Tunable Fabry-Perot Research Articles

Design of near-infrared solid-state tunable Fabry-Perot filters based on VO2/P4VP films

The significant refractive index change of VO2 during phase transition makes it attractive for the design of optical switches and filters, but high absorption of VO2 limits its development in the field of filter. In this paper, we firstly design near-infrared solid-state tunable/switchable single-/dual-band bandpass Fabry-Perot (F-P) filters based on VO2/P4VP composite films using COMSOL software. The simulation results show that the single-passband tunable filter can achieve a continuous thermal tuning range of 19 nm at 1064 nm, the full width at half maxima (FWHM) is 28.8 nm, and the peak transmittance is >30%. On this basis, we simulated a tunable dual-band bandpass filter, the left peak can be heated to achieve a tuning range of 15 nm (945 nm), the right peak is 24 nm (1168 nm), the peak transmittances of both the two peaks are >35%. When boosting the VO2 fraction, the continuous tunability of the above-mentioned single-/dual-band filters will be switchable due to the high absorption of VO2, and then switchable single-/dual-band bandpass filters are designed. This work has guiding significance for the design of novel filter structures and optical tunable devices based on phase change materials such as VO2 in the future.

Multi-component Freon gas detection based on infrared tunable Fabry-Perot detector

A multi-component Freon gas sensing system was developed based on the non-dispersive infrared (NDIR) spectroscopy, which had the advantages of simple structure and low cost. This system mainly consisted of a broadband infrared light source, a tunable Fabry-Perot (FP) detector and a small brass absorption cell. In order to improve the utilization rate of infrared light source, the absorption cell was optimized. H1301, R134a and R410A were simultaneously detected through the measurement of gas absorption spectrum. The spectral range of the FP detector was from 8.0 to 10.5 μm, and the entire spectrum was recorded by wavelength scanning. The area of measured absorbance was directly proportional to the concentration of the target gas, which was used to calibrate the sensing system. The temperature and frequency response characteristics of the system were tested. The experimental results showed that the higher the temperature, the lower the responsiveness. In addition, the system had the best signal-to-noise ratio (SNR) at 10 Hz. The minimum detection limits of H1301, R134a and R410A were achieved to be 2.5 ppm, 5.3 ppm and 4.8 ppm, respectively. The cross-interference among the gases was suppressed by using BP neural network.

Silicon-Based On-Chip Fully Tunable Optical Fabry-Perot Filter Based on Multi-Mode Waveguide

Silicon-Based On-Chip Fully Tunable Optical Fabry-Perot Filter Based on Multi-Mode Waveguide

Hybrid cavity-antenna architecture for strong and tunable sideband-selective molecular Raman scattering enhancement.

Plasmon resonances at the surface of metallic antennas allow for extreme enhancement of Raman scattering. Intrinsic to plasmonics, however, is that extreme field confinement lacks precise spectral control, which would hold great promise in shaping the optomechanical interaction between light and molecular vibrations. We demonstrate an experimental platform composed of a plasmonic nanocube-on-mirror antenna coupled to an open, tunable Fabry-Perot microcavity for selective addressing of individual vibrational lines of molecules with strong Raman scattering enhancement. Multiple narrow and intense optical resonances arising from the hybridization of the cavity modes and the plasmonic broad resonance are used to simultaneously enhance the laser pump and the local density of optical states, and are characterized using rigorous modal analysis. The versatile bottom-up fabrication approach permits quantitative comparison with the bare nanocube-on-mirror system, both theoretically and experimentally. This shows that the hybrid system allows for similar SERS enhancement ratios with narrow optical modes, paving the way for dynamical backaction effects in molecular optomechanics.

On-chip electro-optically tunable Fabry-Perot cavity laser on erbium doped thin film lithium niobate

We demonstrate an on-chip electro-optically tunable Fabry-Perot (FP) cavity laser on Er3+-doped thin film lithium niobate (Er: TFLN). The FP cavity consists of two Sagnac loop reflectors at the two ends with a loaded quality factor of 1.3 × 105 and a free spectral range of 68 pm. The fabricated Er: TFLN FP laser structure is integrated with microelectrodes designed for electro-optically tuning, and a continuous laser wavelength tuning with 24 pm around 1544 nm is achieved by applying a driving voltage from −6 V to 6 V.

Drift calibration method of Fabry-Perot filters using two-stage decomposition and hybrid modeling.

Although tunable Fabry-Perot (F-P) filters are widely acknowledged as fiber Bragg grating (FBG) demodulators, F-P filters exhibit drift error when subjected to ambient temperature and piezo-electrical transducer (PZT) hysteresis. To address the drift issue, the majority of the existing literature makes use of additional devices like the F-P etalon and gas chamber. In this study, a novel drift calibration method based on two-stage decomposition and hybrid modeling is proposed. The initial drift error sequences are broken down into three frequency components using the variational mode decomposition (VMD), and the medium-frequency components are further broken down using the secondary VMD. The initial drift error sequences are significantly simplified by the two-stage VMD. On this foundation, the long short-term memory (LSTM) network and polynomial fitting (PF) are used to forecast the low-frequency and high-frequency drift errors, respectively. The LSTM enables the prediction of intricate nonlinear local behaviors, while the PF method predicts the overall trend. The benefits of LSTM and PF can be effectively utilized in this manner. Compared to the single-stage decomposition, two-stage decomposition achieves superior results. The suggested method is an affordable and effective alternative to the current drift calibration techniques.

Analysis and Design of a High Transmittivity and Narrowband Tunable Lithium Niobate Filter With Double FP Cavities

Tunable Fabry-Perot (FP) filters are being increasingly employed in tunable fiber lasers for wavelength selection and tuning. To address single cavity restrictions on transmittivity and achieve narrowband simultaneously, we propose a narrowband tunable electro-optic (EO) filter based on double FP cavities. Lithium niobate (LiNbO3, LN) platform and MgF2 are utilized as film pairs to effectively eliminate the effect of flat-top respond triggered by two cascaded cavities. Thus we can design the FP cavities with a high transmittivity and narrow passband of approximately 99.9% and 0.3 nm, respectively, making it more tolerant to the loss in the cavities. The resonance wavelength around 1550 nm can be blue shifted by 102 nm when the electric voltage is raised from −150 V to 150 V. The error analysis indicates that the incident angle exhibits a certain tuning effect on the wavelength, and the difference between the optical thicknesses of the cavities should be kept to a minimum. The proposed tunable LN filter with double FP cavities may be used in promising applications such as optical communication and photoelectric integration.

Optical Spectral Shaping Based on Reconfigurable Integrated Microring Resonator-Coupled Fabry–Perot Cavity

We demonstrate a multifunctional optical spectral shaper on a silicon photonic chip. The proposed structure is composed of a tunable microring resonator (MRR) and three tunable Sagnac loop mirrors (SLMs), which can be regarded as a large SLM incorporating an MRR-coupled Fabry–Perot (FP) cavity. To realize flexible tuning, thermo-optically tunable Mach-Zehnder interferometer (MZI) couplers are used to replace conventional directional couplers with fixed coupling coefficients. By controlling the tunable MZI couplers, the proposed structure can be reconfigured as various functional structures including an all-pass MRR with tunable coupling regime, a tunable FP cavity, an SLM incorporating FP cavity, and an MRR-coupled FP cavity. This flexible reconfiguration allows for multifunctional optical spectral shaping including tunable comb filtering, Fano and EIT-like resonances. In particular, the complementary flat-top comb filtering responses can be theoretically obtained in the two ports of this device with same free spectral range (FSR) value, which enable the (de)interleaver operation. The experimental results show that the implemented all-pass MRR has a maximum extinction ratio (ER) of 38.9 dB and the corresponding quality factor is 6.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The comb filter based on configured FP cavity can be switched from narrowband response (0.06 nm) to wideband flat-top response (0.23 nm), with ERs up to 10.6 dB and 22 dB, respectively. Moreover, a dynamic conversion between Lorentz, EIT, and Fano resonance line shapes based on the coupled resonant system can be realized. The demonstrated integrated device holds great potential for various applications such as filtering and switching in optical wavelength-division multiplexing (WDM) communication networks.

Time scrambling and decoy-state quantum key distribution for optical physical layer encryption

We propose an optical physical layer encryption method based on real-time optical signal temporal scrambling and decoy-state quantum key distribution. The real-time optical signal processing is operating with an array of tunable Fabry-Perot cavities by using the updating and synchronization keys. Based on this scheme, an experimental demonstration is given to realize secure communication for optical physical layer in a standard 10 Gbps data transmission with quantum key distribution in real time. An on-line transmitted data over 100 km of a standard single mode fiber is realized with power penalty of as low as 3.45 dB, where the average key generation rate is better than 800 bps. The experimental results indicate that, the proposed encryption scheme of dynamic scrambling with quantum keys exhibits significantly potential for improving the confidentiality of optical physical layer.

Tunable Fabry-Perot interferometer as a dispersing element in spectral devices

Presently, tunable optical filters are widely used in optical and optoelectronic systems and complexes. Tunable optical filters are essential components in a wide range of optical systems. The developed tunable Fabry-Perot interferometer presented the article can be used in various fields of optotechnics. The design of the proposed tunable optical filter is a tunable Fabry-Perot interferometer based on the inverse piezoelectric effect. The optical characteristics of the filter will depend on the optical, electrical and physical characteristics of the components included in its design.

High resolution multispectral spatial light modulators based on tunable Fabry-Perot nanocavities

Spatial light modulators (SLMs) are the most relevant technology for dynamic wavefront manipulation. They find diverse applications ranging from novel displays to optical and quantum communications. Among commercial SLMs for phase modulation, Liquid Crystal on Silicon (LCoS) offers the smallest pixel size and, thus, the most precise phase mapping and largest field of view (FOV). Further pixel miniaturization, however, is not possible in these devices due to inter-pixel cross-talks, which follow from the high driving voltages needed to modulate the thick liquid crystal (LC) cells that are necessary for full phase control. Newly introduced metasurface-based SLMs provide means for pixel miniaturization by modulating the phase via resonance tuning. These devices, however, are intrinsically monochromatic, limiting their use in applications requiring multi-wavelength operation. Here, we introduce a novel design allowing small pixel and multi-spectral operation. Based on LC-tunable Fabry-Perot nanocavities engineered to support multiple resonances across the visible range (including red, green and blue wavelengths), our design provides continuous 2π phase modulation with high reflectance at each of the operating wavelengths. Experimentally, we realize a device with 96 pixels (~1 μm pitch) that can be individually addressed by electrical biases. Using it, we first demonstrate multi-spectral programmable beam steering with FOV~18° and absolute efficiencies exceeding 40%. Then, we reprogram the device to achieve multi-spectral lensing with tunable focal distance and efficiencies ~27%. Our design paves the way towards a new class of SLM for future applications in displays, optical computing and beyond.

Fabry-Perot Interference Fiber Acoustic Wave Sensor Based on Laser Welding All-Silica Glass

Due to the small difference between the thermal expansion coefficients of silica optical fiber and silica glass, they are used as probe materials of optical fiber acoustic wave sensors. According to the light absorption characteristics of a pressure-sensitive silica diaphragm and silica glass, the laser welding of an all-silica Fabry–Perot (FP) interference optical fiber acoustic wave sensor with a CO2 laser is proposed. For understanding the influence of thermal expansion of sealing air in an FP cavity and the drift of interference-intensity demodulation working point of a FP interference acoustic wave sensor, we designed a process for the laser welding of an ultra-thin silica diaphragm and sleeve and optical fiber and sleeve. The exhaust hole of the FP cavity is reserved in the preparation process, and an amplified spontaneous emission light source and a tunable optical-fiber FP filter are introduced to stabilize the working point. The sensor is tested with a 40 kHz sound vibration signal. The results show that the sound pressure sensitivity of the sensor to an acoustic source of 0.02–0.1 W/cm2 is 6.59 mV/kPa. The linearity coefficient is 0.99975, indicating good linearity.

Implementation of a Controller for a Space-Grade, Piezo-Actuated Fabry-Perot Interferometer

A tunable Fabry-Perot interferometer (FPI) can be used as an optical band-pass filter. This type of filter is used in spectrometers and spectral imagers. The transmitted wavelength depends on the optical cavity adjusted by an electronic controller. This cavity, or the gap between the FPI mirrors, is measured using capacitive sensing. The performance of the FPI controller directly affects the FPI transmission spectrum and thus the quality of the spectral data. This work describes the design of the FPI controller for the ultraviolet channel of the ALTIUS hyperspectral imager. The ALTIUS mission is part of the Earth Watch program managed by the European Space Agency, ESA. This article presents a novel combination of building blocks to implement a low-noise, high-stability controller for piezo-actuated FPIs. Special care was taken to guarantee temperature stability and to minimize fluctuation of the FPI gap caused by the controller electronics. With the controller design presented in this paper, temperature variations ranging from &#x2013;50 to +50 &#x00B0;C induce FPI gap deviations of less than 0.1 nm at an electrode distance of 3000 nm, corresponding to a relative temperature drift of 0.3 ppm/&#x00B0;C.

Hysteresis and temperature drift compensation for FBG demodulation by utilizing adaptive weight least square support vector regression.

Hysteresis and temperature drift deteriorate the demodulation performance of tunable Fabry-Perot (F-P) filters. This study addresses a novel adaptive weight least square support vector regression (AWLSSVR) to compensate for the hysteresis and temperature drift of F-P filters. The temperature drift of a referent fiber Bragg grating(FBG) is used to estimate the temperature drifts of other three sensing FBGs, and a novel adaptive weighting strategy with an asymmetric noise interval is proposed, to eliminate the effects of noise in the training dataset. The experimental results show that when the temperature-changing modes of the training and testing datasets were close to each other, the error of the proposed method is reduced to 8.7 pm, while the errors of the other three conventional methods based on LSSVR are more than 10.8 pm. Further, when the temperature-changing modes of the training and testing datasets were partly different, the error of the proposed method was reduced to 5.4 pm, while the errors of other methods were more than 11.9 pm. It was verified experimentally that the proposed AWLSSVR method is more accurate and robust than other versions of WLSSVR for training samples with noise, requires no additional hardware, and covers the entire C band.

Development of triboelectric-enabled tunable Fabry-Pérot photonic-crystal-slab filter towards wearable mid-infrared computational spectrometer

Miniaturized optical spectrometers have been realized by exploiting conventional working principles and advanced nanofabrication technology. Especially in the mid-infrared (MIR) range, chip-scale optical spectrometers enable fast and on-site detection of molecular fingerprints for selective chemical sensing in healthcare and environmental monitoring. This miniaturization is also highly desirable for the wearable devices where the tiny functional parts remain on rigid substrates but the electronics are flexible. In the last decade, the triboelectric nanogenerator (TENG) technology has been proven as an indispensable and enabling technology for wearable self-powered sensors, energy harvesters and voltage sources, etc. Although a few TENG based gas sensors have been demonstrated, each of these sensors can detect a particular gas other than diversified gases. Infrared spectrometer is known as an instrument which can investigate the infrared absorption characteristics of gas molecules. It is the best generic technology to sense multiple gases on the same instrument, or device. In this study, we demonstrate a TENG enabled tunable Fabry-Pérot (FP) photonic-crystal-slab filter aiming for the computational spectrometer in the MIR range. The textile-triboelectric nanogenerator (T-TENG) provides high open-circuit voltage to shift the resonance wavelengths of the electrostatically actuated FP-filter, where this feature provides the sampling bases required for the computational spectrometer. Furthermore, the FP-filter is fabricated by a new transfer-printing method and shows a large wavelength tunability. As a proof of concept, the transmission spectrum of acetone vapor is reconstructed from 5 to 6.5 µm using this TENG enabled FP-filter. The molecular fingerprint of acetone is identified at 5.75 µm. This work paves the way towards the wearable MIR miniaturized optical spectrometer. • A MEMS tunable Fabry-Perot (FP) photonic-crystal-slab filter is fabricated by transfer-printing method. • The computational optical spectrometer is demonstrated for the first time with a single MEMS tunable device. • A textile-TENG is incorporated to tune the resonance of FP filter, forming the sampling bases for computational spectrometer. • The transmission spectra of CO 2 and acetone are reconstructed with their molecular fingerprints identified.

Metal-dielectric-metal multilayer structure with tunable Fabry-Perot resonance for highly sensitive refractive index sensing

The metal-dielectric-metal multilayer structure sensor with a transparent top layer and an opaque bottom layer is proposed, which can provide a perfect narrow-band absorption resonance and is suitable for sensing refractive index change of the liquid to be measured in dielectric layer. The Fabry-Perot resonance analytical model that can accurately reproduce response spectrum and theoretically analyze the mechanism of the dielectric layer thickness to tune resonance wavelength and linewidth of response spectrum is constructed. Theoretical analysis shows that the resonance wavelength is directly proportional to the thickness of dielectric layer, and the full width at half maximum is inversely proportional to the thickness of dielectric layer. The analytical expressions for its resonance wavelength, quality factor, full width at half maximum and sensitivity are also given. When used for the refractive index sensing, the quality factor and figure of merit of the proposed multilayer structure based on the 8th order Fabry-Perot resonance are 2162.8 and 1648.1 RIU&lt;sup&gt;–1&lt;/sup&gt;, respectively. However, due to the influence of the minimum resolution of the spectrometer, the conventional method of measuring resonance wavelength shift to achieve refractive index sensing has a high measurement limit. For the sensing of weaker refractive index perturbation, with the help of superposition of exceptional point degenerate state and tuning mechanism of Fabry-Perot resonance, in this paper proposed is a method of tunably sensing the liquid refractive index by measuring the increase of reflection coefficient or splitting of eigenvalue at a specific wavelength. Here, we take for example the metal-dielectric-metal multilayer structure sensor based on the 8th order Fabry-Perot resonance. According to the calculation results of Fabry-Perot model, when the change in refractive index of liquid to be measured is 10&lt;sup&gt;–4&lt;/sup&gt; RIU, the increase of forward reflection coefficient and the splitting of two eigenvalues of the scattering matrix are 0.319 and 1.1279, respectively.

Applications and research progress of optical fiber grating sensing in thermoplastic composites molding and structure health monitoring

Thermoplastic composites have the characteristics of high strength, fatigue resistance and easy recycling. They have received wide attention and are used in construction, automobile and other fields. An accurate monitoring technique is necessary for monitoring their internal state in the molding process and structure health in the service process. Traditional mechanical and electrical sensors have many disadvantages, such as large size and slow response. Therefore, they are not appropriate for embedded measuring and real-time monitoring. Optical fiber Bragg grating (FBG) sensors present many advantages over traditional and other advanced sensors, such as resistance to electromagnetic interference, light weight and less influence on materials. Generally, FBGs are embedded in composites and/or structures to monitor temperature and strain. The principle of FBG sensor and three key demodulation techniques are introduced firstly, including tunable Fabry-Perot (F-P) filter demodulation, especially the high-speed demodulation technique based on swept wavelength tunable laser, linear filter demodulation and matched grating. Secondly, the progress of monitoring technology based on FBGs for three molding scheme is reviewed, including hot compression molding, fused deposition molding and automated fiber placement molding. Thirdly, the progress of structural health monitoring for thermoplastic composites is also reviewed. Finally, some intelligent thermoplastic composite structures based on FBGs are introduced.

An edge-filter FBG interrogation approach based on tunable Fabry-Perot filter for strain measurement of planetary gearbox

• An improved TFP-based edge-filter FBG interrogation approach is proposed. • A feedback channel is adopted to control the creep of the piezoelectric actuator. • The TFP is driven by both the coarse voltage and fine voltage. • The FBG interrogation approach is applied to the strain measurement of ring gear. Fiber Bragg gratings (FBGs), with smaller size, are suitable to measure the tooth root strain of ring gear which is an ideal signal for fault diagnosis of planetary gearboxes. In order to identify the fault features in the strain signal, a high-speed and high-resolution FBG interrogator is needed. Compared with wavelength-scanning interrogation approach, the edge-filter approach can achieve such a performance more easily and economically. However, conventional edge-filter approaches based on fixed edge filters have low applicability. The adoption of a tunable Fabry-Perot filter (TFP) increases the flexibility of the edge-filter system, but the creep characteristics of the piezoelectric actuator in TFP may cause interrogation errors. This paper proposes an improved TFP-based edge-filter FBG interrogation approach with creep control ability. First, the interrogation principle of the proposed approach is analyzed by comparing with the conventional edge-filter approaches. The creep control method is presented by employing a feedback channel and two kinds of TFP driving voltage. Next, a FBG interrogator based on the proposed approach is established. The creep control performance, static interrogation performance and dynamic interrogation performance are all tested. The results show that the interrogator has the wavelength repeatability of ~ 0.1 pm at 1 kHz and ~ 0.2 pm at 5 kHz respectively. Finally, the proposed edge-filter approach is applied to measure the tooth root strain of ring gear in a planetary gearbox. The measured strain signal has a high quality, and the tooth fault feature can be identified obviously.

Fabrication of 128 × 128 MEMS tunable F-P cavity optical filter array with surface micromachining

In this paper, a tunable Fabry-Perot (F-P) cavity filter with a large 128 × 128 array is successfully fabricated for an infrared (IR) hyperspectral imager via surface micromachining technology. A low-temperature (less than 200 °C) surface micromachining process is developed for manufacturing F-P tunable filter arrays, which has satisfactory compatibility. A suspended micro-bridge structure is created with a polyimide sacrificial layer. To obtain a large tuning range, long support arm structures are studied. The structure also has a compact array of folding arms. The filter can be tuned via an electrostatic force. The filter, which has an initial cavity length of 2.3 μm, has a displacement of 1.5 μm at an applied bias voltage of 8 V. The tuning wavelength of the filter is from 4.7 μm to 2.8 μm with an actuation voltage of less than 2 V. At the centre wavelength of 4 μm, the spectral transmittance of the filter is 73%. The technology for the fabrication of microelectro mechanical systems (MEMS) filter arrays as dispersive elements has potential applications in hyperspectral imaging.

Narrowband photon pairs with independent frequency tuning for quantum light-matter interactions.

We describe a cavity-enhanced spontaneous parametric down-conversion (CE-SPDC) source for narrowband photon pairs with filters designed such that 97.7% of the correlated photons are in a single mode of 4.3(4) MHz bandwidth. Type-II phase matching, a tuneable-birefringence resonator, MHz-resolution pump tuning, and tuneable Fabry-Perot filters are used to achieve independent signal and idler tuning. We map the CE-SPDC spectrum using difference frequency generation to precisely locate the emission clusters, demonstrate CE-SPDC driven atomic spectroscopy, and measure a contribution from unwanted modes of 7.7%. The generated photon pairs efficiently interact with neutral rubidium, a well-developed system for quantum networking and quantum simulation. The techniques are readily extensible to other material systems.