D.T.K. Tong

Experimental demonstration of bipolar optical CDMA system using a balanced transmitter and complementary spectral encoding

We demonstrate a novel balanced differential optical transmitter for spectrally encoded optical code-division multiple-access (CDMA) systems. The proposed structure is suitable for making optical signaling bipolar using complementary spectral encoding. An optical CDMA link with a pair of programmable transmitter and receiver is tested at the OC-3 transmission speed (155 Mb/s) for single-channel transmission. Unmatched code rejection is also demonstrated.

Multiwavelength optically controlled phased-array antennas

A novel multiwavelength scheme is proposed and demonstrated for one-dimensional (1-D) and two-dimensional (2-D) optically controlled phased-array antenna (OCPAA) systems with true time delay (TTD). This hardware-compressive architecture employs a multiwavelength laser source in conjunction with a programmable dispersion matrix (PDM) and switched optical delay lines (SODLs) to generate all the required time delays for beam steering in 2-D phased-array antenna systems. Independent control of elevation and azimuthal scan is achieved by combining wavelength-dependent and wavelength-independent time delays. An experimental prototype of 4/spl times/2 array with 2-b/spl times/2-b resolution is constructed to demonstrate the feasibility of the multiwavelength OCPPA (MWOCPAA). Broadband linear RF phase shift is measured in both elevation and azimuthal planes over the entire bandwidth of the electro-optic (EO) modulator. System issues such as insertion loss, array size, and channel isolation are discussed. Extension of the multiwavelength scheme to a common transmit/receive (T/R) module with TTD is also described.

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.

Modular MEMS-based optical cross-connect with large port-count

We describe and demonstrate a modular microelectromechanical systems (MEMS)-based optical cross-connect (OXC) architecture. The OXC port count increases modularly by adding new optical modules, and a maximum cross-connectivity of /spl sim/ 350 /spl times/ 350 can be achieved in the current design. Each optical module has 16 ports with closed-loop servo-controlled MEMS mirrors. Using a prototype OXC system, mounted in a standard telecommunications equipment bay comprising optical modules, folding mirrors, and other optical elements, we demonstrate switching times of less than 10 ms, excellent optical power stability of less than /spl plusmn/ 0.15-dB variation, and immunity to stochastic vibrations. An automatic power peak-up process is performed when the power falls below 0.5-dB off the maximum coupled power for any connection.

CW injection locking of a mode-locked semiconductor laser as a local oscillator comb for channelizing broad-band RF signals

CW injection locking of mode-locked semiconductor lasers has been experimentally demonstrated. The phases of the mode-locked frequency comb are shown to be coherent with that of the master CW laser. The pulsewidth of the mode-locked laser remains almost unchanged (<2 ps) for a broad range of injection power (-28 to -12 dBm). Pulling of the entire mode-locked frequency comb by 400 MHz has been demonstrated. The coherent multifrequency source can be used as a local oscillator comb for coherent optical channelizers for ultrawide-band RF signals.

Transmit/receive module of multiwavelength optically controlled phased-array antennas

We report on a transmit/receive module of multiwavelength optically controlled phased-array antennas. Both transmit and receive mode of the module employs a single programmable dispersion matrix to provide true time delays for all antenna elements. The multiwavelength receiver combines antenna signals in the optical domain without suffering from coherent interference. Therefore, squint-free receiver over a broad frequency band can be achieved. Experimentally, squint-free beam receiving with 2-b scan angle resolution is demonstrated over an equipment-limited frequency range from dc to 4 GHz.

Two-dimensional symmetric multimode interferences in silicon square waveguides

Symmetric interference in two-dimensional multimode silicon waveguides is experimentally investigated. For a 100/spl times/100 /spl mu/m/sup 2/ cross section, 2700-/spl mu/m-long waveguide fabricated on silicon-on-insulator substrate, an 8/spl times/8 matrix of replicated images with high contrast ratio is demonstrated for 1530-1570 nm wavelength range. Symmetric interference results in reduced device length, and the actual device length is consistent with the theoretical expectation. The device also exhibits stable imaging in terms of good loss uniformity, and low wavelength and polarization dependencies among the replicated images.

Demonstration of an analog fiber-optic link employing a directly modulated semiconductor laser with external light injection

We demonstrate an analog fiber-optic link employing a directly modulated semiconductor distributed-feedback (DFB) laser under optical injection locking. The results show that injection locking can significantly improve performances of analog fiber-optic systems at frequencies considerably beyond the bandwidth of free-running semiconductor lasers.

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.We demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in a free space optical cross-connect with switching times of less than 10 ms, and optical power stability of better than 0.2 dB.

Experimental demonstration of spectrally encoded optical CDMA systems using Mach-Zehnder encoder chains

Summary form only given. Recently, there has been tremendous interest in applying spread spectrum and code division multiple access (CDMA) techniques in optical fiber communication systems. Contrary to radio CDMA systems, which employs electric-field encoding and correlation to achieve orthogonality, most of the optical communication systems use intensity modulation and direct detection. To achieve true orthogonality in optical CDMA systems, the balanced detection scheme and spectral intensity coding need to be used. We shows the block diagram of the bipolar spectrally encoded CDMA system. The transmitter consists of a pair of broadband optical sources connected in a balanced fashion. The input data differentially modulate the intensity of the two balanced sources.