Research On 852nm Tunable Fiber Laser For Cs Atomic Clock Pumping Source

Atomic clock plays a significant role in the accurate guided missile,space positioning systems and flight navigation systems. Since the first atomic clock was developed in 1948, the atomic clock has very important applications in many areas such as national defense,military and space technology, so some scientists think that atomic clock will be more important than atomic bomb. The precision and the accurateness of the atomic clock frequency standard have attracted a lot of interests and studies, with the development of space technology, the demands for the precision of frequency and clock standard will be higher. In the present atomic clocks, Cs atomic clock has the highest precision and the best stability. The Cs atomic clock system is composed of pump source, Cs tube and light detector, where the laser source with the wavelength of 852 nm is used as pump source. Presently, almost all the 852nm lasers are semiconductor lasers, unfortunately, the stability of this kind of laser is poor, while, the fiber laser with the advantages of high stability, high plug in efficiency, high beam quality, as well as compactness, tenability, and flexibility, are the best choice for the atomic clock system. From the 80's of last century, scientists in our country have been trying to develop the Cs atomic clock system of ourselves, up to now, all the key components of the self-determination Cs atomic clock system have been developed except the 852nm laser source.This thesis"Research On 852nm Tunable Fiber Laser for Cs atomic clock pumping source"is under the support of the corresponding national project. With the systematic researches, we gain fruitful results, and the laser system has passed through the appraisement by the experts of General Armaments Department.The major results in the dissertation are obtained as the following:1. The invention of 850nm band fiber couplers is successfully made, in which the fusing taper method is adopted, and 50:50, 60:40 fiber couplers are developed. The 800nm/850nm WDM is successfully developed of which the loss is less than 0.5dB and the isolation degree is more than 40dB. These fiber devices will meet the need of the experiment setup.2. The invention of 850nm single mode fiber Bragg grating is successfully made, of which the center wavelength is near 851nm, the reflectivities range from 30% to 95%, 3dB bandwidth of reflectivity is less than 0.2dB. The FBG provides the frequency selective part for the fiber laser.3. The principle and characteristics of the stress tuning of FBG are investigated. We calculated in theory and selected the organic material for the tuning finally. A beam of uniform strength tuning device is successfully made, of which the stability is good and the tuning range meets the need of experiment.4. The characteristics of the up-conversion of Erbium doped fiber (Si based) is investigated. We proposed that the Er doped fiber is pumped with the bi-wavelength pumping to get 852nm up-conversion laser output for the first time. With bi-direction pumping and bi-wavelength (800nm and 792nm) pumping, some results and conclusions are obtained which will instruct the next experiment.5. By using the semiconductor optical amplifier a fiber laser operating at 852nm is successfully developed. The output power of the fiber laser is higher than 20mW, 3dB bandwidth is less than 0.05nm, side mode suppression is better than 30dB. The fiber laser is compact and stable of which the working wavelength can be tuned from 851nm to 854nm continually. This achievement is passed through the identification and appreciated by the experts of General Armaments Department.The innovative results in this dissertation are as following:1. The 850nm band fiber couplers and WDM are developed. The theory of bragg fiber grating is investigated and the FBG is made by ourselves of which the center wavelength is about 851nm, the highest reflectivity is 95%.2. For the first time we proposed that the Er doped fiber is pumped with the bi-wavelength pumping to get 852nm up-conversion laser output. The characteristics of the up-conversion of Erbium doped fiber (Si based) is investigated. With bi-direction pumping and bi-wavelength (800nm and 792nm) pumping, some results and conclusions are obtained which will instruct the next experiment.3. For the first time we have successfully made out a fiber laser working at 852nm. The fiber laser is compact, stable, easily tunable, of which the output power is higher than 20mW, the side mode suppression is better than 30dB. The fiber laser can be tuned from 851nm to 854nm continually.