This work demonstrates a micro electro mechanical system (MEMS) technology based infrared thin film, which converts absorbed visible light energy into infrared radiation. The principle of the film and the experiment for studying its thermodynamic characteristics are presented. The radiation spectrum of the thin film conforms to the characteristics of blackbody spectrum, and the average emissivity in infrared band is 0.638. The thermal diffusion distance decreases with the decrease of substrate thickness. Moreover, the fabrication of periodic pixel arrays on substrates can effectively reduce the thermal conductivity. The thermal conductivity of the pixel inscribed thin film with a substrate thickness of 360nm is 0.1W/m·K. The temporal constant decreases with the decrease of substrate thickness. The time constant of the film with a substrate thickness of 360nm is 2.72ms while the working temperature is 5 degrees Celsius. These characteristics indicate that the infrared thin film has a promising application prospect in infrared scene projection.

Self-suspended polyimide (PI) composite films were fabricated. Their diameter and thickness were 2.5 in. and 260 nm, respectively. A high ratio of diameter to thickness of 2.4 × 10⁵ was obtained. The multiwalled carbon nanotubes (MWCNTs) were filled into PI to improve the optical absorption and the photothermal response. By using the N-methyl pyrrolidone solvent for both MWCNTs and poly(amic acid), a homogeneous dispersion of MWCNTs with up to 15% content was obtained. Under the thermal treatment of 300 °C, the composite films were successfully synthesized, which was proved by the measurements of Fourier transform infrared spectrum and x-ray diffraction. Compared with the pure PI film, the optical absorption of the composite films at 532 nm wavelength increased from 10% to 28%. The steady and transient photothermal properties of the composite films were investigated. In the steady state, a temperature rise of 145 °C was obtained under 0.7 W/cm² illuminating laser power density. The temperature increased by 29 times compared with that of the pure PI film. The corresponding photothermal conversion efficiency improved to 70.8%. In the transient state, the photothermal response time was 7.5 ms, which was only half that of the pure PI film. The excellent photothermal properties of these self-suspended MWCNT/PI composite films highlight their potential applications in micro- and nanoscale devices for photo detection and thermal imaging.

A new underwater lidar signal-processing method based on wavelet transform (WT) and independent component analysis (ICA) is presented in this letter. The proposed method combines WT and ICA to overcome the drawbacks of ICA and WT applied independently. ICA requires the number of observations equal to or greater than the number of sources to be separated. In the new method, the observation matrix of ICA is constructed by multi-layer wavelet time-domain decomposition from a single measurement, which avoids the uncertainties in multiple measurements caused by the change of measurement conditions. In addition, the new method greatly improves the frequency resolution of the echo signal by introducing wavelet transform. It can remove both the low-frequency scattering and high-frequency electromagnetic noises in the obtained signals. The new approach was tested in an underwater lidar system. A pulsed 532 nm light source operates at a repetition rate of 50 kHz, with an average output power of 3 W and a pulse duration of less than 1 ns. An Avalanche Photo Diode (APD) detector and the acquisition system with a bandwidth of 1 GHz is used to receive the echo signals. Underwater target ranging experiments were conducted when the attenuation length (AL) was 10. The ranging accuracies were compared with different signal processing methods. When there was no scattering suppression algorithm applied, the ranging accuracy was 12 cm; with only ICA, the ranging accuracy was 6.8 cm, with only WT, the accuracy was 5 cm; using the Wavelet-ICA method, the ranging accuracy was improved to 2 cm. The signal processing method can suppress strong scattering clutter in turbid water, thus greatly improve the ranging accuracy.

An infrared scene projector (IRSP) that can operate at an ambient temperature lower than 190 K is developed for the hardware-in-the-loop (HIL) simulation of space-borne IR detection systems. The IRSP is composed of a visible scene generator (VSG), a visible to IR converter, and an IR projection system optimized for cryogenic environments. The core component of the IRSP is a light-driven blackbody micro cavity array (BMCA). The BMCA is a photothermal conversion device. It can transform visible light images into IR images. The BMCA can operate properly in an ultralow temperature environment, and the temperature of the BMCA is the same as the ambient temperature. This property allows the BMCA to generate IR scenes with a pure low temperature background, which is crucial for the ground testing of space-borne IR detection systems. The performance of the IRSP was tested in a vacuum cold chamber. In the cryogenic environment with an ambient temperature of 187.75K, the observed highest temperature of the generated IR scene was 426.15 K, the lowest temperature was 187.75 K, the dynamic range of the IR scene was 38.69 db, and the frame rate of the IR scene reached 76 Hz. The average visible to IR conversion efficiency of BMCA was about 10.6%∼3.1% under different ambient temperatures. The radiation spectrum of the IRSP is close to the standard blackbody radiation spectrum both in the MWIR band and the LWIR band. The IRSP has been applied in a HIL simulation test of a space-borne IR detection system.

The ladar scene projector is a key device in the hardware-in-the-loop (HWIL) simulation system. Ladar scene modeling is a fundamental work of developing a ladar scene projector. A modeling method based on physically based rendering technology and OpenGL is proposed in this paper. This modeling method can quickly generate delay, amplitude, and pulse width data for all return signals in a large-array-scale ladar scene. A $100\times 100$-array-sized ladar scene model with a distance range of 0–3 km is simulated. The average data generation time is only 5.31 ms. Distance resolution is 1.5 m, and the peak-valley error is less than 0.15 m. This method achieves efficient modeling and fast hardware update rates, which greatly improves the real-time performance of the ladar scene projector. It has strong practicality and can be directly applied in the HWIL simulation system.

3D lidar scene projector (LSP) plays an important role in the hardware-in-the-loop (HIL) simulation for autonomous driving system (ADS). It generates a simulated 3D lidar scene in laboratory by generating a 2D array of optical time delay signals. The reconfigurable optical time delay array (ROTDA) is crucial for LSP. However, current ROTDA solutions cannot support a LSP with a spatial resolution more than 10×10. In this paper, we proposed a novel ROTDA design based on the time slicing method. The optical signals with the same time delay but different spatial coordinates were treated as one time slice. Different time slices were superimposed into a composite image by a microlens-array-based imaging system to obtain a 3D lidar scene. And a spatial light modulator (SLM) was utilized to configure the time delay of each lidar scene pixel. We developed a ROTDA prototype with 64×64 pixels, each pixel can be reconfigured with up to 180 different time delays in one frame. The time delay resolution is 1 ns, the maximum time delay is 5000 s, and the 3D frame rate is 20Hz. The prototype can generate a continuous lidar scene with a distance span of 27 m, and can also generate up to 8 short scenes that are separated from each other along the lidar observation direction, each short scene covers a distance span of 3 m or 3.75 m. The design method proposed in this paper can also be applied to other occasions that demand a large number of time delay generators.