Design and characterization of a laser integrated with long on-chip optical feedback usable as compact random number generator

We discuss the design and the dynamics of a semiconductor laser integrated with a long on-chip optical feedback (see also [Verschaffelt et al., Chaos: An Interdisciplinary Journal of Nonlinear Science, vol. 27, pp. 114310, 2017]1). Such lasers with optical feedback are interesting for several applications that make use of their rich dynamical behavior. Moreover, they are ideal test-beds to experimentally study delay induced dynamics, because the system's parameters (such as the laser injection current and the optical feedback strength) can be easily accessed and accurately controlled. The system discussed here uses only standard building blocks of the generic Jeppix platform for photonic integrated lasers. The design is based on a DBR-laser with a spiral delay waveguide. We have included several control pads with which we can tune the fabricated laser's emission wavelength, the feedback strength and phase in order to compensate for fabrication tolerances. We have been able to integrate a 10 cm feedback length on a footprint of 5.5 mm2. We illustrate that this delay is sufficiently long to drive the laser into a chaotic regime, and we analyze the chaotic dynamics based on the spectrum, autocorrelation and permutation entropy. We show - using the NIST statistical test suite for random number generators - that the observed delay dynamics is sufficiently complex for random number generation at a rate of 500 Mbits/s.