QCLs Exhibit Extreme Pulses

Extreme events can take place in tele­communication data streams. In fiber-optic communi­cations where a vast number of spatio-temporal fluc­tuations can occur in transoceanic systems, a sudden surge is an extreme event that must be suppressed, as it can poten­tially alter components associated with the physical layer or disrupt the transmission of private messages. Recently, extreme events have been observed in quantum cascade lasers, as reported by researchers from Télécom Paris (France) in colla­boration with UC Los Angeles and TU Darmstadt (Germany). The giant pulses that charac­terize these extreme events can contribute the sudden, sharp bursts necessary for communi­cation in neuro­morphic systems inspired by the brain’s powerful compu­tational abilities.

Illustration of a quantum cascade photonic device. (Source: Spitz et al., SPIE)

Based on a quantum cascade laser (QCL) emitting mid-infrared light, the researchers deve­loped a basic optical neuron system operating 10,000× faster than biological neurons. Olivier Spitz, Télécom Paris research fellow, notes that the giant pulses in QCLs can be triggered success­fully by adding a pulse-up exci­tation, a short-time small-amplitude increase of bias current. Frédéric Grillot, Professor at Télécom Paris and the Univer­sity of New Mexico, explains that this trig­gering ability is of paramount impor­tance for appli­cations such as optical neuron-like systems, which require optical bursts to be triggered in response to a pertur­bation.

The team’s optical neuron system demons­trates behaviors like those observed in biological neurons, such as thresholding, phasic spiking, and tonic spiking. Fine tuning of modu­lation and frequency allows control of time intervals between spikes. Grillot explains, “The neuro­morphic system requires a strong, super-threshold stimulus for the system to fire a spiking response, whereas phasic and tonic spiking correspond to single or conti­nuous spike firing following the arrival of a stimulus.” To replicate the various biological neuronal responses, inter­ruption of regular succes­sions of bursts corres­ponding to neuronal activity is also required.

Grillot notes that the findings reported by his team demonstrate the increa­singly superior potential of quantum cascade lasers compared to standard diode lasers or VCSELs, for which more complex techniques are currently required to achieve neuro­morphic properties. Experi­mentally demons­trated for the first time in 1994, quantum cascade lasers were originally developed for use under cryogenic tempera­tures. Their develop­ment has advanced rapidly, allowing use at warmer temperatures, up to room temperature. Due to the large number of wave­lengths they can achieve from 3 to 300 microns, QCLs contribute to many industrial applications such as spectro­scopy, optical counter­measures, and free-space communi­cations.

According to Grillot, the physics involved in QCLs is totally different than that in diode lasers. “The advantage of quantum cascade lasers over diode lasers comes from the sub-pico­second electronic transi­tions among the conduc­tion-band states (subbands) and a carrier lifetime much shorter than the photon lifetime,” says Grillot. He remarks that QCLs exhibit completely different light emission behaviors under optical feedback, including but not limited to giant pulse occur­rences, laser responses to modu­lation, and frequency comb dynamics. (Source: SPIE)

Reference: O. Spitz et al.: Extreme events in quantum cascade lasers, Adv. Phot. 2, 066001 (2020); DOI: 10.1117/1.AP.2.6.066001

Link: MirSense: Industrial Quantum Cascade Lasers (QCL) solutions, Palaiseau, France

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