Optical device, optical receiver, and optical transceiver

Abstract

The invention relates to an optical device, an optical receiver and an optical transceiver. A 90-degree hybrid circuit includes a first waveguide and a second waveguide in each of which signal light that has been split by a first coupler propagates. The circuit includes: a third waveguide and a fourth waveguide in each of which local oscillator light that has been split by the second coupler propagates; and a third coupler that multiplexes the signal light that has propagated through the first waveguide and the local oscillator light that has propagated through the third waveguide. The circuit includes: a fourth coupler that multiplexes the signal light that has propagated through the second waveguide and the local oscillator light that has propagated through the fourth waveguide; and a phase adjuster that adjusts a phase of light propagating through at least one of the first to fourth waveguides. A first total value of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a second total value of an optical length of the second waveguide and an optical length of the third waveguide.

Description

Technical Field

[0001] The embodiments discussed herein relate to optical devices, optical receivers, and optical transceivers. Background Art

[0002] For example, an optical receiver adopting a digital coherent reception function includes, as a built-in unit, a 90-degree hybrid circuit that combines signal light and local oscillator light and outputs signal light by splitting the signal light into orthogonal components. Fig.10 is an explanatory diagram illustrating an example of a conventionally used 90-degree hybrid circuit 100 . Fig.10 The 90-degree hybrid circuit 100 shown includes a first optical splitter 110, a second optical splitter 120, a first combiner 130, a second combiner 140, and first to fourth waveguides 101A to 101D.

[0003] The first optical splitter 110 is a 2×2 coupler including a first input port 111A, a second input port 111B, a first output port 111C, and a second output port 111D. The second optical splitter 120 is a 1×2 coupler including 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 including 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 including a first input port 141A, a second input port 141B, a first output port 141C and a second output port 141D.

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

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

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

[0008] The second combiner 140 optically connects the first input port 141A included in the second combiner 140 with the second output port 111D included in the first optical splitter 110 through the second waveguide 101B. The second combiner 140 optically connects the second input port 141B included in the second combiner 140 with the second output port 121C included in the second optical splitter 120 through the fourth waveguide 101D.

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

[0010] The second optical splitter 120 converts the local oscillator light received from the first input port 121A included in the second optical splitter 120 into the local oscillator light of 0 degrees, and outputs the local oscillator light of 0 degrees to the first output port 121B and the second output port 121C included in the second optical splitter 120 .

[0011] The first combiner 130 inputs both the signal light of 0 degrees received from the first optical splitter 110 and the local oscillator light of 0 degrees received from the second optical splitter 120. The first combiner 130 outputs a first signal light for multiplexing the signal light of 0 degrees and the local oscillator light of 90 degrees to a first output port 131C included in the first combiner 130 as a channel CH1 based on the input signal light of 0 degrees and the input local oscillator light of 0 degrees. The first signal light is a signal light having a phase difference of 0 degrees between the signal light and the local oscillator light and having an X1p component.

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

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

[0014] In addition, the second combiner 140 outputs a fourth signal light for multiplexing the signal light of 180 degrees and the local oscillator light of 0 degrees to the second output port 141D included in the second combiner 140 as the channel CH4 based on the input signal light of 90 degrees and the input local oscillator light of 0 degrees. The fourth signal light is a signal light having a phase difference of 270 degrees between the signal light and the local oscillator light and having an XQn component.

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

[0016] When the optical length of the first waveguide 101A is represented by L1, the optical length of the second waveguide 101B is represented by L2, the optical length of the third waveguide 101C is represented by L3, and the optical length of the fourth waveguide 101D is represented by L4, the relationship of the optical lengths L1 = L2 = L3 = L4 holds. In addition, the optical lengths are calculated based on a formula represented by waveguide length × effective refractive index of the waveguide.

[0017] Patent Document 1: Japanese Patent Application Publication No. 2008-193555

[0018] Patent Document 2: U.S. Patent No. 10126498

[0019] Patent Document 3: Japanese Patent Application Publication No. 2001-109023

[0020] Therefore, the 90-degree hybrid circuit 100 outputs the first to fourth signal lights each having a 90-degree phase difference between the signal light and the local oscillator light. However, in the 90-degree hybrid circuit 100, for example, in the first optical splitter 110, the second optical splitter 120, the first combiner 130, the second combiner 140, or the first to fourth waveguides 101A to 101D, a manufacturing error of a waveguide width or the like occurs. Therefore, in the 90-degree hybrid circuit 100, a 90-degree phase difference between the signal light and the local oscillator light cannot be ensured due to a manufacturing error or the like, and a signal loss occurs.

[0021] Therefore, an object of one aspect of an embodiment of the present invention is to provide an optical device or the like capable of suppressing signal loss. Summary of the invention

[0022] According to one aspect of the embodiment, an optical device includes a 90-degree hybrid circuit, which combines signal light and local oscillator light and outputs the signal light by splitting the signal light into orthogonal components. The 90-degree hybrid circuit includes a first coupler that splits the signal light and a second coupler that splits the local oscillator light. The 90-degree hybrid circuit includes a first waveguide, a second waveguide, a third waveguide, a fourth waveguide, a third coupler, a fourth coupler, and a phase adjuster. The signal light that has been split by the first coupler is propagated in each of the first waveguide and the second waveguide. The local oscillator light that has been split by the second coupler is propagated in each of the third waveguide and the fourth waveguide. The third coupler multiplexes the signal light that has been propagated through the first waveguide and the local oscillator light that has been propagated through the third waveguide. The fourth coupler multiplexes the signal light that has been propagated through the second waveguide and the local oscillator light that has been propagated through the fourth waveguide. The phase adjuster adjusts the phase of the light propagated through at least one waveguide among the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide. A first total value of the optical length of the first waveguide and the optical length of the fourth waveguide is shorter than a second total value of the optical length of the second waveguide and the optical length of the third waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to the first embodiment;

[0024] Figure 2 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to the second embodiment;

[0025] Figure 3 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to a third embodiment;

[0026] Figure 4is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to a fourth embodiment;

[0027] Figure 5 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to a fifth embodiment;

[0028] Figure 6 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to a sixth embodiment;

[0029] Figure 7 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to a seventh embodiment;

[0030] Figure 8 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit according to an eighth embodiment;

[0031] Fig. 9 is an explanatory diagram illustrating one example of an optical transceiver according to the present embodiment; and

[0032] Fig.10 is an explanatory diagram illustrating an example of a conventionally used 90-degree hybrid circuit. DETAILED DESCRIPTION

[0033] Preferred embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the present invention is not limited to these embodiments. In addition, the various embodiments can be used in any appropriate combination as long as they do not conflict with each other.

[0034] (a) First Embodiment

[0035] Figure 1 is an explanatory diagram illustrating one example of the 90-degree hybrid circuit 1 according to the first embodiment. Figure 1 The 90-degree hybrid circuit 1 shown is a circuit that combines signal light and local oscillator light, and outputs signal light by splitting the signal light into orthogonal components. The 90-degree hybrid circuit 1 includes a first optical splitter 2, a second optical 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.

[0036] The first optical splitter 2 is a 2×2 coupler, which includes a first input port 21A, a second input port 21B, a first output port 21C, and a second output port 21D. The first optical splitter 2 is a first coupler that splits the signal light and outputs the split signal light to the first waveguide 6A and the second waveguide 6B. The second optical splitter 3 is a 1×2 coupler, which includes a first input port 31A, a first output port 31C, and a second output port 31D. The second optical splitter 3 is a second coupler that splits the local oscillator light, outputs the split local oscillator light to the third waveguide 6C and the fourth waveguide 6D, and outputs the branched local oscillator light. The first combiner 4 is a 2×2 coupler, which includes 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 multiplexes the signal light that has been propagated through the first waveguide 6A and the local oscillator light that has been propagated through the third waveguide 6C. The second combiner 5 is a 2×2 coupler including 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 multiplexes the signal light having propagated through the second waveguide 6B and the local oscillator light having propagated through the fourth waveguide 6D.

[0037] The first optical splitter 2 optically connects the first output port 21C included in the first optical splitter 2 with the first input port 41A included in the first combiner 4 through the first waveguide 6A. The first optical splitter 2 optically connects the second output port 21D included in the first optical splitter 2 with the first input port 51A included in the second combiner 5 through the second waveguide 6B.

[0038] The second optical splitter 3 optically connects the first output port 31C included in the second optical splitter 3 with the second input port 41B included in the first combiner 4 through the third waveguide 6C. The second optical splitter 3 optically connects the second output port 31D included in the second optical splitter 3 with the second input port 51B included in the second combiner 5 through the fourth waveguide 6D.

[0039] The first combiner 4 optically connects the first input port 41A included in the first combiner 4 with the first output port 21C included in the first optical splitter 2 through the first waveguide 6A. The first combiner 4 optically connects the second input port 41B included in the first combiner 4 with the first output port 31C included in the second optical splitter 3 through the third waveguide 6C.

[0040] The second combiner 5 optically connects the first input port 51A included in the second combiner 5 and the second output port 21D included in the first optical splitter 2 through the second waveguide 6B. The second combiner 5 optically connects the second input port 51B included in the second combiner 5 and the second output port 31D included in the second optical splitter 3 through the fourth waveguide 6D.

[0041] When the optical length of the first waveguide 6A is represented by L1, the optical length of the second waveguide 6B is represented by L2, the optical length of the third waveguide 6C is represented by L3, and the optical length of the fourth waveguide 6D is represented by L4, the optical length relationship among the first waveguide 6A to the fourth waveguide 6D is represented by L1 + L4 < L2 + L3. In addition, the optical length is calculated based on the formula represented by the waveguide length of the waveguide × effective refractive index. The optical length L1 of the first waveguide 6A is made shorter than the optical length L2 of the second waveguide 6B. Therefore, the 90-degree hybrid circuit 1 is configured such that, for example, the signal light received from the first output port 21C included in the first optical splitter 2 becomes (0 - d) degrees, and the signal light received from the second output port 21D included in the first optical splitter 2 becomes 90 degrees. The first optical splitter 2 is configured such that by pre-adjusting and setting the optical length of each of the first waveguide 6A and the second waveguide 6B, for example, an error of 10 degrees occurs, that is, a phase difference of 80 degrees is generated as the phase difference of the signal light with respect to the local oscillator light.

[0042] The heater electrode 7 is a phase adjustment part arranged on the first waveguide 6A and adjusts the phase of the signal light propagating through the first waveguide 6A. In addition, the heater electrode 7 is made of an electrode material containing, for example, Ti, TiN, etc. The electrode pads 8 electrically connected to the heater electrode 7 include a first electrode pad 8A arranged near the first optical splitter 2 and a second electrode pad 8B arranged near the first combiner 4. The heater electrode 7 heats the first waveguide 6A due to current flowing through the path between the first electrode pad 8A and the second electrode pad 8B. In the first waveguide 6A, the refractive index changes according to the thermo-optic effect of the first waveguide 6A, and the phase angle of the signal light propagating through the first waveguide 6A becomes higher.

[0043] In addition, the optical length L1 of the first waveguide 6A is different from the optical length L3 of the third waveguide 6C, so the signal light input to the first input port 41A included in the first combiner 4 becomes Sig-d, and the local oscillator light input to the second input port 41B included in the first combiner 4 becomes Lo+d, where "d" represents a change in the phase angle caused by the optical length difference. "d" is set so that, in order to adjust the phase angle of the signal light by driving the heater electrode 7 arranged near the first waveguide 6A, in a state where the heater electrode 7 is not driven, the phase angle of the signal light relative to the local oscillator light is set to be less than -90 degrees at the channel CH1, and is set to be less than +90 degrees at the channel CH2.

[0044] The first optical splitter 2 splits the signal light received from the first input port 21A included in the first optical splitter 2 into a signal light of 0 degrees and a signal light of 90 degrees. The first optical splitter 2 outputs the split signal light of 0 degrees to the first waveguide 6A connected to the first output port 21C included in the first optical splitter 2, and also outputs the split signal light of 90 degrees to the second waveguide 6B connected to the second output port 21D included in the first optical splitter 2.

[0045] The second splitter 3 splits the local oscillator light received from the first input port 31A included in the second splitter 3 and outputs the split local oscillator light as 0-degree local oscillator 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.

[0046] The first combiner 4 inputs both the signal light Sig-d+h of 0 degrees received from the first waveguide 6A and the local oscillator light LO+d of 0 degrees received from the third waveguide 6C. The first combiner 4 outputs the first signal light obtained by multiplexing the signal light Sig-d+h and the local oscillator light LO+90+d to the first output port 41C included in the first combiner 4 as the channel CH1 based on the input signal light and the input local oscillator light. The first signal light is a signal light having a phase difference of 0 degrees between the signal light and the local oscillator light and having an X1p component corresponding to the I component of the X polarized wave.

[0047] Furthermore, the first combiner 4 outputs the second signal light obtained by multiplexing the signal light Sig+90-d+h of 90 degrees and the local oscillator light LO+d of 0 degrees to the second output port 41D included in the first combiner 4 as the channel CH2 based on the input signal light of 0 degrees and the input local oscillator light of 0 degrees. The second signal light is a signal light having a phase difference of 180 degrees between the signal light and the local oscillator light and having an XIn component corresponding to the I component of the X polarized wave.

[0048] The second combiner 5 inputs both the signal light Sig+90 at 90 degrees received from the first optical splitter 2 and the local oscillator light LO+0 at 0 degrees received from the second optical splitter 3. Based on the input signal light at 90 degrees and the local oscillator light at 0 degrees, the second combiner 5 outputs, to a first output port 51C included in the second combiner 5 as channel CH3, a third signal light obtained by multiplexing the signal light Sig+90 at 90 degrees and the local oscillator light LO+90 at 90 degrees. The third signal light is a signal light having a 90-degree phase difference between the signal light and the local oscillator light and having an XQp component corresponding to the Q component of the X polarization wave.

[0049] In addition, based on the input signal light at 90 degrees and the input local oscillator light at 0 degrees, the second combiner 5 outputs, to a second output port 51D included in the second combiner 5 as channel CH4, a fourth signal light obtained by multiplexing the signal light Sig+180 at 180 degrees and the local oscillator light LO+0 at 0 degrees. The fourth signal light is a signal light having a 270-degree phase difference between the signal light and the local oscillator light and having an XQn component corresponding to the Q component of the X polarization wave.

[0050] The heater electrode 7 disposed on the first waveguide 6A heats the first waveguide 6A due to current flowing through the path between the first electrode pad 8A and the second electrode pad 8B. In the first waveguide 6A, the refractive index changes according to the thermo-optic effect of the first waveguide 6A, and the phase angle of the signal light propagating through the first waveguide 6A becomes higher. The heater electrode 7 adjusts the signal light Sig-d entering the first combiner 4 based on the phase change h indicated when the first waveguide 6A is heated. As a result, the 90-degree hybrid circuit 1 correspondingly adjusts the signal light Sig-d+h entering the first combiner 4 so that the phase difference at channel CH1 becomes 0 degrees and the phase difference at channel CH2 becomes 180 degrees.

[0051] When the optical length relationship among the first waveguide 6A to the fourth waveguide 6D is L1+L4 < L2+L3, the phase difference at channel CH1 is less than -90 degrees. If current flows into the heater electrode 7 in this state, the phase difference becomes larger, so that the phase difference at channel CH1 can be made -90 degrees by adjusting the current value. On the contrary, when the optical length relationship among the first waveguide 6A to the fourth waveguide 6D is L1+L4 ≥ L2+L3, the phase difference at channel CH1 is finally equal to or greater than -90 degrees. Even if current flows into the heater electrode 7 in this state, the phase difference only becomes larger, so it is impossible to make the phase difference at channel CH1 -90 degrees.

[0052] For example, in a case where a phase angle change caused by manufacturing errors is represented by "e", "d = d - e" holds. In a case where e < d, heating can be performed by the heater electrode 7 to make the phase angle become the desired phase angle difference (90 degrees). However, in a case where e ≥ d, in a state where the heater electrode 7 is not heated (h = 0), the phase difference between the signal light and the local oscillator light at the channel CH2 becomes 90 degrees - 2(d - e) > 90 degrees. Therefore, if the heater electrode 7 is heated, the result will thus become equal to or greater than 90 degrees. Therefore, in this case, it is impossible to perform adjustment by using the heater electrode 7.

[0053] Therefore, in order to adjust the phase difference at the channel CH1, which includes an error of the initial phase difference caused by manufacturing errors, to -90 degrees by the heater electrode 7, it is necessary to adjust the optical length relationship between the first waveguide 6A to the fourth waveguide 6D to a relationship represented by L1 + L4 < L2 + L3.

[0054] In other words, even in a case where a phase error of d - e occurs between the signal light and the local oscillator light entering the first combiner 4 due to manufacturing errors, by allowing current to flow into the heater electrode 7 and heating the first waveguide 6A, the refractive index of the first waveguide 6A increases. As a result, the phase difference between the signal light propagating through the first waveguide 6A and the signal light propagating through the second waveguide 6B can be adjusted to 90 degrees.

[0055] The 90-degree hybrid circuit 1 according to the first embodiment allows the optical length relationship between the first waveguide 6A to the fourth waveguide 6D to be a relationship represented by L1 + L4 < L2 + L3 and preset. In addition, even in a case where a phase error of d - e occurs between the signal light and the local oscillator light entering the first combiner 4 due to manufacturing errors, the 90-degree hybrid circuit 1 increases the refractive index of the first waveguide 6A by allowing current to flow into the heater electrode 7 and heating the first waveguide 6A. Then, the 90-degree hybrid circuit 1 adjusts the phase difference between the signal light propagating through the first waveguide 6A and the signal light propagating through the second waveguide 6B to 90 degrees by increasing the refractive index of the first waveguide 6A. As a result, even in a case where manufacturing errors occur, signal loss can be suppressed by stably ensuring a 90-degree phase difference.

[0056] In addition, as an example, the case where the optical length is adjusted by adjusting the waveguide length of each of the first waveguide 6A to the fourth waveguide 6D according to the first embodiment has been described, but the embodiment is not limited thereto. The optical length may be adjusted by adjusting the waveguide width, and appropriate modifications are also possible. In this case, the same effect can be obtained by making the waveguide width of the first waveguide 6A narrower than the waveguide width of the second waveguide 6B, and making the waveguide width of the fourth waveguide 6D narrower than the waveguide width of the third waveguide 6C.

[0057] In addition, the case where the 90-degree hybrid circuit 1 according to the first embodiment is configured to have a structure in which the optical length L1 of the first waveguide 6A is made shorter than the optical length L4 of the fourth waveguide 6D has been described as an example. However, the embodiment is not limited thereto, and an embodiment thereof will be described as a second embodiment.

[0058] (b) Second Embodiment

[0059] Figure 2 1 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit 1A according to a second embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the 90-degree hybrid circuit 1 according to the first embodiment, repeated descriptions of their configurations and operations will be omitted. The 90-degree hybrid circuit 1A according to the second embodiment is different from the 90-degree hybrid circuit 1 according to the first embodiment in that the optical length relationship between the first to fourth waveguides 6A, 6B1, 6C, and 6D1 is a relationship represented by L1=L4<L2=L3. The structure of the 90-degree hybrid circuit 1A is configured to have a structure in which 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.

[0060] The first optical splitter 2 splits the signal light received from the first input port 21A included in the first optical splitter 2 into the signal light of 0 degrees and the signal light of 90 degrees. The first optical splitter 2 outputs the split signal light of 0 degrees to the first waveguide 6A connected to the first output port 21C included in the first optical splitter 2, and also outputs the split signal light of 90 degrees to the second waveguide 6B1 connected to the second output port 21D included in the first optical splitter 2.

[0061] The second splitter 3 splits the local oscillator light received from the first input port 31A included in the second splitter 3 and outputs the split local oscillator light as 0-degree local oscillator 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.

[0062] The first combiner 4 inputs both the signal light Sig-d+h of 0 degrees received from the first waveguide 6A and the local oscillator light LO+d of 0 degrees received from the third waveguide 6C. The first combiner 4 outputs the first signal light obtained by multiplexing the signal light Sig-d+h and the local oscillator light LO+90+d to the first output port 41C included in the first combiner 4 as the channel CH1 based on the input signal light and the input local oscillator light. The first signal light is a signal light having a phase difference of 0 degrees between the signal light and the local oscillator light and having a XIp component.

[0063] Furthermore, the first combiner 4 outputs a second signal light obtained by multiplexing the signal light Sig+90-d+h of 90 degrees and the local oscillator light LO+d of 0 degrees to the second output port 41D included in the first combiner 4 as the channel CH2 based on the input signal light of 0 degrees and the input local oscillator light of 0 degrees. The second signal light is a signal light having a phase difference of 180 degrees between the signal light and the local oscillator light and having an XIn component.

[0064] The second combiner 5 inputs both the signal light Sig+90+d of 90 degrees received from the first optical splitter 2 and the local oscillator light LO-d of 0 degrees received from the second optical splitter 3. The second combiner 5 outputs a third signal light obtained by multiplexing the signal light Sig+90+d of 90 degrees and the local oscillator light LO+90-d of 90 degrees to the first output port 51C included in the second combiner 5 as the channel CH3 based on the input signal light of 90 degrees and the input local oscillator light of 0 degrees. The third signal light is a signal light having a 90-degree phase difference between the signal light and the local oscillator light and having an XQp component.

[0065] Furthermore, the second combiner 5 outputs a fourth signal light obtained by multiplexing the signal light Sig+180+d of 180 degrees and the local oscillator light LO-d of 0 degrees to the second output port 51D included in the second combiner 5 as the channel CH4 based on the input signal light of 90 degrees and the input local oscillator light of 0 degrees. The fourth signal light is a signal light having a phase difference of 270 degrees between the signal light and the local oscillator light and having an XQn component.

[0066] The heater electrode 7 disposed on the first waveguide 6A heats the first waveguide 6A as current flows through the path between the first electrode pad 8A and the second electrode pad 8B. In the first waveguide 6A, the refractive index changes according to the thermo-optic effect of the first waveguide 6A, and the phase angle of the signal light propagating through the first waveguide 6A becomes higher. Then, the heater electrode 7 adjusts the signal light Sig–d entering the first combiner 4 based on the phase change h indicated when the first waveguide 6A is heated. As a result, the 90-degree hybrid circuit 1A correspondingly adjusts the signal light Sig-d+h entering the first combiner 4 so that the phase difference at channel CH1 becomes 0 degrees and the phase difference at channel CH2 becomes 180 degrees.

[0067] In the 90-degree hybrid circuit 1A according to the second embodiment, the optical length relationship among the first waveguide 6A to the fourth waveguide 6D1 is set to the relationship represented by L1 = L4 < L2 = L3. The structure of the first waveguide 6A and the structure of the fourth waveguide 6D1 are point-symmetric, while the structure of the second waveguide 6B1 and the structure of the third waveguide 6C are point-symmetric. As a result, the influence of process errors is canceled out, and thus the phase difference change can be suppressed.

[0068] However, in the 90-degree hybrid circuit 1(1A) according to the first and second embodiments, the heater electrode 7 is disposed on the first waveguide 6, so it can be considered that the life of the heater electrode 7 is shortened due to the concentrated heating of the first waveguide 6A. Therefore, an embodiment for solving this situation will be described below as the 90-degree hybrid circuit 1B according to the third embodiment.

[0069] (c) Third Embodiment

[0070] Figure 3 FIG. is an explanatory diagram illustrating an example of the 90-degree hybrid circuit 1B according to the third embodiment. The 90-degree hybrid circuit 1B according to the third embodiment is different from the 90-degree hybrid circuit 1A according to the second embodiment in that: 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.

[0071] The first heater electrode 7A is disposed on the first waveguide 6A. The electrode pads 8 electrically connected to the first heater electrode 7A include a first electrode pad 8A disposed near the first optical splitter 2 and a second electrode pad 8B disposed near the first combiner 4. The first heater electrode 7A heats the first waveguide 6A as current flows through the path between the first electrode pad 8A and the second electrode pad 8B. In the first waveguide 6A, the refractive index changes according to the thermo-optic effect of the first waveguide 6A, and the phase angle of the signal light propagating through the first waveguide 6A becomes higher.

[0072] The second heater electrode 7B is arranged on the fourth waveguide 6D1. The electrode pads 8 electrically connected to the second heater electrode 7B include a third electrode pad 8C arranged near the second combiner 5 and a fourth electrode pad 8D arranged near the second spectrometer 3. The second heater electrode 7B heats the fourth waveguide 6D1 due to the current flowing through the path between the third electrode pad 8C and the fourth electrode pad 8D. In the fourth waveguide 6D1, the refractive index changes according to the thermo-optical effect of the fourth waveguide 6D1, and the phase angle of the signal light propagating through the fourth waveguide 6D1 becomes high.

[0073] The first optical splitter 2 splits the signal light received from the first input port 21A included in the first optical splitter 2 into the signal light of 0 degree and the signal light of 90 degree. The first optical splitter 2 outputs the split signal light of 0 degree to the first waveguide 6A connected to the first output port 21C included in the first optical splitter 2, and also outputs the split signal light of 90 degree to the second waveguide 6B1 connected to the second output port 21D included in the first optical splitter 2. The second optical splitter 3 splits the local oscillator light received from the first input port 31A included in the second optical splitter 3, and outputs the split local oscillator light as the local oscillator light of 0 degree to the third waveguide 6C connected to the first output port 31C and the fourth waveguide 6D1 connected to the second output port 31D.

[0074] The first combiner 4 inputs the signal light Sig-d+h of 0 degrees received from the first waveguide 6A and the local oscillator light LO+d of 0 degrees received from the third waveguide 6C. The first combiner 4 outputs the first signal light obtained by multiplexing the signal light Sig-d+h and the local oscillator light LO+90+d to the first output port 41C included in the first combiner 4 as the channel CH1 based on the input signal light and the input local oscillator light. The first signal light is a signal light having a phase difference of 0 degrees between the signal light and the local oscillator light and having a XIp component.

[0075] Furthermore, the first combiner 4 outputs a second signal light obtained by multiplexing the signal light Sig+90-d+h of 90 degrees and the local oscillator light LO+d of 0 degrees to the second output port 41D included in the first combiner 4 as the channel CH2 based on the input signal light of 0 degrees and the input local oscillator light of 0 degrees. The second signal light is a signal light having a phase difference of 180 degrees between the signal light and the local oscillator light and having an XIn component.

[0076] The second combiner 5 inputs the signal light Sig+90+d of 90 degrees received from the first optical splitter 2 and the local oscillator light LO-d+h of 0 degrees received from the second optical splitter 3. The second combiner 5 outputs a third signal light obtained by multiplexing the signal light Sig+90+d of 90 degrees and the local oscillator light LO+90-d of 90 degrees to the first output port 51C included in the second combiner 5 as the channel CH3 based on the input signal light of 90 degrees and the input local oscillator light of 0 degrees. The third signal light is a signal light having a 90-degree phase difference between the signal light and the local oscillator light and having an XQp component.

[0077] The second combiner 5 outputs a fourth signal light obtained by multiplexing the signal light Sig+180+d of 180 degrees and the local oscillator light LO-d+h of 0 degrees to the second output port 51D included in the second combiner 5 as the channel CH4 based on the input signal light of 90 degrees and the local oscillator light of 0 degrees. The fourth signal light is a signal light having a phase difference of 270 degrees between the signal light and the local oscillator light and having an XQn component.

[0078] The first heater electrode 7A arranged on the first waveguide 6A heats the first waveguide 6A due to the current flowing through the path between the first electrode pad 8A and the second electrode pad 8B. In the first waveguide 6A, the refractive index changes according to the thermo-optical effect of the first waveguide 6A, and the phase angle of the signal light propagating through the first waveguide 6A becomes high. The first heater electrode 7A adjusts the signal light Sig-d entering the first combiner 4 by the phase change h indicated when the first waveguide 6A is heated. As a result, the 90-degree hybrid circuit 1B adjusts the signal light Sig-d+h entering the first combiner 4 so that the phase difference at the channel CH1 becomes 0 degrees, and the phase difference at the channel CH2 becomes 180 degrees.

[0079] The second heater electrode 7B arranged on the fourth waveguide 6D1 heats the fourth waveguide 6D1 due to the current flowing through the path between the third electrode pad 8C and the fourth electrode pad 8D. In the fourth waveguide 6D1, the refractive index changes according to the thermo-optical effect of the fourth waveguide 6D1, and the phase angle of the signal light propagating through the fourth waveguide 6D1 becomes high. The second heater electrode 7B adjusts the local oscillator light LO-d entering the second combiner 5 by the phase change h indicated when the fourth waveguide 6D1 is heated. As a result, the 90-degree hybrid circuit 1B adjusts the local oscillator light LO-d+h entering the second combiner 5 so that the phase difference at the channel CH3 becomes 90 degrees, and the phase difference at the channel CH4 becomes 270 degrees.

[0080] The 90-degree hybrid circuit 1B according to the third embodiment adjusts the phase angle of the signal light by using the first heater electrode 7A arranged on the first waveguide 6A, and also adjusts the phase angle of the local oscillator light by the second heater electrode 7B arranged on the fourth waveguide 6D1, so that the phase difference between the signal light and the local oscillator light can be adjusted to 90 degrees. For example, the phase of the signal light and the phase of the local oscillator light at the input time are not always the same, and change with time. The 90-degree hybrid circuit 1B is capable of adjusting the phase difference between the signal light and the local oscillator light to 90 degrees at a specific channel, so that the phase of the signal light relative to the local oscillator light differs by 90 degrees between channels (for example, between the channel CH1 and the channel CH3). In addition, for example, even in the case of performing an overall adjustment of 10 degrees, the drive adjustment of the heater electrodes can be partially shared by performing an adjustment of 5 degrees at the first heater electrode 7A and an adjustment of 5 degrees at the second heater electrode 7B.

[0081] In the 90 degree hybrid circuit 1B, 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, so that the life of the heater electrodes can be extended by dispersing the temperature increase caused by concentrated heating.

[0082] In addition, in the 90-degree hybrid circuit 1B according to the third embodiment, the case where 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 have been described as an example. However, the embodiment is not limited to this, and an embodiment thereof will be described below as a fourth embodiment.

[0083] (d) Fourth Embodiment

[0084] Figure 4 1 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit 1C according to a fourth embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the 90-degree hybrid circuit 1B according to the third embodiment, repeated descriptions of their configurations and operations will be omitted. The 90-degree hybrid circuit 1C according to the fourth embodiment is different from the 90-degree hybrid circuit 1B according to the third embodiment in that the drive current to the first heater electrode 7A and the second heater electrode 7B is shared by electrically connecting the first heater electrode 7A and the second heater electrode 7B.

[0085] The 90-degree hybrid circuit 1C includes a first electrode pad 8A1 arranged near the first optical 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.

[0086] The wiring 8C1 electrically connects the other end of the first heater electrode 7A to the other end of the second heater electrode 7B. The wiring 8C1 connects the portion between the first heater electrode 7A and the wiring 8C1 through a through hole (not shown) so that the third waveguide 6C is not heated, and also connects the second heater electrode 7B and the wiring 8C1 through the through hole. Figure 4 The vertical direction on the drawing shown in the figure is extended so that the first heater electrode 7A (the second heater electrode 7B) and the wiring 8C1 are both arranged in different layers. As a result, the thermal influence on the wiring 8C1 drawn out toward the third waveguide 6C can be reduced. The wiring 8C1 is a wiring having a lower resistance than, for example, the first heater electrode 7A and the second heater electrode 7B, and is, for example, an aluminum wiring. In addition, the material of the wiring 8C1 is not limited to aluminum, and appropriate modifications are also possible.

[0087] The 90 degree hybrid circuit 1C according to the fourth embodiment electrically connects the first heater electrode 7A and the second heater electrode 7B through the wiring 8C1. As a result, the first heater electrode 7A and the second heater electrode 7B can be driven according to the current flowing through the path between the first electrode pad 8A1 and the second electrode pad 8B1.

[0088] Furthermore, in the 90-degree hybrid circuit 1C according to the fourth embodiment, it is conceivable that the driving power increases due to heat generated at the wiring 8C1 connecting the first heater electrode 7A and the second heater electrode 7B. Therefore, an embodiment that solves this situation will be described below as a fifth embodiment.

[0089] (e) Fifth Embodiment

[0090] Figure 5 1 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit 1D according to the fifth embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the 90-degree hybrid circuit 1C of the fourth embodiment, repeated descriptions of their configurations and operations will be omitted. The 90-degree hybrid circuit 1D according to the fifth embodiment is different from the 90-degree hybrid circuit 1C according to the fourth embodiment in that the wiring width of the wiring 8D1 electrically connecting the first heater electrode 7A and the second heater electrode 7B is made larger than the wiring width of the wiring 8D1. Figure 4 The wiring 8C1 shown has a wider wiring width.

[0091] The 90-degree hybrid circuit 1D according to the fifth embodiment is configured to have a structure in which the wiring width of the wiring 8D1 is made smaller than Figure 4 The wiring 8C1 shown has a wider wiring width, so that the driving electric power required to drive the first heater electrode 7A and the second heater electrode 7B can be suppressed by reducing the resistance.

[0092] In the 90-degree hybrid circuit 1D according to the fifth embodiment, the interval between the first waveguide 6A and the second waveguide 6B is narrow, so that it is conceivable that the effect of phase adjustment is reduced due to the heat generated in the first heater electrode 7A arranged on the first waveguide 6A affecting the second waveguide 6B. Therefore, an embodiment that solves this situation will be described below as a sixth embodiment.

[0093] (f) Sixth Embodiment

[0094] Figure 6 1 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit 1E according to a sixth embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the 90-degree hybrid circuit 1D according to the fifth embodiment, repeated descriptions of their configurations and operations will be omitted. The 90-degree hybrid circuit 1E according to the sixth embodiment is different from the 90-degree hybrid circuit 1D of the fifth embodiment 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.

[0095] The first optical splitter 2 optically connects the first output port 21C included in the first optical splitter 2 with the first input port 41A included in the first combiner 4 through the first waveguide 6A3. The first waveguide 6A3 includes a first input section 12, a first output section 13, and a first straight waveguide 11 connecting the first input section 12 and the first output section 13. The optical length of the first waveguide 6A3 is set to L.

[0096] The first optical splitter 2 optically connects the second output port 21D included in the first optical splitter 2 and the first input port 51A included in the second combiner 5 through the second waveguide 6B3. The second waveguide 6B3 includes a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting the second input section 12A and the second output section 13A. The optical length of the second waveguide 6B3 is set to L+dL. In addition, the optical length dL generates the signal light Sig-d and the signal light Sig+90+d, that is, "d" is generated.

[0097] In the 90-degree hybrid circuit 1E, the propagation direction of the signal light at the first input section 12 as the connection portion of the first waveguide 6A3 connected to the first optical splitter 2 is different from the propagation direction of the signal light at the second input section 12A as the connection portion of the second waveguide 6B3 connected to the first optical splitter 2. As a result, the 90-degree hybrid circuit 1E is constructed to have a structure in which the interval between the first waveguide 6A3 and the second waveguide 6B3 is made wider as the first waveguide 6A3 and the second waveguide 6B3 are respectively away from the first input section 12 and the second input section 12A.

[0098] The second optical splitter 3 optically connects the first output port 31C included in the second optical splitter 3 and the second input port 41B included in the first combiner 4 through the third waveguide 6C3. The third waveguide 6C3 includes a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting the second input section 12A and the second output section 13A. The optical length of the third waveguide 6C3 is set to L+dL. In addition, the optical length dL generates a local oscillator light of LO+d and a local oscillator light of LO-d, that is, generates "d".

[0099] The second optical splitter 3 optically connects the second output port 31D included in the second optical splitter 3 with the second input port 51B included in the second combiner 5 through the fourth waveguide 6D3. The fourth waveguide 6D3 includes a first input section 12, a first output section 13, and a first straight waveguide 11 connecting the first input section 12 and the first output section 13. The optical length of the fourth waveguide 6D3 is set to L.

[0100] In the 90-degree hybrid circuit 1E, the propagation direction of the signal light at the first input section 12 as the connection portion of the fourth waveguide 6D3 connected to the second optical splitter 3 is different from the propagation direction of the signal light at the second input section 12A as the connection portion of the third waveguide 6C3 connected to the second optical splitter 3. As a result, the 90-degree hybrid circuit 1E is constructed to have a structure in which the interval between the third waveguide 6C3 and the fourth waveguide 6D3 is made wide.

[0101] When the optical length of the first waveguide 6A3 is represented by L1, the optical length of the second waveguide 6B3 is represented by L2, the optical length of the third waveguide 6C3 is represented by L3, and the optical length of the fourth waveguide 6D3 is represented by L4, the relationship between the optical lengths of the first waveguide 6A3 to the fourth waveguide 6D3 is L1+L4<L2+L3.

[0102] The first heater electrode 7A is arranged on the first waveguide 6A3. The electrode pads 8 electrically connected to the first heater electrode 7A include a first electrode pad 8A3 arranged near the first combiner 4 and a second electrode pad 8B3 arranged near the first splitter 2.

[0103] The second heater electrode 7B is arranged on the fourth waveguide 6D3. The electrode pads 8 electrically connected to the second heater electrode 7B include a third electrode pad 8C3 arranged near the second combiner 5 and a fourth electrode pad 8D3 arranged 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.

[0104] The first combiner 4 inputs the signal light Sig-d+h of 0 degrees received from the first waveguide 6A3 and the local oscillator light LO+d of 0 degrees received from the third waveguide 6C3. The first combiner 4 outputs the first signal light obtained by multiplexing the signal light Sig-d+h and the local oscillator light LO+90+d to the first output port included in the first combiner 4 as the channel CH1 based on the input signal light and the input local oscillator light. The first signal light has a phase difference of 0 degrees between the signal light and the local oscillator light, and has a XIp component.

[0105] Furthermore, the first combiner 4 outputs a second signal light obtained by multiplexing the signal light Sig+90-d+h of 90 degrees and the local oscillator light LO+d of 0 degrees to the second output port 41D included in the first combiner 4 as the channel CH2 based on the input signal light of 0 degrees and the input local oscillator light of 0 degrees. The second signal light has a phase difference of 180 degrees between the signal light and the local oscillator light, and has an XIn component.

[0106] The second combiner 5 inputs the 90-degree signal light Sig+90+d received from the first optical splitter 2 and the 0-degree local oscillator light LO-d received from the second optical 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 oscillator light LO+90-d to the first output port 51C included in the second combiner 5 as the channel CH3 based on the input 90-degree signal light and the input 0-degree local oscillator light. The third signal light has a phase difference of 90 degrees between the signal light and the local oscillator light, and has an XQp component.

[0107] Furthermore, the second combiner 5 outputs a fourth signal light obtained by multiplexing the signal light Sig+180+d of 180 degrees and the local oscillator light LO-d of 0 degrees to the second output port 51D included in the second combiner 5 as the channel CH4 based on the input signal light of 90 degrees and the input local oscillator light of 0 degrees. The fourth signal light has a phase difference of 270 degrees between the signal light and the local oscillator light, and has an XQn component.

[0108] Therefore, the first heater electrode 7A arranged on the first waveguide 6A3 heats the first waveguide 6A3 due to the current flowing through the path between the first electrode pad 8A3 and the second electrode pad 8B3. In the first waveguide 6A3, the refractive index changes according to the thermo-optical effect of the first waveguide 6A3, and the phase angle of the signal light propagating through the first waveguide 6A3 becomes high. The first heater electrode 7A adjusts the signal light Sig-d entering the first combiner 4 by the phase change h indicated when the first waveguide 6A3 is heated. As a result, the 90-degree hybrid circuit 1E adjusts the signal light Sig-d+h entering the first combiner 4 so that the phase difference at the channel CH1 becomes 0 degrees, and the phase difference at the channel CH2 becomes 180 degrees. In addition, the interval between the first waveguide 6A3 and the second waveguide 6B3 is made wide so that the heat generated in the first heater electrode 7A arranged on the first waveguide 6A3 does not affect the second waveguide 6B3, and therefore, the effect of phase adjustment is enhanced accordingly.

[0109] The second heater electrode 7B arranged on the fourth waveguide 6D3 heats the fourth waveguide 6D3 due to the current flowing through the path between the third electrode pad 8C3 and the fourth electrode pad 8D3. In the fourth waveguide 6D3, the refractive index changes according to the thermo-optical effect of the fourth waveguide 6D3, and the phase angle of the signal light propagating through the fourth waveguide 6D3 becomes high. The second heater electrode 7B adjusts the local oscillator light LO-d entering the second combiner 5 by the phase change h indicated when the fourth waveguide 6D3 is heated. As a result, the 90-degree hybrid circuit 1E adjusts the local oscillator light LO-d+h entering the second combiner 5 so that the phase difference at the channel CH3 becomes 90 degrees, and the phase difference at the channel CH4 becomes 270 degrees. In addition, the interval between the third waveguide 6C3 and the fourth waveguide 6D3 is made wide so that the heat generated in the second heater electrode 7B arranged on the fourth waveguide 6D3 does not affect the third waveguide 6C3, and therefore, the effect of phase adjustment is enhanced accordingly.

[0110] In the 90-degree hybrid circuit 1E according to the sixth embodiment, although the optical length L of each of the first waveguide 6A3 and the fourth waveguide 6D3 on which the heater electrode has been arranged can be adjusted only in the length direction, the optical length L of each of the second waveguide 6B3 and the third waveguide 6C3 on which the heater electrode is not arranged is set to L+dL. As a result, by the heat generated in the heater electrode 7, the optical length L of each of the first waveguide 6A3 and the fourth waveguide 6D3 on which the heater electrode 7 is arranged can be adjusted.

[0111] The 90-degree hybrid circuit 1E adjusts the phase angle of the signal light by the first heater electrode 7A arranged on the first waveguide 6A3, and also adjusts the phase angle of the local oscillator light by the second heater electrode 7B arranged on the fourth waveguide 6D3, so that the 90-degree hybrid circuit 1E can adjust the phase difference between the signal light and the local oscillator light to 90 degrees. The 90-degree hybrid circuit 1E can make adjustments by adjusting the phase difference between the signal light and the local oscillator light to 90 degrees at a specific channel, so that the phase of the signal light relative to the local oscillator light differs by 90 degrees between channels (for example, between the channel CH1 and the channel CH3). In addition, for example, even in the case of performing an overall adjustment of 10 degrees, the drive adjustment of the heater electrodes can be partially shared by performing an adjustment of 5 degrees at the first heater electrode 7A and an adjustment of 5 degrees at the second heater electrode 7B.

[0112] Herein, in the 90 degree hybrid circuit 1E according to the sixth embodiment, the case where the second splitter 3 is composed of a 1×2 coupler has been described as an example, but the second splitter 3 may be composed of a 2×2 coupler, and an embodiment thereof will be described below as a seventh embodiment.

[0113] (g) Seventh Embodiment

[0114] Figure 7 1 is an explanatory diagram illustrating an example of a 90-degree hybrid circuit 1F according to the seventh embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the 90-degree hybrid circuit 1E according to the sixth embodiment, repeated descriptions of their configurations and operations are omitted. The 90-degree hybrid circuit 1F according to the seventh embodiment is different from the 90-degree hybrid circuit 1E according to the sixth embodiment in that the second optical splitter 3A is composed of a 2×2 coupler.

[0115] In the 90-degree hybrid circuit 1F, the first optical splitter 2 and the second optical splitter 3A are configured to have point symmetry, the first waveguide 6A3 and the fourth waveguide 6D3 are configured to have point symmetry, and the second waveguide 6B4 and the third waveguide 6C4 are configured to have point symmetry. As a result, the influence caused by the process error occurring when manufacturing the 90-degree hybrid circuit 1F can be reduced.

[0116] The first optical splitter 2 optically connects the first output port 21C included in the first optical splitter 2 with the first input port 41A included in the first combiner 4 through the first waveguide 6A3. The first waveguide 6A3 includes a first input section 12, a first output section 13, and a first straight waveguide 11 connecting the first input section 12 and the first output section 13. The optical length of the first waveguide 6A3 is set to L.

[0117] The first optical splitter 2 optically connects the second output port 21D included in the first optical splitter 2 with the first input port 51A included in the second combiner 5 through the second waveguide 6B4. The second waveguide 6B4 includes a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting the second input section 12A and the second output section 13A. The optical length of the second waveguide 6B4 is set to L+dL0+dL. In addition, the optical length dL generates an input signal light of Sig-d and an input signal light of Sig+135+d, that is, "d" is generated accordingly. The optical length dL0 of the waveguide length is pre-adjusted so that the phase difference is 90 degrees.

[0118] The second optical splitter 3A optically connects the first output port 31C included in the second optical splitter 3A and the second input port 41B included in the first combiner 4 through the third waveguide 6C4. The third waveguide 6C4 includes a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting the second input section 12A and the second output section 13A. The optical length of the third waveguide 6C4 is set to L+dL0+dL. In addition, the optical length dL generates a local oscillator light of Lo+135+d and a local oscillator light of LO-d, that is, "d". The optical length dL0 adjusts the waveguide length so that the phase difference is 90 degrees.

[0119] The second optical splitter 3A optically connects the second output port 31D included in the second optical splitter 3A and the second input port 51B included in the second combiner 5 through the fourth waveguide 6D3. The fourth waveguide 6D3 includes a first input section 12, a first output section 13, and a first straight waveguide 11 connecting the first input section 12 and the first output section 13. The optical length of the fourth waveguide 6D3 is set to L.

[0120] In the case where the optical length of the first waveguide 6A3 is represented by L1, the optical length of the second waveguide 6B4 is represented by L2, the optical length of the third waveguide 6C4 is represented by L3, and the optical length of the fourth waveguide 6D3 is represented by L4, the optical length relationship between the first waveguide to the fourth waveguide is L1+L4. <L2+L3。

[0121] The second optical splitter 3 according to the sixth embodiment is composed of a 1×2 coupler so that the phase difference between the two outputs becomes 0 degrees, and the first optical splitter 2 is composed of a 2×2 coupler so that the phase difference between the two outputs becomes 90 degrees. If the waveguide lengths of the waveguides connecting the respective optical splitters and combiners are made the same and in the case where the heater electrode is not driven, the phase difference between the signal light and the local oscillator light becomes 0 degrees when input by the first combiner 4, and becomes 90 degrees when input by the second combiner 5.

[0122] In contrast, the first spectrometer 2 and the second spectrometer 3A according to the seventh embodiment are composed of a 2×2 coupler. Therefore, if the waveguide lengths of the waveguides connecting the respective spectrometers and combiners are made the same and when the heater electrode is not driven, the phase difference between the signal light and the local oscillator light becomes -90 degrees when input by the first combiner 4, and becomes +90 degrees when input by the second combiner 5. As a result, between channels (for example, between channel CH1 and channel CH3), the "phase of the signal light relative to the local oscillator light" differs by 180 degrees. In this case, the 90-degree hybrid circuit 1F cannot play the role of a 90-degree hybrid. Therefore, in Figure 7 In the configuration shown, in order to set a phase difference of 90 degrees by using the waveguide length of the waveguide connecting the combiner and the optical splitter, the optical length difference of dL0 described above is used. In order to set a phase difference of 90 degrees, dL0 is set to 1 / 4 of the wavelength of light propagating through the waveguide. An optical length difference of dL0 = λ / 4 is used.

[0123] In order to set the phase difference to 90°, the waveguide length of the waveguide is adjusted in advance. In other words, the 90-degree hybrid circuit 1F is configured so that when the optical length of each of the first waveguide 6A3 and the fourth waveguide 6D3 is set to L, and the optical length of each of the second waveguide 6B4 and the third waveguide 6C4 is set to L+dL0, 2*dL0 becomes 1 / 4 of the wavelength of light. In addition, the optical length difference dL considering the phase difference change is set, and by driving the heater electrode 7, the phase difference can be adjusted to 90°.

[0124] The first heater electrode 7A is arranged on the first waveguide 6A3. The electrode pads 8 electrically connected to the first heater electrode 7A include a first electrode pad 8A3 arranged near the first combiner 4 and a second electrode pad 8B3 arranged near the first splitter 2.

[0125] The second heater electrode 7B is arranged on the fourth waveguide 6D3. The electrode pads 8 electrically connected to the second heater electrode 7B include a third electrode pad 8C3 arranged near the second combiner 5 and a fourth electrode pad 8D3 arranged 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.

[0126] The first combiner 4 inputs the signal light Sig-d+h of 0 degrees received from the first waveguide 6A3 and the local oscillator light LO+135+d of 0 degrees received from the third waveguide 6C3. The first combiner 4 outputs the first signal light obtained by multiplexing the signal light Sig-d+h and the local oscillator light LO+225+d to the first output port 41C included in the first combiner 4 as the channel CH1 based on the input signal light and the input local oscillator light. The first signal light has a phase difference of 0 degrees between the signal light and the local oscillator light, and has a X1p component.

[0127] The first combiner 4 outputs a second signal light obtained by multiplexing the signal light Sig+90-d+h of 90 degrees and the local oscillator light LO+135+d of 0 degrees to the second output port 41D included in the first combiner 4 as the channel CH2 based on the input signal light of 0 degrees and the local oscillator light of 0 degrees. The second signal light has a phase difference of 180 degrees between the signal light and the local oscillator light, and has an XIn component.

[0128] The second combiner 5 inputs the signal light Sig+135+d of 90 degrees received from the first optical splitter 2 and the local oscillator light LO-d of 0 degrees received from the second optical splitter 3A. The second combiner 5 outputs a third signal light obtained by multiplexing the signal light Sig+135+d of 90 degrees and the local oscillator light LO+90-d+h of 90 degrees to the first output port 51C included in the second combiner 5 as the channel CH3 based on the input signal light of 90 degrees and the input local oscillator light of 0 degrees. The third signal light has a phase difference of 90 degrees between the signal light and the local oscillator light, and has an XQp component.

[0129] The second combiner 5 outputs a fourth signal light obtained by multiplexing the signal light Sig+225+d of 180 degrees and the local oscillator light LO-d+h of 0 degrees to the second output port 51D included in the second combiner 5 as the channel CH4 based on the input signal light of 90 degrees and the local oscillator light of 0 degrees. The fourth signal light has a phase difference of 270 degrees between the signal light and the local oscillator light, and has an XQn component.

[0130] Therefore, the first heater electrode 7A disposed on the first waveguide 6A3 heats the first waveguide 6A3 as current flows through the path between the first electrode pad 8A3 and the second electrode pad 8B3. In the first waveguide 6A3, the refractive index changes according to the thermo-optic effect of the first waveguide 6A3, and the phase angle of the signal light propagating through the first waveguide 6A3 becomes higher. The first heater electrode 7A adjusts the signal light Sig-d entering the first combiner 4 based on the phase change h indicated when the first waveguide 6A3 is heated. As a result, the 90-degree hybrid circuit 1F adjusts the signal light Sig-d+h entering the first combiner 4 such that the phase difference at channel CH1 becomes 0 degrees and the phase difference at channel CH2 becomes 180 degrees. In addition, the gap between the first waveguide 6A3 and the second waveguide 6B4 is made wide so that the heat generated in the first heater electrode 7A disposed on the first waveguide 6A3 does not affect the second waveguide 6B4, and thus the effect of phase adjustment is enhanced accordingly.

[0131] The second heater electrode 7B disposed on the fourth waveguide 6D3 heats the fourth waveguide 6D3 as current flows through the path between the third electrode pad 8C3 and the fourth electrode pad 8D3. In the fourth waveguide 6D3, the refractive index changes according to the thermo-optic effect of the fourth waveguide 6D3, and the phase angle of the signal light propagating through the fourth waveguide 6D3 becomes higher. The second heater electrode 7B adjusts the local oscillator light LO-d entering the second combiner 5 based on the phase change h indicated when the fourth waveguide 6D3 is heated. As a result, the 90-degree hybrid circuit 1F adjusts the local oscillator light LO-d+h entering the second combiner 5 such that the phase difference at channel CH3 becomes 90 degrees and the phase difference at channel CH4 becomes 270 degrees. In addition, the gap between the third waveguide 6C4 and the fourth waveguide 6D3 is made wide so that the heat generated in the second heater electrode 7B disposed on the fourth waveguide 6D3 does not affect the third waveguide 6C4, and thus the effect of phase adjustment is enhanced accordingly.

[0132] While setting the relationship state to L1+L4 < L2+L3+λ / 4, the 90-degree hybrid circuit 1F drives the first heater electrode 7A and the second heater electrode 7B to increase L1 and L4 such that the relationship state enters L1+L4 = L2+L3+λ / 4. As a result, the phase difference between the signal light and the local oscillator light can be adjusted to 90 degrees.

[0133] While setting the relationship state to L1 + L4 < L2 + L3 + λ / 4, the 90-degree hybrid circuit 1F according to the seventh embodiment increases L1 and L4 by driving the first heater electrode 7A and the second heater electrode 7B, so that the relationship state enters L1 + L4 = L2 + L3 + λ / 4. As a result, even if each of the first optical splitter 2 and the second optical splitter 3A is constituted by a 2×2 coupler, the phase difference between the signal light and the local oscillator light can be adjusted to 90 degrees by adjusting the refractive index of each of the first waveguide 6A3 and the fourth waveguide 6D3.

[0134] In addition, the 90-degree hybrid circuit 1F has been constructed such that by driving the heater electrode 7 with a waveguide length difference of dL0 = λ / 4, L1 and L4 are increased, thereby obtaining the relationship of L1 + L4 = L2 + L3 + λ / 4. The waveguide length difference of dL0 = λ / 4 indicates that a 90-degree phase difference can be set by the waveguide length of the waveguide provided between the combiner and the optical splitter. However, this embodiment is not limited thereto, and its implementation will be described below as the eighth embodiment.

[0135] (h) Eighth Embodiment

[0136] Figure 8 FIG. is an explanatory diagram illustrating an example of a 90-degree hybrid circuit 1G according to the eighth embodiment. In addition, by assigning the same reference numerals to the components having the same configuration as those in the 90-degree hybrid circuit 1F according to the seventh embodiment, the repeated description of their configuration and operation will be omitted. The 90-degree hybrid circuit 1G according to the eighth embodiment is different from the 90-degree hybrid circuit 1F according to the seventh embodiment in that the phase difference is adjusted to 90 degrees by increasing the optical lengths L2 and L3 in the heater electrode 7 to obtain the relationship of L1 + L4 = L2 + L3 + λ / 4.

[0137] In the 90-degree hybrid circuit 1G, the first optical splitter 2 and the second optical splitter 3A are configured to have point symmetry, the first waveguide 6A3 and the fourth waveguide 6D3 are configured to have point symmetry, and the second waveguide 6B3 and the third waveguide 6C3 are configured to have point symmetry. As a result, the influence caused by the process errors occurring during the manufacture of the 90-degree hybrid circuit 1G can be reduced.

[0138] The first optical splitter 2 optically connects the first output port 21C included in the first optical splitter 2 to the first input port 41A included in the first combiner 4 through the first waveguide 6A3. The first waveguide 6A3 includes a first input section 12, a first output section 13, and a first straight waveguide 11 connecting the first input section 12 and the first output section 13. The optical length of the first waveguide 6A3 is set to L.

[0139] The first optical splitter 2 optically connects the second output port 21D included in the first optical splitter 2 with the first input port 51A included in the second combiner 5 through the second waveguide 6B4. The second waveguide 6B4 includes a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting the second input section 12A and the second output section 13A. The optical length of the second straight waveguide 11A is set to L+dL0-dL. In addition, the optical length dL generates a signal light of Sig+d and a signal light of Sig+135-d, that is, generates "d". By pre-adjusting the waveguide length, the optical length dL0 is constructed so that the phase difference is 90 degrees.

[0140] The second optical splitter 3A optically connects the first output port 31C included in the second optical splitter 3A and the second input port 41B included in the first combiner 4 through the third waveguide 6C4. The third waveguide 6C4 includes a second input section 12A, a second output section 13A, and a second straight waveguide 11A connecting the second input section 12A and the second output section 13A. The optical length of the third waveguide 6C4 is set to L+dL0-dL. In addition, the optical length dL generates a local oscillator light of LO+135-d and a local oscillator light of LO+d, that is, "d". The optical length dL0 of the waveguide length is pre-adjusted so that the phase difference is 90 degrees.

[0141] The second optical splitter 3A optically connects the second output port 31D included in the second optical splitter 3A with the second input port 51B included in the second combiner 5 through the fourth waveguide 6D3. The fourth waveguide 6D3 includes a first input section 12, a first output section 13, and a first straight waveguide 11 connecting the first input section 12 and the first output section 13. The optical length of the fourth waveguide 6D4 is set to L.

[0142] When the optical length of the first waveguide 6A3 is represented by L1, the optical length of the second waveguide 6B4 is represented by L2, the optical length of the third waveguide 6C4 is represented by L3, and the optical length of the fourth waveguide 6D3 is represented by L4, the relationship between the optical lengths of the first waveguide 6A3 to the fourth waveguide 6D3 is L1+L4<L2+L3.

[0143] The first spectrometer 2 and the second spectrometer 3A according to the eighth embodiment are composed of a 2×2 coupler. Therefore, if the waveguide lengths of the waveguides connecting the respective spectrometers and combiners are made the same and in the case where the heater electrode is not driven, the phase difference between the signal light and the local oscillator light becomes -90 degrees when input to the first combiner 4, and becomes +90 degrees when input to the second combiner 5. As a result, between channels (for example, between channel CH2 and channel CH4), the "phase of the signal light relative to the local oscillator light" differs by 180 degrees. In this case, the 90-degree hybrid circuit 1G cannot play the role of a 90-degree hybrid. Therefore, in Figure 8 In the configuration shown, in order to set a phase difference of 90 degrees by using the waveguide length of the waveguide connecting the combiner and the optical splitter, the optical length difference dL0 is used. In order to set a phase difference of 90 degrees, dL0 is set to 1 / 4 of the wavelength.

[0144] In order to set the phase difference to 90°, the waveguide length of the waveguide is adjusted in advance. In other words, the 90-degree hybrid circuit 1G is configured so that when the optical length of each of the first waveguide 6A3 and the fourth waveguide 6D3 is set to L, and the optical length of each of the second waveguide 6B4 and the third waveguide 6C4 is set to L+dL0, 2*dL0 becomes 1 / 4 of the wavelength of light. In addition, the optical length difference dL considering the phase difference change is set, and the phase difference can be adjusted to 90° by driving the heater electrode 7.

[0145] The third heater electrode 7C is arranged on the second waveguide 6B4 . The electrode pads 8 electrically connected to the third heater electrode 7C include a first electrode pad 8A4 arranged near the first splitter 2 and a second electrode pad 8B4 arranged near the second combiner 5 .

[0146] The fourth heater electrode 7D is arranged on the third waveguide 6C4. The electrode pads 8 electrically connected to the fourth heater electrode 7D include a third electrode pad 8C4 arranged near the second splitter 3A and a fourth electrode pad 8D4 arranged near the first combiner 4. The 90-degree hybrid circuit 1G includes a wiring 8E4 electrically connecting the second electrode pad 8B4 and the third electrode pad 8C4.

[0147] The first combiner 4 inputs the signal light Sig+d of 0 degrees received from the first waveguide 6A3 and the local oscillator light LO+135-d+h of 0 degrees received from the third waveguide 6C3. The first combiner 4 outputs the first signal light obtained by multiplexing the signal light Sig+d and the local oscillator light LO+225-d+h to the first output port 41C included in the first combiner 4 as the channel CH1 based on the input signal light and the input local oscillator light. The first signal light has a phase difference of 0 degrees between the signal light and the local oscillator light, and has a X1p component.

[0148] The first combiner 4 outputs a second signal light obtained by multiplexing the signal light Sig+90+d of 90 degrees and the local oscillator light LO+135-d+h of 0 degrees to the second output port 41D included in the first combiner 4 as the channel CH2 based on the input signal light of 0 degrees and the input local oscillator light of 0 degrees. The second signal light has a phase difference of 180 degrees between the signal light and the local oscillator light, and has an XIn component.

[0149] The second combiner 5 inputs the signal light Sig+135-d+h of 90 degrees received from the first optical splitter 2 and the local oscillator light LO+d of 0 degrees received from the second optical splitter 3A. The second combiner 5 outputs a third signal light obtained by multiplexing the signal light Sig+135-d+h of 90 degrees and the local oscillator light LO+90+d of 90 degrees to the first output port 51C included in the second combiner 5 as the channel CH3 based on the signal light of 90 degrees and the input local oscillator light of 0 degrees. The third signal light has a phase difference of 90 degrees between the signal light and the local oscillator light, and has an XQp component.

[0150] The second combiner 5 outputs a fourth signal light obtained by multiplexing the signal light Sig+225-d+h of 180 degrees and the local oscillator light LO+d of 0 degrees to the second output port 51D included in the second combiner 5 as the channel CH4 based on the input signal light of 90 degrees and the local oscillator light of 0 degrees. The fourth signal light has a phase difference of 270 degrees between the signal light and the local oscillator light, and has an XQn component.

[0151] The third heater electrode 7C arranged on the second waveguide 6B4 heats the second waveguide 6B4 due to the current flowing through the path between the first electrode pad 8A4 and the second electrode pad 8B4. In the second waveguide 6B4, the refractive index changes according to the thermo-optical effect of the second waveguide 6B4, and the phase angle of the signal light propagating through the second waveguide 6B4 becomes high. The third heater electrode 7C adjusts the signal light Sig+135-d entering the second combiner 5 by the phase change h indicated when the second waveguide 6B4 is heated. As a result, the 90-degree hybrid circuit 1G adjusts the signal light Sig+135-d+h entering the second combiner 5 so that the phase difference at the channel CH3 becomes 90 degrees, and the phase difference at the channel CH4 becomes 270 degrees.

[0152] The fourth heater electrode 7D arranged on the third waveguide 6C4 heats the third waveguide 6C4 due to the current flowing through the path between the third electrode pad 8C4 and the fourth electrode pad 8D4. In the third waveguide 6C4, the refractive index changes according to the thermo-optical effect of the third waveguide 6C4, and the phase angle of the signal light propagating through the third waveguide 6C4 becomes high. The fourth heater electrode 7D adjusts the local oscillator light LO+135-d entering the first combiner 4 by the phase change h indicated when the third waveguide 6C4 is heated. As a result, the 90-degree hybrid circuit 1G adjusts the local oscillator light LO+135-d+h entering the first combiner 4 so that the phase difference at the channel CH1 is 0 degrees, and the phase difference at the channel CH2 is 180 degrees.

[0153] The 90-degree hybrid circuit 1G sets the relationship state to L1+L4>L2+L3+λ / 4, and increases L2 and L3 by driving the third heater electrode 7C and the fourth heater electrode 7D, so that the relationship state enters L1+L4=L2+L3+λ / 4. As a result, the phase difference between the signal light and the local oscillator light can be adjusted to 90 degrees.

[0154] The 90-degree hybrid circuit 1G according to the eighth embodiment sets the relationship state to L1+L4>L2+L3+λ / 4 by driving the third heater electrode 7C and the fourth heater electrode 7D, increasing L2 and L3 so that the relationship state enters L1+L4=L2+L3+λ / 4. As a result, even if each of the first optical splitter 2 and the second optical splitter 3A is composed of a 2×2 coupler, the phase difference between the signal light and the local oscillator light can be adjusted to 90 degrees by adjusting the refractive index of each of the second waveguide 6B4 and the third waveguide 6C4.

[0155] In the present embodiment, the case where the phase angle of the signal light or the local oscillator light is adjusted by adjusting the refractive index of the waveguide by driving the heater electrode 7 has been described as an example of the phase adjustment portion. However, the phase adjustment portion is not limited to the thermo-optical effect exhibited by the heater electrode 7, and the phase angle of the signal light or the local oscillator light may be adjusted by using a material having an electro-optical effect as a waveguide and adjusting the refractive index by injecting a current into the waveguide, and appropriate modifications are also possible.

[0156] The first to fourth waveguides 6A to 6D may be, for example, channel waveguides, rib waveguides, ridge waveguides, slab waveguides, etc., and appropriate modifications are also possible.

[0157] Fig. 9 is an explanatory diagram illustrating one example of the optical transceiver 70 according to the present embodiment. Fig. 9The optical transceiver 70 shown is connected to an optical fiber provided on the output side and an optical fiber provided on the input side. The optical transceiver 70 includes a light source 71, a digital signal processor (DSP) 72, and an optical transmitter / receiver 73. The optical transmitter / receiver 73 includes an optical transmitter 73A and an optical receiver 73B. The DSP 72 is an electronic component that performs digital signal processing. The DSP 72 performs the following processing: for example, encoding transmission data, etc., generating an electrical signal including transmission data, and outputting the generated electrical signal to the optical transmitter 73A. In addition, the DSP 72 acquires an electrical signal including reception data from the optical receiver 73B, and obtains reception data by performing a process such as decoding the acquired electrical signal.

[0158] The light source 71 includes, for example, a laser diode, etc., generates light having a predetermined wavelength, and supplies the generated light to the optical transmitter 73A and the optical receiver 73B. The optical transmitter 73A modulates the light supplied from the light source 71 by using the electrical signal output from the DSP 72, and outputs the obtained transmission light to the optical fiber. The optical transmitter 73A includes an optical modulator element 73A1 that modulates the light by using the electrical signal input to the optical modulator when the light supplied from the light source 71 propagates through the waveguide, thereby generating transmission light.

[0159] The optical receiver 73B includes an optical receiver element 73B1 that receives an optical signal from an optical fiber and demodulates the received light by using the light provided from the light source 71. Then, the optical receiver 73B converts the demodulated received light into an electric signal and outputs the converted electric signal to the DSP 72. The optical receiver element 73B1 includes, for example, an optical device such as a 90-degree hybrid circuit as a built-in unit.

[0160] The optical device included in the optical transceiver 70 includes a 90-degree hybrid circuit, which combines the signal light and the local oscillator light together and outputs the signal light by splitting the signal light into orthogonal components. The 90-degree hybrid circuit includes a first coupler that splits the signal light and a second coupler that splits the local oscillator light. The 90-degree hybrid circuit includes: a first waveguide and a second waveguide, in each of which the signal light split by the first coupler is propagated; and a third waveguide and a fourth waveguide, in each of which the local oscillator light split by the second coupler is propagated. The 90-degree hybrid circuit includes: a third coupler that multiplexes the signal light that has been propagated through the first waveguide and the local oscillator light that has been propagated through the third waveguide; and a fourth coupler that multiplexes the signal light that has been propagated through the second waveguide and the local oscillator light that has been propagated through the fourth waveguide. The 90-degree hybrid circuit includes a phase adjustment portion that adjusts the phase of light propagating through at least one waveguide among the first waveguide to the fourth waveguide. 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.

[0161] In addition, for the convenience of description, an example has been described in which the optical transceiver 70 includes the optical transmitter 73A and the optical receiver 73B as built-in units, but the optical transceiver 70 may include one of the optical transmitter 73A and the optical receiver 73B as a built-in unit. For example, it is also possible to apply an optical device to the optical transceiver 70 including the optical receiver 73B as a built-in unit, and appropriate modifications are also possible.

[0162] Each component in the unit shown in the drawings is not always physically constructed as shown in the drawings. In other words, the specific shape of the separate or integrated unit is not limited to the drawings; however, depending on various loads or usage conditions, all or part of the unit can be constructed by functionally or physically separating or integrating any unit.

[0163] In addition, all or any part of the various processing functions performed by each unit may also be performed by a central processing unit (CPU) (or a microcomputer, such as a microprocessing unit (MPU) or a microcontroller unit (MCU)). In addition, all or any part of the various processing functions may also be implemented by a program analyzed and executed by the CPU (or a microcomputer, such as an MPU or an MCU), or by hardware of wired logic.

[0164] According to an aspect of the embodiment, signal loss can be suppressed.

Claims

1. An optical device comprising a 90-degree hybrid circuit that combines signal light and local oscillator light and outputs the signal light by splitting the signal light into orthogonal components, wherein: The 90-degree hybrid circuit comprises: a first coupler, the first coupler splitting the signal light; a second coupler for splitting the local oscillator light; a first waveguide and a second waveguide, in each of which the signal light split by the first coupler propagates; a third waveguide and a fourth waveguide, in each of which the local oscillator light split by the second coupler propagates; a third coupler that multiplexes the signal light that has propagated through the first waveguide and the local oscillator light that has propagated through the third waveguide; a fourth coupler that multiplexes the signal light that has propagated through the second waveguide and the local oscillator light that has propagated through the fourth waveguide; and a phase adjuster that adjusts the phase of light propagating through at least one waveguide among the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, and A first total value of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a second total value of an optical length of the second waveguide and an optical length of the third waveguide.

2. The optical device according to claim 1, wherein: The phase adjuster: is arranged on at least one waveguide among the first waveguide and the fourth waveguide, arranged on the first waveguide to adjust the phase angle of the signal light propagating through the first waveguide, and / or The optical fiber is disposed on the fourth waveguide to adjust a phase angle of the local oscillator light propagating through the fourth waveguide.

3. The optical device according to claim 1, wherein The first total value is shorter than a third total value, the third total value corresponds to the sum of the second total value and 1 / 4 of the wavelength of the signal light, and The phase adjuster: is arranged on at least one waveguide among the first waveguide and the fourth waveguide, is arranged on the first waveguide to adjust the phase angle of the signal light propagating through the first waveguide so that the first total value and the third total value are the same, and / or The optical fiber is disposed on the fourth waveguide to adjust a phase angle of the local oscillator light propagating through the fourth waveguide.

4. The optical device according to claim 1, wherein: The waveguide width of each of the first waveguide and the fourth waveguide is configured such that the first total value of the optical length of the first waveguide and the optical length of the fourth waveguide is shorter than the second total value of the optical length of the second waveguide and the optical length of the third waveguide by narrowing the waveguide width of each of the third waveguide and the second waveguide.

5. The optical device according to claim 1, wherein: making the optical length of the first waveguide the same as the optical length of the fourth waveguide, and The optical length of the second waveguide is made the same as the optical length of the third waveguide.

6. The optical device according to claim 1, wherein: The phase adjuster comprises: a first phase adjuster, which is arranged on the first waveguide and adjusts the phase angle of the signal light propagating through the first waveguide; a second phase adjuster that is disposed on the fourth waveguide and adjusts a phase angle of the local oscillator light propagating through the fourth waveguide; and A wiring electrically connects the first phase adjuster and the second phase adjuster.

7. The optical device according to claim 1, wherein: The optical device is constructed to have the following structure: as the first waveguide and the second waveguide are respectively away from a connection portion of the first waveguide connected to the first coupler and a connection portion of the second waveguide connected to the first coupler, an interval between the first waveguide and the second waveguide becomes wider, so that the direction of the signal light propagating at the connection portion of the first waveguide is different from the direction of the signal light propagating at the connection portion of the second waveguide.

8. The optical device according to claim 1, wherein: The first total value is longer than a third total value, the third total value corresponds to the sum of the second total value and 1 / 4 of the wavelength of the signal light, and The phase adjuster: is arranged on at least one waveguide among the second waveguide and the third waveguide, arranged on the second waveguide to adjust the phase angle of the signal light propagating through the second waveguide so that the first total value and the third total value are the same, and / or The optical fiber is disposed on the third waveguide to adjust a phase angle of the local oscillator light propagating through the third waveguide.

9. An optical receiver, comprising an optical receiver element that converts received signal light into an electrical signal, wherein: The optical receiver element includes an optical device including a 90-degree hybrid circuit that combines signal light and local oscillator light and outputs the signal light by splitting the signal light into orthogonal components, The 90-degree hybrid circuit comprises: a first coupler, the first coupler splitting the signal light; a second coupler for splitting the local oscillator light; a first waveguide and a second waveguide, in each of which the signal light split by the first coupler propagates; a third waveguide and a fourth waveguide, in each of which the local oscillator light split by the second coupler propagates; a third coupler that multiplexes the signal light that has propagated through the first waveguide and the local oscillator light that has propagated through the third waveguide; a fourth coupler that multiplexes the signal light that has propagated through the second waveguide and the local oscillator light that has propagated through the fourth waveguide; and a phase adjuster that adjusts the phase of light propagating through at least one waveguide among the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, and A first total value of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a second total value of an optical length of the second waveguide and an optical length of the third waveguide.

10. An optical transceiver, comprising: a light modulator element that modulates the propagating light according to an electrical signal; a light receiver element that converts received reception light into an electrical signal; as well as a signal processing unit that generates an electrical signal to be sent to the optical modulator element and acquires an electrical signal sent from the optical receiver element, wherein The light receiving element includes an optical device including a 90-degree hybrid circuit that combines signal light and local oscillator light and outputs the signal light by splitting the signal light into orthogonal components, wherein The 90-degree hybrid circuit comprises: a first coupler, the first coupler splitting the signal light; a second coupler for splitting the local oscillator light; a first waveguide and a second waveguide, in each of which the signal light split by the first coupler propagates; a third waveguide and a fourth waveguide, in each of which the local oscillator light split by the second coupler propagates; a third coupler that multiplexes the signal light that has propagated through the first waveguide and the local oscillator light that has propagated through the third waveguide; a fourth coupler that multiplexes the signal light that has propagated through the second waveguide and the local oscillator light that has propagated through the fourth waveguide; and a phase adjuster that adjusts the phase of light propagating through at least one waveguide among the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, and A first total value of an optical length of the first waveguide and an optical length of the fourth waveguide is shorter than a second total value of an optical length of the second waveguide and an optical length of the third waveguide.

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