- Fiber-optics; Fiber-optic communications
- Light/photon condensation: Classical, in lasers, and Quantum-based photon Bose-Einstein condensation (BEC) in fiber cavities
- Many-Body Photonics: Statistical-mechanics and quantum-mechanics based study of light and lasers
- Pulse-optics; Pulse-lasers
- Nonlinear Photorefractive-Optics and Phase-Conjugation
Description and examples:
- Fiber-Optics, Fiber-optic communication, Lasers, Nonlinear fiber-optics, Fiber gratings, Tunable lasers, etc. :
Aspects in fiber-optic communications, such as light propagation in fibers, lasers, fiber lasers and amplifiers, special tunable devices, transmitters and filters for WDM (wavelength division multiplexing) networks. Papers elected Publications): 36a, 36b, 39a, 39b, 41, 44, 45, 47, 50, 51, 53, 56, 58, 59, 62, 65, 66, 67, 106 (and 2 Videos for paper 106: Video S1, Video S2, and patents 5, 7, 8, 9.
- Photon thermalization and Quantum-based Bose-Einstein condensation (BEC) in fiber cavities:
Bose-Einstein condensates were demonstrated at low temperatures, mostly with ultra-cold (hundreds of nano-Kelvin) bosonic atoms. We demonstrated quantum-based BEC of photons in a standard fiber cavity at, below and above room temperature.
- Classical condensation phenomena in lasers:
Theoretical and experimental demonstration of classical condensation in three laser systems. They are shown in pulsed (actively mode-locked) and cw-lasers and are based on weighting the modes in a noisy environment in a loss-gain scale (rather than in energy or frequency in quantum-based BEC) in a noisy environment that has the role of temperature.
- Many-body Photonics: Statistical-Mechanics and Quantum-Mechanics based study in Optics and Lasers, Statistical Light-mode Dynamics (SLD):
Basic physical concepts and approaches in electro-optics are incorporated in the study of light behavior in optical systems, including lasers and fibers, provide special insight and results.
An example is our study of many interacting modes in lasers, regarded as a many body system and then learned via Statistical Mechanics. This Statistical Light-mode Dynamics (SLD) approach provides, for example, a new view on how pulses are formed and annihilated in mode-locked lasers, showing that light modes and pulses freeze and melt like gas-liquid-solid or magnetic spin systems, undergoing a first order phase transition (with latent heat, hysteresis, super-cooling and super-heating). The study explains right away the long standing power threshold question in passive mode-locking, as well as the inherent dependence on noise and the quantum limit behavior. It also provides a new statistical mechanics paradigm. Those theoretical ideas were tested and verified in our laboratory.
Multi-pulse formation in a cascade of first order phase transitions (theoretical and experimental). Paper 64.
Watch video from the experiment on cascaded multi-pulse formation and anihilation: Pulse formation and Pulse annihilation that show the formation and annihilation of light pulse quanta in passive mode-locked lasers, as as the noise power (“temperature”) is varied.
Critical exponents: Another development was the theoretical finding and then the experimental demonstration of critical behavior of light in mode-locked lasers. It shows another basic thermodynamic-like side of the light-mode system. The critical exponents were found to be the “classical” mean field values, which are exact in the light system. Papers: 70 and 90.
Videos from the experiment on a pulse tour on the slopes of the the “x-h-T” phase diagram: (Paper 90) on the pulse “jumps” at two points along the coexistence curve (- the boundary with first order phase transitions between the “para-pulse” and the “spontaneous-pulse” phases, that ends at the critical point):
“Mode hyper-combs” (in any dimension, even higher than 3): In another direction we constructed mode hyper-combs of the mode system in actively mode-locked (AML) lasers with multi-frequency modulation. They were mapped to the Spherical-Model of magnetic spins in statistical mechanics, the only soluble model in all dimensions, that has a second order phase transition in dimensions higher than 2. They provide a rare physical realization of the spherical model, and have potential to robust ultra-short light pulse generation.
A popular review of our work on Many-Body Photonics is given in OPN. Paper 98 (Optics & Photonics News (OPN) 24, 40, 2013).
- Localization in optics:
We showed localization for light propagation in two kinds of optical “kicked-rotor” systems – at the temporal frequency domain (for pulses in mode-locked lasers) and at the spatial frequency domain (“kicked” free-space light propagation). In this context, new kind of resonances in pulse lasers were found (“dispersion modes”), that have similar counterparts and roots in quantum “kicked-rotors” and in the optical Talbot effect. Beside the basic interest, those ideas led to applications such as pulse-rate multiplication and pulse compression, useful for WDM in fiber optics communications. Papers: 40, 42, 43, 44, 48, 55.
Another example was an experimental observation of Anderson Localization of light-waves that propagate along an array of randomly located fiber gratings that we fabricated one after one. Paper 74 and Conference paper.
- Nonlinear-Optics in fibers and fiber amplifiers:
Fibers and fiber amplifiers that have had a tremendous impact on the field of optical communication, can also provide strong nonlinear and wave-mixing effects, with many potential “all-optical” applications. For example, we have demonstrated a special fiber laser with an ultra-narrow line-width which is based on nonlinear wave-mixing inside the laser cavity. Another example is a controllable filter based on dynamic gratings in erbium doped fibers. Papers 36a, 36b, 39, 41 and Patents 5, 8.
Real time and all-optical methods are studied for light pulse generation, propagation and characterization. Examples are temporal lens operations, “real time” pulse shaping, spectral analysis via optical Fourier transform, pulse rate multiplication, etc.
- Photorefractive Nonlinear-Optics, Phase-Conjugation and Optical Wave-Mixing:
This research field was probably the most important and large one in photonics from the early nineteen eighties for more than twenty years. Although the activity in the field slowed down in recent years, its beauty and potential will surely attract future interest.
The research is based on nonlinear materials, mostly photorefractive crystals that show strong nonlinear response with low light powers. We formulated the basic and general nonlinear four-wave mixing equations in photorefractive media with solutions, and discovered various photorefractive oscillators and phase conjugate mirrors and phenomena, including the “Self-Pumped (Passive) Phase Conjugate Mirror” and the “Double phase conjugate mirror”. In another work we developed a novel method for imprinting microscopic patterns in crystals, that can be used for image and holographic memory (storage) applications and for determining and relaxing phase matching limitations in nonlinear wave (frequency) mixing. This method led to the possibility of obtaining broadband and controllable second harmonic generation in a broad range of wavelengths. Past activities also included the study of special bacteria called Bacterio-rhodopsin as a novel nonlinear medium. We also studied nonlinear wave mixing in gain (and laser) media like erbium-doped fibers and used it for various “all-optical” applications.