CN105577299A - Multimode fiber bandwidth measurement apparatus and multimode fiber bandwidth measurement apparatus - Google Patents

Multimode fiber bandwidth measurement apparatus and multimode fiber bandwidth measurement apparatus Download PDF

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CN105577299A
CN105577299A CN201510980919.6A CN201510980919A CN105577299A CN 105577299 A CN105577299 A CN 105577299A CN 201510980919 A CN201510980919 A CN 201510980919A CN 105577299 A CN105577299 A CN 105577299A
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bandwidth
multimode fiber
frequency
multimode
sigma
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CN105577299B (en
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张洪喜
朱兴邦
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CETC 41 Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2589—Bidirectional transmission

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  • Physics & Mathematics (AREA)
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  • Computer Networks & Wireless Communication (AREA)
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  • Quality & Reliability (AREA)
  • Testing Of Optical Devices Or Fibers (AREA)

Abstract

The invention provides a multimode fiber bandwidth measurement apparatus, comprising a synthesized sweeping source, an optical transmitter, an optical injection system, a measured multimode fiber, an encircled flux test system, an optical receiver, a spectrum analyzer, a frequency meter and a computer. According to the invention, the encircled flux test system is proposed to be used for estimating whether an optical injection state meets an overfilled launch condition or not, measurement repeatability of the apparatus is guaranteed, optimization to the measurement repeatability of a multimode fiber bandwidth parameter is analyzed and described, uncertainty of a multimode fiber bandwidth measurement result is improved, and a gaussian linear fitting formula of the multimode fiber bandwidth parameter is provided.

Description

A kind of bandwidth for multimode optical fibers measurement mechanism and method
Technical field
The present invention relates to technical field of measurement and test, particularly a kind of bandwidth for multimode optical fibers measurement mechanism, also relate to a kind of multimode fiber wide-band width measurement method.
Background technology
Optical fiber can be regarded as a low pass filter, when high fdrequency component by time will be decayed.A very narrow light pulse comprises a lot of high fdrequency component, and this very narrow light pulse is after one section of multimode fiber, and light pulse can be broadened, so that the identification of the contiguous code of impact.The higher intersymbol interference of speed is more serious, thus limits transmission code speed.
The bandwidth parameter of multimode fiber is in units of MHzkm, refer to one section of optical fiber by the modulating frequency of maximum modulating frequency pulse and the product of fiber lengths.Because bandwidth limits the highest light pulse speed that multimode optical fiber systems channel can transmit, in high speed, large information capacity optical networking, bandwidth of an optical fiber be can not ignore for the impact of transmission range, at this moment multimode fiber can only transmit the distance of hundreds of rice, therefore the bandwidth parameter of Measurement accuracy multimode fiber is extremely important, and this is also the reason that multimode fiber must survey bandwidth parameter when dispatching from the factory.
The method of bandwidth measurement has two kinds: time domain method and frequency domain method.International Telecommunication Union (ITU) recommendation frequency domain method measures the bandwidth parameter of multimode fiber.
GB/T15972.41-2008 " Fiber Optic Test method specification the 41st part: the method for measurement of transmission characteristic and optical characteristics and test procedure---bandwidth " measures the description of bandwidth for multimode optical fibers as shown in Figure 1 to frequency domain method, comprising:
Auxiliary equipment
Suitable auxiliary equipment should be adopted, such as:
A) spectrum analyzer or network analyzer;
B) sinusoidal wave light source.
Program
1. sample end face centering
By optic fibre input end and injection light cone axis centering, and fiber-optic output is aimed at detector surface, make detector can receive whole emergent lights of tested optical fiber.
2. data acquisition and processing (DAP)
Firing test device, records the output optical signal P of tested optical fiber respectively 2(ω) and the output optical signal P of reference optical fiber 1(ω).
3. reference optical fiber
Tested optical fiber is about 2m place apart from injection end and cuts off rear as with reference to optical fiber by available intercept method, also can by data that the are pre-recorded and reference optical fiber of storage.If answer repeated storage reference data when the photoelectricity part of light source or receiver changes.
Calculate
A) according to record result P 1(ω) and P 2(ω), press definition calculate frequency response G (ω);
B) draw width-frequency characteristic curve, and Gaussian function fitting is carried out to curve, to eliminate the irregular impact brought bandwidth measurement result of baseband response curve.On curve ,-3dB (luminous power) point is tested bandwidth of an optical fiber.
GB/T15972.41-2008 " Fiber Optic Test method specification the 41st part: the method for measurement of transmission characteristic and optical characteristics and test procedure---bandwidth " just loosely describes the method for measurement of bandwidth for multimode optical fibers parameter, only enumerate the simple measuring process of bandwidth for multimode optical fibers parameter, not from optimizing measurement reproducibility, improve the aspects such as the uncertainty of measurement result and carry out analyzing and describing, also do not provide the Gaussian lineshape fitting formula of bandwidth for multimode optical fibers.
Summary of the invention
The object of the invention is to propose a kind of bandwidth for multimode optical fibers measurement mechanism and method, when carrying out bandwidth for multimode optical fibers and measuring, proper use of spectrum analyzer, optimizes measurement parameter and arranges, thus improve the measurement reproducibility of multi-mode ribbons width values.The base band frequency response of multimode fiber is Gaussian, The present invention gives the Gaussian lineshape fitting formula of bandwidth for multimode optical fibers parameter, further improves measurement reproducibility and the uncertainty of measurement of multi-mode ribbons width values.
Technical scheme of the present invention is achieved in that
A kind of multimode fiber broadband measuring device, comprising: source, optical sender, light injected system, tested multimode fiber, annular flux test macro, optical receiver, spectrum analyzer, frequency meter, computer are swept in synthesis;
The sine wave signal of setpoint frequency scope is launched in the synthesis source of sweeping, this swept-frequency signal light modulated transmitter, light modulated is after light injected system, incide tested multimode fiber, after Optical Fiber Transmission, monitored by annular flux test macro and adjust light injected system, then demodulating modulation signal by optical receiver, this signal of telecommunication is measured by spectrum analyzer, exports light frequency-domain function P with dB value record 2, and be stored in spectrum analyzer memory B (ω); Then cut off optical fiber, measure input light frequency-domain function P at the place of cutting off 1, and be stored in spectrum analyzer memory A (ω); The dB value of memory A, B subtracts each other the amplitude-versus-frequency curve obtaining optical fiber base band and represent with dB, this curve data substitutes into Mathematical Modeling, and calculating frequency values corresponding to-3dB point by least square method, the length that this frequency values is multiplied by tested multimode fiber is exactly the bandwidth value of tested multimode fiber.
Alternatively, the length of tested multimode fiber is measured by multimode optical time domain reflectometer.
Alternatively, described frequency meter is for calibrating the clock signal of spectrum analyzer.
Alternatively, described smooth injected system comprises mode scrambler, mode filter and cladding mode stripper, wherein mode scrambler adopts strong geometry perturbation motion method, accelerates each pattern and reaches steady-state distribution rapidly, and mode filter and cladding mode stripper are used for the optical mode in filtering high-rder mode and covering.
Alternatively, whether described annular flux test macro meets full injection condition for evaluating light injection state.
Based on said apparatus, the invention allows for a kind of multimode fiber wide-band width measurement method, founding mathematical models based on Gaussian function, draw amplitude-versus-frequency curve, and Gaussian function fitting is carried out to curve, eliminate the irregular impact brought bandwidth measurement result of tested multimode fiber baseband response curve, the frequency that on curve ,-3dB point is corresponding is the bandwidth of tested multimode fiber; Bring bandwidth for multimode optical fibers experiment curv data into Gauss model, thus obtain bandwidth measurement.
Alternatively, the bandwidth of multimode fiber is determined by the least square of Gaussian lineshape, set up a Mathematical Modeling based on Gaussian lineshape, two parameters are had: bandwidth sum peak power in this Mathematical Modeling, from Gauss's mathematical formulae (1) formula, these two parameters are for generation of the Gaussian power Spectral structure relative to frequency f:
P ( f ) = p k a m p ( 0 H z ) exp [ - 1 2 × ( f b a n d w i d t h ) 2 ] - - - ( 1 )
In formula: bandwidth---the bandwidth of multimode fiber;
Pkamp (0Hz)---when frequency is zero hertz, the peak power in Gaussian lineshape;
Adopt least square method, gone out bandwidth and pkamp (0Hz) Two Variables in (1) formula by each data point reverse on bandwidth for multimode optical fibers experiment curv, thus obtain bandwidth value:
bandwidth 2 = 1 2 × ( Σ i = 1 n x i 2 ) 2 - N ( Σ i = 1 n x i 4 ) N Σ i = 1 n x i 2 y i - ( Σ i = 1 n x i 2 ) ( Σ i = 1 n y i ) - - - ( 2 )
p k a m p ( 0 H z ) = exp [ ( Σ i = 1 n x i 2 y i ) ( Σ i = 1 n x i 2 ) - ( Σ i = 1 n x i 4 ) ( Σ i = 1 n y i ) ( Σ i = 1 n x i 2 ) 2 - N ( Σ i = 1 n x i 4 ) ] - - - ( 3 )
In formula: N---sampling number;
X i---each frequency values adopting some correspondence;
Y i---each range value adopting some correspondence.
Alternatively, adopt broadband optical receiver to carry out curve fitting to its frequency response calibration data, obtain the responsiveness of required Frequency point, eliminate optical receiver frequency response to the impact of bandwidth measurement result.
Alternatively, spectrum analyzer is adopted to be used for measuring, analyzing frequency-region signal.
Alternatively, before bandwidth for multimode optical fibers parameter measurement, the calibration of power and frequency calibration are carried out to spectrum analyzer.
The invention has the beneficial effects as follows:
The present invention proposes to use annular flux test macro assessment light to inject state and whether meets full injection condition, the measurement reproducibility of ensuring equipment, analyze and describe the optimization of bandwidth for multimode optical fibers parameter measurement repeatability and the uncertainty improving bandwidth for multimode optical fibers measurement result, and provide the Gaussian lineshape fitting formula of bandwidth for multimode optical fibers parameter.
Accompanying drawing explanation
In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.
Fig. 1 is mode baseband response test device (frequency response) structure chart in prior art;
Fig. 2 is bandwidth for multimode optical fibers measurement mechanism structure chart of the present invention;
Fig. 3 is that bandwidth for multimode optical fibers measures sampling curve and Gauss curve fitting curve analogous diagram.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.
Bandwidth limits the highest light pulse speed that multimode optical fiber systems channel can transmit, and is that multimode fiber must survey parameter when dispatching from the factory.
GB/T15972.41-2008 " Fiber Optic Test method specification the 41st part: the method for measurement of transmission characteristic and optical characteristics and test procedure---bandwidth " just loosely describes the method for measurement of bandwidth for multimode optical fibers, only list the simple measuring process of fiber bandwidth parameter, not from optimizing measurement reproducibility, improve the aspects such as the uncertainty of measurement result and carry out analyzing and describing, also do not provide the Gaussian lineshape fitting formula of bandwidth for multimode optical fibers.
The present invention adopts frequency domain method to measure the bandwidth parameter of multimode fiber, analyzes and describes the optimization of measurement reproducibility and the uncertainty improving measurement result, and provide the Gaussian lineshape fitting formula of bandwidth for multimode optical fibers.
Below in conjunction with Figure of description, the present invention is described in detail.
In multimode fiber, dispersion causes pulse expansion.The dispersion of multimode fiber mainly contains two classes: chromatic dispersion (being caused by wavelength different in light source transmission rate difference in a fiber) and modal dispersion (causing by there is multiple pattern in optical fiber), the dispersion of optical fiber determines bandwidth of an optical fiber.Using laser as in the multimode fiber transmission system of light source, pattern bandwidth is the main determining factor of bandwidth for multimode optical fibers.The present invention determines the bandwidth of multimode fiber by the mode baseband response of measuring multimode fiber.
The baseband response of actual multimode fiber is Gaussian lineshape.On the amplitude frequency curve of baseband response, the frequency that 1 amplitude point is corresponding is light cut-off frequency f c, this frequency is called the-3dB light belt of multimode fiber wide (or-6dB electricity bandwidth), and the length that this value is multiplied by tested optical fiber is the bandwidth of tested multimode fiber.The unit of bandwidth for multimode optical fibers parameter is MHzkm.
As shown in Figure 2, measurement mechanism of the present invention mainly comprises: source, optical sender, light injected system, tested multimode fiber, annular flux test macro, optical receiver, spectrum analyzer, frequency meter, computer etc. are swept in synthesis.
The sine wave signal of setpoint frequency scope is launched in the synthesis source of sweeping, this swept-frequency signal light modulated transmitter, light modulated is after light injected system, incide tested multimode fiber, after Optical Fiber Transmission, monitored by annular flux test macro and adjust light injected system until meet full injection condition, then demodulating modulation signal by optical receiver, this signal of telecommunication is measured by spectrum analyzer, exports light frequency-domain function P with dB value record 2, and be stored in spectrum analyzer B memory (ω).Then cut off optical fiber at distance injection end about 2 meters of, measure input light frequency-domain function P at the place of cutting off 1, and be stored in spectrum analyzer A memory (ω).The dB value of memory A, B is subtracted each other and is obtained measurement result, i.e. the amplitude-versus-frequency curve that represents with dB of optical fiber base band.This curve data substitutes into the Mathematical Modeling set up, and accurately calculates frequency values corresponding to-3dB point by least square method, and the length that this frequency values is multiplied by tested multimode fiber is exactly the bandwidth value of tested multimode fiber.The length of tested multimode fiber is measured by multimode optical time domain reflectometer (OTDR); Frequency meter is for calibrating the clock signal of spectrum analyzer.
Light injected system in measurement mechanism of the present invention comprises mode scrambler, mode filter and cladding mode stripper, wherein mode scrambler adopts strong geometry perturbation motion method, accelerate each pattern and reach steady-state distribution rapidly, mode filter and cladding mode stripper are used for the optical mode in filtering high-rder mode and covering.
Whether the annular flux test macro in measurement mechanism meets full injection condition for evaluating light injection state, and its repeatability for device plays guaranteeing role.
When multimode fiber is subject to random perturbation, is coupled by emergence pattern, makes the superficial velocity of each communication mode be tending towards identical between each communication mode, the light pulse distortion that Mode Coupling causes is changed.In the sufficient situation of Mode Coupling, light pulse is propagated and is obtained stable state propagation in multimode fiber, and in this condition, the broadening of light pulse is directly proportional to the square root of propagation distance.Because the quality of current optical fiber is better, the degree of the Random Coupling in optical fiber between pattern is less, so the transmission range that will reach in multimode fiber needed for stable state propagation is very long, the length of therefore generally getting measuring optical fiber when measuring the bandwidth of multimode fiber is about 2.2km, it is generally acknowledged that between multimode fiber unit length bandwidth and distance be linear dependence in such transmission range.
The measurement of bandwidth for multimode optical fibers parameter wants to obtain repetition, effective result, and injection condition is very important.This is because during multimode transmissions, different model group speed is different, if mode power does not reach stable state or balanced distribution, then the change that incentive condition is very little all can make the power of reception distribute and produce larger change, and the result that base band is measured has very big difference.Full injection mode is adopted to reach the steady-state distribution of received power.Full injected system, for measuring full injection bandwidth, at this moment inject the maximum theoretical numerical aperture that light cone angle is greater than tested multimode fiber, and launch spot diameter is suitable with tested multimode fiber core diameter.Tested multimode fiber should be made without micro-curved, the Energy distribution substantially constant of full injected system output, and have nothing to do (showing that all guided modeses are subject to normal excitation) with being coupled of light source.
In measuring process, in order to can Real-Time Monitoring mode injection condition, purchase high performance annular flux tester, to guarantee that the light injection condition produced meets the requirements, improve systematic survey repeatability.
The method of traditional process bandwidth for multimode optical fibers parameter measurement data is by measuring on amplitude frequency curve than the Frequency point corresponding to the little 3dB of maximum frequency response, obtaining bandwidth for multimode optical fibers measured value.The repeatability of the bandwidth measurement obtained in this way and uncertainty are all poor, this is because two reasons: (1) the method is that the various noises therefore in measuring process can make the repeatability of bandwidth measurement greatly reduce by determining that certain a bit corresponding frequency obtains bandwidth value; (2) due to the impact of spectrum analyzer local oscillator, make measure initial frequency can not be too low, and the power in theory corresponding to zero hertz is maximum power, the bandwidth measurement of such reality also needs to add initial frequency, different initial frequencies can make the uncertainty of bandwidth measurement greatly increase, especially, when the little bandwidth of measurement, this impact is particularly remarkable.
The base band frequency response of multimode fiber is Gaussian, measurement mechanism of the present invention and method founding mathematical models based on Gaussian function, draw amplitude-versus-frequency curve, and Gaussian function fitting is carried out to curve, to eliminate the irregular impact brought bandwidth measurement result of tested multimode fiber baseband response curve, the frequency that on curve ,-3dB point is corresponding is the bandwidth of tested multimode fiber.Bring bandwidth for multimode optical fibers experiment curv data into Gauss model, thus obtain bandwidth measurement accurately.The repeatability of the bandwidth value obtained with measurement mechanism of the present invention and method and uncertainty are all relatively good, have four aspect advantages:
(1) all data points on bandwidth measurement curve are all used to calculate the bandwidth value that will obtain, so the repeatability of result of calculation and uncertainty are all relatively good;
(2) be no longer necessary for and demonstrate power maximum point and-3dB point and very low initial frequency is set;
(3) eliminate the impact of spectrum analyzer local oscillator, can measure by arranging higher initial frequency, thus weaken spectrum analyzer local oscillator to the impact of bandwidth measurement result; And when adopting conventional method to measure, can only by arranging lower initial frequency, less resolution bandwidth and reducing the impact of spectrum analyzer local oscillator longer sweep time;
(4) noise of experiment curv obtains on average, and the indivedual measurement points on frequency response curve have seemed so unimportant (be by determine than maximum power little 3dB power points for conventional method).
The bandwidth of multimode fiber can be determined by the least square of Gaussian lineshape, sets up a Mathematical Modeling based on Gaussian lineshape for this reason.There are two parameters in the model: bandwidth sum peak power (power at zero hertz of place).From Gauss's mathematical formulae (1) formula, these two parameters are for generation of the Gaussian power Spectral structure relative to frequency f.
P ( f ) = p k a m p ( 0 H z ) exp [ - 1 2 × ( f b a n d w i d t h ) 2 ] - - - ( 1 )
In formula: bandwidth---the bandwidth of multimode fiber;
Pkamp (0Hz)---when frequency is zero hertz, the peak power in Gaussian lineshape.
Adopt least square method, gone out bandwidth and pkamp (0Hz) Two Variables in (1) formula by each data point (frequency, the power to) reverse on bandwidth for multimode optical fibers experiment curv, thus obtain bandwidth value accurately:
bandwidth 2 = 1 2 × ( Σ i = 1 n x i 2 ) 2 - N ( Σ i = 1 n x i 4 ) N Σ i = 1 n x i 2 y i - ( Σ i = 1 n x i 2 ) ( Σ i = 1 n y i ) - - - ( 2 )
p k a m = ( 0 H z ) = exp [ ( Σ i = 1 n x i 2 y i ) ( Σ i = 1 n x i 2 ) - ( Σ i = 1 n x i 4 ) ( Σ i = 1 n y i ) ( Σ i = 1 n x i 2 ) 2 - N ( Σ i = 1 n x i 4 ) ] - - - ( 3 )
In formula: N---sampling number;
X i---each frequency values adopting some correspondence;
Y i---each range value adopting some correspondence.
Fig. 3 is that bandwidth for multimode optical fibers measures sampling curve and Gauss curve fitting curve analogous diagram, and in figure, solid line represents sampling curve, represented by dotted arrows Gauss curve fitting curve.
In addition, adopt high sensitivity broadband optical receiver, and its frequency response calibration data is carried out curve fitting, obtain the responsiveness of required Frequency point, thus eliminate optical receiver frequency response to the impact of bandwidth measurement result.High-performance spectrum analyzer is adopted to be used for measuring, analyzing frequency-region signal.In order to reduce the frequency response impact of spectrum analyzer, reduce the uncertainty of measurement that spectrum analyzer is introduced, before bandwidth for multimode optical fibers parameter measurement, the calibration of power and frequency calibration are carried out to the spectrum analyzer in device, also greatly can improve the uncertainty of measurement of system.
It is by determining that the power relative maximum point on base band frequency response curve determines bandwidth value with-3dB point that traditional-3dB puts bandwidth for multimode optical fibers method of measurement.This by putting individually the method determining bandwidth value, its measurement reproducibility is poor.In addition, arranging lower initial frequency can make bandwidth measurement result seriously be subject to the impact of spectrum analyzer local oscillator and depart from the actual value of bandwidth.
The present invention adopts bandwidth for multimode optical fibers to measure frequency response curve Gaussian lineshape fitting technique and measures bandwidth for multimode optical fibers parameter, all data points on experiment curv are all used to calculate the bandwidth value that will obtain, be no longer necessary for and demonstrated power maximum point and-3dB point and very low initial frequency is set, the method obtain the repeatability of bandwidth value and uncertainty all relatively good.
The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1. a multimode fiber broadband measuring device, is characterized in that, comprising: source, optical sender, light injected system, tested multimode fiber, annular flux test macro, optical receiver, spectrum analyzer, frequency meter, computer are swept in synthesis;
The sine wave signal of setpoint frequency scope is launched in the synthesis source of sweeping, this swept-frequency signal light modulated transmitter, light modulated is after light injected system, incide tested multimode fiber, after Optical Fiber Transmission, monitored by annular flux test macro and adjust light injected system, then demodulating modulation signal by optical receiver, this signal of telecommunication is measured by spectrum analyzer, exports light frequency-domain function P with dB value record 2, and be stored in spectrum analyzer memory B (ω); Then cut off optical fiber, measure input light frequency-domain function P at the place of cutting off 1, and be stored in spectrum analyzer memory A (ω); The dB value of memory A, B subtracts each other the amplitude-versus-frequency curve obtaining optical fiber base band and represent with dB, this curve data substitutes into Mathematical Modeling, and calculating frequency values corresponding to-3dB point by least square method, the length that this frequency values is multiplied by tested multimode fiber is exactly the bandwidth value of tested multimode fiber.
2. multimode fiber broadband measuring device as claimed in claim 1, it is characterized in that, the length of tested multimode fiber is measured by multimode optical time domain reflectometer.
3. multimode fiber broadband measuring device as claimed in claim 1, it is characterized in that, described frequency meter is for calibrating the clock signal of spectrum analyzer.
4. multimode fiber broadband measuring device as claimed in claim 1, it is characterized in that, described smooth injected system comprises mode scrambler, mode filter and cladding mode stripper, wherein mode scrambler adopts strong geometry perturbation motion method, accelerate each pattern and reach steady-state distribution rapidly, mode filter and cladding mode stripper are used for the optical mode in filtering high-rder mode and covering.
5. multimode fiber broadband measuring device as claimed in claim 1, is characterized in that, whether described annular flux test macro meets full injection condition for evaluating light injection state.
6. based on the multimode fiber wide-band width measurement method of device described in any one of claim 1 to 5, it is characterized in that, founding mathematical models based on Gaussian function, draw amplitude-versus-frequency curve, and Gaussian function fitting is carried out to curve, eliminate the irregular impact brought bandwidth measurement result of tested multimode fiber baseband response curve, the frequency that on curve ,-3dB point is corresponding is the bandwidth of tested multimode fiber; Bring bandwidth for multimode optical fibers experiment curv data into Gauss model, thus obtain bandwidth measurement.
7. multimode fiber wide-band width measurement method as claimed in claim 6, it is characterized in that, the bandwidth of multimode fiber is determined by the least square of Gaussian lineshape, set up a Mathematical Modeling based on Gaussian lineshape, two parameters are had: bandwidth sum peak power in this Mathematical Modeling, from Gauss's mathematical formulae (1) formula, these two parameters are for generation of the Gaussian power Spectral structure relative to frequency f:
P ( f ) = p k a m p ( 0 H z ) exp [ - 1 2 × ( f b a n d w i d t h ) 2 ] - - - ( 1 )
In formula: bandwidth---the bandwidth of multimode fiber;
Pkamp (0Hz)---when frequency is zero hertz, the peak power in Gaussian lineshape;
Adopt least square method, gone out bandwidth and pkamp (0Hz) Two Variables in (1) formula by each data point reverse on bandwidth for multimode optical fibers experiment curv, thus obtain bandwidth value:
bandwidth 2 = 1 2 × ( Σ i = 1 n x i 2 ) 2 - N ( Σ i = 1 n x i 4 ) N Σ i = 1 n x i 2 y i - ( Σ i = 1 n x i 2 ) ( Σ i = 1 n y i ) - - - ( 2 )
p k a m p ( 0 H z ) = exp [ ( Σ i = 1 n x i 2 y i ) ( Σ i = 1 n x i 2 ) - ( Σ i = 1 n x i 4 ) ( Σ i = 1 n y i ) ( Σ i = 1 n x i 2 ) 2 - N ( Σ i = 1 n x i 4 ) ] - - - ( 3 )
In formula: N---sampling number;
X i---each frequency values adopting some correspondence;
Y i---each range value adopting some correspondence.
8. multimode fiber wide-band width measurement method as claimed in claim 7, is characterized in that, adopts broadband optical receiver to carry out curve fitting to its frequency response calibration data, obtains the responsiveness of required Frequency point, eliminates optical receiver frequency response to the impact of bandwidth measurement result.
9. multimode fiber wide-band width measurement method as claimed in claim 7, is characterized in that, adopts spectrum analyzer to be used for measuring, analyzing frequency-region signal.
10. multimode fiber wide-band width measurement method as claimed in claim 7, is characterized in that, before bandwidth for multimode optical fibers parameter measurement, carry out the calibration of power and frequency calibration to spectrum analyzer.
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