High-yield flip-chip bonding and packaging of low-threshold VCSEL arrays on sapphire substrates

Oxide-confined top-emitting 850 nm and bottom-emitting 980 nm vertical-cavity surface-emitting laser (VCSEL) 8/spl times/8 arrays were designed and fabricated for applications of optical interconnects. The arrays were flip-chip bonded onto sapphire substrates that contain complimentary metal-oxide-semiconductor (CMOS) driver and fan-out circuitries. The off-sited bonding contacts and minimized bonding force produced very high yield of the hybridization process without causing damage to the VCSEL mesas. The hybridized devices were further mounted either on printed circuit board (PCB) or in 68-pin pin-grid-array (PGA) packages. The transparent sapphire substrate allowed optical outputs from the top-emitting VCSEL arrays to transmit directly through without additional substrate removal procedure. Lasing thresholds below 250 /spl mu/A for 850 nm VCSELs and 800 /spl mu/A for 980 nm VCSEL were found at room temperature. The oxide confinement apertures of VCSELs were measured to be around 6 /spl mu/m in diameter. High-speed data transmission demonstrated a bandwidth of up to 1 Gbits/s per channel for these hybridized VCSEL transmitters.     

1.3 /spl mu/m quantum dot vertical-cavity surface-emitting laser with external light injection

A 1.3 /spl mu/m quantum dot vertical-cavity surface-emitting laser (QD VCSEL) with external light injection is presented, having been experimentally demonstrated. The QD VCSEL is fabricated on GaAs substrate. The 3 dB frequency response of the QD VCSEL based on the TO-Can package is enhanced from the free-running 1.75 to 7.44 GHz with the light injection technique.     

1 /spl times/ 12 VCSEL array with optical monitoring via flip-chip bonding

A vertical-cavity surface-emitting laser (VCSEL) 1 /spl times/ 12 array flip-chip bonded to a 1 /spl times/ 12 GaAs monitor photodiode array is demonstrated, and faithful monitoring of the VCSEL threshold current, optical power, and subthreshold emission is recorded. Extremely small monitor crosstalk is measured. This is the first published report of an optically monitored VCSEL array.     

A novel 4/spl times/8 single-mode independently addressable oxide-isolated VCSEL array

We report a novel process to fabricate single-mode independently addressable oxide-isolated vertical-cavity surface-emitting laser (VCSEL) arrays. The array is fabricated with a novel simple two-mask process where a single oxidation layer is used to define the laser aperture and to isolate the interconnects. The 4/spl times/8 VCSEL array has very uniform electrical, modal and geometrical characteristics that make it ideal for two-dimensional (2-D) array applications.     

Flexible optical waveguide film fabrications and optoelectronic devices integration for fully embedded board-level optical interconnects

This paper demonstrates a flexible optical waveguide film with integrated optoelectronic devices (vertical-cavity surface-emitting laser (VCSEL) and p-i-n photodiode arrays) for fully embedded board-level optical interconnects. The optical waveguide circuit with 45/spl deg/ micromirror couplers was fabricated on a thin flexible polymeric substrate by soft molding. The 45/spl deg/ couplers were fabricated by cutting the waveguide with a microtome blade. The waveguide core material was SU-8 photoresist, and the cladding was cycloolefin copolymer. A thin VCSEL and p-i-n photodiode array were directly integrated on the waveguide film. Measured propagation loss of a waveguide was 0.6 dB/cm at 850 nm.     

Long-wavelength monolithic VCSEL arrays with high optical output power

Two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays at 1.55 /spl mu/m wavelength with parallel operation of single- or multimode devices are presented. 3/spl times/3 VCSEL arrays show maximum output powers beyond 30 mW and conversion efficiencies as high as 22%.     

A vertical-cavity surface-emitting laser appliqued to a 0.8-/spl mu/m NMOS driver

An optoelectronic integrated circuit (OEIC) composed of a vertical-cavity surface-emitting laser (VCSEL) appliqued to an NMOS drive circuit was fabricated to form an optical link from the CMOS chip. A custom NMOS circuit was designed and fabricated through the MOSIS foundry service in a standard 0.8-/spl mu/m CMOS process. InGaAs quantum-well VCSELs were grown, fabricated and tested on an n-type GaAs substrate. Next, the VCSELs underwent a substrate removal technique and were appliqued to the NMOS circuitry. The OEIC was tested at the chip level and showed an electrical to optical conversion efficiency of 1.09 mW/V. Modulation results are also discussed.     

Flip-chip bonded 0.85-/spl mu/m bottom-emitting vertical-cavity laser array on an AlGaAs substrate

We report high-performance 0.85-/spl mu/m bottom-emitting vertical-cavity surface-emitting lasers (VCSELs) on an AlGaAs substrate with 2.1 mA threshold current density 4.2 mW maximum output power, 11.7% power conversion efficiency and a maximum operating temperature of 130/spl deg/C. We also demonstrate a flip-chip bonded 0.85-/spl mu/m bottom-emitting VCSEL array, and confirm all pixels across the 8/spl times/8 VCSEL array operate at a f/sub 3/ dB bandwidth of 2.6 GHz at only 4.2 mA.     

Two-dimensional 8×8 photoreceiver array and VCSEL drivers forhigh-throughput optical data links

Two custom GaAs integrated circuits (ICs) have been developed for enabling vertical cavity surface emitting laser (VCSEL) arrays to be used for high throughput spatial division multiplexed (SDM) optical data links. A 16-channel driver IC was developed to drive the VCSEL array and an 8×8 monolithic photoreceiver, which spatially matches the VCSEL array, was developed for receive. Both of these circuits were fabricated in a standard commercial GaAs MESFET process with parasitic photodetectors used for the photoreceivers. Power dissipation and circuit size were primary design challenges for both circuits. The present 8×8 array size along with an estimated usable channel speed of 1 Gb/s allows for an aggregate throughput of 64 Gb/s     

Thermal crosstalk in 4/spl times/4 vertical-cavity surface-emitting laser arrays

We measured thermal crosstalk in 4/spl times/4 VCSEL arrays with a 30-/spl mu/m pitch between devices. The effective thermal resistance of laser diodes in two-dimensional (2-D) arrays is about 50% higher than that of single elements. The output power of the lasers is fairly temperature insensitive under constant voltage operation. From experiments we inferred values for the average thermal conductivity of AlAs-GaAs Bragg reflectors. We found anisotropy in the effective thermal conductivity with numbers of 0.28 W/(cmK) and 0.35 W/(cmK) for the transverse and lateral direction, respectively.     

An 850-nm InAlGaAs strained quantum-well vertical-cavitysurface-emitting laser grown on GaAs (311)B substrate withhigh-polarization stability

The polarization stability of 850-nm InAlGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) grown on GaAs (311)B substrate was investigated by comparing it with that of GaAs unstrained QW VCSEL grown on GaAs (311)B substrate. Photoluminescence measurement showed that strained QWs grown on GaAs (311)B substrate had larger anisotropy in optical gain than unstrained QWs. The VCSEL with strained QWs showed an orthogonal polarization suppression ratio (OPSR) as high as 21 dB under CW operation. Time-dependent OPSR measurement indicated that the strained QW VCSEL had higher polarization stability than the unstrained QW VCSEL under zero-bias modulation     

"Anti" up the aperture [antiguided VCSEL structures]

Coupled vertical cavity surface-emitting laser (VCSEL) arrays are an attractive means to increase the coherent output power of VCSELs. Single-mode VCSELs, with output powers greater than 10 mW, would be useful as telecommunication transmitters /spl lambda/=1.3-1.55 /spl mu/m) or sources for optical interconnects. Commercially available single-mode VCSELs, even at shorter wavelengths /spl lambda/=0.85 /spl mu/m), are generally limited to a few milliwatts of output power. The conventional VCSEL structure incorporates a built-in positive-index waveguide, designed to support a single fundamental mode. Promising results in the 3-5 mW range (/spl lambda/=0.85 /spl mu/m) have been obtained from wet-oxidized, positive-index-guided VCSELs with small emission apertures (less than 3.5 /spl mu/m-dia). The small aperture size leads to a high electrical resistance and high current density, which can impact device reliability. By contrast, antiguided VCSEL structures have shown promise for achieving larger aperture single-mode operation. To obtain high single-mode powers with a larger emitting aperture, the use of a negative-index guide (antiguide) is beneficial. This paper discusses antiguided structures and some of their advantages when incorporated in 2-D VCSEL array structures.     

C-band emission from GaInNAsSb VCSEL on GaAs

The 1.55 /spl mu/m pulsed operation of an optically-pumped GaInNAsSb vertical-cavity surface-emitting laser (VCSEL) is reported. The structure employs a dielectric (SiO/sub 2//TiO/sub 2/) top mirror, while the bottom mirror and active region were grown on GaAs by MBE. Temperature-dependent (10-40/spl deg/C) laser measurements were made for an as-grown sample and an annealed sample, both having a room-temperature lasing wavelength of 1547 nm. Results indicate an annealing-induced blue-shift of the gain peak     

1.3 /spl mu/m GaAs/GaAsSb quantum well laser grown by solid source molecular beam epitaxy

A highly strained GaAs/GaAs/sub 0.64/Sb/sub 0.36/ single quantum well laser has been grown on GaAs (100) substrate by using solid source molecular beam epitaxy. The uncoated broad-area laser demonstrates 1.292 /spl mu/m pulsed operation with a low threshold current density of 300 A/cm/sup 2/. The spontaneous emission of the laser was also studied. The result reveals that the Auger recombination component dominates the threshold current at high temperature.     

Ultralow-threshold sapphire substrate-bonded top-emitting 850-nm VCSEL array

Oxide-confined top-emitting vertical-cavity surface-emitting-laser (VCSEL) 8 /spl times/ 8 arrays were designed and fabricated with ultralow thresholds. The arrays were flip-chip bonded onto sapphire substrates and mounted in pin-grid-array packages as optical transmitter arrays. By using the offset-contact bonding process, we were able to obtain very high yield for hybridized devices without damaging the VCSEL mesas. Room-temperature lasing thresholds below 70 /spl mu/A were found from some of these packaged VCSELs with measured oxide apertures 2.6 /spl mu/m in diameter. The emission spectrum at an injection current of 70 /spl mu/A showed a full-width at half-maximum linewidth of less than 2.5 A. Polarization properties were also confirmed from the output of the device. The superior performance was attributed to the optimized size and placement of the confinement aperture and the precise alignment of the gain profile of the active region to the mode of the resonant cavity.     

Multiple-wavelength vertical-cavity surface-emitting laser arrays with a record wavelength span

Multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays are fabricated using a modified patterned-substrate growth technique in a molecular beam epitaxy (MBE) system. We achieved a large lasing wavelength span of 62.7 nm and highly uniform threshold currents with an average of 2.16/spl plusmn/0.81 mA. High repeatibility of wavelength spacing between 15 arrays with sharp wavelength shift rate 117.14 nm/mm is achieved.     

Optoelectronic and microwave transmission characteristics of indium solder bumps for low-temperature flip-chip applications

This paper describes low-temperature flip-chip bonding for both optical interconnect and microwave applications. Vertical-cavity surface-emitting laser (VCSEL) arrays were flip-chip bonded onto a fused silica substrate to investigate the optoelectronic characteristics. To achieve low-temperature flip-chip bonding, indium solder bumps were used, which had a low melting temperature of 156.7/spl deg/C. The current-voltage (I-V) and light-current (L-I) characteristics of the flip-chip bonded VCSEL arrays were improved by Ag coating on the indium bump. The I-V and L-I curves indicate that optical and electrical performances of Ag-coated indium bumps are superior to those of uncoated indium solder bumps. The microwave characteristics of the solder bumps were investigated by using a flip-chip-bonded coplanar waveguide (CPW) structure and by measuring the scattering parameter with an on-wafer probe station for the frequency range up to 40 GHz. The indium solder bumps, either with or without the Ag coating, provided good microwave characteristics and retained the original characteristic of the CPW signal lines without degradation of the insertion and return losses by the solder bumps.     

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.     

Two-dimensional matrix addressed vertical cavity top-surfaceemitting laser array display

We present the design, fabrication, and demonstration of a 10×10 matrix-addressed vertical-cavity top-surface-emitting laser (VCSEL) array. These arrays are batch-fabricated from full 3-in diameter GaAs/AlGaAs wafers. We show that no performance-penalty is paid using top-contacted matrix addressed pixels over conventional planar VCSEL devices. A computer-controlled display system for electrically addressing the array was designed and constructed to permit video demonstration and array testing     

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.