Optical waveguides – With optical coupler – Particular coupling function
Patent
1997-08-27
1999-08-03
Palmer, Phan
Optical waveguides
With optical coupler
Particular coupling function
385 9, 385 14, 385 15, 385 16, G02B 626
Patent
active
059335548
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention concerns the field of integrated optics and telecommunications. The invention relates to optical--optical switches and wavelength converters having good ON/OFF switching. Optical-optical switches operate with at least two optical signals. To couple these signals into a waveguide, new multimode interference (MMI) couplers are used which can convert at least one signal into a mode of higher order and which can superpose another signal as a fundamental mode with the first signals. These MMIs are very compact.
STATE OF THE ART
Optical signals are transmitted through optical fiber cables for optical telecommunications. Optical signal processing frequently is carried out on integrated optical chips. Illustratively, these chips are composed of polymers, semiconducting thin films, vitreous materials. . . The light is the waveguide boundary conditions and Maxwell's equations is guided. The various allowed discrete states of the light in the waveguide are denoted "optical modes". Depending on the geometry of the intensity distribution and phase distribution within a mode, this mode will be assigned another order. Thus, one speaks of modes as being fundamental, of first order, etc.
One class of waveguide structures is known as Multi-Mode-Interferometers (MMIs). These MMIs are versatile in signal processing. Illustratively,
Recent applications of integrated optics employ modes of higher orders. Mode converters convert fundamental modes into higher-order modes with a further fundamental mode. Mode converters are used as adiabatically
Modes of higher orders also are attractive for optical fast switches and wavelength converters, in particular for so-called optical--optical components. More particularly it has already been shown that cross-phase modulated (XPM) optical--optical switches and wavelength converters allow for this purpose and therefore the procedure is called "optical--optical": on one hand is the input signal to be switched in the switch and on the other hand is an optical control signal providing timing. These signals are fed to a Mach-Zehnder interferometer (MZI) or to a Michelson interferometer (MI) containing non-linear materials (for instance, semiconductor amplifiers etc.) for phase modulation. Depending on whether the control signal is present or absent, the input-signal phase will be modulated in the MZI. Because the phase is shifted only along one arm of
Various designs for achieving this asymmetry have already been suggested, and the following systems have been demonstrated or proposed: splitters, signal is symmetrically guided toward the MZI with the non-linear sub-system, but on the other hand the control signal is asymmetrically guided along one arm of the MZI; the control signal was converted by adiabatic asymmetric Y-arms into a first-order mode (higher order mode).
These systems are based on very promising components. Unfortunately the components generating the higher order mode as well as the optical--optical components incur several drawbacks: superposition of a further optical signal using adiabatic anti-symmetric Y combiners takes place fairly satisfactorily, there are shortcomings on account of the substantial length and the critical manufacturing tolerances. switching ratios; but the above structures are deficient precisely in this respect because they do not take into account the change in intensity entailed by the phase shift. Unless taken into account, this change in intensity in turn leads to poor switching, that is, to poor ON/OFF switching on at least one of the two outputs, and data signals in different waveguides. Therefore, the components may be cascaded only unsatisfactorily on a single chip. Even bidirectional operation is difficult because the control signal interferes with one output of the switch. which reason new, shorter configurations are desirable. the switching rate of the optical--optical switches. A large control signal may so markedly reduce the carriers in a non-linear region of an MZI arm that, at the next signal, the non-linear
REFERENCES:
Bachmann et al. "Overlapping-Image Multimode Interference Couplers With a Reduced Number of SEL-Image for Uniform And Nonuniform Power Splitting" Applied Optics/vol. 34, No. 30/20 Oct. 20, 1995.
Bachmann Maurus
Besse Pierre-Andre
Leuthold Juerg
Farley Walter C.
Palmer Phan
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