An optical dynamic-gain equalizer (DGE) for dense wave-division multiplexing (DWDM) communication systems sets unprecedented performance levels for precision, dynamic range, and reliability. This product, essentially a seamless one-dimensional array of variable optical attenuators (VOAs), is the first such device to employ diffractive microelectromechanical system (MEMS) technology with ultra high-spectral resolution. Its maker, Silicon Light Machines, a subsidiary of Cypress Semiconductor Corp., uses a patented MEMS Grating Light-Valve (GLV) technology developed at Stanford University in California, and now optimized for telecommunications ap-plications.
Essentially, a GLV is a diffraction-type spatial light modulator that's fabricated in a standard CMOS fabrication facility. The model 2200 DGE delivers power accuracy, or residual ripple of ±0.1 dB, with a minimum attenuation step of 1.0 ms. This allows system designers to very accurately attenuate optical power levels and squeeze out any ripple.
Conventional DGEs use a variety of technologies for tight power-level control. Acousto-optic, liquid-crystal, Faraday rotator filter, waveguide, and thermo-optic methods deliver roughly ±0.3 to ±0.5 dB of optical residual ripple. In DWDM systems, subscribers are added or dropped on demand via add/drop multiplexers. Subsequently, power spectrum shapes can change. So, there's a crucial need to save every bit of power gain to flatten out the power signal as much as possible. Even a fraction of a decibel can make a big difference.
Traditionally, gain flattening was done with static devices. Every additional communication channel that's used affects the shape of the power spectrum. These issues are magnified in dynamically changing DWDM systems.
This is where the model 2200 shines. Designed for C-band operation in the 1550-nm spectral region, it independently attenuates optical power over multiple spectral regions, using a single dynamic module instead of a static approach. Future versions are being considered for operation in the L and S bands.
The 2200 is really a subsystem made up of the drive electronics on a board, an optics module that contains the GLV device, and an optical circulator (Fig. 1). This subsystem fits at the mid-stage of a user's gain block--all monitored optically by an external device. Such a setup provides a low-cost-per-channel solution for high-channel-count systems. The DGE's spectral seamlessness means that it's agnostic to channel count.
Aimed at optical system suppliers like Ciena, Lucent Technologies, Nortel, and Alcatel for long-haul and ultra-long-haul communication systems, the 2200 delivers a dynamic range of more than 15 dB. Other impressive specifications of the model 2200 include spectral power ripple within ±0.1 dB, a correction slope of more than 4 dB/nm, less than 6 dB of excess insertion loss, less than 0.25 dB of polarization-dependent loss, and -40 dB of return loss. Equalization time is under 1.0 ms (Fig. 2).
The subsystem dissipates less than 5 W of power and complies with Telecordia's GR-1221 specifications (GR-63 for the control electronics). Moreover, it's designed to operate over a temperature range of -5°C to 70°C.