This study reports the current progress of the novel thermal-actuated tunable focal-length micro polymer (PDMS) lens. The prototype of solid state only tunable lens demonstrates a typical variation of focal length from 1852 mum to 1083 mum under a 60 mA driving current. Moreover, this study also demonstrates the capability to integrate the tunable polymer lens with other optical components such as the conventional and dual-focus Fresnel lens. The resulted compound (PDMS+Fresnel) lens reduced the focal-length of Fresnel lens from 13500 mum to 5038 mum. Moreover the focal-length of compound lens was further dropped to 3523 mum at 60 mA driving current. A dual-focus compound lens was also realized to reduce its focal-length from 8000 mum/4000 mum to 1343 mum/975 mum. The compound lens has potential to further perform beam shaping and remove aberrations.
For the conventional block floating-point quantizer (BFPQ), usually a large block size causes performance degradation and thus small block sizes are preferred, especially when non-uniformly distributed signals are processed. A tunable BFPQ with fractional exponent is proposed in this paper to deal with the problem. We first examine the root cause of degradation through analytic equations and then propose to tune the thresholds for deriving the exponent and fractional exponent of the block so as to strike a good balance between the quantization error and saturation error. An optimal tuning value depending on the block size and mantissa word-length can be obtained. Thus, the tunable BFPQ can achieve better output signal-to-quantization-noise ratio (SQNR) in a wide dynamic range. The analytic equation for the output SQNR of the proposed BFPQ is derived to verify the simulated results. Only one extra multiplication is required for each block to implement the tunable BFPQ. Finally, we show the obvious SQNR improvements compared to the conventional scheme for various settings of block sizes and mantissa word-lengths.
In this letter, the concept of driving tunable solid lens using microthermal actuator is presented. This microoptical device is composed of a flexible polydimethylsiloxane (PDMS) lens, silicon conducting ring, and silicon heater. The mismatching of coefficient of thermal expansion and stiffness between PDMS and silicon will lead to the deformation of polymer lens during heating, so as to further change its focal length. To demonstrate the feasibility of this approach, a microfabrication processes have been established to monolithically fabricate the present microoptical device. The typical experiment results show that the tunable focal length was up to 834 mum with an input current of 70 mA
Synthetic aperture radar possesses the capability to provide two-dimensional imaging for remote sensing and earth observation regardless of weather conditions. The high-resolution SAR image is always desired. However, the data volume of echo signals is huge while the on-board storage or communication bandwidth to ground station is limited. Instead of transmitting raw signals, transmitting region of interest of images can be efficient. Consequently, processing for real-time and high-resolution SAR imaging is essential, either for spaceborne SAR or for airborne SAR [1]. In 2021, Synthetic Aperture Standards Committee (SASC) was approved by IEEE Standards Association for establishing technical standards to enhance its applications.
A novel astigmatism-tunable microlens is reported in this letter. This device is based on a thermal-actuated current-controlled tunable polymer lens. The thermal deformation as well as surface profile of polymer lens is tuned by temperature using the current induced Joule heating. The asymmetric boundary condition is further applied on the silicon conducting ring of the lens to invoke asymmetric deformation of the polymer lens as well as astigmatic change of the polymer lens. To prove the concept, the astigmatism-tunable polydimethylsiloxane lens has been fabricated on the silicon-on-glass wafer. Astigmatism tuning was demonstrated by change of astigmatic focal distance, from 1590 to 44 mum, as input current increased from 0 to 30 mA. In addition, aspect ratios of focal spot shape were varied from -20 to -1.3 and 16 to 1.22 with respect to anterior and posterior focal points. This device provides a feasible solution to the dilemma of astigmatic tuning capability and miniaturization. In summary, the present device has the potential to act as a key component for microelectromechanical systems-based aberration corrector or laser focus-spot shaper.
The range Doppler algorithm (RDA) is widely used for synthetic aperture radar (SAR) imaging. Correct estimation for Doppler centroid is essential for range cell migration correction, azimuth compression, secondary range compression in RDA. This paper presents two methods to assess and improve the Doppler parameter estimation results. The symmetry of the Doppler spectrum is examined to evaluate the quality of coarse estimation of baseband Doppler centroid and the weighted least squares algorithm is used to derive the refined results. Selective window and weighted combining based on the quality index of the average power are adopted for detecting Doppler ambiguity. From the simulation results, we show that the proposed techniques with the appropriate quality index can improve the performance of estimation compared to the conventional schemes for real-time SAR signal processing.
A real-time imaging processor for spaceborne synthetic aperture radar (SAR) is designed and implemented to realize the range Doppler algorithm (RDA) with configurability. The azimuth fast Fourier transform (FFT) decomposition is adopted for full utilization of data after fetching them from high bandwidth memory (HBM) by burst access to achieve streaming input–output for 2-D FFT/inverse FFT (IFFT) processing in all modes. Hybrid datapaths including fixed-point (FP), customized floating-point (CFP), and double-precision (DP) representations are used to achieve the desired signal-to-quantization-noise ratio (SQNR). The 2-D decoupling and scheduling technique is used for complexity reduction of computing spatially varying phase compensation terms. Besides, a multisegment second-order Taylor series expansion is proposed to approximate the migration factor for configurability, which is an essential component in cross-coupling compensation and azimuth compression (AC), especially when squint angle becomes large. Variable range FFT sizes from 8K to 32K are supported to cover different swath widths. The processing times for image sizes of 8K $\times8\text{K}$ , 8K $\times16\text{K}$ , and 8K $\times32\text{K}$ are 0.34, 0.68, and 1.35 s, respectively, which meet the real-time processing requirement. Our implementation demonstrates significant improvement in processing efficiency and hardware efficiency with configurability compared with prior works.
This study demonstrates the possibility of implementing lens system via CMOS process. The ever first CMOS based optical focusing system successfully demonstrated focusing capability, with 5um by 6um focus spot size at 6 Hum, and capable of moving focal point 12um in axial direction. This system is composed of a lens set and an electrothermal actuated optical bench. One PDMS dispensed planar-convex lens and CMOS made Fresnel lens forms lens system to achieve focusing power as NA equals 0.38. This kind of system has potential to monolithically integrate with optical sensing circuitry with low cost.
This study reports a CMOS based optical focusing stage, which incorporates a binary phase-grating Fresnel-lens (PF-Lens). This PF-Lens is the first time implemented in CMOS micro stage. It exploits the superior fine line width and transparent dielectric thin film of CMOS process. Diffraction efficiency of PF-Lens is theoretically fourfold better than that of typical binary amplitude-grating Fresnel-lens (AF-Lens). In addition, by dispensing UV curable transparent polymer onto Fresnel-lens, the resulted compound lens can achieve a shorter focal length of 648 mum (HeNe laser). The integrated micro stage is thermally actuated. It provides 12 mum stroke alone optical-axis and 17.3 mum across optical-axis. It is sufficient to compensate optical alignment error and to speed up precision focus tracking.
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