Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-02-14
2001-06-26
Phan, James (Department: 2872)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S529000, C359S618000, C359S629000
Reexamination Certificate
active
06252718
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical reflector intended for receiving an input beam and transmitting a reverse-direction and parallel output beam, optionally superimposed on the input beam.
BACKGROUND OF THE INVENTION
It is well known that the alignment of the optical components is decisive for the quality of the devices that are fitted with the components. Therefore, any self-alignment, i.e. any assembly in which the properties of the output luminous flux are little sensitive to the orientation or to the position of one or several components, is required.
Among the self-aligned retroreflecting systems known for a long time, the following can be mentioned for exemplification purposes: the cube corner illustrated on
FIG. 1
with which an incident beam
1
,
1
′ on a reflecting orthogonal trihedron
3
produces a parallel output beam
2
,
2
′, whatever the angle of incidence with respect to the diagonal
5
of the cube and the position of the point of incidence
4
.
The so-called ‘cat's eye’ assembly is also well known, consisting of a convergent optical system
8
with optical axis
9
, in the focal plane of which is located a mirror
10
, substantially perpendicular to the axis
9
. A collimated incident beam
11
,
11
′ converges onto the mirror
10
, is reflected on the mirror
10
and then diverges in return onto the optical system
8
that produces an output beam
12
,
12
′, also collimated and parallel to
11
. Such a cat's eye is represented on FIG.
2
.
Both these systems described previously offer self-alignment of the direction of the output beam
2
,
2
′ and
12
,
12
′ on the input beam, respectively
1
,
1
′ and
11
,
11
′ in two dimensions, i.e. in all the planes parallel to the direction of the input beams. In certain systems, one can seek to obtain the self-alignment in a single dimension. In this case, one can use either an orthogonal dihedron instead of the trihedron of
FIG. 1
or a cylindrical cat's eye, i.e. a lens or a cylindrical optical system instead of the spherical optical system
8
in the case of FIG.
2
. The dihedron ensures self-alignment in the plane perpendicular to its edge and the cylindrical cat's eye in the plane perpendicular to the generatrix of its cylindrical lens. In the parallel plane, both these systems behave like a mirror.
Self-aligned separating optical components or devices, which produce two emerging beams, parallel to one another, from a single incident beam, are also known. These may be for instance a periscope or a blade with parallel faces one of which is partially metallized, in order to modify its reflection coefficient on a portion of its surface.
Conventional dihedra and trihedra allow however only total reflection of the beam whereas, in certain applications, a second partial output is required in addition to the first retroreflected output.
SUMMARY OF THE INVENTION
The invention implements an interferometric device of the Sagnac interferometer type, capable of producing two beams, respectively identified as a reciprocal beam and a non-reciprocal beam, in relation to the number of reflections affecting each of the two interfering beams to make the output beams.
The Sagnac interferometers are well known. They consist of a beam splitter and a ring, i.e. a closed optical beam beginning and ending at the beam splitter.
This ring and the beam splitter are arranged so that an input beam is split into two secondary beams, each circulating in the ring, respectively in opposite directions.
Thus, when returning, the waves corresponding to each of these beams interfere and produce two output beams.
This ring often consists of three independent mirrors and it is well known that a reciprocal output is thus produced for which the interfering waves have been subjected to the same number of reflections during their circulation in the ring and a non-reciprocal output for which these waves have been subjected to a number of different reflections.
By ‘matched phase front’, we mean the state of interference obtained when the orientation of the mirrors is adjusted to spread the interferences fringes down to their complete elimination.
The aim of the invention is to provide such a Sagnac interferometer comprising an optical reflector, that benefits from the advantages of a self-aligned reflecting device and that would be then particularly simple to adjust and whose long-term stability is improved.
Another advantage of the invention is to allow the possible construction of wavelength tuneable laser, possibly continuously, that would enable extracting the output luminous beam in optimised conditions, with minimum losses.
According to another embodiment of the invention, it is possible to obtain a laser whose background noise resulting from the ASE (Amplified Spontaneous Emission) is filtered spectrally and that exhibits therefore better efficiency at the emission wavelength of the laser.
The invention also relates to an optical reflector receiving an input beam, transmitting a retroreflected reciprocal output beam and comprising a beam splitter giving a first secondary beam and a second secondary beam, parallel to one another as well as retroreflecting systems each redirecting the secondary beams toward the beam splitter and forming a Sagnac interferometer.
According to the invention, the reflecting system comprises a self-aligned total reflector and the beam splitter is self-aligned.
Preferably, in various embodiments of the invention each having their respective advantages:
the self-aligned total reflector is unidimensional;
the self-aligned total reflector is bidimensional;
the beam splitter is energy-unbalanced, whereas the reflector thus transmits a non-reciprocal output beam;
the optical reflector comprises a diffraction grating forming with the total reflector a Littman-Metcalf system;
the diffraction grating is located between the beam splitter and the total reflector.
The invention also relates to a laser source with external cavity comprising an amplifier medium and a retroreflecting dispersing device comprising an optical reflector formed by a Sagnac interferometer with a total reflector and a Littman-Metcalf configuration grating.
Advantageously:
the amplifier medium is a wave-guide and it is associated with collimation optics thereby collimating the beam that it produces;
the external face of the wave-guide is totally reflecting and the non-reciprocal beam is the single beam transmitted by the source;
the dihedron is mobile in rotation to enable the variation of the wavelength;
the dihedron is mobile in rotation and in translation to enable continuous variation of the wavelength;
the laser source comprises several amplifier guides that are offset at an angle with respect to the retroreflecting-dispersing device and enabling the transmission of the source over several wavelengths.
REFERENCES:
patent: 0030891 (1981-06-01), None
patent: 2724496 (1996-03-01), None
An English language abstract of JP 57 099793., Jun. 1982.
XP 000852817 to T.T. Basiev et al., “Powerful Single Mode Nd Lasers with Self Phase Conjugation”, Proceedings of the International Conference on Lasers '98, Dec. 1998.
Arent Fox Kintner & Plotkin & Kahn, PLLC
Phan James
Photonetics
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