|Ph.D Student||Gershikov Alexander|
|Subject||Optical Components Based on Phase Sensitive Parametric|
|Department||Department of Electrical Engineering||Supervisor||Professor Emeritus Gad Eisenstein|
|Full Thesis text|
In this research we report several experimental photonic systems, based on phase sensitive parametric amplification in fibers. Phase sensitive gain attracts significant attention recently, mostly due to its advantages over conventional, phase insensitive gain. The first and most significant among them is the capability to reach noise figures lower than well-known quantum limit of phase insensitive gain which is 3 dB, meaning that every photon that amplifies the signal is accompanied by two noise photons. During the phase sensitive gain, a process called "mode squeezing" takes place and results in amplification of in-phase signal and simultaneously attenuation of the out of phase elements. The previous works in this field reported sub 3-dB noise figures but the gain region was limited to the spectral vicinity of the pump. We utilized narrow band parametric gain, which is known for the ability to operate at high detuning from the pump, as key process to obtain phase sensitive gain in spectral regions previously unobtainable. The narrow band process was utilized in our previous works as basis for coherent light sources, especially for the 2µm wavelength region. One of the experimental systems we describe in this work improved significantly the performance of optical parametric oscillators for the mentioned wavelength region. The improvement was achieved by the addition of a Thulium doped fiber to the oscillating cavity where it served as an active filter.
However the main emphasis of this work is phase sensitive gain based components. In the first system, we expand the amplifier to the narrow band regime resulting in a gain tenability of more than 400 nm. The amplifier gain was calculated from conversion efficiency of the idler and had a cyclical pattern, with peaks where the phases of the waves match and minima for frequencies where destructive interference takes place. The next step was to expand the phase sensitive gain to the 2µm wavelength region, and characterize it at these wavelengths.
The cyclical pattern of the gain leads to idea to employ it as basis for a parametric oscillators, where each gain period will result in an oscillation line. The setup for both continuous wave and pulsed pump was employed with more than ten oscillation lines on each side of the pump at having a low power variance. Also the capability to control the oscillating lines spectral spacing was demonstrated.
In the last work we modified the setup by utilizing ultra-short pump pulses having, naturally, wide spectral widths. This has two significant consequences. First is a significant, 4-5 times fold, wider amplifier bandwidth. The second is the demonstration of the capability to control amplifier bandwidth. By controlling the pump spectral width (using tunable narrow band filters). This results open possibilities for more completed control over amplifier gain spectra, by using more sophisticated amplitude and phase filters. A gain level between -6 and 6 decibels was measured. A negative gain, similar to the one we measured, is a necessary condition for mode squeezing and key to low noise photonic components.