1,714 research outputs found
Adaptive pumping for spectral control of random lasers
A laser is not necessarily a sophisticated device: Pumping energy into an
amplifying medium randomly filled with scatterers, a powder for instance, makes
a perfect "random laser." In such a laser, the absence of mirrors greatly
simplifies laser design, but control over emission directionality or frequency
tunability is lost, seriously hindering prospects for this otherwise simple
laser. Lately, we proposed a novel approach to harness random lasers, inspired
by spatial shaping methods recently employed for coherent light control in
complex media. Here, we experimentally implement this method in an optofluidic
random laser where scattering is weak and modes extend spatially and strongly
overlap, making individual selection a priori impossible. We show that control
over laser emission can indeed be regained even in this extreme case by
actively shaping the spatial profile of the optical pump. This unique degree of
freedom, which has never been exploited, allows selection of any desired
wavelength and shaping of lasing modes, without prior knowledge of their
spatial distribution. Mode selection is achieved with spectral selectivity down
to 0.06nm and more than 10dB side-lobe rejection. This experimental method
paves the way towards fully tunable and controlled random lasers and can be
transferred to other class of lasers.Comment: 23 pages, 7 figure
Multimode optical feedback dynamics in InAs/GaAs quantum dot lasers emitting exclusively on ground or excited states: transition from short- to long-delay regimes
© 2018 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.The optical feedback dynamics of two multimode InAs/GaAs quantum dot lasers emitting exclusively on sole ground or excited lasing states is investigated. The transition from long- to short-delay regimes is analyzed, while the boundaries associated to the birth of periodic and chaotic oscillations are unveiled to be a function of the external cavity length. The results show that depending on the initial lasing state, different routes to chaos are observed. These results are of importance for the development of isolator-free transmitters in short-reach networks
Time-resolved spectra of a self-pulsing quantum dot laser
Self-sustained pulsations in the output of an InAs quantum dot laser diode in the MHz range are reported for the first time. The characteristics (shape, range and frequency) are presented for the free running laser and when optical feedback in the Littrow configuration is applied. The frequency resolved optical spectra reveal different envelope shifts between the two cases. This might be related to a change of phase-amplitude coupling across the gain maximum in agreement with the expectation for a two level system. The time scale and bifurcation scenario suggest that these are opto-thermal pulsation like those reported in quantum well amplifiers.(1
Modes of Random Lasers
In conventional lasers, the optical cavity that confines the photons also
determines essential characteristics of the lasing modes such as wavelength,
emission pattern, ... In random lasers, which do not have mirrors or a
well-defined cavity, light is confined within the gain medium by means of
multiple scattering. The sharp peaks in the emission spectra of semiconductor
powders, first observed in 1999, has therefore lead to an intense debate about
the nature of the lasing modes in these so-called lasers with resonant
feedback. In this paper, we review numerical and theoretical studies aimed at
clarifying the nature of the lasing modes in disordered scattering systems with
gain. We will discuss in particular the link between random laser modes near
threshold (TLM) and the resonances or quasi-bound (QB) states of the passive
system without gain. For random lasers in the localized regime, QB states and
threshold lasing modes were found to be nearly identical within the scattering
medium. These studies were later extended to the case of more lossy systems
such as random systems in the diffusive regime where differences between
quasi-bound states and lasing modes were measured. Very recently, a theory able
to treat lasers with arbitrarily complex and open cavities such as random
lasers established that the TLM are better described in terms of the so-called
constant-flux states.Comment: Review paper submitted to Advances in Optics and Photonic
Phase conjugate fluorozirconate fibre laser operating at 800nm
We report phase-conjugate feedback into a fluorozirconate optical fiber amplifier at infrared wavelengths. By using a semiconductor laser diode at 807 nm, a grating is established in photorefractive BaTiO3 that, in the ring configuration, provides feedback into the amplifier necessary for laser action. Once written, the grating is self-sustaining, and lasing is observed even after the laser diode is removed
Chaotic mode-competition dynamics in a multimode semiconductor laser with optical feedback and injection
Photonic computing is attracting increasing interest to accelerate
information processing in machine learning applications. The mode-competition
dynamics of multimode semiconductor lasers is useful for solving the
multi-armed bandit problem in reinforcement learning for computing
applications. In this study, we numerically evaluate the chaotic
mode-competition dynamics in a multimode semiconductor laser with optical
feedback and injection. We observe the chaotic mode-competition dynamics among
the longitudinal modes and control them by injecting an external optical signal
into one of the longitudinal modes. We define the dominant mode as the mode
with the maximum intensity; the dominant-mode ratio for the injected mode
increases as the optical injection strength increases. We find that the
characteristics of the dominant mode ratio in terms of the optical injection
strength are different among the modes owing to the different optical feedback
phases. We propose a control technique for the characteristics of the dominant
mode ratio by precisely tuning the initial optical frequency detuning between
the optical injection signal and injected mode. We also evaluate the
relationship between the region for the large dominant mode ratio and injection
locking range. The region for the large dominant mode ratio does not correspond
to the injection-locking range. This discrepancy results from the complex
mode-competition dynamics in multimode semiconductor lasers with both optical
feedback and injection. This control technique of chaotic mode-competition
dynamics in multimode lasers is promising for applications in reinforcement
learning and reservoir computing as photonic artificial intelligence.Comment: 17 pages, 12 figures, 1 tabl
- …