Degeneracy breaking of optical resonance modes in rolled-up spiral microtubes

Abstract

The authors investigate the optical resonance modes (ORMs) generated in semiconductor microtubes of spiral symmetry by using finite-difference time-domain methods. Even though the tube-wall thickness is much smaller than the light wavelength, modes having an electric field parallel to the tube wall can loop around the tube periphery as ORMs. In addition, the degenerated ORMs present in conventional cylindrical cavities such as whispering gallery modes are broken and separated into two modes due to the spiral asymmetry of the rolled-up microtubes.

Optical resonances in tubular microcavities with subwavelength wall thicknesses

“…6 Recently, another kind of microcavities with such whispering gallery modes (WGMs), microtubes, has been fabricated by rolling up prestressed solid thin films. [7][8][9] Unlike other microcavities with WGMs, such tubular microcavities have subwavelength wall thicknesses and thus possess resonances that are very sensitive to ambient refractive index. 10 As a result, microtubes can act as optical sensors for identifying different liquids, promising high potential for lab-on-a-chip applications.…”

“…11,12 Currently, WGM resonances in microtubes have been explored mainly by a waveguide approximation and finitedifference time-domain (FDTD) simulation. [7][8][9]13 However, the two methods cannot present quality (Q) factors of microtubes efficiently, especially for high-Q cases. Hence, a thorough study of WGM resonances in microtubes is absent.…”

Lab-in-a-tube: on-chip integration of glass optofluidic ring resonators for label-free sensing applications

“…The change in RI is more pronounced if a gaseous phase (e.g. 28 The definition of TE and TM modes for our microtubes follows the established classification from Hosoda et al 29 A red shift of 11 nm after changing the microtube's content from air to DI water clearly detects the difference in the refractive indices between air (n # 1) and DI water (n # 1.3330). An example of an optical sensing sequence of air and liquids flowing through the integrated RU-OFRR is depicted in Fig.…”

Three dimensionally confined optical modes in quantum-well microtube ring resonators

“…1͒. 9 Another explanation for the double peak structure might be the existence of axially confined modes of slightly different energy, which spatially overlap or at least cannot be separated by our experimental setup. Such axially localized modes will be thoroughly addressed later in this paper.…”