Lih Y. Lin

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.

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.

High-power high-speed photodetectors-design, analysis, and experimental demonstration

A novel velocity-matched distributed photodetector (VMDP) is proposed to simultaneously achieve high saturation photocurrent and broad bandwidth. Theoretical analysis on the tradeoff between saturation power and bandwidth shows that the VMDP offers fundamental advantages over conventional photodetectors. A comprehensive theoretical model has been developed for the design and simulation of the VMDP. Experimentally, the VMDP with very high saturation (56-mA) photocurrent and instrument-limited 3-dB bandwidth (49 GHz) has been demonstrated. The theoretical analysis and experimental results show that the VMDP is very attractive for high-performance microwave photonic links and high-power optical microwave applications.

Velocity-matched distributed photodetectors with high-saturation power and large bandwidth

A high-power, high-bandwidth photodetector is experimentally demonstrated using a novel velocity-matched distributed photodetector (VMDP). The distributed photodetector structure can achieve large absorption volume and high-saturation power while maintaining the high-speed performance of the fast photodiodes. The VMDP with 56 mA saturation photocurrent and an instrument-limited 3-dB bandwidth of 49 GHz is achieved. The results show that VMDP is ideal for high-performance microwave fiber-optic links and high-power optical-microwave applications.

Micromachined free-space integrated micro-optics

Abstract The surface-micromachining technique has been employed to fabricate novel three-dimensional micro-optical elements for free-space integrated optics. The optical axes of these optical elements are parallel to the substrate, which enables the entire free-space optical system to be integrated on a single substrate. Microscale Fresnel lenses, mirrors, beam splitters, gratings, and precision optical mounts have been successfully fabricated and characterized. In addition, micropositioners such as rotary stages and linear translational stages are monolithically integrated with the optical components using the same surface-micromachining process to provide on-chip optical alignment or optomechanical switching. Self-aligned hybrid integration with semiconductor edge-emitting lasers and vertical cavity surface-emitting lasers are also demonstrated for the first time. This new free-space micro-optical bench (FSMOB) technology could significantly reduce the size, weight, and cost of most optical systems, and could have a significant impact on optical switching, optical sensing and optical data-storage systems as well as on the packaging of optoelectronic components.

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.

Out-of-plane refractive microlens fabricated by surface micromachining

A novel refractive microlens standing perpendicular to the substrate has been fabricated for the first time with surface-micromachining techniques. The microlens has a focal length of 670 /spl mu/m and a diameter of 300 /spl mu/m. The optical axis of the microlens is precisely defined by photolithography and can be pre-aligned to other surface-micromachined micro-optical elements integrated on the same substrate. The focusing and collimating abilities of the lens are successfully demonstrated. The refractive microlens offers higher efficiency compared with diffractive lenses, and is very useful for high-performance free-space micro-optical bench applications.

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.

Layered switch architectures for high-capacity optical transport networks

We propose and analyze layered switch architectures that possess high design flexibility, greatly reduced switch size, and high expandability. The improvement in loss and crosstalk due to the reduced switch size is also discussed. Theoretical models have been developed to compute the network blocking probability using these architectures. Low blocking probability and high network utilization are achieved because of the capability of communication between layers in adjacent switches. The results show that the proposed layered switch architectures are very attractive for high-capacity optical transport networks.

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.