Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1998-06-02
2001-04-17
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S033000, C385S035000, C385S037000
Reexamination Certificate
active
06219473
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates an optical fiber wavelength multiplexer-demultiplexer or router, liable to be used as a component in optical fiber teletransmission installations.
Such multiplexers-demultiplexers are already known; they have been described, then gradually improved, especially in the French patents FR-2.543.768, FR-2.519.148, FR-2.479.981, FR-2.496.260 and in the European patent EP-0.196.963.
The latter document relates more particularly to a multiplexer-demultiplexer in which the input and output fibers are positioned at the immediate vicinity of the focus of a concave mirror. Thus, the diverging light fluxes received from the input fibers are transformed by the concave mirror into parallel light beams which are addressed to a plane diffraction grating, which directs the parallel beams back to the concave mirror and focuses them onto the extremities of the output fibers.
We have sought to reduce the aberrations and, in particular, the spherical aberrations of such a system and it is thus that such a multiplexer-demultiplexer has been suggested, comprising a fiber-holder element, an element carrying the diffraction grating, an intermediate element and a spherical mirror element. The fiber-holder element puts the extremities of the fibers in contact with the element carrying the diffraction grating, the intermediate element which is in contact with the diffraction grating and has the same optical index as the element which carries it, is terminated by a spherical face which is in contact with the mirror.
This device has proven satisfactory, has enabled and still enables numerous embodiments.
However, in certain particular applications, this component has appeared regrettably relatively heavy, as well as its thermal instability produced by the index variation of the different elements of which it consists, in relation to temperature.
OBJECTS AND SUMMARY OF THE INVENTION
The aim of this invention is to remedy these shortcomings and hence to offer a multiplexer-demultiplexer exhibiting the same advantages as that introduced above, with the additional corrections made to spherical and chromatic aberrations, but with reduced weight and, moreover, good thermal stability.
The invention thus relates to an optical fiber wavelength multiplexer-demultiplexer comprising a dispersing system and a reflecting system fitted with a focus. The extremities of the input and output fibers are located close to the focus.
While determining the number of input fibers, of output fibers and the dispersing system, a router can also be produced.
According to the invention, this multiplexer-demultiplexer comprises an optical doublet for correction of the spherical and chromatic aberrations of the assembly.
Thus, a vast portion of the space between the dispersing system and the reflecting system is occupied by air, a gas or vacuum.
The doublet is coupled at the same time to the dispersing system and to the reflecting system, so that a beam emitted by an input fiber crosses several times the doublet. The doublet thus allows successively acting on such a beam during its repeated passages in such a way that the beam resulting from all the passages through the doublet is corrected from its geometrical and chromatic aberrations.
In relation to the previous device, which does not contain any element between the diffraction grating and the mirror, good correction of the spherical aberrations and of the chromatic aberrations can be obtained, which improves significantly the performances of the multiplexer-demultiplexer.
In relation to the other previous device, in which an intermediate optical block links the diffraction grating to the spherical mirror, the device of the invention enables to obtain significant weight reduction of the multiplexer-demultiplexer.
Moreover, the invention device enables to obtain such a multiplexer-demultiplexer exhibiting significantly improved thermal stability.
According to different preferred embodiments each exhibiting their particular advantages:
the doublet is in direct contact with the reflecting optical system,
the doublet operates in the vicinity of the Young points (still known under the name of Weierstrass points) of its input face,
the dispersing system is a grating,
the reflecting optical system is a concave mirror,
the optical doublet is a doublet comprising two lenses whose second lens has a reflecting convex external face,
the first lens is made of a glass known under the reference PSK3 and the second lens is made of a glass known under the reference BaF52,
the second lens has a center thickness equal to 7.66 mm and curves of its external face and of an internal face opposed to that external face which are respectively equal to 401.56 mm and to 748.90 mm, the first lens has a curve of its face opposed to the second lens which is equal to 217.77 mm, and the external face of the second lens and the dispersing system are 271.1 mm apart,
the reflecting system is plane,
the dispersing system, on one hand, and the reflecting system and the doublet, on the other hand, are assembled by means of a material with low expansion coefficient.
Moreover, the device is advantageously used in near infrared, notably at 1550 mm.
REFERENCES:
patent: 4622662 (1986-11-01), Laude et al.
patent: 4675860 (1987-06-01), Laude et al.
patent: 4736360 (1988-04-01), McMahon
patent: 4744618 (1988-05-01), Mahlein
patent: 5305402 (1994-04-01), Hill et al.
patent: 6011884 (2000-01-01), Dueck et al.
patent: 0 242 574 (1987-03-01), None
R. S. Longhurst: “Geometric and Physical Optics”, 1973, Longman, London and New York, pp. 402-406.
M. Born: “Optik”, 1972, Springer, Berlin Heidelberg New York, pp. 58-60.
A.M.J. Koonen: “A Compact Wavelength Demultiplexer Using Both Interference Filters and Diffraction Grating”, 7th European Conference on Optical Communication, Sep. 8-11, 1981, Copenhagen, pp. 8.5-1-8.5-4.
Arent Fox Kintner & Plotkin & Kahn, PLLC
Jobin Yvon Sa
Sanghavi Hemang
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