FR2675269A1 - 3X3 COUPLER WITH OPTICAL FIBERS WITH POLISHED SURFACES. - Google Patents

Abstract

The invention relates to a 3x3 fiber optic coupler (1, 2, 3) with polished surfaces in which the cores (1.1, 2.1, 3.1) of the optical fibers which are assembled together to form said coupler are arranged symmetrically one by one. relative to each other in space and are located, in any plane perpendicular to a common assembly line, on the vertices of an equilateral triangle.

Description

The invention relates to a 3 x 3 fiber optic coupler with polished surfaces.

  3 x 3 optical fiber coupler formed of three optical fibers assembled together along a coupling distance as well as the method of manufacturing such a coupler. We know from document EP O 074 789 or US-PS 4 755

  021 a 2 x 2 coupler or a 4 x 4 coupler in which the fibers opti-

  ques to be assembled are ground on one side to the vicinity of the fiber core and are interconnected by means of their polished surfaces The coupling characteristics of couplers of this type are essentially determined by the distance between the cores and

  by the so-called coupling length within which waves

  miners can pass from one fiber core to another The link does not

  Would two optical fibers require very high precision, the diameter of the core being of the order of 10 gm for single-mode optical fibers and the distance between the cores in the coupling zone being approximately 1 5 gin This also assumes that parallelism

  between the two fiber hearts is as perfect as possible on the

  seems to be the coupling distance For this, in the document EP O O

  74 789, two optic fibers are curved in an arc of circles respectively

  and we grind them in the region from their top to the neighborhood

  from their heart so as to obtain a flat surface We assemble together

  then the two optical fibers along their polished surfaces.

  To make a 4 x 4 coupler, we curve in an arc

  two pairs of optical fibers of this type linked together by the inter-

  medium of polished surfaces and we grind them again in the region

  from their summit to the vicinity of the two hearts contiguously

  re to obtain a flat surface, said polished surface being perpendicular to

  re to the first Then, between them, by means of their polished surfaces, two pairs of optical fibers comprising such a lateral polished surface so as to obtain a coupler whose

  section resembles a four-leaf clover.

  Until now, it was not possible to apply this manufacturing process by analogy to a 3 x 3 coupler since in this case the cores of the optical fibers are purely and simply located

  on an equilateral triangle in the center of the coupling zone The dis-

  tances of optical fibers evolve in a nonlinear way to the right and

  to the left of this center, so that there would be an asymmetry at the ni-

  Calf of the coupling between the three optical fibers This is the reason why the 3 x 3 couplers are generally produced according to another process, namely by twisting followed by fusion The reproducibility

  of these fusion processes remains insufficient, however.

  The objective of the present invention is therefore to propose a

  3 x 3 coupler as well as a process for its production which is reproduced

  tible and offers regular coupling across all three optic fibers

  ques. The problem is solved using a 3 x 3 coupler by the fact

  that, within the limits of the coupling distance, in any plane perpen-

  at the coupling distance, the cores of the optical fibers are

  located on the vertices of an equilateral triangle.

  In the 3 x 3 coupler with polished surfaces according to the invention, the

  cores of the three optical fibers linked together in the coating area

  range are arranged in space symmetrically with respect to each other, that is to say that, in any section perpendicular to the axes of the fibers, the centers of the hearts of the fibers are located on the

  vertices of an equilateral triangle.

  According to the invention, a first and a second optical fiber have curvatures in an arc of a circle in the same

  plane and of the same radius r, the centers of the circles having as co-ordinates

born M (x = r + d and y = O M = (x -r-d

2 =

  d being the minimum distance between the optical fibers at the top of the

  curvature, a third optical fiber linked to the first and second fi

  bres optiques has an elliptical curvature with half-axes a = r 3 and b = r and for center

(X = Y = O)

  y = (r + d) 3 the plane of curvature of said third optical fiber being perpendicular to

  first and second fibers and all optic fibers

  that are connected to each other by straight polished surfaces.

  The 3 x 3 fiber optic coupler is obtained by successively applying the following process steps: a) a curve is formed in an arc having the same radius of

  curvature given a first and a second optical fiber and one furnishes

  the to the vicinity of the core the optical fiber sheath in the region of the apex, so as to obtain a flat surface, b) the first and the second optical fiber are assembled along their polished surfaces, then they are ground again sheath in a plane located at the same distance from the two cores of optical fibers so as to obtain a flat surface,

  c) a third optical fiber is bent into an ellipse and the

  the up to a small distance from the core the optical fiber sheath in the region of the apex of the curvature, so as to obtain a flat surface and

  d) the third optical fiber is assembled along its surface

  this polished with the free polished surface of the first and second op-

  ticks already assembled in such a way that in any plane perpendicular to

  at the common connecting line, the hearts of the fibers are located

  on the angles of an equilateral triangle.

  The invention is described below using an exemplary embodiment

  sation which is shown in the drawings in a partially simplified form The drawings represent: Figure la, a side view of two optical fibers coupled together via polished surfaces, Figure lb, a cross section of an arrangement according to the Figure la and, Figure 2, a cross section of a 3 x 3 coupler with surfaces

polished.

  The coupler with polished surfaces according to the invention is obtained in the following manner: First, we curve in an arc of a circle with a radius of

  curvature r 1 = r 2 = r, according to known methods (for example,

  ment to document EP 0 074 789), two of the three optical fibers to be coupled together (fibers 1 and 2), they are ground in the region from their apex to the vicinity of the cores of fibers 1 1 and 2 1 so as to obtain flat surfaces and the two optical fibers are bonded together by their polished surfaces to obtain the shape shown in FIG. 1a The center of curvature Mi of the optical fiber core 1 1 a

  for coordinates x = r + d, y = O and z = O in the coordinate system

  born represented; analogously, the center of curvature M 2 of the optical fiber core 2 1 has the coordinates x = -r d, y = O and

  z = 0 At any distance from the origin of the coordinates, the dis-

  tance Ax between the two fiber cores is therefore: Ax = 2 (r + d (+) '1 r 2 _ y 2)

  A section of the arrangement according to Figure la, perpendicular to

  re at the y-axis, in the region of the origin of the coordinates, would give the form shown in Figure lb The assembly of the two fibers along their polished surface must be such that the two planes of curvature are located in a common plan, so that the centers of the hearts of

  fibers are always located in the x-y plane.

  When assembling a 2 x 2 coupler thus obtained with a third optical fiber to make a 3 x 3 coupler, care must be taken that the distance of the fiber core 3 3 from the x-y plane in the

  coupling zone is always such that an equilateral triangle is always

  days formed with fiber hearts 1 1 and 1 2 The height h of a tri-

  equilateral side angle Ax is defined by the formula: h = Ax -13/2

  Since the requirement for an equilateral triangle formed in-

  be the centers 1 11, 2 11 and 3 11 of the three fiber cores 1 1, 2 1 and

  3.1 applies to any cut parallel to the x-z plane in the coupling zone

ge of the coupler 3 x 3, z = h = 3/2 Ax

  By introducing into this equation the formula for Ax ci-

above, we get:

z = 3 (r + d (+) 4 Ir 2 _ y 2).

After transformation, it comes:

  lz-43 (r + d) l 2/3 r 2 + y 2 / r 2 = 1.

  This formula describes an ellipse which has half-axes a = 43 r and b = r and, for center, the point M 3 whose coordinates are x = y = O and z = (r + d) 43 It follows that the third optical fiber 3 is bent in accordance with the formula of the ellipse above and that this is ground in the region from the top to the vicinity of the fiber core. Next, a plane grinding of the fibers is carried out. 1 and 2

  pre-assembled in a 2 x 2 coupler perpendicular to their first

  re common polished surface, in the region of their common bond up to

  only to obtain the total distance h according to the above formula (Figure 3).

  When assembling the ground optical fiber 3 with the ground fibers 1 and 2 again, it is only necessary to ensure that the center 3.11 of the fiber core 3 3, seen in the z direction, is located in the middle between the two fiber cores 1 1 and 2 1, that is to say substantially in the plane of the first polished surfaces bonded together from the first and

second optical fiber.

Claims (3)

  1 3 x 3 fiber optic coupler formed by three optical fibers   which are interconnected along a coupling distance, ie   characterized in that, within the limits of the coupling distance, in   any plane perpendicular to the coupling distance, the hearts of the   bres optiques (1, 2, 3) are located on the vertices of an equilateral triangle. 2 3 x 3 fiber optic coupler according to claim 1, characterized in that a first and a second optical fiber (1, 2)   have curvatures in an arc in the same plane and the same   me radius r, the centers of the circles having the coordinates MI = x = r + d) and y = OM 2 = (y = rd d being the minimum distance of the optical fibers (1, 2) from the top of the curvature, that a third optical fiber (3) linked to the first (1) and the second (2) optical fibers has an elliptical curvature having for semi-axes a = r '13 and b = r and for center x = y = O y (r + d)) 3   the plane of curvature of said third optical fiber being perpendicular to   laire to that of the first and second fiber (1, 2) and in that all the optical fibers (1, 2, 3) are interconnected by straight polished surfaces.   3 Method of manufacturing a 3 x 3 fiber optic coupler   according to claim 1 or 2, characterized by the following steps:   a) we curve along an arc having the same radius of   curvature given a first and a second optical fiber and one furnishes   the to the vicinity of the core the optical fiber sheath in the region of the apex, so as to obtain a flat surface, b) the first and the second optical fiber are assembled along their polished surfaces, then they are ground again sheath in a plane located at the same distance from the two cores of optical fibers so as to obtain a flat surface,   c) a third optical fiber is bent into an ellipse and the   the to the vicinity of the core the optical fiber sheath in the region of the apex of the curvature, so as to obtain a flat surface and   d) the third optical fiber is assembled along its surface   this polished with the free polished surface of the first and second op-   ticks already assembled in such a way that, in any plane perpendicular   cular to the common connecting line, the fiber hearts are so-   killed on the angles of an equilateral triangle.