Optical device, optical receiver and optical transceiver

Abstract

To provide an optical device capable of inhibiting signal losses, or the like.SOLUTION: A 90-degree hybrid circuit comprises a first coupler splitting signal light, a second coupler splitting local light, and a first waveguide and a second waveguide through which the signal light split by the first coupler propagates. The 90-degree hybrid circuit comprises a third waveguide and a fourth waveguide through which the local light split by the second coupler propagates, and a third coupler combining the signal light propagating through the first waveguide and the local light propagating through the third waveguide. The 90-degree hybrid circuit comprises: a fourth coupler combining the signal light propagating through the second waveguide and the local light propagating through the fourth waveguide; and a phase adjustment part adjusting a phase of light propagating through at least one waveguide of the first to fourth waveguides. A first total value of optical lengths of the first waveguide and the fourth waveguide is smaller than a second total value of optical lengths of the second waveguide and the third waveguide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical device, an optical receiver, and an optical transceiver. [Background technology]

[0002] For example, an optical receiver employing a digital coherent receiving function has a built-in 90-degree hybrid circuit that mixes a signal light with a local light and separates the signal light into orthogonal components and outputs them. Fig. 10 is an explanatory diagram showing an example of a conventional 90-degree hybrid circuit 100. The 90-degree hybrid circuit 100 shown in Fig. 10 has a first splitter 110, a second splitter 120, a first combiner 130, a second combiner 140, and first to fourth waveguides 101A to 101D.

[0003] The first splitter 110 is a 2×2 coupler having a first input port 111A, a second input port 111B, a first output port 111C, and a second output port 111D. The second splitter 120 is a 1×2 coupler having a first input port 121A, a first output port 121B, and a second output port 121C.

[0004] The first combiner 130 is a 2×2 coupler having a first input port 131A, a second input port 131B, a first output port 131C, and a second output port 131D. The second combiner 140 is a 2×2 coupler having a first input port 141A, a second input port 141B, a first output port 141C, and a second output port 141D.

[0005] The first splitter 110 optically connects a first output port 111C in the first splitter 110 and a first input port 131A in the first combiner 130 via a first waveguide 101A. The first splitter 110 optically connects a second output port 111D in the first splitter 110 and a first input port 141A in the second combiner 140 via a second waveguide 101B.

[0006] The second splitter 120 optically connects between the first output port 121B in the second splitter 120 and the second input port 131B in the first combiner 130 via the third waveguide 101C. The second splitter 120 optically connects between the second output port 121C in the second splitter 120 and the second input port 141B in the second combiner 140 via the fourth waveguide 101D.

[0007] The first combiner 130 optically connects between a first input port 131A in the first combiner 130 and a first output port 111C in the first splitter 110 via a first waveguide 101A. The first combiner 130 optically connects between a second input port 131B in the first combiner 130 and a first output port 121B in the second splitter 120 via a third waveguide 101C.

[0008] The second combiner 140 optically connects between a first input port 141A in the second combiner 140 and a second output port 111D in the first splitter 110 via a second waveguide 101B. The second combiner 140 optically connects between a second input port 141B in the second combiner 140 and a second output port 121C in the second splitter 120 via a fourth waveguide 101D.

[0009] The first splitter 110 splits the signal light from a first input port 111A in the first splitter 110 into a 0-degree signal light and a 90-degree signal light. The first splitter 110 splits and outputs the 0-degree signal light to a first output port 111C in the first splitter 110, and splits and outputs the 90-degree signal light to a second output port 111D in the first splitter 110.

[0010] The second splitter 120 converts the local light from the first input port 121A in the second splitter 120 into 0 degree local light, and branches and outputs the local light to the first output port 121B and the second output port 121C in the second splitter 120.

[0011] The first combiner 130 inputs the 0-degree signal light from the first splitter 110 and the 0-degree local light from the second splitter 120. The first combiner 130 outputs a first signal light obtained by multiplexing the 0-degree signal light and the 90-degree local light based on the input 0-degree signal light and the 0-degree local light as a channel CH1 to a first output port 131C in the first combiner 130. The first signal light is a signal light of an XIp component that is a signal light having a phase difference of 0 degrees between the signal light and the local light.

[0012] Furthermore, the first combiner 130 outputs a second signal light obtained by multiplexing the 90-degree signal light and the 0-degree local light based on the input 0-degree signal light and the 0-degree local light as a channel CH2 to a second output port 131D in the first combiner 130. The second signal light is an XIn component signal light having a phase difference of 180 degrees between the signal light and the local light.

[0013] The second combiner 140 inputs the 90-degree signal light from the first splitter 110 and the 0-degree local light from the second splitter 120. The second combiner 140 outputs a third signal light obtained by multiplexing the 90-degree signal light and the 90-degree local light based on the input 90-degree signal light and 0-degree local light as channel CH3 to a first output port 141C in the second combiner 140. The third signal light is an XQp component signal light in which the phase difference between the signal light and the local light is 90 degrees.

[0014] Furthermore, the second combiner 140 outputs a fourth signal light obtained by multiplexing the 180-degree signal light and the 0-degree local light based on the input 90-degree signal light and 0-degree local light as a channel CH4 to a second output port 141D in the second combiner 140. The fourth signal light is an XQn component signal light in which the phase difference between the signal light and the local light is 270 degrees.

[0015] In other words, the 90-degree hybrid circuit 100 outputs first to fourth signal lights, each of which has a phase difference of 90 degrees between the signal light and the local light, through the first combiner 130 and the second combiner 140 based on the input signal light and local light.

[0016] If the optical length of the first waveguide 101A is L1, the optical length of the second waveguide 101B is L2, the optical length of the third waveguide 101C is L3, and the optical length of the fourth waveguide 101D is L4, then L1=L2=L3=L4 holds true. The optical length is calculated by multiplying the waveguide length of the waveguide by the effective refractive index. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] JP 2008-193555 A [Patent Document 2] U.S. Pat. No. 1,012,6498 [Patent Document 3] JP 2001-109023 A Summary of the Invention [Problem to be solved by the invention]

[0018] The 90-degree hybrid circuit 100 outputs the first to fourth signal lights with the phase difference between the signal light and the local light shifted by 90 degrees. However, in the 90-degree hybrid circuit 100, manufacturing errors occur in the first splitter 110, the second splitter 120, the first combiner 130, the second combiner 140, and the waveguide widths of the first to fourth waveguides 101A to 101D, for example. Therefore, in the 90-degree hybrid circuit 100, a phase difference of 90 degrees between the signal light and the local light cannot be ensured due to manufacturing errors or the like, and signal loss occurs.

[0019] In one aspect, an object of the present invention is to provide an optical device or the like capable of suppressing signal loss. [Means for solving the problem]

[0020] An optical device according to one embodiment includes a 90-degree hybrid circuit that mixes a signal light and a local light and separates the signal light into orthogonal components and outputs the mixed signals. The 90-degree hybrid circuit has a first coupler that branches the signal light, a second coupler that branches the local light, and a first waveguide and a second waveguide through which the signal light branched by the first coupler propagates. The 90-degree hybrid circuit has a third waveguide and a fourth waveguide through which the local light branched by the second coupler propagates, and a third coupler that combines the signal light propagated through the first waveguide and the local light propagated through the third waveguide. The 90-degree hybrid circuit includes a fourth coupler that combines the signal light propagated through the second waveguide with the local light propagated through the fourth waveguide, and a phase adjustment unit that adjusts the phase of the light propagating through at least one of the first to fourth waveguides. A first sum of the optical lengths of the first and fourth waveguides is shorter than a second sum of the optical lengths of the second and third waveguides. Effect of the Invention

[0021] According to one aspect, signal loss can be suppressed. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to a first embodiment. [Diagram 2] FIG. 2 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to the second embodiment. [Diagram 3] FIG. 3 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to a third embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing an example of a 90-degree hybrid circuit according to a fourth embodiment. [Diagram 5] FIG. 5 is an explanatory diagram showing an example of a 90-degree hybrid circuit according to a fifth embodiment. [Figure 6] FIG. 6 is an explanatory diagram showing an example of a 90-degree hybrid circuit according to a sixth embodiment. [Figure 7] FIG. 7 is an explanatory diagram showing an example of a 90-degree hybrid circuit according to a seventh embodiment. [Figure 8] FIG. 8 is an explanatory diagram showing an example of a 90-degree hybrid circuit according to an eighth embodiment. [Figure 9] FIG. 9 is an explanatory diagram illustrating an example of an optical transceiver according to this embodiment. [Figure 10] FIG. 10 is an explanatory diagram showing an example of a conventional 90-degree hybrid circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the embodiments of the optical device and the like disclosed in the present application will be described in detail with reference to the drawings. Note that the present invention is not limited to these embodiments. In addition, the following examples may be appropriately combined as long as no contradiction occurs. EXAMPLES

[0024] Fig. 1 is an explanatory diagram showing an example of a 90-degree hybrid circuit 1 according to a first embodiment. The 90-degree hybrid circuit 1 shown in Fig. 1 is a circuit that mixes a signal light and a local light and separates the signal light into orthogonal components and outputs the components. The 90-degree hybrid circuit 1 includes a first splitter 2, a second splitter 3, a first combiner 4, a second combiner 5, first to fourth waveguides 6A to 6D, a heater electrode 7, and two electrode pads 8.

[0025] The first splitter 2 is a 2×2 coupler having a first input port 21A, a second input port 21B, a first output port 21C, and a second output port 21D. The first splitter 2 is a first coupler that splits and outputs the signal light to the first waveguide 6A and the second waveguide 6B. The second splitter 3 is a 1×2 coupler having a first input port 31A, a first output port 31C, and a second output port 31D. The second splitter 3 is a second coupler that splits and outputs the local light to the third waveguide 6C and the fourth waveguide 6D. The first combiner 4 is a 2×2 coupler having a first input port 41A, a second input port 41B, a first output port 41C, and a second output port 41D. The first combiner 4 is a third coupler that combines the signal light propagated through the first waveguide 6A and the local light propagated through the third waveguide 6C. The second combiner 5 is a 2×2 coupler having a first input port 51A, a second input port 51B, a first output port 51C, and a second output port 51D. The second combiner 5 is a fourth coupler that combines the signal light propagated through the second waveguide 6B and the local light propagated through the fourth waveguide 6D.

[0026] The first splitter 2 optically connects a first output port 21C in the first splitter 2 and a first input port 41A in the first combiner 4 via a first waveguide 6A. The first splitter 2 optically connects a second output port 21D in the first splitter 2 and a first input port 51A in the second combiner 5 via a second waveguide 6B.

[0027] The second splitter 3 optically connects between the first output port 31C in the second splitter 3 and the second input port 41B in the first combiner 4 via a third waveguide 6C. The second splitter 3 optically connects between the second output port 31D in the second splitter 3 and the second input port 51B in the second combiner 5 via a fourth waveguide 6D.

[0028] The first combiner 4 optically connects between the first input port 41A in the first combiner 4 and the first output port 21C in the first splitter 2 with the first optical waveguide 6A. The first combiner 4 optically connects between the second input port 41B in the first combiner 4 and the first output port 31C in the second splitter 3 with the third optical waveguide 6C.

[0029] The second combiner 5 optically connects between the first input port 51A in the second combiner 5 and the second output port 21D in the first splitter 2 with the second optical waveguide 6B. The second combiner 5 optically connects between the second input port 51B in the second combiner 5 and the second output port 31D in the second splitter 3 with the fourth optical waveguide 6D.

[0030] When the optical length of the first optical waveguide 6A is L1, the optical length of the second optical waveguide 6B is L2, the optical length of the third optical waveguide 6C is L3, and the optical length of the fourth optical waveguide 6D is L4, the relationship of the optical lengths of the first to fourth optical waveguides 6A to 6D is L1 + L4 < L2 + L3. Note that the optical length is calculated by the waveguide length of the optical waveguide × the effective refractive index. The optical length L1 of the first optical waveguide 6A is shorter than the optical length L2 of the second optical waveguide 6B. Therefore, the 90-degree hybrid circuit 1 is set such that, for example, the signal light from the first output port 21C in the first splitter 2 is (0 - d) degrees and the signal light from the second output port 21D in the first splitter 2 is 90 degrees. In the first splitter 2, by pre-adjusting and setting the optical lengths of the first optical waveguide 6A and the second optical waveguide 6B in advance, as the phase difference between the signal light and the local light emission, for example, an error of 10 degrees, that is, a phase difference of 80 degrees is set.

[0031] The heater electrode 7 is disposed on the first waveguide 6A and is a phase adjustment unit that adjusts the phase of the signal light propagating through the first waveguide 6A. The heater electrode 7 is made of an electrode material containing, for example, Ti, TiN, or the like. The electrode pad 8 electrically connected to the heater electrode 7 has a first electrode pad 8A disposed near the first splitter 2 and a second electrode pad 8B disposed near the first combiner 4. The heater electrode 7 heats the first waveguide 6A by passing a current between the first electrode pad 8A and the second electrode pad 8B. The refractive index of the first waveguide 6A changes according to the thermo-optic effect of the first waveguide 6A, and the phase angle of the propagating signal light increases.

[0032] In addition, since the optical length L1 of the first waveguide 6A is different from the optical length L3 of the third waveguide 6C, the signal light input to the first input port 41A in the first combiner 4 is Sig-d, and the local light input to the second input port 41B in the first combiner 4 is Lo+d. "d" is the change in phase angle caused by the difference in optical length. "d" is set so that the phase angle of the signal light with respect to the local light is less than -90 degrees in channel CH1 and less than +90 degrees in channel CH2 when the heater electrode 7 near the first waveguide 6A is not driven so that the phase angle of the signal light can be adjusted by driving the heater electrode 7.

[0033] The first splitter 2 splits the signal light from the first input port 21A in the first splitter 2 into 0 degree signal light and 90 degree signal light. The first splitter 2 splits and outputs the 0 degree signal light to the first waveguide 6A connected to the first output port 21C in the first splitter 2, and splits and outputs the 90 degree signal light to the second waveguide 6B connected to the second output port 21D in the first splitter 2.

[0034] The second splitter 3 branches and outputs the local light from the first input port 31A in the second splitter 3 as 0-degree local light to the third waveguide 6C connected to the first output port 31C and the fourth waveguide 6D connected to the second output port 31D.

[0035] The first combiner 4 receives the 0-degree signal light Sig-d+h from the first waveguide 6A and the 0-degree local light LO+d from the third waveguide 6C. Based on the input signal light and local light, the first combiner 4 outputs a first signal light obtained by multiplexing the signal light Sig-d+h and the local light LO+90+d as a channel CH1 to a first output port 41C in the first combiner 4. The first signal light is a signal light of an XIp component that is an I component of X polarization, which is a signal light with a phase difference of 0 degrees between the signal light and the local light.

[0036] Furthermore, the first combiner 4 outputs a second signal light obtained by multiplexing the 90-degree signal light Sig+90-d+h and the 0-degree local light LO+d based on the input 0-degree signal light and 0-degree local light as channel CH2 to a second output port 41D in the first combiner 4. The second signal light is an XIn component signal light that is an I component of X polarization, and has a phase difference of 180 degrees between the signal light and the local light.

[0037] The second combiner 5 inputs the 90-degree signal light Sig+90 from the first splitter 2 and the 0-degree local light LO+0 from the second splitter 3. Based on the input 90-degree signal light and 0-degree local light, the second combiner 5 outputs a third signal light obtained by multiplexing the 90-degree signal light Sig+90 and the 90-degree local light LO+90 as channel CH3 to a first output port 51C in the second combiner 5. The third signal light is an XQp component signal light that is an X-polarized Q component, and is a signal light with a phase difference of 90 degrees between the signal light and the local light.

[0038] Furthermore, the second combiner 5 outputs a fourth signal light obtained by multiplexing the 180-degree signal light Sig+180 and the 0-degree local light LO+0 based on the input 90-degree signal light and 0-degree local light as a channel CH4 to a second output port 51D in the second combiner 5. The fourth signal light is an XQn component signal light that is an X-polarized Q component, and has a phase difference of 270 degrees between the signal light and the local light.

[0039] The heater electrode 7 disposed on the first waveguide 6A heats the first waveguide 6A by causing current to flow between the first electrode pad 8A and the second electrode pad 8B. The refractive index of the first waveguide 6A changes according to the thermo-optical effect of the first waveguide 6A, increasing the phase angle of the propagating signal light. The heater electrode 7 adjusts the signal light Sig-d input to the first combiner 4 by the phase change h when the first waveguide 6A is heated. As a result, the 90-degree hybrid circuit 1 adjusts the signal light Sig-d+h input to the first combiner 4 so that the phase difference of channel CH1 is 0 degrees and the phase difference of channel CH2 is 180 degrees.

[0040] When the relationship of the optical lengths of the first to fourth waveguides 6A to 6D is L1 + L4 < L2 + L3, the phase difference of channel CH1 is less than -90 degrees. In this state, when current is passed through the heater electrode 7, the phase difference increases, and by adjusting the current value, the phase difference of channel CH1 can be made -90 degrees. On the other hand, when the relationship of the optical lengths of the first to fourth waveguides 6A to 6D is L1 + L4 ≥ L2 + L3, the phase difference of channel CH1 becomes -90 degrees or more. In this state, even if current is passed through the heater electrode 7, the phase difference only increases, so the phase difference of channel CH1 cannot be made -90 degrees.

[0041] For example, when the change in the phase angle due to manufacturing error is "e", then "d = d - e". When e < d, the heater electrode 7 can be heated to make the phase angle the预定 phase angle difference (90 degrees). However, when e ≥ d, since the phase difference of the signal light with respect to the local light emission of channel CH2 is 90 degrees - 2(d - e) > 90 degrees in the state where the heater electrode 7 is not heated (h = 0), it becomes greater than 90 degrees when the heater electrode 7 is heated. Therefore, in this case, it cannot be adjusted by the heater electrode 7.

[0042] Therefore, in order to adjust the phase difference of channel CH1 to -90 degrees with the heater electrode 7, including the error of the initial phase difference due to manufacturing error, it is necessary to make the relationship of the optical lengths of the first to fourth waveguides 6A to 6D such that L1 + L4 < L2 + L3.

[0043] That is, even when a phase error d-e occurs between the signal light input to the first combiner 4 and the local light due to manufacturing errors, a current is passed through the heater electrode 7 to heat the first waveguide 6A and increase the refractive index of the first waveguide 6A. As a result, the phase difference between the signal light propagated through the first waveguide 6A and the signal light propagated through the second waveguide 6B can be adjusted to 90 degrees.

[0044] The 90-degree hybrid circuit 1 of Example 1 is set in a state where the relationship of the optical lengths of the first to fourth waveguides 6A to 6D is L1 + L4 < L2 + L3 in advance. Further, even when a phase error d-e occurs between the signal light input to the first combiner 4 and the local light due to manufacturing errors, a current is passed through the heater electrode 7 to heat the first waveguide 6A and increase the refractive index of the first waveguide 6A. Then, the 90-degree hybrid circuit 1 adjusts the phase difference between the signal light propagated through the first waveguide 6A and the signal light propagated through the second waveguide 6B to 90 degrees by increasing the refractive index of the first waveguide 6A. As a result, even when manufacturing errors occur, signal loss can be suppressed by stably ensuring a 90-degree phase difference.

[0045] In addition, although the case where the optical length is adjusted by adjusting the waveguide lengths of the first to fourth waveguides 6A to 6D of Example 1 has been exemplified, the present invention is not limited to this, and the optical length may be adjusted by adjusting the waveguide width, and can be appropriately changed. In this case, the waveguide width of the first waveguide 6A is made narrower than the waveguide width of the second waveguide 6B, and the waveguide width of the fourth waveguide 6D is made narrower than the waveguide width of the third waveguide 6C, so that the same effect can be obtained.

[0046] Also, the 90-degree hybrid circuit 1 of Example 1 has been exemplified as having a structure in which the optical length L1 of the first waveguide 6A is shorter than the optical length L4 of the fourth waveguide 6D. However, the present invention is not limited to this, and the embodiment thereof will be described below as Example 2.

Example

[0047] FIG. 2 is an explanatory diagram showing an example of the 90-degree hybrid circuit 1A of Example 2. The same components as those of the 90-degree hybrid circuit 1 of Example 1 are denoted by the same reference numerals, and the description of the overlapping components and operations is omitted. The difference between the 90-degree hybrid circuit 1A of Example 2 and the 90-degree hybrid circuit 1 of Example 1 is that the optical lengths of the first to fourth waveguides 6A, 6B1, 6C, and 6D1 are in the relationship of L1 = L4 < L2 = L3. The optical length L1 of the first waveguide 6A and the optical length L4 of the fourth waveguide 6D1 are the same, and the optical length L2 of the second waveguide 6B1 and the optical length L3 of the third waveguide 6C are the same.

[0048] The first splitter 2 splits the signal light from the first input port 21A in the first splitter 2 into 0-degree signal light and 90-degree signal light. The first splitter 2 branches and outputs the 0-degree signal light to the first waveguide 6A connected to the first output port 21C in the first splitter 2, and branches and outputs the 90-degree signal light to the second waveguide 6B1 connected to the second output port 21D in the first splitter 2.

[0049] The second splitter 3 branches and outputs the local light emission from the first input port 31A in the second splitter 3 as 0-degree local light emission to the third waveguide 6C connected to the first output port 31C and the fourth waveguide 6D1 connected to the second output port 31D.

[0050] The first combiner 4 inputs the 0-degree signal light Sig-d+h from the first waveguide 6A and the 0-degree local light emission LO+d from the third waveguide 6C. Based on the input signal light and local light emission, the first combiner 4 outputs, as the first signal light in which the signal light Sig-d+h and the local light emission LO+90+d are combined, the first signal light to the first output port 41C in the first combiner 4 as channel CH1. The first signal light is the signal light of the XIp component, which is the signal light with a phase difference of 0 degrees between the signal light and the local light emission.

[0051] Furthermore, the first combiner 4 outputs a second signal light obtained by multiplexing the 90-degree signal light Sig+90-d+h and the 0-degree local light LO+d based on the input 0-degree signal light and 0-degree local light, as a channel CH2 to a second output port 41D in the first combiner 4. The second signal light is an XIn component signal light having a phase difference of 180 degrees between the signal light and the local light.

[0052] The second combiner 5 receives the 90-degree signal light Sig+90+d from the first splitter 2 and the 0-degree local light LO-d from the second splitter 3. The second combiner 5 outputs a third signal light obtained by multiplexing the 90-degree signal light Sig+90+d and the 90-degree local light LO+90-d based on the input 90-degree signal light and the 0-degree local light as channel CH3 to a first output port 51C in the second combiner 5. The third signal light is an XQp component signal light in which the phase difference between the signal light and the local light is 90 degrees.

[0053] Furthermore, the second combiner 5 outputs a fourth signal light obtained by multiplexing the 180-degree signal light Sig+180+d and the 0-degree local light LO-d based on the input 90-degree signal light and 0-degree local light as a channel CH4 to a second output port 51D in the second combiner 5. The fourth signal light is an XQn component signal light in which the phase difference between the signal light and the local light is 270 degrees.

[0054] The heater electrode 7 arranged on the first waveguide 6A heats the first waveguide 6A by passing a current between the first electrode pad 8A and the second electrode pad 8B. The refractive index of the first waveguide 6A changes according to the thermo-optic effect of the first waveguide 6A, and the phase angle of the propagating signal light increases. The heater electrode 7 adjusts the signal light Sig-d input to the first combiner 4 with the phase change h caused when the first waveguide 6A is heated. As a result, the 90-degree hybrid circuit 1A adjusts the signal light Sig-d+h input to the first combiner 4 so that the phase difference of the channel CH1 is 0 degrees and the phase difference of the channel CH2 is 180 degrees.

[0055] In the 90-degree hybrid circuit 1A of Example 2, the optical lengths of the first to fourth waveguides 6A to 6D are set to the relationship of L1 = L4 < L2 = L3, and the configurations of the first waveguide 6A and the fourth waveguide 6D1 are point-symmetrical, and the configurations of the second waveguide 6B1 and the third waveguide 6C are point-symmetrical. As a result, the influence of process errors is canceled, and the variation in the phase difference can be suppressed.

[0056] However, in the 90-degree hybrid circuits 1(1A) of Examples 1 and 2, since the heater electrode 7 is arranged on the first waveguide 6, heating is concentrated on the first waveguide 6A, and it is conceivable that the life of the heater electrode 7 is shortened. Therefore, an embodiment for dealing with such a situation will be described as the 90-degree hybrid circuit 1B of Example 3.

Example

[0057] FIG. 3 is an explanatory diagram showing an example of the 90-degree hybrid circuit 1B of Example 3. The difference between the 90-degree hybrid circuit 1B of Example 3 and the 90-degree hybrid circuit 1A of Example 2 is that the first heater electrode 7A is arranged on the first waveguide 6A, and the second heater electrode 7B is arranged on the fourth waveguide 6D1.

[0058] The first heater electrode 7A is arranged on the first waveguide 6A. The electrode pads 8 that are electrically connected to the first heater electrode 7A include a first electrode pad 8A arranged near the first splitter 2 and a second electrode pad 8B arranged near the first combiner 4. The first heater electrode 7A heats the first waveguide 6A when an electric current flows between the first electrode pad 8A and the second electrode pad 8B. The refractive index of the first waveguide 6A changes according to the thermo-optical effect of the first waveguide 6A, and the phase angle of the propagating signal light increases.

[0059] The second heater electrode 7B is disposed on the fourth waveguide 6D1. The electrode pad 8 electrically connected to the second heater electrode 7B has a third electrode pad 8C disposed near the second splitter 3 and a fourth electrode pad 8D disposed near the second combiner 5. The second heater electrode 7B heats the fourth waveguide 6D1 by a current flowing between the third electrode pad 8C and the fourth electrode pad 8D. The refractive index of the fourth waveguide 6D1 changes according to the thermo-optic effect of the fourth waveguide 6D1, and the phase angle of the propagating signal light increases.

[0060] The first splitter 2 splits the signal light from the first input port 21A in the first splitter 2 into 0-degree signal light and 90-degree signal light. The first splitter 2 splits and outputs the 0-degree signal light to the first waveguide 6A connected to the first output port 21C in the first splitter 2, and splits and outputs the 90-degree signal light to the second waveguide 6B1 connected to the second output port 21D in the first splitter 2. The second splitter 3 splits and outputs the local light from the first input port 31A in the second splitter 3 as 0-degree local light to the third waveguide 6C connected to the first output port 31C and the fourth waveguide 6D1 connected to the second output port 31D.

[0061] The first combiner 4 receives the 0-degree signal light Sig-d+h from the first waveguide 6A and the 0-degree local light LO+d from the third waveguide 6C. Based on the input signal light and local light, the first combiner 4 outputs a first signal light obtained by multiplexing the signal light Sig-d+h and the local light LO+90+d as a channel CH1 to a first output port 41C in the first combiner 4. The first signal light is a signal light of an XIp component that is a signal light with a phase difference of 0 degrees between the signal light and the local light.

[0062] Furthermore, the first combiner 4 outputs a second signal light obtained by multiplexing the 90-degree signal light Sig+90-d+h and the 0-degree local light LO+d based on the input 0-degree signal light and 0-degree local light, as a channel CH2 to a second output port 41D in the first combiner 4. The second signal light is an XIn component signal light having a phase difference of 180 degrees between the signal light and the local light.

[0063] The second combiner 5 receives the 90-degree signal light Sig+90+d from the first splitter 2 and the 0-degree local light LO-d+h from the second splitter 3. The second combiner 5 outputs a third signal light obtained by multiplexing the 90-degree signal light Sig+90+d and the 90-degree local light LO+90-d based on the input 90-degree signal light and 0-degree local light as channel CH3 to a first output port 51C in the second combiner 5. The third signal light is an XQp component signal light in which the phase difference between the signal light and the local light is 90 degrees.

[0064] The second combiner 5 outputs a fourth signal light obtained by multiplexing the 180-degree signal light Sig+180+d and the 0-degree local light LO-d+h based on the input 90-degree signal light and 0-degree local light as a channel CH4 to a second output port 51D in the second combiner 5. The fourth signal light is an XQn component signal light in which the phase difference between the signal light and the local light is 270 degrees.

[0065] The first heater electrode 7A arranged on the first waveguide 6 heats the first waveguide 6A by flowing a current between the first electrode pad 8A and the second electrode pad 8B. The refractive index of the first waveguide 6A changes according to the thermo-optic effect of the first waveguide 6A, and the phase angle of the propagating signal light increases. The first heater electrode 7A adjusts the signal light Sig-d input to the first combiner 4 with the phase change h caused when the first waveguide 6A is heated. As a result, the 90-degree hybrid circuit 1B adjusts the signal light Sig-d+h input to the first combiner 4 so that the phase difference of the channel CH1 is 0 degrees and the phase difference of the channel CH2 is 180 degrees.

[0066] The second heater electrode 7B arranged on the fourth waveguide 6D1 heats the fourth waveguide 6D1 by flowing a current between the third electrode pad 8C and the fourth electrode pad 8D. The refractive index of the fourth waveguide 6D1 changes according to the thermo-optic effect of the fourth waveguide 6D1, and the phase angle of the propagating signal light increases. The second heater electrode 7B adjusts the local light LO-d input to the second combiner 5 with the phase change h caused when the fourth waveguide 6D1 is heated. As a result, the 90-degree hybrid circuit 1B adjusts the local light LO-d+h input to the second combiner 5 so that the phase difference of the channel CH3 is 90 degrees and the phase difference of the channel CH4 is 270 degrees.

[0067] The 90-degree hybrid circuit 1B of the third embodiment adjusts the phase angle of the signal light by the first heater electrode 7A on the first waveguide 6A and adjusts the phase angle of the local light by the second heater electrode 7B on the fourth waveguide 6D1, so that the phase difference between the signal light and the local light can be adjusted to 90 degrees. For example, the phases of the signal light and the local light at the time of input are not necessarily the same, but change from moment to moment. The 90-degree hybrid circuit 1B can adjust the phase difference between the signal light and the local light in a specific channel to 90 degrees so that the phase of the signal light with respect to the local light differs by 90 degrees between channels, for example, between channel CH1 and channel CH3. Also, even if the adjustment is made by 10 degrees overall, the first heater electrode 7A can adjust by 5 degrees and the second heater electrode 7B can adjust by 5 degrees, so that the driving adjustment by the heater electrodes can be shared.

[0068] In the 90-degree hybrid circuit 1B, the first heater electrode 7A is disposed on the first waveguide 6A and the second heater electrode 7B is disposed on the fourth waveguide 6D1, so that the temperature rise caused by concentrated heating can be dispersed, thereby extending the life of the heater electrodes.

[0069] In the 90-degree hybrid circuit 1B of the third embodiment, two electrode pads 8 electrically connected to the first heater electrode 7A and two electrode pads 8 electrically connected to the second heater electrode 7B are arranged. However, the present invention is not limited to this, and an embodiment of the present invention will be described below as a fourth embodiment. EXAMPLES

[0070] 4 is an explanatory diagram showing an example of a 90-degree hybrid circuit 1C of the fourth embodiment. The same components as those in the 90-degree hybrid circuit 1B of the third embodiment are denoted by the same reference numerals, and the description of the overlapping components and operations will be omitted. The 90-degree hybrid circuit 1C of the fourth embodiment differs from the 90-degree hybrid circuit 1B of the third embodiment in that the first heater electrode 7A and the second heater electrode 7B are electrically connected to each other, thereby sharing the driving current to the first heater electrode 7A and the second heater electrode 7B.

[0071] The 90-degree hybrid circuit 1C has a first electrode pad 8A1 arranged near the first splitter 2, a second electrode pad 8B1 arranged near the second combiner 5, and a wiring 8C1. The first electrode pad 8A1 is electrically connected to one end of a first heater electrode 7A arranged on the first waveguide 6A. The second electrode pad 8B1 is electrically connected to one end of a second heater electrode 7B arranged on the fourth waveguide 6D1.

[0072] The wiring 8C1 electrically connects the other end of the first heater electrode 7A and the other end of the second heater electrode 7B. The wiring 8C1 connects the first heater electrode 7A and the wiring 8C1 through a via (not shown) so that the third waveguide 6C is not heated, and also connects the second heater electrode 7B and the wiring 8C1 through a via. Since the via extends in the vertical direction on the drawing shown in FIG. 4, the first heater electrode 7A (second heater electrode 7B) and the wiring 8C1 are arranged in a different layer. As a result, the influence of heat of the wiring 8C1 on the third waveguide 6C can be reduced. The wiring 8C1 is, for example, a wiring having a lower resistance than the first heater electrode 7A and the second heater electrode 7B, for example, an aluminum wiring. The material of the wiring 8C1 is not limited to aluminum and can be changed as appropriate.

[0073] In the 90-degree hybrid circuit 1C of the fourth embodiment, the first heater electrode 7A and the second heater electrode 7B are electrically connected by a wiring 8C1. As a result, the first heater electrode 7A and the second heater electrode 7B can be driven in response to the current flowing between the first electrode pad 8A1 and the second electrode pad 8B1.

[0074] In the 90-degree hybrid circuit 1C of Example 4, it is possible that heat is generated in the wiring 8C1 connecting the first heater electrode 7A and the second heater electrode 7B, resulting in an increase in driving power. Therefore, an embodiment capable of dealing with such a situation will be described below as Example 5. EXAMPLES

[0075] 5 is an explanatory diagram showing an example of a 90-degree hybrid circuit 1D of the fifth embodiment. The same components as those in the 90-degree hybrid circuit 1C of the fourth embodiment are denoted by the same reference numerals, and the description of the overlapping components and operations will be omitted. The 90-degree hybrid circuit 1D of the fifth embodiment differs from the 90-degree hybrid circuit 1C of the fourth embodiment in that the width of the wiring 8D1 electrically connecting the first heater electrode 7A and the second heater electrode 7B is wider than the width of the wiring 8C1 shown in FIG.

[0076] In the 90-degree hybrid circuit 1D of the fifth embodiment, the wiring width of the wiring 8D1 is made wider than the wiring width of the wiring 8C1 shown in FIG. 4, so that the electrical resistance is reduced and the driving power required to drive the first heater electrode 7A and the second heater electrode 7B can be suppressed.

[0077] In the 90-degree hybrid circuit 1D of the fifth embodiment, since the gap between the first waveguide 6A and the second waveguide 6B is narrow, it is possible that the heat generated by the first heater electrode 7A on the first waveguide 6A acts on the second waveguide 6B, thereby reducing the efficiency of the phase adjustment. Therefore, an embodiment for dealing with such a situation will be described below as the sixth embodiment. EXAMPLES

[0078] 6 is an explanatory diagram showing an example of a 90-degree hybrid circuit 1E of Example 6. The same components as those in the 90-degree hybrid circuit 1D of Example 5 are denoted by the same reference numerals, and the description of the overlapping components and operations will be omitted. The 90-degree hybrid circuit 1E of Example 6 differs from the 90-degree hybrid circuit 1D of Example 5 in that the interval between the first waveguide 6A3 and the second waveguide 6B3 and the interval between the third waveguide 6C3 and the fourth waveguide 6D3 are made wider.

[0079] The first splitter 2 optically connects the first output port 21C in the first splitter 2 and the first input port 41A in the first combiner 4 via a first waveguide 6A3. The first waveguide 6A3 has a first input section 12, a first output section 13, and a first straight waveguide 11 connecting between the first input section 12 and the first output section 13. The optical length of the first waveguide 6A3 is L.

[0080] The first splitter 2 optically connects the second output port 21D in the first splitter 2 to the first input port 51A in the second combiner 5 through the second waveguide 6B3. The second waveguide 6B3 has a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting between the second input section 12A and the second output section 13A. The optical length of the second waveguide 6B3 is L+dL. Note that the optical length dL is such that the signal light generates Sig-d and Sig+90+d, i.e., "d".

[0081] In the 90-degree hybrid circuit 1E, the propagation direction of the signal light in the first input section 12, which is the connection portion of the first waveguide 6A3 connected to the first splitter 2, is different from the propagation direction of the signal light in the second input section 12A, which is the connection portion of the second waveguide 6B3 connected to the first splitter 2. As a result, the 90-degree hybrid circuit 1E is structured so that the distance between the first waveguide 6A3 and the second waveguide 6B3 is widened. The distance between the first waveguide 6A3 and the second waveguide 6B3 is structured so that the distance between the first waveguide 6A3 and the second waveguide 6B3 is widened as it moves away from the first input section 12 and the second input section 12A.

[0082] The second splitter 3 optically connects the first output port 31C in the second splitter 3 to the second input port 41B in the first combiner 4 through the third waveguide 6C3. The third waveguide 6C3 has a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting between the second input section 12A and the second output section 13A. The optical length of the third waveguide 6C3 is L+dL. Note that the optical length dL is such that the local light generates LO+d and LO-d, i.e., "d".

[0083] The second splitter 3 optically connects the second output port 31D in the second splitter 3 and the second input port 51B in the second combiner 5 via a fourth waveguide 6D3. The fourth waveguide 6D3 has a first input section 12, a first output section 13, and a first straight waveguide 11 connecting between the first input section 12 and the first output section 13. The optical length of the fourth waveguide 6D3 is L.

[0084] In the 90-degree hybrid circuit 1E, the propagation direction of the signal light at the first input portion 12, which is the connection portion of the fourth waveguide 6D3 connected to the second splitter 3, differs from the propagation direction of the signal light at the second input portion 12A, which is the connection portion of the third waveguide 6C3 connected to the second splitter 3. As a result, the 90-degree hybrid circuit 1E has a structure in which the distance between the third waveguide 6C3 and the fourth waveguide 6D3 is widened.

[0085] If the optical length of the first waveguide 6A3 is L1, the optical length of the second waveguide 6B3 is L2, the optical length of the third waveguide 6C3 is L3, and the optical length of the fourth waveguide 6D3 is L4, the relationship between the optical lengths of the first to fourth waveguides 6A3 to 6D3 is L1+L4. <L2+L3である。

[0086] The first heater electrode 7A is disposed on the first waveguide 6A3. The electrode pads 8 electrically connected to the first heater electrode 7A include a first electrode pad 8A3 disposed near the first combiner 4 and a second electrode pad 8B3 disposed near the first splitter 2.

[0087] The second heater electrode 7B is disposed on the fourth waveguide 6D3. The electrode pads 8 electrically connected to the second heater electrode 7B include a third electrode pad 8C3 disposed near the second combiner 5 and a fourth electrode pad 8D3 disposed near the second splitter 3. The 90-degree hybrid circuit 1E includes a wiring 8E3 electrically connecting the second electrode pad 8B3 and the third electrode pad 8C3.

[0088] The first combiner 4 receives the 0-degree signal light Sig-d+h from the first waveguide 6A3 and the 0-degree local light LO+d from the third waveguide 6C3. The first combiner 4 outputs a first signal light obtained by multiplexing the signal light Sig-d+h and the local light LO+90+d based on the input signal light and local light, as a channel CH1, to a first output port in the first combiner 4. The first signal light is a signal light of an XIp component that is a signal light with a phase difference of 0 degrees between the signal light and the local light.

[0089] Furthermore, the first combiner 4 outputs a second signal light obtained by multiplexing the 90-degree signal light Sig+90-d+h and the 0-degree local light LO+d based on the input 0-degree signal light and 0-degree local light, as a channel CH2 to a second output port 41D in the first combiner 4. The second signal light is an XIn component signal light having a phase difference of 180 degrees between the signal light and the local light.

[0090] The second combiner 5 receives the 90-degree signal light Sig+90+d from the first splitter 2 and the 0-degree local light LO-d from the second splitter 3. The second combiner 5 outputs a third signal light obtained by multiplexing the 90-degree signal light Sig+90+d and the 90-degree local light LO+90-d based on the input 90-degree signal light and the 0-degree local light as channel CH3 to a first output port 51C in the second combiner 5. The third signal light is an XQp component signal light in which the phase difference between the signal light and the local light is 90 degrees.

[0091] Furthermore, the second combiner 5 outputs a fourth signal light obtained by multiplexing the 180-degree signal light Sig+180+d and the 0-degree local light LO-d based on the input 90-degree signal light and 0-degree local light as a channel CH4 to a second output port 51D in the second combiner 5. The fourth signal light is an XQn component signal light in which the phase difference between the signal light and the local light is 270 degrees.

[0092] The first heater electrode 7A arranged on the first waveguide 6A3 heats the first waveguide 6A3 by flowing a current between the first electrode pad 8A3 and the second electrode pad 8B3. The refractive index of the first waveguide 6A3 changes according to the thermo-optic effect of the first waveguide 6A3, and the phase angle of the propagating signal light increases. The first heater electrode 7A adjusts the signal light Sig-d input to the first combiner 4 with the phase change h caused when the first waveguide 6A3 is heated. As a result, the 90-degree hybrid circuit 1E adjusts the signal light Sig-d+h input to the first combiner 4 so that the phase difference of the channel CH1 is 0 degrees and the phase difference of the channel CH2 is 180 degrees. Moreover, since the distance between the first waveguide 6A3 and the second waveguide 6B3 is widened, the heat generated at the first heater electrode 7A on the first waveguide 6A3 does not act on the second waveguide 6B3, thereby improving the efficiency of phase adjustment.

[0093] The second heater electrode 7B arranged on the fourth waveguide 6D3 heats the fourth waveguide 6D3 by flowing a current between the third electrode pad 8C3 and the fourth electrode pad 8D3. The refractive index of the fourth waveguide 6D3 changes according to the thermo-optic effect of the fourth waveguide 6D3, and the phase angle of the propagating signal light increases. The second heater electrode 7B adjusts the local light LO-d input to the second combiner 5 with the phase change h caused when the fourth waveguide 6D3 is heated. As a result, the 90-degree hybrid circuit 1E adjusts the local light LO-d+h input to the second combiner 5 so that the phase difference of the channel CH3 is 90 degrees and the phase difference of the channel CH4 is 270 degrees. Moreover, since the distance between the third waveguide 6C3 and the fourth waveguide 6D3 is widened, the heat generated at the second heater electrode 7B on the fourth waveguide 6D3 does not act on the third waveguide 6C3, thereby improving the efficiency of phase adjustment.

[0094] In the 90-degree hybrid circuit 1E of the sixth embodiment, the optical length L of the first waveguide 6A3 and the fourth waveguide 6D3 in which the heater electrodes are arranged can be adjusted only in the direction of lengthening, but the optical length of the second waveguide 6B3 and the third waveguide 6C3 in which the heater electrodes are not arranged is set to L+dL. As a result, the optical length L of the first waveguide 6A3 and the fourth waveguide 6D3 in which the heater electrode 7 is arranged can be adjusted by heating with the heater electrode 7.

[0095] The 90-degree hybrid circuit 1E adjusts the phase angle of the signal light by the first heater electrode 7A on the first waveguide 6A3, and adjusts the phase angle of the local light by the second heater electrode 7B on the fourth waveguide 6D3, so that the phase difference between the signal light and the local light can be adjusted to 90 degrees. The 90-degree hybrid circuit 1E can adjust the phase difference between the signal light and the local light in a specific channel to 90 degrees, so that the phase of the signal light with respect to the local light differs by 90 degrees between channels, for example, between channel CH1 and channel CH3. Even if the adjustment is made by 10 degrees overall, for example, the first heater electrode 7A can adjust by 5 degrees and the second heater electrode 7B can adjust by 5 degrees, so that the driving adjustment by the heater electrodes can be shared.

[0096] In the 90-degree hybrid circuit 1E of the sixth embodiment, the second splitter 3 is configured as a 1×2 coupler, but it may be configured as a 2×2 coupler, and this embodiment will be described below as the seventh embodiment. EXAMPLES

[0097] 7 is an explanatory diagram showing an example of a 90-degree hybrid circuit 1F of the seventh embodiment. The same components as those in the 90-degree hybrid circuit 1E of the sixth embodiment are denoted by the same reference numerals, and the description of the overlapping components and operations will be omitted. The 90-degree hybrid circuit 1F of the seventh embodiment differs from the 90-degree hybrid circuit 1E of the sixth embodiment in that the second splitter 3A is configured as a 2×2 coupler.

[0098] In the 90-degree hybrid circuit 1F, the first splitter 2 and the second splitter 3A are point-symmetric, the first waveguide 6A3 and the fourth waveguide 6D3 are point-symmetric, and the second waveguide 6B4 and the third waveguide 6C4 are point-symmetric. As a result, the influence of process errors when manufacturing the 90-degree hybrid circuit 1F can be reduced.

[0099] The first splitter 2 optically connects the first output port 21C in the first splitter 2 and the first input port 41A in the first combiner 4 via a first waveguide 6A3. The first waveguide 6A3 has a first input section 12, a first output section 13, and a first straight waveguide 11 connecting between the first input section 12 and the first output section 13. The optical length of the first waveguide 6A3 is L.

[0100] The first splitter 2 optically connects the second output port 21D in the first splitter 2 to the second input port 51B in the second combiner 5 through the second waveguide 6B4. The second waveguide 6B4 has a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting between the second input section 12A and the second output section 13A. The optical length of the second waveguide 6B4 is L+dL0+dL. The optical length dL is such that the input signal light generates Sig-d and Sig+135+d, i.e., "d". The optical length dL0 is set to a phase difference of 90 degrees by adjusting the waveguide length in advance.

[0101] The second splitter 3A optically connects the first output port 31C in the second splitter 3A and the second input port 41B in the first combiner 4 through the third waveguide 6C4. The third waveguide 6C4 has the second input section 12A, the second output section 13A, and the second straight waveguide 11A connecting between the second input section 12A and the second output section 13A. The optical length of the third waveguide 6C4 is L+dL0+dL. The optical length dL is such that the local light generates Lo+135+d and LO-d, i.e., "d". The optical length dL0 is set to a phase difference of 90 degrees by adjusting the waveguide length.

[0102] The second splitter 3A optically connects the second output port 31D in the second splitter 3A and the second input port 51B in the second combiner 5 via a fourth waveguide 6D3. The fourth waveguide 6D3 has a first input section 12, a first output section 13, and a first straight waveguide 11 connecting between the first input section 12 and the first output section 13. The optical length of the fourth waveguide 6D3 is L.

[0103] If the optical length of the first waveguide 6A3 is L1, the optical length of the second waveguide 6B4 is L2, the optical length of the third waveguide 6C4 is L3, and the optical length of the fourth waveguide 6D3 is L4, the relationship between the optical lengths of the first to fourth waveguides is L1+L4. <L2+L3である。

[0104] The second splitter 3 in the sixth embodiment has a 1×2 coupler configuration, so the phase difference between the two outputs is 0 degrees, and the first splitter 2 has a 2×2 coupler configuration, so the phase difference between the two outputs is 90 degrees. When the waveguide lengths of the waveguides connecting the splitters and the combiners are the same and the heater electrodes are not driven, the phase difference between the signal light and the local light is 0 degrees at the input to the first combiner 4 and 90 degrees at the input to the second combiner 5.

[0105] In contrast, the first splitter 2 and the second splitter 3A of the seventh embodiment are configured as 2×2 couplers. Therefore, when the waveguide lengths of the waveguides connecting the splitters and the combiners are the same and the heater electrodes are not driven, the phase difference between the signal light and the local light is −90 degrees at the input of the first combiner 4 and +90 degrees at the input of the second combiner 5. As a result, the “phase of the signal light relative to the local light” differs by 180 degrees between channels, for example, between channel CH1 and channel CH3. In this case, the 90-degree hybrid circuit 1F does not function as a 90-degree hybrid. Therefore, in the configuration of FIG. 7, the optical length difference of dL0 described above is used to provide a phase difference of 90 degrees in the waveguide length of the waveguide connecting the combiner and the splitters. To provide a phase difference of 90 degrees, dL0 should be set to 1 / 4 of the wavelength of the light propagating through the waveguide. An optical length difference of dL0=λ / 4 is used.

[0106] In order to set the phase difference to 90°, the waveguide lengths of the waveguides are adjusted in advance. That is, in the 90-degree hybrid circuit 1F, when the optical length of the first waveguide 6A3 and the fourth waveguide 6D3 is L, and the optical length of the second waveguide 6B4 and the third waveguide 6C4 is L+dL0, 2*dL0 is set to 1 / 4 of the wavelength of light. Then, the optical length difference dL is set in consideration of the variation in the phase difference, and the heater electrode 7 is driven to adjust the phase difference to 90°.

[0107] The first heater electrode 7A is disposed on the first waveguide 6A3. The electrode pads 8 electrically connected to the first heater electrode 7A include a first electrode pad 8A3 disposed near the first combiner 4 and a second electrode pad 8B3 disposed near the first splitter 2.

[0108] The second heater electrode 7B is disposed on the fourth waveguide 6D3. The electrode pads 8 electrically connected to the second heater electrode 7B include a third electrode pad 8C3 disposed near the second combiner 5 and a fourth electrode pad 8D3 disposed near the second splitter 3. The 90-degree hybrid circuit 1F includes a wiring 8E3 electrically connecting the second electrode pad 8B3 and the third electrode pad 8C3.

[0109] The first combiner 4 receives the 0-degree signal light Sig-d+h from the first waveguide 6A3 and the 0-degree local light LO+135+d from the third waveguide 6C3. The first combiner 4 outputs a first signal light obtained by multiplexing the signal light Sig-d+h and the local light LO+225+d based on the input signal light and local light to a first output port 41C in the first combiner 4 as a channel CH1. The first signal light is a signal light of an XIp component that is a signal light having a phase difference of 0 degrees between the signal light and the local light.

[0110] The first combiner 4 outputs a second signal light obtained by multiplexing the 90-degree signal light Sig+90-d+h and the 0-degree local light LO+135+d based on the input 0-degree signal light and 0-degree local light as a channel CH2 to a second output port 41D in the first combiner 4. The second signal light is an XIn component signal light having a phase difference of 180 degrees between the signal light and the local light.

[0111] The second combiner 5 receives the 90-degree signal light Sig+135+d from the first splitter 2 and the 0-degree local light LO-d from the second splitter 3A. The second combiner 5 outputs a third signal light obtained by multiplexing the 90-degree signal light Sig+135+d and the 90-degree local light LO+90-d+h based on the received 90-degree signal light and 0-degree local light, as channel CH3 to a first output port 51C in the second combiner 5. The third signal light is an XQp component signal light having a phase difference of 90 degrees between the signal light and the local light.

[0112] The second combiner 5 outputs a fourth signal light obtained by multiplexing the 180-degree signal light Sig+225+d and the 0-degree local light LO-d+h based on the input 90-degree signal light and 0-degree local light as a channel CH4 to a second output port 51D in the second combiner 5. The fourth signal light is an XQn component signal light in which the phase difference between the signal light and the local light is 270 degrees.

[0113] The first heater electrode 7A arranged on the first waveguide 6A3 heats the first waveguide 6A3 by flowing a current between the first electrode pad 8A3 and the second electrode pad 8B3. The refractive index of the first waveguide 6A3 changes according to the thermo-optic effect of the first waveguide 6A3, and the phase angle of the propagating signal light increases. The first heater electrode 7A adjusts the signal light Sig-d input to the first combiner 4 with the phase change h caused when the first waveguide 6A3 is heated. As a result, the 90-degree hybrid circuit 1F adjusts the signal light Sig-d+h input to the first combiner 4 so that the phase difference of the channel CH1 is 0 degrees and the phase difference of the channel CH2 is 180 degrees. Moreover, since the distance between the first waveguide 6A3 and the second waveguide 6B4 is wide, the heat generated at the first heater electrode 7A on the first waveguide 6A3 does not act on the second waveguide 6B4, thereby improving the efficiency of phase adjustment.

[0114] The second heater electrode 7B disposed on the fourth waveguide 6D3 heats the fourth waveguide 6D3 when current flows between the third electrode pad 8C3 and the fourth electrode pad 8D3. The refractive index of the fourth waveguide 6D3 changes according to the thermo-optical effect of the fourth waveguide 6D3, increasing the phase angle of the propagating signal light. The second heater electrode 7B adjusts the local oscillation light LO-d input to the second combiner 5 with the phase change h when the fourth waveguide 6D3 is heated. As a result, the 90-degree hybrid circuit 1F adjusts the local oscillation light LO-d+h input to the second combiner 5 so that the phase difference of channel CH3 is 90 degrees and the phase difference of channel CH4 is 270 degrees. Moreover, since the distance between the third waveguide 6C4 and the fourth waveguide 6D3 is widened, the heat generated by the second heater electrode 7B on the fourth waveguide 6D3 does not act on the third waveguide 6C4, improving the efficiency of phase adjustment.

[0115] The 90-degree hybrid circuit 1F drives the first heater electrode 7A and the second heater electrode 7B with the relationship of L1+L4<L2+L3+λ / 4 to increase L1 and L4 to the state of L1+L4 = L2+L3+λ / 4. As a result, the phase difference between the signal light and the local oscillation light can be adjusted to 90 degrees.

[0116] The 90-degree hybrid circuit 1F of Example 7 drives the first heater electrode 7A and the second heater electrode 7B with the relationship of L1+L4<L2+L3+λ / 4 to increase L1 and L4 to the state of L1+L4 = L2+L3+λ / 4. As a result, even if the first splitter 2 and the second splitter 3A are configured by 2×2 couplers, the refractive indices of the first waveguide 6A3 and the fourth waveguide 6D3 can be adjusted to adjust the phase difference between the signal light and the local oscillation light to 90 degrees.

[0117] In the 90-degree hybrid circuit 1F, an optical length difference of dL0=λ / 4 is used to provide a phase difference of 90 degrees in the waveguide length of the waveguide between the combiner and the splitter, and the heater electrode 7 is driven to increase L1 and L4 so that the relationship of L1+L4=L2+L3+λ / 4 is satisfied. However, the present invention is not limited to this, and an embodiment thereof will be described below as Example 8. EXAMPLES

[0118] 8 is an explanatory diagram showing an example of a 90-degree hybrid circuit 1G of the eighth embodiment. The same components as those in the 90-degree hybrid circuit 1F of the seventh embodiment are given the same reference numerals, and the description of the overlapping components and operations is omitted. The 90-degree hybrid circuit 1G of the eighth embodiment differs from the 90-degree hybrid circuit 1F of the seventh embodiment in that the optical lengths of L2 and L3 in the heater electrode 7 are increased to satisfy the relationship L1+L4=L2+L3+λ / 4, thereby adjusting the phase difference to 90 degrees.

[0119] In the 90-degree hybrid circuit 1G, the first splitter 2 and the second splitter 3A are point-symmetric, the first waveguide 6A3 and the fourth waveguide 6D3 are point-symmetric, and the second waveguide 6B3 and the third waveguide 6C3 are point-symmetric. As a result, the influence of process errors when manufacturing the 90-degree hybrid circuit 1G can be reduced.

[0120] The first splitter 2 optically connects the first output port 21C in the first splitter 2 and the first input port 41A in the first combiner 4 via a first waveguide 6A3. The first waveguide 6A3 has a first input section 12, a first output section 13, and a first straight waveguide 11 connecting between the first input section 12 and the first output section 13. The optical length of the first waveguide 6A3 is L.

[0121] The first splitter 2 optically connects the second output port 21D in the first splitter 2 to the first input port 51A in the second combiner 5 through the second waveguide 6B4. The second waveguide 6B4 has a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting between the second input section 12A and the second output section 13A. The optical length of the second straight waveguide 11A is L+dL0-dL. Note that the optical length dL is such that the signal light generates Sig+d and Sig+135-d, i.e., "d". The optical length dL0 is set to a phase difference of 90 degrees by adjusting the waveguide length in advance.

[0122] The second splitter 3A optically connects the first output port 31C in the second splitter 3A and the second input port 41B in the first combiner 4 through the third waveguide 6C4. The third waveguide 6C4 has the second input section 12A, the second output section 13A, and the second straight waveguide 11A connecting between the second input section 12A and the second output section 13A. The optical length of the third waveguide 6C4 is L+dL0-dL. Note that the optical length dL is such that the local light generates LO+135-d and LO+d, i.e., "d". The optical length dL0 is set to a phase difference of 90 degrees by adjusting the waveguide length in advance.

[0123] The second splitter 3A optically connects the second output port 31D in the second splitter 3A and the second input port 51B in the second combiner 5 through a fourth waveguide 6D3. The fourth waveguide 6D3 has a first input section 12, a first output section 13, and a first straight waveguide 11 connecting between the first input section 12 and the first output section 13. The fourth waveguide 6D4 The optical length of is L.

[0124] If the optical length of the first waveguide 6A3 is L1, the optical length of the second waveguide 6B4 is L2, the optical length of the third waveguide 6C4 is L3, and the optical length of the fourth waveguide 6D3 is L4, the relationship between the optical lengths of the first to fourth waveguides 6A3 to 6D3 is L1+L4. <L2+L3である。

[0125] The first splitter 2 and the second splitter 3A of the eighth embodiment are configured as a 2×2 coupler. Therefore, when the waveguide lengths of the waveguides connecting the splitters and the combiners are the same and the heater electrodes are not driven, the phase difference between the signal light and the local light is −90 degrees at the input of the first combiner 4 and +90 degrees at the input of the second combiner 5. As a result, the “phase of the signal light relative to the local light” differs by 180 degrees between channels, for example, between channel CH2 and channel CH4. In this case, the 90-degree hybrid circuit 1G does not function as a 90-degree hybrid. Therefore, in the configuration of FIG. 8, an optical length difference of dL0 is used to provide a phase difference of 90 degrees in the waveguide lengths of the waveguides connecting the combiners and the splitters. In order to provide a phase difference of 90 degrees, dL0 should be set to ¼ of the wavelength.

[0126] In order to set the phase difference to 90°, the lengths of the waveguides are adjusted. That is, in the 90° hybrid circuit 1G, when the optical length of the first waveguide 6A3 and the fourth waveguide 6D3 is L, and the optical length of the second waveguide 6B4 and the third waveguide 6C4 is L+dL0, 2*dL0 is set to ¼ of the wavelength of light. Then, the optical length difference dL is set in consideration of the variation in the phase difference, and the heater electrode 7 is driven to adjust the phase difference to 90°.

[0127] The third heater electrode 7C is disposed on the second waveguide 6B4. The electrode pads 8 electrically connected to the third heater electrode 7C include a first electrode pad 8A4 disposed near the first splitter 2 and a second electrode pad 8B4 disposed near the second combiner 5.

[0128] The fourth heater electrode 7D is disposed on the third waveguide 6C4. The electrode pads 8 electrically connected to the fourth heater electrode 7D include a third electrode pad 8C4 disposed near the second splitter 3A and a fourth electrode pad 8D4 disposed near the first combiner 4. The 90-degree hybrid circuit 1G has a wiring 8E4 electrically connecting between the second electrode pad 8B4 and the third electrode pad 8C4.

[0129] The first combiner 4 receives the 0-degree signal light Sig+d from the first waveguide 6A3 and the 0-degree local light LO+135-d+h from the third waveguide 6C3. The first combiner 4 outputs a first signal light obtained by multiplexing the signal light Sig+d and the local light LO+225-d+h based on the input signal light and local light to a first output port 41C in the first combiner 4 as a channel CH1. The first signal light is a signal light of an XIp component that is a signal light with a phase difference of 0 degrees between the signal light and the local light.

[0130] The first combiner 4 outputs a second signal light obtained by multiplexing the 90-degree signal light Sig+90+d and the 0-degree local light LO+135-d+h based on the input 0-degree signal light and 0-degree local light as a channel CH2 to a second output port 41D in the first combiner 4. The second signal light is an XIn component signal light having a phase difference of 180 degrees between the signal light and the local light.

[0131] The second combiner 5 receives the 90-degree signal light Sig+135-d+h from the first splitter 2 and the 0-degree local light LO+d from the second splitter 3A. The second combiner 5 outputs a third signal light obtained by multiplexing the 90-degree signal light Sig+135-d+h and the 90-degree local light LO+90+d based on the input 90-degree signal light and 0-degree local light, as channel CH3 to a first output port 51C in the second combiner 5. The third signal light is an XQp component signal light in which the phase difference between the signal light and the local light is 90 degrees.

[0132] The second combiner 5 outputs a fourth signal light obtained by multiplexing the 180-degree signal light Sig+225-d+h and the 0-degree local light LO+d based on the input 90-degree signal light and 0-degree local light, as a channel CH4 to a second output port 51D in the second combiner 5. The fourth signal light is an XQn component signal light in which the phase difference between the signal light and the local light is 270 degrees.

[0133] The third heater electrode 7C arranged on the second waveguide 6B4 heats the second waveguide 6B4 by flowing a current between the first electrode pad 8A4 and the second electrode pad 8B4. The refractive index of the second waveguide 6B4 changes according to the thermo-optic effect of the second waveguide 6B4, and the phase angle of the propagating signal light increases. The third heater electrode 7C adjusts the signal light Sig+135-d input to the second combiner 5 with the phase change h caused when the second waveguide 6B4 is heated. As a result, the 90-degree hybrid circuit 1G adjusts the signal light Sig+135-d+h input to the second combiner 5 so that the phase difference of the channel CH3 is 90 degrees and the phase difference of the channel CH4 is 27 degrees.

[0134] The fourth heater electrode 7D arranged on the third waveguide 6C4 heats the third waveguide 6C4 by flowing a current between the third electrode pad 8C4 and the fourth electrode pad 8D4. The refractive index of the third waveguide 6C4 changes according to the thermo-optic effect of the third waveguide 6C4, and the phase angle of the propagating signal light increases. The fourth heater electrode 7D adjusts the local light LO+135-d input to the first combiner 4 with the phase change h caused when the third waveguide 6C4 is heated. As a result, the 90-degree hybrid circuit 1G adjusts the local light LO+135-d+h input to the first combiner 4 so that the phase difference of the channel CH1 is 0 degrees and the phase difference of the channel CH2 is 180 degrees.

[0135] The 90-degree hybrid circuit 1G drives the third heater electrode 7C and the fourth heater electrode 7D to increase L2 and L3 in a state where L1+L4>L2+L3+λ / 4 is satisfied, so that the phase difference between the signal light and the local light is adjusted to 90 degrees.

[0136] In the 90-degree hybrid circuit 1G of the eighth embodiment, the third heater electrode 7C and the fourth heater electrode 7D are driven to increase L2 and L3 in a state where L1+L4>L2+L3+λ / 4 is satisfied. As a result, even if the first splitter 2 and the second splitter 3A are configured as 2×2 couplers, the phase difference between the signal light and the local light can be adjusted to 90 degrees by adjusting the refractive indexes of the second waveguide 6B4 and the third waveguide 6C4.

[0137] In this embodiment, a phase adjustment unit is exemplified that adjusts the phase angle of the signal light or the local light by adjusting the refractive index of the waveguide by driving the heater electrode 7. However, the phase adjustment unit is not limited to the thermo-optic effect of the heater electrode 7, and may be modified as appropriate by using a material with an electro-optic effect for the waveguide and adjusting the refractive index by injecting a current into the waveguide to adjust the phase angle of the signal light or the local light.

[0138] The first to fourth waveguides 6A to 6D may be, for example, a channel waveguide, a rib waveguide, a ridge waveguide, a slab waveguide, or the like, and can be appropriately changed.

[0139] FIG. 9 is an explanatory diagram showing an example of an optical transceiver 70 according to the present embodiment. The optical transceiver 70 shown in FIG. 9 is connected to an output optical fiber and an input optical fiber. The optical transceiver 70 includes a light source 71, a DSP (Digital Signal Processor) 72, and an optical transceiver 73. The optical transceiver 73 includes an optical transmitter 73A and an optical receiver 73B. The DSP 72 is an electrical component that performs digital signal processing. For example, the DSP 72 performs processing such as encoding transmission data, generates an electrical signal including the transmission data, and outputs the generated electrical signal to the optical transmitter 73A. The DSP 72 also obtains an electrical signal including reception data from the optical receiver 73B, and obtains reception data by performing processing such as decoding the obtained electrical signal.

[0140] The light source 71 includes, for example, a laser diode, and generates light of a predetermined wavelength and supplies it to the optical transmitter 73A and the optical receiver 73B. The optical transmitter 73A modulates the light supplied from the light source 71 with an electrical signal output from the DSP 72, and outputs the obtained transmission light to an optical fiber. The optical transmitter 73A includes an optical modulator element 73A1 that generates transmission light by modulating the light supplied from the light source 71 with an electrical signal input to the optical modulator when the light propagates through the waveguide.

[0141] The optical receiver 73B has an optical receiver element 73B1 that receives an optical signal from an optical fiber and demodulates the received light using light supplied from the light source 71. The optical receiver 73B then converts the demodulated received light into an electrical signal and outputs the converted electrical signal to the DSP 72. The optical receiver element 73B1 has an optical device built-in, such as a 90-degree hybrid circuit.

[0142] The optical device in the optical transceiver 70 includes a 90-degree hybrid circuit that mixes the signal light and the local light and separates the signal light into orthogonal components and outputs them. The 90-degree hybrid circuit has a first coupler that branches the signal light and a second coupler that branches the local light. The 90-degree hybrid circuit has a first waveguide and a second waveguide through which the signal light branched by the first coupler propagates, and a third waveguide and a fourth waveguide through which the local light branched by the second coupler propagates. The 90-degree hybrid circuit has a third coupler that combines the signal light propagated through the first waveguide and the local light propagated through the third waveguide, and a fourth coupler that combines the signal light propagated through the second waveguide and the local light propagated through the fourth waveguide. The 90-degree hybrid circuit has a phase adjustment unit that adjusts the phase of light propagating through at least one of the first to fourth waveguides. The total value of the optical length of the first waveguide and the optical length of the fourth waveguide is shorter than the total value of the optical length of the second waveguide and the optical length of the third waveguide. As a result, signal loss can be suppressed.

[0143] For convenience of explanation, the optical transceiver 70 has been illustrated as having the optical transmitter 73A and the optical receiver 73B built in, but the optical transceiver 70 may have either the optical transmitter 73A or the optical receiver 73B built in. For example, an optical device may be applied to the optical transceiver 70 having the optical receiver 73B built in, and modifications can be made as appropriate.

[0144] Furthermore, each component of each unit shown in the figure does not necessarily have to be physically configured as shown in the figure. In other words, the specific form of distribution and integration of each unit is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0145] Furthermore, the various processing functions performed by each device may be executed in whole or in part on a CPU (Central Processing Unit) (or a microcomputer such as an MPU (Micro Processing Unit) or an MCU (Micro Controller Unit)). It goes without saying that the various processing functions may be executed in whole or in part on a program analyzed and executed by a CPU (or a microcomputer such as an MPU or an MCU), or on hardware using wired logic. [Explanation of symbols]

[0146] 1 90 degree hybrid circuit 2 First Splitter 3 Second Splitter 4. First Combiner 5 Second Combiner 6A First Waveguide 6B Second Waveguide 6C Third Waveguide 6D 4th Waveguide 7 Heater electrode 7A First heater electrode 7B Second heater electrode 7C Third heater electrode 7D 4th heater electrode

Claims

1. An optical device including a 90-degree hybrid circuit that mixes a signal light and a local light and separates the signal light into orthogonal components and outputs the mixed light, The 90 degree hybrid circuit is a first coupler that branches the signal light; a second coupler that branches the local light; a first waveguide and a second waveguide through which the signal light branched by the first coupler propagates, respectively; a third waveguide and a fourth waveguide through which the local light branched by the second coupler propagates, respectively; a third coupler that combines the signal light propagated through the first waveguide and the local light propagated through the third waveguide; a fourth coupler that combines the signal light propagated through the second waveguide and the local light propagated through the fourth waveguide; a phase adjusting unit that adjusts a phase of light propagating through at least one of the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, an optical device, wherein a first sum of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a second sum of an optical length of the second waveguide and an optical length of the third waveguide.

2. The phase adjustment unit is 2. The optical device according to claim 1, wherein a phase angle adjusting member is disposed in at least one of the first waveguide and the fourth waveguide, the phase angle adjusting member is disposed in the first waveguide to adjust a phase angle of the signal light propagating in the first waveguide, and / or the phase angle adjusting member is disposed in the fourth waveguide to adjust a phase angle of the local light propagating in the fourth waveguide.

3. the first sum is shorter than a third sum which is a sum of the second sum and ¼ of the wavelength of the signal light, The phase adjustment unit is 2. The optical device according to claim 1, wherein a phase angle adjusting member is disposed in at least one of the first waveguide and the fourth waveguide, and is disposed in the first waveguide for adjusting a phase angle of the signal light propagating through the first waveguide and / or is disposed in the fourth waveguide for adjusting a phase angle of the local light propagating through the fourth waveguide so that the first sum value and the third sum value are equal to each other.

4. 2. The optical device according to claim 1, wherein the waveguide widths of the first waveguide and the fourth waveguide are configured to be narrower than the waveguide widths of the third waveguide and the second waveguide, so that a total value of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a total value of an optical length of the second waveguide and an optical length of the third waveguide.

5. 2. The optical device according to claim 1, wherein an optical length of the first waveguide is equal to an optical length of the fourth waveguide, and an optical length of the second waveguide is equal to an optical length of the third waveguide.

6. The phase adjustment unit is a first phase adjustment unit disposed in the first waveguide and configured to adjust a phase angle of the signal light propagating through the first waveguide; a second phase adjustment unit disposed in the fourth waveguide and configured to adjust a phase angle of the local light propagating through the fourth waveguide; a wiring that electrically connects the first phase adjustment unit and the second phase adjustment unit; 2. The optical device according to claim 1, further comprising:

7. 2. The optical device according to claim 1, wherein a distance between the first waveguide and the second waveguide increases with increasing distance from a connection portion of the first waveguide and a connection portion of the second waveguide such that a direction in which the signal light propagates in a connection portion of the first waveguide connected to the first coupler differs from a direction in which the signal light propagates in a connection portion of the second waveguide connected to the first coupler.

8. the first sum is longer than a third sum which is a sum of the second sum and ¼ of the wavelength of the signal light; The phase adjustment unit is 2. The optical device according to claim 1, wherein a phase angle adjustment member is disposed in at least one of the second waveguide and the third waveguide, and is disposed in the second waveguide for adjusting a phase angle of the signal light propagating through the second waveguide and / or is disposed in the third waveguide for adjusting a phase angle of the local light propagating through the third waveguide so that the first sum value and the third sum value are equal.

9. An optical receiver including an optical receiver element that converts a received signal light into an electrical signal, The optical receiver element comprises: an optical device including a 90-degree hybrid circuit that mixes the signal light with a local light and separates the signal light into orthogonal components and outputs the mixed light, The 90 degree hybrid circuit is a first coupler that branches the signal light; a second coupler that branches the local light; a first waveguide and a second waveguide through which the signal light branched by the first coupler propagates, respectively; a third waveguide and a fourth waveguide through which the local light branched by the second coupler propagates, respectively; a third coupler that combines the signal light propagated through the first waveguide and the local light propagated through the third waveguide; a fourth coupler that combines the signal light propagated through the second waveguide and the local light propagated through the fourth waveguide; a phase adjusting unit that adjusts a phase of light propagating through at least one of the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, a first sum of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a second sum of an optical length of the second waveguide and an optical length of the third waveguide; 1. An optical receiver comprising:

10. an optical modulator element that modulates propagating light in response to an electrical signal; an optical receiver element that converts received light into an electrical signal; a signal processing unit that generates an electrical signal to the optical modulator element and acquires the electrical signal from the optical receiver element, The optical receiver element comprises: an optical device including a 90-degree hybrid circuit that mixes a signal light and a local light and separates the signal light into orthogonal components and outputs the mixed light, The 90 degree hybrid circuit is a first coupler that branches the signal light; a second coupler that branches the local light; a first waveguide and a second waveguide through which the signal light branched by the first coupler propagates, respectively; a third waveguide and a fourth waveguide through which the local light branched by the second coupler propagates, respectively; a third coupler that combines the signal light propagated through the first waveguide and the local light propagated through the third waveguide; a fourth coupler that combines the signal light propagated through the second waveguide and the local light propagated through the fourth waveguide; a phase adjusting unit that adjusts a phase of light propagating through at least one of the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, a first sum of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a second sum of an optical length of the second waveguide and an optical length of the third waveguide; 1. An optical transceiver comprising:

Images