IV B.tech,ECE ( DATA TRANSMISSION THROUGH LASERS ) Presented By K.Sai Bhargav Ram

INTRODUCTION Free space optics (FSO/WOC/FSP) is an emerging technology that is gaining acceptance in an increasing number of sectors of science and industry. It has found application in several areas of short communications. It can provide an effective line-of-sight and high bandwidth.

1.Satellite: But this are expensive to make & to maintain. 2.Radio: But we has to use microwave towers around the countrys. 3.Mobile Phone: Data speeds -9.6 kbps is typical.

….. BANDWIDTH when and where required. AND THAT IS ? Over the last 20 years deployment of optical fibre cables in the backbone and metro networks have made huge bandwidth readily available to within one mile of businesses/home in most places. But, HUGE BANDWIDTH IS STILL NOT AVAILABLE TO THE END USERS. The Problem? 4

 Spectrum utilization  Interference  License fees(cost is high)  Wasteful of power  Security  Multipath fading

 The transmission of information using light is actually not a new idea.  In the late nineteenth century, Alexander Bell expanded his "phone-phone" communication (600ft)which modulated by sunlight.. He called it as “Optical Technology”.

An optical wavelength of 1550 nm is often preferential for optical transmission due to eye safety issues.

 Free Space Optics- (FSO) transmits invisible, eye-safe light beams from one "telescope" to another using low power infrared lasers in the tera Hertz spectrum.  Each optical wireless unit uses an optical source, plus a lens or telescope that transmits light trough the atmosphere to another lens Rx the information

 Fig-a: Diode Laser Transmitter Fig- b: Avalanche photo diode receiver  Diode lasers are driven with a DC bias current and the data is on/off keying (OOK).For lasers with output powers below approximately 50 mW.  Detectors are generally either PIN diodes or avalanche photodiodes (APD). For carrier class free-space optics systems, an APD is always advantageous since SNR is good.

 Narrow low power transmit beam  Similar bandwidth/data rate as Optical Fiber  No multi-path induced distortion in LOS  Efficient optical noise rejection and a high optical signal gain  Can support mobile users using steering and tracking capabilities. used for point –point com.  It should be Cheaper Iran

> It is capable of txmting over a distance of over 20 km. Since the camera scans at 60 frames per second, they were only able to receive at 4 bits per second it can be used in villages for txmting data from one to another.. Fig a: The Video Camera, laser pointer combination Fig b: showing a optical Transceiver

 Air Fiber: Hybrid Free- space optic/Radio Light Pointe: Light Pointe: Multi-beam sending process Multi-beam sending process Tera beam: Tera beam: carrier-grade FSO equipment carrier-grade FSO equipment and services

Iran EffectsOptionsRemarks Photon absorption Increase transmit optical power Effect not significant FSO Challenges - Rain = 0.5 – 3 mm

 Getting a laser beam to hit the mark in a laboratory setting is easy, but in the real world it is much harder. 1)Atmospheric turbulence 2)Fog 3)Building movement

 Mie scattering  Photon absorption  Rayleigh scattering  Increase transmit power  Diversity techniques  Effect not severe EffectsSolutionsRemarks dB/km150 dB/km225 dB/km

16 DRIVER CIRCUIT SIGNAL PROCESSING PHOTO DETECTOR Link Range L  Cloud  Rain  Smoke  Gases  Temperature variations  Fog and aerosol By Beer-Lamberts’s law: α : Attenuation coefficient dB/km d 1 and d 2 : Transmit and receive aperture diameters (m) D: Beam divergence (mrad)(1/e for Gaussian beams; FWHA for flat top beams), Dominant term at 99.9% availability Challenge #2—Interrupted signals

High Band width bandwidth THz in the nm range Iran What does It Offer ? No multipath fading - Intensity modulation and direct detection Secure transmission High data rate – In particular line of sight (in and out doors) 205 to 10Gbps Improved wavelength reuse capability Cable free connection 17

Iran DrawbacksDrawbacks Multipath induced dispersion (non-line of sight, indoor) - Limiting data rate Limited transmitted power - Eye safety (indoor) High transmitted power - Outdoor Receiver sensitivity Limited range: Indoor: ambient noise is the dominant (20-30 dB larger than the signal level. Outdoor: Fog and other factors 18

Iran In addition to bringing huge bandwidth to businesses /homes FSO also finds applications in : Multi-campus university Hospitals Others:  Inter-satellite communication  Disaster recovery  Fibre communication back-up  Links in difficult terrains  Temporary links e.g. Conferences  Military applications Cellular communication back-haul FSO challenges… FSO - Applications

Down link Up link Visible-light communication system Distribution of illuminance Visible Light Optical Wireless System with OFDM

FSO equipment currently is being deployed for a variety of applications, such as last-mile connections to buildings, which may provide the greatest opportunity. Since FSO provides the high -speed links that customers need without the costs of laying fiber. FSO provides the optical Connectivity cost effectively, quickly and reliably.

Dept. of ECE, Narayana Engineering college