SU998894A1 - Planar optical waveguide investigation method - Google Patents

Description

The invention relates to optical CMM measurements and can be used both for studying plenary optical waveguides (with a constant or variable refractive index in the waveguide layer), and for physical studies of thin diameters. electrical layers (with constant or variable refractive index) on dielectric substrates having a refractive index less than that of c. layer. .

A known method for determining waveguide parameters by mathematical processing of measurement results of effective refractive indices for guided waveguide modes 1.

However, this method requires the manufacture of special devices for input (output) of radiation, careful collimation of the input beams, ensuring parallelism of the working face of the prismatic communication element and the waveguide surface while maintaining a certain constant gap between the irpaHbra iri surface of the waveguide, place high demands on

the plane of the working face of the prism and the surface of the waveguide.

There is also known a method for investigating a plenary optical waveguide, which includes creating an optical contact between the surface of the waveguide layer and one face of the prism, illuminating the other prism with unparsed light, measuring the third angle of the prism of the angular distribution of the radiation intensity, and calculating the angular distribution of parameters

15 waveguide 2J. . .

However, this method has great complexity and lack of measurement accuracy ..

The purpose of the invention is to simplify the method,.

This goal is realized by the fact that light is scattered on the illuminated edge of the prism, the radiation emitted from the third face is polarized, and the measurement is carried out by determining the interference minima of its spatial Fourier spectrum.

In addition, optical contact is created over the entire total area of contacting surfaces, and optical contact is created with a medium having a refractive index at a working wavelength less than or equal to the refractive index of the prism, but greater than or the refractive index of the waveguide layer at its surface. In this case, the prism is illuminated with light with a coherence length} about the thickness of the waveguide layer,, FIG. Figure 1 shows the optical scheme of the device for implementing the method and the course of the interfering beams for the thin shoulder 6dag waves in FIG. 2 way interfering beams for waveguides with a variable refractive index. The device comprises a prism 1, a waveguide layer 2, a waveguide substrate 3, an input matte face 4, a working face 5, an output face 6, a device for visually controlling or measuring the angular intensity distribution of parallel beams of radiation with the desired field 7 and a layer of liquid 8 In the device, the letters O and b are two arbitrary | HYH. ray. The pairs of rays QI, UQ 1 b4, b interfere. The matted face 4 of the prism 1, which is transparent to the working wavelength range, is illuminated by a beam of non-polarized radiation with the required spectral composition. In optical contact with the working face 5 of the prism, there is a waveguide layer 2 prepared on the substrate 3. The prism refractive index is larger than the waveguide layer refractive index. The prism angle oL is chosen so as to provide a way out of the edge b of the rays that reach the face 5 at angles greater than the critical angle of total internal reflection for the boundary of the prism – substrate medium. For the output side b of the prism is located the device 7 dl. visual control or measurement of the angular distribution of the intensity of parallel beams of radiation with the required polarization, for example, for an electric vector of a wave parallel to the plane of incidence (TM), or for an electric vector of roll, perpendicular to the plane of falling (TE), Device 7 provides research spatial Fourier radiation spectrum of a prism reflected from the optical contact area with a waveguide and past the prism output face 6. The matting of the input face ensures the presence of a large number of rays falling on the working face at angles, wider than the critical angle of total internal reflection for the prism – medium interface of the waveguide. Great. The area of optical contact and the use of a device that fixes the intensity of all that come out of face 6 at a fixed angle f to its normal increases the efficiency of the circuit in terms of the luminous flux. The coherence length of radiation sources should not be significantly less than the optical path difference of the interfering beams. Optical contact of the working face of a prism and a waveguide layer can be accomplished, for example, using a thin layer 8 of immersion liquid, the refractive index of which satisfies the inequality n (0), where Pr is the refractive index of the prism; n (the refractive index of the waveguide layer at its surface (for a thin-film waveguide. P (0) P |).) As the device 7, an optical circuit can be used, including, for example, a polarizer, a lens and a photo-receiver located in the focal plane lens and having a receiving area in the form of a narrow slit parallel to the direction of the interference fringes of equal inclination. Under the above-described conditions of illumination of the S face, such a range of angles of incidence is achieved, at which the rays experience total internal reflection of t waveguide substrate but not yet experiencing such reflection on the surface of the waveguide layer. At angles of incidence where sin (0) / Pr are the rays reflected from both edges of the thin-film waveguide or from the front border and in the thickness of the waveguide layer for the waveguide with variable indicators The refractions interfere, which leads to the appearance of interference minima in the spatial Fourier spectrum of the reflected radiation, using device 7 to determine the exit angles V, for which THESE minima are observed. Exit angles p. from Zan with the angles of incidence E of the same Yauchey on the edge 5 by the ratio--arcsivT CupSih (.6.- ° () where .cL-- is the refracting prism of the prism shown in FIG. 1, knowledge of only three quantities: the refractive angle of the prism, the refractive index of the prism, the angular position of the interference minima. In the process of investigation only the last magnitude is determined, and its determination can be made by known methods with high accuracy.

The value of Ifj is determined using relations (1)

.1ж Irv1P & and -% (0) (0),

where, 1,2, ...;

  the angle of refraction (Fig. 1 and using a mathematical expression, using a value for the waveguide parameters, use the well-known methods to calculate the waveguide parameters using a set of experimental values of Puu, using known methods.

One implementation option. The proposed method is the use of refractometers of the Abbe type of refractometers. | Like Hi; in conventional refractometric measurements, the edge of the measuring prism of the instrument, in this case, is a light source with a white spectrum, however, the observation of the boundary of areas with different levels of light is carried out using a polarizer j between the eye and the eye of the instrument and oriented so as to isolate TM polarization. The compensator built into the device eliminates the difference in interference fringes caused by the dispersion of the prism and the waveguide, and compensation is achieved for a wavelength equal to the D-line sodium wavelength in the ocular field. In this case, a black and white interference pattern is observed near the dark boundary. and a bright area corresponding to the total internal reflection for the boundaries of the prism media — the waveguide substrate. When combining the ocular line of sight with the center of narrow dark lines, the counting device of the device immediately gives the values corresponding to the illumination with the radiation of the D-wave. Observing the interference pattern and counting the number of dark bands makes it possible to estimate the number of waveguide modes for D-sodium and other parameters of the waveguide.

The proposed transmission does not require any adjustment of the sample, especially: but difficult outside the range of the spectrum, special techniques and devices for lighting

and is applicable to wide KJjacca waveguide structures, including waveguides with low scattering or high attenuation. It can be used both for physical studies and for technological control in the production of integrated optical components of fiber-optic communication lines.

Claims (3)

1. A method for studying a planar optical waveguide, thus creating an optical contact between  the surface in the bottom layer and one face of the prism, illumination of the other face of the prism with unpolarized light, measurement of the angular distribution of the radiation intensity beyond the third facet of the prism, which experienced complete internal ignition from the waveguide substrate, and calculating the waveguide parameters so that, in order to simplify the method, the light is scattered on the prismatic side of the prism, the radiation emerging from the third side is polarized, and a measurement is taken by determining the interference minima of its surface spatial furspektra. 2. The method according to claim 1, which means that optical contact is created over the entire total area of the contacting surfaces, we will accept optical contact created by a medium having a refractive index on the working Dlina wave less than or equal to the optical index prism, but greater than or equal to the refractive index of the waveguide layer at its surface, 3. A method according to claim D and about the fact that the prism is illuminated with light with a coherence length of the order of the thickness of the waveguide layer. Sources of information taken into account in the examination 1. Integrated optics. Edited by Tamira. M., Mir, 1978. 2.Appl. Phys. Lett. 1978, No. 32, 12, p. 819 (prototype).