David Seidel

Tunable Optical Frequency Comb with a Crystalline Whispering Gallery Mode Resonator

We report on the experimental demonstration of a tunable monolithic optical frequency comb generator. The device is based on four-wave mixing in a crystalline calcium fluoride whispering gallery mode resonator. The frequency spacing of the comb is given by an integer number of the free spectral range of the resonator. We select the desired number by tuning the frequency of the pumping laser with respect to the corresponding resonator mode. We also observe a rich variety of optical combs and high-frequency hyperparametric oscillation, depending on the experimental conditions. A potential application of the comb for generating tunable narrow band frequency microwave signals is demonstrated.

Mode-locked Kerr frequency combs

We analyze a mode-locked regime in Kerr frequency combs generated in nonlinear microresonators. Using damped driven nonlinear Schrödinger equations we show that the combs can produce subpicosecond optical pulses when the resonators are characterized with a small enough anomalous group velocity dispersion. We provide an analytical solution of the problem for the case of small damping.

Whispering-gallery-mode-resonator-based ultranarrow linewidth external-cavity semiconductor laser

We demonstrate a miniature self-injection locked distributed-feedback laser using resonant optical feedback from a high-Q crystalline whispering-gallery-mode resonator. The linewidth reduction factor is greater than 10,000, with resultant instantaneous linewidth of less than 200 Hz. The minimal value of the Allan deviation for the laser-frequency stability is 3 x 10(-12) at the integration time of 20 micros. The laser possesses excellent spectral purity and good long-term stability.

RF Amplitude and Phase-Noise Reduction of an Optical Link and an Opto-Electronic Oscillator

In this paper we examine the optical sources of noise that degrade high-performance microwave photonic links. In particular, we study the residual phase noise due to laser frequency fluctuations and the detector nonlinearity on microwave signals transmitted on an optical fiber, or generated in the opto-electronic oscillator (OEO). Based on experimental findings, we identify a significant reduction of the relative intensity noise of the laser if the received optical power saturates the photodiode. Furthermore, we suggest the use of a semiconductor optical amplifier in saturation as yet another means to reduce the phase noise induced by laser intensity fluctuations. We also identify the use of multiple photodetectors to reduce the influence of associated 1/f noise, which adds to the phase noise of a transmitted microwave signal, and is the ultimate limitation to the phase noise of the high-performance OEO. Reduction of noise that is due to optical interferences is also addressed.

Generation of near-infrared frequency combs from a MgF₂ whispering gallery mode resonator.

We report on generation of a 20 nm wide, 35 GHz repetition rate optical frequency comb in a magnesium fluoride whispering gallery mode resonator pumped with 2 mW of 1543 nm light. The high efficiency of comb generation is associated with the small anomalous group velocity dispersion of the resonator. Growth dynamics of the comb is studied and compared with earlier theoretical predictions.

Stabilization of a Kerr frequency comb oscillator

We study stability and spectral purity of a microresonator-based Kerr frequency comb oscillator experimentally and observe a correlation between the frequency of the continuous wave laser pumping the nonlinear resonator and the repetition frequency of the comb. This correlation is used in a proof-of-principle demonstration of a Kerr frequency comb stabilized with an optical transition of 87Rb.

Tunable optical single-sideband modulator with complete sideband suppression

We report on the development of a new class of widely tunable resonant single-sideband electro-optical modulators based on interaction of different mode families of a crystalline whispering gallery mode resonator with an externally applied rf field. The tunability comes from the different response of mode families to either the temperature change or the voltage applied to the resonator.

Hard and soft excitation regimes of Kerr frequency combs

We theoretically study the stability conditions and excitation regimes of hyper-parametric oscillation and Kerr frequency comb generation in continuously pumped nonlinear optical resonators possessing anomalous group velocity dispersion. We show that both hard and soft excitation regimes are possible in the resonators. Selection between the regimes is achieved via change in the parameters of the pumping light.

Optomechanics with surface-acoustic-wave whispering-gallery modes.

A surface-acoustic wave (SAW) creates its own high-Q ultrasmall-volume whispering-gallery mode (WGM), different from the usual bulk acoustic WGMs, in an optical dielectric WGM resonator. We show that it is possible to realize an externally controllable, efficient triply resonant optomechanical interaction between two optical WGMs and the SAW WGM and to use such an interaction in various sensor applications.

Narrowband tunable photonic notch filter

We propose a technique for realization of a high-contrast, tunable, low-insertion-loss notch filter using polarization selectivity of whispering-gallery-mode resonators. We demonstrate a 10 MHz filter with 5.5 dB insertion loss and 45.5 dB of in-band rejection. The measured rejection value is limited by the finite (3 kHz) linewidth of our laser. We show that the filter can potentially have tunable bandwidth without significant rejection modification.