WO2005102279A2

WO2005102279A2 - Controlled gap techniques for fiber optics devices

Info

Publication number: WO2005102279A2
Application number: PCT/IB2005/001108
Authority: WO
Inventors: Ram Oron; Anatoly Patlakh
Original assignee: Kilolambda Technologies Ltd.
Priority date: 2004-04-26
Filing date: 2005-04-25
Publication date: 2005-11-03
Also published as: WO2005102279A3

Abstract

A system for preparing a controllable gap between two optical transmission elements (4 and 10) having a common axis by providing the transmission elements (4 and 10) with opposed end surfaces that are not orthogonal to the common axis, and turning the opposed end surfaces relative to each other about the common axis to form a controlled gap between the opposed end surfaces.

Description

CONTROLLED GAP TECHNIQUES FOR FIBER OPTICS DEVICES

FIELD OF THE INVENTION [001] The present invention relates to fiber or waveguide optical devices and methods of production, and particularly to such devices and methods having air gaps or material filled gaps, of precisely controllable dimensions between two fibers and/or waveguides. BACKGROUND OF THE INVENTION [002] Fiber lasers, fiber optics for communication systems, and other systems for light delivery, such as in medical, industrial and remote sensing applications are often using air, or optical material filled gaps, serving as attenuators, mode selectors or beam expanders. Since the gap dimension has to be tightly controlled, and it can assume various dimensions, from a single micrometer to many tens or hundreds of micrometers, different mechanical solutions were proposed for defining the gap, most of them incremental, using a spacer between the fibers. [003] Realizing of an optical gap was done using the following methods; 1. Spacer inserted between fibers 2. Wedge inserted between fibers 3. Micrometric screw 4. Differential screw [004] All of these require inserting external means to adjust the gap width. [005] Better, continuous gap length control techniques, without external means, are needed. The present invention provides a solution accordingly.

SUMMARY OF THE INVENTION [006] It is therefore a broad object of the present invention to provide a controllable gap technique and method for fibers and/or waveguides optic devices as needed in optical systems. [007] It is a further object of the present invention to provide a controllable gap device and method for fibers and/or waveguides where the fabrication of the gap can be executed using only simple mechanical internal means and simple movements, enabling to fabricate the gap, using only one kind of component for the fabrication of many gap sizes at will, where the selection of the gap is continuous. [008] It is still a further object of the present invention to provide a gap for use in a waveguide or optical fiber; the gap is either air or optical material filled. [009] It is still a further object of the present invention to provide a variable gap for use in a waveguide or optical fiber; the gap is either air or optical material filled. [0010] In accordance with one embodiment of the invention, there is provided a system for preparing a controllable gap between two optical transmission elements having a common axis by providing the transmission elements with opposed end surfaces that are not orthogonal to the common axis, and turning the opposed end surfaces relative to each other about the common axis to form a controlled gap between the opposed end surfaces. The transmission elements may be held in a ferrule or ferrulelike holder having an input end leading to an angled ferrule face, placed against a symmetric structure, where both are within a concentrating, e.g. ceramic sleeve. The relative movement, turning about the fiber axis of symmetry, provides the desired gap. [0011] A method for preparation of the gap is presented, as well as the needed tooling. [0012] With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings, making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

BRIEF DESCRIPTION OF THE DRAWINGS [0013] Fig. 1 is a schematic, cross-sectional view of an optical minimal gap between fibers. [0014] Fig. 2 is a schematic, cross-sectional view of an optical maximal gap between fibers. [0015] Fig. 3 is a schematic cross-section view of the method to manufacture the gap. [0016] Fig. 4 is example of a gap-containing device, an attenuator [0017] Fig. 5 is the experimental output of attenuators built in the presented method [0018] Fig. 6 is an example of a gap-containing device, a RL (Reflection/return Loss) Calibrator. [0019] Fig. 7 is the experimental output of calibrators built in the presented method [0020] Fig. 8 is an example of a gap-containing device, a limiter. [0021] Fig. 9 is the experimental output of limiters built using the presented method. [0022] Fig. 10 is a schematic cross-section view of a variable attenuator and back reflector.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT [0023] Turning now to the drawings and referring first to Fig. 1, a gap assembly 2 includes an input optical fiber 4 in a ferrule 6 and an output fiber 8 in a ferrule 10. The ferrules 6 and 10 are angle polished in an angle (e.g. 8°) and pushed into a centering sleeve 12 in a position that ensures their axial and angle match, thus providing a zero gap between them. When the whole assembly 2 is fixed in its position as shown, the gap will stay close to zero, and technically below 0.1 micrometers. When ferrule 6 is turned about its axis of symmetry, ferrule 10 stays in position, and the two ferrules 6 and 10 are held axially together, the gap is increased according to the angle of turning between the two ferrules 6 and 10, until it reaches the maximal gap at 180° position shown in Fig. 2. [0024] Fig. 2 illustrates the device shown in Fig. 1. However, here it reaches the maximal gap 16 at 180° position. Any other gap between the zero gap and the maximal gap 16 can be reached by turning the ferrule 10 at angles between 0-180°. An example is shown using =8° and a ferrule edge diameter of D=l mm, where due to geometry the maximum gap is Gap = £> sin α = 1 x sin 8° = 0.130mm . [0025] Fig. 3 shows a schematic cross-section of a system for assembling the gap-device, where the ferrule 6 is turned about its axis of symmetry using a marked wheel 18. The ferrule 10 stays in position, mounted in a steady rest 20. The two ferrules 6 and 10 are held axially together by spring loading 22. The gap can be increased from zero to a maximum according to the relative angle of turning between the two ferrules 6 and 10, until it reaches the maximal gap at the 180° position. In the procedure, the angle and gap are set to their calculated or pre-measured position, using wheel 18, and the assembly of ferrule 6, ferrule 10 and sleeve 12 is set together using glue at the ends of sleeve 12 or other positions. [0026] Fig. 4 shows a schematic cross-section of a device that uses an air-filled gap as an attenuator. The gap length determines the attenuation value (the attenuation is mainly due to numerical aperture, when passing from the fiber core of the input fiber into the limited aperture or core of the output fiber). The lost light 24 is absorbed in the outer sleeve 12 or transmitted through it and absorbed in the outer containment of the device. [0027] Fig. 5 is a table showing the experimental output of 3 attenuators built as described above, showing a 3dB, 5dB and lOdB attenuation. The gap was controlled by the method illustrated in Fig. 3, and its size appears in the table. The attenuators were tested spectrally and show better spectral stability than prescribed by the Telcordia requirements. The same applies to reflection/return loss and polarization-dependent loss. [0028] Fig. 6 is a schematic cross-section of a gap-containing RL (Reflection/return Loss) Calibrator. The length of the gap 26 is responsible for the back reflection. The gap is followed by a terminator 28, absorbing the passing light (reflecting back less than -60 dB). [0029] Fig. 7 shows the spectral behavior of the reflection/return loss calibrator made for -29 dB reflections. [0030] Fig. 8 is example of a gap-containing limiter. Containing limiting material 34 in the gap, having a gap 16 sized as needed for the limiting value. [0031] Fig. 9 illustrates the experimental output of limiters built as described above. The limit power is 9 dBm. The preferred optical-limiting solid mixture in the gap 16 is composed of light absorbing particles, smaller than the wavelength of visible light (smaller than 0.5 microns) and preferably smaller than 0.1 microns (nano-powder) dispersed in a solid matrix material. The light absorbing particles include at least one metallic or non-metallic material selected from the group consisting of: Ag, Au, Ni, Na, Ti, Co, Cr, C, Re, Si, SmO₂ and mixtures of such materials. The solid matrix material may be a transparent or optical polymer or inorganic glass material, e.g., polymethylmethacrylate ("PMMA") and its derivatives, epoxy resins, glass, spin-on Glass ("SOG"), or other sol-gel materials. The optical-limiting function begins with light absorption in the dispersed powder particles, each according to its absorption spectrum. When the particles are heated by the absorbed light, they conduct heat to their surroundings, leaving hot spots in the volume surrounded by them, and a decreasing temperature gradient in their neighborhood. These hot volumes can decrease the light transmission through the optical-limiting solid mixture by several mechanisms, one of which is scattering due to the refractive index spatial fluctuations created by the hot particle and its surrounding medium of a given, positive or negative, index change with temperature (drø/dT). The scattered light, at angles larger than β (where numerical aperture is sin β) leaves the optical path of the optical system. Some increase in the back-reflected light also may be observed. The light that is not scattered continues along the optical path having lower, "limited" power. When the incident power is reduced, the scattering volume which surrounds each absorbing particle diminishes. The transmittance through the optical-limiting solid mixture returns to its original value, and the scattering process decreases to negligible values. The process may be repeated many times without any permanent damage up to energies that are an order of magnitude or more, larger than the transmitted power limit. [0032] Other light-scattering mechanisms may also occur simultaneously or may dominate with different choices of matrix materials or absorbing particles. These mechanisms include stimulated Raman scattering, in which light is scattered inelastically by thermally induced molecular vibrations, or stimulated Brillouin scattering, in which light is scattered inelastically by local thermally induced acoustic waves. [0033] The light-absorbing particles are dispersed in a transparent matrix such as a monomer which is subsequently polymerized. There are many techniques for preparing such dispersions, such as with the use of dispersion and deflocculation agents added to the monomer mix. One skilled in the art of polymer and colloid science is able to prepare this material for a wide choice of particles and monomers. Similarly, techniques are well known in the art to prepare composite materials with dispersed sub- micron particles in inorganic glass matrices. [0034] Fig. 10 is a schematic cross-section view of a variable attenuator and/or back reflector. The size of the gap 26 is determined by the rotation of a dial 30 with respect to a stable rest 32. The adjustment of the rotation dial 30 creates gaps from zero to a maximum between ferrules 6 and 10, creating a variable attenuator of the light passing through the device. [0035] It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing described and illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes, which come within the meaning and range of equivalency of the claims, are therefore intended to be embraced therein.

Claims

WHAT IS CLAIMED IS: 1. A method of preparing a controllable gap between two optical transmission elements having a common axis, comprising providing said transmission elements with opposed end surfaces that are not orthogonal to said common axis, and turning said opposed end surfaces relative to each other about said common axis to form a controlled gap between said opposed end surfaces. 2. The method of claim 1 wherein said opposed end surfaces are initially continuous over the entire areas of said end surfaces. 3. The method of claim 1 wherein said controlled gap is wedge-shaped. 4. The method of claim 1 wherein said opposed end surfaces are rotated relative to each other by rotating one of said transmission elements about its axis while preventing rotation of the other transmission element. 5. The method of claim 1 wherein said transmission elements are optical fibers or waveguides. 6. The method of claim 1 wherein said transmission elements are mounted to allow relative movement between the two elements in the axial direction, to allow said gap to be formed in response to said relative rotation of said opposed end surfaces. 7. The method of claim 6 wherein said transmission elements are biased toward each other in the axial direction during said relative rotation of said opposed end surfaces. 8. A system for preparing a controllable gap between two optical transmission elements having a common axis and opposed end surfaces that form acute angles with the longitudinal axes of said transmission elements, comprising a device holding said transmission elements in longitudinal alignment with each other while permitting rotational movement of said opposed end surfaces relative to each other, and a biasing device urging said opposed end surfaces toward each other during said relative rotational movement.