Torger Tokle

Wavelength conversion of a 40-Gb/s RZ-DPSK signal using four-wave mixing in a dispersion-flattened highly nonlinear photonic crystal fiber

Wavelength conversion of a 40-Gb/s return-to-zero differential phase-shift keying signal is demonstrated in a highly nonlinear photonic crystal fiber (HNL-PCF) for the first time. A conversion efficiency of -20 dB for a pump power of 23 dBm and a conversion bandwidth of 31 nm, essentially limited by the gain bandwidth of erbium-doped fiber amplifiers, are obtained in only 50-m dispersion-flattened HNL-PCF with nonlinear coefficient equal to 11 W/sup -1//spl middot/km/sup -1/. This experiment demonstrates the potential of four-wave mixing in HNL-PCF as a modulation format and bit rate transparent wavelength conversion mechanism in future high-speed systems.

All-optical wavelength conversion and multichannel 2R regeneration based on highly nonlinear dispersion-imbalanced loop mirror

All-optical wavelength conversion has been achieved to generate a multichannel return-to-zero optical source for wavelength-division-multiplexed (WDM) systems by using a nonlinear optical loop mirror consisting of a common dispersion-shifted fiber. After WDM transmission over 40-km SMF, the WDM signals are successfully regenerated by a novel regenerator including reshaping and reamplification based on a dispersion-imbalanced loop mirror consisting of an SMF and a highly nonlinear dispersion-shifted fiber.

Investigation of Multilevel Phase and Amplitude Modulation Formats in Combination With Polarization Multiplexing up to 240 Gb/s

We present experimental investigations of the receiver sensitivity and dispersion tolerance of multilevel optical communication systems with a symbol rate of 40 Gbaud. Four- and eight-level communication is obtained by combining binary amplitude modulation with either binary or quadrature differential phase modulation. We experimentally compare the dispersion tolerance, and show that multilevel modulation formats offer much better dispersion tolerance compared to binary formats. By combining multilevel modulation with polarization multiplexing, bit rates up to 240 Gb/s were obtained. We demonstrate transmission over 50-km fiber span with no power penalty for a pseudorandom binary sequence length of 27-1 bits

Advanced Modulation Formats for Transmission Systems

DQPSK has shown that multilevel modulation formats can enable new possibilities in optical communication systems. The paper presents several options to go to even more advanced formats using direct detection.

42.8 Gbit/s, 4 Bits per Symbol 16-ary Inverse-RZ-QASK-DQPSK Transmission Experiment without Polmux

We present an experimental implementation of 16-ary 42.8 Gbit/s Inverse-RZ-QASK- DQPSK, using four-level inverse return-to-zero amplitude modulation with four-level differential phase modulation. We demonstrate transmission over a 75 km fibre span with only minor degradation. copy2006 Optical Society of America

Wavelength conversion of 80 Gbit/s optical DQPSK using FWM in a highly non-linear fibre

We present, for the first time, wavelength conversion of 80 Gbit/s optical DQPSK. The wavelength conversion is achieved using FWM in a highly non-linear fibre. We demonstrate a conversion power penalty as low as 2.8 dB.

XPM-Induced Degradation of Multilevel Phase Modulated Channel Caused by Neighboring NRZ Modulated Channels

The impact of XPM from NRZ modulated channels on an 8-level phase modulated channel in a WDM system was investigated. Requirements on launch power are found. 400 km transmission was achieved with negligible penalty.

Transmission of Multilevel 60 Gbit/s Polarization Multiplexed RZ-D8PSK using only 10 Gbit/s equipment

By combining differential 8-ary phase shift keying with polarization multiplexing, we present transmission of multilevel modulation with 6 bits per symbol through a 100 km fiber span with a receiver bit-error-ratio better than 10-9.

Noise filtering in a multi-channel system using a tunable liquid crystal photonic bandgap fiber

This paper reports on the first application of a liquid crystal infiltrated photonic bandgap fiber used as a tunable filter in an optical transmission system. The device allows low-cost amplified spontaneous emission (ASE) noise filtering and gain equalization with low insertion loss and broad tunability. System experiments show that the use of this filter increases for times the distance over which the optical signal-to-noise ratio (OSNR) is sufficient for error-free transmission with respect to the case in which no filtering is used.

Transmission of RZ-DQPSK over 6500 km with 0.66 bit/s/Hz spectral efficiency

Transmission of 12.5 Gbit/s RZ-DQPSK signals over 6500 km with different channel spacings is presented. We demonstrate the feasibility of trans-oceanic transmission using DQPSK in DWDM systems with up to 0.66 bit/s/Hz spectral efficiency. Introduction: Differential quadrature phase shift keying (DQPSK) has recently been suggested as a suitable modulation format for optical communication systems (1). With DQPSK, two bits are transmitted for every symbol, thus the symbol rate and the bandwidth of all electronic and electro-optical components can be halved compared to a binary system. This leads to improved dispersion tolerance and allows for closer channel spacing in wavelength division multiplexing (WDM) systems, and very high spectral efficiency have been obtained in recent experiments (2-4). As differential binary phase shift keying (DBPSK), DQPSK also benefits from a 3 dB improved sensitivity when balanced detection is used. Here, we present a transmission experiment over transoceanic distances using optical DQPSK modulation format with a return-to-zero waveform (RZ-DQPSK). In a 64 channel WDM system experiment, we transmit 12.5 Gbit/s RZ-DQPSK signals over a distance of 6500 km. We investigate channel spacings ranging from 133 to 15 GHz, achieving a maximum spectral efficiency of 0.66 bit/s/Hz, and demonstrate that DQPSK is well suited for dense WDM (DWDM) applications. Experiment: The experimental set-up is illustrated in Fig. 1. In the transmitter, we had a total number of 64 continuous wave (CW) lasers spaced 66 GHz, divided into two groups of odd and even channels. The odd numbered lasers were modulated with a 12.5 Gbit/s information rate (or 6.25 Gbit/s symbol rate) RZ-DQPSK signal. First, a Mach Zehnder (MZ) modulator driven with a 2Vπ data signal (Data1) was used to generate a DBPSK signal. Then, a phase modulator (PM) driven with a ½Vπ data signal (Data2) applied a 90o phase modulation to generate a DQPSK signal. Finally, a MZ driven with a Vπ clock signal was used to generate the RZ waveform. The Data1 and Data2 signals were pre-coded so that a pseudo random bit sequence (PRBS) was obtained at the receiver. Depending on the sign of the 45° phase offset in the demodulator, the received pattern was a 2 15 -1 PRBS or an inverted 2 15 -1 PRBS. Even numbered channels were modulated with a 6.25 Gbit/s RZ-DBPSK with a data pattern different from the odd channels. As 6.25 Gbit/s RZ-DBPSK has the same pulse-shape and similar spectrum as 12.5 Gbit/s RZ-DQPSK, the inter-channel cross-talk was not significantly affected by this simplification. The amplifier chain was 465 km long and consisted of 11 fibre spans made of large effective area fiber with a dispersion of 20 ps/nm/km (D+), and inverse dispersion fibre (IDF) with dispersion of -40 ps/nm/km. The average span length was 45 km, and the respective lengths of the D+ and IDF fibres had been adjusted to get a dispersion map with good dispersion and dispersion slope compensation. To reach longer distances, the fibre link was inserted in a re-circulating loop.