Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-11-01
2001-08-28
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S042000, C385S043000
Reexamination Certificate
active
06282345
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to an arrangement for coupling at least two waveguides to one another with each waveguide having at least one core layer for guiding an optical wave having a specific wavelength &lgr;.
Arrangements for coupling optical waveguides to one another have numerous applications in the realization of components and for offering connections between optical components in integrated optics.
Most arrangements for coupling optical waveguides to one another use butt coupling (see, N. J. Frigo et al “A Wavelength-Division Multiplexed Passive Optical Network with Cost-Shared Components”,
IEEE Photonics Technology Letters
, Vol. 6, No. 11, November 1994, pp. 1365-1367). The end of a waveguide having a specific lateral or transverse structure thereby strikes against another waveguide having a different lateral or transverse structure. The most obvious manufacturing method uses etching for removing the core of a waveguide and epitaxial growth of the second waveguide with MOVPE or MOMBE. The advantage of this method is the independent selection of the material compositions and dimensions of the two waveguides. However, the difficulty of epitaxial crystal growth at the abutting location exists that this requires the utilization of the edge zones of the epitaxially grown material.
When only a slight difference in the material composition of the two waveguides is required such as, for example, for the integration of a laser and modulator, then mask-dependent, selective epitaxy is available as a relatively simple manufacturing method. Compromises must thereby be accepted in the laser function or modulator function (see M. Aoki et al “Monolithic Integration of DFB Lasers and Electroabsorption Modulators Using In-Plane Quantum Energy Control of MQW Structures”,
International Journal of High Speed Electronics and Systems
, Vol. 5, No. 1 (1994), pp. 67-90), such as:
1. Mask-dependent, selective epitaxy allows only slight variation of the wavelength of the photo luminescence (PL) between 1.57 and 1.46 &mgr;m and is coupled with a variation of the layer thickness.
2. Due to the waveguide section in the region of the band edge transition having a length of approximately 50 through 70 &mgr;m corresponding to the gas diffusion length in the MOVPE, additional absorption losses arise (0.5 B at 50 &mgr;m length and 1.55 &mgr;m wavelength).
3. When the modulating electrical field extends in this region with variable PL wavelength and layer thickness, the light that passes through can be spectrally broadened (chirp).
It is simplest to employ the same layer packet for the various optical components (see D. Wake, “A 1550-nm Millimeter-Wave Photodetector with a Bandwidth-Efficiency Produce of 2.4 THz”,
Journal of Lightwave Technology
, Vol. 10, No. 7, July 1992, pp. 908-912; A. Ramdane et al, “Very Simple Approach for High Performance DFT Laser-Electroabsorption Modulator Monolithic Integration”,
Electronics Letters
, Vol. 30, No. 23, Nov. 10, 1994, pp. 1980-1981; and A. Ramdane et al “Monolithic Integration of InGaAsP—InP Strained-Layer Distributed Feedback Laser and External Modulator by Selective Quantum-Well Interdiffusion”,
IEEE Photonics Technology Letters
, Vol. 7, No. 9, September 1995, pp. 1016-1018). In this method, the losses in the component properties are especially high since an optimization can only ensue to a limited extent, for example by employing mechanically stressed quantum wells and barriers or by partial re-ordering (disordering) of quantum wells.
Vertically structured waveguide ends (see G. Müller et al, “Tapered InP/InGaAsP Waveguide Structure for Efficient Fibre-Chip Coupling”,
Electronics Letters
, Vol. 27, No. 20, Sep. 26, 1991, pp. 1836-1837; and G. Wegner et al, “Highly Efficient Multi-Fiber-Chip Coupling with Large Alignment Tolerances by Integrated InGaAsP/InP Spot-Size Transformers”,
ECOC
'92. Berlin, pp. 927-930) or laterally structured waveguide ends (see R. N. Thurston et al, “Two-Dimensional Control of Mode Size in Optical Channel Waveguides by Lateral Channel Tapering”,
Optics Letters
, Vol. 16, No. 5, Mar. 1, 1991, pp. 306-308; J. G. Bauer et al, “High Responsivity Integrated Tapered Waveguide PIN Photodiode”,
Proc.
19
th
Europ. Conf. Opt. Commun
. (
ECOC
'93), Vol. 2, Montreux, Sep. 12-16, 1993, paper Tu 28 (p. 277-280); and R. E. Smith et al, “Reduced Coupling Loss Using a Tapered-Rib Adiabatic-Following Fiber Coupler”,
IEEE Photonics Technology Letters
, Vol. 8, No. 8, August 1996, pp. 1052-1054) are employed for waveguide couplers in other works. The core or a cladding layer of the waveguide is thereby tapered such that the optical field is transferred into other regions of this waveguide.
Arrangements for coupling optical waveguides to one another have numerous applications in the realization of components and for offering connections between optical components in integrated optics.
SUMMARY OF THE INVENTION
The invention which comprises core layers of both waveguides being arranged essentially parallel to one another at a vertical distance from one another relative to the layers that is at least equal to half the wavelength of a wave guided in a core layer and overlap one another in an overlap region and are separated from one another in the overlap region by a cladding layer having a refractive index that is lower relative to the core layers, so that an optical wave guided in the core layer of a waveguide can be coupled over through the cladding layer into the core layer of the other waveguide in the overlap region, and at least one of the two waveguides is a ridge waveguide with a ridge being fashioned on at least one flat side of the core layer of this waveguide, with a longitudinal axis determining the direction of an axis of the propagation of an optical wave guided in this core layer proceeds parallel to this core layer and the ridge waveguide and/or other waveguide comprises a cross-sectional taper in the overlap region in a specific direction of the longitudinal axis of the ridge, on the object of offering an arrangement for coupling optical waveguides to one another that is compatible with planar waveguides, particularly ridge waveguides.
The inventive arrangement connects waveguides that lie vertically above one another. The waveguides respectively have at least one core layer. At least one of the waveguides is fashioned as a ridge waveguide. The waveguides are spatially separated by a cladding layer having a lower retractive index then the core layers. The cladding layer effects an optical coupling of the two waveguides, so that the power of the optical fundamental mode of the coupling structure is guided in both waveguides. When at least a part of the core layer or of a cladding layer of a waveguide is removed or added, then the optical power is displaced into one of the two waveguides. Given an adequately weak modification of the structure of the coupling arrangement along the axis of the wave propagation, the spatial shift of the optical power ensues adiabatically in the coupler, i.e. without losses due to optical emission.
The inventive arrangement advantageously produces a transition from phase mismatching to phase matching between the two waveguides. The transition from phase mismatch to phase match between the two waveguides is effected by the cross-sectional taper within the overlap region of the two waveguides. Given phase matching, in particular, the phase velocities of the optical waves respectively guided in the two waveguides are of the same size.
The inventive arrangement can be utilized on all substrates, for example substrates of SiO
2
, Si
3
N
4
, Al
2
O
3
, SiGe with suitability for optical components. Let a few current applications for such arrangements be cited with reference to the example of semiconductor components having laser-active material such as, for example, GaN, GaAs, InP or more complex mixed crystals:
High-power laser diode with window structure for avoiding “hot spots” at the light exit face.
DBR lasers without butt coupling between amplifier and mirro
Lee John D.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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