CN-116931170-B - Grating end face coupler and design method thereof

CN116931170BCN 116931170 BCN116931170 BCN 116931170BCN-116931170-B

Abstract

The application provides a grating end face coupler and a design method thereof, wherein the grating end face coupler comprises an oxygen burying layer, a lithium niobate layer, a grating layer and an outer cladding layer, wherein the lithium niobate layer is arranged on the oxygen burying layer in a bonding mode, the grating layer is arranged on the lithium niobate layer in a depositing mode, the lithium niobate layer comprises a lithium niobate waveguide layer and a lithium niobate substrate layer, the grating layer comprises a grating waveguide and an output waveguide, and the outer cladding layer is plated on the outer sides of the lithium niobate layer and the grating layer. Therefore, only the material of the grating layer needs to be etched in a large line width and a long period, the process is mature and simple, and the method can be used for solving the technical problems of the existing sub-wavelength grating inverted cone end face coupler that the process is complex and the production cost is too high.

Inventors

XIE ZHENDA
ZHANG CHI
TIAN XIAOHUI
ZHU SHINING
XU ZHICHENG

Assignees

南京大学

Dates

Publication Date: 20260508
Application Date: 20220406

Claims (8)

1. The grating end face coupler is characterized by comprising an oxygen burying layer, a lithium niobate layer, a grating layer and an outer cladding layer, wherein: The grating layer is deposited on the lithium niobate layer, the lithium niobate layer comprises a lithium niobate waveguide layer and a lithium niobate substrate layer, the lithium niobate waveguide layer is arranged on the lithium niobate substrate layer, the grating layer comprises a grating waveguide and an output waveguide, and an outer cladding layer is plated on the outer sides of the lithium niobate layer and the grating layer; The design method of the grating end face coupler comprises the following steps: Determining a first cross-sectional structure and a second cross-sectional structure of a cross section of the grating end-face coupler; determining a first mode and a second mode of the first cross-sectional structure, and a third mode and a fourth mode of the second cross-sectional structure; In the grating region, the first cross-sectional structure and the second cross-sectional structure are arranged to alternately appear, a first equivalent mode is determined according to the first mode and the third mode, and a second equivalent mode is determined according to the second mode and the fourth mode; Determining a first effective refractive index according to the first equivalent mode and a preset duty cycle, and determining a second effective refractive index according to the second equivalent mode and the preset duty cycle, wherein the preset duty cycle is 0.5; Determining a first wave vector according to the first effective refractive index and the wavelength of a preset light source, and determining a second wave vector according to the second effective refractive index and the wavelength; Determining a wave vector mismatch amount according to the first wave vector and the second wave vector; Determining an inverted lattice vector according to the grating period; The design method of the grating end face coupler further comprises the following steps: Judging whether the wave vector mismatch amount is equal to the inverted lattice vector; And if the wave vector mismatch quantity is equal to the inverted lattice vector, the inverted lattice vector compensates the wave vector mismatch quantity, the energy between the first equivalent mode and the second equivalent mode is coupled and converted mutually, the optical field is transferred into the grating layer from the lithium niobate layer, and the mode field is expanded to be matched with the optical fiber mode field.
2. The grating end-face coupler of claim 1, wherein the buried oxide layer is silicon dioxide.
3. The grating end-face coupler of claim 1, wherein the lithium niobate waveguide layer has a trapezoidal structure.
4. The grating end-face coupler of claim 1, wherein the lithium niobate substrate layer is etched from a lithium niobate material.
5. The grating end-face coupler of claim 1, wherein the grating waveguides are etched with a grating of a predetermined pitch according to light of different wavelengths.
6. A grating end-face coupler according to claim 1, wherein the output waveguide is rectangular in overall shape.
7. The grating end-face coupler of claim 1, wherein the grating layer is made of a medium with a refractive index lower than that of the lithium niobate material and higher than that of the outer cladding material, and the grating layer is formed by etching.
8. The grating end-face coupler of claim 1, wherein the outer cladding material is a medium having a refractive index lower than the lithium niobate material and the grating layer material.

Description

Grating end face coupler and design method thereof Technical Field The application relates to the technical field of optical communication devices, in particular to a grating end face coupler and a design method thereof. Background With the rapid development of optical communication technology, the amount of data to be processed and transmitted by an optical communication device is increasing, which requires that the optical communication device has integration, low loss, functional diversity and strong anti-interference capability. In order to meet the above requirements, optical communication devices, especially advanced photonic devices such as high-speed modulators, nonlinear frequency conversion, and frequency comb generation, are often fabricated using lithium niobate (LithiumNiobate on Insulator, LNOI) on an insulator. The optical signal can be well limited to be transmitted in lithium niobate in the LNOI due to a large refractive index difference between an insulator (usually silicon dioxide) and the lithium niobate, and meanwhile, the LNOI is an ideal material for manufacturing an electro-optic modulator due to the high electro-optic coefficient of the lithium niobate, and in addition, the LNOI has the advantages of small bending loss, small transmission loss and compatibility with a complementary metal oxide semiconductor (ComplementaryMetal Oxide Semiconductor, CMOS) process due to the advantages of the lithium niobate in terms of acousto-optic and nonlinearity and the advantages of the LNOI, so that the miniaturization and large-scale integration of a waveguide device can be realized by using the LNOI. According to the current state of the art of optical communications and the advantages of LNOI, it is necessary to make an optical interface based on LNOI featuring low coupling loss between fiber and chip. Currently, optical coupling techniques on lithium niobate films include grating coupling techniques and end-face coupling techniques. The grating coupling technology utilizes the diffraction effect of a periodic grating structure to enable light to be coupled out of the surface of the waveguide through the grating and enter the optical fiber or to be coupled out of the optical fiber and enter the waveguide. The end face coupling technology generally utilizes a conical optical fiber or a lens to focus light spots, and is in butt joint with the end face of the optical waveguide to realize optical coupling, and a coupler positioned at the edge of the optical chip by utilizing the end face coupling technology is an end face coupler. Fig. 1 is a schematic structural diagram of an existing inverse taper end-face coupler for a sub-wavelength grating, based on the characteristics of the grating coupling technology and the end-face coupling technology, a sub-wavelength grating inverse taper structure and a sub-wavelength grating inverse taper end-face coupler are proposed in the prior art, and the sub-wavelength grating inverse taper structure is used for performing alignment on the inverse taper end-face coupler structure to form a sub-wavelength grating. The inverted cone-shaped end face coupler of the sub-wavelength grating reduces the equivalent refractive index of the waveguide by etching the inverted cone-shaped and sub-wavelength grating structure on the lithium niobate crystal, so that the Mode field diameter (Mode FIELDDIAMETER, MFD) of the waveguide is increased, and the waveguide is matched with the small-diameter optical fiber, thereby realizing efficient fiber core coupling. However, the lithium niobate material has great etching difficulty, and the requirements of the inverted cone-shaped and sub-wavelength structures on the photoetching line width and the alignment precision are high, so that the process of the sub-wavelength grating inverted cone-shaped end face coupler is complex, and the production cost is too high. Disclosure of Invention The application provides a grating end face coupler which can be used for solving the technical problem that the existing sub-wavelength grating inverted cone end face coupler is complex in process and high in production cost. In a first aspect, the application provides a grating end-face coupler comprising an oxygen-buried layer, a lithium niobate layer, a grating layer and an outer cladding layer, wherein: The lithium niobate grating structure comprises an oxygen-buried layer, a grating layer, a lithium niobate waveguide layer, an output waveguide layer, an outer cladding layer, a grating layer, an oxygen-buried layer, a lithium niobate layer, an optical grating layer and an optical grating layer, wherein the lithium niobate layer is arranged on the oxygen-buried layer in a bonding mode, the grating layer is arranged on the lithium niobate layer in a depositing mode, the lithium niobate waveguide layer comprises a lithium niobate waveguide layer and a lithium niobate substrate layer, the lithium niobate waveguide layer is arranged on the lithium ni