Search

Chaotic optical communications provide high security for physical layer encryption. We propose a chaotic laser communication system based on a balanced detection optoelectronic delayed feedback system, which has a higher performance compared with one based on single-photodiode detection. Our numerical analysis proves that dynamic behaviors are achieved at only half feedback gain, and the safety hazard chaotic dead zone is eliminated. The generated chaos features high pseudo-randomness and a good capacity to conceal time-delay signatures, which makes it hard for an unauthorized party to remove the chaotic carriers. 10 Gbps message hidden in wideband chaotic carries is transmitted back-to-back, and the BER 10−1 of the eavesdropper achieved at a low feedback gain β=3.2 proves its high confidentiality. Our proposed system has the potential to promote chaotic laser systems to practical appliances with simple structure and high performance. [ABSTRACT FROM AUTHOR]

We proposed a new kind of add-drop multiplexer based on $\pi $ phase-shifted antisymmetric Bragg grating ($\pi $ -ASBG). Light resonance is formed in the $\pi $ -ASBG with mode conversion between backward fundamental transverse electric (TE0) mode and the forward first order transverse electric (T1) mode. With the aid of the TE1 mode generated in the $\pi $ -ASBG, add-drop multiplexer can be designed. As examples, two multiplexer structures based on single- and dual-bus resonator, on silicon-on-insulator (SOI) platform have been studied in detail. Besides, no light is reflected to the input port, if the structure is carefully designed with critical coupling condition satisfied. For the fabricated add-drop multiplexer based on single-bus resonator, the extinction ratio is 23.90 dB and full width at half maximum (FWHM) is 0.33 nm at the through port. For the fabricated add-drop multiplexer based on dual-bus resonator, the extinction ratio is 17.22 dB and FWHM is 0.29 nm at through port. The results show that proposed structures provide a new method to realize add-drop multiplexer and other integrated optical filters for optical communications and sensors. [ABSTRACT FROM AUTHOR]

To evaluate the effect of crosstalk caused by wavelength deviation of reconstruction-equivalent-chirp (REC) integrated multi-wavelength laser arrays (MWLAs) on an optical free-space communication system in which wavelength division multiplexing (WDM) is applied, we derive the model of power penalty caused by the wavelength deviation of REC-MWLAs and the bit error rate (BER) of the system under atmospheric turbulence and conduct a numerical simulation. The two adjacent channels in arranged REC laser arrays are defined as the analysis scope. We find that the power penalty is more sensitive to the deviation of the channel itself than the adjacent channel as the frequency shift increases from 0 to 50 GHz. The numerical relationship between the BER and power penalty is drawn to further investigate the tolerance for wavelength deviation under the requirements of BER < 10 − 6 and BER < 10 − 9. In addition, for a smaller deviation of 5 GHz of the analyzed channel, the linewidth compression of the REC laser can decrease the power penalty from 1.3 to 0.7 dB, improving the system performance and moderating the demands for deviation of REC-MWLAs, and the gemination of channel spacing does not evidently reduce the requirement for deviation. The results of this work demonstrate the feasibility of REC-MWLAs as the light source of WDM free-space communication systems under atmospheric turbulence and provide an effective reference for the allowable deviation in the design and testing of MWLAs. [ABSTRACT FROM AUTHOR]

A simple multi-radio access technology (multi-RAT) capable radio over fiber (RoF) system with $2\times 2$ multiple-input-multiple-output (MIMO) wireless transmission is proposed and experimentally demonstrated. The transmission of sub-6 GHz and 60 GHz millimeter-wave (MMW) services is enabled by a dual-drive Mach–Zehnder modulator (DDMZM) and an optical interleaver. In the central office (CO), sub-6 GHz and 30 GHz signals are applied to the dual branches of the DDMZM which is biased at the quadrature point. After transmission over single-mode fiber (SMF), the two services are separated by the optical interleaver. One output port of the interleaver is used for delivering the sub-6 GHz signal while the other one is used for the generation and transmission of the 60 GHz MMW signal. Furthermore, we also demonstrate the MIMO technology can be used in the proposed architecture to improve the capacity. A proof-of-concept experiment is performed to verify the feasibility of the proposed scheme. In the experiment, a 1.3 Gb/s orthogonal frequency division multiplexing (OFDM) signal at 55 GHz is transmitted over 25 km of SMF and 1 m $2\times 2$ MIMO wireless distance while a 675 Mb/s OFDM signal at 0.375 GHz is delivered over 25 km of SMF at the same time. [ABSTRACT FROM AUTHOR]

A multilongitudinal mode fiber ring laser sensor is proposed and experimentally demonstrated by measuring the strain applied on the laser sensor head. The ring cavity of the laser is formed by a 3-dB coupler, a section of erbium-doped fiber, and one fiber Bragg grating. Photonic generation of beat signals and strain measurement theory are discussed in detail. The strain applied on the fiber ring cavity is obtained by measuring the beat frequency shift. The selection way of the optimal beat signal for strain measurement is obtained by experimental research and discussion. The root-mean-square deviation of the strain and the response of beat frequency to the strain are 2.7 μɛ and 1.5 kHz/μɛ at 1993 MHz, respectively. The proposed sensor scheme offers a cost-effective and high-stability device for strain measurement. [ABSTRACT FROM AUTHOR]

We propose a novel solution for linearly tunable polarization mode dispersion (PMD) compensation by sampled Bragg gratings fabricated with uniform-period phase masks. This all-fiber PMD compensation technique is cost-effective and flexible in designing the differential group delay (DGD) profile. Based on numerical simulations, the efficiency of this PMD compensator is assessed for the 10 Gb/s NRZ transmission system with large DGD. With this compensator, a significant improvement can be achieved in the eye pattern of the received signal. [Copyright &y& Elsevier]

Abstract: An apodized DFB semiconductor laser based on reconstruction-equivalent-chirp (REC) technology is proposed and investigated numerically. By changing the duty cycle of the sampling period, the magnitude of the equivalent index modulation is varied. Thus the equivalent apodization is introduced instead of an actual apodization. This novel DFB structure is advantageous in that it can enlarge the threshold gain difference and improve the mode stability compared with the conventional DFB laser. Moreover, the structure can be easily fabricated by standard holographic technology instead of high cost Electron-beam lithography. [Copyright &y& Elsevier]

A novel method of automatic polarization measurement using electro-optic polarization controllers and fixed polarizers is proposed, featuring in self-calibration, simple set-up, high speed and satisfactory accuracy in real-time SOP measurement of optical fiber devices. Based on this method, higher-order PMD characteristics of the fiber are measured and agree well with theoretical calculations. [Copyright &y& Elsevier]