MACH-ZEHNDER INTERFEROMETRIC OPTICAL MODULATOR WITH SHALLOW RIDGE WAVEGUIDE STRUCTURE AND METHOD FOR MANUFACTURING THE SAME

Disclosed are a Mach-Zehnder interferometric optical modulator and a method for manufacturing the same. The modulator includes first and second lower clad layers stacked on a substrate, a core layer on the first and second lower clad layers, a first upper clad layer on the core layer, a second upper clad layer on the first upper clad layer, and electrodes on the second upper clad layer. The second upper clad layer includes an input waveguide, an output waveguide spaced apart from the input waveguide, branch waveguides branched from the input waveguide and coupled to the output waveguide, and insulating blocks provided on both outer sides of the branch waveguides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 of Korean Patent Application No. 10-2022-0099034, filed on Aug. 9, 2022, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The present disclosure herein relates to an optical modulator and a method for manufacturing the same, and more particularly, to a Mach-Zehnder interferometric optical modulator with a shallow ridge waveguide structure and a method for manufacturing the same.

Recently, with the advent of high-speed Internet and various multimedia services, the volume of global information is expected to increase exponentially. However, profits of network operators are expected to be stagnant, and there is an urgent need to secure optical component technology for achieving high speed, flexibility, small size, and low price of a system in addition to efficiency of network resources. Furthermore, it is required to develop an optical modulator having an ultrahigh transmission speed that may overcome physical and economic limitations of Internet traffic.

SUMMARY

The present disclosure provides a Mach-Zehnder interferometric optical modulator capable of reducing leakage current generated in active waveguides and a method for manufacturing the same.

The present disclosure provides a Mach-Zehnder interferometric optical modulator. The modulator includes: first and second lower clad layers stacked on a substrate; a core layer on the first and second lower clad layers; a first upper clad layer on the core layer; a second upper clad layer on the first upper clad layer; and electrodes on the second upper clad layer. Here, the second upper clad layer may include: an input waveguide; an output waveguide spaced apart from the input waveguide; branch waveguides branched from the input waveguide and coupled to the output waveguide; and insulating blocks provided on both outer sides of the branch waveguides. Each of the branch waveguides may include: active waveguides under the electrodes; and passive waveguides connected between the active waveguides and exposed from the electrodes. The insulating blocks may be provided on both outer sides of the active waveguides.

The insulating blocks may include the same material as the passive waveguides.

According to an example, the insulating blocks and the passive waveguides may include intrinsic InP.

According to an example, the insulating blocks and the passive waveguides may include semi-insulated doped InP.

According to an example, the active waveguides may include conductive doped InP.

According to an example, the first upper clad layer may include conductive doped InP.

According to an example, the first lower clad layer and the second lower clad layer may include conductive doped InP.

According to an example, the core layer may include InGaAsP or InAlGaAs.

According to an example, the Mach-Zehnder interferometric optical modulator may further include an etching stop layer between the first upper clad layer and the second upper clad layer, wherein the etching stop layer may include InGaAsP, InAlAs, or InGaAlAs.

According to an example, the Mach-Zehnder interferometric optical modulator may further include a passivation layer provided on the etching stop layer outside the second upper clad layer.

In an embodiment of the inventive concept, a method for manufacturing a Mach-Zehnder interferometric optical modulator includes: forming first and second lower clad layers on a substrate; forming a core layer on the first and second lower clad layers; forming a first upper clad layer on the core layer; forming a second upper clad layer on the first upper clad layer; and forming electrodes on the second upper clad layer. Here, the forming of the second upper clad layer may include: forming an active layer; forming a passive layer outside the active layer; and patterning the active layer and the passive layer to form active waveguides, passive waveguides between the active waveguides, and insulating blocks on both outer sides of the active waveguides by patterning.

According to an example, the active waveguides may include conductive doped InP, and the passive waveguides and the insulating blocks may include intrinsic InP or semi-insulated doped InP.

According to an example, the second upper clad layer may include: an input waveguide; an output waveguide spaced apart from the input waveguide; branch waveguides branched from the input waveguide and coupled to the output waveguide; and the insulating blocks provided on both outer sides of the branch waveguides.

According to an example, each of the branch waveguides may include: the active waveguides between the insulating blocks; and the passive waveguides between the active waveguides.

According to an example, the method may further include forming an etching stop layer between the first upper clad layer and the second upper clad layer.

According to an example, the active waveguides, the passive waveguides, and the insulating blocks may have a cross-section of a reverse mesa structure.

DETAILED DESCRIPTION

Embodiments of the inventive concept will now be described in detail with reference to the accompanying drawings. The advantages and features of embodiments of the inventive concept, and methods for achieving the advantages and features will be apparent from the embodiments described in detail below with reference to the accompanying drawings. However, the inventive concept may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art, and the inventive concept is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

The terminology used herein is not for delimiting the embodiments of the inventive concept but for describing the embodiments of the inventive concept. The terms of a singular form may include plural forms unless otherwise specified. It will be further understood that the terms “include”, “including”, “comprise”, and/or “comprising” used herein specify the presence of stated elements, steps, operations, and/or devices, but do not preclude the presence or addition of one or more other elements, steps, operations, and/or devices. Furthermore, the terms “clad”, “core”, “waveguide”, and “phase shift region” may be construed as meaning those commonly used in the field of optical communications. Reference numerals, which are presented in the order of description, are provided according to the embodiments and are thus not necessarily limited to the order.

FIG.1illustrates an example of a Mach-Zehnder interferometric optical modulator100according to an embodiment of the inventive concept.FIG.2is a cross-sectional view taken along line I-I′ ofFIG.1.FIG.3is a cross-sectional view taken along line II-II′ ofFIG.1.

Referring toFIGS.1to3, the Mach-Zehnder interferometric optical modulator100of an embodiment of the inventive concept may be a Mach-Zehnder interference modulator with a reverse mesa-type shallow ridge waveguide structure. Alternatively, the Mach-Zehnder interferometric optical modulator100may be a Mach-Zehnder interferometric optical modulator with a mesa structure, but an embodiment of the inventive concept is not limited thereto. According to an embodiment, the Mach-Zehnder interferometric optical modulator100of an embodiment of the inventive concept may include a substrate10, a first lower clad layer20, a second lower clad layer30, a core layer40, a first upper clad layer50, an etching stop layer60, a second upper clad layer70, a passivation layer80, and electrodes90.

The substrate10may be planar. For example, the substrate10may include a silicon wafer. Alternatively, the substrate10may include a glass substrate or a group III-V semiconductor substrate, but an embodiment of the inventive concept is not limited thereto. According to an example, the substrate10may include an input region102, a dividing region104, a phase shifting region106, a coupling region108, and an output region110. The input region102may be a region for receiving light11. The dividing region104may be a region for dividing the light11. The phase shifting region106may be a region for changing a phase of the light11. According to an example, the phase shifting region106may include active regions12and passive regions14. The active regions12may be provided below electrodes90. The active regions12may be regions for modulating the phase of the light11. The passive regions14may be provided between the electrodes90. The passive regions14may be regions for transferring and/or transmitting light. The coupling region108may be a region for causing the light11to interfere. The output region110may be a region for transferring the light to the outside.

The first lower clad layer20may be provided on the substrate10. The first lower clad layer20may include conductive doped InP. For example, the first lower clad layer20may include n-type doped InP.

The second lower clad layer30may be provided on the first lower clad layer20. The second lower clad layer30may include conductive doped InP. The second lower clad layer30may include n-type doped InP. A doping concentration of the second lower clad layer30may be lower than a doping concentration of the first lower clad layer20.

The core layer40may be provided on the second lower clad layer30. The core layer40may have a refractive index higher than refractive indices of the first lower clad layer20and the second lower clad layer30. The core layer40may include InGaAsP. Alternatively, the core layer40may include InAlGaAs, but an embodiment of the inventive concept is not limited thereto.

The first upper clad layer50may be provided on the core layer40. The first upper clad layer50may have a refractive index lower than the refractive index of the core layer40. The first upper clad layer50may include conductive doped InP. For example, the first upper clad layer50may include p-type doped InP.

The etching stop layer60may be provided on the first upper clad layer50. The etching stop layer60may include InGaAsP, InAlAs, or InGaAlAs, but an embodiment of the inventive concept is not limited thereto.

The second upper clad layer70may be provided on the etching stop layer60. The second upper clad layer70may be a ridge waveguide layer that transfers the light11along the core layer40. The second upper clad layer70of a ridge waveguide layer may minimize and/or reduce current leakage that occurs in a sidewall of a typical mesa waveguide. According to an example, the second upper clad layer70may include an input waveguide71, an output waveguide75, branch waveguides73, and insulating blocks76.

The input waveguide71may be connected to one side of the branch waveguides73. The input waveguide71may receive the light11. The input waveguide71may include semi-insulated doped InP. For example, the input waveguide71may include intrinsic InP. Although not illustrated, a waveguide divider may be provided between the input waveguide71and the branch waveguides73. The waveguide divider may receive the light11in the input waveguide71and distribute the light11to the branch waveguides73.

The output waveguide75may be connected to another side of the branch waveguides73. The output waveguide75may transfer the light11to the outside. The output waveguide75may include semi-insulated doped InP. For example, the output waveguide75may include intrinsic InP. Although not illustrated, a waveguide combiner may be provided between the output waveguide75and the branch waveguides73. The waveguide combiner may cause the light11to interfere. The light11may be amplified by constructive interference and dissipated by destructive interference.

The branch waveguides73may be branched from the input waveguide71and may be coupled to the output waveguide75. The branch waveguides73may be parallel with each other. Each of the branch waveguides73may control the phase of the light11using an electric field provided by the electrodes90. The branch waveguides73may have a cross-section of a reverse mesa structure. According to an example, each of the branch waveguides73may include active waveguides72and passive waveguides74.

The active waveguides72may be provided in the active regions12of the substrate10. The active waveguides72may be provided under the electrodes90. The active waveguides72may be phase modulation waveguides. The active waveguides72may be reverse mesa-type shallow ridge waveguides or vertical mesa-type shallow ridge waveguides, but an embodiment of the inventive concept is not limited thereto. The active waveguides72may control the phase of the light11using an electric field between the electrodes90and the substrate10. The active waveguides72may include conductive doped InP. For example, the active waveguides72may include p-type doped InP.

The passive waveguides74may be provided in the passive region14of the substrate10. The passive waveguides74may be provided between the active waveguides72. The passive waveguides74may insulate the active waveguides72. The passive waveguides74may include semi-insulated doped InP. For example, the passive waveguides74may include intrinsic InP.

The insulating blocks76may be provided on both outer sides of the active waveguides72. The insulating blocks76may be parallel with the active waveguides72. The insulating blocks76may be connected in a parallel direction to the active waveguides72, but an embodiment of the inventive concept is not limited thereto. The insulating blocks76may have a cross-section of a reverse mesa structure. The insulating blocks76may be provided below the electrodes90. The insulating blocks76may reduce leakage current generated in the active waveguides72and having a direction intersecting with a travel direction of the light11. The insulating blocks76may have the same material as the passive waveguides74. For example, the insulating blocks76may include intrinsic InP or semi-insulated doped InP. The insulating blocks76may be spaced about 3 m or more apart from the active waveguides72.

Therefore, the Mach-Zehnder interferometric optical modulator100of an embodiment of the inventive concept may reduce leakage current of the active waveguides72using the insulating blocks76.

The passivation layer80may be provided on a sidewall of the branch waveguides73. The passivation layer80may be provided on the insulating blocks76. The passivation layer80may protect the branch waveguides73and the insulating blocks76. Although not illustrated, the passivation layer80may be provided on sidewalls or upper portions of the input waveguide71and the output waveguide75.

The electrodes90may be provided on the active waveguides72. The electrodes90may be provided on the passivation layer80. The electrodes90may modulate the phase of the light11by applying an electric field into the active waveguides72using external power.

A method for manufacturing the Mach-Zehnder interferometric optical modulator100configured as described above is described below.

FIG.4illustrates a method for manufacturing the Mach-Zehnder interferometric optical modulator100of an embodiment of the inventive concept.FIGS.5A to5Dare cross-sectional views illustrating a manufacturing process of the active waveguides72and the insulating blocks76ofFIG.2.FIGS.6A to6Dare cross-sectional views illustrating a manufacturing process of the passive waveguides74ofFIG.3.

Referring toFIGS.4,5A, and6A, the first lower clad layer20is formed on the substrate10(S10). The first lower clad layer20may include n-type doped InP formed using a molecular beam epitaxy (MBE) method or metal-organic vapor phase epitaxy (MOVPE) method.

Next, the second lower clad layer30is formed on the first lower clad layer20(S20). The second lower clad layer30may include intrinsic InP formed using a metal-organic vapor phase epitaxy method.

Next, the core layer40is formed on the second lower clad layer30(S30). The core layer40may include InGaAs formed using a metal-organic vapor phase epitaxy method.

Thereafter, the first upper clad layer50is formed on the core layer40(S40). The first upper clad layer50may include intrinsic InP formed using a metal-organic vapor phase epitaxy method.

Furthermore, the etching stop layer60is formed on the first upper clad layer50(S50). The etching stop layer60may include InGaAsP, InAlAs, or InGaAlAs formed using a metal-organic vapor phase epitaxy method.

Referring toFIGS.1,4,5A, and6A, the second upper clad layer70is formed on the etching stop layer60(S60). The first lower clad layer20, the second lower clad layer30, the core layer40, the first upper clad layer50, and the etching stop layer60may be formed in situ in one chamber (not shown), but an embodiment of the inventive concept is not limited thereto.

FIG.7illustrates an example of forming (S60) the second upper clad layer70ofFIG.1.

Referring toFIGS.1,5B,6B, and7, an active layer77is formed on the etching stop layer60(S62). The active layer77may include p-type doped InP. The active layer77may be formed in the active regions12. Alternatively, the active layer77may be formed in the input region102, the dividing region104, the coupling region108, and the output region110, but an embodiment of the inventive concept is not limited thereto.

Referring toFIGS.1,5C,6C, and7, a passive layer78is formed on the etching stop layer60exposed by the active layer77(S64). The passive layer78may include intrinsic InP or semi-insulated doped InP.

FIG.8illustrates an example of the active waveguides72, the passive waveguides74, and the insulating blocks76ofFIG.1.

Referring toFIGS.5D,6D,7, and8, the active waveguides72, the passive waveguides74, and the insulating blocks76are formed by patterning the active layer77and the passive layer78(S66). The active waveguides72, the passive waveguides74, and the insulating blocks76may have a cross-section of a reverse mesa structure. The insulating blocks76may be spaced about 3 m or more apart from the active waveguides72.

Referring back toFIGS.1to4, the passivation layer80is formed (S70). The passivation layer80may include a silicon oxide film or silicon nitride formed using a chemical vapor deposition method. Alternatively, the passivation layer80may include a polymer formed using spin coating or a sol-gel method, but an embodiment of the inventive concept is not limited thereto.

Furthermore, the electrodes90are formed on the active waveguides72and a portion of the passivation layer80(S80). The electrodes90may include metal formed through a deposition process, a photolithography process, and an etching process. For example, the electrodes90may include at least one of gold (Au), silver (Ag), copper (Cu), aluminum (Al), titanium (Ti), tungsten (W), or tantalum (Ta), but an embodiment of the inventive concept is not limited thereto.

As described above, the Mach-Zehnder interferometric optical modulator and the method for manufacturing the same according to an embodiment of the inventive concept may reduce leakage current of active waveguides by providing, on both outer sides of the active waveguides, insulating blocks having the same material as passive waveguides between the active waveguides.