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Polarization-bistable vertical-cavity surface-emitting lasers : application for optical bit memory

Kawaguchi H.

Opto-Electronics Review

2009

Vol. 17, No. 4

265-274

We summarize recent results on polarization-bistable vertical-cavity surface-emitting lasers (VCSELs) and their application to optical buffer memory. All-optical flip-flop operation with very low switching energies and high repetition rates is achieved. An optical buffer memory consisting of a two-dimensional array of polarization-bistable VCSELs, in which the bit state of the optical signal, ''0'' or ''1'', is stored as a lasing linear polarization state of 0 or 90°. Input data stored as the polarization states of the first VCSEL are transferred to the polarization states of the second VCSEL. In our experiments with 980 nm polarization-bistable VCSELs, 10 Gbit/s optical buffering, 2-bit optical buffering, and a shift register function have been successfully demonstrated.

Theoretical analysis of crosstalk between oxygenated and deoxygenated haemoglobin in focal brain-activation measurements by near-infrared topography

Kawaguchi H., Okui N., Sakaguchi K., Okada E.

Opto-Electronics Review

2008

Vol. 16, No. 4

404-412

The crosstalk between concentration changes in oxygenated haemoglobin and deoxygenated haemoglobin calculated by the modified Lambert-Beer law in near-infrared topography is theoretically investigated. The changes in intensity detected with probe pairs on the scalp caused by the concentration change in either oxygenated or deoxygenated haemoglobin induced by the focal brain activation is predicted by Monte Carlo simulation. The topographic images of the changes in oxygenated and deoxygenated haemoglobin are obtained from the changes in the intensity of light at two wavelengths detected by probe pairs to evaluate the crosstalk. The crosstalk slightly depends on the positional relationship between the probe arrangement and the focal brain activation and is minimised when the focal brain activation is located below a measurement point that is the midpoint between a probe pair. The 690-/830-nm wavelength pair is practically effective for reducing the crosstalk, especially the crosstalk from oxygenated haemoglobin to deoxygenated haemoglobin, in the NIR topography.