A tunable optical 90° hybrid composed of a 2 × 4 multimode interference (MMI), a 2 × 2 MMI coupler and a heater pad is proposed, and a set of formulas was deduced for calculation the light intensity output of the device. The simulation has been performed, and the results show agreement with analytical predication. In the wavelength range of c band, the imbalances are below 0.04dB, the excess loss is less than 0.45 dB, and the phase deviations are below 3°. The fabrication tolerance of width as high as 0.3μm, which is larger than traditional optical 90° hybrid.
The microbolometric exact theoretical output responsivity expression for a focal plane array is obtained for the first time. Based on the physical thermal model for a microbolometer, the temperature change behavior of the microbolometer is analyzed and discussed to get its theoretical temperature change expression under pulse voltage bias. With the temperature change expression and infrared response analysis of the microbolometer, the theoretical output responsivity expression is successfully derived. The theoretical responsivity expression reveals some key factors that affect and determine the infrared sensibility of the microbolometric array, which can be utilized to guide the design optimization for a microbolometric focal plane array.
An optical switch is fabricated based on nanocrystalline vanadium oxide (VOx) thin film using micromachining
technology. An "on" state with semiconducting phase to an "off" state with metallic phase is controlled by applying a
DC power to Aurum electrodes of the optical switch. The optical switching performance for the fabricated device is
investigated at optical communication wavelength of 1.55μm. The heater power requires to achieve switching action is
about 15mW. The testing results show that the extinction ratio and switching response time are 14dB and 2ms,
The readout integrated circuit (ROIC) for micro-bolometric infrared focal plane array (IRFPA) is
commonly fabricated in silicon complementary metal oxide semiconductor field effect transistor (CMOS)
technology. There are three main categories of noise in a typical CMOS ROIC, which are 1/f noise,
KTC noise and fixed pattern noise. These noises in CMOS ROIC can seriously restrain the dynamic
range of the ROIC and degrade the performance of IRFPA. A new CMOS ROIC for micro-bolometric
IRFPA is designed to suppress the noises, and its performance is successfully verified through the theory
analysis and experimental results in this paper.
A complementary metal oxide semiconductor (CMOS) readout integrated circuit (ROIC) for an uncooled focal plane array (UFPA) is presented. The circuit consists of four major parts: a bolometer current direct injection (BCDI) input circuit, a column-shared capacitor feedback transimpedance amplifier (CTIA) integration circuit, a column-shared correlated double sampling (CDS) circuit, and a common output circuit. By applying the BCDI input circuit and the column-shared integration circuit of CTIA structure, high performance (high gain, a highly stable detector bias, and high photon current injection efficiency) is realized with a small pixel size. Moreover, the CDS circuit is utilized to reduce or eliminate noise of the readout circuit, and the common output circuit is utilized to improve the speed performance of the ROIC under low power dissipation. An experimental readout chip for a 45-µm-pitch 64×64 element VO2-based UFPA has been designed and fabricated. The measurement results of the fabricated readout chip at 298 K with 5-V supply voltage have successfully verified the readout function and the performance improvement. The proposed CMOS ROIC can be applied to a micro bolometric UFPA.
Thin films of vanadium dioxide (VO2) were selected for microbolometers. The thin films were fabricated with a novel method mainly including ion-sputtering and annealing. It is found that the electrical properties of these thin films can be controlled by adjusting the time of ion-sputtering and annealing. A standard microbolometer pixel structure of micro-bridge has been applied. Two-dimensional arrays of microbolometers have been fabricated on silicon integrated circuit wafers using a surface micromachining technique. A new type of on-chip readout integrated circuit (ROIC) for 32×32 pixel bolometric detector arrays has been designed and fabricated using a 1.5μm double metal poly complementary metal oxide semiconductor (CMOS) processing. The readout circuit consists of three stages, which provides low noise, a highly stable detector bias, high photon current injection efficiency, high gain, and high speed.
Several prototypes of 32×32 pixel bolometric detector arrays have been designed and fabricated. These arrays consist of detectors with lateral dimensions of 50μm 50μm, and each bolometric detector is on a 100μm pitch. The results of measurement show that the fabricated uncooled infrared focal plane arrays (UIRFPAs) have excellent performance. The frame rate is 50Hz, the pixel operability is above 96%, the responsivity (R) @ f/1 value is up to 15000V/W, the noise equivalent temperature difference (NETD) @ f/1 and 30Hz is about 50mK, and the average power dissipation is only 24.7mW. The results indicate that the technology of fabricating these 32×32 UIRFPAs has potential to be utilized for fabricating low cost and large-scale UIRFPAs.