Multiquantum-well Lasers Research Articles

Carrier transport limited bandwidth of 1.55 μm quantum-well lasers

We present the first measurements of the dynamic response of InGaAs/InGaAsP multiquantum-well lasers which clearly show the effect of the carrier transport phenomena on the modulation response. Using our parasitic-free optical modulation method, we separate an intrinsic RC-like component in the frequency response from normal resonance behavior. The bandwidth is strongly limited by this low-pass rolloff that can be described by a structure-dependent transport time. It is shown that, therefore, the K factor may not be a reasonable quantity for evaluating the ultimate bandwidth.

Calculating the optical properties of multidimensional heterostructures: Application to the modeling of quaternary quantum well lasers

A method for calculating the electronic states and optical properties of multidimensional semiconductor quantum structures is described. The method is applicable to heterostructures with confinement in any number of dimensions: e.g. bulk, quantum wells, quantum wires and quantum dots. It is applied here to model bulk and multiquantum well (MQW) InGaAsP active layer quaternary lasers. The band parameters of the quaternary system required for the modeling are interpolated from the available literature. We compare bulk versus MQW performance, the effects of compressive and tensile strain, room temperature versus high temperature operation and 1.3 versus 1.55 pm wavelength operation. Our model shows that: compressive strain improves MQW laser performance. MQW lasers have higher amplification per carrier and higher differential gain than bulk lasers, however, MQW performance is far from ideal because of occupation of non-lasing minibands. This results in higher carrier densities at threshold than in bulk lasers, and may nullify the advantage of MQW lasers over bulk devices for high temperature operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improvement in the temperature characteristics of 630 nm band InGaAlP multiquantum-well laser diodes using a 15° misoriented substrate

InGaAlP multiquantum-well (MQW) laser diodes were prepared on a (100) GaAs substrate having a 15° misorientation towards the [011] direction. These laser diodes emitted at 632 nm and could operate up to 52°C, under CW conditions. The use of the misoriented substrate was found to improve the MQW heterointerfaces which subsequently enhanced the temperature characteristics of the laser.

Strain effect on K factor, differential gain and nonlinear gain coefficient for InGaAs/InGaAsP strained multiquantum well lasers

The strain effect on the K factor, the differential gain and the nonlinear gain coefficient for InGaAs/InGaAsP tensile-strained and compressive-strained multiquantum well (MQW) lasers is experimentally investigated from the intrinsic modulation response. The differential gain increases with an increase in strain for both types of laser. The strain dependence of the nonlinear gain coefficient is not as high as that of the differential gain. Therefore, the K factor for strained MQW lasers mainly results from the differential gain.

High-power and high-temperature operation of eight-element, monolithic, 780nm MQW laser diode array on 50 μm centres

A 50μm-spaced, eight-element individually addressable laser diode array with an AlGaAs multiquantum well (MQW) active layer lasing at around 780 nm has been fabricated. Highly uniform power/current characteristics up to 100 mW per element at 50°C under CW conditions are realised for the first time. Within the array, variations in the operating currents and the beam characteristics such as the divergence and the wavelength are less than ±4.6% and less than ±2.2%, respectively.

Broadly tunable InGaAsP/InP vertical-coupler filtered laser with low tuning current

A tuning range of 48 nm has been achieved with a tuning current of only 40 mA in a 1.55 mu m InGaAsP/InP multiquantum-well laser based on a grating-assisted vertical coupler intracavity filter. Using a combination of current and voltage tuning a 55 nm tuning range was demonstrated.

Second quantized state oscillation and wavelength switching in strained-layer multiquantum-well lasers

The dependence of lasing wavelength on cavity length has been systemically studied in strained-layer single, double, and triple quantum-well InGaAs lasers. Lasing from the second quantized state has been observed for the first time in double and triple quantum-well lasers. A wide range (∼500 Å) wavelength switching between the first and second quantized states has been demonstrated by controlling the injection current and/or the operation temperature.

Low-threshold 630 nm-band AlGaInP multiquantum-well laser diodes grown on misoriented substrates

Low-threshold AlGaInP (λL = 635.6 nm) multiquantum-well laser diodes have been successfully fabricated by MOCVD using (100) GaAs substrates with a misorientation of 7° towards the (011) direction. A threshold current of 57 mA at 20°C, the lowest value ever reported for 630 nm-band AIGalnP lasers, has been obtained using transverse-mode stabilised laser diodes (stripe width: 5 μm, cavity length: 350 μm).

Circular beam emission from 1.3 mu m InGaAsP strained-multiquantum-well lasers

The beam divergence in the vertical direction from a graded index separate confinement heterostructure (GRINSCH) multiquantum-well (MQW) laser has been studied. It is demonstrated both theoretically and experimentally that a circular beam MQW laser can be produced by choosing appropriate thicknesses for the GRINSCH layers, while maintaining other desired laser characteristics. The beam divergence is found to be more affected by the index change induced by injected carriers than by strain in the MQW active layer. Theoretical results are in good agreement with the measurements for 1.3- mu m InGaAsP strained MQW lasers. >

Theoretical and experimental studies of the effects of compressive and tensile strain on the performance of InP-InGaAs multiquantum-well lasers

The authors have studied, both theoretically and experimentally, the effects of biaxial strain upon the performance characteristics of broad-area InP-InGaAsP-In/sub x/Ga/sub 1-x/As (0.33 >

Periodic stratified structure in a multilayer planar optical waveguide

The contribution of a periodic stratified structure to the optical guiding properties of a multilayer planar waveguide is analyzed. We present an equivalent-layer method for the periodic stratified structure in a multiplayer waveguide that not only allows the whole periodic stratified structure to be treated as a single layer but offers exact solutions for the propagation constant of the waveguide and the power-confinement factor within the periodic stratified structure in a multilayer waveguide. This method is applied to study the optical guiding characteristics of multiquantum-well waveguides, such as the propagation constant, the field distribution, the power-confinement factor, and the group refractive index. The effective indices and the confinement factors of several practical GaInAsP/InP multiquantum-well lasers are calculated and analyzed.

Direct measurement of the transparency current and valence band effective masses in tensile and compressively strained InGaAs/InP multiple quantum-well laser amplifiers

Transparency current densities of 250 and 160 A/cm2 per well at the bandgap wavelength are reported for compressively and tensile strained multi quantum-well laser amplifiers. A strong wavelength dependence of the transparency current is found, due to level broadening, which shows that the threshold current of a quantum-well laser is inherently loss limited, rather than transparency limited. The spectral and polarizational dependence of the gain is measured and analyzed. From this it is concluded that the compressively (1.8%) and tensile (1.6%) strained quantum-well laser amplifiers exhibit valence band effective masses of 0.07 m0 and 0.1 m0, respectively, which shows that they both have a nearly symmetric band structure.

High-frequency modulation in characteristics in 1.5 μm compressively strained multiquantum well lasers with large number of wells

The high-frequency modulation characteristics in 1.5 μm compressively strained multiquantum well (MQW) lasers with a large number of wells (Nw = 20) are measured using an optical modulation technique. The damping K factor and differential gain are improved by increasing the number of wells. The nonlinear gain coefficient is nearly the same. For a 20 well MQW laser with 1.5% strain, the 3 dB bandwidth is estimated to be 29 GHz at 15 mW output.

Gain measurements in InGaAs/InGaAsP multiquantum-well broad-area lasers

The paper describes gain measurements in InGaAs/InGaAsP multiquantum-well lasers at 1.55 μm derived from the spontaneous emission under current injection. The gain spectrum in a broad-area laser device is determined from the spontaneous emission spectrum on using the measured differential quantum efficiency and the loss conditions at the lasing wavelength at threshold. Spectral measurements from 1.0 to 1.7 μm with intensity resolution over four orders of magnitude clearly exhibit contributions from the barriers, and indicate that a nonthermal equilibrium may exist between the well and barrier materials. Band-filling effects in the well can be seen in the absorption spectra for low injection currents. Gain spectra are obtained for carrier injection levels from 1% of threshold to 1.5 times threshold.

Room-temperature operation of MOCVD-grown GaInAs/InP strained-layer multiquantum-well lasers in the 1.8- mu m range

Summary form only given. The authors report the first successful room-temperature pulsed operation of InGaAs strained-layer multiquantum-well (SL-MQW) injection lasers grown by MOVPE (metal-organic vapor-phase epitaxy) on InP substrates in the 1.8- mu m range. The threshold current density and external differential quantum efficiency of 10- mu m-wide ridge waveguide lasers were 2.5 kA/cm/sup 2/ and 5% for 1-mm and 400- mu m-long cavities, respectively. The laser structure consists of four 35-AA-wide In/sub 0.75/Ga/sub 0.25/As SL-QWs separated by 65-AA-wide barrier layers of lattice-matched InGaAs. The MQW is further sandwiched between 150 nm of InGaAsP ( lambda =1.3 mu m) and 2 mu m of InP on both sides. >

1.55 μm multiquantum-well lasers with record performance obtained by atmospheric pressure MOVPE using organometallic phosphorus precursor

The recently available precursor biphosphinoethane (BPE) was used, alongside with phosphine and with tertbutylphosphine (TBP), to grow advanced multiquantum-well (MQW) laser wafers with five quaternary, compressive strained wells. The lowest threshold current densities and the lowest optical losses were obtained with BPE. In particular, the lowest threshold current density, 328 A/cm2, is a record among published values for lasers with five wells. In this comparison, the wafer grown with phosphine came a close second and that grown with TBP was third.

Room-temperature CW operation of 610 nm band AlGaInP strained multiquantum well laser diodes with multiquantum barrier

610 nm band AlGaInP compressively strained multiquantum-well laser diodes with a multiquantum barrier have been successfully fabricated by MOCVD using (100) GaAs substrates with a misorientation of 9° towards the (011) direction. The oscillating wavelength at 25°C is 615nm, which is the shortest ever reported for AlGaInP laser diodes operating at 25°C.

Transverse-mode stabilised 630 nm-band AlGaInP strained multiquantum-well laser diodes grown on misoriented substrates

Transverse-mode stabilised AlGaInP (γL = 638 nm) compressively strained multiquantum-well laser diodes have been successfully fabricated by MOCVD using (100) GaAs substrates with a misorientation of 7° towards the (011) direction. The maximum CW operation temperature was 60°C, which is the highest value for 630 nm-band AlGalnP lasers so far. These lasers operated for more than 2000 h without significant degradation under 3 mW at 40°C.

High-speed 1.5- mu m compressively strained multi-quantum well self-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5- mu m MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9*10/sup -12/ m/sup 3//s. The estimated intrinsic maximum bandwidth is 68 GHz. >

Modulation characteristics of InP-based MQW lasers: the impact of biaxial compressive and tensile strain

The authors relate observed modulation characteristics of strained In/sub x/Ga/sub 1-x/As-InP (0.33<or=x<or=0.73) MQW (multi-quantum-well) separate-confinement-heterostructure (SCH) lasers to properties of the band structures of biaxially strained In/sub x/Ga/sub 1-x/As quantum wells. The differential gain was found to increase significantly for both compressive and tensile strain with respect to its lattice-matched value, indicating that strained devices will have larger 3-dB bandwidths than their lattice-matched counterparts. The authors have also measured the microwave responses of both strained and lattice-matched devices and found that the bandwidth of the lattice-matched devices are 3 and 5 GHz for devices with 63% In in the quantum wells. In addition, by measuring the turn-on delay time at various levels of drive current, the authors have measured a spontaneous lifetime of 0.78 ns for compressively strained ridge waveguide devices. They also calculated Auger coefficients for devices with 73% In in the wells.