CA1289787C - Device for stabilizing the mean wave length of a wide spectrum source and application to an optical fiber gyrometer - Google Patents
Device for stabilizing the mean wave length of a wide spectrum source and application to an optical fiber gyrometerInfo
- Publication number
- CA1289787C CA1289787C CA000522212A CA522212A CA1289787C CA 1289787 C CA1289787 C CA 1289787C CA 000522212 A CA000522212 A CA 000522212A CA 522212 A CA522212 A CA 522212A CA 1289787 C CA1289787 C CA 1289787C
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- Canada
- Prior art keywords
- wave length
- spectrum
- source
- optical fiber
- mean wave
- Prior art date
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-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- G01C19/72—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers
- G01C19/721—Details
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Optics & Photonics (AREA)
- Electromagnetism (AREA)
- Power Engineering (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Gyroscopes (AREA)
- Semiconductor Lasers (AREA)
- Led Devices (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A device is provided for stabilizing the mean wave length of a wide spectrum source including, placed in the optical path of the beam emitted by the source, a filter whose spectrum is centered on the mean wave length of the spectrum emitted by the source but whose width is less than that of the emitted spectrum. Said device finds an application in gyrometers formed of an optical fiber ring interferometer.
A device is provided for stabilizing the mean wave length of a wide spectrum source including, placed in the optical path of the beam emitted by the source, a filter whose spectrum is centered on the mean wave length of the spectrum emitted by the source but whose width is less than that of the emitted spectrum. Said device finds an application in gyrometers formed of an optical fiber ring interferometer.
Description
~ Z ~J~ 7 ~
TITLE OF THE INVENTION
DEVICE FO~ STABILIZING THE MEAN WAVE LENGTH OF A WID~
SPECTR~M SOURCE AND APPLICATION TO AN OPTICAL FIBER
GYROMETER
BACKGROUND OF THE INVENTION
The invention relates to a device for stabilizing 10 the mean wave length of a wide band radiant light source, more especially for a source used in a gyrometer or rate gyro.
It is known that an optical system whose output signal depends on the wave lengths has an unstable scale 15 factor when this latter varies. Among the causes of disturbance temperature variations are generally among the most critical.
Among the applications to which the invention more particularly relates, gyrometers or rate gyros and similar devices come into this category.
A gyrometer is generally formed of a ring interfero-meter.
In a ring interferometer or Sagnac interferometer two beams travel in opposite directions of the same optical path and interfereat the exit from this path. As long as 25 a disturbance in this path has the same characteristics for both directions of propagation and does not vary during the transit time of the light in the interferometer, the two beams are affectedidentically and their relative phase remains unchanged. Disturbances of this type are called 30 "reciprocal". Because the transit time in an inter~erometer is generally very small, the variations of a disturbance during this time, unless it is introduced voluntarily, are generally negligible.
But there exist "non reciprocal" disturbances 35 which have a different amplitude in the two directions of propagation, these are physical effects which, by establishing ,,, ~PJ~
its complete orientation, destroy the symmetry of tha space and of the medium.
Two known effects have this property - the Faraday effect or colinear mayneto-optical effect, by which a magnetic field creates a preferential orientation of the spin of the electrons of the optical material;
- and the Sagnac effect, or relativistic inertial effect, in which the rotation of the interferometer ~lith 10 respect to a Galilean reference destroys the symmetry of the propagation times.
Use of the rotation with respect to the inertial space leads to the construction of optical fiber gyrometers and use of the magnetic field leads to the construction 15 of ampere-metric or magnetometric current sensors.
In recent interferometers, the ring is formed physically by a monomode optical fiber wound on itself so as to form a coil of reduced radius. However, the length of the optical path is directly proportional to the number 20 of turns of the coil. Thus, despite a very reduced volume, a very long optical path may be obtained, typically of the order of a kilometer.
Such an interferometer is used for measuring rotational speeds. This measurement is obtained by measuring 25 the phase shift between the waves travelling through the ring in opposite directions.
Now, as will be described in greater detail hereafter, the formula giving the phase shift between these two waves depends linearly on the wave length thereof and 30 more exactly on the inverse of this wave length.
The waves travelling in the ring originate, after separation, from the same beam generated by a radiant light source generally a semiconductor source. It may for example be a super light~emitting diode.
This source emits a spectrum centered on a mean wave length. Now, this mean value of the wa~e length depends ~PJ~7~7 in its turn on the temperature of the junction.
In the prior art, different methods have been used for stabilizing the emission. These methods have in common the use of feedback circuits which in addition to their complexity require a certain number of adjustments.
The invention aims at overcoming these dra~"backs.
SUMMARY OF THE INVENTION
The invention provides then a device for sta~ilizing the mean wave length of a radiant energy source emitting a wide spectrum beam, comprising, placed in the optical path of said beam, a band pass optical filter with spectrum centered on said mean wave length and of a width less than 15 that of the spectrum of a beam emitted by the source.
The invention also relates to the application of such a device to an optical fiber gyrometer.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other characteristics and advantages will be clear from reading the following description with reference to the accomp~sying Figures in which:
Figure 1 illustrates an example of an interfero-meter of the prior art;
Figure 2 is a diagram illustrating the emission spectrum of ~source and the transmission spectrum of an optical filter; and Figure 3 illustrates schematically a device in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in its preferred application, namely to an optical fiber gyrometer, 37~'7 without this being in any wise limitatiYe.
It seems useful first of all to recall the main characteristics thereof.
Figure 1 illustrates schematically an example S of a ring interferometer of the prior art.
In this Figure 1 can be seen a ring interferometer whose ring is formed from a monomode optical fiber 5, but whose core is formed of traditional optical elements. The addition of a mode filter 3 makes such an interferometer 10 strictly reciprocal. The incident beam 11 produced by a source 10 passes through the mode filter 3 and is separated into two on a semitransparent mirror 4. A part 12 of the beam is fed into the optical fiber 5 through a lens 41 which focuses it on the input 50 of the optical fiber 5, 15 whereas the other part 13 of the beam is fed to the same optical fiber 5 through a lens 42 which focuses it on the input 51 of this optical fiber 5. The two beams travel through the fiber in opposite directions and are taken up in the arms of the interferometer by the semitransparent 20 mirror 4. They pass again through the mode filter 3 and are separated from the incident beam by a semitransparent mirror 2 which feeds them partly into an output arm 6 in which the interference signal is detected by means of a photodetector 60.
The use of a monomode optical fiber 5 as optical path greatly increases the length of this optical path.
In fact, the optical fiber is usually wound so as to form a multiturn coil. Thus very sensitivie gyroscopes can be formed.
However, the separating elements introduce losses and so it has been proposed to replace the discrete elements by integrated optical elements which improves the energy balance. These aspects are outside the scope of the invention.
Associated with photodetector 60 there are provided circuits for processing the electric signals present at .~ 2~ 7 the output of this photodetector (not shown in the Figure~.
These signals come from the photoelectric conversion of the composite beam transmitted through the output arm 6 and picked up by the photodetector 60.
The two beams 12 and 13 interfere depending on their phase state. As was mentioned above, the phase difference between these two beams depends on the non recipro-cal disturbances affecting the waves travelling in the ring.
This phase difference ~ is given by the relation-ship:
~j = l~R)n (1) in which relationship:
- L is the length of the ring, that is to say 15 the length of the optical fiber 5;
- R is the radius of the ring, that is to say the mean radius of the coil formed by the wound turns of optical fibers;
- ~ the wave length in a vacuum of the light 20 energy travelling through the optical fiber 5, - c the velocity of propagation of light in a vacuum;
- and Q the rotational speed measured.
The measurement depends then linearly on the 25 inverse of the wave length ~ . Any variation of this parameter affects the scale factor.
The wave length depends then directly on the emission stability of the source lQo Now, in general, it is a semiconductor source;
30 as is well known, such a source is affected by temperature variations, like any semiconductor elements. It emits a spectrum centered on a mean wave length which will be called hereafter ~O.
The invention aims at stabilizing this mean 35 wave length without having recourse to active feedback elements.
~ ~P~787 By way of non limitative example, we will take the case hereafter of an emission spectrum of Gaussian type in which the variation of the light energy is a function of the wave length described by the relationship:
( ~ _ ~ )2 (2) 2 ~ ~S
in which relationship:-- ~is any wave leng-th of a spectrum;
- ~O the mean wave length;
~ ~ ~S the half width of the spectrum.
Figure 2 illastrates such a spectrum SP~.
The vertical axis represents the light energy W in relative arbitary units and the horizontal axis the 15 wave length.
The width ~ ~ S of the spectrum emitted by source SPS may be defined by the difference between twc extreme wave lengths ~lS and ~2S for which the energy is equal to (l/e), the maximum value being assumed equal 20 to unity.
As illustrated schematically in Figure 3 the invention associates with a source S, emitting in accordance with the spectrum which has just been described, a band pass optical filter Fi with spectrum also centered on the 25 wave length ~ O, but of a width less than the spectrum SPs. An interferential filter is preferably used.
These are filters which use the interference phenomenon for letting pass certain spectral regions or for reflecting them. These filters are formed of a multitude of thin layers whose optical thickness correspo~ds to a quarter of the central wave length or to a multiple of this value. Depending on the kind, on the number, on the thickness and on the arrangement of the layers a large number of band widths may be obtained with high transmission 35 or high reflection.
These filters are available commercially and 7t~7 are available in different variants of construction, for example one of the variants is formed by so called MDI
interferential filters.
These are interferential filters with metal and dielectric components (Metal-dielectric interference filters). These filt~rs are formed of thin metal layers with partial transmission which are separated from each o-ther by dielectric spacing layers free from absorption.
The thickness of the spacing layers determines essentially 10 the spectral situation ~ of the pass band which has the longest wave.
This type of filter is used mostly as band pass filter.
The wave length drifts of the spectra of these 15 filters as ~ function of the temperature depend essentially on geometric variations. The drift coefficient is typically of the order of 10 5/oC and this drift, as will be seen hereafter, may be neglected with regard to the drifts due to the source.
The beam F emitted by source S has then the characteristics of the spectrum SPS described in connection with Figure-2.
In this Figure has also been shown the transmission energy spectrum of the filter Fi.
The half width of the spectrum ~Fi is the difference between two wave lengths ~ lFi and ~ 2Fi way as for the spectrum SPs. The formula describing the transmission coefficient of filter Fi is then of the form:
`2 30 -~ ~ (3) e ~ ~ ~ FiJ
and ~ ~Fi = ~ ~S
wi~h C 1 3 If, following temperature variations, the emitted spectrum SPS shifts in wave length by a value ~O~ at the 3,ZP,~787 output of the filter Fi the beam FFi (Figure 3) will have its mean wave length shifted by a value ~ ~'0 complying with the relationship:
A o = 2 ?~o (5 l+
that is ~ 0 - 2 ~O
if is much smaller than unity.
It can be seen that the variations of the mean wave length of the "source S- filter F" assembly are then very much less than those of the wave length of the beam emitted by source S in accordance with the aim fixed by the invention.
Naturally the optical power picked up by the detector (Figure 1:60) is also reduced by the factor but the disadvantage which results therefrom is not as important as may be assumed from the value of .
In fact, the signal to noise ratio is limited 20 by the photonic noise. This ratio follows a square root law of the detected power. It follows that the signal to noise factor, which is one of the determining parameters to be consideEed, is only reduced by a factor : ff ~ .
To give a general idea, a concrete embodiment 25 will now be described.
As-source a super light-emitting diode is used of the Ga A1 As type (Gallium-Aluminium-Arsenic), emitting a spectrum centered on the wave length ~ 0 = 830 ~m and of a width ~ ~ S= 10 nm.
If we assume a coarse temperature stabilization of this source, typically of the order of a degree celsius, - the ratio ( ~ ~ 0/ ~ 0) is less than 3.10-~.
The option taken in neglecting the wave length drifts proper to the filter is then well justified (10 6/oC).
If we place in front of the detector a filter of width ~ ~Fi = 2 nm, namely = 0.2; then the fluctuations ~I ZPJ~7~7 ( ~ ~ 0/~ 0) of the "source-filter" assembly are reduced in a factor 2 = o 04 and become less than 3.10 6 As far as it is concerned, the signal to noise ratio is only reduced by a factor ~ = 0.45.
The invention allows then a reasonable compromise to be obtained very simply between the stabilization o the scale factor and the sensitivity of the system.
In accordance with the invention, the stabilizing 10 device thus described is applied to an optical fiber gyrometer comprising mainly an interferomeker of the type shown in Figure 1. The stabilizing device is then placed in the path of the light beams 12, 13 coming from the optical fiber 5 after recombination and before detection by the 15 detection means 60. In a preferred embodiment, not shown in the Figure, the stabilizing device is placed in the arm 6 of the interferometer of Figure 1.
The invention is not limited solely to the embodi-ments specificaly described. It applies to any system using 20 a wide spectrum source.
Furthermore, although it has been implicity assumed that it was a question of band pass optical filters operating by transmission, filters operating by reflection may be used just as well if they comply with the conditions 25 proper to the device of the invention: reflected spectrum centered on ~ 0 and of a width less than that of the source.
TITLE OF THE INVENTION
DEVICE FO~ STABILIZING THE MEAN WAVE LENGTH OF A WID~
SPECTR~M SOURCE AND APPLICATION TO AN OPTICAL FIBER
GYROMETER
BACKGROUND OF THE INVENTION
The invention relates to a device for stabilizing 10 the mean wave length of a wide band radiant light source, more especially for a source used in a gyrometer or rate gyro.
It is known that an optical system whose output signal depends on the wave lengths has an unstable scale 15 factor when this latter varies. Among the causes of disturbance temperature variations are generally among the most critical.
Among the applications to which the invention more particularly relates, gyrometers or rate gyros and similar devices come into this category.
A gyrometer is generally formed of a ring interfero-meter.
In a ring interferometer or Sagnac interferometer two beams travel in opposite directions of the same optical path and interfereat the exit from this path. As long as 25 a disturbance in this path has the same characteristics for both directions of propagation and does not vary during the transit time of the light in the interferometer, the two beams are affectedidentically and their relative phase remains unchanged. Disturbances of this type are called 30 "reciprocal". Because the transit time in an inter~erometer is generally very small, the variations of a disturbance during this time, unless it is introduced voluntarily, are generally negligible.
But there exist "non reciprocal" disturbances 35 which have a different amplitude in the two directions of propagation, these are physical effects which, by establishing ,,, ~PJ~
its complete orientation, destroy the symmetry of tha space and of the medium.
Two known effects have this property - the Faraday effect or colinear mayneto-optical effect, by which a magnetic field creates a preferential orientation of the spin of the electrons of the optical material;
- and the Sagnac effect, or relativistic inertial effect, in which the rotation of the interferometer ~lith 10 respect to a Galilean reference destroys the symmetry of the propagation times.
Use of the rotation with respect to the inertial space leads to the construction of optical fiber gyrometers and use of the magnetic field leads to the construction 15 of ampere-metric or magnetometric current sensors.
In recent interferometers, the ring is formed physically by a monomode optical fiber wound on itself so as to form a coil of reduced radius. However, the length of the optical path is directly proportional to the number 20 of turns of the coil. Thus, despite a very reduced volume, a very long optical path may be obtained, typically of the order of a kilometer.
Such an interferometer is used for measuring rotational speeds. This measurement is obtained by measuring 25 the phase shift between the waves travelling through the ring in opposite directions.
Now, as will be described in greater detail hereafter, the formula giving the phase shift between these two waves depends linearly on the wave length thereof and 30 more exactly on the inverse of this wave length.
The waves travelling in the ring originate, after separation, from the same beam generated by a radiant light source generally a semiconductor source. It may for example be a super light~emitting diode.
This source emits a spectrum centered on a mean wave length. Now, this mean value of the wa~e length depends ~PJ~7~7 in its turn on the temperature of the junction.
In the prior art, different methods have been used for stabilizing the emission. These methods have in common the use of feedback circuits which in addition to their complexity require a certain number of adjustments.
The invention aims at overcoming these dra~"backs.
SUMMARY OF THE INVENTION
The invention provides then a device for sta~ilizing the mean wave length of a radiant energy source emitting a wide spectrum beam, comprising, placed in the optical path of said beam, a band pass optical filter with spectrum centered on said mean wave length and of a width less than 15 that of the spectrum of a beam emitted by the source.
The invention also relates to the application of such a device to an optical fiber gyrometer.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other characteristics and advantages will be clear from reading the following description with reference to the accomp~sying Figures in which:
Figure 1 illustrates an example of an interfero-meter of the prior art;
Figure 2 is a diagram illustrating the emission spectrum of ~source and the transmission spectrum of an optical filter; and Figure 3 illustrates schematically a device in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in its preferred application, namely to an optical fiber gyrometer, 37~'7 without this being in any wise limitatiYe.
It seems useful first of all to recall the main characteristics thereof.
Figure 1 illustrates schematically an example S of a ring interferometer of the prior art.
In this Figure 1 can be seen a ring interferometer whose ring is formed from a monomode optical fiber 5, but whose core is formed of traditional optical elements. The addition of a mode filter 3 makes such an interferometer 10 strictly reciprocal. The incident beam 11 produced by a source 10 passes through the mode filter 3 and is separated into two on a semitransparent mirror 4. A part 12 of the beam is fed into the optical fiber 5 through a lens 41 which focuses it on the input 50 of the optical fiber 5, 15 whereas the other part 13 of the beam is fed to the same optical fiber 5 through a lens 42 which focuses it on the input 51 of this optical fiber 5. The two beams travel through the fiber in opposite directions and are taken up in the arms of the interferometer by the semitransparent 20 mirror 4. They pass again through the mode filter 3 and are separated from the incident beam by a semitransparent mirror 2 which feeds them partly into an output arm 6 in which the interference signal is detected by means of a photodetector 60.
The use of a monomode optical fiber 5 as optical path greatly increases the length of this optical path.
In fact, the optical fiber is usually wound so as to form a multiturn coil. Thus very sensitivie gyroscopes can be formed.
However, the separating elements introduce losses and so it has been proposed to replace the discrete elements by integrated optical elements which improves the energy balance. These aspects are outside the scope of the invention.
Associated with photodetector 60 there are provided circuits for processing the electric signals present at .~ 2~ 7 the output of this photodetector (not shown in the Figure~.
These signals come from the photoelectric conversion of the composite beam transmitted through the output arm 6 and picked up by the photodetector 60.
The two beams 12 and 13 interfere depending on their phase state. As was mentioned above, the phase difference between these two beams depends on the non recipro-cal disturbances affecting the waves travelling in the ring.
This phase difference ~ is given by the relation-ship:
~j = l~R)n (1) in which relationship:
- L is the length of the ring, that is to say 15 the length of the optical fiber 5;
- R is the radius of the ring, that is to say the mean radius of the coil formed by the wound turns of optical fibers;
- ~ the wave length in a vacuum of the light 20 energy travelling through the optical fiber 5, - c the velocity of propagation of light in a vacuum;
- and Q the rotational speed measured.
The measurement depends then linearly on the 25 inverse of the wave length ~ . Any variation of this parameter affects the scale factor.
The wave length depends then directly on the emission stability of the source lQo Now, in general, it is a semiconductor source;
30 as is well known, such a source is affected by temperature variations, like any semiconductor elements. It emits a spectrum centered on a mean wave length which will be called hereafter ~O.
The invention aims at stabilizing this mean 35 wave length without having recourse to active feedback elements.
~ ~P~787 By way of non limitative example, we will take the case hereafter of an emission spectrum of Gaussian type in which the variation of the light energy is a function of the wave length described by the relationship:
( ~ _ ~ )2 (2) 2 ~ ~S
in which relationship:-- ~is any wave leng-th of a spectrum;
- ~O the mean wave length;
~ ~ ~S the half width of the spectrum.
Figure 2 illastrates such a spectrum SP~.
The vertical axis represents the light energy W in relative arbitary units and the horizontal axis the 15 wave length.
The width ~ ~ S of the spectrum emitted by source SPS may be defined by the difference between twc extreme wave lengths ~lS and ~2S for which the energy is equal to (l/e), the maximum value being assumed equal 20 to unity.
As illustrated schematically in Figure 3 the invention associates with a source S, emitting in accordance with the spectrum which has just been described, a band pass optical filter Fi with spectrum also centered on the 25 wave length ~ O, but of a width less than the spectrum SPs. An interferential filter is preferably used.
These are filters which use the interference phenomenon for letting pass certain spectral regions or for reflecting them. These filters are formed of a multitude of thin layers whose optical thickness correspo~ds to a quarter of the central wave length or to a multiple of this value. Depending on the kind, on the number, on the thickness and on the arrangement of the layers a large number of band widths may be obtained with high transmission 35 or high reflection.
These filters are available commercially and 7t~7 are available in different variants of construction, for example one of the variants is formed by so called MDI
interferential filters.
These are interferential filters with metal and dielectric components (Metal-dielectric interference filters). These filt~rs are formed of thin metal layers with partial transmission which are separated from each o-ther by dielectric spacing layers free from absorption.
The thickness of the spacing layers determines essentially 10 the spectral situation ~ of the pass band which has the longest wave.
This type of filter is used mostly as band pass filter.
The wave length drifts of the spectra of these 15 filters as ~ function of the temperature depend essentially on geometric variations. The drift coefficient is typically of the order of 10 5/oC and this drift, as will be seen hereafter, may be neglected with regard to the drifts due to the source.
The beam F emitted by source S has then the characteristics of the spectrum SPS described in connection with Figure-2.
In this Figure has also been shown the transmission energy spectrum of the filter Fi.
The half width of the spectrum ~Fi is the difference between two wave lengths ~ lFi and ~ 2Fi way as for the spectrum SPs. The formula describing the transmission coefficient of filter Fi is then of the form:
`2 30 -~ ~ (3) e ~ ~ ~ FiJ
and ~ ~Fi = ~ ~S
wi~h C 1 3 If, following temperature variations, the emitted spectrum SPS shifts in wave length by a value ~O~ at the 3,ZP,~787 output of the filter Fi the beam FFi (Figure 3) will have its mean wave length shifted by a value ~ ~'0 complying with the relationship:
A o = 2 ?~o (5 l+
that is ~ 0 - 2 ~O
if is much smaller than unity.
It can be seen that the variations of the mean wave length of the "source S- filter F" assembly are then very much less than those of the wave length of the beam emitted by source S in accordance with the aim fixed by the invention.
Naturally the optical power picked up by the detector (Figure 1:60) is also reduced by the factor but the disadvantage which results therefrom is not as important as may be assumed from the value of .
In fact, the signal to noise ratio is limited 20 by the photonic noise. This ratio follows a square root law of the detected power. It follows that the signal to noise factor, which is one of the determining parameters to be consideEed, is only reduced by a factor : ff ~ .
To give a general idea, a concrete embodiment 25 will now be described.
As-source a super light-emitting diode is used of the Ga A1 As type (Gallium-Aluminium-Arsenic), emitting a spectrum centered on the wave length ~ 0 = 830 ~m and of a width ~ ~ S= 10 nm.
If we assume a coarse temperature stabilization of this source, typically of the order of a degree celsius, - the ratio ( ~ ~ 0/ ~ 0) is less than 3.10-~.
The option taken in neglecting the wave length drifts proper to the filter is then well justified (10 6/oC).
If we place in front of the detector a filter of width ~ ~Fi = 2 nm, namely = 0.2; then the fluctuations ~I ZPJ~7~7 ( ~ ~ 0/~ 0) of the "source-filter" assembly are reduced in a factor 2 = o 04 and become less than 3.10 6 As far as it is concerned, the signal to noise ratio is only reduced by a factor ~ = 0.45.
The invention allows then a reasonable compromise to be obtained very simply between the stabilization o the scale factor and the sensitivity of the system.
In accordance with the invention, the stabilizing 10 device thus described is applied to an optical fiber gyrometer comprising mainly an interferomeker of the type shown in Figure 1. The stabilizing device is then placed in the path of the light beams 12, 13 coming from the optical fiber 5 after recombination and before detection by the 15 detection means 60. In a preferred embodiment, not shown in the Figure, the stabilizing device is placed in the arm 6 of the interferometer of Figure 1.
The invention is not limited solely to the embodi-ments specificaly described. It applies to any system using 20 a wide spectrum source.
Furthermore, although it has been implicity assumed that it was a question of band pass optical filters operating by transmission, filters operating by reflection may be used just as well if they comply with the conditions 25 proper to the device of the invention: reflected spectrum centered on ~ 0 and of a width less than that of the source.
Claims (5)
1. A device for stabilizing the mean wave length of a radiant energy source emitting a wide spectrum beam, comprising, placed in the optical path of said beam a band pass optical filter with spectrum centered on said mean wave length and of a width less than that of the spectrum of the beam emitted by the source.
2. The device as claimed in claim 1, wherein said band pass optical filter is an interferential filter.
3. The device as claimed in claim 1, wherein said source is a super light emitting diode of the Gallium-Aluminium-Arsenic type emitting in a spectrum centered on a mean wave length of 830 nm and of width 10 nm.
4. The device as claimed in claim 3, wherein said band pass optical filter has a spectrum width equal to 1 nm.
5. A gyrometer formed by a ring interferometer having a monomode optical fiber forming said ring, a radiant energy emission source with wide spectrum centered on a mean wave length, means for separating and mixing the radiation for directing simultaneously and in equal parts the emitted energy to the two ends of the monomode optical fiber and for recombining the radiation emerging from the two ends of the monomode optical fiber and means for detecting this recombined emergent radiation, also including a device for stabilizing the fluctuations of said mean wave length as claimed in claim 1, the band pass optical filter being disposed upstream of the detection means in the optical path of said recombined emergeant radiation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8516601A FR2590035B1 (en) | 1985-11-08 | 1985-11-08 | MEDIUM WAVELENGTH STABILIZER DEVICE OF A WIDE SPECTRUM SOURCE AND APPLICATION TO FIBER OPTIC GYROMETER |
| FR8516601 | 1985-11-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1289787C true CA1289787C (en) | 1991-10-01 |
Family
ID=9324658
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000522212A Expired - Lifetime CA1289787C (en) | 1985-11-08 | 1986-11-05 | Device for stabilizing the mean wave length of a wide spectrum source and application to an optical fiber gyrometer |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0227509A1 (en) |
| JP (1) | JP2511813B2 (en) |
| CA (1) | CA1289787C (en) |
| FR (1) | FR2590035B1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19802095C1 (en) | 1998-01-21 | 1999-08-19 | Litef Gmbh | Method and device for stabilizing the scale factor of a fiber optic gyroscope |
| US6025915A (en) * | 1998-06-25 | 2000-02-15 | Litton Systems, Inc. | Scale factor stabilization of a broadband fiber source used in fiber optic gyroscopes in radiation environments |
| KR100624448B1 (en) * | 2004-12-02 | 2006-09-18 | 삼성전기주식회사 | Semiconductor light emitting device and method thereof |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3148925A1 (en) * | 1981-12-10 | 1983-06-23 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Light source for a ring interferometer |
| JPS58213211A (en) * | 1982-06-04 | 1983-12-12 | Sumitomo Electric Ind Ltd | Noise eliminating system of optical fiber gyro |
| JPS60140115A (en) * | 1983-12-28 | 1985-07-25 | Tech Res & Dev Inst Of Japan Def Agency | Optical fiber rate sensor |
-
1985
- 1985-11-08 FR FR8516601A patent/FR2590035B1/en not_active Expired
-
1986
- 1986-11-04 EP EP86402462A patent/EP0227509A1/en not_active Withdrawn
- 1986-11-05 CA CA000522212A patent/CA1289787C/en not_active Expired - Lifetime
- 1986-11-08 JP JP26649086A patent/JP2511813B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62113010A (en) | 1987-05-23 |
| JP2511813B2 (en) | 1996-07-03 |
| FR2590035B1 (en) | 1988-09-16 |
| FR2590035A1 (en) | 1987-05-15 |
| EP0227509A1 (en) | 1987-07-01 |
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