Optical Devices and Optical Transceivers

Abstract

The present application relates to an optical device and an optical transceiver. An optical device comprises a substrate (W), an RF modulation unit and a phase adjustment unit (220). The RF modulation unit is arranged on the substrate (W) and modulates light according to an RF signal. The phase adjustment unit (220) is arranged on the substrate (W) and adjusts the phase of the optical signal modulated by the RF modulation unit. The phase adjustment unit (220) comprises a heater (2200) and an optical waveguide to be heated (2201). The optical waveguide to be heated (2201) is arranged between a thin film LN substrate (32) and a buffer layer (33) of the substrate (W) and is formed of a material having a thermo-optical effect. The heater (2200) is arranged on the substrate (W) at a position opposite to the optical waveguide to be heated (2201), the buffer layer (33) is located between the heater (2200) and the optical waveguide to be heated (2201), and the heater (2200) heats the optical waveguide to be heated (2201).

Description

Technical Field

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

[0002] For example, Patent Document 1 below discloses a method of using lithium niobate (LiNbO 3 ; LN) Mach-Zehnder optical modulator. In this type of optical modulator, an LN film is provided on a buffer layer, a buffer layer is provided on the LN film, and a signal electrode is provided on the buffer layer. Then, an optical waveguide having a ridge structure (i.e., a thin film LN optical waveguide) is formed on the LN film, and light propagating through the inside of the thin film LN optical waveguide is modulated by an electrical signal supplied via the signal electrode.

[0003] Reference List

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-20953 Summary of the invention

[0006] Technical issues

[0007] Incidentally, at both the electrode for RF modulation and the electrode for phase adjustment, the refractive index of the optical waveguide in the region where each electrode exists is changed by applying a voltage to each electrode. As a result, the effective optical path length of the RF modulation unit and the effective optical path length of the phase adjustment unit are changed, and thus phase modulation can be performed and the phase difference can be adjusted. In addition, as an optical waveguide, it is possible to consider using a structure in which a waveguide formed by using titanium (Ti) is provided between the LN film and the buffer layer (i.e., a Ti diffused optical waveguide). However, because the light confinement effect in the Ti diffused optical waveguide is lower than that in the thin film LN optical waveguide, there is a problem of increased light loss in the Ti diffused optical waveguide. On the contrary, if the optical waveguide is changed from the Ti diffused optical waveguide to the thin film LN optical waveguide, the electric field application efficiency in the RF modulation unit can be improved, and thus the size of the RF electrode for performing RF modulation can be reduced. However, in order to obtain an effective electric field application efficiency in the phase adjustment unit, it is necessary to extend the DC electrode for phase adjustment. However, if the length of the DC electrode increases, it is difficult to reduce the size of the optical modulator.

[0008] On the contrary, in order to reduce the driving power of the phase adjustment unit, it is conceivable to shorten the distance between the DC electrode and the ground electrode. However, considering the manufacturing error, there are some limitations in shortening the distance between the DC electrode and the ground electrode. Therefore, it is difficult to further achieve power saving by shortening the distance between the DC electrode and the ground electrode.

[0009] Therefore, an object of one aspect of an embodiment of the present invention is to provide an optical device and an optical transceiver capable of reducing the size while achieving power saving.

[0010] Technical Solution

[0011] According to one aspect of the embodiment, an optical device includes a substrate, an RF modulation unit and a phase adjustment unit. In the substrate, a first buffer layer, a thin film having an electro-optical effect, and a second buffer layer are formed in this order. The RF modulation unit is arranged on the substrate and modulates light according to an RF signal. The phase adjustment unit is arranged on the substrate and adjusts the phase of the optical signal modulated by the RF modulation unit. The phase adjustment unit includes a first optical waveguide and a heater. The first optical waveguide is arranged between the second buffer layer and the thin film and is formed of a material having a thermo-optical effect. Light that has been modulated by the RF modulation unit or is to be modulated by the RF modulation unit is allowed to pass through the first optical waveguide. The heater is arranged at a position opposite to the first optical waveguide, the second buffer layer is located between the heater and the first optical waveguide, and the heater heats the first optical waveguide.

[0012] Beneficial Effects

[0013] According to an aspect of one embodiment, the size of an optical device can be reduced while achieving power saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a diagram showing an example of an optical transceiver;

[0015] Figure 2 is a diagram showing an example of an optical transmission device;

[0016] Figure 3 is a cross-sectional view showing an example of an RF modulation unit;

[0017] Figure 4 is a cross-sectional view showing an example of a phase adjustment unit;

[0018] Figure 5 is a diagram showing the structure of an optical waveguide in a phase adjustment unit;

[0019] Figure 6 is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0020] Figure 7 is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0021] Figure 8 is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0022] Fig. 9is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0023] Fig.10 is a diagram showing another example of the structure of an optical waveguide in a phase adjustment unit;

[0024] Fig.11 is a diagram showing another example of the structure of an optical waveguide in a phase adjustment unit;

[0025] Fig.12 is a diagram showing another example of the structure of an optical waveguide in a phase adjustment unit;

[0026] Fig.13 is a diagram showing another example of the structure of an optical waveguide in a phase adjustment unit;

[0027] Fig.14 is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0028] Fig.15 is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0029] Fig.16 is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0030] Fig.17 is a diagram showing an example of a manufacturing process of an optical waveguide in a phase adjustment unit;

[0031] Fig.18 is a diagram showing another example of the structure of an optical waveguide in a phase adjustment unit; and

[0032] Fig.19 is a diagram showing another example of the structure of the optical waveguide in the phase adjustment unit.

[0033] Reference numerals list

[0034] W substrate

[0035] T1 Thickness

[0036] T2 Thickness

[0037] W1 Width

[0038] W2 Width

[0039] W3 Width

[0040] 10 Optical transmitter / receiver

[0041] 11 Optical send / receive unit

[0042] 12 LD

[0043] 13 DSP

[0044] 14. Light receiving device

[0045] 20 Optical transmitter

[0046] 200 Optical waveguide

[0047] 201 Input

[0048] 21 RF modulation area

[0049] 210 RF modulation unit

[0050] 2100 Signal Electrode

[0051] 2101 Grounding Electrode

[0052] 211 Terminal Unit

[0053] 22 Phase adjustment area

[0054] 220 Phase adjustment unit

[0055] 2200 Heater

[0056] 2201 Optical waveguide to be heated

[0057] 2201a End face

[0058] 2202 Membrane

[0059] 23 PR

[0060] 24 PBC

[0061] 30 Support substrate

[0062] 31 Buffer layer

[0063] 32 Thin film LN substrate

[0064] 320 spine

[0065] 320a end face

[0066] 321 end DETAILED DESCRIPTION

[0067] 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.

[0068] Configuration of the optical transceiver 10

[0069] Figure 1is a diagram showing an example of an optical transceiver 10. The optical transceiver 10 according to the present embodiment includes an optical transmission / reception unit 11, a laser diode (LD) 12, and a digital signal processor (DSP) 13. The optical transmission / reception unit 11 includes an optical transmission device 20 and an optical reception device 14. The optical transmission device 20 is an example of an optical device.

[0070] The optical transmitting device 20 modulates the light provided from the LD 12 based on the transmission signal output from the DSP 13. Then, the optical transmitting device 20 outputs the optical signal (Tx_out) modulated according to the transmission signal. The optical receiving device 14 receives the optical signal (Rx_in). The received optical signal is polarization-separated, demodulated by using the light provided from the LD 12, converted into an electrical signal, and then output to the DSP 13.

[0071] Configuration of the optical transmission device 20

[0072] Figure 2 is a diagram showing an example of an optical transmitting device 20. The optical transmitting device 20 includes a radio frequency (RF) modulation area 21, a phase adjustment area 22, a polarization rotator (PR) 23, and a polarization beam combiner (PBC) 24. The RF modulation area 21 and the phase adjustment area 22 are arranged on a single substrate W. A plurality of RF modulation units 210 and a terminal unit 211 are arranged in the RF modulation area 21. Each RF modulation unit 210 includes a signal electrode 2100 and a ground electrode 2101. In an embodiment, a plurality of RF modulation units 210 constitute a Mach-Zehnder optical modulator. In the phase adjustment area 22, a plurality of phase adjustment units 220a and a plurality of phase adjustment units 220b are provided. In addition, in the following description, if it is not necessary to distinguish between the phase adjustment unit 220a and the phase adjustment unit 220b, the plurality of phase adjustment units 220a and the plurality of phase adjustment units 220b are collectively referred to as the phase adjustment unit 220. By providing a plurality of RF modulation units 210 and a plurality of phase adjustment units 220 on a single substrate W, the optical transmitting device 20 can be easily manufactured.

[0073] An optical waveguide 200 that propagates light is formed on a substrate W. Light output from the LD 12 is input from an input end 201 of the optical waveguide 200 and then input to each RF modulation unit 210 via the optical waveguide 200. Each RF modulation unit 210 modulates the input light according to an RF signal input from the DSP 13.

[0074] The optical signal that has been modulated by each RF modulation unit 210 is input to the corresponding phase adjustment unit 220b. Each phase adjustment unit 220b adjusts the phase of the optical signal according to the adjustment signal input from the DSP 13. The optical signal whose phase has been adjusted by the corresponding phase adjustment unit 220b is input to the corresponding phase adjustment unit 220a. Each phase adjustment unit 220a further adjusts the phase of the associated optical signal according to the associated adjustment signal input from the DSP 13.

[0075] After the optical signals whose phases have been adjusted by some phase adjustment units 220a are combined, the PR 23 rotates the polarization plane of the combined optical signal. The optical signals whose phases have been adjusted by other phase adjustment units 220a are combined with the optical signals whose polarization planes have been rotated by the PR 23 through the PBC 24 and then output as an optical signal (Tx_out).

[0076] Configuration of RF modulation unit 210

[0077] Figure 3 2 is a cross-sectional view showing an example of the RF modulation unit 210. The RF modulation unit 210 includes a signal electrode 2100 and a ground electrode 2101 provided on a substrate W. In an embodiment, the signal electrode 2100 and the ground electrode 2101 are formed of a material made of, for example, gold, silver, copper, or the like. The substrate W is a multilayer substrate in which a support substrate 30, a buffer layer 31, a thin film LN substrate 32, and a buffer layer 33 are formed in this order. The support substrate 30 is made of, for example, single crystal silicon, etc. The buffer layer 31 and the buffer layer 33 are formed of, for example, a silicon dioxide film, etc. The buffer layer 31 is an example of a first buffer layer, and the buffer layer 33 is an example of a second buffer layer. The thin film LN substrate 32 is made of, for example, LiNbO 3 The thin film LN substrate 32 is formed of a thin film having a large refractive index and an electro-optical effect. A ridge 320 is provided on the thin film LN substrate 32, the thickness of the ridge 320 is greater than the thickness of other regions of the thin film LN substrate 32, and the ridge 320 is formed as a protrusion along the surface of the thin film LN substrate 32. The ridge 320 serves as an optical waveguide 200 that propagates light. The thin film LN substrate 32 and the ridge 320 are formed of the same material. The refractive index of each of the thin film LN substrate 32 and the ridge 320 is greater than the refractive index of each of the buffer layer 31 and the buffer layer 33. The ridge 320 is an example of a second optical waveguide.

[0078] An RF signal having a frequency band of, for example, several tens of gigahertz (GHz) is input from the DSP 13 to the signal electrode 2100. If the RF signal is input to the signal electrode 2100, an electric field is generated between the signal electrode 2100 and the ground electrode 2101. Then, the refractive index of the ridge 320 changes due to the electric field generated between the signal electrode 2100 and the ground electrode 2101. As a result, the phase of light propagating through the ridge 320 changes. By individually changing the phase of light propagating through the ridge 320 in each RF modulation unit 210, the light is modulated according to the RF signal.

[0079] Configuration of the phase adjustment unit 220

[0080] Figure 4 2 is a cross-sectional view showing an example of the phase adjustment unit 220. The phase adjustment unit 220 includes a heater 2200 disposed on a substrate W. In an embodiment, the heater 2200 is made of, for example, titanium, titanium nitride, etc., and is disposed at a position opposite to the optical waveguide 2201 to be heated, and the buffer layer 33 is located between the heater 2200 and the optical waveguide 2201. In addition, in the phase adjustment unit 220 according to the embodiment, the optical waveguide 2201 to be heated is disposed between the heater 2200 and the thin film LN substrate 32, and the optical waveguide 2201 to be heated is formed of a material exhibiting a large thermo-optical effect, which is greater than the thermo-optical effect of the thin film LN substrate 32. The optical waveguide 2201 to be heated is an example of a first optical waveguide. A material having a thermo-optical effect greater than that of the thin film LN substrate 32 is, for example, silicon, a polymer, etc. An example of the polymer used may be, for example, polyimide or polymethyl methacrylate (PMMA) resin.

[0081] Figure 5 2 is a diagram showing an example of the structure of the optical waveguide 200 in the phase adjustment unit 220. Figure 5 , the buffer layer 33 and the heater 2200 are not shown. In the embodiment, the optical waveguide 2201 to be heated is provided on the thin film LN substrate 32 to be continuous in the extension direction of the ridge portion 320. In addition, in the embodiment, the optical waveguide 2201 to be heated is provided on the thin film LN substrate 32 so that the end surface of the optical waveguide 2201 to be heated in the extension direction of the optical waveguide 2201 to be heated is in contact with the end surface of the ridge portion 320 in the extension direction of the ridge portion 320. The refractive index of the optical waveguide 2201 to be heated is larger than the refractive index of each of the thin film LN substrate 32 and the buffer layer 33. Therefore, the light propagating through the ridge portion 320 enters the optical waveguide 2201 to be heated.

[0082] Furthermore, the thermo-optic effect expressed in the optical waveguide to be heated 2201 is larger than the thermo-optic effect expressed in each of the thin film LN substrate 32 and the ridge portion 320. The thermo-optic effect mentioned here is the ratio of the change in the refractive index with respect to the change in temperature, and in the case where the thermo-optic effect is large, this state indicates that the ratio of the change in the refractive index with respect to the change in temperature is large.

[0083] The heater 2200 generates heat according to the size of the adjustment signal input from the DSP 13. By the heat generated from the heater 2200, the optical waveguide 2201 to be heated is heated via the buffer layer 33, and the refractive index of the optical waveguide 2201 to be heated is changed. Therefore, the phase of the light propagating through the ridge 320 is changed. The phase of the optical signal is individually adjusted by individually changing the phase of the light propagating through the optical waveguide 2201 to be heated in each phase adjustment unit 220. In an embodiment, a material such as titanium having a high heat generation efficiency is used for the heater 2200, and a material such as silicon showing a high thermo-optical effect is used for the optical waveguide 2201 to be heated, so that the phase of the light can be adjusted by using low power.

[0084] Method for forming optical waveguide 200 in phase adjustment unit 220

[0085] In the following, reference will be made to Figures 6 to 9 An example of a method of forming the optical waveguide 200 in the phase adjustment unit 220 will be described. Figures 6 to 9 1 and 2 are diagrams each showing an example of a manufacturing process of the optical waveguide 200 in the phase adjustment unit 220 .

[0086] First, for example, Figure 6 As shown in FIG. 1 , on the substrate W formed with the support substrate 30, the buffer layer 31, and the thin film LN substrate 32, a mask 40 is provided at the position of the ridge 320. Then, the thin film LN substrate 32 is etched at a portion other than the portion where the mask 40 is provided, and then the mask 40 is removed. Thus, for example, Figure 7 As shown, a ridge 320 is formed at a position where the mask 40 is provided.

[0087] Then, on the thin film LN substrate 32, a film 2202 formed of the same material as the optical waveguide 2201 to be heated is formed. Then, for example, Figure 8 As shown in FIG. 1 , the film 2202 is polished until the ridge 320 is exposed. Then, a mask 41 is set at a position on the film 2202 where the optical waveguide 2201 to be heated is formed. Then, the film 2202 is etched, and the film 2202 is etched until the thin film LN substrate 32 as the lower layer of the film 2202 is exposed under the process conditions in which the mask 41 and the thin film LN substrate 32 are not etched. Thus, for example, Fig. 9As shown, the optical waveguide 2201 to be heated is formed between the mask 41 and the thin film LN substrate 32. Then, by removing the mask 41, a Figure 5 An optical waveguide 200 is shown.

[0088] In the optical transmitting device 20 according to the embodiment, a material such as titanium that exhibits a large heat generation efficiency is used for the heater 2200, and a material such as silicon that exhibits a large thermo-optical effect is used for the optical waveguide to be heated 2201. As a result, miniaturization of the optical transmitting device 20 and power saving in phase adjustment can be achieved at the same time.

[0089] Effects of implementation methods

[0090] As can be seen from the above description, the optical transmitting device 20 according to the present embodiment includes a substrate W, an RF modulation unit 210, and a phase adjustment unit 220. The substrate W is formed so that the buffer layer 31, the thin film LN substrate 32, and the buffer layer 33 are formed in this order. The RF modulation unit 210 is disposed on the substrate W, and modulates light according to an RF signal. The phase adjustment unit 220 is disposed on the same substrate W as the substrate W on which the RF modulation unit 210 is disposed, and adjusts the phase of the optical signal that has been modulated by the RF modulation unit 210. The phase adjustment unit 220 includes a heater 2200 and an optical waveguide 2201 to be heated. The optical waveguide 2201 to be heated is disposed between the thin film LN substrate 32 and the buffer layer 33, and allows the optical signal modulated by the RF modulation unit 210 to pass through the optical waveguide 2201 to be heated. In addition, the optical waveguide 2201 to be heated is formed of a material having a thermo-optical effect. The heater 2200 is disposed at a position opposite to the optical waveguide 2201 to be heated, the buffer layer 33 is located between the heater 2200 and the optical waveguide 2201 to be heated, and the heater 2200 heats the optical waveguide 2201 to be heated.

[0091] By applying a voltage to each of the electrodes of the RF modulation unit 210 and the phase adjustment unit 220, the refractive index of each of the optical waveguides located in the area where the electrodes are present can be changed. As a result, the effective optical path length of the optical waveguide is changed, and thus phase modulation can be performed and the phase difference can be adjusted. The thin film LN optical waveguide formed by the LN film has a characteristic indicating a high electro-optical effect, and the electric field application efficiency due to RF modulation is also high. Therefore, the size of the RF modulation unit can be reduced. However, in the phase adjustment unit formed by the LN film, it is difficult to reduce power consumption, and therefore it is difficult to improve the electric field application efficiency. Therefore, in the present embodiment, while utilizing the advantages of the thin film LN optical waveguide, with respect to the phase adjustment unit 220, an optical waveguide 2201 to be heated formed of a material having a thermo-optical effect is used instead of using an LN film. As a result, power saving of the optical transmitting device 20 can be achieved.

[0092] In addition, if a thin film LN optical waveguide is used, the electric field application efficiency can be improved in the RF modulation unit 210, so that the size of the signal electrode 2100 for performing RF modulation can be reduced. However, in the phase adjustment unit 220, in order to obtain effective electric field application efficiency, it is necessary to increase the length of the DC electrode used for phase adjustment. Therefore, in the present embodiment, with respect to the phase adjustment unit 220, a light guide 2201 to be heated formed of a material having a thermo-optical effect is used instead of using a LN thin film. In the case of using a thin film LN optical waveguide, the length of the DC electrode of the phase adjustment unit is, for example, 5 mm to 20 mm, while the length of the heater 2200 according to the embodiment using the light guide 2201 to be heated can be reduced to, for example, 0.5 mm to 5 mm. Therefore, the size of the optical transmitting device 20 can be reduced.

[0093] As described above, in the optical transmitting device 20 according to the embodiment, the phase adjustment performed by the phase adjustment unit 220 is achieved by using the thermo-optical effect instead of using the electro-optical effect, thereby achieving a reduction in power consumption and a reduction in size of the optical transmitting device 20. In addition, the phase adjustment performed by the phase adjustment unit 220 according to the embodiment is achieved by the thermo-optical effect instead of using the electro-optical effect, DC drift can be prevented, and thus long-term reliability can also be achieved.

[0094] Furthermore, in the above-described embodiment, the ridge 320 as a protrusion is formed on the thin film LN substrate 32, and the optical signal propagating through the ridge 320 is modulated in the RF modulation unit 210. In the phase adjustment unit 220, instead of the ridge 320, the optical waveguide to be heated 2201 is provided to be continuous in the extending direction of the ridge 320. The end surface of the optical waveguide to be heated 2201 in the extending direction of the optical waveguide 2201 is in contact with the end surface of the ridge 320 in the extending direction of the ridge 320. Therefore, the loss of the optical signal when propagating from the ridge 320 to the optical waveguide to be heated 2201 and the loss of the optical signal when propagating from the optical waveguide to be heated 2201 to the ridge 320 can be reduced.

[0095] Furthermore, in the above-described embodiment, the thermo-optical effect of the optical waveguide 2201 to be heated is greater than the thermo-optical effect of the ridge portion 320. Therefore, the phase of light can be adjusted by using low electric power.

[0096] Furthermore, in the above embodiment, the refractive index of the optical waveguide to be heated 2201 is greater than that of the thin film LN substrate 32. Therefore, a larger amount of optical signal enters the optical waveguide to be heated 2201, so that the phase of the optical signal can be effectively changed.

[0097] other

[0098] In addition, the disclosed technology is not limited to each of the above-described embodiments, and various modifications are possible as long as they do not depart from the spirit of the disclosed technology.

[0099] For example, in the above-mentioned embodiment, at the portion where each of the ridges 320 contacts the optical waveguide 2201 to be heated, the width of the ridge 320 is substantially the same as the width of the optical waveguide 2201 to be heated, however, the disclosed technology is not limited thereto. Fig.10 As shown, in the phase adjustment unit 220, as the end 321 of each ridge 320 gets closer to the end surface 320a of each ridge 320 that contacts the optical waveguide 2201 to be heated, the width of the end 321 of each ridge 320 in the extension direction of the corresponding ridge 320 can be narrowed from width W1 toward width W2. Fig.10 is a diagram showing another example of the structure of the optical waveguide 200 in the phase adjustment unit 220 . Fig.10 The structure of the optical waveguide 200 in the phase adjustment unit 220 is schematically shown when the optical waveguide 200 is viewed from a position opposing the thin film LN substrate 32. Fig.10 In the illustrated example, the width W2 of the end surface 320 a of each ridge 320 in contact with the optical waveguide 2201 to be heated is narrower than the width W3 of the end surface 2201 a of the optical waveguide 2201 to be heated in contact with the ridge 320 .

[0100] The refractive index of the optical waveguide 2201 to be heated is greater than the refractive index of the ridge 320, so that the mode field of light in the optical waveguide 2201 to be heated is narrower than the mode field of light in the ridge 320. Therefore, at the portion where the ridge 320 contacts the optical waveguide 2201 to be heated, by narrowing the width of the ridge 320, it is possible to prevent the optical signal entering the optical waveguide 2201 to be heated from the ridge 320 from becoming a multimode inside the optical waveguide 2201 to be heated. In addition, at the portion where the optical signal enters the ridge 320 from the optical waveguide 2201 to be heated, the width of the ridge 320 gradually increases, so that the loss of the optical signal when entering the ridge 320 from the optical waveguide 2201 to be heated can be prevented, so that the optical signal can be further effectively propagated.

[0101] Furthermore, in the above-described embodiment, at the portion where the ridge portion 320 contacts the optical waveguide 2201 to be heated, the thickness of the ridge portion 320 is substantially the same as the thickness of the optical waveguide 2201 to be heated, however, the disclosed technology is not limited thereto. Fig.11 As shown, in the phase adjustment unit 220 , the thickness T1 of the optical waveguide 2201 to be heated may be thinner than the thickness T2 of the ridge portion 320 . Fig.11 is a diagram showing another example of the structure of the optical waveguide 200 in the phase adjustment unit 220 . Fig.11The structure of the optical waveguide 200 is schematically shown when the optical waveguide 200 is viewed from a direction parallel to the surface of the thin film LN substrate 32. Therefore, it is possible to prevent the optical signal from becoming a multimode when the optical signal propagates through the optical waveguide 2201 to be heated.

[0102] In addition, in the phase adjustment unit 220, as the end 321 of each ridge 320 is closer to each end surface 320a in contact with the optical waveguide 2201 to be heated, the end 321 of each ridge 320 in the extension direction of the corresponding ridge 320 can be, for example, Fig.12 The thickness is shown gradually decreasing from thickness T2 toward thickness T1. Fig.12 is a diagram showing another example of the structure of the optical waveguide 200 in the phase adjustment unit 220 . Fig.12 The structure of the optical waveguide 200 is schematically shown when the optical waveguide 200 is viewed from a direction parallel to the surface of the thin film LN substrate 32. Therefore, the optical signal inside the ridge portion 320 can more efficiently enter the optical waveguide 2201 to be heated.

[0103] In addition, Fig.12 In the example shown, as the end 321 of each ridge 320 is closer to each end surface 320a in contact with the optical waveguide 2201 to be heated, the thickness of the end 321 of each ridge 320 in the extension direction of the corresponding ridge 320 can be thinner than the thickness T1. Therefore, it is possible to prevent the optical signal entering the optical waveguide 2201 to be heated from the ridge 320 from becoming a multi-mode in the optical waveguide 2201 to be heated. In addition, Fig.12 In addition to the structure shown, in the width direction of the optical waveguide 200, the end 321 of each ridge 320 in the extending direction of the corresponding ridge 320 may be configured as, for example Fig.10 That is, the width of the end surface 320a of each ridge 320 in contact with the optical waveguide 2201 to be heated may be configured to be narrower than the width of the end surface of the optical waveguide 2201 to be heated in contact with the ridge 320.

[0104] Furthermore, in the above-described embodiment, the optical waveguide to be heated 2201 is provided to be continuous in the extension direction of the ridge portion 320, and the end surface of the optical waveguide to be heated 2201 in the extension direction of the optical waveguide to be heated 2201 is in contact with the end surface of the ridge portion 320 in the extension direction of the ridge portion 320. However, the disclosed technology is not limited thereto. As another example, for example, Fig.13 As shown, the optical waveguide 2201 to be heated may be disposed between the ridge 320 and the heater 2200 . Fig.133 is a cross-sectional view showing another example of the phase adjustment unit 220. Even with this configuration, the optical signal having propagated through the ridge portion 320 enters the optical waveguide to be heated 2201 having a refractive index greater than that of the ridge portion 320 at the boundary between the ridge portion 320 and the optical waveguide to be heated 2201. Therefore, due to the heat from the heater 2200, the phase of the optical signal propagating through the optical waveguide to be heated 2201 can be changed.

[0105] have Fig.13 The optical waveguide 200 of the configuration shown can be configured according to, for example Figures 14 to 17 The process shown is formed. Figures 14 to 17 Each of the diagrams shows a manufacturing process of the optical waveguide 200 in the phase adjustment unit 220 .

[0106] First, for example, Fig.14 As shown in FIG. 2 , on the substrate W formed with the support substrate 30, the buffer layer 31, and the thin film LN substrate 32, a film 2202 formed of the same material as the optical waveguide 2201 to be heated is formed. Then, a mask 42 is set at the position of the optical waveguide 2201 to be heated. Then, the film 2202 is etched at a portion other than the portion where the mask 42 is set. Thus, for example, Fig.15 As shown, an optical waveguide 2201 to be heated is formed at the position of the mask 42. Then, the mask 42 is removed.

[0107] In the following, for example, Fig.16 As shown in FIG. 1 , a mask 43 is provided at the position of the ridge 320. Then, the thin film LN substrate 32 is etched, and then the thin film LN substrate 32 is etched under the processing conditions where the mask 43 and the optical waveguide 2201 to be heated are not etched. Then, the mask 43 is removed. Thus, for example, Fig.17 As shown, an optical waveguide 200 is formed with an optical waveguide 2201 to be heated disposed on a ridge 320. Fig.17 In the manufacturing process of the optical waveguide 200 shown as an example in FIG. 1 , since the substrate W does not need to be polished, it is different from the method according to, for example, Figure 5 Compared with the optical waveguide 200 of the illustrated embodiment, the number of manufacturing steps can be reduced.

[0108] In addition, Fig.13 and Fig.17 In the optical waveguide 200 shown as an example, as for example Fig.18As shown, the width of the end portion 2203 of the optical waveguide to be heated 2201 in the extending direction of the optical waveguide to be heated 2201 may be narrower as the end portion 2203 is closer to the distal end of the optical waveguide to be heated 2201. Therefore, it is possible to alleviate a sharp change in the refractive index when the optical signal enters the optical waveguide to be heated 2201 from the ridge portion 320 and when the optical signal enters the ridge portion 320 from the optical waveguide to be heated 2201. Therefore, it is possible to reduce the coupling loss of light generated at the boundary between the optical waveguide to be heated 2201 and the ridge portion 320.

[0109] In addition, Fig.18 In the optical waveguide 200 shown as an example, as for example Fig.19 As shown, the width of the ridge 320 at the portion where the optical waveguide 2201 to be heated is provided may be wider than the width of the ridge 320 at the portion where the optical waveguide 2201 to be heated is not provided. Therefore, the optical signal propagating through the ridge 320 can effectively enter the optical waveguide 2201 to be heated. In addition, the width of the ridge 320 at the portion where the optical waveguide 2201 to be heated is provided may be narrowed toward a position associated with a distal end of the optical waveguide 2201 to be heated in the extending direction of the optical waveguide 2201 to be heated. Therefore, the optical signal propagating through the ridge 320 can be prevented from becoming a multimode due to a sharp change in the width of the ridge 320.

[0110] All examples and conditional language herein are intended to help readers understand the teaching purpose of the present invention and the concepts contributed by the inventor to promote the art, and should not be interpreted as limitations on these specific examples and conditions, and the organization of these examples in the specification does not involve the display of advantages and disadvantages of the present invention. Although the embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and modifications may be made thereto without departing from the spirit and scope of the present invention.

Claims

1. An optical device, comprising: A substrate, in which a first buffer layer, a thin film having an electro-optical effect and including a second optical waveguide, and a second buffer layer are sequentially formed; an RF modulation unit which is disposed on the substrate and modulates an optical signal propagating through the second optical waveguide according to an RF signal, the second optical waveguide having an electro-optic effect; and a phase adjustment unit, which is disposed on the substrate and adjusts the phase of the optical signal modulated by the RF modulation unit, wherein: The phase adjustment unit comprises: a first optical waveguide disposed between the second buffer layer and the thin film, formed of a material having a thermo-optical effect, and allowing light that has been modulated by the RF modulation unit or is to be modulated by the RF modulation unit to pass through the first optical waveguide; and A heater is provided at a position opposite to the first optical waveguide, the second buffer layer is located between the heater and the first optical waveguide, and the heater heats the first optical waveguide.

2. The optical device according to claim 1, wherein: The second optical waveguide is formed as a protrusion, The first optical waveguide is arranged to be continuous in the extending direction of the second optical waveguide, and An end face of the first optical waveguide in the direction in which the first optical waveguide extends contacts an end face of the second optical waveguide in the direction in which the second optical waveguide extends.

3. The optical device according to claim 2, wherein: The thermo-optic effect of the first optical waveguide is greater than the thermo-optic effect of the second optical waveguide.

4. The optical device according to claim 1, wherein: The refractive index of the first optical waveguide is greater than the refractive index of the film.

5. The optical device according to claim 2, wherein: The width of the end portion of the second optical waveguide in the extending direction of the second optical waveguide becomes narrower as the end portion of the second optical waveguide is closer to the end face of the second optical waveguide in contact with the first optical waveguide, and The width of the end face of the second optical waveguide in contact with the first optical waveguide is narrower than the width of the end face of the first optical waveguide in contact with the second optical waveguide.

6. The optical device according to claim 2 or 5, wherein: The thickness of the first optical waveguide is thinner than the thickness of the second optical waveguide.

7. The optical device according to claim 1, wherein: The second optical waveguide is formed as a protrusion, and The first optical waveguide is disposed between the second optical waveguide and the heater.

8. The optical device according to claim 7, wherein: The width of an end portion of the first optical waveguide in the extending direction of the first optical waveguide becomes narrower as the end portion of the first optical waveguide is closer to a front end of the first optical waveguide.

9. The optical device according to claim 7 or 8, wherein: The width of the second optical waveguide at a portion where the first optical waveguide is provided is wider than the width of the second optical waveguide at a portion where the first optical waveguide is not provided.

10. The optical device according to claim 9, wherein: The width of the second optical waveguide at a portion where the first optical waveguide is provided gradually narrows toward a position associated with a leading end of the first optical waveguide in an extending direction of the first optical waveguide.

11. An optical transceiver, comprising: The optical device according to any one of claims 1 to 10, used as an optical transmitting device that transmits an optical signal modulated according to an RF signal; as well as A light receiving device receives the light signal and outputs an electrical signal according to the received light signal.

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