Low-threshold operation of 1.34-/spl mu/m GaInNAs VCSEL grown by MOVPE

Low-threshold operation was demonstrated for a 1.34-/spl mu/m vertical-cavity surface-emitting laser (VCSEL) with GaInNAs quantum wells (QWs) grown by metal-organic vapor-phase epitaxy. Optimizing the growth conditions and QW structure of the GaInNAs active layers resulted in edge-emitting lasers that oscillated with low threshold current densities of 0.87 kA/cm/sup 2/ at 1.34 /spl mu/m and 1.1 kA/cm/sup 2/ at 1.38 /spl mu/m, respectively. The VCSEL had a low threshold current of 2.8 mA and a lasing wavelength of 1.342 /spl mu/m at room temperature and operated up to 60/spl deg/C.     

InGaAs-AlAs-AlAsSb coupled quantum well intersubband transition all-optical switch with low switching energy for OTDM systems

We report a novel intersubband transition all-optical switch with low switching energy using InGaAs-AlAs-AlAsSb coupled double quantum wells (C-DQWs) with AlAs spacer layers. Very low saturation energy density of 34 fJ//spl mu/m/sup 2/ was observed for bulk transmittance with wavelength of 1.62 /spl mu/m. Using a waveguide, whose core is 93 periods of the C-DQWs, an all optical switch with a low switching energy of 10 pJ for 10-dB extinction ratio was realized.     

High-efficiency 1.3 /spl mu/m InAsP-GaInP MQW electroabsorption waveguide modulators for microwave fiber-optic links

High-efficiency electroabsorption waveguide modulators have been designed and fabricated using strain-compensated InAsP-GaInP multiple quantum wells at 1.32-/spl mu/m wavelength. A typical 200-/spl mu/m-long modulator exhibits a fiber-to-fiber optical insertion loss of 9 dB and an optical saturation intensity larger than 10 mW. The 3-dB electrical bandwidth is in excess of 20 GHz with a 50-/spl Omega/ load termination. When used in an analog microwave fiber-optic link without amplification, a RF link efficiency as high as -38 dB is achieved at 10 mW input optical carrier power. These analog link characteristics are the first reported using MQW electroabsorption waveguide modulators at 1.32 /spl mu/m.     

Intersubband absorption saturation in InGaAs-AlAsSb quantum wells

We present intersubband absorption saturation studies in InGaAs-AlAsSb quantum wells. We carried out a density matrix calculation to simulate the pulsed excitation condition after including the dephasing time and the short pulse profile to estimate the saturation intensity (I/sub S/). We compare the calculated results with measurements for both resonant and nonresonant excitation. We also present our results on the effect of pulsewidth on Is estimation.     

High-power optically pumped VECSEL using a double-well resonant periodic gain structure

We present the design and fabrication of an optically pumped vertical-external-cavity surface-emitting lasers with double-well resonant periodic gain structure. Each double-well consists of two 4-nm-thick InGaAs strained quantum wells. The double-well provides optimum overlap between the quantum wells and the antinodes of the standing wave of laser signal at high-power and high-temperature operation. The structure is more tolerant to variation of the growth, processing, and operating temperature for maintaining high modal gain. For a 230-/spl mu/m diameter pump spot, over 4-W continuous-wave output with a slope efficiency of 39% is demonstrated at 30/spl deg/C without thermal rollover.     

Room-temperature 2.81-/spl mu/m continuous-wave operation of GaInAsSb-AlGaAsSb laser

GaInAsSb-AlGaAsSb multiple quantum-well (QW) lasers with an emission wavelength of 2.81 /spl mu/m are reported. The ridge waveguide lasers with highly strained QWs show continuous-wave laser emission up to 25/spl deg/C; in pulsed mode, the lasers operate up to 60/spl deg/C. For pulsed operation, a threshold current density of 360 A/cm/sup 2/ is found for devices with 30-/spl mu/m stripe width and 2-mm cavity length at room temperature. A low threshold current density at infinite length of 248 A/cm/sup 2/ is derived.     

1.4-/spl mu/m InGaAsP-InP strained multiple-quantum-well laser for broad-wavelength tunability

InGaAsP-InP strained multiple-quantum-well (MQW) lasers for extended wavelength tunability in external cavity operation were designed, fabricated, and tested. The active layer was a strain compensated structure consisting of three 3.2/spl plusmn/0.3 nm and three 6.4/spl plusmn/0.3 nm 1.0% compressive strained wells and five 10.3/spl plusmn/0.3 nm 0.45% tensile strained barrier layers. A 2-/spl mu/m-wide ridge waveguide laser of length 250 /spl mu/m, when used in a grating external cavity and with no coatings to alter the reflectivity of the facets, was observed to operate over a range >110 nm. The lasers were designed for applications in trace gas and liquid detection with the goal to maximize the tunable range when operated in external cavities and with no facet coatings.     

Performance comparison of GaInNAs vertical-cavity semiconductor optical amplifiers

This paper reports on theoretical and experimental investigations of the influence of the number of GaInNAs quantum wells (QWs) on performance of 1.3-/spl mu/m vertical-cavity semiconductor optical amplifiers (VCSOAs). Full characterization is carried out for two optically pumped VCSOAs with 6 and 15 QWs in the active layer. The 15-QW amplifier is found to be more efficient for amplification purposes but the highest gain to date was obtained for a 6-QW GaInNAs VCSOA, 19-dB on-chip gain in single-mode operation, having a top mirror reflectivity of 97.7%. At high-gain and for low enough reflectivity, the intrinsic noise figure is smaller than 5 dB.     

High-performance 1.06-/spl mu/m selectively oxidized vertical-cavity surface-emitting lasers with InGaAs-GaAsP strain-compensated quantum wells

We present the first room-temperature continuous-wave operation of high-performance 1.06-/spl mu/m selectively oxidized vertical-cavity surface-emitting lasers (VCSEL's). The lasers contain strain-compensated InGaAs-GaAsP quantum wells (QW's) in the active region grown by metalorganic vapor phase epitaxy. The threshold current is 190 /spl mu/A for a 2.5/spl times/2.5 /spl mu/m/sup 2/ device, and the threshold voltage is as low as 1.255 V for a 6/spl times/6 /spl mu/m/sup 2/ device. Lasing at a wavelength as long as 1.1 /spl mu/m was also achieved. We discuss the wavelength limit for lasers using the strain-compensated QW's on GaAs substrates.     

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.     

Feasibility study for degenerate two-photon gain in a semiconductor microcavity

We analyze the magnitude of degenerate two-photon gain of several quantum wells (QWs) in a resonant microcavity which is pumped off-resonantly by an optical field. A set of coupled phenomenological rate equations for electron-hole pairs and photons is derived. In the framework of this model, we make a realistic prediction of the time-integrated two-photon gain and find that a /spl lambda/-cavity containing 11 QWs would give a maximal amplification of /spl sim/2.3% for a peak intensity of /spl sim/80 MW/cm/sup 2/. A better insight into the dependence of the gain on the various physical parameters is given by an analytical formula resulting from various approximations on the rate equations.     

Optical beam steering using InGaAsP multiple quantum wells

We report an efficient optical beam steering device based on InGaAsP multiple quantum wells. An area-selective zinc in-diffusion process is used to define highly localized p-n junctions through which electrical currents are injected into the quantum wells. The extent of the lateral spreading of the electrical carriers can be optimized by selecting the appropriate diffusion depth. Using a twin-parallel-stripe structure, an optical beam at a wavelength of 1.51 /spl mu/m was steered over a 17-/spl mu/m range using dc electrical currents of less than 13 mA.     

Low-threshold piezoelectric-strained InGaAs-GaAs QW lasers grown on (211)B oriented GaAs substrates

We report the operation of strained layer In/sub 0.20/Ga/sub 0.80/As quantum well lasers grown on (211)B GaAs substrates, thus incorporating a piezoelectric field. Growth was by atmospheric pressure metal-organic vapor phase epitaxy (MOVPE). The threshold current density of a 1000 /spl mu/m/spl times/75 /spl mu/m device is 91 A/spl middot/cm/sup -2/ and waveguide transparency is estimated at 32 A/spl middot/cm/sup -2/ for a simple separate confinement heterostructure (SCH) emitting at 982 nm.     

Broad-band superluminescent light-emitting diodes incorporating quantum dots in compositionally modulated quantum wells

We propose and demonstrate a technique for tailoring the emission bandwidth of /spl sim/1.3 /spl mu/m quantum dot superluminescent light-emitting diodes. A broadening of the emission is achieved by incorporating the InAs quantum dot layers in InGaAs quantum wells of different indium compositions. These structures exhibit a broader and flatter emission compared to a simple dot-in well structure comprised of wells of identical indium composition.     

High-power 1.5-/spl mu/m InGaAsP-InP slab-coupled optical waveguide amplifier

We report the first demonstration of a high-power semiconductor optical amplifier (SOA) based on the slab-coupled optical waveguide concept. This concept allows the realization of SOAs having large fundamental optical modes, low loss, and small optical confinement factor. These attributes support large output saturation power, long length for efficient heat removal, and direct butt-coupling to single-mode fibers. The 1.5-/spl mu/m InGaAsP-InP quantum-well amplifier described here has a length of 1 cm, 1/e/sup 2/ intensity widths of 4 /spl mu/m (vertical) and 8 /spl mu/m (horizontal), a fiber-to-fiber gain of 13 dB, and a fiber-coupled output saturation power of 630 mW (+28 dBm). The measured butt-coupling efficiency between the amplifier and SMF-28 is 55%. Thus, the output saturation power of the amplifier itself is approximately 1.1 W (+31 dBm).     

Low noise RF MOSFETs on flexible plastic substrates

We report a low minimum noise figure (NF/sub min/) of 1.1 dB and high associated gain (12 dB at 10 GHz) for 16 gate-finger 0.18-/spl mu/m RF MOSFETs, after thinning down the Si substrate to 30 /spl mu/m and mounting it on plastic. The device performance was improved by flexing the substrate to create stress, which produced a 25% enhancement of the saturation drain current and lowered NF/sub min/ to 0.92 dB at 10 GHz. These excellent results for mechanically strained RF MOSFETs on plastic compare well with 0.13-/spl mu/m node (L/sub g/=80 nm) devices.     

Intersubband χ3 in coupled InGaAs-AlGaAs multiplequantum wells

The third-order nonlinearity, χ³(ω,ω,-ω), is measured for a mid-infrared intersubband transition in strained InGaAs-AlGaAs multiple quantum wells (MQW's). The high conduction band offset of this system allows an intersubband transition at 3.1 μm. The level structure of the quantum well is designed to include a meta-stable trapping level, resulting in a peak saturation intensity of 6 MW/cm² at Brewster's angle, approximately 20 times lower than would be found in a square quantum well with similar linewidth. A near-resonant n₂ of 8.4×10^-7 cm²/W at 3.1 μm is calculated. The off-resonant n₂ is also calculated and shown to be attractive at wavelengths as short as 1.55 μm     

4 W single-transverse mode VECSEL utilising intra-cavity diamond heat spreader

An optically pumped semiconductor vertical external cavity surface emitting laser, with high output power and excellent beam quality operating at a wavelength near 1.05 /spl mu/m, is reported. A transparent diamond heat spreader was used for thermal management of the laser. The gain structure grown by molecular beam epitaxy includes 13 compressively strained InGaAs quantum wells. Maximum output power of 4 W with diffraction-limited beam (M/sup 2//spl les/1.15) was achieved using a 2% output coupler and incident pump power of 20 W. It is shown that power scalability is feasible with the presented laser geometry.     

Blue-chirp electroabsorption modulators with very thick quantum wells

Electroabsorption modulators operating at a wavelength of 1.55 /spl mu/m with very thick quantum wells of 19.6 mm were fabricated using InGaAlAs-InAlAs multiple quantum wells. Blue-chirp (/spl alpha/<0) operation for low applied bias was demonstrated with low insertion loss.     

Vertical-cavity amplifying photonic switch at 1.5 /spl mu/m

The development of a fast amplifying switch operating at 1.55-/spl mu/m wavelength is of particular interest as the active element in optical communication systems. We report the first vertical-cavity amplifying photonic switch (VCAPS) at 1.55-/spl mu/m wavelength, with a 14-dB gain and 10-ps commutation time. This structure is fabricated by the epitaxial lift-off technique and is composed of a resonant periodic gain multiple quantum wells active layers sandwiched between a SiO/sub 2/-Au back mirror based on a Si substrate and a Si-SiO/sub 2/ front mirror.