Jun Sakurai

Single-transverse-mode 3.4-mW emission of oxide-confined 780-nm VCSELs

The authors have fabricated oxide-confined vertical-cavity surface-emitting lasers with metal apertures exhibiting a spatial mode filtering effect. Single-mode continuous-wave output is enhanced up to 3.4 mW by this effect for AlGaAs-based 780-nm vertical-cavity surface-emitting lasers with a 3.5-/spl mu/m-diameter oxide aperture. From numerical calculations, the round-trip loss difference between zeroth- and first-order optical modes as a function of metal aperture size indicates that there is an optimum point; a 4-/spl mu/m metal aperture size is suitable for higher order mode suppression of a 3.5-/spl mu/m oxide aperture device.

VCSEL array-based light exposure system for laser printing

Improving the image quality and speed is an endless demand for printer applications. To meet the market requirements, we have launched the world first laser printer (DocuColor 1256 GA) introducing 780-nm single-mode 8×4 VCSEL arrays in the light exposure system in 2003. The DocuColor 1256 GA features 2400 dots per inch (dpi) resolution which is the highest in the industry and a speed of 50 pages per minute (ppm). A VCSEL array design has an advantage that it can increase the pixel density and also increase the printing speed by simultaneously scanning the 32-beam to the photoconductor in the exposure process. Adopting VCSELs as a light source also contributes to the reduction of the machines power consumption. The VCSELs are industrially manufactured based on the original in-situ monitored oxidation process to control the oxide aperture size. As a result, uniform characteristics with a less than 5% variation in both output power and divergence angle are obtained. Special care is also taken in the assembly process to avoid additional degradation in performance and quality. This technology is currently extended to high-end tandem color machines (2400 dpi, 80 ppm) to grasp on-demand publishing market. This paper will cover the key technologies of the VCSEL based light exposure system as well as its manufacturing process to assure its quality.

Complete Polarization Control of 12×8-Bit Matrix-Addressed Oxide-Confined Vertical-Cavity Surface-Emitting Laser Array

The authors have shown complete polarization control of a 12×8-bit matrix-addressed oxide-confined vertical-cavity surface-emitting laser (VCSEL) array, which has an unstrained active region emitting at 780 nm. By using a combination of an elliptical-shaped post structure fabricated on misoriented substrate and upper p-side metal lines elongated in the substrate off-direction, we observed complete polarization pinning in an index-guide type array device. All of the VCSELs in this array lased in a fundamental transverse mode and linearly polarized along the direction.

High power VCSEL devices for free space optical communications

High power VCSEL (vertical-cavity surface-emitting lasers) as light sources for free space optical communications have been developed. These VCSEL devices have 4, 9, or 16 simultaneously driven spots - similar to a single spot VCSEL and have a single cone-shaped far field pattern (FFP) under high optical output power operations at 10, 20 and 40mW. Since the multispots are driven simultaneously, these devices have a high optical output power even if the optical output power from each spot is small. As a result, the mean time to failure (MTTF) obtained from a 4 spot multimode 850nm VCSEL array is well over 1,000,000 hrs at 70/spl deg/C under a 10mW operation. The VCSEL arrays also show a wide-open 2.5Gbps eye diagram at standard driving conditions - more than sufficient for optical free space communications such as optical wireless HDTV transmission systems. The simultaneously driven 9 and 16 spot multimode 850nm VCSEL arrays also show similar wide-open 2.5Gbps eye diagrams under standard driving conditions. Simultaneously driven multispot VCSEL arrays are useful as light sources for free space optics (FSO) because of their high speed modulation and high reliability under high optical output power operation.

Fabrication of 12×12 matrix-addressed 780 nm oxide-confined VCSEL arrays

Summary form only given. We describe the fabrication process of 12x12 matrix-addressed oxide-confined VCSEL arrays and their characteristics. Complete planarization enabled p(top) and n(bottom) electrodes to be successfully formed across DBR layers whose total thickness is 10 /spl mu/m. As a result, high yield and good uniformity in device performance was achieved. Each VCSEL consists of n and p- semiconductor DBR and MQW active region, which are all AlGaAs 22 /spl mu/m diameter post structure.

VCSELs for optical communication at Fuji Xerox

We introduce the characteristics of vertical-cavity surface-emitting lasers (VCSELs) for use in optical communications. In the field of optical interconnections and networks, 850 nm VCSELs are key optical transmitters due to their high-speed modulation and low power consumption. One promising candidate for achieving high-speed modulations exceeding 50 Gbps is the transverse-coupled-cavity (TCC) VCSEL. In this talk, we demonstrate the characteristics of 850 nm transverse-coupled-cavity VCSELs, which helped us achieve a high 3dB modulation bandwidth (30 GHz) at 0 °C and realize eye-opening at the large-signal modulation rate of 48 Gbps. The VCSELs epilayer structure was grown by MOCVD. The active region consists of three strained InGaAs QWs surrounded by AlGaAs barriers. The n-type and p-type DBRs are composed of AlGaAs/AlGaAs, respectively. A line-shaped H+ ion was implanted at the center of the bowtie-shaped post, dividing it into two cavities. The threshold current of the TCC VCSEL with an oxide aperture of 3.6 μm is 0.33 mA. Only the left-side cavity is pumped, while the right cavity is unpumped. The effect of modulation bandwidth enhancement was observed over a wide temperature range of 120K thanks to an optical feedback in the coupled cavities. These results show the possibility of achieving high-speed VCSELs without any temperature or bias control. We also demonstrate an ultra-compact photodetector-integrated VCSEL with two laterally-coupled cavities. An output power and a photocurrent exhibit similar tendencies under a wide range of temperature changes. This device could be also used for monitoring output power without a conventional photodetector mounted separately.

Developments of VCSELs for printers and optical communications at Fuji Xerox

We review the characteristics of vertical-cavity surface-emitting lasers (VCSELs) for use in printers and optical communications. In 2003, we launched the worlds first laser printer with a 780-nm single-mode 8×4 VCSEL array introduced to the light exposure system in order to meet the market demands for improving the image quality and speed for laser printers. The design of the VCSEL array enabled us to increase the pixel density and the printing speed by projecting 32 beams at a time to the photoconductor in the exposure process. High uniformity with less than 5% of variation has been achieved for both the optical output and the divergence angle. Currently, our high-end color printer is capable of producing the resolution of 2400 dpi (dots per inch) at the speed of 137 ppm (pages per minute). In the field of optical interconnections and networks, 850-nm VCSELs are needed as high-speed optical transmitters (≥10Gbps). In order to address communication traffic that will increase further as well as to reduce their power consumption to an even lower level, we assessed the lasing characteristics of 850-nm VCSELs with InGaAs strained quantum-well (QW) active layers by changing the ratio of Indium composition. As a result, we succeeded in reducing the power consumption per bit to 43 fJ/bit at 10-Gbps, which is much lower than that of commercial GaAs QW VCSELs. Also, we studied 850-nm transverse-coupled-cavity VCSELs, which enabled us to achieve a high 3dB modulation bandwidth (>23 GHz) and realize eye-openings at the large-signal modulation rate of 36 Gbps.

Fabrication of 12/spl times/12 matrix-addressed 780 nm oxide-confined VCSEL arrays

We use undoped 8-degree-off [100] GaAs substrate to [110]. Each VCSEL consists of n- and p-semiconductor DBR and 3QW active regions, which are all Al/sub x/Ga/sub 1-x/As. A post structure is made by dry-etching and then kept in a wet-oxidizing environment to form 3 μm diameter oxide apertures. The pitch of each VCSEL, post size and width of n-electrode and isolation trench were designed corresponding to pixel pitch required for print head application. Each VCSEL was covered by silicon oxynitride and thick polyimide was coated for planarization. The array was packaged into a ceramic dual inline package, and wire bonded to the ceramic package. We investigated array yield, I-L/I-V characteristics and their variations and polarization of the emitted light.