Christopher Perrella

High-efficiency cross-phase modulation in a gas-filled waveguide

Strong cross-Kerr nonlinearities have been long sought after for quantum information applications. Recent work has shown that they are intrinsically unreliable in traveling-wave configurations: cavity configurations avoid this, but require knowledge of both the nonlinearity and the loss. Here we present a detailed systematic study of cross-phase modulation and absorption in an Rb vapor confined within a hollow-core photonic crystal fiber. Using a two-photon transition, we observe phase modulations of up to pi rad with a signal power of 25 mu W, corresponding to a nonlinear Kerr coefficient, n(2), of 0.8 x 10(-6) cm(2)/W, or 1.3 x 10(-6) rad per photon.

Direct core structuring of microstructured optical fibers using focused ion beam milling.

We demonstrate the use of focused ion beam milling to machine optical structures directly into the core of microstructured optical fibers. The particular fiber used was exposed-core microstructured optical fiber, which allowed direct access to the optically guiding core. Two different designs of Fabry-Perot cavity were fabricated and optically characterized. The first cavity was formed by completely removing a section of the fiber core, while the second cavity consisted of a shallow slot milled into the core, leaving the majority of the core intact. This work highlights the possibility of machining complex optical devices directly onto the core of microstructured optical fibers using focused ion beam milling for applications including environmental, chemical, and biological sensing.

Phase-sensitive imaging of cold atoms at the shot-noise limit

We demonstrate simultaneous phase and amplitude imaging of cold atoms using an intrinsically stable interferometer based on polarization beam-displacers. This method allows for the straight-forward retrieval of absorption and phase-shift experienced by an optical probe transmitted through an atomic sample. Furthermore, we show that our technique has a signal-to-noise ratio limited only by photon shot-noise.

Two-color rubidium fiber frequency standard

We demonstrate an optical frequency standard based on rubidium vapor loaded within a hollow-core photonic crystal fiber. We use the 5S(1/2)→5D(5/2) two-photon transition, excited with two lasers at 780 and 776 nm. The sum-frequency of these lasers is stabilized to this transition using modulation transfer spectroscopy, demonstrating a fractional frequency stability of 9.8×10(-12) at 1 s. The current performance limitations are presented, along with a path to improving the performance by an order of magnitude. This technique will deliver a compact, robust standard with potential applications in commercial and industrial environments.

Bidirectional microwave and optical signal dissemination

We describe a technique to disseminate highly stable microwave and optical signals from physically separated frequency standards to multiple locations. We demonstrate our technique by transferring the frequency stability performance of a microwave frequency reference to the repetition-rate stability of an optical frequency comb in a different location. The stabilized optical frequency comb becomes available in both locations for measurements of both optical and microwave signals. We show a microwave frequency stability of 4×10(-15) in both locations for integration times beyond 100 s. The control system uses only a standard Ethernet connection.

Coherent radio-frequency detection for narrowband direct comb spectroscopy

We demonstrate a scheme for coherent narrowband direct optical frequency comb spectroscopy. An extended cavity diode laser is injection locked to a single mode of an optical frequency comb, frequency shifted, and used as a local oscillator to optically down-mix the interrogating comb on a fast photodetector. The high spectral coherence of the injection lock generates a microwave frequency comb at the output of the photodiode with very narrow features, enabling spectral information to be further down-mixed to RF frequencies, allowing optical transmittance and phase to be obtained using electronics commonly found in the lab. We demonstrate two methods for achieving this step: a serial mode-by-mode approach and a parallel dual-comb approach, with the Cs D1 transition at 894 nm as a test case.

Hollow-core fibre frequency standard

Summary form only given. The development of high-quality and low-loss hollow-core photonic-crystal fiber (HC-PCF) offers interesting opportunities to develop robust and compact frequency standards. We are pursuing two different types of frequency standards based on HC-PCF: one based on saturation spectroscopy of iodine, and a second based on two-photon spectroscopy of rubidium. In this presentation we will present the progress with the rubidium-loaded fibre.

High resolution optical spectroscopy in hollow core fibre for use in atomic clocks

We present high resolution measurements of Doppler free features within Rubidium (Rb) filled photonic crystal hollow core fibre (HC-PCF). Measurements within a Rb filled fibre with core diameter of 35μm show broadening of only 1 MHz associated with the transit time effect. This low level of additional broadening opens the door to compact frequency standards. We present initial spectroscopy of the narrow Rb 5S→5D two-photon transition within the fibre which we will use to create a compact frequency standard.

Towards a compact optical fibre clock

We have loaded a hollow core photonic crystal fibre (HC-PCF) with ¹²⁷I<inf>2</inf> and used it to record an absorption spectrum of iodine near 532nm. We will measure the hyperfine structures of the P142 (37-0) transition of ¹²⁷I<inf>2</inf> in a HC-PCF and compare it to measurements made using a traditional ¹²⁷I<inf>2</inf> gas cell to determine how much spectral line broadening is induced in the HC-PCF as a result of gas particle collisions with the walls of the fibre. We aim to provide an estimate of the stability obtainable in a clock based on an ¹²⁷I<inf>2</inf> loaded HCPCF.