Optical waveguides – With optical coupler – Particular coupling structure
Patent
1995-08-04
1997-11-18
Lee, John D.
Optical waveguides
With optical coupler
Particular coupling structure
385 43, 385 47, G02B 626
Patent
active
056895976
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In optics (i.e. in conventional optics, three-dimensional optics, planar optics and waveguide optics), light beams are processed. Important functions are the splitting and combining of light beams. In conventional optics, prisms or pellicle splitters are used for this purpose. Nowadays it is being attempted to reduce the dimensions of the optical components to a considerable extent. On the one hand, it is being attempted in three dimensions to realise the processing of light beams by means of interference phenomena (holography) (free space optics). On the other hand, the technique of integrated optics is developing very rapidly. In this technique, thin-film layers or two-dimensional waveguides are used. It is an object of integrated optics to realise the functionality of the components used in conventional optics by new, integrable optical elements. This research field has found important applications in the field of communication.
In fiber-optical communication, data are transmitted by means of optical signals through glass fibers. The optical signals are processed on integrated optical chips which are placed between the fibers. To manufacture these chips, generally thin-film layers are provided on a support (substrates such as, for example glass, Si, InP, GaAs) and subsequently structured.
In optical waveguides the light is guided through a medium (referred to as the waveguide core). The guidance is realised in that the waveguide core is bounded by a reflecting transition. In cavity waveguides, a metal is used for this purpose. In dielectric waveguides, the total reflection on a surrounding medium having a smaller refractive index (the waveguide cladding) is used. In optical waveguides, only those modes can propagate which fulfil the Maxwell equations. The waveguides are referred to as cut-off, monomode or multimode waveguides, dependent on whether they can guide no mode, only one mode for each polarization or a plurality of modes.
In waveguides, the light propagates in the longitudinal direction (z direction). The x direction is parallel to the waveguide layer and is defined as the horizontal, or lateral direction. Analogously, the y direction is vertical to the waveguide layer and is defined as the vertical, or transversal direction. The propagation of light on the chips is computed by means of numerical methods such as beam propagation (BPM) methods, or mode analysis (MA) methods. In some cases, analytical computations such as the effective index method (EIM) are used. The Maxwell equations are often solved in a scalar approximation. These equations describe the planar optics exactly. Two polarizations can be distinguished: the TE polarization has the E vector in the x direction and the TM polarization has the H vector in the x direction. For the most frequently used two-dimensional dielectric waveguides in integrated optics, the scalar approximation leads to "quasi-TE" and "quasi-TM" modes. In such waveguides, the mode forms and the "effective" indexes may be dependent on the polarization. In many cases it is very much desirable, but very difficult, to produce components which are independent of polarization. It should be noted that "monomode" waveguides often have a mode for each polarization, i.e. overall, there are often two modes in "monomode" waveguides. These are degenerate modes in normal glass fibers.
Important components in integrated optics are the beam splitters and combiners. Generally, one refers to N.times.N splitters. N and N denote the number of inputs and outputs. Ideally, these splitters should have the following properties: they should be compact (having small dimensions), independent of polarization, not very sensitive to manufacturing inaccuracies and easy to produce. Moreover, it should be possible to readily adapt the splitting or combining ratios to the various applications by geometrical changes in the design. Various beam splitters and combiners have already been realised: 50%/50% intensity ratio. Asymmetrical Y branches yield other intensity rat
REFERENCES:
patent: 4200356 (1980-04-01), Hawkes et al.
patent: 4737002 (1988-04-01), Boucouvalas
patent: 5379354 (1995-01-01), Jenkins
patent: 5396570 (1995-03-01), Jenkins et al.
patent: 5428698 (1995-06-01), Jenkins et al.
patent: 5469460 (1995-11-01), Van Roijen et al.
Besse et al, "New 1x2 Multi-Mode Interference Couplers With Free Selection Of Power Splitting Ratios", Proceedings of 20th European Conf. On Optical Commun. (ECOC '94), vol. 2, pp. 669-672, Sep. 1994.
Lee John D.
Tierney Daniel E.
U.S. Philips Corporation
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