E.L. Goldstein

Free-space micromachined optical switches for optical networking

Fiber-optic switches with high port count have emerged as leading candidates for deployment in future optical transport networks, where restoration and provisioning in the optical layer will become increasingly important. This paper reviews the principle and performance of free-space micromachined optical switches (FS-MOS) featuring free-rotating hinged micromirrors. A single-chip FS-MOS that implements the critical function of bridging-essential for restoration in core optical networks is also proposed and demonstrated. The scalability of FS-MOS devices, and the dependence of their insertion losses on mirror-angle, are estimated theoretically. Simulation results suggest that the FS-MOS approach holds considerable promise for being expandable to the port-count values that will be needed in future core-transport lightwave networks.

Performance implications of component crosstalk in transparent lightwave networks

We find both theoretically and experimentally that crosstalk due to small component imperfections in transparent lightwave networks will tend to generate large performance degradations. The most severe degradations, which arise from interference between signal and crosstalk electric fields, are far larger than those predicted from simple power-addition without field interference. Systems corrupted by crosstalk from a single source of optical-field leakage appear to require component crosstalk levels /spl epsiv//spl les/-20 dB, if conventional receivers are used. Since the degradations are believed to depend on N/spl radic//spl epsiv/, where N is the number of crosstalk generators, each producing a crosstalk power level of /spl epsiv/, the problem is expected to grow rapidly severe with network size.<<ETX>>

Free-space micromachined optical switches with submillisecond switching time for large-scale optical crossconnects

Optical crossconnects with large port counts are fast becoming critical components for high-capacity optical transport networks. The free-space micromachined optical switches (FS-MOS) demonstrated in this letter represent a means of filling this network need by combining the advantages of free-space interconnection with the virtues of integrated optics. Featuring free-rotating hinged micromirrors, the switch overcomes the common drawback of mechanical-type switches, namely long switching time. Measurements have revealed switching times less than 700 /spl mu/s, crosstalk less than -60 dB, extinction ratio greater than 60 dB, negligible polarization-dependent loss, and excellent bit-error-rate (BER) performance.

Scaling limitations in transparent optical networks due to low-level crosstalk

As transparent optical networks are scaled up in size, stringent constraints must be placed on the in-band crosstalk generated by their components. Measurements show that transparent networks corrupted by interferometric signal-crosstalk beat noise from only 8 crosstalk fields require component crosstalk levels <-35 dB. Good agreement with theory is shown.<<ETX>>

Opportunities and challenges for MEMS in lightwave communications

Over the remarkably short interval of just a few years, optical microelectromechanical systems (MEMS) have breached the gulf from laboratory curiosity to advanced development and early trial deployment in lightwave-communications systems. This owes largely to the ease with which the technology has demonstrated high optical quality and reasonably fast tuning and switching subsystems that are compact and potentially low in cost. Lightwave micromachines now threaten to make possible functional structures for building tunable lasers and filters, dynamic gain-equalizers, chromatic dispersion-compensators, wavelength-add-drop multiplexers, and polarization-controllers that represent substantial improvements over the conventional state of the art. More extravagant yet, both in promise and in expectations, is the potential of MEMS as a means of building the large-port-count optical switches that are just now becoming needed by emerging mesh-based core transport networks. In this paper, we review the current status and prospects for MEMS in lightwave communications, with particular emphasis on high-port-count core optical cross connects, and discuss challenges that still confront this technology.

On the expandability of free-space micromachined optical cross connects

Free-space micromachined optical-switching technology has emerged as a promising candidate for the large-scale optical cross connects that are needed in next-generation optical-transport networks. Although this technology has demonstrated good optical performance, its ability to expand to the required port-count while remaining within reasonable optical loss budgets has yet to be demonstrated. In this paper, we theoretically analyze the expandability of free-space micromachined optical switches. The chief loss mechanisms-Gaussian-beam divergence and angular misalignment-are analyzed both theoretically and experimentally. We find that micromirror angular repeatability in such a cross connect must be accurate within about 0.1/spl deg/, and show that integrated mechanical structures are capable of achieving this goal. These results in general suggest that free-space micromachined optical-switching technology appears capable of achieving the port-count required by core-transport networks while remaining within cross-office optical-loss budgets.

Fast wavelength-switching of laser transmitters and amplifiers

The authors discuss system aspects and describe experimental demonstrations of nanosecond wavelength tuning in laser diode structures. Both tunable transmitters and tunable filters are considered. The dependence of the refractive index on the carrier density in semiconductors is exploited to obtain fast wavelength tuning. Experimentally, switching times of >

High-density micromachined polygon optical crossconnects exploiting network connection-symmetry

Optical-layer crossconnects with high port count appear to be emerging as key elements for provisioning and restoration in future wavelength-division-multiplexed networks. We demonstrate here a means of achieving high-density optical crossconnects utilizing free-space micromachined optical switches that exploit connection-symmetry in core-transport networks. The micromachined polygon switches proposed here are strictly nonblocking. Measured insertion losses of 3.1-3.5 dB for a 16/spl times/16 (8/spl times/8 bidirectional) switch suggest the promise of scaling to large port count.

Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.

Micro-electro-mechanical systems (MEMS) for WDM optical-crossconnect networks

MEMS (micro-electro-mechanical systems) have shown promise for optical crossconnects in WDM networks. We describe various MEMS optical-switching technologies, their successes in implementing important optical-networking functionalities, and future perspectives.