Salinity is one of the most important characteristic parameters of seawater. The absolute salinity 𝑆𝐴 is defined to be the “Total amount of dissolved material in grams in one kilogram of seawater”, and it is directly related to the seawater density. However, the absolute salinity is difficult to be measured in practice. At present, practical salinity 𝑆𝑃 is calculated by using conductivity, temperature and pressure measured by CTD sensors. The conductivity of seawater is dependent on the ions concentrations. However, the non-ionic components cannot be detected, though they may have significant influence on density. The optical refractive index is sensible to all dissolutions of seawater, therefore it is a good proxy of the concepts of salinity/density. In this paper, urea was used to study the influence of urea on the seawater refractive index based on optical refractive index method. The changes of seawater refractive index versus the urea concentration were studied by a Vgroove refractometer. This method provides a new method for measuring urea in seawater.
The quaternary alloy (AlxGa1-x) y In1-yP is an attractive material due to its bandgap tunability while being lattice-matched to GaAs. Although this direct gap quaternary material is being extensively used for the visible lasers and LEDs due to its unique light absorption/emission properties, the applications in visible photodetectors remain unexplored. In this paper, A symmetric mesa AlInP/AlGaInP/AlInP double-heterostructure has been successfully designed based on the quaternary alloy for visible photodetection. The composition of (AlxGa1-x) y In1-yP was investigated with the help of MATLAB simulation and energy band discontinuity theory giving the values of y=0.48 and x=0.46. By using the first-order approximate data processing method and analogy with other III-V main group quaternary alloy compounds, the simulated values of bandwidth and responsivity are obtained to be 10 GHz and 0.85 A/W respectively at wavelength 560 nm. Meanwhile, by analyzing the influence of doping concentration and thickness of each layer on bandwidth and responsivity, the optimal doping concentration and thickness are obtained to be 2×1018cm-3 and 0.5μm of P layer, 5×1015cm-3 and 1μm of absorption layer, 5×1017cm-3 and 0.5μm of N layer respectively. By selecting optimized parameters, the device exhibits a detectivity of 108 cm√HzW-1 and a noise equivalent power of 10-11W. With high responsivity, high speed, and large bandwidth, the designed photodetector has a good application prospect.
The optical properties of seawater are of great significance to the monitoring of marine safety and marine environment by means of optical sensing. In order to further study the relationship between the refractive index (RI) of different salt solutions, temperature and salinity, two experiments are carried out. The effect of temperature and mass fraction on RI of single component solution, and the effect of type and quantity of ions on the RI of mixed solutions when the mass fraction is kept constant at 3.5% are studied. Experiment results show that mass fraction coefficient of NaCl, MgCl2 and MgSO4 are 1.74×10-4 , 2.54×10-4 and 1.94×10-4 , respectively. Mass fraction coefficient of NaCl is lower than that of MgCl2 and MgSO4. In the second experiment, it is found that the effect of valence state on RI is higher than that of ion number, and the RI of bivalent solution is higher than that of monovalent solution. Not only the temperature and salinity of seawater, but also the components of seawater salt ions have different effects on the RI. Since the intrinsic relationship between RI and salinity is not suitable for different sea areas, the study of the relationship between the RI of single solution or a binary mixed solution and temperature and salinity is of great significance for the modulation process of optical salinity sensing.
In this paper, a new method for measuring the refractive index of seawater based on the V-shaped cavity is proposed. MATLAB software is used to simulate the V-shaped cavity based on the optical thin film transfer matrix. By changing the refractive index of the liquid in the glassware placed in the cavity, the filtering characteristics of the V-shaped cavity are changed. The change of refractive index can be demodulated by monitoring the shift of transmission wavelength of V-shaped cavity. In this paper, the refractive index detection sensitivity is 217nm/RIU, and the refractive index high resolution measurement can be up to 10-8 RIU. In this paper, the empirical formula of the change of refractive index with the change of transmission wavelength shift is given. When the change of refractive index is 10-7 RIU, the accuracy of demodulation using the empirical formula is 0.03%. The outcomes indicate that the new method proposed in this paper has a strong application prospect in the field of high resolution ocean optical sensing.
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.
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.
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, 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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