Abstract
Modulators using atomic systems are often limited in speed by the rate of spontaneous emission. One approach for overcoming this limit is to make use of a buffer gas such as Ethane, which causes rapid fine structure mixing of the P(1/2) and P(3/2) states, and broadens the absorption spectra of the D1 and D2 lines in alkali atoms. Employing this effect, we show that one can achieve high speed modulation using ladder transitions in Rubidium. We demonstrate a 100-fold increase, due to the addition of the buffer gas, in the modulation bandwidth using the 5S-5P-5D cascade system. The observed bandwidth of ~200 MHz is within a factor of 2.5 of the upper bound of ~0.51 GHz for the system used, and is limited by various practical constraints in our experiment. We also present numerical simulations for the system and predict that a much higher modulation speed should be achievable under suitable conditions. In combination with a tapered nano fiber or a SiN waveguide, it has the potential to be used for high-speed, low-power all-optical modulation.
Highlights
All-optical modulation and switching are important for optical communication and quantum information processing [1,2,3,4,5]· We have already demonstrated a cascade system all-optical modulator, polarizer and waveplate at a telecommunication wavelength using the 5S1/2-5P1/26S1/2 system, where the lower leg, at 795 nm, controls the transmission and absorption of the upper leg at 1323 nm [6,7,8]
We proposed a novel scheme for increasing the modulation bandwidth using buffer gas induced rapid fine structure mixing [6]
As a comparison with other techniques for low power all-optical modulation [21,22,23,24], we find that the instability induced switch has an figure of merit (FOM) of 4*104 photons [19] while micro-ring resonators based switches have an FOM of 4*107 photons [20]
Summary
All-optical modulation and switching are important for optical communication and quantum information processing [1,2,3,4,5]· We have already demonstrated a cascade system all-optical modulator, polarizer and waveplate at a telecommunication wavelength using the 5S1/2-5P1/26S1/2 system, where the lower leg, at 795 nm, controls the transmission and absorption of the upper leg at 1323 nm [6,7,8]. We present experimental results for such a modulator using the 5S1/2-5P3/2-5D3/2 system, where the lower leg is at 780 nm and the upper leg is at ~776 nm. The process is aided by the presence of the 5P1/2 level The choice of these particular transitions is primarily determined by the operational wavelength of the devices at our disposal. The principle of operation is the same for any cascade system with two intermediate fine structure levels, and can be used at a wavelength corresponding to the telecommunication band, for example.
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