Jingping Zhu

Compact static Fourier transform imaging spectropolarimeter based on channeled polarimetry

The theoretical operation and experimental demonstration of a Fourier transform imaging spectropolarimeter for real time measurement of the polarization state of light are presented. The spectropolarimeter uses a Wollaston prism as a birefringent interferometer and two high-order retarders to incorporate channeled polarimetry. Compared with previous instruments, the most significant advantage of the described model is that the complete wavelength-dependent polarization is acquired simultaneously along a one-dimensional spatial image by a single snapshot. Also, we show that, in this configuration, we can benefit from the advantages of the model: it is compact and robust, and the birefringent interferometer has a high throughput.

Target detection in turbid medium using polarization-based range-gated technology

Range-gated technology is well known for its good reliability, large field of view (FOV) and low cost in target detection through scattering or turbid medium. However, the tail-gating technology suffers from low signal-to-noise ratio in high turbidity levels due to superposition of photons multiply scattered from the medium and that reflected from the target. In this paper, polarization properties of multiply scattered photons emerging from the turbid medium are studied. Results demonstrate that diffusive photons are almost completely depolarized with no diattenuation and retardance. We combined the tail-gated technology with polarization detection method to effectively image in high level of turbidity. This approach showed about two times enhancement in image contrast as compared with the conventional range-gated technology.

Tests of a compact static Fourier-transform imaging spectropolarimeter.

A compact Fourier-transform imaging spectropolarimeter covering a 450-1000 nm spectral range is presented. The sensor, which is based on two birefringent retarders and a Wollaston interferometer, offers significant advantages over previous implementations. Specifically, with no internal moving parts, electrically controllable or micro polarization components, the full wavelength-dependent state of polarization, spectral and spatial information of a scene can be acquired simultaneously. Outdoor measurements of several cars and plants demonstrate the sensors potential for color measurement, target identification, and agriculture monitoring applications.

Modified polarized geometrical attenuation model for bidirectional reflection distribution function based on random surface microfacet theory

The geometrical attenuation model given by Blinn was widely used in the geometrical optics bidirectional reflectance distribution function (BRDF) models. Blinns geometrical attenuation model based on symmetrical V-groove assumption and ray scalar theory causes obvious inaccuracies in BRDF curves and negatives the effects of polarization. Aiming at these questions, a modified polarized geometrical attenuation model based on random surface microfacet theory is presented by combining of masking and shadowing effects and polarized effect. The p-polarized, s-polarized and unpolarized geometrical attenuation functions are given in their separate expressions and are validated with experimental data of two samples. It shows that the modified polarized geometrical attenuation function reaches better physical rationality, improves the precision of BRDF model, and widens the applications for different polarization.

Comment on the paper “Design and analysis of wide-field-of-view polarization imaging spectrometer”

The corrected approach for increasing the filed-of-view of the polarization imaging spectrometer based on Savart polariscopes is presented.

Design and performance of a compact miniature static Fourier transform imaging spectropolarimeter

We propose a compact, miniature static Fourier transform imaging spectropolarimeter (SFTISP). The spectropolarimeter is formed by cascading two high order crystal retarders and a Wollaston birefringent interferometer. Compared with previous instruments, the most significant advantage of the described model is that without any internal moving parts, electrically controllable or micro-components, the entire wavelength-dependent state of polarization (SOP) is acquired simultaneously along a one-dimensional spatial image by a single snapshot. Also, we show that in this configuration we can benefit from the advantages of the element: compact, robust and high throughput of the Wollaston birefringent interferometer. The theory of the birefringent SFTISP is provided, followed by details of its specific embodiment. A simulation and an experimental demonstration of the sensor are also presented. The core optics of the breadboard sensor is as small as 8×Φ 3.5 cm3 in size. The operation spectral range is from 450 nm to 850 nm. The experiment results were shown to yield accuracy better than 3% over most of the operation spectral band.

A THEORETICAL INVESTIGATION ON PROPAGATION CHARACTERISTICS AND COUPLING EFFICIENCIES OF A COUPLING SYSTEM

In a butt-joint coupling system, a fiber is coupled to a slab waveguide by a fiber ended micro-lens (FEML), so that the electromagnetic field emerging from the FEML is completely different from the fiber mode. The conventional method for calculations of the coupling efficiency, such as the overlap integral method, is not valid. In this paper, a Monte Carlo model for the coupling system is proposed, based not only on the principles of reflection and refraction at media interface plane, but also on the diffractions of micro lens. This model incorporates the geometrical surface of both the fiber end-face micro-lens and slab waveguide, the relative position of the fiber and slab waveguide, and also takes into consideration both the aberration and diffraction effects. The propagation characteristics and coupling efficiencies of the system are simulated. The losses caused by misalignment of the system are also discussed.

Study on the polarization dependency of diffraction efficiency of perfectly conducting blazed gratings

The diffraction properties for blazing -3 order of the perfectly conducting blazed gratings in the Littrow mounting under the polarized incident beam is investigated by numerical simulation. The diffractive electromagnetic fields for S and P polarized incident lights are calculated numerically using TDFD method. The field distribution of the electromagnetic field in the near groove area is analyzed, and the polarization dependency of diffraction efficiency is studied. The spectral characteristics in 1530~1566 nm range is given. It is proved that the efficiency for S polarized incident light is higher than that of P polarized one and it is not sensitive to the blazed angle. The spectral characteristic is flat within the fiber communication spectrum range.

Integrated optical planar waveguide acousto-optic switches

A N X N integrated planar optical waveguide acousto-optical switch design is presented based on waveguide geodesic lenses and acousto-optical deflector. This kind of switches gets over the difficulties occurred in integrated switches based on strip waveguide. It can be integrated in a chip, and the channel numbers N can be up to 218. As an example, a 2 X 2 integrated planar optical waveguide acousto-optical switch has been fabricated and tested. Experiment result shows only one mode is transmitted in the Ti:LiNbO3 waveguide; the chip insertion loss is 0.8 dB; the central acoustic frequency is 150 MHz; the 3 dB bandwidth of IDT is 56 MHz; the chip acoustic frequency resolution is 6 MHz and the chip extinction ratio is larger than 20 dB.

Expression of the degree of polarization based on the geometrical optics pBRDF model

An expression of the degree of polarization (DOP) based on the geometrical optics polarimetric bidirectional reflectance distribution function model is presented. In this expression, the DOP is related to the surface roughness and decreases at different reflection angles because diffuse reflection is taken into consideration. A shadowing/masking function introduced into the specular reflection expression makes the DOP values decrease as the angle of incidence or observation approaches grazing. Different kinds of materials were measured to validate the accuracy of this DOP expression. The measured results suggest that the errors of the DOP are reduced significantly, and the polarized reflection characteristics can be described more reasonably and accurately.