Classification and modulation scheme of laser modulator

Classification and modulation scheme of laser modulator

Laser modulator is a kind of control laser components, it is neither as basic as crystals, lenses and other components, nor as highly integrated as lasers, laser equipment, is a high degree of integration, types and functions of the device class products. From the complex expression of the light wave, it can be seen that the factors affecting the light wave are intensity A(r), phase Φ(r), frequency ω and four aspects of the propagation direction, by controlling these factors can change the state of the light wave, the corresponding laser modulator is the intensity modulator, phase modulator, frequency shifter and deflector.

1. Intensity modulator: used to modulate the intensity or amplitude of the laser, of which optical attenuators, optical gates are the most representative, as well as integrated devices and equipment such as time dividers, power stabilizers, noise attenuators.

2. Phase modulator: used to control the phase of the beam, the phase increase is called lag, the phase decrease is called lead. There are many kinds of phase modulators, and their working principles are very different, such as photoelastic modulators, LN high-speed electro-optical phase modulators, liquid crystal variable phase delay sheets, etc., are all phase modulators based on different working principles.

3. Frequency shifter: used to change the frequency of light waves, is widely used in high-end laser systems or mapping equipment, with acousto-optical frequency shifter as a typical representative.

4. Deflector: used to change the direction of beam propagation, the conventional galvanometer system is one of them, in addition to faster mems galvanometer, electro-optical deflector and acousto-optical deflector.

We have a general concept of the laser modulator, that is, the components that can dynamically control and change some physical properties of the laser, but want to fully introduce the specific products of the laser modulator, only an article is far from enough. So, first of all, focus on the intensity modulator. Intensity modulator as a kind of modulator widely used in all kinds of optical systems, its variety, the different performance can be described as complicated, today to introduce you four common intensity modulator scheme: mechanical scheme, electro-optic scheme, acousto-optic scheme and liquid crystal scheme.

1. Mechanical scheme: mechanical strength modulator is the earliest and most widely used strength modulator. The principle is to change the ratio of s light and p light in the polarized light by rotating the half-wave plate, and to divide the light by the polarizer. From the initial manual adjustment to today’s highly automated and high-precision, its product types and application development have been very mature.

2. Electro-optical scheme: electro-optical intensity modulator can change the intensity or amplitude of polarized light, the principle is based on the Pockels effect of electro-optical crystals. The polarization state of the polarized beam changes after the electro-optic crystal with electric field is applied, and then the polarization is selectively divided by the polarizer. The intensity of the emitted light can be controlled by changing the intensity of the electric field, and the rise/fall edge of ns magnitude can be reached.

3. Acousto-optic scheme: acousto-optic modulator can also be used as an intensity modulator. By changing the diffraction efficiency, the power of 0 light and 1 light can be controlled to achieve the purpose of adjusting the light intensity. Acoustooptic gate (optical attenuator) has the characteristics of fast modulation speed and high damage threshold.

4 Liquid crystal solution: liquid crystal device is often used as a variable wave plate or tunable filter, by applying a drive voltage at both ends of the liquid crystal box to add a precision polarization element, can be made into a liquid crystal shutter or variable attenuator, the product has a large aperture through light, high reliability characteristics.