An optical attenuator (8) includes an input port (1), an output
port (4), a fixed reflector (2), a movable reflector (3),
two detecting means (6, 7) and a driving device (5). The input port
includes a first collimator (13) and a filter (10) attached to the
first collimator. The output port includes a second collimator (41) and
a splitter (42) connected to the second collimator. Input signals are transmitted
from an input fiber (11) through the first collimator and then pass through
the filter. The signals passing through the filter are directed by the fixed and
the movable reflectors to the second collimator. The angular position of the movable
reflector, which is driven by the driving device, determines the proportion of
the signals. reflected by the reflectors that are received by the second collimator,
which determines the size of the output signals transmitted in an output fiber (421).
