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.     

1.27 /spl mu/m metamorphic InGaAs quantum well lasers on GaAs substrates

Pulsed operation at a wavelength of 1.27 /spl mu/m from metamorphic ridge-waveguide (RWG) InGaAs quantum well lasers on GaAs substrates using an alloy graded buffer, grown by molecular beam epitaxy, is demonstrated. Laser performance is anisotropic along the two orthogonal <1/spl plusmn/10> directions with lower threshold currents along the <1-10> direction. Post-growth rapid thermal annealing further reduces threshold currents. For 4 /spl mu/m-wide RWG lasers, minimum threshold current densities are 1-2.5 kA/cm/sup 2/ for cavity lengths 0.6-1.5 mm.     

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.     

Electroabsorption modulator using intersubband transitions in GaN-AlGaN-AlN step quantum wells

We calculate the high-speed modulation properties of an electroabsorption modulator for /spl lambda/=1.55 /spl mu/m based on Stark shifting an intersubband resonance in GaN-AlGaN-AlN step quantum wells. In a realistic simulation assuming an absorption linewidth /spl Gamma/=100 meV we obtain an RC-limited electrical f/sub 3dB//spl sim/60 GHz at an applied voltage swing V/sub pp/=2.8 V. We also show that a small negative effective chirp parameter suitable for standard single-mode fiber is obtained and that the absorption is virtually unsaturable. The waveguide is proposed to be based on the plasma effect in order to simultaneously achieve a strong confinement of the optical mode, a low series resistance, and lattice-matched cladding and core waveguide layers. Extrapolated results reflecting the decisive dependence of the high-speed performance on the intersubband absorption linewidth /spl Gamma/ are also given. At the assumed linewidth the modulation speed versus signal power ratio is on a par with existing lumped interband modulators based on the quantum confined Stark effect.     

High performance 1.28 /spl mu/m GaInNAs double quantum well lasers

The use of multiple quantum wells and GaAs barriers favours the temperature stability and modulation bandwidth of GaInNAs lasers. It is shown that a very low threshold current density and a high characteristic temperature can be achieved for GaInNAs/GaAs double quantum well lasers, emitting at 1.28 /spl mu/m, when grown by molecular beam epitaxy under favourable conditions.     

Electrically-pumped vertical-cavity lasers with Al/sub x/O/sub y/-GaAs reflectors

We have fabricated the first electrically-pumped vertical-cavity surface-emitting lasers (VCSELs) which use oxide-based distributed Bragg reflectors (DBRs) on both sides of the gain region. They require a third the epitaxial growth time of VCSELs with semiconductor DBRs. We obtain threshold currents as low as 160 /spl mu/A in VCSELs with an active area of 8 /spl mu/m/spl times/8 /spl mu/m using a two quantum well InGaAs-GaAs active region. By etching away mirror pairs from the top reflector, quantum efficiencies as high as 61% are attained, while still maintaining a low threshold current of 290 /spl mu/A.     

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.     

Vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

Molecular beam epitaxy-grown 0.98-/spl mu/m vertical-cavity surface-emitting lasers (VCSELs) with a three-stack submonolayer (SML) InGaAs quantum-dot (QD) active region and fully doped Al/sub x/Ga/sub 1-x/As-GaAs DBRs was studied. Large-aperture VCSELs demonstrated internal optical losses less than 0.1% per one pass. Single-mode operation throughout the whole current range was observed for SML QD VCSELs with the tapered oxide apertures diameter less than 2 /spl mu/m. Devices with 3-/spl mu/m tapered-aperture showed high single-mode output power of 4 mW and external quantum efficiency of 68% at room temperature.     

Laterally coupled DBR laser emitting at 1.55 /spl mu/m fabricated by focused ion beam lithography

By using focused ion beam lithography high performance 1.55-/spl mu/m emitting distributed Bragg reflector lasers were realized suitable for high-speed optical telecommunication. Threshold currents of 8 mA and continuous-wave efficiencies of 0.37 W/A for 600-/spl mu/m-long devices were achieved. Stable single-mode emission with sidemode suppression ratios of > 40 dB were observed for the entire operation range. By relative intensity noise measurements an intrinsic 3-dB modulation frequency of > 10 GHz was estimated for a single-mode output power of 23 mW.     

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.     

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-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.     

Low-threshold continuous-wave 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs

We present the first continuous-wave (CW) edge-emitting lasers at 1.5 /spl mu/m grown on GaAs by molecular beam epitaxy (MBE). These single quantum well (QW) devices show dramatic improvement in all areas of device performance as compared to previous reports. CW output powers as high as 140 mW (both facets) were obtained from 20 /spl mu/m /spl times/ 2450 /spl mu/m ridge-waveguide lasers possessing a threshold current density of 1.06 kA/cm/sup 2/, external quantum efficiency of 31%, and characteristic temperature T/sub 0/ of 139 K from 10/spl deg/C-60/spl deg/C. The lasing wavelength shifted 0.58 nm/K, resulting in CW laser action at 1.52 /spl mu/m at 70/spl deg/C. This is the first report of CW GaAs-based laser operation beyond 1.5 /spl mu/m. Evidence of Auger recombination and intervalence band absorption was found over the range of operation and prevented CW operation above 70/spl deg/C. Maximum CW output power was limited by insufficient thermal heatsinking; however, devices with a highly reflective (HR) coating applied to one facet produced 707 mW of pulsed output power limited by the laser driver. Similar CW output powers are expected with more sophisticated packaging and further optimization of the gain region. It is expected that such lasers will find application in next-generation optical networks as pump lasers for Raman amplifiers or doped fiber amplifiers, and could displace InP-based lasers for applications from 1.2 to 1.6 /spl mu/m.     

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.     

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.     

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.     

Broad-stripe near-diffraction-limited mid-infrared laser with a second-order photonic-crystal distributed feedback grating

Electron-beam lithography was used to pattern a second-order photonic-crystal distributed feedback grating onto an antimonide type-II "W" laser emitting at /spl lambda//spl ap/3.7 /spl mu/m. For pulsed optical pumping, the output beam was essentially diffraction-limited up to a stripe width of 150 /spl mu/m, and remained no worse than eight times the diffraction limit for stripes as wide as 600 /spl mu/m. This represents a considerable improvement over all previous mid-infrared semiconductor lasers with such broad stripes.     

Beam steering in high-power CW quantum-cascade lasers

We report the light-current (L-I), spectral, and far-field characteristics of quantum cascade lasers (QCLs) with seven different wavelengths in the /spl lambda/=4.3 to 6.3 /spl mu/m range. In continuous-wave (CW) mode, the narrow-stripe (/spl ap/13 /spl mu/m) epitaxial- side-up devices operated at temperatures up to 340 K, while at 295 K the CW output power was as high as 640 mW with a wallplug efficiency of 4.5%. All devices with /spl lambda//spl ges/4.7 /spl mu/m achieved room-temperature CW operation, and at T=200 K several produced powers exceeding 1 W with /spl ap/10% wallplug efficiency. The data indicated both spectral and spatial instabilities of the optical modes. For example, minor variations of the current often produced nonmonotonic hopping between spectra with envelopes as narrow as 5-10 nm or as broad as 200-250 nm. Bistable beam steering, by far-field angles of up to /spl plusmn/12/spl deg/ from the facet normal, also occurred, although even in extreme cases the beam quality never became worse than twice the diffraction limit. The observed steering is consistent with a theory for interference and beating between the two lowest order lateral modes. We also describe simulations of a wide-stripe photonic-crystal distributed-feedback QCL, which based on the current material quality is projected to emit multiple watts of CW power into a single-mode beam at T=200 K.     

Coupling efficiencies in reflective self-organized lightwave network (R-SOLNET) simulated by the beam propagation method

The reflective self-organized lightwave network (R-SOLNET) enables the formation of self-aligned waveguides in the photorefractive (PR) material between misaligned optical devices by introducing a write beam. The incident write beam from one device and the reflected write beam from the second device induce self-focusing in the PR material and construct a coupling waveguide. A wavelength filter on the waveguide edge is used to facilitate the reflected beam. The beam propagation method reveals that R-SOLNET exhibits higher coupling efficiencies and better tolerances than the one-beam-writing SOLNET and the free-space coupling. The apparent usefulness of R-SOLNET is remarkable for gaps wider than 100 /spl mu/m in 8-/spl mu/m-wide waveguide circuits. For 240-/spl mu/m gap, coupling efficiency better than 50% can be achieved even when the lateral misalignment is as large as 4 /spl mu/m. The results indicate that R-SOLNET may be useful for vertical waveguide constructions of optical z-connections in three-dimensional intrachip optical interconnects and switching systems, as well as for self-aligned optical couplings with devices that cannot emit write beams such as vertical-cavity surface-emitting lasers, photodetectors, and electrooptic switches.     

Low-threshold native-oxide confined narrow-stripe folded-cavity surface-emitting InGaAs-GaAs lasers

Narrow-stripe folded-cavity surface-emitting InGaAs-GaAs lasers are demonstrated, AlAs native-oxide layers above and below waveguide region are employed for current and optical confinement to form narrow-stripe InGaAs-GaAs quantum-well lasers. A low-temperature (400/spl deg/C) selective wet-oxidation technique and an ion-beam-etching technique are used to fabricate insulator confined narrow-stripes and internal 45/spl deg/ deflectors, respectively. Continuous-wave threshold currents as low as 4.5 mA and 59% surface-emitting quantum efficiencies are achieved on the devices with 2-/spl mu/m-wide aperture and a 420-/spl mu/m-long cavity.