Puniu Technology's HiFi-DAS device is a high-performance DAS system developed based on the TGD-OFDR optical reflectometer technology proposed by the fiber sensing research team at Shanghai Jiao Tong University. Through innovative techniques, it has overcome challenges related to spatial resolution and coherent fading noise.

HiFi-DAS system is based on the principle of coherent Rayleigh scattering, utilizing the sensitivity of optical fiber to sound (vibration). When external vibration acts on the sensing fiber, due to the photoelastic effect, the refractive index and length of the fiber will undergo slight changes, resulting in phase changes of the transmitted signal, which in turn causes changes in light intensity. When pipeline leakage (vibration) occurs and causes phase changes, it will lead to changes in signal intensity at that point. By detecting the intensity changes (differential signal) of the signal before and after vibration, vibration events can be detected.

The system consists of a laser, optical modulator, optical amplifier, coherent receiver, and data acquisition and processing components. The light generated by the laser is modulated into broadband frequency-swept optical pulse signals that enter the sensing fiber, and the backward Rayleigh scattering light signal of the optical pulse is detected using coherent detection method. Through data processing, the location and waveform information of the vibration can be obtained.

The problems existing in the distributed optical fiber acoustic sensing system based on Φ-OTDR have been solved.

• The spatial resolution of Φ-OTDR is determined by the pulse width of the probe optical pulse. The shorter the pulse width, the higher the spatial resolution, and vice versa. However, when the peak power of the probe optical pulse is limited, the shorter the pulse width, the lower the average power, which will affect the other three indicators. This is because in Φ-OTDR, the external vibration signal is obtained by demodulating the phase of the Rayleigh backscattering signal (RBS). Therefore, the signal-to-noise ratio of the phase term directly determines the strain sensitivity and sensing distance. The phase term is calculated from the intensity term of RBS, and the detection accuracy of the phase is determined by the signal-to-noise ratio of the intensity term. The signal-to-noise ratio of the RBS intensity term is determined by the energy of the probe optical pulse. Therefore, in Φ-OTDR, improving the spatial resolution will inevitably reduce the strain sensitivity and sensing distance.
• According to the Nyquist sampling theorem, the response bandwidth is determined by the effective transmission frequency of the probe optical pulse. Because the signal-to-noise ratio of the RBS intensity term in Φ-OTDR is very poor, it is necessary to improve the signal-to-noise ratio by averaging multiple transmissions of the probe optical pulse, which will multiply reduce the effective transmission frequency and thus reduce the response bandwidth of the system. Therefore, the spatial resolution and response bandwidth of Φ-OTDR are also contradictory.

Four key performance indicators of distributed optical fiber acoustic sensing system based on TGD-OFDR have been comprehensively improved.

• The probe light pulse in TGD-OFDR is a broadband frequency-sweeping light pulse, meaning the optical frequency of the light pulse changes linearly with time. Before extracting the RBS phase term, the RBS signal is first compressed into a single-frequency pulse signal using a matched filtering algorithm. The pulse width of this single-frequency pulse signal depends on the frequency-sweeping range of the sweeping signal. Therefore, the spatial resolution of TGD-OFDR is independent of the pulse width of the probe light pulse. By emitting a probe light pulse with a large frequency-sweeping range and long duration, high spatial resolution, strain sensitivity, response bandwidth, and long sensing distance can be achieved simultaneously, resulting in a comprehensive improvement of these four important performance indicators.

Eliminating measurement "dead zones" and improving system reliability.

• "Dead zones" refer to areas on the sensing fiber where the signal-to-noise ratio of RBS signals is extremely poor due to optical interference and polarization effects, severely affecting strain sensitivity in these areas and even causing loss of sensing capability. These areas are called "dead zones". The pulse frequency division method and phase rotation averaging method we proposed, combined with polarization diversity receivers, effectively solve the sensing "dead zone" problem caused by optical interference and polarization effects, enabling high-sensitivity, low-noise detection of vibrations and sound waves at any position along the sensing fiber.

• Good linear signal response: The demodulated signal strength is directly proportional to the disturbance signal.
• Low Noise Level: Liquid-cooled design, measured noise level lower than general high-performance laptops;
• Powerful Computing Capability: Built-in SPU V2.0 high-speed signal processing unit, providing superior computing power;
• Internationally Leading Reflectometer Solution: TGD-OFDR technical solution, enabling sound detection and high-fidelity restoration at any point on ordinary optical cables;
• Flexible Architecture: The instrument adopts quick-plug liquid cooling design and excellent dust-proof and shock-absorbing technology, suitable for various operating environments.