NRZ-to-PRZ Conversion of a 10 Gb/s NRZ Signal by Tailoring the Optical Spectrum

Fiber Bragg grating based notch filter for bit-rate-transparent NRZ to PRZ format conversion with two-degree-of-freedom optimization

“…The FBG is operated in transmission mode, acting as a notch filter centered at the carrier wavelength to suppress the carrier and its nearby spectral components. A notch filter scheme, as well as the reported spectra tailor schemes [12,[15][16][17], is essentially based on the following physical mechanism to tailor the spectra. The baseband part of the NRZ spectra (near the carrier) corresponds to the dc and low-frequency components in NRZ pulses, namely the flat top and base of NRZ pulses.…”

“…NRZ to PRZ format conversions are classified into two main categories, one is active, such as the semiconductor optical amplifier (SOA) cascaded filter [7,[9][10][11], and the SOA nonlinear loop mirror (SOALOM) [5]. The other is passive, such as the polarization-diversity loop [8], the optical fiber based Mach-Zehnder interferometer (or optical fiber delay interferometer (DI)) associated with the temperature control device [12], double fiber grating filters cascaded adjustable attenuator [13,14], the fiber Bragg grating (FBG) based detuning filter [15], the FBG-based narrow-band filter [16,17], and the silicon micro-ring resonator based notch filter [18,19]. Active devices mainly employ gain saturation or self-phase modulation of the SOA, usually inevitably introducing the ASE noise and SOA carrier recovery time related pattern effect.…”

“…However, this is hardly ever done. As a result, the experientially selected FBG may suffer from various deficiencies such as over filtering or under filtering of certain components of the NRZ spectra, leading to low extinction ratio (ER) or large duty cycle and obvious pedestal of the converted PRZ signal [16,17], which is undesirable in applications like optical logic operation and add-drop multiplexing.…”