due to stress caused by the electric wiring pattern does not occur, and optical characteristics are not deteriorated due to this.

  There are various types of waveguides that make up optical circuits. In the form described below, an optical circuit based on a silica-based waveguide on a silicon substrate that is most often used as a means for realizing a complex optical circuit. Will be described as an example.

  FIG. 3 shows a phase shifter 300 using the electrical wiring pattern of the basic form of the present invention. In the electric wiring pattern 303 of the present invention, the wiring is routed not only from the heater 302 end to the power supply pad 304 side but also in the opposite direction not connected to the power supply pad 304, and the electric wiring 303 is connected to the waveguide 301 in the vicinity of the waveguide 301. In contrast to the conventional wiring pattern, the wiring pattern is substantially symmetric with respect to the YZ plane including the waveguide.

  In the conventional wiring pattern 103 shown in FIG. 1, since the wiring is routed only from the heater 102 end to the power supply pad 104 side, the upper portion of the waveguide 101 is the edge of the electric wiring 103. When dissimilar materials such as a wiring metal and a clad glass are joined, stress is usually generated in each material because the thermal expansion coefficients of the respective materials are different. In particular, the stress applied to the edge portion of the pattern changes in a complicated manner depending on the location, so that the principal axis of the stress is generally inclined. When patterning the wiring, if patterning is performed by etching such as RIE, not only the wiring but also the cladding may be slightly etched by the etching. That is, the surface of the upper cladding has a step along the wiring pattern edge. In a quartz-based waveguide manufactured on a silicon substrate, a strong horizontal compressive stress is applied to the glass film of the clad or core due to the manufacturing method. If the film is uniform, the stress distribution will be uniform, but if there is a change in the structure such as having a step on the surface, as is well known in the field of structural mechanics, the periphery of the step is complicated. Stress with a proper distribution is added, and the principal axis of the stress is also tilted. Therefore, at the edge portion of the wiring pattern, the birefringent main axis 108 is also inclined with respect to the substrate as shown in the sectional view BB ′ of FIG. There was a coupling between polarized light.

  FIG. 4 is a diagram showing a result 400 of crossed Nicols observation performed to directly examine the state of polarization conversion due to stress. The sample is a quartz-based waveguide fabricated on a silicon substrate 401 (however, in the observed portion, there is no waveguide core and only the cladding 402), the metal wiring 403 is patterned on the surface of the cladding 402, and the waveguide cross section is viewed. Thinly sliced. Cross-Nicol observation is performed by applying TM polarized light to this cross section and analyzing TE polarized light of transmitted light. That is, the place where TM polarized light is converted to TE polarized light by polarization coupling appears bright. As shown in the figure, it can be seen that polarization conversion occurs near the edge of the wiring.

  On the other hand, as shown in FIG. 3, in the wiring pattern 303 of the present invention, the wiring is routed in the opposite direction from the end of the heater 302 to the power supply pad 304 side. Since it can be regarded as being substantially symmetric with respect to the waveguide 301 in the vicinity, the principal axis direction of the stress near the waveguide core 307 is horizontal. Therefore, the birefringent main axis 308 is also always perpendicular to the substrate and does not incline in the projection plane (XY projection plane) perpendicular to the waveguide 301 as shown in the sectional view BB ′ of FIG. There is no coupling between TM polarized light.

  The crossed Nicols observation result shown in FIG. 4 shows that polarization conversion is particularly strong in the range of approximately 25 μm from the wiring edge 404. Therefore, it is better not to place the waveguide in the interferometer at least in this region. Even if the area exceeds 25 μm, the area where the polarization conversion does not become zero immediately does not necessarily become zero. Therefore, if it is allowed in the arrangement, the waveguide should be arranged at a position far enough away with a margin. Is preferred.

  When viewed in the waveguide direction (Z direction), the wiring pattern of the electrical wiring 303 of the phase shifter 300 shown in FIG. 3 also has an edge on the waveguide 301, but the inclination of the principal axis of the stress generated in this portion. Is a tilt in the YZ plane, and the corresponding tilt of the birefringent main axis 308 appears in the YZ plane, and the birefringent main axis is always vertical in the XY projection plane. Accordingly, there is no coupling between TE / TM polarized light.

  FIG. 5 is a diagram showing another example of the wiring pattern of the present invention. In FIG. 5A, the wiring (orthogonal portion wiring) 501 orthogonal to the waveguide direction is not directly connected at the heater end, but the orthogonal portion is connected via the wiring 502 of the extension portion along the waveguide direction. 5B shows a wiring pattern 500 connected to the wiring, FIG. 5B shows a wiring pattern 510 in which the electric wiring 511 is trapezoidal at the heater end, and FIG. 5C shows the electric wiring 521 at the heater end. A wiring pattern 520 having a rectangular shape is shown. These wiring patterns 500, 510, and 520 are characterized in that the electrical wiring is substantially symmetric with respect to the waveguide in the vicinity of the waveguide, that is, the symmetrical pattern with respect to the YZ plane including the waveguide. The point is common with the basic form. In the case of this form, there is a wiring edge near the upper part of the waveguide, so the stress distribution is somewhat complicated compared to the basic form, but because the pattern is symmetrical with respect to the waveguide, it is near the waveguide core. The principal axis direction of the stress is the same as the horizontal direction (X direction). Therefore, similarly to the basic form shown in FIG. 3, the orientations 503, 513, and 523 of the birefringent main axis are always perpendicular to the substrate on the XY projection plane, so that no TE / TM polarization coupling occurs.

Next, an embodiment when the present invention is applied to a phase shifter of an MZI type optical switch will be described in detail.
FIG. 6 shows an MZI type optical switch 600 as an example of a waveguide type optical circuit according to the first embodiment of the present invention. The basic switch configuration is the same as that of the conventional optical switch 200 shown in FIG. 2, but is different from the conventional optical switch in that the wiring pattern of the present invention is applied to the electric wiring 607 of the thermo-optic phase shift heater 606. .

  In the conventional optical switch 200 shown in FIG. 2, the wiring from the thermo-optic phase shift heater 206 is drawn in the direction along the waveguide (Z axis ± direction) and then wired in the direction of the power supply pad (X axis − direction). Pull out. In order to draw a large number of wires in a multiple switch, the wires are usually once drawn in the Z-axis direction in this way. In such a wiring pattern, as shown in FIG. 2, the two arm waveguides pass under the vicinity of the wiring edge over a relatively long area until they are connected to the directional coupler 202. . For this reason, since light propagates over a long distance through the waveguide 201 whose birefringent main axis 202 is inclined, the above-described coupling between TE / TM polarization is particularly likely to occur.

  On the other hand, in the first embodiment using the wiring pattern of the present invention, as shown in FIG. 6, the electrical wiring 607 is once drawn in a direction (X axis ± direction) across the waveguide 601 and then Z direction. The portion of the electrical wiring 607 that is led out in the direction of the first X axis ± is substantially symmetrical with respect to the waveguide 601. For this reason, since the waveguide 601 does not pass under the vicinity of the wiring edge, coupling between TE / TM polarized light does not occur in the interferometer circuit, and the deterioration of optical characteristics due to coupling between polarized lights is suppressed. it can.

  In order to perform the switching operation with the optical switch, it is only necessary to control the phase difference between the arm waveguides. Therefore, it is not necessary to provide the phase shifter in both arm waveguides, and one arm waveguide (usually the short arm side). ) Only in many cases. Limiting to only one arm waveguide is also advantageous in terms of circuit layout because the amount of electrical wiring is halved.

  However, in the waveguide directly under the electrical wiring and under the thermo-optic phase shift heater, the refractive index variation and the birefringence variation are caused by stress as described above, so only one arm waveguide has a phase shifter. That is, when electric wiring or a thermo-optic phase shift heater is loaded only in one arm waveguide, the balance of these fluctuations is lost in both arms. This imbalance in refractive index fluctuation appears as a phase error, and the imbalance in birefringence fluctuation appears as a phase shift in TE / TM polarization, that is, polarization dependence of operation. Similar to the problem, the optical characteristics deteriorate. Therefore, even when only the phase shifter of one arm waveguide is driven, the other arm waveguide is also provided with a dummy thermo-optic phase shift heater and dummy wiring, and the refractive index fluctuation and birefringence due to stress It is preferable to have a configuration that keeps both arms balanced for fluctuation.

  FIG. 7 shows, as a second embodiment of the present invention, an MZI type optical switch 700 having a configuration in which only the phase shifter of one arm waveguide based on the above is driven. In this embodiment, in order to further reduce the electrical wiring, the wiring on the left side of the drawing is combined into one wiring as the common electrical wiring 701. The left side of the thermo-optic phase shift heater 703 of the arm waveguide on the driving side is connected to this common electric wiring, and the right side is connected to the individual electric wiring 702 as in the first embodiment. The left side of the dummy thermo-optic phase-shift heater 704 of the arm waveguide on the non-drive side is connected to the common electric wiring 701, and the dummy electric wiring 705 that is not connected to the power supply pad is connected to the right side. As described above, the dummy thermo-optic phase-shifting heater 704 cannot be driven, but the potential is not indefinite because it is connected to the common electric wiring 701. As shown in the figure, the wiring pattern is substantially symmetrical with respect to the waveguide in the vicinity of the waveguide in the interferometer portion on both the driving side and the dummy side.

  Such a symmetrical wiring pattern and the configuration including the dummy phase shifter 704 do not cause coupling between TE / TM polarized light, but also change in refractive index and birefringence between both arms. Good optical characteristics can be obtained and the number of electrical wirings can be effectively reduced without causing phase error or polarization dependency due to an imbalance in rate fluctuation.

  FIG. 8 shows an MZI type optical switch 800 as an example of a waveguide type optical circuit according to the third embodiment of the present invention. This embodiment is similar to the second embodiment, but in the individual electric wiring 802 connected to the thermo-optic phase shift heater 803 of the arm waveguide on the driving side, the electric power extended in the opposite direction on the power supply pad side. The wiring passes through the arm waveguide on the non-driving side and extends to the point where the electrical wiring can be regarded as being substantially symmetric with respect to the waveguide in the vicinity of the waveguide even when viewed from the arm waveguide on the non-driving side. The point is greatly different from the second embodiment.

  In the second embodiment, the individual electric wiring 702 extending in the opposite direction to the power supply pad side is separated from the electric wiring from the dummy phase shifter 704 of the arm waveguide on the non-driving side, so that it is almost at most of MZI. It stayed at stretching to the center position. If the MZI has a sufficiently wide arm waveguide interval, the edge of the wiring can be arranged at a position sufficiently distant from the waveguide. However, if the MZI has a narrow arm waveguide interval, the MZI has a sufficiently distant position. Difficult to place edges.

  On the other hand, in the present embodiment, since the arm waveguide extends greatly beyond the arm waveguide on the non-drive side, even in the MZI where the distance between the arm waveguides is relatively small, even when viewed from the arm waveguide on the drive side. Even when viewed from the arm waveguide on the non-drive side, the wiring can be arranged substantially symmetrically with respect to the waveguide in the vicinity of the waveguide.

  Also in the present embodiment, as in the second embodiment, the thermo-optic phase shift heater 803 is connected to the common electrical wiring 801, and further changes in refractive index and birefringence due to stress from the thermo-optic phase shift heater 803. In order to balance both arms, it is preferable to provide a dummy thermo-optic phase shift heater 804 in the other arm waveguide and connect it to the common electrical wiring 801. The dummy thermo-optic phase shift heater 804 is not driven by providing a gap 805 in part. Although the gap 805 is small, strictly speaking, the arm balance of the above fluctuation is lost on the driving side and the non-driving side. If this becomes a problem, the right side of the individual electric wiring 802 is shown in FIG. A dummy thermo-optic phase shift heater 806 having a length corresponding to the gap is additionally provided, and the total length of the dummy thermo-optic phase shift heaters 804 and 806 may be aligned on the driving side and the non-driving side.

  FIG. 9 shows an MZI type optical switch 900 as an example of a waveguide type optical circuit according to the fourth embodiment of the present invention. Although this embodiment has a configuration close to that of the third embodiment, a cladding groove 905 for heat insulation is dug around the thermo-optic phase shift heaters 903 and 904, and the dummy thermo-optic phase shift heater 904 The difference from the third embodiment is that a gap for non-driving is provided in a region where the cladding groove 905 is provided.

  The clad groove 905 acts as a heat insulation groove for reducing thermal diffusion and reducing the driving power of the thermo-optic phase shift heater 903, and also acts as a stress relief groove from the thermo-optic phase shift heater 903. Since the stress release groove reduces the refractive index fluctuation and the birefringence fluctuation due to the stress from the thermo-optic phase shift heater, in this embodiment, the total length of the thermo-optic phase shift heaters 903 and 904 is the driving side and the non-driving side. Even though the gaps are not different, there is almost no imbalance in the optical characteristics of both arms. Therefore, the dummy thermo-optic phase shift heater 806 on the right side of the individual electric wiring 802 added in the third embodiment is not necessary, and the element length can be shortened accordingly.

  FIG. 10 shows an MZI type optical switch 1000 as an example of a waveguide type optical circuit according to the fifth embodiment of the present invention. This embodiment is similar to the fourth embodiment except that the individual electric wiring 1002 is guided by the electric wiring both when viewed from the arm waveguide on the driving side and from the arm waveguide on the non-driving side. In the vicinity of the waveguide, the wiring is drawn out in the direction along the waveguide (Z-axis direction) with a thick wiring that can be regarded as being substantially symmetric with respect to the waveguide, and then the wiring is drawn out in the direction of the power supply pad (X-axis direction). The point is greatly different from the fourth embodiment.

  In the fourth embodiment, the individual electrical wiring 902 connected to the thermo-optic phase-shift heater 903 and the dummy thermo-optic phase-shift heater 904 is once drawn in the direction (X-axis direction) across the waveguide and then Z It is pulled out in the axial direction, and then pulled out in the direction of the power feeding pad (X-axis direction). The wiring in the portion extending in the Z-axis direction needs to be disposed at a location sufficiently away from the MZI waveguide so that stress from the edge of the electrical wiring can be ignored, and at the same time, wiring resistance becomes a problem. It is necessary to have a certain width so as not to become. Therefore, if the distance where stress can be ignored is L, the allowable minimum wiring width where wiring resistance does not matter is W, the gap between wirings is G, and the arm waveguide spacing of MZI is S, the multiple optical switches The minimum pitch is S + 2L + W + G.

  On the other hand, in the present embodiment, the edge of the wide portion of the wiring drawn out in the Z-axis direction is the wiring edge closest to the waveguide. Therefore, the distance from the waveguide to the edge of the wide wiring is L. When W <S + 2L (that is, when S + 2L is a sufficient width that does not cause a problem of wiring resistance), the wiring width of the thick portion is S + 2L, and the pitch of the multiple optical switches is S + 2L + G at the minimum. On the other hand, when W ≧ S + 2L, the wiring width of the wide portion is W, and the pitch of the multiple optical switches is W + G at the minimum. In any case, since the optical switches can be arranged at a denser pitch than in the fourth embodiment, a smaller switch chip can be designed. Further, when W <S + 2L, the wiring width of the thick portion becomes a wiring width (S + 2L) larger than the allowable minimum wiring width W, so that unnecessary power consumption due to wiring resistance can be reduced to some extent.

Next, an embodiment when the present invention is applied to a phase shifter for adjusting frequency characteristics of an MZI type multiplexer / demultiplexer will be described in detail.
FIG. 11 shows an MZI type optical multiplexer / demultiplexer 1100 as an example of a waveguide type optical circuit according to the sixth embodiment of the present invention. In the present optical multiplexer / demultiplexer 1100, two 50% directional couplers 1102 and a long arm side waveguide 1106 connecting the two 50% directional couplers 1102 and the short core side are almost the same as the optical switches described in the above embodiments. The MZI configuration is basically composed of two arm waveguides of the waveguide 1107, but the optical path length difference (= effective refractive index neff and waveguide length difference ΔL) between the two arm waveguides 1106 and 1107 is the same as that of the optical switch. A large value is set in comparison. The signal light from the input 1 has a frequency fe (= m · c / {neff · ΔL}; c: speed of light, m: positive integer) to the output 2 and the frequency fo (= The signal light of {m−0.5) · c / {neff · ΔL}) is demultiplexed to the output 1. If the input and output are reversed, the signal light with the frequency fe and the signal light with the frequency fo can be multiplexed. As described above, the multiplexer / demultiplexer 1100 shown in FIG. 11 is also called an interleave filter because it can multiplex / demultiplex even-channel light fe and odd-channel light fo.

  Since the multiplexer / demultiplexer normally does not have a dynamic operation like an optical switch, it is not always necessary to provide a phase shifter in the two arm waveguides. However, when the effective refractive index of the waveguide is shifted due to a manufacturing error or the like and a phase error occurs between the two arm waveguides, a phase shifter is used to correct the phase error.

  Also in the present embodiment, the configuration of the conventional multiplexer / demultiplexer is different from the conventional multiplexer / demultiplexer in that the wiring pattern of the present invention is applied to the electrical wiring of the thermo-optic phase shift heater 1105 as in the embodiment of the optical switch. As shown in FIG. 11, the electrical wiring includes a common electrical wiring 1103 and individual electrical wiring 1104, and has a substantially symmetric pattern with respect to the waveguide 1101. Further, this symmetrical pattern is not only a portion connected to the thermo-optic phase shift heater 1105 but also a portion crossing the interferometer on the routing of the wiring (a portion indicated by an alternate long and short dash line in the figure) Similarly, the pattern is substantially symmetric with respect to the waveguide 1101. For this reason, since the waveguide 1101 does not pass under the vicinity of the wiring edge, coupling between the TE / TM polarized light does not occur in the interferometer circuit, and the deterioration of the optical characteristics due to the coupling between the polarized lights is suppressed. it can. That is, when crossing the waveguide 1101 in the interferometer, it is important to cross in a pattern that is substantially symmetrical with respect to the waveguide.

  Here, the MZI type has been described as an example of the multiplexing / demultiplexing interferometer, but the application of the present invention is not limited to this. For example, the present invention is also effective for a ring resonator type or a Michelson interferometer type. It is.

  Further, in the above embodiment, the optical switch and the optical multiplexer / demultiplexer including the two-beam interferometer have been specifically described. However, unnecessary polarization conversion affects the characteristics. The same applies to, for example, an arrayed waveguide grating (AWG). Therefore, when an electrical wiring is provided for a multi-beam interferometer as well, by adopting a wiring pattern in accordance with the policy of the present invention, polarization conversion due to stress caused by the wiring pattern can be suppressed. Needless to say, the deterioration of the optical characteristics can be prevented as in the embodiment.

Optical Switch with Variable Attenuation Function As Example 1 of the present invention, an optical switch with variable attenuation function 700 according to the second embodiment of the present invention shown in FIG. 7 is conventionally used using a silica-based waveguide on a silicon substrate. The same production method was used. The length of the two arm waveguides is provided with an optical path length difference corresponding to a half wavelength of the operating wavelength, and the shorter arm waveguide is provided with a thermo-optic phase shifter heater 703 on the driving side, A dummy thermo-optic phase shifter heater 704 is provided on the longer arm waveguide as the non-driving side.

  The relative refractive index difference between the core and the clad of the waveguide is 0.75%. The interval between the arm waveguides is 250 μm. The width of the individual electric wiring 702 and the dummy electric wiring 705 is 100 μm, and the gap between the individual electric wiring 702 and the dummy electric wiring 705 is 50 μm. The length of the electrical wiring extending in the X direction inside the MZI is 100 μm for both the individual electrical wiring 702 and the dummy electrical wiring 705. The length of the electrical wiring in the X direction outside the MZI is 100 μm on the dummy electrical wiring 705 side and 150 μm on the individual electrical wiring 702 side (that is, the distance from the drive side arm waveguide to the edge of the individual wiring routed in the Z direction) Is 150 μm). The cap of the dummy electric wiring 705 and the individual electric wiring of the adjacent optical switch is 50 μm. The distance from the waveguide core center to the upper clad surface is about 15 μm.

  In the manufactured optical switch with variable attenuation function of Example 1 of the present invention, the polarization dependent loss (PDL) at the time of 10 dB attenuation in the cross path was about 0.3 dB. For comparison, the polarization dependent loss at the time of 10 dB attenuation in the optical switch 200 with a variable attenuation function in which the electrical wiring is manufactured with the wiring pattern having the conventional configuration shown in FIG. 2 is about 0.6 dB. As described above, the use of the wiring pattern of the present invention greatly improves the polarization dependent loss at the time of attenuation.

Multiple Optical Switch with Variable Attenuation Function The configuration of a multiple optical switch 1200 with a variable attenuation function manufactured as Example 2 of the present invention is shown in FIG. This example was configured based on the fifth embodiment shown in FIG. Also in this embodiment, the length of the two arm waveguides is provided with an optical path length difference corresponding to a half wavelength of the operating wavelength, and the shorter arm waveguide has a thermo-optic phase shifter heater as a driving side. 1205 is provided, and a dummy thermo-optic phase shifter heater 1206 is provided on the longer arm waveguide as a non-driving side.

  The connecting portion between the thermo-optic phase-shifting heaters 1205 and 1206, the common electric wiring 1201 and the individual electric wiring 1202 is provided with an extended wiring along the waveguide 1203 direction shown in FIG. Adopted. This is to prevent heat generated by the thermo-optic phase-shifting heater 1205 from passing through the wiring and entering the arm waveguide on the non-drive side.

  In this embodiment, a disconnection gap for disabling the dummy thermo-optic phase shift heater 1206 is provided in the dummy thermo-optic phase heater 1206. However, since the clad groove 1207 that also acts as a stress relief groove is formed not only in the thermo-optic phase-shifting heaters 1205 and 1206 but also in the periphery of this extended wiring part, even if a disconnection gap is provided in the extended wiring part, the characteristics Since there is no problem, a disconnection gap may be provided here.

Now, the transmittance T of the MZI of the cross path (input 1 → output 2) is the same as that of the phase shifter when the coupling ratio of the directional coupler on the input side and the output side is the same value k (= 0 to 1). When the phase shift amount is φ, T = 4 · k · (1−k) · cos ² ((φ−π) / 2). Therefore, when the phase shifter is not driven (OFF), T = 0 is always set regardless of the value of the coupling rate k. Even if the coupling rate of the directional coupler 1204 deviates from 50% of the design value (k = 0.5) due to a manufacturing error, the MZI property is that the coupling rate of the directional coupler 1204 on the input side and the output side is This means that a switch operation with a high extinction ratio can be obtained as long as the value k is the same, which is a very favorable property.

  As described above, the stress from the electric wirings 1201 and 1202 causes the refractive index fluctuation and the birefringence fluctuation of the waveguide 1203. Therefore, in the directional coupler 1204, these fluctuations cause fluctuations in coupling ratio and coupling ratio. Causes fluctuations in the polarization dependence. Therefore, if the presence or absence of electrical wiring on the upper surface of the directional coupler 1204 is different between the input side and the output side, the coupling rate slightly differs between the input side and the output side. In the present embodiment, in order to prevent such a situation, the common electric wiring 1201 is disposed so as to cover the upper part of the directional coupler 1204, and the thick electric wiring is also connected to the directional coupler 1204 for the individual electric wiring 1202. It was arranged to cover the top of the.

  Similarly to Example 1, the optical switch 1200 with a variable attenuation function of this example was also manufactured using a silica-based waveguide on a silicon substrate. The relative refractive index difference between the core and the clad of the waveguide is 1.5%. The interval S between the arm waveguides is 100 μm, the width of the wide wiring drawn out in the Z direction is 400 μm, that is, the distance L from the arm waveguide to the edge of the wide wiring is 150 μm. The distance from the center of the waveguide core to the upper clad surface is about 15 μm. The gap G between the wirings was 100 μm. The disconnection gap for non-driving the dummy thermo-optic phase shifter was provided with a gap width of 50 μm at a position just in the middle of the region where the cladding groove 1207 is located.

  In the manufactured optical switch 1200 with a variable attenuation function of the present invention, the polarization dependent loss (PDL) at the time of 10 dB attenuation in the cross path was about 0.2 dB. For comparison, the polarization dependent loss at the time of 10 dB attenuation in the optical switch 200 with a variable attenuation function in which the electrical wiring is manufactured with the wiring pattern having the conventional configuration shown in FIG. 2 is about 0.5 dB. Also in this example, the polarization dependent loss at the time of attenuation was greatly improved by using the wiring pattern of the present invention.

Double MZI-type Multiple Variable Attenuator The configurations of double MZI-type multiple variable attenuators 1300 and 1400 manufactured as Example 3 (A) and (B) are shown in FIGS. 13 and 14, respectively. In this embodiment, the MZI type switch elements are double connected, and each of the front stage MZI type switches 1303 and 1403 / the rear stage MZI type switch elements 1304 and 1404 performs an attenuation operation, so that the extinction ratio is doubled. Is obtained, that is, a double-attenuation operation is possible. The configuration of each MZI type switch element is the same as that of the second embodiment. In this embodiment, in order to reduce the wiring to each MZI type switching element, in the configuration of the embodiment 3 (A) shown in FIG. 13, the electric wiring from the common electric wiring 1301 and the individual electric wiring 1302 is connected in parallel. In addition, in the configuration of the embodiment 3 (B) shown in FIG. 14, the electric wirings from the common electric wiring 1401 and the individual electric wiring 1402 are connected in series so that the preceding MZI type switches 1303 and 1403 / the rear MZI type switching elements 1304 1404 is driven simultaneously.

  Although this variable attenuator is a circuit with 1 input and 1 output, it has the function of a changeover switch by pulling out the unconnected waveguide from the front / rear MZI type switch element to the input / output port. It can also be made.

  The variable attenuators 1300 and 1400 of this example were also manufactured using quartz-based waveguides on a silicon substrate, as in Examples 1 and 2. The relative refractive index difference between the core and the clad of the waveguide is 1.5%. The interval S between the arm waveguides is 80 μm, and the width of the clad groove is about 60 μm. The disconnection gap for non-driving the dummy thermo-optic phase shifter was provided with a gap width of 20 μm at a position just in the middle of the region having the cladding groove.

  In the parallel connection example 3 (A), the width of the wide wiring drawn out in the Z direction is 220 μm, that is, the distance from the arm waveguide to the edge of the wide wiring is 70 μm. The width of the narrow wiring portion passing through the side of each MZI element for parallel connection was set to 50 μm, and the minimum gap between the thick and narrow wirings was set to 40 μm.

  In Example 3 (B) connected in series, the width of the wide wiring drawn out in the Z direction is 300 μm, that is, the distance from the arm waveguide to the edge of the wide wiring is 110 μm. The gap between the thick wirings was 50 μm.

  In the manufactured variable attenuators 1300 and 1400 of the present invention, the polarization dependent loss (PDL) at 20 dB attenuation was about 0.3 dB in Example 3 (A) and about 0.2 dB in Example 3 (B). It was. For comparison, the polarization dependent loss at the time of 20 dB attenuation in the variable attenuator 200 in which the electric wiring is manufactured with the wiring pattern having the conventional configuration shown in FIG. 2 was about 0.9 dB. Also in this example, the polarization dependent loss at the time of attenuation was greatly improved by using the wiring pattern of the present invention.

  As described above, in the three examples and embodiments, an optical circuit based on a silica-based waveguide on a silicon substrate has been realized. However, this is excellent in reliability, high connection affinity with an optical fiber, and production technology. This is because it is suitable for mass production with established technology. However, stress due to the provision of electrical wiring to add functionality to other material-based waveguides such as silicon waveguides, lithium niobate (LN) waveguides, polymer waveguides, etc. In the case where the above influences the characteristics, it should be noted that the effects shown in this embodiment and the like can be similarly obtained by devising the electric wiring pattern according to the guidelines of the present invention. .

  In the above examples and embodiments, the directional coupler is used as the coupler constituting the MZI. However, the present invention is not limited to this. For example, a multimode interference (MMI) coupler may be used. good. Further, in a 1 × 2 coupler or a 2 × 1 coupler, a 1 × 2 branching device or a 2 × 1 merger may be used. However, when these are used together in the same MZI, the phase characteristics are different from those of the directional coupler, so that it is necessary to correct the difference as an optical path length difference. In any case, unnecessary polarization coupling is still suppressed by the device of the electric wiring pattern of the present invention.

  In the above example, the wiring pattern that suppresses the coupling between the polarizations has been described with respect to the waveguide in the interferometer. However, when the coupling between the polarizations occurs in the interferometer, the optical characteristics are improved as described above. This is because the influence is great. However, the waveguide that needs to suppress the coupling between the polarizations is not limited to the waveguide in the interferometer. For example, when it is desired to maintain the polarization between the input and output ports, the waveguide type other than the interferometer Needless to say, the application of the present invention is also effective in optical circuits such as splitters (branches), combiners (mergers), and delay lines. In addition, the application of the present invention is effective in the case where it is desired to maintain the polarization in a waveguide outside the interferometer, such as an input / output waveguide portion of the interferometer optical circuit.

It is a figure which shows the phase shifter 100 which is a waveguide type optical circuit provided with the conventional electrical wiring pattern. It is a figure which shows the MZI type | mold optical switch 200 which is a waveguide type optical circuit provided with the conventional electrical wiring pattern. It is a figure which shows the phase shifter 300 which is a waveguide type optical circuit provided with the electrical wiring pattern of this invention. It is a figure which shows the cross Nicol observation result of wiring edge vicinity. It is a figure which shows another example of an electrical wiring pattern of the waveguide type optical circuit of this invention. 1 is a diagram showing an MZI type optical switch 600 as an example of a waveguide type optical circuit according to a first embodiment of the present invention. FIG. It is a figure which shows the MZI type | mold optical switch 700 as an example of the waveguide type optical circuit by the 2nd Embodiment of this invention. It is a figure which shows the MZI type | mold optical switch 800 as an example of the waveguide type optical circuit by the 3rd Embodiment of this invention. It is a figure which shows the MZI type | mold optical switch 900 as an example of the waveguide type optical circuit by the 4th Embodiment of this invention. It is a figure which shows the MZI type | mold optical switch 1000 as an example of the waveguide type optical circuit by the 5th Embodiment of this invention. It is a figure which shows the MZI type | mold optical multiplexer / demultiplexer 1100 as an example of the waveguide type optical circuit by the 6th Embodiment of this invention. It is a figure which shows the multiple optical switch 1200 with a variable attenuation function which is a waveguide type optical circuit of Example 2 of this invention. It is a figure which shows the double MZI type | mold multiple variable attenuator connected in parallel which is the waveguide type optical circuit of Example 3 (A) of this invention. It is a figure which shows the double MZI type | mold multiple variable attenuator connected in series which is the waveguide type optical circuit of Example 3 (B) of this invention.

Explanation of symbols

300 Phase shifters 301, 601, 1101 Waveguides 302, 606, 703, 803, 903, 1105 Thermo-optic phase shift heaters 303, 607 Electrical wiring 304 Feed pads 305, 603 Substrate 306, 604 Glad 307, 605 Waveguide core 308 , 608 Birefringent main axis direction 600,700,800,900,1000 MZI type optical switch 602,1102 Directional coupler 701,801,901,1001,1103 Common electric wiring 702,802,902,1002,1104 Individual electric Wiring 704, 804, 806, 904 Dummy thermo-optic phase shift heater 705 Dummy electric wiring 805 Gap 905 Cladding groove 1100 MZI type optical multiplexer / demultiplexer 1106 Long arm side waveguide 1107 Short arm side waveguide

Claims (9)

  A waveguide-type optical circuit having an electrical wiring in the vicinity of a waveguide, wherein the electrical wiring in the vicinity of the waveguide has a symmetric wiring pattern with respect to the waveguide.   The waveguide optical circuit according to claim 1, wherein the waveguide optical circuit is an optical interferometer including a plurality of waveguides, and the waveguide is a waveguide in the optical interferometer.   The waveguide type optical circuit according to claim 1, wherein the waveguide includes a phase shifter, and the electrical wiring is connected to the phase shifter.   One phase shifter of the plurality of waveguides and the electrical wiring connected to the phase shifter, and one or both of a non-driven dummy phase shifter and dummy electrical wiring connected to the other of the plurality of waveguides The waveguide type optical circuit according to claim 3, comprising:   One phase shifter of the plurality of waveguides and the electric wiring connected to the phase shifter are provided, and the electric wiring is arranged in a pattern on the other of the plurality of waveguides. The waveguide type optical circuit according to claim 3.   5. The waveguide type optical circuit according to claim 4, wherein a clad groove is disposed around the phase shifter, and the dummy phase shifter has a disconnection gap in a region where the clad groove is present. Waveguide type optical circuit.   6. The waveguide optical circuit according to claim 5, wherein the electrical wiring in a direction along the waveguide of the waveguide optical circuit is a pattern that covers the plurality of waveguides.   8. The waveguide optical circuit according to claim 7, wherein the waveguide type optical circuit is an optical interferometer including two couplers on an input side and an output side, and the electric wiring is a pattern covering the two couplers. Waveguide type optical circuit.   2. The waveguide type optical circuit according to claim 1, wherein a range in which symmetry of the electric wiring is ensured is 25 μm or more.

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