CN1042380C - Method for realizing optic fiber ring-shaped cavity bidirection single-mode excitation and optic fiber gyro laser device thereof - Google Patents

Abstract

The present invention relates to an implementation method and a structure design of a novel optical fiber gyroscope laser. The method comprises that a doping optic fiber composite annular laser cavity of bidirectional symmetric optical pumping is adopted, single mode operation is realized by the composite cavity resonance mode selection, by using the near threshold value operation of the laser under weak pumping and saturable absorption characteristics of weak excitation coupling sub-rings, mode fields of clockwise and counterclockwise travelling wave oscillation in the laser are in a weak coupling state, and bidirectional and single mode simultaneous travelling wave oscillation is realized. Compared with the existing optical gyroscope, locking effect of the optical fiber laser gyroscope based on the method is attenuated, the optical fiber laser gyroscope is insensitive to the phase noise interference, and the sensitivity and the accuracy of rotation sensing of the optical fiber laser gyroscope can be greatly improved.

Description

Realize the method and the optic fiber gyro laser device thereof of optic fiber ring-shaped cavity bidirection single-mode excitation

The invention belongs to that the photoelectron technology field is particularly related to the core devices of novel active optics gyro-two-way, single mode swashs the implementation method and the structural design of penetrating optical fiber ring laser simultaneously.

From over more than 30 year of laser appearance, optical gyroscope is greatly developed with the advantage of its many uniqueness as the inertial navigation instrument of new generation in Aeronautics and Astronautics, the naval technology.

The operation principle of optical gyroscope based on the Sagnac effect when a closed optical loop rotates around axis, plane, place, in the loop along clockwise direction (CW) and counterclockwise (CCW) light wave of propagating generation is proportional to the phase difference φ of angular velocity of rotation Ω _s(or difference on the frequency Δ v _s), be expressed as: ${\mathrm{\Δ\φ}}_s=\frac{8\mathrm{\πA}}{{\mathrm{\λ}}_{0}C}\mathrm{\Ω}$ Or ${\mathrm{\Δ\ν}}_s=\frac{4A}{{\mathrm{\λ}}_{0}C}\mathrm{\Ω}---\left(1\right)$ The girth that L and A are respectively loop in the formula with around area λ ₀Be respectively optical wavelength and velocity of wave in the vacuum with C.So, measure Δ φ with method for detecting phases _sOr measure Δ v with the difference frequency detection method _sCan learn the size of angular velocity of rotation Ω

So far, successively three class optical gyroscopes have been developed, though the practicality that has does not all reach its potential high sensitivity and high accuracy.Ring laser gyro (RLG) is to occur the earliest the sixties and commercial optical gyroscope.Its principle signal what Fig. 1.It is the single-frequency He-Ne gas ring laser of a two-way output, and when annular chamber rotated around axis, plane, place, (CW, CCW) sharp penetrated the frequency difference Δ v that light frequency is proportional to generation angular velocity of rotation Ω to suitable, counterclockwise both direction _s. the active device of this active oscillation need not external light source and adopts the difference frequency detection method, and is not too responsive to the disturbance of surrounding environment.Has higher certainty of measurement.But device technology is quite complicated, and light path is limited around area, particularly the optical heterogeneity that is caused by many complicated factors such as discharge excitation, gas turbulence, minute surface 1,2,3 places refractive index sudden changes in the gas laser chamber causes the enhancing of light scattering dorsad, produce so-called " locking " effect, make its variation insensitive, limited its sensitivity minute angular velocities.At present, the drift rate of this gyro reaches 0.01 °/hr.

The interference-type optical fiber optical gyroscope (I-FOG) that grows up the seventies is a kind of passive device, and its operation principle is based on the two-beam interference effect, as shown in Figure 2.Adopting a splitting ratio is that 1: 1 fiber coupler C2 is linked to be Sagnac ring SL with optical fiber, with the 21 ends input of beam of laser from C2.Behind coupler, be divided into aplanatic two bundles, enter fiber optic loop from 23 and 24 two ends respectively, separately in opposite direction the ring in the propagation one week after, arrive 24 and 23 ends respectively, again through the coupler beam split and produce to interfere, (CW will export from 21 ends after CCW) synthetic the two-beam ripple that phase place is identical; When fiber optic loop is rotated, generation is proportional to the phase difference φ of angular velocity of rotation Ω along two-beam suitable, the counter clockwise direction propagation in the ring _sThereby, cause exporting moving of interference of light striped.The distinguishing feature of this gyro is not exist as intrinsic in the laser gyro " locking " effect, and light path is bigger around area, once looks to reaching very high sensitivity and precision.But need the long fiber optic loop of nearly kilometer, and because of adopting the phase-detection technology, intrinsic polarization effect and the extremely sensitive of environmental factor introduced the additive phase interference of noise in the optical fiber for this reason.The drift rate of this gyro is limited in 0.7～0.02 °/hr so far, still not as good as laser gyro.

Ring resonator fiber optics gyro (R-FOG) is the another kind of novel passive optical gyroscope of the development eighties, as shown in Figure 3.Cross-couplings end 32 and 34 and one sections optical fiber of the fiber coupler C3 that coupling ratio is very high are connected to ring resonator, single-frequency laser is imported simultaneously from coupler 31 and 33 two ends, because the branch light action of coupler, the two-way light wave produces multiple-beam interference along suitable, counter clockwise direction respectively in fiber optic loop, and exports from 33 and 31 two ends of coupler respectively.When annular chamber rotates, between the two-beam generation is proportional to the phase difference of angular velocity of rotation Ω, cause relatively moving of two-way output interference of light striped.Because this gyro based on the multiple-beam interference principle, is estimated theoretically, only need the optical fiber of very short (about 10 meters) can reach the same sensitivity of above-mentioned two-beam interference type optic fiber gyroscope, thereby the sensitiveness of environmental interference is reduced relatively.But need to use frequency stabilization narrow linewidth coherent source; And high because of the optical power density in the optical fiber cavity, nonlinear optical effect becomes the adverse factor that limits its sensitivity and precision again, and its drift rate is limited in 0.1 °/hr so far.

Therefore, the technological approaches of exploration novel high-precision optical gyroscope just becomes the important topic of current Aeronautics and Astronautics photoelectron technology.

The objective of the invention is to weak point, proposed the optical fiber ring laser that a kind of new bidirection single-mode is exported, to constitute a kind of novel optical gyro one fiber ring laser gyro at existing three class optical gyroscopes.The advantage that integrates active laser gyro and passive fiber gyro, eliminate " locking " effect in the gas laser gyro to greatest extent, avoid the interference of phase noise in the passive fiber gyro or nonlinear optical effect, in the hope of realizing high sensitivity and high-acruracy survey to angular velocity of rotation.

Realizing the key problem of this gyro, at first is the demonstration that the feasibility of, single mode two-way to optical fiber ring laser, output is simultaneously carried out theory and experiment.

Relevant in the past ring laser bi-directional oscillating The Characteristic Study.Mainly concentrate on on the ring laser of fluid (gas or liquid) as working media: in the theory analysis hypothesis its for the four level system of even broadening or inhomogeneous broadening and with the Doppler effect of molecular motion as basic point of departure; Two-way, the vibration simultaneously of He-Ne gas ring laser is by add isotope Ne in the chamber ²³And realize.

Consider from the notion of traditional laser theory, in the fiber ring laser chamber, because suitable, the mode competition between the capable ripple of two-way counterclockwise, attempt to obtain two-way, single mode, laser output simultaneously almost is impossible.In more than ten years since Rear Earth Doped Fiber Laser is come out, although Chinese scholars has realized single module lasing of optical fiber ring laser by the multiple technologies means, but be stranded competition in its two-way capable wave mode, all bar none at chamber built in light isolator, the laser generation of one of them direction is suppressed, thereby can only be obtained unidirectional laser output.In the ring laser of solid state medium, can realize actually and how to realize research two-way, laser generation simultaneously, still not be reported so far.

Recently, that the application goes into is two-way with regard to fiber ring laser, single mode, simultaneously exciting problem have carried out theoretical research, the theoretical model that adopts with working in the past different is: consider that the solid working media generally has the comprehensive spectral property of even broadening and inhomogeneous broadening concurrently: get typical case's doping (as erbium ion) optical fiber and belong to three level atomic system, and in annular chamber introducing non-uniform excitation mechanism.The time domain specification that utilizes half classical Lamb theory of laser to obtain laser generation mould field in the optic fiber ring-shaped cavity is $E_n\left(t\right)=\frac{1}{2}G\[A_n-S_i\left(f_n\right)(I_n-C_n{I}_{-n})\]E_n+{\mathrm{RE}}_{-n}+q_n\left(t\right)---\left(2\right)$ In the formula subscript n and-n represents respectively along suitable, counterclockwise, E (t) is the light wave electric field, I is the dimensionless light intensity, q _n(t) represent noise, G is a gain index, and A is the factor relevant with gain, and S (f) is the self-saturation factor, and f is a complex frequency, and R is an equivalent cavity internal reflection rate, and C is a coupling coefficient, and (2) formula shows that suitable, the contrary capable mode of two-way field is coupled mutually by coefficient C.Calculate the stable state Probability Distribution P of two-way traveling wave oscillation in the desirable optical cavity according to quantum theory _s(In) pass with coupling coefficient C is $P_n\left(I_n\right)=\frac{\sqrt{\mathrm{\π}}}{M}\exp \[\frac{1}{2}(a_n-a_{-n}C)I_n-\frac{1}{4}(1-C^2)I_n^2+\frac{1}{4}{a}_{-n}^2\]\mathrm{erfc}(\frac{C}{2}{I}_n-\frac{1}{2}{a}_{-n})---\left(3\right)$ A in the formula _n=GA _nIt is the gain coefficient of chamber internal electric field.When C＜1, when promptly being in weak-coupling state, suitable in the annular chamber, the capable wave mode of counter clockwise direction two-way has the identical vibration probability of being close to.The physical factor that the theoretical Mode Coupling of must sening as an envoy to weakens comprises the rotation in weak pumping, low temperature, intracavity reflecting and chamber etc.

Based on the above-mentioned theory result of study, experiment confirm two-way, the single mode of optical fiber ring laser, vibration output simultaneously.For this reason, the present invention proposes a kind ofly to realize that optical fiber ring laser is two-way, single mode, the method for vibration simultaneously, it is characterized in that comprising following measure:

(1) adopt rare-earth doped optical fibre to make the loop laser chamber;

(2) said doped fiber annular chamber is carried out the bi-directional symmetrical optical pumping, constitute symmetric double to the vibration optical fiber ring laser;

(3) in the vibration optical fiber ring laser, introduce mode selection mechanism in said symmetric double, make it work in the single longitudinal mode state;

(4) make in the said monomode fiber ring laser suitable, counterclockwise the weak coupling condition is satisfied in two-way oscillation mode field, i.e. coupling coefficient C＜1 therebetween,, single mode two-way to realize, traveling wave oscillation simultaneously.

The composite fiber annular chamber that optic fiber ring-shaped cavity optic fiber ring-shaped cavity in the said method can adopt the sub-annular chamber of the mutual coupling cascade that is linked to be by two above wavelength division multiplexing (WDM) fiber couplers and doped fiber to constitute; Being positioned at the private end coupler of the sub-annular chamber in end is used for input pumping light and output and swashs and to penetrate light, pump light is gone into the sharp light of penetrating of ring through straight-through fiber segment respectively from two free optical fiber end of end coupler, pump light is gone into ring through straight-through fiber segment respectively from two free optical fiber end of end coupler, the sharp light of penetrating then circulates in the chamber with encircling the pair of cross coupled end that links to each other by it, and partly appears through two free optical fiber end; Public coupler in the middle of being positioned at is about 50% to swashing the power coupling ratio of penetrating light, is used for realizing the effective coupling between the fiber optic loop, and the control size that enters dynatron annular chamber pumping light power.

Said mode selection mechanism can utilize composite fiber annular chamber mode resonance to realize in the said method, said composite fiber annular chamber will have the long L in chamber of two sub-annular chambers equal substantially at least, make the gain spectrum width of the frequency interval Δ v=c/n| Δ L| of its resonance mode, to realize the running of laser single longitudinal mode greater than doped fiber.

Said weak coupling condition can realize by two approach in the said method: the one, make laser close-threshold operation under weak pumping, two pump lights that enter sub-annular chamber by said public coupler are not enough to bleach the wherein light absorption of doped fiber, make it to have the saturable absorption characteristic, play intermode uncoupling effect.

The present invention utilizes said method to design a kind of fiber annular gyro laser device, it is characterized in that the doped fiber segment length between adjacent two couplers of said composite fiber annular chamber is equal substantially, constitutes the symmetrical coupled annular chamber; The input of pump light and the sharp shared end coupler of output of penetrating light, said should identical with other two coupled characteristics respectively chamber of two free optical fiber end of end coupler with it outside the WDM coupler link to each other, its straight-through optical fiber end connects two pump laser source respectively, its cross-couplings optical fiber end is as laser output, and connect an optical isolator respectively, to eliminate the interference of fiber end face reflection to the endovenous laser vibration, the input of pump light and sharp output of penetrating light also can be adopted two end couplers respectively, and two free optical fiber end of an end coupler connect pump laser source respectively.Two free ends of another end coupler are used separately as laser output, and respectively connect an optical isolator.

The WDM coupler of said formation composite fiber annular chamber is the arrowband coupler to excitation wavelength, and promptly it is at the filtering bandwidth of the operation wavelength gain spectrum width less than doped fiber, in order to pressing narrow laser linewidth;

Above-mentioned laser can be selected the doped fiber (as Er-doped fiber) that belongs to three level system for use, has both helped realizing the weak coupling condition, again because of the long influence that helps weakening backscattering of its radiation wavelength (1550nm).

Above-mentioned laser, said mutual coupling cascade fiber optic loop can adopt ordinary optic fibre WDM coupler and doped fiber weldering to connect formation, for eliminating the light feedback that the solder joint loss causes, preferably all adopt doped fiber directly to be coupled into the cascade annular chamber of no solder joint.

The present invention has following effect

The first, to compare with the He-Ne gas ring laser, optical fiber ring laser is made of all solid state medium, can not have any medium refraction index sudden change or medium disturbance factor in the light path, has fabulous optical homogeneity; The doped fiber that can select for use the long wavelength to swash to penetrate is made laser medium, makes in the chamber much weak in the interference ratio He-Ne gas laser of light scattering (wavelength the is 633nm) gyro dorsad, thus usually in the gas laser gyro intrinsic " locking " effect can weaken greatly; And, the fiber ring laser chamber around area can do greatlyyer, thereby can improve rotation sensing sensitivity.

The second, to compare with the passive fiber gyro, optical fiber laser peg-top need not external light source; And adopt the difference frequency technology that angular velocity of rotation is carried out sensing measurement; Can avoid in the common interference optical fiber top since the phase perturbation that polarization, temperature and external environment condition are introduced to the influence of certainty of measurement; Simultaneously, there is not the interference of high light nonlinear optical effect in the chamber as in the resonant cavity type passive fiber gyro yet.

Brief Description Of Drawings:

Fig. 1 is the ring laser gyro structural representation that a kind of two-way output He-Ne gas laser in the prior art constitutes;

Fig. 2 is a kind of interfere type passive fiber gyro structural representation in the prior art;

Fig. 3 is an another kind of passive fiber ring resonator gyroscope structural representation in the prior art;

Fig. 4 is a kind of composite ring of the present invention chamber optical fiber laser peg-top example structure schematic diagram.

The present invention utilizes composite ring mode selection by short-cavity principle to realize single-mode oscillation, and utilize the saturable absorption characteristic of the sub-annular chamber of coupling under weak pumping condition to form intermode weak coupling mechanism, design a kind of Compound Cavity fiber annular gyro laser device embodiment, realized two-way, single mode, output simultaneously.Install as shown in Figure 4:

(LD1 LD2) makes pumping source to adopt the 980nm laser diode of two tail optical fibers output 20mW; Adopt the Er-doped fiber of 1500nm service band, three level system to do laser medium, Optical Fiber Numerical Aperture 0.21 is respectively 4.57dB/m and 3.29dB/m to swashing the absorption coefficient of penetrating optical wavelength (1550nm) and pump light wavelength (980nm).

Adopt two arrowband wavelength division multiplexing optical fiber coupler WDM41 and WDM42 that Er-doped fiber is linked to be main ring 401 and subring 402 formation composite ring resonant cavitys.The filtering bandwidth of coupler at centre wavelength 1550mm place is 20nm (less than Er-doped fiber gain spectrum width 40nm); WDM41 is respectively 0.5% and 99.5% to pump light and the sharp power coupling ratio of penetrating light, and most pumping light powers directly feed in the ring through 411-414 section or 413-412 section, swashs and penetrates light then by the formation of the close coupling between 412-414 low-loss resonance loop; WDM42 is 50% to swashing the power coupling ratio penetrate light, and two optical fiber cavities effectively are coupled, and realizes the resonance modeling, and to coupling ratio＞50% of pump light, makes subring 402 be in weak excited state; The length L of two optical fiber cavities (401,402) ₁And L ₂Be taken as 1 meter.

Two ends, main loop chamber 411 linked to each other with LD2 with pump laser diode LD1 with WDM44 by wavelength division multiplexing optical fiber coupler WDM43 in addition with 413 minutes, and WDM43, WDM44 are respectively 0.5% and 99.5% to pump light and the sharp power coupling ratio of penetrating light.Left side road LD1 pump light is propagated along clockwise direction earlier after the 411-414 section of the 431-434 section of WDM43 and WDM41 leads directly to into optic fiber ring-shaped cavity; Right wing LD2 pump light is propagated in the counterclockwise direction earlier after the 413-412 section of the 444-441 section of WDM44 and WDM41 leads directly to into optic fiber ring-shaped cavity, forms two directional pump symmetrically and evenly.The sharp light (CW) of penetrating along clockwise direction is earlier through the outgoing of the 412-413 of WDM41 section, coupling output through between the 441-443 of WDM44 again; The sharp light (CCW) of penetrating in the counterclockwise direction is earlier from the 414-411 section outgoing of WDM41, coupling output through between the 434-432 of WDM43 again.

Be the interference of the light feedback of eliminating fiber end face, put optical isolator ISO1 and ISO2 respectively at two laser outputs 432 and 443 of WDM43 and WDM44 to the endovenous laser vibration.

Utilize said apparatus, experiment confirm two-way, the single mode of fiber annular gyro laser device, vibration output simultaneously, record laser linewidth＜1GHz (being subjected to the scanning interferometer resolution limit).

Claims (12)

1, two-way, the simultaneously exciting method of single mode of a kind of realization optical fiber ring laser is characterized in that comprising following measure:

(1) adopt rare-earth doped optical fibre to make the loop laser chamber;

(2) said doped fiber annular chamber is carried out the bi-directional symmetrical optical pumping, constitute symmetric double to the vibration optical fiber ring laser;

(3) in the vibration optical fiber ring laser, introduce mode selection mechanism in said symmetric double, make it work in the single longitudinal mode state;

(4) make in the said monomode fiber ring laser suitable, counterclockwise the weak coupling condition is satisfied in two-way oscillation mode field, i.e. coupling coefficient C＜1 therebetween,, single mode simultaneously traveling wave oscillation two-way to realize;

The composite fiber annular chamber that said optic fiber ring-shaped cavity can adopt the sub-annular chamber of the mutual coupling cascade that is linked to be by two above wavelength division multiplexing (WDM) fiber couplers and doped fiber to constitute; Be positioned at the private end coupler of the sub-annular chamber in said composite fiber annular chamber end, being used for input pumping light and output swashs and to penetrate light, pump light enters annular chamber through straight-through fiber segment respectively from two free optical fiber end of end coupler, swash and to penetrate light and then in the chamber, circulate, and partly appear through two free optical fiber end by the pair of cross coupled end that it links to each other with annular chamber.

2, the method for claim 1 is characterized in that public coupler in the middle of the said composite fiber annular chamber is used for realizing the effective coupling between the sub-annular chamber, is about 50% to swashing the power coupling ratio of penetrating light.

3, the method for claim 1 is characterized in that said mode selection mechanism utilizes the Compound Cavity mode resonance to realize, makes the gain spectrum width of the frequency interval of its resonance mode greater than doped fiber.

4, the method for claim 1 is characterized in that said weak coupling condition can adopt that the laser close-threshold operation realizes under weak pumping.

5, the method for claim 1, it is characterized in that said weak coupling condition can make the pumping light power that enters the dynatron annular chamber by said public coupler be not enough to bleach the wherein light absorption of doped fiber, makes it to have had the saturable absorption characteristic of intermode uncoupling effect.

6, a kind of employing fiber annular gyro laser device of method according to claim 1, it is characterized in that the doped fiber segment length between adjacent two couplers is equal substantially, constitute the symmetrical coupled annular chamber, the input of pump light and the sharp shared end coupler of output of penetrating light, the chamber external coupler that two free optical fiber end of said end coupler are identical with it with other two coupled characteristics respectively links to each other, the straight-through optical fiber end of said two chamber external couplers connects pump laser source respectively, and its two cross-couplings optical fiber end as laser output respectively connect an optical isolator.

7, a kind of employing fiber annular gyro laser device of method according to claim 1, it is characterized in that the doped fiber segment length between adjacent two couplers is equal substantially, constitute the symmetrical coupled annular chamber, the input of pump light and sharp output of penetrating light can be adopted two end couplers respectively, two free optical fiber end of one of them end coupler link to each other with pump laser source respectively, and another end coupler respectively connects an optical isolator as two free optical fiber end of laser output.

8, as claim 6 or 7 described lasers, the fiber coupler that its feature also is to constitute said composite fiber annular chamber is to the filtering bandwidth of the excitation wavelength gain spectrum width less than doped fiber.

9, as claim 6 or 7 described lasers, said composite fiber annular chamber will have the long L in chamber of two sub-annular chambers equal substantially at least, makes the gain spectrum width of the frequency interval Δ v=c/n| Δ L| of its resonance mode greater than doped fiber.

10, as claim 6 or 7 described lasers, its feature is that also said composite fiber annular chamber selects the doping of three level system laser medium (as erbium ion) optical fiber for use.

11, as claim 6 or 7 described lasers, its feature is that also said composite fiber annular chamber adopts ordinary optic fibre WDM coupler and doped fiber weldering to connect and constitutes.

12, as claim 6 or 7 described lasers, its feature is that also said composite fiber annular chamber adopts doped fiber directly to be coupled into the cascade annular chamber of no solder joint.

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