CN101275834B - Passive bias optical fiber gyroscope and current sensor - Google Patents
Passive bias optical fiber gyroscope and current sensor Download PDFInfo
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Abstract
In one of embodiments of passive polarizing fiber optic gyroscope and current sensor, the core is a 3X3 ''round''polarization maintaining optic fiber coupler composed of ''round'' polarization maintaining fiber coupler. The coupler realizes light splitting and passive polarization effects simultaneously in Sagnac interference sensor optic fiber loop. A variable 3X3 hybrid optic fiber coupler is composed by two linear polarization maintaining optic fibers and a regular single mode optic fiber, wherein the tail fiber of the two linear polarization maintaining optic fibers are connected in interference optic fiber loop based on the linear polarization maintaining optic fiber, the two ends of the single mode optic fiber are cut into short sections by diagonal angles, in order to form matchingend face on the two ends. In other embodiment of the passive polarizing fiber sensor, the core is an integrated Faraday rotator, comprising accurate magnetic-optic 45 degree rotation unit, of which one end is connected with a one-quarter glass of ''zero-to-rapid'' optic fiber, other end is connected with a one-quarter glass of ''rapid-to-zero'' optic fiber. The main merit of the passive polarization comprises: simple structure, working stability without manually tuning.
Description
Technical field
The present invention relates to Fibre Optical Sensor, the fiber optic interferometric loop, the Sagnac interferometer, gyro, electric current and magnetic field sensor, optical fiber Sagnac interferometer, passive bias optical fiber gyroscope, passive bias optical fiber current sensor, 3 * 3 circle polarization-maintaining fiber couplers, 3 * 3 line polarization-maintaining fiber couplers, meticulous optics magneto-optic Faraday spinner.
Background technology
Fibre Optical Sensor based on the Sagnac optical interference circuit of the present invention mainly is meant two class sensors, promptly based on the speed sensors that revolves of Sagnac effect, and common name gyro and based on the electric current or the magnetic field sensor of Faraday effect.These two kinds of effects all are nonreciprocal effect, thereby these two research fields of gyro and current sensor are being utilized development abreast on the common base in identical Sagnac interference-type optical fiber loop always for a long time.In point of, the research and development of current sensor and technology and exploitation (R﹠amp; D, T﹠amp; D:T is Technology) owing to borrow a large amount of useful technology and be subjected to benifit deeply from history gyro more early.
Past many decades gyro or revolve speed sensors obtained the achievement of making us expressing one's admiration in actual practicality, its optical fiber circuit be with active biased, i.e. piezoelectricity phase-modulator (PZT) or integrated optics piece (Y waveguide device).These technology were also once borrowed the development current sensor, but progress is successful unlike gyro.The main cause why current sensor falls behind can be returned to study carefully and is this fact, that is: the integral body of full optical fibre top structure can all use full-fledged line to protect (retention wire polarization state) optical fiber partially, it is common so-called polarization maintaining optical fibre, but current sensor such as employing help realizing the phase-detection of pin-point accuracy and long-time stability, then can not all use the line polarization maintaining optical fibre, at least wherein the detection optical fiber ring just must be protected (maintenance circular polarization state) optical fiber partially with circle, and the research of this kind optical fiber is then still ripe far away with invention.Although the success of active biased optical fiber Sagnac interfere type gyro in practicality, as above-mentioned, the researcher utilizes the effort of passive biasing never to interrupt for attempting in gyro and current sensor optical interference circuit.This be because, passive biasing has its attracting aspect, comprise simple and strong for structure, low noise, be easy to tuning (majority need not tuning, and by automated system operation), highly sensitive, long-term work stable, and cost is low etc.
Be intended in early days realize that the trial of the passive biasing of Fibre Optical Sensor is to utilize 3 * 3 fiber couplers, it is to be made by three sections conventional single-mode fibers, plays the effect of beam split and the passive biasing of Sagnac optical fiber circuit simultaneously.The sensor construction of Gou Chenging thus, its major defect is: single-mode fiber does not have the function that keeps polarization state, thus make the optical fiber interference type sensor that includes 3 * 3 single-mode optical-fibre couplers can not working stability, so that can not practicality.3 * 3 line polarization maintaining optical fibres have the function of surveying and keeping tested gyro signal on the principle.Yet, up to the present, make 3 * 3 line polarization-maintaining fiber couplers and be adjusted on the accurately parallel process at its three main shafts (be often referred to slow axis, the district forms by the mirror image stress symmetric), run into very big difficulty.Retrieve the commodity of international optoelectronic device, its fiber arm extinction ratio was lower than 20 decibels when the actual measurement coupling mechanism led to the line polarisation, thereby can not meet practical requirement in actual sensor-based system.
Another interferes the technological approaches that uses passive biasing in the loop at optical fiber Sagnac is to adopt nonreciprocal Faraday spinner.At this moment, the complex nature of the problem is how with Faraday spinner incoming fiber optic sensor optical path.Current optical fiber circuit mainly is based on the line polarization maintaining optical fibre, but the Faraday spinner need work in circularly polarized light to obtain the required phase change of pin-point accuracy phase-detection.For this reason, need fiber optic interferometric loop center line polarisation is become rotatory polarization, by conversion loop line polarisation again behind the Faraday spinner.The outer two kinds of methods of the means of present existing conversion polarization state: one is to use Traditional bulk optics quarter-wave plate, and two are to use very short one section (1/4th beat wavelengths) line polarization maintaining optical fibre, with the line polarisation injection of 45 ° of drift angles.Obviously, the inadvisable point of last method is to make optical interference circuit become very complicated on structure and layout, and the basic difficulty of back one method is that the short section of this kind optical fiber is a kind of to the highstrung element of length with regard to physical nature.
The present invention produces on above-mentioned technical background, and its starting point is to avoid having at present defective, complicacy and the technical difficulty of two kinds of passive biasings.Ins and outs of the present invention will be described in following " summary of the invention " and " embodiment " in conjunction with the accompanying drawings.
Summary of the invention
Passive bias optical fiber sensor of the present invention mainly is gyro and current sensor, and one of embodiment is 3 * 3 circle polarization-maintaining fiber couplers.Round polarization maintaining optical fibre wherein is that the previous invention of the inventor is (for example, referring to patent of invention: Chinese ZL01132102.4; The U.S. 5,452,394).The performance index that the laboratory is reached short run sample test data are for being parity with or superiority over 0.95 circularity.The distinct advantages of described 3 * 3 circle polarization-maintaining fiber couplers is that it is made simply, has thoroughly avoided accurately parallel difficult point problem of three pairs of required main shafts of 3 * 3 line polarization-maintaining couplers.
The present invention discloses a kind of very simple and practical Sagnac interferometric sensor based on 3 * 3 circle polarization-maintaining fiber couplers, and wherein coupling mechanism plays the function of beam split and passive biasing simultaneously.The fiber-optic probe ring that is connected to this sensor is also with circle polarization maintaining optical fibre coiled, and its desirable point is both detectable signal and can keep the round polarization-maintaining fiber coil of institute's detectable signal no matter all applicable to current sensor or gyro of this kind structure.
As a kind of conversion, the present invention also discloses a kind of 3 * 3 hybrid fiber coupling mechanisms, and it is made of two line polarization maintaining optical fibres and a conventional single-mode fiber.The tail optical fiber of two line polarization maintaining optical fibres of described coupling mechanism all is connected in the Sagnac interference optical fiber loop based on the line polarization maintaining optical fibre, and two ends of single-mode fiber then all are truncated into short section with the oblique angle, thereby forms the coupling end face at two ends.This short section single-mould fiber is " leaving unused " seemingly, but in fact 120 ° of phase relations between required response function are provided, that is provides passive biasing to the fiber optic interferometric loop.It is easy to be more a lot of than making 3 * 3 line polarization-maintaining fiber couplers to make described special 3 * 3 hybrid fiber coupling mechanisms, because of it contains two slow main shafts is carried out accurately parallel operation.
Another embodiment of the passive biasing device that the present invention is disclosed is a kind of integrated spinner, and it is made of together with both sides additional respectively " zero to fast " 1/4th optical-fibre wave plates and " near zero " 1/4th optical-fibre wave plates meticulous optics magneto-optic Faraday spinner.The ins and outs of relevant optical-fibre wave plate are referring to the authorized patent of invention of the inventor: Chinese ZL01112680.9, the U.S. 4,943,132; 5,096,312; 7,206,468.Term wherein " zero to fast " is the abbreviation of " not being threaded onto fast turn-knob ", and " near zero " is the abbreviation of " being threaded onto not turn-knob soon ".The sample on probation of described integrated spinner, its laboratory data reach at two " zero " and revolve nearly 30 decibels of speed (promptly not revolving) end line polarisation extinction ratio, and meticulous optics magneto-optic part rotatory polarization circularity is better than 0.95 in the centre.The advantage of described assembly is apparent: simple in structure, easy to manufacture, and can onlinely be fused to and interfere in the loop by the ordinary lines polarization maintaining optical fibre, and also insensitive to two ends, 1/4th optical-fibre wave plate tail optical fiber length.These advantages are existing block optics quarter-wave plate and short section of line polarization maintaining optical fibre 1/4th beat wavelength can not compare (know clearly and state as this section leading portion).
Description of drawings
Can understand content of the present invention and meaning from this section more to the simple declaration of accompanying drawing and subsequently " embodiment ".Below narration only is a kind of illustration method, and the present invention is not limited to this narration, that is:
Fig. 1 is the synoptic diagram of an optical fiber interference type sensing arrangement, the line polarisation that light source provides is converted to rotatory polarization feed-in optical fiber circuit via " optical fiber quarter-wave plate ", carry out beam split with 3 * 3 circle polarization-maintaining fiber couplers, simultaneously optical fiber circuit is played the function of passive biasing.
Fig. 2 a is the xsect of the present invention's 3 * 3 circle polarization-maintaining fiber couplers, contained three round polarization maintaining optical fibres, and its fibre core position forms a triangle.
Fig. 2 b is the xsect of the present invention's 3 * 3 circle polarization-maintaining fiber couplers, contained three round polarization maintaining optical fibres, and its fibre core position forms a straight line.
Fig. 3 a is the side view of one 3 * 3 hybrid fiber coupling mechanisms, and wherein single-mode fiber places two either sides near the line polarization maintaining optical fibre, and is punctured into the coupling end face at its two with the oblique angle, thereby only the welding of two line polarization maintaining optical fibres is in the interference-type optical fiber loop.
The xsect of Fig. 3 b presentation graphs 3a, wherein three fibre cores are positioned on the straight line, and wherein two slow main shafts of two line polarization maintaining optical fibres accurately are adjusted into and are parallel to each other.
Fig. 4 shows the xsect of one 3 * 3 hybrid fiber coupling mechanisms, is made of a single-mode fiber and two line polarization maintaining optical fibres, and its three fibre cores are equidistant each other, form a triangle, and two slow main shafts of two line polarization maintaining optical fibres then accurately are adjusted into and are parallel to each other.
Fig. 5 is the synoptic diagram in a fiber optic interferometric loop, and wherein the line polarisation of light source injects light path, and one 3 * 3 hybrid fiber coupling mechanisms play the effect of beam split and the passive biasing of light path simultaneously.
Fig. 6 a is the synoptic diagram of an integrated Faraday spinner, and the intermediate portion is 45 ° of rotary units of meticulous optics magneto-optic, and both sides one are branch one wave plate of " zero to piece " optical fiber four, and one is " being zero soon " optical fiber quarter-wave plate.
Fig. 6 b is the synoptic diagram of an integrated Faraday spinner, and the intermediate portion is 45 ° of spinners of meticulous optics magneto-optic, Yi Bian be branch one wave plate of " zero to piece " optical fiber four, Yi Bian be the circle polarization maintaining optical fibre.
Fig. 6 c is the synoptic diagram of an integrated Faraday spinner, and the intermediate portion is 45 ° of spinners of meticulous optics magneto-optic, and both sides are round polarization maintaining optical fibre.
Fig. 7 is the synoptic diagram of a passive offset sensors structure, and described structure has used integrated Faraday spinner shown in Fig. 6 a as passive bias device.
Fig. 8 is the synoptic diagram of a passive offset sensors structure, and described structure has used integrated Faraday spinner shown in Fig. 6 b as passive bias device.
Embodiment
One embodiment of the present of invention are complete " circle " polarization maintaining optical fibre sensor constructions, and this structure utilizes one 3 * 3 circle polarization-maintaining fiber couplers as passive bias device, as shown in Figure 1.
The cross-sectional structure of described 3 * 3 circle polarization-maintaining fiber couplers is shown in Fig. 2 a.The detailed technology of relevant circle polarization maintaining optical fibre is described, referring to the previous patent of invention of the inventor: Chinese ZL88107839.X, ZL01132102.4 and the U.S. 5,452,394.Among Fig. 2 a, label 1,2,3 show the xsect of three round polarization maintaining optical fibres, 100,200,300 show the fibre core of corresponding optical fiber; Be symmetrical in three of fibre core outside each fibre core and draw the oblique lines circle and represent one group of stressed zone, thereby they rotate in the optical fiber of making around fibre core in the manufacturing process drawing process and produce circular birefringence.The fibre core of three optical fiber of composition 3 * 3 circle polarization-maintaining fiber couplers symmetrically, forms a triangle on its xsect.
In longitudinal direction or direction of principal axis that is transmission direction, it is (not shown among Fig. 2 a that every stressed zone forms a helix around the fibre core rotation.Can be referring to Fig. 6 b right side and Fig. 6 c both sides).Different with 3 * 3 line polarization-maintaining fiber couplers, for 3 * 3 circle polarization-maintaining fiber couplers, its manufacturing course only requires that three fibre cores are accurately parallel in the coupled zone.
In each circle polarization maintaining optical fibre of described coupling mechanism, the cross-section location of three stressed zones forms an equilateral triangle, three round polarization maintaining optical fibres then be close to mutually become a branch of, shown in Fig. 2 a.Note three equilateral triangles (each triangle is made of three stressed zones) among the figure, its direction each other is arbitrarily fully.These characteristics, promptly counter stress zone position unconfined condition is the significant advantage favourable to practical application, makes 3 * 3 to justify the polarization-maintaining fiber coupler very attractive.Make this kind fiber coupler and avoided adjusting the extremely complicated technical matters of many stressed zone geometric relationships fully.These characteristics are fused to also very favourable in the sensor fiber loop of justifying the polarization maintaining optical fibre formation justifying each fiber arm of polarization-maintaining fiber coupler, only require fibre core because of it fibre core is got final product.
Fig. 2 b shows another version of 3 * 3 circle polarization-maintaining fiber couplers, and wherein three optical fiber are in the same plane, and promptly the xsect of three fibre cores is linked to be a straight line.To form leg-of-mutton situation identical with three fibre cores among Fig. 2 a, and rectilinear geometry shown in Fig. 2 b also only requires that to adjust fibre core accurately parallel, and relative how much of three groups of stressed zones are not then had tying requirements.The rectilinear geometry of Fig. 2 b is more simple on technology, because of the anchor clamps of required three optical fiber more simple.On the other hand, circularly polarized light should go into to hold feed-in by optical fiber placed in the middle among Fig. 2 b, is beneficial to incident optical power five equilibrium in two optical fiber.
Described 3 * 3 circle polarization-maintaining fiber couplers, promptly the label among Fig. 1 14 is cores of optical fiber wholecircle polarized light Sagnac interferometric sensor structure, plays the effect of circularly polarized light beam split and the passive biasing of circular polarization light path simultaneously.Label 11 provides the light source of linearly polarized light among Fig. 1, by " zero to fast " optical fiber quarter-wave plate 12 (patent of invention: Chinese ZL01112680.9; The U.S. 7,206,468) be transformed to circularly polarized light, the whole optical fiber wholecircle polarized light loop of feeding.Self-evident, " zero revolves " (promptly not revolving) end of this optical fiber quarter-wave plate 12 can fixedly be connected to linear polarization light source 11, thereby makes both constitute an integrated unit, promptly becomes a special source that circularly polarized light is provided.
Described 3 * 3 circle polarization-maintaining fiber couplers 14 are subjected to circularly polarized light from " revolving soon " termination of described optical fiber quarter-wave plate 12.So this circularly polarized light beam is divided into the three beams circularly polarized light.One light beam directly passes to the other end of coupling mechanism intermediate fibres arm, and (be a mating end, as described above), its power consumption is in this mating end.In the coupling mechanism two optical fiber arms two bundles circularly polarized light then enter into by fiber-optic probe ring (or sensing ring) 15 of circle polarization maintaining optical fibre coiled this fiber optic loop respectively by suitable, counterclockwise go in ring, penetrate from two ends (being alternate ends) in addition of this gauging ring 15 respectively then.What this two bundle was loaded with signal returns circularly polarized light from oppositely entering 3 * 3 circle polarization-maintaining fiber couplers, and the coupled zone is superimposed again and interfere therein, provides luminous power P respectively from two optical fiber arms then
1And P
2, detecting by balance photoelectric detector 13a and 13b, the simple signal through knowing is handled and is obtained by (P
1-P
2)/(P
1+ P
2) representative signal light power.The working point of described wholecircle polarization maintaining optical fibre interferometric sensor is bordering on slope steepest point, its sensitivity and dynamic range and utilize the index of correlation of active biased conventional fiber Sagnac interferometric sensor close.
Passive biasing interfere type sensing arrangement shown in Figure 1 both had been available as current sensor, also was available as gyro.In current sensor application, sensing mechanism depends on the Faraday effect, therefore the gauging ring with circle polarization maintaining optical fibre coiled has unique advantages, the detectable signal that produces owing to phase change, and the signal that has detected can be kept in justifying polarization-maintaining fiber coil.The eigenmodes of circle polarization maintaining optical fibre (patent of invention: the Chinese ZL88107839.X and the U.S. 5,452,394) is dextrorotation and left circularly polarized light.Consider a branch of circularly polarized light to detour in circle polarization maintaining optical fibre gauging ring clockwise or counterclockwise, the transverse field structure of this circularly polarized light beam (being polarization state SOP) remains unchanged in whole transmission course all the time; The amount that is changed only is the phase place of circularly polarized light beam.Find the solution coupled mode equation (referring to Huang Hongjia work Microwave Approach to Highly Inrgeular Fiberoptics, Wiley publishes, 1998, the 159 pages).As can be known:
Wherein
Represent start-phase;
Because of justifying the phase change that the polarization maintaining optical fibre waveguiding effect produces;
Because of the phase change that the Faraday effect produces, (AT) representative produces ampere one number of turn in magnetic field in the formula, and V is the Verdat constant.In addition, importantly, the phase change that occurs because of waveguiding effect
Be a reciprocity process, however the phase change that occurs because of the Faraday effect
It then is one " nonreciprocal " process, therefore respectively at two circularly polarized light beams that pass through circle polarization maintaining optical fibre gauging ring along contrary direction, its reciprocity phase change will be offset, and it promptly equals 2V (AT) owing to " nonreciprocal " phase change that the Faraday effect produces then will double.
For its working mechanism used based on the gyro of Sagnac effect, the current optical fiber interference type gyro of successful operation (being angular-rate sensor) was (comprising the fiber-optic probe ring) to utilize the line polarization maintaining optical fibre to make all.The line polarization maintaining optical fibre is no matter any kind can both keep main axis polarization eigenmodes.Fiber-optic probe ring by line polarization maintaining optical fibre coiled is detectable to go out the phase change that incident main axis polarized light produces because of the Sagnac effect, and the phase change that can keep this to detect.A kind of phenomenological description to the Sagnac effect is: the rotation of fiber optic loop is shortened the circulation path of a branch of light, and makes the circulation path lengthening of another Shu Guang.The rotation of fiber-optic probe ring can not influence the original linear polarization of light beam of going in ring, and what change only is its phase place.
The sensor fiber loop that is shown in Fig. 1 among the present invention is all made by the circle polarization maintaining optical fibre.This kind supports that the sensor construction of circularly polarized light is the same with the optical interference circuit structure that the described Support Line polarized light of being made by the line polarization maintaining optical fibre of epimere transmits, and is equally applicable to gyro and uses.The rotation of circle polarization maintaining optical fibre gauging ring does not influence the polarization state (SOP) of the light beam that goes in ring, just its phase place that is changed.
Described two types gyro, the first be based on the main axis polarized light in the line polarization maintaining optical fibre, its two circularly polarized light that is based in the round polarization maintaining optical fibre, and wherein the phase change that takes place because of the Sagnac effect can be with following phenomenological formulae express:
First and second row refer to transmission of line eigenstate and the transmission of circle eigenstate respectively in the formula, and its polarization state SOP all remains unchanged under two kinds of different eigenstate situations, the just phase place that is changed.(in formula,
With
Represent start-phase respectively, the phase change that phase change that waveguiding effect produces and Sagnac effect are produced.) the Sagnac effect is " nonreciprocal " process equally, thereby preamble is equally applicable to Sagnac effect in the gyro at the described basic difference that changes about reciprocity and non-reciprocal phase of current sense Faraday effect.With reference to Fig. 1, the whole phase shift of being measured by the balance photoelectric detector can be expressed as [2 π LD/ (λ c)] Ω, and wherein L is a fiber lengths; D, the fiber optic loop diameter; λ, free space wavelength; C, the free space light velocity; Ω, the speed of rotation that gyro is surveyed.
From the viewpoint of " integrated optical fiber technology ", optical fibre sensor structure very attractive shown in Figure 1 is because of its whole optical fiber circuits can be made up of two sections round polarization maintaining optical fibres.One section is short fiber, usefulness as 3 * 3 circle polarization-maintaining fiber coupler intermediate fibres arms, its end of going into (only needs core to core with " revolving soon " end welding mutually of optical fiber quarter-wave plate 12, need not the stressed zone on both sides of harmonizing), its end that goes out then blocks with the oblique angle and becomes mating end (general＞10 °, up to 45 ° or more oblique).Another section then is very long one section round polarization maintaining optical fibre, and its total length need comprise the addition length of coupling mechanism two optical fiber arms, in addition, also need comprise the whole round polarization maintaining optical fibre length overall of gauging ring.The center section of this long section circle polarization maintaining optical fibre is used for coiled fiber-optic probe ring, two sections " tail optical fibers " (about 1 meter long or summary weak point) reserved at two, for utilizing ripe technology in next step program, promptly " close up optical fiber; heating and melting is also stretched and drawn ", to make 3 * 3 required circle polarization-maintaining fiber couplers.(only need fibre core parallel, and need not to consider the stressed zone geometrical orientation).So, the both sides fiber arm of coupling mechanism adds that whole fiber optic loop can become one and do not contain welding point or joint.We can say that described jointless basically optical fiber Sagnac interferes the loop, as not utilizing the round polarization maintaining optical fibre of the previous invention of the applicant, then can't constitute.
Circle polarization maintaining optical fibre (patent of invention: Chinese ZL88107839.X is made in the laboratory, the ZL01132102.4 and the U.S. 5,452,394) progress reaches and can keep circularity to be better than 0.95 circularly polarized light, thereby to utilizing wholecircle polarization state optical fiber shown in Figure 1 loop formation current sensor and gyro (speed of rotation) sensor that condition precedent is provided.Obviously, sensor shown in Figure 1 has been represented very simple, the firm and low cost structure that is applicable to current sense and gyro, thereby has very big potential value.
Described wholecircle polarized light sensor structure is owing to its potential superiority, so far-reaching development prospect is arranged.But, at present, the present situation of sensor construction is still mainly set up on the basis of online polarization maintaining optical fibre technology.This is the very important fact, because line polarization maintaining optical fibre technology wants much ripe more than circle polarization maintaining optical fibre technology, and the components and parts overwhelming majority in the optical fiber circuit structure all is to make with the line polarization maintaining optical fibre in now.As for 3 * 3 line polarization-maintaining fiber couplers, before and address, accurately adjustment is parallel owing to not only require three fibre cores on the process in the manufacturing of this kind coupling mechanism, three pairs of mirror image symmetry main shafts that also require simultaneously to be determined by many stressed zones are accurately adjusted parallel, be difficult for reaching practical so its technical difficulty is too big, inside and outside the native land only this kind of only a few commodity come out, and the logical extinction ratio that linearly polarized light reaches of its each fiber arm 20 decibels of less thaies still fail to satisfy practical requirement.Because the technical merit of current this kind 3 * 3 line polarization-maintaining fiber couplers, the present invention discloses a kind of variation of 3 * 3 fiber couplers, promptly a kind of 3 * 3 hybrid fiber coupling mechanisms, and its structure comprises two line polarization maintaining optical fibres in conjunction with a single-mode fiber, be shown in Fig. 3 a, 3b and 4.
Fig. 3 a is a kind of pattern of described hybrid fiber coupling mechanism, and wherein label 4 is joint single-mode fibers, and label 5 and label 6 are two nodel line polarization maintaining optical fibres, draw oblique line on this two nodel lines polarization maintaining optical fibre longitudinal section, are different from single-mode fiber to show it.To every optical fiber, a after the numeral and b represent the end points of this optical fiber.Note single-mode fiber two ends among the figure with greater than 10 ° oblique angle brachymemma, thereby form the coupling end face.This single-mode fiber can be punctured into is enough to all place heat-sealing sleeve pipe 10 inside, makes the outside such as same 2 * 2 line polarization-maintaining fiber couplers of made hybrid fiber coupling mechanism.Perhaps, described single-mode fiber section can still leave the slightly tail optical fiber of length when brachymemma, for example, and as the usefulness of luminous power supervision.In such cases, the tail optical fiber of single-mode fiber section needs to be fixed in the hybrid fiber coupling mechanism, and this is because single-mode fiber does not have the ability of the extraneous perturbation of opposing, even very short its position firm fixation that also requires is to guarantee the stability of polarization state in the sensor fiber loop.
Fig. 3 a is depicted as the side view of 3 * 3 mixing polarization-maintaining fiber couplers.Corresponding cross-sectional view is shown in Fig. 3 b, and wherein three optical fiber 4,5 and 6 place on the isoplanar, so three fibre cores 40,50 and 60 are positioned on the straight line.This structure makes on the technology the used folder mouth that fastens three optical fiber be easy to make.Attention is in Fig. 3 b, and single-mode fiber is not to place between two parties between the polarization maintaining optical fibre of two wires symmetrically, but place two near the either side of line polarization maintaining optical fibre.Take the reason of this layout very simple, exactly in order to make the power coupling conversion between the polarization maintaining optical fibre of two wires more effective.
Fig. 4 shows that 3 * 3 mix the horizontal how much of polarization-maintaining fiber couplers, and wherein single-mode fiber 4 forms a triangle together with two wires polarization maintaining optical fibre 5 and 6 threes; The position of single-mode fiber 4 is symmetrical in the position of line polarization maintaining optical fibre 5 and 6.When making this 3 * 3 mixing polarization-maintaining fiber coupler, three fibre cores all need be adjusted into accurately parallel mutually, and the requirement of " stressed zone is parallel " or " spindle parallel " only relates to two pairs of main shafts of two wires polarization maintaining optical fibre, thereby has greatly simplified the mutually accurate parallel technological difficulties of the desired three pairs of main shafts of original 3 * 3 line polarization-maintaining fiber couplers.Not shown with the corresponding side view of Fig. 4; Abovely the restriction regulation of the short section of single-mode fiber wherein is equally applicable to embodiment shown in Figure 4 in conjunction with Fig. 3 a and 3b are described.
Interferometric sensor structure based on line polarization maintaining optical fibre loop is shown in Fig. 5.The core of this optical fiber circuit promptly is above in conjunction with Fig. 3 a, 3b and 4 described extraordinary hybrid fiber coupling mechanisms.One main axis polarized light injects one of this hybrid fiber coupling mechanism 18 arm.The inclined to one side line of this line light that shakes is provided by light source 11, has passed through the single-mode optical-fibre coupler 16 and the polarizer 17.The hybrid fiber coupling mechanism is divided into the three-beam line polarized light with the incident ray polarized light bundle.A branch of light enters single-mode fiber, leads to mating end always, and consumes its power at this end.Simultaneously, in addition two bundles couple light to the two wires polarization maintaining optical fibre arm of described Special Mixed fiber coupler, enter two ends of detection optical fiber ring thereupon, shown in arrow 20a and 20b, then respectively with along counterclockwise around the detection optical fiber ring.Use for gyro, this fiber optic loop is by line polarization maintaining optical fibre coiled; But for current sensor application, this fiber optic loop then is with circle polarization maintaining optical fibre coiled, and the equal welding of two ends of ring is with the optical fiber quarter-wave plate, so as again with the welding mutually of hybrid fiber coupling mechanism two wires polarization maintaining optical fibre arm.After around the detection optical fiber ring, two linearly polarized light beams reconsolidate and interfere in the coupled section of hybrid fiber coupling mechanism returning with arrow 20a and 20b reverse direction.So the light beam that returns and be loaded with transducing signal is detected by photoelectric detector 13 at last again by the polarizer and single-mode optical-fibre coupler 16.Label 16a is the coupling end face; 19 of labels or be a coupling end face, an or external again detecting device makes it to constitute two-way and detects, thereby strengthens sensitivity and enlarge dynamic range in described interference-type optical fiber loop.
Again with reference to the hybrid fiber coupling mechanism among the figure 5, the section single-mould fiber that it is short-and-medium seems " leaving unused " apparently among the fiber optic interferometric loop.But in fact, this vital role that the single-mode fiber section plays provides required 120 ° of phase relations of " leaving unused ", this indispensable phase relation makes and realized passive biasing in the fiber optic interferometric structure just.
The characteristics of the above embodiment of the invention are to play beam split and passive bias simultaneously with two kind of 3 * 3 fiber coupler in Fibre Optical Sensor.Below disclose another embodiment of the present invention, be characterized in playing bias specially, and before this, then play the branch light action with a routine 2 * 2 line polarization-maintaining fiber couplers with an integrated Faraday spinner.The integrated spinner unit of described passive bias contains a meticulous optics magneto-optic rotary unit, and both sides connect respectively with " zero to fast " and " piece is to zero " optical fiber quarter-wave plate (referring to patent of invention: Chinese ZL01112680.9; The U.S. 7,206,468).The index that laboratory short run sample has reached is, than nearly 30 decibels, is better than 0.95 in the circularity of center section circularly polarized light in the digestion of two ends, integrated spinner unit linearly polarized light.
Fig. 6 a is a kind of sample of described integrated spinner unit, and center section is 45 ° of magneto-optical rotator of a meticulous optics among the figure, and label 22a and 22b are respectively " zero to fast " and " near zero " optical fiber quarter-wave plate.Label 23 is fibre cores; Label 24 is stressed zones.One main axis polarized light enter first optical fiber quarter-wave plate 22a's " zero revolve " promptly do not revolve end, promptly revolve end soon at the end in addition of this optical-fibre wave plate and be transformed to circularly polarized light.This circularly polarized light enters and changes by 45 ° of non-reciprocal phase take place behind the meticulous optical rotator.Then, what the circularly polarized light that penetrates from spinner entered second optical fiber quarter-wave plate 22b revolves end soon, becomes again again after by optical-fibre wave plate to be the main axis polarized light.Obviously, described integrated Faraday spinner is suitable for welding among a conventional interference optical fiber loop that mainly is made of the line polarization maintaining optical fibre.Inserting described integrated Faraday spinner unit in this kind optical fiber circuit only need get final product with the Polarization Maintaining Optical Fiber Fusion Splicer of standard.
Fig. 6 b and 6c are two kinds of variation of described integrated spinner unit.The structure of Fig. 6 b be an edge joint of meticulous optics magneto-optic rotary unit in the centre with optical fiber quarter-wave plate 22a, another side then connects with circle
Polarization maintaining optical fibre 22c.The integrated Faraday spinner of this pattern is suitable for inserting a kind of fiber optic interferometric light path, wherein " zero revolves " of spinner promptly do not revolve end and light path center line polarization maintaining optical fibre element or device welding mutually, and the round polarization maintaining optical fibre end of spinner then with in the light path is justified polarization maintaining optical fibre element or device welding mutually.The structure of Fig. 6 c is that the spinner both sides are round polarization maintaining optical fibre, is fit to insert an optical fiber circuit that mainly is made of the circle polarization maintaining optical fibre.
A typical application of described integrated spinner unit is illustrated in Fig. 7.Comparison diagram 7 and Fig. 5 as seen, Yi Bian the fiber optic interferometric loop shown in this two figure is all very similar with the fiber-optic probe ring on one side at light source.But between among this two figure, partly then be very different.3 * 3 hybrid fiber coupling mechanisms among Fig. 5 singly do not play the branch light action, also cause 120 ° of phase relations simultaneously, thereby the passive phase biasing is provided.But from Fig. 7 as seen, the biasing of beam split and passive phase is then finished by 2 * 2 line polarization-maintaining fiber couplers 25 and collection spinner 21 at 45 respectively.
Optical fiber circuit the right end points is connected to a fiber-optic probe ring (not shown) in the two horizontal arrow 27a on Fig. 7 the right and the 27b presentation graphs.Before described in conjunction with Fig. 5, suitable equally to Fig. 7, that is: in gyro was used, this gauging ring was with line polarization maintaining optical fibre coiled; Then this gauging ring is by circle polarization maintaining optical fibre coiled in current sensor application, but need at the two ends of gauging ring welding two optical fiber quarter-wave plates, so that the suitable counterclockwise two bundle circularly polarized lights that penetrate from gauging ring are transformed to linearly polarized light (shown in two perpendicular arrows the figure), mate mutually with the fiber optic interferometric loop among suitable and Fig. 7.
Fig. 8 shows a kind of version of passive offset sensors structure, contains integrated spinner unit 26, and its one-piece construction is shown in Fig. 6 b.Comparison diagram 8 and Fig. 7 as seen, the two difference only is from the polarization state SOP of integrated spinner unit outgoing beam.For Fig. 8, described SOP is a circular polarization state, and shown in capital C, so the end points 20b of spinner unit can be directly join with a gauging ring by circle polarization maintaining optical fibre coiled, thereby saves " near zero " optical fiber quarter-wave plate of fiber-optic probe ring one end.
Below summary collects the mathematical physics principle of nonreciprocal Faraday spinner at 45.One section passive Faraday rotary unit of meticulous optics magneto-optic in the middle of the integrated spinner, its performance can be expressed as following rotation matrix:
θ is the rotation angle of spinner in the formula, desirable (+) or (-) value, and the one representative turns clockwise, and another is then represented and is rotated counterclockwise.The column matrix of x-main shaft and y-main axis polarized light is:
The column matrix of figure polarized light is:
θ wherein
0Be the start-phase of circularly polarized light, ± represent dextrorotation and left circularly polarized light.
One main shaft (as, x) linearly polarized light of direction becomes after by the Faraday spinner:
This result represents: linearly polarized light keeps its linear polarization and does not produce phase change by the Faraday spinner, just its position angle that is changed.θ is called the Faraday rotation angle in the formula.
One circularly polarized light (as, right-handed rotation) become by the Faraday spinner:
This result represents: circularly polarized light remains its circular polarization state by the Faraday spinner, and what changed is its phase place only, and this is the influence of Faraday effect to circularly polarized light.
Now examine or check the integrated spinner shown in Fig. 6 a, contain both sides " zero to fast " and " near zero " optical fiber quarter-wave plate and meticulous optics magneto-optic rotary unit placed in the middle.Following matrix representation formula about the optical fiber quarter-wave plate is to draw from yellow grand good monograph: Microwave Approach to Highly Inrgeular Fiber Optics, and Wiley InterScience 1998, p.246:
Structure parameter in the formula
Be meant wavelength L
b, revolve apart from L
sFunction with optical fiber total length L;
With ± last subscript represent optical fiber " zero to fast " and " near zero " quarter-wave plate respectively.
One main shaft (as, x) linearly polarized light of direction becomes after by described integrated spinner:
T in the formula
1, T
2It is the transformation matrix of optical fiber " zero to fast " and " near zero " quarter-wave plate; R is the rotation angle θ of Faraday spinner, is taken as 45 °; E
lBe incident x major axes orientation linearly polarized light, its start-phase is θ
0(ρ
1+ ρ
2) be linearly polarized light owing to phase change that the waveguiding effect of two optical fiber quarter-wave plates produces; Last 45 ° is the phase change that the Faraday spinner is produced.An important point that has fundamental property herein is: the phase change that waveguiding effect produced is a reciprocity, and the phase change that the Faraday effect is produced then is a nonreciprocity; Thereby as coming and going twice by integrated spinner unit, it is zero that then total reciprocity phase change will be cancelled each other, and total nonreciprocity phase change then will double.This shows that interfere at optical fiber Sagnac described collection spinner at 45 unit provides a best i.e. passive biasing of 90 ° in the loop.
For the collection spinner at 45 of another form shown in Fig. 6 b, its polarization state behavior is can similar derivation as follows:
Wherein ρ is the structure parameter of optical fiber quarter-wave plate, and this wave plate is excited by the linearly polarized light of an x major axes orientation; ρ
cIt is the phase change that circularly polarized light is produced by output terminal circle polarization maintaining optical fibre section; The meaning of all the other symbols is all with above identical at last formula illustration.
More than be detailed description of the present invention, obviously see that the present invention still can be described in many ways thus.These variations can not think to be different from spirit of the present invention and content, thereby all these all should list the described category of following claim in to the self-evident change of those skilled in the art.
Claims (10)
1. passive bias optical fiber sensor comprises:
One provides the light source of linearly polarized light;
One " not being threaded onto fast turn-knob " optical fiber quarter-wave plate, it does not revolve end and is connected with described light source;
One 3 * 3 circular polarization states keep fiber coupler, and one of fiber arm end is connected with the end that revolves soon of described optical fiber quarter-wave plate in the middle of it, and the other end is punctured into mating end;
One fiber-optic probe ring, its two ends keep each end of fiber coupler two optical fiber arms to be connected with described 3 * 3 circular polarization states; And
A pair of photodetector is connected to each other end that described 3 * 3 circular polarization states keep fiber coupler two optical fiber arms, in order to survey the signal light power that Returning beam carried.
2. sensor according to claim 1, it is characterized in that, described 3 * 3 circular polarization states keep three circular polarization states of fiber coupler to keep the position of optical fiber symmetrical, make the xsect how much of contained three fibre cores become triangle, described three circular polarization states keep among the optical fiber arbitrary all to can be used as and accept the light activated input end of circular polarization.
3. sensor according to claim 1 is characterized in that, described 3 * 3 circular polarization states keep three circular polarization states of fiber coupler to keep optical fiber to be positioned at same plane, makes the xsect of contained three fibre cores become a straight line how much.
4. sensor according to claim 1, it is characterized in that, described fiber-optic probe ring is that circular polarization state keeps the fiber-optic probe ring, in order to survey the slewing rate of this fiber optic loop, two circularly polarized light beams are proportional to tested fiber optic loop slewing rate at phase differential suitable, that produce owing to the Sagnac effect when counterclockwise going in ring in the described fiber optic loop.
5. sensor according to claim 1, it is characterized in that, described fiber-optic probe ring is that circular polarization state keeps the fiber-optic probe ring, in order to survey this fiber optic loop around electric current, two circularly polarized light beams are at ampere-turn suitable, that phase differential that produce owing to the Faraday effect when counterclockwise going in ring is proportional to tested electric current in the described fiber optic loop.
6. passive bias optical fiber sensor.Comprise:
One provides the light source of linearly polarized light;
One 2 * 2 single-mode optical-fibre couplers, wherein a fiber arm is subjected to exciting of described linearly polarized light;
One 3 * 3 hybrid fiber coupling mechanisms that are connected via a polarizer with described 2 * 2 single-mode optical-fibre couplers, contain a single-mode fiber and two linear polarization maintenance optical fiber, these two linear polarization keep optical fiber to play the branch light action, simultaneously produce 120 ° of phase relations, thereby the passive biasing in the sensor interferometer light path is provided because of intercoupling with single-mode fiber;
One fiber-optic probe ring, its two end is connected with two linear polarization maintenance fiber-optic output in described 3 * 3 hybrid fiber coupling mechanisms; And
One photodetector is connected to another fiber arms of described 2 * 2 single-mode optical-fibre couplers, in order to survey the signal light power that Returning beam carried.
7. sensor according to claim 6, it is characterized in that, the cross-sectional structure of described 3 * 3 hybrid fiber coupling mechanisms keeps an optical fiber and a single-mode fiber mutually near forming by two linear polarization, contained three fibre cores are equidistant each other, form a triangle, wherein the single-mode fiber two ends become two mating end with the oblique angle brachymemma.
8. sensor according to claim 6, it is characterized in that, the cross-sectional structure of described 3 * 3 hybrid fiber coupling mechanisms keeps an optical fiber and a single-mode fiber at grade near forming by two linear polarization, contained three fibre cores form a straight line, wherein the single-mode fiber two ends become two mating end with the oblique angle brachymemma.
9. sensor according to claim 6, it is characterized in that, described fiber-optic probe ring is to keep the optical fiber coiled with linear polarization, in order to survey the slewing rate of this fiber optic loop, two linearly polarized light beams are proportional to tested fiber optic loop slewing rate at phase differential suitable, that produce owing to the Sagnac effect when counterclockwise going in ring in the described fiber optic loop.
10. sensor according to claim 6, it is characterized in that, described fiber-optic probe ring is to keep the optical fiber coiled with circular polarization state, and two ends of described fiber optic loop all are connected with two linear polarization maintenance fiber-optic output in described 3 * 3 hybrid fiber coupling mechanisms by " being threaded onto not turn-knob soon " optical fiber quarter-wave plate, thereby make linearly polarized light in the sensor interferometer light path be transformed to circularly polarized light laggard go into fiber optic loop in order to survey this fiber optic loop around electric current, two circularly polarized light beams are suitable in the described fiber optic loop, the phase differential that produces owing to the Faraday effect when counterclockwise going in ring is proportional to the ampere-turn of tested electric current.
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| CN101943630B (en) * | 2009-07-08 | 2012-03-07 | 中国科学院半导体研究所 | Method for analyzing polarization-maintaining characteristic of optical element |
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| CN111238463B (en) * | 2020-01-19 | 2021-10-29 | 湖北三江航天红峰控制有限公司 | Modulation method and device based on random sequence digital closed-loop fiber optic gyroscope |
| CN113687508B (en) * | 2021-08-31 | 2022-06-14 | 华中科技大学 | Single-optical-fiber micro scanning device and driving system thereof |
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