Direct modulation of gas lasers

Direct modulation of gas lasers such as internal modulation, coupling modulation, and phase locking, has been investigated in a 6328 Å He-Ne laser containing a composite modulation element with small insertion loss. It was verified theoretically and experimentally concerning internal modulation that the bandwidth of gas lasers for small perturbation of resonator loss decreases with an increase of resonator loss contrary to the passive circuit case and depends on the dynamic
Q
of the gas laser as an active tuned circuit rather than the resonator
Q
. The measured bandwidth of 6328 Å He-Ne lasers was about 1 Mc/s. Coupling modulation has a flat frequency response above the bandwidth of gas lasers except in the vicinity of harmonics of
c/2L
. Forced phase locking by the frequency
c/2L
is necessary to realize the stable low noise operation of gas lasers. The modulation method simultaneously using the composite modulation element as coupling modulation element and phase-locking element assures a signal transmission of good quality in optical communications.