Automatic tunable chromatic dispersion compensation at 40 gb/s in ASK and DPSK, NRZ, and CSRZ 263-km transmission experiments

Chromatic dispersion (CD) in single-mode optical fiber distorts pulses and is a big obstacle for the installation of long-haul dynamically routed transmission systems, especially at 40 Gb/s. Here the automatic residual CD compensation of a 263-km fiber link in the range -300 to -700 ps/nm is demonstrated for nonreturn-to-zero amplitude-shift keying (NRZ-ASK), carrier-suppressed return-to-zero (CSRZ)-ASK, NRZ differential phase-shift keying (DPSK), and CSRZ-DPSK modulation formats at 40 Gb/s. A thermally tunable dispersion compensator minimizes residual CD, which is measured by a synchronous arrival time detection scheme. The measured transmission penalty with online CD compensation is between /spl plusmn/1.2 dB for various link lengths and compensated CD values.

I. Introduction

Tunable chromatic dispersion (CD) compensation is needed in long-haul and dynamically routed transmission links, especially at 40 Gb/s. Various integrated optical dispersion compensators [1]–[5] have been demonstrated but fiber Bragg gratings (FBGs) exhibit the largest dispersion and lowest insertion loss with an associated tunability. Fig. 1. Chromatic dispersion compensation (CDC) setup for 40-Gb/s ASK and DPSK transmission experiments. Recent advances in FBG technology now allow the realization of single and multichannel tunable devices [6]. Among many CD detection schemes, synchronous arrival time detection with a sensitivity limit of 100 attoseconds [7] is the most promising option because the scheme has an extremely low incremental cost, provides the sign of CD, responds in 1 ms and is usable for various modulation formats [8]. Prior to this, a similar method was reported by Takushima and Kikuchi [9], but arrival time detection was asynchronous. As a consequence, the required frequency deviation was larger, the measurement interval was longer, and the sign of dispersion remained ambiguous.