Waveguide manufacture
A method is provided of manufacturing a waveguide comprising an input port, an output port, a transparent medium having a first refractive index (n 1 ), a first pair of opposing surfaces and a second pair of opposing surfaces. The method comprises polishing at least one surface of the second pair of opposing surfaces to achieve a separation therebetween, bonding a protective layer to at least one polished surface of the second pair of opposing surfaces; and polishing at least one surface of the first pair of opposing surfaces to achieve a separation therebetween.
1 . A method of manufacturing a waveguide, the waveguide comprising:
a waveguiding layer of a transparent medium having a first refractive index (n 1 ), the waveguiding layer having
a first pair of opposing elongate surfaces arranged to guide a wavefront through the transparent medium from the input port to the output port by reflection therebetween in a zig-zag path to provide a plurality of reflections at distinct locations along lengths of the first surface of the first pair of opposing elongate surfaces and the second surface of the first pair of opposing elongate surfaces, and
a second pair of opposing surfaces,
an input port on a first surface or a second surface of the first pair of opposing elongate surfaces,
an output port on the first surface of the first pair of opposing elongate surfaces,
a partially transmissive-reflective coating on the first surface of the first pair of opposing elongate surfaces, arranged such that the wavefront is divided at each reflection and a plurality of replicas of the wavefront are transmitted through a region of the first surface that forms the output port, and
a reflective coating on the second surface of the first pair of opposing elongate surfaces,
the method comprising:
providing a body of the transparent medium having a first pair of opposing elongate surfaces and a second pair of opposing surfaces;
polishing a first surface of the second pair of opposing surfaces of the body of the transparent medium to provide the second pair of surfaces of the waveguiding layer, the second pair of surfaces of the waveguiding layer having a separation therebetween;
bonding a first protective layer to the polished first surface of the second pair of opposing surfaces;
polishing a first surface of the first pair of opposing elongate surfaces and/or a second surface of the first pair of opposing elongate surfaces of the body of transparent medium to provide the first pair of surfaces of the waveguiding layer, the first pair of surfaces having a separation therebetween;
providing the reflective coating on the first surface of the first pair of opposing elongate surfaces, and
providing the partially-transmissive/partially-reflective coating on the second surface of the first pair of opposing elongate surfaces.
2 . A method as claimed in claim 1 wherein the first protective layer is a first cladding having a refractive index (n 2 ) that is less than the first refractive index (n 1 ) of the transparent medium.
3 . A method as claimed in claim 2 wherein the step of bonding the first protective layer to the transparent medium comprises fusion bonding or heating.
4 . A method as claimed in claim 1 wherein the step of bonding the first protective layer to the transparent medium is preceded by a step of applying an optical coating to the at least one surface of the second pair of opposing surfaces, wherein the optical coating has a refractive index (n 2 ) less than the first refractive index (n 1 ) of the transparent medium.
5 . A method as claimed in claim 4 wherein the step of applying the optical coating is followed by a step of adding an adhesive layer, before bonding the protective layer to the transparent medium.
6 . A method as claimed in claim 5 wherein the adhesive layer is partially or totally absorbing to visible light for waveguiding.
7 . A method as claimed in claim 4 wherein the protective layer is formed from the same material same as the transparent medium.
8 . A method as claimed in claim 1 wherein the first protective layer has a thickness sufficient to prevent evanescent loss in the waveguide.
9 . A method as claimed in claim 1 ,
wherein the second pair of opposing surfaces is arranged to guide the wavefront through the transparent medium from the input port to the output port by total internal reflection; and
wherein each surface of the second pair of opposing surfaces is clad with a respective second protective layer of material having a refractive index less than that of the transparent medium.
10 . A method as claimed in claim 9 wherein each second protective layer is a cladding having a second refractive index (n 2 ) that is less than a first refractive index (n 1 ) of the transparent medium.
11 . A method as claimed in claim 10 wherein each second protective layer is fusion-bonded to, or co-moulded with, the transparent medium.
12 . A method as claimed in claim 10 wherein an optical coating is provided between at least one surface of the second pair of opposing surfaces and the respective second portective layer, wherein the optical coating has a refractive index (n 2 ) that is less than the first refractive index (n 1 ) of the transparent medium.
13 . A method as claimed in claim 12 wherein an adhesive layer is provided between the optical coating and the respective second protective layer.
14 . A method as claimed in claim 13 wherein the adhesive layer provided between the optical coating and the respective second protective layer is partially or totally absorbing to visible light for waveguiding.
15 . A method as claimed in claim 12 wherein the protective layer is formed from the same material same as the transparent medium.
16 . A method as claimed in claim 9 wherein each layer of cladding material has a thickness sufficient to prevent evanescent loss in the waveguide.
17 . The method of claim 1 , wherein the input port is at a position on the first surface of the first pair of opposed surfaces that lacks the partially transmissive-reflective coating.
18 . The method of claim 1 , wherein the input port is at a position on the second surface of the first pair of opposed surfaces that lacks the reflective coating.
19 . A method of manufacturing a waveguide comprising
a waveguiding layer of a transparent medium having a first refractive index (n 1 ), the waveguiding layer having
a first pair of opposing elongate surfaces arranged to guide a wavefront through the transparent medium from the input port to the output port by reflection therebetween in a zig-zag path to provide a plurality of reflections at distinct locations along lengths of the first surface of the first pair of opposing elongate surfaces and the second surface of the first pair of opposing elongate surfaces, and
a second pair of opposing surfaces,
an input port on a first surface or a second surface of the first pair of opposing elongate surfaces,
an output port on the first surface of the first pair of opposing elongate surfaces,
a partially transmissive-reflective coating on the first surface of the first pair of opposing elongate surfaces, arranged such that the wavefront is divided at each reflection and a plurality of replicas of the wavefront are transmitted through a region of the first surface that forms the output port, and
a reflective coating on the second surface of the first pair of opposing elongate surfaces,
the method comprising:
providing a body of the transparent medium having a first pair of opposing elongate surfaces and a second pair of opposing surfaces;
polishing a first surface of the second pair of opposing surfaces of the body of the transparent medium to provide the second pair of surfaces of the waveguiding layer, the second pair of surfaces of the waveguiding layer having a separation therebetween and introduce an undesired profile in at least one edge of the first surface of the second pair of opposing surfaces;
applying a first optical coating to the polished first surface of the second pair of opposing surfaces, the optical coating having a refractive index (n 2 ) less than the first refractive index (n 1 ) of the transparent medium;
bonding a first protective layer to the first optical coating, wherein the first protective layer is formed from the same material as the transparent medium; and
polishing a first surface of the first pair of opposing elongate surfaces and/or a second surface of the first pair of opposing elongate surfaces of the body of transparent medium to provide the first pair of surfaces of the waveguiding layer, the first pair of surfaces having separation therebetween and remove the undesired profile.
20 . The method of claim 19 , wherein the undesirable profile in the at least one edge of the first surface of the second pair of opposing surfaces is a rounding or chamfering.