Optical device, optical transmitter, and optical receiver

Abstract

To provide an optical device and the like capable of suppressing an increase in propagation loss of a rib-type optical waveguide.SOLUTION: An optical device comprises: a rib-type optical waveguide including N parallel waveguides connected to outputs of a 1-input×N-output branching coupler; and a first electrode and a second electrode connected to the rib-type optical waveguide. The rib-type optical waveguide includes: a non-conductive slab region formed between the waveguides; and a P-doped region formed in a first slab region located outside one outermost waveguide of the N waveguides and connected to the first electrode. The rib-type optical waveguide includes an N-doped region formed in a second slab region located outside the other outermost waveguide of the N waveguides and connected to the second electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical device, an optical transmitting apparatus, and an optical receiving apparatus. [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. 13 is a schematic plan view showing an example of an optical device 100. Fig. 14 is a schematic cross-sectional view taken along line AA shown in Fig. 13. A VOA 110, which is the optical device 100, 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 in the first slab region 102D, and an N-doped region 102G is formed in 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 a power supply 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 power supply pad 104 is located near the center of the VOA 110, and power is supplied from the power supply pad 104 to the first electrode 103A via a power supply via 104A. In the optical device 100, the ground pad 105 is located near the center of the VOA 110, and power is supplied 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 power supply 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] US Patent Application Publication No. 2022 / 0326586 [Patent Document 2] Japanese Patent Publication No. 2023-075026 [Patent Document 3] Japanese Patent Application Publication No. 2019-191246 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the optical device 100, when the intensity of the signal light input into the rib-type optical waveguide 102 increases, the optical absorption by the Si substrate 121 increases, resulting in an increase in the propagation loss of the rib-type optical waveguide 102. Furthermore, when the intensity of the signal light input into the rib-type optical waveguide 102 increases, the optical absorption by the Si substrate 121 may cause the optical device 100 to malfunction.

[0010] In one aspect, an object is to provide an optical device or the like that can suppress an increase in propagation loss in a rib-type optical waveguide. [Means for solving the problem]

[0011] An optical device according to one embodiment comprises a rib-type optical waveguide having N parallel waveguides connected to the output of a 1-input × N-output branching coupler, and a first electrode and a second electrode connected to the rib-type optical waveguide. The rib-type optical waveguide has a non-conductive slab region formed between the waveguides, and a P-doped region formed in the first slab region outside one of the outermost waveguides of the N waveguides and connected to the first electrode. The rib-type optical waveguide further comprises an N-doped region formed in the second slab region outside the other of the outermost waveguides of the N waveguides and connected to the second electrode. [Effects of the Invention]

[0012] According to one aspect, an increase in propagation loss in a rib-type optical waveguide can be suppressed. [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 plan view illustrating an example of an optical device according to a second embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line AA shown in FIG. [Figure 5]FIG. 5 is a schematic plan view illustrating an example of an optical device according to a third embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view taken along line AA shown in FIG. [Figure 7] FIG. 7 is a schematic cross-sectional view taken along line BB shown in FIG. [Figure 8] FIG. 8 is a schematic plan view showing an example of an optical device according to a fourth embodiment. [Figure 9] FIG. 9 is a schematic cross-sectional view taken along line AA 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 an optical device of a comparative example. [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 an optical device. [Figure 14] FIG. 14 is a schematic cross-sectional view taken along line AA shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Comparative Example] Even if the intensity of the signal light input to the rib-type optical waveguide 102 in the conventional optical device 100 increases, a comparative example VOA that halves the intensity of the signal light input to the rib-type optical waveguide 102 can be considered as a method for suppressing the propagation loss of the rib-type optical waveguide 102. Fig. 11 is a schematic plan view showing an example of an optical device 200 of the comparative example, and Fig. 12 is a schematic cross-sectional view taken along line AA shown in Fig. 11.

[0015] 11 includes a 1×2 branching coupler 150, a first VOA 200A connected to one branch output of the branching coupler 150, and a second VOA 200B connected to the other branch output of the branching coupler 150. The branching coupler 150 is configured with a 1×2 coupler and includes an input unit 151 that inputs a signal light, and a first output unit 152A and a second output unit 152B that branch and output the signal light input from the input unit 151 at a branching ratio of 1:2.

[0016] The first VOA 200A has a Si substrate 221, a rib-type optical waveguide 202 formed on the Si substrate 221, and electrodes 203 connected to both sides of the rib-type optical waveguide 202. Furthermore, the first VOA 200A has a cladding layer 222 formed on the Si substrate 221 and surrounding the rib-type optical waveguide 202 and the two electrodes 203.

[0017] The rib-type optical waveguide 202 has, for example, a waveguide 202A forming a Si core, and a first slab region 202D and a second slab region 202E on either side of the waveguide 202A. The rib-type optical waveguide 202 has an optical input section 202B and an optical output section 202C. The optical input section 202B is an input stage of the rib-type optical waveguide 202 that inputs signal light to the waveguide 202A. The optical output section 202C is an output stage of the rib-type optical waveguide 202 that outputs signal light from the waveguide 202A. A P-doped region 202F is formed in the first slab region 202D, and an N-doped region 202G is formed in the second slab region 202E. The waveguide 202A, the first slab region 202D, and the second slab region 202E are undoped regions. The rib-type optical waveguide 202 has a PIN diode structure with the P-doped region 202F, the undoped region, and the N-doped region 202G.

[0018] The electrode 203 includes a first electrode 203A electrically connected to the P-doped region 202F and a second electrode 203B electrically connected to the N-doped region 202G. The first electrode 203A serves as a signal electrode connected to a power supply pad 204 to which a voltage is applied, and the second electrode 203B serves as a ground electrode connected to a ground pad 205.

[0019] In the first VOA 200A, the feed pad 204 is located near the center of the first VOA 200A, and feeds power from the feed pad 204 to the first electrode 203A via a feed via 204A. In the first VOA 200A, the ground pad 205 is located near the center of the first VOA 200A, and grounding is performed from the second electrode 203B to the ground pad 205 via a ground via 205A1.

[0020] Since the second VOA 200B has the same configuration as the first VOA 200A, the same components and operations are denoted by the same reference numerals and will not be described in detail. The ground pad 205 of the first VOA 200A and the ground pad 205 of the second VOA 200B are connected.

[0021] The branching coupler 150 branches and outputs the input signal light at a branching ratio of 1:2, inputs the signal light branched and output to the first output section 152A to the first VOA 200A, and inputs the signal light branched and output to the second output section 152B to the second VOA 200B.

[0022] When a positive voltage is applied to the first electrode 203A in the first VOA 200A from the power supply pad 204, a current flows from the first electrode 203A to the second electrode 203B. Then, a current flows in the rib-type optical waveguide 202 disposed between the first electrode 203A and the second electrode 203B. As a result, the signal light guided in the rib-type optical waveguide 202 is absorbed by free carrier absorption of the current flowing in the rib-type optical waveguide 202 of the first VOA 205A, and the intensity of the signal light is attenuated.

[0023] Furthermore, when a positive voltage is applied to the first electrode 203A in the second VOA 200B from the power supply pad 204, a current flows from the first electrode 203A to the second electrode 203B. Then, a current flows in the rib-type optical waveguide 202 disposed between the first electrode 203A and the second electrode 203B. As a result, the signal light guided in the rib-type optical waveguide 202 is absorbed by free carrier absorption of the current flowing in the rib-type optical waveguide 202 of the second VOA 205B, thereby attenuating the intensity of the signal light.

[0024] In the optical device 200 of the comparative example, the signal light is branched by the branching coupler 150, and the power of the signal light input to the rib-type optical waveguides 202 in the first VOA 200A and the second VOA 200B can be reduced by half. As a result, in the optical device 200, the light absorption by the Si substrate 221 is reduced, and the signal light can be propagated with low loss.

[0025] However, in the optical device 200 of the comparative example, current needs to be applied to each of the first electrodes 203A of the first VOA 200A and the second VOA 200B, which doubles the power consumption.

[0026] Therefore, there is a demand for optical devices such as VOAs that can suppress the propagation loss of light in optical waveguides while suppressing power consumption. 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 following examples may be combined as appropriate within the scope of not causing any contradiction. [Example]

[0027] Fig. 1 is a schematic plan view showing an example of an optical device 1 according to a first embodiment. Fig. 2 is a schematic cross-sectional view taken along line AA shown in Fig. 1. The optical device 1 shown in Fig. 1 includes a branching coupler 6 and a VOA 10. The VOA 10 includes a Si substrate 21, a rib-type optical waveguide 2 formed on the Si substrate 21, electrodes 3 electrically connected to both sides of the rib-type optical waveguide 2, and a cladding layer 22 formed on the Si substrate 21 and surrounding the rib-type optical waveguide 2 and the two electrodes 3.

[0028] The branching coupler 6 is a 1-input×N-output, e.g., 1-input×2-output, branching coupler. The branching coupler 6 has an input unit 31 that receives signal light, and a first output unit 32A and a second output unit 32B that branch and output the signal light input from the input unit 31 at a branching ratio of 1:2. Of the signal light input from the input unit 31, the branching coupler 6 outputs, for example, X-polarized signal light from the first output unit 32A and, for example, Y-polarized signal light from the second output unit 32B.

[0029] The rib-type optical waveguide 2 is formed of, for example, Si. The rib-type optical waveguide 2 has two parallel waveguides connected to the outputs of the 1×2 branching coupler 6. The two parallel waveguides include 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 with the same width.

[0030] The rib-type 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-type optical waveguide 2 that inputs signal light to the first waveguide 2A and the second waveguide 2B. The optical output section 2D is an output stage of the rib-type optical waveguide 2 that outputs signal light from the first waveguide 2A and the second waveguide 2B.

[0031] The rib-type optical waveguide 2 has a non-conductive slab region 2G formed between the first waveguide 2A and the second waveguide 2B, a first slab region 2E formed outside the first waveguide 2A, and a second slab region 2F formed outside the second waveguide 2B. The width of the non-conductive slab region 2G, i.e., the width between the first waveguide 2A and the second waveguide 2B, is such that the signal light guided through the first waveguide 2A and the signal light guided through the second waveguide 2B are not coupled to each other.

[0032] The rib-type optical waveguide 2 has a P-doped region 2H formed in the first slab region 2E and an N-doped region 2J formed in the second slab region 2F. The P-doped region 2H is a region outside the first slab region 2E that is P-doped and electrically connected to the first electrode 3A. The N-doped region 2J is a region outside the second slab region 2F that is N-doped and electrically connected to the second electrode 3B.

[0033] The first waveguide 2A, the second waveguide 2B, the first slab region 2E, the second slab region 2F, and the non-conductive slab region 2G are undoped regions in the rib-type optical waveguide 2. The rib-type optical waveguide 2 has a PIN diode structure, for example, with a P-doped region 2H, an undoped region, and an N-doped region 2J.

[0034] The electrode 3 includes a first electrode 3A electrically connected to the P-doped region 2H and a second electrode 3B electrically connected to the N-doped region 2J. The first electrode 3A is a signal electrode connected to a power supply pad 4 to which a voltage is applied. The first electrode 3A 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 3B is a ground electrode connected to a ground pad 5. The second electrode 3B 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.

[0035] The cladding layer 22 is made 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.

[0036] In the optical device 1, the power supply pad 4 is located 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 located near the center of the VOA 10, and power is supplied from the second electrode 3B to the ground pad 5 via a ground via 5A.

[0037] When a positive voltage is applied to the first electrode 3A from the power supply pad 4, a current flows from the first electrode 3A to the second electrode 3B. Then, a current flows through the first waveguide 2A and the second waveguide 2B in the rib-type optical waveguide 2, which are arranged between the first electrode 3A and the second electrode 3B. As a result, free carrier absorption of the current flowing through the parallel first waveguide 2A and second waveguide 2B in the rib-type optical waveguide 2 causes the signal light propagating through the first waveguide 2A and the second waveguide 2B to be absorbed, thereby attenuating the intensity of the signal light. In other words, even if the intensity of the signal light input into the rib-type optical waveguide 2 increases, the branching coupler 6 halves the intensity of the signal light input into the first waveguide 2A and the second waveguide 2B. As a result, light absorption by the Si substrate 21 is reduced, thereby suppressing the propagation loss of the rib-type optical waveguide 2.

[0038] The optical device 1 of the first embodiment includes a rib-type optical waveguide 2 having two parallel waveguides connected to the output of a 1-input × 2-output branching coupler 6, and a first electrode 3A and a second electrode 3B connected to the rib-type optical waveguide 2. The rib-type optical waveguide 2 has a non-conductive slab region 2G formed between the first waveguide 2A and the second waveguide 2B. The rib-type optical waveguide 2 further includes a P-doped region 2H formed in the first slab region 2E and connected to the first electrode 3A, and an N-doped region 2J formed in the second slab region 2F and connected to the second electrode 3B. As a result, even when the intensity of the signal light input to the VOA 10 becomes large, the branching coupler 6 can halve the intensity of the signal light input to the first waveguide 2A and the second waveguide 2B, thereby reducing light absorption by the Si substrate 21 and suppressing propagation loss in the rib-type optical waveguide 2. This also ensures high optical input tolerance to the rib-type optical waveguide 2. Moreover, by sharing the electrode 3 that applies voltage to the first waveguide 2A and the second waveguide 2B in the rib-type optical waveguide 2, power consumption can be significantly reduced compared to the optical device 200 of the comparative example.

[0039] In the rib-type optical waveguide 2 of the optical device 1 of Example 1, the rib widths of the first waveguide 2A and the second waveguide 2B are the same, but this is not limited to this, and an embodiment thereof will be described below as Example 2. [Example]

[0040] Fig. 3 is a schematic plan view showing an example of an optical device 1A according to a second embodiment, and Fig. 4 is a schematic cross-sectional view taken along line AA shown in Fig. 3. Note that the same components as those in the optical device 1 according to the first embodiment are denoted by the same reference numerals, and redundant explanations of the components and operations will be omitted.

[0041] The optical device 1A of the first embodiment differs from the optical device 1A of the second embodiment in that the rib width of the first waveguide 2A1 is different from the rib width of the second waveguide 2B1 in the rib-type optical waveguide 2. The rib width of the first waveguide 2A1 is wider than the rib width of the second waveguide 2B1. The width of the first slab region 2E1 of the first waveguide 2A1 is the same as the width of the second slab region 2F1 of the second waveguide 2B1.

[0042] When the rib widths of the first waveguide 2A and the second waveguide 2B in Example 1 are the same, optical coupling may occur between the first waveguide 2A and the second waveguide 2B. Therefore, the rib widths of the first waveguide 2A1 and the second waveguide 2B1 in Example 2 are adjusted to be different. The rib widths of the adjacent first waveguide 2A1 and second waveguide 2B1 are adjusted to be different, so that optical coupling does not occur between the adjacent first waveguide 2A1 and second waveguide 2B1.

[0043] For example, narrowing the rib width of a waveguide weakens the light confinement in the waveguide, and the propagation loss increases due to light absorption in the doped region. Therefore, it is necessary to adjust the rib width within a range that does not increase the propagation loss. Also, widening the rib width of a waveguide allows multimode propagation through the waveguide, which generates noise in the optical signal. Therefore, it is necessary to adjust the rib width within a range that does not cause multimode propagation.

[0044] Therefore, taking these adjustment points into consideration, the rib width of the first waveguide 2A1 is made wider and the rib width of the second waveguide 2B1 is made narrower. Therefore, the difference in the rib widths of the first waveguide 2A1 and the second waveguide 2B1 causes a difference in the effective refractive index between the first waveguide 2A1 and the second waveguide 2B1, and therefore the signal light guided through the first waveguide 2A1 and the signal light guided through the second waveguide 2B1 are not optically coupled.

[0045] In the optical device 1A of the second embodiment, the rib width of the first waveguide 2A1 is widened and the rib width of the second waveguide 2B1 is narrowed, thereby suppressing optical coupling between the signal light guided through the first waveguide 2A1 and the signal light guided through the second waveguide 2B1.

[0046] In the optical device 1A, even when the intensity of the signal light input to the VOA 10A increases, the branching coupler 6 halves the intensity of the signal light input to the first waveguide 2A and the second waveguide 2B. As a result, light absorption by the Si substrate 21 decreases, thereby suppressing propagation loss in the rib-type optical waveguide 2. Moreover, the electrode 3 that applies voltage to the first waveguide 2A and the second waveguide 2B in the rib-type optical waveguide 2 is shared. As a result, power consumption can be significantly reduced compared to the optical device 200 of the comparative example.

[0047] The rib-type optical waveguide 2 in the optical device 1A of Example 2 has been illustrated as having different rib widths for the first waveguide 2A1 and the second waveguide 2B1. For example, if the rib width of the first waveguide 2A1 is widened, the optical confinement of the first waveguide 2A1 is strengthened and the extinction characteristics are improved. On the other hand, if the rib width of the second waveguide 2B1 is narrowed, the optical confinement of the second waveguide 2B1 is weakened and the extinction characteristics are degraded. Therefore, it is conceivable that the extinction characteristics differ between the first waveguide 2A1 and the second waveguide 2B1. Therefore, an embodiment that can address such a situation will be described below as Example 3. [Example]

[0048] Fig. 5 is a schematic plan view showing an example of an optical device 1B of Example 3, Fig. 6 is a schematic cross-sectional view taken along line AA shown in Fig. 5, and Fig. 7 is a schematic cross-sectional view taken along line BB shown in Fig. 5. Note that the same components as those in the optical device 1 of Example 1 are given the same reference numerals, and redundant explanations of the components and operations will be omitted.

[0049] The optical device 1B of Example 3 differs from the optical device 1 of Example 1 in that the rib width of the first waveguide 2A2 varies between the optical input portion 2C and the optical output portion 2D, and the rib width of the second waveguide 2B2 varies between the optical input portion 2C and the optical output portion 2D. Furthermore, the first waveguide 2A2 and the second waveguide 2B2 are configured to be point-symmetrical.

[0050] The first waveguide 2A2 in the optical device 1B has a first rib width X1, which is a wide rib width between the optical input section 2C and the intermediate section, and a second rib width X2, which is a narrow rib width between the intermediate section and the optical output section 2D. The first waveguide 2A2 also has a tapered rib width in the intermediate section, where the rib width gradually changes from the first rib width X1 to the second rib width X2.

[0051] The second waveguide 2B2 in the optical device 1B has a second rib width X2, which is a narrow rib width between the optical input section 2C and the intermediate section, and a first rib width X1, which is a wide rib width between the intermediate section and the optical output section 2D. The second waveguide 2B2 also has a tapered rib width in the intermediate section, where the rib width gradually changes from the second rib width X2 to the first rib width X1. In other words, the first waveguide 2A2 and the second waveguide 2B2 are configured point-symmetrically.

[0052] The width of the first slab region 2E2 of the first waveguide 2A2 varies depending on the rib width of the first waveguide 2A2, and the width of the second slab region 2F2 of the second waveguide 2B2 varies depending on the rib width of the second waveguide 2B2.

[0053] Although the first waveguide 2A2 and the second waveguide 2B2 have different rib widths from the optical input section 2C to the optical output section 2D, the first waveguide 2A2 and the second waveguide 2B2 are configured to be point-symmetrical, so that the extinction ratios at the optical output section 2D can be made the same for the first waveguide 2A2 and the second waveguide 2B2.

[0054] In the optical device 1B of the third embodiment, the rib width of the first waveguide 2A2 varies between the optical input section 2C and the optical output section 2D, and the rib width of the second waveguide 2B2 varies between the optical input section 2C and the optical output section 2D. In the optical device 1B, the first waveguide 2A2 and the second waveguide 2B2 are configured to be point-symmetric. As a result, the extinction ratio at the optical output section 2D can be made the same for the first waveguide 2A2 and the second waveguide 2B2.

[0055] Moreover, in the optical device 1B, the rib width of the first waveguide 2A2 is different from the rib width of the second waveguide 2B2, so that optical coupling between the signal light guided through the first waveguide 2A2 and the signal light guided through the second waveguide 2B2 can be suppressed.

[0056] In the optical device 1B, even when the intensity of the signal light input to the VOA 10B increases, the branching coupler 6 halves the intensity of the signal light input to the first waveguide 2A2 and the second waveguide 2B2. As a result, light absorption by the Si substrate 21 decreases, thereby suppressing propagation loss in the rib-type optical waveguide 2. Moreover, the electrode 3 that applies voltage to the first waveguide 2A2 and the second waveguide 2B2 in the rib-type optical waveguide 2 is shared. As a result, power consumption can be significantly reduced compared to the optical device 200 of the comparative example.

[0057] In the optical device 1 of Example 1, a 1-input x 2-output branching coupler 6 is used and the parallel waveguide has two waveguides, but when a 1-input x N-output branching coupler 6 is used, the parallel waveguide has N waveguides. Therefore, an embodiment in which a 1-input x 3-output branching coupler 6A is used will be described below as Example 4. [Example]

[0058] Fig. 8 is a schematic plan view showing an example of an optical device 1C of Example 4, and Fig. 9 is a schematic cross-sectional view taken along line AA shown in Fig. 8. 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 1C of Example 4 in that a 1-input × 3-output branching coupler 6A is used, and the parallel waveguides are replaced with three waveguides.

[0059] The optical device 1C includes a branching coupler 6A and a VOA 10C. The branching coupler 6A is a 1-input, 3-output branching coupler. The branching coupler 6A includes an input 31, a first output 32A1, a second output 32A2, and a third output 32A3.

[0060] The parallel waveguides in the rib-type optical waveguide 2 in the VOA 10C include 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 rib widths of the first waveguide 2A3 and the second waveguide 2B3 are the same. The rib width of the third waveguide 2K is narrower than the rib width of the first waveguide 2A3.

[0061] The rib-type optical waveguide 2 has a non-conductive slab region 2G31 formed between the first waveguide 2A3 and the third waveguide 2K, and a first slab region 2E3 formed outside the first waveguide 2A3. The rib-type optical waveguide 2 has a non-conductive slab region 2G32 formed between the second waveguide 2B3 and the third waveguide 2K, and a second slab region 2F3 formed outside the second waveguide 2B3.

[0062] The width of the non-conductive slab region 2G31 is the width between the first waveguide 2A3 and the third waveguide 2K, and is a width that prevents coupling between the signal light guided in the first waveguide 2A3 and the signal light guided in the third waveguide 2K. The width of the non-conductive slab region 2G32 is the width between the second waveguide 2B3 and the third waveguide 2K, and is a width that prevents coupling between the signal light guided in the second waveguide 2B3 and the signal light guided in the third waveguide 2K.

[0063] The rib-type optical waveguide 2 has a P-doped region 2H formed in the first slab region 2E3 and an N-doped region 2J formed in the second slab region 2F3. The P-doped region 2H is a region outside the first slab region 2E3 that is P-doped and electrically connected to the first electrode 3A. The N-doped region 2J is a region outside the second slab region 2F3 that is N-doped and electrically connected to the second electrode 3B.

[0064] The first waveguide 2A3, the third waveguide 2K, the second waveguide 2B3, the first slab region 2E3, the second slab region 2F3, the non-conductive slab region 2G31, and the non-conductive slab region 2G32 are undoped regions in the rib-type optical waveguide 2. The rib-type optical waveguide 2 has a PIN diode structure, for example, with a P-doped region 2H, an undoped region, and an N-doped region 2J.

[0065] When a positive voltage is applied to the first electrode 3A from the power supply pad 4, a current flows from the first electrode 3A to the second electrode 3B. Then, a current flows through the first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3 in the rib-type optical waveguide 2 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 by 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-type optical waveguide 2. This results in attenuation of the intensity of the signal light. That is, even if the intensity of the signal light input into the rib-type optical waveguide 2 increases, the branching coupler 6A halves the intensity of the signal light input into the first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3. As a result, light absorption by the Si substrate 21 decreases, and propagation loss in the rib-type optical waveguide 2 can be suppressed.

[0066] The optical device 1C of the fourth embodiment has a rib-type optical waveguide 2 having three parallel waveguides connected to the output of a branching coupler 6A with one input and three outputs. As a result, even when the intensity of the signal light input to the VOA 10C increases, the intensity of the signal light input to the first waveguide 2A3, the second waveguide 2B3, and the third waveguide 2K by the branching coupler 6A is reduced to one-third. Furthermore, light absorption by the Si substrate 21 is reduced, thereby suppressing propagation loss in the rib-type optical waveguide 2. Furthermore, by sharing the electrode 3 that applies voltage to the first waveguide 2A3, the third waveguide 2K, and the second waveguide 2B3 in the rib-type optical waveguide 2, power consumption can be significantly reduced compared to the optical device 200 of the comparative example.

[0067] Next, an optical transceiver 50 employing the optical device 1 of the first to fourth embodiments will be described. FIG. 10 is an explanatory diagram showing an example of an optical transceiver 50 employing the optical device 1 of the present embodiment. The optical transceiver 50 shown in FIG. 10 is connected to an output-side optical fiber FC and an input-side 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 of the acquired electrical signal to obtain the reception data.

[0068] 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.

[0069] 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 built in that guides light.

[0070] 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 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.

[0071] 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.

[0072] 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.

[0073] Furthermore, the various processing functions performed by each device may be executed in whole or in part on a CPU (Central Processing Unit) (or a microcomputer such as an MPU (Micro Processing Unit) or MCU (Micro Controller Unit)). 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 or MCU), or on hardware using wired logic. [Explanation of symbols]

[0074] 1 Optical Devices 2. Rib-type optical waveguide 2A First Waveguide 2B Second waveguide 2E First Slab Area 2F Second slab area 2G Non-conductive slab area 2H P-doped region 2J N-doped region 3A First electrode 3B Second electrode 6-branch coupler 10 VOA

Claims

1. a rib-type optical waveguide having N parallel waveguides connected to the outputs of a 1-input × N-output branching coupler; a first electrode and a second electrode connected to the rib-type optical waveguide; The rib-type optical waveguide is a non-conductive slab region formed between the waveguides; a P-doped region formed in a first slab region outside one of the N waveguides, the first slab region being connected to the first electrode; an N-doped region formed in a second slab region outside the other outermost waveguide of the N waveguides and connected to the second electrode; An optical device comprising:

2. The rib-type optical waveguide is two parallel waveguides connected to the outputs of the branching coupler having one input and two outputs; The width of one of the two waveguides is 2. The optical device according to claim 1, wherein the width of one of said two waveguides is different from that of the other one.

3. The rib-type optical waveguide is two parallel waveguides connected to the outputs of the branching coupler having one input and two outputs; a waveguide width between the input and output of one of the two waveguides is changed; The width of the other of the two waveguides between the input and output is changed, The one waveguide is 2. The optical device according to claim 1, wherein the optical device has a point-symmetrical configuration with respect to the other waveguide.

4. The P-doped region is a first slab region formed outside the one waveguide, the outside of the first slab region being a P-doped region; The N-doped region is 2. The optical device according to claim 1, wherein the second slab region is formed outside the other waveguide, and the outside of the second slab region is an N-doped region.

5. an optical modulation unit that optically modulates light using a transmission signal and transmits the transmission light; an optical device that attenuates the light within the optical modulation unit, The optical device is a rib-type optical waveguide having N parallel waveguides connected to the outputs of a 1-input × N-output branching coupler; a first electrode and a second electrode connected to the rib-type optical waveguide; The rib-type optical waveguide is a non-conductive slab region formed between the waveguides; a P-doped region formed in a first slab region outside one of the N waveguides, the first slab region being connected to the first electrode; an N-doped region formed in a second slab region outside the other outermost waveguide of the N waveguides and connected to the second electrode; An optical transmitting device comprising:

6. an optical receiving unit that receives a reception signal from the received light using light; an optical device that attenuates the light in the optical receiving unit, The optical device is a rib-type optical waveguide having N parallel waveguides connected to the outputs of a 1-input × N-output branching coupler; a first electrode and a second electrode connected to the rib-type optical waveguide; The rib-type optical waveguide is a non-conductive slab region formed between the waveguides; a P-doped region formed in a first slab region outside one of the N waveguides, the first slab region being connected to the first electrode; an N-doped region formed in a second slab region outside the other outermost waveguide of the N waveguides and connected to the second electrode; An optical receiving device comprising:

Images