CZ301215B6 - Connection element and process for producing connecting element for binding signal and pumping into double-tube optical fiber - Google Patents

Abstract

The present invention relates to a connecting element for binding pumping (1) and signal (2) into a double-tube optical fiber (7) for fiber amplifiers and lasers characterized in that it is formed by a signal optical fiber (3), a pumping optical fiber or fibers (9), and a double-tube optical fiber (7) having its face connected to said signal optical fiber (3) and said pumping optical fiber or fibers (9) through the mediation of a weld (8), see Figure. The manufacture of the above-described connecting element is carried out in such a manner that a signal optical fiber (3) and a pumping optical fiber (9) are connected to the face of a double-tube optical fiber (7) by welding in an optical fiber welding machine for a period of 1 to 2 seconds with the use of a welding current amounting to 10 to 18 mA, wherein the fiber overlap in the weld is within the range of 5 to 20 microns and the connected fibers are placed in a retention groove of trapezoidal profile of an optical fiber welding machine. For connecting the pumping optical fiber (9) and the signal optical fiber (3) to the double-tube optical fiber (7), the optical fiber welding machine is a convenient and sufficient device. Another advantage of the arrangement of the present invention results from the shape of the double-tube optical fiber (7), which is at the most adapted to the optical fibers being connected, see the Figure, section B-B. Both, the asymmetrically disposed core and noncircular shape contribute to an effective pumping absorption along the fiber.

Description

A fastener and a method of making a fastener for bonding and pumping into a double-skinned optical fiber

Technical field

BACKGROUND OF THE INVENTION The present invention relates to a novel solution of signal bonding and pumping into a double-layer optical fiber for optical amplifiers and radiation sources, in particular for single- or small-mode waveguide lasers, broadband sources, optical amplifiers, sheath pumping devices, Raman fiber devices.

BACKGROUND OF THE INVENTION

Over four decades since their discovery, lasers have found their place in many areas of human activity. Laser generation is based on the Light Amplification by Stimulated Emission of Radiation (LASER) phenomenon in the active environment. The active environment can be glass fiber optic doped with rare earth elements, then talk about fiber lasers, respectively. fiber amplifiers. The first fiber laser was experimentally demonstrated

J. Koester and E. Snitzer in the early 1960s (C.J. Koester and E. Snitzer, "Amplification in a Fiber Laser", Applied Optics, 3 (9): 1182, 1964),

For a long time, fiber lasers have been seen as a laboratory curiosity that provides interesting operating characteristics but with low output power and few applications. A renewed interest in fiber lasers and amplifiers occurred in the mid-1980s when a research team at the University of Southampton, England, led by David N. Payne, showed that erbia rare earth ions could induce optical amplification in the fibers at a wavelength of about 1550 nm, used in communication systems (RJ Mears, L, Reekie, IM Jauncey, DN Payne, "Low-noise erbium-doped fiber amplifier operating at 1.54 m", Electronics. Lett., 23 (19): 1026—

1028, 1987).

The deployment and development of erbium doped fiber amplifiers (EDFAs) in the early 1990s meant similar breakthroughs in optical communications as mass input of optical fibers into telecommunications about a decade earlier. In addition to typical EDFA applications in backbone optical networks, other fiber amplifier and laser applications in telecommunications and beyond are currently being studied intensively. Fiber amplifiers are being deployed in CATV access and cable television networks. Fiber lasers based on modulation instability can be an attractive source of optical pulses for future high-speed communication systems. Passive medio40 fiber lasers generating hundreds of femtosecond pulses can find use in Raman spectroscopy, and high energy pulsed Q-keyed fiber lasers are part of LID AR (Light Detection And Ranging) detection systems. There are also promising applications in medicine, eye surgery and dentistry.

An important advancement in the development of fiber amplifiers and lasers was the discovery of the multi-mode active environment pumping method in double-ciad (DC) optical fibers (E. Snitzer, H. Po, R. Tumminelli and BC McCollum, “Double-clad, offset core Nd fiber laser ”, in Dígest of Conf. on Optical Fiber Sensors, PD5, New Orleans, USA, 1988; edited by IEEE, New York and E. Snitzer, H. Po, RP Tuminelli and F. Hakimi," Optical fiber lasers " and amplifiers, U.S. Patent 4,815,079, published Mar. 21, 1989).

Since pumping is bonded to a multi-mode inner shell region with a relatively large diameter, and not just to a single-mode core region, high power laser diodes with a large emitting surface and low emissivity can be used for pumping. The discovery of the casing pumping method thus enabled a multiple increase in the average output power of the fiber optic signal

CZ 301215 Bo lasers up to hundreds of watts (V. Dominia, S. MacCormack, R. Waarts, S. Sanders, S. Bicknes,

R. Dohle, E., Wolak, P.S. Yeh, E. Zucker, "110W Fiber Laser", Electronics Lett., 35 (14): 1158—

1160 (1999).

Multitatt wide tunable fiber lasers with sheath pumping technology are suitable signal sources for power testing of optical components for wavelength division multiplexing (WDM) networks. In WDM networks, several dozen signals are transmitted in one optical fiber at a time, the total transmitted power reaches up to hundreds of mW, and testing of component reliability at high optical performance becomes necessary. Yterbium and fiber lasers are used as pumping sources for Raman lasers.

In order to utilize double-sheathed optical fibers in a fiber amplifier, it is necessary to solve the simultaneous coupling of pumping to the inner multi-mode sheath and the signal to the single-mode core. Although several methods have been developed for bonding radiation to double-shell optical fibers, pumping double-shell optical fibers remains a serious problem for many applications.

The methods described so far can be divided into two groups according to the direction of bonding of the pumping. In the first case the pumping is bonded in the direction of the axis of the double-skin optical fiber to its face. Initially, combining the signal and pumping at the active fiber inlet with volumetric optical elements and lenses has been continually improved Η. M. Pask, JL Archambault, DC Hanna, L. Reekiee, PS Russell, JE Townsend and AC Tropper, "Operation of cladding-pumped Yb-doped silica fiber lasers in the l-pm region", Electronics Lett., 30 (11) : 863-865 1994; Clarkson, W. A., Hanna, "Two-mirror beam-shaping technique for high-power diode bars", Optics Lett., 21 (6): 375-377, 1996.

In this case, however, the advantage of propagating the signal through the optical fiber is lost and therefore the challenge is to find another suitable method that preserves the advantages of the fiber optic. Methods have been patented using a directional fiber coupler either made of single-mode and one multi-mode fiber (VP Gapontsev and I. Samartsev, "Coupling arrangement between a multi-mode light source and an optical fiber through an intermediate optical fiber length", US Patent 5 No. 999 673, Dec. 7, 1999), or several multi-mode pumping fibers centered around a single-mode signal fiber (DJ DiGiovanni and AJ Stentz, "Tapered Fiber Bundles for Coupling Light into and Out of Cladding-Pumped Fiber Devices," U.S. Patent No. 5,864 644, wildlife, 26 January 1999, and ΕΡ0 893 862, wildlife 27.1.1999, D. Bayart and L. Berthelot, "Optical coupler for a multimode pump", US Patent 6,778,562, wildlife 10 July 2003; Mac Cormack, VG Dominia, and RG Waart, "Side Coupled Pumping of Double Clad Fiber Gain Media", US Patent No. 6,434,295, wildlife, Aug. 13 ,,2002; BG Fidric, VG Dominie, S. Sanders, "Optical Couple rs for multimode fibers', US Patent No. 6,434,302, game, Aug. 13, 2002; respectively. WO 9 945 419, game. 10.9.1999; Gonthier F., Martineau L., Seguin F., Villeneuve A., Faucher M., Azami N., and

M. Gameau, "Optical coupler comprising multimode fibers and method of making the same", WO 2005029146, game. 31.3. 2005).

The second way is to cross-draw the side of the active fiber by either a diffractive element, eg a prism (T. Weber, W. Luthy, HP Weber, V. Neuman, H. Berthou, G. Kotrotsios, "A longitudinal and side-pumped single transverse- Optical Communications, 115 (1-2): 99-104, 1995), via V-groove (DJ Ripin and L. Goldberg, “High Efficiency Side Coupling of Light into Optical”) fibers using imbedded V-grooves ", Electronics Lett., 31 (25): 2204-2205, 1995; L. Goldberg," Method and Apparatus for Side Dumping in Optical Fiber ", US Patent 5,854,865, game. ), by attaching the obliquely ground pumped fiber to a partially ground double-skin optical fiber sheath (JJ Larsen and G. Vienne, " Side pumping of double-clad photonic crystal fibers ", Opt. Lett. 29 (5): 436-438, 2004) or by embedding the mirror in the double-sheath optical fiber sheath (J. P. Koplow, S.W. Moore and D.A. Kliner, "A New Method for Side-Dumping of Double-Clad Fiber Sources", IEEE J. Quantum Electronics 39 (4): 529-540, 2003).

The clever way is simply to wind up several bare fibers, both pumping multimodal and single-mode rare-earth doped fibers, and surrounding such a fiber braid with a lower refractive index environment that forms the outer casing of the fiber waveguide (AB Grudinin, D. Payne, PW Turner, Μ. N. Zervas, M. Ibsen and K. Durkin,

WO 0 067 350, game. 9. 11.2000; SU Alam, J. Nilsson, PW Turner, M. Ibsen, AB Grudinin and A, Chin, "Low cost multi-port reconfigurable erbium before cladding pumped fiber amplifier", European Conference on Optical Communication, ECOC'2000, Munich, Germany, No. 5.4.3, 2000, used in the products of Southampton Photonics, UK, under the name GTWave technology, see AB Grudinin, DN Payne, P.W., Turner, LJA Nilsson,. N. Zervas, M. Ibsen, Μ. K. Durkin, "Multi-Fiber Arrangement for High Power Fiber Lasers and Amplifiers", U.S. Pat. patent application no. 20050105866, game. 19.5.2005.

Another problem specific to sheath pumping is to provide efficient pumping absorption along erbium-yterbium-doped fibers (erbium-ytterbium-doped fibers) (EYDF). E.g.

in the case of a circular cross-section of the fiber, the so-called meridial beams are selectively absorbed by the center of the pumping, while the scythe (off-axis) beams miss and dampen the core. The attenuation, absorption of the pumping is not homogeneous along the entire fiber, but after absorption of the meridial beams at the beginning of the fiber, the pumping of sin is almost without loss. Fiber with a standard, circular cross-section is therefore the least suitable for pumping through the sheath. A similar situation occurs with the rectangular cross-section of the fiber and other cross-sections. Optimal for dual-layer active fiber applications is to ensure maximum pumping absorption in the fiber, i.e. to ensure a homogeneous attenuation along the entire fiber. This can be achieved by a suitable design of the shape of the inner sheath that provides the so-called chaotic dynamics of beam propagation (V. Doya, O. Legrand and F. Mortessagne, "Optimized absorption in a chaotic double-clad fiber amplifier", Opt, Lett., 26 ( 12): 872-874, 2001;

Leproux, P. Fevrier, V. Doya, P, Roy, and D. Pagnoux, "Modeling and Optimization of Double-Glad Fiber Amplifiers Using Chaotic Propagation of the Pump", Optical Fiber Technology, 7 (4): 324-339 , 2001; P. Peterka, V. Matějec and I. Kašík, “Optimal fiber cross-section shape for sheathed pumped fiber lasers and amplifiers”, was published in the conference proceedings Optical Communications 2003, Prague, 21-22. October, pp. 125-130). The train “chaotic” double-layer optical fiber achieves a statistically uniform distribution of the radiation intensity across the cross-section in any way of excitation.

One of the solutions described herein comprises a coupler in which the input optical fibers are very little conically elongated and then welded to the double-sheathed optical fiber. However, the signal fiber is always in the middle of the optical fiber input beam; it can be said that the core in which the optical signal is propagated is located at the center of the fiber bundle and then at the center of the double-sheathed optical fiber with a circularly symmetrical cross-section. In addition, at least three input optical fibers must always be used to achieve the core position in the center of the cross-section: two pumping optical fibers and one signal optical. When connecting the input fibers to a fiber with a circularly symmetrical cross-section, in many cases the cross-section of the input fiber bundle differs significantly from that of a double-sheathed optical fiber. Finally, according to WO 2005029146, the input fibers are welded together and shaped prior to manufacture of the coupler.

The present invention is fundamentally different from such a solution described. In contrast, the core in which the optical signal propagates is positioned asymmetrically to the center of the double-shell fiber, and both this asymmetric placement of the core and its non-circular shape contribute to efficient absorption of pumping along the fiber. In addition, in the present invention, only two optical fibers (one pumping and one signal optical fiber) are preferably coupled to an asymmetric cross-section optical fiber. In addition, the shape of the double-skinned optical fiber is designed to correspond as closely as possible to the cross-section of the input fibers. Higher arc welding energies can be used to achieve higher weld strength. Into the fiber optic welder, input fibers are unconnected and unshaped, which allows the use of standard fiber optic welder to produce the coupler.

The invention will be explained in more detail with reference to the drawings and figures.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention relates to a device, a coupling element for bonding pumping 1 and signal 2 to a double-shell optical fiber 7 for fiber amplifiers and lasers, characterized in that it comprises a signal-optical fiber 3, pumping optical fiber or fibers 9 and a double-shell optical fiber 7 For example, the signal optical fiber and the pumping optical fiber or fiber are connected through the weld 8.

The claimed fastener is characterized in that the cross-section of the double-skinned optical fiber has the shape of a rectangle (see preform 10 and FIGS. 6 to 9), one or both of the shorter opposing sides and optionally corners thereof may be semicircular chamfered. cross-section of the connected optical input fibers.

The connection is realized in a fiber optic welder. The signal optical fiber and pump optical fiber are connected to the front of the double-skinned optical fiber by welding for 1 to 2 seconds using a welding current of 10 to 18 mA, with the overlap of the fibers in the welding range

5 to 20 microns.

To trap the optical fibers in the welder in such a way as to guarantee their correct orientation, a groove for trapezoidal cross-section, i.e. with a flat bottom, is used, see Fig. 4.

When inserting two optical fibers of circular cross-section into the welder groove, one of the fibers is fastened firmly to the optical welder and the other filament (s) is adjusted by micro-feed so that their faces are flush with the front of the welder. the clamp is firmly fixed by the thrust latch.

This bonding solution is thus fundamentally different from existing methods of simultaneous pumping and signal bonding along the double-layer optical fiber axis, using a special cone-shaped optical fiber coupler as an intermediate stage for the combination of signal fiber and pumping fibers (see U.S. Pat. Nos. 5,864,644, 6,778,562; 6,434,295

US 6,434,302 and WO 2005029146).

The advantage of the solution proposed here is a simpler and more accessible technology that does not require equipment for the production of bicononic welded couplers as with other methods of frontal radiation bonding, nor the introduction of a diffractive element as with the methods of side pumping. A fiber optic welder is sufficient to connect the pump and signal fibers to the double-walled optical fiber. A further advantage of this arrangement results from the shape of the double-skinned optical fiber, which is as adapted as possible to the connected optical fibers, see Figure 1, section B-B. Both the asymmetrically positioned core and the non-circular shape contribute to efficient pumping absorption along the fiber. The double-layer optical fiber preform is produced by MCVD (Modified Chemical Vapor) technology

Deposition) and doping the core with rare earth elements, such as the solution doping technique (erbium and yterbium).

The specific cross-section and asymmetric position of the core is obtained from the initial cylindrical preforms by grinding. The drawing of the fiber from the preform takes place at lower temperatures than is usual with standard fibers in order to maintain the non-circular cross-sectional shape of the preform as much as possible. During drawing, a coating of, for example, a polysiloxane polymer or fluorinated acrylate is applied to the fiber. This cover must have a lower refractive index than the quartz material of the fiber, so that the inner, quartz sheath of the fiber forms a multi-mode waveguide to spread the pumping.

BRIEF DESCRIPTION OF THE DRAWINGS

Giant. 1 shows a coupling element for bonding both pumping i (routed in multi-mode fiber 9) and signal 2 (routed in single- or small-fashioned fiber 3) to one double-layer optical fiber 7. Signal and pump optical fibers are connected to the face of the double-layer optical fiber The weld region is, like the double-skinned optical fiber, covered with a material 4, e.g. a polymer with a lower refractive index than the quartz optical fiber. Thanks to the specific cross-sectional design of the double-sheathed optical fiber, which ensures chaotic beam propagation, the pumping radiation is distributed evenly across the cross-section of the multi-mode and fiber waveguide 5. The signal propagates in the single- or small-mode core 6.

Giant. 2 is an image of a weld of two 125 µm standard diameter optical fibers attached to a double-sheathed optical fiber. This is a top view, in the left part there are two optical fibers which correspond to the single-mode or small-mode fiber-linking fiber 3 and the multi-mode fiber 15 for pumping radiation, and in the right part one double-layer optical fiber 7.

Fig. 3 is a microscope photograph of a kinked fiber end showing a cross-section of a double-sheathed optical fiber 7.

Giant. 4 is a cross-sectional view of the flat bottom fastening groove of the present invention used to retain the optical fibers in the welder so as to ensure their proper orientation relative to each other.

For comparison, FIG. 5 shows a standard mounting groove for holding optical fibers in a welder.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

An embodiment of the invention with a single pumping optical fiber is shown in FIG. 6. It is a connecting element for signal coupling and pumping into a double-skin optical fiber 2, whose preform 10 is ground from a single, circular preform. The cross-section corresponding to the initial circular preform is indicated by dashed lines. The pumping is applied to the double-shell optical fiber by one optical fiber 9 and the signal is also applied to the double-shell optical fiber by one optical fiber 3.

Example 2

An embodiment of the invention with two pumping optical fibers is shown in FIG. 7. It is a connecting element for signal coupling and pumping into a double-skin optical fiber 7, whose preform Γ0 is ground from a single, circular preform. The cross-section corresponding to the initial circular preform is indicated by dashed lines. The pumping is applied to the double-shell optical fiber 7 by two optical fibers 9 and the signal is applied to the double-shell optical fiber by one optical fiber 3.

Example 3

Another embodiment of the invention with a single pumping optical fiber is shown in FIG. 8. It is a connecting element for signal coupling and pumping into double-layer optical fiber

7, whose preform Π) is composed of two ground preforms. Cross-section corresponding to default

circular preforms are indicated by dashed lines. The pumping is applied to the double-shell optical fiber 7 by one optical fiber 9 and the signal is also applied to the double-shell optical fiber by one optical fiber 3.

Example 4

Another embodiment of the invention with two pumping optical fibers is shown in FIG. 9. It is a connecting element for signal coupling and pumping into double-layer optical fiber 17, whose preform 10 is composed of three ground preforms. The cross-section corresponding to the initial circular preforms is indicated by dashed lines. The pumping is applied to the double-shell optical fiber 7 by two optical fibers 9 and the signal is fed to the double-shell optical fiber by one optical fiber 3.

Industrial applicability

The proposed solution can be used both in fiber amplifiers for optical communications and power fiber lasers, which have many other areas of application, in addition to optical communications eg in mechanical engineering (material processing, micro welding) air transport (LI DAR systems), environmental protection (monitoring of air pollution). The method of bonding two fibers with a specific cross section ensuring chaotic beam propagation can be used to construct Y- and X- multi-mode couplers for fiber optic sensors.

Claims (5)

PATENT CLAIMS A coupling element for coupling a signal and pumping into a double-shell optical fiber for fiber amplifiers and lasers, characterized in that it comprises a signal-optical fiber (3), a pumping optical fiber (s) (9) and a double-shell optical fiber (7), the front of which the signaling optical fiber (3) and the pumping optical fiber (s) (9) are connected 35 by means of a weld (8). Fastener according to claim 1, characterized in that the cross-section of the double-skinned optical fiber has the shape of a quadrangle, one or both of the shorter opposing sides and, optionally, its corners can be semicircular beveled and its external dimensions are the same. . A method of manufacturing a fastener according to claims 1 and 2, characterized in that the signal optical fiber and the pumping optical fiber are connected to the front of the double-shell optical fiber by welding in an optical fiber welder for 1 to 2 seconds using a welding 45 to 10 mA, the filament overlap being in the range of 5 to 20 microns. 4. A method of manufacturing a fastener according to claim 3, wherein the spliced optical fibers are fixed in the welder into a mounting groove having a trapezoidal profile. 50, the bottom of which forms a flat bottom with a width corresponding to the width of the optical fibers to be inserted. Method of manufacturing a fastener according to claims 3 and 4, characterized in that when positioning two optical fibers of circular cross-section into the groove of the welder, one of the fibers is fastened firmly to the optical fiber welder and the other fiber or fibers are inserted into the groove 5 are adjusted by means of a micro-feed so that their faces are flush with one another, after which the fibers in the groove are firmly fixed by a thrust latch.