A laser modulation controller (10) modulates the operation of a communications laser circuit and controls the NRZ electrical input into the laser circuit. The electrical modulation controller includes a laser circuit driver (20) for generating and driving input signal to the laser circuit (22). A voltage control circuit (18) controls the laser circuit driver (20) in response to a single input (84). A peak voltage detector circuit (24) responds to the voltage output of the driver circuit (20) and produces a peak voltage signal. A comparison circuit (82) compares the peak voltage signal to a reference signal (78 and 70) and produces from the comparison the control signal input (84) to the voltage control circuit (18). Input circuitry (84) directs the control signal to the voltage control circuit (18) to control the laser circuit driver (20).
Varying Operational Frequency Control Circuit Apparatus With Noise Minimizing Feature
John M. Dugan - Richardson TX Gordon W. Ries - Plano TX
Rockwell International Corporation - El Segundo CA
Many prior control circuits inject a small amplitude control tone into the prime signal path where the distortion added to the prime or main signal by the control tone does not present a significant corruption of the prime signal. This control tone is detected and, based on the detected parameters, the prime signal is adjusted as to one of its parameters such as amplitude. If there are variable frequency spurious signals that may produce products within the bandwidth of the control system, the operation of the control circuit can be completely disrupted. The present invention overcomes the prior art problem by continuously sweeping the frequency of the control tone whereby the detection of the spurious signals in the operation of the control circuit occurs such a small percentage of the time that the control circuit can maintain reliable control operation.
Laser Modulation Controller Using Additive And Amplitude Modulation Control Tones
A laser modulation controller (10) provides laser modulation control by DC bias (54) to a laser (22) with a first control tone (32), amplitude modulating (70) a non-return to zero (NRZ) input working signal (18) to be converted to light output with a second control tone (30), detecting the first control tone from a portion of the light output of the laser (88, 26) as a third signal (58) which is proportional to laser gain, detecting the second control tone (30) from a portion of the light output of the laser as a fourth signal (60) which occurs only if the laser is being modulated in or below the lasing threshold region, and substantively combining the third (58) and fourth (60) signals to generate a fifth signal (84) for use as a control of the amplitude of the NRZ working signal (18).
Control of the amplitude of data modulation applied to a laser diode is critical to prevent excessive wavelength shift and resultant dispersion of the signal in the waveguide at high data rates. The present invention utilizes the intermodulation products of two low frequency signals superimposed upon the modulation signal to produce detected products which are separated into appropriate components and utilized to control the amplitude of the modulation signal such that its logic 0 level occurs at a given optimum point. A further complementary and interacting control loop is utilized to control the bias point or center point for this data modulation signal.
A bandpass filter is used, which closely matches the characteristics of a closed phase lock loop (PLL) so as to provide an acquisition detector output in a PLL being swept. This detector is not activated by noise generated in the loop due to data or other perturbations. This filter includes a differentiator to exacerbate the filtered output and thus, more clearly define the condition being detected. The phase lock acquisition sweep is disabled when the detector output exceeds a predetermined absolute value. The detection scheme works equally well in approaching the lock frequency from above or below actual lock and a latch circuit ensures that the sweep approach always alternates to compensate for an erratic phase detector in the PLL.