A fiber-optic sensing system integrating a Fabry–Perot interferometer (FPI) with an injection-locked optoelectronic oscillator (IL-OEO) is proposed for highly sensitive low-frequency magnetic field detection. The cavity length change of the FPI caused by the magnetostrictive probe is directly coupled into the OEO loop. Through injection locking, a precise mapping from magnetic field-induced frequency shifts to phase variations is realized, and the phase noise of OEO at near-carrier is greatly suppressed, enabling low-noise phase demodulation in the low-frequency range. A phase sensitivity of 21.4 mrad/μT and a magnetic field resolution of 0.97 nT/Hz 1/2 at 100 Hz are achieved, and the relationship between sensitivity and injection ratio is also experimentally investigated. The proposed system offers a promising solution for high-performance low-frequency magnetic field sensing.

An improved phase-generated carrier linear-fitting algorithm arctangent (PGC-LFA-Atan) method for signal demodulation of fiber interferometric sensors under small modulation depth is proposed and demonstrated. By utilizing the random sample consensus algorithm in the linear fitting process and subsequently using a nonlinear fitting curve, the distortion in the demodulated signal caused by modulation depth variation and carrier phase delay under a small modulation depth is greatly suppressed. Experimental results show that the total harmonic distortion of the demodulated signal is lower than 0.4 % and the signal-to-noise and distortion ratio is higher than 48 dB in the modulation range between 0.1 and 0.5 rad. The demodulated phase resolution is 1.78 x 10-5 rad/Hz1/2 @ 100 Hz and the dynamic range reaches 117.12 dB @ 100 Hz when the modulation depth is as low as 0.1 rad.

A high-speed demodulation scheme of a fiber-optic vibration sensor based on cascaded Mach-Zehnder interferometers (MZIs) is proposed and demonstrated. A two-stage cascaded MZIs structure of four-channel outputs with their center wavelengths precisely aligned is implemented for orthogonally demultiplexing the spectral signal of the interferometric vibration sensor. In the digital domain, an orthogonal demodulation algorithm is developed for phase demodulation of fiber-optic interferometric vibration, and its demodulation speed is only limited by the digital sampling rate. In the experiment, a minimum detectable phase shift of 3.96×10-5rad/Hz at 100 Hz and 4.3×10-6rad/Hz at 100 kHz is achieved. Compared to traditional spectral demodulation algorithms, the proposed scheme offers advantages in terms of high demodulation speed, wide bandwidth operation, and ease of implementation, making it highly suitable for industrial and defense applications that demand both high reliability and cost-effectiveness.

A novel signal synthesis system based on optical delay synchronization is proposed to address the requirement of transmitting multiple signals through a single channel. Dual-channel baseband signals are synthesized to an output signal with doubled bit rate, and this basic structure can be cascaded for multi-channel signal synthesis. The synthesized signal is capable of accurately recovering the original multi-channel signals after optical or wireless transmission. The bit error rate (BER) of the transmitted data is evaluated, with the relative error amplitude remaining below 10%. This structure demonstrates the scalability of optical delay synchronization synthesis, providing a solution for multi-channel signal transmission and processing.

A novel fiber Fabry-Perot interferometer (FPI)-based sensing system for dynamic magnetic field detection is proposed and experimentally demonstrated. The FPI is composed of a reflector and a cleaved end face of a single mode fiber, and is fixed on a giant magnetostrictive rod. The significant length change of the FPI cavity caused by external dynamic magnetic field is interrogated by a microwave photonic filter (MPF) system, in which the phase shift of a single-frequency electrical signal within the passband of the MPF is utilized and recorded. Experimental results show that the magnetic field sensitivity and minimum detectable magnetic field reach up to 4.13 x 10(-4) rad/mu T and 1.36 mu T/Hz(1/2) respectively.

A novel coupled optoelectronic oscillator (COEO) with a very-low time jitter and a high side-mode suppression ratio (SMSR) based on optoelectronic co-injection locking (OEIL) is proposed. The phase noise of the COEO at the far carrier is greatly suppressed through the proposed optical injection phase locking of an active mode locked laser (AMLL) with a high-stable and phased-locked distributed feedback laser. The phase noise at the near carrier can be likewise suppressed by electrical injection locking of a radio frequency (RF) source while a high electrical injection ratio will deteriorate the phase noise at far carrier. The phase noise at the near carrier and the far carrier is balanced by locating the optimal electrical injection ratio so as the time jitter of the COEO is minimized. The experiment demonstrates that the OEIL-COEO exhibits an excellent phase noise performance of -135.1 dBc/Hz @ 10 kHz and -157.6 dBc/Hz @ 100 kHz with a center frequency of 10.66 GHz. The optimal electrical injection ratio is experimentally measured to be about -30 dB, under which the calculated root-mean-square (RMS) time jitter reaches 4.3 fs within the offset frequency from 100 Hz to 1 MHz. A high SMSR of 106 dB is obtained compared with that of 52 dB at the free-running state. The Allan deviation converges to 1.2x10(-15) at the average time of 1000 s, indicating the long-term frequency stability.

A fiber Fabry-P & eacute;rot interferometer (FPI)-based sensing system for low-frequency weak magnetic field detection is proposed and experimentally demonstrated. Within the sensor head, a mechanic transform structure is designed and fabricated to amplify the displacement of a magnetostrictive TbDyFe rod under a proper magnetic bias, resulting in significant cavity length change of the FPI with external alternating magnetic field. The dynamic interference spectrum of the FPI is acquired by a spectrometer for high-speed demodulation. A modified Hilbert transform combined with a cumulative average method is performed to recover the signal of magnetic field with suppressed noise. A magnetic field sensitivity of 2.69x10(-4) rad/ mu T and a minimum detectable magnetic field of up to 12.60 nT/Hz (1/2 )at 60 Hz are achieved. The proposed fiber magnetic field sensing system exhibits good linearity and compactness, high sensitivity and resolution, and flat frequency response under 1 kHz; hence, it has great potential in the field of weak magnetic field sensing

Photonic millimeter-wave (mm-wave) signal generation with a wide tuning range based on self-injection locking and Pound-Drever-Hall is proposed. The phase noise of generated heterodyne mm-wave by light beating of two distributed feedback lasers (DFB) is greatly suppressed when two laser lights are frequency-locked to different resonant peaks of a super stable Fabry-P & eacute;rot etalon. Frequency tuning of the mm-wave signal is achieved by simply varying the temperature of one DFB laser so that its light frequency is locked to the tracking resonant modes of the etalon. In the experiment, the generated mm-wave signal tuned from 30 GHz to 87.5 GHz with an interval of 2.5 GHz is observed to be of high flatness less than 0.5 dB. The single-sideband phase noise of the generated mm-wave is proven to be nearly irrelevant to the operating frequency and is measured to be -110 dBc/Hz @ 100 kHz, which is 10 dB lower than that of a commercial 60 GHz analog signal generator. The Allan deviation of generated 60 GHz mm-wave signal reaches 5.1x10(-10) within the average time of 100 s, indicating a long-term frequency stability.

A cost-effective linewidth compressing method for distributed feedback (DFB) laser with a high ratio based on self-injection locking (SIL) and Pound-Drever-Hall (PDH) is proposed. The combination of SIL and PDH helps to reduce the phase noise of the DFB laser, thus a high linewidth compression ratio can be achieved. The experiment results show the single sideband (SSB) phase noise of a commercial DFB laser has been reduced by more than 75-dB in the frequency range from 100-Hz to 10-kHz. The linewidth is narrowed to be around 140-Hz compared with the free-running state of 2.3-MHz, with a high compression ratio of over $1.6\times 10 ^{4}$ . The in-loop Allan deviation (ADEV) of the DFB laser is measured to be $5.4\times 10 ^{-11}$ within the average time of 100 s, indicating the long-term frequency stability.

A finely frequency tunable coupled optoelectronic oscillator (COEO) based on injection locking and phase locked loop is proposed and demonstrated. By investigating a dynamic relation between the frequency locking range and injection locking ratio, an optimum injection locking ratio with sufficient locking range is obtained so as finely frequency tracking and locking with high stability is achieved by tuning the frequency of the injected signal and controlling an optical tunable delay line (OTDL). Through optimizing the injection ratio, a trade-off between the suppression of the near-carrier phase noise and the excellent far-carrier phase noise is realized. In the experiment, a high quality COEO with a tuning range of 1.76 MHz and a precise tuning step of 10 Hz is demonstrated. The measured sidemode suppression ratio (SMSR) at 9.95554 GHz reaches 78.2 dB, and a frequency drift of better than 1 ppb during a 1-hour is observed. The phase noise at 10 kHz offset is measured to be −130.04 dBc/Hz, and the Allan deviation (ADEV) reaches 1.39 × 10 −13 at averaged time of 100 s.

A novel photonic-based tunable broadband signal generator for millimeter wave (mm-wave) signals is demonstrated. An optical frequency comb (OFC) is employed for optical injection locking (OIL) of two slave lasers with different wavelengths. Due to the high gain filtering function provided by the OIL, two salve lasers within the locking range can be tuned and locked by the selected comb lines of the OFC. In the experiment, a 25-line flattened OFC is generated by cascading Mach-Zehnder modulators (MZMs) with a mode spacing of 2 GHz. The locking range of two slave lasers is measured to be 1.1 GHz as injection ratio of -40 dB, consistent with the simulation. The spur suppression ratios (SSRs) are measured to be 60 dB in a span of 10 MHz. The RF power flatness of generated broadband tunable mm-wave signal is tested to be within 3.84 dB for frequency 2 GHz to 48 GHz.

A microwave photonics‐based channelized receiver for broadband vector signals is proposed and experimentally demonstrated. A 4‐line optical frequency comb (OFC) generated by a dual‐parallel Mach‐Zehnder modulator (DPMZM) is used as local oscillator (LO) signal in the in‐phase/quadrature (I/Q) receiver for coherently down‐converting the broadband signal into different channelized bands. By properly setting the frequency difference between the OFC comb line and the broadband signal, either homodyne or heterodyne detection of I/Q receiver is realized. To compensate the amplitude difference and phase difference of adjacent channel signals, an overlap ratio of adjacent slices is introduced for channel equalization and signal reconstruction. The simulated result shows the error vector magnitude of 4‐channel channelization for a reconstructed 8 GBaud quadrature phase shift keying (QPSK) signal is very close to the original one. In the experiment, 2‐channel channelization for a 2 GBaud QPSK is realized and the whole signal is reconstructed successfully. The experimental result also proves the quality improvement of reconstructed signal with an increase of channel overlap ratio.