Optical waveguide sensor based on cascaded phase shift uniform Bragg grating and test method thereof

Abstract

The invention relates to an optical waveguide sensor based on a cascaded phase-shift uniform Bragg grating, and the sensor comprises the cascaded phase-shift uniform Bragg grating which is provided with an input single-mode waveguide and an output single-mode waveguide. A plurality of phase-shift uniform Bragg grating units are arranged between the input single-mode waveguide and the output single-mode waveguide; the phase shift uniform Bragg grating unit comprises a phase shift cavity and periodic refractive index modulation structures symmetrically arranged on the two sides of the phase shift cavity. The optical waveguide structure of the phase shift uniform Bragg grating is not covered by an upper cladding. According to the invention, through the coupling design of cascaded multi-stage harmonic peaks, the quality factor and the detection precision are greatly improved, and the wavelength detection range is widened at the same time. The design without the upper cladding layer is combined with the single-step photoetching etching process, so that the complex process of growing the upper cladding layer or overlaying a sensing window is thoroughly omitted, and the manufacturing cost and the process complexity are greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of optical waveguide sensors, and in particular to an optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings. Background Art

[0002] In the field of optical sensing, Bragg grating sensors utilize the reflection properties of a grating's periodic structure for light of specific wavelengths, monitoring the resonant wavelength shift caused by the external environment. These sensors have been widely used in biochemical testing, environmental monitoring, and other fields. Their advantages lie in their compact structure, ease of integration, and resistance to electromagnetic interference.

[0003] Among them, a uniform Bragg grating with a phase shift can produce a sharp resonant peak within its bandgap, effectively improving the sensor's ability to detect small refractive index changes. However, conventional single-phase-shifted Bragg grating sensors face significant challenges in practical applications. To achieve high-sensitivity sensing, the resonant peak typically requires an extremely high quality factor (Q value) to accurately resolve small wavelength shifts. Improving the Q value of a single grating typically relies on complex structural design or sophisticated fabrication techniques, such as precisely controlling the grating parameters or growing an upper cladding layer of a specific material to expose the sensing window, which undoubtedly increases manufacturing complexity and cost. Cascaded optical resonant structures offer a new approach to addressing these issues. By connecting multiple resonant units (such as phase-shifted Bragg gratings), the optical signal passes through each resonant unit in sequence, achieving superposition and enhancement of the resonant responses. This cascade approach can theoretically effectively amplify the quality factor, improving detection accuracy and range. Existing cascaded grating sensing solutions often rely on complex fabrication processes, such as the need to overlay multiple masks or precisely remove the upper cladding layer in specific areas to form the sensing window, limiting their potential for large-scale application. Therefore, there is an urgent need for a new cascaded Bragg grating sensing structure that can significantly improve the sensing performance (high Q value, large range, and high precision) and greatly simplify the manufacturing process. Summary of the Invention

[0004] To achieve the objective of the present invention, the technical solution adopted by the present invention is: an optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings, comprising: a cascaded phase-shifted uniform Bragg grating, wherein the phase-shifted uniform Bragg grating is provided with an input single-mode waveguide and an output single-mode waveguide, and a plurality of phase-shifted uniform Bragg grating units are provided between the input single-mode waveguide and the output single-mode waveguide; the phase-shifted uniform Bragg grating unit includes a phase-shifted cavity and a periodic refractive index modulation structure symmetrically arranged on both sides of the phase-shifted cavity; the optical waveguide structure of the phase-shifted uniform Bragg grating is not covered by an upper cladding layer.

[0005] Preferably, the periodic refractive index modulation structure is realized by corrugated etching of the waveguide sidewall, and the etching shape is rectangular.

[0006] Preferably, the period Λ of the Bragg grating reflector satisfies the Bragg condition formula: B =2Λn eff , where λ B is the Bragg wavelength, n eff is the average effective refractive index of the waveguide.

[0007] Preferably, both the periodic refractive index modulation structure and the optical waveguide structure are made of silicon.

[0008] Preferably, the periodic refractive index modulation structure includes: a plurality of high refractive index waveguide segments and a plurality of low refractive index waveguide segments, and the high refractive index waveguide segments and the low refractive index waveguide segments are alternately arranged on the phase-shifted uniform Bragg grating unit.

[0009] Preferably, a testing method for an optical waveguide sensor based on a cascaded phase-shifted uniform Bragg grating comprises: coupling an optical signal from a broadband light source to the cascaded phase-shifted uniform Bragg grating; contacting a test agent with the exposed optical waveguide surface, causing a change in the effective refractive index; shifting the resonance peak wavelength of the phase-shift cavity as the refractive index changes, and amplifying the drift in the cascaded structure; and detecting the resonance peak shift of the output spectrum by a spectrum analyzer.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] This invention significantly improves the quality factor and detection accuracy through a coupled design that cascades multiple resonant peaks, while also broadening the wavelength detection range. It further enhances sensitivity by utilizing the transverse magnetic (TM) mode to transmit optical signals, leveraging its high sensitivity to changes in the refractive index of the waveguide surface. The cladding-free design, combined with a single-step photolithography process, eliminates the complex steps of growing the cladding or overlaying the sensing window, significantly reducing manufacturing costs and process complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the overall structure of the optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings in the present invention;

[0013] Figure 2 Schematic diagram of the structure of the phase-shifted uniform Bragg grating in the present invention;

[0014] Figure 3 The transmission spectra of the phase-shifted uniform Bragg gratings with different cascade numbers in the present invention are shown in FIG.

[0015] Figure 4 This is a spectrum drift diagram of the cascaded phase-shifted uniform Bragg grating in the present invention when reagents of different concentrations are passed through it;

[0016] In the figure: 1. Phase-shifted uniform Bragg grating; 2. Phase-shifted uniform Bragg grating unit; 11. Input single-mode waveguide; 12. Output single-mode waveguide; 21. High-refractive-index waveguide; 22. Low-refractive-index waveguide; 23. Phase-shift cavity. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Example:

[0019] like Figures 1 to 4 The present invention provides a technical solution: an optical waveguide sensor based on a cascaded phase-shifted uniform Bragg grating, comprising: a cascaded phase-shifted uniform Bragg grating 1, for improving the resonance peak quality factor and detection accuracy through multi-stage resonance superposition, the phase-shifted uniform Bragg grating 1 is provided with an input single-mode waveguide 11 and an output single-mode waveguide 12, and a plurality of phase-shifted uniform Bragg grating units 2 are provided between the input single-mode waveguide 11 and the output single-mode waveguide 12.

[0020] The phase-shifted uniform Bragg grating unit 2 includes a phase-shift cavity 23 and a periodic refractive index modulation structure symmetrically arranged on both sides of the phase-shift cavity 23. The optical waveguide structure of the phase-shifted uniform Bragg grating is not covered by an upper cladding layer. Both the periodic refractive index modulation structure and the optical waveguide structure are made of silicon. The periodic refractive index modulation structure is achieved by corrugated etching of the waveguide sidewalls, and the etching shape is rectangular. The periodic refractive index modulation structure includes: a plurality of high-refractive index waveguide segments 21 and a plurality of low-refractive index waveguide segments 22, which are alternately arranged on the phase-shifted uniform Bragg grating unit.

[0021] The phase-shifted uniform Bragg grating unit 2 is used to reflect optical signals of a specific wavelength. It consists of a high-refractive-index waveguide 21, a low-refractive-index waveguide 22, and a phase-shift cavity 23. The phase-shift cavity 23 is located between two sections of periodic refractive-index modulation structures. The periodicity is broken by introducing a π / 2 phase shift, forming a narrowband resonance peak.

[0022] The input single-mode waveguide 11 and the output single-mode waveguide 12 are used to guide the input optical signal and output the modulated spectrum respectively. The upper surface of the entire optical waveguide structure is directly exposed to the test environment without upper cladding coverage to maximize the interaction between the evanescent field and the environment.

[0023] The input single-mode waveguide 11, the output single-mode waveguide 12 and the phase-shifted uniform Bragg grating unit 2 adopt the transverse magnetic (TM) mode to transmit optical signals. This mode has a stronger evanescent field intensity and can significantly enhance the refractive index sensing sensitivity.

[0024] High refractive index waveguide 21: reflects the main wavelength to form Bragg reflection conditions.

[0025] Low refractive index waveguide 22: connects to the high refractive index segment, adjusts the grating period, and controls the reflection bandwidth.

[0026] Phase shift cavity 23: introduces a sudden phase change to generate a narrowband transmission window to achieve filtering or resonance.

[0027] The optical signal of the broadband light source is coupled to the cascaded phase-shifted uniform Bragg grating 1 unit via the input single-mode waveguide 11. When the test agent contacts the exposed optical waveguide surface, the effective refractive index of the waveguide changes, causing the resonance peak wavelength of the phase-shift cavity 23 to drift.

[0028] The resonant peak shift of the final output spectrum is detected by a spectrum analyzer. The shift Δλ is linearly correlated with the parameters of the test agent (such as refractive index). Sensing information can be obtained by measuring the change in the central wavelength λ of the cascade spectrum.

[0029] The optical waveguide structure of the cascaded phase-shifted uniform Bragg grating 1 is manufactured based on an SOI platform, with a width of 500 nm and a thickness of 220 nm. The upper cladding is the aqueous solution to be tested (refractive index range 1.33–1.35).

[0030] The period Λ of the Bragg grating reflector satisfies the Bragg condition formula: B =2Λn eff , where λ B is the Bragg wavelength, n eff is the average effective refractive index of the waveguide.

[0031] The period Λ of the phase-shifted uniform Bragg grating is the sum of the waveguide lengths of the high-refractive-index waveguide 21 and the low-refractive-index waveguide 22, and is set to 318.5 nm. The number of cascaded elements N is 5, the period is 40, and the waveguide widths of the high-refractive-index waveguide 21 and the low-refractive-index waveguide 22 are 550 and 450 nm, respectively.

[0032] like Figure 3 As shown, when the number of cascaded phase-shifted uniform Bragg grating units 1 is N=1 and N=5, the corresponding resonance peak quality factors are 3875 and 12000, respectively.

[0033] The cascaded structure significantly improves the quality factor through the superposition effect of multiple resonances. When N = 5, the quality factor Q reaches 3.1 times that of a single unit. This characteristic directly reduces the resonant peak linewidth (the linewidth of a single unit is about 0.4nm, and the cascaded structure is about 0.13nm), thereby improving the refractive index detection accuracy and wavelength resolution. The designed central wavelength under the Λ period is around 1550nm.

[0034] like Figure 4 As shown, when the refractive index of the aqueous solution being measured increases from 1.33 to 1.35, the central wavelength of the resonance peak red-shifts from 1549.53 nm to 1553.80 nm. A linear fit yields a bulk refractive index sensitivity of 210 nm / RIU. Within the 50 nm wavelength detection range of the spectrum analyzer (typically 1530-1580 nm), the sensor covers a refractive index variation range of 0.23 RIU (calculated using the formula: 50 nm / 210 nm / RIU), meeting the needs of a wide range of biochemical detection.

[0035] The embodiments disclosed in the present invention are preferred embodiments, but are not limited to them. Ordinary technicians in this field can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. As long as they do not deviate from the spirit of the present invention, they are all within the scope of protection of the present invention.

Claims

1. An optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings, characterized in that: include: A cascaded phase-shifted uniform Bragg grating is provided with an input single-mode waveguide and an output single-mode waveguide, with a plurality of phase-shifted uniform Bragg grating units arranged between the input single-mode waveguide and the output single-mode waveguide; the phase-shifted uniform Bragg grating unit includes a phase-shift cavity and a periodic refractive index modulation structure symmetrically arranged on both sides of the phase-shift cavity; the optical waveguide structure of the phase-shifted uniform Bragg grating is not covered by an upper cladding layer.

2. The optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings according to claim 1, characterized in that: The periodic refractive index modulation structure is realized by corrugated etching of the waveguide sidewall, and the etching shape is rectangular.

3. The optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings according to claim 1, characterized in that: The period Λ of the Bragg grating reflector satisfies the Bragg condition formula: B =2Λn eff , where λ B is the Bragg wavelength, n eff is the average effective refractive index of the waveguide.

4. The optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings according to claim 1, characterized in that: Both the periodic refractive index modulation structure and the optical waveguide structure are made of silicon.

5. The optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings according to claim 1, characterized in that: The periodic refractive index modulation structure includes: a plurality of high refractive index waveguides and a plurality of low refractive index waveguides, and the high refractive index waveguides and the low refractive index waveguides are alternately arranged on a phase-shifted uniform Bragg grating unit.

6. A method for testing an optical waveguide sensor based on cascaded phase-shifted uniform Bragg gratings according to any one of claims 1 to 5, characterized in that: include: The optical signal from a broadband light source is coupled to a cascaded phase-shifted uniform Bragg grating. The test agent contacts the exposed optical waveguide surface, causing a change in the effective refractive index. The resonant peak wavelength of the phase-shift cavity shifts with the refractive index change, and the cascade structure amplifies the drift. The resonant peak shift of the output spectrum is detected by an optical spectrum analyzer.

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