Abstract
(English)
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The prototype of the Optical Frequency Domain Reflectometer (OFDR) was further characterised. We introduced various improvements on the software level. These enabled to lower the noise by about 10 dB, and to increase the resolution of the instrument below 1 cm (at short range). We identified the main weak points of the instrument, namely polarisation control and resolution at long distance.
We also tested new lasers, developed by our BLISS partner GMMT (Gec-Marconi Materials technology). These lasers are 4-section sample-grating DBR lasers. One of the central sections is the gain section, which is the lasing section, and the second one is the phase section, used for fine frequncy tuning. The front and rear sections are used for coarse frequency tuning. The linewidth of these lasers was supposed to be very small, of the order of one MHz, which should make the lasers suitable for the OFDR. The idea was to use the fine tuning, i.e. the phase section, to generate the continuous frequency scan similar to the one obtained with the current laser, and the coarse tuning, i.e the front and back sections, to change the frequency between scans, as was previously done with a temperature drift. This larger effective frequency scan should have increased the resolution of the instrument. We tested several of these lasers. Unfortunately, the linewidth of about 1 MHz could not be maintained the tuning range. Indeed, during frequency tuning we measured linewidth of up to 100 MHz. Therefore, our conclusion is that, at present, these laser are not suitable for the OFDR.
The OFDR was presented to the BLISS partners during a meeting in Oslo in June, and we got a good feedback from our partners. Two papers were devoted to it during the Symposium on Optical Fiber Measurement in the National Institute of Standards in Boulder (CO). Here again, we got some interesting feedback from several companies. Therefore, the decision was made to carry on with the industrialisation of the instrument. A second-generation prototype, which should be marketable, is now under way.
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