Microcavity Performance Research Articles

Single-mode unidirectional microcavity laser.

In this Letter, we report a suspended whispering gallery mode microdisk with a hole pierced through its surface. The novel disk is made up of Rhodamine B-doped resin, which is fabricated by femtosecond laser direct writing technology. The pierced microcavity achieves highly directional emission of single-mode lasing with a far field divergence angle of about 10 deg, and its high Q factor exceeds 2.6×103. The excellent properties are confirmed by numerical simulation based on the finite-difference time-domain method. The effect of the pierced hole on the microcavity performance is discussed in detail. The method is easy to implement and has a guiding significance for improving the characteristics of an existing microcavity by simple modification.

Influence of crystal anisotropy on subsurface damage in ultra-precision cylindrical turning of CaF2

An optical microcavity, which stores light at a certain spot, is an essential component to realize all-optical signal processing. Single-crystal calcium fluoride (CaF2) theoretically shows a high Q-factor which is a desirable optical property. The CaF2 microcavity can only be manufactured by ultra-precision cylindrical turning (UPCT). The authors have studied UPCT of CaF2 and shown the influence of crystal anisotropy and tool geometry on surface roughness and subsurface damage. The study indicated that a smaller nose radius of the cutting tool led to shallower subsurface damage. Thus, it is inferred that a smaller nose radius compared to the previous nose radius (0.05mm) can further reduce subsurface damage. Nevertheless, the mechanism that causes a difference in subsurface damage due to crystal anisotropy is not sufficiently clear. The influence of subsurface damage on microcavity performance is still unclear. In this study, the UPCT of CaF2 was conducted using a tool with a nose radius of 0.01mm. The subsurface damage was investigated by transmission electron microscope (TEM) observation from the viewpoint of the change in crystal lattice arrangement. In our previous study, fast Fourier transfer (FFT) analysis was used for confirmation of change of crystal structure. In this study, FFT analysis was also used to quantitatively evaluate the depth of subsurface damage. In addition, inverse fast Fourier transfer (IFFT) was used to analyze change of crystal lattice arrangement clearly, which enables discussion of the influence of slip systems. Finally, optical microcavities are manufactured without any crack, and the influence of subsurface damage on microcavity performance is experimentally evaluated using a wavelength tunable laser and power meter.

Performance enhancement of a photonic crystal microcavity and related localization of evanescent Bloch waves

A study is carried out to investigate the possible enhancement of photonic crystal (PC) microcavity performance induced by geometrical and permittivity variations in relation to localization of the associated evanescent Bloch wave. The study is focused on PCs of hexagonally packed dielectric rods. A numerical scheme formulated on the basis of Green's function method with multipole expansion approximation is employed to exhibit explicitly the exponential growth curves of the spontaneous emission rate ($F$) and quality factor ($Q$) of the cavity with respect to increasing number of surrounding layers ($N$), which are characterized by their growth rates ${k}_{F}$. While the same exponential growth pattern is found for PCs with different rod parameters, the associated growth rates do show distinct and significant differences, implying that an appropriate choice of the rod parameters may produce a large performance enhancement for the microcavity or achieve the same performance with a largely reduced surrounding layer number. Meanwhile, the corresponding spatial decay constants of the evanescent Bloch waves, represented by its smallest Im($k$) in the photonic gap, are calculated by means of the extended plane-wave expansion method. The resulting smallest values of Im($k$) show their strong correlation with ${k}_{F}$ as characterized by their linear relation. The study further demonstrates that a judicious choice of the defect rod parameters may also give rise to a remarkable performance enhancement of the microcavity, even at a reduced number of surrounding rod layers. Remarkably, the [${k}_{F},\mathrm{Im}(k)$] values of all PCs considered are located on the same linear correlation line.