CN201242428Y - Apparatus for measuring optical fiber length rapidly - Google Patents

Abstract

The utility model relates to a quick measuring optical fiber length device. The cost of a traditional optical fiber length measuring instrument is higher. An input port of a four-port 3-d B optical fiber coupler in the utility model is connected with a semiconductor laser through an optical fiber separator, the output port thereof is connected with a photodiode, a data acquisition card and a quick fourier transform analyzer in turn, the other two ports of the four-port 3-d B optical fiber coupler are respectively connected on one end of a transitional section single mode fiber and one end of a connecting section single mode fiber, and the other end of the transition section single mode fiber and the other end of the connecting single mode fiber are respectively connected with two ends of a to-be-measured single mode fiber, an electro-optical modulator is inserted in the connecting section single mode fiber, and the electric driving signal port of the electro-optical modulator is electrically connected with a sine-wave signal generator. The utility model overcomes the problem of being unable to meeting the high-precision large-range measuring requirement, and has lower relative cost.

Description

A kind of quick measuring optical fiber length device

Technical field

The utility model belongs to optical technical field, has related to a kind of electrooptic modulator that utilizes and has changed the device that frequency of light wave causes the asymmetric effect measurement fiber lengths of interferometer structure.

Background technology

In the fiber optics field, particularly optical-fibre communications aspect, developing fast, the method and the low-cost equipment of large scale and high accuracy measuring optical fiber length have very significant meaning.

Traditional optical fiber length measuring instrument all is based on the fiber reflection meter, comprise optical time domain reflectometer (OTDR), optimal frequency domain reflectometer (OFDR), optical coherence reflectometer (OCDR), these methods or the pulsed laser light source that need extremely lack and the photoelectric probe of hypervelocity, cost is higher; Perhaps can not reach the requirement of high precision and wide-measuring range simultaneously, difficulty is used for practicality.

Summary of the invention

The utility model is exactly at the deficiencies in the prior art, utilizes electrooptic modulator optical frequency translation technology, and a kind of quick measuring optical fiber length device is provided.

Concrete scheme of the present utility model is: semiconductor laser is connected by the input port light of fibre optic isolater with four port 3-dB fiber couplers, the output port of four port 3-dB fiber couplers is connected with the input end light of photodiode, photodiode output is electrically connected with the input end of data collecting card, and the output terminal of data collecting card is electrically connected with the fast fourier transform analyser.Two other port of four port 3-dB fiber couplers is connected with an end of transition section single-mode fiber and an end of linkage section single-mode fiber respectively, and the length of transition section single-mode fiber is L ₁, the length of linkage section single-mode fiber is L ₂, L ₁L ₂The other end of the other end of transition section single-mode fiber and linkage section single-mode fiber is connected with the two ends of section single-mould fiber to be measured respectively; Electrooptic modulator inserts in the linkage section single-mode fiber, and the electric drive signal mouth of electrooptic modulator is electrically connected with sinusoidal signal generator.

The utility model is applicable to that general fiber lengths measures fast, compares with traditional optical fiber length measuring bill, has overcome and can not satisfy the large scale and high accuracy Testing requirement simultaneously; And owing to do not need the single-mode laser light source and the high-speed photodiode of narrow bandwidth, so relative cost is lower.Because testing fiber is connected in the Sagnac ring, anti-ambient temperature fluctuation of equipment and mechanical disturbance performance are strong.

Description of drawings

Fig. 1 is an one-piece construction synoptic diagram of the present utility model.

Embodiment

As shown in Figure 1, semiconductor laser 1 is connected with the input port light of four port 3-dB fiber couplers 3 by fibre optic isolater 2, the output port of four port 3-dB fiber couplers 3 is connected with the input end light of photodiode 4, the output terminal of photodiode 4 is electrically connected with the input end of data collecting card 5, and the output terminal of data collecting card 5 is electrically connected with fast fourier transform analyser 6.Two other port of four port 3-dB fiber couplers 3 is connected with an end of transition section single-mode fiber 7 and an end of linkage section single-mode fiber 11 respectively, and the length of transition section single-mode fiber 7 is L ₁, the length of linkage section single-mode fiber 11 is L ₂, L ₁L ₂The other end of the other end of transition section single-mode fiber 7 and linkage section single-mode fiber 11 is connected with the two ends of section single-mould fiber 8 to be measured respectively; Electrooptic modulator 10 inserts in the linkage section single-mode fiber 11, and the electric drive signal mouth of electrooptic modulator 10 is electrically connected with sinusoidal signal generator 9.Concrete measuring method may further comprise the steps:

Centre wavelength enters in Sarnia gram (Sagnac) ring after laser that the continuous semiconductor laser instrument of communication band sends is by fibre optic isolater and four port 3-dB fiber couplers.

Laser is divided into two-way after entering the Sagnac ring, wherein one the tunnel enter the known transition section single-mode fiber of length, pass through section single-mould fiber to be measured again, enter the known linkage section single-mode fiber of length then, laser is by after being inserted into the electrooptic modulator in the linkage section single-mode fiber, produce frequency conversion, the sinusoidal signal generator that described electrooptic modulator is modulated by frequency drives; Laser process after the frequency conversion is got back to four port 3-dB fiber couplers at last; The electric field strength E of laser when getting back to four port 3-dB fiber couplers ₁(t) be:

$E_1=-J_1\left(\mathrm{\α}\frac{\mathrm{\π}}{2}\right)\frac{E\left(t\right)}{2}\left\{\begin{array}{c}\exp (i(\mathrm{\ω}-\mathrm{\Ω})t+\mathrm{ni}[\frac{L_1+L_3}{C}\mathrm{\ω}+\frac{L_2}{C}(\mathrm{\ω}-\mathrm{\Ω})])\\ +\exp (i(\mathrm{\ω}+\mathrm{\Ω})t+\mathrm{ni}[\frac{L_1+L_3}{C}\mathrm{\ω}+\frac{L_2}{C}(\mathrm{\ω}+\mathrm{\Ω})])\end{array}\right\}---\left(1\right)$

Wherein α is the normalized amplitude of electrooptic modulator drive signal, J ₁Be that first-order bessel function E (t) is the electric field intensity of light source, ω is the laser angular frequency, and Ω is the angular frequency of electrooptic modulator drive signal.N is the refractive index of single-mode fiber, and C is the light velocity in the vacuum, L ₃Be the length of section single-mould fiber to be measured, L ₁Be the length of transition section single-mode fiber, L ₂Length for the linkage section single-mode fiber.

Another road laser at first enters the known linkage section single-mode fiber of length, produce frequency conversion by electrooptic modulator, after laser after the frequency conversion passes through the transition section single-mode fiber of section single-mould fiber to be measured and known length in proper order, get back to the 3-dB fiber coupler, the electric field strength E of laser when getting back to four port 3-dB fiber couplers ₂(t) be:

$E_2=J_1\left(\mathrm{\α}\frac{\mathrm{\π}}{2}\right)\frac{E\left(t\right)}{2}\left\{\begin{array}{c}\exp (i(\mathrm{\ω}-\mathrm{\Ω})t+\mathrm{ni}[\frac{L_2}{C}\mathrm{\ω}+\frac{L_1+L_3}{C}(\mathrm{\ω}-\mathrm{\Ω})])\\ +\exp (i(\mathrm{\ω}+\mathrm{\Ω})t+\mathrm{ni}[\frac{L_2}{C}\mathrm{\ω}+\frac{L_1+L_3}{C}(\mathrm{\ω}+\mathrm{\Ω})])\end{array}\right\}---\left(2\right)$

The two-way laser of getting back to four port 3-dB fiber couplers interferes the intensity I of transmitted light in four port 3-dB fiber couplers _TFor:

$I_T={J_1}^2\left(\mathrm{\α}\frac{\mathrm{\π}}{2}\right)\frac{{\left|E\left(t\right)\right|}^2}{4}\left[\begin{array}{c}4+2\cos \left[2(\mathrm{\Ωt}+\frac{\mathrm{n\Ω}}{C}{L}_2)\right]+2\cos \left[2(\mathrm{\Ωt}+\frac{\mathrm{n\Ω}}{C}(L_1+L_3))\right]\\ +4\cos \left[(2\mathrm{\Ωt}+\frac{\mathrm{n\Ω}}{C}(L_1+L_2+L_3))\right]+4\cos \left[\frac{\mathrm{n\Ω}}{C}(L_1{+L}_3-L_2)\right]\end{array}\right]---\left(3\right)$

Photodiode is surveyed the transmission light intensity, and light intensity signal is converted into electric signal simultaneously, photodiode be f by frequency _b, f _b＜＜Ω, the light intensity I that receives by photodiode _T:

$I_T={J_1}^2\left(\mathrm{\&alpha;}\frac{\mathrm{\&pi;}}{2}\right)\frac{{\left|E\left(t\right)\right|}^2}{4}\{4+4\cos \left[\frac{\mathrm{n\&Omega;}}{C}(L_1+2{\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="Y200820121529E00071.png"\; state="\{\{state\}\}">L</figure-callout>}}_3+L_2)\right]\}---\left(4\right)$

The driving frequency Ω of electrooptic modulator makes linear change according to 2 π wt, and by linear sweep, transmitted light intensity is pressed cos (ft) and changed

$ft=2\mathrm{\&pi;n}\frac{L_1+L_3-L_2}{C}\mathrm{wt}---\left(5\right)$

Wherein f is the frequency that light intensity changes.

Data collecting card is gathered electric signal, carries out fast Fourier transform (FFT), obtains the corresponding peak of formula (5) on frequency spectrum, obtains the length L of section single-mould fiber to be measured by the frequency f of measuring peak value ₃

${\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="Y200820121529E00071.png"\; state="\{\{state\}\}">L</figure-callout>}}_3=\frac{\mathrm{Cf}}{2\mathrm{\&pi;n\&omega;}}-L_1+L_2---\left(6\right)$

Claims (1)

1, a kind of quick measuring optical fiber length device, it is characterized in that: semiconductor laser is connected by the input port light of fibre optic isolater with four port 3-dB fiber couplers, the output port of four port 3-dB fiber couplers is connected with the input end light of photodiode, photodiode output is electrically connected with the input end of data collecting card, and the output terminal of data collecting card is electrically connected with the fast fourier transform analyser; Two other port of four port 3-dB fiber couplers is connected with an end of transition section single-mode fiber and an end of linkage section single-mode fiber respectively, and the length of transition section single-mode fiber is L ₁, the length of linkage section single-mode fiber is L ₂, L ₁L ₂The other end of the other end of transition section single-mode fiber and linkage section single-mode fiber is connected with the two ends of section single-mould fiber to be measured respectively; Electrooptic modulator inserts in the linkage section single-mode fiber, and the electric drive signal mouth of electrooptic modulator is electrically connected with sinusoidal signal generator.

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