FREE SPACE OPTICAL COMMUNICATION

Abstract— This paper presents an adaptive control scheme for suppressing jitter in laser beams. The variable-order adaptive controller is based on an adaptive lattice filter that implicitly identifies the disturbance statistics from real-time sensor data. The multi-channel adaptive ...

Irradiance fluctuations of an infrared laser beam from a shore-to-ship data link ranging from 5.1 to 17.8 km are compared to lognormal (LN), gamma-gamma (GG) with aperture averaging, and gamma-Laguerre (GL) distributions. From our data analysis, the LN and GG probability density function (PDF) models were generally in good agreement in near-weak to moderate fluctuations. This was also true in moderate to strong fluctuations when the spatial coherence radius was smaller than the detector aperture size, with the exception of the 2.54 cm power-in-bucket (PIB) where the LN PDF model fit best. For moderate to strong fluctuations, the GG PDF model tended to outperform the LN PDF model when the spatial coherence radius was greater than the detector aperture size. Additionally, the GL PDF model had the best or next to best overall fit in all cases with the exception of the 2.54 cm PIB where the scintillation index was highest. The GL PDF model also appears to be robust for off-of-beam cente...

A binary polarization shift-keying scheme with two circle polarization states, circle polarization shift keying (CPolSK), is proposed and discussed. The propagation of the circle-polarized Gaussian Schell model beam is studied based on the cross-spectral density matrix. The results show that the state of polarization remains unchanged and the degree of polarization slightly increases upon propagation in a turbulent atmosphere. The analysis of the bit-error-rate performance shows that the CPolSK system has about a 3 dB lower requirement in signal-to-noise ratio than the on-off keying system. The modulation scheme will be helpful for practical free-space optical communication systems in the future.

In this research, two computers are used to transfer data in free space optical communication system using transmitter and receiver circuits and the distance separation between these computers is 50 m. The transmitter part of the optical communication system contains a drive circuit and semiconductor laser as a light source, while a receiver part of the optical communication system contains a phototransistor and an amplified circuit. In this research, we have designed and constructed an optical system of information transfer between two computers in practice based on the theoretical design circuits A green laser with wavelength of 532 nm and measured output power 26 mW is used. The COM port (RS-232) is used to send and receive data with " advanced serial port " program version 5.5 with a bit rate of 9600Kbps. The results of the optical communication system are achieved as sent a sequence of binary digit 0/1 from one computer to another computer using the measured transmitted power of the laser at a specific distance between computers.

Free Space Optical (FSO) communication technology , also known as Optical Wireless Communications (OWC), has regained a great interest over the last few years. In some cases, FSO is seen as an alternative to existing technologies, such as radio frequency. In other cases, FSO is considered as a strong candidate to complement and integrate with next-generation technologies, such as 5G wireless networks. Accordingly, FSO technology is being widely deployed in various indoor (e.g., data centers), terrestrial (e.g., mobile networks), space (e.g., inter-satellite and deep space communication), and underwater systems (e.g., underwater sensing). As the application portfolio of FSO technology grows, so does the need for a clear classification for FSO link configurations. Most existing surveys and classifications are single-level classifications, and thus not inclusive enough to accommodate recent and emerging changes and developments of different FSO link configurations and systems. In this paper, we propose a multi-level classification framework to classify existing and future indoor, terrestrial, space, underwater, and heterogenous FSO links and systems using common and simple unified notation. We use the proposed classification to review and summarize major experimental work and systems in the area until 2017. Using the proposed classification and survey, we aim to give researchers a jump-start to tap into the growing and expanding realm of the FSO technology in different environments. The proposed classification can also help organize and systematically present the progress in the research on FSO technology. This makes the identification of the market needs for standards an easier task. Moreover, different entities involved in the standardization process including academic, industry, and regulatory organizations can use the proposed classification as a unified language to communicate during the early stages of standard development which require ambiguity-free discussions and exchange of ideas between different standardization entities. We use the proposed classification to review existing standards and recommendations in the field of FSO. It is also envisioned that the proposed classification can be used as a unified framework to define different FSO channel models for simulation tools.

Data centers (DCs) is becoming increasingly an integral part of the computing infrastructures of most enterprises. Therefore, the concept of DC networks (DCNs) is receiving an increased attention in the network research community. Most DCNs deployed today can be classified as wired DCNs as copper and optical fiber cables are used for intra- and inter-rack connections in the network. Despite recent advances, wired DCNs face two inevitable problems; cabling complexity and hotspots. To address these problems, recent research works suggest the incorporation of wireless communication technology into DCNs. Wireless links can be used to either augment conventional wired DCNs, or to realize a pure wireless DCN. As the design spectrum of DCs broadens, so does the need for a clear classification to differentiate various design options. In this paper, we analyze the free space optical (FSO) communication and the 60 GHz radio frequency (RF), the two key candidate technologies for implementing wireless links in DCNs. We present a generic classification scheme that can be used to classify current and future DCNs based on the communication technology used in the network. The proposed classification is then used to review and summarize major research in this area. We also discuss open questions and future research directions in the area of wireless DCs.

Over the last two and half decades free space optical communication is preferred over microwave and radio frequency communication systems because of its license free long range operations. Also it has many advantages such as low cost, high bandwidth and small size and it has few limitations also like beam dispersion, scintillation. A well-known limitation of FSO is the effect of weather condition on it. In this paper we have designed 10gbps FSO system and analyzed of 10gbps FSO system with different weather condition by power and length varying. From the result it is clear, the transmission distance go on decreasing as the weather condition changes from clear to haze, rain and fog and the BER performance of all received signals is also discussed.

Complementing wireless radio networks with free-space optics (FSO) achieves high data rates by modulating radio subcarriers over an optical carrier without expensive optical fiber cabling, enabling a pervasive platform for reaching underserved areas. In this paper, we review the main features of FSO for terrestrial and inter-satellite communications. Simulations of 1 Gbps data transmission through FSO links in both terrestrial and inter-satellite communications have been investigated to highlight potential atmospheric challenges in FSO.

The main project aims is to monitor the mechanical responsivity of the wooden long bow and arrow using optical fiber bragg grating sensors (FBGs). The project considers the time constraint and the availability of the equipments in the lab to develop the sensor system to access the strain endure by the wooden long bow during drawing back. We build a general connecting circuit along the wooden long bow with FBG sensor which consists of optical fiber amplifier, coupler, spectral analyser and optic fiber. The experiment aims to answer the following questions in detail: The relative difference in measurement between tape (3M Micropore TM Tape) and the glue (M.Bond 200 [Vishay] Adhesive which contains cyanocrylate ester) and the strengths and weakness of the tape and glue. The test depends on the strain of the bow. Manual recordings from the Optical Spectrum Analyser (OSA) will be taken to see the shift in wavelength as strain is applied.

We study the characteristics of the FBG Sensors, photodiode, Erbium Amplifier, the relation between responsivity and wavelength. We also analyse the linearity and power level changes that takes place once the Erbium Amplifier is introduced into the circuit. From previous papers, we understand FBG technique is more accurate and reliable for the measurements and discuss the future of it.

In this paper, we consider the problem of space-time (ST) coding with pulse position modulation (PPM). While all the existing ST block codes necessitate rotating the phase or amplifying the amplitude of the transmitted symbols, the proposed scheme can be associated with unipolar PPM constellations without introducing any additional constellation extension. In other words, full transmit diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. The absence of phase rotations renders the proposed scheme convenient for low- cost carrier-less multiple-input-multiple-output (MIMO) time- hopping ultra-wideband (TH-UWB) systems and for MIMO free-space optical (FSO) communications with direct detection. In particular, we propose two families of minimal-delay ST block codes that achieve a full transmit diversity order with PPM. Designate by n the number of transmit antennas and by M the number of modulation positions. For a given set of values of (n, m), the first family of codes achieves a rate of 1 symbol per channel use (PCU) which is the highest possible achievable rate when no constellation extensions are introduced. The second family of codes can be applied with a wider range of (n, m) at the expense of a reduced rate given by: R=1/n+n-1/n log₂(M-1)/n log₂(M).

In this work, a free space optical communications (FSO) link is proposed and utilized to explore and evaluate the FSO link performance under the joint occurrence of the atmospheric scattering and turbulence phenomena for 850 and 1550 nm operation. Diffraction and non diffraction-limited systems are presented and evaluated for both wavelengths' operation, considering far-field conditions under different link distances. Bit error rate, pointing error angles, beam divergence angles, and link distance are the main performance indicators that are used to evaluate and compare the link performance under different system configurations and atmospheric phenomena combinations. A detailed study is performed to provide the merits of this work. For both far-field diffraction-limited and non diffraction-limited systems, it is concluded that 1550 nm system operation is better than 850 nm for the whole presented joint occurrences of atmospheric scattering and turbulence.

Mention optical communication and most people think of fiber optics. But light travels through air for a lot less money. So it is hardly a surprise that clever entrepreneurs and technologists are borrowing many of the devices and techniques developed for fiber-optic systems and applying them to what some call fiber-free optical communication.
A  Free  Space  Optical  transmission  system  is  a  wireless  form  of  connection  designed  for  the interconnection of two points which have a direct line of sight. The systems operate by taking a standard data or telecommunications signal, converting it into a digital format and transmitting it through  free  space.  The  carrier  used  for  the  transmission  of  this  signal  is  Infrared  and  is  generated by either high power LED or laser diode. The basic principles for the transmission of a signal along a fiber are the same as for transmission through free space.

These free-space systems require less than a
fifth the capital outlay of comparable ground-based
fiber-optic technologies. Moreover, they can be up
and running much more quickly. Installing an
FSO system can be done in a matter of days—even
faster if the gear can be placed in offices behind
windows instead of on rooftops. Using FSO, a
service provider can be generating revenue while
a fiber-based competitor is still seeking municipal
approval to dig up a street to lay its cable.
The applications of free-space optics are many
and varied. To cite just a few: • Metro network extensions. Carriers can
deploy FSO to extend existing metropolitan-area
fiber rings, to connect new networks, and, in their
core infrastructure, to complete Sonet rings. •Last-mile access. FSO can be used in highspeed
links that connect end-users with Internet
service providers or other networks. It can also be
used to bypass local-loop systems to provide businesses
with high-speed connections. •Enterprise connectivity. The ease with which
FSO links can be installed makes them a natural for
interconnecting local-area network segments that
are housed in buildings separated by public streets
or other right-of-way property [photo, opposite]. •Fiber backup. FSO may also be deployed in
redundant links to back up fiber in place of a second
fiber link. •Backhaul. FSO can be used to carry cellular
A free-as-air technology
Low-power infrared beams, which do not harm the eyes, are the
means by which free-space optics technology transmits data
through the air between transceivers, or link heads [see drawing,
above], mounted on rooftops or behind windows [see photo,
opposite]. It works over distances of several hundred meters to
a few kilometers, depending upon atmospheric conditions.
Unlike most of the lower-frequency portion of the electromagnetic
spectrum, the part above 300 GHz (which includes
infrared) is unlicensed worldwide and does not require spectrum
fees. The main limitation on its use is that the radiated
power must not exceed the limits established by the Internal.
IEEE SPECTRUM .fiber optic without fiber cable . Michael J. Riezenman. • August 2001 presentation conclusion .
Number One
Physical Obstruction
Construction crane or flying bird comes in path of light beam temporarily
Number Two
Atmospheric Losses
Free space loss
Clear air absorption
Weather conditions (Fog, rain, snow, etc.)
Scattering
Scintillation
Number Three
Building Sway and Seismic activity
Movements of buildings upsets transmitter-receiver alignment
Solution:
Use slightly divergent beam
Divergence of 3-6 milliradians will have diameter of 3-6m after traveling 1km
Active tracking
Feedback mechanism to continuously align transmitter-receiver lenses
Facilitates accelerated installation, but expensive
1.FSO laser beams cannot be detected with spectrum analyzers or RF meters.
2.FSO laser transmissions are optical and travel along a line of sight path that cannot be intercepted easily.
3.The laser beams generated by FSO systems are narrow and invisible, making them harder to find and even harder to intercept and crack.
4.Data can be transmitted over an encrypted connection adding to the degree of security available in FSO network transmissions.

Free Space Optics (FSO) transmits invisible, eye-safe light beams from one "telescope" to another using low power infrared laserin the terahertz spectrum. The beams of light in Free Space Optics (FSO) systems are transmitted by laser light focused on highly sensitive photon detectorreceivers. These receivers are telescopic lenses able to collect the photon stream and transmit digital data containing a mix of Internet messages, video images, radio signals or computer files. Commercially available systems offer capacities in the range of 100 Mbps to 2.5 Gbps, and demonstration systems report data rates as high as 160 Gbps.
Free Space Optics (FSO) systems can function over distances of several kilometers. As long as there is a clear line of sight between the source and the destination, and enough transmitter power, Free Space Optics (FSO) communication is possible.
Academia.

In this paper, simulative analysis of 10Gbps
DWDM system link with FSO channel using different
modulation format under different weather condition has
been performed. A 16×10 DWDM system has been
analyzed with 1nm channel spacing and the effect of
variation in input power and transmission distance is
observed in terms of Q-factor values of received channels.
From the study of variation in input power in the scenario of
different weather condition (clear, haze, rain and fog) the
best modulation format has been identified. It has been
observed that DBNRZ modulation format is best result than
other modulation formats. Similarly in the case of while
varying link distance under different weather conditions, the
best modulation format has been recognized. It has been
observed that CSNRZ modulation format is better result
than the other modulation formats. The BER performance of
all received signals is also discussed.

In this paper investigation has been done on two different photodiodes PIN and APD for use as a receiver in free space fiber optical link. Eye Diagrams have been used to evaluate value of Q- factor in each and every case. Gaussian pulse modulation format has been used in this analysis work. It is clear from the findings of this analysis that value of Q-factor is maximum when APD has been used as the receiving photodiode at 1550nm wavelength and minimum when PIN diode has been used as receiving photodiode at 1550nm wavelength.

Free space optical (FSO) communication shows potential technology for communication.  But
the main weakness is atmospheric turbulence which causes major transmission destruction for
an open air optical communication system. In this paper, the performance of free space optical
(FSO)  is  analyzed  using  subcarrier  multiplexed  QPSK  intensity  modulated  OFS  link  with
optical  intensity  modulation  and  direct  detection  for  a  single  input  single  output  (SISO)
system  considering  strong  atmospheric  turbulence.  To  overcome  the  effect  of  atmospheric
turbulence, multiple input multiple output (MIMO) communication system is introduced here.
The performance results are evaluated and are shown in terms of BER and it is clearly found
that  performance  is  considerably  improved  for  a  multiple  input  multiple  output  (MIMO)
system.

Free-space optical communication (FSO) is an optical communication technology which uses light, propagating in free space to transmit data wirelessly for telecommunications. It is point to point infrared spectrum based optical communication between optical transceivers that are separated by physical medium known as air. FSO links use modulated low power laser beams to transmit information through the free space. This technology is useful where a fiber optic cable is impractical. FSO uses the light of wavelength 780nm to 850nm and 1550nm to 1600nm. 1550nm wavelength produce higher power and more eyes safe compared to 780nm and 850nm. The first part of this paper introduces the free space optic system its block diagram and previous research done on free space optics. The second part informs about the atmospheric conditions that effect the free space optical communication. The last part will describes the previous work done using different modulation techniques.