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.
A compact and light weight liquid-level-measuring system based on fiber-optics sensor technology is presented as
alternative to systems based on float gauges and other conventional level sensors for liquids that pose fire, corrosion and
explosion hazards. These Fresnel reflection based fiber-optic sensors are inherently safer because they do not include
electrical connections inside fuel/chemical tanks, and they exploit changes in internal reflection of guided electromagnetic
modes as a result of contact between the outer surface of optical fiber and a liquid. Discrete changes in light
transmission/reflection are used to indicate that liquid has come into contact with a suitably designed fiber optic probe at
the output end of the fiber. This endeavor presents a quasi-continuous fiber optic level detection system that measures
liquid level to within known increments of depth, by placing the probes of a number of such sensors at known depths in a
tank where each probe effectively serves as a level switch. Due to the fiber optic nature of the design, the system can
operate from cryogenic applications to boiling fluids. Experimental results for liquid nitrogen and water are presented.
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.
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.
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.
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.
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.
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.
Spatial domain multiplexing (SDM) utilizes co-propagation of exactly the same wavelength in optical fibers to increase
the bandwidth by integer multiples. Input signals from multiple independent single mode pigtail laser sources are
launched at different input angles into a single multimode carrier fiber. The SDM channels follow helical paths and
traverse through the carrier fiber without interfering with each other. The optical energy from the different sources is
spatially distributed and takes the form of concentric circular donut shaped rings, where each ring corresponds to an
independent laser source. At the output end of the fiber these donut shaped independent channels can be separated either
with the help of bulk optics or integrated concentric optical detectors. This presents the experimental setup and results
for a four channel SDM system. The attenuation and bit error rate for individual channels of such a system is also
presented.
Free-space optical links are ideal for short-range (1 km to 3 km) communications. An innovative new technique called
Spatial Optical Encryption can be used to secure laser data communications. With this technique, data can be encoded
and transmitted spatially through a single fiber, and then transmitted over a free-space optical link. Different sources of
data could be simultaneously sent over the same fiber. This endeavor demonstrates the design and performance issues of
such a transmitter and receiver using Spatial Optical Encryption over an environmental link of 100 meters.
An optical encryption technique based on polarization property of light is proposed. Many techniques using polarization
beam splitters to encrypt the signal have been proposed earlier. They are based on splitting and interference of two light
signals, namely message and noise. Only by placing suitable mirrors and a second beam splitter in a suitable position,
the two signals are reconstructed at the output. In this paper we report the fiber optic version of a polarization based
encryption technique that also has the potential to double the data carrying capacity of the fiber. Using polarization
dependent couplers in the fiber optic cables, we are able to achieve encryption of the light signal. Theoretical analysis
and simulated results are also presented.
Most developments in data transfer techniques are incremental by nature and the goal of increasing total
capacity in optical communications and networking requires new concepts for basic transmission media. The
transmission data rates can only be enhanced by introducing new modulation and multiplexing techniques. In
this paper different single mode tapered fiber waveguides are used to design a Spatial Multiplexer Unit (SMU)
for a novel optical fiber multiplexing technique called the Spatial Domain Multiplexing (SDM) that allows co-propagation
of two or more channels of exactly same wavelength without interfering with each other. This paper
also presents a CAD model for the SMU and then compares the output beam profiles from different single mode
tapered fibers to determine the optimum geometry for the SMU. Finally experimental and simulated beam
profiles for the SMU are presented.
Spatial reuse of optical frequencies in optical fibers is possible through a novel Spatial Domain Multiplexing
(SDM) technique that enables simultaneous propagation of two or more spatially multiplexed channels of
exactly the same wavelength by confining them to unique spatial locations inside the fiber. Spatial filtering
techniques are employed at the output end to separate the individual optical channels. The SDM channels follow
helical path inside the carrier fiber and do not interfere with each other. This paper presents electromagnetic
wave based model to analyze two such co-propagating SDM channels and then compares the model predictions
to experimental data. The comparison of attenuation and dispersion show a close match to prove that SDM
technique can be used to enhance the bandwidth of optical fiber systems.
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.
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.
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.
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.
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