The National Science Foundation's (NSF) Tokyo Office periodically receives and disseminates reports on research developments in Japan that are related to the Foundation's mission. NSF-sponsored researchers currently working in Japan prepare many of these reports. These reports present information for use by NSF program managers and policy makers; they are not statements of NSF policy. .
Mr. Jeremy A. Palmer, a Ph.D. student in Department of Electrical and Computer Engineering at North Carolina State University, prepared the following report. Mr. Palmer was a participant in the 1999 Summer Institute sponsored in the United States by NSF/NIH/USDA and the Science and Technology Agency and Japan Science and Technology Corporation in Japan. Dr. Hiroyoshi Yajima of Electrotechnical Laboratory, MITI/AIST, located in Tsukuba City hosted Mr. Palmer. Mr. Palmer can be reached via email at: japalmer@eos.ncsu.edu
I. Activities and Findings
I-1. Major Research Activities
In recent years, the optoelectronics research effort of the Electrotechnical Laboratory (ETL) has included the development of edge-emitting, and vertical cavity surface emitting laser diodes (VCSEL’s) possessing a two-dimensional beam steering capability. These devices are viewed as critical to the realization of terabyte data transfer using free-space optical interconnect technology. The objective of this Summer Institute ‘99 research project was to characterize the operation of similar, non-steerable semiconductor laser devices in lieu of evaluations of steerable prototypes.
Figure 1 illustrates the simple twin stripe, and the steerable laser diode structures
(Mukai et. al., 1987).
| Figure 1. |
(a) Simple twin-stripe laser diode structure (b) Edge-emitting steerable laser diode structure |
The infrared beam generated by carrier injection on the cavity/waveguide
portion of the device (LW) can be deflected
by applying current to either of the forward electrodes 1 and
2. The experimental apparatus for characterization of the non-steerable
device is shown in Figure 2.
The characterization procedure established with the simple
diode trials has the following objectives:
The mode of operation described above may also be manifested by a so-called "flip-flop" condition, which may be observed by imaging the light emissions from the forward and rear edges of the laser facet. In this case, quasi-near field intensity patterns from both edges are imaged and compared to confirm the flip-flop effect.
I-2. Major Research Findings
Figure 3 depicts the plot of detector output potential versus carrier injection current for a non-steerable prototype with laser cavity length in excess of 300 mm.
The non-linear region circled in black indicates that modal competition may occur at injection currents less than 450 mA.
II. Contributions
This project offers a contribution to the field of optoelectronics by the development of practical, steerable laser diodes for use in high-density optical data transfer systems. The investigations characterize the operation of such devices, and profile the associated modal behavior in certain regions.