External optical feedback effects on semiconductor injection laser properties
NEC1
TL;DR: In this paper, the effects of external optical feedback on the semiconductor laser properties have been examined, i.e., return of a portion of the laser output from a reflector external to the laser cavity.
Abstract: Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.
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TL;DR: In this paper, a review of the Kuramoto model of coupled phase oscillators is presented, with a rigorous mathematical treatment, specific numerical methods, and many variations and extensions of the original model that have appeared in the last few years.
Abstract: Synchronization phenomena in large populations of interacting elements are the subject of intense research efforts in physical, biological, chemical, and social systems. A successful approach to the problem of synchronization consists of modeling each member of the population as a phase oscillator. In this review, synchronization is analyzed in one of the most representative models of coupled phase oscillators, the Kuramoto model. A rigorous mathematical treatment, specific numerical methods, and many variations and extensions of the original model that have appeared in the last few years are presented. Relevant applications of the model in different contexts are also included.
2,864 citations
TL;DR: High-speed long-distance communication based on chaos synchronization over a commercial fibre-optic channel is demonstrated, showing that information can be transmitted at high bit rates using deterministic chaos in a manner that is robust to perturbations and channel disturbances unavoidable under real-world conditions.
Abstract: Chaos is good, if you are looking to send encrypted information across a broadband optical network. The idea that the transmission of light-based signals embedded in chaos can provide privacy in data transmission has been demonstrated over short distances in the laboratory. Now it has been shown to work for real, across a commercial fibre-optic channel in the metropolitan area network of Athens, Greece. The results show that the technology is robust to perturbations and channel disturbances unavoidable under real-world conditions. Chaotic signals have been proposed as broadband information carriers with the potential of providing a high level of robustness and privacy in data transmission1,2. Laboratory demonstrations of chaos-based optical communications have already shown the potential of this technology3,4,5, but a field experiment using commercial optical networks has not been undertaken so far. Here we demonstrate high-speed long-distance communication based on chaos synchronization over a commercial fibre-optic channel. An optical carrier wave generated by a chaotic laser is used to encode a message for transmission over 120 km of optical fibre in the metropolitan area network of Athens, Greece. The message is decoded using an appropriate second laser which, by synchronizing with the chaotic carrier, allows for the separation of the carrier and the message. Transmission rates in the gigabit per second range are achieved, with corresponding bit-error rates below 10-7. The system uses matched pairs of semiconductor lasers as chaotic emitters and receivers, and off-the-shelf fibre-optic telecommunication components. Our results show that information can be transmitted at high bit rates using deterministic chaos in a manner that is robust to perturbations and channel disturbances unavoidable under real-world conditions.
1,267 citations
Cites methods from "External optical feedback effects o..."
...Optical feedback [11-17], optical injection [18-20] or optoelectronic feedback [21-23] are some of the typical configurations used to generate a high-dimensional chaotic laser output....
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TL;DR: A comprehensive review of the various techniques used for terahertz image formation can be found in this paper, as well as numerous examples which illustrate the many exciting potential uses for these emerging technologies.
Abstract: Within the last several years, the field of terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.
962 citations
TL;DR: It is shown that good quality random bit sequences can be generated at very fast bit rates using physical chaos in semiconductor lasers, which means that the performance of random number generators can be greatly improved by using chaotic laser devices as physical entropy sources.
Abstract: Random number generators in digital information systems make use of physical entropy sources such as electronic and photonic noise to add unpredictability to deterministically generated pseudo-random sequences1,2. However, there is a large gap between the generation rates achieved with existing physical sources and the high data rates of many computation and communication systems; this is a fundamental weakness of these systems. Here we show that good quality random bit sequences can be generated at very fast bit rates using physical chaos in semiconductor lasers. Streams of bits that pass standard statistical tests for randomness have been generated at rates of up to 1.7 Gbps by sampling the fluctuating optical output of two chaotic lasers. This rate is an order of magnitude faster than that of previously reported devices for physical random bit generators with verified randomness. This means that the performance of random number generators can be greatly improved by using chaotic laser devices as physical entropy sources. Random-number generators are important in digital information systems. However, the speed at which current sources operate is much slower than the typical data rates used in communication and computing. Chaos in semiconductor lasers might help to bridge the gap.
823 citations
Additional excerpts
...Single-mode distributed-feedback (DFB) lasers are prepared without standard optical isolators, to allow optical feedback from an external fibre reflector, which reflects a fraction of the light back into the laser, inducing high-frequency chaotic oscillations in the gigahertz regim...
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TL;DR: In this article, the effects of feedback on the spectra of 1.5-μm DFB lasers from feedback power ratios as low as -80 dB up to -8 dB were measured.
Abstract: We have measured the effects of feedback on the spectra of 1.5-μm DFB lasers from feedback power ratios as low as -80 dB up to -8 dB. Five distinct regimes of effects are observed with well defined transitions between them. The dependence of these effects on the distance to the reflection is also investigated.
729 citations
References
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TL;DR: In this article, a saturable resonator is used to switch out the CO2 laser light from its cavity and for repetitive Q•switching for variable length pulses, infinite length pulse trains, logical operations on two signals, and memory functions.
Abstract: Optical resonators containing saturable absorbers (saturable resonators) have nonlinear characteristics and can exhibit hysteresis. This is demonstrated experimentally at 10.6 μ wavelength. A saturable resonator is used to switch out the CO2 laser light from its cavity and for repetitive Q‐switching. Devices are described to obtain variable length pulses, infinite pulse trains, logical operations on two signals, and memory functions.
345 citations
TL;DR: In this paper, a transverse-mode-stabilized AlGaAs laser of a channeled-substrate planar structure was investigated, and the authors found that the intensity distribution and excitation dependence of a non-lasing longitudinal mode have been more complicated than expected from a simple theory.
Abstract: Lasing spectra of a transverse‐mode‐stabilized AlGaAs laser of a channeled‐substrate planar structure have been investigated. These lasers, which oscillate in the fundamental transverse mode, reproducibly operate in a single longitudinal mode. In addition, their linewidth is as narrow as or smaller than 30 MHz when the injection current is ∼1.2 times above threshold. The intensity distribution and excitation dependence of a nonlasing longitudinal mode have been found to be more complicated than expected from a simple theory: sizable dips have been observed in the envelope function, and nonlasing modes have been found to decrease as the injection current is increased above threshold. Furthermore, hysteresis has invariably been observed in the lasing‐wavelength–vs–device‐temperature (or dc current) characteristics. These behaviors are believed to reflect a slightly inhomogeneous nature of the gain spectrum because of a finite thermalization time of injected carriers, as discussed recently by Yamada and Suematsu.
173 citations
TL;DR: In this paper, the optical wave of wide-stripe lasers is found to be guided by changes in the real part of the dielectric constant that are caused by a dip in carrier concentration along the axis of the lasing filament.
Abstract: Experimental measurements of the optical-beam parameters of conventional oxide-insulated GaAs stripe-geometry lasers as a function of stripe width have shown a marked difference in the waveguide mechanism of narrow-stripe ( \simeq10 \mu m) and wide-stripe ( >20 \mu m) lasers. The optical wave of narrow-stripe lasers is guided by the previously reported gain-guiding mechanism. The optical wave of wide-stripe lasers is found to be guided by changes in the real part of the dielectric constant that are caused by a dip in carrier concentration along the axis of the lasing filament. This self-focused guiding has been predicted theoretically. These experimental results strongly support the hypothesis that in all cases the waveguides are formed predominantly by the naturally occurring variations in carrier concentration beneath the stripe. A new and fairly comprehensive mathematical model has been developed based on this assumption. The model predicts the carrier concentration, resultant gain, and dielectric constant profiles together with the optical-beam parameters and light/current characteristics of stripe-geometry lasers. The model is applicable over a wide range of stripe widths and device structures. The results are compared with experiment over the range of stripe widths from 10-20 \mu m and found in reasonable agreement. The effects of narrowing the stripe width below 10 μm are calculated and found to be in qualitative agreement with recently published experimental results. In particular the light-output power at which a predicted "kink" in the light/current characteristic occurs is found to increase rapidly as the stripe width reduces.
169 citations
TL;DR: In this paper, the authors investigated the origin, qualitative, and quantitative properties of low frequency noise appearing in the light output of the laser diode, which is strongly coupled to optical fibers.
Abstract: This paper describes the theoretical investigation of the origin, qualitative, and quantitative properties of the low frequency noise appearing in the light output of the laser diode, which is strongly coupled to optical fibers. This kind of noise has caused serious problems for reliable optical communications, especially for analog-modulation systems. It is shown that there are two different phenomena which generate such noise. One of them is the double cavity state, and the other is the external light injection state. The cause of our noise considered in the double cavity state is the phase variation due to the variation of the equivalent length between the laser and the reflection point generated by mechanical vibrations. On the other hand, the cause in the external light injection state is the random generations of locking and unlocking states due to the frequency variation (or mode jumping) caused by the variation of the internal temperature of the laser diode. We conclude from our theory that an effective method to reduce such noise is to operate the laser diode at well above the threshold current. The complete elimination will be attained by use of the optical isolator inserted between the laser diode and the transmission lines.
158 citations
NEC1
TL;DR: In this paper, a numerical analysis has been carried out on the behavior of semiconductor injection lasers with a stripe geometry double-heterostructure, taking into account spatial hole-burning and its effect on the waveguiding.
Abstract: A numerical analysis has been carried out on the behavior of semiconductor injection lasers with a stripe geometry double-heterostructure, taking into account spatial hole-burning and its effect on the waveguiding. It is shown that spatial hole-burning, the negative dependence of refractive index eta on the excited carrier density n (d_{eta}/ dn , and the lack of complete symmetry in any real laser structure are the three critical factors responsible for the lateral mode instability leading to such anomalous behaviors these lasers exhibit as a "kink" in the light output versus current relation and the lateral shift in the emission spot. Effects of rigid refractive index and gain-loss profiles built into the laser crystal on the mode stability have been examined, and conditions for kink-free, single lateral mode oscillations have been investigated.
112 citations