This PDF file contains the editorial “Guest Editorial: Photonic Switching and Interconnects” for OE Vol. 29 Issue 03

This PDF file contains the editorial “Book Rvw: Principles of Modern Optical Systems," edited by Ivan Andonovic and Deepak Uttamchandani for OE Vol. 29 Issue 03

This PDF file contains the editorial “Book Rvw: Infrared Technology Fundamentals," by Irving J. Spiro and Monroe Schlessinger for OE Vol. 29 Issue 03

It would be tempting to dig out our crystal ball, especially at the start of the last decade of a century, to see what the future might bring to the field of photonic switching and interconnects. I shall not succumb to such a temptation but will merely introduce this special issue. As the title suggests, it is devoted to both photonic switching and interconnects.

As transmission rates in fiber-optic networks increase, routing optical signals using electronic processing will become increasingly difficult. This limitation can be overcome by performing the required processing optically. Self-routing of optical signals through a switching node using optically processed control is demonstrated. Packet headers are encoded with packet destination addresses using either optical code-division or time-division encoding schemes. An optical routing controller reads the destination addresses and appropriately sets the photonic switch using an optical look-up table. The results of several experiments demonstrating optical control of a photonic switch are described.

A multicasting photonic space switch is proposed and demonstrated utilizing acousto-optic Bragg cells in a free-space active splitting, passive combining optical architecture. A 4 x 4 switch is demonstrated at optical wavelength ? = 0.83?m using Te02 Bragg cells. Fiber-to-fiber insertion loss of 15 dB, crosstalk of —20 dB, extinction ratio of >30 dB, and polarization sensitivity of 0.8 dB has been measured. Feasibility of switch operation at 1.3 ?m is also shown for TeO2. Although this design was fabricated as a 4x4, expansion to 14x 14 can be accommodated with modifications to the optical element design. Calculations indicate that a maximum switch size of 20 x 20 and an insertion loss of 11 dB is possible, with crosstalk and extinction ratios greater than 30 dB.

Study of an lnP-based optical switch operating through carrierinduced refractive index change, having suitable features for large-scale integration, polarization independence, and wavelength insensitivity, is briefly summarized. Recent experimental results obtained by an optical switch module (OSM), comprising a packaged version of the 4 x 4 optical switch array with novel fiber arrays [APT (aligned by pyramidal throughholes) fiber arrays], are presented. Preliminary experimental results of module qualification and reliability obtained with the compact OSM are discussed. Finally, an optical asynchronous transfer mode (ATM) switching system architecture using the OSM as a key device is introduced, and high-speed pulse response characteristics of the OSM are examined for its application to the ATM switch system.

An ultrafast switching technique utilizing the optical Kerr effect in optical fibers is described and its switching characteristics are considered, taking into account chromatic and polarization dispersion. Experimental results on picosecond optical Kerr modulation and 2 Gb/s all-optical complete demultiplexing of a 30 ps probe pulse train, as well as all-optical chirping manipulation of ultrashort optical pulses, are presented. Applications of the optical Kerr switching technique to the determination of the nondiagonal component n281 ofthe nonlinear refractive index in nonlinear optical media and to the generation of ultrafast pulse trains are also discussed.

Vertical-cavity electrically pumped surface-emitting microlasers are formed on GaAs substrates at densities greater than two million per square centimeter. Two wafers were grown with ln0.2Ga0.8As active material composing three 80 ? thick quantum wells in one and a single quantum well (SQW) 100 ? thick in the other. Lasing was seen in devices as small as 1 .5 ?m diameter with <0.05 ?m3 active material. SQW microlasers 5 x 5 ?m square had room-temperature cw current thresholds as low as 1.5 mA with 983 nm output wavelength. 10 x 10 ?m square SQW microlasers were modulated by a pseudorandom bit generator at 1 Gb/s with less than 10-10 bit error rate. Pulsed output >170 mW was obtained from a 100?m square device. The laser output passes through the nominally transparent substrate and out its back side, a configuration well suited for micro-optic integration and photonic switching and interchip connections.

A photorefractive interconnect system with coherently erasable synapses (PISCES) is described. Comparing holographic erasure by intensity and phase modulation of the writing beams, we find that the time average technique is most amenable to system implementation. Calculations derived from a simple model of diffraction show that it is possible to find configurations that maximize the interconnection capacity. The PISCES includes Fresnel zone plates for spot array generation, amplitude and phase spatial light modulators based on liquid crystal technology, and detector arrays, in addition to the photorefractive crystal. Alternatives for each of these elements are described.

In this paper, a dynamic information routing architecture, which uses fixed volume holograms accessed by a ferroelectric liquid crystal spatial light modulator (SLM), is presented. The interconnects are therefore reconfigurable at the SLM frame rate. The design of two routing networks is presented, and experimental results are given for each network. Since multiple-exposure holographic recording is necessary to implement these networks, results demonstrating maximum diffraction efficiency holographic recording in LiNbO3 are presented.

A novel static semiconductor laser digital scanner is proposed and demonstrated. The scanner consists of a monolithically integrated semiconductor laser array and an aspheric convex lens. Laser beams are deflected and scanned digitally by the convex lens with no mechanical action. Extremely high scanning speed can be achieved with this scanner because the scanning speed is in principle limited only by semiconductor laser switching time. Scanning angles of the laser beam up to 400 were obtained for a 10-element semiconductor laser array. The array spacing is 300?m, and an aspheric convex lens with 4.5 mm focal length was used. Intensity profiles of the deflected beam coincide with calculations using the ray tracing method.

A method is presented for synthesis of the spectral dependence of infrared sources. Blackbody sources of different temperatures are used as basis functions in this synthesis. The basis functions are linearly combined with appropriate weighting coefficients to approximate the desired spectral distribution. We demonstrate the method by synthesizing blackbody functions of certain temperatures that are not one of the basis functions. The parameters to be determined in the synthesis are the temperatures of the basis functions and the values of the weighting coefficients. Realistic hardware constraints are imposed, such as quantization of the weighting coefficients and the use of a limited number of basis functions. The error in the synthesis is determined as a function of the number of basis sources. The use of four sources was found to be a good compromise, with approximately a 4% error over the 3 to 5 ?m band.

An expression is derived for the complex amplitude transmittance ofthe liquid crystal TV (LCTV) and verified experimentally. It is shown that spatial phase modulation is realizable with good linearity, high transmission efficiency, and small intensity distortion. Although the commercial LCTV does not provide a sufficiently large dynamic range for continuous phase modulation, a dynamic range of 2? can be obtained by making appropriate changes in the design.

Response characteristics of the Knollenberg active scattering aerosol spectrometer ASAS-300X are investigated on monodisperse lightabsorbing aerosols generated by a Berglund-Liu vibrating orifice monodisperse aerosol generator. The responses on the light-absorbing aerosols are in fairly good agreement with Mie scattering theoretical predictions. The response of the Knollenberg ASAS-300X to light-absorbing spherical aerosols is of almost monotonically increasing single-valued behavior compared to the multivalued behavior of nonabsorbing spherical aerosols, and the instrument's response to light-absorbing aerosols is closer to the manufacturer's calibration than is its response to nonabsorbing aerosols.

Petzval curvature plays an important role in the design of a triplet. Its value should be defined at the beginning of the design process, and along with the field of view, it will characterize the type of design. For these reasons, a look at the consequences of choosing various Petzval values is interesting. Different image quality criteria versus the Petzval radius for different glass combinations are studied. It is shown that the natural Petzval radius of a Cooke triplet lies at about — 2.7 times the focal length.

An efficient holographic optical element that combines the beammultiplexing properties of binary-phase computer-generated holograms with the efficiency of volume holograms formed in dichromated gelatin is described. Experimental results for an element that improves both the efficiency and the signal-to-noise ratio of a computer-generated hologram are presented. The possibility of using this element as an optical interconnect is discussed.

We present a general formulation, based on previous work, for calculating the general coherent transfer function (GCTF) of a compound optical system operating under linearity conditions in the Fresnel regime. It should be noted that only under very restrictive conditions on the system (particularly for systems obeying Herschel's condition) can the quadratic phase terms appearing in the Fresnel diffraction regime be neglected. By assuming Gaussian profiles for the refractive indices of the optical media, the GCTF is calculated. The autocorrelation function directly gives the optical transfer function and modulation transfer function distributions. This procedure has been applied to a Tessar-type photolens system.

Optical system modeling is particularly important for simulation of laser beam propagation over large distances. This paper describes the diffraction modeling of the propagation of a laser beam between two points on the surface of the earth, using relay mirrors on one or more satellites. Because of the importance of the atmospheric and propagation effects, computer modeling is necessary to develop understanding of the first-order design parameters. Some of the significant design parameters are characterization of the adaptive mirror for the atmospheric aberration correction, size and finish of the beam expander, apertures of the relay mirror, and acceptable levels of jitter. An example of a propagating laser beam is presented, demonstrating the three-dimensional nature of this model.