Optical Microelectromechanical Systems Research Articles

3D Printing of Glass Micro-Optics with Subwavelength Features on Optical Fiber Tips.

Integration of functional materials and structures on the tips of optical fibers has enabled various applications in micro-optics, such as sensing, imaging, and optical trapping. Direct laser writing is a 3D printing technology that holds promise for fabricating advanced micro-optical structures on fiber tips. To date, material selection has been limited to organic polymer-based photoresists because existing methods for 3D direct laser writing of inorganic materials involve high-temperature processing that is not compatible with optical fibers. However, organic polymers do not feature stability and transparency comparable to those of inorganic glasses. Herein, we demonstrate 3D direct laser writing of inorganic glass with a subwavelength resolution on optical fiber tips. We show two distinct printing modes that enable the printing of solid silica glass structures ("Uniform Mode") and self-organized subwavelength gratings ("Nanograting Mode"), respectively. We illustrate the utility of our approach by printing two functional devices: (1) a refractive index sensor that can measure the indices of binary mixtures of acetone and methanol at near-infrared wavelengths and (2) a compact polarization beam splitter for polarization control and beam steering in an all-in-fiber system. By combining the superior material properties of glass with the plug-and-play nature of optical fibers, this approach enables promising applications in fields such as fiber sensing, optical microelectromechanical systems (MEMS), and quantum photonics.

Low-Temperature Wafer-Level Bonding with Cu-Sn-In Solid Liquid Interdiffusion for Microsystem Packaging

This work demonstrates the potential use of Cu-Sn-In metallurgy for wafer-level low-temperature solid-liquid interdiffusion (LT-SLID) bonding process for microelectromechanical system (MEMS) packaging. Test structures containing seal-ring shaped SLID bonds were employed to bond silicon and glass wafers at temperatures as low as 170 °C. Scanning acoustic microscopy (SAM) was utilized to inspect the quality of as-bonded wafers. The package hermeticity was characterized by cap-deflection measurements and evaluated through finite element modelling. The results indicate the bonds are hermetic, but residual stresses limit the quantitative analysis of the hermeticity. The microstructural studies confirm the bonds contain a single-phase intermetallic Cu6(Sn,In)5 that remains thermally stable up to 500 °C. This work shows Cu-Sn-In based low-temperature bonding method as a viable packaging option for optical MEMS or other temperature-sensitive components.

Theoretical analysis and comparative study of assorted diaphragm primarily based Micro Electro Mechanical System (MEMS) optical pressure sensors

In general, micro pressure sensors use a diaphragm as the sensing element that converts the applied pressure into the required displacement. Displacement is employed to sense real physical phenomena, such as pressure, force with various conduction methods. The conduction is defined as capacitive, piezoresistive, piezoelectric or resonant. Understanding the behavior of structural elements prior to its design is very essential depends on conductive method. The main challenge of parameter optimization of the diaphragm is to attain unsurpassed device performance. Therefore, theoretical analysis of various structures of optical Micro Electro Mechanical System (MEMS) sensor is proposed in this manuscript. Here, diaphragm geometries, like square, rectangular and circular are considered to analyze the structures. The objective of this work is to analyze various structures of optical MEMS sensor measuring pressure theoretically. The displacements of the varied diaphragms are compared for different thicknesses and the graphs are analyzed against their displacements. The best suitable structure of diaphragm for pressure sensor design is obtained. The diaphragm with good characteristics is virtually fabricated using Intellifab. The parameters such as linearity and relationship between pressure and intensity are obtained for the best suited diaphragm.

Optical Interferometric MEMS Accelerometers

AbstractLaser interferometry is one of the most accurate measurement technologies whose displacement resolution can reach the femtometer (fm) level. With the development of Micro‐Electro‐Mechanical Systems(MEMS) technology, many excellent optical interferometric MEMS sensors have emerged, which play an essential role in intelligent manufacturing, aerospace, and many other fields. Among them, optical interferometric MEMS accelerometers develop rapidly due to their high sensitivity, low noise, and anti‐electromagnetic interference advantages. Lots of research in optical interferometric chip design, micro‐nano fabrication process, signal demodulation algorithm, and range extension technology are performed, and different types of MEMS accelerometers based on the optical interferometric principles are developed, which have been demonstrated and applied in the fields of disaster monitoring, equipment operation and maintenance, and resource exploration. This paper reviews the development status of optical interferometric MEMS accelerometers, mainly focusing on the critical problems and solutions that need to be solved in the development process of optical interferometric accelerometers, and finally introduces the typical application scenarios.

MEMS-tunable polarization management in photonic integrated circuits.

Optical fibers are generally polarization-insensitive while photonic integrated circuits (PICs) often exhibit a large polarization dependence due to the high-aspect-ratio and high-index-contrast of integrated waveguides. As PICs become more mature there is an increasing need for tunable polarization management on-chip. Although micro-electro-mechanical systems (MEMS) are increasingly finding application in PICs for optical switching and phase shifting, they have so far not found wide application for polarization management. In this work we propose two optical MEMS architectures for polarization management enabling tunable polarization splitting and rotation - key functions so far lacking in PICs. The first structure consists of a directional coupler with a MEMS-tunable gap enabling a continuously-variable polarization splitting ratio. A second architecture consists of a symmetry-breaking MEMS perturber suspended over an air-cladded waveguide enabling tunable polarization rotation. For both architectures we simulate a polarization extinction exceeding 25 dB, and the operating bandwidth can be as large as 100 nm. We conclude with a discussion of actuation schemes and examine fabrication considerations for implementation in PIC foundries.

Miniature optical MEMS microphone with 14dBA noise floor

This paper explains the fundamental technology used to create an optical microphone transducer. In recent years, microelectromechanical system (MEMS) capacitive microphones have demonstrated improved performance. State-of-the-art capacitive MEMS microphones can achieve SNR in the order of 73 dBA (21 dBA noise floor) with overall dynamic range in the order of 101 dB. There are fundamental challenges to driving the performance of capacitive MEMS microphone technology in very small packages to new heights. Piezoelectric MEMS microphones have not demonstrated SNR performance >65 dBA. The next breakthrough in miniature microphone technology will come from optical MEMS microphone technology. 80dB SNR (14 dBA noise floor) with 132 dB dynamic range (146dB maximum sound pressure level) has been achieved in a very small package. This paper will review the fundamentals of optical acoustic transduction and describe some of the approaches to miniaturization of the technology.

Fiber Optic MEMS Ultrasonic Sensor and its Application in Partial Discharge Detection

In this paper, an optical fiber based ultrasonic sensor was designed and applied to the detection and position of partial discharge (PD). The Fabry-Perot interferometer with a micro-electromechanical system (MEMS) diaphragm has been proven to have high sensitivity, with broadband acoustic frequency response up to 500 kHz and wide directivity. In the PD detection experiment, the minimum detectable pressure (MDP) of the fiber optical MEMS sensor is achieving 0.455μPaHz -1/2. In addition, four ultrasonic sensors are arranged around the ultrasonic source to conduct localization experiments. The results show that the system has excellent localization performance in x, y and z directions. The favourable acoustic performance of the MEMS sensor provides a high-sensitivity and high signal-to-noise ratio (SNR) detection method for PD detection.

Wafer-level hermetically sealed silicon photonic MEMS

The emerging fields of silicon (Si) photonic micro–electromechanical systems (MEMS) and optomechanics enable a wide range of novel high-performance photonic devices with ultra-low power consumption, such as integrated optical MEMS phase shifters, tunable couplers, switches, and optomechanical resonators. In contrast to conventional SiO 2 -clad Si photonics, photonic MEMS and optomechanics have suspended and movable parts that need to be protected from environmental influence and contamination during operation. Wafer-level hermetic sealing can be a cost-efficient solution, but Si photonic MEMS that are hermetically sealed inside cavities with optical and electrical feedthroughs have not been demonstrated to date, to our knowledge. Here, we demonstrate wafer-level vacuum sealing of Si photonic MEMS inside cavities with ultra-thin caps featuring optical and electrical feedthroughs that connect the photonic MEMS on the inside to optical grating couplers and electrical bond pads on the outside. We used Si photonic MEMS devices built on foundry wafers from the iSiPP50G Si photonics platform of IMEC, Belgium. Vacuum confinement inside the sealed cavities was confirmed by an observed increase of the cutoff frequency of the electro-mechanical response of the encapsulated photonic MEMS phase shifters, due to reduction of air damping. The sealing caps are extremely thin, have a small footprint, and are compatible with subsequent flip-chip bonding onto interposers or printed circuit boards. Thus, our approach for sealing of integrated Si photonic MEMS clears a significant hurdle for their application in high-performance Si photonic circuits.

Coarse-to-fine optical MEMS accelerometer design and simulation

A coarse-to-fine optical microelectromechanical systems (MEMS) accelerometer based on the Fabry-Pérot (FP) interferometer is proposed. The mechanical structure consists of a proof mass that is suspended by four L-shaped springs. The deflection of the proof mass due to the applied acceleration is detected using two FP cavities that comprise the system's optical system. Using coarse-to-fine measurement and the dual wavelength method simultaneously increases the sensitivity of the accelerometer as well as the linear measurement range. The optical simulation shows that the sensitivity of the proposed device is 10 times as high as that of a similar optical MEMS accelerometer with one FP cavity. In addition, the proposed optical system is insensitive to the displacements of the proof mass in the orthogonal directions, which considerably reduced the cross-axis sensitivity. The minimum feature size of the structure is 15 µm and the optical signal is conducted completely through the optical fibers, facilitating the device fabrication. Here are the results of the simulation: mechanical sensitivity of 190 nm/g, optical sensitivity of 8 nm/g, linear measurement of ±5g, and first resonance frequency of 1141 Hz.

A Comprehensive Review on the Optical Micro-Electromechanical Sensors for the Biomedical Application.

This study presented an overview of current developments in optical micro-electromechanical systems in biomedical applications. Optical micro-electromechanical system (MEMS) is a particular class of MEMS technology. It combines micro-optics, mechanical elements, and electronics, called the micro-opto electromechanical system (MOEMS). Optical MEMS comprises sensing and influencing optical signals on micron-level by incorporating mechanical, electrical, and optical systems. Optical MEMS devices are widely used in inertial navigation, accelerometers, gyroscope application, and many industrial and biomedical applications. Due to its miniaturised size, insensitivity to electromagnetic interference, affordability, and lightweight characteristic, it can be easily integrated into the human body with a suitable design. This study presented a comprehensive review of 140 research articles published on photonic MEMS in biomedical applications that used the qualitative method to find the recent advancement, challenges, and issues. The paper also identified the critical success factors applied to design the optimum photonic MEMS devices in biomedical applications. With the systematic literature review approach, the results showed that the key design factors could significantly impact design, application, and future scope of work. The literature of this paper suggested that due to the flexibility, accuracy, design factors efficiency of the Fibre Bragg Grating (FBG) sensors, the demand has been increasing for various photonic devices. Except for FBG sensing devices, other sensing systems such as optical ring resonator, Mach-Zehnder interferometer (MZI), and photonic crystals are used, which still show experimental stages in the application of biosensing. Due to the requirement of sophisticated fabrication facilities and integrated systems, it is a tough choice to consider the other photonic system. Miniaturisation of complete FBG device for biomedical applications is the future scope of work. Even though there is a lot of experimental work considered with an FBG sensing system, commercialisation of the final FBG device for a specific application has not been seen noticeable progress in the past.

A Miniature Optical Force Dual-Axis Accelerometer Based on Laser Diodes and Small Particles Cavities.

In recent years, the optical accelerometer based on the optical trapping force effect has gradually attracted the attention of researchers for its high sensitivity and high measurement accuracy. However, due to its large size and the complexity of optical path adjustment, the optical force accelerometers reported are only suitable for the laboratory environment up to now. In this paper, a miniature optical force dual-axis accelerometer based on the miniature optical system and a particles cavity which is prepared by Micro-Electro-Mechanical Systems (MEMS) technology is proposed. The overall system of the miniature optical levitation including the miniature optical system and MEMS particles cavity is a cylindrical structure with a diameter of about 10 mm and a height of 33 mm (Φ 10 mm × 33 mm). Moreover, the size of this accelerometer is 200 mm × 100 mm × 100 mm. Due to the selected light source being a laser diode light source with elliptical distribution, it is sensitive to the external acceleration in both the long axis and the short axis. This accelerometer achieves a measurement range of ±0.17 g–±0.26 g and measurement resolution of 0.49 mg and 1.88 mg. The result shows that the short-term zero-bias stability of the two orthogonal axes of the optical force accelerometer is 4.4 mg and 9.2 mg, respectively. The main conclusion that can be drawn is that this optical force accelerometer could provide an effective solution for measuring acceleration with an optical force effect for compact engineering devices.

Tailorable Stimulated Brillouin Scattering Laser Based on Silicon Ring Waveguides

Stimulated Brillouin scattering (SBS) lasers based on silicon waveguides with large SBS gain, have been widely used in frequency tunable laser emission, mode-locked pulse laser, low-noise oscillator, optical gyroscope, and other fields. However, current SBS lasers still need long waveguide lengths to realize Brillouin laser output, which increases the waveguide losses and is not conductive to be integrated. In this paper, we propose a silicon ring waveguide, in order to tune the frequency of the phonon field of SBS laser based on the silicon substrate of the ring cavity. The simulation results exhibit that the tailorable forward SBS effect is realized in the silicon-based optical waveguide with a large SBS gain up to 1.90 W-1m-1. Particularly, with the mutual restraint between photoelastic and moving boundary effects, the tunable phonon frequencies emitting from 1 to 15 GHz are realized through the conversion among higher order modes by modifying the widths of the ring cavity. Therefore, this silicon waveguide based on ring cavity will provide a new technical scheme for designing tunable SBS lasers by tuning the ring widths. In addition, this enhanced and broadband acoustic radiation will pave the way for hybrid integration in silicon-based optical waveguide, micro-electromechanical system, and CMOS signal processing technology.

Optical Microelectromechanical Systems Technologies for Spectrally Adaptive Sensing and Imaging

AbstractEvolving from past black‐and‐white images, through present red‐green‐blue spectral colors, future remote imaging systems promise spectroscopic functionalities extending well beyond the visible wavelengths. This allows real‐time spectral information to be gathered from multiple wavelength bands that is applicable to numerous remote sensing spectroscopy/imaging applications and aids target recognition. This paper reviews the wavelength tunable microelectromechanical systems (MEMS) optical filter technologies developed for the important infrared and the emerging terahertz wavelength bands of the electromagnetic spectrum with the fabrication effort being enabled by the Western Australian Node of the Australian National Fabrication Facility. A low size, weight and power (SWaP) platform solution is demonstrated delivering mechanically robust, field‐portable, spectroscopic, chem/bio sensing suitable for deployment in remote sensing and imaging applications.

High-resolution micro-optical accelerometer with an electromagnetic driver: design and analysis.

Optical displacement detection is widely used in various micro-electro-mechanical system (MEMS) sensors because of its high sensitivity. The optical accelerometer has a high theoretical resolution. However, due to the small working range of optical detection, the open-loop measuring range of a high-resolution optical accelerometer is usually only tens to hundreds of milligrams. To increase the measurement range, we propose a high-resolution micro-optical accelerometer with electromagnetic force feedback. The optical principle, mechanical structure, and manufacturing process are analyzed. The accelerometer is predicted to work in the first modal with displacement sensitivity at 2.56 µm/g, corresponding to 0th diffraction beam optical sensitivity 1.93%/nm. The designed electromagnetic driver can increase the acceleration measurement range from 0.012 to ±20g. These results provide a theoretical basis for the design and fabrication of a high-resolution micro-optical accelerometer with an electromagnetic driver. The electromagnetic drive scheme introduced effectively improves the dynamic range of high-precision optical accelerometers and can be applied to other optical MEMS sensors.

MEMS enabled miniaturized light-sheet microscopy with all optical control

We have designed and implemented a compact, cost-efficient miniaturised light-sheet microscopy system based on optical microelectromechanical systems scanners and tunable lenses. The system occupies a footprint of 20 × 28 × 13 cm3 and combines off-the-shelf optics and optomechanics with 3D-printed structural and optical elements, and an economically costed objective lens, excitation laser and camera. All-optical volume scanning enables imaging of 435 × 232 × 60 µm3 volumes with 0.25 vps (volumes per second) and minimum lateral and axial resolution of 1.0 µm and 3.8 µm respectively. An open-top geometry allows imaging of samples on flat bottomed holders, allowing integration with microfluidic devices, multi-well plates and slide mounted samples, with applications envisaged in biomedical research and pre-clinical settings.

Optics-on-a-chip for ultrafast manipulation of 350-MHz hard x-ray pulses.

Microelectromechanical systems (MEMS) are miniature devices integrated into a vast range of industrial and consumer applications. Optical MEMS are developed for dynamic spatiotemporal control in lightwave manipulation and communication as modulators, switches, multiplexers, spectrometer, etc. However, they have not been shown to function similarly in sub-nm wavelength regimes, namely, with hard x-rays, as high-brilliance pulsed x-rays have proven powerful for addressing challenges in time-domain science, from energy conversion to neurobiological control. While desirable temporal properties of x-ray pulses can be enhanced by optics, conventional x-ray optics are inherently massive in size, hence, never dynamic. We demonstrate highly ultrafast x-ray optics-on-a-chip based on MEMS capable of modulating hard x-ray pulses exceeding 350 MHz, 103× higher than any other mechanical modulator, with a pulse purity >106 without compromising the spectral brilliance. Moreover, the timing characteristics of the devices can be tuned on-the-fly to deliver optimal pulse properties to create a host of dynamic x-ray instruments and applications, impossible with traditional optics of 109× bulkier and more massive. The advent of the ultrafast optics-on-a-chip heralds a new paradigm of x-ray photonics, time-domain science, and accelerator diagnostics, especially at not only the future-generation light sources that offer coherent and high-frequency pulses but also lab-based facilities that normally do not offer timing structures.

High-sensitivity magnetic sensor based on the evanescent scattering by a magnetorheological film.

We present a simple concept to implement a magnetic sensor that uses evanescent scattering by a suspended magnetorheological (MR) film above a planar waveguide. The soft MR film embedded with ferromagnetic particles is to induce scattering on the evanescent field of a planar waveguide at a proximity distance. This distance can be controlled precisely by a magnetic field. Consequently, the waveguide output power changes in response to the magnetic intensity. Two sensor prototypes of different film thicknesses were designed and tested showing a trade-off between the sensitivity and dynamic sensing range. A maximum sensitivity of ∼2.62dB/mT was obtained. Compared to optical micro-electromechanical systems, the presented sensors feature a simple design, easy fabrication, low cost, and the potential for large-scale production and miniaturization to be integrated into portable devices.

Window Optical Microstructures (Review)

The results of research on the development and application of optical elements placed in the upper part of the window in order to redirect sunlight to the ceiling and into the interior of the room have been summarized and analyzed. There has been a steady trend of transferring such devices to the micro level. The article has described the structures and optical characteristics of three types of the optical microstructures embedded in double-glazed windows: microprismatic films, panels with prismatic microstructures on two sides, and films with embedded micro-mirrors. It has been noted that the use of curved surfaces instead of flat ones in microstructures improves the optical properties and increases the uniformity of the redirected sunlight flux. The designs and properties of optical microelectromechanical systems: switchable micro-mirrors and micro-blinds that were manufactured using microelectronics technology, have been generalized.

A Proposal for a High-Sensitivity Optical MEMS Accelerometer With a Double-Mode Modulation System

A proposal for a high-precision accelerometer based on a silicon optical microelectromechanical system (MEMS) is presented in this article. The device operating principle is that a sensitive mechanical structure senses external vibrations and then the vibrations of the mechanical component cause regular changes in the target modes in the optical system. Through a judicious design of the optical system, we obtain a wide photonic band gap (PBG) (approximately 1.1–2.75 μm) as well as two target modes in the PBG for modulation. Comparison with previously reported works shows that the proposed double-mode accelerometer displays better performance with respect to properties such as sensitivity and resolution. Accurate simulation results obtained by finite element analysis and rigorous coupled wave analysis have obtained the following results: an optical sensitivity of 4.42, a natural frequency of 1032 Hz, a bandwidth from 0 to approximately 900 Hz, a mechanical sensitivity of 0.242 μm/g, an accelerometer sensitivity of 1.017 μm/g, a linear measurement range of ±0.517 g and a resolution of 933.7 ng ( δλ = 1 pm). Due to these optimized performance characteristics, the proposed accelerometer can achieve high precision detection in microvibration applications such as seismic detection.

Triboelectric effect-modulated varifocal liquid lens

Electrically modulated varifocal liquid lenses, which are usually modulated by an external high voltage power source, have attracted much attention due to their bright application prospects in artificial optical systems. Here, a triboelectric nanogenerator (TENG)-based varifocal liquid lens (TVLL) has been demonstrated, in which the focal length can be directly modulated by external mechanical sliding. A dielectrophoretic force is generated by the TENG through the transfer of triboelectric charges in the asymmetric electrodes, which is used to continuously change the shape of the air–liquid interface between concave and convex without any complicated boost converter. Moreover, a triboelectric magnifying glass based on the accurate modulation effect of the TVLL on a light beam has been demonstrated. In this work, the TENG is used as a medium to modulate and accurately control the focal length of the liquid lens by an external mechanical stimulus, which may have great applications in micro-optical-electro-mechanical systems (MOEMS), human–machine interaction, artificial vision systems, etc.