In- & quadrature- phase modulator using polarization modulators

What is it about?

Conventional Mach-Zehnder modulators employ two-mode interference. A polarization modulator also employs two-mode interference between two orthogonal linearly polarized modes. It follows that for every circuit of Mach-Zehnder modulators there is an equivalent circuit of polarization modulators. Previously, we have described a cascade of two Mach-Zender modulators connected by a single coupler equipped with phase shift elements on its ports which provides complex modulation. In this paper we describe an implementation using polarization modulators. It turns out the special coupling element becomes a suitably oriented quarter wave plate.

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Why is it important?

The quarter wave plate my be sandwiched between the two polarisation modulators in a co-linear arrangement The two orthogonally polarised modes share the same physical path which leads to a configuration that is robust to environmental perturbations even when implemented with discrete rather than integrated components. The cascade architecture also has optical and RF power advantages compared to other architectures.

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