We describe a nonlinearly chirped fiber Bragg grating (FBG) based multichannel device that can perform tunable chromatic dispersion compensation. Complex or phase only sampling allows a single grating to operate on multiple DWDM channels. Various key performance parameters are discussed.

SMP^TM technology is described that intelligently uses the spatial nature of light to form fiber-optic components and modules that provide fault-tolerance and improved optical signal setting speeds.

Wireless communications are rapidly becoming the means of data and information transfer for a broad range of applications. As wireless communication applications continue to expand, the information transfer rates are evolving toward the Gigabit per second data rate and, for some applications, there is even a need for terabit per second data rate transfer in the wireless network. In addition, wireless terminals often require instantaneous switching and communications between network members. For most applications directional antennas are needed to support the high data throughput requirements, and phased array antennas are the only high gain, directional antennas that can be rapidly switched to provide instantaneous communications among network members scattered geographically. Wireless terminal equipment is currently designed to operate in the 1 to 60 GHz frequency range and, traditionally, these equipment are designed with RF hardware. More recently, optics technology has been demonstrated to play an important role in RF systems as the True-Time-Delay in the phased array antenna, and, for some systems operating at high data rates, optical interconnects at the baseband level require E-O and O-E conversions. This paper discusses the considerations in using optics technology in the design of the wireless terminal network including optical signal processing, optical backplanes, optical networking, optical interconnects, and optical components. This paper also describes the architecture of an RF wireless communications network using a range of optical technologies.

This paper considers dynamical transient effects in the physical layer of an optical circuit-switched WDM network. These transients of the average transmission power have millisecond time scales. Instead of studying detailed nonlinear dynamics of the network elements, such as optical line amplifiers, a linearized model of the dynamics around a given steady state is considered. System-level analysis in this paper uses modern control theory methods and handles nonlinearity as uncertainty. The analysis translates requirements on the network performance into the requirements to the network elements. These requirements involve a few gross measures of performance for network elements and do not depend on the circuit switching state. One such performance measure is the worst amplification gain for all harmonic disturbances of the average transmission power. Another, is cross coupling of the wavelength channel power variations. The derived requirements guarantee system-level performance for all network configurations and can be used for specifying optical components and subsystems.

Fluorinated polyimide (FPI) is an attractive material for fabricating low-loss optical waveguides at 1.55 micrometers , because of its superior optical and thermal properties. Although FPI planar lightwave circuits (PLCs) are usually fabricated on silicon substrate, such PLCs exhibit relatively high polarization dependence and high transmission loss compared with those of silica PLCs. Use of an FPI substrate overcomes these problems that mainly originate from the difference in thermal expansion coefficient between FPI and silicon. It improves the optical property of FPI waveguides, e.g., the transmission loss and polarization dependent loss for straight waveguides reduce to less than 0.3 dB/cm and 0.1 dB, respectively, in the 1.55-micrometers band. The use of FPI substrates will enable the fabrication of high-optical-quality FPI PLCs such as 1x8 splitters.

A new 2D PBG directional coupler switch is proposed and analyzed by the FDTD method. A 1.55-micrometers device is designed in a square lattice of silicon posts in air. The switching mechanism is a change in the conductance of posts located in the waveguide coupling region, Conductance is induced electrically by carrier injection or is induced optically by electron-hole pair generation. Low insertion loss and optical crosstalk below -23 dB in both the cross and bar switching states are predicted.

In this work, we demonstrated a liquid-crystal WDM (wavelength-division-multiplexing) power equalizer. It provides functionality of optical power equalization and tilting using liquid-crystal modulators and harmonic synthesis approach. The demonstrations show fast gain equalization with a flatness of +/- 0.3dB for several EDFA profiles in C or L bands. The equalization for WDM discrete-channel cases also reached flatness within +/- 0.3dB. The measured polarization dependent losses are less than 0.15dB and 0.1dB for flattened and through-state profiles, respectively. The measured polarization mode dispersions are less than 0.15ps under the through, flattened and 10-dB attenuation states. The measured chromatic dispersion is less than degree(s)7ps/nm.

The Grating Light Valve^TM (GLV^tm) spatial light modulator is a unique and proven CMOS process-compatible optical MEMS device. The modulator employs a dynamically adjustable diffraction grating to manipulate an optical signal. Today, the GLV^TM technology is successfully used in high-resolution display and imaging systems, where its high efficiency, large dynamic range, precise analog attenuation, fast switching speed, high reliability, high yield, and the ability to integrate thousands of channels into a single device are fundamental advantages. These same properties make the GLV^TM device desirable for optical telecommunication applications. The optical properties, functionality, device design, and CMOS processing of the GLV^TM will be presented. Challenges and solutions that arise from adapting the current GLV^TM technology to optical telecommunications wavelengths will be discussed. Measured results will be presented that describe GLV^TM performance parameters, including insertion loss, dynamic range, polarization dependent loss, and spectral attenuation accuracy.

A high-speed/large-scale architecture, 3D Micro Optical Switching System (3D-MOSS), is proposed. A switching network is divided into sub-network blocks, followed by stacking them to construct a multi-layer structure. The inter-block connection is replaced with short-distance vertical optical wiring, that is, optical z-connection. 3D-MOSS, in contrast with conventional planar structures, reduces waveguide cross points, wiring length, and system size. Expected applications are Switching for Fiber Communications, Reconfigurable 3D Micro Optoelectronic System, and so on. 3D-MOSS consists of OE-films, in which thin-film high-speed micro optical switches are embedded. BPM calculation shows that Variable Well Optical Integrated Circuit (VWOIC), with matrix rectangular electrodes or prism-shaped electrodes on an electro-optic slab waveguide, is viable for the optical switch. BPM/FDTD coupled simulation demonstrates an optical z-connection with 2dB loss in a 4-micrometers -width-waveguide- based network. Resource/cost-saving heterogeneous device integration process, SORT, is briefly described.

Optical code division multiple access (O-CDMA) uses very narrow transmission pulses and is thus susceptible to fiber optic link impairments. When the O-CDMA is implemented as wavelength/time (W/T) matrices which use wavelength division multiplexing (WDM) sources such as multi-frequency laser transmitters, the susceptibility may be higher due to: (a) the large bandwidth utilized and (b) the requirement that the various wavelength components of the codes be synchronized at the point of the data modulation and encoding as well as after (optical) correlation. A computer simulation based on the nonlinear Schroedinger equation (developed to study optical networking on the National Transparent Optical Network (NTON)) was modified to characterize the impairments on the propagation and decoding of W/T matrix codes over a link of the NTON. Three critical impairments were identified by the simulation: group velocity dispersion (GVD); the flatness of the optical amplifier gain; and the slope of the GVD. Subsequently, experiments were carried out on the NTON link to verify and refine the simulations as well as to suggest improvements in the W/T matrix signal processing design. The NTON link measurements quantified the O-CDMA dispersion compensation requirements. Dispersion compensation management is essential to assure the performance of W/T matrix codes.

Optical CDMA (O-CDMA) based on matrix codes (e.g., Wavelength/Time, or W/T, matrices) can have a higher capacity and spectral efficiency (bit/s/Hz) than WDM. We have ben exploring the implementation of W/T matrices with WDM components. The wavelength part of the W/T matrices is generated by a WDM laser array consisting of multiple independent laser cavities (each at a distinct ITU frequency) coupled through a semiconductor optical amplifier (SOA). These integrated laser arrays are known as MFLs. The time-like part of the W/T matrix codes is produced by Bragg grating arrays. The W/T matrix implementation requires that the wavelengths be synchronously on-off-keyed (OOF) with a return-to-zero (RZ) modulation of less than 25% duty cycle, and that the synchronicity be retained at the point of correlation (the receiver end). In this paper we explore on- off-keying the MFL SOA in order to achieve a synchronous RZ pulse-train which can then be externally data-modulated. Particular emphasis was placed on determining the smallest achievable pulse-widths and highest pulse repetition rates for the MFLs, since the long MFL cavity lengths may preclude fast modulation formats.

Extremely broadband tunability of semiconductor lasers is achieved. The tuning range covers from 1300 nm to 1540 nm using nonidentical multiple quantum wells (MQWs) in the gain media. The broadband gain medium has two In_0.53Ga_0.47As quantum wells (Qws) near the n-cladding layer and three In_0.67Ga_0.33As_0.72P_0.28 Qws near the p-cladding layer. The sequence of the MQWs is also found to be very influential on the tuning range. For the sequence opposite to the above one, the tuning range is only from 1290 nm to 1450 nm. The reason is because the well sequence influences the carrier distribution. The broadband tunability is possible only when the QW structure could have a better uniformity of carrier distribution.

Based on polymeric materials, the possibilities of monolithic integration of various optical waveguide components are discussed and, especially, the efforts to realize the functions of optical modulation and amplification on a single optical chip are made. Exploration of more capabilities of optical waveguides is also emphasized. The work on exploring functions of optical waveguides for the applications in WDM components and photonic phased-array radar systems are presented and multifunctional optical waveguide chips with the explored functions are fabricated.

Fiber optic based CATV distribution systems may need very high powers prior to distribution. High optical powers can be obtained using a cladding pumped fiber amplifier. The performance of an analog transmission system using a high power cladding pumped fiber amplifier has been investigated. Analog signals from a 120-channel CATV signal generator was used to directly modulate 1550 nm distributed feed back laser. The output was amplified to ~1W using a cladding pumped fiber amplifier. The carrier to noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) of the composite analog signals were measured before and after amplification. No significant change in CNR, CSO and CTB signals were observed which suggests that the amplifier does not introduce any additional non-linearity. Similar experiment was also carried out using a hybrid digital/analog system where the carrier at 223.25 MHz was modulated at 2Mb/s using the BPSK modulation format. Bit error rate (BER) of <10^-9 was obtained for a modulation depth of 2.8% of the BPSK modulated channel. No significant changes in CNR, CSO and CTB were observed for this mixed mode transmission after amplification.

The behavior of a semiconductor optical amplifier (SOA)-based nonlinear loop mirror with feedback has been investigated as a potential device for all-optical signal processing. In the feedback device, input signal pulses (ones) are injected into the loop, and amplified reflected pulses are fed back into the loop as switching pulses. The feedback device has two stable modes of operation - block mode, where alternating blocks of ones and zeros are observed, and spontaneous clock division mode, where halving of the input repetition rate is achieved. Improved models of the feedback device have been developed to study its performance in different operating conditions. The feedback device could be optimized to give a choice of either of the two stable modes by shifting the arrival time of the switching pulses at the SOA. Theoretically, it was found possible to operate the device at only tens of fJ switching pulse energies if the SOA is biased to produce very high gain in the presence of internal loss. The clock division regime arises from the combination of incomplete SOA gain recovery and memory of the startup sequence that is provided by the feedback. Clock division requires a sufficiently high differential phase shift per unit differential gain, which is related to the SOA linewidth enhancement factor.

SOA-based wavelength conversion is obtained in an interferometric device exploiting two synchronous cascaded conversion processes in a SLALOM followed by a nonlinear filter. An accurate analysis and experimental eye-diagrams demonstrate significant signal quality improvement.

We present a device designed to measure laser output wavelength and based on Wollaston prisms and Barium borate (BBO) crystal polarizers. The arrangement generates a localized fringe plane perpendicular to the optic axis at which a CCD array is placed; consequently, good spatial coherence of the light is not a critical requirement for effective operation of the device. The interferogram is recorded with a digital camera allowing complete pixel registration, which results in improved accuracy. After calibration of the arrangement, the wavelength can then be measured with a precision of better than 1 part in 10⁵, and has been shown to track changes in the output wavelength of the laser sources used. In addition, the calibrated wavelength meter was found to be able to measure the absolute value of a series of defined laser lines to an accuracy of 0.18% (+/- 0.86nm).

As data rate of fiber optic communication systems increases to 10Gb/s or higher, chromatic dispersion (CD) of DWDM components becomes increasingly important. It has been shown that chromatic dispersion of passive components could have a detrimental effect on the performance of a 10Gb/s system. In this paper, we discuss chromatic dispersion of an important passive device: interleavers. To achieve better bandwidth efficiency, some system designers have started to evaluate 25GHz interleavers for their next generation products. However, the chromatic dispersion of an uncompensated 25 GHz interleave, regardless of its design, is 16 times larger than that of a 100 GHz interleaver of the same type. For example, if a 100GHz interleaver of certain design has an average CD of 40ps/nm, a 25GHz interleaver (uncompensated) of the same type would have a CD of 640ps/nm several interleavers available on the market. We show that chromatic dispersion of the interleavers is dominated by structural dispersion instead of material dispersion. The CD slopes and ripples of some interleavers can be reduced or completely compensated by innovative designs. We present an interleaver design with extremely small Cd and CD ripple. Finally, we present a 10Gb/s 160-channel transport application by using the low-CD 25GHz interleavers.

We design a hybrid free-space wavelength-division multiplexers (MUX) that favor integration of matured high performance grating-based MUX and planar waveguide devices. By optimizing the component interfaces, we pursuit a divide-and-conquer method in the proposed hybrid integration. Meanwhile, a novel 6-channel coarse MUX based on layered diffractive optics is successfully designed. These two methods combined are promising in integrating multiple optical functions with cost-effective mass production.

A variety of ball-lens based optical add/drop multiplexers (OADMs) are designed and implemented. Insertion losses as low as 0.5 to 0.6 dB for the reflection light-path, and 1.2 to 1.5 dB for the transmission light-path are demonstrated. The 0.5-dB passband and -30 dB stopband for 100-GHz OADM are 0.35 nm and 1.15 nm, respectively. The reflection path has an isolation 15 dB. In addition to the distinct cost advantage of ball lenses over the GRIN lenses, the ball-lens based OADMs also offer a significant simplification in packaging due to the intrinsic spherical symmetry of ball lenses. Optical designs and optics-related packaging issues are discussed in detail.

Communication between computing systems is recognized as the main limitation to increasing the speed of all-electronic systems beyond levels currently achieved in existing supercomputers. Optical interconnects hold great promise in eliminating current communication bottlenecks because of properties that stem from optics inherent parallelism. Wavelength-division multiplexing (WDM) technology, by which multiple optical channels can be simultaneously transmitted at different wavelengths through a single optical transmission medium is a useful means of making full use of optics parallelism over a wide wavelength region. In this talk, we review the working principles of wavelength division (de) multiplexers (WD(D)M) for optoelectronic interconnection in high-throughput optical links and address the optical design issues of Wd9D)Ms. Several grating-based WD9D)M structures are analyzed. We report experimental data for several versions of WD(D)Ms which exhibit low insertion loss, high reliability, and low cost.

An integrated optical wavelength division multiplexer/demultiplexer for the 1.5micrometers telecommunication band is presented using a self-focusing transmission grating as the main dispersive element. The high index contrast between the primary TiO₂ and the secondary Al₂O₃ slab waveguide enables comparatively small devices. In contrast to most other WDM principles like arrayed waveguide gratings or interferometer based devices the optical path may be folded thereby further reducing system dimensions. Plasma assisted metal organic chemical vapor deposition is used to deposit Al₂O₃ and TiO₂ thin films onto oxidized silicon substrates from aluminium acetylacetonate Al(acac) and a prototype precursor cyclopentadienyl-cycloheptatrienyl-titanium CpTiCh, respectively. The grating is realized by an anisotropic plasma etch process. Common input and output channels (respectively input channels and common output for a multiplexer) are numerical aperture matched ridge waveguides and can be coupled to optical fibers. In spite of positioning the outgoing waveguides according to the focal points of the self-focusing grating, the grating itself is designed to meet the layout of the device. The strong impact of the desired arrangement on the grating properties (curvature, size and far field) necessitates a compromise which is found by a hybrid simulation based on the finite element analysis (FEM) and a genetic algorithm.

Poling of nonlinear optical (NLO) film is an important step in building an electro-optic polymer-based modulator. In this paper, an electro-optic modulator based on disperse red 1(DR1) side chained poly(methyl methacrylate) (PMMA/DR1) nonlinear optical film is designed and fabricated using the standard very large scale integration fabrication procedures. The poling methods are discussed and the contact poling is used to poling the nonlinear optical film. The poling voltage is determined by the measurement of break- down voltage. The refractive indices change before and after contact poling is given. The electro-optical coefficient of 12pm/V is obtained.