Niels Henrik David Bohr

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7 October 1885_18 November 1962

contributions in atomic structure and quantum mechanics

Received Nobel Prize in 1922

PRESENTED BY JITTY MARIAM JOSE S8 AEI ROLL NO:24

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INTRODUCTION Light Amplification by Stimulated Emission

Radiation (LASER) is most widely used

Tunable laser is a multi functional laser

Here laser is tuned to required wave length

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CONTENTS LASER Need for tunable laser Tunable laser Types of tunable laser Advantages Applications Future of tunable laser

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LASER Semiconductor materials that give out intense light

at one specific colour

Electrons in excited spontaneously fall down to ground state

Lasers give out energy in the form of photons

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WORKING OF LASER

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NEED FOR TUNABLE LASERIn a WDM network we have 128 different lasers

giving light according to the way in which they are designed

128 spare lasers should be stored for replacement in case of failure

Tunable laser can serve as a backup for multiple channels

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TUNABLE LASER Tunable lasers – laser whose wavelengths can be

tuned

There are two methods of tuning laser

1. Mechanically adjusting the cavity length

2. Changing refractive index of the gain medium

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TYPES OF TUNABLE LASER Distributed Feedback [DFB] laser

Distributed Bragg reflector [DBR] laser

External Cavity Laser Diode [ECDL]

Vertical Cavity Surface Emitting Laser [VCSEL]

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DISTRIBUTED FEEDBACK LASER

Incorporates a diffraction grating directly into the laser chip itself

DFB lasers are tuned by controlling the temperature of the laser diode cavity

Tuning range is limited to 5nm

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DISTRIBUTED BRAGG REFLECTOR LASER

DBR has 3 sections-gain , mirror , phase

Tuning is accomplished by injecting current which changes refractive index

Tuning range is less than 10nm

Wider tuning range up to 40nm achieved by sampled grating

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THE EXTERNAL CAVITY DIODE LASER

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It uses a wavelength selective component such as grating or prism which is adjusted in a way that produces desired wavelength

Wide tuning range of about 40nm

Low tuning rate

VERTICAL CAVITY DIODE LASERMirrors are located in top and bottom of

semiconductor

Light resonates vertically in laser chip

Mainly used in telecommunication and other short reach application

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Comparison LASER ADVANTAGES DISADVANTAGE

SMARKET APPLICATIONS

DFB Wavelength stabilityEstablished fabrication process

Low output powerLimited tuning range

Narrowly tunable applications

DBR Fast switching speedEstablished fabrication process

Broad line widthWavelength instability

Access Switching

SGDBR Broad tuning range Fast switching speed

Low output powerBroad line widthNon continuous tuning

Access Metro Switching

VCSEL Narrow line width(for output)Low power consumptionMode stabilityCircular beam emittedTest at wafer level

Low output powerConfined to short wavelengths

AccessMetro

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ADVANTAGES Reducing risk of human error

Better use of expensive network bandwidth

Flexible provisioning

Simplified capacity planning and expansion

Faster , more responsive provisioning16

APPLICATIONSLaser Radar and 3D ImagingSpectroscopyPhotochemistryatomic vapour laser isotope separationoptical communications

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FUTURE OF TUNABLE LASER Fiber optics is the most emerging technology which

accounts for the high speed and accuracy in data transfer

Tunable laser provides options of multiple channel from 16 to 160 and at a rate of 40Gb/s

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CONCLUSION Due to the ease of fabrication and flexibility ,

ordinary lasers will pave the way for tunable lasers . And hope this is going to become a revolution in the field of communication and technology , especially in the field of optical network.

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REFERENCE1. “Tunable lasers” by Elizabeth Bruce; IEEESpectrum, February 2002.2. Tunable Laser Resonance Raman Spectroscopy of Bacteriorhodopsin by

A Lewis, J Spoonhower, RA … - Proc. Natl. Acad. …, 1974 - National Acad Sciences

3. Tunable laser diode by MC Amann - US Patent 5,325,379, 1994 - Google Patents

4. Monolithic Tunable laser diode LA Coldren - IEEE journal of selected topics in quantum electronics, 2000 - 130.83.66.6

5. Digital phase-measuring interferometry with a tunable laser diode Y Ishii, J Chen, K Murata - Optics letters, 1987 - opticsinfobase.org

6. www.blueskyresearch.com7. www.iolon.com8. www.opticsjournal.com9. www.telcordia.co.in

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