A finely tunable low-drift spurious-free single-loop optoelectronic oscillator (OEO) incorporating injection locking and time delay compensation is proposed and experimentally demonstrated. In the proposed OEO, one mode of a single-loop OEO is injection locked by a tunable electronic oscillator resulting in single-mode oscillation. A time delay compensation system is used to compensate the OEO’s loop length change caused by environmental changes, such as temperature and strain. Tuning of the oscillation frequency is realized by controlling the injection frequency and absolute loop length of the single-loop OEO. In the experiments, when the ambient temperature varies between 22°C and 31°C within 1000 s, an output signal at the frequency of 10.664 GHz with a frequency drift better than $-0.1\mathrm{ppb}$ and side-mode suppression ratio greater than 78 dB has been realized. Also, the OEO can be tuned with a precise frequency step of 10 Hz.

A high-precision and thermal-insensitive strain sensor based on two self-starting optoelectronic oscillators (OEOs) is proposed and experimentally demonstrated. Two OEOs are grouped into a cross-referencing structure by dense wavelength division multiplexing (DWDM); the two OEOs have the same characters and they are placed in the same environment. In this frequency encoded strain sensor, it converts the strain information of the single mode fiber to the frequency information, and the frequency information is acquired by measuring the intermediate frequency (IF) mixed by the two OEOs. The accumulative magnification effect at high-order resonant frequency modes makes the strain sensor achieve high sensitivity, which significantly improves the precision of the measurement strain. The cross-referencing structure of the two OEOs makes the influence of the environment, such as temperature, greatly reduced. In the experiments, measurement errors less than ± 0.3 με at a measurement range of 600 με have been realized, including a drift error due to a variation in the environment such as temperature. Furthermore, a quasi-distributed strain measurement system based on the proposed strain sensor has been designed.

Phase noise measurement of a dual-loop optoelectronic oscillator (OEO) based on a dual- photonic-delay line cross-correlation method is proposed and experimentally demonstrated. The dual-loop OEO and the phase noise measurement system are combined by sharing the transmitter of the optical link, which makes the structure of the system simpler. In part of the dual-loop OEO, the 10 km long fiber is shared by the two loops of the OEO utilizing a wavelength division multiplexing technique. Higher quality factors are obtained simultaneously by the two loops. In part of the phase noise measurement system, a lower phase noise floor is realized through a cross-correlation method. In the experiments, a signal with oscillation frequency of 10.664 GHz and a side-mode suppression ratio of 82.4 dB is generated. Its phase noise is evaluated by the proposed system and PN9000C. The measured results of the two systems are in perfect agreement. The phase noise of the signal is measured as $-122\mathrm{dBc}/\mathrm{Hz}$ at a 10 kHz frequency offset, and the phase noise floor of the 10 μs delay phase noise measurement system is $-148\mathrm{dBc}/\mathrm{Hz}$ at a 10 kHz offset at 10.6 GHz, when the number of averaged results is 100.

To improve the steering precision and angular resolution of liquid-crystal optical phased array, in this paper, we proposed a modified periodic phase controlled method to realize a continuous scanning with a constant angular resolution of less than 20 μrad, meanwhile, its precision is less than 5 μrad (rms). Also, another method we proposed is called subaperture coherence that can realize even better angular resolution less than 5 μrad, which is the limitation of our measurement instrument.

Non-Hermitian photonics based on parity-time (PT) symmetry has been considered an effective solution to achieve mode selection for optical or microwave single-mode oscillation. A PT-symmetric system is usually implemented using two mutually coupled elements with identical geometry or a single element based on precise longitudinal refractive index modulation. In this study, we propose a novel scheme to achieve PT symmetry based on polarization mode manipulation in a single optical loop. By controlling the polarization states of two light waves that are propagating along the clockwise (CW) and counter-clockwise (CCW) directions in the single optical loop, two equivalent mutually-coupled loops with identical geometry and a balanced gain and loss are formed. Based on this concept, a wavelength-tunable single-mode fiber laser with a sub-kHz linewidth is realized. The tunability is achieved by thermally tuning the wavelength of an integrated microdisk resonator (MDR) incorporated in the optical loop. Experimental results show that a continuously tunable single-mode laser with a sub-kHz linewidth of 640 Hz and a wavelength tuning range from 1552.953 to 1554.147 nm is realized. The key advantages of using a single optical loop to implement PT symmetry include greatly simplified implementation and highly improved stability. The demonstration opens new avenues to implement high-performance PT-symmetric systems for applications in photonic and microwave photonic systems.

A frequency-modulated continuous-wave (FMCW) generator with an ultra-large time-bandwidth product (TBWP) is crucial in modern radar systems. Herein we propose and experimentally demonstrate a programmable FMCW generator with an ultra-large TBWP based on two three-electrode distributed Bragg reflector (DBR) laser diodes (LDs) and one photodetector (PD). Thanks to the rapid response of the refractive index to the injection current in the passive phase control section, which is caused by the free-carrier plasma effect, the three-electrode DBR LD takes advantage of programmable and ultra-fast wavelength tuning. In the proposed FMCW generator, a programmable current source injects one three-electrode DBR LD to generate a broadband frequency-chirped optical signal. A constant current source injects the other one to perform a stable optical carrier. By beating the frequency-chirped optical signal and the optical carrier at the PD, a programmable FMCW is generated. Experimental results show that an ultra-wideband FMCW generator with full reconfigurability in modulation type, bandwidth, center frequency, chirp rate, and temporal duration is realized. A chirp rate over 10GHz/μs and a TBWP up to 2×10 ⁷ are experimentally demonstrated. Thanks to the monolithic integration of the critical devices, including two three-electrode DBR LDs and one PD, the demonstration promises breakthroughs in small-size and high-performance FMCW generators, facilitating applications in autonomous vehicles and space exploration systems.