Recently, there has been tremendous interest in excitable optoelectronic devices and in particular excitable semiconductor lasers that could potentially enable unconventional processing approaches beyond conventional binary-logic-based approaches. In parallel, there has been renewed investigation of non-von Neumann architectures driven in part by incipient limitations in aspects of Moore’s law. These neuromorphic architectures attempt to decentralize processing by interweaving interconnection with computing while simultaneously incorporating time-resolved dynamics, loosely classified as spiking (a.k.a. excitability). The rapid and efficient advances in CMOS-compatible photonic interconnect technologies have led to opportunities in optics and photonics for unconventional circuits and systems. Effort in the budding research field of photonic spike processing aims to synergistically integrate the underlying physics of photonics with bio-inspired processing. Lasers operating in the excitable regime are dynamically analogous with the spiking dynamics observed in neuron biophysics but roughly 8 orders of magnitude faster. The field is reaching a critical juncture at which there is a shift from studying single devices to studying an interconnected network of lasers. In this paper, we review the recent research in the information processing abilities of such lasers, dubbed “photonic neurons,” “laser neurons,” or “optical neurons.” An integrated network of such lasers on a chip could potentially grant the capacity for complex, ultrafast categorization and decision making to provide a range of computing and signal processing applications, such as sensing and manipulating the radio frequency spectrum and for hypersonic aircraft control.

Recent progress in semiconductor excitable lasers for photonic spike processing

An in-depth theoretical as well as experimental analysis of the nonlinear dynamics in semiconductor lasers with active optical feedback is presented. Use of a monolithically integrated multisection device of submillimeter total length provides access to the short-cavity regime. By introducing an amplifier section as a special feature, phase and strength of the feedback can be separately tuned. In this way, the number of modes involved in the laser action can be adjusted. We predict and observe specific dynamical scenarios. Bifurcations mediate various transitions in the device output, from single-mode steadystate to self-pulsation and between different kinds of self-pulsations, reaching eventually chaotic behavior in the multimode limit.

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Nonlinear dynamics of semiconductor lasers with active optical feedback.

This paper is a review of applications of delay differential equations to different areas of engineering science. Starting with a general overview of delay models, we present some recent results on the use of retarded, advanced and neutral delay differential equations. An emerging area for modeling with the help of delay equations is real-time dynamic substructuring, or hybrid testing. We introduce the main idea of this technique together with the latest advances. Special emphasis is given to the development of the theory and applications of partial delay differential equations. The review concludes with a summary of some open problems and questions concerning the analysis of spatially extended delayed systems.

On the Use of Delay Equations in Engineering Applications

In this paper, self-pulsation (SP) in a distributed Bragg reflector (DBR) semiconductor laser without a saturable absorber is experimentally and theoretically investigated. Detailed experimental characterizations of the SP DBR laser are reported in the optical and radio-frequency domains. Phase correlation between the longitudinal modes selected by the DBR mirror has been experimentally demonstrated. A theoretical model based on coupled rate equations for three modes has been developed to study the time evolution of phases and amplitudes of the modes. The carrier density modulation, resulting from the beating between adjacent longitudinal modes generates four-wave mixing (FWM) and is responsible for mutual injection locking, leading to passive mode-locking. The calculated power spectral density of the frequency noise derived from the model is in agreement with experimental results and proves that the phases of the longitudinal modes are identically correlated through the FWM process in this type of SP lasers

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Phase Correlation and Linewidth Reduction of 40 GHz Self-Pulsation in Distributed Bragg Reflector Semiconductor Lasers

https://ifisc.uib-csic.es/ingo/Pubs/OptComm-CoupledLasers-05.pdf

Mutually delay-coupled semiconductor lasers: Mode bifurcation scenarios

We present a detailed description and a first theoretical study of an improved concept for high-frequency self-pulsations (SPs) in multisection (MS)-DFB lasers with an integrated phase tuning section. The DFB wavelengths of the two DFB sections are spectrally detuned by nearly the stopband width using two gratings with different grating periods. If both DFB sections are operated at lasing conditions and an appropriate phase is chosen, we obtain beating-type SP with a frequency given by the spectral distance of two lasing modes. Good agreement between theory and experiment is obtained with respect to the role of the detuning, the role of the phase section, as well as the synchronization to external injected signals. The modeling shows a strong nonlinear coupling of the two involved modes via the carrier densities. This effect is important for the mutual coherence and for the observed locking of the beating oscillations to external signals. From the results of the calculations, we draw the conclusion that even higher SP frequencies can be obtained based on the new concept.

Detuned grating multi-section-RW-DFB-lasers for high speed optical signal processing

An integratable version of a self-pulsating AR-coated multisection DFB-laser with a phase-tuning section integrated between two DFB sections is presented. It is shown that the phase current can act as an electrical switch for turning ON and OFF the self-pulsations. In addition, the frequency stability can be improved by properly adjusting the phase current. The frequency of the self-pulsations is electrically tunable over more than one octave continuously.

Electrically switchable self-pulsations in integratable multisection DFB-lasers

Continuously chirped gratings for DFB-lasers fabricated by direct write electron-beam lithography

We demonstrate the first realization of all-active tapered index coupled 1.55-/spl mu/m InGaAsP buried-heterostructure distributed feedback lasers involving chirped gratings. The variation of the effective refractive index along the tapered active stripe is compensated using an optimized continuously chirped grating. The grating has been formed using a novel direct-write electron-beam lithography technique. Lasers with an antireflection/cleaved cavity show stable single-mode operation and high optical output power up to 60 mW. The yield of lasers with a sidemode suppression ration > 40 dB is more than 70%. The -3-dB farfield angles (full-width at half-maximum) amount to 14/spl deg/ and 20/spl deg/ in lateral and vertical direction, respectively.

R. Steingruber

Papers

Detuned grating multi-section-RW-DFB-lasers for high speed optical signal processing

Electrically switchable self-pulsations in integratable multisection DFB-lasers

Continuously chirped gratings for DFB-lasers fabricated by direct write electron-beam lithography

All-active tapered 1.55-μm InGaAsP BH-DFB laser with continuously chirped grating