Optical Modulator

Abstract

The optical modulator (500) of the present disclosure includes a substrate (1), an optical input section (2) provided at an end of the substrate (1), a plurality of phase modulators (20) connected to the optical input section (2) via an optical waveguide (10), a plurality of phase adjusters (30, 40) connected to the plurality of phase modulators (20) via the optical waveguide (10), and a phase adjuster (30, 40) provided at the end of the substrate (1) for emitting light output from the plurality of phase adjusters (30, 40) to the outside. the signal wiring path (60) having an intersection (70) that electrically connects the signal electrode pads (50) and the phase adjuster (30, 40) and intersects with the optical waveguide (10), and the conductive layer (110) and the conductive layer (200) for the signal wiring path intersect with each other at the intersection (70) via the embedded layer (210).

Description

[Technical field]

[0001] The present disclosure relates to optical modulators. [Background technology]

[0002] In recent years, communication traffic has been increasing rapidly due to the widespread use of mobile communication terminals such as smartphones and the diversification of data services resulting from the expansion of cloud services. This has led to a demand for faster and larger capacity optical communication systems.

[0003] In order to meet the demand for higher speed and capacity in optical communication systems, multi-level technology using digital coherent communication technology, in which optical signals modulated in both intensity and phase are transmitted through optical fibers by polarization multiplexing, is being developed. In multi-level optical modulators, Mach-Zehnder type optical modulators are used that can control the amplitude and phase of light and generate optical modulated signals with zero chirp. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2022 / 138845 Summary of the Invention [Problem to be solved by the invention]

[0005] In a Mach-Zehnder type optical modulator, many components are connected to each other via optical waveguides and signal wiring paths on a single substrate, and therefore, intersections between the optical waveguides and the signal wiring paths inevitably occur.

[0006] At such an intersection, an electric field caused by a signal current flowing through the signal wiring path is applied from the signal wiring path intersecting the upper side of the optical waveguide to the optical waveguide below. The phase of the light propagating through the optical waveguide at the intersection changes, albeit slightly, due to the influence of the electric field. In other words, the electric field generated in the signal wiring path unintentionally modulates the phase of the light propagating through the optical waveguide. In addition, the phase of the light propagating through the optical waveguide is unintentionally modulated by the stress generated by the signal wiring path being applied to the optical waveguide.

[0007] At the intersection, the electric field and stress caused by the signal wiring path cause phase modulation of the signal light in the intersecting optical waveguides. Unintended phase modulation of the signal light propagating through the optical waveguide at the intersection becomes noise and may disturb the optical modulation operation. Unintended phase modulation that occurs at such an intersection is called disturbance modulation.

[0008] In the optical waveguide element described in Patent Document 1, the electric field applied to the optical waveguide is reduced by increasing the thickness of the intermediate layer at the intersection between the optical waveguide and the signal electrode (signal wiring path). As a result, the occurrence of disturbance modulation at the intersection between the protruding optical waveguide and the signal electrode (signal wiring path) that propagates an electrical signal is effectively suppressed.

[0009] However, in the configuration of the intersection between the convex optical waveguide and the signal electrode in the optical waveguide element described in Patent Document 1, although the electric field applied to the convex optical waveguide is reduced, the stress is rather increased. As a result, the refractive index of the convex optical waveguide layer through which the signal light is guided still deviates from its original value, which may adversely affect the optical characteristics of the optical waveguide element, specifically the optical modulation characteristics.

[0010] The present disclosure has been made to solve the problems described above, and aims to provide an optical modulator with excellent optical modulation characteristics in which the electric field and stress applied to the optical waveguide layer at the intersection between the optical waveguide and the signal wiring path are alleviated. [Means for solving the problem]

[0011] The optical modulator according to the present disclosure comprises: A substrate; a light input section provided at an end of the substrate, into which light is incident from the outside; a plurality of phase modulators provided on the substrate, connected to the optical input unit via optical waveguides, and configured to modulate the phase of incident light; a plurality of phase adjusters provided on the substrate, connected to the plurality of phase modulators via the optical waveguides, and configured to adjust phases of light emitted from the phase modulators; an optical output unit provided at an end of the substrate, the optical output unit emitting the light output from the plurality of phase adjusters to the outside via the optical waveguide; A plurality of signal electrode pads arranged along an edge of the substrate; a signal wiring path electrically connecting the signal electrode pads and the phase adjuster and having an intersection portion intersecting the optical waveguide; the optical waveguide includes a conductive layer, an insulating layer, a first clad layer, an optical waveguide layer, and a second clad layer formed on the substrate; At the intersection, the conductive layer and the signal wiring conductive layer intersect with each other via a buried layer. Effect of the Invention

[0012] According to the optical modulator of the present disclosure, the intersection of the signal wiring path is made of a semiconductor material and is provided below the optical waveguide, so that the electric field and stress applied to the optical waveguide layer at the intersection of the optical waveguide and the signal wiring path are alleviated, thereby making it possible to obtain an optical modulator with excellent optical modulation characteristics. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a top view of an optical modulator according to first to fourth embodiments. [Diagram 2] 3 is a schematic view of an intersection where an optical waveguide and a signal wiring path intersect in the optical modulator according to the first embodiment. FIG. [Diagram 3] 2 is a cross-sectional view of an optical waveguide constituting a part of an optical modulator according to the first embodiment, in a direction perpendicular to the propagation direction of light. FIG. [Figure 4] 2 is a cross-sectional view of an optical waveguide constituting a part of an optical modulator according to the first embodiment, in a direction perpendicular to the propagation direction of light at an intersection. FIG. [Diagram 5] 2 is a cross-sectional view of an optical waveguide that constitutes a part of an optical modulator according to the first embodiment, taken along the light propagation direction at an intersection. FIG. [Figure 6] 1 is a schematic view of an intersection where an optical waveguide and a signal wiring path intersect in an optical modulator as a comparative example. [Figure 7] 1 is a cross-sectional view of an optical waveguide constituting a part of an optical modulator according to a comparative example, taken along a direction perpendicular to the propagation direction of light. [Figure 8] 11 is a cross-sectional view of an optical waveguide in a direction perpendicular to the propagation direction of light at an intersection in an optical modulator that is a comparative example. FIG. [Figure 9] 11 is a schematic view of an intersection where an optical waveguide and a signal wiring path intersect in an optical modulator according to a second embodiment. FIG. [Figure 10] 11 is a cross-sectional view of an optical waveguide constituting a part of an optical modulator according to a second embodiment, in a direction perpendicular to the propagation direction of light at an intersection. FIG. [Figure 11] 11 is a cross-sectional view of an optical waveguide that constitutes a part of an optical modulator according to a second embodiment, taken along the direction of light propagation at an intersection of the optical waveguide. FIG. [Figure 12] 13 is a schematic view of an intersection where an optical waveguide and a signal wiring path intersect in an optical modulator according to a third embodiment. FIG. [Figure 13] 11 is a cross-sectional view of an optical waveguide constituting a part of an optical modulator according to a third embodiment, in a direction perpendicular to the propagation direction of light at an intersection. FIG. [Figure 14] 11 is a cross-sectional view of an optical waveguide that constitutes a part of an optical modulator according to a third embodiment, taken along the direction of light propagation at an intersection. FIG. [Figure 15] 13 is a schematic view of an intersection where an optical waveguide and a signal wiring path intersect in an optical modulator according to a fourth embodiment. FIG. [Figure 16]13 is a cross-sectional view of an optical waveguide constituting a part of an optical modulator according to a fourth embodiment, in a direction perpendicular to the propagation direction of light at an intersection. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Embodiment 1 <Configuration of the Optical Modulator According to the First Embodiment> FIG. 1 is a top view of an optical modulator 500 according to the first embodiment. The optical modulator 500 according to the first embodiment includes an Fe-doped semi-insulating InP substrate 1, an optical input section 2 that is provided at an end of the Fe-doped semi-insulating InP substrate 1 and into which light is incident from the outside, eight phase modulators 20 that are connected to the optical input section 2 via optical waveguides 10 and phase-modulate the incident light, eight first phase adjusters 30 that are connected to the eight phase modulators 20 via the optical waveguides 10 and adjust the phase of light output from the phase modulators 20, and eight second phase adjusters 30 that are connected to the eight first phase adjusters 30 via the optical waveguides 10. the first phase adjuster 30 and the second phase adjuster 40; two optical output units 3 provided at the ends of the Fe-doped semi-insulating InP substrate 1 and emitting the light output from the four second phase adjusters 40 to the outside via the optical waveguide 10; a plurality of signal electrode pads 50 arranged along the ends of the Fe-doped semi-insulating InP substrate 1; and a signal wiring path 60 electrically connecting the plurality of signal electrode pads 50 to the first phase adjusters 30 and the second phase adjusters 40 and having an intersection 70 that intersects with the optical waveguide 10.

[0015] The phase modulator 20 is a pair of two phase modulators each constituting a Mach-Zehnder type phase modulator. In an example of the optical modulator 500 shown in Fig. 1, the phase modulator 20 is composed of a first Mach-Zehnder type phase modulator corresponding to the XI channel, a second Mach-Zehnder type phase modulator corresponding to the XQ channel, a third Mach-Zehnder type phase modulator corresponding to the YI channel, and a fourth Mach-Zehnder type phase modulator corresponding to the YQ channel.

[0016] FIG. 2 is a schematic view of an intersection 70 where the optical waveguide 10 and the signal wiring path 60 intersect in the optical modulator 500 according to the first embodiment. FIG. 3 is a cross-sectional view of the optical waveguide 10 in a direction perpendicular to the light propagation direction in the optical waveguide 10 constituting a part of the optical modulator 500 according to the first embodiment. FIG. 4 is a cross-sectional view of the optical waveguide 10 in a direction perpendicular to the light propagation direction in the intersection 70 in the optical waveguide 10 constituting a part of the optical modulator 500 according to the first embodiment. FIG. 5 is a cross-sectional view of the optical waveguide 10 along the light propagation direction in the intersection 70 in the optical waveguide 10 constituting a part of the optical modulator 500 according to the first embodiment. For convenience of explanation, the surface protection film 61 is omitted in FIG. 2.

[0017] The optical waveguide 10 includes an n-type InP conductive layer 110 formed on an Fe-doped semi-insulating InP substrate 1, an Fe-doped semi-insulating InP insulating layer 120, an n-type InP first cladding layer 130, an i-type InGaAsP-MQW (Multi Quantum Well) optical waveguide layer 140, and a p-type InP second cladding layer 150. The exposed surface of the Fe-doped semi-insulating InP substrate 1 and the surface and both side surfaces of the optical waveguide 10 are covered with a surface protective film 61. An example of the surface protective film 61 is a SiO2 film. However, the surface protective film 61 may be other than a SiO2 film, for example, a SiN film.

[0018] The n-type InP conductive layer 110 is an example of a conductive layer, and the Fe-doped semi-insulating InP insulating layer 120 is an example of an insulating layer, and may be a conductive layer or insulating layer made of other semiconductor materials. The n-type InP layer constituting the n-type InP conductive layer 110 is an example of an n-type semiconductor layer, and may be composed of other n-type semiconductor layers.

[0019] The cross-sectional shape of the optical waveguide 10 in a direction perpendicular to the light propagation direction is a mesa shape, as shown in Fig. 3. Although an Fe-doped semi-insulating InP substrate is given as an example of the semiconductor substrate, the semiconductor substrate may be other than the Fe-doped semi-insulating InP substrate. Furthermore, the semiconductor substrate may be a substrate made of a material other than a semiconductor material.

[0020] <Configuration of Intersection of Optical Modulator According to First Embodiment> As shown in Figures 2 and 5, at the intersection 70, the n-type InP conductive layer 110 of the optical waveguide 10 and the n-type InP signal wiring conductive layer 200 provided specifically for the intersection 70 intersect with each other via an Fe-doped semi-insulating InP insulating buried layer 210 provided to electrically insulate the n-type InP conductive layer 110 and the n-type InP signal wiring conductive layer 200.

[0021] The n-type InP signal wiring conductive layer 200 has a portion overlapping with the optical waveguide 10 and a portion extending to both side surfaces of the optical waveguide 10. Ends of the n-type InP signal wiring conductive layer 200, i.e., ends of the portions extending to both side surfaces of the optical waveguide 10, are electrically connected to ends of the signal wiring path 60. An example of the metal film constituting the signal wiring path 60 is a metal film consisting of two layers of titanium (Ti) and gold (Au).

[0022] An example of a structure for electrically connecting the signal wiring path conductive layer and the signal wiring path 60 is a structure in which a metal film constituting the signal wiring path 60 is formed on the surface of the n-type InP signal wiring path conductive layer 200 up to a preset distance from the side and tip facing the signal wiring path 60 at the end of the n-type InP signal wiring path conductive layer 200. The signal wiring path 60 made of a metal film extending on the surface of the n-type InP signal wiring path conductive layer 200 is formed so as not to come into contact with the Fe-doped semi-insulating InP insulating layer 120 on the optical waveguide 10 side.

[0023] 2 and 5, Fe-doped semi-insulating InP insulating buried layer 210 is provided on both side surfaces of n-type InP signal wiring conductive layer 200. That is, at intersection 70, n-type InP conductive layer 110, which is a conductive layer, and n-type InP signal wiring conductive layer 200 intersect via Fe-doped semi-insulating InP insulating buried layer 210, which is a buried layer. Note that Fe-doped semi-insulating InP insulating buried layer 210 is an example of an insulating semiconductor layer, and may be a buried layer made of other semiconductor materials.

[0024] Moreover, since the Fe-doped semi-insulating InP insulating layer 120 is provided above the n-type InP signal wiring conductive layer 200 intersecting with the optical waveguide 10, the n-type InP signal wiring conductive layer 200 is electrically insulated from the n-type InP conductive layer 110 and the n-type InP first cladding layer 130. Therefore, the signal current flowing from the signal wiring 60 to the n-type InP signal wiring conductive layer 200 does not flow to the side of the n-type InP conductive layer 110 and the n-type InP first cladding layer 130 constituting the optical waveguide 10.

[0025] <Operation of the Optical Modulator According to the First Embodiment> The operation of the optical modulator 500 according to the first embodiment will be described below. Light incident on the optical input section 2 from outside the optical modulator 500 is guided and branched by the optical waveguide 10, and enters each of the eight phase modulators 20, i.e., four sets of Mach-Zehnder type phase modulators, where the phase of the light is modulated by the phase modulators 20.

[0026] The phase-modulated light is incident on eight first phase adjusters 30 via optical waveguide 10. In the first phase adjuster, a signal current input to signal electrode pad 50 flows through signal wiring path 60 and further flows to first phase adjuster 30 electrically connected to signal wiring path 60, thereby adjusting the phase of the incident light.

[0027] The light whose phase has been adjusted by the first phase adjuster 30 is incident on each of the four second phase adjusters 40 via the optical waveguide 10. In the second phase adjuster 40, a signal current input to a signal electrode pad 50 flows through a signal wiring path 60, and further flows to the second phase adjuster 40 electrically connected to the signal wiring path 60, thereby adjusting the phase of the incident light again.

[0028] The light whose phase has been adjusted again by the second phase adjuster 40 is outputted from the two optical output sections 3 via the optical waveguide 10 to the outside of the optical modulator 500 . The above is an overview of the operation of the optical modulator 500 according to the first embodiment.

[0029] <Functions and Effects of the Optical Modulator According to the First Embodiment> Before describing the operation and effects of the optical modulator 500 according to the first embodiment, the intersection 70a where the optical waveguide 10a and the signal wiring path 60a intersect in the optical modulator 550 of the comparative example will be described below.

[0030] Fig. 6 is a schematic view of an intersection 70a where an optical waveguide 10a and a signal wiring path 60a intersect in an optical modulator 550 as a comparative example. Fig. 7 is a cross-sectional view of the optical waveguide 10a in a direction perpendicular to the light propagation direction in the optical waveguide 10a constituting a part of the optical modulator 550 as a comparative example. Fig. 8 is a cross-sectional view of the optical waveguide 10a in a direction perpendicular to the light propagation direction at the intersection 70a in the optical modulator 550 as a comparative example.

[0031] The optical waveguide 10a of the optical modulator 550, which is a comparative example, includes an n-type InP first cladding layer 130a, an i-type InGaAsP-MQW optical waveguide layer 140a, and a p-type InP second cladding layer 150a formed on an Fe-doped semi-insulating InP substrate 1a, as shown in Fig. 7. The exposed surface of the Fe-doped semi-insulating InP substrate 1a and the surface and both side surfaces of the optical waveguide 10a are covered with a surface protection film 61a. The cross-sectional shape of the optical waveguide 10a in a direction perpendicular to the light propagation direction is mesa-shaped, as shown in Fig. 7.

[0032] 6 and 8, in the optical waveguide 10a of the optical modulator 550 as a comparative example, the signal wiring path 60a is formed on the upper side and both side surfaces of the optical waveguide 10a at the intersection 70a where the optical waveguide 10a and the signal wiring path 60a intersect. That is, the signal wiring path 60a is formed so as to straddle the optical waveguide 10a.

[0033] As described above, at such an intersection 70a, both the electric field and stress generated from the signal wiring line 60a are applied to the i-type InGaAsP-MQW optical waveguide layer 140a of the lower optical waveguide 10a from the signal wiring line 60a intersecting the upper side of the optical waveguide 10a. The reason why an electric field is applied to the i-type InGaAsP-MQW optical waveguide layer 140a is that a potential difference occurs between the signal wiring line 60a and the n-type InP first cladding layer 130a, but since the i-type InGaAsP-MQW optical waveguide layer 140a is located between the signal wiring line 60a and the n-type InP first cladding layer 130a, an electric field generated by the potential difference between them is applied to the i-type InGaAsP-MQW optical waveguide layer 140a.

[0034] The phase of the light propagating through the optical waveguide 10a at the intersection 70a is affected by the electric field and stress and changes slightly but unintentionally. That is, the electric field and stress applied to the i-type InGaAsP-MQW optical waveguide layer 140a unintentionally modulate the phase of the light propagating through the optical waveguide 10a.

[0035] At the intersection 70a, the electric field and stress caused by the signal wiring line 60a cause phase modulation of the signal light in the intersecting optical waveguide 10a. Unintended phase modulation at the intersection 70a of the signal light propagating through the optical waveguide 10a becomes noise, which may disturb the optical modulation operation.

[0036] On the other hand, in the optical modulator 500 according to the first embodiment, as shown in FIGS. 2, 4, and 5, at the intersection 70, the n-type InP conductive layer 110 of the optical waveguide 10 and the n-type InP signal wiring conductive layer 200 provided specifically for the intersection 70 intersect with each other via an Fe-doped semi-insulating InP insulating buried layer 210 provided to electrically insulate the n-type InP conductive layer 110 and the n-type InP signal wiring conductive layer 200.

[0037] In the direction perpendicular to the surface of the Fe-doped semi-insulating InP substrate 1, an Fe-doped semi-insulating InP insulating layer 120 is provided between the n-type InP signal wiring conductive layer 200 and the n-type InP first cladding layer 130. The Fe-doped semi-insulating InP insulating layer 120 functions to electrically insulate the n-type InP signal wiring conductive layer 200 from the n-type InP first cladding layer 130. This is to prevent the signal current flowing through the n-type InP signal wiring conductive layer 200 from flowing to the optical waveguide side.

[0038] 5, Fe-doped semi-insulating InP insulating buried layers 210 are provided on both sides of the n-type InP signal wiring conductive layer 200 along the light propagation direction at the intersection 70. Therefore, the n-type InP signal wiring conductive layer 200 is electrically insulated from the n-type InP conductive layer 110.

[0039] At the intersection 70, a potential difference is generated between the n-type InP signal wiring conductive layer 200, which also serves as the signal wiring path, and the n-type InP first cladding layer 130. However, since the i-type InGaAsP-MQW optical waveguide layer 140 is not located between the n-type InP signal wiring conductive layer 200 and the n-type InP first cladding layer 130, the electric field generated by the potential difference between the two is not directly applied to the i-type InGaAsP-MQW optical waveguide layer 140.

[0040] Furthermore, since the electric field is reduced by the Fe-doped semi-insulating InP insulating layer 120 provided between the n-type InP signal wiring conductive layer 200 and the n-type InP first cladding layer 130, the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140 is also weakened indirectly, so that the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140 is significantly reduced. In other words, the Fe-doped semi-insulating InP insulating layer 120 functions to reduce the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140, which is generated as a signal current flows in the n-type InP signal wiring conductive layer 200.

[0041] Furthermore, the thermal expansion coefficient of the semiconductor material constituting the n-type InP signal wiring conductive layer 200 is extremely close to that of the semiconductor material constituting the i-type InGaAsP-MQW optical waveguide layer 140 constituting the optical waveguide 10. This is because the semiconductor materials constituting the n-type InP signal wiring conductive layer 200 and the i-type InGaAsP-MQW optical waveguide layer 140 are the same InP-based compound semiconductor material. Therefore, the stress generated by providing the n-type InP signal wiring conductive layer 200 is extremely small.

[0042] In other words, the signal wiring path 60 is arranged to penetrate the optical waveguide 10 by passing through the n-type InP signal wiring conductive layer 200 provided on the lower side of the optical waveguide 10. Therefore, the electric field and stress applied from the signal wiring path 60 to the i-type InGaAsP-MQW optical waveguide layer 140 can be significantly reduced as compared with the comparative example in which the signal wiring path 60a crosses the upper side of the optical waveguide 10a.

[0043] The intersection 70 where the optical waveguide 10 and the signal wiring path 60 intersect, which is a part of the optical modulator 500 according to the first embodiment, is formed by a known manufacturing method.

[0044] <Advantages of the First Embodiment> As described above, in the optical modulator of embodiment 1, the signal wiring path that intersects the optical waveguide is connected via a conductive layer for the signal wiring path made of a semiconductor material, and is provided below the optical waveguide. This reduces the electric field and stress applied to the optical waveguide layer at the intersection of the optical waveguide and the signal wiring path, thereby providing an optical modulator with excellent optical modulation characteristics.

[0045] Embodiment 2 Fig. 9 is a schematic view of an intersection 70b where an optical waveguide 10b and a signal wiring line 60b intersect in an optical modulator 600 according to the second embodiment. Fig. 10 is a cross-sectional view of the optical waveguide 10b in a direction perpendicular to the light propagation direction at the intersection 70b in the optical waveguide 10b constituting a part of the optical modulator 600 according to the second embodiment. Fig. 11 is a cross-sectional view of the optical waveguide 10b along the light propagation direction at the intersection 70b in the optical waveguide 10b constituting a part of the optical modulator 600 according to the second embodiment. For convenience of explanation, the surface protection film 61b is omitted in Fig. 9.

[0046] <Configuration of Intersection of Optical Modulator According to Second Embodiment> The optical modulator 600 according to the second embodiment differs from the optical modulator 500 according to the first embodiment in that, instead of the Fe-doped semi-insulating InP insulating burying layer 210 provided on both sides of the n-type InP signal wiring conductive layer 200 of the optical modulator 500 according to the first embodiment, the optical modulator 600 according to the second embodiment has p-type InP burying layers 210b provided on both sides of the n-type InP signal wiring conductive layer 200b. The p-type InP burying layer 210b is an example of a burying layer and may be a burying layer made of other semiconductor materials. The p-type InP layer constituting the p-type InP burying layer 210b is an example of a p-type semiconductor layer and may be a burying layer made of other p-type semiconductor materials.

[0047] As shown in FIG. 11, at the intersection 70b of the optical modulator 600 according to the second embodiment, p-type InP buried layers 210b are provided on both sides of the n-type InP signal wiring conductive layer 200b along the light propagation direction. That is, at the intersection 70b, the n-type InP conductive layer 110b, the p-type InP buried layer 210b, the n-type InP signal wiring conductive layer 200b, the p-type InP buried layer 210b, and the n-type InP conductive layer 110b are arranged in this order along the light propagation direction. In terms of the conductivity type, the n-type InP conductive layer 110b, the p-type InP buried layer 210b, and the n-type InP signal wiring conductive layer 200b have an npn structure. Therefore, no current flows between the n-type InP conductive layer 110b and the n-type InP signal wiring conductive layer 200b because of a reverse bias.

[0048] At the intersection 70b, a potential difference is generated between the n-type InP signal wiring conductive layer 200b, which also serves as the signal wiring path, and the n-type InP first cladding layer 130b. However, since the i-type InGaAsP-MQW optical waveguide layer 140b is not located between the n-type InP signal wiring conductive layer 200b and the n-type InP first cladding layer 130b, the electric field generated by the potential difference between the two is not directly applied to the i-type InGaAsP-MQW optical waveguide layer 140b.

[0049] Furthermore, the electric field is reduced by the Fe-doped semi-insulating InP insulating layer 120b provided between the n-type InP signal wiring conductive layer 200b and the n-type InP first cladding layer 130b, which has the effect of indirectly weakening the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140b. As a result, the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140b is significantly reduced.

[0050] <Advantages of the second embodiment> As described above, in the optical modulator according to the second embodiment, the signal wiring path that intersects the optical waveguide is connected via a conductive layer for the signal wiring path made of a semiconductor material, and is provided below the optical waveguide. This reduces the electric field and stress applied to the optical waveguide layer at the intersection between the optical waveguide and the signal wiring path, thereby providing an optical modulator with excellent optical modulation characteristics.

[0051] Embodiment 3 Fig. 12 is a schematic view of an intersection 70c where an optical waveguide 10c and a signal wiring path 60c intersect in an optical modulator 700 according to the third embodiment. Fig. 13 is a cross-sectional view of the optical waveguide 10c in a direction perpendicular to the light propagation direction at the intersection 70c in the optical waveguide 10c constituting a part of the optical modulator 700 according to the third embodiment. Fig. 14 is a cross-sectional view of the optical waveguide 10c along the light propagation direction at the intersection 70c in the optical waveguide 10c constituting a part of the optical modulator 700 according to the third embodiment. For convenience of explanation, the surface protection film 61c is omitted in Fig. 12.

[0052] <Configuration of Intersection of Optical Modulator According to Third Embodiment> The differences in configuration between the optical modulator 700 according to the third embodiment and the optical modulator 500 according to the first embodiment will be described below.

[0053] In the optical modulator 500 according to the first embodiment, a conductive layer 200 for an n-type InP signal wiring path is provided at the portion intersecting with the optical waveguide 10, and the conductive layer 200 for the n-type InP signal wiring path and the signal wiring path 60 consisting of a metal film are structured so that the metal film constituting the signal wiring path 60 is formed on the surface of the conductive layer 200 for the n-type InP signal wiring path up to a preset distance from the tip of the conductive layer 200 for the n-type InP signal wiring path.

[0054] On the other hand, in the optical modulator 700 according to the third embodiment, as shown in Figs. 12 and 14, the signal wiring path 60c itself is composed of a high-concentration n-type InP wiring layer made of n-type InP having a high concentration of n-type dopant. That is, a part of the signal wiring path 60c also functions as a signal wiring path conductive layer as in the first and second embodiments. The signal wiring path 60c is provided below the optical waveguide 10d, similar to the n-type InP signal wiring path conductive layer 200 in the first embodiment. That is, the signal wiring path 60c fulfills the same function as the n-type InP signal wiring path conductive layer 200 in the first embodiment.

[0055] The doping concentration of the n-type dopant in the high-concentration n-type InP wiring layer constituting the signal wiring path 60c is, for example, 1×10 19 cm -3 The above is desirable because it is necessary to reduce the wiring resistance as much as possible as a signal wiring path.

[0056] Both side surfaces of the signal wiring path 60c at the intersection 70c are provided with a buried layer made of an insulating semiconductor layer such as an Fe-doped semi-insulating InP insulating buried layer 210c, as in the first embodiment. Note that, as in the second embodiment, a buried layer made of a p-type semiconductor layer such as a p-type InP buried layer may be provided instead of the Fe-doped semi-insulating InP insulating buried layer 210c.

[0057] At the intersection 70c, a potential difference is generated between the signal wiring line 60c and the n-type InP first cladding layer 130c. However, since the i-type InGaAsP-MQW optical waveguide layer 140c is not located between the signal wiring line 60c and the n-type InP first cladding layer 130c, the electric field generated by the potential difference between them is not directly applied to the i-type InGaAsP-MQW optical waveguide layer 140c.

[0058] Furthermore, the electric field is reduced by the Fe-doped semi-insulating InP insulating layer 120c provided between the signal wiring line 60c and the n-type InP first cladding layer 130c, which has the effect of indirectly weakening the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140c. As a result, the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140c is significantly reduced.

[0059] In the optical modulator 700 according to the third embodiment, a high-concentration n-type InP wiring layer made of an InP-based compound semiconductor is used as the signal wiring line 60c, and therefore the signal wiring line 60c is made of substantially the same semiconductor material as the optical waveguide 10c. Therefore, the process of forming a metal film and patterning it into a desired shape to form the signal wiring line as in the first and second embodiments can be omitted. As a result, an optical modulator with excellent optical modulation characteristics can be obtained with further cost reduction.

[0060] <Advantages of the Third Embodiment> As described above, in the optical modulator according to the third embodiment, the signal wiring path is made of a semiconductor material and is provided below the optical waveguide. This reduces the electric field and stress applied to the optical waveguide layer at the intersection of the optical waveguide and the signal wiring path, thereby achieving the effect of further reducing costs and obtaining an optical modulator with excellent optical modulation characteristics.

[0061] Embodiment 4 Fig. 15 is a schematic view of an intersection 70d where an optical waveguide 10d and a signal wiring path 60d intersect in an optical modulator 800 according to the fourth embodiment. Fig. 16 is a cross-sectional view of the optical waveguide 10d constituting a part of the optical modulator 700 according to the fourth embodiment, in a direction perpendicular to the light propagation direction at the intersection 70d. For ease of explanation, the surface protection film 61d is omitted in Fig. 15.

[0062] <Configuration of Intersection of Optical Modulator According to Fourth Embodiment> 15 and 16, in the optical modulator 800 according to the fourth embodiment, two via holes 220d penetrating from the front side to the back side of the Fe-doped semi-insulating InP substrate 1d are provided on both side surfaces of the optical waveguide 10d at an intersection 70d where the optical waveguide 10d and the signal wiring path 60d intersect. In addition, a back electrode 230d electrically connecting the two via holes 220d is provided on the back side of the Fe-doped semi-insulating InP substrate 1d.

[0063] Two via holes 220d exposed on the front surface side of the Fe-doped semi-insulating InP substrate 1d are electrically connected to signal wiring paths 60d, respectively.

[0064] In the configuration of the optical modulator 800 according to the fourth embodiment, the Fe-doped semi-insulating InP substrate 1d is present between the optical waveguide 10d and the back electrode 230d, which is a part of the signal wiring path intersecting with the optical waveguide 10d, and therefore the generation of the electric field and the generation of the stress due to the signal wiring path are significantly reduced. Therefore, an optical modulator with excellent optical modulation characteristics can be obtained.

[0065] <Advantages of the Fourth Embodiment> As described above, according to the optical modulator of embodiment 4, two via holes are provided on both side sides of the optical waveguide at the intersection, penetrating from the front side to the back side of the Fe-doped semi-insulating InP substrate and electrically connecting to the signal wiring path, and a back electrode that functions as a signal wiring path is provided by connecting the two via holes to the back side of the Fe-doped semi-insulating InP substrate, thereby achieving the effect of obtaining an optical modulator with superior optical modulation characteristics.

[0066] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.

[0067] Therefore, countless modifications not illustrated are assumed within the scope of the technology of the present disclosure, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment. [Explanation of symbols]

[0068] 1, 1a, 1d Fe-doped semi-insulating InP substrate, 2 optical input section, 3 optical output section, 10, 10a, 10b, 10c, 10d optical waveguide, 20 phase modulator, 30 first phase adjuster, 40 second phase adjuster, 50 signal electrode pad, 60, 60a, 60b, 60c, 60d signal wiring path, 61, 61a, 61b, 61c, 61d surface protection film, 70, 70a, 70b, 70c, 70d intersection, 110, 110b n-type InP conductive layer, 120, 120b, 120c Fe-doped semi-insulating InP insulating layer, 130, 130a, 130b, 130c n-type InP first cladding layer, 140, 140a, 140b, 140c i-type InGaAsP-MQW optical waveguide layer, 150, 150a p-type InP second cladding layer, 200, 200b n-type InP signal wiring conductive layer, 210, 210c Fe-doped semi-insulating InP insulating buried layer, 210b p-type InP buried layer, 220d via hole, 230d back electrode, 500, 550, 600, 700, 800 Optical modulator

Claims

1. A substrate; a light input section provided at an end of the substrate, into which light is incident from the outside; a plurality of phase modulators provided on the substrate, connected to the optical input unit via optical waveguides, and configured to modulate the phase of incident light; a plurality of phase adjusters provided on the substrate, connected to the plurality of phase modulators via the optical waveguides, and adjusting the phases of the light emitted from the phase modulators; an optical output unit provided at an end of the substrate, the optical output unit emitting the light output from the plurality of phase adjusters to the outside via the optical waveguide; a plurality of signal electrode pads arranged along an edge of the substrate; a signal wiring path electrically connecting the plurality of signal electrode pads and the phase adjuster, the signal wiring path having an intersection portion intersecting the optical waveguide; the optical waveguide comprises a conductive layer, an insulating layer, a first clad layer, an optical waveguide layer, and a second clad layer formed on the substrate; an optical modulator, wherein the conductive layer and the signal wiring conductive layer intersect at the intersection via a buried layer;

2. 2. The optical modulator according to claim 1, wherein the buried layer is made of an insulating semiconductor layer.

3. 2. The optical modulator according to claim 1, wherein the buried layer is made of a p-type semiconductor layer, and the conductive layer is made of an n-type semiconductor layer.

4. 4. The optical modulator according to claim 1, wherein an end of the signal wiring conductive layer and an end of the signal wiring are electrically connected.

5. 4. An optical modulator according to claim 1, wherein the conductive layer for the signal wiring path is a part of the signal wiring path, and the conductive layer and the signal wiring path are made of a highly-doped n-type semiconductor layer.

6. A substrate; a light input section provided at an end of the substrate, into which light is incident from the outside; a plurality of phase modulators provided on the substrate, connected to the optical input unit via optical waveguides, and configured to modulate the phase of incident light; a plurality of phase adjusters provided on the substrate, connected to the plurality of phase modulators via the optical waveguides, and adjusting the phases of the light emitted from the phase modulators; an optical output unit provided at an end of the substrate, the optical output unit emitting the light output from the plurality of phase adjusters to the outside via the optical waveguide; a plurality of signal electrode pads arranged along an edge of the substrate; a signal wiring path electrically connecting the plurality of signal electrode pads and the phase adjuster, the signal wiring path having an intersection portion intersecting the optical waveguide; the optical waveguide comprises an n-type first cladding layer, an optical waveguide layer, and a p-type second cladding layer formed on the substrate; An optical modulator characterized in that a plurality of via holes penetrating from the front side to the back side of the substrate are provided on both side sides of the optical waveguide at the intersection, and a back electrode electrically connecting the plurality of via holes is provided on the back side of the substrate.

7. 7. The optical modulator according to claim 6, wherein the plurality of via holes exposed on the surface side of the substrate are electrically connected to the signal wiring paths, respectively.

8. 8. The optical modulator according to claim 1, wherein at least the optical waveguide and the signal wiring path are covered with a surface protection film.

9. 8. The optical modulator according to claim 1, wherein each of the plurality of phase adjusters comprises a first phase adjuster and a second phase adjuster connected to the first phase adjuster via the optical waveguide.

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