Light source with stabilized broadband and associated optical fi

Details Light source with stabilized broadband and associated optical fi Light source with stabilized broadband and associated optical fi

1997-03-12

1999-04-13

Lee, John D.

Coherent light generators

Optical fiber laser

359341, 372 99, H01S 307

Patent

active

058944885

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a broadband light source comprising an amplifying guide structure and an associated optical fiber gyroscope.
A broadband means a range of wavelengths with a typical width of between a few nanometers and a few tens of nanometers. This width contrasts with the width of a laser which is less than a tenth of a nanometer.


BACKGROUND OF THE INVENTION

The invention is particularly applicable to optical fiber gyroscopes.
Several means, known per se, may be used to create broadband light sources. It is thus possible to use a fiber source doped with a rare earth, a super light emitting diode (SLED) or an edge light emitting diode (ELED). These light sources offer spatially single mode guide structures and therefore generating light with a strong spatial coherence due to an amplifier effect.
In the presence of an electrical or optical excitation, any one of these sources spontaneously emits photons in all directions. The applied excitation then entrains an amplification of the spontaneous emission in preferred directions by stimulated emission. This is called amplified spontaneous emission (ASE).
Unlike a laser, light emitted by these sources has low time coherence, in other words they are broadband sources and various means are used to preserve this property and avoid a laser effect.
Therefore one known technique is to use a fiber source 1 doped with a rare earth (particularly erbium) as an amplifying guide structure, as shown in FIG. 1. Fiber 1 with length L has a center line 10 with front end 2 and back end 3, and is symmetric about a transverse plane 4. The front end 2 and back end 3 are terminated by the front face 37 and back face 38 respectively.
A theory of the behavior of this amplifier guide structure assumed to be perfect is given below for information, in order to better identify the invention.
During operation, pump waves 6 and 9 with wavelengths .lambda.p are transmitted symmetrically towards fiber 1 by pump diodes and excite the rare earth. Once excited, the rare earth emits photons by spontaneous emission in all directions. However pump waves 6 and 9 amplify transmissions in the direction of the center line 10, thus creating two opposite preferred directions of propagation. This leads to two ASEs (Amplified Spontaneous Emissions): one 11 towards the front 2 of fiber 1 called the ASE+, and the other 12 towards the back 3 of fiber 1 called the ASE-, producing two light emissions 7 and 8 in front of and behind fiber 1.
Powers P1 and P2 are transmitted along the fiber 1 towards front 2 and towards back 3 respectively, as shown in FIG. 2, in which axis 15 defines the position along axis 10 in FIG. 1 and axis 16 gives the transmitted power.
Curve 13 shows the power P1 transmitted towards front 2. Curve 14 shows the variation of the power P2 transmitted towards back 3.
Emissions 7 and 8 obtained in outputs correspond to the two powers V3-V4 and V2-V1 respectively.
A major problem encountered in these amplification guide structures is that they have spectral instabilities of emitted light, usually due to thermal variations or the sensitivity of emitted light to excitation conditions. The instabilities may also originate from power variations of pump diodes or mode skips, for example.
It is often necessary to have precise control over the average emission wavelength .lambda..sub.m. This is particularly true when using optical fiber gyroscopes, this control being done with a precision of the order of 10.sup.-4 to 10.sup.-6. The stability of the average wavelength .lambda..sub.m is directly related to the stability of an essential characteristic of these gyroscopes, namely the scale factor, which must be precise.
One or several passive filters are usually used in order to successfully stabilize the emission spectrum S around a chosen average wavelength. This type of passive filter appears like a transmission window which is narrower than the emission spectrum window S. It is placed in an arbitrary position between the light source and the receiver. Its use lea

REFERENCES:
patent: 4938556 (1990-07-01), Digonnet et al.
patent: 5108183 (1992-04-01), Fling et al.
patent: 5142660 (1992-08-01), Chang et al.
patent: 5159601 (1992-10-01), Huber
patent: 5283686 (1994-02-01), Huber
patent: 5311603 (1994-05-01), Fidric
Optical Fiber Sensors. Proceedings of the 6th Inter'l Conference OFS '89, Paris, France, Sep. 18-20, 1989, ISBN 3-540-51719-7, 1989, Berlin, West Germany, Springer-Verlag, West Germany, pp. 143-148, XP002017997, Morkel P R: "Erbium-doped fibre superfluorescent source for the fibre gyroscope".
Electronics Letters, vol. 30, No. 8, Apr. 14, 1994, Stevenage GB, pp. 653-654, XP002000367, D.C. Hall et al, "Wavelength Stability Optimisation in Er.sup.3+ -Doped Superfluorescent Fibre Sources".

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