Method for generating a distortion-free, frequency-modulated optical signal and apparatus for the implementation of such a method

An apparatus for generating a frequency modulated optical signal, comprising:

• a semiconductor laser having a pump electrode and a further electrode;
• an electrical voltage that is applied to the pump electrode of the semiconductor laser and that modulates with a modulation frequency, the semiconductor laser having a frequency transfer function with a thermal low-pass part that is dependent on the modulation frequency, said low-pass part effecting a distortion of the generated, frequency-modulated optical signal;
• a high-pass filter means for high-pass filtering of the modulating voltage to be supplied to the pump electrode of the semiconductor laser;
• a low-pass filter means for low-pass filtering of the modulating voltage to be supplied to the further electrode of the semiconductor laser;
• the low-pass filter means having a predetermined low-pass transfer function for the modulation frequency that has a value one for modulation frequencies that are extremely low in comparison to a predetermined frequency and that has a value zero for modulation frequencies that are extremely high in comparison to the predetermined frequency;
• and
• the high-pass means having a high-pass transfer function is equal to a value of one minus the low-pass transfer function of the low-pass filter means;
• wherein the frequency-modulated signal is generated at least partially free of the distortion caused by the thermal low-pass part.

An apparatus for generating a frequency modulated optical signal, comprising:

• a semiconductor laser having at least a pump electrode;
• an electrical voltage that is applied to the pump electrode of the semiconductor laser and that modulates with a modulation frequency, the semiconductor laser having a frequency transfer function with a thermal low-pass part that is dependent on the modulation frequency, said low-pass part effecting a distortion of the generated, frequency-modulated optical signal;
• an amplitude signal that is dependent on an intermediate frequency of an intermediate frequency signal acquired from the superimposed signal being generated such that said amplitude signal with reference to a specific amplitude level has at least two level crossings with slopes inclined in a same direction at two respective specific characteristic frequency values of the intermediate frequency that differ from one another and, when the frequency-modulated optical signal output by the semiconductor laser is undistorted, intermediate frequency values occur that are equal to the characteristic frequency values, and given a frequency-related deviation of the intermediate frequency values from the characteristic frequency values, the intermediate frequency values being in turn at least approximately adjusted back to the characteristic frequency values by a change of the reference frequency of the reference signal that is effected by an output signal generated from a constantly identified amplitude level of the amplitude signal;
• a frequency discriminator for generating the amplitude signal that is dependent on the intermediate frequency from the intermediate frequency signal;
• and
• a control means, whereby a continuously identified amplitude level of the amplitude signal is used as an actual value and a specific amplitude level is used as a rated value, said control means generating an output signal that is dependent on a deviation of this actual value from this rated value that is supplied as a control signal to a frequency-modulatable, optical reference signal transmitter generating the reference signal for the purpose of a change of the reference frequency of the reference signal such that the deviation of the actual value from the rated value is at least approximately eliminated;
• wherein a frequency-modulated signal is generated that is at least partially free of the distortion caused by the thermal low-pass part.

An apparatus for generating a frequency modulated optical signal, comprising:

• a semiconductor laser having at least a pump electrode;
• an electrical voltage that is applied to the pump electrode of the semiconductor laser and that modulates with a modulation frequency, the semiconductor laser having a frequency transfer function with a thermal low-pass part that is dependent on the modulation frequency, said low-pass part effecting a distortion of the generated, frequency-modulated optical signal;
• a signal that corresponds to the modulating voltage being derived from an intermediate frequency signal acquired from the optical superimposed signal, the derived signal being distorted with a low-pass filter part of the frequency transfer function that is dependent on the modulation frequency that is at least approximately equal to a transfer function of the semiconductor laser that is dependent on the modulation frequency, and this distorted signal being employed for generating a frequency modulation impressed on the reference signal for at least partial compensation of the distortion of the frequency-modulated optical signal that is contained in the intermediate frequency signal;
• a means for generating an optical superimposition signal by superimposition of the frequency-modulated optical signal output by the semiconductor laser and the reference signal that is generated by an optical reference semiconductor laser and has the specific reference frequency;
• a means for generating an electrical intermediate frequency signal from the optical superimposition;
• a means for generating the derived signal that at least approximately corresponds to the modulating voltage from the intermediate frequency signal;
• and
• a means for quantized feedback of the derived signal to a reference signal transmitter that generates the reference signal and for distorting the derived signal with the transfer function that is at least approximately equal to the low-pass part of the frequency transfer function the semiconductor laser, the reference signal transmitter being an optical transmitter that can be frequency-modulated by the distorted derived signal from the means for quantized feedback;
• wherein the frequency-modulated signal is generated at least partially free of the distortion caused by the thermal low-pass part.

An apparatus for generating a frequency modulated optical signal, comprising:

• a semiconductor laser having at least a pump electrode;
• an electrical voltage that is applied to the pump electrode of the semiconductor laser and that modulates with a modulation frequency, the semiconductor laser having a frequency transfer function with a thermal low-pass part that is dependent on the modulation frequency, said low-pass part effecting a distortion of the generated, frequency-modulated optical signal;
• a signal that corresponds to the modulating voltage being derived from an intermediate frequency signal acquired from the superimposition signal, the modulating voltage being supplied to the semiconductor laser pre-distorted by a high-pass transfer function for the modulation frequency, the derived signal being distorted by a low-pass transfer function of the modulation frequency that is at least approximately complementary to the high-pass transfer function, and this distorted signal being employed for generating a frequency modulation impressed on the reference signal for at least partial compensation of a distortion of the frequency-modulated optical signal that is contained in the superimposition signal;
• a high-pass filter means having a specific high-pass transfer function for high-pass filtering of the modulating voltage to be applied to the pump electrode of the semiconductor laser;
• a means for generating an optical superimposition signal by superimposing the frequency-modulated optical signal output by the semiconductor laser and the optical reference signal that is generated by an optical reference signal transmitter and has the specific reference frequency;
• a means for generating the derived signal that at least approximately corresponds to the modulation signal from the optical superimposition signal;
• and
• a means for quantized feedback of the derived signal to a reference semiconductor laser that generates the reference signal and for distorting the derived signal with the low-pass transfer function that is at least approximately complementary to the high-pass transfer function, the reference semiconductor laser being an optical transmitter than can be frequency-modulated by the distorted derived signal;
• wherein the frequency-modulated signal is generated at least partially free of the distortion caused by the thermal low-pass part.

An apparatus for generating a frequency modulated optical signal, comprising:

• a semiconductor laser having at least a pump electrode;
• an electrical voltage that is applied to the pump electrode of the semiconductor laser and that modulates with a modulation frequency, the semiconductor laser having a frequency transfer function with a thermal low-pass part that is dependent on the modulation frequency, said low-pass part effecting a distortion of the generated, frequency-modulated optical signal;
• an electrical error signal generated from the frequency-modulated optical signal output by the semiconductor laser, said electrical error signal being at least approximately proportional with a specific proportionality constant to the thermal low-pass part of the frequency transfer function of the semiconductor laser and to the modulating voltage;
• a controllable frequency converter controlled with said error signal, said controllable frequency converter effecting a frequency shift of the signal frequency of the frequency-modulated optical signal, the proportionality constant of the error signal being selected such that the optical frequency of an optical signal at an output of the frequency converter is essentially proportional to the modulated voltage and is independent of the thermal low-pass part of the frequency transfer function of the semiconductor laser;
• an optical splitter for dividing the frequency-modulated optical signal into two signal parts;
• the controllable frequency converter, to which one of the two signal parts is supplied, effecting a frequency conversion at the supplied signal part dependent on a supplied control signal;
• and
• an error signal generator to which the other signal part is supplied and which, dependent on this signal part, generates an error signal that is supplied to the frequency converter as a control signal;
• wherein the frequency-modulated signal is generated at least partially free of the distortion caused by the thermal low-pass part.