At present, an all optical high-order tunable ordinary differential equation (ODE) solver is very difficult to implement. A novel all-optical first to third order linear ODEs solutions with tunable constant coefficients using double Sagnac rings coupled Mach–Zehnder-interferometer (DSMZI) on silicon waveguide chips are proposed. The structural composition and size of the DSMZI have been designed, and the working principles of its first to third order ODEs solutions have been derived. By varying the input electric heating power of the thermal-optical phase shifters of the individual arms of the MZI, the constant-coefficient of the differential equation can be simply tuned in large scope. It is demonstrated that the constant coefficient k ranges from 0.0015/ps to 0.092/ps for the first-order ODE. The constant coefficient p of the second-order ODE solver can be continuously tuned from 0.013/ps to 0.174/ps, correspondingly with the q varying from 0.00004225/ps2 to 0.007569/ps2. Three constant coefficients u, v, and w of the third-order ODE can be continuously tuned from 0.105/ps to 0.252/ps, 0.003675/ps2 to 0.021168/ps2, and 0.00004288/ps3 to 0.0005927/ps3, respectively. The all-optical ODE solvers with the DSMZI can be easily integrated with other optical components based on silicon on insulator, which can provide a path for future artificial intelligence or big data processing systems in optical computing on silicon waveguide chips.
At present, a high-order, reconfigurable photonic signal processor is very difficult to implement. A simple, reconfigurable photonic N-differentiator and integrator based on a unit of the dual-ring coupled Mach–Zehnder interferometer (DRMZI) is proposed first. The reconfigurability is achieved only by controlling the thermo-optic phase shifter (TO-PS) on the two improved micro-ring resonators. The device presents a wide fine-tunable differentiation order range from 0.2 ≤ N ≤ 1.7 reconfigured as a 2 × 2 differentiator after being optimized the TO-PS and the tunable couplers (TC). If it is reconfigured as an integrator, a first-order photonic temporal integrator with 16.1 GHz 3-dB bandwidth and integration time window 38.4 ps is achieved in our design. The 4 × 4 port DRMZI differential unit can be cascaded into k-stage to realize 0.2 × k ≤ N ≤ 1.7 × k order differential function, theoretically approaching any large order. At the same time, the differential signals can be successfully routed to different output ports by reconfiguring the optical path in the structure. The simulation results have shown that a two-stage 4 × 4 photonic temporal differentiator can perform more than two order differential operations, e.g., N = 2.4. Our research can provide a reference for chip-level large-scale integrated photonic processors.
We design and investigate a 10 Gb/s single user hybrid fiber-free space optical (FSO)-fiber experimental system based on optical code division multiple access (OCDMA). The receiving eye diagrams of legitimate user and eavesdropping user are measured, and the reliability and security of the hybrid system are analyzed through the eye diagrams. In order to analyze the security of the hybrid system, a tunable attenuator is used to simulate the eavesdropping situation of eavesdropping user at different position of fiber links. When analyzing the reliability of the system through the eye diagrams of legitimate user under different turbulence effects and different received power, we can see that the system can achieve reliable transmission with low-power reception only under weak turbulence. In the case of middle and strong turbulence, some measures must be taken to ensure the reliable transmission of the system. When analyzing the security of the system, the eye diagrams of eavesdropping user under the different turbulence effects and different eavesdropping distance are measured. It can be seen from the eye diagrams that the eye diagram in the second 20km optical fiber is worse, because Eve's eavesdropping signal in the second section of fiber is affected by the turbulence in FSO channel. The experimental results show that the hybrid fiber-FSO-fiber system based on OCDMA can achieve reliable transmission to ensure reliability, and also shows the good security through the poor eavesdropping.
Ultrafast passive all-optical full-function logic gates (FLOGs), such as AND, NOT, XOR, XNOR, and OR gates, are studied and designed. FLOGs can be realized only by changing the state of input ports in a designed micro-Sagnac waveguide ring unit. The whole chip is internally passive with unified off-chip source fabricated on a silicon-on-insulator substrate. The transmission performance of FLOGs waveguide ring and integrated chip unit are investigated by both the finite-difference time-domain method and beam propagation method. The research shows that FLOGs have the advantages of low power (μW) consuming, multifunctional, and high transmission rate. The simulated device cascades are indicated that the FLOG structure can be well cascaded, which may be used to form the neural network element. There will be potential applications in all-optical communication networks and large-scale integration circuits in the future.
In coherent time-spreading OCDMA, beat noise is the main performance limitation. We propose a novel quasisynchronous
coherent time-spreading optical CDMA, where the synchronization among users can be controlled within
permissible time delay. Within permissible time delay, the mean intensity of aperiodic cross-correlation equals zero, and
the beat noise can be removed. Simulation of four simultaneous users employing LA sequence (156, 8,16) is
demonstrated, where the fiber link consists of 10km single-mode fiber, plus 1 km Dispersion Compensating Fiber. It can
be seen that, beat noise can be removed in quasi-synchronous coherent time-spreading optical CDMA system.
The effects of pulse shape and pulse width on chip-asynchronous coherent time-spreading OCDMA system are evaluated
by the aperiodic cross-correlation function of up-sampled sequence. It can be shown that for chip-asynchronous coherent
time-spreading OCDMA, the shorter optical pulse will obtain better aperiodic cross-correlation properties, which can
reduce multiple-access interference (MAI) and beat noise (BN). For 127-length Gold sequence, normalized throughput
of OCDMA is derived. It can be shown that the shorter optical pulse will obtain larger normalized throughput.
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.
Optical encoders/decoders based on fiber gratings are designed and fabricated. Experiment on one interference user
2.5Gb/s symbol overlapping optical fast frequency-hopping CDMA (SO-FFH OCDMA) system is demonstrated. Multiaccess
interference in SO-FFH OCDMA system is studied, and is compared with that of traditional FFH OCDMA
system. Experiment result shows that multi-access interference will degrade the system performance. With one
interference user, SO-FFH OCDMA can also decode data correctly at data bit rate 2.5Gb/s.
Multiple-access interference (MAI) and beat noise (BN) are analyzed in asynchronous coherent time-spreading OCDMA
system according to the aperiodic cross-correlation function. Relationship between the mean intensity of aperiodic crosscorrelation
and MAI and BN is deduced. Considering the worst system performance, upper bound of BER performance
is evaluated by the maximum value of the mean intensity of aperiodic cross-correlation. For 511 length Gold sequence,
coherent time-spreading OCDMA system can support less than 5 interfering users in the worst performance.
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.
The effects of the PMD and filter control in DMS system are studied theoretically with variational method. Firstly, the DMS transmission of filtering control in constant birefringence fibers is analyzed by Varitional method, from which the evolving rules of characteristically DMS parameters are obtained. Secondly, the stability of DMS transmission and its timing jitter are investigated in the random varying birefringence fibers. At the last, the mean square of DMS timing jitter is gotten, which can be simplfied to no filtering DMS system and to linear transmission systems in considering the effects of PMD. The results reveal that the condition of stability of filter control in DMS system must be satisfied with the relationship of filter strength kf < 2dyP3 Esol ÷ √πB4C2 + 2yP3 Esol C and DMS's timing jitter can be decreased considerably with help of filter strength.
The dispersion managed soliton transmission is a new soliton transmission scheme, but the ultra long-haul WDM system is limited its communication capability for multi-perturbations. In the present, the multi-perturbations including the amplificatory spontaneous emission (ASE) noise, across phase modulation (XPM) between the channels etc are considered. The evolvement characteristics of dispersion managed soliton transmission under control of inline filter are studied with variational method. Then the analysis expressions of timing jitter and equations of DMS's transmission
evolution are gotten. The analysis results indicate that the filter can increase the DMS's transmission rate and stabilize
DMS transmission. At same time, there exist a optimal configure scheme of filter strength and parameters of DMS. If
choosing the parameters (kf",C,B)reasonably, the pulse can be transmitted stable.
A scheme of WDM+OCDMA system employing optical hard-limiter(OHL) is proposed, and its performance of normalized throughput is analyzed. Upper bound of normalized throughput is obtained when all simultaneous users are equally allocated to different wavelength channels. Lower bound of normalized throughput is obtained when all simultaneous users are firstly allocated to same wavelength channels. Compared with the performance of WDM+OCDMA system without OHL, both upper bound and lower bound of normalized throughput in WDM+OCDMA system with OHL can be improved.
KEYWORDS: Medium wave, Dispersion, Signal attenuation, Receivers, Optical signal processing, Optical networks, Process control, Transparency, Local area networks, Channel projecting optics
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.
The three allocated schemes of dispersion managed soliton transmission systems are proposed on standard single-mode fiber. Adopting variational method, the timing jitters induced from the perturbations of amplifier spontaneous-emission (ASE) noise and across-phase modulation (XPM) in multiplexed systems are studied. The results have shown that the dispersion management strength S must be satisfied 2
KEYWORDS: Medium wave, Receivers, Channel projecting optics, Local area networks, Optical networks, Error analysis, Transmitters, Network architectures, Lithium, Analytical research
Estimating the number of simultaneous users on channel, optimum threshold value in multi-wavelength optical CDMA(MW OCDMA) is achieved according to maximum likelihood principle. When MW OCDMA system has large number of simultaneous users on channel, optimum threshold value will vary with the number of simultaneous users, and
the receiver will adjust the optimum threshold accordingly. Theoretical analysis and analogy simulation show that BER of MW OCDMA system will degrade greatly when employing the proposed optimum threshold value by maximum likelihood principle.
Optical encoder and decoder devices based on fiber Bragg gratings is designed. An FFH-OCDMA system scheme is performed with the devices. Transmission of the system is demonstrated over 6.5km of G.652 fiber at data rate 622M bit/s and get the desired results.
A new one-dimensional optical orthogonal codes named extend modified hyperbolic congruence codes(EMHC), is first constructed, and its performance is analyzed. Using EMHC for time spreading and prime codes (PC) for wavelength hopping, a new two-dimensional optical orthogonal codes named EMHC/PC is constructed. Then, the performance of EMHC/PC is analyzed, and is also compared with EQC/PC. It is shown that EMHC/PC has the same code cardinality and code length, but has better cyclic cross-correlation performance. Therefore, EMHC/PC can support more simultaneous users in optical CDMA networks.
The performance of normalized throughput in WDM+OCDMA system is studied. When all simultaneous users are equally allocated to different wavelength channels, upper bound of normalized throughput is obtained. When all simultaneous users are first allocated to same wavelength channels, lower bound of normalized throughput is obtained. However, if there is no central control to allocate wavelength channels equally, WDM+OCDMA system has the in-between performance of normalized throughput.
KEYWORDS: Dispersion, Local area networks, Receivers, Forward error correction, Systems modeling, Signal attenuation, Binary data, Data conversion, Channel projecting optics, Analytical research
The performance of normalized throughput in a hybrid WDMA-OCDMA system is studied. Effect of optical beat noise and dispersion on the normalized throughput is analyzed. The scheme of BCH channel coding is proposed to improve the performance of a hybrid WDMA-OCDMA system. Analysis result shows that the normalized throughput can be improved greatly when traffic load is medium. Furthermore, the maximum normalized throughput will increase for the BCH-coded hybrid WDMA-OCDMA system
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