Optical devices, optical transmitters, and optical receivers

Abstract

To provide an optical device and the like that achieve reduction in the size and power consumption.SOLUTION: An optical device includes: a first waveguide which inputs the first signal light with the first optical characteristic; and a first conversion part which is connected with the first waveguide and converts the first signal light from the first waveguide to the second signal light with the second optical characteristic. The optical device has an optical circuit that is connected with the first conversion part and performs the first optical processing on the second signal light by allowing the second signal light after conversion from the first conversion part to pass therethrough. The optical device includes a second conversion part which is connected with the optical circuit and converts the second signal light after the first optical processing from the optical circuit to the third signal light with the first optical characteristic. The optical device includes: an optical circuit which performs the second optical processing on the third signal light by allowing the third signal light after conversion from the second conversion part to pass therethrough; and a second waveguide which outputs the third signal light after the second optical processing from the optical circuit.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD

[0001] The present invention relates to an optical device, an optical transmitter, and an optical receiver. BACKGROUND ART

[0002] FIG. 30 is an explanatory diagram showing an example of a conventional optical device 200. The optical device 200 shown in FIG. 30 is an optical IC chip. The optical device 200 includes a first waveguide 201, a second waveguide 202, and an optical circuit 203. The first waveguide 201 is a waveguide that guides signal light input to the optical circuit 203. The second waveguide 202 is a waveguide that guides signal light output from the optical circuit 203. The optical circuit 203 converts signal light input from the first waveguide 201 into signal light in different states and outputs the converted signal light in accordance with an external electric signal. Functions of the optical circuit 203 include, for example, an optical modulation (intensity modulation, phase modulation) function, an optical amplification function, an optical attenuation function, and the like. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2000-174699 Patent Document 2 U.S. Patent No. 10468854 Specification Patent Document 3 U.S. Patent Application Publication No. 2020 / 0133034 Specification Patent Document 4 Japanese Unexamined Patent Publication No. 2011-197700 SUMMARY OF THE INVENTION Problem to be Solved by the Invention

[0004] In conventional optical devices 200, the functions of the optical circuit 203 are concentrated in a limited space, resulting in performance limitations. If the optical circuit 203 is, for example, an optical modulator, the driving voltage of the optical modulator is determined by the half-wavelength shift voltage Vπ. However, the product of the half-wavelength shift voltage Vπ and the working length L is determined by the eigenvalue of the element, so the working length needs to be increased. However, there are limitations to reducing the driving voltage with a limited working length.

[0005] Furthermore, if the optical circuit 203 is, for example, a variable optical attenuator (VOA), then in a variable optical attenuator, the light absorption per unit length of the electrode when current is applied is small, so the electrode length needs to be increased to increase the light attenuation. However, if the electrode length is increased, the size of the element increases, and the driving current increases, resulting in higher power consumption. Therefore, in recent years, there has been a demand for miniaturization and power saving in optical devices.

[0006] One aspect of this is to provide optical devices that are miniaturized and power-efficient by shortening the working length of the optical circuit. [Means for solving the problem]

[0007] One embodiment of the optical device includes a first waveguide that receives a first signal light having first optical characteristics, and a first conversion unit connected to the first waveguide that converts the first signal light from the first waveguide into a second signal light having second optical characteristics. The optical device includes an optical circuit connected to the first conversion unit that performs a first optical processing on the second signal light as it passes through the converted second signal light from the first conversion unit. The optical device includes a second conversion unit connected to the optical circuit that converts the second signal light after the first optical processing from the optical circuit into a third signal light having first optical characteristics, and the optical circuit that performs a second optical processing on the third signal light as it passes through the converted third signal light from the second conversion unit. The optical device includes a second waveguide that outputs a third signal light after the second optical processing from the optical circuit. [Effects of the Invention]

[0008] From one perspective, this invention provides optical devices that achieve miniaturization and power saving by shortening the working length of the optical circuit. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an explanatory diagram showing an example of an optical device in Example 1. [Figure 2A] Figure 2A is an explanatory diagram showing an example of the optical device in Example 2A. [Figure 2B] Figure 2B is an explanatory diagram showing an example of the optical device in Example 2B. [Figure 3] Figure 3 is an explanatory diagram showing an example of the optical device in Example 3. [Figure 4] Figure 4 is an explanatory diagram showing an example of the optical device in Example 4. [Figure 5A] Figure 5A is an explanatory diagram showing an example of the first mode conversion unit. [Figure 5B] Figure 5B is an explanatory diagram showing an example of the second mode conversion unit. [Figure 6] Figure 6 is an explanatory diagram showing an example of the optical device in Example 5. [Figure 7] Figure 7 is an explanatory diagram showing an example of the optical device in Example 6. [Figure 8] Figure 8 is an explanatory diagram showing an example of the optical device in Example 7. [Figure 9] Figure 9 is an explanatory diagram showing an example of the optical device in Example 8. [Figure 10] Figure 10 is an explanatory diagram showing an example of the optical device in Example 9. [Figure 11] Figure 11 is an explanatory diagram showing an example of the optical device in Example 10. [Figure 12] Figure 12 is a schematic cross-sectional view of the AA line of the optical device shown in Figure 11. [Figure 13] Figure 13 is an explanatory diagram showing an example of the optical device in Example 11. [Figure 14] Figure 14 is a schematic cross-sectional view of the BB line of the optical device shown in Figure 13. [Figure 15]FIG. 15 is an explanatory diagram illustrating an example of the optical device according to Example 12. [Figure 16] FIG. 16 is a schematic cross-sectional view taken along line C-C of the optical device illustrated in FIG. 15. [Figure 17] FIG. 17 is an explanatory diagram illustrating an example of the optical device according to Example 13. [Figure 18] FIG. 18 is a schematic cross-sectional view taken along line D-D of the optical device illustrated in FIG. 17. [Figure 19] FIG. 19 is an explanatory diagram illustrating an example of the optical device according to Example 14. [Figure 20] FIG. 20 is a schematic cross-sectional view taken along line E-E of the optical device illustrated in FIG. 19. [Figure 21] FIG. 21 is an explanatory diagram illustrating an example of the optical device according to Example 15. [Figure 22] FIG. 22 is a schematic cross-sectional view taken along line F-F of the optical device illustrated in FIG. 21. [Figure 23] FIG. 23 is an explanatory diagram illustrating an example of the optical device according to Example 16. [Figure 24] FIG. 24 is a schematic cross-sectional view taken along line G-G of the optical device illustrated in FIG. 23. [Figure 25] FIG. 25 is an explanatory diagram illustrating an example of the optical device according to Example 17. [Figure 26] FIG. 26 is a schematic cross-sectional view taken along line H-H of the optical device illustrated in FIG. 25. [Figure 27] FIG. 27 is an explanatory diagram illustrating an example of the optical device according to Example 18. [Figure 28] FIG. 28 is an explanatory diagram illustrating an example of the optical device according to Example 19. [Figure 29] FIG. 29 is an explanatory diagram illustrating an example of an optical communication apparatus. [Figure 30] FIG. 30 is an explanatory diagram illustrating an example of a conventional optical device. MODE FOR CARRYING OUT THE INVENTION

[0010] The embodiments of the optical devices and the like disclosed in this application will be described in detail below with reference to the drawings. However, these embodiments do not limit the disclosed technology. Furthermore, the embodiments described below may be combined as appropriate, provided they do not contradict each other. [Examples]

[0011] Figure 1 is an explanatory diagram showing an example of the optical device 1 of Embodiment 1. The optical device 1 shown in Figure 1 includes a first waveguide 2, a second waveguide 3, a first conversion unit 4, an optical circuit 5, a second conversion unit 6, and a folded waveguide 7.

[0012] The first waveguide 2 is a waveguide that inputs, for example, a signal light TE (Transverse Electric field) to the optical device 1. The second waveguide 3 is a waveguide that outputs, for example, a signal light TM (Transverse Magnetic field) after optical processing from the optical device 1. The signal light TE and the signal light TM are orthogonal to each other. Note that if the signal light TE is, for example, a signal light having the first optical characteristics, then the signal light TM is, for example, a signal light having the second optical characteristics.

[0013] The first conversion unit 4 has a first port connected to the first waveguide 2, a second port connected to the optical circuit 5, and a third port connected to the second waveguide 3, and converts the signal light TE from the first waveguide 2 into signal light TM. The first conversion unit 4 outputs the converted signal light TM to the optical circuit 5.

[0014] The optical circuit 5 includes an operating section 31 containing a single waveguide, a first port connecting the first conversion section 4 and the operating section 31, and a second port connecting the second conversion section 6 and the operating section 31. The optical circuit 5 processes the signal light TM converted from the first conversion section 4 with light in the operating section 31 and outputs the signal light TM after light processing to the second conversion section 6.

[0015] The second conversion unit 6 has a fourth port connected to the optical circuit 5, a fifth port connected to one side of the folded waveguide 7, and a sixth port connected to the other side of the folded waveguide 7, and converts the signal light TE from the optical circuit 5 after optical processing into signal light TM. The second conversion unit 6 outputs the converted signal light TE to the folded waveguide 7. The second conversion unit 6 outputs the folded signal light TE from the folded waveguide 7 to the optical circuit 5.

[0016] The optical circuit 5 processes the signal light TE converted from the second conversion unit 6 using the working unit 31, and outputs the processed signal light TE to the first conversion unit 4. The first conversion unit 4 then outputs the signal light TE from the optical circuit 5 to the second waveguide 3.

[0017] The first conversion unit 4 includes a first PR (Polarization Rotator) 11 and a first PBS (Polarization Beam Splitter) 12. The first PR 11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS 12, and converts the signal light TE from the first waveguide 2 into signal light TM, and outputs the converted signal light TM to the first PBS 12. The first PBS 12 has a first port connected to the first PR 11, a second port connected to the optical circuit 5, and a third port connected to the second waveguide 3. The first PBS 12 separates the signal light from the second port into signal light TM and signal light TE, outputs the signal light TM from the first port, and outputs the signal light TE from the third port. In other words, the first PBS12 outputs the signal light TM from the first PR11 to the optical circuit 5, and also outputs the signal light TE from the optical circuit 5 to the second waveguide 3.

[0018] The second conversion unit 6 includes a second PBS 21 and a second PR 22. The second PBS 21 has a fourth port connected to the optical circuit 5, a fifth port connected to the second PR 22, and a sixth port connected to the folded waveguide 7. The second PBS 21 separates the signal light from the fourth port into signal light TM and signal light TE, outputs the signal light TM from the fifth port, and outputs the signal light TE from the sixth port. In other words, the second PBS 22 outputs the signal light TM from the optical circuit 5 to the second PR 22, and outputs the signal light TE from the folded waveguide 7 to the optical circuit 5. The second PR22 has a first port connected to the second PBS21 and a second port connected to the folded waveguide 7. It converts the signal light TM from the second PBS21 into signal light TE and outputs the converted signal light TE to the folded waveguide 7.

[0019] The optical circuit 5 performs optical processing twice in total: once on the signal light TM from the first conversion unit 4 to the second conversion unit 6, and again on the signal light TE from the second conversion unit 6 to the first conversion unit 4. As a result, the functionality of the optical circuit 5 can be doubled, reducing power consumption and miniaturizing the optical device 1. In other words, the efficiency of the optical circuit 5 can be increased.

[0020] For the sake of explanation, the optical device 1 in Example 1 is shown as having a first conversion unit 4 connected to one end of the optical circuit 5 and a second conversion unit 6 connected to the other end of the optical circuit 5. However, the second conversion unit 6 may also be connected to the same end of the optical circuit 5 as the first conversion unit 4, and such an embodiment will be described below as Example 2A. [Examples]

[0021] Figure 2A is an explanatory diagram showing an example of optical device 1A of Embodiment 2A. Components identical to those of optical device 1 in Embodiment 1 are denoted by the same reference numerals, and the explanation of their redundant components and operations is omitted. The optical device 1A shown in Figure 2A includes a first waveguide 2, a second waveguide 3, a first conversion unit 4, an optical circuit 5A, a second conversion unit 6A, and a folded waveguide 7A. The optical circuit 5A includes a forward-side operating unit 31A, a return-side operating unit 31B, and a folded waveguide 32 that optically couples the forward-side operating unit 31A and the return-side operating unit 31B.

[0022] The first conversion unit 4 has a first port connected to the first waveguide 2, a second port connected to the optical circuit 5, and a third port connected to the second waveguide 3. It converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the optical circuit 5.

[0023] The optical circuit 5 has a first port connecting the first conversion unit 4 and the forward-side operating unit 31A, and a second port connecting the second conversion unit 6A and the return-side operating unit 31B. The optical circuit 5 optically processes the converted signal light TM from the first conversion unit 4 and outputs the optically processed signal light TM to the second conversion unit 6A. The forward-side operating unit 31A has a forward-side waveguide and optically processes the signal light guiding the forward-side waveguide with an electrical signal. Furthermore, the return-side operating unit 31B has a return-side waveguide and optically processes the signal light guiding the return-side waveguide with an electrical signal.

[0024] The second conversion unit 6A has a fourth port connected to the return-side operating unit 31B in the optical circuit 5, a fifth port connected to one side of the folded waveguide 7, and a sixth port connected to the other side of the folded waveguide 7. The second conversion unit 6A converts the signal light TM from the optical circuit 5 after optical processing into signal light TE, and outputs the converted signal light TE to the return-side operating unit 31B in the optical circuit 5.

[0025] The optical circuit 5 processes the signal light TE converted from the second conversion unit 6A using optical processing and outputs the processed signal light TE to the first conversion unit 4. The first conversion unit 4 then outputs the signal light TE from the forward-side operating unit 31A within the optical circuit 5 to the second waveguide 3.

[0026] The first conversion unit 4 includes a first PR11 and a first PBS12. The first PR11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS12, and converts the signal light TE from the first waveguide 2 into signal light TM, and outputs the converted signal light TM to the first PBS12.

[0027] The first PBS12 has a first port connected to the first PR11, a second port connected to the forward-side working unit 31A in the optical circuit 5, and a third port connected to the second waveguide 3. The first PBS12 separates the signal light from the second port into signal light TM and signal light TE, outputs signal light TM from the first port, and outputs signal light TE from the third port. In other words, the first PBS12 outputs the converted signal light TM from the first PR11 to the forward-side working unit 31A in the optical circuit 5, and outputs the signal light TE from the forward-side working unit 31A in the optical circuit 5 to the second waveguide 3.

[0028] The second conversion unit 6A includes a second PBS 21A and a second PR 22A. The second PBS 21A has a fourth port connected to the return-side working unit 31B in the optical circuit 5A, a fifth port connected to the second PR 22A, and a sixth port connected to the folded waveguide 7A. The second PBS 21A separates the signal light from the fourth port into signal light TM and signal light TE, outputs the signal light TM from the fifth port, and outputs the signal light TE from the sixth port. In other words, the second PBS 21A outputs the signal light TM from the return-side working unit 31B in the optical circuit 5A to the second PR 22A, and outputs the signal light TE from the folded waveguide 7A to the return-side working unit 31B in the optical circuit 5A.

[0029] The second PR22A has a first port connected to the second PBS21A and a second port connected to the folded waveguide 7A. It converts the signal light TM from the second PBS21A into signal light TE and outputs the converted signal light TE to the folded waveguide 7A.

[0030] The optical circuit 5A performs optical processing on the signal light TM from the first conversion unit 4 and on the signal light TE from the second conversion unit 6A, thereby achieving a total of two optical processing steps. As a result, the functionality of the optical circuit 5A can be doubled, reducing power consumption and miniaturizing the optical device 1A.

[0031] In the optical device 1A of Example 2A, when the waveguide length in the optical circuit 5A is long, the first conversion unit 4 and the second conversion unit 6A are arranged in parallel before and after the optical circuit 5A, thereby enabling miniaturization of the optical device 1A.

[0032] In the optical circuit 5A of the optical device 1A in Example 2A, the first conversion unit 4 converts the signal light TE to signal light TM, and the second conversion unit 6B converts the signal light TM to signal light TE, that is, it is shown as a case of conversion to orthogonal polarization. However, it is not limited to this, and it can also be applied when converting to orthogonal higher-order modes. Therefore, an embodiment of this will be described below as Example 2B.

[0033] Figure 2B is an explanatory diagram showing an example of the optical device 1X of Example 2B. Components identical to those of the optical device 1A in Example 2A are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical device 1X shown in Figure 2B includes a first waveguide 2, a second waveguide 3, a first mode conversion unit 8 which is the first conversion unit 4X, an optical circuit 5A, a second mode conversion unit 9 which is the second conversion unit 6X, and a folded waveguide 7A. The optical circuit 5A has the same configuration as the optical circuit shown in Figure 2A.

[0034] The first mode conversion unit 8 is a mode converter and combiner. The first mode conversion unit 8 has a first port connected to the first waveguide 2, a second port connected to the optical circuit 5A, and a third port connected to the second waveguide 3. It performs higher-order mode conversion of the signal light TE0 from the first waveguide 2 to the signal light TE1, and outputs the signal light TE1 after higher-order mode conversion to the optical circuit 5A. The signal light TE0 and the signal light TE1 are orthogonal to each other. For example, if the signal light TE0 is a signal light having a first optical characteristic, then the signal light TE1 is a signal light having a second optical characteristic.

[0035] The optical circuit 5A has a first port connecting the first mode conversion unit 8 and the forward-side operating unit 31A, and a second port connecting the second mode conversion unit 9 and the return-side operating unit 31B. The optical circuit 5A optically processes the signal light TE1 after mode conversion from the first mode conversion unit 8 and outputs the optically processed signal light TE1 to the second mode conversion unit 9. The forward-side operating unit 31A has a forward-side waveguide and optically processes the signal light guiding the forward-side waveguide with an electrical signal. Furthermore, the return-side operating unit 31B has a return-side waveguide and optically processes the signal light guiding the return-side waveguide with an electrical signal.

[0036] The second mode conversion unit 9 is a mode conversion coupling unit. The second mode conversion unit 9 has a fourth port connected to the return-side operating unit 31B in the circuit 5A, a fifth port connected to one side of the folded waveguide 7A, and a sixth port connected to the other side of the folded waveguide 7A. The second mode conversion unit 9 converts the signal light TE1 after optical processing from the optical circuit 5A into signal light TE0, and outputs the converted signal light TE0 to the return-side operating unit 31B in the optical circuit 5A.

[0037] The optical circuit 5A processes the converted signal light TE0 from the second mode conversion unit 9 and outputs the processed signal light TE0 to the first mode conversion unit 8. The first mode conversion unit 8 then outputs the signal light TE0 from the forward-side operating unit 31A within the optical circuit 5A to the second waveguide 3.

[0038] The optical circuit 5A performs optical processing twice in total: once on the signal light TE1 from the first mode conversion unit 8, and again on the signal light TE0 from the second mode conversion unit 9. As a result, the functionality of the optical circuit 5A can be doubled, reducing power consumption and miniaturizing the optical device 1X.

[0039] In the optical device 1X of Example 2B, when the waveguide length in the optical circuit 5A is long, the first mode conversion unit 8 and the second mode conversion unit 9 are arranged in parallel before and after the optical circuit 5A, thereby enabling miniaturization of the optical device 1X.

[0040] In the optical device 1A of Example 2A, the signal light TM from the first conversion unit 4 and the signal light TE from the second conversion unit 6A, which pass through the optical circuit 5A, travel in reverse. Therefore, for example, due to imperfections in the first PBS 12A and the first PR 11, reflected backlight may occur in which the aliased signal light TE travels in reverse through the first waveguide 2. Accordingly, an embodiment of an optical device that can suppress such reflected backlight will be described below as Example 3. [Examples]

[0041] Figure 3 is an explanatory diagram showing an example of the optical device 1B of Embodiment 3. Note that components identical to those of the optical device 1A in Embodiment 2A are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical device 1B shown in Figure 3 includes a first waveguide 2, a second waveguide 3, a first conversion unit 4, an optical circuit 5A, a second conversion unit 6B, and a folded waveguide 7B. The optical circuit 5A includes a forward-side operating unit 31A, a return-side operating unit 31B, and a folded waveguide 32 that optically couples the forward-side operating unit 31A and the return-side operating unit 31B.

[0042] The first conversion unit 4 has a first port connected to the first waveguide 2, a second port connected to the optical circuit 5A, and a third port connected to the folded waveguide 7B. The first conversion unit 4 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the optical circuit 5A.

[0043] The optical circuit 5A has a first port connecting the first conversion unit 4 and the forward-side operating unit 31A, and a second port connecting the second conversion unit 6B and the return-side operating unit 31B. The optical circuit 5A optically processes the signal light TM converted from the first conversion unit 4 and outputs the optically processed signal light TM to the second conversion unit 6B.

[0044] The second conversion unit 6B has a fourth port connected to the return-side operating unit 31B in the optical circuit 5A, a fifth port connected to the folded waveguide 7B, and a sixth port connected to the second waveguide 3. The second conversion unit 6B converts the signal light TM from the optical circuit 5A after optical processing into signal light TE, and outputs the converted signal light TE to the folded waveguide 7B. The first conversion unit 4 outputs the converted signal light TE from the folded waveguide 7B to the forward-side operating unit 31A in the optical circuit 5A.

[0045] The optical circuit 5A processes the converted signal light TE from the second conversion unit 6B and outputs the processed signal light TE back to the second conversion unit 6B. The second conversion unit 6B then outputs the signal light TE from the return-path operating unit 31B within the optical circuit 5A to the second waveguide 3.

[0046] The first conversion unit 4 includes a first PR11 and a first PBS12. The first PR11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS12. The first PR11 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the first PBS12.

[0047] The first PBS12 has a first port connected to the first PR11, a second port connected to the forward-side working section 31A in the optical circuit 5A, and a third port connected to the folded waveguide 7B. The first PBS12 separates the signal light from the second port into signal light TM and signal light TE, outputs signal light TM from the first port, and outputs signal light TE from the third port. In other words, the first PBS12 outputs the signal light TM from the first PR11 to the forward-side working section 31A in the optical circuit 5A, and also outputs the signal light TE from the folded waveguide 7B to the forward-side working section 31A in the optical circuit 5A.

[0048] The second converter 6B includes a second PBS21B and a second PR22B. The second PBS21B has a fourth port connected to the return-side working unit 31A in the optical circuit 5A, a fifth port connected to the second PR22B, and a sixth port connected to the second waveguide 3. The second PBS21B separates the signal light from the fourth port into signal light TM and signal light TE, outputs the signal light TM from the fifth port, and outputs the signal light TE from the sixth port. In other words, the second PBS21B outputs the signal light TM from the return-side working unit 31A in the optical circuit 5A to the second PR22B, and outputs the signal light TE from the return-side working unit 31A in the optical circuit 5A to the second waveguide 3.

[0049] The second PR22B has a first port connected to the second PBS21B and a second port connected to the folded waveguide 3. It converts the signal light TM from the second PBS21B into signal light TE and outputs the converted signal light TE to the folded waveguide 7B.

[0050] The optical circuit 5A processes the signal light TM from the first conversion unit 4 and the signal light TE from the second conversion unit 6B via the first conversion unit 4, thereby achieving a total of two optical processes in the same direction of propagation. As a result, the functionality of the optical circuit 5A can be doubled, reducing power consumption and miniaturizing the optical device 1B while suppressing the effects of reflected backlight.

[0051] In the optical device 1B of Example 3, when the waveguide length in the optical circuit 5A is long, the first conversion unit 4 and the second conversion unit 6B are arranged in parallel before and after the optical circuit 5A, thereby enabling miniaturization of the optical device 1B.

[0052] Since the optical device 1B connects the second PR22B downstream of the optical circuit 5A to the first PBS12 upstream of the optical circuit 5A, the signal light passes through the waveguide in the optical circuit 5A in the same direction of propagation, first as the signal light TM and second as the signal light TE, thus suppressing the effects of reflected light. This prevents the reflected light of the folded signal light TE from affecting the signal light TE input from the first waveguide 2. Furthermore, it prevents the reflected light of the folded signal light TM from affecting the first signal light TM passing through the optical circuit 5A.

[0053] In the optical circuit 5A of the optical device 1B in Example 3, the first conversion unit 4 converts the signal light TE to signal light TM, and the second conversion unit 6B converts the signal light TM to signal light TE, that is, it is shown as an example of conversion to orthogonal polarization. However, it is not limited to this, and it can also be applied when converting to orthogonal higher-order modes. Therefore, an embodiment of this will be described below as Example 4. [Examples]

[0054] Figure 4 is an explanatory diagram showing an example of the optical device 1C of Embodiment 4. Components identical to those of the optical device 1B of Embodiment 3 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical device 1C shown in Figure 4 includes a first waveguide 2, a first mode conversion unit 8 which is the first conversion unit 4C, an optical circuit 5A, a second mode conversion unit 9 which is the second conversion unit 6C, a folded waveguide 7C, and a second waveguide 3. The optical circuit 5A has the same configuration as the optical circuit shown in Figure 3.

[0055] Figure 5A is an explanatory diagram showing an example of the first mode converter 8. The first mode converter 8 is a mode converter and combiner. The first mode converter 8 has a first port connected to the first waveguide 2, a second port connected to the forward-side operational unit 31A in the optical circuit 5A, and a third port connected to the folded waveguide 7C. The first mode converter 8 converts the signal light TE0 to signal light TE1, for example. The signal light TE0 and signal light TE1 are orthogonal to each other. The first mode converter 8 converts the signal light TE0 from the first waveguide 2 to a higher-order mode of signal light TE1 and outputs the signal light TE1 after higher-order mode conversion to the forward-side operational unit 31A in the optical circuit 5A. The first mode conversion unit 8 outputs the signal light TE0 from the folded waveguide 7C to the forward-side operating unit 31A in the optical circuit 5A.

[0056] The optical circuit 5A has a first port connecting the first mode conversion unit 8 and the forward-side operating unit 31A, and a second port connecting the second mode conversion unit 9 and the return-side operating unit 31B. The optical circuit 5A optically processes the first signal light TE1 after conversion from the first mode conversion unit 8 and outputs the optically processed signal light TE1 to the second mode conversion unit 9. Furthermore, the optical circuit 5A optically processes the second signal light TE0 from the second mode conversion unit 9 via the first mode conversion unit 8 and outputs the optically processed signal light TE0 to the second mode conversion unit 9.

[0057] Figure 5B is an explanatory diagram showing an example of the second mode conversion unit 9. The second mode conversion unit 9 has a fourth port connected to the return-side operating unit 31B in the optical circuit 5A, a fifth port connected to the folded waveguide 7C, and a sixth port connected to the second waveguide 3. The second mode conversion unit 9, for example, mode-converts signal light TE1 to signal light TE0. The second mode conversion unit 9 mode-converts the first signal light TE1 after optical processing from the return-side operating unit 31B in the optical circuit 5A to signal light TE0. The second mode conversion unit 9 outputs the converted signal light TE0 to the first mode conversion unit 8 via the folded waveguide 7C. The second mode conversion unit 9 outputs the second signal light TE0 after optical processing from the optical circuit 5A to the second waveguide 3.

[0058] In other words, the optical circuit 5A processes the first signal light TE1 from the first mode conversion unit 8 and the second signal light TE0 from the second mode conversion unit 9 via the first mode conversion unit 8, thereby achieving a total of two optical processes in the same direction of propagation. As a result, even in higher-order modes, the functionality of the optical circuit 5A can be doubled, reducing power consumption and miniaturizing the optical device 1C while suppressing the effects of reflected backlight.

[0059] In the optical device 1C of Example 4, when the waveguide length in the optical circuit 5A is long, the first mode conversion unit 8 and the second mode conversion unit 9 are arranged in parallel before and after the optical circuit 5A, thereby enabling miniaturization of the optical device 1C. [Examples]

[0060] Figure 6 is an explanatory diagram showing an example of the optical device 1D of Example 5. Note that components identical to those of the optical device 1B of Example 3 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The difference between the optical device 1D shown in Figure 6 and the optical device 1B shown in Figure 3 is that the channel waveguide in the forward-side working section 31A and the channel waveguide in the return-side working section 31B are optically coupled by a folded rib waveguide 32D.

[0061] Since the optical circuit 5D optically couples the channel waveguide in the forward operating section 31A and the channel waveguide in the return operating section 31B using a folded rib waveguide 32D, the optical circuit 5D can be miniaturized. [Examples]

[0062] Figure 7 is an explanatory diagram showing an example of the optical device 1E of Example 6. Note that components identical to those of the optical device 1B of Example 3 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The difference between the optical device 1E shown in Figure 7 and the optical device 1B shown in Figure 3 is that the channel waveguide in the forward-side working section 31A and the channel waveguide in the return-side working section 31B are optically coupled by a folded channel waveguide 32E.

[0063] The optical circuit 5D can be miniaturized because it optically couples the channel waveguide in the forward-side working section 31A with the channel waveguide in the return-side working section 31B using a folded channel waveguide 32E. Moreover, the folded channel waveguide 32E has strong optical confinement and can suppress bending losses. [Examples]

[0064] Figure 8 is an explanatory diagram showing an example of the optical device 1F of Embodiment 7. Note that components identical to those of the optical device 1B of Embodiment 3 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical circuit 5F within the optical device 1F shown in Figure 8 has a forward-side working section 31A1, a return-side working section 31B1, and a folded channel waveguide 32E that optically couples the forward-side working section 31A1 and the return-side working section 31B1.

[0065] The forward-side working section 31A1 includes a forward-side first transforming waveguide 33A1, a forward-side rib waveguide, and a forward-side second transforming waveguide 33A2. The forward-side first transforming waveguide 33A1 connects the channel waveguide on the first PBS12 side with the forward-side rib waveguide and is a tapered waveguide in which the slab width gradually widens from the channel waveguide to the forward-side rib waveguide. The forward-side second transforming waveguide 33A2 connects the forward-side rib waveguide with the return channel waveguide 32E and is a tapered waveguide in which the slab width gradually narrows from the forward-side rib waveguide to the channel waveguide.

[0066] The return-side working section 31B1 includes a first return-side transforming waveguide 33B1, a return-side rib waveguide, and a second return-side transforming waveguide 33B2. The first return-side transforming waveguide 33B1 connects the channel waveguide on the second PBS21A side with the return-side rib waveguide and is a tapered waveguide in which the slab width gradually narrows from the return-side rib waveguide to the channel waveguide. The second return-side transforming waveguide 33B2 connects the return-side rib waveguide with the folded channel waveguide 32E and is a tapered waveguide in which the slab width gradually widens from the channel waveguide to the return-side rib waveguide.

[0067] In the optical device 1F, the forward operating section 31A1 and the return operating section 31B1 are optically coupled by a folded channel waveguide 32E. Therefore, even if the optical confinement in the folded channel waveguide 32E is strong and the radius of curvature of the folded channel waveguide 32E is reduced, the signal light can be folded back without increasing optical loss due to the bending radius.

[0068] Furthermore, in optical circuit 5F, a tapered waveguide with a gradually changing slab width is placed between the channel waveguide and the rib waveguide, thereby suppressing the loss of light between the rib waveguide and the channel waveguide. [Examples]

[0069] Figure 9 is an explanatory diagram showing an example of the optical device 1G of Embodiment 8. The optical device 1G shown in Figure 9 includes a first waveguide 2, a second waveguide 3, a first conversion unit 4, a first folded channel waveguide 10A, an optical circuit 5A, a second folded channel waveguide 10B, a second conversion unit 6G, and a folded channel waveguide 7G. The optical circuit 5A includes a forward-side working unit 31A including the forward-side channel waveguide, a return-side working unit 31B including the return-side channel waveguide, and a folded channel waveguide 32E that optically couples the forward-side working unit 31A and the return-side working unit 31B.

[0070] The first conversion unit 4 has a first port connected to the first waveguide 2, a second port connected to the first folded channel waveguide 10A, and a third port connected to the folded channel waveguide 7G. The first conversion unit 4 converts the signal light TE from the first waveguide 2 into signal light TM. The first conversion unit 4 outputs the converted signal light TM to the first folded channel waveguide 10A. The first folded channel waveguide 10A is connected to the forward-side operating unit 31A in the optical circuit 5A.

[0071] The optical circuit 5A has a first port connecting the first folded channel waveguide 10A to the forward-side working section 31A, and a second port connecting the second folded channel waveguide 10B to the return-side working section 31B. The optical circuit 5A optically processes the signal light TM converted from the first folded channel waveguide 10A and outputs the optically processed signal light TM to the second conversion section 6G.

[0072] The second conversion unit 6G has a fourth port connected to the second folded channel waveguide 10B, a fifth port connected to the folded waveguide 7G, and a sixth port connected to the second waveguide 3. The second conversion unit 6G converts the signal light TM from the second folded channel waveguide 10B after optical processing into signal light TE, and outputs the converted signal light TE to the first folded channel waveguide 10A via the folded waveguide 7G and the first conversion unit 4. The second folded channel waveguide 10B is connected to the forward-side operating unit 31B in the optical circuit 5A.

[0073] The optical circuit 5A processes the converted signal light TE from the first folded channel waveguide 10A using the second conversion unit 6G, and outputs the processed signal light TE to the second conversion unit 6G. The second conversion unit 6G then outputs the signal light TE from the return-side operating unit 31B within the optical circuit 5A to the second waveguide 3.

[0074] The first conversion unit 4 includes a first PR11 and a first PBS12. The first PR11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS12. The first PR11 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the first PBS12.

[0075] The first PBS12 has a first port connected to the first PR11, a second port connected to the first folded channel waveguide 10A, and a third port connected to the folded channel waveguide 7G. The first PBS12 outputs signal light TM from the first PR11 to the first folded channel waveguide 10A, and also outputs signal light TE from the folded channel waveguide 7G to the first folded channel waveguide 10A.

[0076] The second conversion unit 6G includes a second PBS21G and a second PR22G. The second PBS21G has a fourth port connected to the second folded channel waveguide 10A, a fifth port connected to the second PR22G, and a sixth port connected to the second waveguide 3. The second PBS21G outputs the signal light TM from the second folded channel waveguide 10B to the second PR22G and outputs the signal light TE from the second folded channel waveguide 10B to the second waveguide 3.

[0077] The second PR22G has a first port connected to the second PBS21G and a second port connected to the folded waveguide 7G. The second PR22G converts the signal light TM from the second PBS21G into signal light TE and outputs the converted signal light TE to the folded waveguide 7G.

[0078] The optical circuit 5A processes the first signal light TM from the first folded channel waveguide 10A and the second signal light TE from the first folded channel waveguide 10B, thereby achieving a total of two optical processes in the same direction of propagation. As a result, the functionality of the optical circuit 5A can be doubled, reducing power consumption and miniaturizing the optical device 1G while suppressing the effects of reflected light.

[0079] In the optical device 1G of Example 8, the second PR22G downstream of the optical circuit 5A is connected to the first PBS12 upstream of the optical circuit 5A. As a result, the signal light passes through the PIN diode region of the working part in the optical circuit 5A in the same direction of propagation, for the first time as signal light TM and for the second time as signal light TE, thus suppressing the effect of reflected backlight. In other words, it is possible to avoid a situation in which the reflected backlight of the folded signal light TE0 affects the signal light TE0 input from the first waveguide 2. Furthermore, it is possible to avoid a situation in which the reflected backlight of the folded signal light TE1 affects the first signal light TE1 passing through the optical circuit 5A.

[0080] Furthermore, since the optical device 1G has the first conversion unit 4, the optical circuit 5A, and the second conversion unit 6G arranged in parallel, the size of the optical device 1G can be reduced. [Examples]

[0081] Figure 10 is an explanatory diagram showing an example of the optical device 1H of Embodiment 9. The optical device 1H shown in Figure 10 includes a first waveguide 2, a second waveguide 3, a first mode conversion unit 8A, a first folded rib waveguide 10A1, an optical circuit 5A, a second folded rib waveguide 10B1, a second mode conversion unit 9A, and a folded waveguide 7G. The optical circuit 5A includes a forward-side working unit 31A, a return-side working unit 31B, and a folded channel waveguide 32E that optically couples the forward-side working unit 31A and the return-side working unit 31B.

[0082] The first mode conversion unit 8A has a first port connected to the first waveguide 2, a second port connected to the first folded rib waveguide 10A1, and a third port connected to the folded waveguide 7G. The first mode conversion unit 8A performs higher-order mode conversion of the signal light TE0 from the first waveguide 2 to the signal light TE1. The first mode conversion unit 8A outputs the converted signal light TE1 to the first folded rib waveguide 10A1. The first folded rib waveguide 10A1 is connected to the forward-side operating unit 31A in the optical circuit 5A.

[0083] The optical circuit 5A has a first port connecting the first folded rib waveguide 10A1 to the forward-side operating section 31A, and a second port connecting the second folded rib waveguide 10B1 to the return-side operating section 31B. The optical circuit 5A optically processes the signal light TE1 converted from the first mode conversion unit 8A and outputs the optically processed signal light TE1 to the second mode conversion unit 9A.

[0084] The second mode conversion unit 9A has a fourth port connected to the second folded rib waveguide 10B1, a fifth port connected to the folded waveguide 7G, and a sixth port connected to the second waveguide 3. The second mode conversion unit 9A converts the signal light TE1 from the second folded rib waveguide 10B1 after optical processing into signal light TE0, and outputs the converted signal light TE0 to the first folded rib waveguide 10A1 via the folded waveguide 7G and the first mode conversion unit 8A. The second folded rib waveguide 10B1 is connected to the return-side operating unit 31B in the optical circuit 5A.

[0085] The optical circuit 5A processes the signal light TE0 converted by the second mode conversion unit 9A from the first mode conversion unit 8A, and outputs the processed signal light TE0 to the second mode conversion unit 9A. The second mode conversion unit 9A then outputs the second signal light TE0 from the second folded rib waveguide 10B1 to the second waveguide 3.

[0086] The optical circuit 5A processes the first signal light TE1 from the first folded rib waveguide 10A1 and the second signal light TE0 from the first folded rib waveguide 10A1, thereby achieving a total of two optical processes in the same direction of propagation. As a result, the functionality of the optical circuit 5A can be doubled, reducing power consumption and miniaturizing the optical device 1H while suppressing the effects of reflected light.

[0087] In the optical device 1H of Example 9, the second mode conversion unit 9A located downstream of the optical circuit 5A is connected to the first mode conversion unit 8A located upstream of the optical circuit 5A. As a result, the signal light passes through the PIN diode region of the working part within the optical circuit 5A in the same direction of propagation, for the first time as signal light TE1 and for the second time as signal light TE0, thus suppressing the influence of reflected light. In other words, it is possible to avoid a situation in which the reflected light of the folded signal light TE0 affects the signal light TE0 input from the first waveguide 2. Furthermore, it is possible to avoid a situation in which the reflected light of the folded signal light TE1 affects the first signal light TE1 passing through the optical circuit 5A.

[0088] Furthermore, since the optical device 1H has the first mode conversion unit 8A, the optical circuit 5A, and the second mode conversion unit 9A arranged in parallel, the size of the optical device 1H can be reduced.

[0089] Furthermore, since the first folded rib waveguide 10A1 and the second folded rib waveguide 10B1 are rib waveguides, the orthogonality of the modes of the first signal light TE0 and the second signal light TE1 can be maintained.

[0090] Furthermore, various circuits such as DC modulators and phase shifters can be considered as examples of optical circuit 5 for optical device 1 in Examples 1 to 9. However, a VOA (Variable Optical Attenuator) may also be used, and an embodiment of an optical device using a PIN-type VOA will be described below as Example 10. [Examples]

[0091] Figure 11 is an explanatory diagram showing an example of the optical device 1J of Example 10, and Figure 12 is a schematic cross-sectional view of the optical device 1J shown in Figure 11 along line AA. Note that components identical to those of optical device 1 in Example 1 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted.

[0092] The optical device 1J shown in Figure 11 includes a first waveguide 2, a second waveguide 3, a first converter 4, an optical circuit 5 which is a PIN-type VOA, a second converter 6, and a folded waveguide 7. The first converter 4 has a first port connected to the first waveguide 2, a second port connected to the optical circuit 5, and a third port connected to the second waveguide 3. The first converter 4 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the optical circuit 5.

[0093] The second conversion unit 6 has a fourth port connected to the optical circuit 5, a fifth port connected to one side of the folded waveguide 7, and a sixth port connected to the other side of the folded waveguide 7. The second conversion unit 6 converts the signal light TE from the optical circuit 5 after optical attenuation into signal light TM, and outputs the converted signal light TE to the optical circuit 5.

[0094] The first conversion unit 4 includes a first PR11 and a first PBS12. The first PR11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS12. The first PR11 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the first PBS12. The first PBS12 has a first port connected to the first PR11, a second port connected to the optical circuit 5, and a third port connected to the second waveguide 3. The first PBS12 outputs the signal light TM from the first PR11 to the optical circuit 5A and outputs the signal light TE from the optical circuit 5A to the second waveguide 3.

[0095] The second conversion unit 6 includes a second PBS21 and a second PR22. The second PBS21 has a fourth port connected to the optical circuit 5, a fifth port connected to the second PR22, and a sixth port connected to the folded waveguide 7. The second PBS21 outputs the signal light TM from the optical circuit 5 to the second PR22 and outputs the signal light TE from the folded waveguide 7 to the optical circuit 5. The second PR22 has a first port connected to the second PBS21 and a second port connected to the folded waveguide 7, converts the signal light TM from the second PBS21 to the signal light TE, and outputs the converted signal light TE to the folded waveguide 7.

[0096] The optical circuit 5 shown in Figure 12 comprises a Si substrate 51, a SiO2 cladding layer 52 laminated on the Si substrate 51, and a Si rib waveguide 53 disposed within the cladding layer 52. Furthermore, the optical circuit 5 has electrodes 55A and 55B disposed on the first slab 54A and the second slab 54B of the rib waveguide 53. The electrodes consist of a P electrode 55A and an N electrode 55B. The working portion 31 of the optical circuit 5 comprises the rib waveguide 53, the P electrode 55A, and the N electrode 55B.

[0097] The rib waveguide 53 has a P-doped region 54A1 formed in the portion of the first slab 54A that contacts the P electrode 55A, and an N-doped region 54B1 formed in the portion of the second slab 54B that contacts the N electrode 55B. The waveguide width of the rib waveguide 53 between the P-doped region 54A1 and the N-doped region 54B1 is I. Narrowing the waveguide width W improves the efficiency of signal light absorption.

[0098] In the optical circuit 5, when a positive voltage is applied from the P electrode 55A to the N electrode 55B, a current flows through the rib waveguide 53, and the signal light guiding through the rib waveguide 53 is absorbed by the absorption of free carriers. As a result, the intensity of the signal light guiding through the rib waveguide 53 is attenuated in the optical circuit 5.

[0099] The optical circuit 5 has a first port connecting the first conversion unit 4 and the operating unit 31, and a second port connecting the second conversion unit 6 and the operating unit 31. The optical circuit 5 performs optical attenuation processing on the signal light TM converted from the first conversion unit 4 in the operating unit 31, and outputs the signal light TM after optical attenuation processing to the second conversion unit 6.

[0100] The optical circuit 5 performs optical attenuation processing on the signal light TE converted from the second conversion unit 6 using the operating unit 31, and outputs the signal light TE after optical attenuation processing to the first conversion unit 4. The first conversion unit 4 then outputs the signal light TE from the optical circuit 5 to the second waveguide 3.

[0101] The optical circuit 5 performs optical attenuation processing on the signal light TM from the first conversion unit 4 to the second conversion unit 6, and also performs optical attenuation processing on the signal light TE from the second conversion unit 6 to the first conversion unit 4, thereby achieving a total of two optical attenuation processes. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1J.

[0102] Furthermore, in the P-doped region 54A1 and N-doped region 54B1 of the rib waveguide 53 within the optical circuit 5, the resistance decreases as the doping concentration increases, thus reducing power consumption. However, as the doping concentration increases, the absorption of light when no current is flowing increases, resulting in increased light loss. Therefore, an embodiment of an optical device that can suppress light loss is described below as Example 11. [Examples]

[0103] Figure 13 is an explanatory diagram showing an example of the optical device 1K of Example 11, and Figure 14 is a schematic cross-sectional view of the optical device 1K shown in Figure 13 along the BB line. Note that components identical to those of the optical device 1J of Example 10 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The rib waveguide 53 in the optical circuit 5 shown in Figures 13 and 14 has a first slab 54A in contact with the P electrode 55A and a second slab 54B in contact with the N electrode 55B.

[0104] The first slab 54A has a P+ doped region 54A1 adjacent to the ribs of the rib waveguide 53 and a P++ doped region 54A2 in contact with the P electrode 55A. The second slab 54B has an N+ doped region 54B1 adjacent to the ribs and an N++ doped region 54B2 in contact with the N electrode 55B.

[0105] The doping concentrations in the P++-doped region 54A2 and N++-doped region 54B2, which are close to the electrodes, are higher than those in the P+-doped region 54A1 and N+-doped region 54B1.

[0106] In the optical device 1K of Example 11, the signal light TM from the first conversion unit 4 to the second conversion unit 6 is optically attenuated, and the signal light TE from the second conversion unit 6 to the first conversion unit 4 is optically attenuated, thereby achieving a total of two optical attenuation processes. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1K.

[0107] Furthermore, the first slab 54A (second slab 54B) of the rib waveguide 53 in the optical circuit 5 is configured such that the doping concentration is lower in the region closer to the ribs and higher in the region closer to the electrodes 55A (55B). As a result, the efficiency of light absorption when current flows through the optical waveguide is improved while suppressing light loss and narrowing the optical waveguide width W. [Examples]

[0108] Figure 15 is an explanatory diagram showing an example of the optical device 1L of Example 12, and Figure 16 is a schematic cross-sectional view of the CC line of the optical device 1L shown in Figure 15. The optical device 1L shown in Figure 15 has a first waveguide 2, a second waveguide 3, a first conversion unit 4, an optical circuit 5L, a second conversion unit 6, and a folded waveguide 7. The optical circuit 5L has a forward-side working unit 31A1, a return-side working unit 31B1, and a folded-side working unit 32L that optically couples the forward-side working unit 31A1 and the return-side working unit 31B1.

[0109] The first conversion unit 4 has a first port connected to the first waveguide 2, a second port connected to the optical circuit 5L, and a third port connected to the second waveguide 3. The first conversion unit 4 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the optical circuit 5L.

[0110] The optical circuit 5L has a first port connecting the first conversion unit 4 and the forward-side operating unit 31A1, and a second port connecting the second conversion unit 6 and the return-side operating unit 31B1. The optical circuit 5L optically attenuates the converted signal light TM from the first conversion unit 4 and outputs the optically attenuated signal light TM to the second conversion unit 6. The forward-side operating unit 31A1 optically attenuates the signal light TM from the first conversion unit 4 with an electrical signal. The return-side operating unit 32L optically attenuates the optically attenuated signal light TM with an electrical signal. Furthermore, the return-side operating unit 31B1 optically attenuates the optically attenuated signal light TM from the return-side operating unit 32L with an electrical signal.

[0111] The second conversion unit 6 has a fourth port connected to the return-side operating unit 31B1 in the optical circuit 5L, a fifth port connected to one side of the folded waveguide 7, and a fifth port connected to the other side of the folded waveguide 7. The second conversion unit 6 converts the signal light TM from the optical circuit 5L after optical processing into signal light TE, and outputs the converted signal light TE to the return-side operating unit 31B1 in the optical circuit 5L.

[0112] The optical circuit 5L performs optical attenuation on the signal light TE converted from the second conversion unit 6 and outputs the signal light TE after optical attenuation to the first conversion unit 4. The first conversion unit 4 then outputs the signal light TE from the forward-side operating unit 31A1 within the optical circuit 5L to the second waveguide 3.

[0113] The first conversion unit 4 includes a first PR11 and a first PBS12. The first PR11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS12, and converts the signal light TE from the first waveguide 2 into signal light TM, and outputs the converted signal light TM to the first PBS12.

[0114] The first PBS12 has a first port connected to the first PR11, a second port connected to the forward-side working unit 31A1 in the optical circuit 5L, and a third port connected to the second waveguide 3. The first PBS12 outputs the converted signal light TM from the first PR11 to the forward-side working unit 31A1 in the optical circuit 5L, and outputs the signal light TE from the forward-side working unit 31A1 in the optical circuit 5L to the second waveguide 3.

[0115] The second conversion unit 6 includes a second PBS 21 and a second PR 22. The second PBS 21 has a fourth port connected to the return-side working unit 31B1 in the optical circuit 5L, a fifth port connected to the second PR 22, and a sixth port connected to the folded waveguide 7. The second PBS 21 outputs the signal light TM from the return-side working unit 31B1 in the optical circuit 5L to the second PR 22, and also outputs the signal light TE from the folded waveguide 7 to the return-side working unit 31B1 in the optical circuit 5L.

[0116] The second PR22 has a first port connected to the second PBS21 and a second port connected to the folded waveguide 7. It converts the signal light TM from the second PBS21 into signal light TE and outputs the converted signal light TE to the folded waveguide 7.

[0117] The optical circuit 5L includes a Si substrate 51, a cladding layer 52 of SiO2 laminated on the Si substrate 51, a Si rib waveguide 53 arranged within the cladding layer 52, and electrodes arranged on both slabs 54A and 54B of the rib waveguide 53. The electrodes include a P electrode 55A and an N electrode 55B. The working portion 31A1 (32L, 31B1) of the optical circuit 5L includes the rib waveguide 53, the P electrode 55A, and the N electrode 55B.

[0118] The slab of the rib waveguide 53 has a first slab 54A that is in contact with the P electrode 55 and a second slab 54B that is in contact with the N electrode 55B. The first slab 54A has a P+ doped region 54A1 adjacent to the rib of the rib waveguide 53 and a P++ doped region 54A2 that is in contact with the P electrode 55A. The second slab 54B has an N+ doped region 54B1 adjacent to the rib and an N++ doped region 54B2 that is in contact with the N electrode 55B. The doping concentration is reduced in the P+ doped region 54A1 and the N+ doped region 54B1, while the doping concentration is increased in the P++ doped region 54A2 and the N++ doped region 54B2 that are closer to the electrodes.

[0119] The optical circuit 5L performs optical attenuation processing on the signal light TM from the first conversion unit 4 to the second conversion unit 6, and also performs optical attenuation processing on the signal light TE from the second conversion unit 6 to the first conversion unit 4, thereby achieving a total of two optical attenuation processes. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1L.

[0120] Furthermore, the first slab 54A (second slab 54B) of the rib waveguide 53 in the optical circuit 5L is configured such that the doping concentration is lower in the region closer to the ribs and higher in the region closer to the electrodes. As a result, resistance can be reduced while suppressing light loss.

[0121] Furthermore, since the optical circuit 5L within the optical device 1L has a reverse-side working part 32L that optically couples the forward-side working part 31A1 and the return-side working part 31B1, the waveguide length of the VOA can be shortened, thereby enabling miniaturization of the optical circuit 5L.

[0122] Furthermore, in the optical circuit 5L of the optical device 1L in Example 12, the rib waveguide 53 has weak light confinement, and the bending loss increases, especially when the radius of curvature at the folding side working portion 32L is reduced. Therefore, an embodiment of an optical device that addresses this situation will be described below as Example 13. [Examples]

[0123] Figure 17 is an explanatory diagram showing an example of the optical device 1M of Example 13, and Figure 18 is a schematic cross-sectional view of the DD line of the optical device 1M shown in Figure 17. Note that components identical to those of the optical device 1M of Example 12 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical device 1M shown in Figure 17 includes a first waveguide 2, a second waveguide 3, a first converter 4, an optical circuit 5M, a second converter 6, and a folded waveguide 7. The optical circuit 5M includes a forward-side working section 31A2 connected to the first PBS 12 in the first converter 4, and a return-side working section 31B2 connected to the second PBS 12 in the second converter 6. Furthermore, the optical circuit 5M has a folded channel waveguide 32M that optically couples the forward-side working section 31A2 and the return-side working section 31B2.

[0124] The forward-side working section 31A2 shown in Figure 18 includes a forward-side first transforming waveguide 33A1, a forward-side rib waveguide 53A, a forward-side second transforming waveguide 33A2, and forward-side P electrodes 55A and N electrodes 55B. The slab within the forward-side rib waveguide 53A includes a forward-side first slab 54A containing P+ doped regions 54A1 and P++ doped regions 54A2, and a forward-side second slab 54B containing N+ doped regions 54B1 and N++ doped regions 54B2.

[0125] The first forward-side transforming waveguide 33A1 connects the channel waveguide connected to the first PBS12 with the forward-side rib waveguide 53A, and is a tapered waveguide in which the slab width gradually widens as it transitions from the channel waveguide to the rib waveguide. The second forward-side transforming waveguide 33A2 connects the forward-side rib waveguide 53A with the return channel waveguide 32M, and is a tapered waveguide in which the slab width gradually narrows as it transitions from the rib waveguide to the channel waveguide.

[0126] The return-side working section 31B2 shown in Figure 18 includes a first return-side transforming waveguide 33B1, a return-side rib waveguide 53B, a second return-side transforming waveguide 33B2, and return-side P electrodes 55A and N electrodes 55B. The slab within the return-side rib waveguide 53B includes a first return-side slab 54A containing P+ doped regions 54A1 and P++ doped regions 54A2, and a second return-side slab 54B containing N+ doped regions 54B1 and N++ doped regions 54B2.

[0127] The first transforming waveguide 33B1 on the return path connects the channel waveguide connected to the second PBS21 and the rib waveguide 53B on the return path, and is a tapered waveguide in which the slab width gradually widens as it transitions from the channel waveguide to the rib waveguide. The second transforming waveguide 33B2 on the return path connects the rib waveguide 53B on the return path and the folded channel waveguide 32M, and is a tapered waveguide in which the slab width gradually narrows as it transitions from the rib waveguide to the channel waveguide.

[0128] In the optical circuit 5M within the optical device 1M of Example 13, the signal light TM from the first conversion unit 4 to the second conversion unit 6 is optically attenuated, and the signal light TE from the second conversion unit 6 to the first conversion unit 4 is also optically attenuated, thereby achieving a total of two optical attenuation processes. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1M.

[0129] In the optical device 1M, the forward-side working section 31A2 and the return-side working section 31B2 are optically coupled by a folded channel waveguide 32M. As a result, the optical confinement in the folded channel waveguide 32M is strong, and even when the radius of curvature of the folded channel waveguide 32M is reduced, the signal light can be folded back without increasing optical loss due to the bending radius.

[0130] Furthermore, in optical circuit 5M, a first conversion waveguide 33A1 (33B1) and a second conversion waveguide 33A2 (33B2) are arranged, which are tapered waveguides that gradually change the slab width between the channel waveguide and the rib waveguide. As a result, optical loss occurring between the rib waveguide and the channel waveguide can be suppressed.

[0131] In the optical circuit 5M of Example 13, the example shows that the P electrode 55A is arranged separately in the forward-side working section 31A2 and the return-side working section 31B2. However, the P electrode 55A may be shared to reduce the number of electrode terminals, and such an embodiment will be described below as Example 14. [Examples]

[0132] Figure 19 is an explanatory diagram showing an example of optical device 1N in Example 14, and Figure 20 is a schematic cross-sectional view of the EE line of optical device 1N shown in Figure 19. Components identical to those of optical device 1M in Example 13 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted.

[0133] The optical device 1N shown in Figure 19 includes a first waveguide 2, a second waveguide 3, a first converter 4, an optical circuit 5N, a second converter 6, and a folded waveguide 7. The optical circuit 5N includes a forward-side working section 31A3, a return-side working section 31B3, and a folded channel waveguide 32M. The forward-side working section 31A3 and the return-side working section 31B3 each have a single P electrode 55A1 that shares the forward-side P electrode 55A and the return-side P electrode 55A. Furthermore, the forward-side working section 31A3 and the return-side working section 31B3 each have a connecting section 58 that electrically connects the forward-side N electrode 55B and the return-side N electrode 55B.

[0134] The P electrode 55A shown in Figure 20 electrically connects a via 57 electrically connected to the forward P++ doped region 54A2 in the forward working portion 31A3 and a via 57 electrically connected to the return P++ doped region 54A2 in the return working portion 31B3. The connecting portion 58 electrically connects the forward N electrode 55B, which is connected to a via 57 connected to the forward N++ doped region 54B2 of the forward working portion 31A3, and the return N electrode 55B, which is connected to a via 57 connected to the N++ doped region 54B2 of the return working portion 31B3.

[0135] The optical circuit 5N absorbs signal light that is guided through the forward-side rib waveguide 53A in the forward-side working section 31A3 by applying voltage to the forward-side N electrode 55B and the return-side N electrode 55B, causing current to flow from the forward-side N electrode 55B to the P electrode 55A1. Furthermore, the optical circuit 5N absorbs signal light that is guided through the return-side rib waveguide 53B in the return-side working section 31B3 by current flowing from the return-side N electrode 55B to the P electrode 55A1.

[0136] In the optical device 1N of Example 14, the signal light TM from the first conversion unit 4 to the second conversion unit 6 is optically attenuated, and the signal light TE from the second conversion unit 6 to the first conversion unit 4 is also optically attenuated, thereby achieving a total of two optical attenuation processes. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1N.

[0137] In the optical circuit 5N, the P electrode 55A1 is shared between the forward-side working part 31A3 and the return-side working part 31B3, and terminals are placed on the P electrode 55A1, thus reducing the number of terminals on the P electrode side compared to the optical circuit 1M shown in Figure 17. Furthermore, the optical circuit 5N has a connecting part 58 that electrically connects the forward-side N electrode 55B and the return-side N electrode 55B, and terminals are placed on either the N electrode 55B or the connecting part 58, thus reducing the number of terminals on the N electrode side compared to the optical device 1M shown in Figure 17.

[0138] In Example 14, the optical circuit 5N within the optical device 1N illustrates a case where the P++-doped region 54A2 in the forward-side working portion 31A3 and the P++-doped region 54A2 in the return-side working portion 31B3 are connected by a single P electrode 55A1. However, the P++-doped region 54A2 in the forward-side working portion 31A3 and the P++-doped region 54A2 in the return-side working portion 31B3 may be shared, and such an embodiment will be described below as Example 15. [Examples]

[0139] Figure 21 is an explanatory diagram showing an example of optical device 1P in Example 15, and Figure 22 is a schematic cross-sectional view of the FF line of optical device 1P shown in Figure 21. Components identical to those of optical device 1N in Example 14 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted.

[0140] The optical device 1P shown in Figure 21 includes a first waveguide 2, a second waveguide 3, a first converter 4, an optical circuit 5P, a second converter 6, and a folded waveguide 7. The optical circuit 5P has a single P++ doped region 54A3 that connects a P+ doped region 54A1 in the forward operating region 31A3 and a P+ doped region 54A1 on the return side. The P++ doped region 54A3 is electrically connected to a single P electrode 55A via a via.

[0141] The optical circuit 5P applies voltage to the N electrode 55B in the forward-side working section 31A3 and the N electrode 55B in the return-side working section 31B3. As a result, the optical circuit 5P absorbs the signal light that flows from the forward-side N electrode 55B to the P electrode 55A1 and guides the forward-side rib waveguide 53A in the forward-side working section 31A3. Furthermore, the optical circuit 5P absorbs the signal light that flows from the return-side N electrode 55B to the P electrode 55A1 and guides the rib waveguide 53B in the return-side working section 31B3.

[0142] In the optical device 1P of Example 15, the signal light TM from the first conversion unit 4 to the second conversion unit 6 is optically attenuated, and the signal light TE from the second conversion unit 6 to the first conversion unit 4 is also optically attenuated, thereby achieving a total of two optical attenuation processes. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1P.

[0143] In the optical circuit 5P, the P++ doped region 54A3 is shared between the forward-side working portion 31A3 and the return-side working portion 31B3, which allows the distance between the forward-side working portion 31A3 and the return-side working portion 31B3 to be shortened.

[0144] In the optical device 1P of Example 15, the first signal light TM and the second signal light TE travel in reverse at the forward-side working section 31A3 and the return-side working section 31B3 within the optical circuit 5P. Therefore, for example, due to imperfections in the first PBS12 and the first PR11, the folded signal light TE travels in reverse through the first waveguide 2. As a result, the reflected light of the folded signal light TE affects the signal light TE input from the first waveguide 2. Also, for example, due to imperfections in the second PBS21 and the second PR21, the folded signal light TM travels in reverse through the first PR11. As a result, the reflected light of the folded signal light TM affects the first signal light TM passing through the optical circuit 5P. Therefore, an embodiment that suppresses such reflected light will be described below as Example 16. [Examples]

[0145] Figure 23 is an explanatory diagram showing an example of the optical device 1Q of Example 16, and Figure 24 is a schematic cross-sectional view of the optical device 1Q shown in Figure 23 along the GG line. Note that components identical to those of the optical device 1P of Example 15 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical device 1Q shown in Figure 23 includes a first waveguide 2, a second waveguide 3, a first conversion unit 4, an optical circuit 5Q, a second conversion unit 6B, and a folded waveguide 7B. The optical circuit 5Q includes a forward-side operating unit 31A3, a return-side operating unit 31B3, and a folded channel waveguide 32M that optically couples the forward-side operating unit 31A3 and the return-side operating unit 31B3.

[0146] The first conversion unit 4 has a first port connected to the first waveguide 2, a second port connected to the forward-side operating unit 31A3 in the optical circuit 5Q, and a third port connected to the folded waveguide 7B. The first conversion unit 4 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the forward-side operating unit 31A3 in the optical circuit 5Q.

[0147] The optical circuit 5Q has a first port connecting the first conversion unit 4 and the forward-side operating unit 31A3, and a second port connecting the second conversion unit 6B and the return-side operating unit 31B3. The optical circuit 5Q performs optical attenuation on the signal light TM converted from the first conversion unit 4 and outputs the signal light TM after optical attenuation to the second conversion unit 6. The optical circuit 5Q has the same configuration as the optical circuit in Embodiment 15.

[0148] The second conversion unit 6B has a fourth port connected to the return-side operating unit 31B3 in the optical circuit 5Q, a fifth port connected to the folded waveguide 7B, and a sixth port connected to the second waveguide 3. The second conversion unit 6B converts the signal light TM from the return-side operating unit 31B3 in the optical circuit 5Q after optical attenuation processing into signal light TE, and outputs the converted signal light TE to the forward-side operating unit 31B3 in the optical circuit 5Q via the folded waveguide 7B and the first conversion unit 4.

[0149] The optical circuit 5Q performs optical attenuation on the signal light TE converted from the second conversion unit 6B, and outputs the signal light TE after optical attenuation to the second conversion unit 6B. The second conversion unit 6B then outputs the signal light TE from the return-side operating unit 31B3 within the optical circuit 5Q to the second waveguide 3.

[0150] The first conversion unit 4 includes a first PR11 and a first PBS12. The first PR11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS12, and converts the signal light TE from the first waveguide 2 into signal light TM, and outputs the converted signal light TM to the first PBS12.

[0151] The first PBS12 has a first port connected to the first PR11, a second port connected to the forward-side working section 31A3 in the optical circuit 5Q, and a third port connected to the folded waveguide 7B. The first PBS12 outputs the signal light TM from the first PR11 to the forward-side working section 31A3 in the optical circuit 5Q, and also outputs the signal light TE from the folded waveguide 7B to the forward-side working section 31A3 in the optical circuit 5Q.

[0152] The second converter 6B includes a second PBS 21B and a second PR 22B. The second PBS 21B has a fourth port connected to the return-side working unit 31B3 in the optical circuit 5Q, a fifth port connected to the second PR 22B, and a sixth port connected to the second waveguide 3. The second converter 6B outputs the signal light TM from the return-side working unit 31B3 in the optical circuit 5Q to the second PR 22B, and also outputs the signal light TE from the return-side working unit 31B3 in the optical circuit 5Q to the second waveguide 3.

[0153] The second PR22B has a first port connected to the second PBS21B and a second port connected to the folded waveguide 7B. It converts the signal light TM from the second PBS21B into signal light TE and outputs the converted signal light TE to the folded waveguide 7B.

[0154] The optical circuit 5Q performs optical attenuation on the signal light TM from the first conversion unit 4, and also performs optical attenuation on the signal light TE from the second conversion unit 6B via the first conversion unit 4, thereby achieving a total of two optical attenuation processes in the same direction of propagation. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1Q while suppressing the effects of reflected backlight.

[0155] In the optical device 1Q of Example 16, the second PR22B downstream of the optical circuit 5Q is connected to the first PBS12 upstream of the optical circuit 5Q. As a result, the signal light passes through the PIN diode region of the working part 31A3 (31B3) in the optical circuit 5Q in the same direction of propagation, for the first time as signal light TM and for the second time as signal light TE, thus suppressing the effect of reflected backlight. In other words, it is possible to avoid a situation in which the reflected backlight of the folded signal light TE affects the signal light TE input from the first waveguide 2. Furthermore, it is possible to avoid a situation in which the reflected backlight of the folded signal light TM affects the first signal light TM passing through the optical circuit 5Q.

[0156] In the optical circuit 5Q of the optical device 1Q in Example 16, the first conversion unit 4 converts the signal light TE to signal light TM, and the second conversion unit 6B converts the signal light TM to signal light TE, that is, the case where orthogonal polarization is converted is illustrated. However, it is not limited to this, and it can also be applied when converting to orthogonal higher-order modes. Therefore, an embodiment of this will be described below as Example 17. [Examples]

[0157] Figure 25 is an explanatory diagram showing an example of the optical device 1R of Example 17, and Figure 26 is a schematic cross-sectional view of the HH line of the optical device 1R shown in Figure 25. Note that components identical to those of the optical device 1P of Example 15 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted. The optical device 1R shown in Figure 25 includes a first waveguide 2, a second waveguide 3, a first mode conversion unit 8, an optical circuit 5R, a second mode conversion unit 9, and a folded waveguide 7B. The optical circuit 5R has the same configuration as the optical circuit shown in Figure 15.

[0158] The first mode conversion unit 8 has a first port connected to the first waveguide 2, a second port connected to the forward-side operating unit 31A3 in the optical circuit 5R, and a third port connected to the folded waveguide 7B. The first mode conversion unit 8 converts the signal light TE0 from the first waveguide 2 to signal light TE1, and outputs the converted signal light TE1 to the forward-side operating unit 31A3 in the optical circuit 5R. The first mode conversion unit 8 also outputs the signal light TE0 from the folded waveguide 7B to the forward-side operating unit 31A3 in the optical circuit 5R.

[0159] The optical circuit 5R has a first port connecting the first mode conversion unit 8 and the forward-side operating unit 31A3, and a second port connecting the second mode conversion unit 9 and the return-side operating unit 31B3. The optical circuit 5R optically attenuates the first signal light TE1 after conversion from the first mode conversion unit 8 and outputs the signal light TE1 after optical attenuation to the second mode conversion unit 9. Furthermore, the optical circuit 5R optically attenuates the second signal light TE0 from the second mode conversion unit 9 via the first mode conversion unit 8 and outputs the signal light TE0 after optical attenuation to the second mode conversion unit 9.

[0160] The second mode conversion unit 9 has a fourth port connected to the return-side operating unit 31A3 in the optical circuit 5R, a fifth port connected to the folded waveguide 7B, and a sixth port connected to the second waveguide 3. The second mode conversion unit 9 converts the first signal light TE1 from the forward-side operating unit 31A3 in the optical circuit 5R, after optical attenuation processing, into signal light TE0. The second mode conversion unit 9 outputs the converted signal light TE0 to the first mode conversion unit 8 via the folded waveguide 7B. The second mode conversion unit 9 outputs the second signal light TE0 from the optical circuit 5R, after optical attenuation processing, to the second waveguide 3.

[0161] In other words, the optical circuit 5R performs optical attenuation on the first signal light TE1 from the first mode conversion unit 8, and also performs optical attenuation on the second signal light TE0 from the second mode conversion unit 9 via the first mode conversion unit 8, thereby achieving a total of two optical attenuation processes in the same direction of propagation. As a result, even in higher-order modes, the VOA function can be increased by up to twofold, reducing power consumption and miniaturizing the optical device 1R while suppressing the effects of reflected light.

[0162] In the optical device 1R of Example 17, the second mode conversion unit 9 located downstream of the optical circuit 5R is connected to the first mode conversion unit 8 located upstream of the optical circuit 5R. As a result, the signal light passes through the PIN diode region of the working unit 31A3 (31B3) in the optical circuit 5R in the same direction of propagation, for the first time as signal light TM and for the second time as signal light TE, thus suppressing the influence of reflected light. In other words, it is possible to avoid a situation in which the reflected light of the folded signal light TE0 affects the signal light TE0 input from the first waveguide 2. Furthermore, it is possible to avoid a situation in which the reflected light of the folded signal light TE1 affects the first signal light TE1 passing through the optical circuit 5R. [Examples]

[0163] An embodiment for suppressing reflected light is described below as Example 18. Figure 27 is an explanatory diagram showing an example of the optical device 1S in Example 18. Note that components identical to those in the optical device 1P of Example 15 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted.

[0164] The optical device 1S shown in Figure 27 includes a first waveguide 2, a second waveguide 3, a first converter 4S, a first folded channel waveguide 10A, an optical circuit 5S, a second folded channel waveguide 10B, a second converter 6S, and a folded waveguide 7G. The optical circuit 5S includes a forward-side working section 31A4, a return-side working section 31B4, and a folded channel waveguide 32 that optically couples the forward-side working section 31A4 and the return-side working section 31B4.

[0165] The first conversion unit 4S has a first port connected to the first waveguide 2, a second port connected to the first folded channel waveguide 10A, and a third port connected to the folded waveguide 7G. The first conversion unit 4S converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the first folded channel waveguide 10A. The first folded channel waveguide 10A is connected to the forward-side operating unit 31A4 in the optical circuit 5S. The forward-side operating unit 31A4 has a forward-side first conversion waveguide 33A1 that optically couples the first folded channel waveguide 10A and the forward-side rib waveguide 53A, and a forward-side second conversion waveguide 33A2 that optically couples the forward-side rib waveguide 53A and the channel waveguide 32M.

[0166] The optical circuit 5S has a first port connecting the first folded channel waveguide 10A to the forward-side working section 31A4, and a second port connecting the second folded channel waveguide 10B to the return-side working section 31B4. The optical circuit 5S optically attenuates the signal light TM converted from the first conversion section 4S and outputs the signal light TM after optical attenuation to the second conversion section 6S. The return-side working section 31A4 has a first conversion waveguide 33B1 on the return side that optically couples the second folded channel waveguide 10B to the return-side rib waveguide 53B, and a second conversion waveguide 33B2 on the return side that optically couples the forward-side rib waveguide 53B to the channel waveguide 32M.

[0167] The second conversion unit 6S has a fourth port connected to the second folded channel waveguide 10B, a fifth port connected to the folded waveguide 7G, and a sixth port connected to the second waveguide 3. The second conversion unit 6S converts the signal light TM from the second folded channel waveguide 10B after optical attenuation into signal light TE, and outputs the converted signal light TE to the first folded channel waveguide 10A via the folded waveguide 7G and the first conversion unit 4S. The second folded channel waveguide 10B is connected to the forward-side operating unit 31A4 in the optical circuit 5S.

[0168] The optical circuit 5S optically attenuates the signal light TE converted from the first conversion unit 4S to the second conversion unit 6S, and outputs the signal light TE after optical attenuation to the second conversion unit 6S. The second conversion unit 6S then outputs the signal light TE from the return-side operating unit 31A4 within the optical circuit 5S to the second waveguide 3.

[0169] The first conversion unit 4S includes a first PR11 and a first PBS12. The first PR11 has a first port connected to the first waveguide 2 and a second port connected to the first PBS12. The first PR11 converts the signal light TE from the first waveguide 2 into signal light TM and outputs the converted signal light TM to the first PBS12.

[0170] The first PBS12 has a first port connected to the first PR11, a second port connected to the first folded channel waveguide 10A, and a third port connected to the folded channel waveguide 7G. The first PBS12 outputs signal light TM from the first PR11 to the first folded channel waveguide 10A, and also outputs signal light TE from the folded channel waveguide 7G to the first folded channel waveguide 10A.

[0171] The second conversion unit 6S includes a second PBS21G and a second PR22G. The second PBS21G has a fourth port connected to the second folded channel waveguide 10B, a fifth port connected to the second PR22G, and a sixth port connected to the second waveguide 3. The second PBS21G outputs the signal light TM from the second folded channel waveguide 10B to the second PR22G and outputs the signal light TE from the second folded channel waveguide 10B to the second waveguide 3.

[0172] The second PR22G has a first port connected to the second PBS21G and a second port connected to the folded waveguide 7G. It converts the signal light TM from the second PBS21G into signal light TE and outputs the converted signal light TE to the folded waveguide 7G.

[0173] The optical circuit 5S performs optical attenuation on the first signal light TM from the first folded channel waveguide 10A, and also performs optical attenuation on the second signal light TE from the first folded channel waveguide 10A, thereby achieving a total of two optical attenuation processes in the same direction of propagation. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1S while suppressing the effects of reflected light.

[0174] In the optical device 1S of Example 18, the second PR22G downstream of the optical circuit 5S is connected to the first PBS12 upstream of the optical circuit 5S. As a result, the signal light passes through the PIN diode region of the working section 31A4 (31B4) in the optical circuit 5S in the same direction of propagation, for the first time as signal light TM and for the second time as signal light TE, thus suppressing the effect of reflected backlight. In other words, it is possible to avoid a situation in which the reflected backlight of the aliased signal light TE affects the signal light TE input from the first waveguide 2. Furthermore, it is possible to avoid a situation in which the reflected backlight of the aliased signal light TM affects the first signal light TM passing through the optical circuit 5Q.

[0175] Furthermore, since the optical device 1S has the first conversion unit 4S, the optical circuit 5S, and the second conversion unit 6S arranged in parallel, the size of the optical device 1S can be reduced. [Examples]

[0176] An embodiment for suppressing reflected light is described below as Example 19. Figure 28 is an explanatory diagram showing an example of optical device 1T in Example 19. Note that components identical to those in optical device 1P of Example 15 are denoted by the same reference numerals, and the explanation of their overlapping components and operations is omitted.

[0177] The optical device 1T shown in Figure 28 includes a first waveguide 2, a second waveguide 3, a first mode conversion unit 8T, a first folded rib waveguide 10A1, an optical circuit 5T, a second folded rib waveguide 10B1, a second mode conversion unit 9T, and a folded waveguide 7G. The optical circuit 5T includes a forward-side working unit 31A4, a return-side working unit 31B4, and a folded channel waveguide 32M that optically couples the forward-side working unit 31A4 and the return-side working unit 31B4.

[0178] The first mode conversion unit 8T has a first port connected to the first waveguide 2, a second port connected to the first folded rib waveguide 10A1, and a third port connected to the folded waveguide 7G. The first mode conversion unit 8T performs higher-order mode conversion of the signal light TE0 from the first waveguide 2 to the signal light TE1. The first mode conversion unit 8T outputs the converted signal light TE1 to the first folded rib waveguide 10A1. The first folded rib waveguide 10A1 is connected to the forward-side operating unit 31A4 in the optical circuit 5T. The forward-side operating section 31A4 includes a first forward-side conversion waveguide 33A1 that optically couples the first folded rib waveguide 10A1 with the forward-side rib waveguide 53A, and a second forward-side conversion waveguide 33A2 that optically couples the forward-side rib waveguide 53A with the channel waveguide 32M.

[0179] The optical circuit 5T has a first port connecting the first folded rib waveguide 10A1 to the forward-side working section 31A4, and a second port connecting the second folded rib waveguide 10B1 to the return-side working section 31B4. The optical circuit 5T optically attenuates the signal light TE1 converted from the first mode conversion section 8T and outputs the signal light TE1 after optical attenuation to the second mode conversion section 9T. The return-side working section 31A4 has a first conversion waveguide 33B1 on the return side that optically couples the second folded rib waveguide 10B1 to the return-side rib waveguide 53B. The return-side working section 31A4 has a second conversion waveguide 33B2 on the return side that optically couples the return-side rib waveguide 53B to the folded channel waveguide 32M.

[0180] The second mode conversion unit 9T has a fourth port connected to the second folded rib waveguide 10B1, a fifth port connected to the folded waveguide 7G, and a sixth port connected to the second waveguide 3. The second mode conversion unit 9T converts the signal light TE1 from the second folded rib waveguide 10B1 after optical attenuation into signal light TE0, and outputs the converted signal light TE0 to the first folded rib waveguide 10A1 via the folded waveguide 7G and the first mode conversion unit 8T. The second folded rib waveguide 10B1 is connected to the forward-side operating unit 31A4 in the optical circuit 5T.

[0181] The optical circuit 5T optically attenuates the signal light TE0 converted by the second mode conversion unit 9T from the first mode conversion unit 8T, and outputs the signal light TE0 after optical attenuation to the second mode conversion unit 9T. The second mode conversion unit 9T then outputs the second signal light TE0 from the second folded rib waveguide 10B1 to the second waveguide 3.

[0182] The optical circuit 5T performs optical attenuation on the first signal light TE1 from the first folded rib waveguide 10A1, and also performs optical attenuation on the second signal light TE0 from the first folded rib waveguide 10A1, thereby achieving a total of two optical attenuation processes in the same direction of propagation. As a result, the functionality of the VOA can be doubled, reducing power consumption and miniaturizing the optical device 1T, while suppressing the effects of reflected light.

[0183] In the optical device 1T of Example 19, the second mode conversion unit 9T downstream of the optical circuit 5T is connected to the first mode conversion unit 8T upstream of the optical circuit 5T. As a result, the signal light TE1 passes through the PIN diode region of the working unit 31A4 (31B4) in the optical circuit 5T in the same direction of propagation, so the effect of reflected backlight can be suppressed. In other words, it is possible to avoid a situation in which the reflected backlight of the folded signal light TE0 affects the signal light TE0 input from the first waveguide 2. Furthermore, it is possible to avoid a situation in which the reflected backlight of the folded signal light TE1 affects the first signal light TE1 passing through the optical circuit 5T.

[0184] Furthermore, since the optical device 1T has the first mode conversion unit 8T, the optical circuit 5T, and the second mode conversion unit 9T arranged in parallel, the size of the optical device 1T can be reduced.

[0185] Furthermore, the optical device 1 in Embodiment 1 may be modified as appropriate, with the first mode conversion unit 8 replacing the first conversion unit 4 and the second mode conversion unit 9 replacing the second conversion unit 6.

[0186] Figure 29 is an explanatory diagram showing an example of an optical communication device 100. The optical communication device 100 shown in Figure 29 is, for example, an optical coherent transceiver that connects to an output optical fiber 104 and an input optical fiber 105, which are optical fibers. The optical communication device 100 includes an LD (Laser Diode) 101, a communication package 102, and a DSP (Digital Signal Processor) 103. The communication package 102 is, for example, the optical device 1 shown in Figure 1.

[0187] The DSP103 is an electrical component that performs digital signal processing. For example, the DSP103 performs processing such as encoding the transmission data and outputs a data signal corresponding to the processed transmission data to the transmission circuit in the communication package 102. The DSP103 also performs processing such as decoding on the received data corresponding to the data signal obtained from the receiving circuit in the communication package 102.

[0188] LD101 is, for example, an ITLA (Integrated Tunable Laser Assembly) equipped with a tunable laser diode, which generates light of a predetermined wavelength and supplies it to an optical modulator in the transmitting circuit and an optical receiver in the receiving circuit.

[0189] For the sake of explanation, the optical device 102 is shown as an example where both a transmitting circuit and a receiving circuit are built in. However, it may also be equipped with only one of the transmitting circuit or the receiving circuit. If only the transmitting circuit is built in, it is an optical transmitter, and if only the receiving circuit is built in, it is an optical receiver.

[0190] The embodiments including this example are described above, and the following additional notes are disclosed.

[0191] (Note 1) A first waveguide into which a first signal light having a first optical characteristic is input, A first conversion unit connected to the first waveguide converts the first signal light from the first waveguide into a second signal light having second optical characteristics, An optical circuit connected to the first conversion unit, through which the converted second signal light from the first conversion unit passes, performs the first optical processing on the second signal light, A second conversion unit connected to the optical circuit converts the second signal light from the optical circuit after the first optical processing into a third signal light having the first optical characteristics, The optical circuit performs a second optical processing on the third signal light by passing the converted third signal light from the second conversion unit through it, A second waveguide that outputs a third signal light after the second optical processing from the aforementioned optical circuit, An optical device characterized by having (Note 2) The first conversion unit described above is A first port connected to the first waveguide, A second port connected to the aforementioned optical circuit, It has a third port connected to the second waveguide, The second conversion unit described above is: A fourth port connected to the aforementioned optical circuit, A fifth port connected to one side of the folded waveguide connected to the second conversion unit, A sixth port connected to the other side of the aforementioned folded waveguide and The optical device according to Appendix 1, characterized by having the following features. (Note 3) The first optical characteristic and the second optical characteristic represent the polarization state, The first conversion unit described above is: A first PR (Polarization Rotator) is connected to the first waveguide and converts the first signal light from the first waveguide into the second signal light, It includes a first Polarization Beam Splitter (PBS) which is connected to the first PR and outputs the second signal light from the first PR to the optical circuit, and is also connected to the optical circuit and outputs the third signal light from the optical circuit after the second optical processing to the second waveguide, The second conversion unit described above is: A second PBS is connected to the aforementioned optical circuit and outputs the second signal light from the optical circuit after the first photoprocessing to a second PR, The system includes a second PR that connects to the second PBS, converts the second signal light from the second PBS after the first photoprocessing into the third signal light, and outputs the converted third signal light back to the second PBS, The PBS described above is The optical device according to Appendix 1, characterized in that it outputs the third signal light, after conversion from the second PR, to the optical circuit. (Note 4) The first PBS mentioned above is The first port connected to the first PR, A second port connected to the aforementioned optical circuit, It has a third port connected to the second waveguide, The PBS described above is A fourth port connected to the aforementioned optical circuit, A second PR that connects to one side of the folded waveguide, and a fifth port that connects to the second PR, A sixth port connected to the other side of the aforementioned folded waveguide and The optical device according to Appendix 3, characterized by having the following features. (Note 5) The first optical characteristic and the second optical characteristic represent the polarization state, The first conversion unit described above is: A first PR (Polarization Rotator) is connected to the first waveguide and converts the first signal light from the first waveguide into the second signal light, It includes a first PBS (Polarization Beam Splitter) that is connected to the first PR and outputs the second signal light from the first PR to a port of the optical circuit, The second conversion unit described above is: A second PBS is connected to the optical circuit and outputs the second signal light from the optical circuit after the first optical processing to the second PR, and outputs the third signal light from the optical circuit after the second optical processing to the second waveguide, The system includes a second PR that connects to the second PBS and converts the second signal light from the second PBS after the first photoprocessing into the third signal light, and also connects to the first PBS and outputs the converted third signal light to the first PBS, The first PBS described above is The optical device according to Appendix 1, characterized in that the third signal light, after conversion from the second PR, is output to the port of the optical circuit. (Note 6) The first PBS mentioned above is The first port connected to the first PR, A second port connected to the aforementioned optical circuit, It has a third port connected to a folded waveguide which is connected to the second PR, The PBS described above is A fourth port connected to the aforementioned optical circuit, A fifth port connected to the second PR, A sixth port connected to the second waveguide and The optical device according to Appendix 5, characterized by having the following features. (Note 7) The first optical characteristic and the second optical characteristic represent the mode state, The first conversion unit described above is: The system includes a first mode conversion unit that is connected to the first waveguide and converts the first signal light from the first waveguide into a second signal light, and is also connected to the optical circuit and outputs the second signal light after mode conversion to the optical circuit, The second conversion unit described above is: The device has a second mode conversion unit which is connected to the optical circuit and converts the second signal light from the optical circuit after the first optical processing into the third signal light, and also connects to the optical circuit and outputs the third signal light after mode conversion back to the optical circuit. The first mode conversion unit described above is: The optical device according to Appendix 1, characterized in that the third signal light from the optical circuit after the second optical processing is output to the second waveguide. (Note 8) The first mode conversion unit is, A first port connected to the first waveguide, A second port connected to the aforementioned optical circuit, It has a third port connected to the second waveguide, The second mode conversion unit is, A fourth port connected to the aforementioned optical circuit, A fifth port connected to one side of the folded waveguide, A sixth port connected to the other side of the aforementioned folded waveguide and The optical device according to Appendix 7, characterized by having the following features. (Note 9) The first optical characteristic and the second optical characteristic represent the mode state, The first conversion unit described above is: The system includes a first mode conversion unit that connects to the first waveguide and converts the first signal light from the first waveguide into the second signal light, and also connects to the optical circuit and outputs the converted second signal light to a port of the optical circuit. The second conversion unit described above is: The system includes a second mode conversion unit which is connected to the optical circuit and converts the second signal light from the optical circuit after the first optical processing into the third signal light, and is connected to the first mode conversion unit and outputs the converted third signal light to the first mode conversion unit, and outputs the third signal light from the optical circuit after the second optical processing to the second waveguide, The first mode conversion unit described above is: The optical device according to Appendix 1, characterized in that the second mode conversion unit outputs the first signal light after the first optical processing, after mode conversion, to the port of the optical circuit. (Note 10) The first mode conversion unit is, A first port connected to the first waveguide, A second port connected to the aforementioned optical circuit, It has a third port connected to a folded waveguide connected to the second mode conversion unit, The second mode conversion unit is, A fourth port connected to the aforementioned optical circuit, A fifth port connected to the aforementioned folded waveguide, A sixth port connected to the second waveguide and The optical device according to Appendix 9, characterized by having the following features. (Note 11) The optical circuit is, The forward-side working section includes a forward-side rib waveguide connected to the first conversion section, The return-side operating section includes a return-side rib waveguide connected to the second conversion section, A folded waveguide including a rib waveguide connecting the forward operating section and the return operating section, The optical device according to Appendix 1, characterized by having the following features. (Note 12) The optical circuit is, The forward-side working section includes a forward-side rib waveguide connected to the first conversion section, The return-side operating section includes a return-side rib waveguide connected to the second conversion section, A folding waveguide including a channel waveguide connecting the forward operating section and the return operating section, The optical device according to Appendix 1, characterized by having the following features. (Note 13) The optical circuit is, The forward-side working section includes a forward-side rib waveguide connected to the first conversion section, The return-side operating section includes a return-side rib waveguide connected to the second conversion section, A folding waveguide including a channel waveguide connecting the forward operating section and the return operating section, A forward-side conversion waveguide includes a waveguide between the forward-side rib waveguide and the channel waveguide, in which the slab width gradually narrows from the forward-side rib waveguide to the channel waveguide, A return-side conversion waveguide includes a waveguide between the return-side rib waveguide and the channel waveguide, in which the slab width gradually narrows from the return-side rib waveguide to the channel waveguide, The optical device according to Appendix 1, characterized by having the following features. (Note 14) The optical circuit is, A rib waveguide connecting the first conversion unit and the second conversion unit, A first electrode electrically connected to the first slab of the rib waveguide, It has a second electrode electrically connected to the second slab of the rib waveguide, The first slab described above is The rib waveguide has a first portion closer to the rib and a second portion on the side connected to the first electrode, wherein the doping concentration of the second portion is higher than that of the first portion. The second slab is, The optical device according to Appendix 1, comprising a first portion of the rib waveguide closer to the rib and a second portion connected to the second electrode, wherein the doping concentration of the second portion is higher than that of the first portion. (Note 15) The optical circuit is, The forward-side working section includes a forward-side rib waveguide connected to the first conversion section, The return-side operating section includes a return-side rib waveguide connected to the second conversion section, A folding waveguide including a channel waveguide connecting the forward operating section and the return operating section, It has, The aforementioned forward-side operating part is, The forward-side rib waveguide connected to the first conversion unit, A first electrode electrically connected to the first slab of the forward-side rib waveguide, It has a second electrode electrically connected to the second slab of the forward-side rib waveguide, The return-path side operating part is, The return-side rib waveguide connected to the second conversion unit, A first electrode electrically connected to the first slab of the return-side rib waveguide, The optical device according to Appendix 1, characterized by having a second electrode electrically connected to the second slab of the return-side rib waveguide. (Note 16) The optical circuit is, The forward-side working section includes a forward-side rib waveguide connected to the first conversion section, The return-side operating section includes a return-side rib waveguide connected to the second conversion section, A folding waveguide including a channel waveguide connecting the forward operating section and the return operating section, It has, The forward-side operating part and the return-side operating part are, A first electrode is electrically connected to the first slab of the forward-side rib waveguide and to the first slab of the return-side rib waveguide, The optical device according to Appendix 1, characterized in that it has a second electrode that is electrically connected to the second slab of the forward-side rib waveguide and electrically connected to the second slab of the return-side rib waveguide. (Note 17) The optical circuit is, The optical device according to Appendix 1, characterized in that it is a variable attenuator that adjusts the amount of attenuation of the signal light passing through it in accordance with an electrical signal. (Note 18) The optical circuit is, The optical device according to Appendix 1, characterized in that it is a modulator that adjusts the amount of modulation of the signal light passing through it in accordance with an electrical signal. (Note 19) The optical circuit is, The optical device according to Appendix 1, characterized in that it is a phase shifter that adjusts the phase amount of the signal light passing through in accordance with an electrical signal. (Note 20) An optical transmitting device comprising a light source that emits a first signal light, and an optical transmitter that optically processes the first signal light from the light source in accordance with an electrical signal and transmits a third signal light after optical processing, The aforementioned optical transmitter is A first waveguide into which the first signal light having the first optical characteristics is input, A first conversion unit connected to the first waveguide converts the first signal light from the first waveguide into a second signal light having second optical characteristics, An optical circuit connected to the first conversion unit, through which the converted second signal light from the first conversion unit passes, performs the first optical processing on the second signal light, A second conversion unit connected to the optical circuit converts the second signal light from the optical circuit after the first optical processing into a third signal light having the first optical characteristics, The optical circuit performs a second optical processing on the third signal light by passing the converted third signal light from the second conversion unit through it, A second waveguide that transmits the third signal light after the second optical processing from the aforementioned optical circuit, An optical transmitting device characterized by having the following features. (Note 21) An optical receiving device comprising: a light source that emits a first signal light; an optical device that optically processes the first signal light from the light source in accordance with an electrical signal and generates a third signal light after optical processing; and an optical receiver that obtains a received signal from received light using the third signal light after optical processing, The optical device is A first waveguide into which the first signal light having the first optical characteristics is input, A first conversion unit connected to the first waveguide converts the first signal light from the first waveguide into a second signal light having second optical characteristics, An optical circuit connected to the first conversion unit, through which the converted second signal light from the first conversion unit passes, performs the first optical processing on the second signal light, A second conversion unit connected to the optical circuit converts the second signal light from the optical circuit after the first optical processing into a third signal light having first optical characteristics, The optical circuit performs a second optical processing on the third signal light by passing the converted third signal light from the second conversion unit through it, A second waveguide outputs the third signal light, after the second optical processing from the optical circuit, to the receiver. An optical receiving device characterized by having the following features. [Explanation of Symbols]

[0192] 1 Optical devices 2. First waveguide 3. Second waveguide 4. First conversion section 5 Optical circuit 6. Second conversion section 7. Folding waveguide 8. First mode conversion section 9. Second mode conversion section 11. First PR 12. The First PBS 21 The Second PBS 22. Second PR 31A Acting part on the forward path 31B Acting part on the return path 32 Folding Waveguide 53 Rib Waveguides 54A First slab 54B Second Slab 55A First electrode (P electrode) 55B Second electrode (N electrode)

Claims

1. A first waveguide into which a first signal light having a first optical characteristic is input, A first conversion unit connected to the first waveguide converts the first signal light from the first waveguide into a second signal light having second optical characteristics, An optical circuit connected to the first conversion unit, through which the converted second signal light passes from the first conversion unit, performs the first optical processing on the second signal light, A second conversion unit connected to the optical circuit converts the second signal light from the optical circuit after the first optical processing into a third signal light having the first optical characteristics, The optical circuit performs a second optical processing on the third signal light having the first optical characteristics by passing the converted third signal light from the second conversion unit through it, A second waveguide that outputs the third signal light having the first optical characteristics after a second optical processing from the optical circuit, An optical device characterized by having the following features.

2. The first conversion unit is, A first port connected to the first waveguide, A second port connected to the aforementioned optical circuit, It has a third port connected to the second waveguide, which outputs the third signal light having the first optical characteristics after a second optical processing from the optical circuit to the second waveguide, The second conversion unit is, A fourth port connected to the optical circuit, A fifth port connected to one side of the folded waveguide, A sixth port connected to the other side of the aforementioned folded waveguide and The optical device according to claim 1, characterized by having the following features.

3. The first optical characteristic and the second optical characteristic represent the polarization state, The first conversion unit is, A first PR (Polarization Rotator) is connected to the first waveguide and converts the first signal light from the first waveguide into the second signal light, The system includes a first Polarization Beam Splitter (PBS) which is connected to the first PR and outputs the second signal light from the first PR to the optical circuit, and is also connected to the optical circuit and outputs the third signal light from the optical circuit after the second optical processing to the second waveguide, The second conversion unit is, A second PBS (Polarization Beam Splitter) is connected to the aforementioned optical circuit and outputs the second signal light from the optical circuit after the first optical processing to a second PR (Polarization Rotator), The system includes a second PR that is connected to the second PBS, converts the second signal light from the second PBS after the first optical processing into the third signal light, and outputs the converted third signal light back to the second PBS, The second PBS described above is The optical device according to claim 1, characterized in that the third signal light, converted from the second PR, is output to the optical circuit.

4. The first PBS mentioned above is, The first port connected to the first PR, A second port connected to the aforementioned optical circuit, It has a third port connected to the second waveguide, The second PBS described above is A fourth port connected to the optical circuit, A second PR connected to one side of the folded waveguide, and a fifth port connected to the second PR, A sixth port connected to the other side of the aforementioned folded waveguide and The optical device according to claim 3, characterized by having the following features.

5. The first optical characteristic and the second optical characteristic represent the polarization state, The first conversion unit is, A first PR (Polarization Rotator) is connected to the first waveguide and converts the first signal light from the first waveguide into the second signal light, It includes a first PBS (Polarization Beam Splitter) that is connected to the first PR and outputs the second signal light from the first PR to a port of the optical circuit, The second conversion unit is, A second Polarization Beam Splitter (PBS) is connected to the aforementioned optical circuit and outputs the second signal light from the optical circuit after the first optical processing to a second Polarization Rotator (PR), and outputs the third signal light from the optical circuit after the second optical processing to a second waveguide. The system includes a second PR that is connected to the second PBS and converts the second signal light from the second PBS after the first optical processing into the third signal light, and a second PR that is connected to the first PBS and outputs the converted third signal light to the first PBS, The first PBS mentioned above is, The optical device according to claim 1, characterized in that the third signal light, after conversion from the second PR, is output to the port of the optical circuit.

6. The first PBS mentioned above is, The first port connected to the first PR, A second port connected to the aforementioned optical circuit, It has a third port connected to a folded waveguide that is connected to the second PR, The second PBS described above is A fourth port connected to the optical circuit, A fifth port connected to the second PR, A sixth port connected to the second waveguide and The optical device according to claim 5, characterized by having the following features.

7. The first optical characteristic and the second optical characteristic represent the mode state, The first conversion unit is, The system includes a first mode conversion unit that is connected to the first waveguide and converts the first signal light from the first waveguide into the second signal light, and is also connected to the optical circuit and outputs the converted second signal light to the optical circuit, The second conversion unit is, The device has a second mode conversion unit which is connected to the optical circuit and converts the second signal light from the optical circuit after the first optical processing into the third signal light, and also connects to the optical circuit and outputs the third signal light after mode conversion back to the optical circuit. The first mode conversion unit is, The optical device according to claim 1, characterized in that the third signal light after the second optical processing from the optical circuit is output to the second waveguide.

8. The first mode conversion unit is, A first port connected to the first waveguide, A second port connected to the aforementioned optical circuit, It has a third port connected to the second waveguide, The second mode conversion unit is, A fourth port connected to the optical circuit, A fifth port connected to one side of the folded waveguide, A sixth port connected to the other side of the aforementioned folded waveguide and The optical device according to claim 7, characterized by having the following features.

9. The first optical characteristic and the second optical characteristic represent the mode state, The first conversion unit is, The system includes a first mode conversion unit that is connected to the first waveguide and converts the first signal light from the first waveguide into the second signal light, and is also connected to the optical circuit and outputs the converted second signal light to a port of the optical circuit, The second conversion unit is, The optical circuit has a second mode conversion unit which is connected to the optical circuit and converts the second signal light after the first optical processing from the optical circuit into the third signal light, and is connected to the first mode conversion unit and outputs the third signal light after the mode conversion to the first mode conversion unit, and outputs the third signal light after the second optical processing from the optical circuit to the second waveguide. The first mode conversion unit is, The optical device according to claim 1, characterized in that the second mode conversion unit outputs the third signal light after the first optical processing, after mode conversion, to the port of the optical circuit.

10. The first mode conversion unit is, A first port connected to the first waveguide, A second port connected to the aforementioned optical circuit, It has a third port connected to a folded waveguide connected to the second mode conversion unit, The second mode conversion unit is, A fourth port connected to the optical circuit, A fifth port connected to the aforementioned folded waveguide, A sixth port connected to the second waveguide and The optical device according to claim 9, characterized by having the following features.

11. An optical transmitting device comprising: a light source that emits a first signal light; and an optical transmitter that optically processes the first signal light from the light source in accordance with an electrical signal and transmits a third signal light after optical processing, The aforementioned optical transmitter is A first waveguide into which the first signal light having the first optical characteristics is input, A first conversion unit connected to the first waveguide converts the first signal light from the first waveguide into a second signal light having second optical characteristics, An optical circuit connected to the first conversion unit, through which the converted second signal light passes from the first conversion unit, performs the first optical processing on the second signal light, A second conversion unit connected to the optical circuit converts the second signal light from the optical circuit after the first optical processing into a third signal light having the first optical characteristics, The optical circuit performs a second optical processing on the third signal light having the first optical characteristics by passing the converted third signal light from the second conversion unit through it, A second waveguide that outputs the third signal light having the first optical characteristics after a second optical processing from the optical circuit, An optical transmission device characterized by having the following features.

12. An optical receiving device comprising: a light source that emits a first signal light; an optical device that optically processes the first signal light from the light source in accordance with an electrical signal and generates a third signal light after optical processing; and an optical receiver that obtains a received signal from received light using the third signal light after optical processing, The optical device is A first waveguide into which the first signal light having the first optical characteristics is input, A first conversion unit connected to the first waveguide converts the first signal light from the first waveguide into a second signal light having second optical characteristics, An optical circuit connected to the first conversion unit, through which the converted second signal light passes from the first conversion unit, performs the first optical processing on the second signal light, A second conversion unit connected to the optical circuit converts the second signal light from the optical circuit after the first optical processing into a third signal light having the first optical characteristics, The optical circuit performs a second optical processing on the third signal light having the first optical characteristics by passing the converted third signal light from the second conversion unit through it, A second waveguide outputs the third signal light having the first optical characteristics after a second optical processing from the optical circuit to the optical receiver, An optical receiving device characterized by having the following features.

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