Linear Frequency Modulation of Acousto‐Optic Modulator for Heterodyne Demodulation of Interferometric Fiber Optic Sensing Arrays

Bingtao Cai; Wentao Huang; Limin Xiao; Xiaobao Chen

doi:10.3788/CJL241389

Chinese Journal of Lasers, Volume. 52, Issue 10, 1006004(2025)

Linear Frequency Modulation of Acousto‐Optic Modulator for Heterodyne Demodulation of Interferometric Fiber Optic Sensing Arrays

Bingtao Cai¹, Wentao Huang², Limin Xiao^1、*, and Xiaobao Chen^2、**

Author Affiliations

¹Department of Optical Science and Engineering, School of Information Science and Technology, Fudan University, Shanghai 200433, China

²The 23rd Research Institute, China Electronics Technology Group Corporation, Shanghai 201900, China

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Abstract Get PDF(in Chinese)

Figures & Tables(31)

Fig. 1. Principle diagram of ALH algorithm

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Fig. 2. Process of difference frequency carrier with self-mixing interference of LFM light

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Fig. 3. Parameters of 8-TDM array

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Fig. 4. Schematic of 8-term AOM driver signal generation

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Fig. 5. 8 groups of sampled data within carrier cycle

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Fig. 6. Interference signal of single channel after filtering

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Fig. 7. Two orthogonal signals after mixing and filtering. (a) Time domain diagram ; (b) Lissajous figure

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Fig. 8. Demodulation results. (a) Time-domain spectrum;

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Fig. 9. Variations of THD and SINAD for demodulation results under different initial phases

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Fig. 10. Schematic diagram of optical path of digitized amplitude pre-distortion experiment

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Fig. 11. AOM output intensities with different frequencies

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Fig. 12. Block diagram of pre-compensation scheme for DAC

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Fig. 13. Generation of pre-compensation coefficient for DAC

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Fig. 14. Results before digitized amplitude pre-distortion compensation for DAC. (a) Oscilloscope result; (b) generated eight groups of pulse signals

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Fig. 15. Results after digitized amplitude pre-distortion compensation for DAC. (a) Oscilloscope result; (b) generated eight groups of pulse signals

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Fig. 16. Difference frequency carriers corresponding to same sampled point under different OPDs

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Fig. 17. Variations of orthogonal circles under different OPDs. (a) I_X-I_Y plot under different OPDs; (b) normalized I_X-I_Y plot

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Fig. 18. Variations of demodulation result characteristics under different OPDs. (a) THD; (b) SINAD

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Fig. 19. Flow of orthogonal signal normalization algorithm

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Fig. 20. Experimental platform of ALH algorithm

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Fig. 21. Schematic diagram of 8-TDM optical path

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Fig. 22. Schematic of actual sampling in one cycle of 8-TDM optical path

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Fig. 23. Variations of THD and SINAD under different OPDs. (a) THD; (b) SINAD

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Fig. 24. Dynamic range measurement of ALH algorithm

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Fig. 25. Amplitude consistency of 8-channel demodulation results

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Fig. 26. Noise test results of ALH algorithm. (a) Time domain; (b) frequency domain

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Fig. 27. Consistency of demodulation amplitude over 8 h period

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Table 1. Frequency ranges of 8-group frequency modulation signals ( $Δ f$ =50 kHz)
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Table 1. Frequency ranges of 8-group frequency modulation signals ( $Δ f$ =50 kHz)
Group No. 1 2 3 4 5 6 7 8
$f_{s t a r t}$ /MHz 436.15000 452.1125 468.0750 484.0375 500.0000 515.9625 531.9250 547.8875
$f_{e n d}$ /MHz 437.74625 453.7088 469.6713 485.6338 501.5963 517.5588 533.5213 549.4838

Table 2. Difference carrier frequencies generated with different numbers of modulated pulses
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Table 2. Difference carrier frequencies generated with different numbers of modulated pulses
$N^{'}$ 4 5 8 10
Frequency /kHz 100 160 50 40

Table 3. Frequency ranges of 4 groups of swept signals ( $Δ f$ =100 kHz)
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Table 3. Frequency ranges of 4 groups of swept signals ( $Δ f$ =100 kHz)
Group No. $f_{s t a r t}$ /MHz $f_{e n d}$ /MHz
1 436.150 439.3425
2 468.075 471.2675
3 500.000 503.1925
4 531.925 535.1175

Table 4. Generation process of pre-compensation coefficient for DAC

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Table 4. Generation process of pre-compensation coefficient for DAC

Step	Content
Output of DAC	FPGA drives DAC to generate swept signals without amplitude pre-deformation
Output of AOM	Optical signal output by AOM is quantized and collected by ADC after photoelectric conversion
Positive value	Sampled values are subtracted under no light conditions to ensure that all valid sampled points are positive values
Square root	Square root processing is performed on all corrected sampled points
Normalization	Taking reciprocal of processed value and multiplying it by minimum value in sampling array to obtain correction coefficient
Pre-compensation coefficient for DAC	Calculated correction coefficient is input to FPGA to adjust amplitude of DAC output
Repeating	Repeating above process can further achieve high-precision compensation effects

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Bingtao Cai, Wentao Huang, Limin Xiao, Xiaobao Chen. Linear Frequency Modulation of Acousto‐Optic Modulator for Heterodyne Demodulation of Interferometric Fiber Optic Sensing Arrays[J]. Chinese Journal of Lasers, 2025, 52(10): 1006004

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Paper Information

Category: Fiber optics and optical communication

Received: Nov. 10, 2024

Accepted: Jan. 23, 2025

Published Online: May. 17, 2025

The Author Email: Limin Xiao (liminxiao@fudan.edu.cn), Xiaobao Chen (stlcxb@foxmail.com)

DOI:10.3788/CJL241389

CSTR:32183.14.CJL241389

Topics

laser devices and laser physics

Lasers and Laser Optics

Laser physics

laser manufacturing

Instrumentation, Measurement and Metrology

Table 1. Frequency ranges of 8-group frequency modulation signals (Δf=50 kHz)

Table 1. Frequency ranges of 8-group frequency modulation signals (Δf=50 kHz)

Table 2. Difference carrier frequencies generated with different numbers of modulated pulses

Table 2. Difference carrier frequencies generated with different numbers of modulated pulses

Table 3. Frequency ranges of 4 groups of swept signals (Δf=100 kHz)

Table 3. Frequency ranges of 4 groups of swept signals (Δf=100 kHz)

Table 4. Generation process of pre-compensation coefficient for DAC

Table 4. Generation process of pre-compensation coefficient for DAC

Table 1. Frequency ranges of 8-group frequency modulation signals ( $Δ f$ =50 kHz)

Table 1. Frequency ranges of 8-group frequency modulation signals ( $Δ f$ =50 kHz)

Table 3. Frequency ranges of 4 groups of swept signals ( $Δ f$ =100 kHz)

Table 3. Frequency ranges of 4 groups of swept signals ( $Δ f$ =100 kHz)