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What is Mach-Zehnder modulator?

A modulator that splits incoming light into two arms, shifts the phase between them by changing the arms' refractive index with an electrical signal, and recombines them to turn the phase change into an intensity change. A phase difference of 0 gives maximum brightness and π gives minimum. Silicon versions use the plasma dispersion effect and are a few mm long.

Japanese name: マッハツェンダー変調器

Mach-Zehnder modulator appears in 2 practice questions across 1 topic, including Silicon photonics.

Mach-Zehnder modulator Input light Output light Electrode (phase shifter) Voltage changes the arm's index, creating a phase difference Split in two Recombine & interfere Phase diff. 0 Constructive: bright Phase diff. π Destructive: dark
Mach-Zehnder modulator · View in diagrams

Field: Silicon photonics

Try it: questions about Mach-Zehnder modulator

Which correctly describes how a Mach-Zehnder modulator converts a change in optical phase into a change in optical intensity?

  1. AIt splits light into two arms, creates a phase difference between the arms, then recombines them so they interfere
  2. BIt circulates light many times in a ring-shaped resonator so that only specific wavelengths are absorbed
  3. CShining phase-shifted light directly onto a photodetector turns the phase difference into a difference in current
Show answer and explanation

Answer: A. It splits light into two arms, creates a phase difference between the arms, then recombines them so they interfere

In a Mach-Zehnder modulator, incoming light is split equally into two arms, the arms' refractive indices are changed by an electrical signal to create a phase difference, and the light is recombined into one path. If the phase difference between the two beams is 0 they interfere constructively (bright); if it is π (half a wavelength) they cancel (dark); in between, the intensity depends on the phase difference. This places the signal on intensity changes that a photodetector can detect. A photodetector only outputs current according to light intensity and cannot directly detect phase differences. Using a resonator is the approach of the ring modulator.

Mach-Zehnder modulator in the explanations

Questions that mention Mach-Zehnder modulator (2)

  1. Which correctly describes how a Mach-Zehnder modulator converts a change in optical phase into a change in optical intensity?
  2. Which correctly describes the extinction ratio, a measure of optical transmit signal quality?

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Related terms

Extinction ratio C-band Chromatic dispersion CPO (co-packaged optics) Edge coupler Grating coupler O-band Plasma dispersion effect Propagation loss Refractive index

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