To meet the requirements of miniaturization, low cost and high stability of Laser Doppler seawater velocity measurement, a closed-loop feedback laser drive method was studied to achieve a voltage-controlled constant current source based on operational amplifier. The temperature of the laser was collected and controlled by thermal-electric-cooler (TEC). Proportional-Integral-Differential (PID) algorithm was used to set the temperature, so as to realize the closed-loop control of the temperature. The experimental results show that the output optical power of the system was remarkably correlated linearly with the control voltage amplitude at temperature of 25℃, the optical power fluctuation was less than 0.4mW and the wavelength fluctuation was 7pm at the same tuning voltage. The size of the system was 102mm×65mm with a high stability.
Estimation of the wind velocity from the weak aerosol backscattering signals is an important problem in the research of Coherent Doppler lidar (CDL). The signal model and a real correlation random wind field algorithm are explained. The performance of the Maximum likelihood discrete spectral peak (ML DSP) algorithm for Coherent Doppler lidar is applied to simulation signal and summarized by employing the Monte Carlo simulations. The relationships between the SNR, estimation precision, and detection probability under different signal models are simulation and summarized. According to the analysis results of simulated, the ML DSP algorithm performance is the best for Hyperbolic-secant distribution, while Lorentz distribution has the worst performance. To satisfy the 80% detection probability, the turbulence model of Lorentz requires maximum signal-to-noise ratio (-16dB) in very strong turbulence intensity.
Deep ultraviolet (deep-UV) spectroscopy has been proved to be a promising technique for in-situ and real-time nutrient measurement, where key components, such as deuterium lamp light source with wide wavelength range from 190nm to 400nm, has been deployed. For water with multi-contaminations, experimental results indicated that the luminescence emission excited by the wide band light source lead to considerable measurement error. It is desired to develop a narrowband multi-wavelength ultraviolet (UV) light source for a more accurate measurement. However, rare research has been done towards such functional devices, such as wavelength filters and switches, in deep-UV band. Therefore, a novel deep-UV narrow-band filter, based on the deep-UV transparent rectangular single-mode optical waveguide and arrayed waveguide grating (AWG) structure, is proposed and designed in this manuscript. In order to reduce the loss and crosstalk, we optimize the decoupling distance and the number of array waveguide. In conclusion, this deep-UV multiwavelength narrow band-pass filter is designed to be single-channel input and 7-channel output with central wavelengths from 210nm to 240nm, channel spacing of 5nm. This device has -3dB bandwidth of 1.87nm, inter-channel cross-talk of - 23.80dB, and insertion loss of -4.25dB, device size of 40 mm (length) x 10 mm (width) x 2mm (thickness), having integratable interface with waveguide type optical switches and detectors.
Deep ultraviolet (deep-UV, 200nm~300nm) spectrum analysis is an important technique in underwater biochemical sensors. For in-situ exploration, integrated optics based wavelength selective light source would have advantages in obtaining high sensitivity spectrum, compactness and low power consumption. The key components used in forming such wavelength selective light source are optical switch and bandpass filters. However, such optical switch and bandpass filter in deep-UV band have rarely been studied, to our best knowledge. In this paper, we proposed and designed a silica-based optical waveguide structure that can achieve single-mode transmission at 210nm-240nm. Furthermore, we designed and simulated a Mach-Zehnder Interferometer (MZI) switch in deep-UV band for in-situ marine chemical sensing application. In our simulation, a rectangular optical waveguide with single-mode operation has been achieved based on phosphorus (P) and boron (B) co-doped Silica core waveguide with 2.9μm in width and 0.35μm in thickness. The refractive index difference between core and cladding layer is Δn=0.003. Based on this waveguide structure, we also designed a Mach-Zenhder interference (MZI) type optical switch with extinction ratio larger than 26dB at deep-UV band.
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