A novel time-gated digital optical frequency domain reflectometry (TGD-OFDR) technique with high spatial resolution over long measurement range is proposed and experimentally demonstrated. To solve the contradictory between the tuning rate of lightwave frequency, which determines the spatial resolution, and the measurable distance range in traditional OFDR, our proposed scheme sweeps the frequency of probe beam only within a time window, while the local reference remains a frequency-stable continuous lightwave. The frequency-to-distance mapping is digitally realized with equivalent references in data domain. In demonstrational experiments, a 1.6-m spatial resolution is obtained over an entire 110-km long fiber link, proving that the phase noises of the laser source as well as environmental perturbations are well suppressed. Meanwhile, the dynamic range was 26 dB with an average of only 373 measurements. The proposed reflectometry provides a simple-structure and high-performance solution for the applications where both high spatial resolution and long distance range are required.

Time-gated digital optical frequency domain reflectometry with 1.6-m spatial resolution over entire 110-km range

We report a plasma-based strong THz source generated by using intense femtosecond laser pulses to irradiate solid targets at relativistic intensity >10^18W/cm2. Energies up to 50 microJ/sr per THz pulse is observed in the specular direction when the laser pulses are incident onto a copper foil at 67.5 degree. The source appears to be linearly polarized. The temporal, spectral properties of the THz are measured by a single shot, electro-optic sampling method with a chirped laser pulse. The THz radiation is attributed to the self-organized transient fast electron currents formed along the target surface. Such a strong THz source allows potential applications in THz nonlinear physics.

Strong terahertz radiation from relativistic laser interaction with solid density plasmas

An ultrawideband (UWB) radar system for remote ranging based onmicrowave-photonic chaotic signal generation and fiber-optic distribution is proposedand demonstrated experimentally. In this system, an optical-feedback semiconductorlaser with optical injection in the central office generates photonic UWB chaos as probingsignal, and two single-mode fibers transport the optical signal to the remote antennamonitoring terminal and return the corresponding echoed signal back to the centraloffice. In the remote antenna terminal, the photonic signal is transformed into microwavechaos by a fast photodetector and then launched to target by a transmitting antenna,and the echoed signal received by another antenna is converted into optical domain bymodulating a laser diode. The target ranging is achieved at the central office by correlat-ing the echoed signal with the reference signal. We experimentally realize a detectionrange of 8 m, for a free-space target, after 24-km remote distance, and achieve a rang-ing resolution of 3 cm for single target and 8 cm for double targets. In another fiber linkbranch with 15-km fiber transmission, we obtained the 2-cm ranging resolution for asingle target.Index Terms: Chaos, remote radar, semiconductor lasers.

Remote Radar Based on Chaos Generation and Radio Over Fiber

Terahertz (THz) radiation has attracted much attention due to its wide potential applications. Though radiation can be generated with various ways, it is still a big challenge to obtain strong tabletop sources. Plasma, with the advantage of no damage limit, is a promising medium to generate strong THz radiation. This review reports recent advances on strong THz radiation generation from low-density gases and high-density solid targets at different laser intensities.

https://iopscience.iop.org/article/10.1088/1674-1056/21/9/095203/pdf

High power terahertz pulses generated in intense laser—plasma interactions

A fiber-distributed Ultra-wideband (UWB) noise radar was achieved, which consists of a chaotic UWB noise source based on optoelectronic oscillator (OEO), a fiber-distributed transmission link, a colorless base station (BS), and a cross-correlation processing module Due to a polarization modulation based microwave photonic filter and an electrical UWB pass-band filter embedded in the feedback loop of the OEO, the power spectrum of chaotic UWB signal could be shaped and notch-filtered to avoid the spectrum-overlay-induced interference to the narrow band signals Meanwhile, the wavelength-reusing could be implemented in the BS by means of the distributed polarization modulation-to-intensity modulation conversion The experimental comparison for range finding was carried out as the chaotic UWB signal was notch-filtered at 52 GHz and 78 GHz or not Measured results indicate that space resolution with cm-level could be realized after 3-km fiber transmission thanks to the excellent self-correlation property of the UWB noise signal provided by the OEO The performance deterioration of the radar raised by the energy loss of the notch-filtered noise signal was negligible

Fiber-distributed Ultra-wideband noise radar with steerable power spectrum and colorless base station.

We propose and demonstrate a simple scheme for generating the ultrawideband (UWB) signals and reusing the wavelength for upstream service simultaneously by using a distributed polarization modulation-to-intensity modulation convertor. Through adjusting the static phase difference between transverse electric and transverse magnetic modes of the optical carrier (OC) and the angle between the polarization direction of the OC and the principal axis of the polarizers, the UWB doublet-like signals were generated. Meanwhile, the error-free transmission of the upstream signals with bit rate of 1.25 Gbit/s over 10 km fiber is achieved. The power penalty resulting from the interference of downstream signals is less than 0.3 dB.

Implementation of wavelength reusing upstream service based on distributed intensity conversion in ultrawideband-over-fiber system

The dependence of angular distributions of fast electrons generated in the interaction of p-polarized femtosecond laser pulses with foil targets on laser intensities is investigated. A novel fast electron beam along the front target surface is observed for high laser intensity. It is found that the electron acceleration along the target surface is more efficient than those in other directions.

Effective fast electron acceleration along the target surface

The invention discloses a secure communication method based on multichannel signal fragmentization transmission technology. The secure communication method comprises the following steps: dispersing communication data into small fragments in an information transmitting terminal, and then transmitting the small fragments by multiple information channels according to a certain rule; and receiving fragmentization data transmitted by the multiple channels in an information receiving terminal, and integrating the fragmentization data according to the fragmentization rule when the information is sent to obtain complete data transmitted by the transmitting terminal. The dispersion and integration rules of the fragments are determined by keys in the transmission process. By adoption of the secure communication method provided by the invention, on one hand, the difficulty of a third party to intercept complete information from the communication data can be greatly increased, so that the third party is difficult to crack signals via ultrahigh performance calculation; and on the other hand, even if enough information is intercepted by the multiple channels, complete effective data is difficult to be extracted from the encrypted fragmentization information, and it is difficult to recombine and recover the original data, therefore the security is improved.

Secure communication method based on multichannel signal fragmentization transmission technology

The invention discloses a secret communication method and device based on multi-application fragmented transmission, and the method comprises the steps: 1, enabling an information transmission end to generate to-be-transmitted application data; 2, dividing the to-be-transmitted application data into a plurality of application data segments through an encryption key; 3, enabling the plurality of application data segments to be transmitted outwards through a plurality of application channels; 4, enabling an information receiving end to respectively receive the plurality of application data segments through the plurality of corresponding application channels; 5, enabling the plurality of application data segments to be recovered into one piece of data through a decryption key. The method provided by the invention protects communication content from being stolen by a third side.

Secret communication method and device based on multi-application fragmented transmission

The invention discloses a mobile phone communication enciphering mechanism based on a multi-channel signal fragmentation transmission technology. The method comprises the following steps: at an information transmitting end, scattering service data each time into lots of information fragments, mixing the information fragments with random data and sending the mixed data out through two or more SIM cards by a mobile phone antenna; at an information receiving end, receiving these information fragments through the same number of SIM cards and integrating and restoring the original complete service data from the fragment information. The mobile phone communication enciphering mechanism adopted in the invention has the advantages that the difficulty of an eavesdropper in intercepting and capturing complete information can be increased greatly so that the eavesdropper cannot decipher signals through super high performance computing on one hand; even though the eavesdropper intercepts and captures enough information through multi-channel eavesdropping, valid data can be hardly extracted from the enciphered data fragments and the original data cannot be recombined or restored, either.

Wang Sunlong

Papers

Implementation of wavelength reusing upstream service based on distributed intensity conversion in ultrawideband-over-fiber system

Effective fast electron acceleration along the target surface

Secure communication method based on multichannel signal fragmentization transmission technology

Secret communication method and device based on multi-application fragmented transmission

Information enciphering method and device based on multi-channel signal fragmentation transmission technology