||The maximum capacity of an optical fiber transmission system is more than doubled every year to cater the fast-growing communication need. The technology breakthrough in dry fiber fabrication opens the possibility for fiber bandwidth from 1.3 μm to 1.6 μm. The fast increasing demand of communication capacity results in the emergence of wavelength division multiplexing (WDM) technology, which results in the need for ultra-broadband optical amplifier. Cr4+:YAG has a strong spontaneous emission spectrum covers from 1.3 μm to 1.6 μm. In addition, its absorption spectrum is between 0.9 μm to 1.2 μm, which matches with the pumping source in current erbium doped optical amplifier. Such fiber is, therefore, eminently suitable for optical amplifier applications.|
In this thesis, we introduce the development of ultra-broadband optical amplifier using the double-clad Cr4+:YAG crystal fiber, which is grown by the laser heated pedestal growth (LHPG) technique. With the butt-coupling method, a gross gain of 4.0 dB is demonstrated at 1.3W bi-directional pump power at present. Moreover, theoretical models and numerical simulations have been developed to find out a better method for experiments. Numerical simulation indicates that the pump ESA will seriously impede the development of optical amplifier using the double-clad Cr4+:YAG crystal fiber.
In the future, in order to reduce pump ESA we attempt to use clad-pump scheme instead of core-pump scheme, to choose pumping wavelength at 925 nm instead of 1064 nm and to use side deposition of Yb2O3. At the same time, we will also try to grow crystal fiber of smaller core diameter and to extend its length to improve gain performance.