This PDF file contains the front matter associated with SPIE Proceedings Volume 8397, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

A novel multiplexing technique known as Spatial Domain multiplexing (SDM) has been developed in recent years and offers many advantages over its counterparts. With multiple channel transmission of the same wavelength over a single multimode carrier fiber, SDM increases the data capacity by multiple folds. Input channels are launched at appropriate input angles to produce skew ray propagation. The output of the system when projected on a screen is observed as concentric rings. These SDM beams carry orbital angular momentum. Experiments show that two input sources with the same launch conditions, but opposite topological charge take different helical paths inside the transmission fiber. Consequently the shadow of a straight wire does not remain straight. Instead, it is displaced by a specific distance. This endeavor presents a model of such a system by analyzing the shadow distortion, using principles of geometric optics. Experimentally obtained shadow displacement results are quantified and then compared to the model. We also show that when two channels with opposite topological charges are transmitted with same launch conditions, their orbital angular momenta are equal and opposite. As a result orbital Angular momentum based multiplexing can be used to add another degree of freedom to photons.

Bandwidth increase has always been an important area of research in communications. A novel multiplexing technique known as Spatial Domain Multiplexing (SDM) has been developed at the Optronics Laboratory of Florida Institute of Technology to increase the bandwidth to T-bits/s range. In this technique, space inside the fiber is used effectively to transmit up to four channels of same wavelength at the same time. Experimental and theoretical analysis shows that these channels follow independent helical paths inside the fiber without interfering with each other. Multiple pigtail laser sources of exactly the same wavelength are used to launch light into a single carrier fiber in a fashion that resulting channels follow independent helical trajectories. These helically propagating light beams form optical vortices inside the fiber and carry their own Orbital Angular Momentum (OAM). The outputs of these beams appear as concentric donut shaped rings when projected on a screen. This endeavor presents the experimental outputs and simulated results for a four channel spatially multiplexed system effectively increasing the system bandwidth by a factor of four.

A six-user quantum key distribution network based on the auto-compensating plug & play scheme is experimentally demonstrated. The network, which has a bus line topology, uses the BB84 protocol to transmit cryptographic keys encoded unto the phase states of highly attenuated laser light to distances of up to 30.9 km of standard telecommunication-grade fiber. Each user on the network is assigned a unique wavelength for communication with the network server. The quantum bit error rate and sifted key rate measured compares favorably with theory.

Co-site interference is a problem found everywhere from wireless systems and environmental sensors to military communications; it refers to the difficulty of extracting or detecting a weak signal in proximity to a strong transmitter. Traditional interference cancellation techniques are electronics-based and their performance is consequently bandwidthlimited; electronic interference cancellation is also inhibited by the inability to cancel in-band interference. Our group has developed an optical technique for interference cancellation, and our signal processor, called the Opto-Cancellation System (OCS), is capable of cancelling both in-band interference as well as broadband signals over a wide range of frequencies. The OCS has demonstrated >70 dB cancellation of narrowband signals while also cancelling 20 MHz-wide signals by at least 40 dB cancellation over a full 20 MHz range. Proof-of-concept cancellation performance has been previously demonstrated, and to better understand cancellation performance, we explore a theoretical model of our optical interference cancellation. The theoretical model and its projected performance will be compared to experimental results, and various performance parameters will be used to evaluate the limitations and advantages of our RF photonic link approach.

A new design of a variable mechanical optical attenuator is proposed in this paper. Mechanical attenuators are extensively important in designing optical communication systems. It is also highly used in testing and training purposes. The design consists a novel fiber optic splitter-combiner setup. Each branch of the splitter meets a specific branch of the combiner. A fixed distanced multi-window rotary wheel slides between them. Upon rotation the light is either blocked or allowed to pass from a splitter branch to a combiner branch. By changing the number of open gates, the amount of yielded light can be controlled. There is only one moving part. So, the design is easy to manufacture, use or repair. The basic design and work flow is explained. The formula for calculating the attenuation and calibration guideline is also discussed. Then the design is compared with the other design standards based on the areas of application. The possible effects of linear and non-linear properties of light is also discussed. The primary concerns that should be taken if this design is to be fabricated in photonic integrated circuits is also mentioned briefly.

We present experimental demonstration of passively modelocked laser with pulse-repetition frequency tunable using semiconductor optical amplifier as the gain medium. The principle of operation is based on normal mode competition of a coupled cavity comprised of a quantum cavity and an optical cavity represented by a semiconductor gain medium, and a high-birefringence fiber in line with a Faraday mirror respectively. Experimental results are presented for pulse-repetition frequency shows stable tunability over a frequency decade of 93MHz and 1400MHz.

This work shows the process of computing coupling coefficients of first-order distributed feedback (DFB) metalsemiconductor quantum-well lasers. InGaAsP/InP/Au lasers with wavelength 1550 nm for optical communications are studied. The optical waveguide structure for such a laser has semiconductor layers and a built-in grating interface between the metal and semiconductor layers. Such interface has sinusoidal corrugation geometry. To compute the coupling coefficient of the metal-grating waveguide, a model is constructed by the Floquet-Bloch method (FB). The Ray-optics method (RO) is also used to calculate the coupling coefficients. These two methods have close results.

By mixing two lasers together it, is possible to generate RF signals from near DC to hundreds of GHz. Through the use of a narrow-linewidth low-frequency oscillator, optical modulator, and injection locking, much higher frequency outputs can be produced that still retain the narrow linewidth of the low frequency oscillator. Here we focus on the design and implementation of an integrated device including photonic sources and modulators to realize the system described above. Specifically, we report on the creation and mixing of two tunable lasers on a silicon platform with a heterogeneously integrated gain medium realized in a III-V material system.

We present an experimental demonstration of an all optical memory consisting of a coupled system of a semiconductor optical amplifier and a super continuum generator operating in the 1500 nm range. The circuit is designed as a fiber ring consisting of the semiconductor amplifier, a polarization beam splitter, a digital polarization controller, a polarization maintaining fiber and a super continuum generator in series. The P or the S output of the beam splitter is sent to an optical spectrum analyzer to measure the output while the other output completes the ring. The linear polarization is adjusted with a digital polarization controller. The stable state consists of two modes, where the mode amplitude represents the state. Mode 1 corresponds to 1530 nanometers and mode 2 corresponds to 1550 nanometers. A contrast ratio between an "on" and "off" state is measured for each mode. The stable states of the flip flop are [mode1- ON, mode2- ON], [mode 1-ON, mode 2-OFF], [mode1-OFF, mode 2-ON] and [mode 1-OFF, mode 2-OFF] and are controlled by the polarization. We shall present the state diagram for these four states of the flip flop, the effect of power on the system, the effect of the SOA drive current, and the effect of polarization fluctuations.

We report for the first time the use of the well-known coherence modulation of light in two-dimensional arithmetic operations. This method, which allows several signals to be multiplexed on a single light beam, permits parallel real-time all optical subtractions and additions. In the context of an increased need of security, a major application of our multiplexed approach could be the optical encryption of images and multi-modalities techniques in biometric domain. The single-channel optical architecture, which allows carrying out single and multiple arithmetic operations, is described and more results are presented to show the effectiveness of our technique. We have evaluated the performance of the processor in terms of noise level as a function of the continuous optical path-difference ratio.

The paper presents a model of a free space optical transmitter operating in the wavelength range of 8-12 μm. In the transmitter, a quantum cascade laser controlled by a special driver was applied. The driver provides the control of the energy, repetition rate and duration of radiation pulses. In the described transmitter, generation of pulses with high duty cycle is also provided, making it possible to use the data link with either RZ or NRZ coding. In the frame of the study, the impact of laser working conditions on the data link operation was determined.

The paper presents a construction and some investigations results of a new driver for quantum cascade (QC) lasers. The driver is designed to control pulse and CW mode QC lasers. For both laser mode operations, there is the possibility to set a laser current in the range of 0.1 A - 3 A and pulse duration of 30 ns at the frequencies to the level of 25 MHz. The stabilization of the temperature in the range of 50°C ÷ -30°C with accuracy of 1.5 K is also achieved. A full synchronization with external pulses makes the driver very useful in a construction of a free space optical transmission system and of a laser spectroscopy setup.

This paper presents a hybrid opto-electronic asynchronous delta-sigma modulator, implemented in the form of a fiber-optic Analog-to-Digital converter (ADC). This architecture was chosen for its independence of an external clock and ease of demodulation through a single low-pass filter stage. The fiber-optic prototype consists of an input laser (wavelength λ₁) which is modulated with an input RF signal, a high-speed comparator circuit working as bi-stable quantizer, and a fiber-optic loop that includes a SOA and a band-pass filter that act as a leaky integrator. The fiber-optic loop acts as a fiber-ring resonator (FRR), and defines the resonance wavelength λ₂ of the system. The gain within this loop is modified through cross-gain modulation (XGM) by the input wavelength λ₁, and thus achieves the desired modulation effect. The proposed architecture has been constructed and characterized at a sampling rate of 15.4 MS/s processing input analog signals in the range of dc-3 MHz with a signal-to-noise ratio of 36 dB and an effective number of bits of 5.7.