Titanium enhanced Raman microcavity laser

Abstract

Due to their long photon lifetimes, ultra high quality factor (Q) silica microcavities form an ideal platform for microlaser development. Previous work verified that these devices exhibit Raman lasing, because the high Q compensates for the low Raman gain of silica. However, only devices with Q>1E8 are able to achieve microwatt thresholds, limiting the application space. One approach for overcoming this barrier is to increase the inherent Raman gain of the material without degrading the optical performance of the device. To address this challenge, we synthesize a series of titanium (Ti) doped silica sol-gels with different concentrations of Ti, including a null. The refractive indices of the coatings are characterized using spectroscopic ellipsometry and increase linearly with the concentration of Ti from 1.44 to 1.51. We apply the sol-gel as a conformal coating on silica toroidal microcavities and characterize the basic cavity properties (Q) and the lasing behavior, including the lasing threshold and the slope efficiency. All measurements are performed in ambient conditions. Although the cavity Q's are modest (5E6), comparable lasing thresholds (microwatt) to higher Q silica devices are achieved because of the reduction in mode volume and the increase in Raman gain due to the presence of the Ti. Additionally, the efficiency of the laser increases with increasing Ti concentration.

Low threshold anti-Stokes Raman laser on-chip

“…The doping concentrations used here were determined in previous works [26,27] and represent a balance between achieving the maximum increase in Raman gain and in refractive index with the minimum increase in optical loss. An additional consideration is the ability of the sol-gel matrix to support large concentrations of dopants without cracking, which will decrease the Q.…”

“…The film thicknesses are constant (∼400 nm) in all samples. The refractive indices of the coating (ncoating) increase from 1.454 for undoped coating to 1.520 for the 10 mol% of either Zr or Ti-doped coating [26,27].…”

“…The ratio of two peaks indicates the degree of polarization (IP) of silica. The IP values increase from 2.96 (undoped) to 4.87 (10 mol% metal-doped) [26,27], indicating that silica become more polarized with metal dopants. In silica, both SRS and SARS are based on the vibration of phonon.…”

“…1 (b)). Metal dopants enable silica sol-gel layers to exhibit high Raman gain, enhancing Raman lasing efficiencies as high as 40% with lasing thresholds in the sub-mW range [26,27]. These devices could provide a path to overcome the previous hurdles and be the ideal on-chip platform for generating SARS with single pump source.…”

Dissipation Assisted Frequency Comb and Chaos Generation in the Optomechanics

“…Optical microcavity [1], [2], [3] is widely studied for its high quality factor and small mode volume. Recently, the study of microcavity non-linearity including kerr nonlinearity [4], [5], [6], [7], [8], [9], [10], Raman nonlinearity [11], [12], [13], optomechanically induced nonlinearity [14], [15], [16], [17], [18], [19], [20], [21], optomagnonics microcavity [22], [23], [24], [25], [26] become hot points. Combine the nonlinearity and high quality factor of the optical microcavity, various low threshold nonlinear phenomenons such as chaos [27], [28], [29], [30], [31], [32], [33] and frequency comb [34], [35], [36], [37] in the optical microcavity [38], [39] can be observed.…”