Morphological change of a diblock copolymer film induced by selective doping of a photoactive chromophore

Tetrakis‐5,10,15,20‐(4‐carboxyphenyl)porphyrine (TCPP) was position‐selectively introduced into a diblock copolymer film of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) with a sea–island microphase structure. By immersing the PS‐b‐P4VP film into a solution of TCPP/methanol, TCPP was introduced into the island parts comprising P4VP phase. The morphology of the island parts depended on the immersion time and TCPP concentration. A schematic model for the morphological change caused by the phase‐selective introduction of TCPP was proposed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 368–375, 2007     

Degradation behavior in InGaAs/GaAs strained-quantum well lasers

Facet degradation mechanisms of a 980-nm InGaAs/GaAs strained-quantum well laser are analyzed by monitoring the optical-beam induced current. It is clarified that the behavior of defects around the facets govern the long-term stability as well as catastrophic-optical damage generation during operation.     

Light can transform the secondary structure of silk protein

Fibroin is the main component of silk and is expected to be used as a novel functional material in medicine and bioelectronics. The main secondary structures of this protein are of the random-coil and the β-sheet types. In this study, we carried out laser-induced transformation of the secondary structure, from the random-coil type to the β-sheettype, in solid fibroin films. We prepared two types of fibroin films with the random-coil structure. One is a fibroin film doped with a dye as a photosensitizer with a small amount (1 wt %), and the other is a neat fibroin film. The former was excited at 532 nm and the latter was excited at 266 nm. Irradiations were carried out with fluences much lower than each ablation threshold. The excitation of the dye at 532 nm did not affect the secondary structure of the random-coil type. By contrast, 266-nm laser irradiation, which excites tryptophan (an amino-acid residue) involved in fibroin, created the β-sheetdomain in the film. The structural transformation was revealed by infrared absorption spectroscopy and atomic force microscopy. Received: 1 August 2001 / Accepted: 2 August 2001 / Published online: 2 October 2001     

Highly reliable spot-size converter integrated laser diodes over a wide temperature range for access network systems

In this paper, we present highly reliable high-temperature spot-size converter integrated laser diodes (LDs) fabricated using a full-wafer process with dry etching and MOVPE. The lasers lase at 150°C and operate stably for 10,000 h at 85°C and 10 mW. The median lifetime is estimated to be over 10⁵ h. We also demonstrate a novel screening test procedure for a bar configuration of LDs, which can greatly reduce optical module cost.     

Laser diodes integrated with butt-jointed spotsize converterfabricated on 2-in wafer

Laser diodes integrated with spotsize converters by butt-joint technology combined with selective area metal organic vapor phase epitaxial (MOVPE) growth have been successfully fabricated. Satisfactory uniformity, reproducibility (>99%) and tolerance for low threshold current, a narrow emitted beam, and low optical coupling loss to fiber (<-2.4 dB) are obtained by using 2-in full wafer fabrication technology in the experimental fabrication. To investigate the tolerance in fabrication, the characteristic dependence on the variation of the wet etching time just before the butt-joint MOVPE growth and also on the mesa stripe width are investigated. A wide tolerance for these fabrication parameters is confirmed. The results indicate that the butt-joint technology is a useful and reliable process for realizing spotsize converters of the present type and also suggest that the technology is widely applicable to various photonic integrated circuits     

110-GHz, 50%-efficiency mushroom-mesa waveguide p-i-n photodiodefor a 1.55-μm wavelength

A mushroom-mesa structure is proposed to reduce the CR-time constant which originates from the waveguide photodiode structure. Experimental results at a 1.55-μm wavelength show that the multimode waveguide p-i-n photodiode with mushroom-mesa structure has an electrical 3-dB bandwidth of more than 75 GHz in the frequency domain and an electrical 3-dB bandwidth of 110 GHz in the time domain. The external quantum efficiency is 50% or 0.63 A/W, which leads to a record bandwidth-efficiency product of 55 GHz for long wavelength p-i-n photodetectors