Optical sensing circuit and optical sensing method

Abstract

To simplify operation by relaxing the temperature dependence of a resonance peak wavelength in an optical sensing circuit and eliminating the need for oscillation wavelength control between a light source and a ring resonator.SOLUTION: An optical sensing circuit includes a bandpass filter, a reference ring resonator provided with a resistance material as a heater on a clad of a region where the ring resonator is formed, a sensing ring resonator provided with a sensing region, and a photodetection element. Among the light of the resonance wavelength of the reference ring resonator, the light is sent to the input waveguide of the sensing ring resonator in a specific wavelength band extracted by a bandpass filter, and the light of the resonance wavelength of the sensing ring resonator is sent from the output waveguide of the sensing ring waveguide to the photodetection element, and the specific wavelength band extracted by the bandpass filter is less than or equal to the FSR of the sensing ring resonator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical sensing circuit and an optical sensing method, and more particularly to an optical waveguide type optical sensing circuit that can be used as an optical biosensor for measuring minute changes in refractive index accompanying biological reactions such as antigen-antibody reactions, and an optical sensing method that can be used with this optical sensing circuit. [Background technology]

[0002] In recent years, in response to the global spread of the novel coronavirus (COVID-19), biosensor technology has been attracting attention as a means of constantly monitoring hygiene and health conditions to prevent viral infections and chronic lifestyle-related diseases caused by lack of exercise due to increased work from home.

[0003] Biosensors are a general term for chemical sensors that utilize biological molecular recognition mechanisms to convert specific reactions of biomolecules, such as antigen-antibody reactions, into electrical signals for detection. The part that converts these specific reactions into electrical signals is called a transducer, and is the core device in biosensors.

[0004] Optical biosensors are biosensors that use optical devices to detect biological reactions as changes in the amount of fluorescence or refractive index, and are not only non-invasive and non-contact, but also capable of measurement with relatively short waiting times for results (real-time measurement).For these reasons, optical biosensors are becoming increasingly important.

[0005] In contrast to methods that indirectly detect changes due to a reaction by labeling target molecules or recognition molecules with fluorescent molecules or electrochemically active molecules, label-free methods directly measure optical changes or mass changes without labeling. This eliminates the need for the tester to perform tedious labeling procedures and reduces concerns about artifacts, which are measurement fluctuations caused by modification with labeling molecules. In particular, when using optical waveguide devices, by immobilizing antibodies that selectively react only with specific antigens in advance on the sensing cell that functions as the transducer, antigen detection can be instantly captured as a change in refractive index or transmittance, and the output characteristics can be observed with a spectrum analyzer or power meter, allowing measurements to be performed just like a label-free method.

[0006] As mentioned above, with the increasing demand for constant monitoring of sanitary environments and health conditions, sensing devices are required to be label-free, non-contact, real-time, small, and inexpensive, and research and development of optical waveguide-type optical sensing circuits is being actively conducted (see, for example, Non-Patent Documents 1, 2, 3, or 4).

[0007] Silicon (Si) photonics has traditionally attracted attention as a platform technology for optical waveguide devices. Si photonics is characterized by the compactness and integration of optical waveguides and related optical devices such as modulators and photodetectors, which are achieved by utilizing the manufacturing processes of semiconductor devices such as CMOS (Complementary Metal Oxide Semiconductor), and the high productivity achieved by 200mm or 300mm wafer processes that utilize existing semiconductor manufacturing technology. Furthermore, Si waveguides, which have a Si core and a Si oxide film (SiO2) cladding, have a relative refractive index difference of up to 40%, resulting in a high optical confinement effect. In particular, with Si nanowire waveguides, the curvature radius of the bent waveguide and the parallel wiring pitch can be reduced to the order of several microns, enabling the miniaturization of optical circuit layouts. These features make Si photonics suitable for a variety of applications, such as optical transceivers and optical sensing circuits. It is expected that this technology will be applied to various applications (see, for example, Patent Document 1 or 2, and Non-Patent Documents 1, 2, 3, or 4).

[0008] A typical example of an optical waveguide type optical sensing circuit is one that uses a ring resonator.

[0009] A ring resonator is composed of an input waveguide, an output waveguide, and a ring-shaped trace waveguide that can be optically coupled to them. Local directional couplers are formed between the input waveguide and the trace waveguide, and between the output waveguide and the trace waveguide, respectively, causing light to transition between the waveguides. A portion of the light input from the input waveguide couples with the trace waveguide and transitions to the trace waveguide. Furthermore, of the light circulating through the trace waveguide, only light that satisfies specific interference (resonance) conditions couples with the output waveguide and transitions to the output waveguide. The light that transitions to the output waveguide is output via the output waveguide. Because the interference conditions in the trace waveguide are wavelength-dependent, they are observed as spectral peaks. Ignoring optical loss, light that does not satisfy the resonance conditions is output as transmitted light from the port opposite the input port of the input waveguide, in a complementary relationship.

[0010] The operating principle of a conventional optical sensing circuit using a ring resonator will be described with reference to FIG. 15. FIG. 15 is a schematic diagram illustrating the operating principle of the optical sensing circuit. FIGS. 15(A), 15(C), and 15(E) are schematic diagrams illustrating an antibody 560 attached to a ring resonator and how an antigen 570 is captured by the antibody 560. FIGS. 15(B), 15(D), and 15(F) are optical output spectra corresponding to FIGS. 15(A), 15(C), and 15(E), respectively, with wavelength on the horizontal axis and optical output power on the vertical axis. FIGS. 15(A) and 15(B) show the initial state, FIGS. 15(C) and 15(D) show states where the antigen concentration is low, and FIGS. 15(E) and 15(F) show states where the antigen concentration is high. FIG. 15(G) shows the antigen concentration on the horizontal axis and optical output power on the vertical axis.

[0011] As shown in Figure 15(A), an antibody 560 is mounted on the ring resonator. Here, when a tunable wavelength light source is used to tune the output wavelength to the resonance peak wavelength of the ring resonator, the optical output from the output waveguide is maximized (see Figure 15(B)). When the optical output from this output waveguide is maximized, the wavelength of the tunable wavelength light source is fixed to λ0 as the initial state.

[0012] Next, the optical sensing circuit is exposed to the analyte to be sensed, and the antibody 560 mounted on the ring resonator captures the antigen 570 (see Figures 15(C) and (E)). This changes the effective refractive index (equivalent refractive index) of the light propagating through the optical waveguide core, resulting in a shift in the resonant peak wavelength corresponding to the concentration of the substance or antigen (see Figures 15(D) and (F)). At this time, the optical output from the ring resonator's output waveguide is attenuated due to a mismatch between the wavelength of the fixed light source and the resonant peak wavelength of the ring resonator. Therefore, by linking the fluctuation in output power with the fluctuation in the refractive index sensed by the ring resonator, it is possible to estimate the amount of refractive index change. Because analytes have unique refractive indices, the shift in the resonant peak wavelength can be used to identify the detected substance and determine its concentration (see Figure 15(G)).

[0013] As mentioned earlier, ring resonators based on Si photonics can have a radius of curvature that is small enough to be on the order of a few microns, making it possible to realize extremely small ring resonator devices. Furthermore, by using a germanium (Ge) growth device in combination, it is possible to fabricate a photodetector (PD: Photo Diode) on the same wafer, and the elements required for sensing can be integrated and formed in units of 10 or more on a chip that is a few mm square. This makes it possible to simultaneously evaluate multiple samples in a single measurement. However, it is difficult to realize a light source using Si, which is an indirect transition semiconductor and has low luminous efficiency. For this reason, with regard to light sources, currently, methods such as mounting a laser diode (LD: Laser Diode) chip fabricated in a separate process on a Si chip on which a ring resonator device or PD is integrated, or using an external light source as an optical fiber are the only methods available. A method of connecting via fiber or the like is used.

[0014] In waveguide-type optical sensing circuits such as ring resonators, the evanescent wave, which is a component of the transmission mode that leaks from the Si core, overlaps with the sensing specimen, i.e., the refractive index perturbation, causing a change in the equivalent refractive index. Therefore, in order to improve detection sensitivity, it is important to reduce the distance between the specimen and the Si core by thinning the cladding directly above the Si waveguide core using techniques such as etching or chemical mechanical polishing (CMP). [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Publication No. 2018-155863 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-121696 [Non-patent literature]

[0016] [Non-Patent Document 1] CLEO 2018 OSA 2018, JTh2A.60, “High Q Si Slot Waveguide Ring Resonators for Gas Sensing Application” [Non-patent document 2] Japanese Journal of Applied Physics 55, 04EM04 (2016), “Differential Si ring resonators for label-free biosensing” [Non-patent document 3] 11 June 2007 / Vol. 15, No. 12 / OPTICS EXPRESS 7612, “Silicon-on-Insulator microring resonator for sensitive and label-free biosensing” [Non-patent document 4] 13 February 2012 / Vol. 20, No. 4 / OPTICS EXPRESS 4189, “Electrical tracing-assisted dual-microring label-free optical bio / chemical sensors” Summary of the Invention [Problem to be solved by the invention]

[0017] The sensing sensitivity index (Figure of Merit) of a ring resonator is estimated by the product of the spectral Q value (steepness of the resonant peak) and the resonant peak wavelength shift coefficient (Δλ / ΔN) relative to the amount of refractive index change. For example, the detectable refractive index change of a ring resonator with a Q value of 50,000 and Δλ / ΔN=100 [nm / RIU] (RIU: Refractive Index Unit) is approximately 2.0 × 10 -5 [RIU] (see, for example, Non-Patent Document 3). Meanwhile, temperature dependency is also an important factor in terms of detection sensitivity. In a typical Si waveguide device, the coefficient of change (Δλ / ΔT) of the resonance peak wavelength with respect to temperature fluctuation is 0.05 to 0.07 [nm / K]. For example, in a measurement environment where the temperature fluctuation amount ΔT is ±0.1K, this means that wavelength fluctuation of ±0.005 to 0.007 [nm] occurs. In a ring resonator with Δλ / ΔN=100 [nm / RIU], this wavelength fluctuation is 5 to 7 × 10 -5 The refractive index change below this level is buried as temperature-induced measurement noise. In other words, the inherent detection sensitivity of the ring resonator is limited by temperature dependence.

[0018] As such, temperature dependence has a significant impact on the minimum detectable refractive index, and the challenge is how to reduce the temperature dependence of the optical sensing circuit. Furthermore, it is necessary to initially match the light source wavelength with the resonant peak wavelength. The higher the detection sensitivity of the optical sensing circuit, the more strict temperature management and light source oscillation wavelength control are required, making it difficult to operate in general environments.

[0019] The present invention has been made in view of the above-mentioned problems, and aims to alleviate the temperature dependency of the resonance peak wavelength in an optical waveguide type optical sensing circuit and an optical sensing method, and to eliminate the need for oscillation wavelength control between the light source and the ring resonator, thereby simplifying operation. The target. [Means for solving the problem]

[0020] In order to achieve the above-mentioned object, the optical sensing circuit of the present invention is an optical waveguide type optical sensing circuit comprising a support substrate, a clad formed on the support substrate, and an optical waveguide core embedded in the clad and arranged parallel to the upper surface of the support substrate, and is configured to comprise: a bandpass filter; a ring resonator comprising an input waveguide, a ring-shaped trace waveguide, and an output waveguide, a reference ring resonator in which a resistive material is provided as a heater on the clad in the region in which the ring resonator is formed; a sensing ring resonator comprising the input waveguide, the ring-shaped trace waveguide, and the output waveguide, and in which a sensing region is provided; and a light-receiving element.

[0021] Of the light having the resonant wavelength of the reference ring resonator, light in a specific wavelength band extracted by a bandpass filter is sent to the input waveguide of the sensing ring resonator, and light having the resonant wavelength of the sensing ring resonator is sent from the output waveguide of the sensing ring waveguide to the light receiving element, and the specific wavelength band extracted by the bandpass filter is below the FSR (Free Spectral Range) of the sensing ring resonator.

[0022] Furthermore, according to a preferred embodiment of the optical sensing circuit of the present invention, there is provided an optical waveguide type optical sensing circuit comprising a support substrate, a clad formed on the support substrate, and an optical waveguide core embedded in the clad and arranged parallel to the upper surface of the support substrate, the optical sensing circuit comprising: a bandpass filter, a ring resonator comprising an input waveguide, a ring-shaped trace waveguide, and an output waveguide, a reference ring resonator in which a resistive material is provided as a heater on the clad in a region in which the ring resonator is formed; a branching section, a ring resonator comprising an input waveguide, a ring-shaped trace waveguide, and an output waveguide, and a sensing region, N (N is an integer of 2 or more) sensing ring resonators; and N light-receiving elements.

[0023] Of the light of the resonant wavelength of the reference ring resonator, light of a specific wavelength band extracted by the bandpass filter is sent to a branching section, which branches the received light into N branches and sends each branch to the input waveguides of the first to Nth sensing ring resonators, and the light of the resonant wavelength of the first to Nth sensing ring resonators is sent from the output waveguides of the first to Nth sensing ring resonators to the first to Nth light receiving elements, respectively, and the specific wavelength band extracted by the bandpass filter is less than the FSR of the sensing ring resonator.

[0024] According to another preferred embodiment of the optical sensing circuit of the present invention, there is provided an optical waveguide type optical sensing circuit comprising a support substrate, a clad formed on the support substrate, and an optical waveguide core embedded in the clad and arranged parallel to an upper surface of the support substrate, the optical sensing circuit comprising: one or N reference ring resonators each comprising N bandpass filters, an input waveguide, a ring-shaped trace waveguide, and an output waveguide, wherein a resistive material is provided as a heater on the clad in the region where the ring resonator is formed; N sensing ring resonators each comprising an input waveguide, a ring-shaped trace waveguide, and an output waveguide, wherein a sensing region is provided; and N light-receiving elements.

[0025] The light of the wavelength band including each peak of the resonant wavelength of the reference ring resonator extracted by the pth bandpass filter (p is an integer between 1 and N) is sent to the input waveguide of the pth sensing ring resonator, and the light of the resonant wavelength of the pth sensing ring waveguide is sent to the pth light receiving element from the output waveguide of the pth sensing ring resonator. The specific wavelength bands extracted by the first to Nth bandpass filters are respectively the peaks of the resonant wavelength of the first to Nth sensing ring resonators. The wavelength bands include the resonant wavelength, are equal to or less than the FSR, and are different from each other.

[0026] In implementing the above-described optical sensing circuit, the cladding in the sensing region may be partially or entirely thinned.

[0027] Furthermore, in order to achieve the above-mentioned object, the optical sensing method of the present invention is performed using the above-mentioned optical sensing circuit, and includes the steps of using a broadband light source having flat output characteristics over a wide wavelength band as a light source, and changing the temperature of a heater provided in the reference ring resonator as necessary to set the reference ring resonator to an initial state in which the resonant wavelength of the reference ring resonator and the resonant wavelength of the sensing ring resonator match, exposing the sensing ring resonator to a sample, and obtaining the amount of deviation between the resonant wavelength of the reference ring resonator and the resonant wavelength of the sensing ring resonator, and obtaining the concentration of the antigen from the amount of wavelength deviation.

[0028] Here, the shift of the resonant wavelength is preferably acquired based on the attenuation of the light receiving power of the light receiving element from the initial state, or may be acquired based on the heater power when the power supplied to the heater included in the reference ring resonator is changed so that the light receiving power of the light receiving element matches the light receiving power in the initial state. [Effects of the Invention]

[0029] The optical sensing circuit and optical sensing method of this invention enable the use of a broadband light source, eliminating the need to align the light source's oscillation wavelength with the ring resonator's peak wavelength, as in conventional methods. Furthermore, even if the temperature of the measurement environment fluctuates, the two ring resonator devices, the reference ring resonator and the sensing ring resonator, are closely located on the same chip, so the two ring resonators are equally affected by temperature. In other words, the relative relationship between the two resonant peak wavelengths is maintained independently of temperature, so the output characteristics depend only on the refractive index of the sensing sample, eliminating temperature dependence. This mitigates the temperature dependence of the resonant peak wavelength and simplifies operation by eliminating the need to control the oscillation wavelengths of the light source and ring resonator. Furthermore, the inclusion of a bandpass filter prevents degradation of sensing characteristics due to accidental coincidence of the resonant peak wavelengths. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 2 is a schematic plan view of a first light-sensing circuit. [Figure 2] FIG. 2 is a schematic cross-sectional view of a first light-sensing circuit. [Figure 3] FIG. 2 is a diagram illustrating a reference ring resonator and a sensing ring resonator. [Figure 4] FIG. 4 is a schematic diagram for explaining the operation of the first light-sensing circuit. [Figure 5] 10 is a diagram showing the relationship between the shift amount Δλ of the peak wavelengths of the reference ring resonator and the sensing ring resonator and the light receiving power at the light receiving element. FIG. [Figure 6] 10A and 10B are schematic diagrams for explaining the operation of a bandpass filter, showing a resonance spectrum in the case where there is no bandpass filter, and FIG. 10C are schematic diagrams for explaining an arm waveguide having a rib waveguide. [Figure 7] FIG. 2 is a schematic plan view of a bandpass filter. [Figure 8] FIG. 1 is a schematic diagram for explaining the operation of a bandpass filter, showing a resonance spectrum when a bandpass is present. [Figure 9]FIG. 10 is a schematic plan view of another configuration example of the first light-sensing circuit. [Figure 10] FIG. 4 is a schematic diagram for explaining the operation of the second light-sensing circuit. [Figure 11] FIG. 10 is a schematic plan view of a third light-sensing circuit. [Figure 12] FIG. 10 is a schematic plan view of a fourth light-sensing circuit. [Figure 13] FIG. 10 is a schematic diagram for explaining the operation of the fourth light-sensing circuit. [Figure 14] FIG. 10 is a schematic plan view of a fifth light-sensing circuit. [Figure 15] 1A and 1B are schematic diagrams for explaining the operating principle of an optical sensing circuit using a ring resonator. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and positional relationship of each component are merely shown in a schematic manner to enable understanding of the present invention. Furthermore, while preferred configuration examples of the present invention will be described below, the materials and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes and modifications can be made that achieve the effects of the present invention without departing from the scope of the configuration of the present invention.

[0032] (First embodiment) A first embodiment of a light-sensing circuit according to the present invention (hereinafter also referred to as the first light-sensing circuit) will be described with reference to Figures 1 and 2. Figure 1 is a schematic plan view of the first light-sensing circuit, omitting a support substrate and clad, which will be described later, and showing only an optical waveguide core. Note that the support substrate and clad, which will be described later, are also omitted from other schematic plan views. Figure 2 is a schematic cross-sectional view of the first light-sensing circuit. Figure 2(A) is a schematic cross-sectional view taken along line AA in Figure 1, and Figure 2(B) is a schematic cross-sectional view taken along line BB in Figure 1.

[0033] The first light-sensing circuit 100 has a basic structure including a support substrate 10, a cladding 20, and an optical waveguide including an optical waveguide core 30.

[0034] The support substrate 10 is configured as a flat plate made of, for example, single crystal silicon (Si).

[0035] The cladding 20 is provided on the support substrate 10. The cladding 20 covers the upper surface of the support substrate 10 and is formed to encompass the optical waveguide core 30. The cladding 20 is formed from, for example, silicon oxide (SiO2) as a material.

[0036] The optical waveguide core 30 is formed of, for example, Si, which has a refractive index (3.5) higher than the refractive index (1.45) of the cladding 20. As a result, the optical waveguide core 30 and the surrounding cladding 20 function as an optical transmission path (optical waveguide), and light input to the optical waveguide core 30 propagates in a propagation direction according to the planar shape of the optical waveguide core 30.

[0037] The basic structure of this optical waveguide can be easily manufactured by using, for example, an SOI (Silicon On Insulator) substrate. An example of a method for manufacturing an optical waveguide structure will be described below.

[0038] First, an SOI substrate is prepared, which is constructed by sequentially stacking a support substrate layer, an SiO2 layer, and an Si layer. Next, the Si layer is patterned, for example, by dry etching. After that, an SiO2 film is formed on the SiO2 layer to cover the Si layer. As a result, the basic structure of an optical waveguide is obtained, which includes a support substrate 10, a cladding 20, and an optical waveguide core 30.

[0039] The first optical sensing circuit 100 includes an input section 200, a bandpass filter 300, a reference ring resonator 400, a sensing ring resonator 500, a light receiving element 600, and an output section 700.

[0040] Light generated by a light source 900 is input to the first light-sensing circuit 100. The light source 900 may be, for example, a broadband light source (BBLS) having flat output characteristics over a wide wavelength band. A laser diode (LD) or broadband light source (Broad Band Light Source) is used. It is difficult to realize a light source 900 having the above-described output characteristics with Si, which is an indirect transition semiconductor and has low light emission efficiency. For this reason, a method is used in which a laser diode (LD) chip fabricated in a separate process is mounted as the light source 900 on a Si chip on which the light sensing circuit 100 is integrated, or a method is used in which the light source 900 is connected via an optical fiber or the like.

[0041] The input unit 200, which is an input interface of light to the first optical sensing circuit 100, may be an edge-coupling spot size converter (SSC) or a planar coupling grating coupler (GC). A GC with strong polarization selectivity and that can be placed anywhere on the chip is suitable for the input section 200 in order to mitigate the characteristic fluctuations caused by polarization fluctuations in Si waveguide devices, which have a high polarization dependency, and to increase the integration density of ring resonator devices. For this reason, an example in which a GC is used as the input section 200 will be described here.

[0042] Light input from the BBLS, which is the light source 900, through the GC, which is the input unit 200, to the optical sensing circuit 100 is sent to the reference ring resonator 400 via the bandpass filter 300. The bandpass filter 300 has a first input port 301, a first output port 302, and a second output port 303. Details of the bandpass filter 300 will be described later. The input unit 200 is optically connected to the first input port 301 of the bandpass filter 300.

[0043] The reference ring resonator 400 and the sensing ring resonator 500 are both so-called ring resonators. The reference ring resonator 400 and the sensing ring resonator 500 will be described with reference to Fig. 3. Fig. 3 is a diagram for explaining the reference ring resonator 400 and the sensing ring resonator 500. Fig. 3(A) is a schematic diagram for explaining a ring resonator, and Figs. 3(B) and 3(C) are schematic plan views of the reference ring resonator 400 and the sensing ring resonator 500, respectively.

[0044] The ring resonator 1000 includes an input waveguide 1010, a ring-shaped trace waveguide 1020, and an output waveguide 1030. The input waveguide 1010 and the trace waveguide 1020, and the output waveguide 1030 and the trace waveguide 1020, locally form directional couplers 1040 and 1050, respectively, causing light to transition between the waveguides. A portion of the light input from the input waveguide 1010 couples with the trace waveguide 1020 in the directional coupler 1040 and transitions to the trace waveguide 1020. Of the light circulating through the trace waveguide 1020, only light that satisfies a specific interference (resonance) condition couples with the output waveguide 1030 in the directional coupler 1050 and transitions to the output waveguide 1030. The light that transitions to the output waveguide 1030 is output via the output waveguide 1030. The interference condition in this trace waveguide 1020 is wavelength dependent and is therefore observed as a spectral peak. If optical loss is ignored, light that does not satisfy the resonance condition is output as transmitted light from the port opposite the side to which the light was input in the input waveguide 1010, in a complementary relationship.

[0045] The reference ring resonator 400 is configured to include an input waveguide 410, a trace waveguide 420, and an output waveguide 430. The reference ring resonator 400 is also configured to include a heater 440 made of a resistive material such as TiN directly above the trace waveguide 420. When power is supplied to the heater 440 to heat the trace waveguide 420, the resonant wavelength of the reference ring resonator 400 changes.

[0046] The sensing ring resonator 500 is configured to include an input waveguide 510, a trace waveguide 520, and an output waveguide 530. In the sensing ring resonator 500, the optical waveguide core is directly connected to the input waveguide 510. A sensing region 540 is provided on the optical waveguide core 30, which is exposed to the analyte to be sensed. In the sensing region 540, it is preferable that the trace waveguide 520 and the antibody 560, etc. are close to each other to improve the sensitivity of detecting changes in the refractive index. For this reason, the cladding 20 directly above the optical waveguide core 30 is thinned partially or entirely. An antibody, etc. for detecting a specific biological analyte is mounted on this thinned cladding.

[0047] The input waveguide 410 of the reference ring resonator 400 is optically connected to the first output port 302 of the bandpass filter 300. The output waveguide 430 of the reference ring resonator 400 is optically connected to the input waveguide 510 of the sensing ring resonator 500. In addition, the output waveguide 530 of the sensing ring resonator 500 is optically connected to the light receiving element 600.

[0048] The light receiving element 600 is configured by a waveguide type PD made of, for example, Ge.

[0049] The operation of the first optical sensing circuit 100 will be described with reference to Fig. 4. As described with reference to Fig. 15, in the sensing ring resonator 500, the resonance peak spectrum changes depending on the refractive index and concentration of the antibody that has captured the antigen. As an example, three cases are shown here where the deviation Δλ between the peak wavelength of the reference ring resonator and the peak wavelength of the sensing ring resonator is 0.5, 1.0, and 2.0 nm.

[0050] Figures 4(A), (C), and (E) show the resonant peak spectra of the reference ring resonator and the sensing ring resonator, respectively, and Figures 4(B), (D), and (F) show the sum of the resonant peak spectra of the reference ring resonator and the sensing ring resonator. Figures 4(A) and (B) show the case where the deviation Δλ between the peak wavelength of the reference ring resonator and the peak wavelength of the sensing ring resonator is 0.5 nm, Figures 4(C) and (D) show the case where Δλ is 1.0 nm, and Figures 4(E) and (F) show the case where Δλ is 2.0 nm. Figures 4(A) to (F) show wavelength on the horizontal axis and transmittance (unit: dB) on the vertical axis.

[0051] The reference ring resonator 400 at the front stage has a peak spectrum shown by curve I in Figures 4(A), (C), and (E), and the sensing ring resonator 500 at the rear stage has an intrinsic resonance peak spectrum shown by curve II. In this case, the spectrum of light that has passed through the reference ring resonator 400 and the sensing ring resonator 500 is output as the product (sum, in dB notation) of the transmittance of the resonance peak spectrum of the reference ring resonator and the resonance peak spectrum of the sensing ring resonator, as shown in Figures 4(B), (D), and (F).

[0052] Here, the spectrum from the output waveguide 530 of the sensing ring resonator 500 is received by the downstream light receiving element 600, and when a broadband light source is used as the light source 900, the received light power corresponds to the wavelength integral of the sum of the resonance peak spectrum of the reference ring resonator 400 and the resonance peak spectrum of the sensing ring resonator 500. The received light power of the light receiving element 600 depends on the shift Δλ in the peak wavelengths between the reference ring resonator 400 and the sensing ring resonator 500, and is at its maximum when the two peak wavelengths are the same (Δλ=0), and attenuates as the shift Δλ in the peak wavelengths increases.

[0053] FIG. 5 is a diagram showing the relationship between the shift amount Δλ of the peak wavelengths of the reference ring resonator and the sensing ring resonator and the received light power at the light receiving element 600, with the horizontal axis representing the shift amount Δλ (unit: nm) of the peak wavelengths and the vertical axis representing the received light power (unit: dB). Here, the received light power is the relative received light power with the received light power when Δλ=0 as the reference. As shown in FIG. 5, the received light power detected at the light receiving element 600 varies depending on the shift amount Δλ between the two peak wavelengths. For this reason, by linking the shift amount of the peak wavelengths to the refractive index, the horizontal axis can be used to calculate the received light power. The axis can be replaced with the amount of refractive index change, making it possible to estimate the refractive index of the sample.

[0054] In the initial state without a specimen, the reference ring resonator 400 and the sensing ring resonator 500 are designed to have the same wavelength characteristics, such as the resonant peak wavelength and FSR (Free Spectral Range). However, the initial resonant peak wavelength may deviate due to characteristic variations caused by manufacturing errors.

[0055] In this case, a current is passed through the heater 440 mounted on the reference ring resonator 400 to change the resonant peak wavelength of the reference ring resonator 400, and the point at which the light receiving power of the light receiving element 600 reaches its maximum value is set as the initial state. Next, the sensing region 540 of the sensing ring resonator 500 is exposed to the sample, and the output change (attenuation) is monitored. Note that when the difference between the two ring peak wavelengths becomes FSR / 2 or more, the output attenuation curve increases again, and the detectable range becomes half of FSR.

[0056] Next, the bandpass filter 300 will be described with reference to Figs. 6 to 8. Fig. 6 is a schematic diagram for explaining the function of the bandpass filter, showing the resonance spectrum when there is no bandpass filter. Fig. 7 is a schematic plan view for explaining the configuration of a grating-type wavelength filter as an example of a bandpass filter. Fig. 8 is a schematic diagram for explaining the function of the bandpass filter, showing the resonance spectrum when there is a bandpass filter.

[0057] The upper figures in Figures 6(A) and 6(B) and Figures 8(A) and 8(B) show the resonance spectrum of the reference ring resonator, and the lower figures show the resonance spectrum of the sensing ring resonator. Figures 6(A) and 8(A) show the resonance spectrum in the initial state, and Figures 6(B) and 8(B) show the resonance spectrum when a sample is detected.

[0058] In the initial state, the reference ring resonator 400 and the sensing ring resonator 500 are designed to have identical characteristics (see FIGS. 6A and 8A). However, as mentioned above, it is expected that the FSRs of the two ring resonators will differ depending on the refractive index of the antibody. In this case, the Vernier effect may cause wavelengths with matching peaks at wavelengths away from the central observation wavelength (part I in FIG. 6B). In this case, the output attenuation curve may become blunt, reducing sensing sensitivity and narrowing the detectable range of refractive index. For this reason, it is preferable to insert a bandpass filter to narrow the output wavelength range of the light source 900 to around the central observation wavelength.

[0059] A grating-type wavelength filter that exhibits strong selectivity only for a specific wavelength band is preferable as the bandpass filter 300. According to a preferred example of the bandpass filter 300 shown in Fig. 7, the bandpass filter 300 is configured to include a grating 310, a mode filter 320, an input waveguide 330, a first output waveguide 340, and a second output waveguide 350. The input waveguide 330 is optically connected to the input unit 200 in the preceding stage, and the first output waveguide 340 is optically connected to the input waveguide of the reference ring resonator 400 in the subsequent stage.

[0060] In the grating 310, a periodic refractive index modulation structure is applied to the waveguide. In the grating 310, the equivalent refractive indexes of the forward and backward waves of the transmitted light are set to n a and n b and the modulation period of the refractive index is Λ, the Bragg wavelength (λ) that satisfies the following formula (1) is Bragg ) appears as a reflection in the spectrum.

[0061] (n a +n b )Λ=λ Bragg (1) For example, the forward wave of light input from the input waveguide 330 is set to the fundamental mode, and the backward wave is set to a higher-order mode, and the higher-order mode as the backward wave is selectively extracted by the mode filter 320. The extracted light is output from the first output waveguide 340.

[0062] It is preferable to set the wavelength band of the bandpass filter so that it matches the FSR of the resonant peak spectrum of the sensing ring resonator, centered on the peak wavelength of the reference ring resonator. This cuts out output outside the observation wavelength band while using the BBLS, thereby preventing degradation of sensing characteristics due to accidental coincidence of the resonant peak wavelength (see Figure 8(B)).

[0063] Furthermore, when a chip on which the optical sensing circuit 100 is formed is used by fiber mounting, a structure similar to the GC of the input unit 200 can be used as the output unit 700. If the pitch of the array fiber to be mounted is X, by arranging the output unit 700 at a position that is an integer multiple of X away from the array of fibers, the transmitted light that is input from the BBLS and is not bandpass filtered by the bandpass filter 300 and is output from the second output waveguide 350 can be used as tap light and as monitor light during alignment, etc.

[0064] The first light-sensing circuit is not limited to the above-described configuration. Another configuration example of the first light-sensing circuit will be described with reference to Fig. 9. Fig. 9 is a schematic plan view of another configuration example of the first light-sensing circuit.

[0065] In the optical sensing circuit 100a of this other configuration example, the positional relationship between the bandpass filter 300 and the reference ring resonator 400 is different from that of the first optical sensing circuit 100 described with reference to Fig. 1. Other configurations and operations are similar to those of the first optical sensing circuit 100 described with reference to Fig. 1, and therefore, redundant explanations may be omitted.

[0066] In the optical sensing circuit 100a of another configuration example, light input to the optical sensing circuit 100 from the BBLS, which is the light source 900, via the GC, which is the input unit 200, is sent to the reference ring resonator 400. Light that satisfies the resonance condition of the reference ring resonator 400 is sent to the bandpass filter 300. On the other hand, light that does not satisfy the resonance condition of the reference ring resonator 400 is output from the output unit 700.

[0067] The bandpass filter 300 extracts light in a specific wavelength band and sends it to the input waveguide of the sensing ring resonator 500 .

[0068] In this way, in the optical sensing circuit 100a of the other configuration example, as in the first optical sensing circuit 100, light of a specific wavelength band extracted by the bandpass filter 300 from light of the resonant wavelength of the reference ring resonator 400 is sent to the input waveguide of the sensing ring resonator 500. Therefore, the optical sensing circuit 100a of the other configuration example can also achieve the same function as the first optical sensing circuit 100.

[0069] (Second embodiment) A second embodiment of the light-sensing circuit according to the present invention (hereinafter also referred to as a second light-sensing circuit) will be described with reference to Fig. 10. Fig. 10 is a schematic diagram for explaining the operation of the second light-sensing circuit.

[0070] The configuration of the second light-sensing circuit is similar to that of the first light-sensing circuit, and therefore a description thereof will be omitted.

[0071] The first optical sensing circuit utilizes the fact that the received light power of the light receiving element 600 varies depending on the amount of difference between the resonance peak wavelengths of the reference ring resonator 400 and the sensing ring resonator 500. The refractive index and concentration of the specimen are estimated from the amount of fluctuation in the received light power.

[0072] In contrast to this, the second optical sensing circuit estimates the amount of change in refractive index caused by the specimen by sweeping the power applied to the heater 440 mounted on the reference ring resonator 400.

[0073] When a sample is exposed to the sensing region 540 of the sensing ring resonator 500, the resonance peak wavelength of the sensing ring resonator 500 shifts depending on the refractive index and concentration of the sample. On the other hand, the resonance peak wavelength of the reference ring resonator 400 depends on the power applied to the heater 440, i.e., the temperature locally applied to the reference ring resonator 400.

[0074] When this heater power is swept and the correlation between the heater power and the light receiving power of the light receiving element 600 is plotted, the result is as shown in Figure 10(A). The light receiving power of the light receiving element 600 reaches a maximum value when the resonant peak wavelengths of the reference ring resonator and the sensing ring resonator match, and the heater power at that time depends on the specimen. The relationship between the heater power P and the resonant peak wavelength λ of the reference ring resonator is experimentally determined, and is proportional to the relationship shown in Figure 10(B). Using this slope Δλ / ΔP, the horizontal axis (power) in Figure 10(A) can be converted to the amount of shift in the peak wavelength, and a pseudo spectrum such as that shown in Figure 10(C) can be obtained. Furthermore, since the sensing ring resonator has a wavelength shift coefficient Δλ / ΔN with respect to the refractive index change that is specific to the device, the wavelength shift amount Δλ at which the light receiving power is maximized can be calculated. max By dividing Δλ / ΔN by Δλ, it is possible to estimate the amount of refractive index change ΔN due to the specimen.

[0075] (Third embodiment) A third embodiment of the light-sensing circuit according to the present invention (hereinafter also referred to as the third light-sensing circuit) will be described with reference to Fig. 11. Fig. 11 is a schematic diagram for explaining the operation of the third light-sensing circuit. In the following explanation, explanations that overlap with those of the first and second light-sensing circuits may be omitted.

[0076] The third sensing circuit 101 is different from the first optical sensing circuit in that it includes N (N is an integer equal to or greater than 2) sensing ring resonators 500-1 to 500-N and includes a branching section 800 between the reference ring resonator 400 and the sensing ring resonator 500. Note that N is preferably a power of 2.

[0077] The branching unit 800 branches the light sent from the reference ring resonator into N beams and sends them to the first to Nth sensing ring resonators 500-1 to N, respectively. The first to Nth light receiving elements 600-1 to N are optically connected to the subsequent stages of the first to Nth sensing ring resonators 500-1 to N, respectively.

[0078] The branching unit 800 is configured to include a number of couplers necessary to branch the light into N. The couplers are preferably so-called 3 dB couplers. k (k is an integer greater than or equal to 1), the couplers are arranged in log2N stages, log2N -1 is required. The first to log2N-1 stage couplers each split the light received from the previous stage into two and send them to the next stage coupler. The log2N stage couplers each split the light into two and send them to the first to Nth light receiving elements.

[0079] In Figure 11, as an example, N is 4 (=2 2) is shown. The first-stage coupler 810-1 splits the light received from the reference ring resonator into two and sends them to the first coupler 810-2 and second coupler 810-3 of the second stage. The second-stage first coupler 810-2 splits the light received from the first-stage coupler into two and sends them to the first photodetector 600-1 and second photodetector 600-2. The second-stage second coupler 810-3 splits the light received from the first-stage coupler 810-1 into two and sends them to the third photodetector 600-3 and fourth photodetector 600-4. Send to 00-4.

[0080] Here, the first to Nth sensing ring resonators 500-1 to 500-N have the same design but are spatially separated by cladding. This allows independent samples to be used in the sensing region of each sensing ring resonator 500-1 to 500-N. Therefore, by measuring the received light power of each waveguide photodiode in the same way as the first or second optical sensing circuit, multiple samples can be evaluated simultaneously.

[0081] (Fourth embodiment) The fourth light-sensing circuit will be described with reference to Fig. 12 and Fig. 13. Fig. 12 is a schematic plan view of another configuration example of the fourth light-sensing circuit. Fig. 13 is a schematic view for explaining the operation of the fourth light-sensing circuit.

[0082] The fourth sensing circuit differs from the first optical sensing circuit in that it includes N (N is an integer of 2 or more) reference ring resonators 400-1 to 400-N and sensing ring resonators 500-1 to 500-N, and N bandpass filters 300-1 to 300-N connected in series.

[0083] The first to Nth bandpass filters 300-1 to 300-N are connected in series, extract wavelengths in different bands, and send them to the first to Nth reference ring resonators 400-1 to 400-N, respectively. The configuration after the reference ring resonator can be configured based on the same concept as the first to third optical sensing circuits.

[0084] Here, the first to Nth sensing ring resonators 500-1 to 500-N have the same design but are spatially separated by cladding. This allows independent samples to be used in the sensing regions of the respective sensing ring resonators 500-1 to 500-N. Therefore, similar to the first or second optical sensing circuit, multiple samples can be evaluated simultaneously by measuring the received light power of each waveguide photodiode.

[0085] The second to Nth bandpass filters extract wavelengths in a predetermined band from the wavelength bands that were not extracted by the bandpass filters up to the previous stage. Figures 13(A) to 13(D) respectively show the resonant wavelengths of the first to fourth reference ring resonators with solid lines. As shown in Figure 13, the first to Nth sensing ring resonators 500-1 to 500-N use light in different wavelength bands.

[0086] In this way, the fourth light-sensing circuit detects the analyte using light of a wavelength that was not used for analyte detection in the first to third light-sensing circuits, and therefore the light generated by the light source 900 can be used effectively.

[0087] (Fifth embodiment) The fifth optical sensing circuit will be described with reference to Fig. 14. Fig. 14 is a schematic plan view of another configuration example of the fifth optical sensing circuit. The fifth optical sensing circuit differs from the fourth optical sensing circuit in that it includes one reference ring resonator 400 and N sensing ring resonators 500-1 to 500-N, and in the positional relationship between the bandpass filter 300 and the reference ring resonator 400. Other configurations and operations are similar to those of the fourth optical sensing circuit, and therefore, redundant explanations may be omitted.

[0088] Light input to the fifth optical sensing circuit via the input unit 200 is sent to the reference ring resonator 400. Light that satisfies the resonance condition of the reference ring resonator 400 is sent to the first bandpass filter 300-1.

[0089] The first to Nth bandpass filters 300-1 to 300-N are connected in series, extract wavelengths in different bands, and send them to the first to Nth sensing ring resonators 500-1 to 500-N, respectively. The configuration after the sensing ring resonator is the same as that of the fourth optical sensing circuit, so a description thereof will be omitted.

[0090] The light that is not extracted by the Nth bandpass filter 300-N passes through the output section 700 and is output.

[0091] Here, the first to Nth sensing ring resonators 500-1 to 500-N have the same design but are spatially separated by cladding. This allows independent samples to be used in the sensing regions of the respective sensing ring resonators 500-1 to 500-N. Therefore, similar to the first or second optical sensing circuit, multiple samples can be evaluated simultaneously by measuring the received light power of each waveguide photodiode.

[0092] In this way, the fifth optical sensing circuit detects an analyte using light of a wavelength that was not used for analyte detection in the first to third optical sensing circuits, and therefore, similar to the fourth optical sensing circuit, can effectively utilize the light generated by the light source 900. Furthermore, compared to the fourth optical sensing circuit, the number of reference ring resonators can be reduced. [Explanation of symbols]

[0093] 10 Support substrate 20 Clad 30 Optical waveguide core 100, 101 Optical sensing circuit 200 Input section 300 Bandpass Filter 400 Reference Ring Resonator 500 Sensing Ring Resonator 600 photodetector 700 Output Section 800 Branch 810 Coupler 900 light source

Claims

1. A support substrate; a cladding formed on the support substrate; an optical waveguide core embedded in the cladding and provided parallel to an upper surface of the support substrate, N (N is an integer equal to or greater than 2) bandpass filters connected in series; One or N reference ring resonators, each of which is a ring resonator including an input waveguide, a ring-shaped trace waveguide, and an output waveguide, and in which a resistive material is provided as a heater on a clad in a region where the ring resonator is formed; N sensing ring resonators, each of which includes an input waveguide, a ring-shaped trace waveguide, and an output waveguide, and each of which has a sensing region; N light receiving elements Equipped with The light input to the first bandpass filter is transmitted to the Nth bandpass filter in order, light in a wavelength band including each peak of the resonant wavelength of the reference ring resonator, extracted by the pth bandpass filter (p is an integer of 1 to N), is sent to the input waveguide of the pth sensing ring resonator; Light having a resonant wavelength of the p-th sensing ring waveguide is transmitted from the output waveguide of the p-th sensing ring resonator to the p-th light receiving element; The specific wavelength bands extracted by the first to Nth bandpass filters include the resonant wavelengths of the first to Nth sensing ring resonators, respectively, are equal to or less than the FSR (Free Spectral Range), and are mutually different wavelength bands.

1. A light sensing circuit comprising:

2. The bandpass filter is a grating type wavelength filter.

2. The light-sensing circuit according to claim 1, wherein the light-sensing circuit comprises:

3. The number of the reference ring resonators is N, the light extracted by the p-th bandpass filter is sent to the input waveguide of the p-th reference ring resonator; Furthermore, the light is transmitted from the output waveguide of the pth reference ring resonator to the input waveguide of the pth reference ring resonator.

3. The light-sensing circuit according to claim 1 or 2.

4. the number of the reference ring resonators is one, light from the reference ring resonator is sent to a first of the bandpass filters; The light extracted by the pth bandpass filter is sent to the input waveguide of the pth reference ring resonator.

3. The light-sensing circuit according to claim 1 or 2.

5. The cladding of the sensing region is partially or entirely thinned.

5. The light-sensing circuit according to claim 1, wherein the light-sensing circuit comprises: a first electrode;

6. A light sensing method using the light sensing circuit according to any one of claims 1 to 5, If necessary, changing the temperature of a heater included in the reference ring resonator to set the reference ring resonator to an initial state in which the resonant wavelength of the reference ring resonator coincides with the resonant wavelength of the sensing ring resonator; exposing the sensing ring resonator to an analyte; obtaining a shift amount between the resonant wavelength of the reference ring resonator and the resonant wavelength of the sensing ring resonator, and obtaining the concentration of the antigen from the shift amount of the resonant wavelength; An optical sensing method comprising:

7. The amount of shift in the resonant wavelength is obtained by The attenuation is performed based on the amount of attenuation of the light receiving power from the initial state in the light receiving element.

7. The optical sensing method according to claim 6, wherein the optical sensing method comprises:

8. The amount of shift in the resonant wavelength is obtained by The power supplied to the heater of the reference ring resonator is changed so that the light receiving power at the light receiving element coincides with the light receiving power in the initial state.

7. The optical sensing method according to claim 6, wherein the optical sensing method comprises:

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