WHISPERING GALLERY MODE RESONATORS
OEwaves has pioneered the technology of crystalline whispering gallery mode (WGM) optical microresonators, which are used in a variety of our products, including lasers. These mm-scale elements exhibit the highest quality factor (Q) and finesse, beyond what is possible with bulk or integrated optical resonators. Q's in excess of 10^11 and finesse in excess of 17,500 have been demonstrated. OEwaves fabricates WGM resonators from a variety of crystals, including calcium fluoride, lithium tantalate, quartz, silicon, and even diamond. The specific materials serve the specific applications utilizing linear and nonlinear properties of these resonators. For example, magnesium and calcium fluoride can be used for generation of Kerr frequency combs, while lithium tantalate can be used in applications where a change in the index of refraction with voltage is needed, such as for a modulator. Other applications such as harmonic generation are also supported by these crystalline resonators. The high Q of the resonator leads to high sensitivity of the modulator and reduced "effective" V-pi.
The advantage of a crystalline WGM resonator over other approaches, including resonators fabricated with epitaxial growth on chip, is that the ultra-high quality factor allows reduced power (a few mW) to excite linear and nonlinear functionalities. The larger mode volumes of crystalline resonators also reduce the fundamental quantum noise in these structures, compared to ring resonators.