Noise-induced pulse-timing statistics in an integrated two-section semiconductor laser with saturable absorber

We have analyzed and explained the generation of irregularly timed, spontaneous-emission triggered optical pulses from a two-section semiconductor laser with saturable absorber, operating near threshold in a regime of excitability. Here we focus on the statistics of the spontaneously emitted pulses. The numerical simulations and analytical theory are based on the Yamada model. The observed irregular pulse train intervals exhibit an initial refractory time, followed by a time interval until the next emitted pulse. The latter is analyzed in terms of a first-passage-time distribution for the intensity to diffuse from its equilibrium value to hit a larger threshold intensity for the first time. Analytic asymptotic short-time and long-time approximations have been derived

Measurements and modeling of a monolithically integrated self-spiking two-section laser in InP

The self-spiking behavior of an integrated saturable absorber and gain section laser fabricated in an InP technology platform is analyzed. The gain, absorber and intensity dynamics are first inspected using the normalized Yamada model. This model shows excitable behavior as well as the relative refractory period, both of which are also present in biological neurons. Measurements of a two-section laser show irregular spike generation on the millisecond timescale, with a saturable absorber voltage controlled spike density. From our simulations, and from the quasi-random character and millisecond timescale at which these pulses occur, we conclude the laser is triggered by noise, an important characteristic in the operation of biological neurons. Simulations of the laser around the excitability threshold using a newly proposed model with an optical noise term show qualitatively similar self-spiking behavior as measured.</p

Nonlinear semiconductor laser dynamics

This chapter is devoted to the semiconductor laser with a saturable absorber as a device that can operate as an excitable medium. After a short historical introduction, the semiconductor laser and its dynamical properties are treated. Then the focus is shifted toward the laser with a saturable absorber and its excitable dynamics. The feasibility of this system, when implemented on an InP-photonic integration platform, is investigated by simulations with realistic parameter values obtained from experiments. The cascaded operation of a sequence of several laterally coupled lasers with the propagation of spike pulses is demonstrated in simulations. It is shown that the excitability can be robust against the inevitable presence of spontaneous emission noise in a real system. It will be concluded that the semiconductor laser with a saturable absorber is an excellent candidate to serve as a fundamental building block in an all-optical artificial spiking neural network

First-Passage-Time Analysis of the Pulse-Timing Statistics in a Two-Section Semiconductor Laser under Excitable and Noisy Conditions

A two-section semiconductor laser can exhibit excitability for certain parameter settings. When used as a photonic spiking neuron, it is relevant to investigate its sensitivity to noise due to, e.g., spontaneous emission. Under excitable conditions, the system emits irregularly timed noise-triggered pulses. Their statistics is analyzed in terms of a first-passage time distribution for the fluctuating intensity to reach the threshold for excitable response. Two analytic approximations valid for short and long times, respectively, are derived which very well explain measured and simulated pulse-repetition time distributions. This provides physical insight into the noise-triggered spiking mechanism

Measured histogram plot data of First-Passage-Time Analysis of the Pulse-Timing Statistics in a Two-Section Semiconductor Laser under Excitable and Noisy Conditions

Histogram data obtained from measured time traces used to create figure 3. The dataset contains one array with numbers, indicating the temporal difference between pulses (in ΔT, see the paper)