Hiroki Itobe

Dispersion tailoring of a crystalline whispering gallery mode microcavity for a wide-spanning optical Kerr frequency comb

We fabricated a crystalline whispering gallery mode microcavity by using a computer-controlled ultraprecision cutting process to control the cavity cross section. We used a numerical simulation to show that a wide-spanning optical Kerr frequency comb is generated by tailoring the dispersion of a crystalline whispering gallery mode microcavity. To control the dispersion, we designed the cross-sectional shape of the device and fabricated it by using ultraprecision cutting. Both the measured value and the numerical result show that the microcavity has an anomalous dispersion over one octave.

Thermal Effects on Kerr Comb Generation in a CaF 2 Whispering-Gallery Mode Microcavity

We numerically investigate the dynamics of Kerr comb generation in a calcium fluoride whispering gallery mode (WGM) microcavity taking thermal effects into account. Soliton pulse generation is investigated in the presence of thermooptic (TO) and thermal expansion (TE) effects and particularly when the TO effect is negative. We found that, with optimized cavity parameters, self-induced cavity resonance shifts resulting from a negative TO effect allow the system to generate a soliton pulse with no wavelength scanning or dynamic power optimization, which are usually needed to achieve a soliton pulse with silica and other WGM microcavity systems. A negative TO effect automatically tunes the cavity resonance so that the cavity will achieve a soliton state. The competition between the TO and TE effects is also investigated in detail.

Bi-material crystalline whispering gallery mode microcavity structure for thermo-opto-mechanical stabilization

We fabricated a calcium fluoride (CaF2) whispering gallery mode (WGM) microcavity with a computer controlled ultra-precision cutting process. We observed a thermo-opto-mechanical (TOM) oscillation in the CaF2 WGM microcavity, which may influence the stability of the optical output when the cavity is employed for Kerr comb generation. We studied experimentally and numerically the mechanism of the TOM oscillation and showed that it is strongly dependent on cavity diameter. In addition, our numerical study suggests that a microcavity structure fabricated with a hybrid material (i.e. CaF2 and silicon), which is compatible with an ultra-high Q and high thermal conductivity, will allow us to reduce the TOM oscillation and stabilize the optical output.

Dispersion tailoring of a crystalline whispering gallery mode microcavity for optical Kerr frequency comb generation

The generation of an optical Kerr comb in whispering gallery mode (WGM) microcavities has been investigated for applications in frequency metrology, precise spectroscopy, and signal processing. Optical Kerr combs are generated via parametric frequency conversion, thus a high quality factor (Q) is essential for lowering the threshold power, and this can be achieved with crystalline microcavities in, for example, calcium fluoride (CaF 2 ) because of the low absorption coefficient of this material. An optical Kerr comb with a wide span is needed to obtain frequency stabilization with the f-2f self-referencing method, which requires an anomalous dispersion [1]. We used a computer controlled precise cutting machine to fabricate a dispersion controlled CaF 2 microcavity with an anomalous dispersion to obtain exactly the same dispersion as we obtained in the numerical simulation.

Optical nonlinear control at a very low power in ultrahigh-Q microcavity systems

A small optical cavity with a high Q is attractive for optical nonlinear applications. We discuss various applications that utilize or are affected by cavity opto-mechanical coupling.

Soliton pulse formation in a calcium fluoride whispering gallery microcavity without frequency sweeping

We study a way of achieving a soliton pulse from a CaF2 microcavity. We fabricated a dispersion controlled CaF2 cavity and also numerically developed a method to generate soliton pulses without sweeping the input laser.