anhua Ji

The analysis of all-optical logic gates based with tunable femtosecond soliton self-frequency shift

A type of tunable femtosecond soliton logic gate based on fiber Raman Self-Frequency Shift (SFS) is studied in this paper. The Raman SFSs of femtosecond solitons governed by the Newtons cradle mechanism in logic gate are analyzed with an Improved Split-Step Fast Fourier Transform (ISSFFT) algorithm. The impact factors of the solitonic pulse frequency shift and temporal time shift, which are included the Third-Order Dispersion (TOD) effect, are investigated. The existing theoretical equation of SFS is modified into a new expression for this type of soliton logic gate. A lower switching power and the small size of the soliton logic gate device is designed to realize the logic functions of AND, NOT, and XOR. The results demonstrate that the logic gate based on SFS is belonged to the asynchronous system and can be achieved with Milli-Watt switching power and good extinction ratio. ISSFFT is effective and accurately to analyze higher-order dispersive and nonlinear effects in the logic gates.

Construction and performance analysis of a 2D optical orthogonal code

Feature Issue on Optical Code Division Multiple AccessWhat we believe to be a new 2D optical orthogonal code, named PC/OCS, is constructed using PC (prime code) for time spreading and OCS (one-coincidence sequence) for wavelength hopping. Cross-correlation performance of PC/OCS is analyzed. Compared with PC/PC, the number of wavelengths for PC/OCS is not limited to a prime number. PC/OCS can be constructed flexibly and also can use available wavelengths effectively. When the number of available wavelengths is larger than a prime number, PC/OCS not only has a larger code cardinality than PC/PC, but it also has a better cross-correlation performance. Theoretical analysis shows that PC/OCS can reduce the bit error rate and enhance system throughput of multiple-wavelength (MW) optical code-division multiple access networks. When the number of available wavelengths is 16 and code length is 121, code cardinality of PC/OCS can increase approximately 17% more than that of PC/PC, and the peaked throughput can increase approximately 20%.

Code sequence analysis in asynchronous coherent time-spreading optical code-division multiple access

An analysis of the code parameters that are important to asynchronous coherent time-spreading optical code-division multiple-access (OCDMA) systems employing Gold codes is presented. Multiple-access interference (MAI) and beat noise (BN) are analyzed according to the aperiodic cross-correlation function. The relationship between the mean intensity of aperiodic cross-correlation and MAI and BN is deduced. Considering the mean system performance, MAI and BN can be calculated directly from the aperiodic autocorrelation function, and the aperiodic cross-correlation function is not needed. Hence, a computational saving can be achieved. Considering the worst system performance, the upper bound of the bit-error-rate performance is evaluated by the maximum value of the mean intensity of aperiodic cross correlation. For a 511 length Gold sequence, a coherent time-spreading OCDMA system can support 12 interfering users for the mean performance. However, an OCDMA system can support fewer than five interfering users in the worst performance.

Enhanced spontaneous emission of quantum emitter in monolayer and double layer black phosphorus

We theoretically demonstrate that the spontaneous emission rate (SER) of quantum emitter is greatly enhanced in the proximity of single or double layers of black phosphorus (BP). The maximum enhancement factor is on the order of 106, about 3 times larger than that of graphene, due to the large photonic density of states near BP. We also study how the transition frequency, the BP doping level, the distance between emitter and BP, the existence of substrate underneath BP, and the orientation of transition dipole moment influence the SER. With properly designed parameters, both high SER of emitter and low propagation losses of BP surface plasmon polaritons can be achieved in the quantum system, making it a promising candidate for mid-infrared single-photon generation.

Performance analysis of physical-layer security in an OCDMA-based wiretap channel

Based on information-theoretic security, physical-layer security in an optical code division multiple access (OCDMA) system is analyzed. For the first time, the security leakage factor is employed to evaluate the physicallayer security level, and the safe receiving distance is used to measure the security transmission range. By establishing the wiretap channel model of a coherent OCDMA system, the influences of the extraction location, the extraction ratio, the number of active users, and the length of the code on the physical-layer security are analyzed quantitatively. The physical-layer security and reliability of the coherent OCDMA system are evaluated under the premise of satisfying the legitimate user’s bit error rate and the security leakage factor. The simulation results show that the number of users must be in a certain interval in order to meet the legitimate user’s reliability and security. Furthermore, the security performance of the coherent OCDMA-based wiretap channel can be improved by increasing the code length.

Analysis of normalized throughput in WDM-based coherent time-spreading OCDMA system

The performance of normalized throughput in wavelength division multiplexing (WDM) based coherent time-spreading optical code division multiple access (TS-OCDMA) system is studied. The upper bound and lower bound of normalized throughput are obtained with 8 wavelength channels and 127-length Gold code, and with 4 wavelength channels and 511-length Gold code respectively. It is shown that when all simultaneous users are equally allocated to different wavelength channels, WDM+TS-OCDMA has much better performance. However, if there is no central control to allocate wavelength channels equally, WDM+TS-OCDMA system has the in-between performance of normalized throughput.

Performance Analysis of WDM-based Coherent Time-Spreading Optical CDMA System

The performance of WDM-based coherent time-spreading OCDMA system is studied. Upper bound and lower bound of normalized throughput are obtained with 8 wavelength channels and 127 length and 511 length Gold codes. It is shown that when all simultaneous users are equally allocated to different wavelength channels, WDM+ TS OCDMA has much better performance. However, if there is no central control to allocate wavelength channels equally, WDM+ TS OCDMA system has the in-between performance of normalized throughput.

Analysis of the code parameters in asynchronous coherent time-spreading optical CDMA system

An analysis of the code parameters that are important to asynchronous coherent time-spreading OCDMA system is presented. Relationship between the mean intensity of aperiodic cross-correlation and multiple-access interference (MAI) and beat noise (BN) is deduced. Considering the mean system performance, MAI and BN can be calculated directly from aperiodic auto-correlation function, and the aperiodic cross-correlation function is not needed. Hence, a computational saving can be achieved For 511 length Gold sequence, coherent time-spreading OCDMA system can support 12 interfering users for the mean performance.

Performance comparison of WDM+OCDMA and multi-wavelength OCDMA systems

The performance of normalized throughput in WDM+OCDMA is compared with that of MW OCDMA system after considering the effect of chromatic dispersion. Normalized throughput in MW OCDMA system will be reduced after considering the effect of chromatic dispersion. Both WDM+OCDMA and MW OCDMA systems have comparable performance of normalized throughput when traffic load is light. However, WDM+OCDMA system has better performance when traffic load is heavy. Furthermore, the peaked normalized throughput of WDM+OCDMA system is larger than that of MW OCDMA system.

Surface-plasmonic right-angle waveguide amplifiers

We propose a surface-plasmonic right-angle bend waveguide with bismuth ion-doped glass film as core layer and Ag films as cladding layers for first time, to the best of our knowledge. Theoretical analysis shows that the right-angle has bend and absorption losses of 3.17 dB. The rate equations and power evolution equations of high concentration bismuth-doped glass film are setup and solved to analyze the effect of the waveguide length and active ion concentration on the signal gain and Noise Figure (NF). The theoretical results predict that with the pump power 100 mW, the active ion concentration 2.0×1026 ions/m3 and the right-angle waveguide size 1.0 cm×1.0 cm, small-signal unit-length net gain can reach 15.32 dB with NF less than 5.0 dB.