Lars Grüner-Nielsen

Direct continuous-wave measurement of n2 in various types of telecommunication fiber at 1.55 μm

A method for measuring the nonlinear refractive index of optical fibers with an error of less than 5% is demonstrated. The technique is based on measuring the nonlinear phase shift experienced by a dual-frequency beat signal, permitting a simple, highly sensitive, accurate, repeatable, and easily automated measurement procedure and sampling. Measurements of the nonlinear coefficient in standard telecommunication, dispersion-shifted, and a number of dispersion-compensated fibers are presented.

Dispersion-compensating fibers

This paper reviews properties and use of conventional single-mode dispersion-compensating fibers (DCFs). The quality of the dispersion compensation expressed as residual dispersion after compensation is treated. Properties of actual DCFs for discrete compensation including loss and nonlinear effects are discussed. Fiber design with special emphasis on design tradeoffs is considered. The Raman properties of DCFs and their use as a discrete Raman amplifier are also discussed. Finally, DCF for use in dispersion-managed cables (DMCs) is addressed, including optimum fiber design and comparison of different configurations.

73.7 Tb/s (96 x 3 x 256-Gb/s) mode-division-multiplexed DP-16QAM transmission with inline MM-EDFA

Transmission of a 73.7 Tb/s (96 x 3 x 256-Gb/s) DP-16QAM mode-division-multiplexed signal over 119 km of few-mode fiber transmission line incorporating an inline multi mode EDFA and a phase plate based mode (de-)multiplexer is demonstrated. Data-aided 6 x 6 MIMO digital signal processing was used to demodulate the signal. The total demonstrated net capacity, taking into account 20% of FEC-overhead and 7.5% additional overhead (Ethernet and training sequences), is 57.6 Tb/s, corresponding to a spectral efficiency of 12 bits/s/Hz.

Demonstration of massive wavelength-division multiplexing over transoceanic distances by use of dispersion-managed solitons

By combining a special dispersion map that has nearly constant path-average dispersion, a hybrid amplification scheme involving backward-pumped Raman gain, and sliding-frequency guiding filters, we have demonstrated massive wavelength-division multiplexing at 10 Gbits/s per channel, error free (bit-error rate, </=1x10(-9) for all channels), without the use of forward error correction, over greater than 9000 km, using dispersion-managed solitons. The number of channels (27) was limited only by a temporary lack of amplifier power and gain flatness. Terabit capacities are to be expected in the near future.

All-fiber grating-based higher order mode dispersion compensator for broad-band compensation and 1000-km transmission at 40 Gb/s

We use a novel fiber-grating device to demonstrate the first polarization-insensitive all-fiber higher order mode dispersion compensator for broad-band dispersion compensation. Its low loss and high effective area have enabled transmission through 1000 km (10/spl times/100 km) of nonzero dispersion-shifted fiber (NZDSF) at 40 Gb/s.

First demonstration and detailed characterization of a multimode amplifier for space division multiplexed transmission systems

We present the first demonstration of a multimode (two mode-group) erbium-doped fiber amplifier for Space Division Multiplexed (SDM) applications and demonstrate various design and performance features of such devices. In particular we experimentally demonstrate that differential modal gains can be controlled and reduced both by fiber design and control of the pump field distribution. Using a suitably designed fiber we demonstrate simultaneous modal gains of ~20 dB for different pair-wise combinations of spatial and polarization modes in an EDFA supporting amplification of 6 distinct modes.

320-Gb/s single-channel pseudolinear transmission over 200 km of nonzero-dispersion fiber

Single-channel transmission at 320 Gb/s is demonstrated over record length of 200 km of nonzero-dispersion fiber. Typical terrestrial amplifier spacing of 100 km is achieved by using pseudolinear transmission and distributed Raman amplification. Stable semiconductor electroabsorption modulators are used in the transmitter, demultiplexer, and clock recovery, and uncorrelated multiplexing is employed in the OTDM transmitter.

High spectral density long-haul 40-Gb/s transmission using CSRZ-DPSK format

This paper presents an experimental investigation of 40-Gb/s DWDM transmission technologies that can potentially transport multiple terabits of aggregate capacity with ultrahigh spectral efficiency over several thousand kilometers of fiber in a terrestrial optical network. By using carrier-suppressed return-to-zero (CSRZ) differential-phase-shift-keyed (DPSK) modulation format with optimized signal filtering, we have demonstrated transmission of 6.4-Tb/s capacity with 0.8-bit/s/Hz spectral efficiency over 3200 km of fiber using 100-km amplified spans. This transmission was conducted using 160 50-GHz-spaced wavelength channels, each at 42.7 Gb/s, in the standard C + L wavelength bands. Low dispersion-slope TrueWave REACH fiber plus slope-matched dispersion compensating fiber with all-Raman amplification were also employed to achieve this record 20-Pbit/s/km capacity-distance product for terrestrial 40-Gb/s systems. In addition, we used a loop-synchronous polarization controller (PC) to better emulate the polarization effects of a straight-line system.

Amplitude Regeneration of RZ-DPSK Signals in Single-Pump Fiber-Optic Parametric Amplifiers

The input power tolerance of a single-pump fiber-optic parametric amplifier (FOPA) is experimentally shown to be enhanced for return-to-zero differential phase-shift keying (RZ-DPSK) modulation compared to RZ on-off keying modulation at 40 Gb/s. The improved nonlinear tolerance is exploited to demonstrate amplitude regeneration of a distorted RZ-DPSK signal in a gain-saturated FOPA. An optical signal-to-noise ratio penalty of 3.5 dB after amplitude distortion is shown to be reduced to 0.2 dB after the FOPA, thus clearly demonstrating the regenerative nature of saturated FOPAs for RZ-DPSK modulation.

6.4-Tb/s (160 x 42.7 Gb/s) transmission with 0.8 bit/s/Hz spectral efficiency over 32 x 100 km of fiber using CSRZ-DPSK format

Carrier-suppressed, return-to-zero differential-phase-shift-keyed modulation format with strong signal filtering and balanced detection are employed to transmit one-hundred-sixty 40-Gb/s, 50-GHz-spaced channels over 3200 km of TrueWave REACH fiber, a record capacity x distance product of 20 Pbit/s-km for terrestrial 40-Gb/s systems.