Whispering Gallery Mode Microsphere Research Articles

In-Fiber Liquid Microsphere Whispering Gallery Mode Resonator Fabricated by Femtosecond Laser

In-Fiber Liquid Microsphere Whispering Gallery Mode Resonator Fabricated by Femtosecond Laser

Boosted Second Harmonic Generation and Cascaded Sum Frequency Generation from a Surface Crystallized Glass Ceramic Microcavity.

The development of novel materials and structures for efficient second-order nonlinear micro/nano devices remains a significant challenge. In this study, the remarkable enhancement of second-harmonic generation (SHG) and cascaded sum frequency generation in whispering gallery mode microspheres made of surface-crystallized glass with a 6-µm Ba2TiSi2O8 crystal layer are demonstrated. Attributed to the core-shell design, the Ba2TiSi2O8 located on the surface can be efficiently coupled with whispering gallery modes, resulting in a highly efficient micron-scale cavity-enhanced second-order optical nonlinearity. Greatly enhanced SHG of the microcavity is observed, which is up to 80 times stronger than that of a non-resonant sample. Furthermore, owing to the wavelength non-selectivity of random quasi-phase matching, ultra-wideband SHG with a strong response ranging from 860 to 1600nm and high-contrast polarization characteristics is demonstrated. The glass-ceramic-based microsphere cavity also boosts the cascading optical nonlinearity, manifested by a two-magnitude enhancement of cascaded sum frequency generation. This work delineates an efficient strategy for boosting nonlinear optical response in glass ceramics, which will open up new opportunities for applications in photonics and optical communications.

A Reflective Whispering Gallery Mode Microsphere Resonator Integrated With a Thick-Wall Capillary Tube

A Reflective Whispering Gallery Mode Microsphere Resonator Integrated With a Thick-Wall Capillary Tube

Microsphere-Enabled Micropillar Array for Whispering Gallery Mode Virus Detection.

Rapid detection of pathogens and analytes at the point of care offers an opportunity for prompt patient management and public health control. This paper reports an open microfluidic platform coupled with active whispering gallery mode (WGM) microsphere resonators for the rapid detection of influenza viruses. The WGM microsphere resonators, precoated with influenza A polyclonal antibodies, are mechanically trapped in the open micropillar array, where the evaporation-driven flow continuously transports a small volume (∼μL) of sample to the resonators without auxiliaries. Selective chemical modification of the pillar array changes surface wettability and flow pattern, which enhances the detection sensitivity of the WGM resonator-based virus sensor. The optofluidic sensing platform is able to specifically detect influenza A viruses within 15 min using a few microliters of sample and displays a linear response to different virus concentrations.

Fano-like line shape and its tuning effect in a double-handle whispering gallery mode microsphere resonator

Fano-like line shape and its tuning effect in a double-handle whispering gallery mode microsphere resonator

Preparation and controllable tuning of a high-quality factor phonon-laser in the optomechanical microsphere cavity

Low-threshold, narrow linewidth phonon lasers can greatly improve the detection resolution of sensors and have enormous potential for development in classical and quantum sensing fields, as well as information processing. However, its development is limited due to unfavorable factors such as the complex process, low quality factor (Q-factor), difficult tuning, and harsh environments requirements. Here, we report an easy-to-excite phonon laser with an ultra-narrow linewidth in silica whispering gallery mode microsphere optomechanical resonators at room temperature and ambient pressure. The microsphere cavity is fabricated by high-temperature melting with a CO2 laser and designed by controlling the proportion of the sphere to the stem (sphere-to-stem ratio) to reduce mechanical damping. By using a single-frequency laser as the pump source, the microsphere optomechanical resonator exhibited multiple breathing mode phonon lasers with ultra-high optical Q-factor (1.78 × 109), mechanical Q-factor (3.1 × 107), and low threshold (2.4 μW). It is the first time to achieve such a high mechanical Q-factor in the microsphere cavity system of this kind to the best of our knowledge, which opens up an avenue to develop highly sensitive sensors.

Methane Sensor Based on High-Q Microsphere Whispering Gallery Mode

In this paper, the principle of the methane gas enhanced the laser absorption by the WGM of high-Q microsphere was studied. A taper optical fiber was used as a coupler to couple 1653.72 nm laser into a microsphere with a optical fiber handle to form whispering gallery mode(WGM). The resonant wavelength of the microsphere cavity was changed to 1653.72 nm by injecting heating light along the handle, so that one resonant wavelength of the microsphere is just 1653.72 nm. The 1653.72 nm laser forms WGM continuously to surround the microsphere, and the effective optical path is greatly increased, which increases the interaction distance with methane, and thus the sensitivity of methane detection is improved. The results show that the microsphere with WGM can be used as a gas sensor.

Impact of Plasmonic and Dielectric Substrates on the Whispering-Gallery Modes in Self-Assembled Fluorescent Semiconductor Polymer Microspheres.

In this work, the impact of metallic and dielectric conducting substrates, gold and indium tin oxide (ITO)-coated glass, on the whispering gallery modes (WGMs) of semiconductor π-conjugated polymer microspheres is investigated. Hyperspectral mapping was performed to obtain the excitation-position-dependent emission spectra of the microspheres. Substrate-dependent quenching of WGMs sensitive to mode polarization was observed and explained. On a glass substrate, both transverse-electric (TE) and transverse-magnetic (TM) WGMs are quenched due to frustrated total internal reflection. On a gold substrate, however, only the TM WGMs are allowed in symmetry to leak into surface plasmons. An atomically flat gold substrate with subwavelength slits was used to experimentally verify the leakage of WGMs into the surface plasmon polaritons (SPPs). This work provides insight into the damping mechanisms of WGMs in microspheres on metallic and dielectric substrates.

Whispering gallery mode microsphere resonator based on cylindrical air cavity coupling.

In this Letter, an optical fiber whispering gallery mode microsphere resonator based on cylindrical air cavity coupling is proposed and demonstrated. The cylindrical air cavity is vertical to the axis of a single-mode fiber and in touch with the fiber core, fabricated by using femtosecond laser micromachining together with hydrofluoric acid etching. A microsphere is inserted into the cylindrical air cavity and in tangential contact with the inner cavity wall, which is in touch with or inside the fiber core. The light traveling in the fiber core is coupled into the microsphere via an evanescent wave when the light path is tangential to the contacting point of the microsphere and the inner cavity wall, resulting in whispering gallery mode resonance when the phase-matching condition is satisfied. Such a device is highly integrated, robust in structure, low in cost, stable in operation, and has a good quality factor (Q) of 1.44 × 104.

All-optical Tuning of Microsphere Whispering Gallery Mode Resonance Wavelength to Lock to the DFB Laser Wavelength for Using in CH4 Detection

Methane is a flammable and explosive gas, which is the main component of mashgas and natural gas.Methane monitoring plays an important role in coal mine safety and natural gas.The high-Q whispering gallery mode (WGM) of optical microcavity has a long photon lifetime, which greatly prolongs the effective optical path between light and surroundings,and has the potential to be made into miniaturized and highly sensitive gas sensor device.In order to realize the high Q microcavity WGM enhancement light absorption methane gas sensor,the key technology is to lock the resonant frequency of the microsphere cavity to the DFB laser frequency.In order to ensure the intrinsic safety of the CH4 sensor, the resonance wavelength of the all-optically tuning microsphere cavity was studied, so that it was locked to the wavelength of the CH4 absorption peak of 1653.72nm. The resonant wavelength of the microsphere was tuned by injecting light along the fiber handle of the microsphere, and the refractive index of the microsphere was changed by absorbing light and converting heat with the coating of the sphere crown.

Fabrication of Er3+ doped tellurite whispering gallery mode microsphere laser using 0.98 μm and 1.48 μm pump lasers

We reported lasing in Er3+ doped tellurite glass whispering gallery mode microspheres fabricated using the plasma torch method.15Na2O25WO360TeO2 doped with 0.5 mol% Er3+ is used for the fabrication of microspheres. Laser light from the pump is coupled to the microsphere through a half and a full tapered fiber. An optical spectrum analyzer receives the counter propagating light from the microsphere. Pump lasers of 980 nm and 1480 nm are used to achieve the laser emission at 1570 nm.

Ultrahigh-Q WGM microspheres from ZBLAN for the mid-IR band.

The advantages of high-quality-factor (high-Q) whispering gallery mode (WGM) microresonators can be applied to develop novel photonic devices for the mid-infrared (mid-IR) range. ZBLAN (glass based on heavy metal fluorides) is one of the most promising materials to be used for this purpose due to low optical losses in the mid-IR. We developed an original, to the best of our knowledge, fabrication method based on melting of commercially available ZBLAN-based optical fiber to produce high-Q ZBLAN microspheres with the diameters of 250 to 350 μm. We effectively excited whispering gallery modes in these microspheres and demonstrated high quality factor both at 1.55 μm and 2.64 μm. Intrinsic quality factor at telecom wavelength was shown to be (5.4 ± 0.4) × 108 which is defined by the material losses in ZBLAN. In the mid-IR at 2.64 μm we demonstrated record quality factor in ZBLAN exceeding 108 which is comparable to the highest values of the Q-factor among all materials in the mid-IR.

Trapezoidal Angled Fiber Coupler for Microsphere Resonator With Enhancement of Fano Resonance

We propose and demonstrate a trapezoidal angled fiber coupler for excitation of whispering-gallery mode microsphere resonator, with enhanced Fano resonance. The reflection from the angled fiber is enhanced when the oblique angle is greater than critical angle, which is obtained as 30° theoretically for angled fiber. To enhance the endface reflection, the front tip of the angled fiber is polished flat to achieve the trapezoidal angled fiber. Compared with angled fiber, the proportion of Fano lineshape in spectra for trapezoidal angled fiber is nearly doubled and the slope is greatly improved, which reaches 304.55 dB/nm. Moreover, through the coupling of dual microspheres, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> factor is improved severalfold and the thermal tuning efficiency is increased by 50%. With the advantage of low cost, easy fabrication procedure and reflection mode operation, the proposed device shows a great potential for sensing, optical tuning and optical switching applications.

Whispering gallery mode resonator based on dual microspheres in an expanded hollow sphere cavity of capillary tube

A whispering gallery mode microsphere resonator is proposed and demonstrated. The device is based on dual microspheres embedded in an expanded hollow sphere cavity formed by splicing a single-mode fiber and a capillary tube. The whispering gallery mode resonance is excited by the light traveling along the hollow sphere cavity wall and directed out by use of a tapered optical fiber in closing contact with one of the microspheres. The device has a good quality factor (Q) of 2.072 × 103, and a number of asymmetric Fano resonance lines. It is compact in structure, low in cost, simple in fabrication, and convenient in operation.

Radial order dependence of the gas sensing sensitivity of whispering gallery mode microspheres

Silica microspheres were coated with a porous silica layer. The wavelength shift of the whispering gallery modes of the coated microsphere was used to detect small traces of ammonia vapors. The sensing sensitivities of different modes of the same microsphere were found to differ greatly, which is attributed to the modes having different radial indices. This effect was found to be more pronounced in the microspheres coated with thicker coatings.

Caged-Sphere Optofluidic Sensors: Whispering Gallery Resonators in Wicking Microfluidics

The rapid development of optofluidic technologies in recent years has seen the need for sensing platforms with ease-of-use, simple sample manipulation, and high performance and sensitivity. Herein, an integrated optofluidic sensor consisting of a pillar array-based open microfluidic chip and caged dye-doped whispering gallery mode microspheres is demonstrated and shown to have potential for simple real-time monitoring of liquids. The open microfluidic chip allows for the wicking of a thin film of liquid across an open surface with subsequent evaporation-driven flow enabling continuous passive flow for sampling. The active dye-doped whispering gallery mode microspheres placed between pillars, avoid the use of cumbersome fibre tapers to couple light to the resonators as is required for passive microspheres. The performance of this integrated sensor is demonstrated using glucose solutions (0.05–0.3 g/mL) and the sensor response is shown to be dynamic and reversible. The sensor achieves a refractive index sensitivity of ~40 nm/RIU, with Q-factors of ~5 × 103 indicating a detection limit of ~3 × 10−3 RIU (~20 mg/mL glucose). Further enhancement of the detection limit is expected by increasing the microsphere Q-factor using high-index materials for the resonators, or alternatively, inducing lasing. The integrated sensors are expected to have significant potential for a host of downstream applications, particularly relating to point-of-care diagnostics.

Silica Microsphere WGMR-Based Kerr-OFC Light Source and Its Application for High-Speed IM/DD Short-Reach Optical Interconnects

Kerr optical frequency combs (OFCs) based on silica microsphere whispering gallery mode resonator (WGMR) have various applications where they are used as a light source. For telecommunication purposes, WGMR-based Kerr-OFC comb generators can be physically realized using silica microsphere resonators and can be used to replace multiple laser arrays. In such a realization, these novel light sources have the potential to demonstrate an attractive solution for intra-datacenter interconnects (DCI). In this paper, we show an experimental demonstration of a silica microsphere WGMR-based Kerr OFC light source where newly generated 400 GHz spaced carriers together with powerful linear equalization techniques, such as a linear symbol-spaced adaptive decision-feedback equalizer (DFE) with feed-forward (FF) and feedback (FB) taps, provide an alternative to individual lasers ensuring low-cost and low-complexity IM/DD scheme for the transmission of NRZ-OOK modulated signals at data rates up to 50 Gbps/λ over 2 km SMF link. Finally, we demonstrate a record 50 Gbps per λ transmission of NRZ-OOK modulated signals with a novel silica microsphere WGMR-based Kerr-OFC as a light source operating in the optical C-band, surpassing the previously demonstrated data rate record by five times.

Metamaterial engineered silicon photonic coupler for whispering gallery mode microsphere and disk resonators

Optical microresonators with high quality factors are key in photonic circuits requiring fine spectral filtering or resonant storage of optical power. Silicon (Si) photonics provides high-performance optoelectronic circuits but yields planar Si microresonators with rather low quality factors ( Q &lt; 10 5 ). On the other hand, bulk resonators achieve exceptionally high quality factors, Q &gt; --> 10 7 . Si photonic waveguides and bulk resonators have very different sizes and refractive indices that preclude efficient coupling. Here, we show an efficient method to couple bulk resonators and Si waveguides based on subwavelength metamaterial engineering. We demonstrate up to 99% light coupling efficiency for microspheres and microdisks made of silica, lithium niobate, and calcium fluoride, with 0.3 − 3.6 m m diameter. This achievement could enable the heterogeneous integration of bulk resonators and silicon photonic circuits, with potential applications in sensing, communications, and quantum information.

A Stable 1550nm WGM Laser Generated by Yb3+/Er3+ Co-doped Silica Microspheres under μm ASE Source Pumping

The amplified spontaneous emission (ASE) light source at 1 μm was used to excite Yb3+/Er3+ co-doped silica (YEDS) microspheres by evanescent-wave coupling through a taper optical fiber (TOF) to generate a stable 1550 nm laser. Inevitably, the experimental process was accompanied by a frequency up-conversion luminescence whose fluorescence spectrum was collected and analyzed. Pumped by the ASE light source with different power, the system of YEDS microsphere and TOF also generated single-mode laser and multi-longitudinal mode laser. Their peak wavelength, output power of the peak laser, full width at half maximum (FWHM), and side mode suppression ratio (SMSR) were respectively measured. Moreover, the characteristics of a 1550 nm whispering gallery mode (WGM) laser excited by a 1 μm ASE pumping and a tunable laser (TLS) pumping were compared under different variable conditions. It was demonstrated that the ASE pump source has polarization in all directions to excite WGMs in the microsphere cavity, which was different from and superior to the TLS. Therefore, the laser generated by the ASE pump source as an excitation source was not affected by vibration and temperature change. The results show that the 1550 nm laser pumped by ASE can stably output the microsphere WGM mode laser under the interference of vibration and temperature change, which is more suitable for the actual application environment.

A Whispering-Gallery Mode Microsphere Resonator Based on Optical Fiber With an Open Microcavity

A whispering-gallery mode microsphere resonator based on optical fiber with an open microcavity is demonstrated, which is created by use of femtosecond laser micromachining and fusion splicing techniques. When a microsphere is placed into the open microcavity, whispering-gallery mode can be excited through evanescent field coupling. The device can be constructed in either single-mode fiber or multimode fiber, with the insertion loss of ~13.2 and ~21.0 dB, and the quality factor of 4.81X10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 2 X10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> respectively. Because of its features of compact structure, low cost, easy fabrication, convenient operation and high durability, the device is expected to have many photonics applications.