Optical transmitter
AssigneeBritish Telecommunications public limited company
InventorsLeslie D Westbrook, David G Moodie
Life of this patent
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Abstract
An optical transmitter includes a directly modulated semiconductor laser and a non-linear optical intensity modulator which is connected in series with the output of the laser. High frequency analogue modulating signals are applied both to the laser and to the modulator. The modulator has a transfer characteristic such that it cancels intermodulation distortion in the output from the laser, to give a source with an improved dynamic range. The transmitter is suitable for use in an analogue optical distribution system for cellular radio.
Claims22
An optical transmitter comprising:
- (a) a primary input port for receiving an input signal, said input signal being a high frequency and analogue electrical signal,
- (b) a directly modulated semi-conductor laser having a modulation input connected to said primary input port, and
- (c) a non-linear optical intensity modulator optically connected in series with an optical output of said laser, said modulator having a modulator port connected to the primary input port, said modulator having a transfer characteristic arranged to cancel at least partially intermodulation distortion in the optical signal output of the laser,
- (d) wherein a controlled ratio is set between the amplitudes of the signal applied to the modulation input of the laser and a modulating signal applied to the modulator port of the modulator, and an output of the modulator includes modulation by both said laser and said modulator.
A method of generating an optical signal modulated with an input signal, said input signal being a high frequency analogue electrical signal, said method comprising:
- (a) generating an optical signal in a semiconductor laser,
- (b) inputting said input signal into said laser and thereby modulating the optical output of said laser with said input signal,
- (c) inputting said modulated optical output into a non-linear optical intensity modulator connected in series with said semiconductor laser, said modulator having a transfer characteristic arranged to cancel at least partially intermodulation distortion applied by said laser, and
- (d) inputting a signal originating from said input signal into said intensity modulator;
- wherein a controlled ratio is set between the amplitudes of the modulating input of said laser and said signal input to said modulator, and the output of the modulator includes modulation applied by both the laser and the modulator.
A method of generating an optical signal modulated with an input signal, said input signal being a high frequency analogue electrical signal, said method comprising:
- (a) generating an optical signal in a semiconductor laser,
- (b) inputting said input signal into said laser and thereby modulating the optical output of said laser with said input signal,
- (c) inputting said modulated optical output into a non-linear optical intensity modulator connected in series with said semiconductor laser, said modulator having a transfer characteristic arranged to cancel at least partially intermodulation distortion applied by said laser, and
- (d) attenuating said input signal by a controlled ratio and inputting said attenuated signal into said intensity modulator;
- whereby the output of the modulator includes both modulation applied by the laser and the modulator.
Dependencies are inferred from the claim text.