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What is AMPLITUDE Modulation?
Amplitude Modulation (AM) is a photonics technique where the instantaneous peak-to-peak amplitude—or physical height—of an optical carrier wave is systematically varied to encode data or shape a laser profile. While the frequency and phase of the light remain unchanged, the envelope of the optical wave is modified in direct alignment with an incoming electrical signal.
Its primary purpose is to dynamically regulate the power distribution of a continuous laser beam, allowing it to act as an information carrier for data streams or to be carved into highly precise, time-resolved optical pulses.
HOW AMPLITUDE Modulation Works
In high-performance photonic networks, amplitude modulation is executed externally using specialized electro-optic crystals that convert an applied voltage into varying output intensities:
Waveguide Injection
A continuous-wave (CW) laser signal enters an integrated optical circuit on a crystal substrate, most commonly Lithium Niobate (LiNbO3). The incoming light is divided equally into two parallel waveguide pathways forming a Mach-Zehnder interferometer layout.
Voltage-Induced Phase Shifting
An electrical drive signal (RF voltage) is applied to the electrodes flanking the waveguide branches. Through the linear electro-optic effect, this voltage alters the refractive index of the crystal, speeding up the wavefront in one branch while slowing it down in the parallel branch to generate a controllable relative phase shift.
Interferometric Recombination
When the two pathways converge at the output junction, they interfere based on their phase alignment. If the waves arrive perfectly in phase, they merge to create maximum amplitude; if they are driven completely out of phase, they cancel each other out, dropping the amplitude to near-zero. Varying the electrical input between these extremes seamlessly shapes the overall amplitude of the exiting light wave.
