Optical waveguides – With optical coupler – Particular coupling function
Patent
1994-12-06
1996-04-30
Healy, Brian
Optical waveguides
With optical coupler
Particular coupling function
385 14, 385 15, 385 27, 385 43, 385 88, 385 89, 385129, 385130, 385131, G02B 626
Patent
active
055132880
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optical polymer element according to the pre-characterizing clause of the main claim and is preferably used in the coupling of suitable photodiodes onto devices of integrated optics.
The increasing use of integrated-optical components for optical communications, for sensor technology and the computer field lends ever greater significance to the optical connection technique.
Devices of integrated optics (IO) for optical communications (wavelength range 1300 to 1550 nm) and for optical sensor technology (usually in the wavelength range of 633-850 nm) require an optoelectronic signal conversion at the interface between optical and electronic signal processing. This takes place, for example, by coupling the signal light into a photodiode of corresponding spectral sensitivity (for example, InP compounds for optical communications, Si photodiodes for sensor technology).
The usual way of coupling a photodiode onto an optical waveguide consists in a direct coupling of the photodiode onto the waveguide end ("butt coupling"). The light-energy is in this case guided completely into the diode and is transformed there into states of electronic excitation. In addition, an optical waveguide can also be coupled weakly to a photodiode, by only its evanescent field components transferring into the diode ("leaky wave coupling")--the magnitude of the electronic signal response is in this case a function of coupling strength and coupling length. Alternatively, furthermore, an optical waveguide can be passed through an optical semiconductor amplifier (essentially a semiconductor laser diode with antireflection-coated end faces) and the decrease in the charge carrier inversion can be picked off as an electronic signal via the external power supply of the amplifier diode.
The known devices have the disadvantage that they can only be produced in a relatively complex manner.
SUMMARY AND ADVANTAGES OF THE INVENTION
The optical polymer element according to the invention offers in comparison with the known devices, the coupling and fastening of photoelements onto integrated-optical polymeric waveguides is possible, the polymer element is compatible with planar-integrated electronics and great cost advantages are achieved by mass production.
For this purpose, a coupling element, preferably a buffer layer, is provided between the optical waveguide and the photoelement, the buffer layer having, in the region of the photoelement, a refractive index which is less than or equal to the refractive index of the optical waveguide, but is greater than the refractive index of the buffer layer outside the region of the photoelement.
Further advantageous developments are specified in the sub-claims.
A preferred solution is if the photodiodes are integrated by planar and monolithic techniques directly into suitable substrates (for example silicon) by diffusing processes and/or ion implantation. The electrical wiring is advantageously performed directly on the chip. To apply optical waveguides onto a chip electronically processed in this way, first of all an optical buffer layer of lower refractive index than the light-guiding layer is applied. This is followed by the light-guiding polymer layer with the laterally structured optical waveguides and, optionally thereover, an upper covering layer of lower refractive index. If the buffer layer is optically thin (thickness<1/e drop of the field distribution), the evanescent field components extend into the substrate and result in strong intensity losses. If, conversely, the buffer layer is optically thick (thickness>>1/e drop of the field distribution), even in the region of the photodiode there is no light coupled in to the latter.
The necessary high and local coupling of the optical waveguide onto the photodiode is thus achieved by virtue of the fact that the "optically insulating" buffer layer can be optically changed locally over the sensitive window of the photodiode in such a way that the evanescent fields can extend locally far beyond the buffer layer (and in
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Healy Brian
Robert & Bosch GmbH
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