Di Zheng

In conventional microwave photonic (MWP) interrogation based on frequency-domain response analysis, the spatial resolution of fiber Bragg grating (FBG) arrays is inherently limited by the measurement bandwidth. Interrogating spatially dense FBG arrays under narrow bandwidth conditions remains a severe bottleneck. To address this issue, this Letter introduces the estimation of signal parameters via rotational invariance techniques (ESPRIT) into the MWP interrogation scheme. By utilizing the rotational invariance property of the signal subspace to achieve super-resolution extraction of time delays, high spatial resolution FBG interrogation is realized under a narrow measurement bandwidth. In a proof-of-concept experiment, an MWP system comprising three FBG tilt sensors was constructed, with each sensor consisting of two FBGs spaced by merely ~10 cm. Experimental results demonstrate that under a highly restricted measurement bandwidth of only 600 MHz, the proposed method effectively resolves each spatially adjacent grating pair. Within a tilt measurement range of ±12°, the interrogation linearity reaches 0.9992, with a measurement root-mean-square error (RMSE) of ≤0.096°. Under identical parameters, the conventional inverse discrete Fourier transform (IDFT) method completely fails to distinguish the closely spaced FBG pairs. Ultimately, the proposed method breaks the inherent Fourier spatial resolution limit of IDFT schemes, effectively interrogating dense FBG arrays under narrow measurement bandwidths.

Intensity-modulation/direct-detection (IM/DD) optical networks require fiber-optic integrated sensing and communication (F-ISAC) schemes with low hardware complexity and negligible communication penalty. Here, we propose and experimentally demonstrate a simplified F-ISAC scheme enabled by a frequency-swept laser (FSL), which directly generates the periodically swept optical carrier and eliminates the external-modulation-based swept-carrier generation stage. With a single intensity modulator, the system supports 70-Gb/s six-level pulse amplitude modulation (PAM-6) signal transmission and distributed sensing. A sawtooth driving waveform with an inserted transition edge is used to stabilize the FSL output for accurate sensing demodulation. The proposed system retains almost the same forward transmitter and direct-detection receiver as a conventional PAM-based IM/DD link, with only an additional sensing receiver for Rayleigh backscattering detection. Compared with a conventional PAM-based IM/DD system, it increases the optimal launch power by approximately 4 dB and reduces the receiver power penalty by approximately 2 dB at the 7% hard-decision forward-error-correction (HD-FEC) threshold. A spatial resolution of 10 m and a strain sensitivity of 170 pε/√Hz are also achieved.

Ultra-short fiber Bragg gratings (US-FBGs), due to their compact structure and high spatial resolution, have significant application potential in the field of high-density multiparameter sensing networks. Moreover, the demodulation technology with multi-peak detection and good generalization characteristics is the key to promoting US-FBGs into practical engineering applications. Different from the traditional methods, in this paper, the multi-channel characteristics of array waveguide grating (AWG) are first utilized to conduct multi-point spectral sampling of the US-FBG array, and then the spectral reconstruction and multi-peak demodulation are achieved with the aid of convex optimization algorithms and peak-tracing algorithms. The proposed method is validated by demodulating a US-FBG array that combines five US-FBG sensors. The spectral reconstruction and multi-peak demodulation performance of the proposed method were systematically investigated for US-FBG arrays with identical and different bandwidths, respectively. Experimental results indicate high-accuracy spectral reconstruction with an average spectral reconstruction error of 0.13, and multi-peak wavelength demodulation performance with an average wavelength demodulation root mean square error (RMSE) of 10.7 pm under different situations. The proposed demodulation method has great potential in achieving low cost, high performance and high integration.

This study proposes a high-performance fiber Bragg grating (FBG)-based inclinometer with the capability to self-compensate for initial installation deviation. On one hand, the proposed inclinometer, featuring an improved pendulum design and equipped with a pair of FBGs, can accurately identify both the magnitude and direction of inclination, and it exhibits temperature-insensitive characteristics. On the other hand, with the help of a self-developed compact universal joint structure, the issue of the inclinometer's initial tilt angle caused by installation deviation has been effectively resolved. The experimental results demonstrate that a high degree of linearity with a sensitivity of 89.464 pm/° is achieved over a wide range from -20° to 20°. The self-developed universal joint structure is compact and can effectively compensate for initial installation deviation of up to ±5° in any tilt orientation. The developed inclinometer exhibits a high degree of repeatability and long-term stability, demonstrating great potential for practical engineering applications.

Advocating for the voices of the disabled, particularly through wearable artificial throats, has garnered significant attention recently. Such devices necessitate sensors with stretchability, high sensitivity, and excellent skin conformability. In this study, an intelligent photonic artificial throat has been developed. It features a sandwich-structured optical fiber sensor encapsulated in Dragon Skin 20, which has an elastic modulus similar to human tissue and is integrated with sensitivity-enhancing rings and fabric for enhanced wearability. With ultrafast response (response time: 10 ms, recovery time: 32 ms) and high sensitivity (1.92 μW/mN), it detects throat area vibrations and muscle contractions, accurately identifying tones in Mandarin, vowels, words, and sentences in English, achieving accurate bilingual detection. It also distinguishes animal sounds (horse neighing and cuckoo's call) and pop songs when mounted on speakers. Furthermore, the artificial throat can accurately detect subtle movements of the head and neck, and by combining nodding actions with the MORSE code, silent communication between individuals has been successfully achieved. Integrated with an advanced artificial intelligence (AI) algorithm, it recognizes tones (97.50%), vowel letters (97.00%), common words (98.00%) and sentences (96.52%), opening prospects for biomedical applications, language education, speech recognition, motion monitoring, and more.

Personalized health services are of paramount importance for the treatment and prevention of cardiorespiratory diseases, such as hypertension. The assessment of cardiorespiratory function and biometric identification (ID) is crucial for the effectiveness of such personalized health services. To effectively and accurately monitor pulse wave signals, thus achieving the assessment of cardiorespiratory function, a wearable photonic smart wristband based on an all-polymer sensing unit (All-PSU) is proposed. The smart wristband enables the assessment of cardiorespiratory function by continuously monitoring respiratory rate (RR), heart rate (HR), and blood pressure (BP). Furthermore, it can be utilized for biometric ID purposes. Through the analysis of pulse wave signals using power spectral density (PSD), accurate monitoring of RR and HR is achieved. Additionally, utilizing peak detection algorithms for feature extraction from pulse signals and subsequently employing a variety of machine learning methods, accurate BP monitoring and biometric ID have been realized. For biometric ID, the accuracy rate is 98.55%. Aiming to monitor RR, HR, BP, and ID, our solution demonstrates advantages in integration, functionality, and monitoring precision. These enhancements may contribute to the development of personalized health services aimed at the treatment and prevention of cardiorespiratory diseases.