Laser cavity-based sensor and sensing method

Abstract

A laser cavity-based sensor and a sensing method for measuring a measurand are provided. The laser cavity-based sensor includes a laser cavity configured to generate light at a resonant wavelength and having a gain medium and a resonant structure. The resonant structure has a sensing micro-ring resonator (MRR) and a control MRR arranged in a Vernier configuration defining the resonant wavelength of the laser cavity. At least a portion of the sensing MRR is accessible for interaction with said measurand. The sensing method involved operating the laser cavity at an initial resonant wavelength, interacting the measurand with the sensing MRR, tuning the control MRR to operate the laser cavity at a shifted resonant wavelength, and calculating a wavelength shift of the resonance wavelength of the laser cavity induced by the measurand.

Description

[0001] LASER CAVITY-BASED SENSOR AND SENSING METHOD

[0002] TECHNICAL FIELD

[0003] The technical field generally relates to optical sensors and more particularly concerns a laser cavity-based sensor.

[0004] BACKGROUND

[0005] A sensor is a device that detects and measures the presence or concentration of specific measurand by combining a recognition element, such as an enzyme, antibody, or nucleic acid in use case of a biosensor, with a physical transducer, such as an optical or electrical sensor. The recognition element selectively reacts to the presence of the measurand, while the physical transducer converts this reaction into an electrical or optical signal that can be monitored and studied. This method enables the quick, sensitive, and specific detection of target measurand, making sensors an effective tool for a wide range of applications. Over the past two decades, optical sensors formed from microcavity resonators have been used to attain some of the highest sensitivities. They are capable of detecting various measurands including but not limited to molecules, radiations, orientation and acceleration allow for real-time qualitative and quantitative sensing, and integration with electrical processing units. The interaction of the measurand and the recognition element leads to a change in the optical property of the medium and the microcavity transduce it to a change in the resonance mode. The change itself can be used for a label free qualitative detection of the measurand and its value can be interpreted into quantitative sensing. However, this method requires an external tunable laser source which increases the cost and complexity of the system and impedes miniaturization.

[0006] There remains a need in the art for improved optical sensors which alleviate at least some of the drawback of the prior art. SUMMARY

[0007] In accordance with one aspect, there is provided a laser cavity-based sensor for measuring a measurand, comprising: a laser cavity configured to generate light at a resonant wavelength, the laser cavity comprising:

[0008] - a gain medium;

[0009] - a resonant structure comprising a sensing micro-ring resonator (MRR) and a control MRR arranged in a Vernier configuration defining the resonant wavelength of the laser cavity, at least a portion of the sensing MRR being accessible for interaction with said measurand, said interaction changing a spectral response of the sensing MRR; and a tuning mechanism configured to tune a spectral response of the control MRR; and a control and processing unit operatively connected to the tuning mechanism and configured to:

[0010] - operate the laser cavity at an initial resonant wavelength;

[0011] - upon interaction of the measurand with the sensing MRR, tune the control MRR to operate the laser cavity at a shifted resonant wavelength; and

[0012] - calculate a wavelength shift of the resonance wavelength of the laser cavity induced by the measurand.

[0013] In some implementations, the laser cavity is provided in a photonic integrated platform comprising a gain chip hosting the gain medium and at least one reflector chip hosting the sensing MRR and the control MRR.

[0014] The gain chip may include a semiconductor optical amplifier.

[0015] Each of the at least one reflector chip may include a substrate and a cladding extending over the substrate, each of the sensing MRR and the control MRR being embedded in the cladding of one of said at least one reflector chip. The reflector chip hosting the sensing MRR may include a sample enclosure configured to receive a sample containing an analyte embodying the measurand, the at least a portion of the sensing MRR being accessible for interaction with said measurand extending within the sample enclosure. The at least a portion of the sensing MRR accessible for interaction with said measurand may be functionalized so that the analyte attaches thereto.

[0016] In some implementations, the tuning mechanism comprises:

[0017] - a metallic heat resistor in thermal contact with the control MRR;

[0018] - at least one electrode connected to the metallic heat resistor; and

[0019] - an electrical source connected to the at least one electrode.

[0020] In some implementations, the sensing MRR may comprise a metamaterial waveguide,

[0021] In some implementations, the sensing MRR may comprise a cantilever waveguide.

[0022] In some implementations, the laser cavity-based sensor may further comprise:

[0023] - an output port coupled to the resonant structure for extracting an output beam of said light from the laser cavity; and

[0024] - a photodetector coupled to the output port for measuring an optical power of the output beam.

[0025] The control and processing unit may be configured to measure the wavelength shift of the resonance wavelength of the laser cavity based on a monitoring of the optical power of the output beam.

[0026] In accordance with another aspect, there is also provided a sensing method for measuring a measurand, comprising: a) providing a laser cavity-based sensor, the laser cavity-based sensor comprising a laser cavity configured to generate light at a resonant wavelength and having a gain medium and a resonant structure comprising a sensing micro-ring resonator (MRR) and a control MRR arranged in a Vernier configuration defining the resonant wavelength of the laser cavity, at least a portion of the sensing MRR being accessible for interaction with said measurand; b) operating the laser cavity at an initial resonant wavelength; c) interacting the measurand with the sensing MRR; d) tuning the control MRR to operate the laser cavity at a shifted resonant wavelength; and e) calculating a wavelength shift of the resonance wavelength of the laser cavity induced by the measurand.

[0027] In some implementations, interacting the measurand with the sensing MRR comprises inserting a sample containing an analyte embodying the measurand in a sample enclosure provided in said laser cavity-based sensor.

[0028] In some implementations, the at least a portion of the sensing MRR being accessible for interaction with said measurand is functionalized so that the analyte attaches thereto.

[0029] In some implementations, tuning the control MRR comprises injecting a current through a metallic heat resistor in thermal contact with the control MRR.

[0030] In some implementations, the sensing method further comprises measuring an optical power of an output beam from said laser cavity.

[0031] In some implementations, the measurand is one of a concentration of an analyte, a pressure variation, an acceleration, an angular velocity, and a radiation variation.

[0032] Other features and advantages will be better understood upon of reading of detailed embodiments with reference to the appended drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 A is a schematic representation of a laser cavity-based sensor configuration according to one embodiment; FIG. 1 B is a side elevation view in partial transparency of a photonic integrated platform embodying the configuration of FIG. 1A.

[0034] FIGs. 2A and 2B are graphical representations of the individual spectra of two MRRs (FIG. 2A) and their synthesized Vernier reflection spectrum (FIG. 2B).

[0035] FIG. 3A is a schematic representation of a laser cavity-based sensor configuration according to one embodiment using MRRs of different materials; FIG. 3B is a side elevation view in partial transparency of a photonic integrated platform embodying the configuration of FIG. 3A. FIG. 3C is a cross-sectional view in transparency along lines C-C of FIG. 3B; FIG. 3D is a front view of the section of FIG. 3C; FIG. 3E is a cross-sectional view in transparency along lines E-E of FIG. 3B; and FIG. 3F is a front view of the section of FIG. 3E.

[0036] FIG. 4 is a cross-sectional view lines IV-IV of FIG. 1 B.

[0037] FIG. 5 is a schematic representation of a laser cavity-based sensor configuration according to one embodiment using meta-materials in the sensing MRR.

[0038] FIG. 6 is a schematic representation of a laser cavity-based sensor configuration according to one embodiment using a cantilever in the sensing MRR; FIG. 6A is a cross-sectional view along lines A-A of FIG. 6.

[0039] FIG. 7 is a schematic representation of a laser cavity-based sensor configuration according to another embodiment.

[0040] FIGs. 8A to 80 show the evolution of the spectral parameters in one embodiment of a sensing method. FIGs. 9A to 9D show the results of modeling the proposed sensing scheme for a refractive index change of 0.001 Rill, and are graphs respectively illustrating the MRR individual spectra (FIG. 9A) and the Vernier spectrum (FIG. 9B) before the shift, and the MRR individual spectra (FIG. 9C) and the Vernier spectrum (FIG. 9D) after the shift.

[0041] DETAILED DESCRIPTION

[0042] To provide a more concise description, some of the quantitative expressions given herein may be qualified with the term "about". It is understood that whether the term "about" is used explicitly or not, every quantity given herein is meant to refer to an actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including approximations due to the experimental and / or measurement conditions for such given value.

[0043] In the present description, the term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e. the limitations of the measurement system. It is commonly accepted that a 10% precision measure is acceptable and encompasses the term “about”.

[0044] In the present description, when a broad range of numerical values is provided, any possible narrower range within the boundaries of the broader range is also contemplated. For example, if a broad range value of from 0 to 1000 is provided, any narrower range between 0 and 1000 is also contemplated. If a broad range value of from 0 to 1 is mentioned, any narrower range between 0 and 1 , i.e. with decimal value, is also contemplated.

[0045] In accordance with some aspects, there is provided a laser cavity-based sensor for measuring a measurand. A sensing method is also provided. The laser cavity-based sensor may be used in a wide range of sensing applications to cover various stimulus such as pressure, acceleration, angular velocity, radiations, gases, and the like. In some implementations, the measurand may be an analyte in a sample. The sample may be a material with solid, liquid or gas phase. The analyte or measurand may be also a material with a solid, liquid or gas phase or a mixture of them. In other variants, the analyte may alternatively be a mechanical or radiative perturbation.

[0046] In some implementations, the disclosed laser cavity-based sensor may be used for biosensing applications. By way of example, infection diagnostic where the current infection state of the patient is of interest - such as in COVID-19 pandemic rapid tests, the sample may be mucous fluid obtained using swabs from the nose or throat and the analyte is the SARS-CoV-2 antigens. The sensor could similarly be employed to identify other viral infections like influenza or bacterial infections such as Streptococcus from patient samples.

[0047] One skilled in the art will readily understand that the disclosed laser cavity-based biosensor may be used for the discrete measurement of a physical quantities taken at a specific point or period in time, in which case the sampling rate determines how frequently these measurements are taken.

[0048] In addition to biosensing, in some implementations, the sensor’s versatility extends to environmental monitoring. For instance, it may be used to detect various gases such as carbon dioxide, methane, and volatile organic compounds (VOCs) for air quality assessment, providing real-time data critical for regulatory compliance and public health. In water quality monitoring, it can identify contaminants like heavy metals, nitrates, and pathogens. Samples of water can be processed to ensure safe drinking water and healthy aquatic ecosystems.

[0049] In some industrial application implementations, the sensor can be applied to structural health monitoring by detecting pressure, stress, and mechanical perturbations in buildings and bridges. For example, small samples or micro-debris from structural materials can be collected and analyzed using the sensor to provide early warnings of structural failures. It is also useful in process control, where microscale samples of industrial fluids or gases can be analyzed to monitor parameters like temperature, pressure, and gas concentrations, ensuring optimal industrial operations.

[0050] In some aerospace and defense application implementations, the sensor can function as a gyroscope or accelerometer, offering precise measurements of angular velocity and acceleration for navigation systems in aircraft and missiles. Additionally, it can detect ionizing radiation to protecting personnel and equipment in nuclear power plants and defense environments.

[0051] In some agricultural application implementations, for soil health monitoring, microscale samples of soil or water mixed with soil can be analyzed for moisture levels, nutrient content, and contaminants. This aids in irrigation management and fertilization. It can also monitor crop health by analyzing microscale samples of plant fluids for stress indicators such as changes in leaf chemistry or pathogen presence, enabling timely interventions to prevent crop losses.

[0052] The adaptability and precision of the laser cavity-based sensor make it a valuable tool across a myriad of fields. The sensor can provide high sensitivity and accurate measurements in medical diagnostics, environmental monitoring, industrial process control, and aerospace navigation. Its potential to enhance public health, environmental sustainability, and industrial efficiency highlights the importance of further research and development in this technology.

[0053] In some implementations, optical sensor designs are provided based on external cavity lasers (ECLs). In some implementations, the ECL design capitalize on the strengths of silicon photonic integrated circuit (PIC) based platforms, such as Silicon Nitride (SiN), QXP, and Silicon-on-lnsulator (SOI). These ECL based sensor design may incorporate multiple Silicon materials into a single PIC design. In some implementations, each microring resonator (MRR) may be strategically positioned within different material platforms, forming a robust ECL feedback circuit. Some variants may allow to ingeniously merge the compactness and compatibility of an SOI platform with the low propagation loss and high nonlinearity threshold of lower index silicon material platforms (e.g., SiN and QXP), leading to a wealth of benefits, including an enhanced performance with narrower linewidths, a low-noise wideband tunability range, high-side mode suppression ratios, and higher output power. Additionally, implementations of the disclosed ECL-based sensors may leverage the thermal stability advantages of lower index silicon materials while maintaining the rapid switching time and reduced tuning power capabilities of SOI, making it an ideal solution for diverse applications.

[0054] In accordance with one embodiment, the ECL-based sensor uses an ECL configuration based on two MRRs in a Vernier configuration to form the feedback circuit of the ECL. The disclosed configuration employs one of the MRRs as a sensing device within the ECL cavity. The sensing device has the capacity to manipulate lasing conditions. By resetting these laser conditions and understanding the old and new lasing conditions, the presence of measurands that induce changes in the sensing device can detected and quantified. Advantageously, embodiments of the ECL-based sensor can be seamlessly realized using existing fabrication processes (e.g., SiN-on-SOI, QXP-on-SOI), providing practical and accessible designs.

[0055] Laser cavity-based sensor

[0056] Referring to FIGs. 1A and 1 B, there is shown an example of a laser cavity-based sensor 20 according to one embodiment. The laser cavity-based sensor 20 first includes a laser cavity 26 configured to generate light at a resonant wavelength. As will be readily understood by one skilled in the art, a laser cavity typically includes a gain medium 24 apt to amplify light and provided within a resonant structure. In some implementations, as for example shown in FIG. 1 B, the laser cavity is provided within a photonic integrated platform 21. As understood by those skilled in the art, integrated photonics refers to on-chip technology in which at least one component providing an optical function is provided. In the illustrated example, the gain medium 24 is embodied by a waveguide in a gain chip 22. The gain chip 22 may have any structure known in the art. For example, the gain chip 22 be embodied by a Semiconductor Optical Amplifier (SOA) using a direct bandgap lll-V medium such InP or the like, depending on the resonant wavelength of interest. The gain medium 24 may be quantum well-based, quantum dash-based or quantum dot-based. It will be readily understood that in other variants the gain medium 24 may be embodied by any material or structure amplifying light via stimulated emission, the choice of gain medium determining the resonant wavelength of the laser cavity 26. SOAs, such as those based on InP, are for example commonly used in lasers that operate in the 1300-1600 nm wavelength range. A Fabry-Perot laser diode can also be used as the gain medium 24. In other examples gain media without semiconductors may be used, such as EDFAs, etc. The gain medium may have a bandwidth covering the C-band, L-Band, O-band or any other wavelength range providing amplification at the required wavelengths for lasing to occur at the desired resonant wavelength.

[0057] The resonant structure of the laser cavity 26 may be arranged in any configuration providing a resonance of light amplified by the gain medium 24 at a resonant wavelength. In some implementations, such as shown in the illustrated variant of FIGs. 1A and 1 B, the resonant structure has a Fabry-Perot configuration, also understood as a linear cavity. As known in the art, a Fabry-laser Perot cavity may be defined by a pair of light reflectors, or mirrors, provided at opposite ends of the gain medium 24. In some implementations, the pair of light reflectors may include a fixed cavity reflector 28 optically coupled to one extremity 23 of the gain medium 24, and a tunable cavity reflector 32 optically coupled to an extremity 25 of the gain medium 24 opposite the fixed cavity reflector 28.

[0058] The expression “fixed cavity reflector” will be understood by one a skilled in the art as a reflector that is not tunable, or passive. In some implementations, such as shown in FIGs. 1A and 1 B, the fixed cavity reflector 28 may be embodied by a layer of reflective material deposited on a surface at the corresponding extremity 23 of the gain chip 22, embodying a Reflective Semiconductor Optical Amplifier (RSOA) design. It will however be readily understood that the fixed cavity reflector may alternatively be external to the gain chip, and for example includes a separate mirror, a Sagnac loop mirror, or the like.

[0059] In some implementations, the photonics integrated platform 21 may includes one or more reflector chips 30 coupled to the gain chip 22, thereby defining an external cavity laser (ECL) configuration. With particular reference to FIG 1 B, in some embodiments the reflector chip 30 hosts the tunable cavity reflector 32. The reflector chip 30 may be embodied by a SOI structure comprising several layers. In some implementations, the reflector chip 30 may include a substrate 60, for example made of Si, on which is provided a cladding 62, for example made of SiO2. In typical embodiments, the reflector chip 30 includes one of more functional layers 31 embedded in the cladding 62. The functional layers 31 may define waveguide structures and segments allow light circulation through the reflector chip. Optical visa or other coupling elements may be provided to allow light to travel from one functional layer to another.

[0060] In some implementations, the resonant structure of the laser cavity 26 includes a sensing micro-ring resonator (MRR) 34 and a control MRR 36 arranged in a Vernier configuration defining the resonant wavelength of the laser cavity 26. It will be understood that in some implementations, more than one MRR may embody the control MRR 36. As their name entails, each MRR defines a ring-shaped waveguide provided in the reflector chip 30 and forming a closed loop of corresponding radius 7?z. The sensing MRR 34 and the control MRR 36 may be made of a same material, such as for example shown in FIGs 1A and 1 B, or be made of different materials as shown in FIGs. 3A and 3B, or made of same or different materials in which the sensing MRR is based on subwavelength grating metamaterial waveguides, such as shown in FIG. 5. The MRRs 34 and 36 preferably extend generally parallel to the substrate 60 in one of the functional layers 31 of the reflector chip 30. In some implementations, the sensing MRR 34 and the control MRR 36 may extend along a single plane or may respectively extend at different heights h from the substrate 60. In one variant, the sensing MRR 34 and the control MRR 36 may be stacked one above the other, substantially or partially. In other implementations, the sensing MRR 34 and the control MRR 36 may extend laterally offset from each other. In some implementations, the sensing MRR may be a detachable or separate component, remove from the laser cavity for exposure to the measurand and placed back inside for the measuring process.

[0061] The sensing MRR 34 and the control MRR 36 may each be made of any one of a variety of materials. The different materials may be silicon-based such as Si, SiN, or the like. It will however be readily understood by one skilled in the art that any of the embodiments disclosed herein and variants thereof may be implemented using different material or combination of materials. In some implementations, nonsilicon materials may be used, such as Indium Phosphide (InP), Gallium Arsenide (GaAs), Gallium Nitride (GaN), Aluminum Nitride (AIN), along with their respective binary, ternary, and quaternary compounds and alloys. For example, Indium Gallium Arsenide Phosphide (InGaAsP) is used for the C-0 bands (1200 nm - 1700 nm), Indium Gallium Arsenide Antimonide (InGaAsSb) and Mercury Cadmium Telluride (HgCdTe) are suitable for wavelengths above 1700 nm in the mid-infrared region, Gallium Nitride (GaN), Aluminum Nitride (AIN), and their alloys (e.g., InGaN, AIGaN) cover the ultraviolet to blue range (100 nm - 400 nm), and Gallium Arsenide (GaAs) and Aluminum Gallium Arsenide (AIGaAs) are used for the visible to near-infrared range (400 nm - 1200 nm). Additionally, materials like Aluminum Nitride (AIN), SiN, QXP (also referred to as high refractive index silica glass or Hydex, see for example Kues, M., Reimer, C., Roztocki, P. et al. On-chip generation of high-dimensional entangled quantum states and their coherent control. Nature 546, 622-626 (2017)), and Lithium Niobate (LiNbO3), Barium Titanate BaTiO3 (BTO) are notable for their broader wavelength coverage across multiple regions, also providing large Pockels coefficient, and slow wave propagation in the two latter cases for instance.

[0062] In some implementations, the sensing MRR 34 and the control MRR 36 are positioned within the reflector chip 30 so as to perform the reflecting function of the tunable cavity reflector 32. By way of example, FIGs. 1A and 1 B show a configuration where the sensing MRR 34 and control MRR 36 are positioned in a loop mirror configuration. It will be readily understood that this configuration is but one manner of implementing the tunable cavity reflector 32 and that in other variants, the different components of the tunable cavity reflector 32 may be arrange differently than illustrated here, depending on design considerations and target specifications.

[0063] As understood by those skilled in the art, the so-called Vernier Effect uses two (or more) resonators at two (or more) different resonant frequencies having Free Spectral Ranges (FSRs) that are slightly different, such that they overlap perfectly only at multiples of their individual FSR. In some implementations, each MRR has a spectral response defining a comb or scale of wavelength peaks. The FSR of a given ithMRR for light at a wavelength X is given by FSRt=

[0064] I / 7IL fig K ni , where

[0065] FSRt is the FSR of the MRR, Rtis the MRR radius and nggroup index of the MRR waveguide. By convention, the Vernier FSR of a pair of MRRs such as shown in FIG. 1 A is determined by: where m and m-1 are coprime integers for any m in a two MRR Vernier filter. The m and m-1 numbers are known as resonant numbers of the corresponding MRR. m also quantifies the increased tuning efficiency of the Vernier MRRs in comparison to a single

[0066] FIGs. 2A and 2B illustrate the spectral features of two MRRs in a typical Vernier configuration. FIG. 2A shows the individual spectral response or spectra 100 and 102 of the sensing MRR and control MRR with several-nm FSRs. The synthesized spectral response of the two MRRs in a Vernier configuration is shown in FIG. 2B. As can be seen the FSR of the combined MRRs is much broader than their individual ones. This Vernier FSR sets the range for the wavelength tuning of the laser cavity 26. Through a proper selection of the parameters of the laser cavity 26, one of the resonant wavelengths common to both MRRs may be favored, which falls in the gain bandwidth of the gain medium, thereby defining the resonant wavelength 104 of the laser cavity.

[0067] In the context of a laser cavity based on MRRs provided in two different materials, such as for example shown in the embodiment of FIG. 3Aand 3B, their group index difference has an impact on the considerations above. In some implementations, the sensing MRR 34 and control MRR 36 having different radii selected in view of their corresponding group indices. In one embodiment, the radii of the MRRs may be proportional to the ratio of their group indices. For example, for a SiN-on-Si platform, the radii of the MRRs can be approximately related as: which leads to a Vernier FSR of: where Rsi, RsiNare the MRR radii and ng si, ng siNare the group indices of the Si and SiN waveguides, respectively.

[0068] Restating equation (3) and applying it to unspecified different materials, the ratio of the radii of the two MRRs may, in some variants, substantially corresponds to: wherein Ri is the radius of the sensing MRR, R2 is the radius of the control MRR, ngiis the group index of the material of the sensing MRR, ng2 is the group index of the material of the control MRR, and m is a tuning enhancement factor.

[0069] Restating equation (3) and applying it to multiple MRRs in unspecified different materials, the ratio of the radii of the sensing MRR and the control MRRs, which could be more than 1 , may, in some variants, substantially corresponds to: wherein R1 is the radius of the control (first) MRR, R,+iis the radius of the (i+1 )thMRR, ngiis the group index of the material of the first MRR, ng(j+i) is the group index of the material of the (i+1 )thMRR, and rm and other resonant numbers of corresponding MRRs (mi+i) are co-prime numbers. Additional considerations and examples relating to laser configurations with MRRs of different materials can be found in international patent application PCT / CA2024 / 050822 (MARAM el al) filed on June 17, 2024, the entire contents of which is hereby incorporated by reference.

[0070] In some implementations, at least a portion of the sensing MRR 34 is accessible for interaction with said measurand. In some embodiments, for example in the case of biosensing applications, the laser cavity may include a sample enclosure 70 configured to receive a sample 71 containing an analyte 73 embodying the measurand. In some implementations, the sample enclosure 70 may be embodied by a region of the reflector chip 30 where a part of the cladding 62 has been removed, exposing the sensing MRR 34 for interaction with the environment outside of the reflector chip 30. FIGs. 3C and 3D respectively show a tridimensional view and a cross-section view of a portion of the sensing MRR 34 in the configuration of FIG. 3B. As can be seen, the portion of the cladding 62 extending over the sensing MRR 34 has been removed from the reflector chip, for example by etching, leaving the top surface of the sensing MRR 34 exposed so that it will be in contact with the sample 71 when it is inserted inside the sample enclosure 70. For comparison, FIGs. 3E and 3F respectively show a tridimensional view and a cross-section view of a portion of the control MRR 36, which is completely surrounded by the cladding 62. As will be understood by one skilled in the art, although the illustrated variant shows the entire sensing MRR 34 exposed to the environment, in other variants only a portion of the sensing MRR 34 may be so exposed without departing from the scope of protection.

[0071] In some implementations, the portion of the sensing MRR 34 being exposed to the sample 71 within the enclosure 70 is functionalized with functionalizing agents 72 such that the analyte attaches thereto. This can be achieved through several methods. For example, but not limited to, chemical functionalization may use silane chemistry, such as (3-aminopropyl) triethoxysilane (APTES), to introduce reactive groups on the surface of the sensing MRR 34, or may employ polyaniline or polypyrrole as linkers on the MRR surface for effective analyte binding (see for example Kny, Erich, et al. "State of the Art of Chemosensors in a Biomedical Context." Chemosensors 10.6 (2022): 199). Biological molecules, including antibodies and aptamers, may serve as bio-recognition elements to capture specific targets like the SARS-CoV-2 virus, aiding in COVID-19 detection. DNA / RNA probes can also be used for nucleic acid sequence detection. In other implementations, nanomaterials such as gold nanoparticles and functionalized graphene may be used to enhance binding efficiency and detection capabilities (see for example Beraud, Anouk, et al. "Graphene field-effect transistors as bioanalytical sensors: Design, operation and performance." Analyst 146.2 (2021 ): 403-428). Polymer coatings, such as polyethylene glycol (PEG), may also be used to prevent non-specific binding while enabling specific interactions. Conductive polymers may be doped with functional groups for selective analyte binding. Additionally, the surface of the sensing MRR 34 may be functionalized with biotin for ligand / receptor interaction studies, where biotinylated surfaces interact with avidin or streptavidin to model high-affinity binding systems. Advantageously, use of such methods and the like to prepare the surface of the sensing MRR 34 may favor the interaction of the sensing MRR 34 with analytes in a controlled manner, which may significantly improve sensor performance.

[0072] As will be readily understood by one skilled in the art, when the analyte attaches to the sensing MRR 34, or when a measurand interacts with the sensing MRR in a suitable manner, the effective index of the sensing MRR 34 will be affected. This then leads to a shift in the spectral response 100 of the sensing MRR 34, thereby detuning the resonant wavelength 104 of the laser cavity, which provides a means for sensing and measuring the analyte as explained further below.

[0073] By way of example, FIGs. 5 and 6 show 3D illustrations of examples in which appropriate ECL based sensing configurations for different measurands are employed. In particular, FIG. 5 shows a sub-wavelength waveguide grating (SWG), also referred to in the art as a metamaterial waveguide (see Naraine, Cameron M., et al. "Subwavelength grating metamaterial waveguides and ring resonators on a silicon nitride platform." Laser & Photonics Reviews 17.2 (2023): 2200216), as the sensing MRR 34. The metamaterial sensing MRR in this embodiment is covered with a functionalizing layer 74 which may be gas sensitive material, liquid crystal, or electrooptic polymer which is appropriate for gas and radiation sensing applications. Alternatively or additionally, the control MRR may also be a metamaterial waveguide. The use of SWGs in this configuration typically offers enhanced sensitivity, enabling highly sensitive detection of environmental changes. Additionally, the flexible design parameters of SWGs, through the engineering of the effective refractive index and dispersion properties, allow for customizable sensor designs tailored to specific applications. FIGs. 6 and 6A show a cantilevered MRR which is appropriate to measure the clockwise and counter-clockwise resonance modes in Gyroscope application and physical deformations in accelerometer application, is employed as the sensing element. A cantilevered MRR maybe be used as a highly sensitive sensing element due to its ability to detect small changes in resonance modes. In gyroscope applications, the cantilevered MRR can distinguish between clockwise and counter-clockwise resonance modes, to measure angular velocity and rotation. This is achieved by monitoring shifts in the optical resonance wavelength caused by the Coriolis force acting on the rotating structure. In accelerometer applications, the cantilevered MRR detects physical deformations resulting from external accelerative forces, this deformation changes the optical path length within the MRR, which in turn modifies the resonant wavelength of the MRR. By precisely measuring these wavelength shifts, the device can accurately quantify acceleration. Therefore, the cantilevered MRR serves as an effective transducer for converting mechanical movements into measurable optical signals, which then enables high-precision sensing in both gyroscopic and accelerometric contexts.

[0074] Referring back to FIGs. 1 A and 1 B and with additional reference to FIG. 4, in some implementations, the laser cavity-based sensor 20 further comprises a tuning mechanism 50 for tuning the spectral response of the control MRR 36, thereby changing the resonant wavelength of the laser cavity 26.

[0075] In some implementations, the thermo-optic (TO) effect may be used for tuning and switching between adjacent and non-adjacent wavelength channels. The tuning mechanism 50 may for example be embodied by a heater in thermal contact with the control MRR 36, to tune its individual resonances. As best seen on FIG. 4, in the illustrated embodiment the heater 50 includes a metallic heat resistor 52 placed above the control MRR and through which a current is passed to create heat in the resistor 52, whose temperature modifies the index of semiconductor materials. Metals that can be used as metallic heat resistors typically have a higher resistivity than the Cu and Al which typically is used for routing / pads and metallization. TiN, tungsten (W) lines above the waveguide are typically used. In the illustrated implementation the metallic heat resistor 52 is for example embodied by a TiN arch extending within the cladding 62 over a section of the control MRR 36, and having an arched shape matching the portion of the MRR ring underneath. Metal electrodes 54 are provided over the cladding 62 of the reflector chip 30 and are connected to extremities of the TiN arch 52. Metal vias 56 may provide the electrical connection between the electrodes 54 and the TiN arches 52. An electrical source 57, for example a voltage or current source, is connected to the metal electrodes 54 to pass an electrical current to the metallic heat resistor through the metal electrode 54.

[0076] Additionally, a metallic or doped silicon heater can be fabricated beneath or at the same lateral level as the sensing Si or SiN MRR in the SiO2. Heating the sample may allow for temperature-dependent studies of analyte interactions, providing insights into the analyte's behavior under different thermal conditions, thus improving the sensor's accuracy and range of applications such as polymerase chain reaction (PCR). A calibration stage needs to be performed to de-embed the impact of temperature on the index of the MRR waveguide from its impact on the analyte.

[0077] It will be readily understood by one skilled in the art that the tuning mechanism may be embodied by other components and technologies allowing to tune the resonance of the control MRR, without necessarily relying on a thermo-optic effect. Other ways of tuning may for example be based on the plasma dispersion effect or the Pockels effect.

[0078] Referring back to FIG. 1 A, in some implementations the laser cavity-based sensor 20 further includes an output port 45 coupled to the resonant structure for extracting an output beam of light from the laser cavity. The output port 45 may be provided at any point within the laser cavity, such as for example at couplers, reflectors, or at one of the MRRs. The laser cavity-based sensor 20 further includes a photodetector 46, such as a monitoring photodiode coupled to the output port for 45 measuring the optical power of the output beam. It will be noted that in typical embodiment, the laser cavity is only used as a sensing environment and that the generated light does not need to be extracted for any other purpose than monitoring. It will nonetheless be understood by one skilled in the art that multiple output ports may be provided without departing from the scope of protection.

[0079] In some implementations, the laser cavity-based sensor 20 further includes a control and processing unit 80 operatively connected to the tuning mechanism 50. The control and processing unit 80 is configured to:

[0080] - operate the laser cavity at an initial resonant wavelength;

[0081] - upon interaction of the measurand with the sensing MRR, tune the control MRR to operate the laser cavity at a shifted resonant wavelength; and

[0082] - calculate a wavelength shift of the resonance wavelength of the laser cavity induced by the measurand.

[0083] The control and processing unit 80 may be configured for controlling, monitoring, and / or coordinating the functions and operations of various components of the laser cavity-based sensor 20. The control and processing unit is also configured to process and / or analyze signals received from the monitoring photodetector to derive information about the measurand, such as for example the presence and / or concentration of analytes in a sample.

[0084] The control and processing unit 80 can be implemented in hardware, software, firmware, or any combination thereof, and be connected to various components of the laser cavity-based sensor 20 via wired and / or wireless communication links to send and / or receive various types of signals, such as timing and control signals, measurement signals, and data signals. The control and processing unit 80 may be controlled by direct user input and / or by programmed instructions, and may include an operating system for controlling and managing various functions of the laser cavity-based sensor 20. Depending on the application, the control and processing unit 80 may be fully or partly integrated with, or physically separate from, the other hardware components of the laser cavity-based sensor 20. In FIG. 1A, the control and processing unit 80 generally includes a processor 82, a memory 84 and ADCs / DACs for converting analog and digital signals.

[0085] The processor 82 may be able to execute computer programs, also generally known as commands, instructions, functions, processes, software codes, executables, applications, and the like. It should be noted that although the processor 82 in FIG. 1 is depicted as a single entity for illustrative purposes, the term “processor” should not be construed as being limited to a single processor, and accordingly, any known processor architecture may be used. In some implementations, the processor 82 may include a plurality of processing units. Such processing units may be physically located within the same device, or the processor 82 may represent processing functionality of a plurality of devices operating in coordination. For example, the control and processing unit 80 may include a main processor configured to provide overall control and one or more secondary processors configured for dedicated control operations or signal processing functions. Depending on the application, the processor 82 may include or be part of a computer; a microprocessor; a microcontroller; a coprocessor; a central processing unit (CPU); an image signal processor (ISP); a digital signal processor (DSP) running on a system on a chip (SoC); a single-board computer (SBC); a dedicated graphics processing unit (GPU); a special-purpose programmable logic device embodied in hardware device, for example, a field- programmable gate array (FPGA) or an application-specific integrated circuit (ASIC); a digital processor; an analog processor; a digital circuit designed to process information; an analog circuit designed to process information; a state machine; and / or other mechanisms configured to electronically process information and to operate collectively as a processor. The memory 84, which can also be referred to as a computer readable storage medium, is capable of storing computer programs and other data to be retrieved by the processor 82. The terms “computer readable storage medium” and “computer readable memory” are intended to refer herein to a non-transitory and tangible computer product that can store and communicate executable instructions for the implementation of various steps of the methods disclosed herein. The computer readable memory can be any computer data storage device or assembly of such devices, including random-access memories (RAMs); dynamic RAMs; read-only memories (ROMs); magnetic storage devices, such as hard disk drives, solid state drives, floppy disks, and magnetic tapes; optical storage devices, such as compact discs (e.g., CDs and CDROMs), digital video discs (DVDs), and Blu- RayTM discs; flash drive memories; and / or other non-transitory memory technologies. A plurality of such storage devices may be provided, as can be appreciated by those skilled in the art. The computer readable memory may be associated with, coupled to, or included in a computer or processor configured to execute instructions contained in a computer program stored in the computer readable memory and relating to various functions associated with the computer or processor.

[0086] In some implementations, the laser cavity-based sensor 20 may also include one or more user interface devices operatively connected to the control and processing unit 80 to allow the input of commands and queries to the laser cavity-based sensor 20, as well as present the outcomes of the commands and queries. The user interface devices may include input devices (e.g., a touch screen, a keypad, a keyboard, a mouse, a switch, and the like) and output devices (e.g., a display screen, a printer, visual and audible indicators and alerts, and the like).

[0087] Sensing method

[0088] As mentioned above, the laser cavity-based sensor measures the wavelength shift of the resonant wavelength of the laser cavity induced by the measurand. With reference to FIGs. 8A to 80, there is shown an example of the spectral parameters used in some implementations. FIG. 8A illustrates the transfer function of the individual sensing and control MRRs leading to initial lasing conditions before interaction with the measurand, the dashed line indicating the spectral response or spectra 102 of the control MRR and the solid line showing the spectral response or spectra 100 of the sensing MRR. The laser cavity generates light at an initial resonant wavelength Ao, shown at 104 in the bottom graph, corresponding to a common resonance in the spectral responses of both MRRs within the Vernier FSR, and at optical power Hvo. As known in the art, the tuning mechanism may be operated to tune the spectral response of the control MRR so that lasing conditions at the resonant wavelength are met and maintained. Referring to FIG. 8B, the sensing MRR is then exposed to the measurand, for example by inserting a sample in the sample enclosure of the embodiment of FIG. 1 B or 3B. As can be seen in the top graph of FIG. 8B, the interaction of the sensing MRR with the measurand shifts its spectral response 100 to either higher or lower wavelength than Ao (a shift to a higher wavelength is shown in FIG. 8B), the direction of the shift depending on the sample and measurement type. As a result, the laser power will drop by AH due to this shift, since the sensing MRR and control MRR are no longer aligned at the initial resonant wavelength Ao. This drop, shown in the bottom graph of FIG. 8B, may for example be measured using the monitoring photodetector. Next, the control MRR is tuned to operate the laser cavity at a shifted resonant wavelength AO+AAM, for example using the integrated heater of the control MRR, as shown in FIG. 8C. In some implementations, the output power at the shifted resonant wavelength may be slightly lower than the output power at the initial resonant wavelength, due to optical losses induced by the measurand in the sensing MRR. The wavelength shift of the resonance wavelength of the laser cavity induced by the measurand, i.e. the difference AAM between the shifted resonant wavelength and the initial resonant wavelength, can then be calculated.

[0089] Referring to FIG. 7, in some variants the laser cavity-based sensor 20 may include a phase detector 47 for measuring the direction of the wavelength shift induced by the measurand (see FIG. 8D). By way of example, in additional to the output port 45a connected to the monitoring photodiode 46, the laser cavity-based sensor 20 may have two additional output ports 45b and 45b, for example associated with waveguide segments on either sides of the control MRR 36, coupled to the phase detector for measuring a phase difference therebetween. In some implementations, the phase detector 47 may for example be embodied by a 90- degree hybrid coupler (see for example Dong, Po, et al. "Monolithic silicon photonic integrated circuits for compact 100Gb / s coherent optical receivers and transmitters." IEEE Journal of Selected Topics in Quantum Electronics 20.4 (2014): 150-157).

[0090] Different approaches may be used to identify the shifted resonant wavelength. In some implementations, a sweep of the electrical power used to tune the control MRR may be performed, and a peak value of the output power identified (see FIG.8E). In other variants, the wavelength shift may be obtained through calibration, based on the electrical power used to reset the ECL. Other methods to measure the wavelength shift may make use of resonance locking (also known as mode locking) in a stabilized ECL.

[0091] In some implementation, the wavelength shift value may be used to determine the presence of measurands, for example reflected by a wavelength shift above a certain threshold. In other variants, the concentration of analytes in the sample may be calculated from the value of the wavelength shift.

[0092] The laser cavity-based sensors disclosed herein may be used and studied for a variety of applications. In one example of a chemical sensing use-case, the resonance wavelength shift may be studied by covering the sensing MRR with a H2O / D2O solution with different concentrations and studying quantitative chemical sensing. In the next step, ligand / receptor interaction sensing can be assessed by a label free affinity model using avidin (or streptavidin) / biotin interaction. The surface of the sensing MRR may initially be functionalized with biotin, after which samples containing different concentration of avidin (or streptavidin) can be added on the top of the biotinylated surface. Bulk sensitivity or refractive index change can be investigated, for instance in Heavy water measurements using the (D2O) as an absorption or refractive index contrast medium with deionized water. Furthermore, to model the ligand / receptor interaction, avidin (or streptavidin)Zbiotin high affinity system can be used as a model that may be very stable and specific.

[0093] In some implementations, bulk sensitivity of the sensing MRR immersed in a fluid containing the analyte which depends on the configuration of the resonator (i.e. , the analyte solution) can be determined as:

[0094] Based on the sensitivity we find using equation 5 we can define the Limit of Detection (LOD) as: where the standard deviation a represents the system noise floor and can be measured by measuring the signal on a blank sample with a null concentration of analyte. An alternative analytic approach is available which uses the normalised bulk sensitivity, SN= asfollows: res

[0095] In all measurements, noise controlling approaches can be considered as well as signal isolation techniques since the low noise and high linearity are factors of interest in biosensors operating at the high frequency ranges.

[0096] As part of a preliminary feasibility study on a SOI mirroring sensor, an analytical- numerical model was used. FIGs. 9A to 9D show the results of modeling the proposed sensing scheme for a refractive index change as small as 0.001 Rill. FIGs. 9A and 9B shown the MRR individual spectra and the Vernier spectrum before the shift, and FIG. 9C and 9D show the same spectra after the shift, which can be performed in practice by measuring the wavelength shift and retuning the control MRR to reach the well tuned state and measuring the voltage variations comparing initial central wavelength and final wavelength of resonance. By analysing the applied tuning voltage compared to the corresponding baseline voltage in a lookup table, it is possible to calibrate the sensor for detecting clinically relevant concentrations of a target analyte. A significant reduction in the intensity of the resonant wavelength of the laser cavity due to a red shift in the resonance wavelength of the sensing MRR in response to 0.001 Rill changes in the refractive index of cladding theoretically shows the feasibility of the lase cavity-based sensing approach.

[0097] In some embodiments, while the prediction on the performance of SOI based sensors with typical quality factors at the range of 103- 104sounds promising, using a multi-material technology and ultra high quality factor SiN / QXP based MRRs with Q ranges above 7 x 105(i.e. around 2 orders of magnitude higher Q compare to SOI microrings), highly sensitive sensors with very small LOD may be fabricated.

[0098] Implementations of the laser cavity-based sensors proposed here provide intra cavity sensing which presents two main advantages over the conventional optical microcavity resonator-based sensors. Firstly it does not need an external tunable laser source, and is therefore compatible for miniaturization and integration which is necessary in various applications such as portable point of care systems. Second it provides a self-tuning mechanism that each time the resonance condition of the cavity changes to a new state the stability control of lasing mechanism will automatically detune the initial condition to match with the new resonance peak. Therefore, the shift from the original wavelength of operation to the new resonance wavelength of the laser cavity provides the sensing information required. Of course, numerous additional modifications could be made to the embodiments described above without departing from the scope of protection as defined in the appended claims.

Claims

CLAIMS1 . A laser cavity-based sensor for measuring a measurand, comprising: a laser cavity configured to generate light at a resonant wavelength, the laser cavity comprising:- a gain medium;- a resonant structure comprising a sensing micro-ring resonator (MRR) and a control MRR arranged in a Vernier configuration defining the resonant wavelength of the laser cavity, at least a portion of the sensing MRR being accessible for interaction with said measurand, said interaction changing a spectral response of the sensing MRR; and a tuning mechanism configured to tune a spectral response of the control MRR; and a control and processing unit operatively connected to the tuning mechanism and configured to:- operate the laser cavity at an initial resonant wavelength;- upon interaction of the measurand with the sensing MRR, tune the control MRR to operate the laser cavity at a shifted resonant wavelength; and- calculate a wavelength shift of the resonance wavelength of the laser cavity induced by the measurand.

2. The laser cavity-based sensor according to claim 1 , wherein the laser cavity is provided in a photonic integrated platform comprising a gain chip hosting the gain medium and at least one reflector chip hosting the sensing MRR and the control MRR.

3. The laser cavity-based sensor according to claim 2, wherein the gain chip comprises a semiconductor optical amplifier.

4. The laser cavity-based sensor according to claim 2 or 3, wherein each of the at least one reflector chip comprises a substrate and a cladding extending over the substrate, each of the sensing MRR and the control MRR being embedded in the cladding of one of said at least one reflector chip.

5. The laser cavity-based sensor according to claim 4, wherein the reflector chip hosting the sensing MRR comprises a sample enclosure configured to receive a sample containing an analyte embodying the measurand, the at least a portion of the sensing MRR being accessible for interaction with said measurand extending within the sample enclosure.

6. The laser cavity-based sensor according to claim 5, wherein the at least a portion of the sensing MRR being accessible for interaction with said measurand being functionalized so that the analyte attaches thereto.

7. The laser cavity-based sensor according to any one of claims 1 to 6, wherein the tuning mechanism comprises:- a metallic heat resistor in thermal contact with the control MRR;- at least one electrode connected to the metallic heat resistor; and- an electrical source connected to the at least one electrode.

8. The laser cavity-based sensor according to any one of claims 1 to 7, wherein the sensing MRR comprises a metamaterial waveguide.

9. The laser cavity-based sensor according to any one of claims 1 to 8, wherein the sensing MRR comprises a cantilever waveguide.

10. The laser cavity-based sensor according to any one of claims 1 to 9, further comprising:- an output port coupled to the resonant structure for extracting an output beam of said light from the laser cavity; anda photodetector coupled to the output port for measuring an optical power of the output beam.

11. The laser cavity-based sensor according to claim 10, wherein the control and processing unit is configured to measure the wavelength shift of the resonance wavelength of the laser cavity based on a monitoring of the optical power of the output beam.

12. A sensing method for measuring a measurand, comprising: a) providing a laser cavity-based sensor, the laser cavity-based sensor comprising a laser cavity configured to generate light at a resonant wavelength and having a gain medium and a resonant structure comprising a sensing micro-ring resonator (MRR) and a control MRR arranged in a Vernier configuration defining the resonant wavelength of the laser cavity, at least a portion of the sensing MRR being accessible for interaction with said measurand; b) operating the laser cavity at an initial resonant wavelength; c) interacting the measurand with the sensing MRR; d) tuning the control MRR to operate the laser cavity at a shifted resonant wavelength; and e) calculating a wavelength shift of the resonance wavelength of the laser cavity induced by the measurand.

13. The sensing method according to claim 12, wherein interacting the measurand with the sensing MRR comprises inserting a sample containing an analyte embodying the measurand in a sample enclosure provided in said laser cavitybased sensor.

14. The sensing method according to claim 13, wherein the at least a portion of the sensing MRR being accessible for interaction with said measurand is functionalized so that the analyte attaches thereto.

15. The sensing method according to any one of claims 12 to 14, wherein tuning the control MRR comprises injecting a current through a metallic heat resistor in thermal contact with the control MRR.

16. The sensing method according to any one of claims 12 to 15, further comprising measuring an optical power of an output beam from said laser cavity.

17. The sensing method according to any one of claims 12 to 16, wherein the measurand is one of a concentration of an analyte, a pressure variation, an acceleration, an angular velocity, and a radiation variation.

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