Application of additional high-frequency modulation to reduce influence of residual amplitude modulation LiNbO₃ phase modulator on fiber optical gyroscope signal

Residual amplitude modulation in LiNbO₃ phase modulator is one of the key factors that limit the accuracy of highsensitive fiber-optical sensors. A fiber-optical gyroscope is an angular velocity sensor whose sensitivity is better than 0.001 °/h. Optical light intensity changes after phase modulator is a reason for wrong phase difference that introduces an error in the angular velocity signal. Most existing residual amplitude modulation suppression methods are based on reduction of back reflections between an optical fiber and integrated optical waveguide, absorbing groove to suppress or reduce reflection on the bottom face, and algorithmic compensation. In this paper, new approach to reduce residual amplitude modulation in LiNbO₃ for fiber optical gyroscope application is presented. Method feature is an application of additional differential signal modulation with uniform amplitude distribution in the input signal voltage range of the phase modulator. The proposed method allows to suppress residual amplitude modulation of the multifunctional integrated optical circuit phase modulator more than 3 times using additional triangle signal modulation with the frequency f = 200.09 MHz and power P = 36 dBm. This method is suitable for improving fiber optical gyroscope accuracy. Moreover, it could be applied for any fiber-optic sensors based on LiNbO₃ phase modulator. The paper will be of interest to specialists in the field of highly sensitive fiber optical sensors, fiber, and integrated optics.

1. Wei L., Tjin S.C. Special issue «Fiber optic sensors and applications»: An overview. Sensors, 2020, vol. 20, no. 12, pp. 3400. https://doi.org/10.3390/s20123400

2. Fiber Optic Sensors: An Introduction for Engineers and Scientists. Ed. by E. Udd. John Wiley & Sons, lnc., 2006.

3. Lefevre H.C. The Fiber-Optic Gyroscope. Boston, Artech House, 2014, 391 p.

4. Lefevre H.C., Martin P., Morisse J., Simonpietri P., Vivenot P., Arditti H.J. High-dynamic-range fiber gyro with all-digital signal processing. Proceedings of SPIE, 1991, vol. 1367, pp. 72–80. https://doi.org/10.1117/12.24730

5. Novikov A.V. Operation principle of fiber optic gyroscope. GEOSiberia, 2006, vol. 4, pp. 72–75. Available at: https://cyberleninka.ru/article/n/printsip-raboty-volokonno-opticheskogo-giroskopa (accessed: 15.03.2022). (in Russian)

6. Wang D., Sheng F. Residuary intensity modulation of the phase modulator in IFOG and its measurement. Guangdian Gongcheng/ Opto-Electronic Engineering, 2007, vol. 34, no. 7, pp. 26–29.

7. Wang W., Wang J. Study of modulation phase drift in an interferometric fiber optic gyroscope. Optical Engineering, 2010, vol. 49, no. 11, pp. 114401. https://doi.org/10.1117/1.3509360

8. Pogorelaia D.A. Investigation of phase and amplitude distortions influence of an optical signal in an electro-optic modulator on the accuracy characteristics of a fiber optic gyroscope. Dissertation for the degree of candidate of technical sciences. St. Petersburg, ITMO University, 2019, 155 p. (in Russian)

9. Ishibashi C., Ye J., Hall J.L. Analysis/reduction of residual amplitude modulation in phase/frequency modulation by an EOM. Proc. of the Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 2002, pp. 91–92. https://doi.org/10.1109/QELS.2002.1031144

10. Petrov V.M., Shamrai A.V. Microwave Integrated Optical Modulators. Theory and Practice. Moscow, ITMO University, 2021, 225 p. (in Russian)

11. Mondain F., Brunel F., Hua X., Gouzien E., Zavatta A., Lunghi T., Doutre F., De Micheli M.P., Tanzilli S., D’Auria V. Photorefractive effect in LiNbO3-based integrated-optical circuits for continuous variable experiments. Optics Express, 2020, vol. 28, no. 16, pp. 23176–23188. https://doi.org/10.1364/OE.399841

12. Aksarin S.M., Smirnova A.V., Shulepov V.A., Parfenov P.S., Strigalev V.E., Meshkovskiy I.K. The study of spontaneous domain nucleation in the interelectrode gap of phase modulator based on titanium indiffused waveguides in lithium niobate crystals. Scientific and Technical Journal of Information Technologies, Mechanics and Optics, 2021, vol. 21, no. 3, pp. 361–373. (in Russian). https://doi.org/10.17586/2226-1494-2021-21-3-361-373

13. Kuznetsov V.N., Litvinov E.V., Vostrikov E.V., Deyneka I.G. Auxiliary arbitrary waveform generator for fiber optic gyroscope. Scientific and Technical Journal of Information Technologies, Mechanics and Optics, 2022, vol. 22, no. 2, pp. 302–307. (in Russian). https://doi.org/10.17586/2226-1494-2022-22-2-302-307

14. Vázquez C., Vargas E.S., Sanchez Pena J.M. Sagnac loop in ring resonators for tunable optical filters. Journal of Lightwave Technology, 2005, vol. 23, no. 8, pp. 2555–2567. https://doi.org/10.1109/JLT.2005.850793

15. Chan E.H.W., Minasian R.A. Widely tunable, high-FSR, coherencefree microwave photonic notch filter. Journal of Lightwave Technology, 2008, vol. 26, no. 8, pp. 922–927. https://doi.org/10.1109/JLT.2007.912529