Chaos Synchronization of Integrated Five-Section Semiconductor Lasers.

We proposed and verified a scheme of chaos synchronization for integrated five-section semiconductor lasers with matching parameters. The simulation results demonstrated that the integrated five-section semiconductor laser could generate a chaotic signal within a large parameter range of the driving currents of five sections. Subsequently, chaos synchronization between two integrated five-section semiconductor lasers with matched parameters was realized by using a common noise signal as a driver. Moreover, it was found that the synchronization was sensitive to the current mismatch in all five sections, indicating that the driving currents of the five sections could be used as keys of chaotic optical communication. Therefore, this synchronization scheme provides a candidate to increase the dimension of key space and enhances the security of the system.

Photonic reservoir computing with a silica microsphere cavity.

We experimentally demonstrate a photonic reservoir computing (RC) system using a passive silica microsphere cavity. The microsphere cavity exhibits a consistent nonlinear response to the non-return-to-zero signal and the multiple-level signal due to strong interference between numerous whispering gallery modes in the "over-coupling" state. Benefiting from the fact that the long photon lifetime inside the microsphere cavity provides a memory of past inputs, this photonic reservoir does not require a delayed feedback loop. We evaluate the generalization property of the RC system and obtain a correlation coefficient of 0.923. In addition, we obtain a NMSE of 0.06 for the Santa-Fe chaotic time series prediction task and a SER of 0.02 at a SNR of 12 dB for the nonlinear channel equalization task. Moreover, a microsphere cavity with a higher quality factor can provide a larger memory capacity. The application of the silica microsphere cavity as a small-volume passive device in a reservoir furnishes a new avenue for achieving a low-consumption and integrated RC system.

High-entropy-rate broadband chaos generation by using short-resonant-cavity DFB semiconductor laser with optical feedback.

Semiconductor lasers with delayed optical feedback are a promising source of optical chaos for practical applications, owing to simple configurations that are easy to integrate and synchronize. However, for traditional semiconductor lasers, the chaos bandwidth is limited by the relaxation frequency to several gigahertz. Here, we propose and experimentally demonstrate that a short-resonant-cavity distributed-feedback (SC-DFB) laser can generate broadband chaos only with simple feedback from an external mirror. The short distributed-feedback resonant cavity not only enhances laser relaxation frequency but also makes the laser mode more susceptible to external feedback. Experiments obtained a laser chaos with 33.6 GHz bandwidth and a spectral flatness of 4.5 dB. The corresponding entropy rate is estimated as more than 33.3 Gbit/s. It is believed that the SC-DFB lasers will promote development of chaos-based secure communication and physical key distribution.

Feasibility of quasicritical coupling based on LP modes and its application as a filter with tunable bandwidth and stable insertion loss.

The feasibility of the quasicritical coupling based on the high order scalar modes in tapered fiber was presented and discussed in detail theoretically. As its applications, the bandwidth evolution of the coupling process both in the Through port and the Drop port were also included in the calculations and demonstrated in the experiment. As a result, tunable bandwidth filters with stable insertion loss were realized by changing the gap between the few-mode tapered fiber and microcavity working under a state of quasicritical coupling. The bandwidth at the Through port is from 4.8 MHz to 327.1 MHz and that at the Drop port is from 15.3 MHz to 327.1 MHz, with the insertion loss fluctuation less than 10%. The combination of stable efficiency, narrow band, and bandwidth fine tunability may benefit its application in narrow-linewidth lasers, microwave photonics and nonlinear optics.

All-fiber frequency shifter consisting of a fiber Bragg grating modulated via an acoustic flexural wave for optical heterodyne measurement.

We present an all-fiber frequency shifter (AFFS) consisting of a fiber Bragg grating (FBG) modulated via an acoustic flexural wave for optical heterodyne measurement. The AFFS can efficiently generate the frequency-shifted signal due to the resonance peak with a high-reflection efficiency and being completely separated from the reflection spectrum of the original FBG, simultaneously. The experimental result shows that the minimal measurable vibration amplitude and the resolution of the all-fiber optical heterodyne measurement setup constructed with the AFFS are 0.06 nm and 30 pm in the region of tens to hundreds of kilohertz, respectively.

Fast light in the generation configuration of stimulated Brillouin scattering based on high-Q micro-cavities.

In this article, we reported self-pumped stimulated Brillouin scattering (SBS)-induced fast light in a micro-resonator. The optically induced thermal effect in the micro-resonator will lead to a shift of the dispersion spectrum and make the SBS gain occurred in the anomalous dispersion regime. The group delay could be experimentally optimized from -91.0 microsecond to 2.6 microsecond by changing the modulation frequency in a microsphere with its diameter of 175 µm. The experimental results will benefit applications utilizing anomalous dispersion such as gyroscope.

All-fiber narrow-linewidth ring laser with continuous and large tuning range based on microsphere resonator and fiber Bragg grating.

We demonstrate an all-fiber single-longitudinal-mode (SLM) narrow-linewidth ring laser stabilized by a microsphere resonator and fiber Bragg gratings (FBGs) with a large continuous wavelength tuning range from 1540 nm to 1570 nm. In the experiment, stable lasing with a linewidth smaller than 5 kHz was obtained. The laser wavelength was linearly and continuously tuned in the range of 0.15 nm by increasing the pump power and discretely tuning with a step of 0.1 nm by stress-controlled FBGs. The tuning range of the proposed laser configuration was determined by the FBG, and the SLM state was ensured by the coupling between the few-mode tapered fiber and the microsphere, which was simpler in alignment than other ring lasers utilizing microresonators.

Acousto-optic tunable bandpass filter based on acoustic-flexural-wave-induced fiber birefringence.

An acousto-optic tunable bandpass filter was proposed and fabricated based on acoustic-flexural-wave-induced single-mode fiber birefringence via coupling the core mode to a single-cladding vector mode. In the experiment, the resonant wavelength and insertion loss could be electrically tuned with a span of nearly 100 nm and a lowest insertion loss of -1.7 dB. The structure gains advantages of a large tuning range, fast speed, easy fabrication, low insertion loss, and zero frequency shift.

Tunable dual-wavelength fiber laser with unique gain system based on in-fiber acousto-optic Mach-Zehnder interferometer.

A fast tunable dual-wavelength laser based on in-fiber acousto-optic Mach-Zehnder interferometer (AO-MZI) with new fabrication process is proposed. Not only could the center wavelength of the output laser be optimized with enhanced tuning range about 30 nm by tuning the polarization and the driving frequency of the radio frequency (RF) signal accordingly, but also the spectral spacing between the two output wavelengths could be tuned from ~0 nm to 2.65 nm by controlling the power of the RF signal. The tuning mechanism was also discussed.

Tunable in-fiber Mach-Zehnder interferometer driven by unique acoustic transducer and its application in tunable multi-wavelength laser.

An in-fiber Mach-Zehnder interferometer was proposed and fabricated, which was based on a sandwich-like etched single mode fiber driven by only one acoustic transducer. It succeeded the feature of fast tuning and would not introduce frequency shift in the transmission spectrum. Based on it, a fast tuning dual-wavelength laser with a two-wavelength spacing around 3.5 nm was proved with a tuning range of about 3.6 nm, covering wavelengths from 1561.6 nm to 1568.9 nm.

All-fiber tunable laser based on an acousto-optic tunable filter and a tapered fiber.

An all-fiber tunable laser was fabricated based on an acousto-optic tunable filter and a tapered fiber. The structure was of a high signal-to-noise ratio, therefore, no extra gain flattening was needed in the laser. In the experiment, the wavelength of the laser could be tuned from 1532.1 nm to 1570.4 nm with a 3-dB bandwidth of about 0.2 nm. Given enough nonlinearity in the laser cavity, it could also generate a sliding-frequency pulse train. The laser gains advantages of fast tuning and agility in pulse generation, and its simple structure is low cost for practical applications.

Mode conversion in a tapered fiber via a whispering gallery mode resonator and its application as add/drop filter.

Based on the conversion between the fundamental mode (LP01) and the higher-order mode (LP11) in a tapered fiber via a whispering gallery mode resonator, an add/drop filter was proposed and demonstrated experimentally, in which the resonator only interacted with one tapered fiber, rather than two tapered fibers as in conventional configurations. The filter gains advantages of easy alignment and low scattering loss over the other filters based on tapered fiber and resonator, and will be useful in application.