The Andrew and Erna Viterbi Faculty of Electrical & Computer Engineering
Mode selection in multi-mode oscillators by initializing the cavity signal
Multimode continuous wave (CW) oscillators such as long cavity lasers or optoelectronic oscillators (OEOs) can generate signals with ultra-low phase noise. In these devices, the long cavity length highly increases the effective Q-factor of the cavity. However, when the cavity length is increased the mode spacing decreases such that the cavity filter is insufficient to select a specific cavity mode. In multimode oscillators, based on homogenously broadened amplifiers with an instantaneous response time, the oscillator can potentially oscillate in one of a large number of modes. Therefore, when the oscillator is turned on, the steady state mode is randomly selected between a few cavity modes, which experience the highest small signal gain.
In this presentation, we demonstrate a new method to select the oscillation mode in multi-mode oscillators with an instantaneous gain saturation. The method is based on initializing the cavity signal by feeding into the cavity an external signal for a duration that can be as short as the cavity delay. After the external signal is turned off, the steady state oscillation mode is exactly determined by the frequency of the external signal. By changing the external signal frequency, any specific mode can be selected over a broad operating frequency region, which is wider, in our experiments than the FWHM bandwidth of the cavity filter. The method was experimentally demonstrated in an optoelectronic oscillator (OEO) and the results were compared to a comprehensive numerical simulation. A good quantitative agreement between theory and experiments was obtained. A fundamental limit on the minimum duration, which is required to deterministically initialize the cavity signal, is given.
* M.Sc student under the supervision of Prof. Moshe Horowitz.
Join Zoom Meeting: https://technion.zoom.us/j/99476370567
Mon 03 May 2021
Start Time: 14:30
End Time: 15:30
ZOOM Meeting | The Andrew And Erna Viterbi Faculty Of Electrical & Computer Engineering