This PDF file contains the front matter associated with SPIE Proceedings Volume 12314, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

Light wave is of some attractive natures such as huge bandwidth, the possibility to control optical field 2D parallelly by optical free form surface and optical diffraction device. Such nature is very important to many applications such fiber telecommunications, high speed 3D sensing Lidar systems, and VR/AR components. In this talk, those optical devices based on the nature of light wave, including ultra-high speed DFB laser integrated with EA modulators, ultra-wide band lithium niobate thin film optical modulators, and ultra-high speed photodetectors, will be introduced.

Due to the high transmission capacity, optical fiber systems have been widely applied in the modern telecommunication infrastructure to meet the ever-increasing demand of data traffic. Optical amplifiers have been employed to amplify optical signals and to compensate for the transmission losses. They play a key role in relaying the signals in ultra-wideband optical fiber communication systems. However, the amplified spontaneous emission (ASE) noise will be introduced and will pose constraints on the transmission information rates. The mutual information (MI) and the generalized mutual information (GMI) have been applied to evaluate the information rates in communication systems. In this work, we have investigated the impact of ASE noise on the MI and the GMI, and developed corresponding analyses across different modulation formats. Our work aims to explore the limit and requirements on optical amplifiers in next-generation ultra-wideband optical fiber communication systems.

Dual-comb spectroscopy enables spectral measurement with large bandwidth spanning tens of nanometers, but it is limited to measuring absorption spectra and has to trade-off spectral resolution versus acquisition frame rate set by the repetition rate. Here, to alleviate these restrictions, we innovatively propose and demonstrate a hybrid dual-comb emission spectroscopy featuring a spectral resolution of 0.63 pm, a frame rate of 1 MHz, and a measurement bandwidth of 13.6 nm, simultaneously. A mode-locked fiber comb is harnessed to interrogate emission spectral features with high resolution via optical Fourier transform and a soliton microcomb serving as a probe pulse implement parallel multi-point sampling to significantly increase the acquisition rate by nearly 3 orders of magnitude from 1 kHz to 1 MHz. We believe that chip-scale microcombs will make the fast and high-resolution emission spectroscopy presented here a powerful tool for widespread applications.

In order to further enhance the electric field confinement ability of the Bloch surface polariton waveguides, here, a new hybrid Bloch surface polariton waveguide is proposed to reduce the mode size while still maintaining the long-range transmission distance of the conventional Bloch surface polariton waveguide. By incorporating an ellipse dielectric nanowire with the photonic crystal slab combined with a sandwiched dielectric nano-ridge, the weak mode confinement ability of the Bloch surface polariton mode can be compensated effectively. For the considered structural parameters, the modal properties of the hybrid waveguide are quantitatively investigated to demonstrate subwavelength mode confinement ability along with ultra-low propagation loss. The nice optical performance of the presented hybrid waveguide structure could serve as a promising building block for many high-performance integrated optical devices.

A photonic integrated adaptive two-wave mixing (TWM) interferometer is designed for demodulation of FBG acoustic emission sensor signals, whose various optical elements are integrated in a substrate material with photorefractive properties. A ridge waveguide based on InP:Fe is designed. Each component of the photonic integrated TWM interferometer is analyzed and optimized to minimize the loss of light in the transmission of the TWM interferometer and obtain the best demodulation performance. The feasibility of the optimized structure of the photonic integrated adaptive TWM interferometer is verified in theory, and the optimized structure will contribute to the miniaturization and integration of the TWM demodulation system based on InP:Fe.

The performance of traditional silicon oxide based phase shifter is limited by thermo-optic coefficient, making it difficult to achieve high-efficiency phase modulation. A relatively high index contrast (1.5%) SiO2 waveguide is utilized in our work. Thus, the cladding layer could be thinner since a higher confinement can be achieved. The heating efficiency is improved by reducing the thickness of the cladding layer together with the etched air trenches on both sides of the waveguide. The simulation results show that the heating efficiency of the overlay air trench is about 20% higher than the conventional one. Segment heating electrodes are also used to reduce the heating voltages. Mach-Zehnder interferometer (MZI) is fabricated to characterize the performance of the phase shifter, and the measured extinction ratio of MZI is larger than 34 dB with a heating power 69 mW/π.

Spin angular momentum (SAM) and orbital angular momentum (OAM) have opened up new avenues in optical communication and imaging processing. However, detection of these states concurrently requires complicated optical setups. Here, we propose a 12-channel detection for SAM and OAM modes with a dielectric ultracompact metasurface. The phase profile is constructed with both propagation phase and geometric phase. Adopting spin photonic Hall effect and off-axis focusing scheme, light beams carrying different vortices are demultiplexed into several vortex beams with distinct topological charges, and each can be recognized with different focused spots on a transverse plane with unique azimuthal coordinate. The proposed design efficiently demultiplexes the incident with different SAM and OAM modes through a single layer metasurface. We envision this work will pave the way for high-capacity optical communication applications and integrated optical systems.

Defect distribution and their contribution to photocurrent is imaged in commercially available GaP, GaAsP and GaN using phase modulated multi-photon microspectroscopy. Results show that contributions from defects dominate the photocurrent from GaAsP and GaN. In GaP, such contributions are substantially less. Fabrication process of GaAsP and GaN could be optimized to improve their functionality as photodiodes. The method we have implemented can be used as an ‘in-operando’ characterization tool for understanding the underlying processes that contribute to the external signals in semiconductor devices.

Organic-inorganic hybrid perovskite films possess superior optoelectronic properties, including bandgap tunability, high absorption coefficient, well-balanced charge carrier mobility and long electron-hole diffusion length. Hence it can serve as sensitizers in solar cells, photodetectors, pumped lasers and light-emitting diodes. However, the crystallographic defect passivation and suppression of organic-inorganic hybrid perovskite at the grain boundaries are crucial for efficient and stable perovskite photodetectors (PPDs). Herein, a bulk heterojunction (BHJ) fabricated by the two-step spin-coating method facilitates high-quality perovskite film formation while reducing the non-radiative recombination within the photoactive layer, enhancing the photosensitivity performance of PPDs based on BHJ configuration. Specifically, sulfonated graphene (SGA) was used as a functional passivator to interact with Pb²⁺ at the surface and grain boundaries due to its large specific surface area and high binding energy with lead ion, thereby ameliorating the device stability and carrier transport capacity within perovskite films, resulting in a lower dark current density and a higher photocurrent density. Consequently, the PPD based on the BHJ configuration achieves a responsivity of 570 mA/W and the specific detectability of 6.3×10¹¹ Jones under the bias voltage of −1 V with the 532 nm laser illumination intensity of 0.5 μW/cm² and a linear dynamic range of 126 dB. The PPD based on BHJ configuration shows ultrahigh response rates of 0.3 μs and 52.7 μs for the rise and fall times at zero bias, respectively, which is attributed to efficient carrier extraction and the lower defect density. The grain boundary passivation strategy of SGA modification develops a practical approach to ameliorate PPD performance and stability.

Polymer optical waveguide vertical optical coupler and mode division (de)multiplexer on optical printed circuit boards have garnered considerable attention. We have studied a stepped laser-ablation method for the fabrication of concave micromirrors in rectangular optical waveguides. The vertical coupling loss can be reduced to 1.83 dB experimentally. Further, based on gray-tone optical lithography technology combined with the overlay alignment method, a spherical concave micro-mirror has been fabricated, with the vertical coupling loss of 1.39 dB. Furthermore, a polymer three-mode (de)multiplexer with two cascaded waveguide directional couplers is proposed. The device can ensure that the E11 mode of the two narrower waveguides are highly coupled into the E21 and E31 modes of the central waveguide. The fabricated device exhibits coupling ratios of 98.07% and 95.43%. Moreover, a two-mode (de)multiplexer has been studied. The coupling ratio and extinction ratio of the fabricated (de)multi

In this study, a blue Micro-LED chip structure with 1-5 pairs of quantum wells was proposed, and the current-voltage (I-V) curve, electroluminescence (EL) intensity and internal quantum efficiency (IQE) were analyzed for samples with a chip size of 3.5um, respectively. The simulation results show that the IQE value is the highest when the number of pairs of quantum wells is one pair, and the IQE can reach 18% when the current density is 2A/cm².

We have used gold nanostructures to excite various plasmonic modes such as multi-scattering, hot electron injection (HEI) and plasmon-induced resonant energy transfer (PIRET). Together they enable to enhance the utilization of solar light for photocatalytic processes. Detailed experimental and mechanism studies have been conducted to examine the plasmonic enhancement in photocurrent, photodegradation and total water splitting. Our work may find potential applications in optical redox-based sensors and green energy. Acknowledgement: This work is supported by Research Grants Council (RGC) of Hong Kong (15221919, 15215620, N_PolyU511/20) and The Hong Kong Polytechnic University (1-ZE14, 1-ZVGH and 1-CD4V). The technical assistance and facility support of the Materials Research Centre (MRC) and the University Research Facility in Material Characterization and Device Fabrication (UMF) of The Hong Kong Polytechnic University are acknowledged.

In this work, we report the metasurface enabled polarization optics and high-Q chiral metasurface supporting bound state in the continuum

Optical gadgets will take the role of electronic devices in the following decade due to their fast speed, low power consumption, and low heat tolerance. As a consequence, photonic crystal (PhC) based all-optical Buffer, AND, and OR (BAO) logic gates (LoG) were constructed by exploiting square lattice silicon rods with an air background. The suggested LoGs function efficiently by altering the phase of light beams having a wavelength of 1550 nm and are working on the beam-interference principle. The structure is modeled and tested through the finite-difference time-domain (FDTD) approach. For each logic gate, the performance parameter of extinction ratio (ER) is determined by tweaking the silicon rod radius and refractive index over a set of parameters. The suggested all-optical BAO LoG has extinction ratios of 11.84 dB, 33.9 dB, and 11.65 dB, respectively. The response time and operating speeds for each input combination are also calculated and tabulated.

Due to green building railway requirements, sound barrier, as an effective noise reduction measure, has been widely constructed. However, the sound barrier may fall off if its components are damaged or aging. It is critical to accurately detect the early faults of sound barrier. But existing technical solutions have low recognition rate and lack of real-time performance. To solve these problems, a sound barrier fault identification method based on phase-sensitive optical time-domain reflectometry (ϕ-OTDR) is proposed. We propose a novel method based on optimized multi-domain features for feature extraction and feature screening to describe intrinsic information of the vibration signal. A field experiment was carried out in the Hu-Hang Railway. A total of 405 sets of data were obtained. With the help of quadratic discriminant classifier and 5-fold cross-validation, the average recognition accuracy is 82.3% even under complex field environments.

We proposed and demonstrated a high-efficiency Brillouin random fiber laser (BRFL) in a half-open linear random cavity incorporating with a self-inscribed dynamic fiber grating (DFG) for laser frequency stabilization. The DFG can be produced when the ion population distribution along erbium-doped fibers is periodically modulated by two coherent counter-propagating standing waves via the spatial hole-burning effect. Consequently, a BRFL with the linear half-open-cavity exhibited an optimized laser efficiency while the embedded DFG effectively purified the random modes and suppress the frequency drift caused by multiple random mode hopping. With a low laser threshold of 13.9 mW, the laser efficiency of up to 19.3% was observed, which is four times higher than that of the BRFL with a half-open ring cavity. It suggests that the proposed BRFLs could be beneficial to practical applications in fiber-optic sensing and coherent communication

In this manuscript, a 4-N, N-dimethylamino-4′ -N′ -methyl-stilbazolium tosylate (DAST) material assisted electro-optically tuned Bloch Surface Wave Sensor is proposed. The structure is designed using a one-dimensional photonic crystal (1D-PhC) structure. A top defective layer of DAST as an electro-optic material is used. The analysis shows that by illuminating the device with poly-chromatic light at an incident angle of 45.11◦ results in Bloch mode excitation at a 632.8nm operating wavelength. The analytical results also demonstrate the post fabrication 47 nm BSW wavelength tuning by applying only ±5 V potential. The structure also exhibits both wavelength stability (at varying angle) and angular stability (at varying wavelength). Moreover, the structure exhibits 105.71nm/RIU sensitivity at 0V applied bias voltage having very low FWHM of <1nm. Thus, the proposed design possesses the advantage in terms of low voltage wavelength tuning, stable response, easy fabrication, and integration capability in integrated circuits.

Optical modules are the basic building blocks of 5G transport networks, data center intra- and inter-connections. This paper focus on technical solutions and standardization status of 800Gb/s optical modules, as well as the maturity of the industry chain of core optoelectronic chips inside the optical module. First, application scenarios and requirements of 800Gb/s optical modules were analyzed. Second, technical solutions and standardization progress of 8×100Gb/s PAM4, 4×200Gb/s PAM4 and 800Gb/s coherent optical modules with different transmission distances were studied.

Ultra-stable lasers (USLs) based on Fabry-Perot (FP) cavities frequency stabilization take TEM00 mode as the reference frequency. When the laser does not match the FP cavity perfectly, high-order modes will be excited, affecting the performance of USLs. In this paper, influence of different laser alignment conditions on resonant modes of a FP cavity was numerically analyzed using Optical Simulation Containing Ansys Results (OSCAR) code. The relationship between energies of resonant modes and different laser incident conditions was revealed. The results can be a guide for aligning lasers and FP cavities.

Lidar has been widely used in underwater detection, survey, and seabed mapping. However, the performance of underwater lidar is deteriorated by scattering. Scattering not only contributes to attenuation but also worsens ranging accuracy or imaging contrast. Therefore, it was important to suppress scattering in underwater detection. We present investigations of applying a spiral phase plate (SPP) as a spatial filter to suppress scattering in an underwater lidar system. An SPP was inserted in the echo path to separate target-reflected signals from scattering clutters, because, in the echo, the target-reflected light maintained spatial coherence and was converted into an optical vortex ring after passing through the SPP, while the scattering clutters lost their spatial coherence and cannot be converted to the optical vortex but remained a centrally stronger distribution according to the Mie scattering law. A mask was produced by coating a glass sheet with opaque paint, leaving only a transparent ring for light on the optical vortex ring to pass through. Experimentally, the response of the light in the center of the vortex to the RF modulation frequency decreased with the increase of attenuation length, so it was mainly scattered light, while the light on the vortex was measured to maintain RF frequency modulation at high attenuation length, so it was dominated by signal light. The ranging results showed that the ranging error was significantly reduced in a turbid medium by blocking scattering clutters inside and outside the vortex. Moreover, a high-order SPP was more effective in reducing ranging errors. We reduced the ranging error from 30 cm to 6.6 cm with a 24-order SPP when the attenuation length was 15.

Non-metallic mirror, such as semiconductor distributed Bragg reflectors (DBRs), has been widely integrated in the structure of optoelectronic devices. However, constructing conductive DBR in organic optoelectronic device is still scarce, because of the incompatibility of high-temperature processes in the preparation of inorganic DBR. Herein, it is confirmed that organic-oxide hybrid DBR can achieve high conductivity and light manipulation. When thermal evaporated material MoO3 is doped into organic material (1,1-bis[4-[N,N-di(p-tolyl)amino]phenyl]cyclohexane, TAPC), the conductivity of TAPC can be increased by ten thousand times with very small refractive index change. It is shown that 8.5 pairs DBR at 460 nm has a reflectivity of about 95%, and the driving voltage is 8.2 V at the current density of 100 mA cm-2 . Then, a transparent organic light-emitting diode with integrated bottom conductive DBR are fabricated to confirm the functionality of light regulation. Our results confirm that integrated optoelectronic devices with DBR as reflector can be achieved with low operating voltage.

A novel trihedral reflector (also known as hollow cube-corner reflector) with two cylindrical surfaces is proposed. This reflector has bottom side represented by two cylindrical surfaces, which axes constitute a 45° angle. Novel reflector solves the problem of an objects pitch measurement using singular cylindrical cube-corner reflector. Main benefit is that an image of this reflector consists of three lines, allowing to differ more consistently and to measure all three angles of object rotation.

Mode instability phenomenon acts as a common feature in single-frequency fiber ring lasers. Pump power and cavity length are two important control parameters affecting the output SLM stability. In this work, mode instability of an EDFRL has been experimentally investigated by utilizing two effective methods. On the whole, a mode stability map of the EDFRL scaled by pump coefficient is measured and discussed completely through the interferometer scheme, which helps to evaluate the mode stability dependent on pump power in a form of global visualization. Besides, real-time and detailed detection of various mode instability behaviors, including occasional mode hopping, periodic mode hopping and intermittent MLM oscillation, is carried out using the optical heterodyne scheme. The dynamics of mode instability can also be visualized by on-line time-frequency diagrams. This work will contribute to the analysis, understanding and suppression of mode hopping in fiber ring lasers.

Based on a vertical-cavity surface-emitting laser with saturated absorber (VCSEL-SA) subject to optical injection, we proposed an ultrafast pattern recognition scheme of four-bit binary data and theoretically investigated the recognition performances. The results show that, patterns recognition of different four-bit binary data at Gb/s rate can be realized by adjusting the injection weight of each bit number and optimal weight values can be determined. Although noise has some influences on the patterns recognition speed and accuracy, this proposed system has a certain robustness to noise on the whole. These results provide a promising application prospect for VCSEL-SA based ultrafast photonic neuromorphic system in pattern recognition field.

Light detection and ranging (LiDAR) technique is always a building block in the fields of sensing, mapping and autonomous driving navigation. Beam steering devices, which are used for light emission and reception, play a key role in LiDAR system. Lens-assisted beam-steering (LABS) is one of the most competitive candidates among various beam steering technologies. Compared with conventional integrated optical phased array (OPA), LABS unit is with lower optical loss and meanwhile lower control complexity. In this paper, we demonstrate a highly integrated LABS chip based on micro-ring optical switch array with a wide field of view (FoV, 30°×40°) and a narrow beam divergence (<0.1°). A 32×32 micro-ring optical switch array connected with a 1×1024 optical antenna array is integrated in the silicon photonic chip with an overall size of 6×14 mm2. Incident light is routed to one antenna by the micro-ring optical switch array and emitted into the free space, and the emergent light is collimated and steered by a cylindrical lens fixed above the optical antenna array subsequently. On this basis, one-dimensional steering is achieved by switching light to different antennas, while steering in the other dimension is realized via wavelength tuning. Under this circumstance, only two micro-ring switches need to be turned on at one time, leading to a significant reduction of optical loss and control complexity of the proposed chip. Notably, our work demonstrates the feasibility of large-scale integration of optical switch array within LABS chip by adopting compact micro-ring switches, paving a new path for miniatured beam scanners.

Alkali-metal atomic vapor cells are widely used in the precision measurement of magnetic field and inertial rotation. The performance of the atomic sensors is closely related to the partial and total pressures of the mixed gases in atomic vapor cells. The exact composition and quantity of the gas mixture inside the vapor cells can be deduced from the optical absorption spectra, while a high precision wavelength measurement is required. We build a homemade high precision wavelength measurement system which is based on the scanning Fabry-Perot cavity and the saturation absorption peaks. As the laser current is scanning, the interference pattern and the transmission light intensity are recorded synchronously. After scanning, the stride length of all sample points is sequentially calculated from their interference patterns by a dedicated computer program. Patterns of several cycles are averaged to suppress the white noise and improve the precision. Compared with the commercial wavelength meter, which usually has an accuracy of about 50 MHz, our wavelength measurement system can achieve a higher precision below 10 MHz

Microring (MR) devices require thermal stabilization to match their intended operating wavelengths. In this work, we present a scheme for thermal stabilization of MR modulators utilizing integrated temperature sensor and closed-loop control unit based on CMOS integrated circuit. Temperature of the MR modulator is directly monitored by a diode based monolithic temperature sensor. The measured temperature is used in a feedback loop to adjust the thermal tuner of the MR. Thermal steady state and transient simulations are performed showing that temperature tuning range from 30 to 100℃ can be achieved. Considering the relatively slow heat transfer process, unity-gain bandwidth of the control circuit is optimized to ensure loop stability. This design can effectively compensate ambient thermal noise and adjust the deviation of the operating wavelength caused by the process error

In the research process of wireless transmission of retina-like distributed CMOS sensor, a design scheme of SDRAM controller based on FPGA is proposed to solve the problem of large amount of buffered data in real-time image acquisition system. A single-chip SDRAM is used as the data cache device, and the ping-pong read and write operation control scheme is implemented by switching Banks. Its purpose is to improve data transmission stability. And FIFO is used to solve the problem of clock domain crossing. The result of design is simulated by vivado. The waveform finally obtained shows that the design scheme can implement clock domain crossing and SDRAM operations of writing and reading. It can be used as an IP core in the SOC system.

With advance of microwave systems, the optical delay line based on chirped Bragg grating waveguides (CBGWs) have attracted much attention in recent years. However, the loss limits the length of CBGW to achieve larger group delay (GD). In this work, we propose and experimentally demonstrate a novel circulator-free CBGW with low loss and large GD. This CBGW device consists of a 20.11-cm long spiral tapered antisymmetric Bragg grating waveguide (STABGW) and an asymmetric directional coupler (ADC), and is fabricated on a low-loss 800-nm-height silicon nitride platform. The CBGW is realized by linearly increasing the width of Bragg grating waveguide along the length, and its period keeps the same. In our design, the widths of STABGW at two ports are 1.8 and 2.2 μm, respectively and the period is 435 nm. The minimum radius of the waveguide wrapped into Archimedean spiral is 600 μm. The length of ADC is 25 μm, and the widths of two parallel waveguides are 2.3 and 1 μm, respectively, with a 300-nm gap. The experimental results show that a total GD of 2852 ps within the bandwidth of 23 nm is realized. The propagation loss in STABGW is 0.15 dB/cm, and the total insertion loss of the device is 5.4 dB at the wavelength of 1550 nm. The GD is the largest amount achieved by CBGW reported. This integrated device has great potential for diverse applications such as dispersion compensation, all-optical signal processing, and nonlinear optics

Mode-locked fiber lasers based on nonlinear polarization rotation (NPR) have been widely applied due to the simple setup, high performance and rich nonlinear dynamics. However, temperature, vibration, and stress can easily disrupt the optimized mode-locked state. To address this problem, automatic mode-locked lasers using different self-tuning algorithms are proposed in recent years. However, it is relatively difficult to verify and optimize the performance of self-tuning algorithm since the use of actual laser platforms, which hinders the development of intelligent mode-locked fiber laser. In this paper, we demonstrate a simulation platform for NPR mode-locked fiber lasers by using coupled Ginzburg–Landau equation and Jones matrix, which makes the optimization of intelligent self-tuning algorithm easier. As a proof-of-principle demonstration, genetic algorithm and human-like algorithm are implemented to prove the ability of comparing different self-tuning algorithms.

A simple and novel method is proposed for the self-calibrated measurement of high-speed photodetectors (PDs) based on photonic sampling by using a mode-locked laser (MLL). Through the photonic sampling measurements, the uneven response of the MLL can be determined. The prominent advantage of the proposed method lies that the self-reference extraction of the frequency response of the PD can be achieve without the need of any extra electrical/optical transducer standard. In the experiment, a commercial PD is measured by using a MLL with the repetition frequency of 21.936 MHz. The measurement results fit in with the conventional electro-optic frequency sweep measurement.

Acousto-optic dispersive delay line with 4K Nyquist-limited resolution was designed and fabricated for high-definition ultrashort laser pulse shaping. The delay line was optimized for Ti:sapphire laser radiation supporting over 200 nm bandwidth with the transmission passband of 0.18 nm. Experimental assessment and applications of the delay line for time-domain ultrashort pulse modulation are discussed in the report. Arbitrary complex-valued spectral transmission functions of the delay line can be obtained using dispersive Fourier synthesis algorithm for RF waveforms. The results include programmable replication of transform limited femtosecond pulses in 3 ps delay range and time-domain chirped pulse modulation with sub-4-ps rise/fall time of pulse fronts.

In this work, we proposed a ring core fiber (RCF) based all-fiber sensor used for lateral pressure sensing. The sensor is composed of 1-mm coreless fiber (CLF) and 2.5-cm RCF. Then the CL-RC fiber structure is connected to two segments of single-mode fibers (SMFs) to form a Mach-Zehnder interferometer (MZI). One of the SMFs serves as the lead-in fiber which is linked with a broadband laser source (BBS) and the other SMF is connected to the optical spectrum analyzer (OSA) for signal recording. The transmission spectrum of the MZI structure has a large extinction ratio (ER) of up to 20 dB with the free spectral range (FSR) of 9.3 nm. After the fabrication, the MZI sensor is packaged for pressure sensing at room temperature (25 ℃). The weights with different values are applied on the fiber sensor so that the intensities of pressure can be calculated and adjusted. The lateral pressure intensity is tuned from around 1.6 MPa to 9.6 MPa. With the increase of pressure intensity, the spectra of output signals show a linear redshift. The pressure sensitivity of the proposed MZI sensor reaches 607 pm/MPa with good linearity of 0.9839. The proposed pressure sensor formed by RCF has many advantages, such as easy fabrication, low cost, small size, electromagnetic resistance and good sensitivity, which can be potentially applied to diverse fields.

An ultra-high sensitivity separated Fabry-Perot interferometers (FPIs) sensor for gas pressure measurement based on hollow core Bragg fiber (HCBF) and Vernier effect is proposed. The HCBF functions as an FPI cavity and possesses low transmission loss. The sensing unit was prepared by splicing an HCBF at the millimeter scale between the single-mode fiber (SMF) and the hollow silica tube (HST). The reference unit was fabricated by sandwiching the HCBF between two SMFs. Both FPIs with similar free spectral ranges (FSRs) were connected to the 3-dB coupler parallelly to generate the Vernier effect. Experimental results showed that the proposed sensor achieved high gas pressure sensitivity of 77.80 nm/MPa with a linearity of 0.9992. Moreover, a low-temperature crosstalk of ~0.095 kPa/℃ implies that the sensor is temperature insensitive. Compared to the traditional optical fiber gas pressure sensor, the proposed sensor features high sensitivity, stability, easy fabrication, and fast response.