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The linewidth of external cavity diode lasers (ECDLs) is an increasingly important characteristic for experiments in coherent optical communications and atomic physics. The Schawlow--Townes and time-averaged linewidths depend on free parameters of the design, such as cavity length, power, and grating characteristics. We show that the linewidth is also sensitive to the focus, set by the distance between the laser and the collimating lens, due to the effect on the external cavity backcoupling efficiency. By considering these factors, a simple ECDL can readily achieve linewidths below 100kH. [c] 2009 Optical Society of America OCIS codes: 140.2020, 140.3410, 140.3600.

Efficient coupling of coherent plane waves into single-mode fibers is a key technology for free-space optical communication at 1550 nm. Here we deal with the influence of random angular jitter on a plane wave to single-mode fiber coupling. The expression of mean-coupling efficiency in the presence of random jitter is handled in the pupil plane. First, an analytical expression of the mean-coupling efficiency is derived for the zero bias error case. Then the bias error was taken into account. By minimizing the coupling efficiency penalty, the optimum value of design parameter [beta] of fiber-coupled optical systems in the presence of random jitter is obtained. The results obtained here will be useful in facilitating parametric estimation and optimization of fiber-coupled optical systems. OCIS codes: 060.2310, 060.4510, 010.3310.

A high-speed low-complexity Reed--Solomon (RS) decoder architecture based on the recursive degree computationless modified Euclidean (rDCME) algorithm is presented in this brief. The proposed architecture has very low hardware complexity compared with the conventional modified Euclidean and degree computationless modified Euclidean (DCME) architectures, since it can reduce the degree computation circuitry and replace the conventional systolic architecture that uses many processing elements (PEs) with a recursive architecture using a single PE. A high-throughput data rate is also facilitated by employing a pipelining technique. The proposed rDCME architecture has been designed and implemented using SMIC 0.18-[micro]m CMOS technology. Synthesized results show that the proposed RS (255, 239) decoder requires only about 18K gates and can operate at 640 MHz to achieve a throughput of 5.1 Gb/s, which meets the requirement of modern high-speed optical communications. Index Terms--Degree computationless, error-correction codes, modified Euclidean (ME) algorithm, optical communications, recursive, Reed--Solomon (RS) decoder.

The optical constants [beta], [delta] of the complex refractive index ([??] = 1 [delta] + i[beta]) of Dy were obtained in the 2-830 eV energy range using a novel transmittance method. Si/W/Dy/W films were deposited by dc-magnetron sputtering on Si photodiode substrates, and the transmittance was characterized using synchrotron radiation. The extinction coefficients [beta] of Dy and the transmittance of a Si capping layer and two W interface barrier layers as functions of energy were solved simultaneously using a nonlinear optimization routine. The measured transmittances of the capping and barrier layers were primarily used as indicators for any flaws in the transmittance results. The dispersion coefficients [delta] of Dy were calculated using the Kramers--Kronig integral, and a complete set of [beta] values required for this integral was obtained by combining the present data with data from the literature. Sum rule tests on Dy show some deficiencies in the present data, which may be attributed to lower film density compared with the bulk value. Similar procedures were applied to previously measured transmittances of [B.sub.4]C/La, Si/Tb, Si/ Nd, and Si/Gd films, where [B.sub.4]C or Si were used as capping layers on those reactive rare-earth films. The improved sets of transmittance values of [B.sub.4]C and Si capping layers were used as input in the optimization routine to solve for more accurate [beta] values of La, Tb, Nd, and Gd. The revised optical constants of these materials, tested for consistency with partial sum rules, are also reported. of America OCIS codes: 310.6860, 340.7480.

Time-average TV holography is widely used method for vibration measurement. The method generates speckle correlation time-averaged [J.sub.0] fringes that can be used for full-field qualitative visualization of mode shapes at resonant frequencies of an object under harmonic excitation. In order to map the amplitudes of vibration, quantitative evaluation of the time-averaged fringe pattern is desired. A quantitative evaluation procedure based on the phase-shifting technique used in two beam interferometry has also been adopted for this application with some modification. The existing procedure requires a large number of frames to be recorded for implementation. We propose a procedure that will reduce the number of frames required for the analysis. The TV holographic system used and the experimental results obtained with it on an edge-clamped, sinusoidally excited square aluminium plate sample are discussed. OCIS codes: 120.3940, 120.6165, 120.5060, 120.5050, 120.2650, 120.7280.

This paper introduces the dynamic spot diffusing (DSD) configuration for high-speed indoor wireless optical communications. In this configuration, data are modulated onto a moving spot which is translated over the ceiling. A multi-element imaging receiver is pointed upward and acquires data whenever the transmitter spot is in its field-of-view (FOV). We develop expressions for the channel capacity of such DSD links and discuss design techniques to maximize these information theoretic bounds. Rather than tracking the transmitter spot, we apply rateless erasure correcting codes to approach the capacity of the simulated DSD links. This technique is demonstrated to have better flexibility, greater multipath immunity, higher data rates and simpler transmitters than previously defined multi-spot and diffuse architectures. In a 6 x 6 x 3 m room, simulated data rates vary between 7 Mbps to 25 Mbps at different positions using a single 100 Mbps transmitter and between 35 Mbps to 84 Mbps using 6 spots and the designed erasure correction code. Using power efficient modulation and power gain due to the spot motion of the DSD system, proportionally higher rates are estimated when faster 1 Gbps and 10 Gbps transmitters are employed. Index Terms--Wireless infrared channel, indoor diffuse infrared communication, optical intensity modulation, spot diffusing architecture.

In optical burst switched (OBS) networks, the queueing delay in ingress edge node is an important performance measure. In this paper, we propose a deterministic delay model and derive the upper bound of the burst queueing delay in an edge node. On this basis, the edge-to-edge delay guarantee framework for premium services is further outlined. Index Terms--Optical burst switching, deterministic QoS, delay analysis.

A modified dilated Benes network composed of directional couplers is proposed. This structure is introduced to improve the signal-to-noise ratio (SNR) characteristics of dilated Benes networks. A new estimation of the SNR for dilated Benes networks is derived, and it is shown that this SNR is much worse than that previously known. The SNR for modified dilated Benes networks is estimated and compared to dilated Benes and other network architectures. Some other properties including the number of switching elements required, number of crossovers, and system attenuation are also derived and analyzed. Most of the characteristics are shown to be similar to dilated Benes networks and better than those of other well-known networks fabricated in Ti: LiNb[O.sub.3]. Index Terms - Communications switching, directional couplers, photonic switching networks.

In this paper, we study the use of multiuser detection and blind detection techniques to improve the performance of optical code-division multiple-access (OCDMA) systems. First, a new multiuser receiver known as the interference suppression receiver is proposed. Second, we study the use of blind detection by proposing a blind receiver for OCDMA systems. While previous studies on multiuser detection are limited to systems with p-i-n detectors, avalanche photodiode detectors are also included here. Index Terms - Avalanche photodiode detectors, code division multiple access, multiple-access interference, multiuser detection, optical communications.

All-optical communication requires all-optical interconnections, thus leading to reliable, fast, and flexible modular communication means in future systems. Free-space approaches are advantageous since they fully use the two dimensions optics offer. A folded architecture based on a polarization code is proposed for dynamic optical interconnection. The suggested systems are compact and appropriate for both intracomputer and intercomputer communication. The modularity of the proposed architecture is presented, and a growth rule for the fully connected versions of the system is introduced. The proposed approach significantly reduces both the price of the interconnection systems and their complexity. Presented are 4 x 4 and 8 x 8 fully connected switches, a rearrangeable nonblocking 4 x 4 switch, and a crossbar architecture.

Ultralong distance soliton transmission is effected by soliton transmission control techniques in time and frequency domains. Synchronous modulation is used in the realization of soliton transmission control in the time domain. This is a re-timing technique, and eliminates jitter and nonlinear interaction between adjacent solitons. The soliton pulse is stabilized by soliton transmission control in the frequency domain. This can be realized only by the use of a band pass optical fiber.

In this paper, we examine the use of differential pulse-position modulation (DPPM) for optical communication systems using intensity modulation with direct detection in the presence of additive white Gaussian noise. We present expressions for the error probability and power spectral density of DPPM. We show that for a given bandwidth, DPPM requires significantly less average power than pulse-position modulation (PPM). We also examine the performance of DPPM in the presence of multipath intersymbol interference (ISI). We find that the ISI penalties incurred by PPM and DPPM exhibit very similar dependencies upon the channel rms delay spread. We discuss the use of chip-rate and multichip-rate equalization to combat ISI. Finally, we describe potential problems caused by the nonuniform bit-rate characteristic of DPPM, and we propose several solutions. Index Terms - Differential pulse-position modulation, intensity modulation, wireless optical communication.