S.B. Poole

Highly programmable wavelength selective switch based on liquid crystal on silicon switching elements

We present a novel wavelength selective switch (WSS) based on a liquid crystal on silicon (LCOS) switching element. The unit operates simultaneously at both 50 and 100 GHz channel spacing and is compatible with 40 G transmission requirements.

Dispersion Trimming in a Reconfigurable Wavelength Selective Switch

We experimentally demonstrate dispersion compensation in a wavelength selective switch, and characterize the bandwidth-dispersion product. At a channel bit-rate of 80 Gbit/s, we compensate for various amounts of dispersion (up to ±60 ps/nm), tunable for each wavelength division multiplexed channel, solely by adjusting the phase front of the optical signal inside the wavelength selective switch. Error-free operation is obtained for all of the channels, and for each output port after propagation over various lengths of dispersive fiber.

Pump excited-state absorption in erbium-doped fibers

Ground-state and excited-state absorption spectra covering the wavelength range of 450-1050 nm are presented for erbium-doped silica fibers with four different core codopants: GeO(2), GeO(2)/B(2)O(3), GeO(2) /P(2)O(5), and Al(2)O(3). It is shown that the host glass influences the excited-state absorption spectra and that P(2)O(5)- or A1(2)O(3)-codoped fibers are the preferred choice for 514.5-, 655-, or 807-nm pump wavelengths owing to reduced pump excited-state absorption. However, excited-state absorption is still significant at the 807-nm wavelength. Pump wavelengths of 524, 532, and 980 nm appear ideal because of the strong ground-state absorption and lack of excited-state absorption.

Tunable single-mode fiber lasers

Tunable laser action has been obtained in Nd3+- and Er3+-doped single-mode fiber lasers. In the case of the Nd3+-doped fiber, an extensive tuning range of 80 nm has been achieved. Tunable CW lasing also has been observed for the first time in an Er3+-doped fiber laser, which has an overall tuning range of 25 nm in the region of \lambda = 1.54 /mu m.

Fabrication and characterization of low-loss optical fibers containing rare-earth ions

Low-loss fibers containing rare-earths have been produced with high absorption levels in the visible and near infrared regions. Although containing relatively large quantities of rare-earth impurity dopants, the fibers possess low-loss windows where the attenuation is similar to that observed in undoped fibers. This attribute makes the fibers attractive for use in long distributed sensors, as well as low-threshold fiber lasers. Fiber characteristics relevant to these two applications are uniformity of dopant incorporation, absorption and fluorescence spectra, and fluorescence lifetime. These measurements are presented, together with their respective temperature dependences. The fiber fabrication method is described and results given for Nd3+-, Er3+-, and Tb3+-doped fibers.

Er/sup 3+/-Yb/sup 3+/ and Er/sup 3+/ doped fiber lasers

Single-mode fiber lasers operating at approximately 1.57 mu m are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er/sup 3+/ and Yb/sup 3+/) and erbium on its own. The performance of Er/sup 3+/-Yb/sup 3+/ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 mu m are available from diode pumped Er/sup 3+/-Yb/sup 3+/ systems. >

Spectral modeling of channel band shapes in wavelength selective switches

A model for characterizing the spectral response of the passband of Wavelength Selective Switches (WSS) is presented. We demonstrate that, in contrast to the commonly used supergaussian model, the presented model offers a more complete match to measured results, as it is based on the physical operation of the optical system. We also demonstrate that this model is better suited for calculation of WSS channel bandwidths, as well as predicting the final bandwidth of cascaded WSS modules. Finally, we show the utility of this model in predicting channel shapes in flexible bandwidth WSS channel plans.

Wavelength-Selective Reconfiguration in Transparent Agile Optical Networks

The development of wavelength-selective switching (WSS) technologies is enabling the next generation of transparent optical networks, with remote reconfiguration of the mesh network providing optimal network utilization. Whereas first generations of networks were based on the ITU-defined fixed 50/100-GHz grids, true spectral transparency becomes possible with the introduction of Flexible Grid (FG) wavelength switching within the mesh network. Optical architectures that support the addition and dropping at any node of bandwidth-variable channels will allow optimal spectral utilization in transmission of legacy and next-generation transmission formats.

High performance `Drop and Continue' functionality in a Wavelength Selective Switch

We demonstrate for the first time channel-selective optical power sharing between a designated express-port and any drop-port of a 1×9 50 Channel WSS. Bit-Error Rate testing shows that this drop- and-continue functionality can be implemented with negligible system penalty.

Characterization of special fibers and fiber devices

Methods for characterizing birefringent fibers (both those with high circular or linear birefringence and those with negligible intrinsic birefringence) are presented, and their relative merits are discussed. Fibers with high nonlinear coefficients exhibit interesting optical phenomena, and methods are developed to determine second harmonic, Pockels and Kerr effects, parametric phenomena, and the Verdet constant of silica and higher-loss, nonsilica fibers. Fibers containing rare-earth ions are of interest both as active (laser and amplifiers) and passive systems. Techniques are developed to characterize these devices, and conventional methods are modified to quantify dopant parameters within the fiber. Techniques for the measurement of the diverse properties of all these different fibers are presented with results, and, where appropriate, the problems with their characterization are discussed. >