Leda M. Lunardi

Tunable dispersion compensation at 40-Gb/s using a multicavity etalon all-pass filter with NRZ, RZ, and CS-RZ modulation

We present a multichannel tunable dispersion compensator (TDC) based on multicavity all-pass etalons that is capable of operation at 40 Gb/s. The device has a tuning range of +200/-220 ps/nm with a group delay ripple < /spl plusmn/5 ps over a channel bandwidth of 80 GHz, an overall loss of < 5.2 dB, very low insertion loss ripple, and can operate on any channel on a 200-GHz grid over the C-band. In addition, we present system performance results at 40 Gb/s using NRZ, RZ, and CS-RZ modulation, compensating up to 45 km of nonzero dispersion shifted fiber (NZDSF). Our results show that this device introduces very little excess system penalty with signal frequency drifts of up to 20 GHz when operated near the center of its tuning range. For single channel experiments with fiber, the system penalty increase versus signal detuning is more significant, but can be reduced by dynamically optimizing the device dispersion during detuning. Finally, we demonstrate simultaneous compensation of 4 channels across the C-band over 25 km of NZDSF.

Advanced components and sub-system solutions for 40 Gb/s transmission

With the commissioning of the latest 10-Gb/s systems, vendors are now in the process of developing architectures for their next-generation products. 40-Gb/s components and subsystems are currently in development to address the necessities of these next-generation systems. The top three challenges associated with 40-Gb/s transmission are optical signal-to-noise ratio, dispersion, and high-speed components. In order to realize 40-Gb/s transmission, new component and subsystem developments are crucial. This paper reviews the latest transmission technologies and dispersion compensation techniques developed to fulfill 40-Gb/s transmission system requirements.

40 nm broadband SOA-Raman hybrid amplifier

A hybrid SOA-Raman amplifier scheme with over 40 nm operational bandwidth has been demonstrated. This novel and simple configuration can significantly increase span length and optical signal-to-noise ratio. Q-factors are measured to optimize the operating condition for the two schemes. The performance is related to crosstalk in SOA and overall OSNR.

Bi-directionally pumped broadband Raman amplifier

A two-wavelength bi-directional Raman pump scheme is proposed and tested. Gain flatness of better than 1.5 dB over the C-band was achieved. The new schemes improved signal-to-noise ratio and no noticeable BER penalty due to pump-signal crosstalk was observed.

Tunable dispersion compensation at 10 Gb/s and 40 Gb/s using multicavity all-pass etalons

Our tunable dispersion compensator devices based on multiple cavity all-pass etalons are designed to compensate all channels throughout the C- and L-bands and appropriate for 10 Gb/s and 40 Gb/s applications. Detailed characterization of devices and system experimental results will be presented.

Optimization of Operating Conditions of Semiconductro Optical amplifier for Single Wavelength and WDM Applications

We studied saturation behavior of semiconductor optical amplifier (SOA) and its impact on amplifier performance. Optimal operating conditions of SOA in both single channel and WDM applications were explored.

10-Gbit/s RZ pulses using an all-silicon nonlinear transmission line integrated circuit

We demonstrate 25 ps wide electrical pulses using a nonlinear transmission line (NLTL) integrated circuit fabricated on high-resistivity silicon. These pulses are modulated electrically and used to drive a LiNbO/sub 3/ Mach-Zehnder modulator to create optical 10 Gbit/s RZ data with 27 ps pulse width.

Semiconductor devices for fiber optic communication systems

We review the state-of-the-art of heterojunction-based integrated circuit technologies that have potential applications for time division multiplexing (TDM) and wavelength division multiplexing (WDM) fiber optic communication systems.

Raman tilt and nonideal tilt control function of C-band erbium-doped fiber amplifiers

Due to stimulated Raman scattering, shorter wavelength channels will pump longer wavelength channels, and so transfer their energy to longer wavelength channels. A tilt occurs when a flat DWDM signals travel through transmission fiber. We characterized the Raman tilt for 100 km SSMF and LEAF fiber at composite input powers ranging from 13 dBm to 22 dBm with a 40-channel laser source with 100 GHz spacing. Raman tilt with different fiber length at different composite launch power for SSMF is fully studied. In order to compensate the positive Raman gain tilt generated in the transmission fiber, a negative tilt is required. A tilt control function is available in some EDFAs. The mechanism of this tilt control is to use a tunable attenuator to change the internal loss of the amplifier. Unfortunately, the negatively tilted gain spectrum achieved by this mechanism is not a straight line. From the simulation result, the tilted gain curve actually can be regarded as two straight lines with a junction at about 1538 nm in good approximation. By combining the Raman output spectrum with the EDFA output spectrum, tilt is eliminated, but a non-flat spectral shape is generated with a dip at 1538 nm. This combined spectral shape agrees quite well with the measured spectral shape in actual system. This study reveals imperfection with this tilt compensation mechanism. A new tilt compensation solution is proposed and tested. Test results shown significant flatness improvement.

Challenges in component testing for optical systems

We discuss several examples that have been obtained from testing components in system-like conditions from our point of view as a component maker. First, we examine the conventional bidirectional transmission using interleaved signals for two directions within same band. One advantage of the bidirectional interleaving transmission, over separate band bidirectional transmission is the reduction of the four wave mixing phenomenon, which occurs between narrowly spaced copropagating adjacent channels, and is mitigated due to the copropagating channel space doubling. In both uni- and bidirectional cases, separate paths and amplifiers for the traffic in the two directions are used at the amplification nodes. This, in turn, is not cost effective, and if not properly filtered could easily form a loop for Rayleigh backscattering. This limitation is almost entirely removed with the development of a birefringent interleaver filter, which can be combined with a non-reciprocal birefringent filter to deliver near-complete blockage of backreflected channels. The resulting components (i.e., bidirectional isolator, bidirectional circulator, four-port interleaver) enable the use of standard unidirectional optical components to create bidirectional networks that deliver twice the spectral efficiency of unidirectional networks. We also illustrate some of the technical challenges that face the designer of 40 Gbit/s systems but can only be overcome with new types of components, such as tunable dispersion compensators and low dispersion components.