On the dynamics of population inversion for 3 μm Er3+lasers

A generalized model for 3-μm (⁴I_11/2 →⁴I_13/2)Er lasers is proposed. The essential energy transfer processes present in the single-doped Er ³⁺ systems (up-conversion from ⁴I_13/2, up-conversion from ⁴ I_11/2, cross-relaxation from ⁴S _3/2), as well as those present in Cr³⁺ codoped Er ³⁺ systems, are taken into account. In the frame of this model, the main features of 3 μm Er³⁺ lasers, such as long pulse or CW operation, the change of emission wavelength as a function of pumping conditions, and the effects of codoping with Ho³⁺ or Tm³⁺ ions, are explained     

Room-temperature operation of InAs quantum-dash lasers on InP (001)

The first self-assembled InAs quantum dash lasers grown by molecular beam epitaxy on InP (001) substrates are reported. Pulsed room-temperature operation demonstrates wavelengths from 1.60 to 1.66 μm for one-, three-, and five-stack designs, a threshold current density as low as 410 A/cm² for single-stack uncoated lasers, and a distinctly quantum-wire-like dependence of the threshold current on the laser cavity orientation. The maximal modal gains for lasing in the ground-state with the cavity perpendicular to the dash direction are determined to be 15 cm^-1 for single-stack and 22 cm^-1 for five-stack lasers     

Characteristics of GaAsSb single-quantum-well-lasers emitting near1.3 μm

We report data on GaAsSb single-quantum-well lasers grown on GaAs substrates. Room temperature pulsed emission at 1.275 μm in a 1250-μm-long device has been observed. Minimum threshold current densities of 535 A/cm² were measured in 2000-μm-long lasers. We also measured internal losses of 2-5 cm^-1, internal quantum efficiencies of 30%-38% and characteristic temperatures T₀ of 67°C-77°C. From these parameters, a gain constant G₀ of 1660 cm^-1 and a transparency current density J_tr of 134 A/cm² were calculated. The results indicate the potential for fabricating 1.3-μm vertical-cavity surface-emitting lasers from these materials     

Differential gain in bulk and quantum well diode lasers

Differential gain (g^') of bulk and single-quantum-well (SQW) lasers was determined from threshold current density and differential quantum efficiency measurements. The threshold measurement technique was used to show that g^' is a function of cavity length (L) in SQW lasers and independent of L in bulk lasers. It was found that g^' of long SQW lasers (1000 μm) is about 7×10^-16 cm² , approximately two times that of bulk lasers. At short cavity lengths (250 μm), g^' is about the same for both laser types     

Low threshold voltage vertical-cavity lasers fabricated byselective oxidation

Novel vertical-cavity surface emitting lasers fabricated using selective oxidation to form a current aperture under a top monolithic distributed Bragg reflector mirror are reported. Large cross-sectional area lasers (259 μm²) exhibit threshold current densities of 150 A/cm² per quantum well and record low threshold voltage of 1.33 V. Smaller lasers (36 μm²) possess threshold currents of 900 μA with maximum output powers greater than 1 mW. The record performance of these oxidised vertical-cavity lasers arises from the low mirror series resistance and very efficient current injection into the active region     

Distributed Bragg-reflector Pb1-xSnxTe/PbSeyTe1-ydiode lasers

Distributed Bragg-reflector (DBR) diode lasers were designed and fabricated from lattice-matched Pb1-xSnxTe/PbSeyTe1-ysingle heterostructures grown by liquid-phase epitaxy. These DBR lasers operated in a single longitudinal mode within a limited range of heat-sink temperatures, 8.5-38 K, with a threshold current density of ∼3 kA/cm²at 20 K. Single longitudinal mode operation was maintained up to more than three times the threshold current. Continuous tuning of the laser output frequency over a range of ∼6 cm^-1, near 775 cm^-1(12.9 μm), was acheived by varying the heat-sink temperature. The average tuning rate was 0.21 cm^-1/K, and it was much smaller than the rate for corresponding Fabry-Perot lasers, which was 2.3 cm^-1/K. The measured effective mode index of the DBR lasers agrees well with the calculated one.     

Auger recombination rates in compressively strainedInxGa1-xAs/InGaAsP/InP(0.53⩽x⩽0.73) multiquantum well lasers

The authors have experimentally determined Auger recombination rates in compressively strained In_xGa_1-xAs/InGaAsP/InP MQW lasers for the first time. The Auger recombination rates were derived from the measured turn-on delay times during large-signal modulation of single-mode lasers. The Auger coefficient increases from 5±1×10^-30 to 13±1×10^-30 cm⁶ s^-1 as the indium composition in the quantum well active region, x, increases from 0.53 to 0.73     

High power and high efficiency operation of Al-freeInGaAs/GaInAsP/GaInP GRINSCH SQW lasers (λ≃0.98 μm)

High power and high quantum efficiency Al-free InGaAs/GaInAsP/GaInP GRINSCH SQW lasers emitting at 0.98 μm are reported. A CW output power as high as 580 mW and single lateral mode power up to 280 mW were achieved for the Al-free ridge waveguide lasers at room temperature. The lasers exhibited a high internal quantum efficiency of 99% and low internal waveguide loss of 3.2 cm^-1. A high characteristic temperature of 217 K and low threshold current density of 109 A/cm² were also obtained. The results are the best obtained for Al-free 0.98 μm pumping lasers     

Er3+-Yb3+ and Er3+ doped fiberlasers

Single-mode fiber lasers operating at ~1.57 μm are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er³⁺ and Yb³⁺) and erbium on its own. The performance of Er³⁺-Yb³⁺ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 μm are available from diode pumped Er³⁺ -Yb³⁺ systems     

The spatial distribution of high-order harmonics from solid surfaceplasmas

Investigations have been performed on harmonic generation from solid-vacuum interfaces using a 2.2-ps 1054-nm laser pulse at maximum intensities of ~2×10¹⁷ W·cm^-2. It is found that the divergence of the harmonics gradually increases at intensities between Iλ²=2×10¹⁵ and 2×10¹⁶ W·cm^-2·μm². We experimentally observe that the divergence of the harmonics decreases as the order of the harmonic increases. We also found that the divergence of the third harmonics emission is smaller for 2.2-ps pulsewidth for the driving lasers as compared with those for 100-ps pulsewidth lasers     

Room-temperature pulsed operation of triple-quantum-well GaInNAslasers grown on misoriented GaAs substrates by MOCVD

The lasing operation of three-quantum-well GaInNAs stripe geometry lasers grown by MOCVD on 0° and 6° misoriented (100) GaAs substrates, respectively, have been demonstrated and their performance is compared for the first time. Both devices achieved room temperature, pulsed lasing operation at an emission wavelength of 1.17 μm, with a threshold current density of 667 A/cm² for lasers grown on 6° misoriented substrates, and 1 kA/cm² for lasers grown on 0° misoriented substrates. The threshold for the lasers grown on 6° misoriented substrates compares favorably with the best results for GaInNAs lasers. Lasers with narrower stripe width and a planar geometry have also been demonstrated by the use of lateral selective wet oxidation for current confinement, with a threshold current density of 800 A/cm² for 25-μm-wide devices     

Optical and RF characteristics of short-cavity-lengthmultiquantum-well strained-layer lasers

The optical and RF characteristics of short-cavity, strained-layer In_0.3Ga_0.7As graded-index separate-confinement-heterostructure (GRINSCH) multiple-quantum-well ridge waveguide lasers are described. Short-cavity-length strained-layer lasers with four In_0.3Ga_0.7As quantum wells have been fabricated using chemically assisted ion beam etching (CAIBE). These lasers have a very low K factor of 0.14 ns and a high differential gain of 1.1×10^-15 cm². A 3 dB modulation bandwidth of 23.5 GHz has been measured on a 50 μm cavity-length device. This is the highest reported bandwidth for a quantum well laser     

Tensile-strained GaAsP/GaInAsP/GaInP quantum well lasers

Tensile-strained GaAsP/GaInAsP/GaInP separate-confinement-heterostructure single-quantum-well (SCH-SQW) lasers are reported for the first time. A low threshold current density of 261 A/cm² and a high characteristic temperature of 190 K were obtained for a 1600-μm long broad-area laser having ~0.3% lattice strain. The internal quantum efficiency was as high as 93% and internal waveguide loss 3.3 cm^-1. Some primary results of unstrained GaAs/GaInAsP and compressive-strained (1.4%) InGaAs/GaInAsP SCH-SQW lasers are also presented. Both the tensile and compressive-strained lasers exhibited higher quantum efficiency than the unstrained lasers. On the other hand, the tensile-strained lasers had nearly the same internal waveguide loss and threshold current as the unstrained lasers     

Absorption loss coefficient of the active layer for 1.48-μm bulkand MQW lasers

It is shown that the absorption loss coefficient of the active layer for 1.48-μm bulk lasers is 66 cm^-1 which is between 45 and 107 cm^-1 for 1.3-μm bulk lasers and for 1.55-μm bulk lasers, respectively. It is also described that the absorption loss coefficient of the active layer for 1.48-μm multiple-quantum-well (MQW) lasers is 28 cm^-1 which is about two-fifths of that for 1.48-μm bulk lasers. Therefore, the high slope efficiency of the 1.48-μm MQW lasers is attributed not only to the small optical confinement factor but also to the small absorption loss coefficient of the active layer     

1.3 μm InGaAs/GaAs strained quantum well lasers with InGaPcladding layer

Using MOVPE, we fabricated strained quantum well 1.3 μm lasers with an InGaP cladding layer on a GaAs substrate. The lasers had a high gain coefficient of 60 cm^-1. Lasers with high reflection facets had a low threshold current density of 500 A/cm², and a high characteristic temperature of 100 K     

Low-threshold strain-compensated InGaAs(N) (λ = 1.19-1.31μm) quantum-well lasers

Highly strained (Δa/a ~ 2.5%) In_0.4Ga_0.6 As and In_0.4Ga_0.6As_0.995N_0.005 -quantum-well (QW) active lasers utilizing strain-compensating InGaP-GaAsP buffer layers and GaAs_0.85P_0.15 barrier layers, grown by metal-organic chemical vapor deposition (MOCVD), are demonstrated with lasing emission wavelength of 1.185 and 1.307 μm, respectively. Threshold and transparency current density for the strain compensated InGaAsN QW lasers, with emission wavelength of 1.295 μm, are measured to be as low as 290 A/cm² (L = 1500 μm) and 110 A/cm², respectively, with characteristic temperature of T₀ and T₁ of 130 K and 400 K     

Modulation characteristics of high speed (f-3 dB=20 GHz)tunneling injection InP/InGaAsP 1.55 μm ridge waveguide lasersextracted from optical and electrical measurements

High-performance multiquantum-well 1.55 μm InP-based tunneling injection lasers are fabricated using a conventional single mode ridge waveguide fabrication process and characterized. The lasers consist of an eight quantum-well strain-compensated gain region and a 30-Å InP tunneling barrier. The bandwidth of these lasers is measured to be 20 GHz with a damping limited bandwidth extracted from the K-factor (determined from optical modulation measurements) of 26 GHz. To our knowledge, this is the highest measured bandwidth recorded for an InP-based simple ridge waveguide structure. The differential gain is measured to be as high as 1×10^-15 cm², with a measured gain compression coefficient ϵ of 5×10^-17 cm³. It is shown that the K-factor can also be extracted solely from measurements of the small signal electrical impedance. The carrier escape time τ_esc is determined to be 0.5 ns, independent of bias. This high frequency performance is achieved with a very simple device structure at room temperature under constant drive currents     

Fabrication, characterization and analysis of low threshold currentdensity 1.55-μm-strained quantum-well lasers

Tertiarybutylarsine and tertiarybutylphosphine are less hazardous alternatives to arsine and phosphine as group V sources for crystal growth of In_xGa_1-xAs_yP_1-y alloys by metalorganic chemical vapor deposition. Compressive and tensile-strained quantum-well lasers emitting at 1.55 μm have been fabricated using these sources. Threshold current density as low as 93 A/cm², transparency current density as low as 38 A/cm² and internal efficiency of 91% were obtained for 1.5% compressive-strained single quantum-well lasers. These devices represent the best lasers emitting at this wavelength that have been reported in the literature. An analysis of some of the characteristics of these devices such as transparency current, differential gain and nonradiative recombination is also presented in this paper     

New direct optical pump schemes for multiatmosphere CO2and N2O lasers

Nine schemes for direct optical pumping of multiatmosphere CO₂ and N₂O lasers at pump wavelengths in the 1.4-3.6-μm region are discussed. Most of these wavelengths can be generated by solid-state lasers, which are more attractive pump sources than the chemical lasers (HBr, HF) used previously to pump high-pressure CO₂ and N₂O lasers. Including previously studied pump schemes, there are altogether 14 possible pump transitions in CO ₂ and N₂O in the 1.4-4.5-μm region. Numerical laser simulations are carried out to compare all of these pump schemes. Assuming 10 J/cm² pump energy in a pulse of 100 ns FWHM, and 5% output coupling as the only resonator loss, the calculated energy conversion efficiencies are in the range of 6-40%. The pump thresholds are in the range of 0.1-3.1 J/cm²