Microfiber Cavity Research Articles

Ultracompact all-fiber self-transceiving ultrasonic probe with an enhanced working distance.

All-optical ultrasonic probes exhibit notable benefits in ultrasonic detection and imaging. Typically, two separate optical fibers are used for excitation and detection, yet limited research has explored the integration of both functionalities within a single fiber. In this Letter, to our knowledge, a new method for fabricating an all-fiber self-transceiving ultrasonic probe is proposed with a lateral dimension of less than 500 µm. Double cladding fiber (DCF) is spliced with a short segment of thin-diameter single-mode fiber (TDSMF), which is then embedded into a fiber bubble to form a Fabry-Perot cavity, and the bubble surface is coated with a composite material layer. The pulsed laser propagates through the inner cladding of DCF and leaks from the splicing point of DCF-TDSMF, inducing the material excitation for efficient ultrasound generation. The core-guided detection laser is directed to the TDSMF end, entering the bubble microcavity and inducing an optical interference for weak echo detection. The emitting functionality produces an ultrasound with a -6 dB bandwidth of 17.5 MHz and a peak frequency of 6.29 MHz, which is well-matched with the fiber microcavity's response frequency of 3.29 MHz. Through self-transceiving experiments, low-noise pulse-echo signals are captured at varying working distances of up to 3.78 cm. The proposed probe exhibits great potential in biomedical and industrial fields due to its all-fiber miniaturization and enhanced-distance detection capability.

Light control of a movable microbubble in an ethanol-filled fiber microcavity for displacement measurement.

An optical fiber displacement sensor based on a light-controlled microbubble in an ethanol-filled fiber microcavity is proposed. The single-frequency 1550 nm laser in the side-lead-in single-mode fiber (SMF) produces an uneven temperature gradient by side irradiation in the ethanol-filled fiber microcavity. The microbubble shifts to the laser irradiation position along the microcavity due to the Marangoni effect and finally stops at the laser irradiation position. When the side-lead-in SMF moves, the microbubble follows. The surfaces of the microcavity and microbubble form a Fabry-Perot interferometer (FPI). The optical path difference (OPD) of the FPI is demodulated by the position of the side-lead-in SMF, which can be used for the displacement measurement with ultrahigh sensitivity (1.1 × 10-3 nm-1/µm). What is more, the proposed structure is only sensitive to a one-dimensional direction and has the advantages of non-contact, large range, and high resolution, which makes it a perfect candidate for displacement sensors.

Label-Free DNA Hybridization Detection Using a Highly Sensitive Fiber Microcavity Biosensor.

A novel label-free optical fiber biosensor, based on a microcavity fiber Mach-Zehnder interferometer, was developed and practically demonstrated for DNA detection. The biosensor was fabricated using offset splicing standard communication single-mode fibers (SMFs). The light path of the sensor was influenced by the liquid sample in the offset open cavity. In the experiment, a high sensitivity of -17,905 nm/RIU was achieved in the refractive index (RI) measurement. On this basis, the probe DNA (pDNA) was immobilized onto the sensor's surface using APTES, enabling real-time monitoring of captured complementary DNA (cDNA) samples. The experimental results demonstrate that the biosensor exhibited a high sensitivity of 0.32 nm/fM and a limit of detection of 48.9 aM. Meanwhile, the sensor has highly repeatable and specific performance. This work reports an easy-to-manufacture, ultrasensitive, and label-free DNA biosensor, which has significant potential applications in medical diagnostics, bioengineering, gene identification, environmental science, and other biological fields.

Thermal Locking Cascaded Fiber Microcavities for Ultrasensitive Acoustic sensing

Thermal Locking Cascaded Fiber Microcavities for Ultrasensitive Acoustic sensing

Fiber Mach-Zehnder interferometer micro-cavity length adjustment in tens of nanometers for sensing system miniaturization

Fiber Mach-Zehnder interferometer (FMZI) micro-cavity length adjustment in tens of nanometers by chemical etching for refractive index sensing system miniaturization was firstly reported. This etching process is capable of adjusting the length of micro-structure at the order of tens of nanometers, and achieving such high precision without involving complicated and expensive nano-fabrication facilities. The chemical etching opens up the fiber micro-cavity and redshifts its resonant wavelength at the rate of 3.6 nm/min, upon an estimated etching speed of 41.5 nm/min. The shift of the micro-cavity’s resonant wave-length close to the LD’s emitting wavelength is achieved by such precise length adjustment for sensing system miniaturization. The miniaturized FMZI is experimentally applied to the refractive index sensing for ethanol solutions. The measured transmission is in good linearity with regards to the solution index and the sensitivity is -12.8 dB for 0.0043 RIU (refractive index unit) difference in this study. The miniaturized FMZI index-sensing system can be portable and operating at a fast speed, which is well suited for practical field applications.

Single-longitudinal-mode lasing based on enhanced scattering in eccentric-hole microstructured optical fiber resonators

In this paper, we propose a dual-core eccentric-hole fiber (DCEHF) microresonator to achieve single-longitudinal-mode (SLM) laser emission based on enhanced pump light field induced by scattering effect of the two fiber cores. The directional dependences of the scattered pump field distribution on incident angle as well as overlap integrals between scattered pump light fields and WGMs have been theoretical investigated, and the calculation results show that when the incident angle of the pump light is close to 180°, significant discrepancies would occur in the overlap integrals between WGMs and the scattered field. And consequently, specific mode having the largest overlap integral would outperform through the mode competition process to excite SLM lasing. We have experimentally obtained SLM lasing emission when the DCEHF-based microresonator is rotated by 206°, which is in good accordance with our calculation results. Additionally, experimental observation of the output laser spectrum shows that the proposed fiber microcavity supports highly stable SLM laser emission. The proposed microresonator based on DCEHFs possesses several desirable merits such as compact size, good laser stability, single-mode operation, and good compatibility with existent fiber-optic systems, which make it a good candidate for applications as functional photonic device in future micro-optics systems.

Carrier, spin and optical propagation properties of CsPbBr3 hexagonal nanocrystals

The shape of nanocrystals can effectively adjust their photo-physical properties, which becomes a route to improve the nanocrystal-based semiconductor device. Herein, we further dig the photo-physical properties of CsPbBr3 hexagonal nanocrystals (HNCs), in which CsPbBr3 cubic nanocrystals (CNCs) serves as a reference. It is found that the activity of carrier in CsPbBr3 HNCs is higher than that of CsPbBr3 CNCs, owing to the slow energy dissipation path related to the phonon energy, which slows down the carrier temperature cooling process and accelerate the carrier recombination behavior simultaneously. Moreover, the spin flip process may occur in the CsPbBr3 HNCs, whose lifetime is longer than that of CsPbBr3 CNCs owing to the weakening of phonon scattering of Elliott-Yafet mechanism. In addition, the photoluminescence test of CsPbBr3 HNCs in optical fiber microcavity shows that its light wave-guiding performance is determined by the self-absorption effect and the conventional light wave-guiding effect, which are both super to those of CsPbBr3 CNCs, benefiting from its high PL quantum yield. Our research suggests that the CsPbBr3 HNCs exhibits a huge potential in the field of optoelectronics, spintronics and photo-communication.

Experimental realization of strong coupling between a cold atomic ensemble and an optical fiber microcavity

Experimental realization of strong coupling between a cold atomic ensemble and an optical fiber microcavity

High-Resolution Optical Fiber Salinity Sensor With Self-Referenced Parallel Fabry–Perot Fiber Microcavity

A high-resolution salinity sensor based on a self-referenced parallel Fabry–Perot fiber microcavity is proposed. The sensor is fabricated by inserting a short piece of exposed-core microstructure fiber (ECF) between multimode fiber (MMF) and single-mode fiber (SMF). Due to the unique exposed-core fiber structure and the specially designed SMF-MMF-ECF-SMF structure, two prominent parallel Fabry–Perot interferometers (FPIs) are constructed. Besides, a self-referenced differential phase-demodulation technology is proposed to eliminate the wavelength uncertainty of the spectra measurement devices. Enhanced demodulation system stability and accuracy are achieved by analyzing the phase shift responses of the reflection spectrum. A high salinity-phase sensitivity of 17.36 deg/ ‰ in the range from 0 ‰ to 35 ‰ is obtained, and the corresponding refractive index (RI) sensitivity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.04} \times {10} ^{{5}}$ </tex-math></inline-formula> deg/RIU. The salinity resolution and RI resolution are as low as 0.0058 ‰ and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${9.6} \times {10} ^{-{7}}$ </tex-math></inline-formula> RIU, respectively, which gives a great potential for harsh environmental monitoring and label-free biochemical analysis.

Feedback and compensation scheme to suppress the thermal effects from a dipole trap beam for the optical fiber microcavity.

Cavity quantum electrodynamics (cavity QED) with neutral atoms is a promising platform for quantum information processing and optical fiber Fabry-Pérot microcavity with small mode volume is an important integrant for the large light-matter coupling strength. To transport cold atoms to the microcavity, a high-power optical dipole trap (ODT) beam perpendicular to the cavity axis is commonly used. However, the overlap between the ODT beam and the cavity mirrors causes thermal effects inducing a large cavity shift at the locking wavelength and a differential cavity shift at the probe wavelength which disturbs the cavity resonance. Here, we develop a feedback and compensation scheme to maintain the optical fiber microcavity resonant with the lasers at the locking and probe wavelengths simultaneously. The large cavity shift of 210 times the cavity linewidth, which makes the conventional PID scheme ineffective can be suppressed actively by a PIID feedback scheme with an additional I parameter. Differential cavity shift at the probe wavelength can be understood from the photothermal refraction and thermal expansion effects on the mirror coatings and be passively compensated by changing the frequency of the locking laser. A further normal-mode splitting measurement demonstrates the strong coupling between 85Rb atoms and cavity mode after the thermal effects are suppressed, which also confirms successful delivery and trapping of atoms into the optical cavity. This scheme can solve the thermal effects of the high-power ODT beam and will be helpful to cavity QED experimental research.

Spectrally programmable fiber microcavity laser with dye-doped liquid crystals

Envelope shaping and wavelength tuning for resonance modes of lasers have always been promising topics, especially, in extending the functionalities of microcavities which are popular platforms for light confinement and generation. In this paper, a scattering-assisted fiber microcavity laser is proposed with function of spectral shaping. The fiber microcavity supports a liquid crystal micropillar with flexibly controllable scattering, which plays an important role to enhance the laser emission and enable whispering-gallery-mode lasing with variable spectral envelope that is defined by controlling the state of liquid crystal molecules. Our results show that external fields can change refractive index and disorder of the liquid crystal, and the resonant wavelengths of the whispering-gallery-mode laser exhibit opposite tuning regularity under the action of voltage and temperature. Moreover, using a patterned voltage control, spectrally definable hybrid laser emission is realized, laying a solid foundation for the research of spectral programmable soft-materials based lasers.

Novel fiber-tip micro flowmeter based on optofluidic microcavity filled with silver nanoparticles solutions

Abstract A novel fiber-tip micro flowmeter based on optofluidic microcavity filled with silver nanoparticles solutions (SNS) is proposed. CW fiber laser was used to heat SNS that can emit heat obviously due to the excellent optic-thermo effect. The heat generated by the silver nanoparticles would be taken away as the microfluidic flows over the fiber microcavity until thermal balance is established under different velocity. The effective refractive index (RI) of the SNS changed followed by temperature of the thermal balance. The dips of the Fabry–Perot interference spectrum shift and the flow velocity can be demodulated. Moreover, the sensor can measure the flow rate with a high sensitivity due to the superior thermal conductivity and specific heat capacity of sidewalls. The max flow rate sensitivity can reach 1.5 nm/(μL/s) in the large range of 0–5 μL/s with a detection limitation (DL) of 0.08 μL/s. The Micron scale probe-type flowmeter has strong robustness and can be used to measure flow rate in tiny space. The heating medium also has an excellent biological compatibility and is not contact with the fluidics directly. As such, we believe that the proposed fiber-tip micro flowmeter has great application potentials in haematology, oil prospecting, ocean dynamics and drug research.

Dynamic manipulation of WGM lasing by tailoring the coupling strength.

Miniaturized lasing with dynamic manipulation is critical to the performance of compact and versatile photonic devices. However, it is still a challenge to manipulate the whispering gallery mode lasing modes dynamically. Here, we design the quasi-three-dimensional coupled cavity by a micromanipulation technique. The coupled cavity consists of two intersection polymer microfibers. The mode selection mechanism is demonstrated experimentally and theoretically in the coupled microfiber cavity. Dynamic manipulation from multiple modes to single-mode lasing is achieved by controlling the coupling strength, which can be quantitatively controlled by changing the coupling angle or the coupling distance. Our work provides a flexible alternative for the lasing mode modulation in the on-chip photonic integration.

Strong mode coupling-enabled hybrid photon-plasmon laser with a microfiber-coupled nanorod.

Laser based on single plasmonic nanoparticle can provide optical frequency radiation far beyond the diffraction limit and is one of the ultimate goals of nanolasers, yet it remains a challenge to be realized because of the inherently high Ohmic loss. Here, we report the direct observation of lasing in microfiber-coupled single plasmonic nanoparticles enabled by strong mode coupling. We show that, by strongly coupling a gold nanorod (GNR) with the whispering gallery cavity of a dye-doped polymer microfiber (with diameter down to 2.0 μm), the substantially enhanced optical coherence of the hybrid photon-plasmon mode and effective gain accumulated from the active microfiber cavity enable single-mode laser emission from the GNR at room temperature with a threshold as low as 2.71 MW/cm2 and a linewidth narrower than 2 nm.

A microfluidic system for analysis of electrochemical processing using a highly sensitive optical fiber microcavity

Microfluidics provide unique possibilities to control tiny volumes of liquids and their composition. In this work we combined a microfluidic system with a microcavity in-line Mach-Zehnder interferometer (µIMZI) induced in the side surface of a single-mode optical fiber using a femtosecond laser micromachining. The µIMZI shows capability for investigating optical properties of volumes down to picoliters with an exceptionally high refractive index sensitivity. Here we report numerical analysis and experimental results that show that when the µIMZI is incorporated with the microfluidic system the measurements can be performed with sensitivity exceeding 14,000 nm/RIU which is similar to measurements done under static conditions. In a flow injection system, we show the influence of flow rate and injection volume on the response, and that the orientation of the cavity versus the flow direction has only a minor impact on the results. Finally, we have supported the system by band electrodes making it possible to induce redox reactions in the microchannel to detect the flowing products of the reactions optically. It has been found that thanks to the high sensitivity of the µIMZI the products of the reactions can be clearly detected both electrochemically and optically even when the only part of the flowing redox probe is oxidized at the band electrode. The capability for monitoring the products was shown for a standard redox probe, potassium ferricyanide, as well as for the neurotransmitter dopamine. This work shows that the proposed solution may offer highly sensitive optical measurements, even when the chemical reactions are not effective in the whole volume of the system.

Hermetic Welding of an Optical Fiber Fabry-Pérot Cavity for a Diaphragm-Based Pressure Sensor Using CO2 Laser.

A diaphragm-based hermetic optical fiber Fabry–Pérot (FP) cavity is proposed and demonstrated for pressure sensing. The FP cavity is hermetically sealed using one-step CO2 laser welding with a cavity length from 30 to 100 μm. A thin diaphragm is formed by polishing the hermetic FP cavity for pressure sensing. The fabricated FP cavity has a fringe contrast larger than 15 dB. The experimental results show that the fabricated device has a linear response to the change in pressure, with a sensitivity of −2.02 nm/MPa in the range of 0 to 4 MPa. The results demonstrate that the proposed fabrication technique can be used for fabricating optical fiber microcavities for sensing applications.

Temperature and Pressure Sensor Based on Polished Fiber-Optic Microcavity

A single-optic-fiber temperature and pressure sensor based on a side-polished optical fiber microcavity coated with a polydimethylsiloxane (PDMS) film has been proposed and fabricated. This sensor integrates two Mach-Zehnder interferometers (MZIs), where the first MZI is formed by path 1 in the inside coating, and the second MZI is constructed by path 1 and path 2 in the waist region. The formation mechanism of the dual MZIs is simulated by using the finite-difference beam propagation method, and the sensitivities of the dual MZIs are predicted by simulations. Experimental results indicate the temperature sensitivity of –1.19 nm/℃ for the first MZI and pressure sensitivity of –3.96 nm/MPa for the second MZI, respectively. By monitoring the dual wavelength shifts corresponding to the dual MZIs, temperature and pressure can be simultaneously measured. Due to the good sensitivities, simple fabrication and robust structure, the proposed sensor shows promising potential for optofluidic sensing and ocean detection.

A multi-angle torsion sensor based on seven-core fiber microcavity structure

A multi-angle torsion sensor based on seven-core optical fiber(SCF) microcavity structure is proposed. An end of SCF is treated with microcavity processed and cascaded with single-mode fiber(SMF) and multi-mode fiber(MMF). Among them, the MMF1 and MMF2 at both ends of SCF realize the beam splitting and combining functions between SMF and SCF, and the microcavity structure mainly plays the role of beam splitting. Experiments results show that the intensity loss of the transmission spectrum changes significantly in the torsion range of 0°–360°, and the maximum torsion sensitivity is 0.04685 dB/°. The experimental results agree with the theoretical simulation. The sensor has simple structure and easy preparation, and can be widely used in the field of outdoor safety detection and bridge monitoring.

Temperature Sensitivity of Polymer Fiber Microlasers

There are many kinds of materials or methods used to make optical microcavities, and they have many different geometric structures. And electrospinning technique has become a very convenient and easy one to prepare polymer fiber. Based on this situation, PM597-doped polymer solution was prepared into high-performance fibers with different diameters by electrospinning technology in our work. In order to better study the temperature sensing of polymer fiber whispering gallery mode, we have placed it on two different substrates with gold and aluminum. A 532 nm pulsed laser beam was used to excite a single fiber in the radial direction, then the whispering gallery mode (WGM) laser was observed and the distribution of WGM was determined by theoretical calculations. The threshold of samples on aluminum substrate is 0.4 μJ. In addition, it is found that the samples on aluminum substrate performed better in temperature sensing, and the value is 0.13 nm/°C. As a result, WGM polymer fiber microcavities on aluminum substrate made by electrospinning technology have very broad development prospects in biosensing, optical pump lasers and other applications.

Graphene/Epoxy Composite Based Broadband All-Optical Tunable Fiber Microcavity Filter

A graphene/epoxy composite based broadband all-optical tunable fiber microcavity filter is presented. The graphene/epoxy composite based microcavity shows the excellent all-optical controlability. Since the light acts on the graphene/epoxy composite directly, the microcavity has stronger optical Kerr effect and photothermal effect induced by the optical pump. Experimental results show that its wavelength tuning range and tuning step reach 25.54 nm and −832 pm/mW, respectively. It is expected to be applied in the fields of tunable optical filters, optical communication, optical sensors, fiber lasers, and spectrum scanning.