Micro-ring filter based on polymer cladding and preparation method thereof

Abstract

The invention relates to a micro-ring filter based on a polymer cladding. The micro-ring filter comprises an upper cladding, a micro-ring filter and a lower cladding, the upper cladding layer is a PDMS (Polydimethylsiloxane) polymer; the lower cladding is made of silicon dioxide; the micro-ring filter comprises an input grating coupler connected with an input light source, and the input light source sequentially passes through the input grating coupler, an input conical waveguide, a straight-through waveguide and a straight-through end output conical waveguide and is finally output from a straight-through end output grating coupler; and the straight waveguide is matched with an annular waveguide. Through the complementary design of the negative thermo-optical coefficient of the PDMS upper cladding and the positive thermo-optical coefficient of the silicon core layer, the self-shielding of the micro-ring resonant wavelength to the external temperature change is realized.

Description

Technical Field

[0001] This invention relates to the field of optical waveguide sensor technology, and more specifically to a microring filter based on polymer cladding. Background Technology

[0002] Microring resonant cavity filters, as core devices in integrated photonics, have significant application value in wavelength division multiplexing systems, optical interconnect networks, and optical sensing. Their working principle is based on evanescent field coupling between a ring waveguide and a straight waveguide, utilizing resonance conditions to achieve wavelength-selective filtering. Traditional silicon-based microring filters typically use silicon dioxide (SiO2) as the upper and lower cladding materials, and silicon (Si) as the core waveguide material, utilizing the high refractive index difference of silicon to achieve strong optical field confinement. However, this structure has significant technical bottlenecks: First, temperature sensitivity is the main factor limiting the practical application of the device. Silicon material has a large positive thermo-optic coefficient at a wavelength of 1550 nm, while the thermo-optic coefficient of the SiO2 cladding is extremely low, causing the resonant wavelength to drift by as much as 100 pm / K with temperature. When operating over a wide temperature range, the channel center wavelength shift can reach 12.5 nm, far exceeding the 0.1 nm tolerance specified by the International Telecommunication Union, forcing the system to add a complex temperature control module, significantly increasing power consumption and size. Second, traditional processes suffer from cladding stress mismatch problems. The difference in thermal expansion coefficients between SiO2 and silicon introduces interfacial stress during high-temperature processes, leading to increased waveguide birefringence and worsening polarization-dependent losses. Furthermore, SiO2 deposition requires high-temperature processes, resulting in poor compatibility with CMOS back-end processes and limiting large-scale photonic integration. To overcome the temperature drift problem, existing technologies have attempted two solutions: one is active compensation using thermally tunable electrodes, but this consumes up to 10mW per channel and has limited response speed; the other is passive compensation using a dual-ring coupling structure, but at the cost of sacrificing FSR (free spectral range) (reducing it by more than 50%). Regarding cladding materials, silicon nitride (SiN) has been used as a buffer layer, but its positive thermo-optic coefficient is still insufficient to effectively compensate for the thermal drift of silicon.

[0003] In view of the above-mentioned technical problems, an improved technical solution is proposed. Summary of the Invention

[0004] To achieve the objective of this invention, the technical solution adopted by this invention is: a polymer-clad microring filter, comprising: an upper cladding layer, a microring filter, and a lower cladding layer;

[0005] The upper cladding layer is PDMS polymer; the lower cladding layer is silicon dioxide;

[0006] The micro-ring filter includes: an input grating coupler connected to the input light source, the input light source passing sequentially through the input grating coupler, an input tapered waveguide, a straight-through waveguide, and a straight-through output tapered waveguide, and finally outputting from the straight-through output grating coupler;

[0007] The through waveguide is coupled with a ring waveguide.

[0008] Preferably, the bottom of the lower cladding layer is supported by silicon.

[0009] Preferably, a ring waveguide is used to selectively allow or suppress optical signals of a specific wavelength;

[0010] When the optical path difference of a light wave propagating through a ring waveguide is an integer multiple of the light wave wavelength, resonance enhancement will occur, that is, the resonance condition L×neff=mλ will be satisfied.

[0011] Conversely, when the optical path difference is a half-integer multiple of the wavelength of the light wave, i.e., L×neff=(m+1 / 2)×λ, the light signal of a specific wavelength will be suppressed;

[0012] Where L is the length of the ring waveguide, neff is the effective refractive index of the waveguide, m is the resonant order, and λ is the resonant wavelength.

[0013] Preferably, the waveguide transmission mode of the microring filter adopts the transverse electric mode.

[0014] Preferably, a method for fabricating a polymer-clad microring filter includes:

[0015] On the surface of SOI silicon-based material, a silicon core layer waveguide structure is formed by photolithography and reactive ion etching.

[0016] Electron beam lithography was used to define micro-ring filters of different radii and straight waveguide structures with coupling spacing.

[0017] Liquid PDMS prepolymer is spin-coated onto the surface of a silicon waveguide and cured by step heating to form a 10μm thick upper cladding, thus achieving full waveguide sealing.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. By complementing the negative thermo-optic coefficient of the PDMS cladding with the positive thermo-optic coefficient of the silicon core layer, the microring resonant wavelength is self-shielded from external temperature changes.

[0020] 2. The mechanical support structure of silicon dioxide underlayer and silicon substrate is adopted, combined with flexible packaging of PDMS polymer, which effectively absorbs thermal stress, suppresses waveguide deformation and reduces cost.

[0021] 3. The free spectral range (FSR) can be adjusted through flexible design of micro-ring radius, and the dynamic filtering function can be reconstructed by combining physical size and refractive index control. Attached Figure Description

[0022] Figure 1This is a schematic diagram of the polymer-clad microring filter of the present invention;

[0023] Figure 2 This is a schematic diagram illustrating the variation of the temperature waveguide coefficient with waveguide width according to the present invention;

[0024] Figure 3 This is a schematic diagram illustrating the temperature response of the present invention as a function of waveguide width;

[0025] Figure 4 This is the spectrum of the micro-ring filter of the present invention.

[0026] Figure 5 This is a diagram showing the effect of the radius of the present invention on the free spectral range.

[0027] In the figure: 1. PDMS polymer upper cladding; 2. Micro-ring filter; 3. Lower cladding; 21. Input grating coupler; 22. Input tapered waveguide; 23. Micro-ring resonator; 24. Through-end output tapered waveguide; 25. Through-end output grating coupler; 26. Download end output tapered waveguide; 27. Download end output grating coupler. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, the present invention provides a technical solution: a polymer-clad microring filter, comprising: a PDMS polymer upper cladding 1, a microring filter 2, and a lower cladding 3. The waveguide of the microring filter 2 includes: an input grating coupler 21, an input tapered waveguide 22, a ring waveguide 23, a through-end output tapered waveguide 24, a through-end output grating coupler 25, a download-end output tapered waveguide 26, and a download-end output grating coupler 27.

[0030] The input light source passes sequentially through the input grating coupler 21, the input tapered waveguide 22, the straight waveguide, and the straight-through output tapered waveguide 24, and is finally output from the straight-through output grating coupler 25; the straight waveguide is coupled with the ring waveguide 2.

[0031] The input grating coupler 21 and the through-end output grating coupler 25 are used for optical coupling into the waveguide and the output waveguide.

[0032] The input tapered waveguide 22 and the straight-through output tapered waveguide 24 are used to connect two waveguides of different widths, realizing the conversion of different widths of optical waveguides.

[0033] The ring waveguide 23 is used to selectively pass or suppress optical signals of specific wavelengths, thereby achieving the filtering function of optical signals of specific wavelengths. According to the resonance condition L×n eff =mλ, at a specific wavelength, resonance enhancement will occur, satisfying L×n eff The wavelength under the condition (m+1 / 2)×λ will be suppressed.

[0034] Where L represents the length of the ring waveguide 23, and n eff Let n represent the effective refractive index of the ring waveguide, m represent the resonant order, and λ represent the resonant wavelength of the constructive or destructive interference. When n is adjusted regularly... eff The size of the PN junction can be adjusted to achieve filtering functions for different wavelengths. A common method is to adjust it through the electro-optic effect, such as when a voltage is applied to the PN junction, the change in carrier concentration causes n... eff The changes.

[0035] In the micro-ring filter, the upper cladding 1 is made of PDMS polymer, the core waveguide material is silicon, the lower cladding 3 waveguide material is silicon dioxide, and the bottom is made of Si material as mechanical support.

[0036] A method for fabricating a polymer-clad microring filter, comprising:

[0037] On the surface of SOI silicon-based material, a silicon core layer waveguide structure is formed by photolithography and reactive ion etching.

[0038] Electron beam lithography was used to define micro-ring filters of different radii and straight waveguide structures with coupling spacing.

[0039] Liquid PDMS prepolymer is spin-coated onto the surface of a silicon waveguide and cured by step heating to form a 10μm thick upper cladding layer 1, thus achieving full waveguide sealing.

[0040] like Figure 2 As shown, this is a schematic diagram of how the temperature waveguide coefficient changes with the width of the annular waveguide 2 in this invention, wherein the height of the annular waveguide 2 is set to 220 nm.

[0041] The temperature waveguide coefficient Sw represents the effect of temperature change δT on the effective refractive index, i.e., Sw = δn eff / δT. The effective refractive index is determined by the properties of the ring waveguide 2 itself.

[0042] Therefore, both the PDMS polymer cladding layer 1 and the Si core layer simultaneously affect n. eff The size of the PDMS polymer coating 1 is shown. The PDMS polymer coating 1 exhibits a large negative thermo-optic coefficient of -4.5 × 10⁻⁶ around 1550 nm. -4 / ℃, while the thermo-optical coefficient of the core waveguide silicon at a wavelength of 1550nm is approximately +1.86×10. -4 / ℃.

[0043] Therefore, when the width of the ring waveguide 2 is greater than 353 nm, the positive thermo-optic effect of the core silicon plays a dominant role, and the effective refractive index increases as the temperature rises.

[0044] When the width of the ring waveguide 2 is less than 353 nm, the negative thermo-optical effect of the cladding PDMS plays a dominant role.

[0045] When the width of the ring waveguide 2 is equal to 353nm, the positive thermo-optical effect of the core silicon and the negative thermo-optical effect of the cladding PDMS cancel each other out, and Sw = 0.

[0046] When the temperature changes, the spectral response S of the micro-ring filter may undergo a redshift or blueshift, which is reflected in the change of the spectrum. S = Sw × λ / ng, where ng represents the group refractive index of the waveguide.

[0047] like Figure 3 The diagram illustrates the temperature response as a function of waveguide width in this invention. When the width of the ring waveguide 2 is 353 nm, the spectrum of the micro-ring filter responds to temperature zero, thus achieving shielding of the micro-ring filter from external temperature changes.

[0048] The negative thermo-optic effect of the PDMS polymer cladding 1 is stronger than that of the silicon core layer. The ring waveguide 2 of the micro-ring filter adopts a transverse electric mode for transmission. This transmission mode greatly reduces the negative temperature response of the PDMS polymer cladding 1 to the device itself, thus making the micro-ring filter almost unaffected by temperature.

[0049] like Figure 3 The image shows the transmission spectra of the through-pass and download ends of the micro-ring filter in this invention. In practical use, the resonant wavelength of the micro-ring filter is not affected by temperature. By changing the physical dimensions and refractive index of the micro-ring, the resonant wavelength of the resonant cavity can be tuned, thereby changing the passband and stopband of the filter.

[0050] like Figure 4 As shown, by designing microrings of different radii, the free spectral range (FSR) of the microring filter can be adjusted, achieving selective transmission to specific wavelengths. According to the formula, FSR = γ... 2 / L·ng Ming can adjust the FSR by adjusting the radius of the ring waveguide 2 (different radii can be selected during the design phase).

[0051] The larger the radius, the smaller the FSR. Due to the temperature-independent nature of the waveguide, the value of ng cannot be adjusted by the thermo-optical effect, but it can be adjusted by the electro-optical effect, ultimately achieving the purpose of adjusting the FSR.

[0052] Furthermore, the micro-ring filter proposed in this patent possesses temperature insensitivity, which allows it to maintain stable filtering characteristics even in environments with fluctuating temperatures. This improves system reliability and performance, and reduces signal distortion and system calibration requirements caused by temperature variations. In addition, the micro-ring resonator-based design not only enhances the performance of optical communication systems but also reduces reliance on temperature control, effectively decreasing energy consumption and cost. This design has significant theoretical research and practical application value for realizing high-performance, low-cost optical communication systems.

[0053] The embodiments disclosed herein are preferred embodiments, but are not limited thereto. Those skilled in the art can readily grasp the spirit of the present invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A polymer-cladding- mode-based micro-ring filter, characterized by, Comprise: Upper cladding layer, micro-ring filter and lower cladding layer; The upper cladding layer is a PDMS polymer; The lower cladding layer is silica; The micro-ring filter comprises: an input grating coupler connected with an input light source, the input light source sequentially passing through the input grating coupler, an input tapered waveguide, a straight-through waveguide and a straight-through end output tapered waveguide, and finally outputting from a straight-through end output grating coupler; The straight-through waveguide is matched with a ring waveguide.

2. The polymer-cladding- mode-based micro-ring filter according to claim 1, wherein The bottom of the lower cladding layer is supported by silicon.

3. The polymer-cladding- mode-based micro-ring filter according to claim 1, wherein The ring waveguide is used to realize selective passing or suppression of specific wavelength optical signals; When the optical wave propagates one round in the ring waveguide, the optical path difference is an integer multiple of the wavelength of the optical wave, resonance enhancement occurs, that is, the resonance condition Lxneff=mλ is met; On the contrary, when the optical path difference is a half integer multiple of the wavelength of the optical wave, that is, Lxneff=(m+1 / 2)×λ, the specific wavelength optical signal is suppressed; Wherein, L is the length of the ring waveguide, neff is the effective refractive index of the waveguide, m is the resonance order, and λ is the resonance wavelength.

4. The polymer-cladding- mode-based micro-ring filter according to claim 1, wherein The waveguide transmission mode of the micro-ring filter adopts transverse electric mode.

5. A method for manufacturing the polymer-cladding-based micro-ring filter according to any one of claims 1 to 4, characterized by, Comprise: On the surface of SOI silicon-based material, a silicon core layer waveguide structure is formed by photolithography technology and reactive ion etching process; An electron beam lithography is used to define a micro-ring filter with different radii and a straight waveguide structure with different coupling distances; A liquid PDMS prepolymer is spin-coated on the surface of the silicon waveguide, and a thickness of 10μm upper cladding layer is formed by stepwise temperature curing to realize full sealing of the waveguide.

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