Abstract
Polarization-insensitive wavelength conversion, as well as the conversion of return-to-zero (RZ) ON-OFF keying (RZ-OOK) to RZ binary phase-shift keying (RZ-BPSK), has been simultaneously achieved at 40 Gb/s for the first time by cross-phase modulation (XPM) in a highly birefringent, nonlinear photonic crystal fiber (PCF). A 10-9-BER receiver sensitivity conversion penalty of < 3 dB was achieved for a polarization scrambled, 40 Gb/s 25%-RZ-OOK pump, when the 40 Gb/s RZ probe was launched at 45 degrees with respect to the birefringence axes of the PCF and when the pump-probe detuning was greater than about 6 nm.
Highlights
Wavelength conversion may be used to facilitate the full utilization of the bandwidths of fibers deployed in dense wavelength division multiplexed (DWDM) networks, as well as to minimize network blocking probability, and to enhance network interoperability
As some networks have been upgraded from RZ-OOK to RZ-differential phase-shift keying (RZDPSK) due to the latter’s 3-dB optical signal-to-noise ratio (OSNR) advantage as well as its superior performance in DWDM transmission, interoperability with other networks still carrying RZ-OOK can lead to mixed-modulation format transmission over the long-haul backbone [1]
To carry out RZ-OOK-to-RZ binary phase-shift keying (RZ-BPSK) format conversion in photonic crystal fiber (PCF), a pump-probe configuration was employed in which the pump was a wavelength-tunable, 40 Gb/s, 231-1 pseudo-random bit sequence; and the probe, a 40 Gb/s optical clock fixed at 1553 nm (Fig. 3)
Summary
Wavelength conversion may be used to facilitate the full utilization of the bandwidths of fibers deployed in dense wavelength division multiplexed (DWDM) networks, as well as to minimize network blocking probability, and to enhance network interoperability. Apart from perfectly matching the SOPs of the pump and the probe over the length of the PCF, other techniques have been suggested to alleviate the polarization dependence of XPM: Using two crosspolarized pumps [11]; launching the pump circularly polarized in a spun, circularly birefringent fiber [12]; through polarization diversity [9, 13]; and by pump depolarization [14]. Another means of obtaining polarization insensitive operation is to utilize the birefringence of the nonlinear fiber itself, when possible. A 45o pump launch by itself is inadequate to compensate the polarization sensitivity of XPM, and requires a minimum pump-probe detuning (PPD) as will be clarified in the ensuing section
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