This work was to introduce a reference mechanism in fiber based-SPR (surface plasmon resonance)
sensors to increase their sensitivity. We fabricated two tandem SPR sections in a single optical fiber and
coated one of the sections with a reference material to split a regular single resonant peak into two peaks,
one in regular wavelength range for sensing and another one in longer wavelength range for referencing.
By using the referencing peak to specifically detect the SPR changes caused by uncontrolled factors, such
as temperature variation, non-specific bonding, we were able to subtract the contribution of these factors
to the sensing peak using an established relationship, and thus increase the sensitivity of the sensing dip. With the method, we have demonstrated a fiber-based SPR humidity sensor whose sensitivity is immune to the variation of environment temperature.
Fabrication of flat, free-standing silicon diaphragms as micromirrors using etching processes is the key in the
development of optical Micro-Elecro-Mechanical System(MEMS) devices, such as tunable F-P(Fabry-Perot) filters. It is
very important for etching process to get smooth surface and uniform depth because they greatly affect the performance
of the final device. In this paper, we report the experimental results about roughness and flatness of silicon micromirror
fabricated by wet and dry etching processes. The investigated process involved wet-etching process in self-prepared
KOH solution, and dry etching process with such machines as ALCATEL 601E DRIE(Deep Reactive Ion Etching) and
STS ICP (Inductivity Coupling Plasma). It was found that wet etching process could supply more uniform etching depth,
whereas the better surface roughness was gotten by dry etching. For a 30μm target depth, surface roughness less than
3-nm and maximal depth difference less than 0.3-μm were obtained by STS ICP and KOH respectively.
A novel structure of optical fiber accelerometer based on MEMS torsional micro-mirror is introduced, including MEMS
torsional micro-mirror and optical signal detection. The micro-mirror is a non-symmetric one, which means that the
torsional bar supporting the micro-mirror is not located in the axis where the center of the micro-mirror locates. The
optical signal detection is composed of PIN diode and dual fiber collimator, which is very sensitive to the coupling angle
between the input fiber and output fiber. The detection principle is that acceleration is first transformed into torsional
angle of the micro-mirror, then, optical insertion loss of the dual fiber collimator caused by the angle can be received by
PIN. So under the flow of acceleration to torsional angle to optical signal attenuation to optical power detection, the
acceleration is detected. The theory about sensing and optical signal detect of the device are discussed in this paper. The
sensitive structure parameters and performance parameters are calculated by MATLAB. To simulate the static and modal
analysis, the finite element analysis, ANSYS, is employed. Based on the above calculation, several optimization methods
and the final structure parameters are given. The micro-mirror is completed by using silicon-glass bonding and deep
reactive ion etching (DRIE). In the experiment, the acceleration is simulated by electrostatic force and the test results
show that the static acceleration detection agrees with the theory analysis very well.
Large-scale micro-electromechanical systems (MEMS) scanning mirrors play a primary role in many fields of
manipulating light beam scanning, such as rapid optical spectrum analyzers (OSAs) based on dispersive gratings using in
near infrared (NIR) region. According to the applications, a high speed electromagnetically actuated MEMS scanning
mirror with large mirror area of 9×6mm2 has been developed. The MEMS scanning mirror chip, which is fabricated
using bulk silicon micromachining process and electroplating technique, is immersed in a constant 365 mT magnetic
field parallel to the coil plane and generates the maximum optical deflection angle of ±11.15° at the 1.39 kHz resonant
frequency. The quality factor, Q, of 77 is achieved in air corresponding to a low power consumption of 102.6 mW. In
addition, the surface roughness of less than 20nm for scanning mirror has been measured and the optical reflectivity at
the wavelength of 1550nm is high up to 87%. The results show that the device is adequate for mm-sized scanning
systems and compatible with smart OSAs applications.
In this paper we design and fabricate the first mirror-integrated silicon-on-insulator-based (SOI-based) arrayed-waveguide grating (AWG) with working functions. The fabricated AWG has a channel spacing of 1.6 nm centered at 1556 nm. We substitute the bent waveguides array in the traditional AWG configuration by adopting the structure of the mirror-integrated straight waveguides. Theoretical advantages of the new structure are demonstrated. Detailed description of the design procedure and the fabrication process is provided. Test results of both the traditional AWG and this design are delineated and analyzed, which shows that the total length of the waveguide array is reduced from 3.14 cm to 2.53 cm, and the holistic structure also becomes more compact. The crosstalk of the fabricated 1x8 AWG is better than -20 dB. The typical on-chip insertion loss is about 10 dB. Losses caused by the mirrors and the waveguides transmission are about 4.2 dB, both of which resulted from the imprecision in the fabrication process.
A 1×8 multimode interference coupler with a strong confinement structure in the multimode region was proposed and fabricated on silicon-on-insulator material. In the multimode region, the waveguide was etched to the buried silica layer so as to realize the strong confinement and obtain better resolution of the self-imaging effect, while in the input/output ports, the rib waveguides with the large cross-section rib structure were designed to satisfy the single-mode condition, with which the device could be efficiently coupled with single-mode fibers or other waveguide devices. The fabrication process was also specially designed to eliminate the photolithography alignment error.
We have reported a novel 1x2 MEMS optical switch for telecommunication application. A vertical mirror was fabricated by wet anisotropic etching in (110)-oriented silicon wafer. Using DRIE (Deep Reactive Ion Etching) technique, we make a torsional actuator to turn a vertical mirror with a small angle. The actuator was composed of a cantilever beam and two electrodes with curved shape edges. The mirror size was 500 um (L) x 125 um (H) x 50 um (W), and the cantilever dimension was 3000 um (L) x 125 um (H) x 10 um (W). In the optical switch, ball lenses were added in the optics system to extend working distance of fibers. We also fabricated a micro optical platform integrated with the device to simplify the coupling. On the platform, a U-shape groove and fiber clamps were fabricated to accommodate and fix the SMF (single mode fiber). The surface roughness (Ra) of etched mirror was tested below 10 nm. The optical switch was tested on electric and optical characteristics: switching voltage 78.5V, resonance frequency 2.3 kHz, insertion loss 4 - 5 dB, crosstalk 45dB. The device can perform the switching function by the large.
A novel self-aligning SIOB (SIlicon Optical Bench) for fully passive alignment of optical components is proposed for integrated transceiver modules. The coupling efficiency from laser diode directly to fiber is about 8% in theory because of severe mode mismatch and large NA difference. To pursue high coupling efficiency, a ball lens is added between laser diode and fiber. The calculations and simulations are done to optimize the optical system according to optical component specifications. The coupling efficiency is up to 45%. We designed the layout and fabricated the SIOB in (100) silicon wafer to obtain the demanding cavities by MEMS technology.
A new method is presented in this paper to fabricate Fabry-Perot (FP) cavity with MEMS bulk wet-etching technology, through which FP cavities can be achieved with the cavity length from several microns to tens of microns. The parallelism of mirror elements can be well achieved without electrostatic control. Some FP cavities were achieved that the insertion loss was less than -8dB, the full width half maximum (FWHM) was about 2 nm, and the efficient finesse is up to 50. Some factors which influence the finesse have also been analyzed. The further work is ongoing.
Planar lightwave circuits based on silicon are playing important roles in integrated optical systems. The integrated waveguide turning mirror (IWTM) is essential component for the compactness of optical devices. We designed and fabricated an integrated waveguide turning mirror with a 90° directional change in SOI. The mirror was etched by induct-coupled-plasma etching (ICP) first. Then the surface was enhanced by wet anisotropic etching. This two-step process introduced a compact IWTM with smooth and vertical surface. Compared with the mirror fabricated by wet anisotropic etching only, the mirror fabricate by the two-step process is better to meet the requirement of compact design.
An integrated grating-assisted optical add/drop multiplexer (OADM) based on an innovative phase-compensated coupler is proposed. This device can get high performance, while the grating is not needed to be critical positioning. Therefore, it can be fabricated with feasibility.
White-light interferometry (WLI) is a powerful technique for distributed fiber-optic sensing system. The sensing regions are determined by the optical path difference between two polarization modes of dual-mode optical fiber and the coupling coefficients are measured by detecting the interferogram. However, the performance of the system is limited by the coherent length of low-coherent source and the crosstalk among the sensing units. In this paper, we propose a method to process interferogram to improve resolution and eliminate crosstalk in distributed sensing system.
Radon transform can transform orthogonal coordinate space to Radon space with simple rotation and shift coordinate transform relationship. Radon transform followed by MeIlin transform, i.e., Radon-Mellin transform, is shown to provide scale, rotation and shift invariant correlation in Joint transform correlator by a series of one-dimensional (1-D) MeBin transformed projection correlations to utilize many excellent devices for 1-D signal processing with the advantage of change of reference pattern in real-time and without utilizing complicated synthesized filters.