Amar R. Bhagwat

Low-light-level optical interactions with rubidium vapor in a photonic band-gap fiber

We show that rubidium vapor can be produced within the core of a photonic band-gap fiber yielding an optical depth in excess of 2000. Our technique for producing the vapor is based on coating the inner walls of the fiber core with organosilane and using light-induced atomic desorption to release Rb atoms into the core. As an initial demonstration of the potential of this system for supporting ultralow-level nonlinear optical interactions, we perform electromagnetically induced transparency with control-field powers in the nanowatt regime, which represents more than a 1000-fold reduction from the power required for bulk, focused geometries.

Nonlinear optics in hollow-core photonic bandgap fibers

Hollow-core photonic-bandgap fibers provide a new geometry for the realization and enhancement of many nonlinear optical effects. Such fibers offer novel guidance and dispersion properties that provide an advantage over conventional fibers for various applications. In this review we summarize the nonlinear optics experiments that have been performed using these hollow-core fibers.

Generation of large alkali vapor densities inside bare hollow-core photonic band-gap fibers

We demonstrate the ability to generate extremely large rubidium densities in uncoated hollow-core photonic band-gap fibers using light-induced atomic desorption. Once the fiber is exposed to Rb vapor for 1-2 weeks, and this atomic source is removed, the fiber yields large desorbable densities for an extended period of time. We show that optical depths greater than e(-1200) can be created within seconds. Our observed Rb densities are several orders of magnitude larger than any previously reported to be generated optically, and allow for the demonstration of a relatively easy-to-use fiber-based vapor cell capable of producing large optical depths without the need for thermal tuning.

Spectroscopy of Rb atoms in hollow-core fibers

Recent demonstrations of light-matter interactions with atoms and molecules confined to hollow waveguides offer great promise for ultralow-light-level applications. The use of waveguides allows for tight optical confinement over interaction lengths much greater than what could be achieved in bulk geometries. However, the combination of strong atom-photon interactions and nonuniformity of guided light modes gives rise to spectroscopic features that must be understood in order to take full advantage of the properties of such systems. We use light-induced atomic desorption to generate an optically dense Rb vapor at room temperature inside a hollow-core photonic band-gap fiber. Saturable-absorption spectroscopy and passive slow-light experiments reveal large ac Stark shifts, power broadening, and transit-time broadening, that are present in this system even at nanowatt powers.

All-optical modulation of four-wave mixing in an Rb-filled photonic bandgap fiber.

We demonstrate efficient all-optical modulation using Rb vapor confined to a hollow-core photonic bandgap fiber. The intensity of a signal field participating in the four-wave-mixing process is modulated using a weak switching field. We observe 3 dB of attenuation in the signal field with only 3600 photons of switching energy, corresponding to 23 photons per atomic cross section lambda(2)/(2pi). Modulation bandwidths as high as 300 MHz are observed.

Chip-based optical interactions with Rubidium vapor

We demonstrate tightly confined interactions with Rb atoms on a chip of silicon nitride nanowires. Optical depths of 2 are observed, and absorption spectroscopy reveals strong effects of transit-time broadening and Van der Waals shifts.

Nonlinear optical interactions with Rubidium atoms confined in a hollow-core photonic crystal fiber

We use light-induced atomic desorption to produce an appreciable density of Rubidium atoms in a hollow-core photonic bandgap fiber and demonstrate electromagnetically induced transparency at very low light levels.

All-optical modulation of four wave mixing in a Rb-filled hollow-core photonic band-gap fiber

We demonstrate efficient modulation of four-wave mixing in a Rb-waveguide system via application of a weak “switching” field. We observe 3 dB attenuation of the signal field with only 3600 photons of “switching” energy.

Diffusion and redistribution of rubidium in hollow-core photonic bandgap fibers

We characterize the diffusion and redistribution processes that Rb atoms undergo on the inner silica surface of hollow-core photonic bandgap fibers by investigating the dynamics of fiber-transmission and light-induced atomic desorption.

Ultralow-Power Nonlinear Optics with Rb-Filled Photonic Band-Gap Fibers

Using light-induced atomic desorption, we generate an optically-dense Rb vapor on-demand inside a hollow-core photonic bandgap fiber for ultralow power nonlinear optical interactions. We demonstrate electromagnetically-induced-transparency, four-wave-mixing and efficient all-optical modulation in this system.