Heterogeneously integrated microdisk lasers for optical interconnects and optical logic

Optical interconnect and optical packet switching systems could take advantage of small footprint, low power lasers and optical logic elements. Microdisk lasers, with a diameter below 10 mu m and fabricated in InP membranes with a high index contrast, offer this possibility at the telecom wavelengths. The lasers are fabricated using heterogeneous integration of InP membranes on silicon-on-insulator (SOI) passive waveguide circuits, which allows to combine the active elements with compact, high-index contrast passive elements. The lasing mode in such microdisk lasers is a whispering gallery mode, which can be either in the clockwise (CW) or counter clockwise direction (CCW) or in both. The coupling to the SOI wire waveguides is through evanescent coupling. Predefined, unidirectional operation can be achieved by terminating the SOI wires at one end with Bragg gratings. For all-optical flip-flops, the laser operation must be switchable between CW and CCW, using short optical pulses. Unidirectional operation in either direction is only possible if the coupling between CW and CCW direction is very small, requiring small sidewall surface roughness, and if the gain suppression is sufficiently large, requiring large internal power levels. All-optical flip-flops based on microdisk lasers with diameter of 7.5 mu m have been demonstrated. They operate with a CW power consumption of a few mW and switch in 60ps with switching energies as low as 1.8fJ. Operation as all-optical gate has also been demonstrated. The surface roughness is limited through optimized etching of the disks and the large internal power is obtained through good heat sink

Apoptosis in cervical squamous carcinoma: predictive value for survival following radiotherapy

Background—Apoptosis, or programmed cell death, can be induced by radiotherapy. The extent of apoptosis in a tumour before treatment may have important implications for response to radiotherapy and long term survival. Aim—To examine the extent of apoptosis in tumour tissue from patients with squamous carcinoma of the cervix before radiotherapy, and to correlate this with response to treatment and prognosis. Methods—The percentage of apoptotic cells was assessed in 146 carcinomas of the cervix from patients scheduled to receive radiotherapy. The CAS 200 static image analysis system was used to count the number of tumour nuclei per high power field, while the numbers of apoptotic cells in the same field were visualised simultaneously on the image analyser and recorded manually. Results—The median apoptotic level was 0.73%. Patients were divided into two groups around the median. There was no statistically significant difference in outcome between the two groups as determined by long term survival following radiotherapy. Conclusions—The CAS 200 static image analyser system can be used to assist in the rapid semiautomated assessment of apoptosis in conventionally prepared tissue. The results suggest that the apoptotic state of a tumour before treatment is of no value in predicting response to radiotherapy and subsequent prognosis. Tumour stage, size, and BrdU labelling index, as a measure of proliferation rate, remain the most important prognostic factors in terms of predicting local tumour control. Key Words: apoptosis • uterine cervix • squamous cell carcinom