JP2002541474A - Optical fiber characteristics measurement device - Google Patents

Abstract

(57) [Summary] An apparatus for measuring characteristics of an optical waveguide fiber is disclosed. The device according to the invention is free of the mirrors, lenses and apertures normally required for measuring the properties of a particular waveguide fiber. The device according to the invention uses one optical switch at the input end of the optical fiber under test and another optical switch at the output end of the optical fiber under test. Both switches maintain the mode power distribution of the light passing through the switches, especially the spot size. The device can be used to measure the attenuation or wavelength width of a multimode waveguide fiber, both properties being affected by the incident and detected mode power distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Citation of related application]

This application is related to US Provisional Application No. 60 / 128,50, filed April 9, 1999.
No. 4 and US Provisional Application No. 60 / 129,706, filed Apr. 16, 1999.
Claim the benefit of the issue.

[0002]

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to an apparatus for measuring optical properties of a waveguide fiber. In particular, it relates to an apparatus using an optical switch for a light source or a detector.

[0003]

[Technical background]

Optical measurement of waveguide fibers is always a costly part of the manufacturing process. Bandwidth, attenuation, numerical aperture, core diameter, and differential mode delay (diff
This is particularly significant in the measurement of multi-mode fiber including rental mode delay. Conventional optical measurement systems use an optical bench, and use large optical components including a lens and a movable mirror that turn an optical path and connect various measurement signals. One connection to the fiber under test has been established by using an XYZ translation stage in front of the final lens in front of the detector. It is known that translation stages are temperature sensitive and can cause backlash in the movable optical path. The connection at the light input end of the fiber is made to a light source appropriate for the desired measurement.

Because certain multi-mode fiber optical properties, ie, bandwidth and attenuation, are sensitive to incident conditions, measurements using more than one incident condition are usually desired.
Furthermore, since measurements at more than one wavelength are usually desired, the connection at the input end must be made many times. Therefore, it is well known that these measuring stands are difficult and laborious to adjust and maintain, and are of large size with a surface area of approximately square meters. In order to maintain reliability, the above-mentioned measuring table must be periodically calibrated against a reference measuring table using standardized fibers. Repeated measurements that are time consuming and costly are often required.

[0005] Currently, standard optical specifications, which are the norm for the characteristics of multimode fibers, include measurements performed using incident conditions with spot sizes and numerical apertures that excite all modes of the multimode waveguide fiber. include. This incident state is called an overfilled state and is defined in the industry standard Fiber Optic Testing Procedure (FOTP) 54. Attenuation measurements are performed using limited or limited incidence, referred to as limited phase spatial incidence (LPS) and FOTP5
0 is defined. LPS incidence is similar to 30 μm spot size incidence described below.

[0006] More recently, the demand for multimode fibers optimized for laser light sources has increased the number of different incident states for bandwidth measurements. In other words, the number of connections on the measurement table is gradually increased, and the problem on the measurement table is increased. Therefore, there is a need for a fiber optic measurement device that provides ease of adjustment and connection of the components of the device and the fiber under test. Switching the input end of the waveguide fiber between a plurality of light sources having different wavelengths or different input states needs to be performed at high speed and reliably.

The present invention meets the need for lower cost, faster, and more repeatable waveguide fiber measurements.

[0008]

Summary of the Invention

One feature of the present invention is an optical waveguide fiber measuring apparatus, wherein an Nx1 optical switch is used at an input end of a fiber under test, and a 1xM optical switch is used at a detection end of the fiber under test. Light sources having the desired wavelength and incident state, ie, spot size and numerical aperture, are each connected to the N ports of the Nx1 switch. The detector is connected to each of the M ports of the Mx1 switch. as a result,
The fiber connects between the two switches and allows all desired measurements to be performed as is.

The entrance end switch is selected to maintain the incident state of the light source, ie, the mode power distribution. The sensing end switch is selected to maintain the mode power distribution emitted from the fiber under test. For a particular measurement, a reference fiber is first connected between the switches to establish, for example, a reference line for the incident power and an incident pulse width. Next, in the bandwidth measurement, the pulse width of the pulse passing through the fiber under test is compared with the reference pulse width. A similar comparison is performed in the attenuation measurement, except that the power emitted from the fiber under test is compared with the incident power in this measurement.

In embodiments of the present invention, the spot size or numerical aperture of the incident light varies between one light source and another. Further, in some cases, the light source is a single mode laser. In a preferred embodiment, the single mode laser light source is approximately 8 μm to 30 μm.
It has a spot size in the range of m. In other embodiments, it is possible to limit either the spot size or the numerical aperture of the incident light, so that some of all modes of the multimode fiber propagate and excite power.

[0011] A further embodiment of the measuring device is an O connected to a switch via a 1x2 coupler.
Includes TDR. As a result, a small amount of reflected power can be the light incident on each of the fiber ends. Details of the OTDR connection will be described in the description of FIG. 1 below. Additional features and advantages of the invention will be set forth in the following Detailed Description, most of which are readily apparent to one of ordinary skill in the art from the detailed description, or may be included in the accompanying drawings. In addition, it will be understood by practicing the invention from the description including the claims and the embodiments of the invention.

The foregoing general description and the following detailed description of the embodiments are merely exemplary of the invention, and are not intended to be construed as an overview or understanding of the nature and characteristics of the invention as set forth in the appended claims. It will be appreciated that it has been contemplated to provide an arrangement. The attached drawings are
It is included to provide a further understanding of the invention and is incorporated in and constitutes part of this specification. The drawings illustrate embodiments of the invention and, together with the description, provide a description of the principles and operation of the invention.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The reference material details preferred embodiments of the invention. Examples are set forth in the accompanying drawings. A preferred embodiment of the measuring device of the present invention is illustrated in FIG. 1 and generally designated by the reference numeral 10.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

According to the present invention, the waveguide fiber measuring apparatus of the present invention includes an Nx1 switch 2 for inputting power to the fiber under test. As shown in the embodiment of the present invention and as shown in FIG. 1, each of the light sources 4 is optically connected to N input ports of an N × 1 switch via a 1 × 2 connector 12. In the case of OTDR 6, the second optical connection is implemented via switch 12 to the output of 1 × M switch 8. This arrangement allows one port to obtain OTDR traces from each end of the fiber under test. Also shown at the N input ports of the switch 2 is a light source 14 for measuring the differential mode dispersion (DMD) of the fiber under test at one or more wavelengths.

The fiber can be optically connected to the measuring device 10 by means of a splice 18. These can be fusion splices or a number of known mechanical splices. The variable attenuator 20 may be placed in the optical path for use when the power of the incident light is very strong relative to the detector 22. Overuse of the detector is most likely to occur when acquiring the aforementioned reference optical signal. The switch 24 is arranged to send optical power from the detector in use to the data storage and analysis means 26. Generally, the analyzing and storing means includes an oscilloscope and a computer having an analog-digital interface. These analytical means, including the calculation programs used to calculate bandwidth and attenuation, are known (see the description of FOTP above),
Therefore, it will not be described further here.

Examples of the incident state or mode power distribution used in the apparatus of FIG. 1 are as follows. In a strictly limited incident state where the spot size is approximately 9.3 μm and the numerical aperture (NA) is approximately 0.14, a standard step index type single mode fiber is connected to an optical fiber This can be achieved by using it as a tail 28. Multiple restricted launches can be achieved by using standard single mode fiber with the multimode fiber under test and offsetting the single mode fiber core relative to the core of the multimode fiber.

A reasonably limited incidence condition can be achieved by using a 50 μm core multimode fiber wound around a mandrel as the pigtail 28. Five revolutions of the fiber around a 5 mm diameter mandrel provided a spot size (diameter) of 30 μm and a numerical aperture of 0.13. The overfilled light is injected into the pigtail 28 of a step index type multimode fiber having a core diameter larger than about 100 μm and a numerical aperture larger than about 0.30.
Achieved by using as

[0018]

【Example】

The measurement was performed using the device described in FIG. Switch 2 is a JDS D
P8T switch, PN: SC1618-D2SP SN: B6B036
It was 6. The test was performed using PN: SW12-Z000 switches each manufactured by JDS.
311 SN: 1x2 switch of JC034991 and PN: SB0108-Z
[000329] A 1 × 8 switch of SN: GB029604 was used as switch 2 and was repeatedly implemented. The variable attenuator 20 is made of JDS and has a PN: H
A9-Z046 SN: KC000660. The four different incident states are:
The core was 62.5 μm and the outer diameter was used to measure the bandwidth of a 125 μm fiber. The four states are as described above: a standard overfill as defined by the TIA / EIA FOTP; and a 30 μm spot achieved by 5 turns of a 50 μm core fiber around a 5 mm diameter mandrel. A moderately constrained launch condition providing: a limited launch condition caused by offsetting the core of a standard step index single mode fiber by 4 μm for a 62.5 μm core fiber; And the strictly limited launch conditions created by the use of step index single mode fiber.

The results of the test are set forth in Table 1. The percent difference in bandwidth measurement was measured by creating a standard benchmark for each incident condition and each switch type. The percent difference in bandwidth measurement generated by the variable attenuator is given in the last column of Table 1. The percent difference is the bandwidth 850 nm / bandwidth 1300 nm (BW85
0 nm / BW1300 nm). Measurements at 1300 nm wavelength were not made using single mode fiber (SMF) injection.

[0020]

[Table 1] The effect of the attenuator at the end of the system is shown very small, less than 5% in all conditions. Many switches show a low percentage difference, especially in the case of overfilled incidence. In summary, the present invention provides a method of connecting a light source at multiple wavelengths and with multiple incidence states via a fiber optic switch, thus eliminating the need for large optical components outdoors. The present invention provides a means for measuring the multimode fiber bandwidth by performing a single connection of the fiber under test to a test apparatus that performs a complete measurement by combining all the states.

The present invention further provides a means for connecting a plurality of optical measurements using fiber optic switch technology. That is, a plurality of measurements can be performed by connecting to the test device once. For example, measurement of optical time domain scatter (OTDR) or differential mode delay (DMD) can be performed simultaneously by connecting them to an additional port of the switch, so that hand width and attenuation can be performed simultaneously.

This design removes the optical bench and uses a single electrical mount for the components. A single connection provides a means to switch between different wavelengths, different measurements and different incident conditions without the need for outdoor optical components. This further boosts the dynamic range of the measurement by eliminating the power lost in the outdoor optical path. The dynamic range, known as the magnitude of the attenuation, can be replaced by the measurement path while maintaining the signal-to-noise ratio at which the performance of the measurement is allowed.

The dynamic range of the measurement system translates directly into a fiber length that can be measured. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. That is, the present invention
It is intended to cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[Brief description of the drawings]

FIG. 1 is a schematic view of an embodiment of a waveguide fiber measuring apparatus according to the present invention.

[Description of Signs] 2, 8 Optical switch 4 Light source 18 Splice 20 Variable attenuator 22 Detector 26 Data storage and analysis means

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD, GE , GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, U G, UZ, VN, YU, ZA, ZW

Claims (11)

[Claims] A first optical switch having N input ports and at least one output port; a plurality of laser or light emitting diode light sources each optically connected to the N input ports; A second optical switch having at least one input port and M output ports; a plurality of photodetectors each optically connected to the M output ports of the second optical switch; An optical measuring means optically connected to receive light from any one of the devices, wherein the reference optical fiber piece or the optical fiber piece to be tested is: , Optically connected between at least one output port of the first switch and at least one input port of the second switch, wherein the first and second switches pass through a switch. An optical characteristic measuring apparatus for a waveguide fiber, wherein a mode power distribution of light is maintained. 2. In measuring a multimode fiber, a spot size and a numerical aperture of a mode power distribution incident on the multimode fiber are sufficient to input power to all allowable modes of the multimode fiber. 2. The apparatus for measuring optical characteristics of a waveguide fiber according to claim 1, wherein: 3. When measuring a multimode fiber, the spot size or the numerical aperture of the mode power distribution is limited so as not to propagate the power of some allowable modes of the multimode fiber. The optical fiber measuring device according to claim 1, wherein 4. The laser of claim 3, wherein a preselected number of the lasers are single mode lasers and provide light having a spot size in a range of approximately 8 μm to 30 μm. For measuring optical characteristics of a waveguide fiber. 5. The apparatus of claim 1, further comprising a variable attenuator optically connected to an optical path starting at one of said light sources and ending at one of said photodetectors. 2. An optical characteristic measuring apparatus for a waveguide fiber according to claim 1. 6. The optical fiber measuring apparatus according to claim 1, wherein said optical measuring means is configured to measure a bandwidth of a multimode fiber to be tested. 7. An optical characteristic measuring apparatus for a waveguide fiber according to claim 1, wherein said optical measuring means is configured to measure attenuation of a multimode fiber to be tested. 8. A third switch having at least one input port and at least two output ports, and an OTD optically connected to at least one input port of the third switch.
R, wherein one of the at least two output ports of the third switch is optically connected to an input port of the first switch, and one of the at least two output ports is 2. The optical fiber measuring device according to claim 1, wherein the optical fiber is optically connected to an output port of the second switch. 9. The apparatus according to claim 1, wherein the first or second switch is a modular unit. 10. The apparatus according to claim 1, further comprising means for automatically switching between two of the N input ports of the first coupler. 11. An apparatus for measuring optical characteristics of a waveguide fiber, comprising:
11. The optical fiber measuring apparatus according to claim 1, further comprising means for automatically switching between the two output ports.