Observation of switching and pulsed behaviour in a noise-driven resonant tunneling diode excitable optoelectronic oscillator

Summary form only given. Excitability is a well-established nonlinear dynamical concept in biological (neurons), and chemical (Belousov-Zhabotinsky reaction) systems [1]. The all-or-none response of an excitable system is a key effect of information processing in excitable oscillators. Excitability has been reported in lasers with promising applications in photonics such as clock recovery and pulse reshaping [2]. However, slow speed operation and bulky schemes make most of them too complex and slow for current and future information processing needs.In this work, we present a novel, compact, and simple excitable optoelectronic oscillator consisting of a AlAs/InGaAs double barrier quantum well (DBQW) resonant tunneling diode (RTD) driving a 1550 nm communications laser diode (LD) [3], Figs. 1(a) and (b). RTD-LD excitable optoelectronic systems exhibit a current-voltage (I-V) curve with a pronounced negative differential resistance (NDR), Fig. 1(c), and can operate at greater than GHz speeds [3] (RTDs can work up to THz). Here we present noise activated induced excitable and pulsed dynamics in both electrical and optical domains using RTD-LDs operating at room temperature. The RTD-LD is first DC biased, VDC, slightly below the peak, Fig. 1(c), i.e., in a non-oscillating equilibrium situation. For purposes of demonstration and experimental convenience, the driving signal consists of a stochastic voltage signal generated by a Gaussian white noise source, Vnoise, with a cut-off frequency of 80 MHz. The driving signal can be also injected optically, taking advantage of the optical input port of the RTD ridge waveguide [3], Fig. 1(a). The RTD-LD can emit excitable pulses in both electrical and optical outputs when the amplitude of the stochastic perturbation exceeds a given threshold, as presented in Fig. 1(d), showing upward and downward electrical pulses due to noise-induced RTD-LD switching from the peak-to-valley regions. The LD intensity output follows the switching - urrent modulation induced by the RTD with a sequence of downward pulses of decreasing intensity with a FWHM around 200 ns. The FWHM of the pulses can go below 1 ns if an appropriate RTD-LD refractory time is chosen, determined by the circuit´s resonant tank. For a given range of noise input the pulsed behavior is more regular, Fig. 2(a), with a time repetition determined by the RTD-LD refractory time. Interestingly, Fig. 2(b) shows multi-pulsing “bursting” behavior as a result of the asymmetric IV curve when the RTD-LD is DC biased closed to the valley region, which can be explored in novel applications such as signal pattern generation. We also present the numerical simulations of a system of differential equations comprising a nonlinear Liénard´s oscillator that models the electrical circuit [3], stochastically driven by means of white Gaussian noise, Dξ(t) (D is the noise dimensionless amplitude, and ξ(t) the Gaussian function), and LD single mode laser rate equations [3]. As seen in Figs. 2(c) and (d), the Liénard oscillator-laser diode model subjected to stochastic fluctuations is in a very good agreement with the experimental results.We have shown excitability in a simple and compact RTD-LD optoelectronic circuit configuration. Since RTDs and LDs can be monolithic integrated, and the I-V N-shape of the optoelectronic system extends over a wide bandwidth, this approach can provide compact designs at GHz high-speed with improved performance for emerging applications in neural emulation, signal processing, and switching in optical networks.