Use of fiber helical coils to obtain polarization insensitive fiber devices

• Fiber pigtails are coiled to produce polarization insensitive devices.
• These devices allow the development of systems with full control of polarization.
• The device polarization sensitivity limits the polarization control.

Using a new model for the description of the birefringence of a helical coil, it is shown that the birefringence effect on the signal polarization introduced by a fiber device can be canceled out by introducing two helical coils at the required orientation. Experimental results obtained using this modification in a polarization insensitive device (optical isolator) and in a non-polarization insensitive device working at two different wavelengths (wavelength division multiplexer) are presented and discussed. Such modified devices were used in the construction of an erbium-doped fiber amplifier (EDFA) with a full control of the input signal and pump states of polarization.