We present a fast shape measurement of micro-parts based on depth discrimination in imaging with LED illumination. It is based on a 4f-setup with an electrically adjusted tunable lens at the common Fourier plane. Using such a configuration, the opportunity to implement a fast depth scan by means of a tunable lens without the requirement of mechanically moving parts and depth discrimination using the limited spatial coherence of LED illumination is investigated. The technique allows the use of limited spatially partially coherent illumination which can be easily adapted to the test object by selecting the geometrical parameters of the system accordingly. Using this approach, we demonstrate the approach by measuring the 3D form of a tilted optically rough surface and a cold-formed micro-cup. The approach is robust, fast since required images are captured in less than a second, and eye-safe and offers an extended depth of focus in the range of few millimetres. Using a step height standard, we determine a height error of ±1.75 μm (1σ). This value may be further decreased by lowering the spatial coherence length of the illumination or by increasing the numerical aperture of the imaging system.A vector ray-tracing model (VRT) has been developed to compute the optical caustics associated with the primary rainbow for an oblate spheroidal water drop illuminated by a Gaussian beam. By comparing the optical caustic structures (in terms of limiting rainbow and hyperbolic umbilic fringes) for a water drop with a Gaussian beam (GB) illumination with that for the same drop, but with parallel beam (PB) illumination, the influence of the Gaussian beam on the optical caustics is investigated. For a water drop with GB illumination and different drop/beam ratios (i.e., the ratio between the drop equatorial radius and the Gaussian beam waist), the location of cusp points and the curvature of the limiting rainbow fringe are also studied. We anticipate that these results not only confirm the approach to compute optical caustics for oblate spheroidal drops illuminated by a shaped beam, but may also lead to a new method for measuring the aspect ratio of spheroidal drops.A novel hollow fiber temperature sensor (HFTS) based on long-range surface plasmon resonance is presented. The HFTS consists of a dielectric/Ag-coated hollow fiber filled with the thermosensitive liquid and two multimode fibers connected at both ends. By measuring the transmission spectra under different temperatures, the performances, including sensitivity and figure of merit (FOM) of the sensors with different structural parameters, such as thermosensitive liquid property, ethylene-vinyl acetate (EVA) and silver layer thicknesses, were investigated experimentally. check details The results shows that the sensitivity of the optimized HFTS is 1.60nm/°C to 5.21nm/°C in the range from 20°C to 60°C, and the FOM is up to 0.0453°C-1. Both performances are higher than most reported optical fiber temperature sensors based on surface plasmon resonance. Moreover, the performance of the HFTS is not sensitive to the dielectric layer thickness, which greatly reduces the difficulty of fabrication.Conventional beam scanning systems employing a microlens array (MLA) suffer from the problem that only discrete diffraction angles can be addressed because of the periodic structure of the MLA. In this paper, an adaptive fiber-optics collimator (AFOC) that continuously adjusts the position of light source (optic fiber output) is used in front of the periodic structure as a moving linear phase shifter to overcome this discrete scanning angle problem. By introducing the AFOC into the beam scanning system employing MLA, a beam scanning system with continuous scanning capability and high resolution is fulfilled. Theoretical simulations and experimental results both demonstrate the continuous high-resolution scanning capacity of the beam scanning system employing both MLA and AFOC. The proposed beam scanning system is expected to find wide applications in space optical communication, optical interconnection, power projection, and coherent beam combining.Self-referenced biosensing based on mode-splitting on a microring resonator is experimentally demonstrated. A Bragg grating integrated on the surface of the ring provides coupling between the clockwise and counterclockwise travelling modes of the pristine ring resonator lifting their degeneracy. The amount of mode-splitting is directly related to the reflectivity of the grating and it is only affected by structurally modifying the grating. Environmental perturbations to the surroundings of the gratings, such as temperature and bulk refractive index variations, have a minor effect on the amount of mode-splitting. This principle allows the realization of a self-referenced sensing scheme based on the detection of variations of the mode-splitting induced by structural changes to the grating. In this work, a polymethyl methacrylate (PMMA) Bragg grating is integrated onto a ring resonator in Al2O3. It is shown both theoretically and experimentally that the amount of splitting of a resonance varies minimally under temperature or bulk refractive index perturbations. However, the structural change of attaching a layer of biomolecules inside the grating does affect its reflectivity and the amount of mode splitting present. This result represents the first proof-of-concept demonstration of an integrated mode-splitting biosensor insensitive to temperature and refractive index variations of the liquid matrix where the molecules to be detected are embedded. The reported results pave the road towards the realization of truly self-referenced biosensors.We theoretically investigate the preparation of mid-infrared (MIR) spectrally-uncorrelated biphotons from a spontaneous parametric down-conversion process using doped LN crystals, including MgO doped LN, ZnO doped LN, and In2O3 doped ZnLN with doping ratio from 0 to 7 mol%. The tilt angle of the phase-matching function and the corresponding poling period are calculated under type-II, type-I, and type-0 phase-matching conditions. We also calculate the thermal properties of the doped LN crystals and their performance in Hong-Ou-Mandel interference. It is found that the doping ratio has a substantial impact on the group-velocity-matching (GVM) wavelengths. Especially, the GVM2 wavelength of co-doped InZnLN crystal has a tunable range of 678.7 nm, which is much broader than the tunable range of less than 100 nm achieved by the conventional method of adjusting the temperature. It can be concluded that the doping ratio can be utilized as a degree of freedom to manipulate the biphoton state. The spectrally uncorrelated biphotons can be used to prepare pure single-photon source and entangled photon source, which may have promising applications for quantum-enhanced sensing, imaging, and communications at the MIR range.