Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
1999-12-10
2001-03-27
Spyrou, Cassandra (Department: 2872)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
C385S024000, C372S043010, C372S050121
Reexamination Certificate
active
06208793
ABSTRACT:
SUMMARY OF THE INVENTION
An object of the present invention is an optoelectronic apparatus which operates on different wavelength channels whose wavelengths can be individually varied. Apparatus, i.e., components of this kind play a key role in wavelength multiplexing techniques when working with fiber-optic data transmission. Such optoelectronic components may, for example, be in the form of laser arrays, laser lines, amplifier arrays and filter arrays. An object of the present invention is to develop a structure for an optoelectronic component having the aforementioned characteristics.
An optoelectronic component array designed according to the invention serves a maximum of n channels whose characteristic wavelengths are individually tunable by control currents. Examples of such component arrays are wavelength-tunable laser arrays, wavelength-tunable amplifier arrays, wavelength-tunable filter arrays, wavelength-tunable detector arrays and wavelength-tunable converter arrays. Each individual channel corresponds to an individually bent optical waveguide. For each of these optical waveguides, an individual function y
i
(x) defines the course of the maximum of the conducted light field in the xy plane, i.e. the individual waveguide bends, where i is an integer, in the range 1≦i≦n. The axial direction i follows the bending of the optical waveguide of ordinal number i, i.e. there is a curved coordinate in the xy plane. In the case of a laser array, each optical waveguide is composed of the laser-active zone
3
and the surrounding materials which, in the xz plane, are distant at most by the lightwave length from the center of the light field. Above or below the xy plane is a feedback grating
4
whose grating lines are tilted with respect to a preferential direction by the tilt angle &phgr;. The grating area is bounded in the x-direction by two boundary surfaces at x=0 and at x=L, these two boundary surfaces being perpendicular to the x-axis. Feedback grating
4
is in an area in which the amount of the intensity of the light field conducted in the optical waveguide is greater than I
0
(x)/100, I
0
(x) being the intensity in the maximum of the light field in the yz plane at position x. For the length of the grating area L in the x-direction, 0.2≦K·L≦7 is applicable for the feedback thus achieved, where K is the coupling coefficient of feedback grating
4
. Feedback grating
4
is DFB-like (DFB=distributed feedback), DBR-like (DBR=distributed Bragg reflector) or it has a sampled grating. In the last-mentioned case, there are additionally a defined number of grating-free areas in the direction of light propagation. Feedback grating
4
may produce, for example, purely real index coupling, purely imaginary index coupling or complex coupling (real and imaginary coupling). The cross-sectional form of feedback grating
4
(in planes which perpendicularly intersect the xy plane) is either triangular, rectangular or sinusoidal. Suitable mixed forms are also possible, such as a rectangular form with rounded corners. For a homogeneous feedback grating
4
or a homogeneous partial area of a grating, &Lgr;
0
is the grating period. Wavelength tuning is achieved by the multi-sectioning of each individual optical waveguide, each individual section being pumped with its own control current. Typically, there are two to three sections per optical waveguide, i.e., the emission wavelength of a channel is set using two to three different control currents. In this context, the wavelength of channel i is tunable approximately in the wavelength range &Dgr;&lgr;
i
. An example of this is a DFB semiconductor laser array emitting from n optical waveguides on n different wavelengths &lgr;
i
, where i runs from l to n. In other words, the optoelectronic component is capable of operating simultaneously on n different frequency channels. The wavelength interval &Dgr;&lgr;
i
of the waveguide of ordinal number i is preset in its absolute wavelength position by the tilt of the feedback grating (tilt angle (&phgr;), by the grating and by the &Lgr;
0
of the feedback grating and the corresponding bending function of the optical waveguide y
i
(x). Finally, the emission wavelength &lgr;
i
is fine-tuned by the control currents corresponding to the optical waveguide of ordinal number i. The same applies analogously to the other optical waveguides of the component array. It is possible to precisely set both the absolute wavelengths of the n channels and the wavelength spacings of the individual channels i in relation to each other. This makes it possible, for example, to implement component arrays having equidistant frequency or wavelength spacings for WDM, i.e., wavelength division multiplex, applications.
The angle &agr;
li,i
describes the angle between the optical waveguide of ordinal number i and the normal onto the component facet at position x=0, (left end of the grating area). The angle &agr;
re,i
describes the angle between the optical waveguide of ordinal number i and the normal onto the component facet at position x=L, (right end of the grating area). The widths of the optical waveguides may differ, this having an influence on the effective refractive index N
eff,i
. The left and right grating boundaries (boundary surfaces) shown in the figures stand for directions which are preferred crystallographically or from the standpoint of the component geometry. The boundary surfaces may be cleaved, etched or lithographic grating boundaries, cleaved or etched component boundaries, cleaved semiconductor wafer boundaries or etched boundaries on the semiconductor wafer. If the component does not end at the boundary surfaces, the optical waveguides may continue outside the grating area. There may be branches, combiners, switches, tapers, etc. in the grating-free area. In this case, the area shown in the figures represents a section of an integrated optoelectronic circuit.
For the sake of clarity, the component dimensions, the angles, the waveguide widths, the waveguide bends and the corrugation periods are not shown to scale in the illustrations. Typically, the lateral wavelength width is considerably greater than the grating period in the feedback grating.
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Hillmer Hartmut
Klepser Bernd
Cherry Euncha
Deutsche Telekom AG
Kenyon & Kenyon
Spyrou Cassandra
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