Photonic Mach-Zehnder Modulator

Electro-Optic Drive

Bias V_bias / V_π 0.50

Drive swing V_pp / V_π 0.60

Drive frequency (visual) 0.30 Hz

Drive Topology

Transfer Function

P_bar = cos²(Δφ/2) vs Δφ/π

Live Readout

Output power (bar)

Cross-port power

Phase diff. Δφ/π

0.00

Extinction ratio

0 dB

How it works

A Mach-Zehnder modulator (MZM) splits an input optical wave 50/50 into two waveguide arms, applies an independent electro-optic phase shift to each arm, then recombines them in a second coupler. The output power depends only on the phase difference between the arms:

Δφ(V) = π · V / Vπ
P_bar   = cos²(Δφ / 2)
P_cross = sin²(Δφ / 2)   (P_bar + P_cross = 1, energy conserved)

Vπ is the "half-wave voltage" — the drive needed to swing the output from fully bright to fully dark. Driving the device at V = Vπ/2 (Δφ = π/2) sits on the steepest, most linear part of the cos² curve — the usual quadrature bias point for analog and digital modulation.

Bias sets the DC operating (quadrature) point on the transfer curve.
Drive swing is the peak-to-peak RF voltage riding on top of the bias, in units of Vπ.
Push-pull drives the two arms with equal and opposite voltage (±V/2), reaching the same Δφ as a single-arm drive of V but with half the voltage swing per arm — the standard silicon-photonics topology because it also cancels residual optical-frequency chirp.
Extinction ratio is 10·log₁₀(P_max/P_min) of the bar port sampled over one drive cycle — how dark the "off" state gets relative to the "on" state.

Real-world relevance: this exact cos² transfer function governs the silicon-photonic and lithium-niobate MZMs used to encode data onto laser light in every fiber-optic transceiver and data-center interconnect.

Input / arm light Bar output Cross output

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