Flat-gain wide-band erbium doped fiber amplifier by combining two difference doped fibers

A new erbium-doped fibre amplifier (EDFA) is demonstrated using a combination of newly developed Erbium Zirconia co-doped fiber (Zr-EDF) and the commercial silica-based Erbium-doped fiber (Si-EDF) as the gain medium. Both fibers have a very high concentration of erbium ion. A compact amplifier operating in C-band region is firstly reported using a double-pass configuration. It is shown that average gains of the proposed Zr-EDF amplifier are obtained at approximately 18 dB with a gain variation of +-2 dB within C-band region. A flat-gain and wide band operation is achieved by configuring the amplifier in two stages comprising a 2 m long Zr-EDF and 9 m long Si-EDF optimised for C- and L-band operations, respectively, in a double-pass parallel configuration. A chirp fibre Bragg grating (CFBG) is used in both stages to ensure double propagation of the signal and thus to increase the attainable gain in both C- and L-band regions. At an input signal power of 0 dBm, a flat gain of 15 dB is achieved with a gain variation of less than 0.5 dB within a wide wavelength range from 1530 to 1605 nm. The corresponding noise figure varies from 6.2 to 10.8 dB within this wavelength regio

Flat-gain wide-band erbium doped fiber amplifier by combining two difference doped fibers

A new erbium-doped fibre amplifier (EDFA) is demonstrated using a combination of newly developed Erbium Zirconia co-doped fiber (Zr-EDF) and the commercial silica-based Erbium-doped fiber (Si-EDF) as the gain medium. Both fibers have a very high concentration of erbium ion. A compact amplifier operating in C-band region is firstly reported using a double-pass configuration. It is shown that average gains of the proposed Zr-EDF amplifier are obtained at approximately 18 dB with a gain variation of ±2 dB within C-band region. A flat-gain and wide band operation is achieved by configuring the amplifier in two stages comprising a 2 m long Zr-EDF and 9 m long Si-EDF optimised for C- and L-band operations, respectively, in a double-pass parallel configuration. A chirp fibre Bragg grating (CFBG) is used in both stages to ensure double propagation of the signal and thus to increase the attainable gain in both C- and L-band regions. At an input signal power of 0 dBm, a flat gain of 15 dB is achieved with a gain variation of less than 0.5 dB within a wide wavelength range from 1530 to 1605 nm. The corresponding noise figure varies from 6.2 to 10.8 dB within this wavelength region

Broad optical bandwidth based on nonlinear effect of intensity and phase modulators through intense four-wave mixing in photonic crystal fiber

This work investigates the advantages of nonlinear optics of a cascaded intensity modulator (IM) and phase modulator (PM) to generate an initial optical frequency comb. The results show that when the direct current bias to amplitude ratio, α = 0.1 , and the IM and PM have the same modulation index and are equal 10, seed comb is achieved; it is generated by the modulation of two continuous wave lasers. Hence, based on these parameters, an intense four-wave mixing is created through 9 m of photonic crystal fiber. Moreover, a broadband spectrum was achieved, spaced by a 30-GHz microwave frequency

Multi premises network based on coding technique

In this article optical code division multiple access (OCDMA) was chosen as multiplexing technique because it's considered as the next-generation optical access network. A multi premises downstream optical network was implemented using direct detection method based on OCDMA technique. The users encoded by modified prime code at C band with channel spacing 50 GHz. In this article low error rate transmission at high data rate for distances up to 25 km is demonstrated. Variation in the results was studied when varied fiber length, data rate and different effective power were applied. It has been shown that OCDMA is capable of providing gigabit-per-second for each user. Nevertheless, the results have indicated that direct detection OCDMA technique is capable to support multi premises network

Multi premises network based on spectral amplitude coding optical CDMA systems

The aim of this article is to introduce multi downstream passive optical network based on optical code division multiple access (OCDMA) technique, which is considered as a next-generation optical access network. Hence, incorporating this technique with passive optical network (PON) will enable the system to support higher bandwidth compared to the standard PON. The decoder is configured based on spectral coding because of its good noise suppression properties. Since the most important aspect of PON architecture is its simplicity, a multi PON access network each PON comprises 9 users encoded by modified quadratic congruence (MQC) codes at the C band for downstream signals with channel spacing 25/50 GHz is simulated. In this article low error rate transmission at high data rate for distances up to 28 km is demonstrated. Variation in the results was studied when varied fiber length, data rate and different effective power were applied. It has been shown that OCDMA is capable of providing gigabit-per-second for each user. The receiver sensitivity is affected by the multi premises system, where the best system performance can only be achieved when the effective power is -1dBm. Nevertheless, the results have indicated that the proposed PON based on spectral amplitude coding OCDMA technique is capable to support multi premises network

Compensation of Chromatic Dispersion and Nonlinear Phase Noise Using Iterative Soft Decision Feedback Equalizer for Coherent Optical FBMC/OQAM Systems

In this article, we propose an iterative soft decision feedback (ISDF) equalizer to compensate for the chromatic dispersion and nonlinear phase noise effects in 30-Gbaud coherent optical filter bank multicarrier with off-set quadrature amplitude modulation (FBMC/OQAM) system. Conventional optical FBMC/OQAM system usually uses a 1-tap zero-forcing equalizer per subcarrier to combat the inter-symbol interference (ISI) caused by the chromatic dispersion (CD) in optical fiber. However, residual ISI and inter-carrier interference (ICI) still remain in the system and have significant impact on the system performance. To overcome this problem, a new ISDF N-tap frequency sampling (FS) equalizer is proposed to jointly mitigate the residual ISI and ICI which permits a better trade-off between performance and complexity. Simulation results show that, the proposed technique is capable of suppressing the interference more effectively than using only 1-tap equalizer. The feedback branch of the proposed ISDF equalizer can be exploited further to compensate for the nonlinear effect of the optical fiber. With compensation of linear and nonlinear impairments the proposed technique acts as a backpropagation method for optical FBMC/OQAM system

Successive Interference Cancellation for DS-Optical PPM-CDMA Systems

In this paper we introduce a successive interference cancellation (SIC) scheme for direct sequence optical code division multiple access (DS-OCDMA) systems using pulse position modulation (PPM). Considering double-padded modified prime code (DPMPC) as a signature sequence code, results show that the system has better performance in terms of both capacity and bit error rate (BER) as compared to the one without cancellation scheme, where the system with SIC scheme can support up to 88 users while the system without SIC scheme can support only 38 users at similar BER=10−9. Although the receiver sensitivity is affected by the overlapping between users, which limits the system performance, the theoretical analysis of this issue indicates the influence of the size of M-ary PPM on OCDMA system. Hence, the BER value is still sufficient for good system performance

Performance analysis of a hybrid optical CDMA/DWDM system against inter-symbol interference and four wave mixing

This paper reports the implementation and theoretical model for analyzing an optical CDMA/DWDM hybridsystem to reduce two major problems, the Inter-Symbol Interference (ISI) and the Four Wave Mixing (FWM)effects and improve the performance of optical subscriber access networks by using Zero Cross Correlation (ZCC)optical codes, which helps to reduce the effect of the Multiple Access Interference (MAI). A squeezing method isused in the proposed hybrid system to completely suppress the ISI. In this method, the sequence interval of thesignature code is squeezed into a duration of less than one-bit. The hybrid system is capable of accommodating120 optical CDMA users carried by only 10 DWDM wavelengths spaced by 0.2 nm with 60 Gb/s/wavelengthtransmitted over 105.075 km of opticalfiber. The result shows that the optimum interval of the code sequence is aquarter (i.e., 25%) of the bit duration. Moreover, the results reveal that the CDMA technology based on the spreadspectrum is capable of increasing the nonlinear tolerance of the proposed hybrid system as the energy of bits isdistributed over the chip sequence code. Also, the number of ones/weight and the positions between them have asignificant effect on the performance of the proposed hybrid system

Suppression of inter and intra channel four wave mixing effects in optical CDMA over DWDM hybrid system

In this study, a hybrid system of optical Code Division Multiple Access(optical CDMA) and Dense Wavelength Division Multiplexing(DWDM) is proposed with a comprehensive investigation into the effect of four-wave mixing(FWM). In such system, two major FWM problems exist, inter and intra-channel FWM, including multiple access interference(MAI) and inter-symbol interference(ISI). Results show that the optimum transmitted power is 18dBm in order to control the trade-off between inter and intra-channel FWM, where an increase in the BER of the hybrid system at transmitted power above 18 dBm is indicated. Hence, an electro-optic phase modulator(EOPM) module is proposed and placed after the WDM multiplexer to simultaneously modulate the phase of all wavelengths signals to increase the nonlinear tolerance in the hybrid system by suppressing the impact of intra-channel FWM, which is shown to greatly improve the performance of the optical CDMA-DWDM hybrid system based OOK transmission. In addition, the effect of MAI can be reduced by the use of multi-diagonal(MD) identification sequence code, due to the zero cross-correlation property of MD. The results also reveal that the CDMA technology in conjunction with chromatic dispersion helps to reduce the effect of inter-channel FWM. Moreover, the identification sequence code interval plays crucial role in the mitigating of ISI as the results expose that the best performance of the proposed hybrid system can be achieved when the identification sequence code interval squeezed into 25% of bit duration where the avoidance of ISI is guaranteed