RU2796501C1 - METHOD FOR ANTIREFLECTION OF ENDS OF ACTIVE Cr:ZnS WAVEGUIDES BASED ON SURFACE MICROSTRUCTURING - Google Patents

Abstract

FIELD: optical materials.

SUBSTANCE: obtaining antireflection microstructures on optical surfaces. Methods for obtaining antireflection microstructures on optical surfaces of active Cr:ZnS waveguides in the mid-infrared (from 2 to 10 mcm) range. Claimed method of antireflection of the ends of active Cr:ZnS waveguides based on surface microstructuring is designed to suppress the reflection and scattering of electromagnetic waves from 2 to 10 mcm, falling on the surface of the substrate at angles in the range from 0 to 40 degrees, from the surface of the end of the active Cr:ZnS waveguide and thus increasing the transmission of electromagnetic waves through the active Cr:ZnS waveguide, by modifying the flat surface of the end face of the active Cr:ZnS waveguide using direct laser ablation with single ultrashort laser radiation pulses, which uses a laser producing ultrashort laser radiation pulses, a lens for focusing ultrashort pulses laser radiation relative to the upper boundary of the substrate, a positioner that moves the substrate in three coordinates relative to the focusing point of ultrashort laser radiation pulses. The method includes placing an active Cr:ZnS waveguide relative to the focusing point of ultrashort laser radiation pulses, where the end face of the active Cr:ZnS waveguide is directly exposed to ultrashort laser radiation pulses, and ultrashort laser radiation pulses physically affect the surface of the active Cr:ZnS waveguide end face to remove material from the end surface of the active Cr:ZnS waveguide by ablation, forming a hole or a depression. The positioner continuously moves the end of the active Cr:ZnS waveguide, synchronized with the repetition rate of ultrashort laser pulses, to form holes on the flat top surface of the substrate. At the same time, the created surface microstructure has distances between holes less than the shortest wavelength of electromagnetic waves, and the depth of the holes is greater than the shortest wavelength of electromagnetic waves. Moreover, the effective refractive index of the surface microstructure monotonically increases from the environment to the material substrate.

EFFECT: reduction of losses during transmission of electromagnetic waves due to reflection from the microstructure of the surface topography at the ends of active Cr:ZnS waveguides by 15%.

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Description

The mid-infrared range (mid-IR range, from 2 to 10 µm) is a technologically important spectral range for sensing, imaging and communication. In the last few years, there has been a surge of interest in new optical materials in the mid-IR range, as well as in devices based on them that meet the ever-increasing requirements of these applications. A wide range of recent technological advances in this area covers the functions of generating, propagating, manipulating and detecting mid-IR light in free space, as well as in fiber optic and planar platforms. Today, the world's leading laboratories are actively developing new materials for the mid-IR range: laser crystals, semiconductors, glasses, plasmonic metals, nanostructures.

However, optical materials used to create mid-IR optics and photonic components typically have a high refractive index that results in significant Fresnel reflection losses at the material-air interface. The latter leads to a decrease in the energy efficiency of individual components of optics and photonics in the mid-IR range and limits the efficiency of systems as a whole.

Traditional coatings, which are dielectric multilayer thin films, have significant drawbacks associated with a narrow spectral range of antireflection, a strong dependence of the transmittance on the angle of incidence of rays, low radiation strength, and high requirements for adhesion of films to the surface of materials, which is a critical limitation on the use of such coatings. in a number of cases. In this regard, the problem of ultrawideband antireflection of the surfaces of optical materials in the mid-IR range, which would remove the above limitations, becomes of great relevance.

Also today, the direction of compact waveguide lasers in the mid-IR range is actively developing. In particular, a waveguide Cr:ZnS laser [N. Tolstik, A. Okhrimchuk, M. Smayev, V. Likhov, E. Sorokin, and I. Sorokina, "Single-mode depressed cladding buried waveguide laser based on single-crystal Cr:ZnS," in CLEO: Science and Innovations, ( Optical Society of America, 2019), pp.STh1E-6.]. The optical material used to create a waveguide Cr:ZnS laser has a characteristic feature associated with relatively high values of the refractive index, which leads to significant Fresnel reflection losses at the material-air interface, however, the development of a method for broadband coated surfaces of the ends of Cr:ZnS waveguides remained an insurmountable problem.

Patent CN104816099A is known from the prior art. The invention discloses a device for preparing a subwavelength antireflection structure. The device consists of a computer control module and a laser device, an optical transmission component, a galvanometer component, a focusing system component and a processing platform, while the optical transmission component, the galvanometer component and the focusing system component are arranged in series along the laser light path. The laser device is controlled by the computer control module, the operations of the galvanometer component and the processing platform are also controlled by the computer control module, and an anti-reflection structure is prepared on the surface to be treated. The device for preparing the subwavelength anti-reflection structure provided by the invention has the advantages that the device and the process are simple, the preparation of the plate and mask is not required, the size of the subwavelength structure can be accurately controlled, the processing accuracy is smaller than the element size, the preparation efficiency is high, the process preparation can be completed in one step, and laser light sources have high selective efficiency and low cost.

The authors propose a method for antireflection of the ends of active Cr:ZnS waveguides (Fig. 1) based on surface microstructuring, designed to suppress the reflection and scattering of electromagnetic waves from the surface of the end of an active Cr:ZnS waveguide and, thus, increase the transmission of electromagnetic waves through the active Cr:ZnS waveguide. In this case, electromagnetic waves have known wavelengths; The method is based on the process of modifying the flat surface of the end of an active Cr:ZnS waveguide using direct laser ablation (evaporation) with single ultrashort laser radiation pulses, which uses a laser of ultrashort laser radiation pulses, an objective for focusing ultrashort laser radiation pulses relative to the upper boundary of the substrate, a positioner , which moves the substrate in three coordinates relative to the focus point of ultrashort laser radiation pulses; the process includes: placement of the active Cr:ZnS waveguide relative to the focusing point of ultrashort laser radiation pulses, where the end face of the active Cr:ZnS waveguide is directly exposed to ultrashort laser radiation pulses, and ultrashort laser radiation pulses act on the surface of the active Cr:ZnS waveguide end face physically to removal of material from the end surface of the active Cr:ZnS waveguide by ablation (evaporation), forming a recess of a given depth and shape, the positioner continuously moves the end of the active Cr:ZnS waveguide in accordance with a certain algorithm, synchronized with the repetition rate of ultrashort laser radiation pulses, to form holes with a certain period on the flat top surface of the substrate; the process uses one ultra-short pulse of laser radiation to form each individual hole on the substrate; wherein the generated surface microstructure has a certain distribution of the distance between the holes and the depth of the holes, where the distance between the holes is less than the shortest wavelength of electromagnetic waves; while the depth of the structure is several times greater than the shortest wavelength of electromagnetic waves; in this case, the effective refractive index of the surface microstructure usually increases monotonically from the environment to the material substrate; moreover, for electromagnetic waves incident on the substrate surface at angles in the range from 0 to 40 degrees, the transmission loss of electromagnetic waves due to reflection from the microstructure of the surface relief is less than 1%.

The method differs from the analogue in that it allows creating not subwavelength microstructures, but recesses with a greater depth than one fourth of the radiation wavelength. The method presented in the analog of the invention, allows you to make enlightenment only one wavelength, and the method proposed by the authors is designed for enlightenment in a wide spectral range (from 2 to 10 microns). The analog also uses a galvanic scanner, which limits the area of application of the microstructure. In the method proposed by the authors, there is no such limitation, since an air cushion nanopositioner is used.

List of figures

Fig. 1 - method of antireflection of the ends of active Cr:ZnS waveguides based on surface microstructuring.

Claims (1)

A method for antireflection of the ends of active Cr:ZnS waveguides based on surface microstructuring, designed to suppress the reflection and scattering of electromagnetic waves from 2 to 10 μm, incident on the substrate surface at angles in the range from 0 to 40 degrees, from the surface of the end of an active Cr:ZnS waveguide and , thus increasing the transmission of electromagnetic waves through the active Cr:ZnS waveguide, by modifying the flat surface of the end face of the active Cr:ZnS waveguide using direct laser ablation with single ultrashort laser radiation pulses, which uses a laser of ultrashort laser radiation pulses, a lens for focusing ultrashort pulses laser radiation relative to the upper boundary of the substrate, a positioner that moves the substrate in three coordinates relative to the focus point of ultrashort laser radiation pulses; the method includes: placing an active Cr:ZnS waveguide relative to the focusing point of ultrashort laser radiation pulses, where the end face of the active Cr:ZnS waveguide is directly exposed to ultrashort laser radiation pulses, and ultrashort laser radiation pulses physically affect the surface of the active Cr:ZnS waveguide end face to removing material from the end surface of the active Cr:ZnS waveguide by ablation, forming a hole or depression, the positioner continuously moves the end of the active Cr:ZnS waveguide, synchronized with the repetition rate of ultrashort laser radiation pulses, to form holes on the flat top surface of the substrate; wherein the generated surface microstructure has distances between holes less than the shortest wavelength of electromagnetic waves, and the depth of the holes is greater than the shortest wavelength of electromagnetic waves; also, in this case, the effective refractive index of the surface microstructure monotonically increases from the environment to the material substrate.

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