Abstract—This paper describes a MEMS-based tunable Fabry-Perot filter that can be directly integrated on a detector. The Fabry-Perot filter consists of two parallel mirrors and lets the light with particular wavelength pass through. The wavelength depends on the gap between the mirrors. The gap of the micromechanical Fabry-Perot filter can be changed by applying a voltage to the mirrors, an electrostatic force inducing an attraction between the substrate and the top mirror. Based on the comprehensive analysis of the working principle of the micro F-P cavity filter, the optimum tuning scheme of micro F-P cavity filter is established. A simulation of the mechanical behavior was performed based on finite elements, using ANSYS software. We finally establish the L-arm type cantilever to support cavity structure, the micro-bridge can achieve a considerable range of tuning; relatively high fill factor, filter light leakage is avoided; the high abilityto keep parallel can achieve high precision filtering effect; structural stability, it can resist the residual stress of manufacture. This MEMS F-P tunable filter can be a potential application in spectroscopic sensing and optical communication system.
A compact two-dimensional laser scanner based on piezoelectric actuators is presented. The scanner consists of two single-axis laser scanners placed perpendicular to each other, which exhibit the advantages of small size, large angle, high scanning speed, and high linearity. The mechanical structure and principle of the scanner are introduced and the performance of the scanner is experimentally investigated. The result shows that the maximum angle of the scanner is approximately 9.315 deg with a main resonant frequency of 1242 Hz. An open-loop controller based on a hysteresis compensation algorithm and analog notch filter is proposed. Its nonlinearity is reduced to ±0.5% after compensation. High frequency scanning and the step response of the scanner are also studied to demonstrate the performance and effectiveness of the scanner.
Vanadium oxide uncooled bolometer with gold black absorber of high long-wave-infrared-rays absorption has been fabricated and optimized. The fabrication processes for mirobolometer were developed with surface micromachining below 350°C. We evaluated gold black film reflectance by Fourier transform infrared spectroscopy. Low reflectance shows that gold black has good absorption at 8 to 14 μm infrared window. Detector tests show that a bolometer with gold black absorber, compared with the one without gold black, had better performance, with maximum responsivity and detectivity of 8.4×104 V/W and 6.16×108 cm Hz1/2/W, respectively, at 13 Hz chopper frequency and bias current 67 μA.
Voice coil actuators (VCAs) are applied in a fast steering mirror (FSM), precision positioning platform, etc. These applications demand that the VCAs used are simple, inexpensive, reliable, and efficient. In this paper, we report a novel VCA with concentration flux-line structure. The VCA greatly reduces the magnet leakage and has less electromagnetic interference with other electronic devices. The output force sensitivity of the VCA is 4.17 N/A with a coil of 300 turns and the stroke is ±2.5 mm. Driven by this VCA, the mechanical scanning angle of the FSM can achieve ±4.9 deg when the scanning frequency is 100 Hz.
The laser scanning system of a lidar usually needs a laser scanner with characteristics such as fast linear scanning, small
size and small rotational inertia moment. Traditional laser scanners, such as galvanometer and rotating multi-faceted
mirror, are difficult to achieve fast linear scanning with low moment of inertia. In order to solve these problems, a
piezoelectric optical scanner based on novel piezoelectric actuator is designed in this paper. First of all, the scanner
system components based on self-learning feed-forward controller is introduced. Furthermore, the principle and method
of amending the scanner hysteresis loop are analyzed. Finally, one-dimensional linear scanning in a wide range of
frequencies using the control platform with the core of digital signal processor TMS320F2812 is achieved. The
experimental results show that the hysteresis characteristics have been restrained and scanning linear performance of the
piezoelectric optical scanner has been remarkably improved in low frequencies. In high frequencies, the nonlinearity of
triangle wave scanning is reduces by adding a notch filter circuit which restrained the structure resonance of the scanner.
The piezoelectric optical scanner also has other advantages such as large optical scanning angle, high first step
resonance frequency, small size and simple structure.
In this paper, 3 types of laser beam scanner are introduced. One is transmissive beam scanner, which is composed of
convex and concave microlens arrays (MLAs). By moving the concave lens in the plane vertical to the optical axis, the
incident beam can be deflected in two dimensions. Those two kinds of MLAs are fabricated by thermal reflow and
replication process. A set of mechanical scanner frame is fabricated with the two MLAs assembling in it. The testing
result shown that the beam deflection angles are 9.5° and 9.6°, in the 2 dimension(2D) with the scanning frequency of 2
HZ and 8 HZ, respectively. The second type of laser beam scanner is actuated by voice coil actuators (VCAs). Based on
ANSOFT MAXWELL software, we have designed VCAs with small size and large force which have optimized
properties. The model of VCAs is built using AutoCAD and is analyzed by Ansoft maxwell. According to the simulation
results, high performance VCAs are fabricated and tested. The result is that the force of the VCAs is 6.39N/A, and the
displacement is ±2.5mm. A set up of beam scanner is fabricated and actuated by the designed VCAs. The testing result
shown that the two dimensional scanning angle is 15° and 10° respectively at the frequency of 60HZ. The two
dimensional scanning angle is 8.3° and 6° respectively at the frequency of 100HZ. The third type of scanner is actuated
by amplified piezoelectric actuators (APAs). The scanning mirror is actuated by the piezoelectric (PZ) actuators with the
scanning frequency of 700HZ, 250HZ and 87HZ respectively. The optical scanning angle is ±0.5° at the three
frequencies.
A simple method is reported to manufacture a planar compound eye using a microlens array. The compound eye, inspired by insects, consists of a microlens array and a waveguide coupled with it. A microlens array with lenses of 50 µm in diameter is fabricated by melting AZ1500 photoresist and then transferring it onto SU-8. With the self-focus method applied, a waveguide array is formed, and each is exactly coupled to a lens. The formation of the waveguide is simulated using finite difference time domain (FDTD) arithmetic, resembling the ommatidia produced in our experiment. The ommatidia is also testified to astrict beam, just as the natural compound eyes do.
Rotational prisms or reflectors are used for conventional optical scanners. Their disadvantages are large size, low scanning speed and high power consumption. In the paper a microoptical scanner based on the integration of piezoelectrical driver and microlens arrays is described. The microlens arrays consist of a convex microlens array and a cocave microlens array with 256×256 elements respectively. Each element dimension is 50×50 μm2. The scanner is driven by a piezoelectrical(PZT) crystal. A PA90 amplifier is controlled by an input signal produced by a single chip computer. The amplifier supplies a high voltage pulse signal to driving the PZT. The scanning frequency can reach 200Hz to 300Hz and the scanner's size is a few cubic centimeters.
Nanostructural vanadium dioxide thin films are investigated as intelligent window coatings. The films are fabricated using reactive sputtering and post annealing. A reversible semiconductor to metal phase transition for as-deposited VO2 nanostructure films with grain size of ~8nm takes place at a temperature of 35°C, which lowers about 33°C in comparison with a phase transition temperature of 68°C in conventional VO2 films with a grain size of 1-2 μm. The results indicate that the nanostructural VO2 films are more suitable to the application for smart thermochromic glazing of windows than that of conventional VO2 films.
This paper reports the preliminary results for an on-going program in wafer-level MEMS package. In this particular paper, three closed-loop microheaters of 5μm, 7μm and 9μm width were designed. By reactive ion sputtering technique, two classes of samples were presented. The first one was first co-sputtered with nickel / chromium (Ni/Cr) alloy and then sputtered with gold(Au) metal as heating material; the second one was sputtered with Cr, tin (Sn) and Au respectively as heating material. The bonding of the former sample based on the Ni/Cr and Au heating material failed. The eutectic bonding experiment of the later sample based on the Cr, Sn and Au heating material by global heating method was completed in annealing oven at temperature of about 400 deg. C. for 20 minutes. The SEM testing result showed the eutectic bonding of Au-Sn by global heating was successful. More results will be reported in future.
The infrared focal plane array (IRFPA) imaging system is the trend of IR imaging technology. However the most difficult problem associated with the IRFPA is intrinsic spatial photo-response nonuniformity. Practicable and real-time nonuniformity correction (NUC) is a key technology in the application of IRFPA. The main specifications and parameters of IRFPA nonuniformity are researched, and a real-time new nonuniformity correction method by using the field programmable gate array (FPGA) technology is presented in this paper. It has the advantage of large dynamic range, small storage capacity, high processing speed and high corrective accuracy, etc. Then the correction principle and main steps are described in detail. The block diagram of hardware circuit and the working processes were introduced. The experimental results are satisfactory, showing advantage of this method.
A new method, self-alignment process is introduced to fabricate microlens arrays. By this method, during fabrication process, the rigorous alignment, which has great effect on diffraction efficiency in the conventional multi-photolithography process, is avoided. The large arrays of 1500 × 640 element silica microlens with 8-phase-level are manufactured by this method. The measurement results show that the 8-phase-level microlens arrays diffraction efficiency is as high as 93%, which is higher than by the conventional method.
For the first time, diffractive rectangle-based multilevel steps Si microlens arrays are fabricated by a new method, named part etching. The new method proposed can increase focal length of diffractive microlenses arrays. The 256x256 element microlens arrays are designed for a center wavelength of 4micrometers , with 40micrometers (Horizontal) x 30micrometers (Vertical) quadrate pixel dimension and a speed (F number) of F/2.53 (in air). The focal length of the microlens array is 400micrometers in Si material, much longer than focal length of the microlens arrays of the same size fabricated by conventional binary optics method. The method also includes photolithography and ion beam milling process. The 256x256 element microlens arrays and the same 256x256 element PtSi IR Focal Plan Arrays (FPAs) are monolithic integrated on the same wafer. The IR response characteristics of the integration device are improved greatly.
The IR spectrum from 3 to 5micrometers has numerous applications in both military and civil industries. High performance at high operating temperature is often important in these applications. Conventional Focal Plane Arrays (FPAs) without integration with concentrator such as microlens have poor sensitivity and low signal-to-noise ratio because of their lower fill factor. The binary optics microlens arrays reported in this paper are designed for integration with FPAs. Thus, the FPAs' fill factor, sensitivity, and signal- to-noise ratio can be improved while retaining a given image resolution and optical collection area. In the paper, we discussed the 256(Horizontal)x290(Vertical) microlens arrays designed for a center wavelength of 4micrometers , with 50micrometers (Horizontalx33micrometers (Vertical) quadrate pixel dimension and a speed (F number) of F/1.96. PtSi FPAs were fabricated on the front side of a 400-micrometers -thick Si substrate. The designed diffractive microlens arrays will be etched on the back side of the same wafer in a register fashion and it will be reported in other paper. Considering the diffraction efficiency, 8-phase-level approximation is enough. For the diffraction efficiency of 8-phase-level diffractive microlens reaches 95%. The process only need three mask-level, so we designed and fabricated three masks with the same dimension 4'x4'. Also, a set of fine verniers was designed and fabricated on each mask to allow accurate alignment during the fabrication process. Through a computer simulation, the microlens arrays are nearly diffraction limited, with the diffraction efficiency of 93%, a bit lower than the theoretical value of 95%. Introduction of microlens arrays has the ability to increase the FPAs' fill factor to 100%, while it is only about 21.6% without microlens. To our knowledge, this is the first trial of integration large area microlens arrays with FPAs at home.
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