Optical device, optical transmission device, and optical reception device

Abstract

The invention relates to an optical device, an optical transmission device and an optical receiving device. In one embodiment, an optical device includes: a ribbed optical waveguide including N parallel waveguides connected to the output of a 1 input * N output shunt coupler; and a first electrode and a second electrode, the first electrode and the second electrode being connected to the rib-shaped optical waveguide. The ribbed optical waveguide includes a non-conductive slab region, a P-type doped region, and an N-type doped region formed between the waveguides. The P-type doped region is formed in a first plate region outside one of the outermost waveguides of the N waveguides, and is connected to the first electrode. The N-type doped region is formed in a second plate region outside another one of the outermost waveguides of the N waveguides, and is connected to the second electrode.

Description

TECHNICAL FIELD

[0001] The embodiments discussed herein relate to optical devices, optical transmission devices, and optical receiving devices. BACKGROUND

[0002] With recent increases in communication capacity, the demand for optical fiber communication has also increased. Accordingly, optical devices typified by silicon photonics have been actively developed. Known examples of such optical devices include optical attenuators, such as variable optical attenuators (VOAs), which attenuate the intensity of signal light guided through an optical waveguide in accordance with an electric signal.

[0003] Figure 13 is a schematic plan view of an example of an optical device 100. Figure 14 is a schematic cross-sectional view taken along the line A-A shown in Figure 13 The VOA 110, which is an example of the optical device 100, has a Si substrate 121, a rib-shaped optical waveguide 102 formed on the Si substrate 121, and electrodes 103 connected to the rib-shaped optical waveguide 102 at both sides. The VOA 110 also has a cladding layer 122 formed on the Si substrate 121 and surrounding the rib-shaped optical waveguide 102 and the periphery of the two electrodes 103.

[0004] For example, the rib-shaped optical waveguide 102 has a waveguide 102A that forms a Si core, and a first flat plate region 102D and a second flat plate region 102E located at both sides of the waveguide 102A. The rib-shaped optical waveguide 102 has an optical input portion 102B and an optical output portion 102C. The optical input portion 102B is an input stage of the rib-shaped optical waveguide 102 that is where signal light is input to the waveguide 102A. The optical output portion 102C is an output stage of the rib-shaped optical waveguide 102 that is where signal light is output from the waveguide 102A. A P-type doped region 102F that has been P-type doped is formed in the first flat plate region 102D, and an N-type doped region 102G that has been N-type doped is formed in the second flat plate region 102E. The waveguide 102A, a portion of the first flat plate region 102D, and a portion of the second flat plate region 102E are undoped regions. The P-type doped region 102F, the undoped regions, and the N-type doped region 102G located in the rib-shaped optical waveguide 102 have a PIN diode structure.

[0005] The electrodes 103 have a first electrode 103A electrically connected to the P-type doped region 102F, and a second electrode 103B electrically connected to the N-type doped region 102G. The first electrode 103A is a signal electrode connected to a power supply pad 104 for applying a voltage, and the second electrode 103B is a ground electrode connected to a ground pad 105.

[0006] In the optical device 100, the power supply pad 104 is positioned near the center of the VOA 110, and power is supplied from the power supply pad 104 to the first electrode 103A via the power supply via hole 104A. In the optical device 100, the ground pad 105 is positioned near the center of the VOA 110, and grounding is achieved from the second electrode 103B to the ground pad 105 via the ground via hole 105A.

[0007] In a case where a positive voltage is applied from the power supply pad 104 to the first electrode 103A, current flows from the first electrode 103A to the second electrode 103B, and thus current will flow through the rib-shaped optical waveguide 102 arranged between the first electrode 103A and the second electrode 103B. As a result, the intensity of the signal light is attenuated due to absorption of the signal light guided through the rib-shaped optical waveguide 102 by free carrier absorption of the current flowing through the rib-shaped optical waveguide 102.

[0008] Patent Document 1: U.S. Patent Application Publication No. 2022 / 0326586

[0009] Patent Document 2: Japanese Patent Application Publication No. 2023-075026

[0010] Patent Document 1: Japanese Patent Application Publication No. 2019-191246

[0011] However, when the intensity of the signal light input into the rib-shaped optical waveguide 102 increases in the optical device 100, light absorption through the Si substrate 121 increases, and thus propagation loss in the rib-shaped optical waveguide 102 increases. In addition, when the intensity of the signal light input into the rib-shaped optical waveguide 102 increases, the optical device 100 can malfunction due to light absorption through the Si substrate 121.

[0012] Therefore, it is an object of one aspect of an embodiment of the present application to provide an optical device that, for example, is capable of minimizing an increase in propagation loss in a rib-shaped optical waveguide. SUMMARY

[0013] According to an aspect of the embodiments, an optical device includes a rib-shaped optical waveguide including N parallel waveguides connected to outputs of a 1-input by N-output splitter coupler, and first and second electrodes connected to the rib-shaped optical waveguide. The rib-shaped optical waveguide includes a non-conductive slab region formed between the waveguides, a P-type doped region, and an N-type doped region. The P-type doped region is formed in a first slab region outside one of the outermost waveguides of the N waveguides and is connected to the first electrode. The N-type doped region is formed in a second slab region outside another of the outermost waveguides of the N waveguides and is connected to the second electrode. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a schematic plan view of an example of an optical device according to a first embodiment;

[0015] Figure 2 is a schematic cross-sectional view taken along the line A-A shown in Figure 1

[0016] Figure 3 is a schematic plan view of an example of an optical device according to a second embodiment;

[0017] Figure 4 is a schematic cross-sectional view taken along the line A-A shown in Figure 3

[0018] Figure 5 is a schematic plan view of an example of an optical device according to a third embodiment;

[0019] Figure 6 is a schematic cross-sectional view taken along the line A-A shown in Figure 5

[0020] Figure 7 is a schematic cross-sectional view taken along the line B-B shown in Figure 5

[0021] Figure 8 is a schematic plan view of an example of an optical device according to a fourth embodiment;

[0022] Figure 9 is a schematic cross-sectional view taken along the line A-A shown in Figure 8

[0023] Figure 10 is a diagram showing an example of an optical transceiver having adopted an optical device according to the embodiments;

[0024] Figure 11 ​​​​​is a schematic plan view of an example of the optical device according to the comparative example;

[0025] Figure 12 is a schematic cross-sectional view taken along the line A-A shown in Figure 11

[0026] Figure 13 is a schematic plan view of an example of the optical device; and

[0027] Figure 14 is a schematic cross-sectional view taken along the line A-A shown in Figure 13 DETAILED DESCRIPTION

[0028] The VOA according to the comparative example can be considered as a method capable of reducing the propagation loss in the rib-shaped optical waveguide 102 even when the intensity of the signal light input to the rib-shaped optical waveguide 102 in the conventional optical device 100 increases, which makes it possible to halve the intensity of the signal light input to the rib-shaped optical waveguide 102. is a schematic plan view of an example of the optical device 200 according to the comparative example, and

[0029] is a schematic cross-sectional view taken along the line A-A shown in Figure 11 Figure 12 Figure 11

[0030] Figure 11 The optical device 200 shown in FIG. 10 has a 1x2 branching coupler 150, a first VOA 200A connected to one of the branching outputs of the branching coupler 150, and a second VOA 200B connected to the other of the branching coupler 150. The branching coupler 150 is a 1x2 coupler, and has an input portion 151 to which signal light is input, and a first output portion 152A and a second output portion 152B to which the signal light input from the input portion 151 is branched and output at a splitting ratio of 1:2.

[0031] The first VOA 200A has a Si substrate 221, a rib-shaped optical waveguide 202 formed on the Si substrate 221, and electrodes 203 connected to the rib-shaped optical waveguide 202 at both sides. The first VOA 200A also has a cladding layer 222 formed on the Si substrate 221 and surrounding the periphery of the rib-shaped optical waveguide 202 and the two electrodes 203.

[0032] ​​​​For example, the rib-shaped optical waveguide 202 has a waveguide 202A that forms a Si core and a first flat plate region 202D and a second flat plate region 202E positioned on both sides of the waveguide 202A. The rib-shaped optical waveguide 202 has an optical input portion 202B and an optical output portion 202C. The optical input portion 202B is an input stage of the rib-shaped optical waveguide 202 that is a place where signal light is input to the waveguide 202A. The optical output portion 202C is an output stage of the rib-shaped optical waveguide 202 that is a place where signal light is output from the waveguide 202A. A P-type doped region 202F that has been P-type doped is formed in the first flat plate region 202D, and an N-type doped region 202G that has been N-type doped is formed in the second flat plate region 202E. The waveguide 202A, a portion of the first flat plate region 202D, and a portion of the second flat plate region 202E are undoped regions. The P-type doped region 202F, the undoped region, and the N-type doped region 202G in the rib-shaped optical waveguide 202 have a PIN diode structure.

[0033] The electrode 203 has a first electrode 203A that is electrically connected to the P-type doped region 202F and a second electrode 203B that is electrically connected to the N-type doped region 202G. The first electrode 203A is a signal electrode that is connected to a power supply pad 204 for applying a voltage, and the second electrode 203B is a ground electrode that is connected to a ground pad 205.

[0034] In the first VOA 200A, the power supply pad 204 is positioned near the center of the first VOA 200A, and power is supplied from the power supply pad 104 to the first electrode 203A via a power supply via 204A. In the first VOA 200A, the ground pad 205 is positioned near the center of the first VOA 200A, and grounding is achieved from the second electrode 203B to the ground pad 205 via a ground via 205A1.

[0035] The second VOA 200B has the same configuration as the first VOA 200A, so any redundant description of the configuration and operation thereof will be omitted by assigning the same reference numerals. The ground pad 205 of the first VOA 200A and the ground pad 205 of the second VOA 200B are connected to each other.

[0036] The branching coupler 150 branches and outputs signal light input thereto at a splitting ratio of 1:2, inputs signal light branched and output to the first output portion 152A to the first VOA 200A, and inputs signal light branched and output to the second output portion 152B to the second VOA 200B.

[0037] In a case where a positive voltage is applied from the power supply pad 204 to the first electrode 203A in the first VOA 200A, current flows from the first electrode 203A to the second electrode 203B. Then, the current will flow through the rib-shaped optical waveguide 202 arranged between the first electrode 203A and the second electrode 203B. As a result, the intensity of the signal light is attenuated due to the absorption of the signal light guided through the rib-shaped optical waveguide 202 by the free carrier absorption of the current flowing through the rib-shaped optical waveguide 202 of the first VOA 200A.

[0038] In a case where a positive voltage is applied from the power supply pad 204 to the first electrode 203A in the second VOA 200B via the power supply via hole 204B, current flows from the first electrode 203A to the second electrode 203B. Then, the current will flow through the rib-shaped optical waveguide 202 arranged between the first electrode 203A and the second electrode 203B. As a result, the intensity of the signal light is attenuated due to the absorption of the signal light guided through the rib-shaped optical waveguide 202 by the free carrier absorption of the current flowing through the rib-shaped optical waveguide 202 of the second VOA 200B.

[0039] In the optical device 200 according to the comparative example, the signal light is split by the branching coupler 150, and the power of the signal light input to the rib-shaped optical waveguide 202 in the first VOA 200A and the second VOA 200B can be halved. As a result, the absorption of light by the Si substrate 221 is reduced, and the propagation of the signal light is achieved with reduced loss in the optical device 200.

[0040] However, since in the optical device 200 according to the comparative example, the current will be supplied to the first electrode 203A in the first VOA 200A and the second VOA 200B, the power consumption is doubled.

[0041] Therefore, there is a need for an optical device such as a VOA that can minimize the propagation loss of light in an optical waveguide while minimizing power consumption. Preferred embodiments of the present application will be explained with reference to the accompanying drawings. The following embodiments can be appropriately combined with each other as long as the combination does not cause contradiction.

[0042] (a) First Embodiment

[0043] Figure 1 is a schematic plan view of an example of the optical device 1 according to the first embodiment. Figure 2 is a schematic cross-sectional view taken along the line A-A shown in Figure 1 Figure 1 ​The optical device 1 shown in FIG. 1 has a branching coupler 6 and a VOA 10. The VOA 10 has a Si substrate 21, a rib-shaped optical waveguide 2 formed on the Si substrate 21, electrodes 3 electrically connected to the rib-shaped optical waveguide 2 at both sides, and a cladding layer 22 formed on the Si substrate 21 and surrounding the periphery of the rib-shaped optical waveguide 2 and the two electrodes 3.

[0044] The branching coupler 6 is a 1-input x N-output (for example, 1-input x 2-output) branching coupler. The branching coupler 6 has an input section 31 where input signal light is present, and a first output section 32A and a second output section 32B where signal light input from the input section 31 is branched and output at a branching ratio of 1:2. The branching coupler 6 outputs signal light of, for example, X polarization from the first output section 32A, and signal light of, for example, Y polarization from the second output section 32B, both of which are signal light input from the input section 31.

[0045] The rib-shaped optical waveguide 2 is formed of, for example, Si. The rib-shaped optical waveguide 2 has two parallel waveguides connected to the output of the 1 x 2 branching coupler 6. The two parallel waveguides have a first waveguide 2A connected to the first output section 32A, and a second waveguide 2B parallel to the first waveguide 2A and connected to the second output section 32B. The first waveguide 2A and the second waveguide 2B have a linear structure of the same width.

[0046] The rib-shaped optical waveguide 2 has an optical input section 2C and an optical output section 2D. The optical input section 2C is an input stage of the rib-shaped optical waveguide 2, which is where signal light is input to the first waveguide 2A and the second waveguide 2B. The optical output section 2D is an output stage of the rib-shaped optical waveguide 2, which is where signal light is output from the first waveguide 2A and the second waveguide 2B.

[0047] The rib-shaped optical waveguide 2 has a non-conductive flat-plate region 2G formed between the first waveguide 2A and the second waveguide 2B, a first flat-plate region 2E formed outside the first waveguide 2A, and a second flat-plate region 2F formed outside the second waveguide 2B. The width of the non-conductive flat-plate region 2G, that is, the width between the first waveguide 2A and the second waveguide 2B, is a width that does not allow signal light guided through the first waveguide 2A and signal light guided through the second waveguide 2B to be coupled to each other.

[0048] The rib-shaped optical waveguide 2 has a P-type doped region 2H formed in the first flat-plate region 2E and an N-type doped region 2J formed in the second flat-plate region 2F. The P-type doped region 2H is a region electrically connected to the first electrode 3A, which is obtained by P-type doping of a portion outside the first flat-plate region 2E. The N-type doped region 2J is a region electrically connected to the second electrode 3B, which is obtained by N-type doping of a portion outside the second flat-plate region 2F.

[0049] The first waveguide 2A, the second waveguide 2B, a portion of the first slab region 2E, a portion of the second slab region 2F, and the non-conductive slab region 2G in the rib-shaped optical waveguide 2 are undoped regions. For example, the P-type doped region 2H, the undoped region, and the N-type doped region 2J in the rib-shaped optical waveguide 2 have a PIN diode structure.

[0050] The electrode 3 has a first electrode 3A electrically connected to the P-type doped region 2H and a second electrode 3B electrically connected to the N-type doped region 2J. The first electrode 3A is a signal electrode connected to a power supply pad 4 for applying a voltage. The first electrode 3A includes a material having electrical resistance, such as a metal such as aluminum or a semiconductor material such as silicon. The second electrode 3B is a ground electrode connected to a ground pad 5. The second electrode 3B also includes a material having electrical resistance, such as a metal such as aluminum or a semiconductor material such as Si or Ge.

[0051] The cladding layer 22 is formed of, for example, SiO2. The power supply pad 4 is an electrode pad connected to the first electrode 3A. The ground pad 5 is an electrode pad connected to the second electrode 3B.

[0052] In the optical device 1, the power supply pad 4 is positioned near the center of the VOA 10, and power is supplied from the power supply pad 4 to the first electrode 3A via a power supply via 4A. In the optical device 1, the ground pad 5 is positioned near the center of the VOA 10, and grounding is achieved from the second electrode 3B to the ground pad 5 via a ground via 5A.

[0053] In a case in which a positive voltage is applied from the power supply pad 4 to the first electrode 3A, current flows from the first electrode 3A to the second electrode 3B. Then, the current will flow through the first waveguide 2A and the second waveguide 2B, which are in the rib-shaped optical waveguide 2 and are arranged between the first electrode 3A and the second electrode 3B. As a result, the signal light guided through the first waveguide 2A and the second waveguide 2B is absorbed due to free carrier absorption of the current flowing through the parallel first waveguide 2A and the second waveguide 2B in the rib-shaped optical waveguide 2, so that the intensity of the signal light is attenuated. That is, even in a case in which the intensity of the signal light input into the rib-shaped optical waveguide 2 is increased, the signal light input to the first waveguide 2A and the second waveguide 2B is halved by the branching coupler 6. As a result, light absorption of the Si substrate 21 is reduced, and it is possible to reduce the propagation loss in the rib-shaped optical waveguide 2.

[0054] The optical device 1 according to the first embodiment has a rib-shaped optical waveguide 2 including two parallel waveguides that are parallel to each other and connected to outputs of a 1-input x 2-output branching coupler 6, and a first electrode 3A and a second electrode 3B connected to the rib-shaped optical waveguide 2. The rib-shaped optical waveguide 2 has a non-conductive slab region 2G formed between a first waveguide 2A and a second waveguide 2B. Further, the rib-shaped optical waveguide 2 has a P-type doped region 2H formed at a first slab region 2E and connected to the first electrode 3A, and an N-type doped region 2J formed at a second slab region 2F and connected to the second electrode 3B. As a result, even in a case where the intensity of signal light input to the VOA 10 increases, the branching coupler 6 halves the intensity of signal light input to the first waveguide 2A and the second waveguide 2B, thereby reducing light absorption of the Si substrate 21, and thus it is possible to reduce propagation loss in the rib-shaped optical waveguide 2. Therefore, the rib-shaped optical waveguide 2 has a high light input tolerance. Further, compared to the optical device 200 according to the comparative example, the electrodes 3 for applying a voltage to the first waveguide 2A and the second waveguide 2B in the rib-shaped optical waveguide 2 are able to significantly reduce power consumption.

[0055] As an example, the case where the first waveguide 2A and the second waveguide 2B have the same rib width has been described with respect to the rib-shaped optical waveguide 2 of the optical device 1 according to the first embodiment, but is not limited to this example, and a second embodiment will be described below as an embodiment related to their rib widths.

[0056] (b) Second Embodiment

[0057] Figure 3 is a schematic plan view of an example of an optical device 1A according to the second embodiment, and Figure 4 is a schematic cross-sectional view taken along the line A-A shown in Figure 3 . By assigning the same reference numerals to components that are the same as those of the optical device 1 according to the first embodiment, any redundant description of the same components and their operations will be omitted.

[0058] The optical device 1A according to the second embodiment differs from the optical device 1 according to the first embodiment in that a first waveguide 2A1 and a second waveguide 2B1 in the rib-shaped optical waveguide 2 of the optical device 1A have rib widths different from each other. The rib width of the first waveguide 2A1 is wider than the rib width of the second waveguide 2B1. A first slab region 2E1 of the first waveguide 2A1 has the same width as a second slab region 2F1 of the second waveguide 2B1. The rib-shaped optical waveguide 2 has a non-conductive slab region 2G1 formed between the first waveguide 2A1 and the second waveguide 2B1.

[0059] In the case of the first embodiment in which the first waveguide 2A and the second waveguide 2B have the same rib width, the coupling of light can occur between the first waveguide 2A and the second waveguide 2B. Therefore, in this second embodiment, the rib widths of the first waveguide 2A1 and the second waveguide 2B1 have been adjusted to be different from each other. Adjusting the rib widths of the first waveguide 2A1 and the second waveguide 2B1 adjacent to each other prevents the coupling of light between the first waveguide 2A1 and the second waveguide 2B1 adjacent to each other.

[0060] For example, reducing the rib width of the waveguide weakens the confinement of light in the waveguide, and the propagation loss increases due to the increased absorption of light in the doped region. Therefore, the rib width is adjusted so that the propagation loss does not increase. Increasing the rib width of the waveguide enables multimode propagation in the waveguide, and generates noise in the optical signal. Therefore, the rib width is adjusted so that multimode propagation does not occur.

[0061] Therefore, in view of these adjustment points, the rib width of the first waveguide 2A1 has become wider, and the rib width of the second waveguide 2B1 has become narrower. Therefore, the difference between the rib widths of the first waveguide 2A1 and the second waveguide 2B1 generates a difference between the effective refractive indices of the first waveguide 2A1 and the second waveguide 2B1, thereby preventing the coupling of light between the signal light guided through the first waveguide 2A1 and the signal light guided through the second waveguide 2B1.

[0062] Since in the optical device 1A according to the second embodiment, the rib width of the first waveguide 2A1 has become wider, and the rib width of the second waveguide 2B1 has become narrower, it is possible to reduce the coupling of light between the signal light guided through the first waveguide 2A1 and the signal light guided through the second waveguide 2B1.

[0063] Even in the case in which the intensity of the signal light input to the VOA 10A in the optical device 1A increases, its branching coupler 6 halves the intensity of the signal light input to the first waveguide 2A and the second waveguide 2B. As a result, the light absorption through the Si substrate 21 thereof is reduced, and it is possible to reduce the propagation loss in the rib-shaped optical waveguide 2. Furthermore, the electrodes 3 for applying voltages to the first waveguide 2A and the second waveguide 2B in the rib-shaped optical waveguide 2 are shared. As a result, it is possible to greatly reduce the power consumption compared to the optical device 200 according to the comparative example.

[0064] The case in which the first waveguide 2A1 and the second waveguide 2B1 of the rib-shaped optical waveguide 2 in the optical device 1A according to the second embodiment have different rib widths from each other has been described as an example. For example, in a case in which the rib width of the first waveguide 2A1 is made wider, the light confinement in the first waveguide 2A1 increases, and the extinction performance is improved, and in a case in which the rib width of the second waveguide 2B1 is made narrower, the light confinement in the second waveguide 2B1 decreases, and the extinction performance is reduced. Thus, the first waveguide 2A1 and the second waveguide 2B1 can have different extinction performances from each other. Therefore, the third embodiment described below is an embodiment that addresses such a case.

[0065] (c) Third Embodiment

[0066] Figure 5 is a schematic plan view of an example of an optical device 1B according to the third embodiment, Figure 6 is a schematic cross-sectional view taken along the line A-A shown in Figure 5 , and Figure 7 is a schematic cross-sectional view taken along the line B-B shown in Figure 5 . By assigning the same reference numerals to components that are the same as those of the optical device 1 according to the first embodiment, any redundant description of the same components and their operations will be omitted.

[0067] The optical device 1B according to the third embodiment differs from the optical device 1 according to the first embodiment in that the optical device 1B is configured such that the rib width of its first waveguide 2A2 changes between its optical input portion 2C and optical output portion 2D, and the rib width of its second waveguide 2B2 changes between the optical input portion 2C and the optical output portion 2D. Further, the first waveguide 2A2 is configured to be point-symmetrical to the second waveguide 2B2.

[0068] The first waveguide 2A2 in the optical device 1B has a first rib width XI that is wider from the optical input portion 2C to an intermediate portion, and a second rib width X2 that is narrower from the intermediate portion to the optical output portion 2D. Further, the intermediate portion of the first waveguide 2A2 has a tapered rib width that gradually changes from the first rib width XI to the second rib width X2.

[0069] The second waveguide 2B2 in the optical device 1B has a second rib width X2 that is narrower from the optical input portion 2C to an intermediate portion, and a first rib width XI that is wider from the intermediate portion to the optical output portion 2D. Further, the intermediate portion of the second waveguide 2B2 has a tapered rib width that gradually changes from the second rib width X2 to the first rib width XI. That is, the first waveguide 2A2 and the second waveguide 2B2 are configured to be point-symmetrical to each other.

[0070] The width of the first slab region 2E2 of the first waveguide 2A2 is changed according to the rib width of the first waveguide 2A2. The width of the second slab region 2F2 of the second waveguide 2B2 is changed according to the rib width of the second waveguide 2B. The rib-shaped optical waveguide 2 has a non-conductive slab region 2G2 formed between the first waveguide 2A2 and the second waveguide 2B2.

[0071] The rib widths of the first waveguide 2A2 and the second waveguide 2B2 are different from each other between the optical input portion 2C and the optical output portion 2D, but the first waveguide 2A1 and the second waveguide 2B2 are configured to be point-symmetrical to each other. As a result, it is possible to make the extinction ratios of the first waveguide 2A2 and the second waveguide 2B2 the same at the optical output portion 2D.

[0072] The optical device 1B according to the third embodiment is configured so that the rib width of the first waveguide 2A2 is changed between the optical input portion 2C and the optical output portion 2D, and the rib width of the second waveguide 2B2 is changed between the optical input portion 2C and the optical output portion 2D. In the optical device 1B, the first waveguide 2A2 is configured to be point-symmetrical to the second waveguide 2B2. As a result, it is possible to make the extinction ratios of the first waveguide 2A2 and the second waveguide 2B2 the same at the optical output portion 2D.

[0073] Further, since the rib width of the first waveguide 2A2 and the rib width of the second waveguide 2B2 are different from each other in the optical device 1B, it is possible to reduce the optical coupling between the signal light guided by the first waveguide 2A1 and the signal light guided by the second waveguide 2B.

[0074] Even in a case where the intensity of the signal light input to the VOA 10B is increased in the optical device 1B, the signal light input to the first waveguide 2A2 and the second waveguide 2B2 is halved by the branching coupler 6. As a result, the light absorption by the Si substrate 21 thereof is reduced, and it is possible to reduce the propagation loss in the rib-shaped optical waveguide 2. Further, the electrode 3 for applying a voltage to the first waveguide 2A2 and the second waveguide 2B2 in the rib-shaped optical waveguide 2 is shared. As a result, it is possible to greatly reduce the power consumption compared to the optical device 200 according to the comparative example.

[0075] With respect to the optical device 1 according to the first embodiment, the case where the branching coupler 6 of 1 input x 2 outputs is used and the parallel waveguides have two waveguides has been described as an example, but in a case where the branching coupler 6 of 1 input x N outputs is used, the parallel waveguides have N waveguides. Therefore, the fourth embodiment described below is an embodiment in a case where the branching coupler 6A of 1 input x 3 outputs is used.

[0076] (d) Fourth Embodiment

[0077] Figure 8is a schematic plan view of an example of the optical device 1C according to the fourth embodiment, and Figure 9 is a schematic cross-sectional view taken along Figure 8 the line A-A shown in FIG. 10. By assigning the same reference numerals to the same components as those of the optical device 1 according to the first embodiment, any redundant description of the same components and their operations will be omitted. The optical device 1C according to the fourth embodiment differs from the optical device 1 according to the first embodiment in that a 1-input x 3-output branching coupler 6A is used in the optical device 1C, and parallel waveguides have three waveguides.

[0078] The optical device 1C has the branching coupler 6A and a VOA 10C. The branching coupler 6A is a 1-input x 3-output branching coupler. The branching coupler 6A has an input section 31, a first output section 32A1, a second output section 32A2, and a third output section 32A3.

[0079] The parallel waveguides in the rib optical waveguide 2 in the VOA 10C have a first waveguide 2A3 connected to the first output section 32A1, a second waveguide 2B3 connected to the second output section 32A2, and a third waveguide 2K connected to the third output section 32A3. The first waveguide 2A3 has the same rib width as the second waveguide 2B3. The third waveguide 2K has a rib width narrower than the rib width of the first waveguide 2A3.

[0080] The rib optical waveguide 2 has a non-conductive flat region 2G31 formed between the first waveguide 2A3 and the third waveguide 2K, and a first flat region 2E3 formed outside the first waveguide 2A3. The rib optical waveguide 2 has a non-conductive flat region 2G32 formed between the second waveguide 2B3 and the third waveguide 2K, and a second flat region 2F3 formed outside the second waveguide 2B3.

[0081] The non-conductive flat region 2G31 has a width that is the width between the first waveguide 2A3 and the third waveguide 2K, and does not allow signal light guided through the first waveguide 2A3 and signal light guided through the third waveguide 2K to be coupled to each other. The non-conductive flat region 2G32 has a width that is the width between the second waveguide 2B3 and the third waveguide 2K, and does not allow signal light guided through the second waveguide 2B3 and signal light guided through the third waveguide 2K to be coupled to each other.

[0082] The rib-shaped optical waveguide 2 has a P-type doped region 2H formed in the first slab region 2E3 and an N-type doped region 2J formed in the second slab region 2F3. The P-type doped region 2H is a region electrically connected to the first electrode 3A, which is obtained by P-type doping of a portion outside the first slab region 2E3. The N-type doped region 2J is a region electrically connected to the second electrode 3B, which is obtained by N-type doping of a portion outside the second slab region 2F3.

[0083] In the rib-shaped optical waveguide 2, the first waveguide 2A3, the third waveguide 2K, the second waveguide 2B3, a portion of the first slab region 2E3, a portion of the second slab region 2F3, the non-conductive slab region 2G31, and the non-conductive slab region 2G32 are undoped regions. For example, the P-type doped region 2H, the undoped regions, and the N-type doped region 2J in the rib-shaped optical waveguide 2 have a PIN diode structure.

[0084] In a case where a positive voltage is applied from the power supply pad 4 to the first electrode 3A, current flows from the first electrode 3A to the second electrode 3B. Then, the current will flow through the first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3, which are located in the rib-shaped optical waveguide 2 and arranged between the first electrode 3A and the second electrode 3B. As a result, the signal light guided through the first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3 is absorbed due to the free carrier absorption of the current flowing through the parallel first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3 in the rib-shaped optical waveguide 2. Therefore, the intensity of the signal light is attenuated. That is, even in a case where the intensity of the signal light input into the rib-shaped optical waveguide 2 is increased, the signal light input to the first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3 is halved by the branching coupler 6A. As a result, the light absorption through the Si substrate 21 is reduced, and it is possible to reduce the propagation loss in the rib-shaped optical waveguide 2.

[0085] The optical device 1C according to the fourth embodiment has a rib-shaped optical waveguide 2 including three parallel waveguides that are parallel to each other and connected to the output ends of the 1-input x 3-output branching coupler 6A. As a result, even in a case where the intensity of the signal light input into the VOA 10C is increased, the intensity of the signal light input to the first waveguide 2A3, the second waveguide 2B3, and the third waveguide 2K becomes 1 / 3 at the branching coupler 6A. Then, the light absorption through the Si substrate 21 is reduced, and thus it is possible to reduce the propagation loss in the rib-shaped optical waveguide 2. Furthermore, compared to the optical device 200 according to the comparative example, the electrode 3 for applying a voltage to the first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3 in the rib-shaped optical waveguide 2 can significantly reduce power consumption.

[0086] Next, an optical transceiver 50 employing the optical device 1 according to any one of the first to fourth embodiments will be described. Figure 10 is a diagram showing an example of the optical transceiver 50 employing the optical device 1 according to the embodiment. Figure 10 The optical transceiver 50 shown in FIG. 8 is connected to an output optical fiber FC and an input optical fiber FC. The optical transceiver 50 has a digital signal processor (DSP) 51, an optical transmitter 53, and an optical receiver 54. The DSP 51 is an electronic component that performs digital signal processing. For example, the DSP 51 performs processing such as encoding on transmitted data, and outputs a generated electric signal to the optical transmitter 53. Further, the DSP 51 obtains an electric signal including received data from the optical receiver 54, and obtains reception data by performing processing such as decoding on the obtained electric signal.

[0087] The optical transmitter 53 outputs transmission light obtained by modulating light supplied to the optical transmitter 53 using an electric signal output from the DSP 51 to the optical fiber FC. The optical transmitter 53 has an optical modulation unit 53A that generates transmission light by modulating light supplied to the optical modulation unit 53A using an electric signal input to the optical modulator when the light propagates through a waveguide.

[0088] The optical receiver 54 has an optical receiving unit 54A that receives an optical signal from the optical fiber FC and demodulates the received light by using light supplied to the optical receiving unit 54A. The optical receiver 54 converts the demodulated reception light into an electric signal, and outputs the converted electric signal to the DSP 51. The optical device serving as an optical waveguide has been built in the optical transmitter 53 and the optical receiver 54.

[0089] For ease of description, a case where the optical transmitter 53 and the optical receiver 54 are built in the optical transceiver 50 has been described as an example, but either one of the optical transmitter 53 or the optical receiver 54 can be built in the optical transceiver 50. For example, the example can be appropriately modified, and the optical device 1 can be applied to an optical transceiver 50 in which the optical transmitter 53 is built, or to an optical transceiver 50 in which the optical receiver 54 is built.

[0090] In the present embodiment, the rib-shaped optical waveguide 2 can be: a planar lightwave circuit (PLC) having a core and cladding layers both of SiO2; an InP waveguide; or a GaAs waveguide. For example, the core can be Si or Si3N4, the lower cladding layer can be SiO2, and the upper cladding layer can be SiO2or air.

[0091] The components of each part shown in the drawings can not be physically configured as shown in the drawings. That is, the specific separation and integration mode of the components is not limited to those shown in the drawings, for example, all or part of the components can be configured to be functionally or physically separated or integrated in any unit according to various loads and use cases.

[0092] All or any part of various processing functions implemented on each device can be executed on a central processing unit (CPU) (or microcomputer, such as a micro processing unit (MPU) or a micro controller unit (MCU)). All or any part of the various processing functions can be executed on a program analyzed and executed by the CPU (or microcomputer, such as an MPU or MCU), or on hardware through wired logic.

[0093] According to one aspect, an increase in propagation loss in a rib-shaped optical waveguide can be minimized.

Claims

1. An optical device, comprising: A rib-shaped optical waveguide comprising N parallel waveguides connected to output ends of a branch coupler having 1 input end and N output ends; as well as a first electrode and a second electrode, the first electrode and the second electrode being connected to the rib-shaped optical waveguide, wherein The rib-shaped optical waveguide comprises: a non-conductive slab region formed between the waveguides; a P-type doped region formed in a first slab region outside one of the outermost waveguides of the N waveguides and connected to the first electrode; and An N-type doping region is formed in a second slab region outside another outermost waveguide of the N waveguides and is connected to the second electrode.

2. The optical device according to claim 1, wherein The rib-shaped optical waveguide includes two parallel waveguides connected to the output end of the branch coupler of 1 input end × 2 output ends, and One of the two waveguides has a waveguide width different from a waveguide width of the other of the two waveguides.

3. The optical device according to claim 1, wherein The rib-shaped optical waveguide includes two parallel waveguides connected to the output end of the branch coupler of 1 input end×2 output ends, The waveguide width of one of the two waveguides varies between the input end and the output end, The waveguide width of the other of the two waveguides changes between the input end and the output end, and The one waveguide of the two waveguides is arranged point-symmetrically with respect to the other waveguide of the two waveguides.

4. The optical device according to claim 1, wherein The P-type doping region is a region formed in the first slab region outside the one outermost waveguide in the waveguides, and the region is obtained by P-type doping of a portion outside the first slab region, and The N-type doping region is a region formed in the second slab region outside the other outermost waveguide in the waveguide, and is obtained by N-type doping of a portion outside the second slab region.

5. An optical transmission device, comprising: an optical modulator that optically modulates light by using a transmitted signal and transmits the transmitted light; as well as an optical device that attenuates light in the optical modulator, wherein The optical device comprises: a rib-shaped optical waveguide comprising N parallel waveguides connected to output terminals of a 1-input-terminal×N-output-terminal branch coupler; and a first electrode and a second electrode, the first electrode and the second electrode being connected to the rib-shaped optical waveguide, and The rib-shaped optical waveguide comprises: a non-conductive slab region formed between the waveguides; a P-type doped region formed in a first slab region outside one of the outermost waveguides of the N waveguides and connected to the first electrode; and An N-type doping region is formed in a second slab region outside another outermost waveguide of the N waveguides and is connected to the second electrode.

6. An optical receiving device, comprising: an optical receiver that receives a reception signal from reception light by using light; as well as an optical device that attenuates light in the optical receiver, wherein The optical device comprises: a rib-shaped optical waveguide comprising N parallel waveguides connected to output terminals of a 1-input-terminal×N-output-terminal branch coupler; and a first electrode and a second electrode, the first electrode and the second electrode being connected to the rib-shaped optical waveguide, and The rib-shaped optical waveguide comprises: a non-conductive slab region formed between the waveguides; a P-type doped region formed in a first slab region outside one of the outermost waveguides of the N waveguides and connected to the first electrode; and An N-type doping region is formed in a second slab region outside another outermost waveguide of the N waveguides and is connected to the second electrode.

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