Query: On-chip single-mode high-Q terahertz whispering gallery mode resonator

Candidate papers:

abstract: The chip scale terahertz (THz) devices and systems are helpful to enable actual applications in THz communication and sensing. Here, we demonstrate an on chip THz whispering gallery mode resonator (WGMR) delivering a high quality (Q) factor TE single mode, fabricated on a high resistivity float zone silicon wafer by complementary metal oxide semiconductor compatible technology. For a TE mode in a WGMR, it is the first time to achieve a Q factor of 1210 at 0.4925 THz with 28 dB extinction ratio, to the best of our knowledge. With this excellent WGMR, we have demonstrated a stable and highly sensitive sensor for particle distance estimation. Our investigation provides an effective approach to fabricate high performance integrated THz WGMRs for chip scale systems.
author_names: Ziwei Wang

Shixing Yuan

Gaoneng Dong

Ruolan Wang

Liao Chen

Xiaojun Wu

Xinliang Zhang
title: On chip single mode high Q terahertz whispering gallery mode resonator
venue: Optics Letters
year: 2019

abstract: We report on Fano resonances in a high quality (Q) whispering gallery mode (WGM) spherical resonator coupled to a multi mode waveguide in the terahertz (THz) frequency range. The asymmetric line shape and phase of the Fano resonances detected with coherent continuous wave (CW) THz spectroscopy measurements are in excellent agreement with the analytical model. A very high Q factor of 1600, and a finesse of 22 at critical coupling is observed around 0.35 THz. To the best of our knowledge this is the highest Q factor ever reported for a THz WGM resonator.
author_names: Dominik Walter Vogt

Rainer Leonhardt
title: Fano resonances in a high Q terahertz whispering gallery mode resonator coupled to a multi mode waveguide.
venue: Optics letters
year: 2017

abstract: We report on the coupling of a free space Gaussian beam to symmetric high quality (Q) whispering gallery mode resonators (WGMRs) for terahertz (THz) radiation. We achieve very high excitation efficiencies up to 50% to THz WGMs with a Q factor of 1.5x104 at 0.7 THz. The high coupling efficiencies have been realized by leveraging a Gaussian beam with a nearly diffraction limited focal spot, as well as readily available low loss, high index silicon spheres with diameters comparable to the wavelength. The results convincingly underline the viability of free space coupling in the THz frequency range.
author_names: Dominik Walter Vogt

Angus Harvey Jones

Rainer Leonhardt
title: Free space coupling to symmetric high Q terahertz whispering gallery mode resonators.
venue: Optics letters
year: 2019

abstract: We report on the first experimental demonstration of terahertz (THz) whispering gallery modes (WGMs) with an ultra high quality (Q) factor of $1.5 \times {10}{4} at 0.62THz. The WGMs are observed in a high resistivity float zone silicon (HRFZ Si) spherical resonator coupled to a sub wavelength silica waveguide. A detailed analysis of the coherent continuous wave (CW) THz spectroscopy measurements combined with a numerical model based on Mie Debye Aden Kerker (MDAK) theory allows to unambiguously identify the observed higher order radial THz WGMs.
author_names: Dominik Walter Vogt

Rainer Leonhardt
title: Ultra high Q terahertz whispering gallery modes in a silicon resonator
year: 2018

abstract: We investigate mode coupling effects of terahertz whispering gallery modes (WGMs) in a multi mode resonator using an extended transfer matrix method. Coupling effects between two WGMs are successfully observed on a well designed high Q terahertz Teflon ring resonator that supports low order WGMs. The extended transmission matrix method is adopted to model, analyze, and reproduce terahertz single band resonance and asymmetric dual band resonances caused by mode coupling. Moreover, the terahertz splitting effect based on coupling of two modes in a multi mode resonator is theoretically illustrated. This detailed analysis not only contributes to understanding physical phenomena, such as mode splitting, but also helps in identifying parameters when designing terahertz devices, such as dual band filters.
author_names: Shixing Yuan

Liao Chen

Ziwei Wang

Ruolan Wang

Xiaojun Wu

Xinliang Zhang
title: Mode coupling in a terahertz multi mode whispering gallery mode resonator.
venue: Optics letters
year: 2019

abstract: We report on prism coupling of high quality (high Q) terahertz (THz) whispering gallery modes (WGMs) in spherical high resistivity float zone grown silicon (HRFZ Si) resonators over two octaves from 0.2 THz to 1.1 THz. The WGMs are excited using a HRFZ Si prism and show unprecedented quality factors of up to 2.2 x 104. A detailed discussion of the phase and mode matching criteria of the prism coupling scheme implemented in the continuous wave THz spectroscopy system is presented. The results provide numerous opportunities for passive ultra broadband high Q devices operating in the THz frequency range.
author_names: Dominik Walter Vogt

Angus Harvey Jones

Harald G L Schwefel

Rainer Leonhardt
title: Prism coupling of high Q terahertz whispering gallery modes over two octaves from 0.2 THz to 1.1 THz.
venue: Optics express
year: 2018

abstract: We investigate thermal tuning of an ultra high quality (Q) terahertz (THz) whispering gallery mode resonator (WGMR) made of low loss silicon. The Si THz WGMR can be continuously tuned with a rate of about 29 MHz/K in the frequency range from 650 GHz to 666 GHz. Furthermore, we utilize the Si WGMR to extract the thermo optic coefficient of Si at 459 GHz and 659 GHz in the temperature range from 295 K to 363 K.We investigate thermal tuning of an ultra high quality (Q) terahertz (THz) whispering gallery mode resonator (WGMR) made of low loss silicon. The Si THz WGMR can be continuously tuned with a rate of about 29 MHz/K in the frequency range from 650 GHz to 666 GHz. Furthermore, we utilize the Si WGMR to extract the thermo optic coefficient of Si at 459 GHz and 659 GHz in the temperature range from 295 K to 363 K.
author_names: Dominik Walter Vogt

Angus Harvey Jones

Rainer Leonhardt
title: Thermal tuning of silicon terahertz whispering gallery mode resonators
year: 2018

abstract: A tunable integrated terahertz (THz) filter is one of the basic elements for realizing integrated reconfigurable THz communication systems. The state of the art tunable THz filters are discrete or vertically pumped for integrated devices. Here, we propose and demonstrate voltage actuated thermally tunable on chip THz bandpass and bandstop filters based on a whispering gallery mode resonator. The quality factors of the bandpass and bandstop filters attain 1867 and 1909, respectively, at approximately 0.4795 THz. Widely continuous tunability is realized by adjusting the voltage applied to a micro heater. As far as we know, this is the first Letter on on chip tunability in the THz domain. It provides a simple and reliable tuning method for on chip THz devices. Furthermore, the implementation of tunable bandpass and bandstop filters plays an important role in THz signal processing.
author_names: Ziwei Wang

Gaoneng Dong

Shixing Yuan

Liao Chen

Xiaojun Wu

Xinliang Zhang
title: Voltage actuated thermally tunable on chip terahertz filters based on a whispering gallery mode resonator.
venue: Optics letters
year: 2019

abstract: A monolithic lab on a chip fabricated by femtosecond laser micromachining capable of label free biosensing is reported. The device is entirely made of fused silica, and consists of a microdisk resonator integrated inside a microfluidic channel. Whispering gallery modes are excited by the evanescent field of a circular suspended waveguide, also incorporated within the channel. Thermal annealing is performed to decrease the surface roughness of the microstructures to a nanometric scale, thereby reducing intrinsic losses and maximizing the Q factor. Further, it is used to position, with submicrometric precision, the waveguide tangent to the resonator and within the critical coupling regime. With this fabrication method and geometry, the alignment between the waveguide and the resonator is robust and guaranteed at all instances. A maximum sensitivity of 121.5 nm/RIU was obtained at a refractive index of 1.363, whereas near the refractive index range of water based solutions the sensitivity is 40 nm/RIU. A high Q factor of 105 is kept throughout the entire measurement range.
author_names: Joao M Maia

Vitor A Amorim

Duarte Viveiros

Paulo V S Marques
title: Femtosecond Laser Micromachining of an Optofluidics based Monolithic Whispering Gallery Mode Resonator Coupled to a Suspended Waveguide
year: 2021

abstract: Fano resonance is widely discussed in designing novel terahertz components, such as sensors, filters, modulators, and group delay modules. Usually, high quality (Q) factor and flexible tunability of Fano resonance are key requirements for these applications. Here, we present tunable terahertz Fano resonance with a Q factor of 2095 at 0.439 THz in coupled terahertz whispering gallery mode resonators (WGMRs) Coupling between a relatively low Q (578) quartz ring and a high Q (2095) silicon ring is employed to generate the Fano resonance. The resonant frequency of the Fano resonance can be actively manipulated by tuning the resonant frequency of the high Q WGMR, which is achieved through utilizing an electrical thermo optic tuning method, meanwhile, the resonance intensity of the Fano resonance can be engineered by adjusting the coupling strength between two WGMRs. This coupled WGMR scheme delivers high Q tunable Fano resonance and may contribute to the design of high performance configurable terahertz devices.
author_names: Shixing Yuan

Liao Chen

Ziwei Wang

Ruolan Wang

Xiaojun Wu

Xinliang Zhang
title: Tunable high quality Fano resonance in coupled terahertz whispering gallery mode resonators
venue: Applied Physics Letters
year: 2019