The quality factor is tuned by changing the properties of the cavity’s two walls. When the quality factor is reduced, light can get in. By raising the quality factor, the light is trapped inside. The opening and closing of the cavity must be done within the same time scale as that of the incoming light pulse, to prevent the light from escaping back. In a recent letter, the authors trapped and released a pulse in the same direction it came from. In this paper, the authors demonstrate capturing a 4 ps pulse for 332 ps, and then releasing it in a different direction. To achieve this, the two sides of the cavity need to be tuned.
The tuning was done by changing the Silicon refractive index with free carriers. The free carriers were created using a light pulse of short wavelength that hit the cavity on its appropriate side. The authors found that the main limitation of their method is free carrier absorption. If free carriers exist in the period of time when the light is trapped inside the cavity, the energy slowly dissipates. In their method, this problem cannot be avoided, and can only be minimized by restricting the free carriers to the opening and closing intervals, which enables the light to be captured for longer periods of time.
Developing such methods to integrate optical components is a key enabling technology and constitutes a crucial step in advancing other fields such as parametric and quantum-information processes.
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