Shuiying Xiang

Microwave Generation With Photonic Frequency Sextupling Based on Cascaded Modulators

A novel scheme to optically generate a microwave signal with frequency sextupling is proposed. The proposed scheme is based on cascading an intensity modulator (IM) and a dual-parallel Mach-Zehnder modulator (DPMZM), without any optical or electrical filter. The low frequency local oscillator signal is divided into two paths, with one path driving the IM at the minimum transmission point and the other path driving the upper arm of the DPMZM. By controlling the three dc biases of the DPMZM, the third-order sidebands are generated, with other sidebands well suppressed. A 20-dB electrical spurious suppression ratio is demonstrated in the experiment. The phase noise measurements show that the phase noise performance of the generated microwave signal is not deteriorated by the optical system. The proposed scheme has no strict requirements for the modulation indexes and the generated signal exhibits advantages of high frequency tunability and purity.

Compensation of the Dispersion-Induced Power Fading in an Analog Photonic Link Based on PM–IM Conversion in a Sagnac Loop

An analog photonic link with the compensation of the dispersion-induced power fading is proposed and demonstrated based on phase modulation to intensity modulation conversion in a Sagnac loop. Due to the velocity mismatch of the modulator, only the incident light wave along the clockwise direction is effectively modulated by the radio frequency signals, while the counterclockwise light wave is not modulated. After combining the two light waves in a polarizer, an intensity modulated optical signal is generated, which can be directly detected. In addition, the phase difference between the two light waves can be adjusted through the polarization controller before the polarizer. This feature is used to shift the frequency response of a dispersive link to compensate the dispersion-induced power fading at any working frequency. Experimental results show that the power fading after transmission over both 25 and 50 km lengths of fiber in a conventional intensity modulated link can be successfully compensated in the proposed link, and thus, a high and constant link gain over a large frequency range is achieved. The spur-free dynamic ranges of the link before and after fiber transmission are also measured.

Photonic Microwave Generation With Frequency Octupling Based on a DP-QPSK Modulator

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated using a dual-polarization quadrature phase shift keying modulator. By properly setting the phase difference between the two drive signals, the working points of the modulator, and the polarization state of the light wave after the modulator, an optical signal with only ±4th order sidebands is generated. A pure 24-GHz microwave signal with low-phase noise is experimentally obtained using a 3-GHz local oscillator signal. The proposed photonic frequency octupling system also exhibits good frequency tunability as no electrical or optical filter is used.

Suppression of Chaos Time Delay Signature in a Ring Network Consisting of Three Semiconductor Lasers Coupled With Heterogeneous Delays

The properties of chaos time delay signature (TDS) in a ring network consisting of three mutually coupled semiconductor lasers (MCSLs) are investigated numerically, where heterogeneous coupling delays are proposed to obtain the TDS concealment from the intensity chaos in wide parameter regions. The evolution of the TDS patterns, which are quantified via the autocorrelation function, for a ring network with identical coupling delays as well as that with heterogeneous coupling delays is compared. By analyzing the effects of the coupling strength, frequency detuning, and injection current on the TDS, the parameter regions for successful TDS concealment are identified. It is found that the intensity chaos with a desirable TDS concealment can be generated in the proposed ring network in which the TDS is mainly affected by the injection current and coupling strength, but is not so sensitive to the frequency detuning. In particular, a larger injection current and smaller coupling strength are preferable to obtain chaos with a low TDS. Besides, the ring network with heterogeneous coupling delays allows for better TDS concealment in much wider parameter regions, compared to that with identical coupling delays, and, thus, is highly desirable for the chaos-based random bit generators.

Photonic Generation of Triangular Pulses Based on Phase Modulation and Spectrum Manipulation

A photonic triangular pulse generation method based on spectrum manipulation of phase-modulated signals is proposed and experimentally demonstrated. A light wave is first phase modulated by a sinusoidal signal to generate optical sidebands. Then, the optical spectra are manipulated by attenuating the optical carrier and one of the first-order sidebands with the same suppression ratio. By choosing a proper modulation index, a full-duty-cycle triangular pulse train with a repetition rate equal to the frequency of the drive signal can be generated. To improve the practical feasibility and the repetition-rate tunability, the spectrum manipulation is realized using a Sagnac loop and a fiber Bragg grating (FBG). In the experiment, four full-duty-cycle triangular pulse trains with different repetition rates (3-6 GHz) are successfully generated, and the repetition rate can be further improved if larger bandwidth measuring instruments are used. In addition to the large and tunable repetition rate, the proposed scheme also features the advantages of simple structure, low cost, and freedom from bias drift.

An Analog Photonic Link With Compensation of Dispersion-Induced Power Fading

A simple and low cost analog photonic link with the compensation of dispersion-induced power fading is proposed and demonstrated using a dual-electrode Mach-Zehnder modulator. In the proposed link, the modulator is single-electrode driven to realize a novel double-sideband (DSB) modulation. By adjusting the dc bias of the modulator, the frequency response of a dispersive link can be controlled to compensate the power fading at any working frequency. Experimental results show that the power fading in a conventional DSB modulated link after fiber transmission over 25 and 50 km can be both successfully compensated in the proposed link, and the spurious-free dynamic range at 12 GHz of a link with 25 km of single-mode fiber is improved by 11.6 dB.

Simulation of Multi-bit Extraction for Fast Random Bit Generation Using a Chaotic Laser

Multi-bit extraction schemes for fast random bit generation using a semiconductor laser subject to delayed optical feedback are numerically investigated. The simulation shows that the statistical properties of the chaotic signal significantly influence the generation of random bit sequences. More importantly, bit sequences with verified randomness at hundreds of gigabit per second, even up to the order of terabit per second could be numerically generated utilizing some effective postprocessing techniques even though the original statistical distribution substantially differs from a symmetric distribution. Such numerical results frequently required for developing ultrafast random bit generators as the first stage help to evaluate the experimental implementations of the corresponding schemes.

Emulation of Spiking Response and Spiking Frequency Property in VCSEL-Based Photonic Neuron

The dynamical response properties of photonic neuron based on vertical-cavity surface emitting lasers (VCSELs) subject to orthogonal polarized optical pulse injection stimuli have been numerically investigated. Based on the well-known spin flip model, we first reproduce some experimental findings of neuron-like dynamics in VCSELs, such as phasic spiking with a single abrupt pulse, and tonic spiking with multiple periodic pulses. Besides, we further go beyond in three directions and obtain several novel results. The operating parameter ranges corresponding to different neuron-like dynamics are identified by extensive bifurcation analysis. In addition, the effect of the time-varying pump current on the neuron-like dynamics for VCSELs under given optical injecting pulse strength is also discussed. For a given pump current, the spiking frequency dependence on the stimuli strength is further revealed in VCSELs with time-varying optical pulse injection. Such controllable neuron-like response dynamics and spiking frequency dependence in VCSELs are interesting and valuable for ultrafast photonic neuromorphic systems and neuron-inspired photonic information processing.

Quantifying the Complexity of the Chaotic Intensity of an External-Cavity Semiconductor Laser via Sample Entropy

This paper presents detailed numerical investigations of quantifying the complexity of the chaotic intensity obtained from the well-known Lang-Kobayashi model for an external-cavity semiconductor laser (ECSL) using sample entropy (SampEn). We demonstrate that the modified SampEn could be an alternative to quantify the underlying dynamics of an ECSL under the condition that the dimension, radius, and time delay of the delayed vectors are properly selected. The numerical results are supported by the earlier numerical studies using the permutation entropy and Kolmogorov-Sinai entropy. Furthermore, we also confirm that the SampEn shows certain robustness to the additive observational noise.

Photonic microwave frequency measurement with a tunable range based on a dual-polarization modulator

This paper presents a novel photonic-assisted microwave frequency measurement scheme based on an integrated dual-polarization Mach-Zehnder modulator (DPol-MZM). The DPol-MZM is used to obtain a polarization multiplexing signal modulated by the microwave signal with the frequency to be identified. The obtained signal is split into two channels after propagating along a single mode fiber. The two divided parts are used to establish an amplitude comparison function (ACF) which provides frequency-power mapping. The proposed scheme is experimentally verified. The frequency responses of the two branches are nearly complementary; thus, a relatively steep ACF is obtained. A frequency measurement range from 2 to 28 GHz with an error of ±0.2  GHz is achieved. Moreover, the measurement range can be tuned by simply adjusting the polarization state of one channel. The proposed system is simple, and the measurement range can be easily adjusted.