Changlun Hou

MOEMS Accelerometer Based on Microfiber Knot Resonator

A microelectromechanical system (MEMS)-based optical accelerometer combined with a microfiber knot resonator (MKR) is proposed and demonstrated. The 386-mum-diameter MKR, fabricated by a 1.1-mu m-diameter microfiber, has a high quality factor (Q-factor) of 8500 and acts as the sensing device for vibration measurement of the MEMS structure. The experimental results show that such an accelerometer has a sensitivity of 654.7 mV/g, and a dynamic range of 20 g. This sensitivity can be further improved by increasing the Q-factor of the MKR, which can be achieved by optimizing the optical and geometrical parameters of the microfiber.

Novel high sensitivity accelerometer based on a microfiber loop resonator

An optical accelerometer with a bulk-micromachined silicon proof mass and a microfiber loop resonator (MLR) sensor was developed. The MLR was fixed on the surface of the cantilever beam. The proof mass and cantilever beam were fabricated with a two-mask process. An accelerometer with a range of ±20 g and output sensitivity 624.7 mV/g was fabricated. The design, simulation, fabrication, and preliminary results are presented.

Nanometer-scale displacement sensor based on phase-sensitive diffraction grating.

In this paper, a nanometer-scale displacement sensor based on a phase-sensitive diffraction grating with interferometeric detection is described and experimentally demonstrated. The proposed displacement sensor consists of a coherent light source, a microstepping motor controller, an integrated grating, a mirror, and a differential circuit. Experimental results show that the displacement sensor has a sensitivity of about 6 mV/nm and a resolution of less than 1 nm. This displacement measurement is an attractive technology with high sensitivity, broad dynamic range, good reliability, and immunity to electromagnetic interference.

Long focal-length measurement using divergent beam and two gratings of different periods

A new accurate method for long focal-length measurement based on Talbot interferometry is proposed. A divergent beam and two Ronchi gratings of different periods are employed, as the alternative of the collimated beam and two identical gratings, to achieve higher measurement accuracy. Moreover, with divergent beam, lenses of large aperture can be easily measured without scanning, which is required when it comes to traditional collimated beam. Numerical analysis and experiments were carried out. The results demonstrate the proposed method features remarkably high accuracy and repeatability.

Compact optical correlator based on one phase-only spatial light modulator

An optical correlator that utilizes one phase-only spatial light modulator (SLM) combined with a mirror is proposed and demonstrated. This system is compressed by displaying the input and filter pattern on different parts of the same SLM. The background noise is separated from the correlation signal by superimposing a high-frequency carrier with the filter pattern except in the zero-frequency regions, which will improve the signal-to-noise ratio in pattern recognition. Our architecture is compact and the cost is relatively low by utilizing only one SLM.

Optical accelerometer based on grating interferometer with phase modulation technique

In this paper, an optical accelerometer based on grating interferometer with phase modulation technique is proposed. This device architecture consists of a laser diode, a sensing chip and an optoelectronic processing circuit. The sensing chip is a sandwich structure, which is composed of a grating, a piezoelectric translator and a micromachined silicon structure consisting of a proof mass and four cantilevers. The detected signal is intensity-modulated with phase modulation technique and processed with a lock-in amplifier for demodulation. Experimental results show that this optical accelerometer has acceleration sensitivity of 619 V/g and high-resolution acceleration detection of 3 μg in the linear region.

Laser direct writing using submicron-diameter fibers.

In this paper, a novel direct writing technique using submicron-diameter fibers is presented. The submicron-diameter fiber probe serves as a tightly confined point source and it adopts micro touch mode in the process of writing. The energy distribution of direct writing model is analyzed by Three-Dimension Finite-Difference Time-Domain method. Experiments demonstrate that submicron-diameter fiber direct writing has some advantages: simple process, 350-nm-resolution (lower than 442-nm-wavelength), large writing area, and controllable width of lines. In addition, by altering writing direction of lines, complex submicron patterns can be fabricated.

Optical tilt sensor with direct intensity-modulated scheme

An optical tilt sensor based on a phase-sensitive diffraction grating with direct intensity-modulated scheme is proposed in this paper. The tilt sensor consists of a coherent light source, an integrated grating, a mechanical sensing part, and an optical signal processing circuit. The mechanical sensing part consists of a bulk proof mass and two cantilevers that can be fabricated with a two-mask process on a silicon-on-insulator substrate. A phase-sensitive diffraction grating, which was formed with the integrated grating and the upper surface of the proof mass, acts as the sensing element for the tilt measurement. Experimental results show this tilt sensor provides the optimal tilt sensitivity of 1.15 V/° and resolution of about 0.0046°, and a measurement range of ±20° in a rotational plane that is perpendicular to the direction of the earths gravity.

Novel diffractive optical element: binary photon sieve

In this paper, we developed a novel photon sieve consisting of a large number of precisely positioned holes distributed according to an underlying Fresnel zone plate (FZP) geometry, while the holes at transparent and opaque circular rings of the FZP have a π phase shift. Compared to a conventional photon sieve which we call an amplitude-photon sieve (PS), the binary photon sieve has a transmission two times more amplitude-PS and a diffractive efficiency approximately four times than amplitude-PS. A 70-mm diameter, f/10 binary photon sieve has been fabricated for operation at visible light. Details of design, fabrication, and performance of the binary photon sieve are presented.

MOEMS accelerometer based on microfiber knot resonator

A MOEMS (Micro-Optical Electronic Mechanical System) accelerometer based on a microfiber knot resonator is proposed and demonstrated in this paper, and the microfiber knot resonator acts as the sensing device for vibration measurement of the MOEMS structure. The diameters of the microfiber and microfiber knot are 1.1um and 386um, respectively. The experimental results show that such an accelerometer has a sensitivity of 654.7 mV/g, and a dynamic range over ±25g. This sensitivity can be increased significantly by increasing the Q factor of the microfiber knot resonators, which can be achieved by improving fabrication of the microfiber.