Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2000-10-30
2003-03-25
Dang, Hung Xuan (Department: 2873)
Optical waveguides
With optical coupler
Plural
C385S017000, C385S018000, C385S031000, C385S033000, C359S199200, C359S199200
Reexamination Certificate
active
06539145
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
Increasing use is being made of wavelength multiplexing/demultiplexing techniques for the purpose of more effective utilization of the transmission capacity of optical conductors. In this case, several mutually independent optical signals of different wavelengths are transmitted over a common optical conductor. Multiplexing/demultiplexing techniques are then used to combine and separate these signals at the receiver and/or transmitter. One possibility for separating and/or combining optical signals of different wavelengths is to use narrowband optical bandpass filters.
Such filters mostly consist of dielectric layer systems which are mounted on suitable carrier substrates, generally glass substrates. Their transmission and/or return characteristics for a specific wavelength region are specifically set by selecting the thicknesses and refractive indices of the individual layers and their arrangement.
The reflectivity and/or transmissivity of optical bandpass filters of different center wavelengths is illustrated schematically and in an idealized fashion in
FIG. 9
as a function of the wavelength of the light. In this case, &lgr;
1
to &lgr;n stand for the center wavelengths of the filters F
1
to Fn, &lgr; stands for the wavelength of the light, and R and T stand for the reflectance and transmittance. The transmittance is illustrated with unbroken lines, and the reflectance with dashed lines. It holds that R≈1−T. These filters have a particularly high transmission in a specific region about their center wavelength, but reflect light of wavelengths outside this region. They therefore act as wavelength-selective mirrors. The center wavelength is a function in this case of the angle of incidence of the light beams.
A multiplexing/demultiplexing arrangement having optical filters, which is known in the prior art, is illustrated in FIG.
10
. The optical signal emerging from an optical conductor F
1
, as a rule a glass fiber, of wavelengths &lgr;
1
-&lgr;n is collimated by an imaging system L
1
, rendered parallel and coupled into a filter system. As a rule, the imaging system in this case comprises a lens, mostly a graded-index lens. The filter system comprises optical filters Fi
1
, Fi
2
, Fi
3
, which are fitted at a fixed spacing from one another onto the mutually opposite sides of a plane-parallel glass plate
8
and in a fashion offset relative to one another. The light coupled into the glass plate
8
by the imaging system L
1
at a specific angle then runs to and fro inside the glass plate in a zigzag fashion between the mutually opposite filters Fi. Light of a specific wavelength is coupled out of the beam path at each filter Fi and coupled into an optical conductor F
2
, F
3
, F
4
by the associated imaging system L
2
, L
3
, L
4
.
It is a disadvantage of such arrangements that a special filter of a specific center wavelength must be used respectively for each wavelength. Several different filters are required depending on the wavelength separation and bandwidth of the individual signals to be separated and/or combined, and in this case only very small fault tolerances are permissible in producing the filters. This leads, on the one hand, to an increased rejection of filters for specific wavelengths and thus to increased production costs and, on the other hand, requires high costs for storing individual special filters.
SUMMARY OF THE INVENTION
The object of the present invention is to make available a module for multiplexing and/or demultiplexing optical signals in which there is a reduction in the number of the filters of a different characteristic which are required for a multiplexing/demultiplexing arrangement, and in which it is possible to use filters with higher manufacturing tolerances.
It is provided in accordance therewith that at least one wavelength-selective filter can be set with reference to the angle of incidence of the light beams. The desired center wavelength of the respective filter can be set exactly in this case via the angle of incidence. This has two advantages. Firstly, individual special filters can be used as multiplexing elements for several wavelengths, the selected wavelength being set via the angle of incidence of the light beams. By using identical filters for different wavelength channels, it is possible to reduce the total number of different filters to be produced, and thus to lower the costs of production and storage.
Secondly, it is possible to use filters with higher tolerances with reference to the center wavelength, since the desired center wavelength can be set precisely by appropriately tilting the filter even in the case of high tolerance values. Consequently, the rejection in filter production can be substantially reduced, and costs can be saved correspondingly.
In a preferred refinement of the invention, the light is coupled into or out of the module by means of optical conductors, each optical conductor being assigned at least one imaging element which is arranged between the optical conductor and a filter. In this case, the optical axes of the optical conductors and the optical axes of the imaging elements assigned to the optical conductors are preferably arranged parallel to one another. Both the adjustment and the fixing of the individual components are facilitated in this way by a parallel arrangement.
In a first development of this refinement of the invention, in each case the imaging element is a lens which is transirradiated off-axis by the light of the assigned optical conductor. The beam deflection required for the functioning of the multiplexing/demultiplexing arrangement is achieved in this case by means of a parallel offset of the optical axis of the optical conductor and assigned imaging element. Such an arrangement is of particularly simple design and is therefore also simple in terms of production engineering and can be executed with a low outlay on adjustment. In this case, use is also made in some circumstances of more complicated, multistage lens systems, for example, to reduce imaging errors resulting from the off-axis transirradiation of the lens.
In a second development, in each case the imaging element is a lens which is transirradiated axially by the light of the assigned optical conductor. Imaging errors owing to off-axis transirradiation of the lens are thereby avoided. However, in order to retain the parallelism of the optical axes of the optical conductors there is then additional need for at least one optical element which can be tilted with reference to the angle of incidence of the light beam and deflects light reflected by the filter in the direction of the lens and the assigned optical conductor. The tiltable optical element is, in particular, a mirror or prism arranged in the beam path between the filter and lens. In this case, by comparison with the use of a prism, the use of a mirror has the advantage of avoiding an additional wavelength dependence on the basis of the dispersion of the glass. Mirrors, prisms and also the wavelength-selective filters should have a weak dependence on polarization.
The arrangements described for producing a beam deflection have the advantage that it is possible in a multichannel multiplexing/demultiplexing arrangement having cascades of optical conductors, imaging systems and tiltable filters to avoid the direct adaptation, which is very complicated in terms of production engineering, of the angular settings of the optical axes of the imaging systems and optical conductors to the tilted filter/filters.
Particularly compact designs are provided by arrangements in which either several filter cascades or filter and mirror/prism cascades are combined. The individual filters of a cascade can be filtered either individually or in common in this case. In the cascaded arrangements, the respective optical conductors are preferably arranged parallel to one another in accordance with the above-described beam deflecting arrangements, and can thereby easily be adjusted and fixed.
A first such advantageous arrangeme
Auracher Franz
Baumann Ingo
Dang Hung Xuan
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
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