To measure a Faraday rotation angle of the CdSe QDs doped
optical fiber, a linearly polarized light from a 660 nm laser diode
was launched through a linear polarizer into the fiber of the effective
length of 183 cm under magnetic field generated by a
DC solenoid. Note that the CdSe QDs doped optical fiber was
wound around the solenoid to increase the length of the fiber,
which is the total length of the fiber under the same direction of
magnetic field. The output power was applied to the polarimeter
(PA510: Thorlabs, USA) and the Faraday rotation angle was determined
by using a Poincare sphere. Experimental set-up with
the fiber isolator configuration is shown in Fig. 3, where the LD
output power was . The reflected output optical spectrum
by the reflection mirror (Silver coated mirror) was monitored
by the optical spectrum analyzer (OSA, resolution: 1 nm).
The CdSe QDs doped optical fiber was single mode at the wavelength
of 660 nm and a fiber type linear polarizer (operating at
660 nm, OZ Optics Ltd.) was directly spliced with the fiber.
Optical loss of the present fiber isolator was less than 1.7 dB,
including of insertion loss of the linear polarizer, 0.6
dB of propagation loss in the CdSe QDs doped fiber of 183 cm
length, and of splicing loss between the linear polarizer
and the CdSe QDs doped fiber. The propagation loss of the
fiber can be decreased by shortening the length of the fiber by
using a strong magnet tube instead of the lengthy DC solenoid
and that would make all-optical fiber isolator with less than 1
dB of insertion loss.