This thesis presents a study of two aspects of ring laser gyroscopes: Correction of systematic errors due to optical backscatter, and development of solid-state ring laser gyroscopes. Backscatter at the optical surfaces of ring laser gyroscopes causes systematic measurement errors. These errors were modelled and corrected for in large ring lasers. The model included backscattering, hole burning and dispersion in the gain medium. The model predictions were used in conjunction with measurements of the intensity modulation of each beam and the phase difference between these modulation to correct the measured Sagnac frequency of the large ring lasers, PR-1 and G-0. Dramatic improvements in the sensitivity of both lasers were achieved. Most current laser gyroscopes use He-Ne plasma as the gain medium. This makes the devices fragile, the plasma creates UV light that degrades the cavity mirrors and the gas itself degrades over time. As a alternative, solid state materials might be used as the gain medium for the gyroscope. Both neodymium doped and erbium ytterbium co-doped phosphate glass lasers were constructed. Initially linear cavity designs were constructed to test the suitability of the gain media. Both laser systems employed longitudinal laser diode pumping. Thirty six perimeter ring lasers were then developed using both gain media. In both cases successful rotation sensing was achieved on a turntable which provided external rotation. For rotation rates between 0.1 and 0.85 rad/s, the gyroscope built using Er-Yb and Nd phosphate glass are superior to Nd:YAG (the only other material known to have been used in a continuous wave solid state gyroscope). This improvement is due to the use of thin heavily doped gain medium, which decreases the detrimental effect caused by gain gratings.

M.Phil. / This dissertation describes the design and experimental realization of an all-optical active Q-switched Erbium-doped fibre ring laser. The aim of this research is to propose an approach of Q-switching mechanism for a fibre laser. The Q-switch device combines a fibre Bragg grating and a tunable fibre Fabry-Perot filter. The Q-switching principle is based on dynamic spectral overlapping of two filters, namely FBG based filter and tunable F-P filter. When the spectra overlap, the filter system has the maximum transparency, the laser cavity has minimal losses and it can release the stored power in the form of the giant impulse. A series of experiments are performed to optimize the all-optical active Q-switched Erbium-doped ring laser system in term of output peak power and time duration of laser pulses. Two different Erbium-doped fibres having different Erbium ion concentration are used in this experimental investigation. The first fibre, with an Erbium ion concentration of 2200 ppm and pump absorption of 23.4 at 980 nm is referred to as “high concentration” and the second with an Erbium ion concentration of 960 ppm and pump absorption of 12.4 at 980 nm is referred to as “low concentration” To optimize the Q-switched fibre laser system, different parameters were investigated such as the length of the Erbium-doped fibre, the output coupling ratio, the repetition rate of pulses and the concentration of the Erbium Doped Fibres. The achieved output laser pulse characteristics, peak power and time duration, were 580 mW and 13 μs respectively, at 1 kHz of repetition rate. These characteristics were obtained using a length of 3.5 m “low concentration” Erbium-doped fibre in a ring laser cavity; the output coupling is 90 %, for a pump power of 80 mW. Employing this all-optical Q-switching approach, a simple, robust all-optical active Q-switched Erbium-doped laser is demonstrated.