Phase Generated Carrier Technique Research Articles

An improved high stability and low distortion phase generated carrier demodulation algorithm for phase-sensitive optical time-domain reflectometers

The phase generated carrier (PGC) demodulation technique for phase-sensitive optical time-domain reflectometry (Ф-OTDR) has significant potential in applications involving distributed optical fiber sensing and imaging. An improved PGC demodulation algorithm for a Ф-OTDR combined with an unbalanced Michelson interferometer system is presented in this letter. This modified PGC technique uses the one output signal as a fundamental carrier frequency signal with mathematical transformations, and another output is the modulated signal, which enable the two signals to be output synchronously from the interferometer. Theoretical simulations and experiments demonstrate that the linear and nonlinear distortion caused by phase modulation depth and carrier phase delay are well suppressed by the proposed algorithm with high stability and low distortion. The signal-to-noise-and-distortion ratio of sensors using the proposed method in the same conditions achieve gains of 12.98 dB, 30.82 dB and 6.93 dB over PGC-Arctan, PGC-differential-and-cross-multiplying and PGC-single-path differential division method, respectively. Experimental verification shows that the proposed demodulation system can exactly recover the original signals of multiple vibration positions simultaneously, and the system employing the ameliorated PGC demodulation algorithm has the noise level of about 1.83 × 10−4 rad (√Hz)−1 and a large dynamic range of 65.72 dB @ 800 Hz, which provides a new choice for distributed optical fiber sensing technology.

A long-haul and high-accuracy fiber length measurement technology based on Mach–Zehnder and Sagnac hybrid interferometer

In this paper, an optical fiber length measurement system based on phase-modulated pulse time of flight method is proposed. The fiber length is calculated by measuring the flight time of the phase-modulated pulse in the fiber under test. The measurement system is based on the interference structure of Mach–Zehnder hybrid Sagnac to obtain stable interference effects. To improve the signal-to-noise ratio of the system, the phase-generated carrier technique is utilized to effectively eliminate the parasitic Rayleigh scattering noise along the optical fiber. Finally, a balance of long measurement distance and high measurement precision is achieved in the system, and a measurement resolution of 0.2 m is realized within the measurement range of 100 km.

Distortion-corrected phase demodulation using phase-generated carrier with multitone mixing.

We present a novel phase generated carrier (PGC) demodulation technique for homodyne interferometers which is robust to modulation depth variations and source intensity fluctuations. By digitally mixing the waveform with a multitone synthetic function (a linear combination of harmonics of the modulating signal), distortion can become negligible even in presence of large variations of the modulation depth. The technique only requires two mixers and can also provide the DC component of the phase in real time, without needing any previously recorded data or ellipse-fitting algorithms. We validate the technique with simulated waveforms and with experimental data from a wavelength metering experiment using an integrated unbalanced interferometer on-chip, showing that the technique corrects distortion without increasing the noise with respect to the standard PGC technique.

Modified phase-generated carrier demodulation compensated for the propagation delay of the fiber

In this paper, a modified phase generated carrier (PGC) demodulation technique based on Mach–Zehnder interferometer (MZI) is proposed, the related simulation and experiment results show that this technique can restrain the influence of the time delay between carrier signals and disturbance signals. Combined with 3×3 coupler, the modified PGC technique uses the two of three output signals as fundamental carrier frequency signal and second-harmonic carrier frequency signal by mathematical transformations, and another output is modulated signal, which enable the three signals output simultaneously from the interferometer. Meanwhile, in order to raise further the signal to noise ratio (SNR), the influences of differential-and-cross-multiplying (DCM) and Arctangent (ATAN) between the modified technique and the traditional technique, time delay, and laser sources with different line-width on demodulation effects are discussed. We believe this work will provide some new methods for the technological research in the field of fiber optical communication.

Silicon Photonic Biochemical Sensor on Chip Based on Interferometry and Phase-Generated-Carrier Demodulation

Integrated biochemical sensors based on Mach-Zehnder interferometers (MZIs) rely on the evanescent field detection principle to monitor the phase shift induced by a refractive index change on the surface of the sensing arm, providing a high sensitivity thanks to the long interaction length with the analyte. This paper presents an integrated refractive index and biochemical sensor based on a pair of balanced MZIs realized on silicon-on-insulator. The device includes a thermal phase modulator in one of the branches of each MZI to extract univocally the induced phase change by applying active phase detection based on the phase generated carrier technique. The direct modulation of the MZI results in a simple configuration of the sensor, only requiring a fixed wavelength laser and a photodetector, enabling the possibility of full monolithic integration. The results of refractive index measurements show a detection limit down to 4.88 × 10–7 RIU. Additionally, an immunoassay reports the binding of anti-bovine serum albumin (BSA) to BSA, with anti-BSA concentrations down to 33.33 nM.

Interrogation of Extrinsic Fabry–Perot Sensors Using Path-Matched Differential Interferometry and Phase Generated Carrier Technique

Fiber optic extrinsic Fabry-Perot interferometer (EFPI) sensors utilizing the state-of-the-art MEMS technology have been intensively studied on sensor fabrication for various applications, whereas the signal interrogation technique is still inadequate for some particular applications especially those involving dynamic sensing with high frequency. In this paper, we proposed a white light path-matched differential interferometer system utilizing phase generated carrier (PGC) demodulation method for dynamic EFPI sensors interrogation. A fiber Michelson interferometer (MI) is cascaded with the EFPI sensor as a readout interferometer. One arm of the MI contains a step-motor-assisted movable mirror-collimator pair to realize exactly path matching, and another arm is wound on a piezoelectric transducer ring to introduce the carrier signal for PGC demodulation. The general design principles of the system are presented in detail. Experimental results shown that the sensing signal can be correctly recovered with low distortion. The spectrum level of the phase noise is as low as -103 dB re. rad/√Hz at 1 kHz. The presented interrogation scheme may find promising applications in lots of dynamic EFPI sensing fields, such as acoustic and vibration sensing etc.

Proposal for eliminating the external disturbance via digital PGC technique in a multiplexed fiber interferometer measurement system

We demonstrate a multiplexed fiber interferometer measurement system for eliminating the external disturbance using the digital phase generated carrier (PGC) demodulation technique. By applying two fiber Bragg gratings (FBG) and two fiber interferometers that share the reference arm and part of the sensing arm in this measurement system, we find that the system can be used for detecting the useful signal and the external disturbances is reduced by 26dB. Thus, our work may provide some new possibilities for technological applications in vibration measurement.

Stimulated Brillouin scattering-induced phase noise in an interferometric fiber sensing system

Stimulated Brillouin scattering-induced phase noise is harmful to interferometric fiber sensing systems. The localized fluctuating model is used to study the intensity noise caused by the stimulated Brillouin scattering in a single-mode fiber. The phase noise structure is analyzed for an interferometric fiber sensing system, and an unbalanced Michelson interferometer with an optical path difference of 1 m, as well as the phase-generated carrier technique, is used to measure the phase noise. It is found that the phase noise is small when the input power is below the stimulated Brillouin scattering threshold, increases dramatically at first and then gradually becomes flat when the input power is above the threshold, which is similar to the variation in relative intensity noise. It can be inferred that the increase in phase noise is mainly due to the broadening of the laser linewidth caused by stimulated Brillouin scattering, which is verified through linewidth measurements in the absence and presence of the stimulated Brillouin scattering.

用于探测极低频信号的光纤传感器相位生成载波解调方法

A high resolution ultra low frequency phase generated carrier(PGC) demodulation technique for interferometric fiber sensors is proposed. The differential cross multiplication(DCM) algorithm and the Arctangent algorithm of PGC technique are analyzed theoretically and simulated by computer for ultra low frequency demodulation. And the results show that an unnecessary random direct current(DC) drift is induced in the recovered signal of DCM-PGC, but it doesn't exit in that of Arctangent-PGC. To demonstrate the conclusion, an optical fiber interferometer-based ultra low frequency sensing system is set up, and the comparable experiments of DCM-PGC and Arctangent-PGC are carried out. The experimental results show that only Arctangent-PGC can be used for ultra low frequency demodulation, for it avoids the problem of DC drift as DCM-PGC. At last the ultra low frequency demodulation system is achieved by Arctangent-PGC, and the testing results show that the system has the lowest frequency of0.01 Hz, a minimum detectable phase shift of4×10-4 rad/√Hz, a dynamic range of110 dB@1 Hz and a linearity of99.99%.

Improvement on phase generated carrier technique for passive demodulation of miniature interferometric sensors

Theoretical and experimental results show the errors inherent in the passive “phase generated carrier, differentiate-cross-multiply” technique for interferometric sensors. A better choice of the value of the laser is suggested giving significant improvement in this error.

Multiplexing of interferometric sensors using phase-generated carrier techniques

The multiplexing of four interferometric sensor outputs on a single optical fibre using a phase-generated carrier technique is demonstrated. Low crosstalk ( – 60 dB) and high performance (minimum detectable phase shifts of 2–18 μrad) were achieved with this configuration. This technique is expandable to large numbers of sensors.

Multiplexing of interferometric sensors using phase carrier techniques

This paper demonstrates the multiplexing of fiber-optic interferometric sensors using a CW phase generated carrier technique. The technique employs modulated diode laser sources at different carrier frequencies, nearly balanced interferometers (∼4-cm path difference), and phase generated carrier demultiplexing demodulation. This approach leads to a simple all-passive sensor array which has intrinsically low crosstalk. The system is analyzed in terms of shot noise performance and crosstalk. An experimental all optical implementation of a four sensor array was demonstrated; both the single sensor and multisensor arrays were limited by the laser phase noise to a sensitivity of \sim 18 \mu rad/ \sqrt{Hz} . Crosstalk between individual channels was better than -60 dB and crosstalk between three sensors and the test sensor was better than -55 dB. In the absence of laser phase noise the demodulator/demultiplexer demonstrated \sim 2-\mu rad performance with both single sensor and four element array operation.