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Conference on Lasers and Electro-Optics

Optical bistability in active distributed—feedback structures: an experimental and theoretical study

Richard R. Wyatt, Mike J. Adams

Published Jan 1, 1986• 4 citations
Publisher

Abstract

Optical bistability in active semiconductor devices has attracted considerable interest recently due to the possibility of combining microwatt switching powers with nanosecond switching times. We present experimental and theoretical results of optical bistability in a distributed-feedback (DFB) laser amplifier operating in reflection at 1.5 μm; switch-on delay followed by a sharp transient overshoot is predicted and observed. Minimum switching energies are in the femtojoule region.

DOI
10.1364/cleo.1986.mb5

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Optical bistability in distributed feedback semiconductor laser amplifiers

M.J. Adams, Richard R. Wyatt

New theoretical and experimental results are presented for optical bistability in distributed feedback amplifiers at 1.5 μm. The onset of bistability occurs at input powers as low as 1 μW, a factor of about 1000 times less than the input predicted for passive DFB structures. The transient response exhibits a large spike as the amplifier goes through a resonance, in good agreement with the theoretical prediction.

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Optical Bistability in 1.55 μm Semiconductor Laser Amplifiers

M.J. Adams, H.J. Westlake, M.J. O’Mahony

Dispersive bistability arising from the carrier-dependence of the refractive index has been observed in semiconductor lasers operated just below threshold with a small injected optical signal. The minimum optical input required for switch-up is as low as 1 μW for InGaAsP amplifiers at 1.55 μm(1) and 1.3 μm(2) (cf 30 μW for GaAs devices(3)). As yet, reliable measurements of the dynamic response are not (4) available, although we predict recovery times to be on the order of carrier lifetimes, ie a few nanoseconds at room temperature. This contribution will review our experimental and theoretical work on 1.55 μm amplifier bistability and set it in the context of other semiconductor bistable optical devices.

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Time characteristics of bistable DFB amplifiers for all-optical switching

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In all-optical switching systems bistable distributed-feedback (DFB) amplifiers are being used experimentally as memory cells and signal regenerators. In this frame a single section DFB amplifier (with one AR coated facet) operating around threshold at 1549 nm is pumped by a similar laser with a carefully controlled frequency detuning. The polarization controlled pump beam is modulated by a Mach-Zehnder switch (2.5 GHz bandwidth) to avoid source frequency chirp. The measurement of a pump reference and of the beam reflected from the amplifier is performed through a fiber directional coupler inserted between the two DFB diodes. Optical bistability has been observed both in transmission and in reflection for a sinewave modulated input in the 1-200 MHz frequency range. The output square wave exhibits up and down switching times lower than 1 ns and about 2 ns, respectively. The latter figure is consistent with the carrier recombination time in InGaAsP active structures, which is the main limit to the recovery time of bistable amplifiers. Work is in progress to investigate this feature in other types of amplifiers (e.g., multisection DFBs and quantum well structures).

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It has recently become clear that OB in semiconductor laser amplifiers has many potential advantages for applications in optical logic and signal processing. Foremost among these advantages may be listed (i) ready availability (compared with other bistable devices [1]), (ii) wavelength compatibility with optical communications systems, (iii) inherent optical gain (for serial processing), and (iv) a combination of microwatt switching powers and nanosecond switching times leading to femtoule optical switching energies [2,3]. In support of item (ii) on this list, it is worth noting that amplifier OB has been reported at 0.8 μm [4], 1.3 μm [5], and 1.5 μm [6], all of which are wavelengths employed for optical communications systems.

Topical Meeting on Optical Bistability (OB)•Jan 1, 1988•0 citations

Optical Bistability in a Traveling-Wave SOA Connected to a DFB Laser Diode: Theory and Experiment

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We investigate the bistable response of a traveling-wave semiconductor optical amplifier (SOA) connected bidirectionally to a distributed feedback (DFB) laser diode. By contrast to dispersive DFB amplifiers, bistability is possible for a broad wavelength range of the injected optical signal. A theoretical analysis clarifies the origin of the phenomenon and the conditions under which it occurs. Numerical simulations and experimental results confirm the theoretical analysis. Experimentally obtained step heights up to 25 dB and widths of the bistability domain of 1-4 dB have been found

IEEE Journal of Quantum Electronics•Jul 11, 2006•14 citations

Effect of end reflections on distributed- feedback bistable optical devices

Herbert G. Winful

We recently presented a theory of bistability in a nonlinear distributed-feedback (DFB) structure,1 in that work the coupling between forward and backward propagating waves was provided solely by Bragg-scattering from a periodic index perturbation built into the otherwise homogeneous medium. With the recent demonstration of bistability in the high-index semiconductors GaAs2 and InSb,3 it is clear that the external feedback due to Fresnel reflections will play a major role in any practical DFB bistable optical device. These end reflections have already been considered in the case of semiconductor DFB lasers.4 In this paper we show that even minor end reflections can drastically alter the switching threshold of DFB bistable optical devices.

Conference on Lasers and Electro-Optics•Jan 1, 1981•0 citations
Optical bistability in active semiconductor devices has attracted considerable interest recently due to the possibility of combining microwatt switching powers with nanosecond switching times. We present experimental and theoretical results of optical bistability in a distributed-feedback (DFB) laser amplifier operating in reflection at 1.5 μm; switch-on delay followed by a sharp transient overshoot is predicted and observed. Minimum switching energies are in the femtojoule region.
Dispersive bistability arising from the carrier-dependence of the refractive index has been observed in semiconductor lasers operated just below threshold with a small injected optical signal. The minimum optical input required for switch-up is as low as 1 μW for InGaAsP amplifiers at 1.55 μm(1) and 1.3 μm(2) (cf 30 μW for GaAs devices(3)). As yet, reliable measurements of the dynamic response are not (4) available, although we predict recovery times to be on the order of carrier lifetimes, ie a few nanoseconds at room temperature. This contribution will review our experimental and theoretical work on 1.55 μm amplifier bistability and set it in the context of other semiconductor bistable optical devices.
In all-optical switching systems bistable distributed-feedback (DFB) amplifiers are being used experimentally as memory cells and signal regenerators. In this frame a single section DFB amplifier (with one AR coated facet) operating around threshold at 1549 nm is pumped by a similar laser with a carefully controlled frequency detuning. The polarization controlled pump beam is modulated by a Mach-Zehnder switch (2.5 GHz bandwidth) to avoid source frequency chirp. The measurement of a pump reference and of the beam reflected from the amplifier is performed through a fiber directional coupler inserted between the two DFB diodes. Optical bistability has been observed both in transmission and in reflection for a sinewave modulated input in the 1-200 MHz frequency range. The output square wave exhibits up and down switching times lower than 1 ns and about 2 ns, respectively. The latter figure is consistent with the carrier recombination time in InGaAsP active structures, which is the main limit to the recovery time of bistable amplifiers. Work is in progress to investigate this feature in other types of amplifiers (e.g., multisection DFBs and quantum well structures).
It has recently become clear that OB in semiconductor laser amplifiers has many potential advantages for applications in optical logic and signal processing. Foremost among these advantages may be listed (i) ready availability (compared with other bistable devices [1]), (ii) wavelength compatibility with optical communications systems, (iii) inherent optical gain (for serial processing), and (iv) a combination of microwatt switching powers and nanosecond switching times leading to femtoule optical switching energies [2,3]. In support of item (ii) on this list, it is worth noting that amplifier OB has been reported at 0.8 μm [4], 1.3 μm [5], and 1.5 μm [6], all of which are wavelengths employed for optical communications systems.
We investigate the bistable response of a traveling-wave semiconductor optical amplifier (SOA) connected bidirectionally to a distributed feedback (DFB) laser diode. By contrast to dispersive DFB amplifiers, bistability is possible for a broad wavelength range of the injected optical signal. A theoretical analysis clarifies the origin of the phenomenon and the conditions under which it occurs. Numerical simulations and experimental results confirm the theoretical analysis. Experimentally obtained step heights up to 25 dB and widths of the bistability domain of 1-4 dB have been found
We recently presented a theory of bistability in a nonlinear distributed-feedback (DFB) structure,1 in that work the coupling between forward and backward propagating waves was provided solely by Bragg-scattering from a periodic index perturbation built into the otherwise homogeneous medium. With the recent demonstration of bistability in the high-index semiconductors GaAs2 and InSb,3 it is clear that the external feedback due to Fresnel reflections will play a major role in any practical DFB bistable optical device. These end reflections have already been considered in the case of semiconductor DFB lasers.4 In this paper we show that even minor end reflections can drastically alter the switching threshold of DFB bistable optical devices.