2. INTRODUCTION  Tunable lasers are different to traditional lasers because they can continuously change their emission wavelength, or color, in a given spectral range.  As such, these quantum devices have found numerous applications in many diverse fields.  In particular, tunable lasers have played a crucial and sustained role in advancements of fundamental physics and science.  A Tunable laser is a laser whose wavelength of operation can be altered in a controlled manner.laserwavelength  While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range.laser gain media

3. DEFINITION  Tunable lasers as the name suggests are lasers whose wavelengths can be tuned or varied.  They play an important part in optical communication networks  Recent improvements in tunable laser technologies are enabling highly flexible and effective utilization of the massive increases in optical network capacity brought by large-scale application of dense wavelength division multiplexing.  The distributed feedback laser (DFB), the external cavity diode laser, the vertical cavity diode laser and the micro electro mechanical system (MEMS) technology  Tunable lasers are still a relatively young technology, but as the number of wavelengths in networks increases so will their importance.

4.  A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner.laserwavelength  Tunable lasers are now widely used as light sources in DWDM systems.  the tunable lasers are used both as a light source in the transmitter and as a local oscillator in the receiver.  We can use this tunable lasers are enabling highly flexible and effective utilization of the massive increases in optical network capacity brought by large-scale application of dense wavelength division multiplexing  Tunable lasers are still a relatively young technology, ADVANTAGES OF TUNABLE LASER

5. APPLICATIONS  1.spectroscopyspectroscopy  2.photochemistryphotochemistry  3.atomic vapor laser isotope separation,atomic vapor laser isotope separation  4. optical communicationsoptical communications  5.Spectroscopic Applications of Pulsed Tunable Optical Parametric Oscillators.  6.Solid-State Dye Lasers  7.Tunable Lasers Based on Dye-Doped Polymer Gain Media Incorporating 8.Homogeneous Distributions of Functional Nanoparticles

6. CONCLUSIONS  For the 100-Gbit/s system now being developed as a next-generation optical communication system,  we have160 kHz was demonstrated using a TLA with 1500-μm-long DFB lasers . In addition to the line width characteristics described here, the tunable laser requires higher power, a wider tuning range, and lower power consumption.  Research and development will continue with the aim of obtaining tunable lasers with even better performance

7. REFERENCES  [1] H. Ishii et al., Quasicontinuous wavelength tuning in superstructure- grating (SSG) DBR lasers, IEEE Journal of Quantum Electronics, Vol. 32, pp. 433-441 (1996)  [2] G. Morthier et al., A lambda/4-shifted sampled or superstructure grating widely tunable twin-guide laser, IEEE Photonics Technol. Lett.Vol. 13, p. 1052-1054,(2001)  [3] J.-O. Wesström et al., Design of a Widely Tunable Modulated Grating Y-branch Laser using the Additive Vernier Effect for Improved Super-Mode Selection, accepted to the IEEE International Semiconductor Laser Conference