Optical bistable switching using frequency modulation (A)

Frederic A. Hopf, Sami A. Shakir

Riccardo A. Calvani, M. Calzavara, Renato Caponi

In all-optical switching systems bistable distributed-feedback (DFB) amplifiers are being used experimentally as memory cells and signal regenerators. In this frame a single section DFB amplifier (with one AR coated facet) operating around threshold at 1549 nm is pumped by a similar laser with a carefully controlled frequency detuning. The polarization controlled pump beam is modulated by a Mach-Zehnder switch (2.5 GHz bandwidth) to avoid source frequency chirp. The measurement of a pump reference and of the beam reflected from the amplifier is performed through a fiber directional coupler inserted between the two DFB diodes. Optical bistability has been observed both in transmission and in reflection for a sinewave modulated input in the 1-200 MHz frequency range. The output square wave exhibits up and down switching times lower than 1 ns and about 2 ns, respectively. The latter figure is consistent with the carrier recombination time in InGaAsP active structures, which is the main limit to the recovery time of bistable amplifiers. Work is in progress to investigate this feature in other types of amplifiers (e.g., multisection DFBs and quantum well structures).

Saad S. M. Hassan, S.P. Tewari

Nasser N. Peyghambarian, H. M. Gibbs, Daniele Hulin +3 more

Leonardo Del Bino, Niall Moroney, Pascal Del’Haye

The Kerr nonlinearity can be a key enabler for many digital photonic circuits as it allows access to bistable states needed for all-optical memories and switches. A common technique is to use the Kerr shift to control the resonance frequency of a resonator and use it as a bistable, optically-tunable filter. However, this approach works only in a narrow power and frequency range or requires the use of an auxiliary laser. An alternative approach is to use the asymmetric bistability between counterpropagating light states resulting from the interplay between self- and cross-phase modulation, which allows light to enter a ring resonator in just one direction. Logical high and low states can be represented and stored as the direction of circulation of light, and controlled by modulating the input power. Here we study the switching speed, operating laser frequency and power range, and contrast ratio of such a device. We reach a bitrate of 2 Mbps in our proof-of-principle device over an optical frequency range of 1 GHz and an operating power range covering more than one order of magnitude. We also calculate that integrated photonic circuits could exhibit bitrates of the order of Gbps, paving the way for the realization of robust and simple all-optical memories, switches, routers and logic gates that can operate at a single laser frequency with no additional electrical power.

Vijay Bhatt, Sabur A. Barbhuiya, Pradip K. Jha +1 more

Abstract We theoretically explore optical bistability for the possible signature of all-optical switching and their performance in a hybrid quantum optomechanical system comprising of two semiconductor microcavities coupled optically. One of the cavity is driven by an external amplitude-modulated pump laser while the second cavity, which contains a quantum dot (QD), is indirectly driven by light transmitted from the first cavity and a transverse optical field. The generated bistable behavior due to optomechanical nonlinearity shows a typical optical switching behavior and it can be controlled by changing the laser power, QD cavity coupling, modulating amplitude/frequency and the optomechanical coupling. A clear signature of energy exchange between the mechanical and optical modes is visible from the mechanical displacement spectrum. These results suggest that the present system can be used in sensitive optical switches and optical sensors.