CN202676133U - High-precision optical fiber length measuring system - Google Patents

Abstract

The utility model provides a high-precision optical fiber length measuring system. An existing optical fiber length measuring system OTDR (optical time domain reflectometer) has shortcomings that measurement precision is low, equipment is huge and short-distance optical fibers cannot be measured; and an OFDR (optical frequency domain reflectometer) and an OLCR (optical low coherence reflectometer) have shortcomings of expensive manufacturing cost, low stability and the like. The high-precision optical fiber length measuring system can overcome the shortcomings. The high-precision optical fiber length measuring system is mainly characterized in that continuous light emitted from a laser light source is modulated via an electro-optic modulator so as to form time domain short-pulse signals, by the aid of a beam splitter, a beam of light enters an optical circulator, an optical fiber to be measured and a Faraday rotator mirror enter a detector, and another beam of light directly enters the detector. Time difference of a light pulse running through the optical fiber and a light pulse without running through the optical fiber are respectively measured, so that the length of the optical fiber can be accurately measured. Measurement precision can reach a centimeter rank. Besides, the system is simple, and the stability is high.

Description

The high-precision optical fiber length measuring system

Technical field

The present invention relates to a kind of high-precision optical fiber length measuring system.

Background technology

The high-precision optical fiber length measuring system has important using value in optical fiber telecommunications system.Traditional optical fibre measuring method mainly comprises optical time domain reflectometer (OTDR), optical frequency territory reflectometer (OFDR), the low coherent reflection instrument (OLCR) of light etc.

Wherein OTDR is based on backward Rayleigh scattering and the Fresnel reflection principle is made, and is the present instrument of measuring optical fiber length the most widely.The advantage of OTDR is to measure length can reach kilometers up to a hundred, and shortcoming is that degree of accuracy is relatively poor, can only reach the magnitude of rice, and immeasurability short distance optical fiber, and equipment volume is huge.

Although the measuring accuracy of OFDR and OLCR is relatively high, can reach respectively millimeter and tens micron dimensions, stability and the reliability ratio of practical operation are lower.In addition, complicated structure and high cost have also limited their application to a certain extent.

Summary of the invention

The invention provides a kind of high-precision optical fiber length measuring system, mainly solved existing measuring system complex structure, cost height, and when fiber lengths was measured, precision was low, the problem of poor stability.

Concrete technical solution of the present invention is as follows:

This high-precision optical fiber length measuring system comprises the pulse generating unit for generation of pulse laser, pulse generating unit is connected with beam splitter, be provided with two output terminals on the beam splitter, beam splitter the first output terminal is connected with optical circulator the first port, beam splitter the second output terminal is connected with oscillograph by the second photodetector, optical circulator the second port connects with testing fiber and faraday rotation mirror successively, and optical circulator the 3rd port is connected with oscillograph by the first photodetector.

Above-mentioned pulse generating unit is LASER Light Source, Polarization Controller and the electrooptic modulator that connects successively, or pulsed laser light source.

Above-mentioned LASER Light Source can be selected the continuous laser source of 1550nm or 1310nm.

Advantage of the present invention is:

1, this optical fiber length measuring system accuracy depends on the pulse width of electrooptic modulator modulation, and used pulse width is narrower, and rising edge of a pulse is more precipitous, and the result who obtains is more accurate.If get the light pulse signal that pulsewidth is 1ns, precision can reach a centimetre magnitude.

2, this optical fiber length measuring system utilizes pulse to have propagation delay in testing fiber to come measuring optical fiber length.Simple in structure, used optical device relative low price, easy to use, cost performance is high.

3, this optical fiber length measuring system does not reflect or principle of interference based on weak signal, and is lower to the incident light requirement, and preferably stability and reliability are arranged.

Description of drawings

Fig. 1 is the structural representation of high-precision optical fiber length measuring system;

Fig. 2 is when not connecing testing fiber, the oscillograph output image;

Fig. 3 is when connecing the testing fiber of 10026.4m, the oscillograph output image.

Embodiment

The continuous light that the DFB LASER Light Source of 1550nm or 1310nm is sent enters electrooptic modulator afterwards through Polarization Controller (PC), is modulated the light pulse signal with certain pulsewidth by electrooptic modulator; Light pulse signal is divided into two bundles by 90/10 beam splitter, and (splitting ratio of beam splitter is determined by the loss that testing fiber length causes.If the laser of LASER Light Source output is enough strong, then beam splitter arbitrary proportion splitting ratio all can.) 90% a branch ofly enter testing fiber through optical circulator 1 port to 2 port, the light pulse that is reflected back by faraday rotation mirror enters a photodetector through optical circulator 2 port to 3 ports; A branch of another photodetector that directly enters of 10%; By the time delay of oscillograph detecting optical pulses, calculate the length of testing fiber.Wherein the effect of Polarization Controller is to make the laser that enters electrooptic modulator have good polarization characteristic; The splitting ratio of beam splitter is determined by the loss that testing fiber length causes; Faraday rotation mirror plays the effect of catoptron in this system, simultaneously can steady reflection polarisation of light attitude.

Be located at and do not connect in the testing fiber situation, the total length that beam splitter 90% port is connected to optical circulator 1 port is L ₁, the total length that optical circulator 2 ports are connected to faraday rotation mirror is L ₂, the total length that optical circulator 3 ports are connected to electrooptic modulator is L ₃, the total length that beam splitter 10% port is connected to electrooptic modulator is L ₄, the length of testing fiber is L.Do not connecing in the testing fiber situation, the mistiming that oscillograph detects two signal pulses is Δ t ₁, then

${\mathrm{\&Delta;t}}_1=\frac{L_1+{2\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000142027650000011.png,HDA0000142027650000012.png"\; state="\{\{state\}\}">L</figure-callout>}}_2+L_3-L_4}{c/n}---\left(1\right)$

Wherein, c is the light velocity in the vacuum, and n is optical fibre refractivity.

Have in the testing fiber situation, the mistiming that oscillograph detects two signal pulses is Δ t ₂, then

${\mathrm{\&Delta;<figure-callout\; id="2"\; label="t"\; filenames="HDA0000142027650000011.png,HDA0000142027650000012.png"\; state="\{\{state\}\}">t</figure-callout>}}_2=\frac{L_1+2L+{2\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000142027650000011.png,HDA0000142027650000012.png"\; state="\{\{state\}\}">L</figure-callout>}}_2+L_3-L_4}{c/n}---\left(2\right)$

(2)-(1),

$\mathrm{\&Delta;t}={\mathrm{\&Delta;t}}_2-{\mathrm{\&Delta;t}}_1=\frac{2\mathrm{Ln}}{c}---\left(3\right)$

Thus, can obtain testing fiber length is:

$L=\frac{\mathrm{c\&Delta;t}}{2n}=\frac{c({\mathrm{\&Delta;t}}_2-{\mathrm{\&Delta;t}}_1)}{2n}---\left(4\right)$

This high-precision optical fiber length measuring system measuring accuracy can reach a centimetre magnitude, does not interfere and weak reflection because not existing in the system, so stability and reliability are all very high.

Embodiment:

The continuous light of LASER Light Source incident is the light pulse of 1ns through the electrooptic modulator output pulse width; Testing fiber is G652 type single-mode fiber (refractive index is 1.4685), and nominal length is 10026.4m.When not connecing testing fiber, oscillograph is exported as shown in Figure 2, according to the output data, can calculate Δ t ₁=26.612ns; During testing fiber, oscillograph is exported as shown in Figure 3 in the connection, according to the output data, can calculate Δ t ₂=98221.191ns.The light velocity in the vacuum is got 299792458m/s, and the fiber lengths that calculates according to formula (4) is 10025.98m, and error is 4/100000ths.

Claims (3)

1. high-precision optical fiber length measuring system, comprise the pulse generating unit for generation of pulse laser, it is characterized in that: described pulse generating unit is connected with beam splitter, be provided with two output terminals on the beam splitter, beam splitter the first output terminal is connected with optical circulator the first port, beam splitter the second output terminal is connected with oscillograph by the second photodetector, optical circulator the second port connects with testing fiber and faraday rotation mirror successively, and optical circulator the 3rd port is connected with oscillograph by the first photodetector.

2. high-precision optical fiber length measuring system according to claim 1, it is characterized in that: described pulse generating unit is LASER Light Source, Polarization Controller and the electrooptic modulator that connects successively, or pulsed laser light source.

3. high-precision optical fiber length measuring system according to claim 2, it is characterized in that: described LASER Light Source is the continuous laser source of 1550nm or 1310nm.

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