Optical transmission system

#The invention relates to an optical transmission system comprising an optical transmitter coupled via a glass fibre to at least an optical receiver, the optical transmitter comprising an electro-optical converter and linearization means for linearizing the relation between an electric input signal of the electro-optical converter and a parameter of an optical output signal of the electro-optical converter. The invention likewise relates to an optical transmitter to be used in such a transmission system.

#A transmission system as defined in the opening paragraph is known from the journal article "Comparison of direct and external modulation for CATV Lightwave transmission at 1.5 .mu.m wavelength" in Electronics Letters 24, September 1992, Vol. 28, No. 20 pp. 1875-1876.

#In the known transmission system an electrical input signal is applied to an electro-optical converter which converts the input signal into changes of a parameter of the light emitted by the electro-optical converter. This parameter may be, for example, the intensity (power), frequency, phase or a combination of these parameters. The electro-optical converter may comprise, for example, a laser or LED directly controlled by the input signal. Alternatively, it is conceivable that the electro-optical converter comprises a laser or LED which continously generates a light signal that is modulated by an external modulator which is controlled by the input signal.

#The invention will now be further explained with reference to the drawing Figures, in which:

#FIG. 1 shows a transmission system in which the invention is used;

#FIG. 2 shows a first embodiment for the optical transmitter 1 shown in FIG. 1;

#In the transmission system shown in FIG. 1 each first input of modulators 2 to N is supplied with a corresponding transmit signal S.sub.2 to S.sub.N. A second input of each modulator 2 to N is supplied with a carrier signal having a frequency f.sub.2 to f.sub.N. The modulated outputs of the modulators 2 to N are connected to inputs of an adder circuit 6. The output of the adder circuit 6 is connected to an input of an optical transmitter 8. A signal V.sub.S is the input signal of the optical transmitter 8. The optical transmitter 8 is connected to a plurality of sub-stations 12 to 18 via a glass fibre network 10.

#The signals S.sub.2 to S.sub.N may be, for example, video signals such as used in cable television distribution, or data signals. The modulators 2 to N modulate each signal S.sub.2 to S.sub.N on its own carrier. This modulation may be performed by known modulation techniques such as various forms of amplitude modulation (for example, AM, VSB, SSB, ASK) or various forms of angle modulation (for example, FM, PM, FSK, PSK). By adding the output signals of the modulators 2 to N together, a frequency-multiplexed signal V.sub.S is obtained. The optical transmitter 8 converts this signal to a light signal of which a parameter, for example, wavelength, or intensity, is modulated in dependence on the signal V.sub.S.

#This light signal is distributed to the sub-stations 12 to 18 via the glass fibre network 10. In each of the sub-stations 12 to 18 there is an optical receiver which converts the received light signal to a replica of the frequency-multiplexed signal V.sub.S. This replica may further be processed by known means to a suitable signal for a terminal station such as, for example, a television set, a telephone set or a personal computer.