LBTEK's mechanical three-loop polarization control is based on the principle of birefringence induced in optical fibers under external force. The three loops function equivalently as λ/4, λ/2, and λ/4 waveplates respectively. By adjusting the rotation angles of these three loops in coordination, the polarization state of incident light can be transformed into any desired polarization state. The retardation effect caused by birefringence is primarily determined by the fiber cladding radius, fiber loop radius, and the wavelength of the input light. The number of fiber loops required for different wavelengths can be calculated using the formula provided in the technical specifications. LBTEK offers two options for polarization controllers: empty polarization controllers and pre-installed fiber polarization controllers. The polarization controllers are mainly designed for use with fibers protected by Ø900 µm sleeves.

LBTEK offers two types of squeeze-type polarization controllers, primarily designed for fibers with Ø900 µm protective sleeves or Ø250 µm bare fibers. Each polarization controller consists of a rotatable fiber squeezer and two fiber clamping blocks. The polarization controller generates stress-induced birefringence within the fiber through mechanical squeezing, effectively functioning as a rotatable variable waveplate. The equivalent waveplate's polarization angle and retardation can be adjusted according to user requirements, enabling the conversion of any input polarization state into the desired output polarization state. The squeeze-type polarization controller reduces inherent loss and back-reflection loss, serving as an alternative to traditional free-space polarization controllers composed of two quarter-wave plates and one half-wave plate. Among them, the FT-P007-N and FT-P008-N models feature knob screws for fiber locking, offering more convenient operation compared to the FT-P000-N model with cross screws for fiber locking.