Floquet-based silicon-based integrated compact polarization beam splitter

Abstract

A Floquet-based silicon-based integrated compact polarization beam splitter comprises a silicon layer, a silicon oxide layer, a pair of coupling waveguides located on the silicon oxide layer, input ports corresponding to the coupling waveguides and output ports corresponding to the coupling waveguides, the silicon layer, the silicon oxide layer, the coupling waveguides, the input ports and the output ports are sequentially arranged from bottom to top, any input port inputs a TE mode or a TM mode, a first output port outputs the TM mode, and a second output port outputs the TE mode. Through periodical modulation of the waveguide width, the suppression of TE mode power exchange and the maximization of TM mode power exchange can be realized by regulating and controlling the phase between the coupling waveguides within the coupling length of only 6 microns.

Description

Technical Field

[0001] The present invention relates to a technology in the field of photon communication, specifically a silicon-based integrated compact polarization beam splitter based on Floquet. Background Art

[0002] Traditional silicon-based polarization beam splitters (PBS) generally adopt multimode interference (MMI), directional coupling (DC) structures or subwavelength (SWG) structures, but face various bottlenecks in practical applications: First, in order to meet the phase matching condition, the multimode interference and directional coupling schemes need to design a coupling length exceeding 10 micrometers, resulting in the device footprint being difficult to meet the requirements of high-density photon integration; Second, although the existing subwavelength structures can regulate the mode refractive index through the equivalent medium theory, they are highly sensitive to process errors and rely on high-precision electron beam lithography technology. These defects severely restrict the application of silicon-based PBS in large-scale photon integrated circuits such as data center interconnection and coherent optical communication. Summary of the Invention

[0003] Aiming at the above deficiencies of the existing technology, the present invention proposes a silicon-based integrated compact polarization beam splitter based on Floquet. Through the periodic modulation of the waveguide width, within a coupling length of only 6 micrometers, by regulating the phase between the coupled waveguides, the suppression of TE mode power exchange and the maximization of TM mode power exchange can be achieved.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a silicon-based integrated compact polarization beam splitter based on Floquet, including: a silicon layer, a silicon oxide layer, and a pair of coupled waveguides located on the silicon oxide layer, and their corresponding input ports and output ports, which are arranged in sequence from bottom to top, wherein: any input port inputs TE or TM mode, the first output port outputs TM mode, and the second output port outputs TE mode.

[0006] The width of the coupled waveguides changes according to a sine function while keeping the spacing equal.

[0007] When changing according to the sine function, the initial phases of the two waveguides differ by π.

[0008] The length of the coupled waveguides is 6 micrometers.

[0009] The central operating wavelength of the coupled waveguides is near 1550 nm, and the bandwidth is above 53 nm. Technical Effects

[0010] Floquet theory is a theory based on a periodic potential field. In the present invention, the width of the coupled waveguides varies periodically and can be considered as a Floquet system, similar to a one-dimensional photonic crystal. According to Floquet theory, when the phase difference of the periodic changes between two adjacent waveguides is exactly π, the quasi-energy collapses, and at this time, the energy exchange between the waveguides is suppressed. The present invention realizes the function of polarization beam splitting by designing parameters such as the amplitude and period of the sinusoidal variation of the waveguide width, so that the exchange of the TE mode between the waveguides is suppressed while the exchange of the TM mode is not affected. Compared with the prior art, the present invention further reduces the required coupling length of the device while ensuring a large polarization beam splitting ratio, realizing a compact polarization beam splitter. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the whole of the present invention;

[0012] In the figure: 1 input port, 2 input port, input TE / TM mode, 3 TM mode output port, 4 TE mode output port, 5 TE mode transmission waveguide, width modulation phase is π, 6 silicon oxide layer, 7 silicon layer, 8 TM mode transmission waveguide, width modulation phase is 0;

[0013] Figure 2 is a top view of the coupling region of the present invention;

[0014] Figure 3 is a cross-sectional view of the coupling region of the present invention;

[0015] Figures 4 - 7 is a schematic diagram of the effect of the embodiment;

[0016] Figure 4 is the spectral response of the device when the TE mode is input; Figure 5 is the spectral response of the device when the TM mode is input. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] As Figures 1 - 3 shown, this embodiment relates to a silicon-based integrated compact polarization beam splitter based on Floquet, including: a silicon layer 7, a silicon oxide layer 6 arranged in sequence from bottom to top, and a pair of coupled waveguides on the silicon oxide layer 6, namely a TE mode transmission waveguide 5 and a TM mode transmission waveguide 8 and their corresponding input ports 1, 2 and output ports 3, 4, wherein: any input port inputs a TE or TM mode, the first output port 3 outputs the TM mode, and the second output port 4 outputs the TE mode.

[0018] The distance between the TE mode transmission waveguide 5 and the TM mode transmission waveguide 8 is 705 nm, the width of the waveguide varies according to a sine function, and the initial phases of the two waveguides differ by a π.

[0019] This embodiment relates to a manufacturing method of a silicon-based integrated compact polarization beam splitter based on Floquet, including:

[0020] Step 1: Perform simulation using the finite-difference time-domain (FDTD) method: Based on the silicon-on-insulator (SOI) platform, set the top silicon thickness to 220 nm, the silicon oxide thickness to 3 microns, the overlying layer to air, the waveguide height to 220 nm, the average width to 500 nm, the distance between two waveguides to 705 nm, and the width of the waveguide also varies according to the sine function. By the FDTD method, set the incident light modes to TM and TE modes, and the wavelength range to 1500 - 1600 nm, and the spectral responses of the device in the two modes can be obtained.

[0021] As Figure 4 and Figure 5 shown, in the simulation results, the polarization extinction ratio of the TM mode > 12.5 dB, the polarization extinction ratio of the TE mode > 23.5 dB, and the bandwidths of both can reach 100 nm.

[0022] For the said sine function, its amplitude is 50 nm, the period is 6 microns, and the initial phases of the two waveguides differ by a π.

[0023] Step 2: Based on the standard silicon-on-insulator (SOI) platform, complete the preparation of the grating and waveguide structures through two independent patterning processes, specifically including:

[0024] 2.1 Spin-coat an electron beam photoresist on the surface of the SOI substrate, use electron beam lithography (EBL) technology to define the grating pattern, and transfer the pattern to the silicon layer through dry etching.

[0025] 2.2 Thoroughly remove the residual photoresist and repeat spin-coating. Define the waveguide structure through the secondary EBL process, and form the waveguide geometric profile through dry etching.

[0026] 2.3 Use the plasma ashing process to remove all photoresist residues to ensure the cleanliness of the device surface. This process is compatible with the conventional silicon photonics process, does not require complex masks or special materials, and has good mass production feasibility.

[0027] Step 3: Perform performance testing of the device through an optical link system: In the experiment, use a C-band tunable laser source to construct an optical link system, and connect a polarization controller, the device under test, a 3 dB optical splitter, and an optical power meter in sequence. During the test, optimize the polarization state of the input light by adjusting the polarization controller, make the incident light be in the TE and TM modes respectively, and record their maximum output powers. Utilize the wavelength scanning function of the tunable laser to continuously collect the transmission spectral response of the device within the target band, and then calculate the polarization extinction ratio of the device according to the spectral response.

[0028] Through specific actual experiments, within the bandwidth range of 1507 - 1560 nm (53 nm), the polarization extinction ratios of the TM mode and TE mode of the present invention reach >10 dB and >20 dB respectively, and the corresponding insertion losses reach <2 dB and <1 dB respectively, as shown in Figure 7 , Figure 6 respectively. This result provides a feasible solution for realizing small-sized and more compact photonic integrated circuits.

[0029] Compared with the prior art, the present device exhibits stable beam splitting characteristics within a wide wavelength range. Considering the manufacturing errors of the device and experimental measurement errors, it can be considered that the experiments and simulations are basically consistent, verifying the effectiveness of the Floquet phase modulation mechanism and the reliability of the process implementation.

[0030] Those skilled in the art can make partial adjustments to the above specific implementation in different ways without departing from the principles and purposes of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific implementation. All implementation solutions within its scope are subject to the present invention.

Claims

1. A Floquet-based silicon-integrated compact polarization beam splitter, characterized in that, Comprising: A silicon layer, a silicon oxide layer, and a pair of coupled waveguides located on the silicon oxide layer, as well as corresponding input ports and output ports, which are arranged from bottom to top in sequence. Among them: TE or TM mode is input through any input port, TM mode is output through the first output port, and TE mode is output through the second output port.

2. The Floquet-based silicon-integrated compact polarization beam splitter according to claim 1, characterized in that, The width of the coupled waveguide changes according to a sine function while maintaining equal spacing.

3. The Floquet-based silicon integrated compact polarization beam splitter according to claim 2, characterized in that, For the change according to the sine function, the initial phases of the two waveguides differ by π.

4. The Floquet-based silicon-integrated compact polarization beam splitter according to claim 1 or 2, characterized in that, The length of the coupled waveguide is 6 microns.

5. The Floquet-based silicon-integrated compact polarization beam splitter according to claim 4, wherein The center operating wavelength of the coupled waveguide is near 1550 nm, and the bandwidth is above 53 nm.

6. A method for manufacturing a Floquet-based silicon-integrated compact polarization beam splitter according to any one of claims 1-5, characterized in that, Comprising: Step 1: Perform simulation using the finite-difference time-domain (FDTD) method: Based on the silicon-on-insulator (SOI) platform, set the top silicon thickness to 220 nm, the silicon oxide thickness to 3 microns, the overlying layer to air, the waveguide height to 220 nm, the average width to 500 nm, the distance between the two waveguides to 705 nm, and the width of the waveguide also changes according to a sine function. Through the FDTD method, set the incident light modes to TM and TE modes, and the wavelength range to 1500 - 1600 nm to obtain the spectral response of the device in the two modes. Step 2: Based on the standard silicon-on-insulator (SOI) platform, complete the preparation of the grating and waveguide structure through two independent patterning processes, specifically including: 2.1 Spin-coat an electron beam photoresist on the surface of the SOI substrate, use electron beam lithography (EBL) technology to define the grating pattern, and transfer the pattern to the silicon layer through dry etching. 2.2 Thoroughly remove the residual photoresist and repeat the spin-coating. Define the waveguide structure through the secondary EBL process, and form the waveguide geometric profile through dry etching. 2.3 Use a plasma ashing process to remove all photoresist residues and ensure the cleanliness of the device surface.

7. The method of the Floquet-based silicon-integrated compact polarization beam splitter according to claim 6, characterized in that For the sine function, its amplitude is 50 nm, the period is 6 microns, and the initial phases of the two waveguides differ by a π.

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