Electrical and thermal tuning of quality factor and free spectral range of optical resonance of nematic liquid crystal microdroplets

Abstract

We experimentally study the effect of temperature and electric field on the quality (Q) factor and free spectral range (FSR) of whispering-gallery-mode optical resonance of dye-doped nematic liquid crystal microdroplets. Both the Q factor and the FSR are highly sensitive to the temperature and electric field and are tunable. The Q factor decreases, whereas the FSR increases substantially, with increasing temperature and electric field. The variation of the Q factor and FSR is understood based on the change in the effective refractive index and the dynamic size of the microdroplets.

Electrically switchable whispering gallery mode lasing from ferroelectric liquid crystal microdroplets

“…5 With the aim of exploring and expanding the versatile usage of liquid crystal droplets, we studied the electrical and thermal tuning of the quality factor (Q) and the free spectral range (FSR) of WGM resonance. 6 We also reported on the magnetic field tuning of lasing in ferromagnetic nematic droplets. 7 Among the liquid crystals, the ferroelectric liquid crystals (FLCs) show outstanding performance for fast electro-optical applications due to the spontaneous polarisation of the smectic layers.…”

“…1,2 If the pumping energy exceeds a certain threshold, the dye gives stimulated emission and the resonator emits multimode laser light. Liquid crystal microdroplets have drawn considerable attention across various scientific disciplines owing to their potential applications in tunable optical microcavities [2][3][4][5][6][7][8][9][10][11][12][13][14][15] and sensors. [16][17][18][19][20][21][22] They could well fit into the integrable photonics as essential optical components in miniaturised devices and hence serve widespread applications such as electrically or magnetically tunable lasers, filters, and sensors.…”

“…The details of the experimental setup are presented in our previous reports. 5,6 For electric field studies, the dc field is provided by a high voltage supply. The switching response time of lasing was measured with the help of a photomultiplier tube connected to a digital storage oscilloscope.…”

“…It is observed that the WGM spectrum of FLC is significantly different from that usually observed in the case of nematic or smectic-A microdroplets. 2,6,8 The modes have a lower linewidth and are not equally spaced. This is attributed to the inhomogeneity in the refractive index of the cavity that occurs due to the complex elastic deformation of the smectic layers.…”

Thermally tunable and electrically switchable solid sphere shell three-layer 3D Bragg microcavity laser based on cholesteric-liquid-crystals

“…Such a WGMs peak wavelength shift behavior can be attributed to the fact that the CLC molecules tend to gradually align in the electric field direction and the effective index of the CLCs decreases when the applied electric field is above a threshold value (0.33 V μm −1 ). 28) Finally, the CLC molecules were arranged along the direction of the applied electric field, and the effective refractive index of CLCs did not change any more.…”