Optical devices and methods of manufacture thereof

• US 20020181910A1
• Filed: 06/03/2002
• Published: 12/05/2002
• Est. Priority Date: 12/03/1999
• Status: Active Grant

• Current Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Original Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Inventors: Holmes, Melanie
• Granted Patent: US 6,922,513 B2
• Time in Patent Office: Days
• US Class Current: 385/124
• CPC Class Codes: G02B 6/0281 Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core G02B6/0288, G02B6/0286 take precedence
• CPC Class Codes: G02B 6/0283 Graded index region external to the central core segment, e.g. sloping layer or triangular or trapezoidal layer G02B6/0288, G02B6/0286 take precedence
• CPC Class Codes: G02B 6/03633 arranged - -
• CPC Class Codes: G02B 6/03694 Multiple layers differing in properties other than the refractive index, e.g. attenuation, diffusion, stress properties
• CPC Class Codes: G02B 6/13 Integrated optical circuits characterised by the manufacturing method
• CPC Class Codes: G02B 6/262 Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
• CPC Class Codes: G02B 6/29307 components assembled in or forming a solid transparent unitary block, e.g. for facilitating component alignment
• CPC Class Codes: G02B 6/29308 Diffractive element having focusing properties, e.g. curved gratings Rowland circle spectrometers G01J3/20
• CPC Class Codes: G02B 6/2931 Diffractive element operating in reflection
• CPC Class Codes: G02B 6/3512 the optical element being reflective, e.g. mirror
• CPC Class Codes: G02B 6/3546 NxM switch, i.e. a regular array of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/3548 1xN switch, i.e. one input and a selectable single output of N possible outputs
• CPC Class Codes: G02B 6/3582 Housing means or package or arranging details of the switching elements, e.g. for thermal isolation
• CPC Class Codes: G02B 6/3833 Details of mounting fibres in ferrules; Assembly methods; Manufacture

Abstract

An optical fiber (12), which presents a beam expanding feature, has a core, an inner cladding, an outer cladding and a sheath. The inner cladding is doped with a photosensitive material like germanium. By using ultra-violet radiation (16) from a copper laser (18) having a Gaussian energy distribution, a refractive index taper may be created inside the fiber. Therefore the tapered fiber has a larger effective area in the coupling region (20), and insertion losses are reduced.

Claims

1. An optical fibre having a core, a photosensitive inner cladding and a further cladding surrounding the photosensitive inner cladding, the core being arranged to permit a light beam to travel therethrough, the fibre having a first end zone in which the inner cladding has a plurality of refractive indices along a longitudinal axis of the fibre, the fibre further having a second end at which it is compatible with a standard fibre, said refractive indices being such that in use the light beam travels along the fibre, the refractive indices defining a taper such that at a free-space end of the fibre the diameter of the core is increased to a enlarged core diameter equal to that of the core plus the inner cladding;

and whereby at said free-space end the fibre has a V number greater than that of the standard fibre, wherein the outer dimension of the fibre is unchanged along its length.

2. An optical fibre according to claim 1, wherein the inner cladding has refractive indices in the said zone which have an approximately Gaussian distribution between a minimum refractive index and a maximum, said maximum being at a free-space end of the fibre.

3. An optical fibre according to claim 1 or 2, said core having a centre, wherein the inner cladding has a photosensitivity which reduces with distance from the centre of the core.

4. An optical fibre according to any preceding claim, wherein the inner cladding comprises deuterium loaded germanosilicate glass.

8. An array of beam-steering elements for steering light from an array of input fibres to an array of output elements wherein the input fibres are in accordance with any of claims 1-4, wherein each said beam-steering element has a width defined as a given multiple of the spot size of the input fibres, and wherein the input fibres have a ratio of separation-to-spot size, which ratio is selected to be equal to the given multiple times the square root of 2.

5. A method of increasing the offset coupling tolerance of an optical fibre, comprising

providing said optical fibre having first and second ends, wherein said fibre has a core, a photosensitive inner cladding and an outer cladding, wherein the refractive index of the core is greater than that of the inner cladding and that of the outer cladding, wherein at least at one end the fibre is compatible with a standard fibre;

illuminating the optical fibre with electromagnetic radiation on the end face at the other end of the fibre, whereby the refractive index of the photosensitive inner cladding increases along the fibre to said end face such that at the end face the index of the inner cladding matches onto that of the core, whereby the core diameter at said end face is raised to that of the core plus the inner cladding, wherein the V number at the end face is greater than that of a standard fibre, the increased V number and core diameter increasing the spot size and the coupling tolerance.

7. A method according to claim 5 or 6, wherein the electromagnetic radiation is uv laser radiation.

6. A method of increasing the offset coupling tolerance of an optical fibre, comprising:

providing said optical fibre having first and second ends, wherein said fibre has a core, a photosensitive inner cladding and an outer cladding, wherein the refractive index of the core is greater than that of the inner cladding and that of the outer cladding, wherein at least at one end the fibre is compatible with a standard fibre;

illuminating the optical fibre in the other end region thereof with electromagnetic radiation transverse the length of the fibre, whereby the refractive index of the photosensitive inner cladding increases along the fibre to said end such that at the end the index of the inner cladding matches onto that of the core, whereby the core diameter at said end face is raised to that of the core plus the inner cladding, wherein the V number at the end face is greater than that of a standard fibre, the increased V number and core diameter increasing the spot size and the coupling tolerance.