A Mach-Zehnder modulator driven on one arm has half-wave voltage

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Polarisation and anisotropic media · Polarisation and anisotropic media

What an Instrument Can See, Ch Modulating light: electro-optic, acousto-optic and magneto-optic devices

Problem

A Mach-Zehnder modulator driven on one arm has half-wave voltage Vπ=4.0 VV_\pi=4.0\ \mathrm V, so its transmission is T=cos⁡2(πV/2Vπ)T=\cos^2(\pi V/2V_\pi). ((a)) Find the smallest positive bias voltage that puts the modulator at quadrature, T=12T=\tfrac12. ((b)) A small signal swings the voltage 0.40 V0.40\ \mathrm V either side of that bias. Find TT at the two extremes of the swing. ((c)) Compare your answers with the straight-line estimate T≈12−(π/2Vπ) ΔVT\approx\tfrac12-(\pi/2V_\pi)\,\Delta V from the slope at quadrature, and say what the comparison shows about the choice of bias.

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