CN116990906A - MZ structure-based lithium niobate hybrid integrated electro-optic modulator and preparation method thereof - Google Patents

Abstract

The application relates to a lithium silicon niobate hybrid integrated electro-optic modulator based on an MZ structure and a preparation method thereof, wherein the modulator comprises a substrate, a silicon waveguide layer, an isolation layer, a lithium niobate layer and a metal layer from bottom to top; the lithium niobate layer is composed of a ridge waveguide structure of a bottom slab and an upper rib. The application reduces the insertion loss of the whole device, and simultaneously reduces the material limitation of light transmission in the silicon waveguide, such as two-photon absorption effect and the like; in addition, the minimum linewidth of the lithium niobate waveguide of the device is 2um, the requirement on the etching precision of the lithium niobate is reduced under the condition of maintaining the excellent performance of the device, and the tolerance of the device to the etching process is increased.

Description

MZ structure-based lithium niobate hybrid integrated electro-optic modulator and preparation method thereof

Technical Field

The application belongs to the field of photonic chips, and particularly relates to a lithium silicon niobate hybrid integrated electro-optical modulator based on an MZ structure and a preparation method thereof.

Background

With the vigorous development of application fields such as 5G communication, high-capacity information centers, quantum computation, artificial intelligence and the like, higher demands are put forward on the transmission and processing of information in an optical communication system which is a mainstream communication technology at present. In the optical interconnection, photons are used as a transmission carrier of information, and the optical interconnection has the advantages of high speed, high bandwidth, small delay and low power consumption. The electro-optical modulator performs the function of converting electrical signals into optical signals, and is one of the core devices of optical interconnection, optical computing and optical communication networks.

Compared with the current mature material platform SiPH, the lithium niobate material has strong electro-optic effect, so that the lithium niobate material is more suitable for an electro-optic modulator. The disadvantage is that lithium niobate is not easily etched with precision, which limits to a certain extent the further development of lithium niobate modulators. The method which is generally known at present is to mix lithium niobate with silicon base, which not only utilizes the excellent electro-optic modulation performance of lithium niobate, but also utilizes the capacity of silicon maturation

Disclosure of Invention

The application aims to solve the technical problem of providing a lithium niobate hybrid integrated electro-optical modulator based on an MZ structure and a preparation method thereof, wherein the electro-optical modulator reduces the insertion loss of the whole device and simultaneously reduces the material limitation of light transmission in a silicon waveguide, such as two-photon absorption effect and the like; in addition, the minimum linewidth of the lithium niobate waveguide of the device is 2um, the requirement on the etching precision of the lithium niobate is reduced under the condition of maintaining the excellent performance of the device, and the tolerance of the device to the etching process is increased.

The application provides a lithium silicon niobate hybrid integrated electro-optic modulator based on an MZ structure, which comprises a substrate, a silicon waveguide layer, an isolation layer, a lithium niobate layer and a metal layer from bottom to top; the lithium niobate layer is composed of a ridge waveguide structure of a bottom slab and an upper rib.

And the silicon oxide isolation layer is arranged above the silicon waveguide layer along the direction vertical to the substrate, and a silicon oxide isolation layer is arranged between the two waveguide layers.

The metal layer is positioned on the surface of the lithium niobate layer slide layer.

The application also provides a preparation method of the lithium silicon niobate hybrid integrated electro-optic modulator based on the MZ structure, which comprises the following steps:

etching a silicon layer on an SOI wafer to prepare a grating coupler, depositing a silicon oxide cladding layer and polishing; bonding LNOI, polishing the lithium niobate thin film; etching a ridge waveguide pattern and 1 x 2MMI in the LN layer by using an EBL method; and preparing the metal electrode on the lithium niobate layer by an ultraviolet lithography method.

Advantageous effects

The optical interface grating coupler of the modulator is arranged on a silicon layer, the insertion loss of the current silicon grating coupler is about 3dB, and the insertion loss of the lithium niobate grating coupler is about 8 dB. By adopting the method, the insertion loss of the whole device is reduced, and meanwhile, the material limitation of light transmission in the silicon waveguide, such as two-photon absorption effect and the like, is reduced; in addition, the minimum linewidth of the lithium niobate waveguide of the device is 2um, the requirement on the etching precision of the lithium niobate is reduced under the condition of maintaining the excellent performance of the device, and the tolerance of the device to the etching process is increased.

Drawings

FIG. 1 is a cross-sectional view of an electro-optic modulator of the present application;

FIG. 2 is a top view of an electro-optic modulator of the present application;

FIG. 3 shows the voltage length product as a function of lithium niobate waveguide etch depth Hrib and electrode spacing gap;

FIG. 4 shows the variation of metal absorption loss with the lithium niobate waveguide etch depth Hrib and electrode spacing gap;

FIG. 5 is a graph showing the variation of the high frequency signal S11 of the electro-optic modulator according to the present application with frequency;

FIG. 6 is a graph showing the variation of the high frequency signal S21 of the electro-optic modulator according to the present application with frequency;

FIG. 7 is a calculated electro-optic response curve for an electro-optic modulator of the present application;

fig. 8 is a diagram of a 1 x 2mmi optical mode transmission;

FIG. 9 shows the transmittance of a single output waveguide of a 1 x 2MMI as a function of wavelength;

FIG. 10 is a transmission diagram of an optical mode of a silicon/lithium niobate interlayer coupler;

FIG. 11 is a graph showing the insertion loss of a silicon/lithium niobate interlayer coupler as a function of process error;

FIG. 12 is a graph showing transmittance of a silicon grating coupler as a function of wavelength;

fig. 13 is a schematic diagram of a process flow for manufacturing an electro-optic modulator according to the present application.

Detailed Description

The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the teachings of the present application, and such equivalents are intended to fall within the scope of the application as defined in the appended claims.

Example 1

As shown in fig. 1 and 2, the embodiment provides a MZ structure-based lithium niobate hybrid integrated electro-optical modulator, which includes, from bottom to top, a substrate (725 um), a silicon waveguide layer (220 nm), a silicon dioxide isolation layer (160 nm), a lithium niobate layer (600 nm), and a metal layer (1 um). The silicon waveguide layer is arranged on the surface of the substrate, the lithium niobate waveguide layer is composed of a ridge waveguide structure of a bottom slab and an upper rib, the lithium niobate waveguide layer is arranged above the first waveguide layer along the direction vertical to the substrate, and a silicon dioxide isolation layer is arranged between the two waveguide layers. The metal layer is positioned on the surface of the lithium niobate waveguide slab layer. Light enters a grating coupler of a silicon layer from an optical fiber, is coupled into the LN layer through an interlayer coupler formed by a silicon tip-LN ridge type straight waveguide, is split by 1 x 2MMI of the LN layer, and enters a CPW modulation area. After the light is modulated, the light is combined by 1 x 2MMI, and then is coupled into a silicon layer by a lithium niobate/silicon tip interlayer coupler, and is coupled to an optical fiber by a silicon grating.

As shown in fig. 13, the preparation method comprises the following steps:

etching a silicon layer on an SOI wafer to prepare a grating coupler, depositing a silicon oxide cladding layer and polishing; bonding LNOI, polishing the lithium niobate thin film; etching a ridge waveguide pattern and 1 x 2MMI in the LN layer by using an EBL method; and preparing the metal electrode on the lithium niobate layer by an ultraviolet lithography method.

Through simulation optimization, the TE mode is realized under 1550nm wavelength, the electro-optic bandwidth exceeding 200GHz, and the product of half-wave voltage length is 2.27 Vcm. Fig. 3 shows the calculated voltage length product of the device as a function of the lithium niobate waveguide etching depth htib and the electrode spacing gap, and the asterisks correspond to the dimensions selected in the design. Fig. 4 is a simulation result of the variation of the metal absorption loss with the electrode gap and the lithium niobate waveguide etching depth hcib. Fig. 5 and fig. 6 show simulation results of the high-frequency characteristics S11 and S21 of the device, where S11 is less than 20dB, and the fact that the designed device realizes good impedance matching and the fact that the 3dB electro-optic response bandwidth of the designed device exceeds 200GHz is predicted by the corresponding frequency when S21 is attenuated to 6.4 dB.

The simulation optimizes the structure of the related passive device, and comprises the following steps: 1. a silicon grating coupler with an insertion loss of 3.47dB, which simulates the change in transmission efficiency with wavelength, is shown in fig. 12. 2. An interlayer coupler with an insertion loss of 0.03dB is shown in a simulation mode field diagram as shown in fig. 9, transmission efficiency as shown in fig. 10, and the change of the insertion loss along with the dislocation process error within 300nm as shown in fig. 11. 3. 1 x 2MMI with insertion loss of 0.22dB, simulation mode field diagram shown in figure 7 and single-ended output transmission efficiency shown in figure 8.

Claims (4)

1. The utility model provides a lithium niobate silicon mixes integrated electro-optical modulator based on MZ structure which characterized in that: the semiconductor device comprises a substrate, a silicon waveguide layer, an isolation layer, a lithium niobate layer and a metal layer from bottom to top; the lithium niobate layer is composed of a ridge waveguide structure of a bottom slab and an upper rib.

2. An electro-optic modulator as claimed in claim 1, wherein: and the silicon oxide isolation layer is arranged above the silicon waveguide layer along the direction vertical to the substrate, and a silicon oxide isolation layer is arranged between the two waveguide layers.

3. An electro-optic modulator as claimed in claim 1, wherein: the metal layer is positioned on the surface of the lithium niobate layer slide layer.

4. A preparation method of a lithium silicon niobate hybrid integrated electro-optic modulator based on an MZ structure comprises the following steps:

etching a silicon layer on an SOI wafer to prepare a grating coupler, depositing a silicon oxide cladding layer and polishing; bonding LNOI, polishing the lithium niobate thin film; etching a ridge waveguide pattern and 1 x 2MMI in the LN layer by using an EBL method; and preparing the metal electrode on the lithium niobate layer by an ultraviolet lithography method.