Optical device.

The invention relates to an optical device according to the preamble of claim 1.

Such devices are known as interferential working length or angle of a variety of publications.

As examples of the DE-A1 36 33 574 and EP-A1 0163362 may be mentioned. In the latter document, a position measuring device is described in which the index grating is a phase grating in which by varying the ridge to furrow ratio and the phase depth, the intensity ratio of two diffracted partial beams of different orders and the phase relationship between the 0th and 1st order can be adjusted.

In measurement systems which are based on the two-beam interference of the partial beams of different diffraction orders, a phase grating of this type have the considerable disadvantage of very different diffraction efficiencies, resulting in a poor degree of modulation.

Object of the invention, each of devices of the type mentioned, which are based on the two-beam interference to provide a Rekombinationsgitter that does not have this drawback, and that is so designed that by interference of the diffracted partial beams both equal signals defined phase relationship have, as well as equal modulation levels can be generated.

This object is achieved by a device having the features of claim 1.

Advantages of the invention lie in the improved efficiency and greater reliability, because the modulation degree of the interference signals can be increased considerably.

Advantageous embodiments of the invention are specified in the dependent claims.

With the aid of embodiments the invention with reference to the drawings will be explained in more detail below.

It shows<dl id="dl0001"><dt>figure 1</dt><dd>a schematic representation of a position; </dd><dt>figure 2</dt><dd>a variant of a position;</dd><dt>figure 3</dt><dd>a position measuring device in Auflichtanordnung;</dd><dt>figure 4</dt><dd>different diffraction grating sections;</dd><dt>figure 5</dt><dd>a diffraction grating with asymmetrically arranged lattice discontinuities and</dd><dt>figure 6</dt><dd>another diffraction grating section.</dd></dl>

In the position-shown in Figure 1 in transmitted light arrangement a phase grating 2 is from a light source 1, which emits narrow-band light, at an angle α illuminates the grating normal 0th The angle α is determined by the formula sin .alpha = l / 2 d, where l is the wavelength of light used and d the division period. Behind the phase grating 2 formed by diffraction two partial beams A and B of the diffraction orders "0" and "1". This sub-beams A and B meet a further grid 3, which is preferably also formed as a phase grating. This phase grating 3 is designed so that no zero diffraction order arises. This interpretation can be done in a known manner by the choice of the lattice parameters of the phase grating. 3 Of the costs incurred at the phase grating 3 by diffraction partial beams only to the grating normal 0 sat bent partial beams A and B are used. The partial light beams A and B take on another phase grating 4 and are there again flexed. Behind the phase grating 4 is thus obtained diffracted partial beams (A / +. 2) - (B / + 1.) (A / + 1.) - (B / 0th), (A / 0th) - (B / . -1), (A (-1.) - (B / -2.) two of the partial beams have the same direction and can thus interfere with each other..

On displacement of the phase grating 3 towards the phase gratings 2 and 4, the diffracted at the phase grating 3 partial beams A and B receive a phase shift. By moving the grating 3 just one grating period formed behind the grid 4, two complete sinusoidal intensity modulations. The purpose of the phase grating 4 is to produce the desired intensities and degrees of modulation, and between these selected directions the desired phase relationships in the selected directions.

The phase grating 4 and its variants are shown in Figures 4, 5 and 6 and will be described later.

The interfering partial beams falling on photovoltaic cells 5, 6, 7, 8 and are converted into electrical signals, which are evaluated with incremental position measuring systems in a known manner.

In Figure 2 is even more schematically a variant of a position shown in which the back mixing diffraction grating in the X direction is movable. This should be made clear that it does not matter which is moved to the grid - that forms the scale.

The position measuring system shown schematically in Figure 2 has an illumination device 21 of the illumination beam capable of generating interference two beams A and B by splitting at a phase grating 22 and subsequent deflection at a second grid 23 are formed. These interfere with the passage through a further phase grating 24 with each other. The diffracted and interfering partial beams (A / + 2.) - (B / 0th), (A / + 1.) - (B / -1.) (A / 0th) - (B / -2.) meet detector devices 25, 26, 27, which convert them into another phase-shifted measurement signals.

Notwithstanding the Transparency-illustrated embodiments, the invention can also be realized in Auflichtgeräten, requiring a modified geometric arrangement of the components.

This variant is shown in Figure 3 in analogy to the ones already described. Corresponding components of the figure index is again put forward.

From a light source 31 coming a lighting beam is split by a phase grating 32 in partial light beams A and B, running in different directions.

The special feature of this embodiment is a triple prism 33, which is located between the diffraction gratings 32 and 34th In this triple prism 33, the tip is removed, and the partial beams A and B occur - not as usual at the base, but - on the side opposite the base surface, which is caused by the capping of the tip.

Excluding the different refractive indexes - which, as you will be neglected in the other embodiments - through the partial light beams A and B unaffected the triple prism, so to speak from behind and hit the phase grating 34, which is constructed in this case as a reflection grating. At this reflection grating 34, the partial beams A and B are aligned by diffraction in parallel and are now, from the bottom up into the triple prism 33 a. They go through the triple prism 33 and meet as parallel partial beams A and B back to the reflection grating 34. There they are again diffracted and reflected by the base of the triple prism 33 opposing surface on the phase grating 32nd They interfere and the light-dark modulation can be detected.

Changes in distance of the two phase gratings 32 and 34 follow in this example to proportional retardation differences of interfering partial beams A and B, whose light-dark modulation provides the distance measurement signal.

4 shows different cross sections are shown by phase gratings, as they can be implemented as a diffraction grating 4, 24, 32, 34 in the embodiments.

Given the graduation period d the bars of the phase grating are the first example of Figure 4 4a narrower than the grooves. The land / groove ratio differs so markedly from 1: ex. 1

In the second example, the phase grating 4b is d structured differently with the same grating period; it has twice as many lattice discontinuities, as the first phase grating 4a. By adding a web within the graduation period d this is achieved. The profile, however, remains symmetrical.

A third example is a further structured phase grating 4c, in which the number of lattice discontinuities is doubled within the graduation period d again. Although the profile is symmetrical, the positions of lattice discontinuities may be randomly distributed.

Although structured in this manner phase grating may be symmetrical within the graduation period, but they need not be symmetrical, as the phase grating shown in Figure 4d. 5

The structuring of this phase grating is made by mathematical laws and it can be more intensity ratios of diffracted in different orders partial beams and the phase angle between the different diffraction orders to adjust.

If varies with a phase grating 4e according to Figure 6 in addition to the above structure also the height h1, h2 of the lands that the phase depth is also arbitrary between the higher orders of diffraction phase relationships can be set.