Optical device, optical transmitter and optical receiver

Abstract

To provide an optical device and the like capable of suppressing change in tapping rate even when the wavelength of signal light changes.SOLUTION: The optical device includes a first coupler, a second coupler, and a monitor part. The first coupler includes a first input port, a first bar port located to the first input port in a bar direction, and a first cross port located to the first input port in a crossing direction. Many pieces of signal light on a short wavelength side are tapped from the first input port to the first bar port. The second coupler includes a second input port, a second bar port located to the second input port in the bar direction, and a second cross port located to the second input port in the crossing direction. Many pieces of signal light on a long-wavelength side are tapped from the second input port to the second cross port. The monitor part is connected to the first bar port or the second cross port, and monitors signal light outputted from the first bar port or the second cross port.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] For example, coherent optical communication technology enables high-speed, large-capacity communication in optical fiber communication networks. Optical transceivers for coherent optical communication monitor the power of the signal light propagating through the optical waveguide of the optical device used therein, and control the internal circuitry, for example, adjusting the attenuation, based on the monitoring results. Therefore, optical transceivers require an optical tap to tap a portion of the signal light propagating through the optical waveguide.

[0003] As a method for realizing an optical tap, for example, a tapered directional coupler has been proposed (see, for example, Patent Document 1). In the optical device of Patent Document 1, for example, SiO2 in a BOX (Buried Oxide) layer on a substrate of an SOI (Silicon-On-Insulator) wafer is used as a lower cladding, and the Si in the SOI layer is etched to form a core of any shape. Furthermore, by depositing SiO2 from above, an upper cladding is formed, and an optical device based on silicon photonics technology can be manufactured.

[0004] Patent Document 1 discloses a device consisting of two parallel tapered waveguides, in which light input to one tapered waveguide gradually transfers its optical power to the other adjacent tapered waveguide along the propagation direction. This is because the device uses evanescent waves, which cause light to leak out of the core. Another reason is that at a certain cross section (perpendicular to the propagation direction of light) within the two tapered waveguides, the effective refractive indices of light guided through each tapered waveguide match, and the magnitude relationship between the effective refractive indices of light guided through each of the two tapered waveguides is reversed before and after this cross section.

[0005] In Patent Document 1, the evanescent wave of TM0 seeps out from the core more widely than TE0, and by utilizing this, only TM0 (almost 100%) transitions to the other adjacent tapered waveguide, while TE0 minimizes light transition. As a result, the optical device of Patent Document 1 enables polarization separation between TM0 and TE0. This is because the greater the light seepage due to the evanescent wave, the stronger the optical coupling to the adjacent tapered waveguide, making nearly 100% transition possible with a shorter taper length. Another reason is that this utilizes the fact that if the optical coupling to the adjacent tapered waveguide is weak, only a small amount of transition occurs with the same taper length.

[0006] Here, TE0 is the light in the TE mode where the electric field component parallel to the substrate is the main component and the effective refractive index is the maximum, and TM0 is the light in the TM mode where the electric field component perpendicular to the substrate is the main component and the effective refractive index is the maximum. When focusing on the operation when TE0 is input, some of the input power will transition to the other adjacent tapered waveguide, but the remaining power will not transition and will remain in one tapered waveguide and be optically tapped.

[0007] In optical devices, for example, when the wavelength of the signal light is 1520 nm, the tapping ratio, which indicates the proportion of the signal light guided in the adjacent waveguide that is tapped, is approximately 2.2%, and when it is 1580 nm, the tapping ratio is approximately 3.5%. In other words, in conventional optical devices, when the wavelength of the guided signal light changes, the tapping ratio also changes. The reason for this is that the longer the wavelength, the greater the leakage of light due to evanescent waves, and the stronger the optical coupling to the other adjacent tapered waveguide.

[0008] In other words, in an optical device that functions as an optical tap by optically coupling one tapered waveguide to another adjacent tapered waveguide via an evanescent wave, the longer the wavelength, the stronger this optical coupling becomes, so the tap ratio changes in response to changes in wavelength. Note that, for convenience of explanation, a tapered directional coupler is used as an example, but the tap ratio also changes in response to changes in wavelength in a normal directional coupler that is not tapered. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2016 / 052343 [Patent Document 2] Japanese Patent Application Publication No. 8-234032 [Patent Document 3] Japanese Patent Application Publication No. 4-212108 [Patent Document 4] US Patent Application Publication No. 2018 / 0372957 [Patent Document 5] U.S. Patent Application Publication No. 2021 / 0181419 Summary of the Invention [Problem to be solved by the invention]

[0010] However, coherent optical transceivers must operate over a wide wavelength range of signal light to support wavelength division multiplexing communications, so the tap ratio changes significantly depending on the wavelength of the signal light. Therefore, there is a need for optical devices that can suppress changes in the tap ratio even when the wavelength of the signal light changes.

[0011] In one aspect, an object is to provide an optical device or the like that can suppress a change in tap ratio even when the wavelength of signal light changes. [Means for solving the problem]

[0012] An optical device according to one embodiment includes a first coupler, a second coupler, and a monitor unit. The first coupler has a first input port, a first bar port located in the bar direction relative to the first input port, and a first cross port located in the cross direction relative to the first input port. In the first coupler, signal light on the shorter wavelength side from the first input port is tapped mostly to the first bar port. The second coupler has a second input port, a second bar port located in the bar direction relative to the second input port, and a second cross port located in the cross direction relative to the second input port. In the second coupler, signal light on the longer wavelength side from the second input port is tapped mostly to the second cross port. The monitor unit is connected to the first bar port or the second cross port, and monitors the signal light output from the first bar port or the second cross port. [Effects of the Invention]

[0013] According to one aspect, even when the wavelength of the signal light changes, the change in the tap ratio can be suppressed. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of an optical device according to a first embodiment. [Figure 2] FIG. 2 is a schematic plan view showing an example of the first coupler. [Figure 3] FIG. 3 is a schematic cross-sectional view showing an example of the portion taken along line AA shown in FIG. [Figure 4] FIG. 4 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of the first coupler. [Figure 5] FIG. 5 is a schematic plan view showing an example of the second coupler. [Figure 6] FIG. 6 is a schematic cross-sectional view showing an example of the portion of line BB shown in FIG. [Figure 7] FIG. 7 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of the second coupler. [Figure 8] FIG. 8 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of an optical device. [Figure 9] FIG. 9 is a schematic plan view showing an example of a coupler of a comparative example. [Figure 10] FIG. 10 is a schematic cross-sectional view showing an example of the CC line portion shown in FIG. [Figure 11] FIG. 11 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of a coupler of a comparative example. [Figure 12] FIG. 12 is an explanatory diagram illustrating an example of an optical device according to a second embodiment. [Figure 13] FIG. 13 is an explanatory diagram illustrating an example of an optical device according to a third embodiment. [Figure 14] FIG. 14 is an explanatory diagram showing an example of an optical transceiver according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the optical device and the like of the present invention will be described with reference to the drawings. Note that the disclosed technology is not limited to these embodiments. Furthermore, the embodiments shown below may be combined as appropriate within the scope of not causing any contradiction. [Example]

[0016] FIG. 1 is an explanatory diagram illustrating an example of an optical device 1 according to a first embodiment. The optical device 1 illustrated in FIG. 1 includes a first coupler 2, a second coupler 3, a first PD (Photo Detector) 4A(4), a second PD 4B(4), and an adder 5. The first coupler 2 includes a first input port 21, a first bar port 22 located in the bar direction relative to the first input port 21, and a first cross port 23 located in the cross direction relative to the first input port 21. The first coupler 2 is, for example, a 2×2 coupler in which a portion of the signal light, mainly having a short wavelength, from the first input port 21 is tapped to the first bar port 22. That is, in the first coupler 2, a larger amount of the signal light on the short wavelength side from the first input port 21 is tapped to the first bar port 22 compared to the signal light on the long wavelength side.

[0017] The second coupler 3 has a second input port 31, a second bar port 32 located in the bar direction relative to the second input port 31, and a second cross port 33 located in the cross direction relative to the second input port 31. The second coupler 3 is, for example, a 2×2 coupler in which a portion of the signal light, mainly of long wavelengths, from the second input port 31 is tapped to the second cross port 33. In other words, in the second coupler 3, more of the signal light on the long wavelength side from the second input port 31 is tapped to the second cross port 33 than the signal light on the short wavelength side.

[0018] The first PD4A is a monitor unit connected to the first bar port 22 of the first coupler 2 and performs current conversion on a portion of the signal light tapped at the first bar port 22. The second PD4B is a monitor unit connected to the second cross port 33 of the second coupler 3 and performs current conversion on a portion of the signal light tapped at the second cross port 33.

[0019] The adder 5 adds together the current value mainly consisting of short wavelengths from the first PD 4A and the current value mainly consisting of long wavelengths from the second PD 4B, and outputs the added current value as a monitor output to the control circuit via an A / D converter (not shown).

[0020] Fig. 2 is a schematic plan view showing an example of the first coupler 2, and Fig. 3 is a schematic cross-sectional view showing an example of the AA line portion shown in Fig. 2. The first coupler 2 is a tapered directional coupler having a first waveguide 11 that inputs signal light as a first input port 21, and a second waveguide 12 adjacent to the first waveguide 11. The first waveguide 11 is, for example, a tapered waveguide whose waveguide width narrows from the input stage to the output stage. The second waveguide 12 is, for example, a tapered waveguide whose waveguide width widens from the input stage to the output stage.

[0021] The first coupler 2 shown in FIG. 3 includes a Si substrate (not shown), a lower cladding layer 13 made of, for example, SiO2, laminated on the Si substrate, and a first waveguide 11 and a second waveguide 12, each of which is a core 14 made of, for example, Si, formed on the lower cladding layer 13. The first coupler 2 further includes an upper cladding layer 15 made of, for example, SiO2, laminated on the lower cladding layer 13, the first waveguide 11, and the second waveguide 12. The waveguide width of the first waveguide 11 shown in FIG. 3 is, for example, (0.36+X) μm, and the waveguide width of the second waveguide 12 is, for example, (0.46+X) μm, where X is 0 to 0.1 μm. The height of the first waveguide 11 and the second waveguide 12 is, for example, 0.22 μm. Furthermore, the spacing between the parallel sections of the first waveguide 11 and the second waveguide 12 is, for example, 0.21 μm.

[0022] The parallel section in which the first waveguide 11 and the second waveguide 12 are parallel to each other in the first coupler 2 has a start point and an end point. The waveguide width of the first waveguide 11 at the start point is equal to the waveguide width of the second waveguide 12 at the end point. The waveguide width of the first waveguide 11 at the end point is equal to the waveguide width of the second waveguide 12 at the start point. The first waveguide 11 and the second waveguide 12 have a point-symmetric structure. The parallel section is 100 μm long. The S-bend at the first bar port of the first waveguide 11 and the S-bend at the input stage of the second waveguide 12 have a radius of 60 μm.

[0023] In a tapered directional coupler, for example, when the waveguide length corresponding to the parallel section is made shorter than the reference length, only a portion of the signal light guided in the first waveguide 11 transitions from the first waveguide 11 to the second waveguide 12. In contrast, in a tapered directional coupler, when the waveguide length corresponding to the parallel section is made longer than the reference length, the signal light guided in the first waveguide 11 transitions to the second waveguide 12. When the waveguide length corresponding to the parallel section is the reference length, the rate at which the power of the signal light transitions from the first waveguide 11 to the second waveguide 12 increases as the wavelength increases and the proportion of evanescent waves increases.

[0024] In the first coupler 2, the waveguide length of the parallel section is set to 100 μm, so the power of the signal light steadily shifts from the first waveguide 11 to the second waveguide 12, reducing the power of the signal light that can be tapped from the first bar port 22. In the first coupler 2, as the wavelength of the signal light propagating through the first waveguide 11 becomes longer, it tends to shift to the second waveguide 12, but short wavelengths remain in the first waveguide 11, so that the power of the signal light with a short wavelength is mainly tapped at the output end of the first bar port 22. As a result, the first coupler 2 functions as the first cross port 23, outputting the signal light from the second waveguide 12, and as the first bar port 22, mainly tapping the signal light with a short wavelength from the first waveguide 11.

[0025] 4 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of the first coupler 2. The tap ratio of the first coupler 2 to the first PD 4A side, i.e., the ratio of the optical power tapped to the first bar port 22 connected to the first PD 4A side relative to the input signal light power, was calculated using the finite-difference time-domain method. The calculation results show that mainly short-wavelength signal light is tapped at the first bar port 22 of the first coupler 2.

[0026] Fig. 5 is a schematic plan view showing an example of the second coupler 3, and Fig. 6 is a schematic cross-sectional view showing an example of the BB line portion shown in Fig. 5. The second coupler 3 shown in Fig. 5 is a tapered directional coupler having a first waveguide 11 that inputs signal light as a second input port 31, and a second waveguide 12 adjacent to the first waveguide 11. The first waveguide 11 is, for example, a tapered waveguide whose waveguide width narrows from the input stage to the output stage. The second waveguide 12 is, for example, a tapered waveguide whose waveguide width widens from the input stage to the output stage.

[0027] The second coupler 3 shown in FIG. 6 includes a Si substrate (not shown), a lower cladding layer 13 made of, for example, SiO2, etc., laminated on the Si substrate, and a first waveguide 11 and a second waveguide 12, each of which is a core 14 made of, for example, Si, formed on the lower cladding layer 13. The second coupler 3 also includes an upper cladding layer 15 made of, for example, SiO2, etc., laminated on the lower cladding layer 13, the first waveguide 11, and the second waveguide 12. The waveguide width of the first waveguide 11 shown in FIG. 6 is, for example, (0.36+X) μm, and the waveguide width of the second waveguide 12 is, for example, (0.46+X) μm, where X is 0 to 0.1 μm. The height of the first waveguide 11 and the second waveguide 12 is, for example, 0.22 μm. Furthermore, the width of the parallel section between the first waveguide 11 and the second waveguide 12 is, for example, 0.21 μm.

[0028] The parallel section in which the first waveguide 11 and the second waveguide 12 are parallel to each other in the second coupler 3 has a start point and an end point. The waveguide width of the first waveguide 11 at the start point is equal to the waveguide width of the second waveguide 12 at the end point. The waveguide width of the first waveguide 11 at the end point is equal to the waveguide width of the second waveguide 12 at the start point. The first waveguide 11 and the second waveguide 12 have a point-symmetric structure. The parallel section is 6 μm. The S-bend at the second bar port 32 of the first waveguide 11 and the S-bend at the input stage of the second waveguide 12 have a radius of 60 μm.

[0029] When the waveguide length corresponding to the parallel section is the reference length, the rate at which the power of the signal light shifts from the first waveguide 11 to the second waveguide 12 increases with wavelength, which increases the proportion of evanescent waves. In the second coupler 3, when the waveguide length of the parallel section is short (6 μm), the power of the signal light is less likely to shift from the first waveguide 11 to the second waveguide 12, and the power of the signal light that can be tapped from the second cross port 33 decreases. Therefore, since the second coupler 3 is prone to leakage as the wavelength of the signal light propagating through the first waveguide 11 increases, the power of the signal light with a longer wavelength is primarily tapped at the output end of the second cross port 33. As a result, the second coupler 3 outputs the signal light from the first waveguide 11 as the second cross port 32, and primarily taps the signal light with a longer wavelength from the second waveguide 12 as the second cross port 33.

[0030] To begin with, the input to the first coupler 2 in the optical device 1 is not a simultaneous input of signal light of a plurality of wavelengths, but rather a single signal light among a plurality of wavelengths is input on a wavelength-by-wavelength basis.

[0031] When a signal light of a single wavelength is input to the first coupler 2, the signal light mainly consisting of a short wavelength is tapped from the first bar port 22, and the signal light transitioned from the first waveguide 11 is output from the first cross port 23. When the signal light mainly consisting of a short wavelength tapped from the first bar port 22 is present, the first PD 4A converts the signal light mainly consisting of a short wavelength into a current and outputs the current value mainly consisting of a short wavelength after the current conversion to the adder 5.

[0032] Furthermore, the second coupler 3 taps the signal light mainly consisting of long wavelengths from the second cross port 33 out of the signal light input from the first cross port 23 of the first coupler 2, and outputs the remaining signal light from the second cross port 32. When the signal light mainly consisting of long wavelengths tapped from the second cross port 33 is present, the second PD 4B converts the signal light mainly consisting of long wavelengths into a current and outputs the current-converted current value mainly consisting of long wavelengths to the adder 5. When the signal light mainly consisting of short wavelengths is present, the adder 5 monitors and outputs the current value mainly consisting of short wavelengths, and when the signal light mainly consisting of long wavelengths is present, it monitors and outputs the current value mainly consisting of long wavelengths.

[0033] 7 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of the second coupler 3. The tap ratio of the second coupler 3 to the second PD 4B side, i.e., the ratio of the optical power output to the second cross port 33 connected to the second PD 4B side relative to the input optical power, was calculated using the finite-difference time-domain method. The calculation results show that signal light mainly having long wavelengths is tapped at the second cross port 33 of the second coupler 3.

[0034] In the adder 5 of the optical device 1, a current value corresponding to the signal light mainly composed of a short wavelength tapped at the first cross port 22 of the first coupler 2 is added to a current value corresponding to the signal light mainly composed of a long wavelength tapped at the second cross port 33 of the second coupler 3. FIG. 8 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of the optical device 1. In the optical device 1, when the signal light input to the first coupler 2 is, for example, in the wavelength range of 1.524 μm to 1.572 μm, the minimum tap ratio is 16.6%, the maximum tap ratio is 18.7%, and the ratio of the minimum tap ratio to the maximum tap ratio is 1.12. In other words, it can be seen that in the optical device 1, fluctuations in the tap ratio can be suppressed even when the wavelength changes.

[0035] The time it takes for the signal light to reach the adder 5 via the first PD 4A after input to the first input port 21 of the first coupler 2 is defined as a first arrival time D1. The time it takes for the signal light to reach the adder 5 via the second coupler 3 and the second PD 4B after input to the first input port 21 is defined as a second arrival time D2. The optical wiring and electrical wiring of the optical device 1 are adjusted so that the first arrival time D1 and the second arrival time D2 are approximately equal. Specifically, the lengths of the optical wiring and electrical wiring are determined so that the sum of the light arrival time from the input to the first coupler 2 to each PD 4 and the electrical arrival time from each PD 4 to the adder 5, which is the current summing portion, is approximately equal for all PD currents. As a result, when the PD currents are summed, speed degradation of the PDs 4 due to pulse delays of each PD current can be suppressed.

[0036] Here, the differences between the characteristics of the first coupler 2 and the second coupler 3 and the characteristics of the comparative coupler 100 will be described. Fig. 9 is a schematic plan view showing an example of the comparative coupler 100, and Fig. 10 is a schematic cross-sectional view showing an example of the CC line portion shown in Fig. 9. The coupler 100 shown in Fig. 9 is a tapered directional coupler having a first waveguide 111 for inputting signal light and a second waveguide 112 adjacent to the first waveguide 111.

[0037] 10 includes a Si substrate (not shown), a lower cladding layer 113 stacked on the Si substrate, and a first waveguide 111 and a second waveguide 112, which are cores 114 formed on the lower cladding layer 113. The coupler 100 further includes an upper cladding layer 115 stacked on the lower cladding layer 113, the first waveguide 111, and the second waveguide 112. The first waveguide 111 has a width of, for example, (0.36+X) μm, and the second waveguide 112 has a width of, for example, (0.46+X) μm, where X is 0 to 0.1 μm. The heights of the first waveguide 111 and the second waveguide 112 are, for example, 0.22 μm. Furthermore, the width of the parallel section between the first waveguide 111 and the second waveguide 112 is, for example, 0.21 μm. The parallel section is 8.6 μm. The S-bend at the output stage of the first waveguide 111 and the S-bend at the input stage of the second waveguide 112 each have a radius of 60 μm.

[0038] In the coupler 100, the tap ratio, which indicates the proportion of the signal light tapped from the first waveguide 111 or the second waveguide 112, varies in accordance with a change in the wavelength of the guided signal light. Fig. 11 is an explanatory diagram showing an example of the relationship between the wavelength and the tap ratio of the comparative coupler 100. In the coupler 100, when the input signal light is in the wavelength range of 1.524 μm to 1.572 μm, for example, the minimum tap ratio is 16.6% and the maximum tap ratio is 24.2%, and the ratio of the minimum tap ratio to the maximum tap ratio is 1.45. In other words, it can be seen that in the coupler 100, the tap ratio varies greatly when the wavelength changes.

[0039] Therefore, in the wavelength range of 1.524 μm to 1.572 μm, the ratio of the minimum tap ratio to the maximum tap ratio in the coupler 100 of the comparative example is 1.45, whereas in the optical device 1 of this example, the ratio of the minimum tap ratio to the maximum tap ratio is 1.12. Therefore, in the optical device 1 of this example, fluctuations in the tap ratio can be suppressed even when the wavelength of the signal light fluctuates.

[0040] On the other hand, in the comparative coupler 100, the tap rate fluctuates significantly when the wavelength of the guided signal light changes, so the A / D converter that digitally converts the current value of the signal light tapped by the coupler 100 requires a wide dynamic range, resulting in large quantization noise.

[0041] In contrast, in the optical device 1 of the first embodiment, fluctuations in the tap rate can be suppressed even when the wavelength of the guided signal light changes, so that the A / D converter does not require a wide dynamic range and, assuming the same number of quantization bits, the quantization noise is reduced. As a result, the optical device 1 is useful for A / D converters used in optical transceivers whose signal light operates over a wide wavelength range.

[0042] The optical device 1 of Example 1 combines a first coupler 2 that makes it easier to tap signal light with a short wavelength and a second coupler 3 that makes it easier to tap signal light with a long wavelength, and by adding up the current values ​​of the light tapped by each coupler, it is possible to realize a tap with little wavelength dependency.

[0043] The first coupler 2 and the second coupler 3 are optically coupled via evanescent waves, utilizing the characteristic that the tap ratio is greater on the long wavelength side than on the short wavelength side. In the first coupler 2, the first cross port 22 is connected to the first PD 4A to mainly tap light on the short wavelength side, and in the second coupler 3, the second cross port 33 is connected to the second PD 4B to mainly tap light on the long wavelength side. Then, by combining the outputs of the first PD 4A and the second PD 4B, a tap with little wavelength dependency can be achieved.

[0044] In the first embodiment, the input of the optical device 1 is the first input port 21 of the first coupler 2, and the first cross port 23 of the first coupler 2 is connected to the second input port 31 of the second coupler 3. However, this is not limiting. For example, the input of the optical device 1 may be the second input port 31 of the second coupler 3, and the second cross port 32 of the second coupler 3 may be connected to the first input port 21 of the first coupler 2, and other suitable modifications may be made.

[0045] Although the first coupler 2 and the second coupler 3 are exemplified as 2×2 couplers, they may be 1×2 couplers with at least one input, and may be changed as appropriate.

[0046] The cross-sectional shapes of the first coupler 2 and the second coupler 3 do not have to be those shown in Figures 3 and 6 and can be changed as appropriate. By adjusting the cross-sectional shape, for example, to a shape of a waveguide other than a rectangular waveguide, such as a rib waveguide, the degree of freedom in designing the tap ratio and its wavelength dependency can be increased.

[0047] Furthermore, the first coupler 2 and the second coupler 3 are not limited to the first waveguide 11 and the second waveguide 12 shown in Figures 2 and 5 being linearly tapered, and can be modified as appropriate. The first waveguide 11 and the second waveguide 12 may, for example, have a width that changes in a quadratic curve with respect to the light propagation direction, may connect waveguides with different tapered structures along the way, or may be linear waveguides, i.e., non-tapered waveguides. Furthermore, one of the waveguides may not be tapered. In any case, it is obvious that optical coupling by evanescent waves is maintained.

[0048] The first coupler 2 and the second coupler 3 may be configured as ordinary directional couplers that are not tapered, and can be changed as appropriate. Since ordinary directional couplers are easier to design than tapered directional couplers, they are preferable from the viewpoint of simplifying the design.

[0049] In the optical device 1 of Example 1, an example is shown in which the optical device 1 has a first PD 4A connected to the first bar port 22 of the first coupler 2 and a second PD 4B connected to the second cross port 33 of the second coupler 3. For example, it is not necessary for the first bar port 22 and the second cross port 33 to all be connected to different PDs 4, and such an embodiment will be described below as Example 2. [Example]

[0050] FIG. 12 is an explanatory diagram illustrating an example of an optical device 1A according to a second embodiment. The same components as those in the optical device 1 according to the first embodiment are denoted by the same reference numerals, and descriptions of the overlapping components and operations will be omitted. The optical device 1 according to the first embodiment differs from the optical device 1A according to the second embodiment in that the first PD 4A, the second PD 4B, and the adder 5 are configured as a single detector 6. The detector 6 is connected to the first bar port 22 of the first coupler 2 and also to the second cross port 33 of the second coupler 3. The detector 6 combines the short-wavelength signal light mainly tapped at the first bar port 22 and the long-wavelength signal light mainly tapped at the second cross port 33, converts the combined signal light into a current, and outputs the converted current value for monitoring. An example of a single detector is known from U.S. Patent Application Publication No. 2019 / 0391006.

[0051] The time it takes for the signal light to reach the detector 6 after being input to the first input port 21 of the first coupler 2 is defined as a third arrival time D3. The time it takes for the signal light to reach the detector 6 after passing through the second coupler 3 after being input to the first input port 21 is defined as a fourth arrival time D4. The optical wiring and electrical wiring of the optical device 1A are adjusted so that the third arrival time D3 and the fourth arrival time D4 are equal. Specifically, the lengths of the optical wiring and electrical wiring are determined so that the sum of the time it takes for the light to reach the detector 6 after being input to the first coupler 2 and the time it takes for the electricity to reach the sum of the converted light-to-current portions inside the detector 6 is approximately equal for all PD currents. As a result, when the PD currents are summed, degradation of the PD speed in the detector 6 due to delays in the pulses of each PD current can be suppressed.

[0052] The detector 6 in the optical device 1A of the second embodiment is connected to the first bar port 22 of the first coupler 2 and also to the second cross port 33 of the second coupler 3. Furthermore, the detector 6 multiplexes the signal light mainly consisting of a short wavelength tapped at the first bar port 22 and the signal light mainly consisting of a long wavelength tapped at the second cross port 33, converts the signal light into a current, and outputs the current value after the current conversion as a monitor. As a result, it is possible to reduce the number of PD elements compared to the optical device 1 of the first embodiment, which contributes to the miniaturization of the optical device 1A.

[0053] Incidentally, the optical device 1 of Example 1 has been illustrated as having a single first coupler 2 and a single second coupler 3, but is not limited to this, and an embodiment thereof will be described below as Example 3. Note that the same components as those of the optical device 1 of Example 1 are given the same reference numerals, and descriptions of the overlapping components and operations will be omitted. [Example]

[0054] Fig. 13 is an explanatory diagram showing an example of an optical device 1B according to Example 3. The optical device 1B shown in Fig. 13 includes two first couplers 2 (2A, 2B), two second couplers 3 (3A, 3B), two first PDs 4A (4A1, 4A2), two second PDs 4B (4B1, 4B2), and three adders 5 (5A, 5B, 5C).

[0055] One first coupler 2A connects the first bar port 22 to one first PD4A1 and connects the first cross port 23 to the first input port 21 of the other first coupler 2B. The other first coupler 2B connects the first bar port 22 to the other first PD4A2 and connects the first cross port 23 to the second input port 31 of one second coupler 3A.

[0056] One of the first PD4A1 converts the signal light mainly composed of short wavelengths tapped by one of the first couplers 2A into a current and inputs the current value mainly composed of short wavelengths after the current conversion to the first adder 5A. The other of the first PD4A2 converts the signal light mainly composed of short wavelengths tapped by the other of the first couplers 2B into a current and inputs the current value mainly composed of short wavelengths after the current conversion to the first adder 5A. The first adder 5A adds the current value mainly composed of short wavelengths from one of the first PD4A1 and the current value mainly composed of short wavelengths from the other of the first PD4A2 and outputs the result to the second adder 5B.

[0057] One second coupler 3A connects the second cross port 33 to one second PD 4B1 and connects the second bar port 32 to the second input port 31 of the other second coupler 3B. The other second coupler 3B connects the second cross port 33 to the other second PD 4B2.

[0058] The second PD4B1 converts the signal light mainly composed of long wavelengths tapped by the second coupler 3A into a current and inputs the current-converted current value mainly composed of long wavelengths to the second adder 5B. The other second PD4B2 converts the signal light mainly composed of long wavelengths tapped by the second coupler 3B into a current and inputs the current-converted current value mainly composed of long wavelengths to the third adder 5C. The second adder 5B adds the current value mainly composed of short wavelengths from the first adder 5A and the current value mainly composed of long wavelengths from the second PD4B1, and outputs the result to the third adder 5C. The third adder 5C adds the current value from the second adder 5B and the current value mainly composed of long wavelengths from the other second PD4B2, and outputs the result for monitoring.

[0059] The time required for the current value to reach the third adder 5C after passing through the first PD4A1, the first adder 5A, and the second adder 5B from the input of the signal light at the first input port 21 of the first coupler 2A is defined as a first arrival time D1. The time required for the current value to reach the third adder 5C after passing through the other first coupler 2B, the other first PD4A2, the first adder 5A, and the second adder 5B from the input of the signal light at the first input port 21 is defined as a second arrival time D2.

[0060] The time it takes for the current value to reach the third adder 5C after passing through the other first coupler 2B, one second coupler 3A, one second PD4B1, and second adder 5B from the input of the signal light at the first input port 21 is defined as a third arrival time D3. The time it takes for the current value to reach the third adder 5C after passing through the other first coupler 2B, one second coupler 3A, the other second coupler 3B, and second PD4B2 from the input of the signal light at the first input port 21 is defined as a fourth arrival time D4.

[0061] In the optical device 1B, the optical wiring and electrical wiring are adjusted so that the first arrival time D1, the second arrival time D2, the third arrival time D3, and the fourth arrival time D4 are the same. Specifically, the lengths of the optical wiring and electrical wiring are determined so that the sum of the optical arrival time from the input to the first coupler 2 to each PD 4 and the electrical arrival time from each PD 4 to the third adder 5C, which is the current summing portion, is approximately equal for all PD currents. As a result, when the PD currents are summed, speed degradation of the PDs 4 due to pulse delays of each PD current can be suppressed.

[0062] In the optical device 1B of the third embodiment, a tap with little wavelength dependency can be realized by using a plurality of first couplers 2 and a plurality of second couplers 3 and adding up the current values ​​of the light tapped by each coupler.

[0063] In the optical device 1B of the third embodiment, two first couplers 2 and two second couplers 3 are used, but the present invention is not limited to this and may be configured with, for example, M first couplers 2 and N second couplers 3, and this can be changed as appropriate. In addition, for example, M≦1, N≦1, M≠N, or M=N can also be used, and this can be changed as appropriate.

[0064] The waveguides used in the first coupler 2 and the second coupler 3 may be, for example, a rib waveguide, a ridge waveguide, a rectangular waveguide, or a high mesa waveguide. A rib waveguide is preferable because it allows light to seep into the slab portion, making it less susceptible to the effects of rough core sidewalls and enabling low-loss propagation. A rectangular waveguide is preferable because it has strong optical confinement, resulting in low loss even when the bending radius R is small. The waveguide may also be a low-loss curved waveguide, and can be changed as appropriate.

[0065] The waveguides used in the first coupler 2 and the second coupler 3 may be PLC, InP waveguides, or GaAs waveguides, each with a SiO2 core and clad. Alternatively, the core may be Si, the lower clad may be SiO2, and the upper clad may be SiO2 or air. Alternatively, a Si waveguide such as SiN may be used. Si waveguides are preferred because they have a large relative refractive index difference, resulting in strong optical confinement, making it possible to realize a low-loss bent waveguide even with a small bending radius R, which allows for the miniaturization of optical devices.

[0066] Next, an optical transceiver 50 employing the optical device 1 of this embodiment will be described. FIG. 14 is an explanatory diagram showing an example of the optical transceiver 50 of this embodiment. The optical transceiver 50 shown in FIG. 14 includes an optical transmitter / receiver 51 and a DSP (Digital Signal Processor) 52. The optical transmitter / receiver 51 includes an optical modulator element 54, a driver circuit 55, an optical receiver element 56, and a TIA (Transimpedance Amplifier) ​​57. The optical transmitter / receiver 51 includes an optical transmitter and an optical receiver. The DSP 52 controls the entire optical transmitter / receiver 51. The DSP 52 is an electrical component that performs digital signal processing, such as IQ modulation of a transmission signal and demodulation of a reception signal.

[0067] The DSP 52 performs processing such as encoding of transmission data, generates an electrical signal including the transmission data, and outputs the generated electrical signal to the driver circuit 55. The driver circuit 55 drives the optical modulator element 54 in response to the electrical signal from the DSP 52. The optical modulator element 54 optically modulates the signal light. The optical modulator element 54 includes, for example, an optical device 1. The optical transmitter includes at least the optical modulator element 54.

[0068] The optical receiver element 56 uses an optical signal to obtain signal light from the received light and converts the obtained signal light into an electrical signal. The optical receiver element 56, for example, has an optical device 1 built in. The optical receiver has at least the optical receiver element 56 built in. The TIA 57 amplifies the electrical signal after the electrical conversion and outputs the amplified electrical signal to the DSP 52. The DSP 52 performs processing such as decoding of the electrical signal obtained from the TIA 57 to obtain received data.

[0069] For ease of explanation, the optical transceiver 50 is exemplified as incorporating an optical modulator element 54 and an optical receiver element 56, but the optical transceiver 50 may be an optical transmitter incorporating only the optical modulator element 54 or an optical receiver incorporating only the optical receiver element 56, and may be modified as appropriate.

[0070] 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.

[0071] 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]

[0072] 1 Optical Devices 2. First Coupler 3 Second Coupler 4A First PD 4B Second PD 21 First input port 22 First Bar Port 23 First Crossport 31 Second input port 32 Second Bar Port 33 Second Crossport 50 Optical Transceiver 54 Optical modulator element 56 Optical receiver element

Claims

1. a first coupler having a first input port, a first bar port in a bar direction relative to the first input port, and a first cross port in a cross direction relative to the first input port, wherein a signal light on a short wavelength side from the first input port is mostly tapped to the first bar port; a second coupler having a second input port, a second bar port in a bar direction relative to the second input port, and a second cross port in a cross direction relative to the second input port, wherein a larger amount of signal light on the long wavelength side from the second input port is tapped to the second cross port; a monitor unit connected to the first bar port or the second cross port and configured to monitor the signal light output from the first bar port or the second cross port; An optical device comprising:

2. The first cross port of the first coupler comprises:

2. The optical device according to claim 1, wherein the optical device is connected to a first input port of a different first coupler or a second input port of the second coupler.

3. The second bar port of the second coupler comprises:

2. The optical device according to claim 1, wherein the optical device is connected to a first input port of the first coupler or a second input port of a different second coupler.

4. 2. The optical device according to claim 1, wherein a first arrival time of the signal light from the first input port of the first coupler to the monitor unit is equal to a second arrival time of the signal light from the first input port to the monitor unit via the second cross port of the second coupler.

5. The first coupler comprises: a first waveguide serving as the first input port to which the signal light is input; a second waveguide adjacent to the first waveguide and optically coupled to the first waveguide by an evanescent wave; 2. The optical device according to claim 1, wherein the signal light is output from the second waveguide as the first cross port, and a large amount of the signal light on the short wavelength side is tapped from the first waveguide as the first bar port.

6. The second coupler comprises: a first waveguide for inputting the signal light as the second input port; a second waveguide adjacent to the first waveguide and optically coupled to the first waveguide by an evanescent wave; 2. The optical device according to claim 1, wherein the second cross port outputs the signal light from the first waveguide, and the second cross port taps a large amount of the signal light on the long wavelength side from the second waveguide.

7. The first coupler comprises: a first waveguide serving as the first input port to which the signal light is input; a second waveguide adjacent to the first waveguide, Within a section in which the first waveguide and the second waveguide are arranged in parallel, the waveguide width of the first waveguide at the start point of the section is equal to that of the second waveguide at the end point of the section, and the waveguide width of the first waveguide at the end point is equal to that of the second waveguide at the start point, and the first waveguide and the second waveguide have a point-symmetric structure; 2. The optical device according to claim 1, wherein the signal light is output from the second waveguide as the first cross port, and a large amount of the signal light on the short wavelength side is tapped from the first waveguide as the first bar port.

8. The second coupler comprises: a first waveguide for inputting the signal light as the second input port; a second waveguide adjacent to the first waveguide, Within a section in which the first waveguide and the second waveguide are arranged in parallel, the waveguide width of the first waveguide at the start point of the section is equal to that of the second waveguide at the end point of the section, and the waveguide width of the first waveguide at the end point is equal to that of the second waveguide at the start point, and the first waveguide and the second waveguide have a point-symmetric structure; 2. The optical device according to claim 1, wherein the second cross port outputs the signal light from the first waveguide, and the second cross port taps a large amount of the signal light on the long wavelength side from the second waveguide.

9. An optical transmitter comprising an optical modulation unit that modulates an optical signal using an electrical signal, and that transmits signal light modulated by the optical modulation unit, The optical device in the optical transmitter comprises: a first coupler having a first input port, a first bar port in a bar direction relative to the first input port, and a first cross port in a cross direction relative to the first input port, wherein a signal light on a short wavelength side from the first input port is mostly tapped to the first bar port; a second coupler having a second input port, a second bar port in a bar direction relative to the second input port, and a second cross port in a cross direction relative to the second input port, wherein a larger amount of signal light on the long wavelength side from the second input port is tapped to the second cross port; a monitor unit connected to the first bar port or the second cross port and configured to monitor the signal light output from the first bar port or the second cross port; An optical transmitter comprising:

10. An optical receiver including an optical receiving unit that acquires signal light from received light using an optical signal and converts the acquired signal light into an electric signal, The optical device in the optical receiver includes: a first coupler having a first input port, a first bar port in a bar direction relative to the first input port, and a first cross port in a cross direction relative to the first input port, wherein a signal light on a short wavelength side from the first input port is mostly tapped to the first bar port; a second coupler having a second input port, a second bar port in a bar direction relative to the second input port, and a second cross port in a cross direction relative to the second input port, wherein a larger amount of signal light on the long wavelength side from the second input port is tapped to the second cross port; a monitor unit connected to the first bar port or the second cross port and configured to monitor the signal light output from the first bar port or the second cross port; An optical receiver comprising:

Images