Due to the lack of supply of wavelength division multiplexer components and emerging communications protocols, single- mode fiber coarse wavelength division multiplexers (WDMs), multimode fiber WDMs, and single-mode fiber dense WDMs are being considered in the metropolitan core and metropolitan access networks. This paper describes the evolving specifications for WDMs placed in metropolitan transport equipment. Comparisons of WDM components from various technologies such as arrayed waveguides, bulk grating, thin film filters, and fiber bragg gratings will be presented.

The ever-increasing demand for higher speed communications has led us to the dense wavelength multiplexing architecture and high-speed transmissions. Arrayed waveguide gratings (AWGs) have proven to be an important building block for high performance DWDM networks. In such high-speed applications, the dispersion of the AWG is a critical parameter. In this paper, we review the dispersion properties of AWGs based on its filtering properties. We also report the methods employed for measurement of chromatic dispersion and polarization mode dispersion in AWGs. In particular, we discuss the effect of different measurement parameters on the results, and ways to improve the accuracy. In conclusion, AWGs can offer low dispersion (chromatic dispersion < 15 ps/nm and differential group delay < 0.2 ps), which makes them highly suitable for high-speed applications.

In this paper, we first review the working principle of grating-base wavelength division (de)multiplexers (WD(D)M) for optical networks. Then key device parameters for WDM multiplexers, including insertion loss, isolation, channel passband, wavelength accuracy, polarization-dependent loss and temperature sensitivity are provided to evaluate the performance for the devices. After that, issues regarding optical design of grating-based WD(D)Ms for commercial uses are addressed. Next, several grating-based WD(D)M structures are analyzed with the procedures to optimize design of grating-based wavelength division (de)multiplexers. Based on these designs and analyses, we give the procedures of optimal design of devices with experimental data.

We construct a passive grating-based wavelength-division (de)multiplexer (MUX/DMUX) for single-mode-fiber networks. The MUX/DMUX has almost identical bi-directional filtering characteristics on optical signals at wavelengths around 1550 nm. With total insertion loss less than 3 dB and an enlarged passing band of each channel, the encapsulated device exhibits very stable performance under temperature variation and is immune from mechanical vibration. The insertion loss of this device changes about 1 dB at temperatures from 25 degree(s)C to 60 degree(s)C, while the enter wavelength of each channel drifts about 8.3 X 10^-4 nm/(nm(DOT) degree(s)C). Better results are expected with further optimization on the design. The device successfully demultiplexes 2³¹ -1 PRBS signals up to 3.5 Gb/s per channel in an emulated amplifier-free local- area networks (LAN's) and metropolitan-area networks transmission. It is plausible the cost-effective MUX/DEMUX is an excellent candidate to meet 10 Gb/s all-optical multi- wavelength short-link applications.

Both a 160-channel DWDM system integrating a 1 X 4 25-GHz nonlinear Fourier Filter Flat-top (F³T) interleaver with four 1 X 40 100-GHz AWGs and a 4-channel NWDM system were investigated for 10 Gbit/s transmission experiments.

DWDM networks consist of many densely packed wavelength channels propagating independently (and even bi- directionally) within the physical fibers making up a given system. The `virtual fibers' within a DWDM transport network, aside from providing higher bandwidth capability, are able to expand overall network flexibility as well as improve reliability. Bandwidth increase is satisfied by adding wavelength channels via increasing the density of channels and/or by expanding the spectral region for incorporating additional channels. The increased flexibility addresses complex and continuously varying topologies and the frequent need to flexibly add/drop channels and re- provision channels. Further, the incorporation of non- intrusive monitoring of all optical wavelengths s improves network reliability by enabling element control, improved network management, and predictive network failure capability.

We describe the design and performance of a multimode 8- channel, 200 GHz-spaced dense wavelength division demultiplexer using a high order blazed grating. The mean insertion loss of this DEMUX is 1.95 dB. Adjacent crosstalk is measured to be better than -45 dB. The temperature test cycling from 20 to 60 degree(s)C indicates that the wavelength thermal drift is less than 0.00033 nm/ degree(s)C. The device has multi-mode fibers for both input and output, which is good for the optical networks in both metropolitan and local areas. The device is not sensitive to the disturbance of temperature and environment, so no temperature controller is needed.

The central role of photonics in the new millennium, which has often been predicted is now becoming a reality. The Wavelength Division Multiplexing or the WDM revolution is upon us. Sprouting everywhere are the new technologies, companies and devices that keep, in this revolutionary internet era, information as photons for as many transfer operations as possible. The critical components that are poised to fuel the photonics explosion are already in view (see Figure 1).

In this paper a study of the design of wide area optical networks is presented, more specifically the problem of design of the virtual topology in optical networks. A network with a small number of nodes was analyzed through a Mixed-Integer Linear Programming formulation for the problem of the virtual topology design. Heuristic methods were then applied for a hypothetical optical network with a larger number of nodes plausibly located on the Brazilian territory. The work resulted in some suggested guidelines for the design of virtual topologies.

All-optical 2R regeneration and wavelength conversion is demonstrated in a simple SOA/DFB laser device. A regenerated Q factor improvement of 2.5 is reported.

Multiwavelength Optical Orthogonal Codes in optical CDMA networks were constructed by Yang and Kwong (1997) in which every pulse of a 2D code word (matrix) is enclosed in a distinct wavelength and it exhibits better bit error performance under heavy traffic load conditions. This system performance evaluation focused on the influences due to the multiple users interference alone, neglecting the negative effects of system noise. In this paper, a theoretical investigation is carrier out considering the effects of phase noise and relative intensity noise of laser source, modal noise in the multimode fiber channel, APD noise and receiver thermal noise, in addition to MUI, in direct- detection asynchronous fiber-optic CDMA communication system.

Research and engineering are underway for incorporating thermooptic waveguide elements into product-quality silica planar-lightwave circuits to enable dynamic functions such as switches and programmable attenuators as integrable components. One of the initial targets for this technology is to integrate an AWG dense wavelength multiplexer with an array of programmable variable optical attenuators in order to preset the spectral power distribution in a dense wavelength-division multiplexed channel.

A wavelength conversion experiment based on Bragg grating fiber external cavity laser at 2.5 Gb/s rate is introduced. The primary result of 5 nm up-conversion and clear eye diagram is obtained. The laser is sealed in common DIP-14 package. This method shows advantages of simplicity and stable converted wavelength.

Chromatic dispersion in optical fibers limits the transmission distance of high bit-rate optical communications systems. A virtually imaged phase array (VIPA) can perform chromatic dispersion compensation on multiple WDM channels simultaneously. A VIPA is generated by a tilted etalon with a perfectly reflective coating on one side and a partially transmissive coating on the other side. Light is focused into the etalon through an anti-reflection coated input/output window on the reflective side. The etalon produces large angular dispersion which is converted into chromatic dispersion using a lens and mirror. The insertion loss and bandwidth of the VIPA chromatic dispersion compensation system is governed by the shape of the etalon's transmissive coating. Numerical simulations evaluate the insertion loss and bandwidth of a VIPA chromatic dispersion compensator configured with three different transmissive coating designs. Overall, a 2-level coating is superior to both constant and linear coatings. The constant coating exhibits wide bandwidth but high insertion loss. The linear coating demonstrates low insertion loss but narrow bandwidth. The constant coating features both low insertion loss and wide bandwidth.

High concentration erbium-doped silica fibers were developed for amplification of L-band optical signals. Power conversion efficiency as a function of erbium-doping concentration for various erbium-doped silica fibers was analyzed and characterized at a wavelength of 1585 nm and at a pump wavelength of 1480 nm by using a two-stage amplifier and a C-band ASE filter. The experimental results are consistent with the simulation results. High Al doping and optimization of NA and erbium-doped region can help reduce the pair-induced quenching effects and improve the efficiency.

We propose a new design for introducing a tunable chirp on a uniform fiber Bragg grating by a controllable temperature gradient. The device consists of an unchirped Bragg grating in a bare fiber that is mounted in a plastic sleeve whose surface is coiled with a length of wire heater. The desired temperature distribution produces a chirp on the grating and at a rate that can be adjusted by varying the current. We have demonstrated an electrically tunable chirped sampled fiber Bragg grating that enables a tuning range of chirp rate up to 0.4 nm/cm with an electrical power of 3.3 W.

Compact integrated optical circuits for signal routing and signal processing are currently the subjects of much active research. Multimode interference (MMI) couplers are widely used as splitters and combiners since they possess the desirable attributes of small size, low excess loss, well- defined slitting, dimensional tolerance and ease of fabrication. Recently there has been renewed interest in employing MMI devices within Mach-Zehnder structures to achieve splitting and switching functions. However, the extent of the switching capabilities achieved so far has been quite limited. This paper highlights how the switching capabilities of these Mach-Zehnder switches can be extended and presents design techniques for this type of photonic switch.

A Dense Wavelength Division Multiplexing (DWDM) nonblocking OXC devices developed by us are presented in this paper. Some experimental results are shown and discussed.

A new technology invented at JPL of color filtering and beam scanning device based on electro-optical switching of internal-reflection states have been proposed for use in DWDM, display and measurement applications.

Single-mode waveguides based on planar silica have found increasing application in passive optical components such as arrayed waveguide gratings (AWG), couplers, and splitters. Key aspects of these devices are their low insertion losses and relative insensitivity to temperature. Planar polymer waveguides present a complementary technology that is finding deployment in thermally activated components such as thermo-optic switches, variable attenuators and tunable filters. This results from the large thermo-optic effects and low thermal conductivities in polymers that lead to low power, compact and rapid thermal activation.

A promising polarization-insensitive thermo-optic switch based on multi-mode polymeric waveguides is reported. This device has a packing density of 40 channels/cm. Simulation result shows that an extinction ratio of greater than 20 dB can be achieved with the device-electrode interaction length of 30 mm. The thermo-optic switch operating at wavelengths of 632.8 nm and 1.3 micrometers has been demonstrated experimentally with extinction ratios of 21 dB and 22 dB, respectively. Such a device has an intrinsic wide optical bandwidth due to the large dynamic range of the phase- matching condition implied by the multi-mode waveguides.

A new wavelength conversion technique using the amplified spontaneous emission of a semiconductor optical amplifier is proposed. The technique allows signals of a particular wavelength to be converted to many wavelengths simultaneously without the need of any probe laser. A 622 Mb/s one-to-six wavelength conversion system has been demonstrated over a bus network.

A novel single-fiber bi-directional optical add-drop multiplexer is proposed for wavelength division multiplexing distribution networks. It includes only two optical circulators and two sets of fiber Bragg grating, with advantages of passive, low insertion loss and cost- effective. Self-healing function can be provided passively to the distribution ring network with only one fiber. Very small degradation of bit-error-rate (power penalty < 0.1 dB) is observed when it is used for bi-directional add-drop and transmission.