Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
1999-07-02
2003-10-28
Nguyen, Thong (Department: 2872)
Optical waveguides
Optical fiber waveguide with cladding
C385S011000
Reexamination Certificate
active
06640035
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to dispersion compensation fibers for compensation of dispersion in glass fiber
BACKGROUND INFORMATION
Dispersion comensation fibers are described, for example, by D. M. Pataca, M. L. Rocha, K. Smith, T. J. Whitley, R. Wyatt in “Actively modelocked Pr
3+
-doped fluoride fibre laser”
Electr. Lett.,
30 (1994) 2, p. 964.
The use and design of such dispersion compensation fibers (DC fibers) for compensation of the dispersion of the active fibers of the fiber laser with a fiber laser structure such as that presented in
FIG. 1
, for example, is already known. The phase modulator in the laser resonator requires both at the input and at the output defined linear polarized light which must be produced. Previously, this has been achieved using polarization convertors, which is generally complex and laborious.
As the radiation source of ultra-high bit rate transmission systems and as a source of solitons, modelocked fiber lasers are used to advantage. The most important prerequisite is that the pulse width over time must be as small as possible, i.e., it must not exceed a few ps. Various authors, such as D. M. Pataca, M. L. Rocha, K. Smith, T. J. Whitley, R. Wyatt: “Actively modelocked Pr
3+
-doped fluoride fibre laser”
Electr. Lett.,
30 (1994) 2, p. 964, have demonstrated that the chromatic dispersion of the active fibers of the fiber laser has a pulse widening effect. The formulas by D. J. Kuizenga, A. E. Siegman: “FM and AM Mode Locking of the Homogeneous Laser—Part I: Theory.”
IEEE J. Quant. Electr.
6 (1970), p. 694 with the supplement by G. Geister: “Integrierte optische Modulation von Nd-Faserlasem” [Integrated optical modulation of Nd fiber lasers]
Fortschrittsberichte VDI Reihe
[VDI Progress Reports Series] 10 (1990) 140, 1, 102 describe the dependence of pulse half-width &tgr;
p
over time on modulation frequency f
m
, modulation index &dgr;
c
, laser wavelength &lgr;, length of active fiber L
a
, gain coefficient g and spectral half-width &Dgr;&lgr; of the fluorescence spectrum:
τ
p
=
2
2
ln
2
π
[
1
f
m
2
δ
c
]
1
/
4
[
(
λ
2
L
a
2
π
c
D
)
2
+
(
g
π
2
Δ
f
2
)
2
]
1
/
8
The extension by Geister is expressed by the additional term with D, taking into account chromatic dispersion.
FIG. 2
shows the negative influence of dispersion D on pulse half-width for the case of a Pr
3+
ZBLAN glass fiber laser. This means that D must disappear in order to minimize &tgr;
p
, i.e., dispersion must be compensated. This can be accomplished by using a chirped fiber Bragg grating as the laser reflector, e.g., as the decoupling reflector. However, this method is very problematical. The reflecting power of the chirped fiber grating is precisely defined by optimizing the fiber laser and must thus be verified because otherwise the laser threshold is increased and the output power is reduced. To compensate for the dispersion of the active fibers the spectral half-width must be >10 nm according to estimates; otherwise &tgr;
p
is increased. These technological requirements cannot be met at the present time.
SUMMARY OF THE INVENTION
An object of the present invention is to permit a combination of the effects of dispersion compensation and definition of the linear polarization state in a glass fiber that has high birefringence of the DC fibers and is linked to the active fiber.
The present invention provides a dispersion compensation fiber for compensation of dispersion in a glass fiber, which is accommodated in the fiber laser resonator and linked to the active fiber, characterized in that it is formed by a selected doping in the preform and by a controlled elliptical shaping of the core for geometric birefringence which allows only the propagation of the two orthogonal linear polarization states, both for dispersion compensation as well as for definition of the linear polarization state.
REFERENCES:
patent: 5261016 (1993-11-01), Poole
patent: 5371815 (1994-12-01), Poole
patent: 5450427 (1995-09-01), Fermann et al.
patent: 5482525 (1996-01-01), Kajioka et al.
Nakano et al., “Dispersion-Compensator Incorporated Optical Fiber Amplifier,”IEEE Photonics Technolgy Letters, Bd. 7, Nr. 6, Jun. 1, 1995.
Fermann et al., “Generation of Pulses Shorter than 200 FS from a Passively Mode-Locked ER Fiber Laser,” Optics Letters, Bd. 18, Nr. 1, Jan. 1, 1993.
Pataca et al., “Actively Modelocked PR3+-Doped Fluoride Fibre Laser,” Electronics Letters, Bd. 30, Nr. 12, Jun. 9, 1994 Mentioned in specification.
Poole et al., “Elliptical-Core Dual-Mode Fiber Dispersion Compensator,” IEEE Photonics Techology Letters, Bd. 5, Nr. 2, Feb. 1, 1993.
Youwei et al., “Triple-Clad Single-Mode Fibers for Dispersion Flattening,” Optical Engineering, Bd. 33, Nr. 12, Dec. 1, 1994.
Kuizenga et al., “FM and AM Mode Locking of the Homogeneous Laser-Part I: Theory,” IEEE J. Quant. Electr. 6 (1970), p. 694 with the supplement by G. Geister, “Integrierte optische Modulation von Nd-Faserlasern,” [Integrated optical modulation of Nd fiber lasers] etc. Mentioned in specification.
Boness et al., “Tailoring of dispersion-compensation fibers with high compensation ratios up to 30,” Pure Appl. Opt. 5 (1995) 333 Mentioned in specification.
Vengsarkar et al., “Fundamental-mode dispersion-compensating fibers: design considerations and experiments,” OFC '94. Optical Fiber Communication, vol. 4 Technical Digest Series Mentioned in specification.
Gisin et al., Polarization Mode Dispersion of Short and Long Single-Mode Fibers, J. Lightw. Technol. 9 (1991) 7, p. 821*.
Vobian et al., Different aspects of the polarization mode dispersion measuring technique, Proc. EFOG&N 94, Heidelberg 1994, p. 174 Mentioned in specification.
Deutsche Telekom AG
Kenyon & Kenyon
Lavarias Arnel C.
Nguyen Thong
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