CA2233242C - Physical-contact optical fiber connector - Google Patents

Physical-contact optical fiber connector Download PDF

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Publication number
CA2233242C
CA2233242C CA 2233242 CA2233242A CA2233242C CA 2233242 C CA2233242 C CA 2233242C CA 2233242 CA2233242 CA 2233242 CA 2233242 A CA2233242 A CA 2233242A CA 2233242 C CA2233242 C CA 2233242C
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CA
Canada
Prior art keywords
optical fiber
physical
protective film
recited
fiber connector
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA 2233242
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French (fr)
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CA2233242A1 (en
Inventor
Walter Heitmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Deutsche Telekom AG
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Deutsche Telekom AG
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Filing date
Publication date
Application filed by Deutsche Telekom AG filed Critical Deutsche Telekom AG
Priority to CA 2233242 priority Critical patent/CA2233242C/en
Publication of CA2233242A1 publication Critical patent/CA2233242A1/en
Application granted granted Critical
Publication of CA2233242C publication Critical patent/CA2233242C/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24Coupling light guides
    • G02B6/36Mechanical coupling means
    • G02B6/38Mechanical coupling means having fibre to fibre mating means
    • G02B6/3807Dismountable connectors, i.e. comprising plugs
    • G02B6/3833Details of mounting fibres in ferrules; Assembly methods; Manufacture
    • G02B6/3847Details of mounting fibres in ferrules; Assembly methods; Manufacture with means preventing fibre end damage, e.g. recessed fibre surfaces

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
  • Surface Treatment Of Glass Fibres Or Filaments (AREA)

Abstract

An physical-contact optical fiber connector for optical fibers has improved long-term stability. The fiber surface ends of the optical fibers are coated with a thin, absorption-free film made of very hard material, whereby the resistance to scoring is considerably increased. The thickness of the protective film is such that interfering reflection losses due to differences in the refraction indices are largely avoided. The hardness of the film is greater than that of the optical fiber material. Its optical thickness is also small compared to the operating wavelength. For optical fibers made of quartz glass, a protective film of Al2O3 is used. Other oxides, nitrides, borides, and carbides are also used. For optical fibers made of multicomponent glass or plastic, the protective film is made of an absorption-free material of greater hardness.
The optical thickness of the protective film is between 1/1000 and 1/10 of the operating wavelength. The films are applied using ion-supported processes or ion-beam sputtering or the MicroPlasma process. Due to the small diameter of the rods, a large number can be placed into the coating system and coated at the same time. Thus physical-contact optical fiber connectors are obtained that have virtually unlimited service life and have extremely small insertion losses or connection losses.

Description

[234513 6]
Physical-camtact Optical Fiber Connector Field of the Invention The present invention rel;rtes to a physical-contact optical fiber connector.
Related Technolo~v Physical-contact optical fiber connectors are known and are widely used in communication technology. Known plugs with one optical fiber, two optical fibers, for example for home wiring or computer wiring, or with four to twenty-four optical fibers are used not only for data and information transmission, but also for video and speech 'transmission. Physical-contact optical fiber connectors are designed on the following principle: The optical ~_iber with a typical outside diameter of 125 ~m is secured in the center of a hard metal or ceramic rod having a diameter of 2.5 mm or 1.25 mrn. The end face of the optical fiber, polished to a spherical cap, projects somewhat forward at the end face of the rod. The rods are mounted together using a cylindrical sleeve, so that the offset of the fiber cores is less than 1 ~.m.
The fibers are inserted with a slight amount of pressure, which causes the spherical caps to flatten in the center. Clean end surfaces result in optical contact with low insertion loss and very small back-reflection. In T. Shintak et al. "Highly Stable Physical-Contact Optical Fiber Connectors with Special Convex Ends." Journal of Lightwave Techno:(ogy 11, 2 (1993) 241., which is hereby incorporated by reference herein, there is a detailed description of the principles and manufacturing of physical-contact connectors.
'Typical data and embodiments of physical-contact optical fiber connectors for an optical fiber are described and compiled in the brochure of the Swiss company Diamond "Lichtwellenleiter-Komponenten (Optical Fiber Components) 002-037-104P007 (1995)." According to this publication, insertion losses of new and clean physical-contact connectors is 0.:? dB to 0.4 dB for single-mode fibers.
Service life is given as 1000 connection cycles, i.e., the insertion loss should not increase by more than 0.2 dE: after 1000 insertions under clean surface and ambient conditions.
In practice, however, much higher inse~.rtion loss values are obtained with known physical-contact optical fiber connectors. In loss measurements in the DTAG
operating network, insertion losses between 0.3 dB and 0.9 dB were found, as can be S seen in the following publications: VV. Heitmann and H. Gruhi:
"Dampfun~;smessungen an der optischen Kabelstrecke Miinchen-Passau-Scharding (Osterreich), 15.02.1996" (Loss measurements on the Munich-Passau-Schardina (Austria) optical fiber line. 02/ 15/ 1996), H. Gruhl: ''Dampfungsmessungen an der Telekom-LWL Trasse Munchen-Passau-Scharding / Projekt Photon, Bitest bed, 27.11.1996" (Loss measurements on the Munich-Passau-Scharding Telekom-L WL
route / Photon Project, Bitest bed, 11 /27/1996), and H. Gruhl:
''Experimentierschleife vom Labor 801 Gebaude ~3 TZ fiber Rodermark 10, 30.12.1996" (Experimental loop from Lab 801 Building 33 TZ via Riidermark 10, 12/30/1996), with values up to ~. dB
having been measured in the Austrian Telekom network.
Insertion losses of physical-contact optical fiber connectors are mostly due to contamination of and damage to the contact area between the fiber end surfaces, causing high insertion losses. The measurement results of the systems according to the above three publications refer to standard single-mode optical fibers, a fiber type used almost exclusively in telecomrrmnication company networks. The mode field diameter, i.e., the diameter in which the predominant part of the optical power is conducted i.n the optical fiber, and thus also in the contact surface, is approximately 10 pm.
Slight contamination of the contact surface can considerably increase the insertion loss. Whereas films of contaminants can be removed by cleaning the end surfaces, this is not possible for surfaces that are scored. Scored surfaces are caused by dust particles that get onto the contact surface during insertion in a dusty environment and damage the surfaces when the spherical caps are pressed together.
Such damages have been relatively infrequent, since the operating networks are serviced by trained personnel and reconnections are relatively infrequent. In local networks, building systems and computer networks a high number of connections are needed on relatively short segments. which must also be frequently reconnected. In addition, reconnection is often performed by untrained personnel, so that in the case of ten physical-contact connections, for example, additional losses and interruption in the connection may easily result.
Summarv of the Invention Ar.~ object of the present invention is therefore to increase the long-term stability of physical-contact optical fiber connectors, avoid high insertion losses. and make repeated reconnections possible even by untrained personnel without negative consequen~,ces.
The present invention therei:ore provides a physical-contact optical fiber connector for optical fibers with end face contacts, characterized in that the end faces of the optical fiber are provided with a thin, absorption-free protective film with a hardness that is greater than that of the optical fiber material and whose optical thickness :is small compared to the operating wavelength.
Aalditional advantageous embodiments of the present invention include that:
a) the optical fibers are made of quartz glass and the protective film is made of corundum (A1,0;);
b) the optical fibers are made of quartz glass and the protective film is made of o:Kides, nitrides, borides, o:r carbides;
c) the optical fibers are made of multicomponent glasses or plastic and the protective film is made of a harder absorption-free organic or inorganic material.
d) the optical thickness of the protective film is between 1 / 1000 and 1 / 10 of the operating wavelength;
e) the fiber surfaces of an optical fiber are coated with a thin, absorption-free protective film made of very herd material, the thickness of the protective film being suitably small to avoid interfi:ring reflection losses due to differences in the refraction indices;
f) the protective film of the optical fiber is made of oxides such as Y,O;, Scz03, ZrO,, and HfO,:, and g) ion-supported processes or ion-bea~~n sputtering or the MicroPlasma process are used for producing the protective film.
The resistance to scoring of the optical fiber is considerably increased by coating the optical fiber surfaces with a thin, absorption-free film made of a very hard material. The thickness of the protective film is so small that interfering reflection losses due to refraction index differences are largely avoided. The thickness of the protective film is selected to be so small that interfering reflection losses due to differences in the refraction indices are largely avoided. The book by F.
Kohlrausch:
"Praktische Physik"(Practical Physics), Teubner Verlag Stuttgart, 22°d edition (1968) 23, discloses that, for example, A1,0; (corundum) has a Knoop hardness of 1800, so that a quartz glass sand grain cannot score a surface made of this material.
Since the film coating is very thin. light is virtually unaffected by it, so that reflections of the boundary surfaces remain almost unchanged. The protective films can be produced and applied using ion-supported processes, ion-beam sputtering, or a MicroPlasma process. The optical fiber can be built into the plug rod in advance and the spherical caps at the end surfaces can be polished. Due to the small diameter of the rods, a large number can be placed and coated in the coating system simultaneously.
The coating time is relatively short due to the small thickness of the protective filin.
Opposite fiber ends can then be spliced to the optical fiber.

In accordance with this invention, there is provided a physical-contact optical fiber connector for use in an optical fiber network having an operating wavelength comprising: at least one optical fiber having an end face and an optical fiber hardness; and a thin, absorption-free protective film at the end face, the protective film having a hardness greater than the optical fiber hardness and having an optical thickness small compared to the operating wavelength.
Brief Description of the Drawing The present invention is now explained with reference to an embodiment as shown in:
Fig. l, which shows schematically a side view of part of a connector according to the present invention, although not to scale for purposes of clarity.
Detailed Description Fig. 1 shows a connector 1 in which an end surface 2 of an optical fiber 3 is coated with a thin, absorption-free film 4 made of a very hard material, whereby the scoring resistance is substantially increased. It should be understood that a plurality of 4a optical fibers 3 may be provided. The thickness of the protective film 4 is such that interfering reflection losses due to differences in the refraction indices are lary~ely avoided. ~Che decisive factor for the resistance of a material to surface damage is its hardness. Optical fibers are usually made of quartz glass, which is a relatively stable glass, but its hardness is exceeded by many materials, so that it becomes scored over time when used in physical-contact optical connectors. In a study reported in the publication by Y. Taga: "Recent progress of optical thin films in the automobile industry," Applied Optics 32, 28 (1'93) X519, dealing with the stability of coated automobile windshield surfaces, it was determined that A1,0- films with a thickness of 8 nm are sufficient to considerably increase the scoring resistance of glass surfaces.
The Knoo~~ hardness of' quartz glass is given as 820, while the value for A1,0;
(corundum) is 1800, according to F. Kohlrausch "Praktische Physik," Teubner Verlag Stuttgart, :?2th edition ( 1968)23. According to this publication, a quartz glass sand grain will not score an A1,0; film applied to a glass surface. The optical thickness of the protective layer, i.e., the refraction index n multiplied by the geometric thickness d of the film, must be small compared to 1/4 of the wavelength ~, used for the transmissi~~n. Reflection attains a maximum at an optical thickness of ~,/4 if the refraction index of the protective film is greater than that of the quartz glass. The refraction indices of quartz glass and A1203 are approximately 1.45 and 1.7, respective:~y. Thus an 8-nm geometric thickness of A1,0; corresponds to an optical thickness of approximately 14 nm. T'he operating wavelengths of optical communication systems typically we 1300 nm and greater. This results in an optical thickness of at least 325 nm for a ~.I4 film. For an optical protective film with a thickness of 14 nm, or when the optical thicknesses of the end faces add up to 28 nm upon contact, such an arrangement is still less than 10% of the optical thickness of the ~,/4 film. l~.ight is practically unaffected by such a thin layer, so that the reflection of the bound~uy layer remains unchanged. A small increase of about 0.3 dB in reflection would still be in the admissible ran~;e if it helped achieve long-term stability of the contact sw-faces, as is the case here. T'he back-reflection occurring then can be reduced to sufficiently small values by slightly angling the spherical caps.

In addition to A1,0;, all absorption-free materials with even greater hardnesses may be considered as materials for the protective layer to be applied. Suitable oxides include Y,03, Sc,O;, ZrO,. and HfO,. as set forth in the publication by N. Kaiser "Dunne Schichten fur den ultravioletten Spektralbereich (T'hin films for the ultraviolet spectral range)," Laser and Optoelektronik :'.8, 2 ( 1996) ~2. In the publication by F.
Richter:
"Superhan:e dunne Schichten (Superhard thin films)", Physikalische Blatter 52, (1996) 35_'>, a number of substances are listed, such as nitrides, borides, and carbides, having handnesses between that of f~1,0; and diamond.
Among other methods, ion-supported processes, such as described in the two last-mentioned publications, ion-beam sputtering, such as described in the publication by R. Henking et al.: "Ionenstrahl-~:erstauben: Ein Beschichtungsverfahren fiir Laserkomponenten der Zukunft (Ion-beam sputtering: a coating process for laser components of the future)," Laser and Optoelektronik 28, 2 ( 1996) 43, or the MicroPlasma process according to the publication by M.A. Scobey et al.:
''Passive DWDM components using MicroPlasma optical interference filters,'' Optical Fiber Conference OFC 1996, Thk 1242, can be used. It is recommended that the optical fiber be built into the connector rod in advance and the spherical caps be polished at the end faces. Due to the small diameter (2.5 mm or 1.25 mm) of the rods, a large number can be placed and coated in the coating system at the same time. The required coating time is relatively short due to the small thickness of the protective layer. The opposite ends of the fibers can then be spliced to the optical fiber lead. A
typical value for the splice loss is currently 0.05 dB.

Claims (12)

1. A physical-contact optical fiber connector for use in an optical fiber network having an operating wavelength comprising:
at least one optical fiber having an end face and an optical fiber hardness;
and a thin, absorption-free protective film at the end face, the protective film having a hardness greater than the optical fiber hardness and having an optical thickness small compared to the operating wavelength.
2. The physical-contact optical fiber connector as recited in claim 1 wherein the at least one optical fiber is made of quartz glass and the protective film is made of corundum.
3. The physical-contact optical fiber connector as recited in claim 1 wherein the at least one optical fiber is made of quartz glass and the protective film is made of at least one of oxides, nitrides, borides, and carbides.
4. The physical-contact optical fiber connector as recited in claim 1 wherein the at least one optical fiber is made of multicomponent glasses or plastic and the protective film is made of a harder absorption-free material.
5. The physical-contact optical fiber connector as recited in claim 1 wherein the optical thickness of the protective film is between 1/1000 and 1/10 of the operating wavelength.
6. The physical-contact optical fiber connector as recited in claim 1 wherein the fiber protective film is made of a very hard material and coats fiber surfaces of the at least one optical fiber, a physical thickness of the fiber protective film being suitably small to avoid interfering reflection losses due to differences in refraction indices.
7 7. The physical-contact optical fiber connector as recited in claim 6 wherein the protective film is made of oxides.
8. The physical-contact optical fiber connector as recited in claim 7 wherein the protective film is made of at least one of Y2O3, Sc2O3, ZrO2, and HfO2.
9. The physical-contact optical fiber connector as recited in claim 1 wherein the protective calm is deposited by at least one of an ion-supported process. ion-beam sputtering, and a MicroPlasma process.
10. The physical-contact optical fiber connector as recited in claim 1 wherein the protective film is made of oxides.
11. The physical-contact optical fiber connector as recited in claim 10 wherein the protective film is made of at least one of Y2O3, Sc2O3, ZrO2, and HfO2.
12. The physical-contact optical fiber connector as recited in claim 6 wherein the at least one optical fiber includes a plurality of optical fibers.
CA 2233242 1998-03-27 1998-03-27 Physical-contact optical fiber connector Expired - Fee Related CA2233242C (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA 2233242 CA2233242C (en) 1998-03-27 1998-03-27 Physical-contact optical fiber connector

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Application Number Priority Date Filing Date Title
CA 2233242 CA2233242C (en) 1998-03-27 1998-03-27 Physical-contact optical fiber connector

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CA2233242A1 CA2233242A1 (en) 1999-09-27
CA2233242C true CA2233242C (en) 2006-11-28

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