Flip-chip bonded arrays of monolithically integrated, microlensedvertical-cavity lasers and resonant photodetectors

We present flip-chip bonded arrays of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The VCLs and photodetectors are integrated using a novel structure that allows through-the-substrate emission and detection without compromising device performance. Substrate-side microlenses have been integrated to take advantage of the through-the-substrate architecture. Flip-chip bonded VCLs exhibit threshold currents as low as 135 μA with differential efficiencies of ~53%. The detectors have the same operating wavelength as the VCLs and responsivities of 0.48 A/W, corresponding to 60% absorption, with optical bandwidths of 7 nm     

Monolithic integration of microlensed resonant photodetectors andvertical cavity lasers

Monolithic integration of high performance microlensed resonant photodetectors and vertical cavity lasers (VCLs) from a single epitaxial growth is presented. The VCLs have sub-200 μA threshold currents. Adjacent detectors have the same operating wavelength and responsivities of ~0.4 A/W with ~6 nm optical bandwidths     

Monolithic vertical-cavity laser/p-i-n photodiode transceiver arrayfor optical interconnects

The design, fabrication, and characterization of a 16-element monolithic 850-nm vertical-cavity laser/p-type-intrinsic-n-type (VCL/p-i-n) photodiode transceiver array for optical interconnects are described. The packaged VCL/p-i-n array exhibits excellent array uniformity over a large temperature range. Packaged VCLs display up to 1 mW of single-mode power and a relative intensity noise below -120 dB/Hz for all currents above threshold at a measuring bandwidth of 2 GHz. The p-i-n photodiodes exhibit a responsivity of 0.535 A/W and a -3-dB bandwidth of 2.3 GHz. A microlens array integrated into the packaged VCL/p-i-n device decreases the VCL beam divergence six to seven times. Polarization control with a mean rejection ratio of 22 dB across the VCL array is achieved with the use of oval aperture VCLs     

Low-threshold 840-nm laterally oxidized vertical-cavity lasers using AlInGaAs-AlGaAs strained active layers

We explore the use of a novel strained AlInGaAs-AlGaAs material system to achieve low-threshold current in oxide-apertured vertical-cavity lasers (VCLs) emitting near 850 nm. We report a low continuous-wave (CW) room-temperature threshold current of 290 /spl mu/A from top-emitting, 840-nm VCLs with a 5-/spl mu/m-wide thin-oxide aperture. The low-threshold current has been attributed to the use of strained active layers, which increase the gain and reduce the transparency current. We also studied the effects of post-growth rapid thermal annealing (RTA) on the characteristics of AlInGaAs-AlGaAs VCLs and found that RTA improves the material quality and significantly enhances VCL performance.     

Fabrication and performance of selectively oxidized vertical-cavitylasers

We report the high yield fabrication and reproducible performance of selectively oxidized vertical-cavity surface emitting lasers. We show that linear oxidation rates of AlGaAs without an induction period allows reproducible fabrication of buried oxide current apertures within monolithic distributed Bragg reflectors. The oxide layers do not induce obvious crystalline defects, and continuous wave operation in excess of 650 h has been obtained. The high yield fabrication enables relatively high laser performance over a wide wavelength span. We observe submilliamp threshold currents over a wavelength range of up to 75 nm, and power conversion efficiencies at 1 mW output power of greater than 20% over a 50-nm wavelength range     

A single transverse-mode monolithically integrated long vertical-cavity surface-emitting laser

We present a fully monolithic long vertical-cavity surface-emitting laser operating in the fundamental TEM/sub 00/ transverse mode with output powers up to 7.8 mW. The lasing wavelength is 980 nm and the threshold is 9.1 mA. Pump currents from threshold to rollover produce an output beam with an M/sup 2/<1.08. The laser consists of an InGaAs-GaAs-AlGaAs gain region/semiconductor mirror bonded to a 0.5-mm-thick glass substrate with an integrated curved mirror.     

Single-mode distributed-feedback 761-nm GaAs-AlGaAs quantum-welllaser

We have developed single-mode distributed-feedback 761-nm GaAs-AlGaAs quantum well lasers as sources for O₂ sensing through laser absorption spectroscopy. Devices containing a 4-μm-wide ridge waveguide exhibit low threshold currents of 25 mA and quantum efficiencies greater than 35% at output powers in excess of 25 mW. The spectral linewidths of these devices are 12.0 MHz at 15 mW. Temperature- and current-tuning rates are 0.06 nm/°C and 0.0075 nm/mA (-3.9 GHz/mA), respectively. The devices display smooth, continuous, single-mode wavelength tuning over a 4.2 nm interval     

Resonant cavity-enhanced InGaAs-AlGaAs heterojunctionphototransistors with an optical design for high uniformity and yield

We present uniformity data on resonant cavity-enhanced InGaAs-AlGaAs heterojunction phototransistors (HPT's) with an optical design that promotes high uniformity and yield. The HPT's operate in the wavelength region where the GaAs substrate is transparent and the data show the HPT's to be suitable for vertical integration with optical emitters or modulators to form two-dimensional arrays of smart pixels operating in transmission mode. The absorbing region of the HPT consists of an InGaAs multiple-quantum-well structure where the quantum wells (QW's) have been distributed to make the total absorption in the cavity insensitive to growth variations as well as the spatial matching of the standing wave and absorbing QW's. Theoretically, we estimate the absorption to be 39%±1% of the incident optical power, even at wafer nonuniformities of 12.5%. With these nonuniformities, the resonant wavelength moves ±25 nm, making postgrowth tuning of the wavelength necessary. Experimentally, we show postgrowth tuning of the resonance wavelength without loss in uniformity. The arrays have good uniformity as well as very high responsivities. The average responsivity is 160 A/W ±15% from 927-955 nm. The standard deviation of a typical array is 0.5 nm in resonant wavelength and about 5% of the average responsivity. The difference between maximum and minimum values for an array is typically 3 nm in resonant wavelength and ±10% of the average responsivity     

Low threshold current 1.5-μm buried heterostructure lasers usingstrained quaternary quantum wells

Buried heterostructure lasers operating at a wavelength of 1.5 μm with four compressively strained quaternary quantum wells (strain ~1.8%, thickness ~90 Å) and current blocking layers were made using atmospheric pressure metalorganic chemical vapor deposition. Pulsed room-temperature threshold currents for uncoated devices as low as 4.1 mA and as low as 0.8 mA for devices with high reflectivity mirror coatings are reported. The dependence of threshold current on active region width is consistent with broad-area laser measurements     

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.     

Modeling and performance of wafer-fused resonant-cavity enhancedphotodetectors

We discuss wavelength tuning and its corresponding quantum efficiency modulated by the standing wave effects in a resonant-cavity enhanced (RCE) photodetector. Specific design conditions are made for a thin In_0.53Ga_0.47As (900 Å) photodetector wafer-fused to a GaAs-AlAs quarter wavelength stacks (QWS). Analytic expressions for the calculation of resonant wavelength and standing wave effects are derived, using a hard mirror concept of fixed phase upon reflection, and are found to agree reasonably well with the exact numerical approach, using a transmission matrix method. We then experimentally demonstrate that wavelength tuning as large as 140 nm and its corresponding quantum efficiency modulated by the standing wave effects are clearly observed in our wafer-fused photodetectors, consistent with the predictions. The external quantum efficiency at 1.3 μm wavelength and absorption bandwidth for the wafer-fused RCE photodiodes integrated with an amorphous Si-SiO₂ dielectric mirror are measured to be 94% and 14 nm, respectively. This technique allows the formation of multichannel photodetectors with high quantum efficiency and small crosstalk, suitable for application to wavelength demultiplexing and high-speed, high-sensitivity optical communication systems     

Monolithic oxide-confined multiple-wavelength vertical-cavitysurface-emitting laser arrays with a 57-nm wavelength grading rangeusing an oxidized upper Bragg mirror

Monolithic, oxide-confined, multiple-wavelength vertical-cavity surface-emitting laser arrays with a very large periodic, wavelength grading span of 57 nm (from 968 to 1025 nm) have been achieved under room temperature, continuous-wave operation, with threshold currents of 4.5 mA±1.5 mA. Almost linear wavelength grading is achieved by organometallic vapor phase epitaxial growth on a patterned substrate. An extended wavelength range is achieved by minimizing the optical loss dispersion by scaling the growth rate of all the epilayers and using a selectively-oxidized upper DBR mirror with a flattened optical reflectance spectrum, plus the higher differential optical gain provided by compressively-strained In_0.2Ga_0.8As-GaAs quantum wells     

GaInAsP dual wavelength laser

The fabrication and performance characteristics of a dual wavelength laser emitting near 1.3 μm and 1.55 μm are described. The lasers are of the etched mesa buried heterostructure type, and utilise semi-insulating InP layers both the lateral optical confinement and current confinement. The 1.55 μm emission is at a single wavelength by virtue of the frequency selective feedback provided by a grating etched on the substrate. The lasers have threshold currents in the 20 to 40 mA range, and have quantum efficiencies comparable to single emitter lasers     

Design and realization of InGaAs/GaAs strained layer DFB quantumwell lasers

Optical waveguiding in an InGaAs/GaAs strained-layer distributed feedback (DFB) quantum well laser is investigated using the one-dimensional shooting method presented. The numerical approach is used to optimize the waveguide geometry and to calculate the corrugation period and the coupling factor for the integrated Bragg grating. The quantum well DFB structure designed according to the numerical calculations for an emission wavelength of 982 nm was realized for the first time entirely by molecular beam epitaxy (MBE) growth. Thus, side-mode suppression ratios of 49 dB, threshold currents of 7 mA and quantum efficiencies of 0.4 mW/mA were achieved     

Diode-pumped and packaged acoustooptically tunableTi:Er:LiNbO3 waveguide laser of wide tuning range

Design, fabrication, and properties of an acoustooptically tunable Ti:Er:LiNbO₃ waveguide laser of up to 31-nm tuning range in the wavelength band 1530 nm<λ<1575 nm are discussed. The laser cavity is formed by an Au mirror and a dielectric mirror as output coupler, both vacuum-deposited on the polished waveguide endfaces. As tunable intracavity wavelength filter with zero frequency shift, two monolithically integrated single-stage acoustooptical TE-TM-mode converters are used together with two polarization splitters operated as TE- and TM-pass polarizers, respectively. The minimum threshold of about 54 mW (coupled) pump power is obtained at λ≈1561-nm emission wavelength for diode laser pumping at λ_p≈1480 nm. With about 110-mW coupled pump power, up to 320-μW output power is achieved; the emission linewidth is 0.3 nm     

Tunable GaInNAs lasers with photonic crystal mirrors

We present results of tunable GaInNAs lasers with photonic crystal (PhQ mirrors, fabricated from GaAs-AlGaAs layers with a double GaInNAs quantum well emitting at IR wavelength. The devices are realized as ridge waveguide lasers with two coupled segments and a total length between 240 and 580 pm. PhC blocks with different thicknesses are used for the back and front mirror as well as for the intermediate reflector between the two segments. The lasers have threshold currents around 20 mA and output powers up to 6 mW. Tuning of the laser emission over 30 nm is achieved by a variation of the currents injected into the two segments.     

The perylene derivative BASF-241 solution as a new tunable dyelaser in the visible

Basic optical properties of the perylene derivative BASF-241 solution in chloroform relevant to its application as a dye laser were measured. The fluorescence spectrum, excited by frequency-doubled (532-nm) Nd:YAG laser pulses, shows three pronounced peaks centered at 540, 580, and 630 nm, with a Stokes shift and mirror image in relation to the absorption spectrum. The quantum yield was about a unity, with a lifetime of 5.0±0.5 ns. Addition of trichloroacetic acid (CCl₃COOH) causes a red shift of absorption and fluorescence spectra by about 750 cm^-1-L/mol. In a cavity consisting of a ~100% reflecting back mirror and an 8% reflecting output coupler, lasing was obtained at 577 nm, with a threshold of ~10 μJ/pulse. Using a grating, a tuning range of almost 20 nm was obtained, centered at the 0-1 fluorescence emission peaks     

Butt-coupling efficiency of VCSELs into multimode fibers

We report a detailed study on butt coupling efficiencies of vertical-cavity surface-emitting lasers (VCSELs) to standard graded index multimode silica fibers. Coupling efficiency strongly depends on active laser diameter as well as index guiding and transverse mode spectrum of the laser. For typical active laser diameters of 16-20-/spl mu/m coupling efficiencies of about 90% are obtained with weakly index guided proton-implanted vertical-cavity lasers (VCLs) whereas stronger index guided oxidized lasers show considerably lower coupling efficiencies between 75% and 55%, depending on driving currents.     

Contact reflectivity effects on thin p-clad InGaAs singlequantum-well lasers

Thin p-clad InGaAs quantum-well (QW) lasers with either Au or Ni as the p-contact metal have been fabricated. Due to reduced contact reflectivity, the Ni contact lasers hare significantly higher threshold currents and lower slope efficiencies than the Au contact lasers. In addition, operating wavelength differences greater than 50 mn are observed for cavity lengths between 250 and 700 microns, with large wavelength jumps occurring at shorter and longer cavity lengths. The measured wavelength effects are explained by incorporating the optical mode loss difference between the two laser types into quantum-well laser theory     

Surface-normal electroabsorption reflection modulators usingasymmetric Fabry-Perot structures

The authors discuss a family of surface-normal electrooptic reflection modulators using asymmetric Fabry-Perot (ASFP) structures with GaAs-AlGaAs multiple quantum wells (MQWs) as the active medium. When an optimized top mirror reflectivity (~75%) is used, a voltage swing as low as 2 V is enough to change the device reflectivity by more than 40% with a contrast ratio of 50. A comparison with various Fabry-Perot structures shows that the ASFP is the best structure in terms of its operating voltage requirement and optical bandwidth. A sensitivity analysis shows that tolerances of 2 nm in operating wavelength, 0.5 V in operating voltage, 0.3% in layer thickness control or 10°C in temperature variation can be expected from ASFPs with a finesse ~10