CN214067429U - Waveguide array based on lithium niobate - Google Patents

Abstract

The utility model discloses a waveguide array based on lithium niobate, include: a silicon-based substrate; a silicon dioxide buffer layer deposited on the silicon-based substrate; a core layer on the silica buffer layer; a silica cladding layer located on and covering the core layer; wherein the core layer comprises: the two lithium niobate wide waveguides are bilaterally symmetrical, and the first lithium niobate grating and the second lithium niobate grating are arranged on the same plane; the first lithium niobate grating and the second lithium niobate grating are positioned between the two lithium niobate wide waveguides; the first lithium niobate grating is positioned on the left side of the second lithium niobate grating. The utility model discloses can realize that crosstalk between the suppression waveguide of 1550nm optical band realizes high transmissivity, low insertion loss.

Description

Waveguide array based on lithium niobate

Technical Field

The utility model relates to a waveguide array based on lithium niobate.

Background

Integrated on-chip Optical Phased Arrays (OPAs) are one of the key components of light detection and ranging (Lidar), and are used in many applications, such as unmanned, aerial mapping, and optical communications, due to their solid-state beam steering capabilities.

With the rapid growth of network traffic, low optical loss, low driving voltage and compact space occupation of OPAs are important. The traditional silicon optical phased array adopts thermo-optic modulation, so that the energy consumption is high and the requirement on processing precision is high. In contrast, thin film Lithium Niobate (LN) is one of the best materials for achieving high performance OPA due to its high electro-optic efficiency and low optical loss. In addition, the lithium niobate material has large second-order nonlinear optical coefficient, can adopt an electro-optic modulation technology, has the characteristics of high speed, low energy consumption and the like, and has relatively low material cost, so that the integrated OPA based on the lithium niobate material has obvious advantages in the aspect of high-speed modulation.

For the conventional lithium niobate optical phased array, in order to realize the large-angle wide-field light beam scanning range, the distance between adjacent waveguides is very small, and due to the low contrast between the core layer and the cladding material, the adjacent waveguides are very easy to couple, the crosstalk is large, and the independent phase or amplitude control is difficult to carry out. However, setting the waveguide pitch to 3-4 μm to mitigate crosstalk can make the beam scanning angle range limited. There is therefore a strong compromise between the angle of deflection of the beam and the spacing between adjacent waveguides. For small pitch OPA, cross talk is suppressed by reducing the transmission length, the size of which is of no value for commercial applications. Therefore, research on the OPA with low crosstalk is of great value on the premise of narrow spacing between adjacent waveguides and large transmission length.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a waveguide array based on lithium niobate can realize to crosstalk between 1550nm optical band suppression waveguide, realizes high transmissivity, low insertion loss.

The technical scheme for realizing the purpose is as follows:

a lithium niobate-based waveguide array, comprising:

a silicon-based substrate;

a silicon dioxide buffer layer deposited on the silicon-based substrate;

a core layer on the silica buffer layer; and

a silica cladding layer located on and covering the core layer;

wherein the core layer comprises: the two lithium niobate wide waveguides are bilaterally symmetrical, and the first lithium niobate grating and the second lithium niobate grating are arranged on the same plane;

the first lithium niobate grating and the second lithium niobate grating are positioned between the two lithium niobate wide waveguides; the first lithium niobate grating is positioned on the left side of the second lithium niobate grating.

Preferably, the lithium niobate wide waveguide is a straight waveguide, the width is 0.5 μm, the height is 0.3 μm, and the gap between the two lithium niobate wide waveguides is 1.46 μm.

Preferably, the core layer further comprises: and the lithium niobate thin film is positioned on the silicon dioxide buffer layer and positioned below the lithium niobate wide waveguide, the first lithium niobate grating and the second lithium niobate grating, and the thickness of the lithium niobate thin film is 0.1 mu m.

Preferably, the period of the first lithium niobate grating is 0.35-0.45 μm, the duty ratio is 0.85-0.95, the width is 0.24-0.28 μm, the grating number is 250, and the wide waveguide distance between the first lithium niobate grating and the lithium niobate on the left side is 0-0.05 μm;

the period of the second lithium niobate grating is 0.8-0.9 μm, the duty ratio is 0.15-0.25, the width is 0.05-0.15 μm, the grating number is 150, and the wide waveguide distance between the second lithium niobate grating and the lithium niobate on the right side is 0.4-0.45 μm;

the distance between the first lithium niobate grating and the second lithium niobate grating is 0.14-0.18 μm.

Preferably, the device further comprises a metal electrode attached to the silica cladding.

The utility model has the advantages that: 1) the utility model discloses compact structure, preparation technology and semiconductor processing technology are compatible. The lithium niobate material has wide transparent window, low absorption loss, high nonlinear optical coefficient, excellent electrooptical modulation characteristic, high modulation efficiency and low energy consumption, and can be produced in large batch and at low cost; 2) the device can be expanded into a phased array with 8 waveguide arrangements, millimeter-scale transmission length is realized, crosstalk is low, and the device is significant for practical application; 3) the utility model can realize the crosstalk among the inhibiting waveguides in the 1550nm optical band, realize high transmittance and low insertion loss, and has important application prospect in the fields of optical phased array, optical communication and the like; 4) the utility model keeps lower insertion loss and crosstalk within the range of 1520 + 1600nm wavelength, and the bandwidth reaches 80 nm; 5) an angle of around ± 45 ° can be achieved in terms of beam deflection.

Drawings

Fig. 1 is a cross-sectional view of a lithium niobate-based waveguide array of the present invention;

FIG. 2 is a structural diagram of the core layer of the present invention;

fig. 3 is a field distribution diagram of the present invention, which is based on the finite difference time domain method and uses simulation software to simulate the TE mode light incidence and the light beam transmission only between the lithium niobate wide waveguides when the central wavelength is 1550 nm;

fig. 4 is a field distribution diagram of the present invention based on the finite difference time domain method, which uses simulation software to simulate the incident of TE mode light and the transmission of light between the lithium niobate array waveguides when the central wavelength is 1550 nm;

fig. 5 is a field distribution diagram of the utility model, which is based on the finite difference time domain method and uses simulation software to simulate the incident TE mode light and the transmission of light beam between eight lithium niobate wide waveguide arrangements when the central wavelength is 1550 nm;

fig. 6 is a field distribution diagram of the present invention based on the finite difference time domain method, which uses simulation software to simulate the incident TE mode light and the light transmission between eight lithium niobate array waveguides when the central wavelength is 1550 nm;

FIG. 7 is a far field light beam scanning range diagram of the present invention based on finite difference time domain method using simulation software at 1550nm wavelength;

fig. 8 is a manufacturing flow chart of the lithium niobate-based waveguide array according to the present invention.

Detailed Description

The present invention will be further explained with reference to the accompanying drawings.

Referring to fig. 1-2, the present invention relates to a lithium niobate-based waveguide array, comprising: a silicon-based substrate 1, a silica buffer layer 2, a core layer 3 and a silica cladding layer 4.

A buffer layer 2 of silicon dioxide is deposited on the silicon-based substrate 1. The core layer 3 is located on the silica buffer layer 2. The silica cladding layer 4 is located on the core layer 3 and covers the core layer 3. The core layer 3 includes: two bilaterally symmetrical lithium niobate wide waveguides 31, a first lithium niobate grating 32 and a second lithium niobate grating 33.

The first lithium niobate grating 32 and the second lithium niobate grating 33 are located between the two lithium niobate wide waveguides 31; the first lithium niobate grating 32 is located to the left of the second lithium niobate grating 33.

The utility model discloses a wavelength is when 1550nm, and the direct waveguide arrival coupling waveguide of the lithium niobate of TE polarized light source through the design (two wide waveguides of lithium niobate 31), through adding grating structure (first lithium niobate grating 32 and second lithium niobate grating 33) between it, the coupling between suppression waveguide realizes reducing the function of crosstalking between the array waveguide.

Through experiments and multiple times of verification, in the embodiment, the lithium niobate wide waveguide 31 is a straight waveguide, the width is 0.5 μm, the height is 0.3 μm, and the gap between two lithium niobate wide waveguides 31 is 1.46 μm. The length of the lithium niobate wide waveguide 31 is 100 μm.

The core layer 3 further includes: and a lithium niobate thin film having a thickness of 0.1 μm, which is located on the silica buffer layer 2 and below the lithium niobate wide waveguide 31, the first lithium niobate grating 32, and the second lithium niobate grating 33.

The period of the first lithium niobate grating 32 is 0.4 μm, the duty ratio is 0.9, the width is 0.26 μm, the grating number is 250, and the distance between the first lithium niobate grating 32 and the left lithium niobate wide waveguide 31 is 0 μm; the period of the second lithium niobate grating 33 is 0.85 μm, the duty ratio is 0.2, the width is 0.1 μm, the grating number is 150, and the distance from the second lithium niobate grating 33 to the lithium niobate wide waveguide 31 on the right side is 0.44 μm; the pitch between the first lithium niobate grating 32 and the second lithium niobate grating 33 is 0.16 μm. Two grating structures with different parameters are added, so that larger mode mismatch is generated between the waveguides, and the coupling between the waveguides is inhibited. A metal electrode 5 is applied to the silica cladding 4.

As shown in fig. 8, the method for manufacturing the lithium niobate-based waveguide array includes the following steps:

step one, depositing a silicon dioxide buffer layer 2 on a silicon-based substrate 1, and depositing a lithium niobate layer on the silicon dioxide buffer layer 2; the thickness of the silicon dioxide buffer layer 2 may be set to 2 μm. The thickness of the lithium niobate layer was set to 400 nm.

Adding photoresist (photoresist) on the lithium niobate layer, then performing Electron Beam Lithography (EBL) on a mask, then bombarding the lithium niobate layer by argon plasma (Ar +) to perform plasma etching (RIE) and monitoring the etching depth in real time to form a core layer 3;

step three, carrying out wet chemical process (RCA) cleaning on the surface of the core layer 3 to remove impurities on the surface of the lithium niobate;

depositing a silicon dioxide cladding layer 4 on the core layer 3 by using a Plasma Enhanced Chemical Vapor Deposition (PECVD) method;

and fifthly, photoetching a mask, and attaching the metal electrode 5 to the silicon dioxide cladding 4 by applying a corresponding photoresist drying process and a metal stripping technology.

Fig. 3 is the utility model discloses use simulation software simulation when central wavelength is 1550nm based on the finite difference method of time domain, TE mode light incidence, the field distribution diagram of optical transmission between the lithium niobate wide waveguide.

Fig. 4 shows that the utility model discloses use emulation software simulation when central wavelength is 1550nm based on the finite difference method of time domain, TE mode light incidence, lithium niobate array waveguide between optical transmission's field distribution diagram.

Fig. 5 shows a field distribution diagram of the present invention, which is based on the finite difference time domain method and uses simulation software to simulate the incident TE mode light when the central wavelength is 1550nm, and the light beam is transmitted only between the eight lithium niobate wide waveguide arrangements.

Fig. 6 shows a field distribution diagram of the present invention, which is based on the finite difference time domain method and uses simulation software to simulate the incident TE mode light and the light transmitted between eight lithium niobate array waveguides when the central wavelength is 1550 nm.

Fig. 7 is a diagram of a far-field light beam scanning range of the present invention at 1550nm wavelength based on the finite difference time domain method using simulation software, which can realize an angle of ± 45 ° in terms of light beam deflection.

The utility model discloses in, adjacent lithium niobate is wide to be led the interval and is less than a wavelength. It contains only two basic repeating elements, namely a pair of substantially phase-mismatched lithium niobate wide waveguides, of exactly the same width, but two asymmetrically placed lithium niobate gratings in the gap. When the two lithium niobate gratings are correctly positioned, the change of the mode refractive index can cause strong phase mismatch, thereby inhibiting power transmission between the waveguides. The asymmetric placement of these lithium niobate gratings also helps to extend the dual waveguide design of this nanostructure, forming a low crosstalk lithium niobate waveguide array by alternately flipping the position of two lithium niobate gratings in the waveguide array gap. The theoretical study of the present invention shows that for TE (transverse electric mode) polarized light, this array exhibits-20.96 dB peak crosstalk and-0.3 dB Insertion Loss (IL) between nearest neighbor waveguides at a wavelength of 1550nm when the length is 200 μm. Furthermore, the utility model discloses can realize the angle of 45 in the aspect of the light beam deflects. This opens up opportunities for solid-state lidar applications that achieve wide field-of-view scanning ranges.

The above embodiments are provided only for the purpose of illustration, not for the limitation of the present invention, and those skilled in the relevant art can make various changes or modifications without departing from the spirit and scope of the present invention, therefore, all equivalent technical solutions should also belong to the scope of the present invention, and should be defined by the claims.

Claims (5)

1. A lithium niobate-based waveguide array, comprising:

a silicon-based substrate;

a silicon dioxide buffer layer deposited on the silicon-based substrate;

a core layer on the silica buffer layer; and

a silica cladding layer located on and covering the core layer;

wherein the core layer comprises: the two lithium niobate wide waveguides are bilaterally symmetrical, and the first lithium niobate grating and the second lithium niobate grating are arranged on the same plane;

the first lithium niobate grating and the second lithium niobate grating are positioned between the two lithium niobate wide waveguides; the first lithium niobate grating is positioned on the left side of the second lithium niobate grating.

2. The lithium niobate-based waveguide array of claim 1, wherein the lithium niobate wide waveguides are straight waveguides having a width of 0.5 μ ι η and a height of 0.3 μ ι η, and a gap of 1.46 μ ι η between two of the lithium niobate wide waveguides.

3. The lithium niobate-based waveguide array of claim 1, wherein the core layer further comprises: and the lithium niobate thin film is positioned on the silicon dioxide buffer layer and positioned below the lithium niobate wide waveguide, the first lithium niobate grating and the second lithium niobate grating, and the thickness of the lithium niobate thin film is 0.1 mu m.

4. The lithium niobate-based waveguide array of claim 1, wherein the first lithium niobate grating has a period of 0.35 to 0.45 μ ι η, a duty cycle of 0.85 to 0.95, a width of 0.24 to 0.28 μ ι η, a grating number of 250, and a wide waveguide spacing from the left lithium niobate of 0 to 0.05 μ ι η;

the period of the second lithium niobate grating is 0.8-0.9 μm, the duty ratio is 0.15-0.25, the width is 0.05-0.15 μm, the grating number is 150, and the wide waveguide distance between the second lithium niobate grating and the lithium niobate on the right side is 0.4-0.45 μm;

the distance between the first lithium niobate grating and the second lithium niobate grating is 0.14-0.18 μm.

5. The lithium niobate-based waveguide array of claim 1, further comprising a metal electrode attached to the silica cladding.

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