Resonant Mirror Research Articles

Simultaneous measurement of temperature and refractive index using microfiber knot resonators in Hi-Bi fiber loop mirrors

Based on the large evanescent field of microfibers, a novel fiber sensor using a microfiber knot resonator embedded in a Hi-Bi fiber loop mirror is proposed for simultaneous measurement of the temperature and refractive index of solutions. Due to the different responses of the microfiber knot resonator and fiber loop mirror to temperature and refractive index variations, the fiber sensor can measure temperature and refractive index simultaneously by utilizing the sensitivity matrix. The experimental measurements show that the sensitivities of the microfiber knot resonator and the fiber loop mirror to temperature are 5.6 pm/°C and −464.1 pm/°C, respectively. The sensitivity of the microfiber knot resonator to the refractive index of dilute solutions is 116 nm/RIU. The sensor has a higher sensitivity to refractive index variations than LPGs and has potential for use in the field of biochemistry.

Time-varying optical vortices enabled by time-modulated metasurfaces

Abstract In this paper, generation of optical vortices with time-varying orbital angular momentum (OAM) and topological charge is theoretically demonstrated based on time-modulated metasurfaces with a linearly azimuthal frequency gradient. The topological charge of such dynamic structured light beams is shown to continuously and periodically change with time evolution while possessing a linear dependence on time and azimuthal frequency offset. The temporal variation of OAM yields a self-torqued beam exhibiting a continuous angular acceleration of light. The phenomenon is attributed to the azimuthal phase gradient in space-time generated by virtue of the spatiotemporal coherent path in the interference between different frequencies. In order to numerically authenticate this newly introduced concept, a reflective dielectric metasurface is modelled consisting of silicon nanodisk heterostructures integrated with indium-tin-oxide and gate dielectric layers on top of a mirror-backed silicon slab which renders an electrically tunable guided mode resonance mirror in near-infrared regime. The metasurface is divided into several azimuthal sections wherein nanodisk heterostructures are interconnected via nanobars serving as biasing lines. Addressing azimuthal sections with radio-frequency biasing signals of different frequencies, the direct dynamic photonic transitions of leaky-guided modes are leveraged for realization of an azimuthal frequency gradient in the optical field. Generation of dynamic twisted light beams with time-varying OAM by the metasurface is verified via performing several numerical simulations. Moreover, the role of modulation waveform and frequency gradient on the temporal evolution and diversity of generated optical vortices is investigated which offer a robust electrical control over the number of dynamic beams and their degree of self-torque. Our results point toward a new class of structured light for time-division multiple access in optical and quantum communication systems as well as unprecedented optomechanical manipulation of objects.

Stimulated Acoustic Light Scattering in the Externally Excited Optical Resonator

Dynamics of Stokes radiation generation in a nanodispersed medium within an optical resonator excited by external monochromatic radiation is investigated for the first time. Conversion of incident radiation results from ponderomotive buildup of intrinsic acoustic pulsations of the dispersed particles. It is assumed that the resonator mirrors reflect well the frequencies of the incident radiation and the first Stokes component.

Lasing in a medium with the properties of a Christiansen filter.

Dye lasing in a dense slurry-like mixture, similar to the optical medium of the Christiansen filter, is first reported. A cuvette with lithium fluoride (LiF) crystal particles and an immersion liquid containing pyrromethene 567 dye was placed in a two plane mirror resonator and pumped by pulses of the second harmonic of the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Twenty nanosecond pulses at 545-570 nm wavelengths with energies up to 0.6 mJ were obtained at the output of this slurry laser. The central part of the laser beam with a divergence of 6 mrad was usually accompanied by a ring structure of scattered radiation. The conditions of the generation development and formation of the output beam profile in a slurry laser as well as its possible applications are discussed.

Hadamard transform-based hyperspectral imaging using a single-pixel detector.

In this paper, a single-pixel hyperspectral imager is developed based on the Hadamard transformation. The imager's design, fabrication, signal processing method, and experimental results are discussed. The single-pixel hyperspectral imager works in pushbroom mode and employs both spatial encoding and spectral encoding to acquire the hyperspectral data cube. Hadamard encoding patterns, which are known for their multiplexing advantage to achieve high signal-to-noise ratio (SNR), are used in both encoding schemes. A digital micromirror device (DMD) from Texas Instruments (TI) is used for slow spatial encoding and a resonant scanning mirror in combination with a fixed Hadamard mask is used for fast spectral encoding. In addition, the pushbroom operation can be achieved internally by spatially shifting the location of the Hadamard encoded slit on the DMD, thus the imager is able to acquire 3D data cubes without the need to scan it across the object. Although our experimental results demonstrate the hyperspectral data cubes of various objects over a 450 nm ∼ 750 nm visible spectral range, the proposed imager can be easily configured to be used at other wavelengths due to the single-pixel detection mechanism used.

Critical assessment of relevant methods in the field of biosensors with direct optical detection based on fibers and waveguides using plasmonic, resonance, and interference effects

Direct optical detection has proven to be a highly interesting tool in biomolecular interaction analysis to be used in drug discovery, ligand/receptor interactions, environmental analysis, clinical diagnostics, screening of large data volumes in immunology, cancer therapy, or personalized medicine. In this review, the fundamental optical principles and applications are reviewed. Devices are based on concepts such as refractometry, evanescent field, waveguides modes, reflectometry, resonance and/or interference. They are realized in ring resonators; prism couplers; surface plasmon resonance; resonant mirror; Bragg grating; grating couplers; photonic crystals, Mach-Zehnder, Young, Hartman interferometers; backscattering; ellipsometry; or reflectance interferometry. The physical theories of various optical principles have already been reviewed in detail elsewhere and are therefore only cited. This review provides an overall survey on the application of these methods in direct optical biosensing. The “historical” development of the main principles is given to understand the various, and sometimes only slightly modified variations published as “new” methods or the use of a new acronym and commercialization by different companies. Improvement of optics is only one way to increase the quality of biosensors. Additional essential aspects are the surface modification of transducers, immobilization strategies, selection of recognition elements, the influence of non-specific interaction, selectivity, and sensitivity. Furthermore, papers use for reporting minimal amounts of detectable analyte terms such as value of mass, moles, grams, or mol/L which are difficult to compare. Both these essential aspects (i.e., biochemistry and the presentation of LOD values) can be discussed only in brief (but references are provided) in order to prevent the paper from becoming too long. The review will concentrate on a comparison of the optical methods, their application, and the resulting bioanalytical quality.

High-Speed and Large-Amplitude Resonant Varifocal Mirror

We design, fabricate, and measure high-speed resonant varifocal mirrors for a reflective type focus scanning optical element. A circumference supported type mirror and a node supported type mirror with a 1 mm diameter driven by an electrostatic actuator are investigated. In the node supported type, a larger amplitude compared to that of the circumference supported type was obtained. The fabricated mirror could operate at approximately 450 kHz with axisymmetric deformation. The focal length was calculated to be ±28 mm at an applied total voltage amplitude of 150 V.

Simultaneous measurement of displacement, pitch, and yaw angles of a cavity output mirror based on phase measuring deflectometry.

Accurate and high dynamic range measurement of the three attitude variations (i.e., displacement, pitch, yaw angles) has been widely researched based on various approaches to meet different application requirements. However, none of the existing methods can detect these three attitude variations at the same time. This paper proposes a method based on a classical phase measuring deflectometry (PMD) system and a double iteration algorithm to simultaneously measure the three variations of the output mirror in a laser resonator. The relationship between the attitude variations and the lateral displacement parameters (LDP) of the imaged structural fringes is derived in the PMD system. Through the established relationship, the attitude variations could be calculated once the LDP are detected. Furthermore, a two-step measuring scheme combining the four-step shifting phase and the color-coded fringe is proposed to effectively detect the LDP. Finally, an experiment is conducted to verify the feasibility of the proposed method.

Linear Modeling and Control of Comb-Actuated Resonant MEMS Mirror With Nonlinear Dynamics

This article presents a novel method to derive and identify an accurate small perturbation model of a comb-actuated resonant microelectromechanical system (MEMS) mirror with highly nonlinear dynamics. Besides the nonlinear stiffness and damping, the comb-drives add nonlinearities due to their electrostatic nature and their effect on the dynamic mirror amplitude over frequency behavior. The proposed model is based on a period to period energy conservation and applies for most nonlinearities present in an oscillator such as MEMS mirrors. It is shown that for specific nominal operation points with square wave excitation, the small perturbation model is linear for a wide range. The full dynamics of the derived linear model are parametrized by three constants, that can be estimated by the phase locked loop (PLL), performing a proposed identification method only based on phase measurements. An analysis of control laws usually applied in a PLL provides important information for the proper design of controllers to meet the desired behavior for individual applications.

A single-pixel hyperspectral imager using two-stage Hadamard encoding

This paper presents a hyperspectral imaging approach using a single-pixel detector. The system consists of a two-stage encoding system based on the concept of Hadamard transform. In contrast with conventional hyperspectral imaging methods where wavelength filters or Fourier spectroscopy is usually adopted, the spectral imaging system in this design uses an encoded slit, a resonant scanning mirror, and a fixed encoder mask to reconstruct the spectral image. The proposed method provides a novel way to set up an easily-controllable single-pixel approach that allows the imager to operate at any wavelength. We present a complete single-pixel hyperspectral imaging system with experimental results to demonstrate its working performance.

Inverse design of all-dielectric parallel-plane mirror optical resonator

Inverse-design algorithms can be used to design compact and high-performance complex photonic structures. In this study, we propose the design of an all-dielectric optical resonator based on the concept of the parallel mirror resonator by using the objective-first inverse design algorithm. Light is strongly confined using a predefined objective function that creates symmetric mirror regions acting as reflective layers for the fundamental transverse-electric polarization mode. Thanks to the flexibility of the algorithm, segments of the cavity and dielectric mirror are designed in a simulation region by choosing a cavity of an appropriate length. A time-domain analysis of the proposed structure was carried out using the two-dimensional finite-difference time-domain method. The proposed structure has a configuration with a footprint of 13.394 × 0.592 μm2. The algorithm generates an inverse-designed structure to obtain a resonance peak at the target wavelength without any intuitive scanning of the complete parameter space. As a result, the first-order mode is strongly localized in the region of the cavity for the defined design wavelength. Moreover, the application of the inversely designed resonator as refractive index sensor is examined to show that the proposed structure has the potential for use in integrated photonic devices. Thus, the objective-first inverse design algorithm is promising for use in the design of a variety of photonic structures.

Ultra-Compact Microsystems-Based Confocal Endomicroscope.

Point-of-care medical diagnosis demands immediate feedback on tissue pathology. Confocal endomicroscopy can provide real-time in vivo images with histology-like features. The working channel in medical endoscopes are becoming smaller in dimension. Microsystems methods can produce tiny mechanical scanners. We demonstrate a flexible fiber instrument for in vivo imaging as an endoscope accessory. The optical path is folded on-axis to reduce length while allowing the beam to expand and achieve a numerical aperture of 0.41. A high-speed parametric resonance mirror produces large deflection angles > 13°, and is mounted on a 2 mm diameter chip designed with clamp structures for reduced space. A compact lens assembly provides diffraction-limited lateral and axial resolution of 1.5 and [Formula: see text], respectively. A working distance of [Formula: see text] and field-of-view of [Formula: see text] m are achieved. Miniature apparatus is fabricated to assemble and align the scanhead components. The optics and scanner are packaged in a distal tip with 2.4 mm diameter and 10 mm rigid length. These dimensions allow the endomicroscope to pass forward easily through the 2.8 mm diameter working channel in medical endoscopes commonly used in clinical practice. Fluorescence images are collected in vivo at 10 frames per second in the colon of genetically-engineered mice that spontaneously develop adenomas. A FITC-labeled peptide heterodimer is administered intravenously to provide specific contrast. Sub-cellular structures are visualized to distinguish pre-malignant from normal mucosa. These results demonstrate use of microsystems methods to produce an ultra-compact instrument with sufficiently small dimensions for broad use.

Complex Valued State Space Model for Weakly Nonlinear Duffing Oscillator with Noncollocated External Disturbance

This paper proposes a slow flow model for a weakly nonlinear and parametrically driven Duffing oscillator and a complex valued state space model for the oscillator with noncollocated external disturbances. The combination of the parametrically driven duffing oscillator and noncollocated disturbances can be observed in resonant MEMS mirrors with a reinforcement structure to reduce dynamic mirror deformation. The model is based on a rational function approximation for the angular derivative of the out-of-plane comb drive capacitance, enabling qualitative analysis at large amplitudes while the stability analysis is maintained as the conventional cubic function approximation. The slow flow model is extended including a single tone noncollocated disturbance and is linearized at an equilibrium point for a small disturbance. The linearized disturbance model is reformulated by a complex valued state space model to cope with general wideband disturbances, allowing various analytic methods in traditional system theory. The simulation results demonstrate a good agreement between the proposed models and the ODE simulation, verifying the accuracy and benefits of the proposed models.

Capacitive Charge-based Self-Sensing for Resonant Electrostatic MEMS mirrors

This paper proposes capacitive charge-based self-sensing by integration of the comb drive intrinsic displacement current for resonant electrostatic MEMS mirrors in order to solve the problem of robust feedback for laser scanning in mobile light detection and ranging (Lidar) application. A two-channel switched current integrator circuit is implemented to determine the deflection angle and to distinguish the rotation direction from the asymmetric comb drive charge. Parameters of the MEMS mirror are calibrated with the deflection angle by an optical PSD setup. The resonant electrostatic MEMS mirror is parametrically driven by a square wave high voltage signal, which means, that the charge measurement is only available during the time with non-zero drive signal. From the partly available charge measurements, a nonlinear observer is developed to estimate the mirror state at all time for a potential feedback control. The feasibility for online position estimation is proven by simulation using experimental charge and deflection angle measurements resulting in less than 2% error at full amplitude operation. Finally, the performance of the proposed method is discussed for realization of active MEMS mirror feedback control, overcoming imprecise motions due to structural nonlinearities as well as external disturbances like vibration and climate variation.

Validating the Critical Point of Spontaneous Parametric Downconversion for Over 600 Scanning MEMS Micromirrors on Wafer Level

Sensors and actuators based on resonant micro-electro-mechanical systems (MEMS), such as scanning micro mirrors, are well-established in automotive and consumer products. As the areas of application broaden, the requirements for the MEMS are increasing. Devices outside of the performance specifications have to be rejected which is costly due to the high processing times of MEMS technologies. In particular, nonlinear system behavior is often found to cause unexpected device failure or performance issues. Thus, accurate simulation or rather system models which account for nonlinear sensor dynamics can not only increase process yield, but more importantly, lead to a comprehensive understanding of the underlying physics and to improved MEMS design. We have studied [1] the possibility of a rather drastic device failure induced by nonlinearities on the example of a resonant scanning MEMS micro mirror. On the level of a few selected chips, we have carefully measured the complex nonlinear system behavior and modeled it by a nonlinear mode-coupling phenomenon known as spontaneous parametric down-conversion (SPDC). The most intriguing feature of SPDC is the sudden change from a rather linear to a nonlinear system behavior at the critical oscillation amplitude. However, the threshold only lies within the range of the mirror's operational amplitude, if certain frequency resonance conditions regarding the mechanical modes are met. Thus, the critical amplitude strongly depends on the frequency spectrum of the MEMS design which in turn is largely influenced by fabrication imperfections. We validate the dependence of the critical amplitude on the resonance condition by measuring it for over 600 micro mirrors on wafer-level. Our work does not only validate the theory of SPDC with measurements on such a large scale, but also demonstrates modeling strategies which are essential for MEMS product design.

Mode locking in an optomechanical cavity

We experimentally study a fiber-based optical ring cavity integrated with a mechanical resonator mirror and an optical amplifier. The device exhibits a variety of intriguing nonlinear effects including synchronization and self-excited oscillation. Passively generated optical pulses are observed when the frequency of the optical ring cavity is tuned very close to the mechanical frequency of the suspended mirror. The optical power at the threshold of this process of mechanical mode locking is found to be related to quantum noise of the optical amplifier.

Design and Calibration of a Fast Flying-Dot Projector for Dynamic Light Transport Acquisition

The light transport captures a scene's visual complexity. Acquiring light transport for dynamic scenes is difficult, since any change in viewpoint, materials, illumination or geometry also varies the transport. One strategy to capture dynamic light transport is to use a fast “flying-dot” projector; i.e., where an impulse light-probe is quickly scanned across the scene. We have built a novel fast flying-dot projector prototype using a high speed camera and a scanning MEMS (Micro-electro-mechanical system) mirror. Our contributions are calibration strategies that enable dynamic light transport acquisition at near video rates with such a system. We develop new methods for overcoming the effects of MEMS mirror resonance. We utilize new algorithms for denoising impulse scanning at high frame rates and compare the trade-offs in visual quality between frame rate and illumination power. Finally, we show the utility of our calibrated setup by demonstrating graphics applications such as video relighting, direct/global separation, and dual videography for dynamic scenes such as fog, water, and glass. Please see our accompanying video for dynamic scene results.

Electro-optical Amplitude and Phase Modulators Based on Tunable Guided-Mode Resonance Effect

Here, electrically tunable amplitude and phase modulators are designed by the hybridization of indium tin oxide (ITO) into a guided-mode resonance mirror (so-called GMRM), which consists of a high-...

Fast micron-scale 3D printing with a resonant-scanning two-photon microscope

3D printing allows rapid fabrication of complex objects from digital designs. One 3D-printing process, direct laser writing, polymerises a light-sensitive material by steering a focused laser beam through the shape of the object to be created. The highest-resolution direct laser writing systems use a femtosecond laser, steered using mechanised stages or galvanometer-controlled mirrors, to effect two-photon polymerisation. Here we report a new high-resolution direct laser writing system that employs a resonant mirror scanner to achieve a significant increase in printing speed over current methods while maintaining resolution on the order of a micron. This printer is based on a software modification to a commercially available resonant-scanning two-photon microscope. We demonstrate the complete process chain from hardware configuration and control software to the printing of objects of approximately 400 × 400 × 350 μm, and validate performance with objective benchmarks. Released under an open-source license, this work makes micron-scale 3D printing available at little or no cost to the large community of two-photon microscope users, and paves the way toward widespread availability of precision-printed devices.

High-order cylindrical vector beams with tunable topological charge up to 14 directly generated from a microchip laser with high beam quality and high efficiency

Large topological charge optical vortex beams carrying orbital angular momentum have potential applications on optical trapping, optical communication with high capacity, quantum information processing. However, the beam quality is degraded in vortex beams generated with spiral phase plates or resonator mirrors with defect spots and optical conversion efficiency in solid-state lasers is sacrificed by controlling the loss of resonator. It is a big challenge for generating high beam quality, high-order cylindrical vector beams with large topological charge in compact solid-state lasers. Here, high-order cylindrical vector beams [Laguerre-Gaussian (LG) modes with zero degree and order of l, LG0,l] with tunable topological charges up to 14 have been generated in an annular beam pumped Yb:YAG microchip laser by manipulating the pump power-dependent population inversion distribution. Efficient performance with optical efficiency of 17.5% has been achieved. The output power is 1.36 W for a vector-vortex laser with 14 topological charges. The pump power dependent wavelength tunable and dual-wavelength laser oscillation in vector-vortex beams has been observed by controlling the reabsorption loss at 1030 nm. Wavelength tunable, dual-wavelength (1030 and 1050 nm) laser oscillation has been achieved for vector-vortex beams with topological charges of 8, 9, and 10. The laser beam quality factor M2 close to the theoretical value (l + 1) has been achieved for LG0,l vector-vortex beams with tunable topological charges up to 14. This work provides a new effective method for generating large topological charge high-order cylindrical vector beams in solid-state microchip lasers with high efficiency and high beam quality.