CN1346990A - Process for preparing optical fibre based on single-mode optical fibre to implement different performance of acousto-optic filter - Google Patents

Abstract

A process based on single-mode transmitting optical fibre for preparing the optical fibre to implement different performance of acousto-optic filter includes using a commercially available optical fibre for transmission purpose, determining needed external diameter and etching speed, and etching the optical fibre by controlling etch time to change its refractivity in acousto-optical action region. Its advantages are simple process, easy control, high effect, no damage to core of optical fibre, and low loss of optical fibre.

Description

Realize the method for preparing optical fiber of different acousto-optic filter performances based on the transmission single-mode fiber

Technical field

The invention belongs to the photoelectron technology field, particularly based on the design of the acousto-optical device serviceability of transmitting single-mode fiber and the method for realization.

Background technology

In the last few years, along with the optical WDM communication technology extensively obtains practicality, corresponding photoelectron technology industry had become one of major industry of current high-tech sector.Next step target of optical fiber telecommunications system development be the broadband, at a high speed, high capacity and networking.In the high speed fibre network in future, in order to overcome speed of electronics ink-bottle effect on the low side, many control function such as route exchanging that originally on the aspect of electricity, realize, Add/drop Voice Channels etc. will be realized on the aspect of light, but this just needs the relevant device of wavelength of a class dynamic change, as optical filter, photoswitch, optical attenuator, optical wavelength changer etc.This class device seems to be different, and in fact their denominator is a wavelength selectivity, and their common device bases are adjustable light wave-filters.

As a kind of basic device, tunable optic filter has following leading indicator: filtering bandwidth, tunable range, tuning speed, extinction ratio etc.The leading indicator that different application scenarios is concerned about is generally different, such as, when being used for the wavelength selector spare of wavelength-division multiplex system, require filtering bandwidth very narrow; When being used for adjustable optical attenuator, generally wish attenuation characteristic and Wavelength-independent, i.e. the non-constant width of bandwidth of operation; Be used for then requiring the filtering spectrum shape arbitrarily to adjust when amplifier gain is balanced.In addition, consider requirement of actual application and environment etc., generally also require the volume of device little, the insertion loss is little, low in energy consumption etc.

For many years, people once studied the multiple wave filter that can be used for fibre system, comprise the F-P wave filter of regulating by micromechanics or piezoelectric effect, based on the wave filter of twin-beam or multiple-beam interference, based on the optical filter of electrooptical effect or acoustooptic effect and fiber grating etc.By their working mechanism and the decision of factor such as technology difficulty, these wave filters respectively have relative merits, and are being applied with different occasions in various degree, still, still do not have to be competent at a high speed and dynamic adjustable, and the device that loss is little, volume is little, power consumption is little.Such as, though obtain using more widely at present based on the wave filter in piezoelectric effect F-P chamber, its tuned speed can not satisfy the requirement of following high-speed light network in the millisecond magnitude.Based on the wave filter of the electrooptical effect or the acoustooptic effect of body device, tuned speed is higher, but the insertion loss that the optical fiber pigtail coupling is introduced is about number dB.The volume of fiber grating is little, and the insertion loss is little, and bandwidth and filtering spectrum shape have very strong designability, but can only adjust by temperature in using, and dynamic range is limited.

1986, people such as H.J.Shaw reported the acoustooptic effect that realizes for the first time on optical fiber.Up to now, appeared in the newspapers having of leading on the dual mode optical fiber, on the general single mode fiber, on the birefringence fiber and fuse tapered fiber and fuse the acoustooptic effect that realizes on the fiber coupler.This class can realize the function that the multi-wavelength is correlated with based on the device of optical fiber acoustooptic effect, can realize wavelength tuning and amplitude adjusted by changing frequency of sound wave or intensity of acoustic wave, and tuning range can reach tens nanometer, and tuning speed can reach the microsecond magnitude.Wherein, based on transmission with the acousto-optical device of commercially available single-mode fiber because the cost of material is low, technology is simple, it is little to insert loss, is easy to the fibre-optic transmission system (FOTS) compatibility the most attractive.

Light transmitting fiber (abbreviation optical fiber) is made of optical fiber fuse and the covering that wraps in optical fiber fuse outside, and fiber cores and covering are glass (silicon dioxide) material, and the refractive index ratio covering of fuse is slightly high, to form optical waveguide.In order to increase pliability, the covering outside also has one deck overlay.By general international standard, transmission is 125 μ m with the cladding diameter (abbreviation external diameter) of single-mode fiber, and fuse diameter (abbreviation core diameter) is about several microns, and the refractive index of some optical fiber gradually changes along radius, does not have clear and definite core diameter.The about 250 μ m or bigger of the diameter of overlay do not have strict regulation.

The basic device of existing acousto-optical device based on the transmission single-mode fiber as shown in Figure 1,11 expression transmission single-mode fibers among the figure, the fiber segment of overlay is peelled off in 12 expressions, this is the zone of acousto-optic interaction, 13 expression aluminium awls, 14 expression electroacoustics transducers.The sound wave that electroacoustics transducer produces with of the transmission of compressional wave form through an aluminium awl after, concentration of energy is at cone tip part, and is coupled into optical fiber at cone tip part.Sound wave is the form transmission (arrow 15 expressions among the figure) to scratch capable ripple in optical fiber, has caused equivalent variations in refractive index, as shown in Figure 2.21 are illustrated in one section optical fiber that deformation has taken place under the effect of scratching capable sound wave among Fig. 2, and 22,23 and 24 represent the situation of each point place deformation in the deformation optical fiber respectively, and wherein coordinate y represents the coordinate axis on the cross section of optic fibre, and coordinate n represents refractive index.This deformation can equivalence be the change of refractive index.The effect of this periodic refractive index perturbation that produces under acoustic wave action is similar to long period fiber grating, if the optical fiber that uses is single-mode fiber, then can cause the coupling of core to cladding mode.The refractive index perturbation of long period fiber grating that different is is fixed, and can only regulate slightly by expanding with heat and contract with cold in the use; And the perturbation that acoustic wave action produces can change by voltage and the frequency that is added on the electroacoustics transducer.Because scratching the refractive index perturbation that capable sound wave causes is non-circle symmetry, the cladding mode that participates in coupling also is non-circle symmetry, normally core LP ₀₁To cladding mode LP ₁₁ ^Cl, LP ₁₂ ^Cl, LP ₁₃ ^ClDeng coupling.By the conditional decision that acoustooptic effect produces, the core, cladding mode and the sound wave three that produce coupling must satisfy the wave vector matching condition, so the Mode Coupling under the acoustic wave action is the relevant process of a wavelength.Light through being coupled into covering runs into overlay and can be absorbed when the continuous transmission of Optical fiber relay, do not satisfy the light that the wave vector matching condition is not coupled into covering and pass through then losslessly, and this has just formed the light filtering of band resistance type.The bat length that the phase-matching condition here refers to two light wave patterns that participate in coupling equals the wavelength of sound wave, under certain frequency of sound wave, the part of different wave length may satisfy phase-matching condition respectively simultaneously with different cladding modes in the core, so might see several bandreject filterings peak simultaneously under a certain frequency of sound wave, they correspond respectively to core LP ₀₁To LP ₁₁ ^Cl, LP ₁₂ ^Cl, LP ₁₃ ^ClCoupling etc. several different cladding modes.Satisfying the centre wavelength annex of phase matching, because matching condition can not be satisfied fully, coupling efficiency diminishes relatively, therefore forms the filtering spectrum with certain bandwidth.When frequency of sound wave changes, the centre wavelength of Satisfying Matching Conditions changes, and the filtering peak is moved, the tunable characteristic of Here it is acousto-optic filter.

Shown in Figure 3 is the resulting filtering spectrum of Lucent TrueWave single-mode fiber (non-zero dispersion displacement optical fiber) that adopts 30cm long.This optical fiber is a kind of single-mode fiber of transmitting of being used in optical fiber telecommunications system.Adding frequency of sound wave during measurement is 2.9MHz.Can see simultaneously among the figure that at 1500nm, 1534nm and 1594nm place three filtering peaks are arranged, they correspond respectively to LP ₀₁→ LP ₁₁ ^Cl(peak 31), LP ₀₁→ LP ₁₂ ^Cl(peak 32) and LP ₀₁→ LP ₁₃ ^ClThe mode switch at (peak 33).Carefully measure these three filtering peaks-three dB bandwidth is respectively 1.04nm, 1.33nm and 1.46nm.Remeasure the peak wavelength at three filtering peaks behind the slight modification frequency of sound wave, the wavelength tuning degree that can obtain them is respectively 0.11nm/kHz, 0.123nm/kHz and 0.148nm/kHz.The insertion loss of whole device is below 0.1dB.

The above results has proved uses transmission to realize that with single-mode fiber acousto-optic filtering is possible, but also has some problems:

1) parameters such as the relation of the spectral property of these acousto-optic filtering shown in Figure 3 such as bandwidth, frequency of sound wave and filtering peak center wavelength and tuning degree depend primarily on the index distribution (refractive index is along the variation of radius on the optical fiber cross section) of optical fiber, and the optical fiber that uses different refractivity to distribute can obtain different device performances.Transmission at present has general single mode fiber, dispersion shifted optical fiber, non-zero dispersion displacement optical fiber with single-mode fiber, and dispersion compensating fiber etc. are multiple, and their index distribution is different according to different performance requirements.But all transmission are to design at the needs of transport property with single-mode fiber, their difference difference for acoustooptic effect is not too big, result and Fig. 3 of obtaining under acoustic wave action are similar, therefore, directly adopt the merchant to sell the wave filter that Transmission Fibers can not realize different performance.If adopt the optical fiber of non-transmission usefulness or, but can introduce bigger insertion loss when being connected, lose meaning with the fibre-optic transmission system (FOTS) compatibility with Transmission Fibers for the optical fiber of acoustooptic effect particular design might obtain the performance of filters of different requirements.

2) on the principle, along with frequency of sound wave changes, light filter peak wavelength can arbitrarily move.But it is identical with the cardinal principle that Fig. 3 shows to adopt the merchant to sell the filtering spectrum that Transmission Fibers obtains, exist simultaneously owing to be coupled to many filtering peak of different cladding modes formation, therefore the tunable range of actual spendable unimodal region has only tens nanometer, for example, among Fig. 3,31 32 have only 34nm to the peak from the peak.

3) with based on the acousto-optical device of body material comparing, is very high based on the acousto-optic coupling efficiency of optical fiber.But, sell in the Transmission Fibers the merchant, the distributed areas of sound wave are 125 μ m (external diameters of optical fiber), and the distributed areas of core light wave are about 10 μ m, and the overlapping degree of sound wave and light wave is still little, limited the raising of acousto-optic coupling coefficient, in order to reach enough acousto-optic conversion efficient, the length in acousto-optic interaction district can not be too short, for example, for obtaining result shown in Figure 3, the acousto-optic interaction section length is 30cm.

In a word, based on transmission with the benefit that single-mode fiber designs and produces acousto-optic filter be and the optical fiber telecommunications system compatibility, shortcoming is that optical fiber parameter is fixing, and component characteristic parameter correspondingly determines all that also programmable leeway is little.Therefore need to seek a kind of way that can change optical fibre refractivity partly, can only change index distribution in the acousto-optic interaction district like this to realize different device performances; And the optical fiber that keeps other parts is constant with the advantage of maintenance with the transmission system compatibility.

At present, what seen reported in literature can the local way that changes Refractive Index Profile o be the method for drawing awl that fuses, and is about to the optical fiber spot heating, drawing-down under the state that melts.Since can only local drawing-down, taper must be formed, and the uniform zone of diameter can not be very long; And along with the external diameter core diameter that attenuates diminishes simultaneously, when external diameter little to a certain degree the time core district almost disappear, at this moment, what form between external diameter and the air is the optical waveguide of one section multimode.

Summary of the invention

The objective of the invention is for overcoming the weak point of prior art, propose a kind of new optical fiber designs and preparation method who realizes different acousto-optic filter performances based on the transmission single-mode fiber.This method technology is simple, and than being easier to control, the long even acousto-optic interaction district of realization, and the core district of optical fiber does not easily destroy, and not only can realize the performance that device is different but also can keep the low advantage of single-mode fiber loss; In addition the optical fiber external diameter can arbitrarily design, and can also adopt different single-mode fibers, has brought the design leeway of very big device performance.

The present invention proposes a kind ofly to realize it is characterized in that the method for preparing optical fiber of different acousto-optic filter performances based on the transmission single-mode fiber, adopts the merchant to sell transmission and uses single-mode fiber, and its external diameter is carried out etching; Specifically comprise: require its external diameter size of decision according to device performance, demarcate etch rate in advance according to lithographic method of being taked and actual process condition, external diameter size as requested and etch rate reduce the external diameter of this optical fiber partly by the control time then, change the Refractive Index Profile o in acousto-optic interaction district equivalently with realization.

The said lithographic method of the present invention comprises chemical etching or method for etching plasma, all belongs to the routine techniques means; Saidly demarcate the method that etch rate reaches various outer diameter by the control time then in advance according to process conditions and also belong to the routine techniques means.

Principle of work of the present invention and effect:

The experimental provision of the acousto-optic filter that the single-mode fiber that uses the present invention to prepare constitutes as shown in Figure 4.Wherein: 41 is original single-mode fiber section, and 42 for peelling off the fiber segment of overlay, and 43 is the fiber segment through over etching.44 and 45 are respectively aluminium awl and electroacoustics transducer, and sonic transmissions is as shown in arrow 46.Except that through the fiber segment of over etching, this installs with shown in Figure 1 identical.The optical fiber that uses the inventive method etching to cross, the performance of device can have following change:

1, the raising of coupling conversion efficiency $\mathrm{\&eta;}=\frac{{\mathrm{\&kappa;}}_0^2}{{\mathrm{\&kappa;}}_0^2+{\mathrm{\&delta;}}^2}{\sin }^2\left[L{({\mathrm{\&kappa;}}_0^2+{\mathrm{\&delta;}}^2)}^{1/2}\right]----\left(1\right)$ ${\mathrm{\&kappa;}}_0=\frac{\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sqrt{\frac{{\mathrm{\&epsiv;}}_0}{{\mathrm{\&mu;}}_0}}{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="A0113667200122.png,A0113667200131.png"\; state="\{\{state\}\}">n</figure-callout>}}_0\underset{A}{\&Integral;}{\mathrm{\&psi;}}_1(x,y)\mathrm{\&Delta;n}(x,y){\mathrm{\&psi;}}_2(x,y)\mathrm{dxdy}----\left(2\right)$ Coupling efficiency eta under the acoustic wave action between optical fiber core and a certain cladding mode is represented by (1) formula.Wherein, δ is the phase mismatch factor, and L is the length in coupling district.κ ₀Be coupling coefficient, it is by the core mould field, the cladding mode mould field ψ that participate in coupling ₁(x, y), ψ ₂(x, y) and the refraction index changing Δ n that causes of sound wave (x, overlapping integration decision y), as the formula (2).After the optical fiber jacket etching reduced, core mould field was constant substantially, and the cladding mode field becomes concentrates, and the zone of acoustic wave action is also concentrated, therefore the coupling coefficient κ that obtains under the identical acoustic power ₀Become big, the raising of the efficiency eta that helps being coupled.

Optical fiber external diameter lithographic method of the present invention is passed through in theoretical and experimental result explanation, and the power consumption of sound wave is reduced about an order of magnitude, perhaps can reduce active region length under identical power consumption condition, helps the reduction of device volume like this, is convenient to practicality.

2, the increasing of the variation of resonant acoustic wave frequency and tuning range $L_B\left(\mathrm{\&lambda;}\right)=\frac{2\mathrm{\&pi;}}{{\mathrm{\&beta;}}_{01}-{\mathrm{\&beta;}}_{1\mathrm{\&mu;}}}----\left(3\right)$ $f=\frac{\mathrm{\&pi;R}{C}_{\mathrm{ext}}}{{L_B}^2}----\left(4\right)$ Participate in the long L of bat of two light wave patterns of acousto-optic mode switch _BRepresent by (3) formula.β wherein ₀₁And β _{1 μ}Expression participates in the core (subscript 01) of coupling and the propagation constant of cladding mode (subscript 1 μ) respectively.Diminish when the external diameter of optical fiber is etched, the propagation constant of core is approximate constant and propagation constant cladding mode changes with external diameter, and therefore difference of them increases claps diminishing of personal attendant.(4) formula is represented the resonant acoustic wave frequency f and is clapped long L _BRelation.In the formula, C _ExtBeing the velocity of sound of elastic wave, is a constant relevant with material, and R is a fiber radius.

(4) formula explanation, one side optical fiber external diameter diminishes frequency of sound wave is reduced, and claps long shortening on the other hand frequency of sound wave is raise.Shown in Figure 5 is the LP that Theoretical Calculation obtains ₀₁→ LP ₁₁ ^Cl(curve 51), LP ₀₁→ LP ₁₂ ^Cl(curve 52) and LP ₀₁→ LP ₁₃ ^ClThe relation (optical wavelength 1550nm) that the resonant acoustic wave frequency changes with etching optical fiber external diameter under (curve 53) three kinds of Mode Coupling situations.Curve shows among the figure, when the optical fiber external diameter was big, the variation of optical fiber external diameter played a major role, and after the optical fiber external diameter is reduced to a certain degree, clapped long variation and played a major role, and it is 25 μ m (LP that the minimum value of resonant acoustic wave frequency occurs in external diameter respectively ₀₁-LP ₁₁ ^ClMould, f=860kHz), 61 μ m (LP ₀₁-LP ₁₂ ^ClMould is f=1.84MHz) with 97 μ m (LP ₀₁-LP ₁₃ ^ClMould, f=2.79MHz).As can be seen, core is different to the speed that the resonant acoustic wave frequency of different cladding modes coupling reduces to change along with the optical fiber external diameter.If consider in the acousto-optic frequency scope than the 0～5MHz that is easier to realize, when the optical fiber external diameter just can not consider that core is to LP less than 40 μ m the time ₁₃ ^ClThe coupling of mould, and, only need to consider that core is to LP when optical fiber external diameter the time less than 20 μ m ₁₁ ^ClThe coupling of mould.

Put it briefly, along with reducing of optical fiber external diameter, basic mode is increasing to the difference of the resonant acoustic wave frequency of different cladding mode couplings, just under identical frequency of sound wave, it is increasing at interval that core is changed pairing centre wavelength to different cladding modes, thereby the tunable range of unimodal region that can be practical is also big more.

3, the change of dispersion parameters and bandwidth $\mathrm{\&Delta;\&lambda;}=\frac{0.8L_B}{L}\frac{1}{N}\mathrm{\&lambda;}----\left(5\right)$ $N=\frac{\&PartialD;L_B}{\&PartialD;\mathrm{\&lambda;}}/\frac{L_B}{\mathrm{\&lambda;}}----\left(6\right)$ (5) formula is represented single filtering peak-three dB bandwidth Δ λ, and L is the fiber lengths of active region in the formula, and λ is an optical wavelength.N is the CHROMATIC DISPERSION IN FIBER OPTICS parameter, is represented by (6) formula, and mainly the intermode dispersion characteristic by optical fiber determines.When the optical fiber external diameter is etched when diminishing, the propagation constant of cladding mode changes thereby the CHROMATIC DISPERSION IN FIBER OPTICS characteristic also changes thereupon.Shown in Figure 6 is the LP that Theoretical Calculation obtains ₀₁→ LP ₁₁ ^ClCurve 61), LP ₀₁→ LP ₁₂ ^Cl(curve 62) and LP ₀₁→ LP ₁₃ ^ClThe relation (optical wavelength 1550nm) that the fibre-optical dispersion parameter N of (curve 63) three kinds of Mode Coupling correspondences changes with etching optical fiber external diameter.As seen, reduce along with the optical fiber external diameter is etched, dispersion parameters reduces, and by (5) formula, the bandwidth at single filtering peak increases.Therefore by the suitable optical fiber external diameter of design, can obtain the filtering bandwidth that needs.

4, the change of special external diameter value and tuning characteristic $\mathrm{\&Delta;\&lambda;}=\sqrt{\frac{\frac{0.8}{L}\&CenterDot;L_B^2\left({\mathrm{\&lambda;}}_0\right)}{\frac{{\&PartialD;}^2{L}_B\left(\mathrm{\&lambda;}\right)}{\&PartialD;{\mathrm{\&lambda;}}^2}}}----\left(7\right)$ $T=\frac{\&PartialD;\mathrm{\&lambda;}}{\&PartialD;f}=-\frac{\mathrm{\&lambda;}}{2f}\frac{1}{N}----\left(8\right)$ Can also see from Fig. 6, when the optical fiber external diameter is very little, dispersion parameters N=-1.To the coupling of each cladding mode, each exists one to make that N value is zero critical external diameter value for core, and they are respectively 19.6 μ m (LP ₀₁-LP ₁₁ ^Cl, the resonant acoustic wave frequency f=897KHz), 31 μ m (LP ₀₁-LP ₁₂ ^Cl, f=2.64MHz) with 43 μ m (LP ₀₁-LP ₁₃ ^Cl, f=4.86MHz).When the optical fiber external diameter was got these values, (5) formula was no longer suitable, at this moment-three dB bandwidth can calculate by (7) formula, and result of calculation illustrates that its value can reach hundreds of nanometers.(8) formula represents that acousto-optic filter centre wavelength is with sound wave change of resonance frequency, i.e. tuning degree.

Along with the optical fiber external diameter diminishes, the dispersion parameters value diminishes; The filtering peak that the change of unit frequency of sound wave obtains moves increase, and promptly tuning degree increases.When the optical fiber external diameter is big,, moves frequency of sound wave to short wavelength's direction along with increasing the filtering peak; After external diameter was less than critical value, dispersion parameters N value was got negative, and the filtering peak moves to long wavelength's direction with the frequency of sound wave increase.In the N value is near zero, claps longly to that is to say that not with wavelength shift frequency of sound wave does not have selectivity to wavelength, and filtering bandwidth can reach hundreds of nanometers.

Description of drawings

Fig. 1 is the basic device synoptic diagram of existing optical fiber acousto-optical device;

Fig. 2 is that the equivalent refractive index of optical fiber under the acoustic wave action changes synoptic diagram;

The acousto-optic filtering spectrum curve map of Fig. 3 on single-mode fiber, obtaining without etching;

Fig. 4 is for adopting the experimental provision synoptic diagram of etching type optical fiber acousto-optic filter of the present invention;

The graph of relation that the resonant acoustic wave frequency changes with etching optical fiber external diameter under three kinds of Mode Coupling situations that Fig. 5 obtains for Theoretical Calculation;

The graph of relation that the dispersion parameters N of single-mode fiber changes with etching optical fiber external diameter under three kinds of Mode Coupling situations that Fig. 6 obtains for Theoretical Calculation;

Fig. 7 is the actual measurement acousto-optic filtering spectrum curve map of the covering coupling single-mode fiber of 72 μ m for the external diameter of embodiments of the invention 1 preparation;

Fig. 8 is the actual measurement acousto-optic filtering spectrum curve map of the covering coupling single-mode fiber of 56 μ m for embodiment 1 external diameter of the present invention's preparation;

Fig. 9 is the actual measurement acousto-optic filtering spectrum curve map of the covering coupling single-mode fiber of 25 μ m for embodiment 1 external diameter of the present invention's preparation;

Figure 10 is the actual measurement acousto-optic filtering spectrum curve map of the covering coupling single-mode fiber of 21 μ m for embodiments of the invention 2 preparation external diameters;

Figure 11 is the actual measurement acousto-optic filtering spectrum curve map of the dispersion compensation single-mode fiber of 50 μ m for embodiments of the invention 3 preparation external diameters.

Embodiment

Of the present inventionly realize that based on the transmission single-mode fiber preparation process and effect thereof that the method for preparing optical fiber of different acousto-optic filter performances reaches three kinds of embodiment in conjunction with the accompanying drawings are described in detail as follows:

Embodiment 1:

The external diameter of three sections covering coupling single-mode fibers is adopted chemical etching method, be etched to 72 μ m, 56 μ m and 25 μ m respectively partly, the length of etching section is 8 centimetres.The method for designing of etching optical fiber external diameter value is: the active region length of bandwidth as requested and permission calculates the N value by (5) formula, is determined the external diameter of etching optical fiber then by Fig. 6 response curve.The original outer diameter of used optical fiber is 125 μ m, and core diameter is 8.3 μ m, and core district and cladding region refractive index difference are 0.33%.The hydrofluorite of working concentration about 40% is demarcated under the room temperature and is obtained etch rate and be about-60 μ m/30 minutes, controls the external diameter size that etching time obtains every section optical fiber requirement then.The filtering spectrum that records with experimental provision shown in Figure 4 is shown in Fig. 7, Fig. 8 and Fig. 9 respectively.

Fig. 7 is the acousto-optic filtering spectrum that the optical fiber external diameter records when being 72 μ m, and used frequency of sound wave is 1430kHz, and piezoelectric ceramics voltage is 25V, and electrical power consumed is 120mW; Recording filtering peak center wavelength is 1526nm, and the centre wavelength tuning degree is 0.31nm/kHz, and bandwidth is 6.4nm.Fig. 8 is the acousto-optic filtering spectrum of optical fiber external diameter when being 56 μ m, and used frequency of sound wave is 1020kHz, and piezoelectric ceramics voltage is 14V, and electrical power consumed is 35mW; Recording filtering peak center wavelength is 1574.8nm, and the centre wavelength tuning degree is 0.53nm/kHz, bandwidth 7.6nm.Fig. 9 is the acousto-optic filtering spectrum of optical fiber external diameter when being 25 μ m, and used frequency of sound wave is 818kHz, and piezoelectric ceramics voltage is 2.5V, and electrical power consumed is 1.1mW; Recording filtering peak center wavelength is 1540.8nm, and the centre wavelength tuning degree is 2.75nm/kHz, and bandwidth is 30.2nm.

Sum up above-mentioned 3 test results as seen, along with external diameter reduces, electrical power consumed reduces, and the resonant acoustic wave frequency descends, and bandwidth increases.Meet above result of theoretic analysis.

Embodiment 2:

With one section with the used identical covering coupling single-mode fiber of embodiment 1 with the method for conventional plasma etching with external diameter local etching to 21 μ m (LP as shown in Figure 6 ₀₁-LP ₁₁ ^ClThe critical value of pattern is about 19.5 μ m), the length of etching section is 5.5cm.The filtering spectrum that uses experimental technique shown in Figure 4 to obtain is shown in Fig. 8.Used frequency of sound wave is 867kHz, and piezoelectric ceramics voltage is 2.4V, and electrical power consumed is about 1.1mW, records bandwidth 349nm.

As seen, when external diameter was etched to the critical value annex, the filtering bandwidth that obtains had the increase on the magnitude.

Embodiment 3:

The external diameter of one section dispersion compensating fiber is adopted method local etching to the 50 μ m identical with embodiment 1, and the length of etching section is 8cm.The original outer diameter of this optical fiber is 125 μ m, and dispersion measure is 80ps/nm/km.Use filtering spectrum that experimental technique shown in Figure 4 obtains as shown in figure 11.Used frequency of sound wave is 1.935MHz during measurement, and piezoelectric ceramics voltage is 20V.Among the figure, the centre wavelength at peak 111 is 1464.4nm, corresponding LP ₀₁-LP ₁₁ ^ClMode Coupling, the centre wavelength at peak 112 are 1590.6nm, corresponding LP ₀₁-LP ₁₂ ^ClMode Coupling.The bandwidth at two peaks all is about 2nm, and centre wavelength is at a distance of 126nm, and like this, changing the available unimodal region of frequency of sound wave tunable range is 126nm.

Compare without the filtering spectrum of the non-zero dispersion displacement optical fiber of etching with employing shown in Figure 3, the resulting filtering spectrum width of present embodiment is more or less the same, but the tunable range of actual spendable unimodal region increases to 126nm from 34nm shown in Figure 3.

Claims (1)

1, a kind ofly realizes it is characterized in that the method for preparing optical fiber of different acousto-optic filter performances, adopt the merchant to sell transmission and use single-mode fiber, its external diameter is carried out etching based on the transmission single-mode fiber; Specifically comprise: require its external diameter size of decision according to device performance, demarcate etch rate in advance according to lithographic method of being taked and actual process condition, external diameter size as requested and etch rate reduce the external diameter of this optical fiber partly by the control time then, change the Refractive Index Profile o in acousto-optic interaction district equivalently with realization.

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