Fri, 01 Sep 2000
Vincent Coude du Foresto
Dear FLUOR users,

This message may not be important to you for the moment, but please read it whenever you are about to use FLUOR again.

The FLUOR triple coupler box is back on Mt Hopkins, after having been inspected and tested by Le Verre Fluore. I join in attachment the
transmission measurements made by the manufacturer, which show that the venerable couplers are as chromatic as they were 9 years ago, and that the overall loss of the triple coupler box ranges between 0.41 and 1.25dB (90 to 75% overall transmission), depending on the input/output pair and wavelength considered.

Now we had long suspected that the triple coupler did not transmit that much, and indeed it was found that the connectors were **extremely dirty**,  most notably those at the output end of the triple coupler box. The contamination source was found to be (mostly) tiny bits of foam from the shipping crate! Therefore after cleaning and repolishing the triple coupler was shipped back in a sealed wrapping, and this problem should now be taken care of. The good news, of course, is that the sensitivity of FLUOR should improve, maybe by up to one magnitude (to be confirmed......).

But there remains the risk of contamination by the dusty IOTA environment. For the output ports of the triple coupler box this is annoying as it is almost impossible to clean them without getting into the risky business of opening the box. So a few precautions are needed in order to avoid  contamination:
        - Never leave the output ports open. They should always be connected to a fiber, or have a clean dummy connector (blue key),
        - Do not connect/disconnect unless it is absolutely necessary. At the output of the triple coupler, only two fibers need to be
           disconnected (typically once a night) for alignment purposes. The other two fibers should never be manipulated (next time I go
           the mountain I plan to remove a short piece of plastic that will make the disconnection impossible).
        - Leave the patchcord fibers inserted into the output ports when FLUOR is stored for long periods of time.

Similar recommandations also hold, of course, for the connector sockets at the telescope feeds. The fiber ends themselves are in principle protected, when not connected, by a small cap in the connector, but a fiber end plugged into the socket is exposed to dusty air. So if FLUOR is not going  to be used for a long time, the fiber ends should be removed (and replaced by a clean blue key) from the sockets and the connectors inserted into a small plastic bag for extra protection. If dirty, fiber ends can in principle be cleaned, but there is always the risk of scratching the fiber core. This would not be catastrophic, but serious (the fibers would need to be sent back for repolishing).

The case of the patchcord output is more problematic: it cannot be removed easily from its socket, so the best is probably to leave it there but to carefully cover the socket with a plastic bag for protection.

vincent foresto

Fluor Photometric Coupler (P1/T1)
Fluor Photometric Coupler (P2/T2)
Fluor Interferometric Coupler I1/(I1+I2)

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