Abstract

When used in the analog RF photonics links, frequency modulation (FM ) offers a benefit of larger SIN ratio compared to intensity (IM ) modulation. Large FM gain had been achieved in an analog links comprising a FM diode laser and an optical FM discriminator.¹ The frequency discriminator converts an FM signal into IM one so that direct (incoherent ) detection can be employed. The linearity of the discriminator response is pivotal to achieving a high performance of the link, characterized by a high FM gain and low distortion. The most common FM discriminator, an unbalanced Mach-Zehnder interferometer (MZI), is simple and integratable,² but pos-esses inherently large third order harmonic distortion that restricts the dynamic range of the link. Other approaches using chirped gratings or MZI combinations³ do reduce nonlinearity, but increase complexity and severely reduce bandwidth. We propose a FM discriminator, consisting of MZI with ring resonators in its arms, in which the third-order inter-modulation distortion is completely cancelled; yet the bandwidth is hardly affected.

© 2002 Optical Society of America