First-order polarization mode dispersion compensator using two independent feedback signals enabling separation of principal states of polarization and differential group delay controls.

We propose and demonstrate a novel first-order polarization mode dispersion (PMD) compensator separating principal-states-of-polarization (PSP) control from differential-group-delay (DGD) control by using two independent feedback monitoring signals. To verify the proposed operating principle, we fabricated an automatically adaptive module-type 40-Gb/s PMD compensator on printed circuit boards. The results show that unlike previous typical compensation method of controlling alternately PSP and DGD, the proposed scheme provides independent continuous PSP tracking regardless of DGD control by delay line under rapidly varying PSP condition, thus resulting in stable compensated signal with reduction in compensation time.

Noncontact detection of ultrasonic waves using fiber optic Sagnac interferometer.

This paper describes a fiber optic sensor suitable for noncontact detection of ultrasonic waves. This sensor is based on the fiber optic Sagnac interferometer, which has a path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence using a fiber polarization controller.