Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-02-19
2001-06-19
Hofsass, Jeffery (Department: 2736)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06249364
ABSTRACT:
This invention relates to optical wave-guide wavelength multiplexers and demultiplexers.
These devices become more and more important with the development of optical fiber telecommunications. Indeed, wavelength multiplexing and demultiplexing technologies enable transmission of an increased volume of information in the same optical fiber. Direct optical amplification is now reliable and allows one to amplify a set of channels, at different wavelengths, with a single optical amplifier. It does not require any more to demultiplex the channel wavelengths for amplifying them separately as it would be the case with electronic amplifiers. Such dense wavelength division multiplexing (D-WDM) is particularly efficient in the 1530 nm-1565 nm window of erbium-doped-fiber amplifier (EDFA).
The operation of a device according to the previous art is illustrated on
FIGS. 1 and 2
.
FIG. 1
represents a multiplexer. Input single-mode fibers
1
to
5
have their ends located on a plane
6
constituting the input plane of the multiplexer. This multiplexer comprises a dispersing element or grating
7
, a collimation optical element
8
, a reflector system
9
and produces an output beam
10
collected by an output single-mode fiber
61
. The optical elements of the multiplexer, the grating
7
and the collimation optical elements
8
as well as the reflector optical system
9
are laid out in such a way that the input beams, spatially separate in the input plane
6
, are superimposed at the output point
62
and coupled in the output fiber
61
. This arrangement with a grating and a reflector is usually called the Littman-Metcalf configuration.
On
FIG. 2
, each of the input single-mode fibers
1
to
5
ends has been represented, together with their optical cores
11
,
21
,
31
,
41
,
51
, their claddings
12
,
22
,
32
,
42
,
52
and their coatings
13
,
23
,
33
,
43
,
53
. In such a system, the input plane
6
defines, in its geometrical dimension x, the input function F(&lgr;) of the multiplexer, represented approximately on
FIG. 2
, each of the fibers cutting through an associated elementary passband
14
,
24
,
34
,
44
and
54
.
The widths &Dgr;&lgr;1, . . . , &Dgr;&lgr;5 of each of these elementary bands depend on the diameters of the cores
11
,
21
,
31
,
41
,
51
of each single-mode optical fiber
1
to
5
and are generally small in relation to the distance d(&lgr;1, &lgr;2), . . . , d(&lgr;4, &lgr;5) separating the central wavelengths &lgr;1, . . . , &lgr;5 of the elementary bands, consecutive to the beams provided by each input fiber
1
to
5
and superimposed on the output fiber
61
.
We shall designate later on by &Dgr;&lgr; the width of the elementary bands &Dgr;&lgr;i, . . . , &Dgr;&lgr;n and by d(&lgr;i, &lgr;i+1) the distance between the central wavelengths of two consecutive elementary bands.
The preferred embodiment of the invention is described with optical fibers for making the wave-guides. However, integrated optics also makes it possible to manufacture wave-guides and the invention can be implemented with any kind of optical wave-guide.
The purpose of the invention is to suggest an optical wave-guide wavelength optical multiplexer-demultiplexer which exhibits a significant improvement of the &Dgr;&lgr;/d(&lgr;i, &lgr;i+1) ratio, is easy to manufacture, can be realized with standard components easy to obtain and has a low loss.
It is another purpose of the invention to construct such multiplexing-demultiplexing device in which the elementary passband associated to each fiber is widened and shows front edges towards low frequencies and towards high frequencies which are as steep as possible and in which each transmitted wavelength undergoes the same attenuation. Such an elementary transfer function, ideally rectangular in shape, enables to obtain accurate delimitation of the passband and uniform transmission within this band.
To obtain this result, one has to increase the &Dgr;&lgr;/d(&lgr;i, &lgr;i+1) ratio and various propositions have been made in that direction.
The preferred embodiment described here uses a microlens array for increasing this ratio.
When this ratio is high, other problems are to be addressed:
In practice, industrialization requires that the geometrical spacings between the wave-guides ends are equal and that, in the meantime, the wavelength spacings are also equal. It is a first object of the invention to satisfy these two conditions by using a prism, for allowing satisfactory increase of &Dgr;&lgr;/d(&lgr;i, &lgr;i+1).
Gratings usually introduce polarization effects depending of the wavelength that are detrimental to the multiplexer/demultiplexer quality. The higher the &Dgr;&lgr;/d(&lgr;i, &lgr;i+1) is the more important is the sensitivity of the multiplexer/demultiplexer to these effects. It is a second object of the invention to avoid these effects by using a polarization splitter.
To this end, the invention relates to an optical wave-guide wavelength multiplexing device comprising;
an array of input single-mode wave-guides designed for carrying light beams at different wavelengths (&lgr;1, &lgr;2, . . . , &lgr;n),
an output single-mode wave-guide designed for carrying the whole set of such light beams,
a dispersing system receiving light beams from the input wave-guides in an end plane and generating superimposed light beams designed for the output wave-guide in an output plane,
a collimating lens which produces collimated beams from the input wave-guides whose respective central axes are converging to be superposed on the rear reflector of the dispersing system,
a refracting prism located between the dispersing system and the collimating lens.
According to the invention, it is also possible to construct a demultiplexing device. The device according to the previous art described above with reference to
FIGS. 1 and 2
can also operate in reverse direction, as a demultiplexer. The single-mode fiber
61
is then an input wave-guide carrying a light beam at various wavelengths and the fibers
1
to
5
become thus output wave-guides, each receiving a beam at a given wavelength, separated spatially from the beams coming out at the other wavelengths. Thus, although it will be mainly described embodied as a multiplexer, the invention can also be applied to such a demultiplexer.
The device according to the invention is then an optical wave-guide wavelength demultiplexing device comprising:
an array of output single-mode wave-guides designed for carrying light beams at different wavelengths (&lgr;1, &lgr;2, . . . , &lgr;n),
an input single-mode wave-guide designed for carrying the whole set of such light beams,
a dispersing system receiving the light beam from the input wave-guide in an end plane and generating spatially separate light beams designed for the output wave-guides in an output plane,
a collimating lens receives collimated beams whose respective central axes are diverging from the rear reflector of the dispersing system where they are superposed and produces converging beams whose respective central axes are parallel and directed to the output wave-guide array,
a refracting prism located between the dispersing system and the collimating lens.
The device according to the invention is then an optical wave-guide wavelength multiplexing device comprising:
an array of input single mode waveguides designed for carrying light beams at different wavelengths (&lgr;1, &lgr;2, . . . , &lgr;n),
an output single-mode wave-guide designed for carrying the whole set of such light beams,
a dispersing system receiving light beams from the input wave-guides in an end plane and generating superimposed light beams designed for the output wave-guide in an output plane,
a collimating lens which produces collimated beams from the input wave-guides whose respective central axes are converging to be superposed on the rear reflector of the dispersing system,
a polarization splitter between the input single-mode wave-guides array and the grating.
The device according to the invention is then an optical wave-guide wavelength
LaLoux Bernard
Lefevre Herve
Martin Philippe
Merigot Bertrand
Arent Fox Kintner & Plotkin & Kahn, PLLC
Hofsass Jeffery
Photonetics
Tweel , Jr. John
LandOfFree
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