The dependence of phase and modulation depth on the frequency and intensity of an optical signal is examined for the case of transmission by a saturable absorber.
All-optical data processing continues to attract significant interest as a way to overcome the electronic signal processing bottleneck of fiber telecommunication networks. Nonlinear optical devices such as limiters and saturable absorbers rely on intensity-dependent attenuation of light. However, making such devices using intensity-dependent multiphoton dissipation processes is an issue as these make complete absorption and transmission impossible. Here, we show that nonlinear phase retardation in an optical fiber can control the dissipation of coherent light waves interacting on a thin plasmonic absorber from total absorption to perfect transmission. The fiber’s instantaneous Kerr nonlinearity and the femtosecond coherent absorption time scale make this approach ultrafast. We report proof-of-principle demonstrations of all-optical intensity discrimination, power limiting, pulse restoration, pulse splitting, and signal transfer between carrier wavelengths within a fiber circuit. Our results indicate that nonlinear control of coherent absorption can imitate and outperform saturable and multiphoton absorption in terms of bandwidth and contrast.
We investigate the coherent population trapping resonance induced by a polychromatic optical field with an asymmetric spectrum, i.e., whose sidebands equidistant from the carrier have unequal powers. A situation is considered where a modulation is used to provide the so-called in-phase and quadrature signals in the optical field's transmission, which are used for stabilization of the local oscillator's frequency in chip-scale atomic clocks. In a general case, the frequencies of the signals nonlinearly depend on the optical field's intensity due to the asymmetry of the resonance. In this work, we demonstrate a) that this effect stems from a multi-peak structure of the resonance; b) a linear dependence of the frequency on the optical field's intensity at high modulation values; c) that the regime of the resolved structure has more advantages than suppression of the frequency shift due to the spectrum asymmetry.
Abstract When a 787‐nm signal light with constant optical intensity is superimposed with a control light of the same wavelength in an Er‐doped optical fiber, optical switchoff occurs. The optical intensity of the control light for switch‐off is 1.4 and 25 W/cm2. As the optical intensity increases, the optical transmission of the fiber decreases. When the optical intensity is 25 W/cm2, the optical transmission is lowest. A numerical analysis based on the four‐level double absorption model indicates that this nonlinear transmission characteristic takes place because the excited absorption due to the 2H11/2‐4I13/2 transition of Er3+ is predominating in the 4I9/24I15/2 and 2H11/2‐4H13/2 double absorptions. The optical switch‐off phenomenon is regarded as the first‐order phase transition phenomenon due to complex saturable absorbers with negative optical intensity dependence in optical transmission.