Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
  • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
  • G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
  • G01M11/3127—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using multiple or wavelength variable input source
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/02—Testing optical properties
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
  • G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
  • G01M11/335—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face using two or more input wavelengths

Definitions

• the present invention relates generally to an apparatus for measuring optical properties of waveguide fiber, and particularly to an apparatus that employs optical switching of light sources or detectors.
• Waveguide fiber optical measurements have always been a costly part of the manufacturing process. This is particularly true of multimode fiber measurements that include bandwidth, attenuation, numerical aperture, core diameter, and differential mode delay.
• Traditional optical measurement systems have used optics benches and bulk optic components consisting of lenses and movable mirrors to fold optical paths and to combine signals for the various measurements.
• One connection to the test fiber is established using an XYZ translation stage in front of a final lens before the detector. Translation stages are known to be temperature sensitive and subject to backlash in their movable parts.
• the connection at the light launch end of the fiber is made to a source of light appropriate for the desired measurement.
• the multimode fiber optical properties viz., bandwidth and attenuation
• bandwidth and attenuation are launch sensitive
• measurements using more than one launch condition are desired.
• measurements at more than one wavelength are usually desired so that the launch end connection may have to be made numerous times.
• standard optical specifications for multimode fiber performance criteria include measurements made using a launch condition having a spot size and numerical aperture which excites all of the modes of the multimode waveguide fiber.
• This launch condition is called the overfilled condition and is defined in the industry standards Fiber Optic Test Procedure (FOTP) 54.
• Attenuation measurements are made using a limited or restricted launch, referred to as Limited Phase Space Launch (LPS) and defined in FOTP 50.
• LPS Limited Phase Space Launch
• the LPS launch is similar to the 30 urn spot size launch described below.
• One aspect of the present invention is an apparatus for measuring optical waveguide fiber that makes use of an N X 1 optical switch at the launch end of the fiber under test and a 1 X M optical switch at the detector end of the fiber under test.
• the light sources having the desired wavelengths and launch conditions, i.e., spot size and numerical aperture, are each connected to one of the N ports of the N X 1 switch.
• the detectors are each connected to one of the M ports of the M X1 switch. The result is, the fiber may be connected between the two switches and remain connected while all of the desired measurements are made.
• the launch end switch is selected to preserve the launch conditions, i.e., the mode power distribution, of the sources.
• the detector end switch is selected to preserve the mode power distribution of the light exiting the fiber under test.
• a reference fiber is first connected between the switches to establish, for example a baseline launch power or launch pulse width.
• the pulse width of a pulse passing through the fiber under test is compared to the reference pulse width.
• the same comparison is made for the attenuation measurements, except that in this measurement the power exiting the fiber under test is compared to the launched power.
• the spot size or numerical aperture of the launched light varies from one light to another source.
• certain of the sources are single mode lasers.
• the single mode laser sources have a spot size in the range of about 8 ⁇ m to 30 ⁇ m.
• either the spot size or the numerical aperture of the launched light may be restricted so that not all modes of a multimode fiber carry power, that is, are excited.
• a further embodiment of the measurement apparatus includes an OTDR coupled to the switches via a 1 X 2 coupler so that a trace of reflected power can be made of light launched into each end of the fiber.
• Figure 1 is a schematic of an embodiment of the invented waveguide fiber measurement apparatus.
• FIG. 1 An exemplary embodiment of the measurement apparatus of the present invention is shown in Figure 1 , and is designated generally throughout by reference numeral 10.
• the present invention for an apparatus to measure waveguide fiber includes an N X 1 switch 2 for launching power into the fiber under test.
• each of light sources 4 are optically coupled through 1 X 2 connector 12 to one of the N input ports of the N X 1 switch.
• a second optical connection is made through switch 12 to the output end of the 1 X M switch, 8. This arrangement allows one to obtain an OTDR trace from each end of the fiber under test.
• DMD differential mode dispersion
• the fiber may be optically connected into the measurement apparatus 10 by means of splices 18. These may be fusion splices or any one of the many mechanical splices known in the art.
• Variable attenuator 20 may be placed in the circuit for use in cases where the launched light power is too high for the detectors 22. Overdriving the detectors is most likely to occur when acquiring the reference light signal mentioned above.
• Switch 24 is positioned to send light power from the detector in use to data storage and analysis means 26.
• the analysis and storage means include an oscilloscope and a computer having an analogue to digital interface.
• a very restricted launch condition of spot size about 9.3 ⁇ m and numerical aperture (NA) about 0.14 may be achieved using a standard step index single-mode fiber as optical fiber pigtail 28 at one input port of switch 2.
• a plurality of restricted launches may then be achieved by using the standard single mode fiber in conjunction with a multimode fiber under test and offsetting the single mode fiber core relative to the multimode fiber core.
• Moderately restricted launch conditions can be achieved using as pigtail 28 a 50 ⁇ m core multimode fiber wrapped about a mandrel. Five turns of such fiber wrapped around a 5 mm diameter mandrel provided a spot size (diameter) of 30 urn and a numerical aperture of 0.13. An over filled launch was achieved using as pigtail 28 a step index multimode fiber having a core diameter greater than about 100 urn and a numerical aperture greater than about 0.30.
• Switch 2 was a JDS, DP8T switch PN: SC1618-D2SP SN: B6B0366. Testing was repeated using as switch 2 the respective JDS switches, 1x2 switch PN: SW12-Z000311 SN: JC034991 , and 1x8 switch PN: SB0108-
• Variable attenuator 20 was a JDS, PN: HA9-Z046 SN: KC000660.
• Four different launch conditions were used to measure bandwidth of a 62.5 micron core, 125 ⁇ m outside diameter fiber. These were as described above: • a standard overfilled defined by TIA/EIA FOTP ;
• Results of the test are set forth in Table 1.
• the percent difference of the bandwidth measurement from that made on a reference bench are given for each launch condition and each switch type.
• the percent difference in bandwidth measurement caused by the variable attenuator is given in the last row of Table 1.
• the percent differences are presented as BW850 nm/BW1300 nm. Measurements at 1300 nm wavelength were not made using the single mode fiber (SMF) launch.
• SMF single mode fiber
• Attenuator The impact of the attenuator at the end of the system was shown to be quite small, less than 5% in all cases. Most switches show a low percent difference, especially in the case of the overfilled launch.
• the invention provides a way of combining sources at multiple wavelengths and with multiple launch conditions through a fiber optic switch, thus eliminating the need for open air, bulk optical components.
• This provides the means for making a multimode fiber bandwidth measurement whereby a test fiber must undergo one connection to the test apparatus for a complete measurement under all permutations of these conditions.
• the invention also provides a means of combining multiple optical measurements using fiber optic switch technology.
• multiple measurements can be performed. For example, an optical time domain reflectometer (OTDR) or differential mode delay (DMD) measurement can be combined with bandwidth and attenuation by connecting them to additional ports of the switches.
• OTDR optical time domain reflectometer
• DMD differential mode delay
• This design eliminates the optical bench and utilizes a single electronic equipment rack for the components.
• One connection then provides means to switch in the various launch conditions, various wavelengths and various measurements without the need for open air optics.
• the dynamic range is known in the art to be the amount of attenuation which can be placed in a measurement path while retaining a signal to noise ratio that allows a measurement to be made.
• Dynamic range of a measurement system thus translates directly into the length of fiber which can be measured.

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• 2000
  • 2000-03-23 MX MXPA01010149A patent/MXPA01010149A/es unknown
  • 2000-03-23 KR KR1020017012847A patent/KR20020021085A/ko not_active Application Discontinuation
  • 2000-03-23 EP EP00928128A patent/EP1166075A1/en not_active Withdrawn
  • 2000-03-23 AU AU46409/00A patent/AU4640900A/en not_active Abandoned
  • 2000-03-23 CA CA002369006A patent/CA2369006A1/en not_active Abandoned
  • 2000-03-23 BR BR0009406-4A patent/BR0009406A/pt not_active Application Discontinuation
  • 2000-03-23 JP JP2000611047A patent/JP2002541474A/ja active Pending
  • 2000-03-23 WO PCT/US2000/007900 patent/WO2000062033A1/en not_active Application Discontinuation
  • 2000-03-23 CN CN00810209A patent/CN1360676A/zh active Pending

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