In a fiberoptical network, for example in a LAN, spread spectrum modulation is
used, for example, CDMA, by providing an electrical digital data signal to a spreading
device including a multiplier also receiving the spreading code. Then a modulation
is made of the spread signal at radio frequencies, the signal being multiplied
by a subcarrier wave generated in a oscillator, whereby the data signal is carried
on an RF subcarrier. A control channel signal from a control unit is added to the
modulated signal, so that the control signal will be located in the baseband. The
added signal is converted to an optical signal transmitted on an output fiber.
The control channel signal can be TDMA-modulated using collision detection. Making
spectrum spreading in the electrical domain allows the use of standard components
developed for example for mobile telephone systems. No wavelength control and no
optical filters are necessary, which allows a low cost system to be constructed.
Alternatively, the spreadspectrum data signal can be located in the baseband and
the control channel on a subcarrier or both the data and the control channel can
be put on subcarriers.
