Optical device including optical modulator and optical transceiver

Abstract

An optical device including an optical modulator and an optical transceiver. An optical device including an optical modulator formed on a substrate. The optical device includes: a signal electrode for the optical modulator formed on the substrate; a ground electrode for the optical modulator formed on the substrate; an optical waveguide disposed in a region between the signal electrode and the ground electrode; a first buffer zone formed between the optical waveguide and the substrate; and a second buffer zone formed between the optical waveguide and the signal electrode and between the optical waveguide and the ground electrode. The dielectric constant of the second buffer zone is higher than the dielectric constant of the first buffer zone.

Description

Technical Field

[0001] The embodiments discussed herein relate to an optical device and an optical transceiver including an optical modulator. Background Art

[0002] Figure 1 An example of an optical device including an optical modulator is illustrated. In this example, the optical modulator generates a polarization multiplexed optical signal. In this regard, the optical modulator includes a pair of mother Mach-Zehnder interferometers X and Y. Each of the mother Mach-Zehnder interferometers X and Y includes a pair of Mach-Zehnder interferometers. Therefore, the optical modulator includes four Mach-Zehnder interferometers XI, XQ, YI, and YQ. When an electrical signal is provided, each Mach-Zehnder interferometer XI, XQ, YI, and YQ can work as an optical modulator.

[0003] The optical modulator is formed using a LiNbO 3 (LN) substrate 1. In this regard, each Mach-Zehnder interferometer is constructed by forming an optical waveguide 2 in a surface region of the LN substrate 1.

[0004] The optical modulator includes a signal electrode 3, a DC electrode 4 and a ground electrode. A signal electrode 3 is provided for each Mach-Zehnder interferometer XI, XQ, YI and YQ. Each signal electrode 3 is provided with an RF signal indicating transmission data. The RF signal can be generated by a digital signal processor (not shown). The description of the DC electrode 4 is omitted here. The ground electrode is formed in a region on the surface of the LN substrate 1 where neither the signal electrode 3 nor the DC electrode 4 is formed. The ground electrode is electrically connected to GND. Note that the ground electrode is omitted in the drawings for visibility.

[0005] Figure 2 An example of a conventional light modulator is illustrated. Figure 2 Draw out Figure 1 Any of the four sub-modulators of the optical modulator shown (i.e., any of the Mach-Zehnder interferometers XI, XQ, YI, and YQ). For example, Figure 2 Can indicate Figure 1 AA section of sub-modulator XI shown.

[0006] like Figure 1 and Figure 2 As shown, the optical modulator includes a pair of optical waveguides WGa and WGb forming a Mach-Zehnder interferometer, a signal electrode 3 and a ground electrode 5. The optical waveguides WGa and WGb are implemented by a coplanar waveguide (CPW). In this example, the coplanar waveguide is composed of two linear or linear-like conductors (i.e., WGa and WGb) formed parallel to each other.

[0007] exist Figure 2In the example shown, the LN substrate 1 is an X-cut LN substrate. The signal electrode 3 is formed on a region between a pair of optical waveguides forming a Mach-Zehnder interferometer. Figure 2 In the example shown, the signal electrode 3 is formed on the region between the optical waveguides WGa and WGb. At the same time, the ground electrode 5 is formed in the other region on the surface of the LN substrate 1. Therefore, the signal electrode 3 and each ground electrode 5 are formed so that the corresponding optical waveguide is placed therebetween. In other words, the optical waveguide is provided in the region between the signal electrode 3 and the ground electrode 5. Note that a buffer layer 6 such as an oxide film is formed on the surface of the LN substrate 1, and the signal electrode 3 and the ground electrode 5 are formed on the surface of the buffer layer 6.

[0008] When a voltage is applied between the signal electrode 3 and the ground electrode 5 in the optical device, an electric field is generated in the surface area of ​​the LN substrate 1. In this case, because the LN substrate 1 is an X-cut LN substrate, a strong electric field is generated in the direction along the surface of the LN substrate 1. Therefore, Figure 2 As shown, for example, when an electric field is generated in the +Z direction in the optical waveguide WGa, an electric field is generated in the -Z direction in the optical waveguide WGb. Therefore, the directions of the electric fields generated in the optical waveguides WGa and WGb are opposite to each other. These electric fields change the refractive index (or optical path length) of the optical waveguides WGa and WGb, respectively, and change the phase of the light to be output from the optical waveguides, respectively. Therefore, a desired modulated optical signal can be generated by appropriately adjusting the phase of light propagating through the Mach-Zehnder interferometer using an electrical signal.

[0009] For example, Japanese Laid-Open Patent Publication No. 2004-133311 describes an optical modulator formed using an X-cut LN substrate. International Publication Pamphlet WO 2012 / 124830 describes an example of an optical modulator element.

[0010] In recent years, in order to realize large-capacity data communication, an electric signal with a bandwidth of several tens of GHz is applied to a signal electrode. For an electric signal with such a wide bandwidth, a coplanar structure can be used to obtain a preferable transmission characteristic.

[0011] exist Figure 2 In the example shown, the optical waveguides WGa and WGb having a coplanar structure are formed by diffusing a metal such as titanium from the surface of the LN substrate 1. However, in this structure, it is difficult to sufficiently confine light within the optical waveguide, so the efficiency of applying the electric field is reduced. Therefore, it is necessary to increase the amplitude of the input electrical signal to generate an optical signal with a specified amplitude. Therefore, the driving voltage of the optical modulator increases, resulting in large power consumption of the optical modulator.

[0012] An object of one aspect of the present invention is to reduce the driving voltage of an optical modulator. Summary of the invention

[0013] According to one aspect of the embodiment, an optical device includes an optical modulator formed on a substrate. The optical device includes: a signal electrode for the optical modulator formed on the substrate; a ground electrode for the optical modulator formed on the substrate; an optical waveguide disposed in a region between the signal electrode and the ground electrode; a first buffer zone formed between the optical waveguide and the substrate; and a second buffer zone formed between the optical waveguide and the signal electrode and between the optical waveguide and the ground electrode. The dielectric constant of the second buffer zone is higher than the dielectric constant of the first buffer zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 An example of an optical device including an optical modulator is illustrated;

[0015] Figure 2 An example of a conventional light modulator is illustrated;

[0016] Figure 3A and Figure 3B This example shows how to solve the problem caused by Figure 2 Examples of optical modulators with problems caused by the structures shown;

[0017] Figure 4 It is an illustration of the propagation of light and signals;

[0018] Figure 5 An example of an optical device including an optical modulator according to an embodiment of the present invention is illustrated;

[0019] Figure 6 An example of a cross-sectional structure of an optical modulator according to an embodiment of the present invention is illustrated;

[0020] Figure 7 An effect obtained according to an embodiment of the present invention is illustrated;

[0021] Figure 8 A variation of the optical modulator according to the embodiment of the present invention is illustrated;

[0022] Fig. 9A and 9B illustrates other variations of the optical modulator according to the embodiment of the present invention; and

[0023] Fig.10 An example of an optical transceiver according to an embodiment of the present invention is illustrated. DETAILED DESCRIPTION

[0024] Figure 3A and Figure 3B This example shows how to solve the Figure 2 The structure shown is an example of the problems caused by the light modulator. Figure 3A and Figure 3BIt also shows Figure 1 Any one of the four sub-modulators of the optical modulator shown in (ie, any one of the Mach-Zehnder interferometers XI, XQ, YI and YQ).

[0025] exist Figure 3A In the illustrated configuration, a buffer layer 11 is formed on an LN substrate 1, and a thin film LN crystal layer 12 is formed on the buffer layer 11. Optical waveguides WGa and WGb are formed by etching the thin film LN crystal layer 12. The optical waveguides WGa and WGb are rib waveguides and include a flat plate. A buffer layer 13 is formed on the upper side of the thin film LN crystal layer 12. The buffer layers 11 and 13 may be SiO2 films. A signal electrode 21 is formed above the region between the optical waveguides WGa and WGb. A ground electrode 22 is formed in the outer region of the optical waveguides WGa and WGb.

[0026] In this configuration, the optical waveguides WGa and WGb are surrounded by the buffer layers 11 and 13, so the light will be sufficiently confined within the optical waveguides. Figure 2 Compared with the configuration shown in , the conversion efficiency from the input electrical signal to the optical signal is improved, and the driving voltage of the optical modulator can be reduced.

[0027] However, as described above, the optical waveguides WGa and WGb (ie, rib waveguides) are formed by etching the thin film LN crystal layer 12. It is necessary to precisely control the depth at which etching is performed to form the rib optical waveguide, and thus it is difficult to produce an optical modulator.

[0028] exist Figure 3B In the optical modulator shown, a channel waveguide is formed to replace Figure 3A In this case, the optical waveguides WGa and WGb are formed by etching away the thin film LN crystal surrounding the optical waveguides WGa and WGb. Therefore, there is no need to accurately control the depth at which etching is performed, so the production of the optical modulator is relatively easy.

[0029] However, in this configuration, the buffer layer 13 provided in the region between the electrodes 21 and 22 and the optical waveguides WGa and WGb is formed of, for example, SiO2, as is the buffer layer 11. The effective refractive index of the optical waveguides WGa and WGb formed of LN crystal is different from the effective refractive index of the buffer layer 13 formed of SiO2. Specifically, the effective refractive index of the LN crystal is about 2.2, and the effective refractive index of SiO2 is about 1.5. The propagation speed of electromagnetic waves depends on the effective refractive index. Therefore, the speed of light propagating through the optical waveguide WGa or WGb does not match the speed of the electromagnetic wave propagating through the buffer layer 13. Specifically, the speed of the electromagnetic wave propagating through the buffer layer 13 is higher than the speed of the light propagating through the optical waveguide WGa or WGb.

[0030] Figure 4is an example diagram of propagation of light and signals. In this example, light propagates through a pair of optical waveguides WGa and WGb forming a Mach-Zehnder interferometer. A signal electrode 21 is formed in a region between the optical waveguides WGa and WGb. A ground electrode 22 is formed in a region outside the optical waveguides WGa and WGb. An RF signal is provided to the signal electrode 21. The RF signal indicates transmission data. The propagation direction of light is the same as the propagation direction of the RF signal.

[0031] When an RF signal is supplied to the signal electrode 21, an electric field caused by the RF signal is generated between the signal electrode 21 and the ground electrode 22. The electric field passes through the optical waveguides WGa and WGb. The change in the electric field propagates as the RF signal propagates. The propagation direction of the electric field change is the same as the propagation direction of the RF signal.

[0032] However, in Figure 3B In the configuration shown in which the buffer layer 13 is formed in the region between the electrodes 21 and 22 and the optical waveguides WGa and WGb, the speed of light propagating through the optical waveguides WGa and WGb will not match the speed of the electromagnetic wave propagating through the buffer layer 13. For example, when the effective refractive index of the buffer layer 13 is lower than the effective refractive index of the optical waveguides WGa and WGb, the speed of the electromagnetic wave propagating through the buffer layer 13 is higher than the speed of light propagating through the optical waveguides WGa and WGb. When the speed of light propagating through the optical waveguides WGa and WGa does not match the speed of the electromagnetic wave propagating through the buffer layer 13, the input RF signal needs to have a larger amplitude to obtain a specified light amplitude. Therefore, it is necessary to increase the driving voltage of the optical modulator.

[0033] Implementation

[0034] Figure 5 An example of an optical device including an optical modulator according to an embodiment of the present invention is illustrated. The optical modulator 100 according to an embodiment of the present invention is Figure 1 The optical modulators shown are substantially the same. Therefore, the optical modulator 100 includes a pair of mother Mach-Zehnder interferometers X and Y for generating polarization multiplexed optical signals. Each mother Mach-Zehnder interferometer X and Y includes a pair of Mach-Zehnder interferometers. Therefore, the optical modulator 100 includes four Mach-Zehnder interferometers XI, XQ, YI and YQ. When an electrical signal is provided, each Mach-Zehnder interferometer XI, XQ, YI and YQ can work as an optical modulator.

[0035] The optical modulator 100 is formed on an LN substrate 1. In this regard, each Mach-Zehnder interferometer is constructed by forming an optical waveguide in a surface region of the LN substrate 1. The LN substrate 1 may be, but is not particularly limited to, an X-cut LN substrate.

[0036] The optical modulator 100 includes a signal electrode 21, DC electrodes 4a and 4b, and a ground electrode. The signal electrode 21 is provided for each Mach-Zehnder interferometer XI, XQ, YI, and YQ. Each signal electrode 21 is provided with an RF signal indicating transmission data. The RF signal is generated by a digital signal processor (not shown), provided to the corresponding signal electrode 21 via a driver 51, and terminated by a terminator 52.

[0037] A DC electrode 4a is provided for each Mach-Zehnder interferometer XI, XQ, YI and YQ. A DC voltage for adjusting the operating point of the Mach-Zehnder interferometers XI, XQ, YI and YQ is applied to the DC electrode 4a. A DC electrode 4b is provided for each mother Mach-Zehnder interferometer X and Y. A DC voltage for adjusting the phase difference is applied to the DC electrode 4b. For example, a DC voltage for adjusting the phase difference between the Mach-Zehnder interferometers XI and XQ may be applied to the DC electrode 4b for the mother Mach-Zehnder interferometer X, and a DC voltage for adjusting the phase difference between the Mach-Zehnder interferometers YI and YQ may be applied to the DC electrode 4b for the mother Mach-Zehnder interferometer Y. For example, the phase difference may be π / 2.

[0038] The ground electrode is formed in a region on the surface of the LN substrate 1 where neither the signal electrode 21 nor the DC electrodes 4a and 4b are formed. The ground electrode is electrically connected to GND. Note that for the purpose of visibility, Figure 5 The ground electrode is omitted.

[0039] In the optical modulator 100, the electrical signals are provided to the Mach-Zehnder interferometers XI, XQ, YI and YQ, respectively. In response thereto, the Mach-Zehnder interferometers XI, XQ, YI and YQ output modulated optical signals XI, XQ, YI and YQ, respectively. The modulated optical signal X is generated from the modulated optical signals XI and XQ, and the modulated optical signal Y is generated from the modulated optical signals YI and YQ. The polarization beam combiner (PBC) 53 combines and outputs the modulated optical signals X and Y.

[0040] Figure 6 An example of a cross-sectional structure of the optical modulator 100 according to an embodiment of the present invention is illustrated. Figure 6 Shows Figure 5 Any one of the four sub-modulators of the optical modulator 100 shown (i.e., any one of the Mach-Zehnder interferometers XI, XQ, YI, and YQ). For example, Figure 6 Can indicate Figure 5 AA section of sub-modulator XI shown.

[0041] A buffer layer 11 is formed on the surface of the LN substrate 1. The buffer layer 11 may be, but is not particularly limited to, an oxide film. In this example, the oxide film is SiO2.

[0042] The optical waveguides WGa and WGb are formed on the surface of the buffer layer 11. In this example, the optical waveguides WGa and WGb are formed of LN crystal as with the LN substrate 1. For example, a thin film X-cut LN crystal may be formed on the surface of the buffer layer 11. Then, the thin film X-cut LN crystal is selectively removed by etching or the like to form the optical waveguides WGa and WGb. For example, each of the optical waveguides WGa and WGb may be 2-3 μm in height and 1-4 μm in width.

[0043] The buffer zone 31 is formed on the side of each optical waveguide WGa and WGb. The height of the buffer zone 31 is equal to the height of the optical waveguides WGa and WGb. For example, the buffer zone 31 may be 1-5 μm in width.

[0044] The buffer region 32 is formed on the upper sides of the optical waveguides WGa and WGb and the buffer region 31. For example, the buffer region 32 may be formed of the same material as the buffer layer 11. That is, the buffer region 32 may also be formed of SiO2.

[0045] As described above, each of the optical waveguides WGa and WGb is surrounded by the buffer layer 11, the buffer layer 31, and the buffer layer 32. In this regard, the refractive index of the optical waveguides WGa and WGb is higher than that of the buffers 11, 31, and 32. Therefore, the optical waveguides WGa and WGb function as cores, and the buffers 11, 31, and 32 function as claddings.

[0046] The buffer region 31 and the buffer layer 11 are formed of different materials. Specifically, the dielectric constant of the buffer region 31 is different from the dielectric constant of the buffer layer 11. In this example, the dielectric constant of the buffer region 31 is higher than the dielectric constant of the buffer layer 11.

[0047] The dielectric constant of the buffer layer 31 is determined to be close to the dielectric constant of the optical waveguides WGa and WGb compared to the buffer layer 11. For example, when the buffer layer 11 is formed of SiO2, the relative dielectric constant of the buffer layer 11 may be 4-6. For example, it is assumed that the relative dielectric constant of the LN crystal forming the optical waveguides WGa and WGb is 30. In this case, the buffer layer 31 is formed to have a relative dielectric constant higher than the dielectric constant of SiO2 and close to 30.

[0048] For example, the buffer region 31 may be formed of a material obtained by mixing SiO2 with a substance having a higher dielectric constant than SiO2. In this case, the buffer region 31 may be formed of a material obtained by mixing SiO2 with TiO2. The relative dielectric constant of TiO2 is about 50-80. Therefore, the relative dielectric constant of the buffer region 31 may be determined to be a desired value by adjusting the mixing ratio between SiO2 and TiO2.

[0049] The signal electrode 21 is disposed in a region between the optical waveguides WGa and WGb. The ground electrode 22 is formed in a region outside the optical waveguides WGa and WGb. Therefore, each of the optical waveguides WGa and WGb is disposed in a region between the signal electrode 21 and the ground electrode 22. The buffer region 31 is disposed between the signal electrode 21 and each of the optical waveguides WGa and WGb. Similarly, the buffer region 31 is provided between the ground electrode 22 and each of the optical waveguides WGa and WGb. In other words, the buffer region 31a is formed on one side of each of the optical waveguides WGa and WGb, and the signal electrode 21 is formed to be connected to the buffer region 31a. The buffer region 31b is formed on the other side of each of the optical waveguides WGa and WGb, and the ground electrode 22 is formed to be connected to the buffer region 31b.

[0050] As described above, each optical waveguide WGa and WGb is provided between the signal electrode 21 and the ground electrode 22. A buffer zone 31 is provided in the region between the electrodes (21 and 22) and the optical waveguide (WGa and WGb). In this example, the optical waveguide is formed of a thin film X-cut LN crystal. Therefore, when a voltage is applied between the signal electrode 21 and the ground electrode 22, a strong electric field is generated in the optical waveguide in a direction substantially parallel to the surface of the LN substrate 1.

[0051] The dielectric constant of the buffer zone 31 is close to the dielectric constant of the optical waveguides WGa and WGb. Specifically, the dielectric constant of the buffer zone 31 is determined so that the speed of light propagating through the optical waveguides WGa and WGb matches or approaches the speed of the electromagnetic wave propagating through the buffer zone 31. Therefore, the speed of light propagating through the optical waveguides WGa and WGb matches or approaches the speed of the electromagnetic wave propagating through the buffer zone 31. As a result, Figure 3A and Figure 3B Compared with the configuration shown in FIG. 1 , the amplitude of the input RF signal required to obtain a specific light amplitude can be reduced. Therefore, the driving voltage of the optical modulator can be reduced, thereby reducing the power consumption of the optical modulator.

[0052] In an embodiment of the present invention, Figure 4 The "buffer layer" shown corresponds to the buffer region 31. Here, increasing the dielectric constant of the buffer region 31 increases the effective refractive index of the buffer region 31 to microwaves, so that the speed of microwaves propagating through the buffer region 31 can be close to the speed of light propagating through the optical waveguide.

[0053] Figure 7 An effect obtained according to an embodiment of the present invention is illustrated. The horizontal axis of the graph represents the frequency of the RF signal used to drive the optical modulator. The vertical axis represents the E / O response. The E / O response represents the intensity or amplitude of the output optical signal relative to the amplitude of the input electrical signal (in this example, the RF signal).

[0054] exist Figure 3B In the optical modulator shown, when the frequency of the RF signal is high, the E / O response deteriorates. Figure 7 In the example shown, when the frequency of the RF signal exceeds 30 GHz, the E / O response deteriorates sharply. In contrast, in the embodiment of the present invention, even when the frequency of the RF signal is high, the deterioration of the E / O response is mild. Figure 3B Compared with the configuration shown, the driving voltage of the input RF signal required to obtain a specified light amplitude can be reduced. This effect is particularly prominent when the frequency of the RF signal (ie, the bit rate of the transmitted data) is high.

[0055] As described above, in the embodiment of the present invention, the dielectric constant of the buffer region 31 is higher than the dielectric constant of the buffer layer 11, so the speed of light propagating through the optical waveguides WGa and WGb matches or approaches the speed of the electromagnetic wave propagating through the buffer region 31. In this regard, the difference between the propagation speed of the electromagnetic wave through the buffer region 31 and the propagation speed of the light through the optical waveguides WGa and WGb is smaller than the difference between the propagation speed of the electromagnetic wave through the buffer layer 11 and the propagation speed of the light through the optical waveguides WGa and WGb. Therefore, it is possible to reduce the driving voltage of the input RF signal required to obtain a specified light amplitude. As a result, the power consumption of the optical modulator is reduced. Alternatively, assuming Figure 3B The driving voltage of the optical modulator in the structure shown is the same as the corresponding driving voltage in the embodiment of the present invention. Figure 3B Compared with the structure shown in FIG. 1 , the length of the signal electrode formed along the optical waveguide can be reduced. In this case, the size of the optical device can be reduced.

[0056] Note that increasing the dielectric constant of the buffer region 31 can improve Figure 7 However, excessively increasing the dielectric constant of the buffer region 31 will deteriorate the E / O response. Therefore, it is preferable to determine the dielectric constant of the buffer region 31 to an appropriate value so that the E / O response is enhanced.

[0057] In addition, as a general rule, in order to sufficiently confine light within the optical waveguides WGa and WGb, the refractive index of the optical waveguides WGa and WGb is preferably sufficiently higher than the refractive index of the buffer zone surrounding the optical waveguides WGa and WGb. Therefore, the material of the buffer zone 31 is preferably determined so that the light is sufficiently confined within the optical waveguides WGa and WGb. However, if the light cannot be sufficiently confined within the optical waveguides WGa and WGb, it is considered that the E / O response will deteriorate. Therefore, determining the material of the buffer zone 31 to enhance the E / O response (preferably, optimize the E / O response) will allow the driving voltage of the input RF signal required to obtain a specified light amplitude to be reduced.

[0058] Figure 8 A variation of the optical modulator according to the embodiment of the present invention is illustrated. Figure 6 Compared with the structure shown in Figure 8 In the illustrated configuration, no buffer 32 is provided. This means that no buffer 32 needs to be provided. Figure 6 The buffer layer 32 shown in FIG. 1 only needs to achieve speed matching between light and microwaves, and there is no need to provide a buffer layer on the upper side of the optical waveguides WGa and WGb.

[0059] exist Figure 8 In the illustrated configuration, no process for providing the buffer 32 is required, and therefore, Figure 6 Compared with the configuration shown, the method for producing the optical modulator can be simplified. However, since the surfaces of the optical waveguides WGa and WGb are not protected by the buffer layer, light scattering may occur.

[0060] Fig. 9A and Fig. 9B Other variations of the optical modulator according to the embodiment of the present invention are illustrated. Fig. 9A Shows Figure 6 A variation of the configuration shown in . Fig. 9B Shows Figure 8 A variation of the configuration shown in .

[0061] exist Figure 6 and Figure 8 In the configurations shown, the edge positions of the buffer region 31 match the edge positions of the electrodes (21, 22) respectively. In these configurations, there may be a gap between the buffer region 31 and the electrodes (21, 22) due to production errors, etc. Here, the gap between the buffer region 31 and the electrodes (21, 22) can reduce the conversion efficiency from electrical signals to optical signals, thereby increasing the driving voltage of the input RF signal required to obtain a specified optical amplitude.

[0062] exist Fig. 9A and Fig. 9BIn the illustrated configuration, a portion of the signal electrode 21 overlaps a portion of the corresponding buffer region 31, and a portion of the ground electrode 22 overlaps a portion of the corresponding buffer region 31. In this case, even in the case of a production error such as a production error in which the width of the buffer region 31 is smaller than a design value or a production error in which the distance between the signal electrode 21 and the ground electrode 22 is larger than a design value, a gap will not be likely to be formed between the buffer region 31 and the electrodes (21, 22). Therefore, since the conversion efficiency from an electrical signal to an optical signal is not reduced, an increase in the driving voltage of an input RF signal required to obtain a specified optical amplitude is suppressed. Note that the process of forming the signal electrode 21 and the ground electrode 22 preferably includes a process of depositing a metal such as Ti on the side surface of the buffer region 31.

[0063] Fig.10 An example of an optical transceiver according to an embodiment of the present invention is illustrated. The optical transceiver 200 includes a light source (LD) 201 , an optical modulator 202 , an optical receiver 203 , and a digital signal processor (DSP) 204 .

[0064] The light source 201 is, for example, a laser light source and generates a continuous wave light of a specified frequency. The optical modulator 202 generates a modulated optical signal by modulating the continuous wave light generated by the light source 201 with a transmission signal provided from the DSP 204. The optical modulator 202 may correspond to Figure 5 2. The optical modulator 100 shown in FIG. 20 is a coherent receiver and demodulates the received optical signal by using the continuous wave light generated by the light source 201. The DSP 204 generates a transmission signal according to the data provided from the application. The transmission signal is provided to the optical modulator 202. The DSP 204 restores the data from the received signal demodulated by the optical receiver 203.

[0065] Therefore, the optical transceiver 200 includes the optical device according to the embodiment of the present invention as an optical modulator. Therefore, it is possible to simultaneously achieve a reduction in power consumption of the optical transceiver and a reduction in size of the optical transceiver.

Claims

1. An optical device, comprising an optical modulator formed on a substrate, the optical device comprising: A signal electrode, the signal electrode is used for the optical modulator, and the signal electrode is formed on the substrate; A ground electrode, the ground electrode is used for the optical modulator, and the ground electrode is formed on the substrate; an optical waveguide disposed in a region between the signal electrode and the ground electrode; a first buffer zone formed between the optical waveguide and the substrate; as well as A second buffer zone is formed between the optical waveguide and the signal electrode and between the optical waveguide and the ground electrode, wherein: The optical waveguide, the signal electrode, the ground electrode and the second buffer region are arranged side by side on the substrate in a direction parallel to a surface of the substrate, and The dielectric constant of the second buffer area is higher than the dielectric constant of the first buffer area.

2. The optical device according to claim 1, wherein: The optical waveguide is formed from thin film X-cut LN crystal.

3. The optical device according to claim 1, wherein: The first buffer zone is formed of SiO2, and The second buffer region is formed of a material including SiO 2 and a substance having a higher dielectric constant than SiO 2 .

4. The optical device according to claim 1, wherein: The difference between the propagation speed of the electromagnetic wave through the second buffer zone and the propagation speed of the light through the optical waveguide is smaller than the difference between the propagation speed of the electromagnetic wave through the first buffer zone and the propagation speed of the light through the optical waveguide.

5. The optical device according to claim 1, wherein: A portion of the signal electrode and a portion of the ground electrode are respectively formed to overlap with the second buffer region.

6. The optical device according to claim 1, further comprising: A third buffer region is formed of the same material as the first buffer region and is disposed on an upper side of the optical waveguide.

7. The optical device according to claim 6, wherein: A portion of the signal electrode and a portion of the ground electrode are respectively formed on an upper surface of the third buffer region to overlap the second buffer region.

8. An optical transceiver, comprising an optical modulator and an optical receiver, wherein: The optical modulator comprises: substrate, A signal electrode, the signal electrode is used for the optical modulator, and the signal electrode is formed on the substrate; A ground electrode, the ground electrode is used for the optical modulator, and the ground electrode is formed on the substrate; an optical waveguide disposed in a region between the signal electrode and the ground electrode; a first buffer region formed between the optical waveguide and the substrate; and A second buffer zone is formed between the optical waveguide and the signal electrode and between the optical waveguide and the ground electrode, wherein: The optical waveguide, the signal electrode, the ground electrode and the second buffer region are arranged side by side on the substrate in a direction parallel to a surface of the substrate, and The dielectric constant of the second buffer area is higher than the dielectric constant of the first buffer area.

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