Optical sensor based on groove type waveguide and cascade micro-ring resonant cavity structure

Abstract

The invention relates to the technical field of optical sensors, in particular to an optical sensor based on a groove type waveguide and a cascade micro-ring resonant cavity structure. The optical sensor comprises an input waveguide, an output waveguide, a groove type micro-ring resonant cavity and a reference micro-ring resonant cavity. According to the invention, the refractive index sensitivity of 9264 nm / RIU and the detection limit of 2.91 * 10 <-5 > RIU are realized through optimization design. The invention has the characteristics of compact structure and compatible preparation process with a CMOS platform, and can be widely applied to the fields of biomolecular detection, medical diagnosis, environmental monitoring and the like.

Description

Technical Field

[0001] This invention relates to the field of optical sensor technology, and specifically to an optical sensor based on a slotted waveguide and a cascaded microring resonant cavity structure. Background Technology

[0002] Biosensors, as important tools in modern medical diagnosis, environmental monitoring, and food safety testing, have been widely researched and applied in recent years. Traditional biosensors mostly rely on electrochemical or fluorescence methods, which, while performing well in some scenarios, have limitations in sensitivity, real-time performance, and interference resistance. In contrast, optical biosensors, with their advantages of being label-free, having fast detection speeds, strong resistance to electromagnetic interference, and enabling real-time monitoring, are gradually becoming an important development direction for next-generation high-performance biosensing technology. The basic principle of optical biosensors is to characterize the concentration or refractive index changes of a target substance by detecting changes in optical parameters (such as wavelength drift and intensity changes) caused by the interaction of light waves with the analyte. With their high sensitivity and integrability, these sensors have broad application prospects in early clinical disease diagnosis, environmental pollutant detection, and food safety supervision.

[0003] Currently, common optical biosensors mainly include Mach-Zehnder interferometers (MZI), photonic crystal sensors, surface plasmon resonance (SPR) sensors, and microring resonator (MRR) sensors. MZIs have a relatively simple structure and can achieve high refractive index sensitivity, but their large size and insufficient on-chip integration hinder miniaturization and large-scale integration. Photonic crystal sensors can achieve extremely high sensitivity, but their fabrication process is complex and costly, and they suffer from shortcomings in mass production and long-term stability. SPR sensors rely on the surface plasmon resonance effect at the metal-dielectric interface, offering high sensitivity, but the inherent high loss of metallic materials results in a low quality factor, limiting detection accuracy and signal-to-noise ratio. Compared to the above structures, MRR sensors combine high Q-factor, compact structure, easy compatibility with CMOS processes, and suitability for integration, making them superior in overall performance and thus a key research focus in recent years.

[0004] However, despite the significant potential of microring resonators in the field of optical biosensing, several problems remain to be solved. First, the light field in traditional MRRs is primarily confined within high-refractive-index waveguides, limiting the interaction area with the analyte and resulting in insufficient sensitivity, making it difficult to detect low concentrations of biomolecules. Second, there is an inherent trade-off between the Q-factor and free spectral range (FSR) of MRRs: a larger microring radius helps improve the Q-factor but significantly reduces the FSR; conversely, reducing the microring radius increases the FSR but leads to a decrease in the Q-factor. Therefore, a single microring structure cannot simultaneously achieve a high Q-factor and a large FSR. Finally, due to insufficient light-matter interaction and limited dynamic range, it is difficult to meet the high demands of applications such as early clinical diagnosis and trace contaminant monitoring. Thus, existing optical biosensors still have significant shortcomings in terms of sensitivity, dynamic range, and detection limit. How to achieve a significant improvement in sensitivity and an expansion of the FSR while maintaining a high Q-factor remains a critical technical challenge that needs to be overcome in this field. Summary of the Invention

[0005] To address the issues of insufficient sensitivity, inherent trade-offs between quality factor and free spectral range, and high detection limits in existing optical biosensors, this invention proposes a high-sensitivity optical biosensor based on a cascaded slotted microring resonator. This sensor enhances the interaction between light and the analyte by introducing a slotted waveguide on a silicon-based platform and utilizes the vernier effect of the double-ring cascade to achieve a balance between high sensitivity, quality factor, and wide dynamic range, thereby significantly improving sensing performance.

[0006] The present invention provides an optical sensor based on a slotted waveguide and a cascaded microring resonator structure. The optical sensor includes: an input waveguide (1), an intermediate waveguide (11), an output waveguide (7), a slotted microring resonator (SMRR) (5), and a reference microring resonator (8). The slotted microring resonator (5) and the reference microring resonator (8) are arranged side by side on the same plane, and are coupled to the input waveguide (1), the intermediate waveguide (11) and the output waveguide (7) respectively. The sensor is placed on a silicon-on-insulator substrate, which is composed of a top silicon layer (9) and a buried oxide layer (10).

[0007] In this invention, the slotted microring resonant cavity (5) is composed of an inner ring waveguide (4) and an outer ring waveguide (3); The inner ring waveguide (4) and the outer ring waveguide (3) are a pair of concentric circles. The inner radius of the inner ring waveguide (4) is 6.8 ~ 7.0 μm, and the width of both the inner ring waveguide (4) and the outer ring waveguide (3) is 0.2 μm. There is a groove region between the inner ring waveguide (4) and the outer ring waveguide (3), with a groove width of 0.06~0.12 μm, and the groove region is filled with air; In the actual operation of the present invention, the inner radius of the inner ring waveguide (4) is preferably 6.90 μm; the slot width is preferably 0.06 μm; The groove region is filled with air, forming a high-intensity area of ​​concentrated light field. This concentrates light energy within the groove region, significantly enhancing the interaction between the light and the analyte. The grooved waveguide structure provided by this invention increases the proportion of light field leakage into the groove region, significantly increasing the area of ​​interaction between the light field and the analyte. Therefore, this invention achieves a refractive index sensitivity as high as 9264 nm / RIU, with the detection limit reduced to 2.91 × 10⁻⁶. -5 The RIU has significant advantages over existing single-ring resonant cavity structures.

[0008] In this invention, the inner ring radius (R2) of the reference microring resonator (8) is 5.6~5.8 μm, and the width (W) is... r2 The value is 0.4 μm; In the actual operation of the present invention, the inner ring radius of the reference microring resonator (8) is preferably 5.7 μm.

[0009] In this invention, the width (W1) of the input waveguide (1), the intermediate waveguide (11) and the output waveguide (7) is 0.3 ~ 0.5 μm; The coupling gap (gap1) between the input waveguide (1), the intermediate waveguide (11) and the outer ring waveguide (3) is 0.09 ~ 0.11 μm; The coupling gap (gap2) between the intermediate waveguide (11), the output waveguide (7) and the reference micro-ring resonator (8) is 1.0~1.5 μm; In the actual operation of the present invention, the width of the input waveguide (1), the intermediate waveguide (11) and the output waveguide (7) is preferably 0.4 μm; The coupling gap between the input waveguide (1), the intermediate waveguide (11) and the outer ring waveguide (3) is preferably 0.10 μm; The coupling gap between the intermediate waveguide (11), the output waveguide (7) and the reference microring resonator (8) is preferably 0.10 μm.

[0010] In this invention, the thickness of the top silicon layer (9) is 0.22 μm and the thickness of the buried oxide layer (10) is 2.00 μm.

[0011] In this invention, the optical biosensor further includes a sensing area (2) and a test object (6).

[0012] In the actual operation of this invention, when the input light is coupled into the sensing SMRR and the reference MRR respectively, due to the slight difference in the free spectral range of the two rings, a new envelope peak will form in the output spectrum, thereby producing an equivalently amplified free spectral range. In the design of this invention, the free spectral range of a single SMRR is approximately 15.43 nm, while the free spectral range after cascading is amplified to 152.06 nm, approximately 10 times that of a single ring. Simultaneously, the quality factor of this structure can still be maintained at around 5622, ensuring detection accuracy.

[0013] The present invention also provides the application of the above-mentioned optical sensor in early clinical diagnosis.

[0014] The present invention also provides the application of the above-mentioned optical sensor in detecting hemoglobin concentration, wherein the detection sensitivity is 0.8875 nm / (g / L).

[0015] In practical applications, this invention was validated using hemoglobin solution as the detection target. The results showed that the sensor has a good ability to distinguish different concentrations of hemoglobin, with a concentration sensitivity of 0.8875 nm / (g / L). It can effectively distinguish between normal, mild, moderate and severe abnormal states, indicating its potential for application in early clinical diagnosis.

[0016] The beneficial effects of this invention are: Compared with existing technologies, this invention proposes a high-sensitivity optical biosensor based on a cascaded slotted microring resonator (MRR). By introducing a slotted waveguide structure into the MRR, the light field can be more fully leaked into the low-refractive-index slot region, thereby significantly enhancing the interaction between light and the analyte and improving the sensor's refractive index sensitivity. Simultaneously, this invention employs a cascaded double microring structure and utilizes the Vernier Effect to achieve an equivalent amplification of the free spectral range. While maintaining a high quality factor, it achieves a dynamic detection range far greater than that of a single microring structure, fundamentally overcoming the physical limitations of traditional MRRs in terms of sensitivity and detection range. Based on this structural optimization, the detection limit of this invention is significantly reduced, enabling accurate detection of trace biomolecules and meeting the high-precision sensing requirements of early clinical diagnosis and environmental monitoring. Furthermore, this invention is designed and manufactured based on a silicon-on-insulator (SiI) platform, which has good compatibility with existing CMOS processes, facilitating subsequent integration and miniaturization. This process characteristic makes this invention not only valuable for research and verification under laboratory conditions but also feasible for practical detection applications. Attached Figure Description

[0017] Figure 1This is a conceptual diagram illustrating the application of the cascaded slotted microring resonator in hemoglobin concentration detection in this invention. Figure (a) shows the overall architecture of the cascaded slot microring resonator; Figure (b) shows the top view of the cascaded slot microring resonator; and Figure (c) shows the waveguide cross-section. Figure 2 This is the sensing unit portion of the cascaded slotted microring resonator of the present invention; Figure (a) shows the structure of the slot-type micro-ring resonator; Figure (b) shows the field strength diagram of the slot-type micro-ring resonator. Figure 3 This invention provides simulation verification of the free spectrum range based on a cascaded slot microring resonator. Figure (a) is a schematic diagram of a cascaded slot microring resonator; Figure (b) is a transmission spectrum of a cascaded slot microring resonator. Figure 4 This invention provides sensitivity simulation verification based on a cascaded slotted microring resonator. Figure (a) shows the transmission spectrum of the cascaded slot microring resonator under different refractive indices; Figure (b) shows the sensitivity fitting line of the cascaded slot microring resonator. Figure 5 Simulation verification of the hemoglobin concentration detection based on a cascaded slotted microring resonator, as per the present invention; Figure (a) shows the transmission spectrum of the cascaded groove microring resonator at different protein concentrations; Figure (b) shows the fitted line graph of the hemoglobin concentration of the cascaded groove microring resonator. Detailed Implementation

[0018] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0019] Example like Figure 1 As shown, this invention proposes an optical biosensor based on a cascaded slotted microring resonator (CSMRR). Its overall structure includes an input waveguide, an output waveguide, a slotted microring resonator (SMRR), and a reference microring resonator (MRR). The SMRR enhances the interaction between the optical field and the external analyte, and the cascaded reference MRR with the SMRR constitutes the Vernier Effect, thereby significantly expanding the free spectral range while maintaining a high quality factor. Figure 1 (a) shows the overall architecture. Figure 1 (b) is a top view. Figure 1 (c) is a cross-sectional view of the waveguide, which clearly shows that the groove region is set at the center of the waveguide, forming a region with a strong and concentrated distribution of optical field.

[0020] like Figure 2As shown, the sensing unit of the present invention is an SMRR. Figure 2 (a) shows the structure of the SMRR. The microring consists of a pair of high-refractive-index silicon waveguides with a low-refractive-index groove region with a width of approximately 0.06 μm in the middle. The microring has a radius of 6.9 μm, a waveguide width of 0.2 μm, and is connected to the input / output waveguides through a coupling gap of 0.1 μm. Figure 2 (b) shows the field intensity distribution in the groove region. It can be seen that the light field is mainly confined to the groove region and interacts strongly with the test object in the external environment, thereby significantly improving the refractive index sensitivity.

[0021] like Figure 3 As shown, this is the structure of CSMRR and its transmission spectrum simulation verification. Figure 3 (a) shows a schematic diagram of the cascaded SMRR and reference MRR, where the reference microring has a radius of 5.7 μm, a waveguide width of 0.4 μm, and a coupling gap of 0.1 μm. Due to the difference in the free spectral ranges of the two microrings, the output signals form a Vernier envelope peak after superposition, significantly amplifying the free spectral range of the CSMRR. Simulation results are as follows... Figure 3 As shown in (b), the FSR of a single grooved microring is 15.43 nm, while the FSR of the cascaded structure of the present invention is extended to 152.06 nm, which is about 10 times higher, while the Q factor is maintained at around 5622, achieving a balance between high resolution and wide dynamic range.

[0022] like Figure 4 As shown, the present invention uses the simulation software Lumerical to verify the sensing sensitivity. Figure 4 (a) shows the transmission spectrum at different refractive indices. As the refractive index increases, the resonant wavelength gradually redshifts. Figure 4 (b) shows the fitted curve, indicating that the sensor's refractive index sensitivity reaches 9264 nm / RIU, and the detection limit is reduced to 2.91 × 10⁻⁶. -5 RIU has significant advantages over existing single-ring resonators.

[0023] like Figure 5 As shown, this invention is further applied to hemoglobin concentration detection. In the simulation, it is assumed that the refractive index of the cladding covering the surface of the sensing area changes with different hemoglobin concentrations. By simulating the refractive index environments corresponding to seven different hemoglobin concentrations, the concentration range is from 0 (g / l) to 180 (g / l), mainly including 0 (g / l), 80 (g / l), 100 (g / l), 120 (g / l), 140 (g / l), 160 (g / l) and 180 (g / l). Figure 5(a) shows the transmission spectra of hemoglobin solutions at different concentrations, with the resonant wavelength gradually shifting as the concentration increases. Figure 5 (b) shows the fitting curve of concentration versus resonant wavelength. The sensitivity is 0.8875 nm / (g / L), which can effectively distinguish between normal, mild, moderate and severe abnormal concentration ranges, proving the feasibility of this structure in medical clinical testing.

[0024] In this embodiment, the specific optimal parameter values ​​of the slot width, SMRR inner and outer ring widths, SMRR radius, slot width, reference MRR ring width, reference MRR radius, input / output straight waveguide width, and input / output coupling gap marked in the above figure were obtained by scanning and optimization through the Ansys Lumerical simulation platform. The parameters are shown in Table 1.

[0025] Table 1 Parameters of Cascaded Slotted Microring Resonators Parameter name numerical values slot width 0.06 μm SMRR inner and outer ring width 0.20 μm SMRR radius 6.90 μm Reference MRR ring width 0.40 μm Reference MRR radius 5.70 μm Input / output straight waveguide width 0.40 μm Input / output coupling gap 0.10 μm In the implementation of this invention, the key to the cascaded slotted microring resonator's ability to maintain a high Q factor while maximizing its free spectral range and sensitivity lies in: achieving a suitable value for the inner and outer ring widths of the SMRR and the width of the slot region, thus confining the optical field within the low-refractive-index slot region and enhancing the interaction between the optical field and the external analyte; by controlling the ring widths and radii of the SMRR and the reference MRR, utilizing the Vernier Effect caused by the cascaded structure, a difference in the free spectral range of the two microrings is created, and the output signals, after superposition, form a Vernier envelope peak, expanding the free spectral range of the CSMRR to ten times that of a single SMRR; and achieving phase matching between the input / output straight waveguides and the SMRR and reference MRR, enabling efficient coupling of the CSMRR by scanning their coupling gap.

[0026] In summary, the CSMRR described in this embodiment, by combining the enhanced optical field effect of a slotted waveguide and the Vernier effect to extend the free spectral range, achieves a balance of high sensitivity, low detection limit, and wide dynamic range while maintaining a high Q factor. Compared to typical optical biosensor structures in the prior art, such as the embedded racetrack-type MRR (sensitivity 297 nm / RIU, LOD 7.40 × 10⁻⁶), this approach offers significant advantages. -5 Compared to conventional runway-type MRR (sensitivity 185 nm / RIU) and standard runway-type MRR (sensitivity 185 nm / RIU), the sensitivity of the CSMRR in this embodiment is significantly improved to 9264 nm / RIU, an improvement of more than an order of magnitude; at the same time, its detection limit is as low as 2.91 × 10⁻⁶. -5 RIU is superior to dual-slot cascaded MRR (4.88×10). -6(RIU). In addition, the free spectral range (FSR) of CSMRR reaches 152.06 nm, which is about 10 times that of the traditional single-ring structure, while its Q-factor remains at a high level of 5622. This fully demonstrates the comprehensive balance advantage of this structure in terms of sensitivity, detection limit and spectral range, and can effectively break through the performance bottleneck of existing optical biosensors.

[0027] Although specific embodiments of the present invention have been described in detail, those skilled in the art can make further modifications and substitutions to the details of the technical solutions of the present invention based on all the teachings disclosed, and all such modifications and substitutions are within the scope of protection of the present invention. The full scope of the present invention is given by the appended claims and any equivalents.

Claims

1. An optical sensor based on a grooved waveguide and a cascaded microring resonant cavity structure, characterized in that, The optical sensor includes: an input waveguide (1), an intermediate waveguide (11), an output waveguide (7), a slotted microring resonator (5), and a reference microring resonator (8). The channel-type microring resonator (5) and the reference microring resonator (8) are arranged side by side on the same plane; The sensor is placed on a silicon-on-silicon insulator substrate, which is composed of a top silicon layer (9) and a buried oxide layer (10).

2. The optical sensor according to claim 1, characterized in that, The slotted microring resonant cavity (5) is composed of an inner ring waveguide (4) and an outer ring waveguide (3); The inner ring waveguide (4) and the outer ring waveguide (3) are a pair of concentric circles. The inner radius of the inner ring waveguide (4) is 6.8 ~ 7.0 μm, and the width of both the inner ring waveguide (4) and the outer ring waveguide (3) is 0.2 μm. There is a groove between the inner ring waveguide (4) and the outer ring waveguide (3), with a groove width of 0.06~0.12 μm, and the groove is filled with air.

3. The optical sensor according to claim 1, characterized in that, The inner ring radius of the reference microring resonator (8) is 5.6~5.8 μm and the width is 0.4 μm.

4. The optical sensor according to claim 1, characterized in that, The widths of the input waveguide (1), intermediate waveguide (11) and output waveguide (7) are 0.3 ~ 0.5 μm; The coupling gaps between the input waveguide (1), the intermediate waveguide (11), and the outer ring waveguide (3) are all 1.0~1.5 μm; The coupling gap between the intermediate waveguide (11), the output waveguide (7) and the reference microring resonator (8) is 1.0~1.5μm.

5. The optical sensor according to claim 1, characterized in that, The thickness of the top silicon layer (9) is 0.22 μm, and the thickness of the buried oxide layer (10) is 2.0 μm.

6. The optical sensor according to claim 1, characterized in that, The optical biosensor also includes a sensing area (2) and a analyte (6).

7. The application of the optical sensor according to any one of claims 1 to 6 in early clinical diagnosis.

8. The application of the optical sensor according to any one of claims 1 to 6 in detecting hemoglobin concentration, characterized in that, The sensitivity of the detection is 0.8875 nm / (g / L).

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