MOGlabs CEF, Manual

Page: 28 / 60

14
Chapter 3. Operation and Optimisation
with 90 to 95% typical at 780 nm.
M1
M2
Faraday
isolator
Fibre
coupler
Cylindrical
telescope
Figure 3.6:
Schematic of the extended chassis laser showing Faraday isolator,
and two mirrors used for aligning the beam to a single-mode fibre.
The isolator rotates the polarisation of the laser beam by 45
◦
(90
◦
for a
double-stage isolator). For lasers with fibre coupling, or with dual beam
output (using a PBS polarising beamsplitter cube), the isolator will in most
cases have an internal half-wave retardation waveplate. The waveplate is
mounted inside the end-cap of the isolator (see figure 3.7). On older (EOT)
isolators, the waveplate is in the final silver-coloured metal element of the
retarder.
The waveplate angle may need adjustment, for example to vary the power
ratio for the two beams exiting the PBS or to align the polarisation to
a more convenient horizontal or vertical axis for experiments, or to align
to a polarisation preserving fibre. To adjust the waveplate angle, loosen
the radial set screw holding the waveplate, rotate, and restore set screw
tension. Older isolators use a 0.035” or 0.9 mm hex key; newer MOGL abs
isolators require a 1.5 mm hex key.
A second waveplate holder is available, which mounts directly before the
exit face of the laser. The waveplate allows separate polarisation control
for the beam reflected from M1.