CS233165B1 - Method of selecting raw material for electrooptical modulators - Google Patents

Abstract

A method of selecting raw material for electro-optic modulators, in particular lithium niobate, by marking defects on the examined crystal, made visible on a screen, where the goal is achieved by exposing the crystal of the selected raw material, provided with two parallel polished surfaces, parallel to the optical axis Z of the crystal, preferably corresponding to the crystallographic surfaces (100) or (010), to a beam of expanded, possibly divergent, gas plasma light, linearly polarized so that the frequency direction of the laser light is identical to the direction of the optical axis Z of the crystal.

Description

The invention relates to a process for selecting raw material of birefringent crystals, in particular lithium niobate, for the production of electro-optical modulators.

So far, the selection of the raw material for this purpose has been made by evaluating macrospocic inhomogeneities such as bubbles, impurities, cracks and cords in the functional direction of the optical Z-axis in white natural light or when observed in laser monochromatic light. This method of raw material selection does not provide sufficiently reliable results, and the modulators of the raw material so selected, which exclude areas of said inhomogeneities, do not achieve the necessary extinction ratio and greatly deform the wavefront of transmitted light.

Other methods of selecting a raw material are known, for example the method of selecting the raw material for the ruby resonators of U.S. Patent No. 135,108 based on assessing the shape and cross-section of the gas laser beam after passing through the selected raw material provided with straight, parallel polished surfaces at both ends; selection of raw material for optically uniaxial crystal cuts according to the author's certificate no.

156,203, based on the evaluation of the isochrome symmetry violation when viewed in wedge-converging light.

Even these methods do not provide sufficiently reliable results for selecting the raw material for the manufacture of electro-optical modulators.

Reliable results in the selection of the raw material, especially lithium niobate for electro-opic modulators, are achieved by the method according to the invention characterized by defects on the crystal under investigation, visible on the screen, the principle being that the crystal of the raw material is provided with two parallel polished surfaces. parallel to the optical Z-axis of the crystal, preferably corresponding to the crystallographic surfaces (100) or (010), is exposed to a beam of expanded or divergent light of a gas laser linearly polarized so that the laser light frequency is coincident with the optical-Z direction.

Example

The lithium niobate monocrystal of 25 mm diameter and 80 mm length was provided with two adjacent, parallel surfaces, which were polished as is common in pptical practice with transparent windows, which were parallel to the optical Z-axis of the crystal and corresponded to crystallographic ^r areas <100 ). The treated crystal was exposed to a parallel beam of gas laser beams such that the frequency of transmitted light was identical to the direction of the optical axis Z of the crystal. The projection of the raw material was observed on a screen where regions of optical inhomogeneities were clearly displayed and these regions were marked with a marker directly on the selected crystal. For further processing into electro-optical modulators, the areas so marked were excluded from the processing and the modulators produced from the selected raw material complied with their parameters, in particular the extinction ratio of 95% of all produced. Electro-optical modulators produced from and from selected raw material complied with their parameters only in a maximum of 50% of the produced ones.

Claims (1)

SUBJECT OF THE INVENTION 233 163 Method for selecting a raw material, in particular lithium niobate crystals for electro-optical modulators by marking defects on the investigated crystal visible on the screen, characterized in that the selected raw material crystal has two parallel polished surfaces parallel to the optical Z axis of the crystal, preferably corresponding to crystallographic surfaces (100) or (010) exposed to a beam of expanded or divergent gas laser light linearly polarized such that the laser light frequency is coincident with the direction of the optical axis Z of the crystal.