Optical modulator
By setting a signal line made of semiconductor material at the intersection of the optical waveguide and the signal line and setting an insulating layer below the optical waveguide, the effects of electric field and stress at the intersection of the optical waveguide and the signal line are solved, the optical characteristics of the optical modulator are improved and noise interference is reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2023-12-01
- Publication Date
- 2026-06-26
Smart Images
Figure CN122295618A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to optical modulators. Background Technology
[0002] The proliferation of mobile communication terminals, such as smartphones, and the diversification of data services brought about by the expansion of cloud services have led to a rapid increase in communication traffic in recent years. This has created a demand for higher speeds and larger capacities in optical communication systems.
[0003] To meet the demands for high speed and large capacity in optical communication systems, multi-valued techniques are being developed for digital coherent communication, which uses polarization multiplexing of optical signals modulated in both intensity and phase within optical fibers. Multi-valued optical modulators utilize Mach-Zehnder type optical modulators that can separately control the amplitude and phase of light and generate zero-chill optical modulation signals.
[0004] Patent Document 1: International Publication No. 2022 / 138845
[0005] In Mach-Zehnder type optical modulators, multiple components on a single substrate are interconnected via optical waveguides and signal wiring. Therefore, intersections between optical waveguides and signal wiring are inevitable.
[0006] In this intersection, an electric field generated by the signal current flowing in the signal lines is applied from the signal lines crossing the upper side of the optical waveguide to the lower side. The phase of the light propagating in the optical waveguide at the intersection is slightly changed by the electric field. That is, the electric field generated in the signal lines unintentionally modulates the phase of the light propagating in the optical waveguide. Furthermore, even when stress generated by the signal lines is applied to the optical waveguide, the phase of the light propagating in the optical waveguide is unintentionally modulated.
[0007] At the intersection, phase modulation of the signal light occurs within the crossed optical waveguide due to the electric field and stress caused by the signal wiring. This unwanted phase modulation of the signal light propagating in the optical waveguide at the intersection becomes noise, potentially disrupting the optical modulation process. Such unwanted phase modulation at the intersection is called perturbation 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 of the optical waveguide and the signal electrode (signal wiring). As a result, the generation of disturbance modulation at the intersection of the protruding optical waveguide and the signal electrode (signal wiring) that propagates the electrical signal is effectively suppressed.
[0009] However, in the structure of the intersection between the convex waveguide and the signal electrode in the optical waveguide element described in Patent Document 1, although the electric field applied to the convex waveguide is reduced, the stress is increased instead. As a result, since the refractive index of the convex waveguide layer through which the signal light propagates still deviates from its original value, it may negatively affect the optical characteristics of the optical waveguide element, specifically its optical modulation characteristics. Summary of the Invention
[0010] This disclosure is made in order to eliminate the aforementioned problems, and its purpose is 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 of the optical waveguide and the signal wiring are relieved.
[0011] The optical modulator disclosed herein is characterized by having:
[0012] substrate;
[0013] A light input section is provided at the end of the aforementioned substrate and receives light from the outside;
[0014] Multiple phase modulators are disposed on the substrate and connected to the light input unit via optical waveguides to modulate the phase of the incident light.
[0015] Multiple phase adjusters are disposed on the substrate and connected to the multiple phase modulators via the optical waveguide to adjust the phase of the light emitted from the phase modulators.
[0016] A light output section is provided at the end of the substrate, and light output from the plurality of phase adjusters is emitted to the outside via the optical waveguide.
[0017] Multiple signal electrode pads are arranged along the ends of the aforementioned substrate; and
[0018] The signal wiring electrically connects the aforementioned multiple signal electrode pads to the aforementioned phase adjuster, and has a crossover portion that intersects with the aforementioned optical waveguide.
[0019] The aforementioned optical waveguide is composed of a conductive layer, an insulating layer, a first cladding layer, an optical waveguide layer, and a second cladding layer formed on the aforementioned substrate.
[0020] In the aforementioned intersection, the conductive layer and the conductive layer for signal routing intersect via an embedded layer.
[0021] According to the optical modulator disclosed herein, since the intersection of the signal wiring is made of semiconductor material and is disposed on the lower side of the optical waveguide, the electric field and stress applied to the optical waveguide layer at the intersection of the optical waveguide and the signal wiring are relieved, thus achieving the effect of obtaining an optical modulator with excellent optical modulation characteristics. Attached Figure Description
[0022] Figure 1 This is a top view of the optical modulators involved in embodiments 1 to 4.
[0023] Figure 2 This is a general view of the intersection where the optical waveguide and signal wiring intersect in the optical modulator according to Embodiment 1.
[0024] Figure 3 This is a cross-sectional view of the optical waveguide in the direction perpendicular to the direction of light propagation in the optical waveguide that constitutes part of the optical modulator according to Embodiment 1.
[0025] Figure 4 This is a cross-sectional view of an optical waveguide in a direction perpendicular to the direction of light propagation in the intersection, which is part of the optical modulator according to Embodiment 1.
[0026] Figure 5 This is a cross-sectional view of an optical waveguide along the direction of light propagation in the intersection, which is part of the optical modulator according to Embodiment 1.
[0027] Figure 6 This is a general view of the intersection where the optical waveguide and signal wiring cross in the optical modulator used as a comparative example.
[0028] Figure 7 This is a cross-sectional view of the optical waveguide in a direction perpendicular to the direction of light propagation, which is part of the optical modulator used as a comparative example.
[0029] Figure 8 This is a cross-sectional view of the optical waveguide in the optical modulator used as a comparative example, in a direction perpendicular to the direction of light propagation in the intersection.
[0030] Figure 9 This is a general view of the intersection where the optical waveguide and signal wiring intersect in the optical modulator according to Embodiment 2.
[0031] Figure 10 This is a cross-sectional view of an optical waveguide in a direction perpendicular to the direction of light propagation in the intersection, which is part of the optical modulator according to Embodiment 2.
[0032] Figure 11 This is a cross-sectional view of an optical waveguide along the direction of light propagation in the intersection, which is part of the optical modulator according to Embodiment 2.
[0033] Figure 12 This is a schematic diagram of the intersection of the optical waveguide and the signal wiring in the optical modulator according to Embodiment 3.
[0034] Figure 13This is a cross-sectional view of the optical waveguide in the direction perpendicular to the direction of light propagation in the intersection, which is part of the optical modulator according to Embodiment 3.
[0035] Figure 14 This is a cross-sectional view of the optical waveguide along the direction of light propagation in the intersection, which is part of the optical modulator according to Embodiment 3.
[0036] Figure 15 This is a general view of the intersection where the optical waveguide and signal wiring intersect in the optical modulator according to Embodiment 4.
[0037] Figure 16 This is a cross-sectional view of an optical waveguide in a direction perpendicular to the direction of light propagation in the intersection, which is part of the optical modulator according to Embodiment 4. Detailed Implementation
[0038] Implementation method 1.
[0039] <The configuration of the optical modulator according to Embodiment 1>
[0040] Figure 1 This is a top view of the optical modulator 500 according to Embodiment 1.
[0041] The optical modulator 500 according to Embodiment 1 includes: an Fe-doped semi-insulating InP substrate 1; a light input section 2 disposed at the end of the Fe-doped semi-insulating InP substrate 1, through which light is incident from the outside; eight phase modulators 20 connected to the light input section 2 via optical waveguides 10, for phase modulation of the incident light; eight first phase adjusters 30 connected to the eight phase modulators 20 via optical waveguides 10, for adjusting the phase of the light emitted from the phase modulators 20; and four second phase adjusters 40 connected to the eight first phase adjusters via optical waveguides 10. The 30 are connected to each other to further adjust the phase of the light emitted from the 8 first phase adjusters 30; 2 light output sections 3 are disposed at the ends of the Fe-doped semi-insulating InP substrate 1 and emit the light emitted from the 4 second phase adjusters 40 to the outside via the optical waveguide 10; a plurality of signal electrode pads 50 are arranged along the ends of the Fe-doped semi-insulating InP substrate 1; and a signal wiring 60 electrically connects the plurality of signal electrode pads 50 to the first phase adjusters 30 and the second phase adjusters 40, and has a cross portion 70 that intersects with the optical waveguide 10.
[0042] For phase modulator 20, the two phase modulators form a pair and each constitutes a Mach-Zehnder type phase modulator. Figure 1In one example of the optical modulator 500 shown, the phase modulator 20 is composed of a first Mach-Zehnder phase modulator corresponding to the XI channel, a second Mach-Zehnder phase modulator corresponding to the XQ channel, a third Mach-Zehnder phase modulator corresponding to the YI channel, and a fourth Mach-Zehnder phase modulator corresponding to the YQ channel.
[0043] Figure 2 This is a schematic view of the intersection 70 where the optical waveguide 10 and the signal line 60 intersect in the optical modulator 500 according to Embodiment 1. Figure 3 This is a cross-sectional view of the optical waveguide 10 in the direction perpendicular to the direction of light propagation in the optical waveguide 10 that constitutes part of the optical modulator 500 according to Embodiment 1. Figure 4 This is a cross-sectional view of the optical waveguide 10, which is part of the optical modulator 500 according to Embodiment 1, in a direction perpendicular to the direction of light propagation in the intersection 70. Figure 5 This is a cross-sectional view of the optical waveguide 10, which is part of the optical modulator 500 according to Embodiment 1, along the direction of light propagation in the intersection 70. In this view, Figure 2 For ease of explanation, the surface protective film 61 has been omitted.
[0044] The optical waveguide 10 comprises: an n-type InP conductive layer 110, 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 formed on an Fe-doped semi-insulating InP substrate 1. The exposed portion of the surface of the Fe-doped semi-insulating InP substrate 1, the surface of the optical waveguide 10, and both sides are covered by a surface protective film 61. An example of the surface protective film 61 is a SiO2 film. However, the surface protective film 61 can also be a film other than SiO2, such as a SiN film.
[0045] 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. The conductive and insulating layers can also be made of other semiconductor materials. Furthermore, the n-type InP layer constituting the n-type InP conductive layer 110 is an example of an n-type semiconductor layer, and can also be made of other n-type semiconductor layers.
[0046] like Figure 3As shown, the cross-sectional shape of the optical waveguide 10 in the direction perpendicular to the direction of light propagation is mesa-shaped. As an example of a semiconductor substrate, an Fe-doped semi-insulating InP substrate is cited, but the semiconductor substrate can also be a substrate other than an Fe-doped semi-insulating InP substrate. Furthermore, it can also be a substrate made of a material other than a semiconductor material.
[0047] <The configuration of the cross section of the optical modulator according to Embodiment 1>
[0048] like Figure 2 as well as Figure 5 As shown, in the intersection 70, the n-type InP conductive layer 110 of the optical waveguide 10 and the n-type InP signal routing conductive layer 200 specially provided in the intersection 70 cross via an Fe-doped semi-insulating InP insulating buried layer 210 provided to electrically insulate the n-type InP conductive layer 110 from the n-type InP signal routing conductive layer 200.
[0049] The n-type InP signal routing conductive layer 200 has a portion overlapping with the optical waveguide 10 and portions extending to both sides of the optical waveguide 10. The ends of the n-type InP signal routing conductive layer 200, i.e., the ends of the portions extending to both sides of the optical waveguide 10, are electrically connected to the ends of the signal routing line 60. As an example of a metal film constituting the signal routing line 60, a metal film composed of two layers of titanium (Ti) and gold (Au) can be cited.
[0050] As a structure for electrically connecting the conductive layer for signal routing to the signal routing line 60, an example is a structure in which a metal film constituting the signal routing line 60 is formed on the surface of the n-type InP conductive layer 200 at a predetermined distance from the side opposite to the signal routing line 60 and the front end. In this case, the signal routing line 60, formed of a metal film extending on the surface of the n-type InP conductive layer 200, is formed so that it does not contact the Fe-doped semi-insulating InP insulating layer 120 on the optical waveguide 10 side.
[0051] like Figure 2 as well as Figure 5 As shown, Fe-doped semi-insulating InP insulating buried layers 210 are provided on both sides of the n-type InP signal routing conductive layer 200. That is, in the intersection 70, the n-type InP conductive layer 110, which serves as a conductive layer, and the n-type InP signal routing conductive layer 200 intersect via the Fe-doped semi-insulating InP insulating buried layer 210, which serves as a buried layer. The Fe-doped semi-insulating InP insulating buried layer 210 is an example of an insulating semiconductor layer, but it can also be a buried layer made of other semiconductor materials.
[0052] Furthermore, since an Fe-doped semi-insulating InP insulating layer 120 is provided above the n-type InP signal routing conductive layer 200 that intersects with the optical waveguide 10, the n-type InP signal routing 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 routing line 60 to the n-type InP signal routing conductive layer 200 does not flow towards the n-type InP conductive layer 110 and the n-type InP first cladding layer 130 constituting the optical waveguide 10.
[0053] <Operation of the optical modulator according to Embodiment 1>
[0054] The operation of the optical modulator 500 according to Embodiment 1 will be described below.
[0055] Light incident from outside the optical modulator 500 onto the optical input section 2 passes through the optical waveguide 10 and is branched, and is respectively incident onto 8 phase modulators 20, i.e. 4 sets of Mach-Zehnder type phase modulators, and the phase of the light is modulated by the phase modulators 20.
[0056] Phase-modulated light is incident on eight first phase modulators 30 via optical waveguide 10. In the first phase modulator, the signal current input to the signal electrode pad 50 flows in the signal wiring 60 and then flows to the first phase modulator 30 electrically connected to the signal wiring 60, thereby adjusting the phase of the incident light.
[0057] The light whose phase has been adjusted by the first phase adjuster 30 is incident on the four second phase adjusters 40 via the optical waveguide 10. In the second phase adjuster 40, the signal current input to the signal electrode pad 50 flows in the signal wiring 60 and then flows to the second phase adjuster 40 which is electrically connected to the signal wiring 60, thereby adjusting the phase of the incident light again.
[0058] The light, which is phase-adjusted again by the second phase adjuster 40, is output from the two light output sections 3 to the outside of the light modulator 500 via the optical waveguide 10.
[0059] The above is a summary of the operation of the optical modulator 500 according to Embodiment 1.
[0060] <The function and effects of the optical modulator involved in Implementation Method 1>
[0061] Before explaining the function and effect of the optical modulator 500 according to Embodiment 1, the following describes the intersection 70a where the optical waveguide 10a and the signal line 60a intersect in the optical modulator 550 of the comparative example.
[0062] Figure 6This is a general view of the intersection 70a where the optical waveguide 10a intersects with the signal line 60a in the optical modulator 550, which is used as a comparative example. Figure 7 This is a cross-sectional view of the optical waveguide 10a in the direction perpendicular to the direction of light propagation in the optical waveguide 10a that constitutes part of the optical modulator 550 as a comparative example. Figure 8 This is a cross-sectional view of the optical waveguide 10a in the optical modulator 550, which is used as a comparative example, in a direction perpendicular to the direction of light propagation in the cross section 70a.
[0063] like Figure 7 As shown, the optical waveguide 10a of the optical modulator 550, as 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. The exposed portion of the Fe-doped semi-insulating InP substrate 1a, the surface of the optical waveguide 10a, and both sides are covered by a surface protective film 61a. Figure 7 As shown, the cross-sectional shape of the optical waveguide 10a in the direction perpendicular to the direction of light propagation is a table shape.
[0064] As a comparative example, the optical waveguide 10a of the optical modulator 550 is as follows: Figure 6 as well as Figure 8 As shown, in the intersection 70a where the optical waveguide 10a and the signal routing line 60a intersect, the signal routing line 60a is formed on the upper side and both sides of the optical waveguide 10a. That is, the signal routing line 60a is formed to cross the optical waveguide 10a.
[0065] As described above, in such a crossover 70a, the electric field and stress generated by the signal line 60a are applied from the signal line 60a crossing the upper side of the optical waveguide 10a to the i-type InGaAsP-MQW optical waveguide layer 140a on the lower side. The electric field is applied to the i-type InGaAsP-MQW optical waveguide layer 140a because a potential difference is generated between the signal line 60a and the n-type InP first cladding layer 130a. Since the i-type InGaAsP-MQW optical waveguide layer 140a is located between the signal line 60a and the n-type InP first cladding layer 130a, it is subjected to the electric field generated by the potential difference between the two.
[0066] The phase of light propagating in the optical waveguide 10a at the intersection 70a is slightly but unexpectedly altered by the electric field and stress. That is, the electric field and stress applied to the i-type InGaAsP-MQW optical waveguide layer 140a will unexpectedly modulate the phase of light propagating in the optical waveguide 10a.
[0067] In the intersection 70a, phase modulation of the signal light occurs within the crossed optical waveguide 10a due to the electric field and stress caused by the signal wiring 60a. This unintended phase modulation of the signal light propagating in the optical waveguide 10a at the intersection 70a becomes noise and may disturb the optical modulation operation.
[0068] On the other hand, in the optical modulator 500 according to Embodiment 1, such as Figure 2 , Figure 4 as well as Figure 5 As shown, in the intersection 70, the n-type InP conductive layer 110 of the optical waveguide 10 and the n-type InP signal routing conductive layer 200 specially provided in the intersection 70 cross via an Fe-doped semi-insulating InP insulating buried layer 210 provided to electrically insulate the n-type InP conductive layer 110 from the n-type InP signal routing conductive layer 200.
[0069] An Fe-doped semi-insulating InP insulating layer 120 is disposed between the n-type InP signal routing conductive layer 200 and the n-type InP first cladding layer 130 in a direction perpendicular to the surface of the Fe-doped semi-insulating InP substrate 1. The Fe-doped semi-insulating InP insulating layer 120 functions to electrically insulate the n-type InP signal routing conductive layer 200 from the n-type InP first cladding layer 130. This is to prevent the signal current flowing in the n-type InP signal routing conductive layer 200 from flowing to the optical waveguide side.
[0070] In addition, such as Figure 5 As shown, along the direction of light propagation in the intersection 70, Fe-doped semi-insulating InP insulating embedded layers 210 are respectively provided on both sides of the n-type InP signal routing conductive layer 200. Therefore, the n-type InP signal routing conductive layer 200 is electrically insulated from the n-type InP conductive layer 110.
[0071] In the cross section 70, although a potential difference is generated between the n-type InP signal routing conductive layer 200, which also serves as a signal routing line, and the n-type InP first cladding layer 130, since the i-type InGaAsP-MQW optical waveguide layer 140 is not located between the n-type InP signal routing 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.
[0072] Furthermore, since the Fe-doped semi-insulating InP insulating layer 120 disposed between the n-type InP signal routing conductive layer 200 and the n-type InP first cladding layer 130 reduces the electric field, it also weakens the electric field indirectly applied to the i-type InGaAsP-MQW optical waveguide layer 140. Therefore, 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 in a way that reduces the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140 in the electric field generated in the n-type InP signal routing conductive layer 200 as the signal current flows.
[0073] Furthermore, the coefficient of thermal expansion of the semiconductor material constituting the n-type InP signal routing conductive layer 200 is extremely close to that of the semiconductor material constituting the i-type InGaAsP-MQW optical waveguide layer 140, which constitutes the optical waveguide 10. This is because the semiconductor materials constituting both the n-type InP signal routing 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 the provision of the n-type InP signal routing conductive layer 200 is significantly small.
[0074] That is, since the signal line 60 is configured to penetrate the optical waveguide 10 through the n-type InP signal line conductive layer 200 disposed on the lower side of the optical waveguide 10, the electric field and stress applied to the i-type InGaAsP-MQW optical waveguide layer 140 from the signal line 60 can be significantly reduced compared to the configuration in the comparative example where the signal line 60a crosses on the upper side of the optical waveguide 10a.
[0075] In this embodiment, the intersection 70 where the optical waveguide 10, which is part of the optical modulator 500, intersects with the signal line 60 is formed by a known manufacturing method.
[0076] <Effects of Implementation Method 1>
[0077] According to the optical modulator of Embodiment 1, since the signal wiring that intersects with the optical waveguide is connected by a conductive layer made of semiconductor material and is disposed on the lower side of the optical waveguide, the electric field and stress applied to the optical waveguide layer at the intersection of the optical waveguide and the signal wiring are relieved, thus achieving the effect of obtaining an optical modulator with excellent optical modulation characteristics.
[0078] Implementation method 2.
[0079] Figure 9This is a schematic diagram of the intersection 70b of the optical waveguide 10b and the signal line 60b in the optical modulator 600 according to Embodiment 2. Figure 10 This is a cross-sectional view of the optical waveguide 10b, which is part of the optical modulator 600 according to Embodiment 2, in a direction perpendicular to the propagation direction of light in the intersection 70b. Figure 11 This is a cross-sectional view of the optical waveguide 10b along the light propagation direction in the intersection 70b, which is part of the optical modulator 600 according to Embodiment 2. Figure 9 For ease of explanation, the surface protective film 61b has been omitted.
[0080] <The configuration of the cross section of the optical modulator according to Embodiment 2>
[0081] The difference in configuration between the optical modulator 600 of Embodiment 2 and the optical modulator 500 of Embodiment 1 lies in the fact that, instead of the Fe-doped semi-insulating InP insulating buried layer 210 disposed on both sides of the n-type InP signal routing conductive layer 200b of the optical modulator 500 of Embodiment 1, a p-type InP buried layer 210b is disposed on both sides of the n-type InP signal routing conductive layer 200b of the optical modulator 600 of Embodiment 2. The p-type InP buried layer 210b is an example of a buried layer, but it can also be a buried layer made of other semiconductor materials. Furthermore, the p-type InP layer constituting the p-type InP buried layer 210b is an example of a p-type semiconductor layer, but it can also be other p-type semiconductor materials.
[0082] like Figure 11 As shown, in the intersection 70b of the optical modulator 600 according to Embodiment 2, p-type InP buried layers 210b are respectively provided on both sides of the n-type InP signal routing conductive layer 200b along the light propagation direction. That is, in the intersection 70b, the n-type InP conductive layer 110b, the p-type InP buried layer 210b, the n-type InP signal routing conductive layer 200b, the p-type InP buried layer 210b, and the n-type InP conductive layer 110b are arranged sequentially along the light propagation direction. In terms of conductivity type, the n-type InP conductive layer 110b, the p-type InP buried layer 210b, and the n-type InP signal routing conductive layer 200b form an npn structure. Therefore, no current flows between the n-type InP conductive layer 110b and the n-type InP signal routing conductive layer 200b because they are reverse biased.
[0083] In the cross section 70b, although a potential difference is generated between the n-type InP signal routing conductive layer 200b, which also serves as a signal routing line, and the n-type InP first cladding layer 130b, since the i-type InGaAsP-MQW optical waveguide layer 140b is not located between the n-type InP signal routing 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.
[0084] Furthermore, since the electric field is reduced by the Fe-doped semi-insulating InP insulating layer 120b disposed between the n-type InP signal routing conductive layer 200b and the n-type InP first cladding layer 130b, the electric field indirectly applied to the i-type InGaAsP-MQW optical waveguide layer 140b is also weakened. Therefore, the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140b is significantly reduced.
[0085] <Effects of Implementation Method 2>
[0086] According to the above, in the optical modulator according to Embodiment 2, since the signal wiring that intersects with the optical waveguide is connected by a conductive layer made of semiconductor material and is disposed on the lower side of the optical waveguide, the electric field and stress applied to the optical waveguide layer at the intersection of the optical waveguide and the signal wiring are relieved, thus achieving the effect of obtaining an optical modulator with excellent optical modulation characteristics.
[0087] Implementation method 3.
[0088] Figure 12 This is a schematic diagram of the intersection 70c of the optical waveguide 10c and the signal line 60c in the optical modulator 700 according to Embodiment 3. Figure 13 This is a cross-sectional view of the optical waveguide 10c, which is part of the optical modulator 700 according to Embodiment 3, in a direction perpendicular to the direction of light propagation in the intersection 70c. Figure 14 This is a cross-sectional view of the optical waveguide 10c, which is part of the optical modulator 700 according to Embodiment 3, along the direction of light propagation in the intersection 70c. Figure 12 For ease of explanation, the surface protective film 61c has been omitted.
[0089] <The configuration of the cross section of the optical modulator according to Embodiment 3>
[0090] The following describes the differences in the configuration between the optical modulator 700 of Embodiment 3 and the optical modulator 500 of Embodiment 1.
[0091] In the optical modulator 500 according to Embodiment 1, an n-type InP signal routing conductive layer 200 is provided at the portion intersecting with the optical waveguide 10. The n-type InP signal routing conductive layer 200 and the signal routing line 60 made of a metal film are configured such that the metal film constituting the signal routing line 60 is formed on the surface of the n-type InP signal routing conductive layer 200 from the front end of the n-type InP signal routing conductive layer 200 to a predetermined distance.
[0092] On the other hand, in the optical modulator 700 according to embodiment 3, such as Figure 12 as well as Figure 14 As shown, the signal routing line 60c itself is composed of a high-concentration n-type InP wiring layer, which is composed of n-type InP with a high concentration of n-type dopant. That is, a portion of the signal routing line 60c also functions as a conductive layer for signal routing lines as in Embodiments 1 and 2. Like the n-type InP conductive layer 200 for signal routing lines in Embodiment 1, the signal routing line 60c is disposed on the lower side of the optical waveguide 10d. In other words, the signal routing line 60c performs the same function as the n-type InP conductive layer 200 for signal routing lines in Embodiment 1.
[0093] The doping concentration of the n-type dopant in the high-concentration n-type InP wiring layer constituting the signal wiring 60c is preferably 1 × 10⁻⁶. 19 cm -3 That's all. This is because signal cabling needs to minimize wiring resistance.
[0094] Similar to Embodiment 1, a buried layer composed of an insulating semiconductor layer, such as an Fe-doped semi-insulating InP insulating buried layer 210c, is provided on both sides of the signal routing line 60c in the intersection 70c. Alternatively, as in Embodiment 2, a buried layer composed 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.
[0095] In the cross section 70c, although a potential difference is generated between the signal line 60c and the n-type InP first cladding 130c, since the i-type InGaAsP-MQW optical waveguide layer 140c is not located between the signal line 60c and the n-type InP first cladding 130c, the electric field generated by the potential difference between the two is not directly applied to the i-type InGaAsP-MQW optical waveguide layer 140c.
[0096] Furthermore, since the electric field is reduced by the Fe-doped semi-insulating InP insulating layer 120c disposed between the signal line 60c and the n-type InP first cladding layer 130c, the electric field indirectly applied to the i-type InGaAsP-MQW optical waveguide layer 140c is also weakened. Therefore, the electric field applied to the i-type InGaAsP-MQW optical waveguide layer 140c is significantly reduced.
[0097] In the optical modulator 700 according to Embodiment 3, since a high-concentration n-type InP wiring layer made of InP-based compound semiconductor is used as the signal wiring 60c, it is made of a semiconductor material that is substantially the same as that of the optical waveguide 10c. Therefore, the processes of forming metal films and patterning them into desired shapes to form signal wiring as in Embodiments 1 and 2 can be omitted. As a result, an optical modulator with lower cost and excellent optical modulation characteristics can be obtained.
[0098] <Effects of Implementation Method 3>
[0099] According to the above, in the optical modulator according to Embodiment 3, since the signal wiring is made of semiconductor material and disposed at the lower part of the optical waveguide, the electric field and stress applied to the optical waveguide layer at the intersection of the optical waveguide and the signal wiring are relieved, thus achieving the effect of obtaining an optical modulator with lower cost and excellent optical modulation characteristics.
[0100] Implementation method 4.
[0101] Figure 15 This is a general view of the intersection 70d where the optical waveguide 10d and the signal line 60d intersect in the optical modulator 800 according to Embodiment 4. Figure 16 This is a cross-sectional view of the optical waveguide 10d, which is a part of the optical modulator 700 according to Embodiment 4, in a direction perpendicular to the propagation direction of light in the intersection 70d. Figure 15 For ease of explanation, the surface protective film 61d has been omitted.
[0102] <The configuration of the cross section of the optical modulator according to Embodiment 4>
[0103] In the optical modulator 800 according to embodiment 4, such as Figure 15 as well as Figure 16 As shown, two through-holes 220d are provided on both sides of the intersection 70d where the optical waveguide 10d and the signal routing line 60d intersect. These through-holes extend from the surface side of the Fe-doped semi-insulating InP substrate 1d to the back side. Additionally, a back electrode 230d is provided on the back side of the Fe-doped semi-insulating InP substrate 1d, electrically connecting the two through-holes 220d.
[0104] Two through-holes 220d exposed on the surface side of the Fe-doped semi-insulating InP substrate 1d are electrically connected to the signal routing line 60d.
[0105] In the configuration of the optical modulator 800 according to Embodiment 4, since there is an Fe-doped semi-insulating InP substrate 1d between the optical waveguide 10d and the back electrode 230d, which is part of the signal wiring that intersects with the optical waveguide 10d, the generation of electric field and stress caused by the signal wiring is significantly reduced. Therefore, an optical modulator with excellent optical modulation characteristics can be obtained.
[0106] <Effects of Implementation Method 4>
[0107] According to the optical modulator of Embodiment 4, since two through holes are provided on both sides of the optical waveguide at the intersection, extending from the surface side of the Fe-doped semi-insulating InP substrate to the back side and electrically connected to the signal wiring, and a back electrode is provided on the back side of the Fe-doped semi-insulating InP substrate to function as a signal wiring by connecting the two through holes, an optical modulator with superior optical modulation characteristics is obtained.
[0108] This disclosure describes various exemplary embodiments and examples, but the various features, forms and functions described in one or more embodiments are not limited to the application of a specific embodiment, and can also be applied to the embodiments alone or in various combinations.
[0109] Therefore, numerous variations, not illustrated, can be conceived within the scope of this disclosure. These include variations, additions, or omissions of at least one constituent element, as well as extraction of at least one constituent element and combination with constituent elements of other embodiments.
[0110] Explanation of reference numerals in the attached figures
[0111] 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 modulator; 40...Second phase modulator; 50...Signal electrode pads; 60, 60a, 60b, 60c, 60d...Signal wiring; 61, 61a, 61b, 61c, 61d...Surface protective 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 conductive layer for signal routing; 210, 210c... Fe-doped semi-insulating InP insulating buried layer; 210b... p-type InP buried layer; 220d... via; 230d... back electrode; 500, 550, 600, 700, 800... optical modulator.
Claims
1. An optical modulator, comprising: have: substrate; A light input section is disposed at the end of the substrate and receives light from the outside; Multiple phase modulators are disposed on the substrate and connected to the light input section via optical waveguides to modulate the phase of the incident light; Multiple phase adjusters are disposed on the substrate and connected to the multiple phase modulators via the optical waveguide, respectively, to adjust the phase of the light emitted from the phase modulators; A light output section is disposed at the end of the substrate, and emits light output from the plurality of phase adjusters to the outside via the light waveguide; Multiple signal electrode pads are arranged along the ends of the substrate; as well as The signal routing circuit electrically connects the plurality of signal electrode pads to the phase adjuster and has a crossover portion that intersects with the optical waveguide. The optical waveguide is composed of a conductive layer, an insulating layer, a first cladding layer, an optical waveguide layer, and a second cladding layer formed on the substrate. In the intersection, the conductive layer and the conductive layer for signal routing intersect via an embedded layer.
2. The optical modulator according to claim 1, characterized in that, The embedded layer is composed of an insulating semiconductor layer.
3. The optical modulator according to claim 1, characterized in that, The buried layer is composed of a p-type semiconductor layer, and the conductive layer is composed of an n-type semiconductor layer.
4. The optical modulator according to any one of claims 1 to 3, characterized in that, The end of the conductive layer for the signal wiring is electrically connected to the end of the signal wiring.
5. The optical modulator according to any one of claims 1 to 3, characterized in that, The conductive layer for the signal wiring is part of the signal wiring, and the conductive layer and the signal wiring route are composed of a high-concentration n-type semiconductor layer.
6. An optical modulator, comprising: have: substrate; A light input section is disposed at the end of the substrate and receives light from the outside; Multiple phase modulators are disposed on the substrate and connected to the light input section via optical waveguides to modulate the phase of the incident light; Multiple phase adjusters are disposed on the substrate and connected to the multiple phase modulators via the optical waveguide, respectively, to adjust the phase of the light emitted from the phase modulators; A light output section is disposed at the end of the substrate, which emits light from the plurality of phase adjusters to the outside via the light waveguide; Multiple signal electrode pads are arranged along the ends of the substrate; and The signal routing circuit electrically connects the plurality of signal electrode pads to the phase adjuster and has a crossover portion that intersects with the optical waveguide. Multiple through holes are provided on both sides of the optical waveguide at the intersection, extending from the surface side of the substrate to the back side. A back electrode is provided on the back side of the substrate to electrically connect the multiple through holes.
7. The optical modulator according to claim 6, characterized in that, The plurality of through holes exposed on the surface side of the substrate are electrically connected to the signal wiring.
8. The optical modulator according to any one of claims 1 to 7, characterized in that, At least the optical waveguide and the signal wiring are covered with a surface protective film.
9. The optical modulator according to any one of claims 1 to 8, characterized in that, The plurality of phase adjusters are each composed of a first phase adjuster and a second phase adjuster connected to the first phase adjuster via the optical waveguide.