Charles Wong

FERROELECTRIC LIQUID CRYSTAL FIBER WAVEGUIDE

Abstract In this paper, we present the results on the fabrication and characterization of the FLC-in-fiber waveguides, in which hollow core optical fibers with typical core diameters of 2 to 10 μms are filled with FLCs. Proper alignment of the FLC inside the fiber core, allows for the electro-optic modulation of the liquid crystal refractive index resulting in a new class of devices for optical communication and sensors. We describe the fabrication process of the FLC-in-fiber waveguides. The propagation loss is measured to be 3.5 dB/cm. Linear modulation of the tilt angle up to 10 degrees is obtained by applying the electric fields up to 5 volts/μm. And a 10/24 μsecs rise/fall time is demonstrated with an E-field of 1 volt/μm applied across a fiber of 1 cm in length.

A liquid crystal-based Fourier optical spectrum analyzer

We propose a liquid crystal (LC)-based cost-effective Fourier optical spectrum analyzer (FOSA) without moving parts. Unlike normal spectrometers, the LC FOSA retrieves the spectrums Fourier coefficients instead of the direct spectrum measurement by changing different LC states in a number of stages. Besides the common applications, the LC FOSA can precisely read and recover the envelope of a dense wavelength-division-multiplexing spectrum to act as a spectral monitor and then work with a gain-flattening device to control the optical network instantly and dynamically.

Dynamic channel blocker/equalizer with high blocking extinction ratio

The effect of an interpixel gap on light leakage in a free-space liquid-crystal-based dynamic channel blocker/equalizer is studied. The electric field components along the driving electric field within the liquid crystal interpixel gap are numerically calculated. The results show nonuniform distributions in both width and thickness. The numeric results on the relation between gap width and electric field distribution are also presented. A 20-channel, 200-GHz channel-spacing blocker/equalizer on the C band with flat tops and a 40-dB extinction ratio is fabricated and examined.

Study of chromatic dispersion ripples in birefringent crystal-based optical interleavers

We report the study of chromatic dispersion ripples in birefringent crystal-based optical interleavers. The simulation indicates that for a 99.8% transmittance AR coating surface, the chromatic dispersion ripples caused by the Rhomb etalon effect could be as high as ±30 ps/nm. The experimental results are in agreement with the simulation results. We also demonstrate a practical approach to eliminate the chromatic dispersion ripples to be coupled into the output collimators. The overall interleaver chromatic dispersion, of less than 15 ps/nm within the passband, is demonstrated.

Liquid crystal fiber phase modulator

In the following, we present the fabrication techniques of the liquid crystal fibre phase modulator using liquid crystal fibre (LCF), working theory and measurement on the fiber phase modulation using LCF. We also present the measurement of the propagation loss of the LCF.

Effect of an imperfect antireflection coating on a birefringent interleaver in an optical communications system

The effect of an imperfect antireflection AR coating on a birefringent interleaver an important optical communication component and on an optical communications system containing such a birefringent interleaver is investigated. We demonstrate how the imperfect AR coat- ing on the rhomb surfaces affects the birefringent interleavers intensity spectrum and generates undesirable chromatic dispersion CD ripples for an interleaver that should be dispersion-free by design. Our results show that a rhomb with a close-to-perfect AR surface coating T =99.8% can still generate a ±30-ps/nm CD ripple, causing a nonneg- ligible power penalty in an optical communications system. We also demonstrate a simple and practical approach to reduce the CD ripple caused by the imperfect AR coating.

Liquid crystal-based dynamic channel blocker/equalizer for optical networks

Inter-channel crosstalk for a liquid crystal-based dynamic channel blocker/equalizer has been experimentally studied. With the optimal interpixel width, a 32-channel, 100-GHz channel-spacing sample is fabricated and characterized. The maximum insertion loss (IL) of 5 dB and the polarization dependent loss (PDL) of 0.5 dB within the ITU ± 14 GHz are achieved. The 45 dB extinction ratio is obtained. The variations of the IL and PDL within the temperature range from - 5°C to 65°C cross the C-band are less than 1 dB and 0.4 dB respectively.

Network performance for cascaded dispersion-free slicers

The impact of cascaded spectral Slicers on network performance is investigated in this paper. For a dispersive spectral Slicer, its dispersion is inversely proportional to the square of its channel spacing. When many narrow-band spectral Slicers are cascaded together, the total dispersion can cause significant penalty on system performance. We demonstrated the deleterious effects on system performance caused by the dispersion of cascaded spectral Slicers. To solve this problem, we applied a signal processing technique to design theoretically dispersion-free spectral Slicers. The design principle and simulation results of dispersion-free spectral Slicers are presented. Based on this signal processing technique, six dispersion-free 50-GHz Slicers were made and cascaded together. The total group delay ripples across spectrum within ±12GHz around center frequencies are less than ±0.8ps, which are much less than the group delay variation of ±14ps within the same bandwidth for dispersive Slicers. The power penalty of cascade dispersion-free Slicers is investigated by deploying them in a 16-channel OC-192 WDM (wavelength-multiplexing division) link. The measurement result shows no noticeable power penalty.