Hongzhi Jia

Research of optical rotation measurement system based on centroid algorithm

An optical rotation measurement system based on digital signal processor, modulated laser, and step motor rotating stage is established. Centroid algorithm featured fast and simple calculation is introduced to process light signals with or without sample to obtain the optical rotating angle through the step difference between two centroids. The system performance is proved experimentally with standard quartz tubes and glucose solutions. After various measurements, the relative error and precision of the system are determined to 0.4% and 0.004°, which demonstrates the reliable repeatability and high accuracy of whole measurement system.

A low confinement loss double-photonic crystal fibre over 850 nm bandwidth with 26 orbital angular momentum modes transmission

ABSTRACT In this paper, a new double-photonic crystal fibre (D-PCF) is proposed and numerically investigated, result shows that can support angular momentum (OAM) mode transmission up to 26. Based on As2S3 substrate, the proposed D-PCF is composed of three well-ordered air-hole rings in the cladding and another several air-hole rings at the centre. Due to the large effective index difference greater than 10−4 between eigenmodes, OAM can be well separated with the proposed D-PCF. In addition, the confinement loss of less than 7 × 10−9 dB/m for all eigenmodes is obtained with wavelengths spanning from 1.25 to 2.1 µm, where the optical wave can be confined closely within the core of D-PCF. With these beneficial properties, the designed D-PCF could enable large-capacity transmission in high-speed communications.

Theoretical proposal of a low-loss wide-bandwidth silicon photonic crystal fiber for supporting 30 orbital angular momentum modes

We propose a novel four-ring hollow-core silicon photonic crystal fiber (PCF), and we systematically and theoretically investigate the properties of their vector modes. Our PCF can stably support 30 OAM states from the wavelength of 1.5 μm to 2.4 μm, with a large effective refractive index separation of above 1×10−4. The confinement loss is less than 1×10−9 dB/m at the wavelength of 1.55 μm, and the average confinement loss is less than 1×10−8 dB/m from the wavelength of 1.2 μm to 2.4 μm. Moreover, the curve of the dispersion tends to flatten as the wavelength increases. In addition, we comparably investigate PCFs with different hole spacing. This kind of fiber structure will be a potential candidate for high-capacity optical fiber communications and OAM sensing applications using fibers.

Novel method for determination of optical rotatory dispersion spectrum by using line scan CCD

A novel method is presented for rapid measurement of optical rotatory dispersion (ORD). Light passes through a polarizer, sample and analyzer, to a transmission grating that disperses the collimated light beam. A step-motor rotating stage controlled by a digital signal processor changes the analyzer orientation. The light power is measured by a charge-coupled device (CCD) after each rotating-stage step. The optical rotation angle for each wavelength is determined from the shift between two Malus curves obtained from each CCD pixel. The ORD spectrum is obtained by transforming the optical rotation angle into specific rotation. The ORD spectrum for a standard quartz tube demonstrates good continuity and agreement with reference data.

Analysis of the bandwidth of resonant spectra for tilted fiber grating

Abstract Based on the coupled-mode equations, the formula of null-null bandwidth for tilted fiber grating is deduced in this paper. Numerical simulations and theoretical analysis of the effects of the tilt angle on bandwidth and maximum reflectivity are performed. Furthermore, under the maximum reflection of 95%, the relation of bandwidth with the tilt angle, modulation amplitude, and the needed length of grating are demonstrated in two three-dimensional diagrams. It reveals that the grating tilt can obviously narrow the bandwidth, especially in the case of large modulation amplitude and grating length, which is meaningful to its application in optical communications and fiber sensing.