Experiment Pockels effect and electro-optic modulation with He-Ne laser

Induced birefringence by an electric field: use the Pockels effect to encode and transport information on an optical carrier.

Topics covered:
- Polarization and change of light polarization state
- Natural birefringence and induced by an electric field
- Polarization modulation, amplitude modulation
- Electro-optic modulator, Lithium Niobate crystal (LiNbO3), Pockels effect
- Half-wave voltage (Vp), measurement of the electro-optic coefficient by different methods
- Optical transmission in free space, demodulation

Principles and objectives:
A laser beam is linearly polarized at 45° to the (X,Y) axes of the Lithium Niobate crystal. The beam passes through this crystal along its optical axis (Z).
An applied voltage to the modulator allows for the linear modification of one of the refractive indices of the LiNbO3 crystal (Pockels effect). The natural birefringence of the material is then modified, causing a phase shift between the ordinary and extraordinary waves propagating in the crystal. This phase shift induces a change in polarization at the modulator ouExperimentut. The analyzer placed before the detector transforms this polarization variation into intensity variation.
The transfer function of the setup (transmitted intensity / incident intensity) is measured experimentally either by rotating the analyzer or by applying a continuous voltage to the crystal.
The curve obtained is used to study its operating points or to determine the half-wave voltage and the electro-optic coefficient (r22) of the material.

This product was developed in collaboration with the LMOPS laboratory in Metz.

Composition:
▪ 1 electro-optic modulator (Pockels cell, LiNbO3 crystal) with 2 SMA-SMA cables
▪ 1 control generator-amplifier for Pockels cell
▪ 1 amplified detector with adjustable gain
▪ 1 meter-long prism bench with adjustable feet set (ref.202519)
▪ 5 standard prism riders (ref.202234)
▪ 1 prism rider with lateral adjustment (ref.202392)
▪ 1 He-Ne laser 632.8 nm <1mW, polarized with power supply (ref.204886)
▪ 1 laser support on rod (ref.202674)
▪ 1 polarizer in graduated mount (ref.202374)
▪ 1 632.8nm crystalline quarter-wave plate in graduated rotating mount (ref.202380)
▪ 1 multimedia kit (radio + speakers + all necessary connections for proper functioning)
▪ 1 experiment manual