Syed H. Murshid

Experimental results from copropagating analog channels of same wavelength over 600-meter-long standard step index multimode fiber

Spatial domain multiplexing is a new dimension in fiber optic multiplexing with the potential to greatly increase the data-carrying capacity of optical fiber communication systems. Spatially multiplexed channels follow helical paths inside the fiber and do not interfere with each other as optical energy from individual channels is distributed in the radial direction at different distances from the origin of the fiber. The resultant output appears as concentric circles when projected on a screen. The experimental setup and results for two spatially modulated analog channels of the same wavelength over approximately 600 m of standard 62.5/125-µm multimode fiber, using 635-nm pigtail laser sources and 30-MHz sinusoidal modulation, are reported here.

Simultaneous transmission of two channels operating at the same wavelength in standard multimode fibers

Spatial domain multiplexing is a novel multiplexing technique providing a method to transmit multiple channels of same wavelength inside an optical fiber. Two such analog channels on optical fibers for LAN applications are reported.

Tapered Optical Fiber Quadruples Bandwidth of Multimode Silica Fibers Using Same Wavelength

Four co-propagating optical channels of same wavelength have been spatially multiplexed and de-multiplexed over a step index multimode silica fiber to quadruple the bandwidth. This presents experimental setup and results for such a system.

Orbital angular momentum in four channel spatial domain multiplexing system for multi-terabit per second communication architectures

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.

SDM propagation model for multiple channels using electromagnetic theory and vortex analysis

Spatial Domain Multiplexing (SDM) is a novel technique in optical fiber communications. Single mode fibers are used to launch Gaussian beams of the same wavelength into a multimode step index fiber at specific angles. Based on the launch angle, the channel follows a helical path. The helical trajectory is explained with the help of vortex theory. The electromagnetic wave based vortex formation and propagation is mathematically modeled for multiple channels and the results are compared against experimental and simulated data. The modeled output intensity is analyzed to show a relationship between launch angle and the electric field intensity.

SDM propagation model for multiple channels using ray theory

Spatial Domain Multiplexing (SDM) is a novel optical fiber multiplexing technique where multiple channels of the same wavelength are launched at specific angles inside a standard step index multimode carrier fiber. These channels are confined to specific locations inside the fiber and they do not interfere with each other while traversing the length of the fiber. Spatial filtering techniques are employed at the output end to separate, route and process the individual channels. These skew ray channels inside the SDM system follow a helical trajectory along the fiber. The screen projection of the skew rays resembles a circular polygon. A ray theory based mathematical model of the SDM system is presented and simulated as well as experimental data is compared to the model predictions. This ray theory model utilizes launch point, input incidence angle, and point of incidence on fiber to explain the behavior of the individual channels. Thus the vector approach to propagation allows us to predict the effects of pulse spreading in the SDM system. The results showed that the skew ray trajectory is sensitive to input incidence angle. Similarly changing the launch point, while maintaining the angle of incidence constant with the z axis, can drastically affect the skew ray trajectory.

CAD model for co-propagating spatially multiplexed channels of same wavelength over standard multimode fibers

Spatial Domain Multiplexing (SDM) is a novel technique that allows co-propagation of two or more optical communication channels of the same wavelengths over a single strand of optical fiber cable by maintaining spatial separation between the channels. Spatial multiplexer known as the beam combiner module (BCM) supports helical propagation of light to ensure spatial separation between the channels. It is inserted at the input end of the system. Spatial de-multiplexing is achieved by a unit named beam separator module (BSM). This unit is inserted at the receiving end of the system and it routes the optical energy from individual channels to dedicated receivers. Spatially multiplexed channels exhibit negligible crosstalk. The bandwidth of the fiber optic systems employing SDM technique increases by multiple folds. CAD model of a beam combiner module for a two channel system using commercially available simulation tools is presented here. Simulated beam profile of the output is compared to the experimental data.

Architecture of an all optical de-multiplexer for spatially multiplexed channels

Multiple channels of light can propagate through a multimode fiber without interfering with each other and can be independently detected at the output end of the fiber using spatial domain multiplexing (SDM). Each channel forms a separate concentric ring at the output. The typical single pin-diode structure cannot simultaneously detect and demultiplex the multiple channel propagation supported by the SDM architecture. An array of concentric circular pindiodes can be used to simultaneously detect and de-multiplex the SDM signals; however, an all optical solution is generally preferable. This paper presents simple architecture for an all optical SDM de-multiplexer.

Mathematical modeling and experimental analysis of multiple channel orbital angular momentum in spatial domain multiplexing

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.

Spatial Combination of Optical Channels in a Multimode Waveguide

Spatial domain multiplexing allows co-propagation of multiple channels of same wavelength over a single strand of optical fiber. Spatial multiplexer in multimode waveguides is presented and contrasted with spatial multiplexers in the branching waveguides.