Application Cases

Experiment Name: Tunable Laser Demodulation Experiment

Research Direction: Fiber Bragg Grating (FBG) Sensing, Tunable Lasers

Experiment Objective:
Based on the Buneman frequency estimation demodulation algorithm using a spectrometer, a demodulation program suitable for the tunable laser demodulation method was developed as a reference for comparison of demodulation results. The study analyzed issues in FBG demodulation with fast tunable laser sources, including the impact of data acquisition delays on demodulation accuracy and the influence of sampling value jumps on demodulation results. The theoretical analysis of the demodulation algorithm was validated through simulations and experiments, and a comparison between the two algorithms was conducted.

Testing Equipment:
Signal generator, ATA-105 power amplifier, laser light source, fiber Bragg grating sensors, piezoelectric ceramics, etc.

Experimental Procedure:
In this experiment, a piezoelectric ceramic (PZT) driven by an ATA-105 power amplifier was used to generate vibration signals. An FBG sensor was fixed onto the PZT using resin for the experiment. The PZT sensor primarily utilizes the axial strain applied to the fiber Bragg grating during piezoelectric ceramic vibration, causing a shift in the central wavelength to detect vibration signals. The fiber Bragg grating sensor is the core component. When the vibration platform oscillates, it drives a mass block to vibrate, and the vibration at the mass block end induces axial strain in the fiber Bragg grating attached to a steel cantilever beam, leading to a shift in the central wavelength. By detecting changes in the central wavelength, relevant parameters of the vibration itself can be obtained.

Figure 1: Hardware System of the Experiment

Experimental Setup:
The system consists of a signal generator, power amplifier, piezoelectric ceramics, grating sensors, and software. This experiment employed both adhesive-type vibration sensors and cantilever beam-type vibration sensors. The software used was the fast tunable laser source multi-point sampling FBG demodulation algorithm program developed in this study. Additionally, the second channel utilized a Buneman frequency estimation FBG demodulation program adapted for the tunable laser used in this experiment. Dual-channel demodulation was performed, and the corrected demodulation results were compared, displayed, and analyzed. The fiber Bragg grating sensor detects changes in the measured parameter by monitoring the positional shift of its spectral reflection peak. In this experiment, three FBG sensors were used for high-frequency vibration tests with piezoelectric ceramics, low-frequency vibration tests with an exciter, and acceleration tests with an exciter. The light source used was a Modulated Grating Y-branch (MG-Y) tunable semiconductor laser, which is essentially a monolithically integrated distributed Bragg reflector (DBR) laser based on the vernier tuning principle.

Figure 2: Designs of the Two Vibration Test Sensors

Experimental Results:
The variations in sampled values and demodulation results for the five-frequency vibration experiment output are as follows:

Figure 3: Spectral Reflection Sampling Values at Five Fixed Wavelengths Under 3500 mV Signal Intensity and 60 Hz Vibration Frequency

Multiple repeated vibration experiments were conducted using Sensor 1 and Sensor 2. For Sensor 1, a sampling interval of 0.096 nm was selected to sample the high-frequency vibration signal. Demodulation was performed using both the Buneman frequency estimation method and the multi-point sampling demodulation method proposed in this study. The results were then compared and processed, yielding the following figures:

Figure 4: Comparison of Demodulation Results for 7 kHz–2 V High-Frequency Vibration Experiment with Piezoelectric Ceramics at a 0.096 nm Sampling Interval

Figure 5: Comparison of Demodulation Results for 8 kHz–2 V High-Frequency Vibration Experiment with Piezoelectric Ceramics at a 0.096 nm Sampling Interval

From Figures 4 and 5, it can be observed that the amplitude of the central wavelength vibration increases with the signal intensity. The fast tunable laser source multi-point sampling fiber Bragg grating demodulation algorithm proposed in this study demonstrates a higher demodulation range and accuracy compared to the Buneman frequency estimation demodulation algorithm. Moreover, in demodulation with wide sampling intervals, this algorithm further highlights its advantages in terms of large range, high precision, and high stability.

Figure: Specifications of the ATA-100 Series Power Amplifier