Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1995-04-28
1996-06-11
Boudreau, Leo
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359187, 375296, H04B 1000
Patent
active
055261590
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In optical telecommunication systems with signal transmission via optical fibers, the interaction of laser chirp, on the one hand, and fiber dispersion, on the other hand, leads to possibly substantial signal distortion which, in particular in the case of analog signal transmission (for example, AM-CATV) in the wavelength window around 1.55 .mu.m via standard monomode fibers, can restrict the range of such systems to a few hundred meters.
Laser chirp, that is to say the modulation-dependent frequency deviation of a laser, can be circumvented by the use of external modulators, but this entails an appreciable outlay. An attempt can be made to combat fiber dispersion, that is to say the wavelength-dependent spread of the signal propagation time in the optical fiber, by splicing in fiber pieces having a dispersion opposite to that of the standard fiber, but it is then necessary to accept an appreciable additional attenuation. A further approach to a solution is offered by electronic compensation measures; thus, an all-pass and a low-pass filter structure (with a varactor diode) for compensating the fiber dispersion by corresponding signal delays are known from ELECTRONICS LETTERS 27 (1991) 5 dated 28.02.1991, pages 421 to 423.
By contrast, the invention adopts a different approach for the purpose of electric compensation of signal distortion in an optical telecommunication system caused by laser chirp and fiber dispersion.
SUMMARY OF THE INVENTION
The invention relates to a method and a circuit arrangement for electric compensation of signal distortion caused by laser chirp and fiber dispersion. The method is characterized in that a correction signal is derived from the electric transmission and/or reception signal by squaring followed by differentiation and is added to the electric transmission signal and/or reception signal, respectively, after a level correction necessary per se in the form of a signal attenuation; the circuit arrangement is characterized according to the invention in that, branching from the electric transmission and/or reception signal path is a correction signal path which has a squaring element and a downstream differentiating element and opens out again into the electric signal path after a downstream level correction circuit via an adding input, it being the case that in a further embodiment of the invention a level adapting circuit can be connected upstream of the squaring element in the correction signal path.
The invention, which proceeds from a relationship between the light output and the optical frequency of the laser which is linear and phase-locked at least to a good approximation, and is based on the finding that a signal occurring at the end of a dispersive transmission link essentially comprises the original signal and an interference term which can be simulated electrically in a very simple way, is attended by the advantage that signal distortion caused by laser chirp and fiber dispersion can be compensated electrically at the receiving end and/or (given a defined length of link) at the transmission end in a very effective way independently of the mean signal level with a very low outlay on circuitry .
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with further objects and advantages, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several Figures of which like reference numerals identify like elements, and in which:
FIG. 1 shows a circuit arrangement for electric compensation at the transmission end, and FIG. 2 shows a circuit arrangement for electric compensation at the reception end of signal distortion induced by laser chirp and fiber dispersion.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Represented diagrammatically in FIG. 1 to an extent required in order to understand the invention is an exemplary embodiment of a circui
REFERENCES:
patent: 5418637 (1995-05-01), Cuo
patent: 5430969 (1995-07-01), Blauvelt et al.
Gysel, "Electrical Predistortion to Compensate for Combined Effect Chirp of Laser and Fibre Dispersion", Electronics Letters, vol. 27, No. 5, Feb. 28, 1991, pp. 421-423.
Wedding, "Reduction of Bit Error Rate in High Speed Optical Transmission Systems Due to Optimized Electrical Drive Pulse Shaping", 14th European Conference On Optical Communications, Sep. 1988, pp. 187-190.
Petermann et al, "Chirp Reduction in Intensity-Modulated Semiconductor Lasers for Maximum Transmission Capacity of Single-Mode Fibres", Archiv Fur Elektronik und Ubertraagungstechnik, Sep. 1986, pp. 283-288.
Walker et al, "Wide Bandwidth, Long Distance Fibre-Optic Communication Systems", Agard Conference Proceedings No. 383, Guided Optical Structures In The Military Enviroment, Sep. 1985, pp. 27.1-27.9.
Boudreau Leo
Negash Kinfe-Michael
Siemens Aktiengesellschaft
LandOfFree
Method and circuit arrangement for electric compensation of sign does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and circuit arrangement for electric compensation of sign, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and circuit arrangement for electric compensation of sign will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-357265