Cavity ring-up spectroscopy for dissipative and dispersive sensing in a whispering gallery mode resonator

In whispering gallery mode resonator sensing applications, the conventional way to detect a change in the parameter to be measured is by observing the steady state transmission spectrum through the coupling waveguide. Alternatively, cavity ring-up spectroscopy (CRUS) sensing can be achieved transiently. In this work, we investigate CRUS using coupled mode equations and find analytical solutions with a large spectral broadening approximation of the input pulse. The relationships between the frequency detuning, coupling gap and ring-up peak height are determined and experimentally verified using an ultrahigh \textit{Q}-factor silica microsphere. This work shows that distinctive dispersive and dissipative transient sensing can be realised by simply measuring the peak height of the CRUS signal, which might improve the data collection rate

Optomechanical Transduction and Characterization of a Silica Microsphere Pendulum via Evanescent Light

Dissipative optomechanics has some advantages in cooling compared to the conventional dispersion dominated systems. Here, we study the optical response of a cantilever-like, silica, microsphere pendulum, evanescently coupled to a fiber taper. In a whispering gallery mode resonator the cavity mode and motion of the pendulum result in both dispersive and dissipative optomechanical interactions. This unique mechanism leads to an experimentally observable, asymmetric response function of the transduction spectrum which can be explained using coupled-mode theory. The optomechanical transduction, and its relationship to the external coupling gap, are investigated and we show that the experimental behavior is in good agreement with the theoretical predictions. A deep understanding of this mechanism is necessary to explore trapping and cooling in dissipative optomechanical systems.Comment: 5 page

Whispering gallery resonators for optical sensing

In recent years, whispering gallery mode devices have extended their functionality across a number of research fields from photonics to sensing applications. Here, we will discuss environmental sensing applications, such as pressure, flow, and temperature using ultrahigh Q-factor microspheres fabricated from ultrathin optical fiber and microbubbles fabricated from pretapered glass capillary. We will discuss device fabrication and the different types of sensing that can be pursued using such systems. Finally, we will introduce the concept of using cavity ring-up spectroscopy to perform dispersive transient sensing, whereby a perturbation to the environment leads to a frequency mode shift, and dissipative transient sensing, which can lead to broadening of the mode, in a whispering gallery mode resonator

Hollow whispering gallery resonators

In recent years, whispering gallery mode (WGM) devices have extended their functionality across a number of research fields from photonics device development to sensing applications. Here, we will discuss some such recent applications using ultrahigh Q-factor hollow resonators fabricated from pretapered glass capillary. We will discuss device fabrication and different applications that can be pursued such as bandpass filtering, nanoparticle detection, and trapping. Finally, we will introduce our latest results on visible frequency comb generation

TeraHz tuning of whispering gallery modes in a PDMS, stand-alone, stretchable microsphere

We report on tuning the optical whispering gallery modes in a poly dimethyl siloxane-based (PDMS) microsphere resonator by more than a THz. The PDMS microsphere system consists of a solid spherical resonator directly formed with double stems on either side. The stems act like tie-rods for simple mechanical stretching of the microresonator over tens of microns, resulting in tuning of the whispering gallery modes by one free spectral range. Further investigations demonstrate that the whispering gallery mode shift has a higher sensitivity (0.13 nm/{\mu}N) to an applied force when the resonator is in its maximally stretched state compared to its relaxed state.Comment: 3 pages, 4 figures, submitted to Optics Letter

Whispering gallery mode microcavities: from fabrication to applications

Trapping and cooling macroscopic objects using light has attracted great interest recently as it may enable us to see quantum mechanical features in large systems. A microsphere pendulum is one such system to put it to test. This thesis work is devoted to solving many of the steps necessary for future trapping and cooling works of a microsphere pendulum using a whispering gallery mode (WGM) cavity-based photonic molecule scheme. In the course of implementing this scheme, microcavity devices, such as microspheres and microbubbles were studied for topics as diverse as optomechanics, photonics, laser tuning and spectroscopy. The WGMs in the microsphere pendulum sense its mechanical mode through fibre taper coupling of light. Its properties in the evanescent light fields and its optomechanical transduction characteristics were investigated. This system is highly dissipative - a feature which could prove to be very useful for cavity cooling applications. Owing to its pressure tuning capability, a microbubble cavity can be used as a means of finding co-resonances as needed to achieve a photonic molecule and mode splitting. By locking a laser to a WGM of a microbubble resonator, linear tuning and stability characteristics of the WGM via pressure were studied. A fast method of sensing and estimation of dissipation and dispersion individually in an optomechanical system with minimal invasion was required. In this regard, cavity-ringup spectroscopy (CRUS) was investigated by simply measuring the peak height of the CRUS signal, enabling ultrafast sensing applications. Finally, a coupled, two cavity system, known as a photonic molecule, was studied for its optomechanical transduction properties in CMIT, ATS and their intermediate regimes making way for understanding the trapping capabilities of such a system. The range of studies in this thesis also illustrate the versatility of WGM-based resonators in optics measurements extending from fundamental optomechanics to applied photonics