Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

Mode-Locked Fiber Lasers for Optical Time-Domain Reflectometry and Sensing

“…In contrast, B = 2 for a circularly birefringent fiber (θ = π/2). Figure 2.17 Works in the literature have reported the use of nonlinear polarization rotation (NPR) to generate a passive mode-locked laser [11,12,[80][81][82]. Figure 2.18 shows an experimental schematic using an SOA as an NPR device.…”

“…Figure 2.18 shows an experimental schematic using an SOA as an NPR device. Nonlinear polarization rotation in the SOA followed by polarization projection is employed as the mode-locking mechanism [11,82]. In this way, the SOA not only acts as an amplifying element, but also provides the nonlinearities needed for pulse compression [12].…”

“…Such laser configuration has been shown to produce subpicosecond pulses [11]. The physical mechanisms that guarantee mode-locked in PML fiber lasers are the nonlinear polarization rotation [11,[79][80][81][82]. This is accomplished in a ring topology, where an SOA and an erbium doped fibre amplifier (EDFA) act as gain media while the NPR effect is enforced by the SOA.…”

“…When a highpower optical pulse impinges on the SOA, the pulse's leading edge can deplete the SOA gain and saturate the device, so that a much lower gain is provided for the trailing edge of the pulse. Hence, as the SOA provides polarisation dependent gain, the refractive index saturation will also be polarisation dependent so that SOA will act as a nonlinear polarization rotation device [11,12,[79][80][81][82]. This feature can be used as a pulse compression mechanism by properly adjusting light polarisation along the cavity.…”