High-Q whispering gallery traveling wave resonators for oscillator frequency stabilization

Usually a frequency-stabilized standing wave resonator-oscillator incorpora ting a resonator as a frequency discriminator requires a circulator to sepa rate the injected and reflected wave. A ferrite circulator is a noisy devic e and can limit the phase noise or frequency stability. Moreover, we show t hat the noise in a circulator varies, and detailed low noise measurements a re necessary to choose an appropriate quiet circulator. Thus, by realizing a configuration that does not require a circulator, an improvement in perfo rmance and reliability can be obtained. A solution to this problem is to de sign a high-Q whispering gallery traveling wave (WGTW) resonator. This devi ce naturally separates the injected and reflected wave in the same way as a ring cavity at optical frequencies, without degrading the frequency discri mination. Q-factor measurements of a WGTW sapphire resonator are presented, along with a derivation of critical parameters to maximize the frequency d iscrimination. New measurements of noise in ferrite circulators and isolato rs have also been made, which is followed with a discussion on oscillator d esign.