These fixed chirp modulators are fabricated from Titanium Indiffused Z-Cut LiNbO3, which creates an inequality in the push-pull phase shift between the two arms of the Mach-Zehnder interferometer. This results in a phase/frequency shift (chirp) in the output in addition to the intensity modulation. These fixed chirp modulators down-chirp the pulse, which can be useful when the optical fiber in the network has a positive dispersion coefficient. The down-chirped pulse traveling through an optical fiber with a positive dispersion coefficient will be compressed until a minimum is reached. Beyond that point the dispersion term will dominate. Since chirping the pulse increases the spectral width of the pulse, the chirped pulse will eventually be broader than an unchirped pulse traveling through the same optical fiber. This fixed chirp intensity modulator is ideal for applications requiring improved power penalty (less than two dB for +1600 ps/nm) performance over zero-chirp devices.
These zero chirp modulators are fabricated from X-Cut Titanium Indiffused LiNbO3, which allows for both arms of the Mach-Zehnder interferometer to be symmetrically modulated. This symmetry ensures that the modulated output of the intensity modulator is not also shifted in phase/frequency (chirped). Chirp is an important factor in high-data-rate, long-distance telecommunication systems. The optimum value (typically zero or ~0.6) depends signficantly upon the overall system architecture. Zero-chirp intensity modulators, in particular, are ideal for use in metro and long-haul DWDM applications requiring less than a 2 dB power penalty for ±1200 ps/nm dispersion.
