Optical devices and optical communication equipment

Abstract

The present application relates to an optical device and an optical communication device. An optical device includes: a plurality of first Si optical waveguides that split and output an optical signal received from an input unit; a plurality of LN optical waveguides that are included in an LN modulator and transmit the optical signal split and output by the first Si optical waveguide; a plurality of second Si optical waveguides that multiplex and output associated optical signals output from a plurality of corresponding LN optical waveguides. The device includes: an output unit that outputs the optical signal multiplexed by the second Si optical waveguide; and a plurality of Mach-Zehnder interferometers that are respectively arranged on each optical waveguide connected by the first Si optical waveguide, the LN optical waveguide, and the second Si optical waveguide. When there is a difference between the waveguide lengths of the LN optical waveguides, the device is configured to make the optical path lengths of the optical waveguides of the respective Mach-Zehnder interferometers equal.

Description

Technical Field

[0001] The embodiments discussed herein relate to optical devices and optical communication equipment. Background Art

[0002] In general, for example, an optical device such as an optical modulator sometimes includes an optical modulator chip, on the surface of which an optical waveguide is formed. A signal electrode is provided on the optical waveguide formed on the optical modulator chip, and if a voltage is applied to the signal electrode, an electric field is generated inside the optical waveguide in a perpendicular direction relative to the surface of the optical modulator chip. The refractive index of the optical waveguide changes due to the electric field; therefore, the phase of light propagating in the optical waveguide is changed, and thus the light can be modulated. That is, the optical waveguide formed on the optical modulator chip constitutes, for example, a Mach-Zehnder interferometer, and is capable of outputting, for example, an IQ signal that has undergone XY polarization division multiplexing based on the phase difference of light between a plurality of optical waveguides arranged in parallel.

[0003] If the optical modulator chip performs high-speed modulation, a high-speed signal having a frequency band of, for example, several tens of gigahertz (GHz) is input to a signal electrode disposed along an optical waveguide. Therefore, a coplanar waveguide (CPW) structure capable of obtaining broadband transmission characteristics is sometimes used for the signal electrode. That is, sometimes, a signal electrode and a pair of ground electrodes sandwiching the signal electrode are disposed above the optical waveguide.

[0004] On the contrary, sometimes, an optical waveguide is formed at a position overlapping with the position of the signal electrode by spreading, for example, a metal such as titanium from the surface of the substrate. Also, sometimes, an LN optical waveguide using a thin film of lithium niobate (LN) crystal is formed at a position overlapping with the position of the signal electrode. The LN optical waveguide can more strongly confine light than a diffused optical waveguide using diffused metal, can improve the efficiency of applying an electric field, and can reduce the driving voltage.

[0005] Figure 7 is a schematic plan view illustrating a configuration example of the light modulator 100 . Figure 7The optical modulator 100 shown has a configuration in which an optical fiber extending from a light source is connected to the input side of the optical modulator 100, and an optical fiber for outputting a transmission signal is connected to the output side of the optical modulator 100. The optical modulator 100 has an optical input unit 110, an LN modulation unit 120, and an optical output unit 130. The optical input unit 110 includes a first Si optical waveguide 111 and a first LN-Si waveguide junction unit 112. The first Si optical waveguide 111 has a single Si optical waveguide connected to the optical fiber on the input side, two Si optical waveguides branched from the single Si optical waveguide, four Si optical waveguides branched from the associated two Si optical waveguides, and eight Si optical waveguides branched from the associated four Si optical waveguides. The first LN-Si waveguide joining unit 112 joins portions between eight Si optical waveguides included in the first Si optical waveguide 111 and corresponding eight LN optical waveguides included in the LN optical waveguide 121 included in the LN modulation unit 120 and outputs optical signals received from the Si optical waveguides to the LN optical waveguides.

[0006] The LN modulation unit 120 has an LN optical waveguide 121, a signal electrode 122, and an RF terminator 123. When the light provided from the first Si optical waveguide 111 is transmitted through the LN optical waveguide 121, the LN modulation unit 120 modulates the light by an electric field applied by the signal electrode 122. The LN optical waveguide 121 is an optical waveguide formed by using, for example, a thin film LN substrate, and has 8 LN optical waveguides arranged in parallel and joined to the corresponding first LN-Si waveguide joining unit 112 in the optical input unit 110. The light modulated by being transmitted through the LN optical waveguide 121 is output to the optical output unit 130.

[0007] The signal electrode 122 is a transmission path having a CPW structure provided at a position overlapping with the position of the LN optical waveguide 121, and applies an electric field to the LN optical waveguide 121 according to an electric signal having, for example, tens of gigahertz (GHz) output from a digital signal processor (DSP). A terminal portion of the signal electrode 122 is connected to an RF terminator 123. The RF terminator 123 is connected to the terminal portion of the signal electrode 122 and prevents unnecessary reflection of a signal transmitted by the signal electrode 122.

[0008] The optical output unit 130 has a second LN-Si waveguide joint unit 131, a second Si optical waveguide 132, eight sub-side Mach-Zehnder (MZ) segments 133 and four parent-side MZ segments 134. In addition, the optical output unit 130 has a polarization rotator (PR) 135 and a polarization beam combiner (PBC) 136. The second LN-Si waveguide joint unit 131 joins eight LN optical waveguides 121 in the LN modulation unit 120 and corresponding eight second Si optical waveguides 132 together. The second Si optical waveguide 132 has eight Si optical waveguides connected to the second LN-Si waveguide joint unit 131 and includes four Si optical waveguides merged with two Si optical waveguides among the eight Si optical waveguides. In addition, the second Si optical waveguide 132 has two Si optical waveguides merged with two Si optical waveguides among the four Si optical waveguides, and includes a single Si optical waveguide merged with the two Si optical waveguides and connected to the optical fiber on the output side.

[0009] The eight Si optical waveguides included in the second Si optical waveguide 132 are provided with a sub-side MZ segment 133 for each Si optical waveguide. By applying a bias voltage to a DC electrode on the Si optical waveguide, a group of sub-side MZ segments 133 adjust the bias voltage so that the on / off of the electric signal is associated with the on / off of the optical signal, and then, an I signal or a Q signal is output. Each of the four Si optical waveguides included in the second Si optical waveguide 132 is provided with a father-side MZ segment 134 for each Si optical waveguide. By applying a bias voltage to a DC electrode on the Si optical waveguide, a group of father-side MZ segments 134 adjust the bias voltage so that the on / off of the electric signal is associated with the on / off of the optical signal, and then, an I signal or a Q signal is output.

[0010] The PR 135 rotates the I signal or Q signal input from one of the combinations of the parent-side MZ segments 134 by 90 degrees, and obtains a vertically polarized light signal rotated by 90 degrees. Then, the PR 135 inputs the vertically polarized light signal to the PBC 136. The PBC 136 multiplexes the vertically polarized light signal input from the PR 135 and the horizontally polarized light signal input from another set of the parent-side MZ segments 134, and then outputs a polarization division multiplexed signal.

[0011] The LN optical waveguide 121 is capable of generating an electric field by applying a high-frequency signal to the signal electrode 122 and modulating light transmitted through the LN optical waveguide 121 by changing the refractive index of the LN optical waveguide 121. In addition, a thin-film LN substrate (not shown) and the LN optical waveguide 121 are stacked on a buffer layer (not shown); therefore, the light intensity can be confined in the LN optical waveguide 121, and thus the driving voltage applied to the signal electrode 122 can be reduced.

[0012] However, the length of the LN modulation unit 120 including the LN optical waveguide 121 increases, so that the size of the optical modulator chip from the optical input unit 110 to the optical output unit 130 increases. Therefore, the size of the chip is reduced by using a U-shaped structure for the LN optical waveguide 121A included in the LN modulation unit 120A, and the input end of the optical input unit 110A and the output end of the optical output unit 130A are arranged in parallel at one end of the optical modulator 100A. Figure 8 1 is a schematic plan view illustrating a configuration example of an optical modulator 100A including an LN optical waveguide 121A having a U-shaped structure. Figure 7 Components of the same configuration as those in the illustrated optical modulator 100 are assigned the same reference numerals, and repeated description of their configuration and operation will be omitted.

[0013] Figure 8 The LN modulation unit 120A shown has the following structure: Figure 7 The LN optical waveguide 121A having a long waveguide length of the LN modulation unit 120 shown uses a U-shaped structure. In addition, the LN optical waveguide 121A has a U-shaped structure so that the input end of the optical input unit 110A and the output end of the optical output unit 130A are arranged in parallel at one end of the optical modulator 100A. Therefore, even if the waveguide length of the LN optical waveguide 121A becomes longer, the size of the optical modulator chip can be prevented from increasing by using the U-shaped structure.

[0014] Patent Document 1: Japanese Patent Application Publication No. 2014-112171

[0015] Patent Document 2: Japanese Patent Application Publication No. 2019-15791

[0016] exist Figure 8 In the optical modulator 100A shown, a nested Mach-Zehnder interferometer is constructed by eight optical waveguides connecting the first Si optical waveguide 111, the LN optical waveguide 121A, and the second Si optical waveguide 132, and the waveguide lengths of the eight optical waveguides are different between the inner side and the outer side of the eight optical waveguides having a U-shaped structure. In addition, if the waveguide length of the optical waveguide forming the Mach-Zehnder interferometer increases, the bias point or loss in the Mach-Zehnder interferometer significantly differs depending on the wavelength of the optical signal. Therefore, in order to cope with this state, the waveguide length is adjusted by providing a delay device in the LN optical waveguide on the inner side of the LN optical waveguide 121A having a U-shaped structure. However, an area for arranging the delay device is required on the LN optical waveguide 121A, so that the size of the LN modulation unit 120A increases. Therefore, the chip size of the optical modulator chip is increased.

[0017] Therefore, an object of one aspect of an embodiment of the present invention is to provide an optical device or the like capable of preventing an increase in chip size even when an LN optical waveguide is used. Summary of the invention

[0018] According to one aspect of the embodiment, an optical device includes: an input unit that inputs an optical signal; a plurality of first silicon (Si) optical waveguides that divide and output the optical signal received from the input unit; a plurality of LN (LiNbO3) optical waveguides that are included in an LN modulation unit and transmit the optical signal divided and output by the first Si optical waveguide; a plurality of second Si optical waveguides that multiplex and output the associated optical signals output from the plurality of corresponding LN optical waveguides; an output unit that outputs the optical signal multiplexed by the second Si optical waveguide; and a plurality of Mach-Zehnder interferometers that are respectively provided on each optical waveguide connected by the first Si optical waveguide, the LN optical waveguide, and the second Si optical waveguide. When there is a difference between the waveguide lengths of the LN optical waveguides, the optical path lengths of the optical waveguides of the respective Mach-Zehnder interferometers are configured to be equal. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a block diagram illustrating a configuration example of an optical communication device according to the present embodiment;

[0020] Figure 2 is a schematic plan view illustrating the configuration of an optical modulator according to a first embodiment;

[0021] Figure 3 is a schematic plan view illustrating a configuration example of an optical modulator according to a second embodiment;

[0022] Figure 4 is a schematic plan view illustrating a configuration example of an optical modulator according to a third embodiment;

[0023] Figure 5 is a schematic plan view illustrating a configuration example of an optical modulator according to a fourth embodiment;

[0024] Figure 6 is a schematic plan view illustrating a configuration example of an optical modulator according to a fifth embodiment;

[0025] Figure 7 is a schematic plan view illustrating a configuration example of a light modulator; and

[0026] Figure 8 is a schematic plan view illustrating a configuration example of an optical modulator including an LN optical waveguide having a U-shaped structure. DETAILED DESCRIPTION

[0027] Preferred embodiments of the present invention will be explained with reference to the accompanying drawings. In addition, the present invention is not limited to these embodiments.

[0028] [a] First Embodiment

[0029] Figure 1 is a block diagram illustrating a configuration example of an optical communication device 1 according to an embodiment. Figure 1 The optical communication device 1 shown is connected to an optical fiber 2A (2) provided on the output side and an optical fiber 2B (2) provided on the input side. The optical communication device 1 has a digital signal processor (DSP) 3, a light source 4, an optical modulator 5, and an optical receiver 6. The DSP 3 is an electronic component that performs digital signal processing. The DSP 3 performs processing such as encoding transmission data, generates an electrical signal including the transmission data, and outputs the generated electrical signal to the optical modulator 5. In addition, the DSP 3 acquires an electrical signal including reception data from the optical receiver 6, and performs processing for decoding the acquired electrical signal, so that the DSP 3 obtains reception data.

[0030] The light source 4 includes, for example, a laser diode, etc., generates light having a predetermined wavelength, and supplies the generated light to the optical modulator 5 and the optical receiver 6. The optical modulator 5 is an optical device that modulates the light supplied from the light source 4 using the electrical signal output from the DSP 3 and outputs the obtained optical transmission signal to the optical fiber 2A. The optical modulator 5 includes, for example, an LN optical waveguide 31 and a signal electrode 32 having a microstrip line (MSL) structure. When the light supplied from the light source 4 propagates via the LN optical waveguide 31, the optical modulator 5 generates an optical transmission signal by modulating the light by the electrical signal input to the signal electrode 32.

[0031] The optical receiver 6 receives an optical signal from the optical fiber 2B and demodulates the received optical signal by using the light supplied from the light source 4. Then, the optical receiver 6 converts the demodulated received optical signal into an electrical signal and then outputs the converted electrical signal to the DSP 3.

[0032] Figure 2 is a schematic plan view illustrating a configuration example of the light modulator 5 according to the first embodiment. Figure 2 The optical modulator 5 shown has the following configuration: an optical fiber 4A from a light source 4 is connected to the input side and an optical fiber 2A for outputting a transmission signal is connected to the output side. The optical modulator 5 includes an optical input unit 11, an LN modulation unit 12, and an optical output unit 13. The input end of the optical input unit 11 and the output end of the optical output unit 13 are arranged in parallel at one end of the optical modulator 5 (at Figure 2The optical input unit 11 includes an input unit 20, a first Si optical waveguide 21, a first LN-Si waveguide junction unit 22, and a plurality of parent-side Mach-Zehnder (MZ) segments 23. The input unit 20 is connected to the optical fiber 4A on the input side. The first Si optical waveguide 21 includes a single Si optical waveguide connected to the input unit 20, two Si optical waveguides branched from the single Si optical waveguide, four Si optical waveguides branched from the associated two Si optical waveguides, and eight Si optical waveguides branched from the associated four Si optical waveguides. The parent-side MZ segment 23 is arranged on each of the four Si optical waveguides included in the first Si optical waveguide 21. By applying a bias voltage to the DC electrode on the Si optical waveguide, a group of parent-side MZ segments 23 adjust the bias voltage so that the on / off of the electrical signal is associated with the on / off of the optical signal, and then outputs an I signal or a Q signal. The first LN—Si waveguide joint unit 22 joins portions between eight Si optical waveguides included in the first Si optical waveguide 21 and eight LN optical waveguides included in the LN optical waveguide 31 , and outputs optical signals received from the Si optical waveguides to the LN optical waveguides.

[0033] The LN modulation unit 12 includes an LN optical waveguide 31, a signal electrode 32, and an RF terminator 33. The LN optical waveguide 31 has a U-shaped structure in which the LN optical waveguide 31 is bent from the optical input unit 11 toward the optical output unit 13, so that the LN optical waveguide 31 has a waveguide length sufficient to appropriately change the refractive index of the LN optical waveguide 31. In addition, the LN optical waveguide 31 has a U-shaped structure; therefore, the curvature radius of the inner LN optical waveguide of the LN optical waveguide 31 is small, and the curvature radius of the outer LN optical waveguide of the LN optical waveguide 31 is large, and therefore, the waveguide length of the inner LN optical waveguide is different from the waveguide length of the outer LN optical waveguide.

[0034] When the optical signal supplied from the first Si optical waveguide 21 is transmitted via the LN optical waveguide 31, the LN modulation unit 12 modulates the object optical signal by using the electric field applied from the signal electrode 32. The LN optical waveguide 31 is an optical waveguide formed by using, for example, a thin film LN substrate (not shown), and includes 8 parallel LN optical waveguides. The light modulated while being transmitted via the LN optical waveguide 31 is output to the light output unit 13.

[0035] The signal electrode 32 is a transmission path having an MSL structure and disposed at a position overlapping with that of the LN optical waveguide 31, and applies an electric field to the LN optical waveguide 31 according to the electric signal output from the DSP 3. A terminal portion of the signal electrode 32 is connected to the RF terminator 33. The RF terminator 33 is connected to the terminal portion of the signal electrode 32 and prevents unnecessary reflection of a signal transmitted by the signal electrode 32.

[0036] The optical output unit 13 includes an output unit 40, a second LN-Si waveguide joint unit 41, a second Si optical waveguide 42, eight sub-side MZ segments 43, a PR 44, and a PBC 45. The output unit 40 is connected to the optical fiber 4B. The second LN-Si waveguide joint unit 41 joins the portion between the LN optical waveguide 31 included in the LN modulation unit 12 and the second Si optical waveguide 42, and outputs the optical signal received from the LN optical waveguide 31 to the second Si optical waveguide 42. The second Si optical waveguide 42 includes eight Si optical waveguides connected to the second LN-Si waveguide joint unit 41, and also includes four Si optical waveguides merged with two Si optical waveguides among the eight Si optical waveguides. In addition, the second Si optical waveguide 42 includes two Si optical waveguides merged with two Si optical waveguides among the four Si optical waveguides, and a single Si optical waveguide merged with the two Si optical waveguides. The single Si optical waveguide is connected to the output unit 40. The eight Si optical waveguides included in the second Si optical waveguide 42 are provided with a sub-side MZ segment 43 for each Si optical waveguide. By applying a bias voltage to a DC electrode on the Si optical waveguide, a group of sub-side MZ segments 43 adjust the bias voltage so that the on / off of the electric signal is associated with the on / off of the optical signal, and outputs an I signal having an in-phase component or a Q signal having an orthogonal component.

[0037] The PR 44 rotates the I signal or Q signal input from one of the two groups of sub-side MZ segments 43 by 90 degrees and obtains a vertically polarized light signal rotated by 90 degrees. Then, the PR 44 inputs the vertically polarized light signal to the PBC 45. The PBC 45 multiplexes the vertically polarized light signal input from the PR 44 and the horizontally polarized light signals input from the other two groups of sub-side MZ segments 43, and then outputs a polarization division multiplexed signal.

[0038] The four father-side MZ segments 23 provided on the first Si optical waveguide 21 and the eight child-side MZ segments 43 provided on the second Si optical waveguide 42 constitute a nested Mach-Zehnder interferometer.

[0039] In the following, the configuration of the optical modulator 5 according to the first embodiment will be described in detail. The LN optical waveguide 31 included in the LN modulation unit 12 has a U-shaped structure so that the waveguide length is different between the inner LN optical waveguide and the outer LN optical waveguide. That is, there is a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31. Therefore, in the present embodiment, in order to make the optical path lengths of the eight optical waveguides from the first Si optical waveguide 21 to the second Si optical waveguide 42 connected to each of the LN optical waveguides 31 equal, the waveguide length of each of the eight Si optical waveguides 21A included in the first Si optical waveguide 21 is adjusted. The single optical waveguide is an optical waveguide of the Mach-Zehnder interferometer extending from the first Si optical waveguide 21 to the second Si optical waveguide 42 via the first LN-Si waveguide junction unit 22, the LN optical waveguide 31, and the second LN-Si waveguide junction unit 41. Furthermore, the Si optical waveguide strongly confines light and can be bent to a small radius, so that the area required for delay adjustment can be reduced compared to the LN optical waveguide 31. In order to make the optical path lengths of the optical waveguides equal, the curvature can be adjusted in addition to adjusting the waveguide length of each Si optical waveguide 21A included in the first Si optical waveguide 21, and appropriate modification is also possible.

[0040] It is assumed that the effective refractive index inside the optical waveguide of the first Si optical waveguide 21 and the second Si optical waveguide 42 is represented by N(Si), and the effective refractive index inside the optical waveguide of the LN optical waveguide 31 is represented by N(LN). In addition, it is assumed that the waveguide length inside the optical waveguide of the first Si optical waveguide 21 and the second Si optical waveguide 42 is represented by L(Si), and the waveguide length inside the optical waveguide of the LN optical waveguide 31 is represented by L(LN). The optical path length of a single optical waveguide can be realized by N(Si)×L(Si)+N(LN)×L(LN). Therefore, in order to make the optical path lengths of the eight optical waveguides equal by adjusting the optical path length inside the optical waveguide, the waveguide length of each Si optical waveguide 21A included in the first Si optical waveguide 21 is adjusted.

[0041] A high-frequency signal associated with the electric signal output from the DSP 3 is transmitted by the signal electrode 32, so that an electric field is generated in a direction from the signal electrode 32 toward the ground electrode, and the generated electric field is applied to the LN optical waveguide 31. Therefore, the refractive index of the LN optical waveguide 31 changes according to the electric field applied to the LN optical waveguide 31, and thus light transmitted via the LN optical waveguide 31 can be modulated.

[0042] The optical modulator 5 according to the first embodiment is configured so that the optical path lengths of the optical waveguides of the respective Mach-Zehnder interferometers are equal even if there is a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31 by using, for example, a U-shaped structure for the LN optical waveguide 31. Therefore, even if there is a difference between the waveguide lengths of the LN optical waveguides 31, it is possible to prevent the chip size of the optical modulator 5 from increasing.

[0043] The first Si optical waveguide 21 included in the optical modulator 5 has a waveguide length that makes the optical path length of the optical waveguide of each Mach-Zehnder interferometer equal by using the Si optical waveguide 21A included in the first Si optical waveguide 21. Therefore, even if there is a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31, it is possible to prevent the chip size of the optical modulator 5 from increasing. In addition, it is possible to prevent the number of modules of the optical communication device 1 including the built-in optical modulator 5 from increasing.

[0044] The optical modulator 5 has a configuration in which the input unit 20 and the output unit 40 are arranged in parallel, and a U-shaped structure is used for the LN optical waveguide 31 so that the LN optical waveguide 31 is bent from the input unit 20 toward the output unit 40 to create a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31; therefore, an increase in the chip size of the optical modulator 5 can be prevented.

[0045] Furthermore, for convenience of description, in the optical modulator 5 according to the first embodiment, the case where the waveguide length inside the optical waveguide of the Si optical waveguide 21A included in the first Si optical waveguide 21 is adjusted so that the optical path length of each optical waveguide of the Mach-Zehnder interferometer is equal has been described as an example. However, the curvature inside the optical waveguide of the optical waveguide of the first Si optical waveguide 21 may be adjusted, and appropriate modification is possible.

[0046] Furthermore, the case where the waveguide length inside the optical waveguide of the first Si optical waveguide 21 is adjusted in the optical modulator 5 to make the optical path length of each optical waveguide of the Mach-Zehnder interferometer equal has been described as an example. However, it may also be possible to adjust the waveguide length inside the optical waveguide of the second Si optical waveguide 42 instead of the first Si optical waveguide 21. Furthermore, it is also possible to adjust the waveguide length inside the optical waveguide of each of the first Si optical waveguide 21 and the second Si optical waveguide 42, and an embodiment thereof will be described as a second embodiment. Figure 3 2 is a schematic plan view illustrating a configuration example of the optical modulator 5A according to the second embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the optical modulator 5 according to the first embodiment, repeated description of the configuration and operation thereof will be omitted.

[0047] [b] Second Embodiment

[0048] exist Figure 3 In the optical modulator 5A shown, in order to make the optical path length of each optical waveguide of the Mach-Zehnder interferometer equal, the waveguide length of each optical waveguide inside the Si optical waveguide 21A included in the first Si optical waveguide 21 and the Si optical waveguide 42A included in the second Si optical waveguide 42 is adjusted.

[0049] Hereinafter, the configuration of the optical modulator 5A according to the second embodiment will be described in detail. The LN optical waveguide 31 included in the LN modulation unit 12 has a U-shaped structure so that the waveguide length of the inner LN optical waveguide is different from the waveguide length of the outer LN optical waveguide. In this embodiment, the optical path lengths of the eight optical waveguides from the first Si optical waveguide 21 to the second Si optical waveguide 42 connected to each LN optical waveguide 31 are equal. Then, in order to make the optical path lengths of the eight optical waveguides equal, the waveguide length of each of the eight Si optical waveguides 21A included in the first Si optical waveguide 21 and the waveguide length of each of the eight Si optical waveguides 42A included in the second Si optical waveguide 42 are adjusted. For example, the waveguide lengths of the Si optical waveguides 21A and 42A connected to the inner LN optical waveguide are lengthened, and the waveguide lengths of the Si optical waveguides 21A and 42A connected to the outer LN optical waveguide are shortened so that the optical path lengths of the respective optical waveguides are equalized by an amount corresponding to N(Si)×L(Si)+N(LN)×L(LN).

[0050] Furthermore, in order to make the optical path lengths of the optical waveguides equal, in addition to adjusting the waveguide length inside each Si optical waveguide 21A included in the first Si optical waveguide 21 and the waveguide length inside each Si optical waveguide 42A included in the second Si optical waveguide 42, it is also possible to adjust the curvature, and appropriate modifications are also possible.

[0051] The Si optical waveguide 21A included in the first Si optical waveguide 21 and the Si optical waveguide 42A included in the second Si optical waveguide 42 included in the optical modulator 5A according to the second embodiment have waveguide lengths such that the optical path lengths of the optical waveguides of the respective Mach-Zehnder interferometers are equal. Therefore, even if there is a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31, it is possible to prevent the chip size of the optical modulator 5A from increasing.

[0052] Furthermore, as an example, the case has been described in which the optical modulator 5 according to the first embodiment adjusts the waveguide length inside the optical waveguide included in the first Si optical waveguide 21 so that the optical path length of each optical waveguide of the Mach-Zehnder interferometer is equal. However, it is also possible to adjust the DC electrode 23A of the father-side MZ segment 23 provided on the first Si optical waveguide 21 and the DC electrode 43A of the child-side MZ segment 43 provided on the second Si optical waveguide 42, and an embodiment thereof will be described as a third embodiment. Figure 4 3B is a schematic plan view illustrating a configuration example of an optical modulator 5B according to the third embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the optical modulator 5 according to the first embodiment, repeated description of the configuration and operation thereof will be omitted.

[0053] [c] Third Embodiment

[0054] In order to make the optical path lengths of the waveguides of the Mach-Zehnder interferometer equal, Figure 4 The optical modulator 5B illustrated in FIG. 4 adjusts the waveguide length of the optical waveguide included in the first Si optical waveguide 21 and the second Si optical waveguide 42, and also adjusts the DC electrodes 23B and 43B of the father-side MZ segment 23 and the daughter-side MZ segment 43. For example, the optical modulator 5B adjusts the waveguide length inside the Si optical waveguide 21A included in the first Si optical waveguide 21 and the waveguide length inside the Si optical waveguide 42A included in the second Si optical waveguide 42. In addition, the optical modulator 5B adjusts the DC electrode 23B of the father-side MZ segment 23 provided on the first Si optical waveguide 21 and the DC electrode 43B of the daughter-side MZ segment 43 provided on the second Si optical waveguide 42.

[0055] Hereinafter, the configuration of the optical modulator 5B according to the third embodiment will be described in detail. The LN optical waveguide 31 included in the LN modulation unit 12 has a U-shaped structure so that the waveguide length of the inner LN optical waveguide is different from the waveguide length of the outer LN optical waveguide. Therefore, in the present embodiment, the optical path lengths of the eight optical waveguides from the first Si optical waveguide 21 to the second Si optical waveguide 42 connected to each LN optical waveguide included in the LN optical waveguide 31 are equal. Then, in order to make the optical path lengths of the eight optical waveguides equal, the waveguide length of each of the eight Si optical waveguides 21A included in the first Si optical waveguide 21 and the waveguide length of each of the eight Si optical waveguides 42A included in the second Si optical waveguide 42 are adjusted. In addition, the DC electrode 23B of the father-side MZ segment 23 provided on the first Si optical waveguide 21 and the DC electrode 43B of the child-side MZ segment 43 provided on the second Si optical waveguide 42 are adjusted. Furthermore, adjusting the DC electrodes 23B and 43B is to adjust, for example, the electrode length (waveguide length) or curvature of each of the DC electrodes 23B and 43B. The DC electrodes 23B and 43B are adjusted by, for example, lengthening the waveguide length of the Si optical waveguides 21A and 42A connected to the inner LN optical waveguide so that the optical path length of each optical waveguide is equal to an amount corresponding to N(Si)×L(Si)+N(LN)×L(LN). Furthermore, the DC electrodes 23B and 43B are adjusted by, for example, shortening the waveguide length of the Si optical waveguides 21A and 42A connected to the outer LN optical waveguide so that the optical path lengths are equal.

[0056] The optical modulator 5B according to the third embodiment has a configuration in which the Si optical waveguide 21A included in the first Si optical waveguide 21, the Si optical waveguide 42A included in the second Si optical waveguide 42, and the DC electrodes 23B and 43B of the father-side MZ segment 23 and the daughter-side MZ segment 43 are respectively adjusted so that the optical path lengths of the optical waveguides are equal. The DC electrode 23B of the father-side MZ segment 23 or the DC electrode 43B of the daughter-side MZ segment 43 has an electrode length that makes the optical path lengths of the optical waveguides equal. Therefore, even if there is a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31, the chip size of the optical modulator 5A can be prevented from increasing.

[0057] Furthermore, for the convenience of description, the case where the optical modulator 5B adjusts the Si optical waveguide 21A included in the first Si optical waveguide 21, the Si optical waveguide 42A included in the second Si optical waveguide 42, and the DC electrodes 23B and 43B of the father-side MZ segment 23 and the child-side MZ segment 43, respectively, so that the optical path length of each optical waveguide is equal has been described as an example. However, in order to make the optical path length of each optical waveguide equal, it is also possible to adjust only the DC electrodes 23B and 43B of the father-side MZ segment 23 and the child-side MZ segment 43, respectively, or alternatively, it is also possible to adjust one of the DC electrodes 23B and 43B of the father-side MZ segment 23 and the child-side MZ segment 43, respectively, and appropriate modifications are also possible.

[0058] The case where the optical modulator 5 according to the first embodiment adjusts the waveguide length inside the optical waveguide included in the first Si optical waveguide 21 to make the optical path lengths of the optical waveguides equal has been described as an example. However, it is also possible to adjust the position of the branch waveguide 21B provided on the first Si optical waveguide 21, and an embodiment thereof will be described as a fourth embodiment. Figure 5 is a schematic plan view illustrating a configuration of an optical modulator 5C according to a fourth embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the optical modulator 5 according to the first embodiment, repeated description of the configuration and operation thereof will be omitted.

[0059] [d] Fourth Embodiment

[0060] Figure 5 The optical modulator 5C shown adjusts the waveguide length inside the Si optical waveguide 21A included in the first Si optical waveguide 21 and the waveguide length inside the Si optical waveguide 42A included in the second Si optical waveguide 42 of each optical waveguide in order to make the optical path length of the optical waveguide of the Mach-Zehnder interferometer equal. In addition, the optical modulator 5C adjusts the DC electrode 23B of the father-side MZ segment 23 provided on the first Si optical waveguide 21 and the DC electrode 43B of the child-side MZ segment 43 provided on the second Si optical waveguide 42. In addition, the optical modulator 5C adjusts the position of the branch waveguide 21B included in the first Si optical waveguide 21 by moving the branch waveguide 21B in the traveling direction of the optical signal. In addition, the optical modulator 5C adjusts the position of the multiplexing waveguide 42B included in the second Si optical waveguide 42 in the traveling direction of the optical signal.

[0061] Hereinafter, the configuration of the optical modulator 5C according to the fourth embodiment will be described in detail. The LN optical waveguide 31 included in the LN modulation unit 12 has a U-shaped structure so that the waveguide length of the inner LN optical waveguide is different from the waveguide length of the outer LN optical waveguide. Therefore, in the present embodiment, the optical path lengths of the eight optical waveguides from the first Si optical waveguide 21 to the second Si optical waveguide 42 connected to the LN optical waveguide included in the LN optical waveguide 31 are equal. Then, in order to make the optical path lengths of the eight optical waveguides equal, the waveguide length of each of the eight Si optical waveguides 21A included in the first Si optical waveguide 21 and the waveguide length of each of the eight Si optical waveguides 42A included in the second Si optical waveguide 42 are adjusted. In addition, in order to make the optical path lengths of the optical waveguides of the Mach-Zehnder interferometer equal, the DC electrode 23B of the father-side MZ segment 23 provided on the first Si optical waveguide 21 and the DC electrode 43B of the child-side MZ segment 43 provided on the second Si optical waveguide 42 are adjusted. Furthermore, adjusting the DC electrodes 23B and 43B is adjusting, for example, the electrode length (waveguide length) or the curvature of the DC electrodes 23B and 43B.

[0062] Furthermore, among the four Si optical waveguides included in the first Si optical waveguide 21, the position of the branch waveguide 21B of the Si optical waveguide including the inner LN optical waveguide included in the LN optical waveguide 31 is adjusted by moving the branch waveguide 21B in the traveling direction of the optical signal. That is, the waveguide length is shorter than the waveguide length of the optical waveguide including the outer LN optical waveguide; therefore, the branch waveguide 21B on the Si optical waveguide is located at a position behind the traveling direction of the optical signal. Furthermore, by moving the multiplexing waveguide 42B among the four Si optical waveguides included in the second Si optical waveguide 42 in the traveling direction of the optical signal, the position of the multiplexing waveguide 42B on the optical waveguide including the outer LN optical waveguide included in the LN optical waveguide 31 is adjusted. That is, the waveguide length is longer than the waveguide length of the optical waveguide including the inner LN optical waveguide; therefore, the multiplexing waveguide 42B of the Si optical waveguide is set to be located at a position behind the traveling direction of the optical signal.

[0063] The optical modulator 5C according to the fourth embodiment is configured to adjust the Si optical waveguide 21A included in the first Si optical waveguide 21, the Si optical waveguide 42A included in the second Si optical waveguide 42, and the DC electrodes 23B and 43B of the father-side MZ segment 23 and the child-side MZ segment, respectively, so that the optical path lengths of the optical waveguides are equal. The optical modulator 5C adjusts the position of the branch waveguide 21B on the Si optical waveguide among the four Si optical waveguides included in the first Si optical waveguide 21, and adjusts the position of the multiplexing waveguide 42B on the Si optical waveguide among the four Si optical waveguides included in the second Si optical waveguide 42, so that the optical path lengths of the optical waveguides are equal. That is, by setting the position of the branch waveguide 21B included in the first Si optical waveguide 21 in the traveling direction of the optical signal, the first Si optical waveguide 21 has a waveguide length that makes the optical path lengths of the optical waveguides equal. By arranging the position of the multiplexing waveguide 42B included in the second Si optical waveguide 42 in the direction opposite to the traveling direction of the optical signal, the second Si optical waveguide 42 has a waveguide length that makes the optical path lengths of the optical waveguides equal. Therefore, even if there is a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31, it is possible to prevent the chip size of the optical modulator 5C from increasing.

[0064] Furthermore, the case where, in the optical modulator 5C according to the fourth embodiment, the position inside the branch waveguide 21B provided on the first Si optical waveguide 21 and the position inside the multiplexing waveguide 42B provided on the second Si optical waveguide 42 are adjusted so that the optical path length of each optical waveguide is equal has been described as an example. However, one of the position inside the branch waveguide 21B on the first Si optical waveguide 21 and the position inside the multiplexing waveguide 42B on the second Si optical waveguide 42 may be adjusted so that the optical path length of each optical waveguide is equal, and appropriate modification is also possible.

[0065] For example, the loss in the LN optical waveguide 31 depends on the curvature of the curved waveguide having the U-shaped structure, and the loss in the waveguide having a small radius of curvature increases. In contrast, an excessive loss is generated in the PR 46 on the second Si optical waveguide 42. Therefore, in order to cope with such a situation, the following embodiment will be described as a fifth embodiment: in the optical modulator 5C, the PR 46 is provided on the optical waveguide including the LN optical waveguide having a large radius of curvature among the eight LN optical waveguides 31 having the U-shaped structure. Figure 6 5D according to the fifth embodiment. In addition, by assigning the same reference numerals to components having the same configuration as those in the optical modulator 5C according to the fourth embodiment, repeated description of the configuration and operation thereof will be omitted.

[0066] [e] Fifth Embodiment

[0067] In order to make the optical path lengths of the waveguides of the Mach-Zehnder interferometer equal, Figure 6 The optical modulator 5D shown adjusts the waveguide length inside the Si optical waveguide 21A included in the first Si optical waveguide 21 and the waveguide length inside the Si optical waveguide 42A included in the second Si optical waveguide 42 of each optical waveguide. In addition, the optical modulator 5D adjusts the DC electrode 23B of the father-side MZ segment 23 provided on the first Si optical waveguide 21 and the DC electrode 43B of the child-side MZ segment 43 provided on the second Si optical waveguide 42. In addition, the optical modulator 5D adjusts the position by moving the position of the branch waveguide 21B included in the first Si optical waveguide 21 in the traveling direction of the optical signal. In addition, the optical modulator 5D adjusts the position by moving the position of the multiplexing waveguide 42B included in the second Si optical waveguide 42 in the traveling direction of the optical signal. Furthermore, the optical modulator 5D disposes the PR 46A on the optical waveguide including the LN optical waveguide having the larger curvature radius (ie, the LN optical waveguide disposed on the outer side) among the eight LN optical waveguides 31 having the U-shaped structure.

[0068] Hereinafter, the configuration of the optical modulator 5D according to the fifth embodiment will be described in detail. The LN optical waveguide 31 included in the LN modulation unit 12 has a U-shaped structure so that the waveguide length of the inner LN optical waveguide is different from the waveguide length of the outer LN optical waveguide. Therefore, in the present embodiment, the optical path lengths of the eight optical waveguides from the first Si optical waveguide 21 to the second Si optical waveguide 42 connected to the LN optical waveguide included in the LN optical waveguide 31 are equal. Then, in order to make the optical path lengths of the eight optical waveguides equal, the waveguide length of each of the eight Si optical waveguides 21A included in the first Si optical waveguide 21 and the waveguide length of each of the eight Si optical waveguides 42A included in the second Si optical waveguide 42 are adjusted. In addition, in order to make the optical path lengths of each optical waveguide of the Mach-Zehnder interferometer equal, the DC electrode 23B of the father-side MZ segment 23 provided on the first Si optical waveguide 21 and the DC electrode 43B of the child-side MZ segment 43 provided on the second Si optical waveguide 42 are adjusted. Furthermore, adjusting the DC electrodes 23B and 43B is adjusting, for example, the waveguide length or curvature of each of the DC electrodes 23B and 43B.

[0069] Furthermore, among the four Si optical waveguides included in the first Si optical waveguide 21, the position of the branch waveguide 21B of the Si optical waveguide including the inner LN optical waveguide included in the LN optical waveguide 31 is adjusted by moving the position in the traveling direction of the optical signal. Furthermore, among the four Si optical waveguides included in the second Si optical waveguide 42, the position of the multiplexing waveguide 42B of the optical waveguide including the outer LN optical waveguide included in the LN optical waveguide 31 is adjusted by moving the position in the traveling direction of the optical signal.

[0070] Furthermore, the optical modulator 5D sets the PR 46A on the optical waveguide including the LN optical waveguide having a larger curvature radius (i.e., arranged on the outer side) among the eight LN optical waveguides 31 having the U-shaped structure. The loss in the optical waveguide including the LN optical waveguide having a smaller curvature radius (i.e., arranged on the inner side) increases, so that the PR 46A with increased loss is not set. Therefore, among the waveguides having the U-shaped structure included in the LN optical waveguide 31, the difference between the loss in the optical waveguide including the outer LN optical waveguide and the loss in the optical waveguide including the inner LN optical waveguide is set small. Therefore, the loss balance between the vertically polarized wave and the horizontally polarized wave can be ensured.

[0071] The optical modulator 5D according to the fifth embodiment is configured to adjust the Si optical waveguide 21A included in the first Si optical waveguide 21, the Si optical waveguide 42A included in the second Si optical waveguide 42, and the DC electrodes 23B and 43B of the father-side MZ segment 23 and the child-side MZ segment 43, respectively, so that the optical path lengths of the optical waveguides are equal. The optical modulator 5D adjusts the position of the multiplexing waveguide 42B provided on the Si optical waveguide among the four Si optical waveguides included in the second Si optical waveguide 42, and adjusts the position of the branch waveguide 21B provided on the Si optical waveguide among the four Si optical waveguides included in the first Si optical waveguide 21, so that the optical path lengths of the optical waveguides are equal. The optical modulator 5D provides the PR 46A on the optical waveguide including the LN optical waveguide having a larger curvature radius (i.e., provided on the outside) among the eight LN optical waveguides 31 having a U-shaped structure. Therefore, the loss between the optical waveguides caused by the loss caused by providing the PR 46A can be reduced. Furthermore, even if there is a difference between the waveguide lengths of the LN optical waveguides included in the LN optical waveguide 31 , it is possible to prevent the chip size of the optical modulator 5D from increasing.

[0072] In addition, for the sake of convenience of description, the following case has been described as an example: in the optical modulator 5 of the first embodiment, directional coupling is used for the portion between the first Si optical waveguide 21 and the LN optical waveguide 31; however, the portion between the first Si optical waveguide 21 and the LN optical waveguide can also be coupled using butt coupling, and appropriate modifications are also feasible.

[0073] According to one aspect of an embodiment of an optical device and the like disclosed in the present application, it is possible to prevent an increase in chip size even when an LN optical waveguide is used.

Claims

1. An optical device, comprising: An input unit that inputs an optical signal; a plurality of first Si optical waveguides that divide and output the optical signal received from the input unit; a plurality of LN optical waveguides which are included in the LN modulator and transmit the optical signal split and output by the first Si optical waveguide, and have differences in waveguide lengths; a plurality of second Si optical waveguides that multiplex and output associated optical signals output from the plurality of corresponding LN optical waveguides; an output unit, the output unit outputting the optical signal multiplexed by the second Si optical waveguide; as well as a plurality of Mach-Zehnder interferometers, wherein the plurality of Mach-Zehnder interferometers are respectively arranged on optical waveguides connected by the first Si optical waveguide, the LN optical waveguide and the second Si optical waveguide, The first Si optical waveguide and the second Si optical waveguide of each of the Mach-Zehnder interferometers are configured to have equal optical path lengths by adjusting the effective refractive index and waveguide length inside at least one of the first Si optical waveguide and the second Si optical waveguide.

2. The optical device according to claim 1, wherein: The first Si optical waveguide or the second Si optical waveguide has a waveguide length such that optical path lengths of the optical waveguides are equal.

3. The optical device according to claim 1, wherein: The first Si optical waveguide or the second Si optical waveguide has a curvature that makes the optical path lengths of the optical waveguides equal.

4. The optical device according to claim 1, wherein: The LN optical waveguide is configured to have a U-shaped structure such that the input unit and the output unit are arranged in parallel, the LN optical waveguide is bent from the input unit toward the output unit, and a difference is generated between waveguide lengths of the LN optical waveguide.

5. The optical device according to claim 4, wherein: A polarization rotator that performs polarization rotation on an optical signal transmitted via the optical waveguide is provided on a Si optical waveguide connected to an LN optical waveguide disposed on an outer side among the LN optical waveguides having the U-shaped structure.

6. The optical device according to claim 1, wherein: Each of the Mach-Zehnder interferometers comprises: a plurality of first Mach-Zehnder segments, the plurality of first Mach-Zehnder segments being disposed on respective first Si optical waveguides, and a plurality of second Mach-Zehnder segments, the plurality of second Mach-Zehnder segments being arranged on each second Si optical waveguide, and The DC electrode of the first Mach-Zehnder segment or the DC electrode of the second Mach-Zehnder segment has an electrode length that makes the optical path lengths of the optical waveguides equal.

7. The optical device according to claim 1, wherein: Each of the Mach-Zehnder interferometers comprises: a plurality of first Mach-Zehnder segments, the plurality of first Mach-Zehnder segments being disposed on respective first Si optical waveguides, and a plurality of second Mach-Zehnder segments, the plurality of second Mach-Zehnder segments being arranged on each second Si optical waveguide, and The DC electrode of the first Mach-Zehnder segment or the DC electrode of the second Mach-Zehnder segment has a curvature that makes the optical path lengths of the optical waveguide equal.

8. The optical device according to claim 6, wherein: The first Mach-Zehnder segment is a nested parent-side Mach-Zehnder segment, and the second Mach-Zehnder segment is a nested child-side Mach-Zehnder segment.

9. The optical device according to claim 6, wherein: The first Mach-Zehnder segment is a nested child Mach-Zehnder segment, and the second Mach-Zehnder segment is a nested parent Mach-Zehnder segment.

10. The optical device according to claim 1, wherein: The first Si optical waveguide has a waveguide length that makes the optical path lengths of the optical waveguides equal by arranging the positions of the branch waveguides included in the first Si optical waveguide in the traveling direction of the optical signal.

11. The optical device according to claim 1, wherein: The second Si optical waveguide has a waveguide length that makes the optical path lengths of the optical waveguides equal by arranging the position of the multiplexing waveguide included in the second Si optical waveguide in the direction opposite to the traveling direction of the optical signal.

12. An optical communication device, comprising: a processor that performs signal processing on the electrical signal; a light source, the light source generating light; as well as an optical device that modulates light generated from the light source by using an electrical signal output from the processor, Wherein, the optical device comprises: An input unit that inputs an optical signal; a plurality of first Si optical waveguides that divide and output an optical signal received from the input unit; a plurality of LN optical waveguides which are included in the LN modulator and transmit the optical signal split and output by the first Si optical waveguide, and have differences in waveguide lengths; a plurality of second Si optical waveguides that multiplex and output optical signals output from the plurality of corresponding LN optical waveguides; an output unit that outputs the optical signal multiplexed by the second Si optical waveguide; and a plurality of Mach-Zehnder interferometers, each of which is disposed on an optical waveguide connected by the first Si optical waveguide, the LN optical waveguide, and the second Si optical waveguide, and The first Si optical waveguide and the second Si optical waveguide of each of the Mach-Zehnder interferometers are configured to have equal optical path lengths by adjusting an effective refractive index and a waveguide length inside at least one of the first Si optical waveguide and the second Si optical waveguide.

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