A bragg grating based non-volatile reconfigurable filter

Abstract

This invention relates to a non-volatile reconfigurable filter based on a Bragg grating. The filter includes an SOI substrate, a waveguide, a phase-shifted Bragg grating structure, a first non-volatile phase change material (PVMT) film, and a second non-volatile PVMT film. The waveguide, containing the phase-shifted Bragg grating structure, is disposed above the SOI substrate. The first PVMT film is disposed in the phase-shifted region above the phase-shifted Bragg grating structure, and the second PVMT film is disposed in the uniform grating region above the phase-shifted Bragg grating structure. The first PVMT film is disposed between the second PVMT films. This filter achieves both constant transmission power with center wavelength shift and constant transmission center wavelength with power tuning while maintaining a transmission loss of only 0.76 dB.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor and optoelectronic integration, and specifically relates to a non-volatile reconfigurable filter based on a Bragg grating. Background Technology

[0002] As the size of silicon-based transistors continues to shrink, current integrated circuit chips are facing bottlenecks in both power consumption and speed. Photonic integrated chips, with their advantages of high speed, high parallelism, and low power consumption, have the potential to become the next-generation hardware platform that breaks through the limitations of traditional integrated circuits. Silicon-based optoelectronics, utilizing the highly developed CMOS manufacturing process in the microelectronics industry, can integrate optical, electrical, and optoelectronic devices on the same silicon substrate, and is the main development direction for realizing large-scale photonic integrated chips.

[0003] Silicon photonic filters are key components in silicon-based optoelectronic chips, enabling the selection of input light wavelengths and playing a crucial role in applications such as wavelength division multiplexing (WDM) systems and on-chip optical signal processing. Existing research has focused on technologies for realizing silicon photonic filters, including Mach-Zehnder interferometers, photonic crystal nanobeam microcavities, microring resonators, and Bragg gratings. However, the transmission characteristics of these devices are entirely determined by their structural parameters and cannot be altered to meet application requirements after fabrication. These devices also typically exhibit high process sensitivity; if process errors cause deviations in transmission characteristics from the design, compensation can only be achieved through external heating or electrical stimulation, increasing overall power consumption. Existing reconfigurable silicon photonic filters often utilize thermo-optic or electro-optic effects to alter the material's refractive index, resulting in low modulation efficiency and introducing additional losses. Furthermore, their adjustable functions are largely limited to wavelength shifts. Therefore, researching and designing novel low-power reconfigurable silicon photonic filters has become a key technology for the development of silicon photonic integrated circuits.

[0004] Phase change materials (PCMs) are non-volatile materials with high optical contrast. They can be rapidly and repeatedly tuned between amorphous and crystalline phases by applying nanosecond-level electro / optical pulses, and retain their final material properties even after the external excitation is turned off. Introducing PCMs with specific optical properties into traditional silicon photonics filters can realize multifunctional reconfigurable silicon photonics filters with zero static power consumption. In 2021, S. Hadi Bardi et al. achieved an 8.8 nm wavelength redshift by integrating the PCM material Ge2Sb2Te5 (GST) onto a Bragg grating waveguide, while the transmission amplitude could be modulated from 0.544 to 0.007. However, the high insertion loss of GST is detrimental to the application of filters in large-scale integration, and the transmission amplitude tuning achieved by resonant wavelength redshift can introduce crosstalk to signals in other wavelength channels. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a non-volatile reconfigurable filter based on a Bragg grating to overcome the shortcomings of existing reconfigurable silicon-based optical filters, such as limited tuning function and high static power consumption.

[0006] This invention provides a non-volatile reconfigurable filter based on a Bragg grating, comprising an SOI substrate, a waveguide, a phase-shifted Bragg grating structure, a first non-volatile phase change material film, and a second non-volatile phase change material film. The waveguide is disposed above the SOI substrate, and the waveguide contains the phase-shifted Bragg grating structure. The first non-volatile phase change material film is disposed in the phase-shifted region above the phase-shifted Bragg grating structure, and the second non-volatile phase change material film is disposed in the uniform grating region above the phase-shifted Bragg grating structure. The first non-volatile phase change material film is disposed between the second non-volatile phase change material films.

[0007] Preferably, the SOI substrate comprises a silicon substrate, a buried oxide layer, and a top silicon layer.

[0008] Preferably, the filter further includes an upper cladding layer disposed above the first non-volatile phase change material film and the second non-volatile phase change material film.

[0009] Preferably, the upper cladding layer is a silicon dioxide thin film.

[0010] Preferably, the first non-volatile phase change material film is a Ge2Sb2Se4Te1 film.

[0011] Preferably, the second non-volatile phase change material film is an Sb2Se3 film.

[0012] The aforementioned first non-volatile phase change material thin film and second non-volatile phase change material thin film can be made of other phase change materials with different optical properties according to different device functional requirements.

[0013] Preferably, the waveguide comprises a silicon waveguide and / or a silicon nitride waveguide.

[0014] Preferably, the waveguide thickness is 200–240 nm.

[0015] Preferably, the thickness of the first non-volatile phase change material film and the second non-volatile phase change material film is 10-50 nm.

[0016] Preferably, the Bragg grating period is 300-330 nm, the Bragg grating duty cycle is 0.3-0.7, and the sidewall etching depth of the Bragg grating is 10-100 nm.

[0017] Preferably, the waveguide is a doped waveguide; the doped waveguide is an N-type doped and a P-type doped waveguide.

[0018] Preferably, the phase-shifting Bragg grating structure is a π-phase-shifting Bragg grating structure.

[0019] Preferably, the waveguide is a single-mode waveguide.

[0020] This invention also provides a method for fabricating a non-volatile reconfigurable filter based on a Bragg grating, comprising:

[0021] (1) Provide an SOI substrate, select a region with equal width of Bragg grating period above the SOI substrate, form a first non-volatile phase change material region window by electron beam exposure, grow a first non-volatile phase change material thin film, and peel off the photoresist.

[0022] (2) A second non-volatile phase change material thin film is grown in the regions on both sides of the first non-volatile phase change material above the substrate by electron beam exposure to form a second non-volatile phase change material region window, and the photoresist is peeled off. The first non-volatile phase change material thin film is disposed between the second non-volatile phase change material thin film.

[0023] (3) Waveguide structure and Bragg grating structure are formed by electron beam exposure and etching;

[0024] (4) Forming a PIN-doped region by ion implantation;

[0025] or

[0026] (1) Provide an SOI substrate and form waveguide and Bragg grating structures by electron beam exposure and etching;

[0027] (2) Forming a PIN-doped region by ion implantation;

[0028] (3) A second non-volatile phase change material thin film is grown in a window formed by electron beam exposure in the uniform Bragg grating region of the waveguide, and the photoresist is stripped off.

[0029] (4) A first non-volatile phase change material thin film is grown in the waveguide center phase shift region by electron beam exposure to form a first non-volatile phase change material region window, and the photoresist is peeled off. The first non-volatile phase change material thin film is disposed between the second non-volatile phase change material thin film.

[0030] Preferably, the upper cladding is prepared on the Bragg grating.

[0031] The present invention also provides an application of the above-mentioned non-volatile reconfigurable filter based on Bragg grating in wavelength division multiplexing systems, spectral shaping, or on-chip signal processors.

[0032] The Bragg grating structure involved in this invention can be used to design optical filters suitable for various wavelength bands, depending on the operating wavelength requirements of the device.

[0033] Beneficial effects

[0034] This invention employs the superposition of non-volatile phase change materials (e.g., the superposition of lossless Sb₂Se₃ and lossy Ge₂Sb₂Se₄Te₁, which are only lossy in their crystalline state) to simultaneously achieve center wavelength shift with constant transmission power (wavelength adjustment range ~10nm) and power tuning with constant transmission center wavelength (power adjustment range ~15dB) while ensuring a transmission loss of only 0.76dB. A lossless second non-volatile phase change material film disposed in the uniform grating region above the uniform Bragg grating structure ensures that no additional insertion loss is introduced during wavelength tuning. Meanwhile, a first non-volatile phase change material film, which can transition from lossless to lossy, is disposed in the phase-shifting region above the Bragg grating structure. This film absorbs incident light to achieve tuning of the incident light intensity. Unlike extinction achieved by tuning the resonant wavelength, this method does not introduce crosstalk to adjacent optical channels. Attached Figure Description

[0035] Figure 1 The images show a cross-sectional view (a) and a top view (b) of a prior art filter.

[0036] Figure 2 The images show a cross-sectional view (a) and a top view (b) of the filter structure of the present invention.

[0037] Figure 3 This is a cross-sectional view of the SOI substrate.

[0038] Figure 4 This is a cross-sectional view of the structure after growing an Sb2Se3 thin film on the substrate and peeling off the photoresist in Example 1.

[0039] Figure 5 The images show a cross-sectional view (a) and a top view (b) of the structure after growing a Ge2Sb2Se4Te1 thin film on the substrate and removing the photoresist in Example 1.

[0040] Figure 6 This is a top view of the structure formed by electron beam exposure and etching to create a single-mode waveguide structure and a Bragg grating structure in Example 1.

[0041] Figure 7 This is a top view of the structure after the PIN doped region is formed by ion implantation in Example 1.

[0042] Figure 8 This is a cross-sectional view of the structure after a silicon dioxide film was prepared as an upper cladding layer in Example 1.

[0043] Figure 9The images show a cross-sectional view (a) and a top view (b) of the structure formed by electron beam exposure and etching to create a single-mode waveguide structure and a Bragg grating structure in Example 2.

[0044] Figure 10 This is a top view of the structure after the PIN doped region is formed by ion implantation in Example 2.

[0045] Figure 11 This is a top view of the structure after growing an Sb2Se3 thin film on the waveguide and peeling off the photoresist in Example 2.

[0046] Figure 12 This is a top view of the structure after growing a Ge2Sb2Se4Te1 thin film on the waveguide and peeling off the photoresist in Example 2.

[0047] Figure 13 This is a cross-sectional view of the structure after a silicon dioxide film was prepared as an upper cladding layer in Example 2.

[0048] Figure 14 The resonant wavelength of the reconstructed filter in Examples 1 and 2 is tuned when the crystallinity of the Sb2Se3 region changes synchronously.

[0049] Figure 15 This refers to the tuning of the extinction ratio of the reconstruction filters in Examples 1 and 2 while keeping the resonant wavelength constant. Detailed Implementation

[0050] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0051] Example 1

[0052] A method for fabricating a non-volatile reconfigurable filter based on a Bragg grating includes:

[0053] (1) Provide an SOI substrate, including a silicon substrate, a buried oxide layer, and a top silicon layer, such as Figure 3 As shown, these are the initial materials used in the manufacturing process;

[0054] (2) A 20 nm thick Ge2Sb2Se4Te1 thin film was grown in a selected region with an equal width of the Bragg grating period above the substrate using electron beam exposure to form a Ge2Sb2Se4Te1 region window. The photoresist was then stripped off. Figure 4 As shown;

[0055] (3) A 20 nm thick Sb2Se3 film was grown in the Ge2Sb2Se4Te1 region on both sides of the substrate using electron beam exposure to form Sb2Se3 region windows. The photoresist was then removed. Figure 5 As shown, the Ge2Sb2Se4Te1 thin film is disposed between the Sb2Se3 thin films;

[0056] (4) A single-mode ridge silicon waveguide structure with a width of 500 nm, a height of 220 nm, and a ridge height of 70 nm is formed by electron beam exposure and etching, as well as a Bragg grating structure. Figure 6 As shown;

[0057] (5) A PIN-doped region is formed on the waveguide ridge by ion implantation, with a doping concentration of 10. 20 cm -3 ,like Figure 7 As shown;

[0058] (6) Prepare a 2µm thick silicon dioxide film on it as the upper cladding layer, such as Figure 8 As shown.

[0059] Example 2

[0060] A method for fabricating a non-volatile reconfigurable filter based on a Bragg grating includes:

[0061] (1) Provide an SOI substrate, including a silicon substrate, a buried oxide layer, and a top silicon layer, such as Figure 3 As shown, these are the initial materials used in the manufacturing process;

[0062] (2) A single-mode ridge silicon waveguide structure and a Bragg grating structure with a width of 500 nm, a height of 220 nm, and a ridge height of 70 nm are formed by electron beam exposure and etching, such as Figure 9 As shown;

[0063] (3) A PIN-doped region is formed on the waveguide ridge by ion implantation, with a doping concentration of 10. 20 cm -3 ,like Figure 10 As shown;

[0064] (4) A 20nm thick Sb₂Se₃ thin film is grown in a Sb₂Se₃ region window formed by electron beam exposure in a uniform grating region above the waveguide, and the photoresist is peeled off, such as... Figure 11 As shown;

[0065] (5) A 20nm thick Ge2Sb2Se4Te1 thin film is grown in the phase-shifting region above the waveguide using electron beam exposure to form a Ge2Sb2Se4Te1 region window. The photoresist is then stripped off. Figure 12 In this case, the Ge2Sb2Se4Te1 thin film is disposed between the Sb2Se3 thin films;

[0066] (6) Prepare a 2µm thick silicon dioxide film on it as the upper cladding layer, such as Figure 13 As shown.

[0067] Figure 14 and 15 The results were obtained using the 3D Finite Difference Time Domain (FDTD) method in Lumerical software. See the results below. Figure 14 and 15 It achieves both constant transmission power with center wavelength shift (wavelength adjustment range ~10nm) and constant transmission center wavelength with power tuning (power adjustment range ~16dB) while ensuring a transmission loss of only 0.76dB.

Claims

1. A non-volatile reconfigurable filter based on a Bragg grating, characterized in that, The device includes an SOI substrate, a waveguide, a phase-shifted Bragg grating structure, a first non-volatile phase change material (PVC) film, and a second non-volatile PVC film. The waveguide, containing the phase-shifted Bragg grating structure, is disposed on the phase-shifted region above the PVC structure. The first non-volatile PVC film is disposed on the phase-shifted region above the PVC structure, and the second non-volatile PVC film is disposed on the uniform grating region above the PVC structure. The first non-volatile PVC film is disposed between the second non-volatile PVC films. The first non-volatile PVC film is a Ge2Sb2Se4Te1 film, and the second non-volatile PVC film is an Sb2Se3 film.

2. The non-volatile reconfigurable filter based on a Bragg grating according to claim 1, characterized in that, The SOI substrate includes a silicon substrate, a buried oxide layer, and a top silicon layer.

3. The non-volatile reconfigurable filter based on a Bragg grating according to claim 1, characterized in that, The filter further includes an upper cladding layer disposed above the first non-volatile phase change material film and the second non-volatile phase change material film.

4. The non-volatile reconfigurable filter based on a Bragg grating according to claim 3, characterized in that, The upper cladding layer is a silicon dioxide thin film.

5. The non-volatile reconfigurable filter based on a Bragg grating according to claim 1, characterized in that, The waveguide thickness is 200–240 nm; the thickness of the first non-volatile phase change material film and the second non-volatile phase change material film is 10–50 nm; the Bragg grating period is 300–330 nm, the Bragg grating duty cycle is 0.3–0.7, and the sidewall etching depth of the Bragg grating is 10–100 nm.

6. The non-volatile reconfigurable filter based on a Bragg grating according to claim 1, characterized in that, The waveguide is a doped waveguide; the doped waveguide is an N-type doped waveguide and a P-type doped waveguide.

7. A method for fabricating a non-volatile reconfigurable filter based on a Bragg grating as described in claim 1, comprising: (1) Provide an SOI substrate, select a region with equal width of Bragg grating period above the SOI substrate, form a first non-volatile phase change material region window by electron beam exposure, grow a first non-volatile phase change material thin film, and peel off the photoresist. (2) A second non-volatile phase change material thin film is grown in the regions on both sides of the first non-volatile phase change material above the substrate by electron beam exposure to form a second non-volatile phase change material region window, and the photoresist is peeled off. The first non-volatile phase change material thin film is disposed between the second non-volatile phase change material thin film. (3) Waveguide structure and Bragg grating structure are formed by electron beam exposure and etching; (4) Forming a PIN-doped region by ion implantation; or (1) Provide an SOI substrate and form waveguide and Bragg grating structures by electron beam exposure and etching; (2) Forming a PIN-doped region by ion implantation; (3) A second non-volatile phase change material thin film is grown in a window formed by electron beam exposure in the uniform Bragg grating region of the waveguide, and the photoresist is stripped off. (4) A first non-volatile phase change material thin film is grown in the waveguide center phase shift region by electron beam exposure to form a first non-volatile phase change material region window, and the photoresist is peeled off. The first non-volatile phase change material thin film is disposed between the second non-volatile phase change material thin film.

8. The method according to claim 7, characterized in that, The upper cladding is prepared on the Bragg grating.

9. An application of the non-volatile reconfigurable filter based on a Bragg grating as described in claim 1 in wavelength division multiplexing systems, spectral shaping, or on-chip signal processors.

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