High‐accuracy system for spectral measurement of small‐area‐contrast and low‐light‐level display screens

Abstract— A double‐monochromator spectroradiometer with a photon‐counting detector will be described. The system captures spectroradiometric data with near‐perfect linearity over six decades of intensity and with wavelength uncertainties of under 0.05 nm. It enables accurate measurement of spectral radiance data and small‐area contrast with an uncertainty less than 0.002 in chromaticity (x,y) and 2% in luminance for a typical CRT spectrum.     

Compensation of Frequency Offset for Differentially Encoded 16- and 64-QAM in the Presence of Laser Phase Noise

The compensation of frequency offset for differentially encoded 16- and 64-ary quadrature amplitude modulation (QAM) in the presence of laser phase noise is investigated. Differential encoding is employed to solve the four-fold phase ambiguity problem in a nondata-aided transmission system with square QAM constellations. Simulation results show that frequency offset and phase noise can successfully be compensated using a second-order digital filter loop for the square QAM constellations.      

Intensity and phase measurements of asymmetric mode profiles and the transform in the near- to far-field transitions

A fast and accurate measurement technique employing a calibrated CCD array is described to measure the intensity and phase distributions of the asymmetric mode profiles associated with optical waveguides. A Shack-Hartmaan wavefront sensor incorporated in the system provides the phase information. The transform describing the near-field (NF) to far-field (FF) transitions of the asymmetric mode profiles is investigated both experimentally and theoretically. The simulated NF to FF transitions using the transform are compared with the measured profiles at different positions from the end face of the waveguide. Good agreement is obtained between the measured and the computed profiles proving the accuracy of the measurement technique and also the transform used for propagation of the asymmetric mode profiles.     

Numerical simulation of intensity and phase noise from extracted parameters for CW DFB lasers

A self-consistent numerical approach is demonstrated to analyze intensity and phase noise from experimentally extracted parameters for a continuous-wave distributed feedback (DFB) laser. The approach takes into account the intrinsic fluctuations of the photon number, carrier number, and phase. Values for the parameters appearing in the rate equations are extracted from the measured relative intensity noise spectra and linewidth of the laser. The simulation of the frequency spectra of intensity and phase noise of the DFB laser are performed by fast Fourier transform and exhibit good agreement with experimental results. The model presented here can readily be extended for the purpose of system simulations.