Showing papers on "Slope efficiency published in 2020"

Niobium disulfide as a new saturable absorber for an ultrafast fiber laser

Abstract: Group VB transition metal dichalcogenides (TMDCs) are emerging two-dimensional materials and have attracted significant interests in the fields of physics, chemistry, and material sciences. However, there are very few reports about the optical characteristics and ultrafast photonic applications based on group VB TMDCs so far. In this work, we have calculated the niobium disulfide (NbS2) band structure by the density functional theory (DFT), which has revealed that NbS2 is a metallic TMDC. In addition, we have prepared an NbS2-microfiber device and the nonlinear optical characteristics have been investigated. The modulation depth, saturation intensity and non-saturable loss have been measured to be 13.7%, 59.93 MW cm−2 and 17.74%, respectively. Based on the nonlinear optical modulation effect, the Er-doped fiber (EDF) laser works in the soliton mode-locking state with the pump power of 94–413 mW. The pulse duration of 709 fs and the maximum average output power of 23.34 mW have been obtained at the pump power of 413 mW. The slope efficiency is as high as 6.79%. Compared to the recently reported studies based on TMDCs comprehensively, our experimental results are better. These experimental results demonstrate that NbS2 with excellent nonlinear optical properties can be used as a promising candidate to advance the development of ultrafast photonics.

Effects of Lateral Optical Confinement In GaN VCSELs With Double Dielectric DBRs

Abstract: Two types of GaN vertical-cavity surface-emitting lasers (VCSELs), with and without lateral optical confinement (LOC) structure, were fabricated and their performances were compared. Compared with the VCSEL without LOC, the device with LOC showed a great improvement in threshold current, slope efficiency, output power and differential quantum efficiency, which was mainly due to the reduction of internal loss. Devices with LOC showed clear and multi-transversal mode structures. However, thermal dissipation became worse. The effects of such a design on thermal resistance and transverse modes were discussed.

8-kW single-stage all-fiber Yb-doped fiber laser with a BPP of 0.50 mm-mrad

Abstract: Single-mode fiber lasers with excellent beam quality and several-kilowatts output power are expected to realize both extraordinary processing speed and high aspect ratio in the material processing field. In this paper, we report an 8-kW output single-stage Yb-doped fiber laser with a BPP of 0.50 mm-mrad. The laser has a delivery fiber with a length of 3 m. To realize an 8-kW single-mode output without excess a stimulated Raman scattering threshold, fibers with a considerably large effective core area are employed. An ytterbium doped fiber is directly pumped by newly developed high-power laser diode modules with a total available pump power over 10 kW through a bi-directional pumping scheme. The laser has a high slope efficiency of 81%. The power of the SRS light around 1120 nm was 22 dB smaller than the fundamental laser power at 1070 nm. To the best of our knowledge, it is the smallest BPP with more than 8 kW output power pumped by an end-pumping regime. We believe the laser will contributes laser processing using a galvano scanner for high speed and high aspect ratio welding.

550 W single frequency fiber amplifiers emitting at 1030 nm based on a tapered Yb-doped fiber.

Abstract: In this paper, we report a high power single frequency 1030 nm fiber laser with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). The T-YDF has advantages of effectively suppressing stimulated Brillouin scattering (SBS) while maintaining good beam quality. As a result, a record output power of 379 W single frequency, linearly polarized, nearly single-mode fiber amplifier operating at 1030 nm is demonstrated. The polarization extinction ratio is as high as 16.3 dB, and the M2 is measured to be 1.12. Further, the dependence of the thermal-induced mode instability (TMI) threshold on the polarization state of an input signal laser is investigated for the first time. By changing the polarization state of the injected seed laser, the output power can increase to 550 W while the beam quality can be maintained well (M2=1.47). The slope efficiency of the whole amplifier is about 80%. No sign of SBS appears even at the highest output power and the further brightness scaling of both situations is limited by the TMI effect. To the best of our knowledge, this result is the highest output power of all-fiberized single frequency fiber amplifiers.

Close look on cubic Tm:KY 3 F 10 crystal for highly efficient lasing on the 3 H 4 → 3 H 5 transition

Abstract: We report on Czochralski growth, detailed ground- and excited-state absorption and emission spectroscopy and highly-efficient mid-infrared (∼2.3 µm) laser operation of a cubic potassium yttrium fluoride crystal, Tm:KY3F10. The peak stimulated-emission cross-section for the 3H4 → 3H5 transition is 0.34×10−20 cm2 at 2345 nm with an emission bandwidth exceeding 50 nm. The excited-state absorption spectra for the 3F4 → 3F2,3 and 3F4 → 3H4 transitions are measured and the cross-relaxation is quantified. A continuous-wave 5 at.% Tm:KY3F10 laser generated 0.84 W at 2331-2346 nm by pumping at 773 nm, with a record-high slope efficiency of 47.7% (versus the incident pump power) owing to the efficient action of energy-transfer upconversion leading to a pump quantum efficiency approaching 2. The first Tm:KY3F10 laser with ESA-assisted upconversion pumping (at 1048 nm) is also demonstrated. Due to its broadband emission properties, Tm:KY3F10 is promising for ultrashort pulse generation at ∼2.3-2.4 µm.

MXene-Ti 3 C 2 T x for watt-level high-efficiency pulse generation in a 2.8 μm mid-infrared fiber laser

Abstract: We report a watt-level passively Q-switched 2.8 μm mid-infrared multi-mode fiber laser by employing multi-layered two-dimensional MXene-Ti3C2Tx as the saturable absorber (SA). The MXene-Ti3C2Tx is fabricated by selectively etching aluminum layers in Ti3AlC2. The non-saturable loss, modulation depth, and saturable intensity of the SA at 2866 nm were measured to be 25.0%, 33.2%, and 0.043 GW/cm2, respectively. The maximum average output power of the Ti3C2TxQ-switched fiber laser reached 1.09 W at 28.23% slope efficiency. The pulse repetition rate, shortest pulse width, pulse peak power, and single-pulse energy were 78.12 kHz, 1.04 μs, 13.4 W, and 13.93 μJ, respectively. This is the first demonstration of watt-level pulse generation in a mid-infrared fiber laser using low dimensional materials, to the best of our knowledge. These results indicate that the Ti3C2Tx is a reliable and superior broadband SA for high power mid-infrared pulsed laser generation.

High-power hybrid GaN-based green laser diodes with ITO cladding layer

Abstract: Green laser diodes (LDs) still perform worst among the visible and near-infrared spectrum range, which is called the “green gap.” Poor performance of green LDs is mainly related to the p-type AlGaN cladding layer, which on one hand imposes large thermal budget on InGaN quantum wells (QWs) during epitaxial growth, and on the other hand has poor electrical property especially when low growth temperature has to be used. We demonstrate in this work that a hybrid LD structure with an indium tin oxide (ITO) p-cladding layer can achieve threshold current density as low as 1.6 kA/cm2, which is only one third of that of the conventional LD structure. The improvement is attributed to two benefits that are enabled by the ITO cladding layer. One is the reduced thermal budget imposed on QWs by reducing p-AlGaN layer thickness, and the other is the increasing hole concentration since a low Al content p-AlGaN cladding layer can be used in hybrid LD structures. Moreover, the slope efficiency is increased by 25% and the operation voltage is reduced by 0.6 V for hybrid green LDs. As a result, a 400 mW high-power green LD has been obtained. These results indicate that a hybrid LD structure can pave the way toward high-performance green LDs.

Fabrication, microstructures, and optical properties of Yb:Lu2O3 laser ceramics from co-precipitated nano-powders

Abstract: The Yb:Lu2O3 precursor made up of spherical particles was synthesized through the co-precipitation method in the water/ethanol solvent. The 5 at% Yb:Lu2O3 powder is in the cubic phase after calcination at 1100 °C for 4 h. The powder also consists of spherical nanoparticles with the average particle and grain sizes of 96 and 49 nm, respectively. The average grain size of the pre-sintered ceramic sample is 526 nm and that of the sample by hot isostatic pressing grows to 612 nm. The 1.0 mm-thick sample has an in-line transmittance of 81.6% (theoretical value of 82.2%) at 1100 nm. The largest absorption cross-section at 976 nm is 0.96×10−20 cm2 with the emission cross-section at 1033 nm of 0.92×10−20 cm2 and the gain cross sections are calculated with the smallest population inversion parameter β of 0.059. The highest slope efficiency of 68.7% with the optical efficiency of 65.1% is obtained at 1033.3 nm in quasi-continuous wave (QCW) pumping. In the case of continuous wave (CW) pumping, the highest slope efficiency is 61.0% with the optical efficiency of 54.1%. The obtained laser performance indicates that Yb:Lu2O3 ceramics have excellent resistance to thermal load stresses, which shows great potential in high-power solid-state laser applications.

Efficient visible laser operation of Tb:LiYF4 and LiTbF4.

Abstract: We report laser operation of two Tb3+-activated gain media, Tb:LiYF4 and LiTbF4, in yellow or/and green spectral region. A record-high slope efficiency of 63% among Tb3+-lasers and maximum output power of 1.17 W (incident power of 2.79 W) at around 544 nm were obtained with a c-cut 15%Tb:LiYF4 crystal. The yellow laser characteristics in σ-polarization were studied. A slope efficiency of 21% at 582 nm was achieved. More importantly, we succeeded in laser operation of LiTbF4 for the first time to the best of our knowledge. Laser oscillation at around 544 nm yielded a maximum slope efficiency of 45%. This points toward the possibility of producing high-energy pulsed lasers using LiTbF4, which features a high active-ion concentration as well as relatively long lifetime.

Generation of Q-switched and mode-locked pulses with Eu2O3 saturable absorber

Abstract: In this paper, Europium Oxide (Eu2O3) is used as a saturable absorber (SA) to produce Q-switched and mode-locked pulses in an erbium-doped fiber laser (EDFL) cavity. The Eu2O3 was synthesized using casting technique and the resulting Eu2O3 thin film was introduced between two optical fiber ferrule connectors to form a SA. Then the SA was positioned in the EDFL ring cavity. A stable Q-switched operation was achieved by controlling the loss and gain of the cavity. As the pumping power was increased from 84.0 mW to 125.0 mW, the repetition frequency increased from 60.1 kHz to 68.6 kHz and pulse width reduced from 4.5 μs to 3.6 μs respectively. The Q-switched EDFL was operating at the center wavelength of 1568 nm, had a 162 nJ maximum pulse energy and 10.24% slope efficiency. Adding a 100 m SMF in the ring cavity initiated a self-starting mode-locked EDFL and the pulses remained stable within a range of 104.6 to 145.8 mW pump power. At the threshold pump power of 104.6 mW, the mode-locked EDFL operated at a central wavelength of 1565 nm with a repetition rate of 1.8 MHz and a pulse width of 3.51 ps. The results show that Eu2O3 can be deployed as a SA for both Q-switching and mode locking generations.

2.5 kW Narrow Linewidth Linearly Polarized All-Fiber MOPA With Cascaded Phase-Modulation to Suppress SBS Induced Self-Pulsing

Abstract: As a major limitation for power scaling of high power narrow linewidth fiber master oscillator power amplifiers (MOPAs), Stimulated Brillouin Scattering (SBS) induced self-pulsing in polarization maintaining (PM) fiber amplifiers is well characterized and analyzed in this paper by comparing different white noise signal (WNS) phase-modulated modes in experiments. It is found that the self-pulsing effect is not observed in the PM-amplifier with single-frequency laser seed injection, and cascaded WNS modulation provides superior self-pulsing suppression than single WNS modulation with similar output linewidth. Moreover, the experimental results indicate that the self-pulsing threshold can hardly be predicted only by the output linewidth or the defined SBS threshold in a WNS phase modulated fiber amplifier system. As self-pulsing is originated from the spectral spikes in WNS modulated system, we theoretically analyzed characteristics of these spikes in different phase-modulation modes. It indicates the spectral peak intensity can be reduced by cascaded modulation, for which self-pulsing can be suppressed. The theoretical predictions agree well with the experimental results. At the same time, in order to suppress the mode instability effect, a plum blossom shaped bending mode selection device is used in this high-power narrow linewidth fiber amplifier system. Finally, a 32 GHz cascaded WNSs modulated, over than 2.5 kW linearly polarized all-fiber amplifier with a slope efficiency of 86.7% is demonstrated. The polarization extinction ratio (PER) is measured larger than 14 dB and the beam quality factor M2 maintains lower than 1.3 in the power scaling process.

Kilowatt-level ytterbium-Raman fiber amplifier with a narrow-linewidth and near-diffraction-limited beam quality

Abstract: By focusing on a typical emitting wavelength of 1120 nm as an example, we present the first, to the best of our knowledge, demonstration of a high-efficiency, narrow-linewidth kilowatt-level all-fiber amplifier based on hybrid ytterbium-Raman (Yb-Raman) gains. Notably, two temporally stable, phase-modulated single-frequency lasers operating at 1064 nm and 1120 nm, respectively, were applied in the fiber amplifier, to simultaneously alleviate the spectral broadening of the 1120 nm signal laser and suppress the stimulated Brillouin scattering effect. An over 1 kW narrow-linewidth 1120 nm signal laser was obtained with slope efficiency of ${\sim}{77}\% $∼77% and beam quality of ${\rm M}_x^2\sim {1.25}$Mx2∼1.25, ${\rm M}_y^2 \sim {1.17}$My2∼1.17. The amplified spontaneous emission (ASE) noise in the fiber amplifier was effectively suppressed by incorporating an ASE-filtering system between the seed laser and the main amplifier. Furthermore, the experimental results demonstrate that the spectral linewidth broadening effect is tightly related to the injected power ratios between the two seed lasers. Overall, this setup could provide a reference on obtaining and optimizing high-power narrow-linewidth fiber lasers operating in the long wavelength extreme of the Yb gain spectrum.

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

Abstract: 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 μm2) 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 (M2∼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.

Tunable in the range of 4.5-6.8 µm room temperature single-crystal Fe:CdTe laser pumped by Fe:ZnSe laser.

Abstract: We report a laser operation from a Fe:CdTe single crystal, pumped by 40-ns pulses of a 4.12-µm Fe:ZnSe laser. The maximum output energy of 5.8 mJ was produced at 5.4 µm with 30% absorbed energy slope efficiency. A record 2300-nm-wide smooth and continuous wavelength tunability over 4.5-6.8 µm range was demonstrated, being the longest wavelength tuning achieved for Fe2+-doped chalcogenide lasers. We also discuss the features of the oscillation spectra.

Highly efficient Er:YAP laser with 6.9 W of output power at 2920 nm

Abstract: We report on the efficient high-power operation of a laser-diode-pumped Er3+-doped yttrium aluminum perovskite (Er:YAP) laser in the 3 μm spectral region at room temperature. 6.9 W of continuous-wave (CW) output power was obtained at 2920 nm. The slope efficiency was as high as 30.6% with respect to the absorbed pump power, which is close to the quantum defect limit (33.4%). To the best of our knowledge, this is the highest CW output power generated from 3 μm Er3+-doped solid state lasers at room temperature. Furthermore, our analysis has shown that more than 10 W of output power based on Er:YAP is possible by further mitigating the thermal lens effect.

2.9 µm lasing from a Ho 3+ /Pr 3+ co-doped AlF 3 -based glass fiber pumped by a 1150 nm laser

Abstract: Ho3+/Pr3+ co-doped AlF3-based glass fibers were fabricated by using a rod-in-tube method based on the matrix glass composition of AlF3-BaF2-CaF2-YF3-SrF2-MgF2-LiF-ZrF4-PbF2. Under the pump of a 1150 mW Raman fiber laser, a 2.9 µm laser was observed in a 19 cm long Ho3+/Pr3+ co-doped AlF3-based glass fiber with an output power of 173 mW and a slope efficiency of 10.4%. Ho3+/Pr3+ co-doped AlF3-based glasses were fabricated to investigate the deactivation effects of Pr3+ ions on the Ho3+:5I7 level. Our results showed that the Ho3+/Pr3+ co-doped AlF3-based glass fibers are potential gain media for ∼2.9µm lasers.

Ultrafast Yb-Doped Fiber Laser Using Few Layers of PdS2 Saturable Absorber.

Abstract: Two-dimensional (2D) transition metal dichalcogenide (TMD) materials have exceptional optoelectronic and structural properties, which allow them to be utilized in several significant applications in energy, catalyst, and high-performance optoelectronic devices. Among other properties, the nonlinear optical properties are gaining much attention in the research field. In this work, a unique pentagonal TMD material, palladium disulfide (PdS2), is employed as a saturable absorber (SA) in an ytterbium-doped fiber (YDF) laser cavity and mode-locked laser pulse is generated. At first, liquid phase exfoliation is performed to prepare PdS2 nanoflakes. Afterward, the PdS2-nanoflakes solution was incorporated in the side-polished fiber (SPF) to form SPF-based PdS2-SA. By utilizing this SA, a highly stable mode-locked laser pulse is realized at pump power of 160 mW, which has a center wavelength of 1033 nm and a 3-dB spectral bandwidth of 3.7 nm. Moreover, the pulse duration, maximum power output and corresponding single-pulse energy were determined as 375 ps, 15.7 mW and 0.64 nJ, respectively. During the experiment, the mode-locked pulse remained stable till the pump power reached a value of 400 mW and, for the regulation of power, the slope efficiency is calculated at about 4.99%. These results indicate that PdS2 material is a promising nonlinear optical material for ultrafast optical applications in the near-infrared (NIR) region.

Room-temperature operation of c-plane GaN vertical cavity surface emitting laser on conductive nanoporous distributed Bragg reflector

Abstract: Technological feasibility of III-nitride vertical cavity surface emitting laser (VCSEL) has been hindered by the lack of an electrically conductive, easily manufacturable, wide reflection stop band distributed Bragg reflector (DBR). Here, we present the first electrically injected III-nitride VCSEL on an electrically conductive DBR using nanoporous (NP) GaN. The measured threshold current density and the maximum light output power were 42 kA/cm2 and 0.17 mW, respectively, at 434 nm. Vertical injection was demonstrated and showed no deterioration in the threshold current density or slope efficiency, demonstrating the feasibility of vertical injection in NP GaN VCSELs. Filamentary lasing was observed, and its effect on the slope efficiency and the lasing linewidth is studied. Initial measurements showing the correlation between the measured high threshold current density and surface undulations are presented and discussed.

Highly efficient LD-pumped 607 nm high-power CW Pr3+: YLF lasers

Abstract: We demonstrated a 607 nm high-power continuous-wave (CW) orange laser based on a 12-mm-long a-cut Pr3+:YLF crystal with high slope efficiency and a low doping level. A maximum output power of 4.88 W with a slope efficiency of ~49% was achieved at an absorbed pump power of 12.15 W, and no output saturation power was observed. To improve the laser beam quality, we designed a concave-plane cavity and achieved an output power of 3.80 W with M2 factors of ~1.7 and ~2.2 in the horizontal and vertical directions, respectively, by means of a novel output coupler with tunable transmission. In addition, theoretical analyses were conducted to explain our designs, and the corresponding simulated results were presented.

Passively Q-switched Tm:YAlO3 laser based on WS2/MoS2 two-dimensional nanosheets at 2 μm

Abstract: A comparison of the pulsed laser performances of 2 μm passively Q-switched Tm:YAlO3 (YAP) lasers based on the use of tungsten disulfide (WS2) and molybdenum disulfide (MoS2) two-dimensional (2D) nanosheets as saturable absorbers is reported. The novel nanosheets were prepared by chemical vapor deposition (CVD) technology. The microstructure and optical characteristics of the nanosheets were investigated experimentally. In a continuous-wave (CW) operation, the maximum output power of 2.8 W was obtained at an absorbed pump power of 6.9 W, with a corresponding slope efficiency of 46.4%. In a passively Q-switched operation at a pump power of 1.45 W, the average output power, pulse width, repetition rate, pulse energy, and peak power for the Tm:YAP/WS2 laser were 0.11 W, 2.65 μs, 34.7 kHz, 2.9 μJ, and 1.23 W, respectively. As for the Tm:YAP/MoS2 laser, the corresponding values were 0.10 W, 2.5 μs, 24.0 kHz, 3.8 μJ, and 1.55 W.

Preparation and properties of Tm-doped SiO2 -ZrO2 phase separated optical fibers for use in fiber lasers

Abstract: Zirconium oxide (ZrO2) is a perspective co-dopant of rare-earth ions in silica fibers for use in fiber lasers. ZrO2 nanoparticles increase the solubility of rare-earth ions and enhance their luminescence properties. In this paper, we report on the fabrication of Zr-Tm codoped silica fibers using the MCVD method combined with modified solution-doping technique. Several fibers with different dopant concentrations were prepared and their optical properties were studied. It was found that increasing Zr concentration leads to the creation of larger ZrO2 nanoparticles which causes unwanted attenuation. Optimal Zr concentration was found to be 1 at. %. The fiber with optimal Zr concentration and Tm concentration of 260 ppm exhibited 1.8 µm fluorescence lifetime of 420 ± 10 µs. For the first time in literature, we have demonstrated laser operation in a Zr/Tm-codoped silica fiber. The threshold for laser operation was determined to be 233 mW and the slope efficiency of 72.7% was achieved. MCVD combined with modified solution doping proved to be a feasible method of preparation of Tm-doped SiO2-ZrO2 optical fibers for use in fiber lasers.

55 W kilohertz-linewidth core- and in-band-pumped linearly polarized single-frequency fiber laser at 1950 nm.

Abstract: Based on core- and in-band-pumped polarization-maintaining ${{\rm Tm}^{3 + }}$Tm3+-doped single-cladding fiber (PM-TSF, the core diameter is 9 µm) by a 1610 nm fiber laser and a distributed Bragg reflector seed laser, a linearly polarized single-frequency fiber laser (LP-SFFL) at 1950 nm with an output power of 55.3 W and a laser linewidth of 6.95 kHz is demonstrated. The output beam qualities of ${M}_x^2$Mx2 and ${ M}_y^2$My2 are measured to be 1.01 and 1.03, respectively. The slope efficiency with respect to the launched pump power is 71.0%, in comparison with a theoretical quantum efficiency of 82.6%. A polarization-extinction ratio of 19 dB and an optical signal-to-noise ratio of 58 dB are obtained from the 1950 nm LP-SFFL. To the best of our knowledge, to date, this is the highest power of 2.0 µm SFFL output directly from a strict single-mode active fiber. Our experiment offers a promising solution to the current limitations of the high-performance fiber lasers at 2.0 µm, which is particularly essential for coherent detection.

High-efficiency ∼2 µm CW laser operation of LD-pumped Tm3+:CaF2 single-crystal fibers.

Abstract: The Tm:CaF2 single-crystal fibers were successfully grown by modified temperature gradient technique method. The J-O intensity parameters, spontaneous radiative transition rates, radiative lifetimes and fluorescence branching ratios of Tm3+ were calculated with Judd-Ofelt theory. A systematic study of the fluorescence characteristics has been carried out. Simulated emission cross-sections of the 3F4 → 3H6 transition were calculated to be 6.68×10−21 cm−2 and 4.65×10−21cm−2 for crystal doped with 3 at.% and 4 at.% Tm3+. The 64.4% slope efficiency with output power of 2.23W was achieved in 3 at.% Tm:CaF2 single-crystal fiber. The slope efficiency decreased to 44.5% and maximum output power decreased to 1.65W in 4 at.% Tm:CaF2 single-crystal fiber. Obtained results show that Tm-doped CaF2 single-crystal fibers are promising materials for IR laser action generation.

254 W laser-diode dual-end-pumped Tm:YAP InnoSlab laser.

Abstract: A compact laser-diode dual-end-pumped 3 at. % a-cut Tm:YAP InnoSlab laser with the output power of 254 W in 1.99 µm has been demonstrated. The slope efficiency with respect to the incident pumped power is 45.9%, and the optical-to-optical conversion efficiency is 36.5%. The RMS stability of the maximum output power is better than 0.1% in 30 min. Beam quality factors M2 are 250 in the x direction and 4.7 in the y direction. Additionally, the shape of the output laser spot is rectangular.

Theoretical Study on the Effects of Dislocations in Monolithic III-V Lasers on Silicon

Abstract: In this work, we present an approach to modelling III-V lasers on silicon based on a travelling-wave rate equation model with sub-micrometer resolution. By allowing spatially resolved inclusion of individual dislocations along the laser cavity, our simulation results offer new insights into the physical mechanisms behind the characteristics of 980 nm In(Ga)As/GaAs quantum well (QW) and 1.3 μm quantum dot (QD) lasers grown on silicon. We identify two effects with particular importance for practical applications from studying the reduction of the local gain in carrier-depleted regions around dislocation locations and the resulting impact on threshold current increase and slope efficiency at high dislocation densities. First, a large minority carrier diffusion length is a key parameter inhibiting laser operation by enabling carrier migration into dislocations over larger areas, and secondly, increased gain in dislocation-free regions compensating for gain dips around dislocations may contribute to gain compression effects observed in directly modulated silicon-based QD lasers. We believe that this work is an important contribution in creating a better understanding of the processes limiting the capabilities of III-V lasers on silicon in order to explore suitable materials and designs for monolithic light sources for silicon photonics.

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

Abstract: 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.