Optical device, optical transmitter, and optical receiver

Abstract

To provide an optical device in which an element size is reduced in size.SOLUTION: An optical device includes a first rib type optical waveguide including a first doped region and a second doped region, a second rib type optical waveguide including a third doped region and a fourth doped region, and a bending waveguide that optically connects between the first rib type optical waveguide and the second rib type optical waveguide. The optical device includes a first electrode electrically connected to the first doped region, a second electrode electrically connected to the second doped region, a third electrode electrically connected to the third doped region, and a fourth electrode electrically connected to the fourth doped region. The bending waveguide includes a first bending electrode electrically connecting between the first electrode and the third electrode, and a second bending electrode electrically connecting between the second electrode and the fourth electrode. The distance between a rib waveguide of the bending waveguide and the first bending electrode disposed on an outer peripheral side of the bending waveguide is longer than the distance between a rib waveguide of the first rib type optical waveguide and the first electrode disposed on the same side as the outer peripheral side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, the demand for optical fiber communications has increased along with the increase in communication capacity. Therefore, the development of optical devices, typified by silicon photonics, has been actively pursued. Known examples of such optical devices include optical attenuators such as variable optical attenuators (VOAs), which attenuate the intensity of signal light propagating through an optical waveguide in response to an electrical signal.

[0003] Fig. 16 is a schematic plan view showing an example of an optical device 100, and Fig. 17 is a schematic cross-sectional view taken along line AA shown in Fig. 16. A VOA 110, which is the optical device 100 shown in Fig. 16, has a Si substrate 121, a rib-type optical waveguide 102 formed on the Si substrate 121, and electrodes 103 connected to both sides of the rib-type optical waveguide 102. Furthermore, the VOA 110 has a cladding layer 122 formed on the Si substrate 121 and surrounding the rib-type optical waveguide 102 and the two electrodes 103.

[0004] The rib-type optical waveguide 102 has, for example, a waveguide 102A forming a Si core, and a first slab region 102D and a second slab region 102E on either side of the waveguide 102A. The rib-type optical waveguide 102 has an optical input section 102B and an optical output section 102C. The optical input section 102B is the input stage of the rib-type optical waveguide 102 that inputs signal light to the waveguide 102A. The optical output section 102C is the output stage of the rib-type optical waveguide 102 that outputs signal light from the waveguide 102A. A P-doped region 102F is formed at the outer end of the first slab region 102D, and an N-doped region 102G is formed at the outer end of the second slab region 102E. The waveguide 102A, the first slab region 102D, and the second slab region 102E are undoped regions. The rib-type optical waveguide 102 has a PIN diode structure with the P-doped region 102F, the undoped region, and the N-doped region 102G.

[0005] The electrode 103 includes a first electrode 103A electrically connected to the P-doped region 102F and a second electrode 103B electrically connected to the N-doped region 102G. The first electrode 103A serves as a signal electrode connected to an input pad 104 to which a voltage is applied, and the second electrode 103B serves as a ground electrode connected to a ground pad 105.

[0006] In the optical device 100, the input pad 104 is located near the center of the VOA 110, and power is supplied from the input pad 104 to the first electrode 103A via an input via 104A. In the optical device 100, the ground pad 105 is located near the center of the VOA 110, and grounding is provided from the second electrode 103B to the ground pad 105 via a ground via 105A.

[0007] When a positive voltage is applied to the first electrode 103A from the input pad 104, a current flows from the first electrode 103A to the second electrode 103B, and therefore a current flows in the rib-type optical waveguide 102 disposed between the first electrode 103A and the second electrode 103B. As a result, the signal light guided through the rib-type optical waveguide 102 is absorbed by free carrier absorption of the current flowing through the rib-type optical waveguide 102, and the intensity of the signal light is attenuated. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-145184 [Patent Document 2] US Patent Application Publication No. 2007 / 0172189 [Patent Document 3] Special Publication No. 2022-516194 Summary of the Invention [Problem to be solved by the invention]

[0009] In the optical device 100, in order to reduce the driving power of the VOA, it is necessary to increase the length of the electrodes and the PIN region in the VOA. Therefore, in the optical device 100, the VOA has a linear structure as shown in Fig. 16, which increases the size of the element. Furthermore, in the optical device 100, the size of the element is not limited to the PIN region, and in fact, reduction in element size is required even in the PIP region or NIN region.

[0010] In one aspect, an object is to provide an optical device or the like that is capable of reducing the element size. [Means for solving the problem]

[0011] An optical device of one embodiment includes a first rib-type optical waveguide disposed on a substrate, the first rib-type optical waveguide having a first doped region formed in a first slab region, a second doped region formed in a second slab region, and a first rib waveguide formed between the first and second slab regions. The optical device also includes a second rib-type optical waveguide disposed on the substrate, the second rib-type optical waveguide having a third doped region formed in a third slab region, a fourth doped region formed in a fourth slab region, and a second rib waveguide formed between the third and fourth slab regions. The optical device also includes a bent waveguide disposed on the substrate, the bent waveguide having a third rib waveguide optically connecting the first rib-type optical waveguide and the second rib-type optical waveguide. The optical device includes a first electrode conducting current to the first doped region, a second electrode conducting current to the second doped region, a third electrode conducting current to the third doped region, and a fourth electrode conducting current to the fourth doped region. The optical device also includes a first bend electrode provided adjacent to the bend waveguide and conducting current between the first electrode and the third electrode, and a second bend electrode provided adjacent to the bend waveguide and conducting current between the second electrode and the fourth electrode. The distance between the third rib waveguide and the first bend electrode, which is located on the outer periphery of the bend waveguide, is longer than the distance between the first rib waveguide and the first electrode, which is located on the same side as the outer periphery. [Effects of the Invention]

[0012] According to one aspect, the size of the element is reduced. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic plan view showing an example of an optical device according to a first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line AA shown in FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view taken along line BB shown in FIG. [Figure 4] FIG. 4 is a schematic plan view illustrating an example of an optical device according to a second embodiment. [Figure 5] FIG. 5 is a schematic cross-sectional view taken along line AA shown in FIG. [Figure 6] FIG. 6 is a schematic cross-sectional view taken along line BB shown in FIG. [Figure 7] FIG. 7 is a schematic plan view illustrating an example of an optical device according to a third embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view taken along line AA shown in FIG. [Figure 9] FIG. 9 is a schematic cross-sectional view taken along line BB shown in FIG. [Figure 10] FIG. 10 is an explanatory diagram showing an example of an optical transceiver that employs the optical device of this embodiment. [Figure 11] FIG. 11 is a schematic plan view showing an example of the optical device of Comparative Example 1. As shown in FIG. [Figure 12] FIG. 12 is a schematic cross-sectional view taken along line AA shown in FIG. [Figure 13] FIG. 13 is a schematic plan view showing an example of the optical device of Comparative Example 2. As shown in FIG. [Figure 14] FIG. 14 is a schematic cross-sectional view taken along line AA shown in FIG. [Figure 15] FIG. 15 is a schematic cross-sectional view taken along line BB shown in FIG. [Figure 16] FIG. 16 is a schematic plan view showing an example of an optical device. [Figure 17] FIG. 17 is a schematic cross-sectional view taken along line AA shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] In optical devices, reducing the driving power of the optical device requires increasing the length of the electrodes and PIN regions in the optical device, which results in an increase in element size. Therefore, the optical device of Comparative Example 1, in which the electrodes and PIN regions are divided, can be considered as a method for reducing the element size of the optical device.

[0015] [Comparative Example 1] Fig. 11 is a schematic plan view showing an example of an optical device 200 of Comparative Example 1, and Fig. 12 is a schematic cross-sectional view taken along line AA shown in Fig. 11. The optical device 200 shown in Fig. 11 is, for example, an optical attenuator such as a VOA (Variable Optical Attenuator). The optical device 200 has a first VOA 210A with a linear structure, a second VOA 210B with a linear structure, and a curved waveguide 220 that optically connects the first VOA 210A and the second VOA 210B. The optical device 200 is a VOA with an L-shaped structure.

[0016] 12 includes a Si substrate 231, a first rib-type optical waveguide 210A1 formed on the Si substrate 231, and a first electrode 214A and a second electrode 214B electrically connected to both sides of the first rib-type optical waveguide 210A1. The first VOA 210A is formed on the Si substrate 231 and includes a cladding layer 232 surrounding the first rib-type optical waveguide 210A1, the first electrode 214A, and the second electrode 214B.

[0017] The first rib type optical waveguide 210A1 is formed of, for example, Si. The first rib type optical waveguide 210A1 has a waveguide 211A that forms a core. The waveguide 211A has a linear structure with the same width. The first rib type optical waveguide 210A1 has an optical input section 211A1 and an optical output section 211A2. The optical input section 211A1 is an input stage of the first rib type optical waveguide 210A1 that inputs signal light to the waveguide 211A. The optical output section 211A2 is an output stage of the first rib type optical waveguide 210A1 that outputs signal light from the waveguide 211A.

[0018] The first rib-type optical waveguide 210A1 has a first slab region 212A formed on one outer side of the waveguide 211A and a second slab region 212B formed on the other outer side of the waveguide 211A. The first rib-type optical waveguide 210A1 has a P-doped region 213A formed in the first slab region 212A and an N-doped region 213B formed in the second slab region 212B. The P-doped region 213A is a region outside the first slab region 212A that is P-doped and electrically connected to the first electrode 214A. The N-doped region 213B is a region outside the second slab region 212B that is N-doped and electrically connected to the second electrode 214B.

[0019] In the first rib type optical waveguide 210A1, the waveguide 211A, the first slab region 212A, and the second slab region 212B are undoped regions. The rib type optical waveguide 210A1 has a PIN diode structure with, for example, a P-doped region 213A, an undoped region, and an N-doped region 213B.

[0020] The electrodes include a first electrode 214A electrically connected to the P-doped region 213A and a second electrode 214B electrically connected to the N-doped region 213B. The first electrode 214A is a signal electrode connected to a first input pad 241A to which a voltage is applied. The first electrode 214A is made of a material having electrical resistance, for example, a metal such as aluminum or a semiconductor material such as silicon. The second electrode 214B is a ground electrode connected to a first ground pad 242A. The second electrode 214B is also made of a material having electrical resistance, for example, a metal such as aluminum or a semiconductor material such as silicon or germanium.

[0021] The cladding layer 232 is formed of, for example, SiO2. The first input pad 241A is an electrode pad connected to the first electrode 214A via an input via 241A1. The first ground pad 242A is an electrode pad connected to the second electrode 214B via a ground via 242A1.

[0022] 12 includes a Si substrate 231, a second rib-type optical waveguide 210B1 formed on the Si substrate 231, and a third electrode 214C and a fourth electrode 214D electrically connected to both sides of the second rib-type optical waveguide 210B1. The second VOA 210B is formed on the Si substrate 231 and includes a cladding layer 232 surrounding the second rib-type optical waveguide 210B1, the third electrode 214C, and the fourth electrode 214D.

[0023] The second rib type optical waveguide 210B1 is formed of, for example, Si. The second rib type optical waveguide 210B1 has a waveguide 211B that forms a core. The waveguide 211B has a linear structure with the same width. The second rib type optical waveguide 210B1 has an optical input section 211B1 and an optical output section 211B2. The optical input section 211B1 is an input stage of the second rib type optical waveguide 210B1 that inputs signal light to the waveguide 211B. The optical output section 211B2 is an output stage of the second rib type optical waveguide 210B1 that outputs signal light from the waveguide 211B.

[0024] The second rib-type optical waveguide 210B1 has a third slab region 212C formed on one outer side of the waveguide 211B and a fourth slab region 212D formed on the other outer side of the waveguide 211B. The second rib-type optical waveguide 210B1 has a P-doped region 213C formed in the third slab region 212C and an N-doped region 213D formed in the fourth slab region 212D. The P-doped region 213C is a region outside the third slab region 212C that is P-doped and electrically connected to the third electrode 214C. The N-doped region 213D is a region outside the fourth slab region 212D that is N-doped and electrically connected to the fourth electrode 214D.

[0025] In the second rib type optical waveguide 210B1, the waveguide 211B, the third slab region 212C, and the fourth slab region 212D are undoped regions. The second rib type optical waveguide 210B1 has a PIN diode structure with, for example, a P-doped region 213C, an undoped region, and an N-doped region 213D.

[0026] The electrodes include a third electrode 214C electrically connected to the P-doped region 213C and a fourth electrode 214D electrically connected to the N-doped region 213D. The third electrode 214C is a signal electrode connected to the second input pad 241B to which a voltage is applied. The third electrode 214C is made of a material having electrical resistance, for example, a metal such as aluminum or a semiconductor material such as silicon. The fourth electrode 214D is a ground electrode connected to the second ground pad 242B. The fourth electrode 214D is also made of a material having electrical resistance, for example, a metal such as aluminum or a semiconductor material such as silicon or germanium.

[0027] The cladding layer 232 is formed of, for example, SiO2. The second input pad 241B is an electrode pad connected to the third electrode 214C via an input via 241B1. The second ground pad 242B is an electrode pad connected to the fourth electrode 214D via a ground via 242B1.

[0028] The curved waveguide 220 is formed of, for example, Si. The curved waveguide 220 has a waveguide 221 forming a core. The waveguide 221 is a curved optical waveguide that optically connects the waveguide 211A of the first rib-type optical waveguide 210A1 and the waveguide 211B of the second rib-type optical waveguide 210B1. The curved waveguide 220 has a fifth slab region 222A formed on one outer side of the waveguide 221 and a sixth slab region 222B formed on the other outer side of the waveguide 221.

[0029] In the first VOA 210A, the first input pad 241A is located near the center of the first VOA 210A, and power is supplied from the first input pad 241A to the first electrode 214A via the input via 241A1. In the first VOA 210A, the first ground pad 242A is located near the center of the first VOA 210A, and power is supplied from the second electrode 214B to the first ground pad 242A via the ground via 242A1.

[0030] When a voltage is applied to the first electrode 214A from the first input pad 241A, a current flows from the first electrode 214A to the second electrode 214B. Then, a current flows in the waveguide 211A in the first rib-type optical waveguide 210A1 disposed between the first electrode 214A and the second electrode 214B. As a result, in the first VOA 210A, the signal light guided in the waveguide 211A is absorbed by free carrier absorption of the current flowing in the waveguide 211A, and the intensity of the signal light is attenuated.

[0031] In the second VOA 210B, the second input pad 241B is located near the center of the second VOA 210B, and power is fed from the second input pad 241B to the third electrode 214C via an input via 241B1. In the second VOA 210B, the second ground pad 242B is located near the center of the second VOA 210B, and power is fed from the fourth electrode 214D to the second ground pad 242B via a ground via 242B1.

[0032] When a voltage is applied to the third electrode 214C from the second input pad 241B, a current flows from the third electrode 214C to the fourth electrode 214D. Then, a current flows in the waveguide 211B in the second rib-type optical waveguide 210B disposed between the third electrode 214C and the fourth electrode 214D. As a result, in the second VOA 210B1, the signal light guided in the waveguide 211B is absorbed by free carrier absorption of the current flowing in the waveguide 211B, and the intensity of the signal light is attenuated.

[0033] The optical device 200 of Comparative Example 1 has an L-shaped structure, which is divided into a first VOA 210A and a second VOA 210B, and the first VOA 210A and the second VOA 210B are optically connected by a bent waveguide 220. As a result, the element size of the optical device 200 can be reduced.

[0034] However, the optical device 200 of Comparative Example 1 has a first connection line electrically connecting the first input pad 241A and the second input pad 241B, and a second connection line electrically connecting the first ground pad 242A and the second ground pad 242B. The first connection line and the second connection line are generated in a layer different from the electrode layer, resulting in a two-layer structure. This results in a complex wiring pattern. Therefore, the optical device 300 of Comparative Example 2, in which the wiring pattern is simplified, will be described.

[0035] Comparative Example 2 Fig. 13 is a schematic plan view showing an example of an optical device 300 of Comparative Example 2, Fig. 14 is a schematic cross-sectional view taken along line AA shown in Fig. 13, and Fig. 15 is a schematic cross-sectional view taken along line BB shown in Fig. 13. Note that the same components as those in the optical device 200 of Comparative Example 1 are given the same reference numerals, and redundant explanations of the components and operations will be omitted.

[0036] The optical device 200 of Comparative Example 1 and the optical device 300 of Comparative Example 2 differ in that a first bending electrode 224A and a second bending electrode 224B are provided in addition to the bending waveguide 220A.

[0037] The bent waveguide 220A is disposed on the periphery of the fifth slab region 222A and has a first bent electrode 224A electrically connecting the first electrode 214A and the third electrode 214C. The bent waveguide 220A is disposed on the periphery of the sixth slab region 222B and has a second bent electrode 224B electrically connecting the second electrode 214B and the fourth electrode 214D.

[0038] The optical device 300 of Comparative Example 2 includes a first bent electrode 224A that electrically connects the first electrode 214A and the third electrode 214C, and a second bent electrode 224B that electrically connects the second electrode 214B and the fourth electrode 214D. As a result, wiring layers for the first and second connecting lines are not required, simplifying the wiring pattern on layers other than the electrode layers. Moreover, the optical device 300 requires only two pads, the second input pad 241B and the second ground pad 242B, thereby reducing the complexity of the wiring.

[0039] However, the waveguide 221 of the Si bent waveguide 220 has a larger refractive index change than the cladding layer 232, causing the mode field of light to expand in the slab portion and, moreover, because the light confinement is weaker in the bent portion, the mode field shifts toward the outer periphery. As a result, in the optical device 300, the mode field of the signal light shifts toward the outer periphery in the waveguide 221 in the bent waveguide 220 and is absorbed by the first bent electrode 224A, resulting in optical loss. Therefore, there is a demand for an optical device 1 that can reduce optical loss.

[0040] Hereinafter, examples of optical devices and the like disclosed in the present application will be described in detail with reference to the drawings. Note that the disclosed technology is not limited to these examples. Furthermore, the examples shown below may be combined as appropriate within the scope of not causing any contradiction. [Example]

[0041] FIG. 1 is a schematic plan view showing an example of an optical device 1 of Example 1, FIG. 2 is a schematic cross-sectional view taken along line AA shown in FIG. 1, and FIG. 3 is a schematic cross-sectional view taken along line BB shown in FIG. 1. The optical device 1 shown in FIG. 1 is, for example, an optical attenuator such as a VOA (Variable Optical Attenuator). The optical device 1 has a first VOA 2A with a linear structure, a second VOA 2B with a linear structure, and a curved waveguide 3 that optically connects the first VOA 2A and the second VOA 2B. The optical device 1 is a VOA with an L-shaped structure.

[0042] 2 includes a Si substrate 31, a first rib-type optical waveguide 2A1 formed on the Si substrate 31, and a first electrode 14A and a second electrode 14B electrically connected to both sides of the first rib-type optical waveguide 2A1. The first VOA 2A is formed on the Si substrate 31 and includes a cladding layer 32 surrounding the first rib-type optical waveguide 2A1, the first electrode 14A, and the second electrode 14B.

[0043] The first rib type optical waveguide 2A1 is formed of, for example, Si. The first rib type optical waveguide 2A1 has a first rib waveguide 11A that forms a core. The first rib waveguide 11A has a linear structure with the same width. The first rib type optical waveguide 2A1 has an optical input section 11A1 and an optical output section 11A2. The optical input section 11A1 is an input stage of the first rib type optical waveguide 2A1 that inputs signal light to the first rib waveguide 11A. The optical output section 11A2 is an output stage of the first rib type optical waveguide 2A1 that outputs signal light from the first rib waveguide 11A.

[0044] The first rib-type optical waveguide 2A1 has a first slab region 12A formed on one outer side of the first rib waveguide 11A and a second slab region 12B formed on the other outer side of the first rib waveguide 11A. The first rib-type optical waveguide 2A1 has a P-doped region 13A formed in the first slab region 12A and an N-doped region 13B formed in the second slab region 12B. The P-doped region 13A is a region outside the first slab region 12A that is P-doped and electrically connected to the first electrode 14A. The N-doped region 13B is a region outside the second slab region 12B that is N-doped and electrically connected to the second electrode 14B.

[0045] In the first rib type optical waveguide 2A1, the first rib waveguide 11A, the first slab region 12A, and the second slab region 12B are undoped regions. The rib type optical waveguide 2A1 has a PIN diode structure with, for example, a P-doped region 13A, an undoped region, and an N-doped region 13B.

[0046] The electrodes include a first electrode 14A electrically connected to the P-doped region 13A and a second electrode 14B electrically connected to the N-doped region 13B. The first electrode 14A is a signal electrode to which a voltage is applied. The first electrode 14A is made of a material having electrical resistance, for example, a metal such as aluminum or a semiconductor material such as Si. The second electrode 14B is a ground electrode. The second electrode 14B is also made of a material having electrical resistance, for example, a metal such as aluminum or a semiconductor material such as Si or Ge. The cladding layer 32 is formed of, for example, SiO2.

[0047] 2 includes a Si substrate 31, a second rib-type optical waveguide 2B1 formed on the Si substrate 31, and a third electrode 14C and a fourth electrode 14D electrically connected to both sides of the second rib-type optical waveguide 2B1. The second VOA 2B also includes a cladding layer 32 formed on the Si substrate 31 and surrounding the second rib-type optical waveguide 2B1, the third electrode 14C, and the fourth electrode 14D.

[0048] The second rib type optical waveguide 2B1 is formed of, for example, Si. The second rib type optical waveguide 2B1 has a second rib waveguide 11B that forms a core. The second rib waveguide 11B has a linear structure with the same width. The second rib type optical waveguide 2B1 has an optical input section 11B1 and an optical output section 11B2. The optical input section 11B1 is an input stage of the second rib type optical waveguide 2B1 that inputs signal light to the second rib waveguide 11B. The optical output section 11B2 is an output stage of the second rib type optical waveguide 2B1 that outputs signal light from the second rib waveguide 11B.

[0049] The second rib optical waveguide 2B1 has a third slab region 12C formed on one outer side of the second rib waveguide 11B and a fourth slab region 12D formed on the other outer side of the second rib waveguide 11B. The second rib optical waveguide 2B1 has a P-doped region 13C formed in the third slab region 12C and an N-doped region 13D formed in the fourth slab region 12D. The P-doped region 13C is a region outside the third slab region 12C that is P-doped and electrically connected to the third electrode 14C. The N-doped region 13D is a region outside the fourth slab region 12D that is N-doped and electrically connected to the fourth electrode 14D.

[0050] In the second rib optical waveguide 2B1, the second rib waveguide 11B, the third slab region 12C, and the fourth slab region 12D are undoped regions. The second rib optical waveguide 2B1 has a PIN diode structure with, for example, a P-doped region 13C, an undoped region, and an N-doped region 13D.

[0051] The electrodes include a third electrode 14C electrically connected to the P-doped region 13C and a fourth electrode 14D electrically connected to the N-doped region 13D. The third electrode 14C is a signal electrode connected to an input pad 41B to which a voltage is applied. The third electrode 14C is made of a material having electrical resistance, such as a metal such as aluminum or a semiconductor material such as silicon. The fourth electrode 14D is a ground electrode connected to the ground pad 42B. The fourth electrode 14D is also made of a material having electrical resistance, such as a metal such as aluminum or a semiconductor material such as silicon or germanium.

[0052] The cladding layer 32 is formed of, for example, SiO2. The input pad 41B is an electrode pad connected to the third electrode 14C via an input via 41B1. The ground pad 42B is an electrode pad connected to the fourth electrode 14D via a ground via 42B1.

[0053] The curved waveguide 3 is made of, for example, Si. The curved waveguide 3 has a waveguide 21 forming a core. The waveguide 21 is a curved optical waveguide that optically connects the first rib waveguide 11A of the first rib type optical waveguide 2A1 and the second rib waveguide 11B of the second rib type optical waveguide 2B1. The curved waveguide 3 has a fifth slab region 22A formed on one outer side of the waveguide 21 and a sixth slab region 22B formed on the other outer side of the waveguide 21.

[0054] The bent waveguide 3 is disposed on the outer periphery of the fifth slab region 22A and has a first bent electrode 24A that electrically connects the first electrode 14A and the third electrode 14C. The bent waveguide 3 is disposed on the outer periphery of the sixth slab region 22B and has a second bent electrode 24B that electrically connects the second electrode 14B and the fourth electrode 14D. As shown in FIG. 3, the lower part of the second bent electrode 24B is disposed on the sixth slab region 22B, but a portion of the first bent electrode 24A is disposed on the fifth slab region 22A.

[0055] The spacing between the third rib waveguide 21 and the first bending electrode 24A of the bending waveguide 3 is defined as S2. The spacing between the first rib waveguide 11A and the first electrode 14A of the first rib type optical waveguide 2A1 is defined as S1. The spacing between the second rib waveguide 11B and the third electrode 14C of the second rib type optical waveguide 2B1 is defined as S1. The spacing S2 is longer than the spacing S1. That is, the spacing between the first bending electrode 24A and the third rib waveguide 21 is longer. As a result, absorption by the first bending electrode 24A of the mode field of light shifting from the third rib waveguide 21 toward the first bending electrode 24A is suppressed, thereby suppressing optical loss.

[0056] In the optical device 1 of Example 1, the spacing distance S2 between the third rib waveguide 21 and the first bending electrode 24A in the bending waveguide 3 is longer than the spacing distance S1 between the first rib waveguide 11A and the first electrode 14A in the first rib optical waveguide 2A1. As a result, the first bending electrode 24A on the outer periphery side of the third rib waveguide 21 is spaced away from the third rib waveguide 21, suppressing absorption by the first bending electrode 24A of the mode field of light shifted toward the outer periphery in the bending waveguide 3, thereby suppressing optical loss. Moreover, the wiring pattern can be simplified while the device size can be reduced.

[0057] In the optical device 1, the spacing distance S2 between the third rib waveguide 21 and the first bending electrode 24A in the bending waveguide 3 is longer than the spacing distance S1 between the second rib waveguide 11B and the third electrode 14C in the second rib optical waveguide 2B1. As a result, the first bending electrode 24A on the outer periphery side of the third rib waveguide 21 is spaced away from the third rib waveguide 21, suppressing absorption by the first bending electrode 24A of the mode field of light shifting toward the outer periphery of the bending waveguide 3, thereby suppressing optical loss.

[0058] In the optical device 1 of Example 1, if the thicknesses of the fifth slab region 22A and the sixth slab region 22B of the curved waveguide 3 are large, the confinement of light will be weakened, resulting in a large shift of the mode field of light toward the outer periphery of the curved waveguide 3. As a result, it may not be possible to suppress light absorption by the first curved electrode 24A. Therefore, even if the thicknesses of the fifth slab region 22A and the sixth slab region 22B are large, the distance between the third rib waveguide 21 of the curved waveguide 3 and the curved electrode 24A may be further increased, and this embodiment will be described below as Example 2. [Example]

[0059] Fig. 4 is a schematic plan view showing an example of an optical device 1A of Example 2, Fig. 5 is a schematic cross-sectional view taken along line AA in Fig. 4, and Fig. 6 is a schematic cross-sectional view taken along line BB in Fig. 4. Note that the same components as those in the optical device 1 of Example 1 are given the same reference numerals, and descriptions of the overlapping components and operations will be omitted. The optical device 1 of Example 1 differs from the optical device 1A of Example 2 in that a spacing distance S4 between the third rib waveguide 21 in the bending waveguide 3 and the first bending electrode 24A1 is longer than a spacing distance between the third rib waveguide 21 and the outer periphery of the fifth slab region 22A.

[0060] The distance between the third rib waveguide 21 in the bend waveguide 3 and the inner circumferential end of the first bend electrode 24A1 on the outer circumferential side of the bend waveguide 3 is defined as S4. The distance between the third rib waveguide 21 and one end of the fifth slab region 22A on the outer circumferential side of the bend waveguide 3 is defined as S3. As shown in FIGS. 5 and 6 , the first bend electrode 24A is disposed on the substrate 31 with the inner circumferential end of the first bend electrode 24A1 spaced apart from the outer circumferential end of the fifth slab region 22A. The distance S4 is longer than the distance S3. As a result, the distance between the first bend electrode 24A1 and the third rib waveguide 21 is large, which suppresses absorption by the first bend electrode 24A1 of the mode field of light shifting from the third rib waveguide 21 toward the first bend electrode 24A1, thereby reducing optical loss.

[0061] In the optical device 1A of the second embodiment, the spacing distance S4 between the third rib waveguide 21 and the first bending electrode 24A1 in the bending waveguide 3 is set longer than the spacing distance S3 between the third rib waveguide 21 and the outer circumferential edge of the fifth slab region 22A. As a result, even if the thicknesses of the fifth slab region 22A and the sixth slab region 22B are increased, the absorption by the first bending electrode 24A1 of the mode field of light that shifts to the outer circumferential side of the bending waveguide 3 can be suppressed, thereby suppressing optical loss.

[0062] In the optical device 1A of Example 2, the doped regions of the fifth slab region 22A1 and the sixth slab region 22B are interrupted at the curved waveguide 3 between the first VOA 2A and the second VOA 2B, which may reduce the attenuation efficiency of the VOA. Therefore, an embodiment that can improve the attenuation efficiency of the VOA will be described below as Example 3. [Example]

[0063] Fig. 7 is a schematic plan view showing an example of an optical device of Example 3, Fig. 8 is a schematic cross-sectional view taken along line AA shown in Fig. 7, and Fig. 9 is a schematic cross-sectional view taken along line BB shown in Fig. 7. The optical device 1A of Example 2 and the optical device 1B of Example 3 differ from each other in that the optical device 1A of Example 2 has a P-doped region 23A formed on the fifth slab region 22A1 of the curved waveguide 3B and an N-doped region 23B formed on the sixth slab region 22B1.

[0064] The P-doped region 23A electrically connects the P-doped region 13A in the first rib optical waveguide 2A1 to the P-doped region 13C in the second rib optical waveguide 2B1. The N-doped region 23B electrically connects the N-doped region 13B in the first rib optical waveguide 2A1 to the N-doped region 13D in the second rib optical waveguide 2B1. In the optical device 1B, the P-doped region 13A connects to the P-doped region 13C via the P-doped region 23A, and the N-doped region 13B connects to the N-doped region 13D via the N-doped region 23B. As a result, a PIN structure is formed over the first VOA 2A, the second VOA 2B, and the bend waveguide 3B.

[0065] The spacing distance between the third rib waveguide 21 of the bent waveguide 3B and the fifth doped region 23A formed on the outer periphery of the bent waveguide 3B is defined as Sd2. The spacing distance between the first rib waveguide 11A of the first rib optical waveguide 2A1 and the first doped region 13A on the same side as the outer periphery is defined as Sd1. The spacing distance between the second rib waveguide 11B of the second rib optical waveguide 2B1 and the third doped region 13C on the same side as the outer periphery is defined as Sd1. The spacing distance Sd2 is longer than the spacing distance Sd1.

[0066] In the optical device 1B of the third embodiment, a P-doped region 23A connecting the P-doped region 13A and the P-doped region 13C is disposed in the curved waveguide 3B, and an N-doped region 23B connecting the N-doped region 13B and the N-doped region 13D is disposed in the curved waveguide 3B. Since the P-doped region and the N-doped region are longer, the extinction ratio of the VOA is increased, thereby improving the attenuation efficiency.

[0067] In the optical device 1B, the spacing distance Sd2 between the third rib waveguide 21 and the P-doped region 23A is longer than the spacing distance Sd1 between the first rib waveguide 11A and the P-doped region 13A. As a result, the first bent electrode 24A2 and the third rib waveguide 21 are spaced apart, which suppresses absorption by the first bent electrode 24A1 of the mode field of light shifting from the third rib waveguide 21 to the outer periphery, thereby suppressing optical loss.

[0068] In the optical device 1B, the spacing distance Sd2 between the third rib waveguide 21 and the P-doped region 23A is longer than the spacing distance Sd1 between the second rib waveguide 11B and the P-doped region 13C. As a result, the first bend electrode 24A2 and the third rib waveguide 21 are spaced apart, which suppresses absorption by the first bend electrode 24A1 of the mode field of light shifting from the third rib waveguide 21 to the outer periphery, thereby suppressing optical loss.

[0069] For ease of explanation, the optical device 1 is illustrated as having a PIN diode structure with a P-doped region, an undoped region, and an N-doped region. However, the optical device can also be applied to a PIP diode structure with a P-doped region, an undoped region, and a P-doped region. The optical device can also be applied to an NIN diode structure with an N-doped region, an undoped region, and an N-doped region.

[0070] Furthermore, although a VOA has been exemplified as the optical device 1, the optical device is not limited to a VOA and can also be applied to a high-order filter.

[0071] Next, an optical transceiver 50 employing the optical device 1 (1A, 1B) of the first to third embodiments will be described. FIG. 10 is an explanatory diagram showing an example of an optical transceiver 50 employing the optical device 1 (1A, 1B) of the present embodiment. The optical transceiver 50 shown in FIG. 10 is connected to an output optical fiber FC and an input optical fiber FC. The optical transceiver 50 includes a DSP (Digital Signal Processor) 51, an optical transmitter 53, and an optical receiver 54. The DSP 51 is an electrical component that performs digital signal processing. For example, the DSP 51 performs processing such as encoding transmission data, generates an electrical signal including the transmission data, and outputs the generated electrical signal to the optical transmitter 53. The DSP 51 also acquires an electrical signal including reception data from the optical receiver 54 and performs processing such as decoding the acquired electrical signal to obtain the reception data.

[0072] The optical transmitter 53 modulates the supplied light with the electrical signal output from the DSP 51 and outputs the obtained transmission light to the optical fiber FC. The optical transmitter 53 has an optical modulation unit 53A that generates transmission light by modulating the supplied light with the electrical signal input to the optical modulator as the light propagates through the waveguide.

[0073] The optical receiver 54 has an optical receiving section 54A that receives an optical signal from the optical fiber FC and demodulates the received light using the supplied light. The optical receiver 54 then converts the demodulated received light into an electrical signal and outputs the converted electrical signal to the DSP 51. The optical transmitter 53 and the optical receiver 54 each have an optical device 1 (1A, 1B) built in that attenuates light, for example.

[0074] For convenience of explanation, the optical transceiver 50 has been illustrated as having a built-in optical transmitter 53 and an optical receiver 54, but the optical transceiver 50 may have a built-in optical transmitter 53 or an optical receiver 54. For example, the optical device 1 (1A, 1B) may be applied to an optical transceiver 50 having a built-in optical transmitter 53 or an optical transceiver 50 having a built-in optical receiver 54, and modifications can be made as appropriate.

[0075] In the embodiment, the rib-type optical waveguide 2 may be a PLC (Planar Lightwave Circuit) in which both the core and clad are made of SiO2, an InP waveguide, or a GaAs waveguide. The core may be Si or Si3N4, the lower clad may be SiO2, and the upper clad may be SiO2 or air, etc.

[0076] Furthermore, the components of each unit shown in the figure do not necessarily have to be physically configured as shown in the figure. In other words, the specific form of distribution and integration of each unit is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0077] Furthermore, the various processing functions performed by each device may be executed in whole or in part on a CPU (Central Processing Unit) (or a microcomputer such as an MPU (Micro Processing Unit), MCU (Micro Controller Unit), or DSP). Needless to say, the various processing functions may be executed in whole or in part on a program analyzed and executed by a CPU (or a microcomputer such as an MPU, MCU, or DSP), or on hardware using wired logic. [Explanation of symbols]

[0078] 1 Optical Devices 2A1 First rib-type optical waveguide 2B1 Second rib-type optical waveguide 3. Bent waveguide 11A First rib waveguide 11B Second rib waveguide 12A First slab region 12B Second slab region 12C Third Slab Region 12D Fourth Slab Region 13A P-doped region 13B N-doped region 13C P-doped region 13D N-doped region 14A First electrode 14B Second electrode 14C Third electrode 14D Fourth electrode 21 Third rib waveguide 22A Fifth Slab Region 22B 6th Slab Region 23A Fifth doped region 23B sixth doped region 24A First bent electrode 24B Second curved electrode

Claims

1. a first rib-type optical waveguide disposed on a substrate, the first rib-type optical waveguide having a first doped region formed in a first slab region, a second doped region formed in a second slab region, and a first rib waveguide formed between the first slab region and the second slab region; a second rib-type optical waveguide disposed on the substrate, the second rib-type optical waveguide having a third doped region formed in a third slab region, a fourth doped region formed in a fourth slab region, and a second rib waveguide formed between the third slab region and the fourth slab region; a bent waveguide disposed on the substrate and having a third rib waveguide that optically connects the first rib-type optical waveguide and the second rib-type optical waveguide; a first electrode conducting current to the first doped region; a second electrode conducting current to the second doped region; a third electrode conducting current to the third doped region; a fourth electrode conducting current to the fourth doped region; a first bent electrode provided in parallel with the bent waveguide and conducting current between the first electrode and the third electrode; a second bend electrode provided in parallel with the bend waveguide and conducting current between the second electrode and the fourth electrode; The distance between the third rib waveguide and the first bend electrode arranged on the outer periphery of the bend waveguide is an optical device, characterized in that the distance is longer than the distance between the first rib waveguide and the first electrode on the same side as the outer periphery;

2. The curved waveguide is a fifth slab region and a sixth slab region formed on both sides of the curved waveguide; The distance between the third rib waveguide and one end of the first bend electrode on the outer periphery of the bend waveguide is 2. The optical device according to claim 1, wherein the distance is longer than the distance between the third rib waveguide and one end of the fifth slab region on the outer periphery side of the bent waveguide.

3. The curved waveguide is a fifth slab region and a sixth slab region formed on both sides of the curved waveguide; a fifth doped region formed in the fifth slab region and a sixth doped region formed in the sixth slab region; The distance between the third rib waveguide and the fifth doped region formed on the outer periphery of the bent waveguide is 2. The optical device according to claim 1, wherein the distance is longer than the distance between the first rib waveguide and the first doped region on the same side as the outer periphery.

4. The first rib-type optical waveguide comprises: a first P-doped region as the first doped region and a first N-doped region as the second doped region; The second rib-type optical waveguide comprises: a second P-doped region as the third doped region and a second N-doped region as the fourth doped region; 2. The optical device according to claim 1, wherein:

5. The first rib-type optical waveguide comprises: a first P-doped region as the first doped region and a second P-doped region as the second doped region; The second rib-type optical waveguide comprises: a third P-doped region as the third doped region, and a fourth P-doped region as the fourth doped region; 2. The optical device according to claim 1, wherein:

6. The first rib-type optical waveguide comprises: a first N-doped region as the first doped region and a second N-doped region as the second doped region; The second rib-type optical waveguide comprises: a third N-doped region as the third doped region, and a fourth N-doped region as the fourth doped region; 2. The optical device according to claim 1, wherein:

7. an optical modulation unit that optically modulates light using a transmission signal and transmits the transmission light; an optical device disposed in the optical modulation unit, The optical device is a first rib-type optical waveguide disposed on a substrate, the first rib-type optical waveguide having a first doped region formed in a first slab region, a second doped region formed in a second slab region, and a first rib waveguide formed between the first slab region and the second slab region; a second rib-type optical waveguide disposed on the substrate, the second rib-type optical waveguide having a third doped region formed in a third slab region, a fourth doped region formed in a fourth slab region, and a second rib waveguide formed between the third slab region and the fourth slab region; a bent waveguide disposed on the substrate and having a third rib waveguide that optically connects the first rib-type optical waveguide and the second rib-type optical waveguide; a first electrode conducting current to the first doped region; a second electrode conducting current to the second doped region; a third electrode conducting current to the third doped region; a fourth electrode conducting current to the fourth doped region; a first bent electrode provided in parallel with the bent waveguide and conducting current between the first electrode and the third electrode; a second bend electrode provided in parallel with the bend waveguide and conducting current between the second electrode and the fourth electrode; The distance between the third rib waveguide and the first bend electrode arranged on the outer periphery of the bend waveguide is The distance is longer than the distance between the first rib waveguide and the first electrode on the same side as the outer periphery.

1. An optical transmitter comprising:

8. an optical receiving unit that receives a reception signal from the received light using light; an optical device disposed in the optical receiving section, The optical device is a first rib-type optical waveguide disposed on a substrate, the first rib-type optical waveguide having a first doped region formed in a first slab region, a second doped region formed in a second slab region, and a first rib waveguide formed between the first slab region and the second slab region; a second rib-type optical waveguide disposed on the substrate, the second rib-type optical waveguide having a third doped region formed in a third slab region, a fourth doped region formed in a fourth slab region, and a second rib waveguide formed between the third slab region and the fourth slab region; a bent waveguide disposed on the substrate and having a third rib waveguide that optically connects the first rib-type optical waveguide and the second rib-type optical waveguide; a first electrode conducting current to the first doped region; a second electrode conducting current to the second doped region; a third electrode conducting current to the third doped region; a fourth electrode conducting current to the fourth doped region; a first bent electrode provided in parallel with the bent waveguide and conducting current between the first electrode and the third electrode; a second bend electrode provided in parallel with the bend waveguide and conducting current between the second electrode and the fourth electrode; The distance between the third rib waveguide and the first bend electrode arranged on the outer periphery of the bend waveguide is The distance is longer than the distance between the first rib waveguide and the first electrode on the same side as the outer periphery.

1. An optical receiver comprising:

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