Long wavelength GaInAsSb-AlGaAsSb distributed-feedback lasers emitting at 2.84 /spl mu/m

Room-temperature continuous-wave operation of a singlemode GaInAsSb/GaSb/AlGaAsSb distributed feedback (DFB) laser is presented at a record long emission wavelength for this material system of 2.843 /spl mu/m. The threshold current at 20/spl deg/C is 75 mA. Mode selection was realised by metal gratings laterally patterned to a ridge waveguide. By varying the grating period, DFB emission from 2.738 up to 2.843 /spl mu/m is obtained.     

Room-temperature low-threshold type-II quantum-well lasers at 4.5 /spl mu/m

We report optically pumped InAs-InGaSb-InAs-AlSb type-II quantum-well lasers at 3.84-4.48 /spl mu/m. Lasing was observed at temperatures up to 300 K with a characteristic temperature T/sub 0/ of 61.6 K. The average absorbed threshold power was only 0.7 mW at 220 K, and 2.7 mW at 300 K with a pulselength of 650 ns and a repetition rate of 2 kHz. At 49 K, the continuous-wave (CW) output power was 4.2 mW/facet with an absorbed threshold pump power of 31.5 mW and an absorbed pump power of 62 mW, indicating a differential quantum efficiency of 54% for two facets.     

Study on high-temperature performances of 1.3-/spl mu/m InGaAsP-InP strained multiquantum-well buried-heterostructure lasers

Stripe-width and cavity length dependencies of high-temperature performances of 1.3-/spl mu/m InGaAsP-InP well-designed buried-heterostructure strained multiquantum-well (MQW) lasers were investigated. The threshold currents as low as 4.5/10.5 mA and slope efficiencies as high as 0.48/0.42 mW/mA at 25/spl deg/C/85/spl deg/C were obtained in the MQW lasers with 1.5-/spl mu/m width, 250-/spl mu/m length, and 0.3/0.85 facet reflectivity. With temperature increasing from 25/spl deg/C to 85/spl deg/C, the MQW lasers exhibited lower output power degradation, the minimum value was 1.78 dB at an operation current of 45 mA. The MQW lasers were suitable for application in optical access networks.     

Improved high-temperature performance of 1.3-1.5-/spl mu/m InNAsP-InGaAsP quantum-well microdisk lasers

We report for the first time lasing action in the InNAsP-InGaAsP material system. Dramatic improvement in lasing action in a microdisk cavity was observed at elevated temperature up to 70/spl deg/C, which is about 120/spl deg/C higher than that of InGaAs-InGaAsP microdisk. This resulted in the first optically pumped InNAsP-InGaAsP microdisk lasers capable of above room-temperature lasing. The improvement of lasing temperature can be attributed to a large conduction band offset between the quantum well and barriers in the InNAsP-InGaAsP material system.     

2.5-mW single-mode operation of 1.55-/spl mu/m buried tunnel junction VCSELs

We present 1.55-/spl mu/m wavelength buried tunnel junction InGaAlAs-InP vertical-cavity surface-emitting lasers with low threshold current and high efficiency. An improved mirror design is accomplished with high-reflective low-loss epitaxial InGaAlAs-InAlAs and hybrid dielectric CaF/sub 2/-ZnS-Au layer stacks, respectively. Lasers with aperture diameters of only around 5 /spl mu/m exhibit continuous-wave single-mode output powers at room temperature well beyond 2 mW. Threshold voltages and series resistances as low as 0.9 V and 30-40 /spl Omega/ have been measured. The spectral behavior shows excellent performance over the relevant current and temperature range.     

Room-temperature CW operation of distributed-feedback buried-heterostructure InGaAsP/InP lasers emitting at 1.57 ?m

Room temperature CW operation of distributed-feedback buried-heterostructure InGaAsP/InP lasers emitting at 1.57 ?m was achieved. A DC threshold of about 250 mA at 25°C and a temperature coefficient of the lasing wavelength of 1.0 ?/°C were obtained. Some of these lasers manifested single longitudinal mode operation both in DC condition and in deeply modulated condition at 500 Mbit/s.     

90/spl deg/C continuous-wave operation of 1.83-/spl mu/m vertical-cavity surface-emitting lasers

Excellent lasing performance is demonstrated for a 1.83-/spl mu/m InGaAlAs-InP vertical-cavity surface-emitting laser (VCSEL) utilizing the buried tunnel junction technology. Threshold currents as low as 190 /spl mu/A at 20/spl deg/C and operating temperatures as high as 90/spl deg/C have been measured. These values are the best ones reported so far for long-wavelength VCSELs.     

Dispersion-induced ultrafast pulse reshaping in 1.55-/spl mu/m InGaAs-InGaAsP optical amplifiers

Using the Foreman effective mass Hamiltonian, the electronic structure of the valence band and the interband dipole matrix elements in In/sub x/Ga/sub 1-x/As-In/sub y/Ga/sub 1-y/As/sub z/P/sub 1-z/ quantum-well optical amplifiers are calculated, taking into account the valence band mixing and the biaxial strain. The optical field of the amplified pulse is calculated by solving the wave equation with the computed polarization as a source term. A novel wavelet transform is introduced in analyzing the pulse chirp imposed by the optical amplifier. In the linear propagation regime, the spectrum of the amplified pulse can be either red-shifted or blue-shifted with respect to its initial center frequency, depending on the local gain dispersion spanned by the pulse spectrum. The output pulse shape can be retarded or advanced, depending on the local gain and group velocity dispersion. Furthermore, an initially unchirped pulse centered in the tail of the gain spectrum is significantly reshaped after propagating 600 /spl mu/m, and its spectrum is broadened and distorted considerably. In the spectral region where both gain and group velocity change rapidly, the frequency chirp for a linearly chirped input pulse is significantly weakened after propagation.     

Doping-type dependence of turn-on delay time in 1.3-/spl mu/m InGaAsP-InP modulation-doped strained quantum-well lasers

The dependence of turn-on delay time on doping type in 1.3-/spl mu/m InGaAsP-InP modulation-doped (MD) strained quantum-well (QW) lasers is theoretically investigated, based on the detailed band structure model including the band mixing effects. It is found that the turn-on delay time in n-type MD lasers is reduced to 1/4 that of undoped lasers due to both a lower threshold current and a reduced carrier lifetime. The reduction of the delay time is smaller in p-type MD lasers, however, because of the increased threshold current. These results show that the n-type MD-QW lasers are superior for high-speed modulation under zero-bias conditions.     

80/spl deg/C continuous-wave operation of 2.01-/spl mu/m wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers

Electrically pumped buried tunnel junction InGaAlAs-InP vertical-cavity surface-emitting lasers (VCSELs) with self-adjusted lateral current and optical confinement and record emission wavelengths beyond 2 /spl mu/m are presented. Front and back side mirrors are realized using 31.5 epitaxial layer pairs of alternating InGaAs-InAlAs and a dielectric 2.5 pair CaF/sub 2/-a-Si layer stack. The devices show single-mode continuous-wave operation up to heat sink temperatures over 80/spl deg/C. The maximum output power at 20/spl deg/C reaches 0.43 mW, threshold current and voltage are as low as 0.66 mA and 0.73 V, respectively. To reach the long emission wavelength, we use an optimized active region comprising heavily strained quantum wells. High-resolution X-ray diffraction and photoluminescence measurements reveal excellent material quality without relaxation in the quantum wells.     

High-T/sub 0/ strain-compensated InGaAsSb-AlGaAsSb quantum-well lasers emitting at 2.43 /spl mu/m

Strain-compensated InGaAsSb-AlGaAsSb quantum-well (QW) lasers emitting near 2.5 /spl mu/m have been grown by solid-source molecular beam epitaxy. The relatively high arsenic composition causing a tensile strain in the Al/sub 0.25/GaAs/sub 0.08/Sb barriers lowers the valence band edge and the hole energy level, leading to an increased hole confinement and improved laser performance. A 60% external differential efficiency in pulsed mode was achieved for 1000-/spl mu/m-long lasers emitting at 2.43 /spl mu/m. A characteristic temperature T/sub 0/ as high as 163 K and a lasing-wavelength temperature dependence of 1.02 nm//spl deg/C were obtained at room temperature. For 2000 /spl times/ 200 /spl mu/m/sup 2/ broad-area three-QW lasers without lateral current confinement, a low pulsed threshold of 275 A/cm/sup 2/ was measured.     

Lasing characteristics of GaInAsP-InP strained quantum-well microdisk injection lasers with diameter of 2-10 /spl mu/m

We have obtained pulsed lasing operation in 2-5-/spl mu/m diameter microdisk injection lasers using GaInAsP-InP compressively-strained multiple-quantum-well (MQW) wafers around room temperature. The effective cavity volume of the 2-/spl mu/m-diameter device is the smallest among those for any type of electrically-pumped lasers. The threshold current of this device was as low as 0.2 mA. Cavity modes in emission spectra observed under CW conditions coincide well with theoretically predicted whispering gallery modes. Further reduction of diameter to less than 1.5 /spl mu/m will realize the condition for spontaneous emission almost coupling into a single mode, which results in thresholdless lasing operation.     

High-temperature 4.5-/spl mu/m type-II quantum-well laser with Auger suppression

Laser emission at 4.2-4.5 /spl mu/m has been observed at temperatures up to 310 K in pulsed optical pumping experiments on type-II quantum-well (QW) lasers with four constituents in each period (InAs-Ga/sub 1-x/In/sub x/Sb-InAs-AlSb). The characteristic temperature, T/sub 0/, is 41 K, and a peak output power exceeding 2 W/facet is observed at 200 K. The power conversion efficiency per facet of /spl ap/0.2% up to 200 K is within a factor of 2 of the theoretical value. The 300 K Auger coefficient of 4/spl times/10/sup -27/ cm/sup 6//s extracted from the threshold pump intensity demonstrates that Auger losses have been suppressed by a factor of four.     

1.5-/spl mu/m InGaAsP-InP slab-coupled optical waveguide lasers

We report the demonstration of high-power semiconductor slab-coupled optical waveguide lasers (SCOWLs) operating at a wavelength of 1.5 /spl mu/m. The lasers operate with large (4/spl times/8 /spl mu/m diameter) fundamental mode and produce output power in excess of 800 mW. These structures have very low loss (/spl sim/0.5 cm/sup -1/) enabling centimeter-long devices for efficient heat removal. The large fundamental mode allows 55% butt-coupling efficiency to standard optical fiber (SMF-28). Comparisons are made between SCOWL structures having nominal 4- and 5-/spl mu/m-thick waveguides.     

Continuous-wave operation of GaInNAsSb distributed feedback lasers at 1.5 /spl mu/m

GaAs-based singlemode emission at 1.5 /spl mu/m has been realised for the first time in continuous-wave operation. GaInNAsSb active-layer material and GaAsN strain-compensating barriers have been used in combination with lateral distributed feedback. Laser diodes with a threshold current of 95 mA, an external efficiency of 0.15 W/A and a maximum output power of more than 10 mW could be demonstrated. A sidemode suppression ratio better than 31 dB could be realised at a singlemode emission wavelength of 1496 nm.     

High-speed Modulation of InGaAs: Sb-GaAs-GaAsP quantum-well vertical-cavity surface-emitting lasers with 1.27-/spl mu/m emission wavelength

1.27-/spl mu/m InGaAs: Sb-GaAs-GaAsP vertical-cavity surface-emitting lasers (VCSELs) were grown by metal-organic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% as the temperature raised from room temperature to 70/spl deg/C. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is measured to be 10.7 GHz with modulation current efficiency factor (MCEF) of /spl sim/5.25 GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C.     

Continuous-wave operation up to 36/spl deg/C of 1.3-/spl mu/m GaInAsP-InP vertical-cavity surface-emitting lasers

We introduced ion-beam assisted deposition in order to improve the quality of Al/sub 2/O/sub 3/ and SiO/sub 2/, which were used as part of the mirrors of 1.3-/spl mu/m GaInAsP-InP vertical-cavity surface-emitting lasers (VCSELs). The refractive index of Al/sub 2/O/sub 3/ was improved to 1.63 from 1.56 and the one of SiO/sub 2/ increased to 1.47 from 1.45. Low-threshold room-temperature continuous-wave (CW) operation of 1.3-/spl mu/m VCSEL with the improved mirrors was demonstrated. The threshold current was 2.4 mA at 20/spl deg/C. The CW operating temperature was raised to 36/spl deg/C, which is a record high temperature for 1.3-/spl mu/m VCSEL.     

Coherence-collapse threshold of 1.3-/spl mu/m semiconductor DFB lasers

The onset of the coherence-collapse threshold is theoretically and experimentally studied for monomode 1.3-/spl mu/m antireflection/high reflection distributed-feedback lasers taking into account facet phase effects. The variation of the coherence collapse from chip to chip due to the facet phase is in the range of 7 dB and remains almost independent of the grating coefficient. Lasers that operate without coherence collapse under -15-dB optical feedback, while exhibiting an efficiency as high as 0.30 W/A, are demonstrated. Such lasers are adequate for 2.5 Gb/s isolator-free transmission without under the International Telecommunication Union recommended return loss.     

Recombination mechanisms in 1.3-/spl mu/m InAs quantum-dot lasers

We measure, in real units, the radiative and total current density in high performance 1.3-/spl mu/m InAs quantum-dot-laser structures. Despite very low threshold current densities, significant nonradiative recombination (/spl sim/80% of the total recombination) occurs at 300 K with an increasing fraction at higher current density and higher temperature. Two nonradiative processes are identified; the first increases approximately linearly with the radiative recombination while the second increases at a faster rate and is associated with the loss of carriers to either excited dot states or the wetting layer.     

1.55-/spl mu/m spot-size converter integrated laser diode with conventional buried-heterostructure laser process

A 1.55-/spl mu/m spot-size converter integrated laser diode is demonstrated with conventional buried-heterostructure laser process. For the spot-size converter, we employed a double-waveguide structure in which a ridge-based passive waveguide was incorporated. The passive waveguide was optically combined with a laterally tapered active waveguide to control mode size. The threshold current was measured to be 5 mA together with high slope efficiency of 0.45 W/A. The beam divergence angles in the horizontal and vertical directions were as small as 9.0/spl deg/ and 7.8/spl deg/, respectively.