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Metrology System for Characterization of Lensed Optical Fibers

IP.com Disclosure Number: IPCOM000051266D
Publication Date: 2005-Feb-10
Document File: 7 page(s) / 179K

Publishing Venue

The IP.com Prior Art Database

Abstract

This document discloses a metrology system useful for characterizing the shape and relative position of a cylindrical lens fashioned onto the tip of glass optical fibers. The system is comprised of a combination of measurement techniques that enables characterization of the lens, including video microscopy, machine vision processing, illumination, and far-field beam analysis. Also important is the integration of mechanical adjustments that enable the lensed fiber to be positioned and oriented efficiently and with a high degree of repeatability.

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Metrology System for Characterization of Lensed Optical Fibers

Technical Field

This document discloses a metrology system useful for characterizing the shape and relative position of a cylindrical lens fashioned onto the tip of glass optical fibers.  The system is comprised of a combination of measurement techniques that enables characterization of the lens, including video microscopy, machine vision processing, illumination, and far-field beam analysis.  Also important is the integration of mechanical adjustments that enable the lensed fiber to be positioned and oriented efficiently and with a high degree of repeatability.

Background

The coupling of highly divergent, edge-emitting diode lasers to single- and multi-mode optical fibers can be significantly improved by forming a lens on the end of the optical fiber.  Because diode lasers typically emit a highly elliptical beam, the lens formed on the tip of the fiber is typically a cylindrical wedge lens.  The efficiency of power coupling between the laser and the fiber is, in part, determined by the radius of curvature of the lens, the wedge angle of the lens, the degree to which the lens is centered on the core of the fiber, and the surface roughness of the lens.

Single-mode optical fiber is constructed of a concentric series of structures including a glass core (3-6 μm in diameter), a glass cladding (125 μm in diameter), and a polymer jacket (250 μm in diameter).  The lens is fashioned directly on the end of the outer glass portion of the fiber. The nature of the metrology problem posed in the manufacture of lenses of this type is suggested by the presentation of typical lens geometry and specifications for some currently commercialized products in Figure 1 and Table 1, respectively.

Figure 1                .                       Illustration of Radius (R), Wedge Angle (A), Perpendicularity (P), and Centration (C) of a Lensed Optical Fiber


Table 1. Typical Lens Specifications

Parameter

Symbol

Description

Target Values

Typical Tolerance

Radius

R

Lens Radius of Curvature

4 – 20 mm

+/- 1 mm

Wedge Angle

A

Half-angle of wedge face relative to longitudinal axis of fiber

23 – 45o

+/- 1o

Perpendicularity

P

Angle of lens axis relative to longitudinal axis of fiber

90o

+/- 1o

Centration

C

Lateral offset between axis of lens and fiber core

0 mm

+/- 0.5 mm

Explanation and Problems of Current Technology

There a number of microscopy, surface profilometry, and laser beam profiling techniques that one might consider for the application of interest.  Vendor technology is extremely mature in the microscopy and profilometry areas and relatively mature in the beam profiling areas.

Microscopy techniques (optical and electron) are widely used for a variety of measurement and inspection applications.  Automating a measurement typically requires implementation of software and image processing algorithms.  While microscopy can be used to measure the geometric shape of the lens,...