Modified quadratic congruence codes for fiber Bragg-grating-based spectral-amplitude-coding optical CDMA systems

Abstract

We have constructed a series of new code families for the spectral-amplitude-coding optical code-division multiple-access (CDMA) system, and proposed new transmitter and receiver structures based on tunable chirped fiber Bragg gratings (FBGs). The proposed system has been analyzed by taking into account the effects of phase-induced intensity noise, shot noise, and thermal noise. We have also compared the performance of this system with that of a former system where a Hadamard code is used. It has been shown that the new code families can suppress the intensity noise effectively and improve the system performance significantly. When the effective power is large (i.e., 10 dBm), the intensity noise is the main factor that limits the system performance. When the effective power is not sufficiently large, thermal and shot noise sources become the main limiting factors and the effect of thermal noise is much larger than that of shot noise.

IP transmission over optical spectral amplitude‐coding CDMA links

“…Therefore, although MUI can be canceled by using a reference decoder when sequences with a fixed in-phase cross correlation are used in an optical spectral amplitude-coding CDMA system, the existing PIIN still severely degrades the overall system performance. To suppress its effect, a new code, referred to as modified quadratic congruence (MQC) code, has been proposed [5]. It can suppress the effect of PIIN because it has ideal in-phase cross correlation.…”

“…When the effects of phase-induced intensity noise (PIIN) of an ideally unpolarized thermal source and the associated receiver shot and thermal noises are considered, variance of the generated photocurrent can be expressed as [5] …”

“…ᑬ ϭ (e)/(hv c ) is the responsivity of the photodetector, where is the photodetector's quantum efficiency, h is the Plank's constant, e is the electron charge, and v c is the central frequency of the original optical pulse. With the use of the Gaussian approximation, the corresponding bit error rate (BER) can be expressed as [5] P ek ͑k͒ ϭ 1 2 erfc͑ ͱSNR͑k͒/8͒.…”

“…It can suppress the effect of PIIN because it has ideal in-phase cross correlation. When MQC codes are used in a spectral amplitude-coding system, the receiver signalto-noise ratio (SNR) taking into account PIIN, thermal noise, and shot noise can be expressed as [5] SNR ͑k͒ ϭ…”

“…Recent relevant works about the scattering behavior of targets above rough surfaces include the multipole expansion method discussed by B. R. Johnson et al for the case in which the incident light wave is incident upon a dielectric flat surface with a spherical particle on it [4]. A four-path model for electromagnetic scattering from a rectangular dielectric box above a dielectric half space was used by J. T. Johnson to clarify the scattering interactions for both frequency and time domain [5], and in his next work, the study was extended to the case of the rough interface by using the coupled canonical grid/discrete dipole approach [6]. Chiu et al present an analytical solution for predicting the near-field interaction between a dielectric cylinder and a slightly rough surface based on the reciprocity theorem [7], and the second moments of the backscatter fields from a circular dielectric cylinder above a slightly rough surface with inhomogeneous dielectric profile are derived.…”