Mingjiang Zhang

Precise Fault Location in WDM-PON by Utilizing Wavelength Tunable Chaotic Laser

We propose a method to locate precisely faults in wavelength-division-multiplexing (WDM) passive optical network (PON) by using a wavelength tunable chaotic laser. The chaotic laser consists of a multiple-longitudinal-mode Fabry-Perot (FP) laser diode whose modes match the channels of WDM-PON, and an optical feedback loop including a filter. The loop feeds a proportion of light of one mode that passes through the filter back into laser cavity to generate chaotic light. By adjusting the filter frequency, we can tune the wavelength of the chaotic light, and diagnose the corresponding branch of WDM-PON. We demonstrate a proof-of-concept experiment for detection of three ITU channels. Fault location is realized by correlating the back-reflected light with its time-delayed duplicate. The results show that spatial resolution of 2 cm and dynamic range of about 20.8dB can be achieved. In addition, we have experimentally studied the effects of the strength level and wavelength mismatching of the feedback light on the chaotic output of the FP laser.

Can Fixed Time Delay Signature be Concealed in Chaotic Semiconductor Laser With Optical Feedback

External-cavity lasers are usually used for chaos encryption in optical chaos-based communication systems. The external-cavity round-trip time (the time delay in the laser dynamics) is often regarded as an additional key to encode messages, which is a critical security parameter. The feasibility of identifying the time delay has been a crucial issue in chaotic optical communication. Some researchers propose that the time delay can be hidden by modulating the value of feedback strength or increasing the number of feedback cavities. In this paper, we experimentally and numerically demonstrate that the time delay signatures cannot be concealed in optical feedback semiconductor lasers. Whether single or double optical feedback, the time delay signatures can all be identified by the power spectrum analysis method. Furthermore, adjusting the feedback strength, the pumping current and the time-delay value, we find that the extraction of the time delay signatures still cannot be influenced.

A robust random number generator based on differential comparison of chaotic laser signals

We experimentally realize a robust real-time random number generator by differentially comparing the signal from a chaotic semiconductor laser and its delayed signal through a 1-bit analog-to-digital converter. The probability density distribution of the output chaotic signal based on the differential comparison method possesses an extremely small coefficient of Pearsons median skewness (1.5 × 10⁻⁶), which can yield a balanced random sequence much easily than the previously reported method that compares the signal from the chaotic laser with a certain threshold value. Moveover, we experimently demonstrate that our method can stably generate good random numbers at rates of 1.44 Gbit/s with excellent immunity from external perturbations while the previously reported method fails.

Generation of Broadband Chaotic Laser Using Dual-Wavelength Optically Injected Fabry–Pérot Laser Diode With Optical Feedback

Chaotic laser with a flat power spectrum up to 32.3 GHz has been generated by using a dual-wavelength optically injected Fabry-Pérot laser diode with optical feedback. The Fabry-Pérot laser diode with fiber ring cavity is utilized to generate the chaotic light. The bandwidth of the chaotic laser, due to dual-wavelength optical injection, is enhanced roughly four times as much as that of the chaotic laser without optical injection.

Generation of flat-spectrum wideband chaos by fiber ring resonator

We present a simple method to generate spectrally uniform wideband chaos by injecting chaotic laser into a fiber ring resonator. The resonator is a single-coupler ring equipped with an optical filter and amplifier, which adjust the optical field circulating in the ring. The incoherent interference of the circulating fields produces wideband chaos with uniform power spectrum density distribution. We experimentally achieved a chaotic spectrum that extends over 26.5 GHz (limited by measurement bandwidth) and fluctuates within ±1.5 dB. In addition, tuning the filter frequency can control the spectral profile so as to meet different application needs.

Photonic ultrawideband signal generator using an optically injected chaotic semiconductor laser

We propose and demonstrate a method to generate ultrawideband (UWB) signals in the optical domain based on the chaotic dynamics of an optically injected semiconductor laser with optical feedback. The chaotic-UWB pulses with a fractional bandwidth of 116% and central frequency of 6.88 GHz are experimentally generated by controlling the injection strength and frequency detuning of the chaotic laser. The spectrum of the UWB signals is in full compliance with the Federal Communications Commission spectral mask, and the experimental results are qualitatively consistent with the simulated results.

Direct generation of all-optical random numbers from optical pulse amplitude chaos

We propose and theoretically demonstrate an all-optical method for directly generating all-optical random numbers from pulse amplitude chaos produced by a mode-locked fiber ring laser. Under an appropriate pump intensity, the mode-locked laser can experience a quasi-periodic route to chaos. Such a chaos consists of a stream of pulses with a fixed repetition frequency but random intensities. In this method, we do not require sampling procedure and external triggered clocks but directly quantize the chaotic pulses stream into random number sequence via an all-optical flip-flop. Moreover, our simulation results show that the pulse amplitude chaos has no periodicity and possesses a highly symmetric distribution of amplitude. Thus, in theory, the obtained random number sequence without post-processing has a high-quality randomness verified by industry-standard statistical tests.

Photonic generation of ultrawideband pulse using semiconductor laser with optical feedback

We propose and demonstrate an approach to the generation of an ultrawideband (UWB) pulse utilizing the nonlinear dynamics of a semiconductor laser (SL). The output UWB chaotic optical pulses generated by the SL with optical feedback can be controlled when the feedback strength and driving current of the SL are tuned. Our experiment proves that the spectrum characteristics of the UWB pulses satisfy Federal Communications Commission regulations, and the experimental results are consistent with the simulated results based on the lasers rate equations.

Location of Wire Faults Using Chaotic Signal

We propose a method for testing wire fault using a chaotic signal. The fault is detected by correlating the chaotic signal back-reflected from the fault with its delayed duplicate. Centimeter-level spatial resolution and antijamming can be achieved, benefiting from the broadband and randomness of the chaotic waveform. We experimentally proved that our method can be used to locate the impedance discontinuities of several different kinds of electric cables. Preliminary experiments obtained 0.5-m resolution with a data acquisition bandwidth of 120 MHz. Further, we demonstrate the ability for testing live wires using our method.

Remote Radar Based on Chaos Generation and Radio Over Fiber

An ultrawideband (UWB) radar system for remote ranging based on microwave-photonic chaotic signal generation and fiber-optic distribution is proposed and demonstrated experimentally. In this system, an optical-feedback semiconductor laser with optical injection in the central office generates photonic UWB chaos as probing signal, and two single-mode fibers transport the optical signal to the remote antenna monitoring terminal and return the corresponding echoed signal back to the central office. In the remote antenna terminal, the photonic signal is transformed into microwave chaos 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 by modulating a laser diode. The target ranging is achieved at the central office by correlating the echoed signal with the reference signal. We experimentally realize a detection range of 8 m, for a free-space target, after 24-km remote distance, and achieve a ranging resolution of 3 cm for single target and 8 cm for double targets. In another fiber link branch with 15-km fiber transmission, we obtained the 2-cm ranging resolution for a single target.