Spatial domain multiplexing (SDM) offers a degree of photon freedom to optical fibers. One variant of SDM utilizes ring-like output profiles, created through specific oblique input angles, and shows high-performance gains. Conventional modeling of this system utilizes Laguerre–Gaussian based models; however, these models are more suitable for free-space environments as opposed to fiber propagation. Therefore, a diffraction-based approach to deriving a Bessel–Gaussian beam solution is presented that adheres well to experimental data while maintaining continuity requirements. The derived model shows an input angle to azimuthal index relationship proportional to the transverse wave number of the carrier optical fiber region of SDM architectures.
Free-space optical (FSO) communications provide point-to-point connectivity while offering many advantages in size, weight, and power as compared to radio frequency. It has the potential to provide fiber-optic data rates without the need for lengthy fiber cables. Omnidirectional FSO, also known as O-FSO systems, provide a non-line-of-sight option for data communications. They are gaining popularity in short-distance networks. Most existing O-FSO links range from 1 to 100 m and present experimental/simulated data rates ranging between 5 kb/s and 1 Mb/s. A 2.5-Gb/s O-FSO system was recently reported with a range of 25 cm. This paper employs a fiber bundle as an O-FSO receiver. The energy collected by the receiver is related to the acceptance cone of each fiber. The fiber bundle integrates the optical power gathered by the individual fibers and couples it to the photodetector. Experimental data rates approaching 100 kb/s over a meter long system are presented, whereas simulated results support a data rate up to 52 Mb/s for distances approaching a kilometer. Theoretical and experimental optical power versus range is also presented for the proposed O-FSO architecture, using on-off keying.
Spatial domain multiplexing (SDM), also known as space division multiplexing, adds a new degree of photon freedom to existing optical fiber multiplexing techniques by allocating separate radial locations to different channels of the same wavelength as a function of the input launch angle. These independent MIMO channels remain confined to their designated locations while traversing the length of the carrier fiber owing to helical propagation of light inside the fiber core. As a result, multiple channels of the same wavelength can be supported inside a single optical fiber core, thereby allowing spatial reuse of optical frequencies and multiplication of fiber bandwidth. It also shows that SDM channels of different operating wavelengths continue to follow an output pattern that is based on the input launch angle. As a result, the SDM technique can be used in tandem with wavelength division multiplexing (WDM), to achieve higher optical fiber bandwidth through increased photon efficiency and added degrees of photon freedom. This endeavor presents the feasibility of a hybrid optical fiber communication architecture in which the spectral efficiency of the combined system increases by a factor of “n” when each channel of an “n” channel SDM system carries the entire range of WDM spectra.
Spatial domain multiplexing/space division multiplexing (SDM) can increase the bandwidth of existing and futuristic optical fibers by an order of magnitude or more. In the SDM technique, we launch multiple single-mode pigtail laser sources of the same wavelength into a carrier multimode fiber at different angles. The launching angles decide the output of the carrier fiber by allocating separate spatial locations for each channel. Each channel follows a helical trajectory while traversing the length of the carrier fiber, thereby allowing spatial reuse of optical frequencies. We launch light from five different single-mode pigtail laser sources (of same wavelength) at different angles (with respect to the axis of the carrier fiber) into the carrier fiber. Owing to helical propagation, five distinct concentric donut-shaped rings with negligible crosstalk at the output end of the fiber were obtained. These SDM channels also exhibit orbital angular momentum (OAM), thereby adding an extradegree of photon freedom. We present the experimental data of five spatially multiplexed channels and compare them with simulated results to show that this technique can potentially improve the data capacity of optical fibers by an order of magnitude: A factor of five using SDM and another factor of two using OAM.
Vertical takeoff and landing (VTOL) aircrafts such as helicopters and drones, add a flexible degree of operation to
airborne vehicles. In order to operate these devices in low light situations, where it is difficult to determine slope of the
landing surface, a lightweight and standalone device is proposed here. This small optical device can be easily integrated
into current VTOL systems. An optical projector consisting of low power, light weight, solid state laser along with
minimal optics is utilized to illuminate the landing surface with donut shaped circles and coaxial centralized dot. This
device can placed anywhere on the aircraft and a properly placed fiber system can be used to illuminate the surface
beneath the bottom of the VTOL aircraft in a fashion that during operation, when the aircraft is parallel to the landing
surface, the radius between the central dot and outer ring(s) are equidistant for the entire circumference; however, when
there the landing surface of the VTOL aircraft is not parallel to the landing strip, the radial distance between two
opposite sides of the circle and central dot will be unequal. The larger this distortion, the greater the difference will be
between the opposite sides of the circle. Visual confirmation or other optical devices can be used to determine relative
alignment of the projector output allowing the pilot to make proper adjustments as they approach the landing surface to
ensure safe landings. Simulated and experimental results from a prototype optical projector are presented here.
Lasercomm or Free Space Optical (FSO) communication has the potential to provide fiber optic data rates without the
need for wired physical connectivity. This paper investigates the feasibility of an Omnidirectional FSO (O-FSO)
communications link that utilizes fiber bundles for improved omni-directionality and compares experimental data with
modeled results. Current state of the art O-FSO link ranges are limited to 100 meters or so, with data rates of only a
few100 kbits/sec. The proposed architecture is formed from commercially available fiber bundle that collects
omnidirectional light due to the hemispheric nature of the fiber bundle by exploiting the acceptance cones of the
individual fiber exposed to the optical radiation. The experimental transmitter is composed of an LED source that is
driven by an On-Off-Keying signal. This paper presents the received optical power while varying the range between the
transmitter and receiver. The omni-directionality of this architecture is also verified. The measured results are then
compared to the model predictions for omni-directionality and range.
Spatial domain multiplexing (SDM) is a system that allows multiple channels of light to traverse a single fiber, utilizing
separate spatial regions inside the carrier fiber, thereby applying a new degree of photon freedom for optical fiber
communications. These channels follow a helical pattern, the screen projection of which is viewable as concentric rings
at the output end of the system. The MIMO nature of the SDM system implies that a typical pin-diode or APD will be
unable to distinguish between these channels, as the diode will interpret the combination of the SDM signals from all
channels as a single signal. As such, spatial de-multiplexing methods must be introduced to properly detect the SDM
based MIMO signals. One such method utilizes a fiber consisting of multiple, concentric, hollow core fibers to route
each channel independently and thereby de-mux the signals into separate fibers or detectors. These de-mux fibers consist
of hollow core cylindrical structures with beveled edges on one side that gradually taper to route the circular, ring type,
output energy patterns into a spot with the highest possible efficiency. This paper analyzes the beveled edge by varying
its length and analyzing the total output power for each predetermined length allowing us to simulate ideal bevel length
to minimize both system losses as well as total de-mux footprint. OptiBPM simulation engine is employed for these
analyses.
Spatial Domain Multiplexing/Space Division Multiplexing (SDM) can increase the bandwidth of existing and futuristic
optical fibers by an order of magnitude or more. In the SDM technique, we launch multiple single mode pigtail laser
sources of same wavelength into a carrier fiber at different angles. The launching angles decide the output of the carrier
fiber by allocating separate spatial locations for each channel. Each channel follows a helical trajectory while traversing
the length of the carrier fiber, thereby allowing spatial reuse of optical frequencies. In this endeavor we launch light from
five different single mode pigtail laser sources at different angles (with respect to the axis of the carrier fiber) into the
carrier fiber. Owing to helical propagation we get five distinct concentric donut shaped rings with negligible crosstalk at
the output end of the fiber. These SDM channels also exhibit Orbital Angular Momentum (OAM), thereby adding an extra
degree of photon freedom. We present the experimental data of five spatially multiplexed channels and compare them with
simulated results to show that this technique can potentially improve the data capacity of optical fibers by an order of
magnitude: A factor of five using SDM and another factor of two using OAM.
Spatial domain multiplexing (SDM) also known as space division multiplexing adds a new degree of photon freedom to
existing optical fiber multiplexing techniques by allocating separate radial locations to different MIMO channels as a
function of the input launch angle. These independent MIMO channels remain confined to the designated location while
traversing the length of the carrier fiber, due to helical propagation of light inside the fiber core. The SDM technique can
be used in tandem with other multiplexing techniques, such as time division multiplexing (TDM), and wavelength division
multiplexing in hybrid optical communication schemes, to achieve higher optical fiber bandwidth by increasing the photon
efficiency due to added degrees of photon freedom. This paper presents the feasibility of a novel hybrid optical fiber
communications architecture and shows that SDM channels of different operating wavelengths continue to follow the
input launch angle based radial distribution pattern.
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.
Free Space Optical (FSO) communication is the fusion of wireless technology and optical fiber communications systems. It has the potential of providing fiber optic data rates without the physical restraints of optical fiber cables. This endeavor presents a novel receiver structure with potential for omnidirectional free space optical communications. Interesting approaches for accomplishing omnidirectional free space lasercomm such as direct detection and solar blind non-line of sight UV scattering have been reported over the last few years. However, these technologies have resulted in limited distances of the order of 10 to 100 meters and data rates often limited to less than 1 Mb/s. This endeavor reports the architecture of an omnidirectional receiver setup by integrating an off the shelf detector and a fiber bundle, where the fiber bundle couples omnidirectional photons within its field of view and delivers these photons to the detector. The coupling of light from all directions into a detector is regulated by the cone of the acceptance angle of the fiber. Multiple fibers with overlapping acceptance angles provide the necessary coverage that may be needed to extract the optical signal from the free space optical channel. Simulated results showing the normalized power pattern of the system is presented to demonstrate omnidirectional potential of the structure. Theoretical power level versus distance plot for an FSO System employing On-O Keying (OOK) is also presented.
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