Optical signal scrambling

Details Optical signal scrambling Optical signal scrambling

2000-04-28

2001-12-25

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Having particular chemical composition or structure

C359S313000, C372S026000, C372S027000

Reexamination Certificate

active

06333808

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to optical signal scrambling of optical communication signals for improving transmission capabilities over optical fibre.
BACKGROUND TO THE INVENTION
It is well known that in long distance optical communication systems degradation of the signal results from a range of different factors and variations of such factors result in signal fading. This results in reduction of signal to noise ratio and, in digital systems, an increase in the average bit error rate of detection at a receiving station. This phenomena and some methods of reduction of such problems is detailed in U.S. Pat. No. 5,361,270 the whole content of which is included herein by reference.
The invention disclosed in U.S. Pat. No. 5,361,270 employs two concatenated lithium niobate phase modulators with a 45° phase shifting coupling therebetween, each phase modulator being modulated by a different wavelength signal. There is a problem with the concatenation of two phase modulators that requires two different drive frequencies to overcome modulator overlap. Such phase modulators are extremely expensive and the present invention seeks to simplify the design of a scrambler thereby to significantly reduce costs of manufacture.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided an optical signal scrambler comprising an optical phase modulator having a common input/output for an optical signal an input for a modulating signal and a common output/input coupled to a 45° Faraday mirror whereby an optical signal input to the input/output of the modulator is returned as an output which is phase scrambled.
The scrambler may comprise coupling means for routing the optical signal to the input/output of the modulator and for coupling the returned signal to an optical transmission line. The coupling means may comprise a three port circulator having a first port for receiving the optical signal a second port coupled to the common input/output of the modulator and a third port for connection the optical transmission line. Alternatively the coupling means may comprise a 3 dB coupler.
The scrambler may comprise a modulating signal generator coupled to the modulating input. Two modulating signal generators of different frequencies may be coupled to the modulating input. In one advantageous arrangement the modulator is arranged to be a travelling wave configuration with a modulating electrode having an input at each end, each of which ends is coupled to a different one of the modulating signal generators thereby to modulate the signal each in a different direction of passage through the modulator. The modulator may be a lithium niobate phase modulator.
The invention also includes an optical signal generator having a scrambler, as previously defined, coupled to a laser signal generator source. A further refinement is the provision of an optical signal generator having a scrambler as previously defined and a plurality of laser signal generators each of a different wavelength coupled via a multiplexer to the scrambler.
The invention also includes a method of phase scrambling of an optical signal including the steps of passing the signal in one direction through an optical phase modulator, modulating the phase of the signal during passage through the modulator to a Faraday reflector, reflecting the modulated signal back through the modulator for further phase modulation thereby to scramble the signal irrespective of its original polarisation.


REFERENCES:
patent: 5159481 (1992-10-01), Maeda
patent: 5327511 (1994-07-01), Heismann et al.
patent: 5361270 (1994-11-01), Heismann
patent: 5515199 (1996-05-01), Farina
patent: 5657151 (1997-08-01), Swan et al.
patent: 6008922 (1999-12-01), Gautheron et al.

Affiliated with

Also associated with

Rating

Optical signal scrambling does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical signal scrambling, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical signal scrambling will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2570609