Optical modulation format identification is critical in the next generation of heterogeneous and reconfigurable optical networks. Here we present a blind modulation format identification method by applying fast density-peak-based pattern recognition in the autonomous receiver of elastic optical networks. In this paper, we find different modulation format types show different energy level features which can be used as a metric to identify these modulation formats in 2D Stokes plane. The proposed method does not require training symbols, and is insensitive to carrier phase noise, frequency offset as well as polarization mixing. The effectiveness is verified via numerical simulations and experiments with PDM-BPSK, PDM-QPSK, PDM-8PSK, PDM-16PSK, PDM-8QAM, PDM-16QAM. The results show that high identification accuracy can be realized using our proposed method over wide optical signal-to-noise ratio (OSNR) ranges. Meanwhile, we also discuss the influence of the residual CD, PMD, PDL impairments to our proposed method. We believe that the simple and flexible identification method would certainly bring great convenience to the future optical networks.

Phase-sensitive optical time domain reflectometry (Ф-OTDR) attracts much attention due to its capability of telling the type and position of an intrusion simultaneously. In recent decades, coherent Ф-OTDR has been demonstrated to realize long-distance detection. For coherent Ф-OTDR, there are three typical demodulation schemes in the reported studies. However, they still cannot realize real-time monitoring to satisfy practical demands. A simple and effective demodulation method based on self-mixing has been put forward to demodulate the beat signal in coherent Ф-OTDR. It not only saves a local electrical oscillator and frequency locked loop, but also demodulates the beat signal without residual frequency. Several vibrations with different frequency were separately applied at the same location of a 42.5 km fiber. The spatial resolution of 10 m and frequency response range from 8 Hz to 980 Hz have been achieved. The precise location with signal-to-noise ratio of 21.4 dB and broadband measurement demonstrate the self-mixing scheme can demodulate the coherent Ф-OTDR signal effectively.

A photonic method to estimate the angle-of-arrival (AOA) of microwave signals based on optical phase scanning is proposed and experimentally demonstrated. At remote antenna unit (RAU), one received high-frequency microwave signal is directly applied to a phase modulator (PM), and another received high-frequency microwave signal coupled with a low-frequency large-voltage sawtooth-wave signal is applied to another PM. The sawtooth-wave signal is used to scan the phase of the optical sideband from 0 to 2π. After transmission over a segment of fiber link, the AOA parameter can be estimated by processing the received low-frequency electrical signals at central office (CO). Such scheme can be applicable to either single-tone or wideband microwave signals. Experimental results show that the AOA measurement errors are less than 2.27° and 4.45° for a single-tone signal at 10 GHz and a 2-GHz broadband signal with the center frequency of 18 GHz, respectively.

An optical fiber temperature and torsion sensor has been proposed by employing the Lyot-Sagnac interferometer, which was composed by inserting two sections of high-birefringence (HiBi) fiber into the Sagnac loop. The two inserted sections of HiBi fiber have different functions; while one section acts as the temperature sensitive region, the other can be used as reference fiber. The temperature and twist sensor based on the proposed interferometer structure have been experimentally demonstrated. The experimental results show that the envelope of the output spectrum will shift with the temperature evolution. The temperature sensitivity is calculated to be −17.99 nm/°C, which is enlarged over 12 times compared to that of the single Sagnac interferometer. Additionally, the fringe visibility of the spectrum will change due to the fiber twist, and the test results reveal that the fringe visibility and twist angle perfectly conform to a Sine relationship over a 360° twist angle. Consequently, simultaneous torsion and temperature measurement could be realized by detecting the envelope shift and fringe visibility of the spectrum.

A chaos-based communication scheme allowing for multiaccess message transmission is proposed. In this scheme, two mutually coupled semiconductor lasers (MCSLs) are identically driven by an external cavity semiconductor laser (ECSL). The MCSLs isochronally synchronize with each other through symmetric operation, and they laggardly synchronize to the ECSL through injection-locking. When external modulation is adopted, strong chaos pass filtering effects that are not restricted by the relaxation oscillation frequencies of the MCSLs are observed, which enables us to achieve high bit-rate multiaccess chaos communication. Moreover, the security can be improved by making use of the multiaccess ability. This scheme can be used as a rudiment of chaos communication networks.

In strain measurement applications, the matched fiber Bragg gratings (FBG) method is generally used to reduce temperature dependence effects. The FBG parameters have to be designed to meet the requirements by the particular application. The bandwidth and slope of the FBG has to be balanced well, according to the measurement range, accuracy and sensitivity. A sensitivity enhanced strain demodulation method without sacrificing the measurement range for FBG sensing systems is proposed and demonstrated utilizing a pair of reference FBGs. One of the reference FBGs and the sensing FBG have almost the same Bragg wavelength, while the other reference FBGs has a Bragg wavelength offset relative to the sensing FBG. Reflected optical signals from the sensing FBG pass through two reference FBGs, and subtract from each other after the detection. Doubled strain measurement sensitivity is obtained by static rail load experiments compared to the general matched grating approach, and further verified in dynamic load experiments. Experimental results indicate that such a method could be used for real-time rail strain monitoring applications.