Multi-fiber light guide, device with a multi-fiber light guide and method for producing the same

An optical sensor arrangement, comprising:

• a housing including a multi-fiber light guide, the multi-fiber light guide including:
• a plurality of light guiding fibers, each of the plurality of light guiding fibers including a glass core which is elongated, the plurality of light guiding fibers thereby including a plurality of the glass core which includes a glass;
• a glass cladding which includes a glass, the plurality of the glass core being surrounded by the glass cladding such that the glass cladding with the plurality of the glass core form a glass element which is rigid and continuous, the plurality of the glass core having a higher refractive index than the glass cladding and thereby being configured such that a light can be guided by a total reflection along the plurality of the glass core, the glass element of the multi-fiber light guide including two abutting faces, with the plurality of the glass core ending in respective ones of the two abutting faces and thereby being configured such that the light can be guided along the plurality of the glass core from a respective one of the two abutting faces to another respective one of the two abutting faces, the glass element further including a glass shell which encompasses the glass cladding with the plurality of the glass core which are embedded, the glass shell extending between the two abutting faces;
• and
• an ion exchange layer at each of the two abutting faces, the glass of the plurality of the glass core and the glass of the glass cladding including a plurality of alkali ions, which are at least partly exchanged by a plurality of alkali ions of a higher atomic number within the ion exchange layer at each of the two abutting faces, exchanged ones of the plurality of alkali ions within the ion exchange layer imparting a compressive stress at the two abutting faces, the ion-exchange layer also extending along the glass shell of the glass element;
• a sensor element encased in the housing, the multi-fiber light guide configured for guiding a light from outside of the housing to the sensor element.

A method for producing a multi-fiber light guide, the method comprising the steps of:

• providing a first preform with at least one rod of a first glass and at least one first glass element of a second glass having a lower refractive index than the first glass, the first preform being assembled such that the at least one rod is surrounded by the second glass;
• heating the first preform and fusing the at least one rod to the at least one first glass element;
• drawing the first preform to increase a length of the first preform and to reduce a lateral dimension of the at least one rod;
• cutting the first preform, which has been drawn, into a first plurality of sections;
• assembling the first plurality of sections to form a second preform;
• cutting a second plurality of sections from the second preform to obtain a plurality of second glass elements comprising a plurality of light guiding fibers including a core of the first glass surrounded by a cladding of the second glass, the core being a glass core, the cladding being a glass cladding;
• and
• immersing the plurality of second glass elements into a salt bath including a plurality of alkali ions to effect an ion exchange with a plurality of alkali ions in a plurality of glasses of respective ones of the plurality of second glass elements and to form an ion exchange layer at a surface of the respective ones of the plurality of second glass elements which exerts a compressive stress to the plurality of glasses, wherein the respective ones of the plurality of second glass elements each including two abutting faces and a glass shell, a plurality of the glass core ending in respective ones of the two abutting faces and thereby being configured such that a light can be guided along the plurality of the glass core from a respective one of the two abutting faces to another respective one of the two abutting faces, the glass shell encompassing the glass cladding with the plurality of the glass core which are embedded, the glass shell extending between the two abutting faces, the ion-exchange layer also extending along the glass shell.