Bose-Einstein condensation of photons in a long fiber cavity.

We demonstrate photon Bose-Einstein condensation (photon-BEC) at a broad temperature range that is valid also in the long 1D fiber cavity limit. It is done with an erbium-ytterbium co-doped fiber (EYDF) cavity by overcoming the challenging requirement of sublinear light dispersion for BEC in 1D using a chirped-gratings Fabry-Perot. We experimentally show with a square-root mode-dispersion, a quadratic temperature dependence of the critical power for condensation (compared to a linear dependence in finite regular fiber-cavities) between 90 K and 382 K, as the theory predicts.

Nonlinear light mode dispersion and nonuniform mode comb by a Fabry-Perot with chirped fiber gratings.

We demonstrate a nonlinear light mode dispersion and a nonuniform frequency mode comb by a chirped fiber Bragg gratings (CFBG) Fabry-Perot (FP) at the 1550 nm wavelength regime. We give analytical expressions for the general chirp case, and an experimental demonstration with a linear chirp, showing a square-root dependence of the dispersion as a function of the FP mode number. Such sublinear dispersion is required, for example, for photon Bose-Einstein condensation (BEC) in a one-dimensional (1D) system like fiber cavities.

Bose-Einstein condensation of photons in an erbium-ytterbium co-doped fiber cavity.

Bose-Einstein condensation (BEC) is a special many-boson phenomenon that was observed in atomic particles at ultra-low temperatures. Later, BEC was also shown for non-atomic bosons, such as photons. Those experiments were usually done in micron-size cavities, where the power (particle number) was varied, and not the temperature, until condensation was reached.

Thermalization of one-dimensional photon gas and thermal lasers in erbium-doped fibers.

We demonstrate thermalization and Bose-Einstein (BE) distribution of photons in standard erbium-doped fibers (edf) in a broad spectral range up to ~200nm at the 1550nm wavelength regime. Our measurements were done at a room temperature ~300K and 77K. It is a special demonstration of thermalization of photons in fiber cavities and even in open fibers.

CW laser light condensation.

We present a first experimental demonstration of classical CW laser light condensation (LC) in the frequency (mode) domain that verifies its prediction (Fischer and Weill, Opt. Express20, 26704 (2012)). LC is based on weighting the modes in a noisy environment in a loss-gain measure compared to an energy (frequency) scale in Bose-Einstein condensation (BEC).

Experimental observation of critical phenomena in a laser light system.

We experimentally demonstrate critical behavior of a passively mode-locked laser with properties that are similar to those of gas-liquid and magnetic spin systems. The laser light modes provide a special nonthermodynamic many-body system where noise takes the role of temperature. It is also a rare opportunity of an experimental pure one-dimensional system.

Laser light condensate: experimental demonstration of light-mode condensation in actively mode locked laser.

We have recently predicted (R. Weill, B. Fischer and O.

Picosecond flat-top pulse generation by low-bandwidth electro-optic sinusoidal phase modulation.

We report the first experimental demonstration to our knowledge of a microwave frequency upshifting system based on phase modulation. A sequence of flat-top optical and RF pulses at a repetition rate of 18.22 GHz, each with a FWHM time width of approximately 25 ps, is generated from a sinusoidal RF tone of only 3.

Data storage in optical fibers and reconstruction by use of low-coherence spectral interferometry.

We demonstrate optical data storage in optical fibers and reconstruction by use of low-coherence spectral interferometry. The information was stored by means of writing fiber Bragg gratings with different central wavelengths at different locations of the fiber. We need only a single short pulse is needed to read all the stored data.

Temporal differentiation of optical signals using a phase-shifted fiber Bragg grating.

We propose and experimentally demonstrate an all-optical (all-fiber) temporal differentiator based on a simple pi-phase-shifted fiber Bragg grating operated in reflection. The proposed device can calculate the first time derivative of the complex field of an arbitrary narrowband optical waveform with a very high accuracy and efficiency. Specifically, the experimental fiber grating differentiator reported here offers an operation bandwidth of approximately 12 GHz.

Complete characterization of optical pulses by real-time spectral interferometry.

We demonstrate a simple method for complete characterization (of amplitudes and phases) of short optical pulses, using only a dispersive delay line and an oscilloscope. The technique is based on using a dispersive delay line to stretch the pulses and recording the temporal interference of two delayed replicas of the pulse train. Then, by transforming the time domain interference measurements to spectral interferometry, the spectral intensity and phase of the input pulses are reconstructed, using a Fourier-transform algorithm.

Reconfigurable generation of high-repetition-rate optical pulse sequences based on time-domain phase-only filtering.

We propose and demonstrate a fiber-based phase-only filtering technique for programmable optical pulse shaping, in which the filtering operation is implemented in the time domain by means of an electro-optical (EO) phase modulator. The technique has been applied for generating customized ultrahigh-repetition-rate optical pulse sequences (>40 GHz) from single input pulses by driving the EO phase modulator with a periodic electronic waveform (RF tone). The generated output pulses are replicas of the input pulse and both the repetition rate and the envelope profile of the generated sequences can be controlled and tuned electronically using this approach.

Frequency shifting of microwave signals by use of a general temporal self-imaging (Talbot) effect in optical fibers.

A simple and practical microwave frequency-shifting technique based on a general temporal self-imaging (GTSI) effect in optical fiber is proposed, formulated, and experimentally demonstrated. The proposed technique can be applied to an arbitrary periodic microwave signal (e.g.

Spectral Fraunhofer regime: time-to-frequency conversion by the action of a single time lens on an optical pulse.

We analyze a new regime in the interaction between an optical pulse and a time lens (spectral Fraunhofer regime), where the input pulse amplitude is mapped from the time domain into the frequency domain (time-to-frequency conversion). Here we derive in detail the conditions for achieving time-to-frequency conversion with a single time lens (i.e.

Measuring temperature profiles in high-power optical fiber components.

We demonstrate a new method for measuring changes in temperature distribution caused by coupling a high-power laser beam into an optical fiber and by splicing two fibers. The measurement technique is based on interrogating a fiber Bragg grating by using low-coherence spectral interferometry. A large temperature change is found owing to coupling of a high-power laser into a multimode fiber and to splicing of two multimode fibers.