Tokuo Umeda

Optical waveguides using GaAs-AlxGa1−xAs multiple quantum well

Abstract For the purpose of using the multiple quantum well structure as an optical waveguide of nonlinear-optical devices, GaAs-Al x Ga 1- x As MQW structure is investigated theoretically. The composition ratios of the composing compound semiconductors can provide flexibility for the design of those devices. The numerically calculated result of the field distributions of the MQW waveguide structures showed that they can be approximated by replacing the MQW core section with a uniform material whose refractive index equals the root-mean-square value of the refractive indices of the MQW core section when the MQW structural (quantum wells and barriers) dimensions are less than ∼ 200 A for the near-infrared region.

Observation of chaos in a semiconductor laser with delayed feedback

Abstract By feeding the output from a semiconductor laser back onto its own output facet with an appropriate delay, the oscillation was able to be brought into a chaotic regime. Observed waveforms and accompanying spectra did not show distinct behavior to reach chaos, but the dimensionality test of the waveforms gave a strong evidence that the observed waveforms were chaos.

Time and flow study results before and after installation of a hospital information system and radiology information system and before clinical use of a picture archiving and communication system.

The effectiveness of a hospital information system (HIS) and a radiological information system (RIS) was evaluated to optimize preparation for the planned full clinical operation of a picture archiving and communication system (PACS), which is now linked experimentally to the HIS and the RIS. One thousand IC (integrated circuit) cards were used for time studies and flow studies in the hospital. Measurements were performed on image examination order entry, image examination, reporting, and image delivery times. Even though after the HIS and the RIS operation only a small amount of time savings were realized in each time fraction component, such as in the patient movement time, examination time, and film delivery time, the total turn-around time was shortened markedly, by more than 23 hours on average. It was verified that the HIS and the RIS was beneficial in the outpatient clinics of the orthopedic department. Our method of measurement employing IC cards before and after HIS and RIS operations can be applied in other hospitals.

TM-mode propagation and form birefringence in a GaAs-AlGaAs multiple quantum well optical waveguide

Abstract On optical waveguides having GaAs-AlGaAs MQW structures, the linear optical guiding property is investigated theoretically, particularly on TM-modes. Dispersion properties and field distributions are calculated either exactly or in a three-layer slab waveguide approximation with a virtual uniform core section. The form birefringence property of the waveguide is discussed. The three-layer slab waveguide treatment gives sufficient approximations for GaAs-AlGaAs MQW optical waveguide having small MQW period.

Picosecond HEMT Pholodetector

A short and narrow gate GaAs/AlGaAs MESFET with a HEMT structure was tested as a picosecond photodetector. Its impulse response was measured by the autocorrelation technique and found as fast as 22 ps in FWHM.

Effect of Incident Light Illumination Shape on Responsivity of GaAs MESFET Photodetector

Photoresponsivity of a GaAs MESFET is investigated. By matching the incident light illumination shape to the electrode shape of the device, an improvement of a factor ~3 in the photoresponsivity was observed. This suggests that the photoresponsivity of GaAs MESFETs is substantially due to a channel current caused by a direct optically-induced modulation of depletion layer.

HIS:RIS contribution to image diagnosis and maximization of efficacy of PACS when coupled with HIS:RIS

To maximize the efficacy of the PACS coupled with the HIS/RIS and to clarify the effectiveness of the PACS itself, the amount of contribution of the HIS/NS to image diagnosis was measured beforehand. Video-tape recorders were used to record the CRT display of the HIS/RIS terminals and the simultaneous conversation between a patient and his physician in the clinics of our hospital. Consultation time and entry time for image examination order were measured for each case by replay of the tape. Consultation time was approximately 10 min, while order time was 2-3.5 min depending on whether the physician was an internist or an orthopedist. Detailed description on an order was closely related to detailed reports. The HIS/RIS contributed to image diagnosis even before the PACS was coupled. Concrete methods of efficacy maximization of the PACS were pointed out by internists and orthopedists in terms of modalities, outpatient clinics and wards.

Multi-media PACS integrated with HIS/RIS employing magneto-optical disks

A multi-media magneto-optical disk filing system which stores the voice of image interpretation and order of image diagnosis issued at physicians departments has been developed. The advantages of these 5.25 in., 600 MB disks are rewritability and compactness; they are applicable to circulation media as well as filing media inside hospitals. In this paper, the status of magneto-optical disk (MOD) application to medical images involving standardization activity is briefly introduced. Results of system analysis of the hospital at Osaka University School of Medicine are presented, and the design of HIS/RIS/PACS and role of MOD through HIS/RIS/PACS are described. The result of the experiments -- oral reporting accommodation, together with medical images, interchangeability check, and hand carry acceptance check -- are also reported. Technology assessment steps and future development are further discussed in terms of speed, security, file integration, and operability.

Development and evaluation of oral reporting system for PACS

Experimental workstations for oral reporting and synchronized image filing have been developed and evaluated by radiologists and referring physicians. The file media is a 5.25-inch rewritable magneto-optical disk of 600-Mb capacity whose file format is in accordance with the IS&C specification. The results of evaluation tell that this system is superior to other existing methods of the same kind such as transcribing, dictating, handwriting, typewriting and key selections. The most significant advantage of the system is that images and their interpretation are never separated. The first practical application to the teaching file and the teaching conference is contemplated in the Osaka University Hospital. This system is a complete digital system in terms of images, voices and demographic data, so that on-line transmission, off-line communication or filing to any database will be easily realized in a PACS environment. We are developing an integrated system of a speech recognizer connected to this digitized oral system.

Linewidth enhancement factor dependence of the instability in semiconductor lasers with delayed feedback and its influence on the analyses

Abstract The instability enhancement due to the linewidth enhancement factor (α-parameter) in semiconductor lasers with delayed feedback on the regime IV are explained in terms of the laser emission suppression caused by the feedback field using the phasor representation. The discrepancy of the unstable condition due to the adiabatic-following approximation (AFA) is also examined.