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This study aims at optimising the graphene coverage in a microresonator for the design of an efficient modulator by using a combination of graphene induced losses and phase shift. The graphene integration in the ring can provide tunability by means of altering the loss and coupling coefficient by changing the graphene coverage or its chemical potential. The fundamental parameters of graphene integrated all‐pass ring resonator are extracted based on the transmission characteristics using finite‐difference time‐domain method. As compared to conventional graphene‐oxide‐semiconductor straight waveguide, graphene integrated on an all‐pass ring resonator shows enhanced optical absorption and phase shift due to field enhancement factor. A modulator based on graphene tunable loss and phase shift is investigated taking into account the field enhancement factor. For 1.55 μm radiation and ring radius of 3.75 μm with 22% graphene coverage, a maximum modulation depth of 12.6 dB is demonstrated based on electrostatic control of graphene chemical potential. The proposed modulator can feature operational speed in the range of 10 GHz that is useful in a variety of electro‐optic applications. [ABSTRACT FROM AUTHOR]

The authors proposed a flexible microresonator based on nanowires composed of Ⅱ–Ⅵ compounds to detect the small strain caused by external motion. The nanowire ring resonator is embedded in polydimethylsiloxane (PDMS) flexibility to improve the coupling efficiency. In this work, CdS nanowire is fabricated onto a PDMS flexible substrate. With the help of a fibre tip, the single nanowire is manipulated under a microscope, allowing the curved line to be a ring and making the litter overlapping. This overlap increases coupling efficiency and sensor performance. The ring cavity has the parameters of diameter 1 µm, length 75 µm and radius ∼10 µm. Experiments demonstrated the process of fabricating a strain sensor and detected peak shifts. This resonant wavelength appeared red‐shift and linear tuned when stretching the flexible substrate. The quality factor was about 2000 and the gauge factor was about 80 nm per stretching unit. Being a small structure and high sensitivity, the sensor can be integrated into the chip. This promotes the development of miniaturisation to some extent. As a result, this work is beneficial to optical manipulation, further being extended to the tunable light source. [ABSTRACT FROM AUTHOR]

High frequency large scanning angle electrostatically actuated microelectromechanical systems (MEMS) mirrors are used in a variety of applications involving fast optical scanning. A 1-D parametrically resonant torsional micromirror for use in biomedical imaging is analyzed here with respect to operation by duty-cycled square waves. Duty-cycled square wave excitation can have significant advantages for practical mirror regulation and/or control. The mirror's nonlinear dynamics under such excitation is analyzed in a Hill's equation form. This form is used to predict stability regions (the voltage-frequency relationship) of parametric resonance behavior over large scanning angles using iterative approximations for nonlinear capacitance behavior of the mirror. Numerical simulations are also performed to obtain the mirror's frequency response over several voltages for various duty cycles. Frequency sweeps, stability results, and duty cycle trends from both analytical and simulation methods are compared with experimental results. Both analytical models and simulations show good agreement with experimental results over the range of duty cycled excitations tested. This paper discusses the implications of changing amplitude and phase with duty cycle for robust open-loop operation and future closed-loop operating strategies. [ABSTRACT FROM AUTHOR]

We present an integrated beam steering system with a microlens scanner and a vertical cavity surface-emitting laser (VCSEL) source. The scanner and the VCSEL are assembled with an alignment sphere process and with an accuracy of 121 ± 7μm defined by precision microspheres. The microlens scanner employs an electrostatic comb-drive actuator with prebent springs to extend the maximum displacement to 83 μm; 60% larger than that with standard folded springs. This translates to an angular scan range of ±9.6° with the double sided comb-drive scanner. The mechanical resonance with lens is measured to be 236 Hz. [ABSTRACT FROM AUTHOR]

A tunable slow-light hollow-core photonic crystal fiber (HPCF), applicable to miniaturized microstructure spectroscopic gas sensors is proposed. In the proposed structure, we have taken the advantage of the microfluidic infiltration technique to tune the slow-light regime so as to match the reference absorption line of the target gas sample, which is required for designing miniaturized gas sensors with reconfigurable detection sensitivity. The main feature of this structure is that the enhanced electrical field is strongly localized in the hollow-core of a photonic crystal fiber for any gas samples due to tunability of slow-light modes. We discuss the potential of slow light in HPCF for realizing compact and tunable gas sensor devices with low and high loss material. In particular, we present numerical results showing how this optofluidic microstructure can be used for detecting CO, CO2, H2S, CH4, SO2, and N2O gases. [ABSTRACT FROM AUTHOR]

We propose a scheme to utilize a multimode microdisk resonator in silicon controlled through free-carrier injection for continuous fast-to-slow light tuning. Two nearby resonant modes are employed, i.e., undercoupling and overcoupling. The optical properties of a device are analytically investigated considering the resonance spacing, bandwidth, and density change of free carriers. Pulse propagation simulations are implemented, and the pulse delay/advance is studied for wavelengths between the two resonances. As the density of injected free carriers increases, a continuous transition from fast to slow light occurs for a range of wavelengths. Consequently, a microdisk resonator in silicon is experimentally realized with the desired two resonances, exhibiting electrooptical tuning with a fast response. The experimental results agree well with the simulation in power transmission, and the tunable time delay and advance are also predicted. [ABSTRACT FROM PUBLISHER]

Microelectromechanical system (MEMS) technology, and surface micromachining in particular, have led to the development of miniaturized optical devices with a substantial impact in a large number of application areas. The reason is the unique MEMS characteristics that are advantageous in fabrication, systems integration, and operation of micro-optical systems. The precision mechanics of MEMS, microfabrication techniques, and optical functionality all make possible a wide variety of movable and tunable mirrors, lenses, filters, and other optical structures. In these systems, electrostatic, magnetic, thermal, and pneumatic actuators provide mechanical precision and control. The large number of electromagnetic modes that can be accommodated by beam-steering micromirrors and diffractive optical MEMS, combined with the precision of these types of elements, is utilized in fiber-optical switches and filters, including dispersion compensators. The potential to integrate optics with electronics and mechanics is a great advantage in biomedical instrumentation, where the integration of miniaturized optical detection systems with microfluidics enables smaller, faster, more-functional, and cheaper systems. The precise dimensions and alignment of MEMS devices, combined with the mechanical stability that comes with miniaturization, make optical MEMS sensors well suited to a variety of challenging measurements. Micro-optical systems also benefit from the addition of nanostructures to the MEMS toolbox. Photonic crystals and microcavities, which represent the ultimate in miniaturized optical components, enable further scaling of optical MEMS. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of different masking parameters onto the surface quality of the {111} sidewalls in order to generate specifically deep cavities by wet-anisotropic-etching of bulk silicon, for optical sensors using cavity sidewalls as reflectors. Mask alignment with crystal planes prior to wet-etching is found to be essential in order to avoid the appearance of additional planes during long etching. Mask deposition processes have been also evaluated. Among the different employed mask materials, Cr/Au gives the best results. It is then shown that cavities as deep as 1 mm with low roughness sidewalls can be simply produced with potassium hydroxide solution with periodic piranha cleaning. [ABSTRACT FROM AUTHOR]

We discuss relevant design considerations for the fabrication of electromechanically tunable photonic crystal cavities based on double semiconductor slabs. A simple optical and electromechanical model of the device based on coupled-mode theory and electrostatics is discussed and used jointly with 3-D finite-element calculations of optical cavity modes to extract the tuning-range dependence on geometrical parameters. A design rule, which avoids the sticking of membranes due to capillary forces and keeps a large tunability, is defined. The details of the fabrication process and a summary of the experimental results on GaAs and InGaAsP/InP material systems are given. We also address the problem of nonsymmetric devices, where the thicknesses of the membranes are not exactly the same, resulting in an imbalanced power emission of coupled modes. [ABSTRACT FROM AUTHOR]

A large displacement piston motion micromirror is designed, fabricated, and tested with device features tuned to applications requiring ultralow tilt. The fabricated MEMS mirror is based on electrothermal actuation and has a footprint of 1.9 mm × 1.9 mm with a mirror aperture of 1 mm. The application optimized device holds key features of ultralow maximum tilt of 0.25 ° and a strongly linear motion of 90 μm achievable at only 1.2 V. This device is further characterized in an interferometric system to determine the piston mode and the accurate piston displacement as a function of voltage, power, and frequency. [ABSTRACT FROM AUTHOR]

Speckle noise is a major obstacle for the application of laser light sources in projection displays and illumination. In this paper, a method for speckle reduction using a Micro-Electro-Mechanical Systems (MEMS) diffuser device is presented. The MEMS device consists of a random reflective pattern on the top surface of a moving mass that is vibrated in-plane by an electrostatic push-pull comb drive. The harmonic in-plane motion of the MEMS diffuser creates time-varying speckle patterns that are averaged by the camera or the eye, thus reducing speckle noise. The device is fabricated using Silicon-On-Insulator (SOI) technology. The measured device shows good agreement with analytical calculation and simulation. Using a red He-Ne laser, speckle contrast is measured both for free space geometry and for light pipe geometry. Speckle contrast reduction up to 43.08% for the free space geometry and 26.8% for the light pipe geometry is achieved. [ABSTRACT FROM AUTHOR]

We describe a microelectromechanical systems-based actuator for three-dimensional (3D) positioning of a polymer microlens implemented using silicon-on-glass technology. The actuator combines comb drives for lateral tracking with electrostatic parallel plates for out-of-plane focusing as well as tilting of a polymer microlens, yielding fully 3D actuation. The complete actuator is fabricated using wafer bonding of silicon and pyrex wafers; the lens is integrated using polymer dispensing techniques. The 3 DOF positioning of the lens for focusing, tracking, and tilting are experimentally characterized, furthermore, the layout and symmetry would allow 4 DOF movement, demonstrating how this actuation system combined with an integrated lens may be particularly useful for new generations of optical pickups. [ABSTRACT FROM AUTHOR]

A novel method to fabricate microchannels into fused silica capillaries and hollow fibres by a high‐voltage high‐frequency corona discharge induced by a Tesla coil is demonstrated. Channels as narrow as 2.2 μm are successfully made in capillaries with 2 μm inner and 125 µm outer diameters. [ABSTRACT FROM AUTHOR]

Scanned laser pico projectors utilising laser light sources and microelectromechanical systems mirror devices introduce geometric distortion to the displayed images because of nonlinear mirror driving methods. A pre‐processing algorithm is proposed that corrects the nonlinear geometric distortion of scanned laser pico projectors. The distortion is modelled as blockwise homography transforms. The geometry of the images being displayed is pre‐distorted using the pixel indices obtained by the backward blockwise homography transforms. The pre‐distorted images are displayed by the pico projector whose geometrical distortion undoes the pre‐distortion such that distortion‐free images can be displayed. The proposed algorithm requires a small amount of information stored in the memory and three bilinear interpolations per pixel, thus providing an efficient way to correct nonlinear distortion without additional optical components, such as aspherical lenses. [ABSTRACT FROM AUTHOR]