Single-mode Laser Emission Research Articles

Extremely lower lasing threshold in Er3+/Yb3+ co-doped phosphate dual glass microspheres

Erbium-doped glass microsphere laser systems hold significant promise in the applications of bio-medicine and optical fiber sensing. However, their development has been hindered by the relatively high laser pump threshold. In this study, we proposed a unique dual microsphere system where two microspheres are affixed to a single-mode fiber taper and achieved a remarkably low lasing threshold of 19 μW for single-mode laser emission at 1544 nm. This is in sharp contrast with the lasing threshold of 56 μW observed in single microspheres. Our findings represent a significant achievement in the development of low-threshold, compact infrared laser sources for emerging applications in photonics.

Development of pedestal-free large mode area fibers withTm3+ doped silica nanostructured core.

We present the pedestal-free thulium doped silica fiber with a large nanostructured core optimized for fiber lasers. The fiber is composed of over 6 thousand thulium doped silica nanorods with a diameter of 71 nm each which form a nanostructured step-index core. We study the influence of non-continuous distribution in nanoscale active areas on gain, beam quality, and fiber laser performance. The proof-of-concept fiber is effectively single mode for wavelength above 1.8 µm. We demonstrate the performance of the fiber in a laser setup pumped at 792 nm. Single mode laser emission with a slope efficiency of 29% at quasi-continuous output power of 4 W with M2 = 1.3 at the emission spectrum 1880-1925 nm is achieved.

Silicon-thulium hybrid microdisk lasers with low threshold and wide emission wavelength range.

We demonstrate low-threshold and wide emission wavelength range hybrid-integrated silicon-thulium microdisk lasers based on a pulley-coupled design. The resonators are fabricated on a silicon-on-insulator platform using a standard foundry process and the gain medium is deposited using a straightforward, low-temperature post-processing step. We show lasing in 40- and 60-µm diameter microdisks with up to 2.6 mW double-sided output power and bidirectional slope efficiencies of up to 13.4% with respect to 1620 nm pump power launched to the bus waveguides. We observe thresholds less than 1 mW versus on-chip pump power and both single-mode and multimode laser emission spanning across wavelengths from 1825 to 1939nm. These low threshold lasers with emissions over a > 100 nm range open the door to monolithic silicon photonic integrated circuits with broadband optical gain and highly compact and efficient light sources in the emerging ∼1.8-2.0 µm wavelength band.

Simulations of single-mode laser emission along a waveguide connected to cross-coupled microresonators

ObjectiveSingle-mode operation is very important for laser emissivity; to exceed the emissivity of a single laser, the phase locking of all lasers in an array can be achieved only when the laser array is coupled and operated in single-mode. MethodsIn this study, a single-mode laser emitted along the waveguide was realized through cross-coupling microspheres connected to a straight waveguide. Whispering-gallery modes were formed at the equators of the two microspheres when their resonance conditions were simultaneously satisfied. Compared with a single microcavity, the FSR of the coupled microcavities was significantly increased owing to the Vernier effect. Moreover, when the waveguide was coupled with the microspheres in the weak field of the resonance modes, the whispering-gallery modes near the equator were significantly suppressed, and a new quadrilateral mode was formed. ResultThe energy in the coupling microspheres was concentrated in the stable quadrilateral mode and the Q factor was high (∼104). The single-mode laser energy in the waveguide accounted for 82 % of the total optical radiation energy of the device. This work has application prospects in laser switches and on-chip light sources.

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.

Low-threshold single-mode laser in perovskite microdiscs direct-synthesized into planar microcavity

Low-threshold single-mode laser in CsPbBr3 microdiscs grown between two distributed Bragg reflectors (DBRs) is realized at room temperature. The CsPbBr3 microdiscs are directly synthesized on the surface of prepared first-half DBRs microcavity by a chemical vapor deposition method. This scheme avoids possible surface damage or contamination caused by the traditional transfer of sample into the DBRs. The single-mode laser with low threshold (∼1.3 μJ/cm2) was obtained in the CsPbBr3 microdiscs sandwiched in DBRs and measured by using the micro-photoluminescence spectroscopy. The length of the resonant cavity is short enough to support a large free spectral range, which ensures only one mode in the bandwidth of the optical gain. Moreover, by modulating the thickness of the CsPbBr3 microdiscs, the wavelength of single-mode laser emission can be broadly tuned from 529.6 to 544.1 nm. This work provides a method of fabricating single-mode laser in DBRs, which may have potential applications in on-chip integration of optoelectronic devices and signal processing.

Design of a mid-infrared single-mode laser based on parity-time symmetry breaking in air-clad hollow-core ZBLAN fiber micro-resonator

In this paper, we propose a single-mode laser operating in the mid-infrared regime by exploiting parity-time (PT) breaking in a whispering gallery mode (WGM) micro-resonator based on air-clad hollow-core ZBLAN fibers. By introducing alternate gain–loss modulation regions with refractive indices respectively having the same real parts but opposite imaginary parts into the air hole clad region of the hollow-core fiber infiltrated with optical functional materials, a PT symmetry system could be set up and specific WGM in PT-broken state whose electric field distribution matches the gain–loss modulation pattern can be excited to realize single-mode laser emission around 5 μm. And moreover, simulation results indicate that high precision laser wavelength tuning with a sensitivity of 1.623 nm RIU−1 can be achieved by adjusting the refractive index of the functional materials filled into the cladding air holes.

Single-Mode Lasing in Plasmonic-Enhanced Woven Microfibers for Multifunctional Sensing.

Single-mode plasmonic lasing has great potential for use in photonic and sensing applications. In this work, single-mode lasing is realized using a plasmonic-enhanced woven microfiber that shows ultrahigh sensitivity to the ambient environment. This plasmonic-enhanced microfiber is fabricated by spraying Ag nanospheres onto rhodamine 6G-doped polymer microfibers. Single-mode laser emission with an ultranarrow linewidth (0.1 nm) and a low threshold (18.8 kW/mm2) is achieved in the microfiber using the effects of mode selection and plasmonic enhancement provided by the Ag nanospheres. A large wavelength shift in the single-mode lasing is observed when the proposed laser is used as a sensor and exposed to a humid or acidic environment. The wavelength shift is attributed to refractive index variations in the microfiber caused by either moisture absorption or chemical reactions. In humidity sensing, the laser's sensitivity is as high as 826.6 pm/% relative humidity (RH) and the detection limit is 0.051% RH. An innovative strategy for acetic acid gas sensing is proposed that uses the chemical reaction with rhodamine 6G, and its minimum response time is 5 min. Because of the microfiber's excellent fabric compatibility, a wearable sensor is fabricated by weaving the plasmonic-enhanced microfiber into clothes, and this sensor demonstrates extreme bending stability. The results reported here provide a novel approach to the design and fabrication of ultrasensitive wearable sensors for multifunctional sensing applications.

On-chip ultra-narrow-linewidth single-mode microlaser on lithium niobate on insulator.

We report an on-chip single-mode microlaser with a low threshold fabricated on erbium doped lithium-niobate-on-insulator (LNOI). The single-mode laser emission at 1550.5 nm wavelength is generated in a coupled microdisk via the inverse Vernier effect at room temperature, when pumping the resonator at 977.7 nm wavelength. A threshold pump power as low as 200 μW is demonstrated due to the high quality factor above 106. Moreover, the measured linewidth of the microlaser reaches 348 kHz without discounting the broadening caused by the utilization of optical amplifiers, which is, to our knowledge, the best result in LNOI microlasers. Such a single-mode microlaser lithographically fabricated on chip is in high demand by the photonics community.

Superior single-mode lasing in a self-assembly CsPbX3 microcavity over an ultrawide pumping wavelength range

All-inorganic perovskite micro/nanolasers are emerging as a class of miniaturized coherent photonic sources for many potential applications, such as optical communication, computing, and imaging, owing to their ultracompact sizes, highly localized coherent output, and broadband wavelength tunability. However, to achieve single-mode laser emission in the microscale perovskite cavity is still challenging. Herein, we report unprecedented single-mode laser operations at room temperature in self-assembly CsPbX 3 microcavities over an ultrawide pumping wavelength range of 400–2300 nm, covering one- to five-photon absorption processes. The superior frequency down- and upconversion single-mode lasing manifests high multiphoton absorption efficiency and excellent optical gain from the electron–hole plasma state in the perovskite microcavities. Through direct compositional modulation, the wavelength of a single-mode CsPbX 3 microlaser can be continuously tuned from blue-violet to green (427–543 nm). The laser emission remains stable and robust after long-term high-intensity excitation for over 12 h (up to 4.3 × 10 7 excitation cycles) in the ambient atmosphere. Moreover, the pump-wavelength dependence of the threshold, as well as the detailed lasing dynamics such as the gain-switching and electron–hole plasma mechanisms, are systematically investigated to shed insight into the more fundamental issues of the lasing processes in CsPbX 3 perovskite microcavities.

Topological charge of finite-size photonic crystal modes

Topological charges are the winding numbers of polarization vectors around the vortex centers of far-field radiation. In this work, the topological charge of photonic crystal modes is theoretically analyzed using an envelope function approach. A group of modes is discovered with unique polarization properties dictated by their non-trivial envelope functions. Experimentally, lasing operation on such mode is demonstrated in an electrically pumped mid-infrared photonic crystal surface-emitting laser with high slope efficiency. The topological charge is directly observed from the polarization properties of single-mode laser emission.

1.88 μm laser emission from Tm3+ doped fluorosilicate glass microspheres with excellent stability and high damage threshold

In this letter, high Q factor microsphere resonators with excellent stability and high damage threshold are fabricated from Tm3+ doped fluorosilicate glasses using the traditional melt-quenching and fiber heating techniques. Intense 1.88 μm photoluminescence and single mode laser emission are obtained under the excitation of an 808 nm laser. The Q factor of the microsphere resonator is measured to be as high as 1.4 × 106. Models for photoluminescence and lasing are proposed using spectroscopic data from the absorption and emission spectra. The excellent resistance to humidity and temperature are characterized from the transmittance spectra under different environmental conditions. Differential thermal analysis (DTA), measured in four different glass samples proves the high damage threshold. The proposed glass microsphere resonator laser can find application in optical sensors and micro lasers, especially in complex environments.

Al2O3:Yb3+ integrated microdisk laser label-free biosensor

Whispering gallery mode resonator lasers hold the promise of an ultralow intrinsic limit of detection. However, the widespread use of these devices for biosensing applications has been hindered by the complexity and lack of robustness of the proposed configurations. In this work, we demonstrate biosensing with an integrated microdisk laser. Al2O3doped with Yb3+ was utilized because of its low optical losses as well as its emission in the range 1020-1050 nm, outside the absorption band of water. Single-mode laser emission was obtained at a wavelength of 1024 nm with a linewidth of 250 kHz while the microdisk cavity was submerged in water. A limit of detection of 300 pM (3.6 ng/ml) of the protein rhS100A4 in urine was experimentally demonstrated, showing the potential of the proposed devices for biosensing.

Near-Infrared Luminescence and Single-Mode Laser Emission From Nd3+ Doped Compound Glass and Glass Microsphere

In this letter, an Nd3+-doped compound fluorosilicate glass was successfully fabricated with the method of melt-quenching. Under the excitation of a 808 nm laser, enhanced near-infrared photoluminescence emission at the range from 1065 to 1140 nm was observed in the glass sample. To characterize its stability and resistance to environmental effects, transmission spectra at the range of NIR-MIR were measured under different environments, including humidity and temperature. In addition, the obtained fluorosilicate glass was also developed as a microsphere resonator by using CO2 laser heating method. When the diameter of the microsphere was controlled at 61.5 μm, coupling with a tapered fiber, single-multimode lasing in the wavelength range λ1056-1071 nm was achieved with a low lasing threshold of 1.5 mW. Compared to the traditional compound tellurate and fluoride glasses, this fluorosilicate glass has higher transition temperature; means that this resonator can be pumped by higher power. Therefore, using it as the raw material, the developed microsphere resonator offers a high transition temperature and with a low lasing threshold, which are promising it for high performance sensing and detection applications.

Whispering gallery mode microlaser based on a single polymer fiber fabricated by electrospinning

Electrospinning is a very simple method of preparing polymer solutions into high performance fibers. In this work, PM597-doped polymer fibers with different diameters have been fabricated by electrospinning technology. Whispering gallery mode (WGM) lasing emission was observed when a 532 nm pulse laser beam radially excited the single electrospun polymer fiber (EPF) created by this method. The distribution of WGMs is also quantitatively confirmed through theoretical calculation. Additionally, the number of WGM laser peaks decrease as the diameter of the EPF decreases. Single longitudinal mode laser emission can be obtained when the EPF diameter decreases to 8.8 µm. It has also been found that the WGM laser from the single EPF has relatively low thresholds and good lifetime compared to droplet lasers or other fiber lasers. Moreover, EPF networks have unique research prospects in photonic devices, optical pump lasers and biosensing due to their very large surface to volume ratio.

Enhanced single-mode fiber laser emission by nano-crystallization of oxyfluoride glass-ceramic cores

We have demonstrated enhanced 1.55 μm single-mode fiber laser output in KYF4:Er3+/Yb3+ nanocrystal embedded oxyfluoride glass ceramic fibers.

Evanescent-wave pumped single-mode microcavity laser from fiber of 125 μm diameter

A microcavity laser based on evanescent-wave-coupled gain is formed using a silica fiber with a diameter of 125 μm in a rhodamine 6G ethanol solution. When the fiber is sticking to the cuvette wall by capillary force, using the excitation of a 532 nm nanosecond pulsed laser, single-mode laser emission is observed. While increasing the distance between the fiber and the cuvette wall, the typical multi-peak whispering-gallery-mode (WGM) laser emission can also be demonstrated. On the other hand, while increasing the refractive index of the solution by mixing ethanol and ethylene glycol with different ratios as a solvent, the single-mode emission would evolve to multi-peak WGM laser emission controllably.

Single mode compound microsphere laser

Single mode laser is demonstrated based on compound microspheres. The two coupled microspheres, corresponding to the diameters of 32.7 μm and 49.2 μm, are both made from Er3+/Yb3+ co-doped phosphate glass. Based on the Vernier effect, single mode laser emission has been realized at 1544.43 nm with the side-mode suppression ratio of 45.1 dB and the threshold of only 163 μW. This compound microspheres scheme can effectively select one laser emission mode among various modes, which can potentially used in micro-size laser source, high precision sensor and other frontier fields.

Broadband 2-µm emission on silicon chips: monolithically integrated Holmium lasers.

Laser sources in the mid-infrared are of great interest due to their wide applications in detection, sensing, communication and medicine. Silicon photonics is a promising technology which enables these laser devices to be fabricated in a standard CMOS foundry, with the advantages of reliability, compactness, low cost and large-scale production. In this paper, we demonstrate a holmium-doped distributed feedback laser monolithically integrated on a silicon photonics platform. The Al2O3:Ho3+ glass is used as gain medium, which provides broadband emission around 2 µm. By varying the distributed feedback grating period and Al2O3:Ho3+ gain layer thickness, we show single mode laser emission at wavelengths ranging from 2.02 to 2.10 µm. Using a 1950 nm pump, we measure a maximum output power of 15 mW, a slope efficiency of 2.3% and a side-mode suppression ratio in excess of 50 dB. The introduction of a scalable monolithic light source emitting at > 2 µm is a significant step for silicon photonic microsystems operating in this highly promising wavelength region.

2 μm Doppler wind lidar with a Tm:fiber-laser-pumped Ho:YLF laser.

A 2μm Ho-doped ytrrium lithium fluoride (Ho:YLF) laser end-pumped by a 1.94μm Tm:fiber laser was developed. A laser system of a ring resonator oscillator and amplifier was operated at repetition rates of 200-5000Hz at room temperature. The Q-switched outputs were 7.4W at 5000Hz and 4.25W at 200Hz. Injection seeding was applied to the ring resonator, and single-mode laser emission was obtained. The Tm:fiber-laser-pumped Ho:YLF laser was first used for Doppler wind lidar measurements, and wind profiles were obtained up to ranges of about 15km in a range resolution of 96m and an integration time of 1s.