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

Realizing Einstein's Mirror: Optomechanical Damping with a Thermal Photon Gas

Einstein described the damping and thermalization of the center-of-mass motion of a mirror placed inside a blackbody cavity by collisions with thermal photons. While the time for damping even a microscale or nanoscale object is so long that it is not experimentally viable, we show that this damping is feasible using the high-intensity light from an amplified thermal light source with a well-defined chemical potential. We predict this damping of the center-of-mass motion will occur on timescales of tens of seconds for small optomechanical systems.

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.

Photon thermalization and a condensation phase transition in an electrically pumped semiconductor microresonator

We report on an experimental study of photon thermalization and condensation in a semiconductor microresonator in the weak-coupling regime. We measure the dispersion relation of light and the photon mass in a single-wavelength, broad-area resonator. The observed luminescence spectrum is compatible with a room-temperature, thermal-equilibrium distribution. A phase transition, identified by a saturation of the population at high energies and a superlinear increase of the occupation at low energy, takes place when the phase-space density is of order unity. We explain our observations by Bose-Einstein condensation of photons in equilibrium with a particle reservoir and discuss the relation with laser emission.

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. Here we demonstrate BEC of photons in a few-meters-long one-dimensional (1D) erbium-ytterbium co-doped fiber cavity at, below and above room temperature, between 100 K and 415 K. The experiments were done at about the 1550 nm wavelength regime having a few to tens of μW intra-cavity light power (10⁷-10⁸ photons). By varying the power and also the temperature, we found linear dependence of the condensation on power for various temperatures and of the critical power (for condensation) on temperature. These findings agree, functionally and quantitatively, with the theoretical BEC prediction without any adjustable parameter.