DE2650500A1 - Polarisation colour filter device - has specific polarisation optical elements for filtering or separating discrete laser lines of laser beam - Google Patents

Abstract

A polarisation colour filter is used for separating discrete spectral lines of a laser beam. It has polarisation specific optical elements. A colour dispersive optically active crystal is used which as a function of its thickness changes the polarisation state of specific laser lines differently through a rotation of the polarisation directions. The polarisation directions are determined by means of polarisation specific optical elements for filtering, or separating the lines. A quartz body (Q) with the optic axis positioned in the direction of the laser beam rotates the polarisation direction or plane of a light beam by an angle which increases linearly.

Description

"Polarized color filter device"

The invention relates to a polarized color filter device for filtering out or separating discrete laser lines of a laser beam with polarization-specific ones optical means.

Lasers are used more and more frequently as light sources in information display devices such as B. the laser displays in digital light deflectors. When these displays are multicolored should be, the ion lasers (Ar and Kr) are used, which at the same time several discrete laser lines of different Generate wavelength can; z. B. the argon ion laser emits 6 lines in broadband mode over the spectral range blue - green.

In general, only a few of this line variety are used Lines required, with the argon laser z. B. the two strongest lines 488nm (blue) and 514nm (green). In this case, a filter arrangement is required that eliminates the unwanted Laser lines suppressed.

In principle, such a filtering is with the dispersion effects known as color splitting by means of a prism or grid.

Absorption filters or interference filters are also used for these purposes known. However, the first ones need longer distances, unless one uses in addition Lenses. In the second case, the space requirement is small, but there must be high light losses be accepted.

The use of so-called Lyot filters is also possible.

Here, a birefringent plate is used in the linearly polarisist Light beam brought (optical axis of the plate perpendicular to the direction of the beam), the due to different phase shifts for two different wavelengths (different colors) ensures that the two colors are perpendicular to each other polarized leave the plate. These two colors can then continue accordingly are processed.

However, such waveplates have lengths for given wavelengths extremely small thickness tolerances and are therefore complex and expensive.

The object of the invention is to provide a more straightforward polarizing color filter device to create, the dimensions of which are not critical, so that an easier production is possible.

This object is achieved in that a color-dispersing optical active crystal is used, the polarization state depending on its thickness certain laser lines in the sense of a rotation of the polarization directions different changed that with polarization-specific optical means for filtering or Separation of the lines can be noted.

The drawings represent exemplary embodiments. They show: Fig. 1 shows a device with one optically active quartz; FIG. 2 shows a device with two optically active crystals.

The optical activity, which is dependent on the thickness, is used for filtering of a crystal e.g. B. used by crystalline quartz. A quartz body Q with a layer of the optical axis o in the direction of the laser beam rotates the direction of polarization or plane of a light beam at an angle a linearly with the thickness d des Quartz body Q grows. The value for G depends on the wavelength, see above that a thickness can always be specified for two specified wavelengths X 1 '2, at which the two colors leave the quartz body polarized perpendicular to each other (P1, P2, Fig. 1). This enables a simple separation of both colors with polarization-specific Averaging e.g. a polarization splitter cube PT is possible.

The values for the separation of the argon lasers are an example 514.5 nm and 496.5 nm are given: It is used for exactly orthogonal polarization of both Lines a thickness d of 38.7 mm (deep quartz) are required. With an additional polarization filter one color can now be 100% (excluding reflection losses) and the other Color at 0 5 ', i.e. not allowed through.

The quartz thickness may deviate from the specified value by up to 0.2 mm, if deviations of the intensities of 1% are permitted.

The comparable thickness tolerances for Lyot filters are on the other hand in the m range.

To filter out certain lines from a large number of predefined lines, several such filters must be arranged one behind the other, as shown in Fig. 2 is shown schematically. Here, for example, a four-color laser beam hits the Wavelengths on ... on to the quartz body Q1 with a thickness of d1, over the Polarization splitter PT1, the waves X 1 and X2 are split off, while the waves W3 and W4 hit the quartz body Q2 with the thickness d2, in order then in the polarization splitter PT2 to be disconnected.

The light losses are despite the larger number occurring here of interfaces is not significant, since the light beam hits all interfaces falls vertically and thereby with modern reflection-reducing broadband layers the light loss per interface can be reduced to about 0.3%.

PATENT SEARCH:

Claims (4)

PATENT CLAIMS: 1. Polarizing color filter device for filtering out or separation of discrete laser lines of a laser beam with polarization-specific ones optical means, characterized. that a color dispersing optically active Crystal is used, the polarization state depending on its thickness certain laser lines in the sense of a rotation of the polarization directions different changed that with polarization-specific optical means for filtering or Separation of the lines can be noted. 2. Color filter device according to claim 1, characterized in that that the optically active crystal is a quartz body, the optical axis of which is in the direction of the beam runs and its thickness is chosen so that an orthogonal polarization of two predetermined discrete laser lines takes place. 3. Color filter device according to claim 1 or 2, characterized in that that a polarization splitter cube is provided as a polarization-specific optidws means is. 4. polarization device according to claim 1, characterized in that that several quartz bodies of different thicknesses with each arranged in between Polarization parts are arranged one behind the other.