Demonstration of 3-×8×10 Gbps WDM/DPSK-OCDMA using 31 -chip, 640 Gchip/s SSFBG en/decoder for 10 G flexible access

Abstract

We demonstrate a high data-rate SSFBG-based WDM/OCDMA experiment (3 wavelengths with 100 GHz spacing, 8 OCDMA, 10 Gbps/user) using 31-chip, 640 Gchip/s en/decoders, DPSK modulation, time gating and FEC. Introduction Optical code division multiple access (OCDMA) is a promising candidate for next-generation broadband access network [1~2]. Recently, coherent OCDMA using ultra-short optical pulse is receiving increasing attention with the progress of reliable and compact en/decoder devices, such as planar lightwave circuit (PLC), spatial light phase modulator (SLPM) [3], micro ring resonator (MRR) [4], superstructured fiber Bragg grating (SSFBG) [5] and arrayed waveguide grating (AWG) multi-port device [6]. The SSFBG was used mainly for time spreading (TS) OCDMA, while SLPM and MRR were used for spectral encoding (SPE) OCDMA schemes. The SSFBG-based TSOCDMA scheme is very attractive because the SSFBG en/decoders have the ability of ultra-long optical code (OC) generation, polarization independent operation, good compactness and low loss. The longer the code length is, more the active users can be accommodated [5]. However, it’s difficult to achieve high throughput in this scheme because of the compromise between code length and data-rate [7]. Previously, the highest throughput of SSFBGbased TS-OCDMA system was 10×1.25 Gbps [5]. To our knowledge, there has been no report on multiuser SSFBG en/decoder-based OCDMA with above 10 Gbps data-rate. Generally, in an OCDMA system the asynchronous access capability is essential for providing low latency access with simplified management and soft capacity on demand. However, total capacity (and the throughput) is limited by high multiple-accessinterference (MAI) and beat noises for the asynchronous operation [5~6]. Using differentialphase-shift-keying (DPSK) and forward-errorcorrection (FEC) could significantly enhance the system performance [3~4, 6]. On the other hand, if high throughput and the degree of security are the major considerations, synchronous SPE-OCDMA using slotor chiplevel timing coordination and time gating can mitigate the impairments of MAI and beat noise to achieve high throughput OCDMA [3~4]. These techniques have not been used in SSFBGbased multi-user TS-OCDMA system. In this paper, we demonstrate for the first time a 10 Gbps/user multi-user SSFBG-based TS-OCDMA system with 31-chip, 640 Gchip/s en/decoders, DPSK modulation and time gating. By combining with WDM technique [4,6,8] and FEC, high throughput SSFBGbased TS-OCDMA system will be achieved. Experiment Figure 1 shows the experimental setup. 10.7 GHz optical pulses were generated by a super-continuum (SC) light source and a 15 nm band pass filter (BPF) centred at 1550.8 nm. This signal was then modulated by Lithium Niobate phase modulator (LNPM) with optical transmission network (OTN) frame, which contains of 2-1 pseudo random bit sequence (PRBS) payload data and FEC parity. Then the data were split into 3 paths to a multi-user WDM/OCDMA setup with SSFBGs serving as WDM multiplexer and OCDMA encoders simultaneously [8]. The three paths are for signals at wavelengths of λ1(1550nm), λ2(1550.8nm) and λ3(1551.6nm), respectively. The upper branch is for λ2. Encoder 1 to 4 are 31chip, 640 Gchip/s SSFBGs with central wavelength of λ2 to generate four different BPSK 31-chip Gold codes, the first row in Fig. 2 shows the waveforms of the generated four codes. The duration of the generated OCs is about 50 ps. The waveforms of auto-correlations and several cross-correlations are shown in the second and third rows of Fig. 2, respectively. The peak discrimination ratio between auto-/cross-correlation is very high. The user adjust units consist of fixed fiber delay lines, tunable optical Time, 10 ps/div a. u.