Torben N. Nielsen

Integrated tunable fiber gratings for dispersion management in high-bit rate systems

Dispersion management is becoming paramount in high-speed wavelength-division-multiplexed lightwave systems, that operate at per-channel rates of 40 Gb/s and higher. The dispersion tolerances, in these systems, are small enough that sources of dispersion variation, that are negligible in slower systems, become critically important to network performance. At these high-bit rates, active dispersion compensation modules may be required to respond dynamically to changes occurring in the network, such as variations in the per-channel power, reconfigurations of the channels path that are caused by add-drop operations, and environmental changes, such as changes in ambient temperature. We present a comprehensive discussion of an emerging tunable dispersion compensating device, based on thermally actuated fiber gratings. These per-channel devices rely on a distributed on-fiber thin film heater, deposited onto the outer surface of a fiber Bragg grating. Current flowing through the thin film generates resistive heating at rates that are governed by the thickness profile of the metal film. A chirp in the grating is obtained by using a thin-film, whose thickness varies with position along the length of the grating in a prescribed manner; the chirp rate is adjusted by varying the applied current. The paper reviews some of the basic characteristics of these devices and their implementation, in a range of different applications, including the mitigation of power penalties associated with optical power variations. We present detailed analysis of the impact of group-delay ripple and polarization-mode dispersion on systems performance, and present results from systems experiments, that demonstrate the performance of these devices at bit rates of 10, 20, 40 and 160 Gb/s. We also discuss advantages and disadvantages of this technology, and compare to other devices.

Tunable dispersion compensation in a 160-Gb/s TDM system by a voltage controlled chirped fiber Bragg grating

We demonstrate for the first time a device that enables practical dispersion management of a 160-Gb/s time-division multiplexer system (return-to-zero duty cycle: 30%). The dynamic dispersion is provided by an integrated chirp-tunable Bragg grating which is capable of recovering 2-ps pulses over a tuning range of 50 ps/nm with system power penalty less than 1.3 dB.

OFC 2004 workshop on optical and electronic mitigation of impairments

This paper provides an overview of OFC 2004 Workshop on Optical and Electronic Mitigation of Impairments from the perspective of the invited speakers. The workshop was held on February 23, 2004.

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.

Optoelectronic phase-locked loop with balanced photodetection for clock recovery in high-speed optical time-division-multiplexed systems

An optoelectronic phase-locked loop (PLL) for clock recovery in high-speed optical time-division-multiplexed (OTDM) systems is proposed and experimentally demonstrated. The proposed scheme incorporates a pair of balanced photodetector through which the polarity ambiguity in error signal is resolved, and the cancellation of laser noise enables clock recovery with low timing jitter. Using an electroabsorption modulator as a phase detector, a 10-GHz clock signal with root-mean-square (rms) timing jitter of 300 fs is successfully extracted from 40 and 80 Gb/s return-to-zero (RZ) data stream. A 40- to 10-Gb/s demultiplexing is performed by using the recovered clock signal with no penalty introduced in the bit error rate performance.

320 Gbit/s single-channel pseudo-linear transmission over 200 km of nonzero-dispersion fiber

Single-channel transmission at 320 Gbit/s is demonstrated over record length of 200 km (2/spl times/100 km) of nonzero-dispersion fiber. Semiconductor based transmitter, demultiplexer and clock recovery is employed as well as uncorrelated multiplexing in the transmitter.

All-fiber active add-drop wavelength router

We describe a fiber Bragg grating Mach-Zehnder interferometer (FBG-MZI) which utilizes active phase control. The active FBG-MZI is operated as a wavelength router, where the grating-selected wavelength channel can be actively routed. We believe this is the first demonstration of an all fibre FBG-MZI wavelength router.

Electrically tunable power efficient dispersion compensating fiber Bragg gratings for dynamic operation in nonlinear lightwave systems

We demonstrate a power efficient (<0.5 W) tunable dispersion compensating fiber Bragg grating device and show for the first time dynamic optimization of dispersion in a nonlinear lightwave system. Operation is demonstrated in a 20 Gbit/s single channel NRZ system where the device was used to adjust the dispersion to the power-dependent optimal dispersion required for optimum performance.

Dense wavelength-division multiplexed transmission in "zero-dispersion" DSF by means of hybrid Raman/erbium-doped fiber amplifiers

Transmission of 25 and 50 equally 100-GHz and 50-GHz spaced 10-Gb/s (OC-192) channels on the ITU grids is demonstrated over eight and four 83.8-km long spans, respectively, of DSF with the zero-dispersion wavelength within the signal wavelength band. Significant performance improvements are obtained with a pump power of only 440 mW with 55-/spl mu/m/sup 2/ dispersion-shifted fibers because of their relatively high Raman efficiency.

Integrated planar waveguide amplifier with 15 dB net gain at 1550 nm

A packaged Er-doped aluminosilicate planar optical waveguide amplifier (POWA) has shown net gain of 15 dB (22 dB) at 1550 nm (1532 nm) with 150 mW/980 nm pump. Low loss (0.25 dB) mode converters that couple between the POWA and standard P-glass waveguides are also demonstrated.