This methodology applies to many systems utilizing intensity modulation of laser beams.

Aset of equations has been formulated to enable quantification of several aspects of the performance of an analog photonic communication link as affected by laser noise. A procedure for measuring the laser noise has been devised to provide laser-noise data for use in the equations. The equations and procedure are generally applicable to diverse analog photonic links, in the design and operation of which laser noise is of great concern. Analog photonic links have been found to be useful as subsystems, radio-antenna-arraying systems, optoelectronic oscillators, and wide-band signal-processors.

Figure 1. In an Analog Photonic Link of the type of interest here, RF intensity modulation is effected by use of a Mach-Zehnder modulator and the RF signal is detected by a photodiode.

The equations are derived from first principles, using what is known of (1) the optical response of a generic Mach- Zehnder modulator to the DC bias and RF modulation input voltages and (2) the RF response of a generic photodiode to the modulated laser signal, along with a few simplifying assumptions. The forms of the equations have been chosen to emphasize the effects of laser noise.

In addition to laser noise, thermal noise at the input and output ends of the link and shot noise originating in the photodiode are taken into account. The equations include adjustable parameters, representing magnitudes of various components of the modulator and photodiode responses that must be determined empirically. There are also adjustable parameters for the laser power, the proportionality between the square root of the laser power and the electric field in the laser beam, and the fractions of laser-beam power remaining after incurring losses in propagation through the Mach-Zehnder modulator and the optical fiber. The performance measures calculated by the equations include the RF gain, RF noise figure, compression dynamic range, and spurious-free dynamic range.