Distortion in linearized electrooptic modulators

Abstract

Abstruct-Intermodulation and harmonic distortion are calculated for a simple fiber-optic link with a representative set of link parameters and a variety of electrooptic modulators: simple Mach-Zehnder, linearized dual and triple Mach-Zehnder, simple directional coupler (two operating points), and linearized directional coupler with one and two dc electrodes. The resulting dynamic ranges, gains, and noise figures are compared for these modulators. A new definition of dynamic range is proposed to accommodate the more complicated variation of intermodulation with input power exhibited by linearized modulators. The effects of noise bandwidth, preamplifier distortion, and errors in modulator operating conditions are described.

High Linearity Wideband Coherent Amplitude Modulation (AM) Radio Frequency (RF)-Photonic Links

“…The photonic shot noise at each detector, however, is uncorrelated, and so doesn't subtract. Thus the REN noise term disappears from equation (9), but the shot noise term does not. The equation for the SFDR of a system using a balanced detector is therefore…”

“…This occurs because for all linearization schemes there is an operational point where one can actually achieve a SFDR value that is several dB larger than that achieved by a simple removal of the 3 rd order distortional term. However, operation about this point leads to "cliffs" in the SFDR map [9] that are more confusing than useful, so we have avoided this issue by designing for a removal of the third order term only. In Figure 40, the use of a sub-optimum value of s and the sweep in frequency allows one to pass through this operating point, and pick up the few extra dB of SFDR that are available.…”

“…Other linearization schemes that use two or more modulators in series or in parallel [9] operate by using a secondary modulator to generate a distortional component of the same magnitude but opposite sign of that generated in the primary modulator. When the signals are combined, the two distortional components cancel, thus providing a degree of linearization.…”

Silicon photonics devices for integrated analog signal processing and sampling

“…In particular, for analog applications, a high degree of linearity is often important, and linearity is often limited by the optical modulator [46]. Many schemes have been proposed to create more linear modulators (see for example [46,47] and [48]). These schemes can generally be split into two different categories: electrical schemes (such as pre-emphasis, feedback schemes, and post-processing fixes) and optical schemes (cascaded MZ modulators, splitting and recombining signals, adding other optical elements).…”

Performance evaluation of analog signal transmission in an integrated optical vortex emitter to 36-km few-mode fiber system

“…SFDR is an important common judgment criteria to measure the linearity level of an analog link [23,24]. SFDR is defined by the RF input power range at the left and right boundaries of which the fundamental RF power and SHD/THD power are equal to the noise floor [25,26]. In generally, a higher SFDR system facilitates a more linear signal transmission.…”