CN111399118A

CN111399118A - Integrated polarization beam splitter based on thin-film lithium niobate waveguide

Info

Publication number: CN111399118A
Application number: CN202010105406.1A
Authority: CN
Inventors: 时尧成; 许弘楠
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-02-20
Filing date: 2020-02-20
Publication date: 2020-07-10
Anticipated expiration: 2040-02-20
Also published as: CN111399118B

Abstract

The invention discloses an integrated polarization beam splitter based on a thin-film lithium niobate waveguide, which is formed by sequentially cascading a 1 × 2 multi-mode interference coupler, a multi-section phase shifter and a 2 × 2 multi-mode interference coupler to form a Mach-Zehnder interference coupler structure, wherein the 1 × 2 multi-mode interference coupler is formed by a first tapered waveguide, a second tapered waveguide, a third tapered waveguide and a multi-mode waveguide, the 2 × 2 multi-mode interference coupler is formed by a first tapered waveguide, a second tapered waveguide, a third tapered waveguide, a fourth tapered waveguide and a multi-mode waveguide, the multi-section phase shifter is formed by a first interference arm and a second interference arm, the first interference arm is formed by a first connecting waveguide, a first phase shifting waveguide, a second connecting waveguide, a second phase shifting waveguide and a third connecting waveguide, the second phase shifting waveguide and the third connecting waveguide are sequentially connected, the second interference arm is formed by a fourth connecting waveguide, a third phase shifting waveguide, a fifth connecting waveguide, a fourth phase shifting waveguide and a sixth connecting waveguide.

Description

Integrated polarization beam splitter based on thin-film lithium niobate waveguide

Technical Field

The invention particularly relates to an integrated polarization beam splitter based on a thin-film lithium niobate waveguide, which is suitable for application occasions requiring polarization beam splitting, polarization beam combining and polarization filtering in optical fiber communication, on-chip optical communication, optical sensing systems and quantum optical systems.

Background

Lithium niobate has a strong electro-optic effect, a strong nonlinear effect and good thermal stability, and is widely applied to integrated optical devices such as electro-optic modulators, wavelength converters and the like. In recent years, with the maturity of thin-film lithium niobate processing and preparation processes, ultra-small integrated optical devices based on thin-film lithium niobate waveguides are rapidly developed. Because the thin film lithium niobate waveguide has higher refractive index difference and smaller spot size, the waveguide has stronger birefringence, so that most of integrated optical devices based on the thin film lithium niobate waveguide have stronger polarization correlation and can only work under the condition of single polarization. Therefore, it is necessary to separate different polarization states in the input signal by using a polarization beam splitter, or to filter out polarization states other than the working polarization. In addition, the thin film lithium niobate waveguide has better polarization maintaining characteristic, and crosstalk is not generated in the transmission process of different polarization states. Therefore, for an optical communication system, signals can be loaded on different polarization states, and the signals are combined by using a polarization beam splitter, so that the capacity of a channel is doubled without increasing wavelength channels. For the optical sensing system, because the sensitivities of different polarization states to the change of the environmental parameters are different, the polarization beam splitter can be used for monitoring a plurality of environmental parameters simultaneously. For quantum optical systems, quantum entanglement between different polarization states can be achieved using a polarizing beam splitter.

At present, the design idea of the integrated polarization beam splitter is mostly based on an asymmetric coupler structure, and one polarization state meets the phase matching condition by adjusting the structural parameters of the coupler, and the other polarization state is mismatched in phase, so that different polarization states are separated. However, lithium niobate is an anisotropic material and typically requires the use of x-cut thin films to ensure maximum electro-optic modulation efficiency and wavelength conversion efficiency, resulting in thin film lithium niobate waveguides of different transmission directions typically having different effective refractive indices, which greatly increases the design difficulty of asymmetric couplers. Therefore, a new technical solution is needed for realizing an integrated polarization beam splitter based on a thin film lithium niobate waveguide.

Disclosure of Invention

The invention aims to provide an integrated polarization beam splitter based on a thin-film lithium niobate waveguide. By cascading a polarization insensitive multimode interference coupler and a multi-section phase shifter and regulating and controlling the transmission direction and the transmission length of a thin film lithium niobate waveguide in the phase shifter, the independent control of the transmission phase of a TE fundamental mode and a TM fundamental mode in the phase shifter is realized, and the TE polarization state and the TM polarization state in input light are further separated.

The integrated polarization beam splitter based on the thin-film lithium niobate waveguide is characterized in that a Mach-Zehnder interferometer structure is formed by sequentially cascading a 1 × 2 multi-mode interference coupler (I), a multi-section phase shifter (II) and a 2 × 2 multi-mode interference coupler (III), wherein an input waveguide (0) is connected with a first tapered waveguide (31) in the 1 × 2 multi-mode interference coupler (I), a second tapered waveguide (32) and a third tapered waveguide (33) in the 1 × 2 multi-mode interference coupler (I) are respectively connected with a first tapered waveguide (11) and a fourth tapered waveguide (14) in the multi-section phase shifter (II), a third tapered waveguide (13) and a sixth tapered waveguide (16) in the multi-section phase shifter (II) are respectively connected with a first tapered waveguide (41) and a second tapered waveguide (42) in the 2 × 2 multi-mode interference coupler (III), a second tapered waveguide (13) and a fourth tapered waveguide (42) in the 2 × 2 multi-mode interference coupler (III), a third tapered waveguide (43), a fourth tapered waveguide (44) and a fourth tapered waveguide (23) and a fifth tapered waveguide (15) in the multi-phase shift coupler (II), a third tapered waveguide (23) and a fifth tapered waveguide (15) are respectively connected with a second tapered waveguide (15) and a third tapered waveguide (15) and a fourth tapered waveguide (15) in the multi-phase shift waveguide (11) in the multi-phase shift waveguide (15) in the multi-phase shift interference coupler (II), and a fifth tapered waveguide (15) in the multi-phase shift waveguide (II) in the multi-phase shift waveguide (15) in the multi-mode interference coupler (II) in the multi-.

In the present invention, after input light is transmitted from an input waveguide (0) to a polarization insensitive 1 × 2 multimode interference coupler (I), the input light is divided into two beams with the same intensity and phase, and enters a first interference arm (II-1) and a second interference arm (II-2), wherein an optical signal input into the first interference arm (II-1) sequentially passes through a first connecting waveguide (11), a first phase-shifted waveguide (21), a second connecting waveguide (12), a second phase-shifted waveguide (22), a third connecting waveguide (13), and enters a 2 × 2 multimode interference coupler (III) through a first tapered waveguide (41), an optical signal input into the second interference arm (II-2) sequentially passes through a fourth connecting waveguide (14), a third phase-shifted waveguide (23), a fifth connecting waveguide (15), a fourth phase-shifted waveguide (24), a sixth connecting waveguide (16), and enters a 2 multimode interference coupler (II) through a second tapered waveguide (42), the optical signal after the optical signal is transmitted through the first phase-shifted waveguide (21) and the second phase-shifted waveguide (24), the fundamental mode-shifted waveguide (II-2) is transmitted through the second fundamental mode-shifted waveguide (z) after the input light is transmitted through the fundamental mode-2), the fundamental mode-shifted waveguide (z) and the fundamental mode-shifted waveguide (z) so that the optical signal is transmitted through the fundamental-2 fundamental-2, the fundamental-shifted waveguide (24), the fundamental-mode-phase-shifted waveguide (24), the fundamental-shifted waveguide (II-shifted waveguide (III) after the optical waveguide (90) and the fundamental-waveguide (24), the optical-fundamental-waveguide (24) and the optical-fundamental.

The invention has the beneficial effects that:

(1) the transmission phase of the TE-based mode and the TM-based mode in the multi-section phase shifter can be independently controlled by regulating and controlling the transmission direction and the transmission length of the thin-film lithium niobate waveguide, so that the complete separation of the TE polarization state and the TM polarization state is realized.

(2) Has the advantages of simple structure, simple design and convenient processing.

(3) The waveguide has the excellent performances of high extinction ratio (more than 40dB), low loss (less than 0.9dB), large working bandwidth (more than 200nm), large processing tolerance (waveguide width tolerance of-10 nm to +10nm) and the like.

Drawings

FIG. 1 shows a schematic diagram of an integrated polarization beam splitter based on a thin-film lithium niobate waveguide according to the present invention;

in the figure, I, 1 × 2 multimode interference coupler, II, multi-section phase shifter, III, 2 × 2 multimode interference coupler, II-1, first interference arm, II-2, second interference arm, 0, input waveguide, 1, first output waveguide, 2, second output waveguide, 11, first connecting waveguide, 12, second connecting waveguide, 13, third connecting waveguide, 14, fourth connecting waveguide, 15, fifth connecting waveguide, 16, sixth connecting waveguide, 21, first phase shifting waveguide, 22, second phase shifting waveguide, 23, third phase shifting waveguide, 24 and fourth phase shifting waveguide.

FIG. 2 is a schematic diagram of the structure of 1 × 2 multimode interference coupler (I);

in the figure: 31. a first tapered waveguide, 32, a second tapered waveguide, 33, a third tapered waveguide, 34, a multimode waveguide.

FIG. 3 is a schematic structural diagram of a 2 × 2 multimode interference coupler (III);

in the figure: 41. a first tapered waveguide, 42, a second tapered waveguide, 43, a third tapered waveguide, 44, a fourth tapered waveguide, 45, a multimode waveguide.

FIG. 4 is a schematic cross-sectional view of a single-mode lithium niobate waveguide;

in the figure: 51. lithium niobate core layer, 52, silicon dioxide substrate layer and upper cladding layer

Fig. 5 is a graph showing a simulation of transmittance spectrum for each output port.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and the implementation examples of the integrated polarization beam splitter based on the thin film lithium niobate waveguide.

The method comprises the steps of selecting a thin-film lithium Niobate waveguide based On a lithium Niobate Insulator (L ituum-Niobate On Insulator, L NOI) material, wherein a core layer is made of the lithium Niobate material and has the thickness of 700nm, a substrate layer is made of a silicon dioxide material and has the thickness of 2 mu m, an upper cladding layer is made of the silicon dioxide material and has the thickness of 2 mu m, in the embodiment, the side wall inclination angles of all waveguide structures are 70 degrees, and the widths of all single-mode thin-film lithium Niobate waveguides in the multi-stage phase shifter (II) are 300 nm.

The transmission directions of the input waveguide (0), the first output waveguide (1) and the second output waveguide (2) are all the y direction. The first phase shift waveguide (21) and the third phase shift waveguide (23) are both composed of a curved waveguide and a straight waveguide for y-direction transmission. The second phase shift waveguide (22) and the fourth phase shift waveguide (24) are both composed of a curved waveguide and a straight waveguide for z-direction transmission. The length difference between the first phase-shifting waveguide (21) and the third phase-shifting waveguide (23) is-13.79 μm, and the length difference between the second phase-shifting waveguide (22) and the fourth phase-shifting waveguide (24) is +13.64 μm. The radius of all the curved waveguides in the first interference arm (II-1) and the second interference arm (II-2) is 25 μm.

The opening widths of a first tapered waveguide (31), a second tapered waveguide (32) and a third tapered waveguide (33) in the 1 × 2 multimode interference coupler (I) are all 700nm, the opening widths of a multimode waveguide (34) in the 2 mu m.1 × 2 multimode interference coupler (I) are all 4.5 mu m, the opening widths of a first tapered waveguide (41), a second tapered waveguide (42), a third tapered waveguide (43) and a fourth tapered waveguide (44) in the 9.3 mu m.2 × 2 multimode interference coupler (III) are all 700nm, the opening widths of a multimode waveguide (45) in the 2 mu m.2 × 2 multimode interference coupler (III) are all 4.5 mu m, and the length of the multimode waveguide is 20.4 mu m.

The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are within the spirit of the invention and the scope of the appended claims.

Claims

1. An integrated polarization beam splitter based on a thin-film lithium niobate waveguide is characterized by being formed by combining a first 1 × 2 multi-mode interference coupler (I), a multi-section phase shifter (II) and a 2 × 2 multi-mode interference coupler (III) which are sequentially cascaded to form a Mach-Zehnder interference coupler structure, wherein the 1 × 2 multi-mode interference coupler (I) is formed by a first tapered waveguide (31), a second tapered waveguide (32), a third tapered waveguide (33) and a multi-mode waveguide (34), the first tapered waveguide (31) in the 1 × 2 multi-mode interference coupler (I) is connected with an input waveguide (0), the 2 × 2 multi-mode interference coupler (III) is formed by a first tapered waveguide (41), a second tapered waveguide (42), a third tapered waveguide (43), a fourth tapered waveguide (44) and a multi-mode waveguide (45), the third tapered waveguide (43) and a fourth tapered waveguide (44) in the 2 × 2 multi-mode interference coupler (III) are respectively connected with a first tapered waveguide (44), a fourth tapered waveguide (11), a second tapered waveguide (II) and a third tapered waveguide (13), a fourth tapered waveguide (13), a third tapered waveguide (13), a fourth tapered waveguide (II), a fourth tapered waveguide (13), a third tapered waveguide (13), a fifth tapered waveguide (13), a fourth tapered waveguide (II), a fifth tapered waveguide (15) and a sixth tapered waveguide (15) are sequentially connected with a third tapered waveguide (13), a second tapered waveguide (13), a third tapered waveguide (11-phase shifting waveguide (13) and a fourth tapered waveguide (13) and a second waveguide (13).

2. The integrated polarization beam splitter based on the thin film lithium niobate waveguide of claim 1 is characterized in that after input light is transmitted to the polarization insensitive 1 × 2 multimode interference coupler (I) through the input waveguide (0), the input light is split into two beams with the same intensity and phase, and the two beams enter the first interference arm (II-1) and the second interference arm (II-2), wherein an optical signal input into the first interference arm (II-1) sequentially enters the first connection waveguide (11), the first phase shift waveguide (21), the second connection waveguide (12), the second phase shift waveguide (22), the third connection waveguide (13) through the first tapered waveguide (41) and enters the 2 × 2 multimode interference coupler (III), an optical signal input into the second interference arm (II-2) sequentially enters the fourth connection waveguide (14), the third phase shift waveguide (23), the fifth connection waveguide (15), the fourth phase shift waveguide (24), the sixth connection waveguide (16) through the fourth connection waveguide (14), the third phase shift waveguide (23), the fourth connection waveguide (24) and the sixth connection waveguide (16), and the optical signal enters the multimode interference coupler (TE-2) through the second phase shifter (II-2) after the fundamental mode, the fundamental mode of the second interference waveguide (TE-2), the second interference waveguide (21) is transmitted through the fundamental mode, the fundamental mode of the optical waveguide (TE-2), the optical waveguide (90) and the fundamental mode of the optical waveguide (TE-2), the fundamental waveguide (III) are all controlled by the fundamental mode, the fundamental mode of the fundamental optical waveguide (TE-90) and the fundamental mode, the fundamental optical waveguide (TE-2), the fundamental optical waveguide (21) after the fundamental optical waveguide (90) and the fundamental optical waveguide, the fundamental optical waveguide (III) are transmitted through the fundamental optical waveguide, the fundamental optical waveguide (90) and the fundamental optical waveguide (21), the fundamental optical waveguide (III) are transmitted in the fundamental optical waveguide, the fundamental optical waveguide (TE-fundamental optical waveguide (21) and the fundamental optical waveguide, the fundamental optical waveguide (III) and the fundamental optical waveguide, the.

3. The integrated polarization beam splitter based on the thin-film lithium niobate waveguide of claim 1 or 2, wherein the first phase-shifting waveguide (21) and the third phase-shifting waveguide (23) are both formed by a curved waveguide and a straight waveguide for y-direction transmission; the second phase shift waveguide (22) and the fourth phase shift waveguide (24) are both composed of a curved waveguide and a straight waveguide for z-direction transmission.

4. The integrated polarization beam splitter based on thin-film lithium niobate waveguide of claim 3, wherein the length difference of the first phase-shifting waveguide (21) and the third phase-shifting waveguide (23) and the length difference of the second phase-shifting waveguide (22) and the fourth phase-shifting waveguide (24) can ensure that the TE fundamental mode generates a phase difference of-90 ° and the TM fundamental mode generates a phase difference of +90 °.

5. The integrated polarization beam splitter based on thin film lithium niobate waveguide of claim 3, wherein the TE-based mode inputted in the input waveguide (0) can be transmitted to the first output waveguide (1).

6. The integrated polarization beam splitter based on thin film lithium niobate waveguide of claim 1, wherein the TM fundamental mode inputted in the input waveguide (0) is capable of being transmitted to the second output waveguide (2).