Akemi Murakami

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.

Single-Mode Oxide-Confined VCSEL for Printers and Sensors

The 850nm single-mode oxide-confined VCSEL with a metal aperture as a spatial mode filter is reported. The OPTALO (optical probing technique for AlAs lateral oxidation) process was adopted to manufacture a small oxide aperture in VCSEL with high reproducibility. The combination of a metal-aperture and an oxide-aperture brought good performance to 850nm single-mode VCSEL. The fundamental transverse mode oscillation was obtained up to 4.7mW output power. The SMSR is larger than 27dB. No kinks in the L-I curves were observed under -40 to 95degC temperature range. The laser beam is selectively polarized in parallel to the lang0.1-1rang orientation of the GaAs substrate. We also developed the 780nm single-mode VCSEL array (8times4) for laser beam printer application. The polygon scanner system incorporating this 780nm single-mode VCSEL array made it possible to achieve 2400 DPI high dense printing together with 80ppm high speed print

A New Flying Optical Head

A new flying optical head was developed for attaining the high speed accessing. The weight of the moving part of the flying optical head is reduced to less than 10 gr by using the flying slider. The variation of distance between an objective lens and a disk is largely reduced by floating the objective lens on the disk surface. The autofocusing is done by axially moving one of the relay lenses, which is mounted on the fixed part of the head. The moving part is carried by a linear motor to do track-following as well as track-seeking. The mechanical resonant frequency for the linear motor is as high as more than 5 kHz, and it can sufficiently follow disk tracks under the condition of the radial runout of ±45 µm and the rotational speed of 1800 rpm. The new flying optical head is successfully applied for read/write of optical disk data.

New flying optical head for high-speed accessing

A flying optical head has been developed to attain high speed accessing, the important issue in applying optical disks for computer file memories, because the head weight could be ultimately reduced. And it was successfully applied for writing and reading of optical disks for the first time. The moving part of the head consists of an objective lens, mirror, flying slider and moving coil of a voice coil motor and a linear bearing, which total weight is as light as 3.6gr. The flying slider makes the objective lens follow on a disk surface, so the variation of the distance between the lens and the optical disk caused by the axial runout of the disk is largely reduced. Autofocusing is done by axial moving of relay lenses which are placed in the fixed part of the head. The resonant frequency of the moving part has been improved to more than 10kHz by reducing its weight, which enables it to do track-following as well as track-seeking. Seek time of less than 20 ms for a 130mm disk was achieved with the flying optical head.

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.

Characteristics and Reliability of 10 Gbps/Channel 1 ×10 Vertical-Cavity Surface-Emitting Laser Array of 850 nm Wavelength

A 10 Gbps/channel 1 ×10 vertical-cavity surface-emitting laser (VCSEL) array of 850 nm wavelength was demonstrated for a 100 Gbps (10 Gbps × 10) local area network. The VCSEL array was oxidized using an in situ probing technique. The threshold current of each VCSEL on the array is approximately 0.5 mA with the oxide and metal apertures of 8 and 6 µm, respectively. The temperature characteristic of lasing from -40 to 120 °C was stable and the f-3 dB cutoff frequency exceeded 10 GHz at 6 mA. The data transmission test through the conventional multimode fiber of 300 m length was carried out. We also investigated the reliability of the VCSEL array at an ambient temperature of 120 °C and a dc current of 15 mA. We could achieve a failure rate over a decade below 1% at a temperature and current of 60 °C and 7 mA, respectively.