Abstract
A novel coherent optical code-division multiple access (OCDMA) scheme is proposed that uses spectral line pairing to generate signals suitable for heterodyne decoding. Both signal and local reference are transmitted via a single optical fiber and a simple balanced receiver performs sourceless heterodyne detection, canceling speckle noise and multiple-access interference (MAI). To validate the idea, a 16 user fully loaded phase encoded system is simulated. Effects of fiber dispersion on system performance are studied as well. Both second and third order dispersion management is achieved by using a spectral phase encoder to adjust phase shifts of spectral components at the optical network unit (ONU).
Highlights
Code-division multiple access (CDMA) is widely used in wireless communications because of its spectral efficiency, system capacity, signal quality, security, and flexibility [1]
A number of attempts at optical CDMA (OCDMA) have been made; performance has been limited by speckle noise and multiple access interference (MAI) generated in receivers that are not fully coherent
In what is commonly referred to as coherent OCDMA, the encoding is fully coherent, and waveforms can be generated by performing encoding in the time domain through a superstructured fiber Bragg grating (SSFBG) [7,8]; or by performing phase or amplitude encoding in the frequency domain [2], adopting either programmable liquid crystal modulators (LCM) [9], micro-ring resonators [10], or arrayed wave-guild gratings (AWG) [11]
Summary
Code-division multiple access (CDMA) is widely used in wireless communications because of its spectral efficiency, system capacity, signal quality, security, and flexibility [1]. The high autocorrelation peak requires a fast nonlinear threshold detector to capture the ultra-short optical pulse Both time spread OCDMA (TS-OCDMA) and SPECTS-OCDMA require a fast phase or amplitude modulator [3], and the auto-correlation in TS-OCDMA produces a sharp peak, and low level sidelobes [2]. We proposed a new coherent OCDMA combining spectral phase encoding (SPE) and phase and polarization diversity (PPD) [1] detection This scheme inherits the attributes for SPE-OCDMA, while making obsolete the requirement for a phase-locked loop (PLL) and nonlinear threshold. It has been shown that the system is able to eliminate MAI and speckle noise and achieve high spectral efficiency [1] Such a homodyne system requires has a complex receiver design and requires two fibers to convey the reference comb and signal comb separately [1,12,13].
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