High Slope Efficiency Research Articles

All-solid-state widely wavelength-tunable and high-efficiency Yb:YSr3(PO4)3 laser.

We demonstrate an all-solid-state widely wavelength-tunable Yb:YSr3(PO4)3 (Yb:YSP) laser with high efficiency. The free-running Yb:YSP laser oscillating at multiple wavelengths in the range of 1024-1054 nm is realized with different crystal lengths and output coupler transmittances. The maximum output power of 2.72 W is obtained under the absorption pump power of 7.30 W. The highest slope efficiency is 66.9%, using the crystal of 6.5-mm-length. Simultaneous dual-wavelength operation can be realized as well. Furthermore, the widely wavelength-tunable Yb:YSP laser with a range of more than 60 nm (from 1004 to 1066 nm) is achieved using a birefringent filter. The experimental results indicate that the Yb:YSP crystal can be a promising candidate for ultrafast lasers in the 1 µm region.

Research on the Asymmetric Corrugation-Pitch-Modulated HR-AR DFB Lasers With Sampled Gratings

A distributed feedback (DFB) laser for high-speed modulation with asymmetric corrugation-pitch-modulated (ACPM) grating structure and high-reflection and anti-reflection coating (HR-AR) coating is demonstrated theoretically and experimentally in this paper. The ACPM gating structure is fabricated by the reconstruction equivalent chirp (REC) technology, which is with low cost. The impact of the longitudinal spatial hole burning (LSHB) effect and the facet phase on the characteristics of the ACPM DFB laser is discussed in detail. The numerical simulation results show that the proposed ACPM DFB laser can suppress the LSHB effect significantly. Comparing with the conventional HR-AR DFB laser, the ACPM DFB laser can achieve higher output efficiency, better single-mode yield, and wider modulation bandwidth. The modulation eye diagrams of HR-AR DFB lasers with different grating structures are also presented. The experimental results show that the LSHB effect in the HR-AR DFB laser with ACPM structure is suppressed effectively. The laser with ACPM structure fabricated by the REC technique has high slope efficiency, stable single longitudinal mode operation, and wide modulation bandwidth.

Broadband Sheet Parametric Oscillator for χ (2) Optical Frequency Comb Generation via Cavity Phase MatchingSupported by the National Key Research and Development Program of China (Grant Nos. 2019YFA0705000 and 2017YFA0303700), the Key R&D Program of Guangdong Province (Grant No. 2018B030329001), the Leading-Edge Technology Program of Jiangsu Natural Science Foundation (Grant No. BK20192001), and the National Natural Science Foundation of China

We demonstrate a broadband optical parametric oscillation, using a sheet cavity, via cavity phase-matching. A 21.2 THz broad comb-like spectrum is achieved, with a uniform line spacing of 133.0 GHz, despite a relatively large dispersion of 275.4 fs2/mm around 1064 nm. With 22.6% high slope efficiency, and 14.9 kW peak power handling, this sheet optical parametric oscillator can be further developed for χ (2) comb.

Study of asymmetric biconical fiber tapers for in-fiber Mach-Zehnder interferometers and applications in single-frequency fiber lasers.

In this paper, asymmetric biconical fiber tapers (ABFTs) for in-fiber Mach-Zehnder interferometers (IFMZIs) are proposed and analyzed to enhance the interference effect. The proposed ABFT-IFMZIs are fabricated, tested, and demonstrated in applications of single-frequency (SF) emissions when incorporated into an all-fiber laser cavity as the frequency selecting component. In comparison with the traditional IFMZIs composed of all symmetric biconical fiber tapers (SBFTs), higher average transmittance and fringe contrast have been demonstrated with the ABFT-based IFMZIs. When applied to the SF fiber laser emission, lower pump threshold and higher slope efficiency have also been confirmed with the ABFT-IFMZI device. The theoretical and experimental results have indicated that the interference effect of IFMZIs can indeed be improved by the designated asymmetry of conical taper angles in ABFTs that can offer an extra flexibility in fiber taper design, fabrication, and applications.

Over 255 mW single-frequency fiber laser with high slope efficiency and power stability based on an ultrashort Yb-doped crystal-derived silica fiber

A single-frequency distributed Bragg reflector (DBR) fiber laser at 1030 nm has been demonstrated using a 0.7 cm long homemade Yb:YAG crystal-derived silica fiber (YCDSF). The absorption and emission cross sections of the YCDSF are 4.93 × 10 − 20 cm 2 at 980 nm and 1.1 × 10 − 20 cm 2 at 1030 nm. Using this gain fiber, an over 255 mW continuous-wave lasing in the constructed laser has been obtained at single transverse and longitudinal mode operation. The slope efficiency and the pump threshold of the fiber laser were up to ∼35% and as low as 25 mW, respectively. The fiber laser also demonstrated an optical signal-to-noise ratio of 79 dB and a beam quality factor of 1.016 in two orthogonal directions. Its power fluctuation at 210.5 mW was less than 0.85% of the average power within 13 h. Moreover, the relative intensity noise and linewidth of the laser are also investigated at the different pump powers. The results indicate that the single-frequency DBR fiber laser has potential applications in high-quality seed sources and high-precision optical sensing.

High content Er3+ doped ZBLAN glass: The spectral characteristics and high slope efficiency MIR laser investigation

The ZBLAN glass with high content of Er3+ was prepared and studied. The glass has a wide infrared transmittance range of 2.5–8.0 µm, which means a lower maximum phonon energy. By testing and analyzing the fluorescence spectrum and lifetime curves under different penetration depths, the intrinsic emission spectrum and lifetime of the sample are obtained without the influence of sub-absorption. Under 980 nm excitation, the maximum emission cross section and the lifetime of 2.7 µm are 6.10 × 10−21 cm2 and 6.49 ms, indicating that high-concentration doping has a larger laser quality factor. According to the rate equation and transmission equation, cascaded and non-cascaded fiber laser models are established to conduct research on 2.7 µm fiber lasers. The slope efficiency can reach 40.38% at a pump wavelength of 980 nm and a fiber background loss of 0.1 dB/m. The high emission cross section, long fluorescence lifetime and high slope efficiency output make ZBLAN glass heavily doped with Er3+ an ideal host material for mid-infrared lasers.

Design and fabrication of 905 nm vertical cavity surface emitting laser with high power conversion efficiency

Vertical cavity surface emitting lasers (VCSELs) have lots of excellent properties, such as circular beam, low threshold, single longitudinal mode, high speed modulation and monolithic array fabrication capability. The VCSELs have been widely used in data communication and short-distance optical interconnection. In the fields of distance detection and automatic driving, high accuracy lidars have become an indispensable component. In practical applications, 905 nm laser exhibits little absorption by the water vapor in the air. In addition, the 905 nm laser can match with both inexpensive Si detector and high response avalanche photodiode (APD). Therefore, the 905 nm semiconductor laser has become a key light source of lidar. This paper presents the design and fabrication of 905 nm VCSEL with high power conversion efficiency. First, the main factors influencing the power conversion efficiency (PCE) of VCSEL are analyzed theoretically. It is concluded that the slope efficiency contributes to the PCE most. In order to achieve a high slope efficiency, strained InGaAs is used as a quantum well material. Due to the wavelength redshift caused by the thermal effect, the lasing peak wavelength of the multiple quantum well (MQW) is designed to be about 892 nm by optimizing the In composition. The active region consists of three pairs of In<sub>0.123</sub>Ga<sub>0.88</sub>As/Al<sub>0.3</sub>Ga<sub>0.7</sub> MQWs. The N-distributed Bragg reflectors (DBRs) are designed to have 40 pairs of Al<sub>0.9</sub>Ga<sub>0.1</sub>As/Al<sub>0.12</sub>Ga<sub>0.88</sub>As, and the P-DBRs are designed to have 20 pairs of Al<sub>0.9</sub>Ga<sub>0.1</sub>As/Al<sub>0.12</sub>Ga<sub>0.88</sub>As. The epitaxial structure is designed and grown by metal organic chemical vapor deposition (MOCVD). The cavity mode of the epitaxial wafer is around 903.7 nm. The photoluminescence (PL) spectrum is also measured. The peak wavelength is approximately 893.7 nm, and the full width at half maximum is 21.6 nm. Then, the 905 nm VCSELs with different apertures (6–18 μm) are fabricated via semiconductor technologies such as photolithography, evaporation, inductively coupled plasma (ICP), wet oxidation, electroplating, etc. Finally, the L-I-V characteristics and spectra of VCSELs with different apertures are tested. The obtained maximum slope efficiency and PCE of the devices are 1.12 W/A and 44.8%, respectively. In addition, the influences of aperture size on the far-field profiles and spectra of the devices are investigated. These 905 nm VCSELs with high PCE are potential for the miniaturization and lowing the cost of LiDAR.

Lasing characteristics of highly bend compensated large mode area ytterbium doped modified hybrid multi trench fiber

In this article, lasing characteristics of a newly designed ytterbium-doped modified hybrid multi trench fiber (YDMHMTF) has been numerically investigated for strongly pumped conditions. The designed YDMHMTF is maintained single-mode condition with an effective mode area of 1300μm2 at the wavelength of 1064 nm for the compact bending radius of 7.5 cm. The radius of doped region is varied up to a maximum core size of ~19 µm through numerical simulations to achieve maximum conversion efficiency for the straight and bending cases. The effective signal overlap factor is ensured by introducing a high-index arc in the inner trench of fiber along with a maximum doped core region. A 1.5 m length of highly bend LMA YDMHMTF shows slope efficiency of 74% and conversion efficiency of 75% when pumped with a laser source of 975 nm. Further, the high slope efficiency of 81% and conversion efficiency of 80% are achieved with aid of a 2 m length YDMHMTF for the straight and practical bending conditions. Therefore, the proposed YDMHMTF can be utilized to develop an efficient compact laser system suitable for industrial lasing applications. Moreover, the fabrication feasibility of our proposed YDMHMTF becomes easier than the photonic crystal fiber and Bragg fiber based designs.

A Directly Modulated Laterally Coupled Distributed Feedback Laser Array Based on SiO2 Planarization Process

Low-cost and high-speed single-mode semiconductor lasers are increasingly required as wide-band access fiber communication expands in recent years. Here, a high-speed laterally coupled distributed feedback (LC-DFB) laser array is achieved based on a SiO2 planarization process. The device exhibits low threshold currents of about 12 mA and high slope efficiencies over 0.26 W/A. Stable single mode operation and high-speed performance are realized with side mode suppression ratios (SMSR) over 45 dB, and 3-dBe bandwidths exceed 14 GHz for all four channels. Such a high-speed and process simple LC-DFB laser array shows great potential to the low-cost fiber communication networks.

STUDY OF Nd: YAG SOLAR LASER OUTPUT PERFORMANCE IN END PUMPING AND SIDE PUMPING CONFIGURATIONS

Since the report of the first sun-pumped solid-state laser, several pumping schemes have been proposed for enhancing the solar-laser performance. Although the most efficient laser systems have end-pumping approaches, side-pumping configurations are very suitable for reducing the thermal loading problems and consequently producing higher laser beam quality. Here we report a study of the Nd: YAG solar-lasers performance by using either end-pumping or side-pumping techniques. The end-pumping configuration provides simultaneously, in multimode regime, the maximum laser power (120 W continuous wave), the highest collection efficiency (32.1 W/m2), the highest slope efficiency (8.9 %), the lowest threshold pump power (192 W) and in monomode operation the highest fundamental-mode collection efficiency (7.9 W/m2) the highest solar laser brightness (6.5 W). However, the side-pumping approach is very preferred for achieving high laser beam quality in monomode operation (M2 < 1.05). Keywords: Solar irradiance; parabolic mirror; Fresnel lenses; solar-pumped laser; end-pumping configuration; side-pumping method; solar-laser power.

Fabrication, microstructure and optical properties of Yb:LuxY3-xAl5O12 transparent ceramics

In this paper, we reported mixed garnet laser ceramic gain media with composition of 15 at.% Yb:Lu x Y 3-x Al 5 O 12 (x = 0, 0.75, 1.5, 3.0, Yb:LuYAG) fabricated by the solid state reactive sintering in vacuum. After being sintered at 1850 °C for 30 h, all the Yb:LuYAG ceramics have dense microstructure and high optical quality. The in-line transmittances of the 1.6 mm thick ceramics with x = 0, 0.75, 1.5 and 3.0 are 84.8%, 84.1%, 82.4% and 83.4% at 1100 nm wavelength, respectively. The influences of the Lu 3+ content on the absorption and emission spectra were discussed. With the increase of Lu 3+ content, the crystal field increases, causing a blue shift of position and bigger absorption coefficient of the about 938 nm absorption peaks. The main emission peaks for all Yb:LuYAG ceramics retain at 1030 nm. The samples have shown a high laser emission slope efficiency, near to exceeding 60% in optimized output coupling conditions. The comparable optical properties and excellent thermo-mechanical qualities mean that the Yb:LuYAG ceramics are promising gain media used for high power laser application. • Yb:LuYAG ceramics with the in-line transmittance over 82% at 1100 nm were fabricated by reactive sintering. • The introduction of Lu 3+ caused the blue shift and bigger absorption for Yb:Lu x Y 3-x Al 5 O 12 ceramics at ~938 nm. • For Yb:Lu x Y 3-x Al 5 O 12 ceramics with x = 0.75, the laser outpower of 8.7 W and the slope efficacy of 65.6% were obtained.

High absorption large-mode area step-index fiber for tandem-pumped high-brightness high-power lasers

A short absorption length ytterbium (Yb)-doped large-mode area (LMA) fiber is presented as a step forward to mitigate the stern problem of nonlinear scatterings in a tandem pumping scheme adopted for high-power fiber laser. The short absorption length was realized by incorporating high Yb concentration in the fiber core. Furthermore, by replacing the inherent silica cladding with a Ge-doped cladding, we were able to obtain low core numerical aperture (NA) and negate the detrimental effect of index-raising by high Yb concentrations. This overcomes the long-standing limitation in step-index Yb-doped fibers (YDFs) where high cladding absorption inevitably results in high NA, thus hampering single-mode operation. We report an LMA ( ∼ 575 μm 2 ) YDF with NA of 0.04 and absorption of 27 dB/m at 976 nm—both traits promote power scaling of single-mode tandem pumped fiber lasers. To our knowledge, this is the highest cladding absorption attained in a low-NA step-index fiber to date. An all-fiber tandem-pumped amplifier was built using only ∼ 14 m of the YDF. The amplifier delivered a near-Gaussian beam ( M 2 ∼ 1.27 ) at 836 W output power (pump power limited) with a high slope efficiency of ∼ 83 % . Thanks to the short length and the tandem pumping, no indication of limiting factors such as stimulated Raman scattering, photodarkening, and transverse mode instability was observed.

Plasmonic random laser from dye-doped cholesteric liquid crystals incorporating silver nanoprisms.

Plasmonic random lasers have been demonstrated in combining dye-doped cholesteric liquid crystals (DD-CLCs) and silver nanoparticles (AgNPs). The DD-CLC laser reveals the lowest threshold and highest slope efficiency through the localized surface plasmon resonance of AgNPs with the best coupling of the emission spectrum of lasing dye and resonance of electron oscillation on the metal surface. Thermal control of the DD-CLC lasers has been achieved to simultaneously shift the long- and short-edge lasing peaks. By the α-stable analysis, the DD-CLC random laser (RL) reveals heavy tail distribution with relatively low α∼1.06 to show the Lévy behavior. Owing to its low spatial coherence, the DD-CLC RL has been demonstrated to produce a speckle-reduced image with a lower contrast of about 0.04.

Enhancement of the laser emission efficiency of Yb:Y2O3 ceramics via multi-step sintering method fabrication

Highly transparent 5.0 at.% Yb:Y2O3 ceramics were successfully fabricated by using an optimal content of La2O3 and ZrO2 sintering additives and multi-step sintering method. The sintering process of the ceramics was based on a combination of two-step sintering in air followed by vacuum sintering. In-line optical transmission reached 78.5% at 1100 nm and 80% at 2000 nm. The absorption cross-section at 978 nm and the stimulated emission cross-section at 1032 nm were determined to be 2.23 × 10−20 cm2 and 1.42 × 10−20 cm2, respectively. Laser emission at 1.03 μm with a high slope efficiency of 33% was obtained from a 1.5 mm thick Yb:Y2O3 uncoated ceramic medium under quasi-continuous wave pumping at 971 nm with a fiber-coupled diode laser.

Vertical Integration of Nitride Laser Diodes and Light Emitting Diodes by Tunnel Junctions

We demonstrate the applications of tunnel junctions (TJs) for new concepts of monolithic nitride-based multicolor light emitting diode (LED) and laser diode (LD) stacks. The presented structures were grown by plasma-assisted molecular beam epitaxy (PAMBE) on GaN bulk crystals. We demonstrate a stack of four LDs operated at pulse mode with emission wavelength of 453 nm. The output power of 1.1 W and high slope efficiency of 2.3 W/A is achieved for devices without dielectric mirrors. Atomically flat surface after the epitaxy of four LD stack and low dislocation density is measured as a result of proper TJ design with optimized doping level. The strain compensation design with InGaN waveguides and AlGaN claddings is shown to be crucial to avoid cracking and lattice relaxation of the 5 µm thick structure. Vertical connection of n-LDs allows for cascade emission of photons and increases the quantum efficiency n-times. The two-color (blue and green) LEDs are demonstrated. Application of TJs simplifies device processing, reducing the need for applications of p-type contact. The key factor enabling demonstration of such devices is hydrogen-free PAMBE technology, in which activation of buried p-type layers is not necessary.

High-efficiency Er-doped yttrium gallium garnet laser resonantly pumped by a laser diode at 1.47 µm.

The spectroscopic and laser properties of an Er3+-doped yttrium gallium garnet crystal, Y3Ga5O12 (YGG), are studied. The stimulated emission cross section is 1.4×10-21cm2 at 1.65 µm. A continuous-wave laser resonantly pumped by a laser diode at 1.47 µm is demonstrated, delivering a maximum output power of 3.34 W. Benefiting from the low phonon energy of the YGG host, the corresponding slope efficiency is as high as ∼42%. To the best of our knowledge, this is the highest slope efficiency from the laser-diode resonantly pumped Er lasers at room temperature in the 1.6 µm spectral range.

Towards Highly Efficient Polymer Fiber Laser Sources for Integrated Photonic Sensors

Lab-on-a-Chip (LoC) devices combining microfluidic analyte provision with integrated optical analysis are highly desirable for several applications in biological or medical sciences. While the microfluidic approach is already broadly addressed, some work needs to be done regarding the integrated optics, especially provision of highly integrable laser sources. Polymer optical fiber (POF) lasers represent an alignment-free, rugged, and flexible technology platform. Additionally, POFs are intrinsically compatible to polymer microfluidic devices. Home-made Rhodamine B (RB)-doped POFs were characterized with experimental and numerical parameter studies on their lasing potential. High output energies of 1.65 mJ, high slope efficiencies of , and -lifetimes of ≥900 k shots were extracted from RB:POFs. Furthermore, RB:POFs show broad spectral tunability over several tens of nanometers. A route to optimize polymer fiber lasers is revealed, providing functionality for a broad range of LoC devices. Spectral tunability, high efficiencies, and output energies enable a broad field of LoC applications.

Efficient operation near the quantum limit in external cavity diamond Raman laser

We realize efficient operation of the first Stokes (1240.3 nm) and the second Stokes (1485.8 nm) in external cavity diamond Raman lasers (DRLs) through efficient cavity coupling management and study their output performance. Firstly, an output pulse energy of 0.26 mJ at the first Stokes is generated and the slope efficiency is 84.3%, which closely approaches the quantum limit of 85.8%. Secondly, an output pulse energy of 0.26 mJ at the first Stokes and 0.18 mJ at the second are generated simultaneously. The total Raman output pulse energy is 0.44 mJ with a slope efficiency of 73.0%. To our knowledge, this is the highest slope efficiency in dual-wavelength external cavity DRLs. At the maximum pump level, by managing the cavity coupling, the energy ratio of the second Stokes to the first can be changed from 0.69 to 1.92. Highly efficient operation in external cavity DRLs is very important in practical applications, such as remote sensing, scanning lidar and laser range finding.

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.

Efficient near-infrared laser emission and nonlinear optical properties of a newly developed Yb:LYSB laser crystal

Herein, we report on the growth and characterization of La0.78Y0.32Yb0.04Sc2.86(BO3)4 (Yb:LYSB) crystal as bifunctional laser and nonlinear optical (NLO) medium. High quality Yb:LYSB crystal with non-congruent melting has been grown by the Czochralski technique. Structural, linear and NLO properties, and near-infrared (NIR) laser emission performances of the grown crystal are presented. The absorption cross-section at 980 nm for σ-polarization was evaluated to be 0.6 × 10−20 cm2, and emission cross-section around 1080 nm in π-polarization and σ-polarization amounted to 3.6 × 10−21 cm2 and 1.33 × 10−21 cm2, respectively. The spectroscopic investigations revealed the existence of two different Yb3+ centers in the LYSB crystal matrix. Efficient laser emission at 1028 nm was obtained with a c-cut 4 at.% Yb:LYSB uncoated sample with a thickness of 3.5 mm. Employing the pump at 971.5 nm with a fiber-coupled diode laser, the Yb:LYSB medium yielded laser pulses with 1.5 mJ energy at 4.25 mJ energy of the absorbed pump pulse, corresponding to an overall optical-to-optical efficiency of 0.35. The laser operated with a high slope efficiency of 0.57. The refractive indexes were measured and the NLO properties of Yb:LYSB crystal for second harmonic generation of 1028 nm laser radiation were determined. The results of this work indicate Yb:LYSB as a promising crystal to design new laser sources in the NIR and green (∼514 nm) spectral ranges based on direct laser emission and self-frequency doubling processes, respectively.