DE3742331C2 - - Google Patents

Description

The invention relates to a method for decoupling at least visible light from one consisting of a glass core and a coat organic material existing first optical fiber in a second optical fiber using the temperature in a coupler for light modulation or for temperature measurement with a large measuring range according to the preamble of claim 1.

Such a method for temperature measurement is known from US 41 51 747 known.

However, with the optical fibers used there Temperature measurement limited to the range of high temperatures.  

GB 20 73 439 describes a method for temperature measurement with the aid of optical fibers specified. However, with the optical fibers used the measuring range is limited to values T <-100 ° C, since at lower temperatures, the attenuation of the optical fiber is so strong increases that the signal is no longer measurable. An optical fiber according to GB 20 73 439 it is 9 m long.

From GB 21 84 859 it is known that in the form of a biconical Tapers is a temperature controlled coupler within a monomode fiber can be made. However, the physical Structure of the optical fiber can be changed.

If one uses the biconical taper according to GB 21 84 859 for temperature measurement, then one in the measuring range of the interval

29 ° CT55 ° C

limited.

The biconical taper according to GB 21 84 859 is also usable as a modulator.

Starting from a method according to the preamble of the claim 1 is an object of the invention, the method for use in to further develop a larger temperature and wavelength range, without the mechanical structure of the first optical fiber needs to be changed.

This task is in the process according to the preamble of Main claim through the characterizing part of the main claim solved. Further advantageous embodiments of the invention are characterized in more detail in the subclaims. An approx 1 m long piece of the optical fiber enables temperature measurements in the area -196 ° C <T <+ 20 ° C.

The invention is explained with reference to FIGS. 1-3, and in particular reference to the embodiment of FIG. 3 in more detail.

Fig. 1 shows the temperature behavior of the refractive indices,

Fig. 2 shows the transmission behavior of the optical fibers and

Fig. 3 shows an arrangement for coupling optical radiation.

The refractive index n is plotted against the temperature T in the diagram shown in FIG. 1. The refractive index of the quartz core n _K at room temperature (20 ° C), corresponding to the right end of the curves, is greater than the refractive index of the silicone cladding n _{M of} the multimode step index fiber PCS from Quartz in Bad Pyrmont. The difference becomes smaller as the temperature falls and tends towards zero at a limit temperature T _g . From this temperature onwards, it is no longer possible to guide optical radiation in the core, since no total reflection can occur at the interface between the core and the jacket.

The diagrams in FIG. 2 show the transmitted light power P as a function of the length l of the optical waveguide PCS that has cooled to -196 ° C. with liquid air. The wavelength of the transmitted light is an essential parameter. Fig. 2a (2b) applies to = 0.7425 µm (1.5 µm). In Fig. 2c, the continuous spectrum of a black body with T = 2000 K (0.4 micrometers <λ <2.2 microns) was used in the measurement.

Fig. 3 shows an arrangement for extracting light at any point of the optical waveguide 1, to damage mechanically without this. The optical waveguide 1 consists of the quartz core 11 and the silicone jacket 12 . A terminal 2 encloses the optical waveguide 1 with its glass jaws 21 and 22 . The jacket 12 and the inside of the glass jaws 21 and 22 are coated with a transparent plastic known under the registered trademark Tefzel.

An outcoupling optical waveguide 3 with the core 31 and the jacket 32 opens into one of the glass jaws.

Via a pipe system 4 , which consists of an inner pipe 41 and an outer pipe 42 arranged concentrically to this, the liquid air required for cooling is supplied (inner pipe 41 ) and discharged (outer pipe 42 ).

Claims (4)

1. A method for decoupling at least visible light from a first optical waveguide consisting of a glass core and a jacket made of organic material into a second optical waveguide by means of the temperature in a coupler for light modulation or for temperature measurement in a large measuring range, characterized in that the glass of the core Quartz and the organic material of the silicone sheath is that the coupler is cooled, that the first optical waveguide in the coupler is intact, that low temperatures are measured and that IR light can also be used. 2. The method according to claim 1, characterized in that the coupler comprises a clamp ( 2 ) with glass jaws ( 21, 22 ) through which liquid air flows, into which the second optical waveguide ( 3 ) is inserted and the glass jaws of the first optical waveguide ( 1 ) enclose. 3. The method according to claim 1, characterized in that the first optical waveguide ( 1 ) is the temperature sensor and shorter than one meter. 4. The method according to claim 3, characterized in that Temperatures between + 20 ° C and -196 ° C can be measured.