In order to achieve high-precision, long-term and in-situ monitoring of nitrate concentration in seawater, a new method based on deep ultraviolet spectroscopy is presented to measure the absorbance of multi-component seawater samples at 200nm-400nm, and the measurement models are established using least square algorithm and kernel partial least square algorithm respectively. It is proved that kernel partial least square algorithm is better and the predicted concentration of nitrate is more accurately by comparing the two models. The research results show that the kernel partial least square algorithm can better extract the nonlinear relationship between the absorbance of different wavelengths and the nitrate concentration hidden in the spectrum of multi-component seawater, with better goodness of fit as well as prediction accuracy.
Salinity of seawater is one of the most important ocean parameters. Salinity of seawater is mainly obtained by conductivity measurement using CTD (Conductivity-Temperature-Depth). Conversion accuracy between conductivity and salinity relies on the assumption that components of seawater are fixed, as well as high accuracy and synchronism measurements of conductivity, temperature and pressure. The study of seawater salinity based on the V-block optical refractive index method provides a total different principle for salinity measurement. Achieving high resolution seawater optical refractive index measurements could help to study factors affecting the accuracy of salinity measurement. In this paper, the various instrument parameters that affect the accuracy of seawater refractive index measurement are analyzed and the optical refractometer is optimized based on the components on the shelf. This paper systematically analyzed the resolution and tolerance of refractive index measurement on the parameters of V-block refractometer, such as incident angle, external environment and prism refractive index, etc. The optical refractometer with an air film layer on both sides of the V-block was proposed for seawater salinity measurement. With such an optimization, the measurement accuracy is further improved and the tolerance is increased. The theoretical resolution to the seawater refractive index and salinity are 1.8×10-6 and 0.01‰, respectively. Experimentally, we have achieved 3.9×10-6 and 0.021‰ respectively, and a good linearity. The difference between theoretical and experimental results are analyzed.
A laser radar used in an automatic driving system was designed to operate normally in rainy and foggy weather while ensuring eye safety. The laser radar uses the principle of triangulation to measure the distance while adjusting the position of the focused light source by the beam expanding and focusing module. The laser radar used a home-made passively Q-switched Er:YAG laser that used a home-made TiS2 as a saturable absorber with an operating wavelength of 1645 nm. At an absorption pump power of 10.54 W, the passively Q-switched Er:YAG laser had a pulse repetition frequency of 37 kHz, a maximum average output power of 1.44 W, a pulse duration of 1.1 μs, and a pulse energy of 36.39 μJ.
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.