TH59448B - Bias control built-in modulator and optical transmitter - Google Patents

Abstract

DC60 (07/04/60) A device and a method for controlling bias in an optical modulator are disclosed. The method is particularly applicable to the control of a multi-wavelength modulator and a tunable transmitter. At the calibration stage, the modulator is optically operated as desired, and the amplitude of the peak-to-peak variation of the output optical signal in a predetermined dithering amount is stored in memory as a reference. At the operating stage, the optical modulator controller adjusts the modulator bias voltage until the measured peak-to-peak variation of the optical signal matches the reference value stored in the calibration stage. For a multi-wavelength modulator and a tunable transmitter, the calibration is repeated at each wavelength, and the corresponding peak-to-peak variation of the optical signal is stored in memory. Edit 07/04/2017 A device and a method for controlling bias in an optical modulator are disclosed. The method is particularly applicable to the control of a multi-wavelength modulator and a tunable transmitter. In the modulator calibration stage, the desired optical operation is performed, and the amplitude of the peak-to-peak variation of the output optical signal in a predetermined dithering amount is stored in the memory as a reference. In the operating stage, the optical modulator controller adjusts the modulator bias voltage until the measured peak-to-peak variation of the optical signal matches the reference value stored in the calibration stage. For multi-wavelength modulators and tunable transmitters, the calibration is repeated at each wavelength, and the corresponding peak-to-peak variation of the optical signal is stored in the memory. --------------------------

Claims (1)

1. Claims (all) that do not appear on this advertisement page: Edited 07/04/2017 1. A method for controlling an optical modulator, comprising: (a) feeding a first optical signal, a first bias signal, and a first RF modulator signal to the optical modulator and measuring its performance parameters, wherein the magnitude of the first bias signal is selected to obtain a predetermined value of the measured performance parameter; (b) feeding a dither signal to the optical modulator and measuring the variation in the target peak-to-peak optical power of the first optical signal due to the dither signal, while feeding the first optical signal, a first RF modulator signal, and a first bias signal of the magnitude chosen in step (a) to the optical modulator; (c) storing the magnitude of the first bias signal and the measured target peak-to-peak optical power variation in memory; (d) applying a second optical signal, a second RF signal, a second bias signal, and a dither signal to the optical transducer, and measuring the operational peak-to-peak optical power variation of the second optical signal due to the applied dither signal, when steps (a) to (c) are completed; and (e) adjusting the second bias signal, to minimize the difference between the operational peak-to-peak optical power variation measured in step (d) and the target peak-to-peak optical power variation stored in step (c), thus obtaining predetermined values of the performance parameters without the need to remeasure the performance parameters, where steps (a) to (c) are performed during the calibration of the optical transducer, and steps (d) and (e) are performed during subsequent operations of the optical transducer. 2. The method of claim 1, wherein the magnitude of the second bias signal applied in step (d) is equal to the magnitude of the first bias signal stored in step (c). 3. The method of claim 2, wherein the calibration of the optical modulator includes (f) measuring the dependence of the peak-to-peak power variation of the first optical signal due to the dither signal applied on the magnitude of the bias signal applied to the optical modulator, wherein step (e) includes calculating, adjusting the second bias signal, based on the operational peak-to-peak power variation measured in step (d) and the dependence measured in step (f). 4. The method of claim 1, further including (g) collecting the magnitude of the second bias signal after the adjustment in step (e). 5. The method of claim 4, further including (h) initializing the electro-optical modulator, after step (g) is completed; and (i) repeating steps (d) and (e), when step (h) is completed, wherein the repeated step (d) includes feeding a second bias signal with the magnitude stored in step (g) to the optical modulator. 6. The method as stated in claim 1, wherein the optical modulator is intended to operate at the plurality of wavelengths, wherein the method further comprises repeating steps (a) and (b) while feeding an optical signal at each wavelength of the plurality of wavelengths, and storing the magnitude in step (c) of the first bias signal and the measured peak-to-peak power variation corresponding to each wavelength of the plurality of wavelengths, wherein in step (d), the second optical signal is at the first wavelength of the plurality of wavelengths, and in step (e), the targeted peak-to-peak power variation corresponding to the first wavelength. 7. The method of claim 6, further comprising (j) calculating the difference between the magnitudes of the first and second bias signals, and storing the difference in memory, when step (d) is completed; 8. The method of claim 7, further comprising (k) changing the wavelength of the second optical signal from the first wavelength to the second wavelength of that plurality of wavelengths, when step (j) is completed; (i) repeating steps (d) and (e), when step (k) is completed, wherein in step (d) the second bias signal is the sum of the first bias signal at the second wavelength and the difference stored in step (j); 9. The method of claim 1, wherein step (b) includes adjusting the ratio of the amplitude of the dither signal and the RF modulator signal, to obtain a predetermined value of the target peak-to-peak optical power variation. 10. The method as described in claim 1, wherein the targeted peak-to-peak power variation of step (b) and the operational peak-to-peak power variation of steps (d) and (e) are averaged using a boundary impulse response filter. 11. A control unit for controlling a multi-wavelength optical modulator, comprising: a dither unit for feeding a dither signal to the optical modulator; a measurement unit for measuring the peak-to-peak power variation at the output of the optical modulator due to the dither signal fed by the dither unit, when the optical signal is fed to the input of the optical modulator; a memory for storing the measured target peak-to-peak power variation by the measurement unit for each of the plurality of wavelengths of the optical signal; and a feedback loop controller operationally coupled with the memory, the dither unit, and the measurement unit, to feed a bias signal to the optical modulator, depending on the wavelength of the optical signal. 12. The control unit as stated in claim 11, wherein the feedback loop controller comprises a suitably programmed microcontroller. 13. The control unit as stated in claim 11, wherein the feedback loop controller comprises a PID controller 14. A tunable transmitter comprising: a control unit as described in claim 11; a tunable laser light source for providing an optical signal; a multi-wavelength optical modulator coupled to the tunable laser light source, controlled by the control unit; and a wavelength lock coupled to the control unit for locking the wavelength of the tunable laser light source to a plurality of wavelengths, wherein the control unit is adjusted to provide a wavelength control signal for adjusting the wavelength of the tunable laser light source to a plurality of wavelengths, using the wavelength lock to generate a wavelength error signal proportional to the wavelength deviation of the tunable laser light source from the plurality of wavelengths, and to adjust the bias signal applied to the multi-wavelength optical modulator to minimize the difference between the peak-to-peak power variation measured by the measurement unit and the target peak-to-peak power variation stored in memory, corresponding to the plurality of wavelengths. 15. The tunable transmitter as stated in claim 14, wherein the wavelength locking comprises a Febry-Perot interferometer and first and second light detectors for detecting light signals reflected from and transmitted through the Febry-Perot interferometer, wherein the wavelength error signal is proportional to the difference in the photocurrents of the first and second light detectors, and wherein the peak-to-peak variation of the light power is proportional to the peak-to-peak variation of the sum of the photocurrents of the first and second light detectors. 16. The tunable transmitter as stated in claim 15, wherein the multi-wavelength light modulator comprises a Maksender modulator. (Mach-Zehnder) of a plane waveguide integrated into a unit with a tunable laser light source on a common substrate 1. 7. The tunable transmitter as stated in claim 16, wherein the tunable laser light source includes a semiconductor optical amplifier coupled to a planar waveguide Mach-Zehnder modulator, wherein a control unit is adjusted to adjust the output optical power of the tunable transmitter by adjusting the gain of the semiconductor optical amplifier, using the sum of the photocurrents of the first and second photodetectors as the measurable quantity of the output optical power. 18. The tunable transmitter as stated in claim 16, wherein the planar waveguide Mach-Zehnder modulator has two arms, each with an electrode for adjusting the optical phase of the optical signal propagated therein. 19. The tunable transmitter as stated in claim 18, wherein the control unit comprises Furthermore, a dithering unit is electrically coupled to the optical driver unit to adjust the optical phase in both arms of the planar waveguide mach-sender modulator 2. The adjustable transmitter as described in claim 19, wherein the dithering unit is electrically coupled to the optical driver unit to feed the dithering signal to the planar waveguide mach-sender modulator. --------------------------