Application and analysis of optical thin films

Optical thin film is a kind of functional thin film that works by using the effect of thin film on light. Optical thin film can realize the functions of spectral transmission, spectral reflection, spectral absorption, light reflection reduction, reflection increase, beam splitting, high pass, low pass, narrow band filtering and so on in changing light intensity.

Optical thin film is a kind of functional thin film that works by using the effect of thin film on light. Optical thin film can realize the functions of spectral transmission, spectral reflection, spectral absorption, light reflection reduction, reflection increase, beam splitting, high pass, low pass, narrow band filtering and so on in changing light intensity.There are many types of optical films, these films give optical elements a variety of performance, in the realization of the function of optical instruments and affect the quality of optical instruments play an important or decisive role.

Traditional optical thin film is an important part of modern optical instruments and various optical devices. By plating a layer or multiple layers of thin film on the surface of various optical materials, the interference effect of light is used to change the light intensity, polarization state and phase change of transmitted light or reflected light.The film can be plated on the surface of various materials such as optical glass, plastic, optical fiber, and crystal. Its thickness can range from a few nm to tens or hundreds of μm.Optical film can get good fastness, optical stability, the cost is relatively low, almost does not increase the volume and weight of the material, so it is the preferred method to change the optical parameters of the system, it can even be said that there is no optical film without modern optical instruments and various optical devices.In the course of more than two hundred years of development, optical thin films have formed a complete set of optical theory - thin film optics. Optical thin films have been widely used in various optical devices (such as laser resonators, interference filters, optical lenses, etc.), and its important role in the field of optoelectronics has gradually been recognized by people.

1. Beamsplitter coating

A device that divides a beam of light into two parts is called a spectroscope. The working part of the spectroscope is generally a coated plane, which has a specific reflectivity and transmittance in a certain wavelength range. Usually this plane is tilted so that the incident light and the reflected light are separated. The predetermined reflectance and transmittance values of the spectroscope vary according to its use.

For different spectroscopes there is often a different transmittance and reflectivity ratio T/R, that is, the spectral ratio. The most commonly used is a neutral spectroscope, T/R=50/50, which divides a beam of light into two beams of the same spectral composition.Because it has the same transmittance and reflectance ratio for each wavelength in a certain wavelength region, the reflected light and transmitted light do not have color and are neutral.The commonly used neutral spectroscope has two structures: one is coated with a spectroscopic film on a transparent flat substrate, and the other is coated with a film layer on two right Angle prisms, and then the film is glued to the surface of the film into a cube. There are two common types of metal spectroscope and medium spectroscope. The spectral width of the metal film spectroscope is wide, the disadvantage is that the absorption loss is large, the spectral efficiency is low, and the dielectric spectroscope is characterized by high spectral efficiency, obvious polarization effect, and obvious spectral dispersion.