A high-Q microwave photonic filter by using an SOA-based active mode-locked fiber ring laser

A high-Q microwave photonic filter using a semiconductor optical amplifier (SOA)-based mode-locking fiber ring laser is proposed, analyzed and experimentally demonstrated. The proposed microwave photonic filter can realize a high-Q frequency response, it is compact without an optical source, and it can be easily tuned by adjusting an optical variable delay line in a ring cavity. A result with a Q-factor of about 236 and a rejection ratio of about 45 dB is obtained. The measured results and the theoretical estimations agree very well.     

A dispersion flattened fiber front-haul transmission system with high bitrate signal at low input optical power

We propose a dispersion flattened fiber (DFF) front-haul transmission system with high bitrate, polarization multiplexing (PM) and quadrature amplitude modulation (QAM) signal at low input optical power. The modulation format of the system is PM-16QAM, and the bitrate is 256 Gbit/s. The transmission characteristics over DFF link system are experimentally studied, which are compared with those over non-zero dispersion shifted fiber (NZDSF) link and standard single mode fiber (SSMF) link. The experimental results show that the error vector magnitude (EVM) of 256 Gbit/s and PM-16QAM signal over 25 km DFF link is 0.75% better than that over 25 km NZDSF link at least, and the bit error rate (BER) and Q-factor are much better than those of NZDSF. Their EVM and BER are both decreased with the increase of input optical power, and the Q-factor is increased. Those characteristics over 25 km SSMF are the worst at the same case. The larger the dispersion is, the more the constellation points are deviated from their respective centers and the worse the constellation characteristics are. The greater the attenuation of the DFF is, the smaller the input power of the DFF is, the more the constellation points are deviated from their centers and the worse the constellation characteristics are. This study provides a new idea and experimental support for long span front-haul propagation in mobile communication.     

Noise performance of erbium-doped fiber amplifier pumped at 1.49μm, and application to signal preamplification at 1.8 Gbit/s

Direct measurements of the noise figure of an erbium-doped fiber amplifier are described. With an amplifier gain as high as 36 dB, a noise figure as low as 4.1 dB was measured. Noise figures remained below 6 dB for signal wavelengths within the high gain (G>20 dB) region of the amplifier. An optical receiver sensitivity of -43 dBm at 1.8 Gb/s, corresponding to 215 photons/b, was achieved using the fiber amplifier as an optical preamplifier for a direct detection receiver     

Optimized Quality Factor of Graphene Oxide-Reinforced PVC Nanocomposite

Graphene oxide (GO)-reinforced polyvinyl chloride (PVC) composite films were prepared by solution blending. The homogeneity of GO dispersion with PVC was confirmed by an optical microscope. Quality factor (Q-factor) as a function of temperature (40–150 °C) was measured within a broadband frequency range of 50–35 MHz. The controlled GO loading demonstrates a crucial impact on the optimization of the Q-factor, resonance frequency (f ₀) and wide bandwidth. This nanocomposite may be well suited for electronic applications. The further development of GO-reinforced polymer nanocomposites based on an optimized Q-factor may result in a material for electromagnetic frequency radiation shields for radar and communication towers/devices.     

Nonlinear effect mitigation based on PAPR reduction using electronic pre-distortion technique in direct-detection optical OFDM system

The nonlinear effect induced by the Mach–Zehnder modulator (MZM) and optical self-phase modulation (SPM) in the presence of high peak-to-average power ratio (PAPR) is investigated theoretically. We theoretically and experimentally investigate the direct-detection optical orthogonal frequency-division multiplexing (DD-OOFDM) system with an electronic pre-distortion technique of companding transform (CT) to reduce the peak-to-average power ratio (PAPR) of OFDM signals and improve the receiver sensitivity. Experimental results show that the PAPR reduction can reach about 3 dB when the complementary cumulative distribution function is 1 × 10⁻⁴, which means the number of random OFDM signals is 1 × 10⁴, and the receiver sensitivity is improved by 0.7, 1.7, and 2.4 dB for the launch power of 2, 6 and 10 dB m, respectively, at the BER of 1 × 10⁻⁴ after transmission over 100-km single-mode fiber with the μ of 2. It shows that the PAPR reduction can mitigate not only the nonlinearity of MZM, but also the nonlinear phase noise in the fiber link when the optical power into fiber is high.     

Combining self-phase modulation and optimum modulation conditionsto improve the performance of 10-Gb/s transmission systems using MQWMach-Zehnder modulators

For 10-Gb/s transmission over nondispersion shifted fiber, the combined use of self-phase modulation (SPM) and joint optimization of the bias and modulation voltages to increase the dispersion limited transmission distance is considered for multiple quantum well Mach-Zehnder modulators. For the dual drive (push-pull) modulation format, the dependence of the receiver sensitivity on fiber length and average transmitted optical power is determined for both conventional and π phase-shift modulators with either symmetric or asymmetric Y-branch waveguides. When SPM is negligible and the optical extinction ratio is maximized, the modulator design must he considered carefully in order to increase the transmission distance. By combining SPM and optimum modulation conditions, the dependence of the system performance on the modulator design is reduced substantially. For an average transmitted optical power of 12.5 dBm, the receiver sensitivity for transmission over 140 km of fiber varies by only 0.3 dB for the different modulator designs. This compares with a variation of 3.1 dB for maximum extinction ratio modulation     

Hybrid Link/Path-Based Design for Translucent Photonic Network Dimensioning

The advancement of ultralong-haul transmission technology has dramatically enhanced the all-optical reaches. However, the actual situations of installed fiber and sites for terrestrial network often prevent implementing a purely transparent network, and thus, opaque reshaping retiming regenerating (3R) regeneration is required to guarantee optical signal reachability. Since 3R regenerators based on optical/electrical/optical conversion tend to dominate the total network costs, an efficient network design method that allocates a minimum number of 3R regenerators to optimum locations is essential to build a cost-effective photonic network. In this paper, we propose such a network-dimensioning method by combining the advantages of link-based and path-based design approaches. It first guarantees optical signal reachability for any possible traffic demand in each segmented linear link. After combining all the links, excessive regenerators are eliminated based on the optical signal quality check with -factor calculation for each wavelength path. A trial design of a large-scale mesh network demonstrated a significant cost savings of more than 30% in comparison with a conventional link-based design. In the trial, the impact of fiber loss coefficient over the total network cost was investigated quantitatively, addressing the importance of such quantitative modeling and analysis.     

Long-span repeaterless transmission systems with optical amplifiersusing pulse width management

This paper proposes pulse width management in order to extend the repeater spacings of repeaterless transmission systems with optical amplifiers. First, the dependency of receiver sensitivity on duty ratio, receiver response, and fiber dispersion is clarified by numerical analysis. Next, the calculation results of sensitivity as a function of signal format and receiver basedband response are verified experimentally. Moreover, we show that pulse width management which uses return-to-zero (RZ) format with large duty ratio (~0.7) at the transmitter and pulse compression at the receiver increases the repeater gain by ~4.5 dB compared to conventional systems employing nonreturn-to-zero (NRZ) format. Record repeater spacing of 300 km is realized at 10 Gb/s by utilizing pulse width management     

Apodized chirped fiber Bragg grating for postdispersion compensation in wavelength division multiplexing optical networks

In this paper, a postdispersion compensation unit is proposed leading to a better performance for the optical communication systems. This unit utilizes a chirped fiber Bragg grating (CFBG). For enhanced performance of the CFBG, a proper apodization function is chosen to improve the quality factor (Q‐factor) and the bit error rate (BER) of the system. A 110‐km wavelength division multiplexing (WDM) optical link is investigated. The system performance is evaluated through its Q‐factor, eye diagram, and BER showing best performance when using the Hamming apodization function.     

A PAPR reduction scheme based on a new spreading code in optical direct detection OFDM system

In this paper, we propose and experimentally demonstrate a peak-to-average power ratio (PAPR) reduction scheme based on a new spreading code in direct detection optical orthogonal frequency division multiplexing (OFDM) system. The new spreading code with low cross correlation and high auto-correlation can support \(2N+1\) users. Thus, \(2N+1\) users or data symbols can be transmitted over only N subcarriers. The experimental results show that, after transmission over 70 km single-mode fiber, at the bit error rate of \(10^{-3}\), with fiber launch power of 2.75 dBm, the receiver sensitivity can be improved 2.1 dB by using the proposed scheme based on new spreading code. The PAPR can be reduced about 4.6 dB, compared with the original OFDM signal at a complementary cumulative distribution function of \(10^{-4}\).     

Design and analysis of all-optical up- and down-wavelength converter based on FWM of SOA-MZI for 60 Gbps RZ data signal

In this paper, the design and analysis of the all-optical up- and down-wavelength converter based on four-wave mixing (FWM) effect of semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI) have been presented. The return-to-zero (RZ) modulated data signal at a bit rate of 60 Gbps has been evaluated for error-free operation to show the feasibility of proposed system at different pump wavelength. The converted signal power and quality factor are investigated as the function of variable signal power and pump power. The optimized operating input signal power of ?5 dBm with Q-factor of \(\sim \)28 dB for RZ modulated signal by using SOA-MZI structure with enhanced FWM effect. The important contribution of these investigations that it is possible to expand the optical network with limited available channel bandwidth by utilizing the wavelength converter and gives an approach to implement wavelength converter for future hybrid optical access networks.     

Design tables for two active RC circuits realizing low-pass polyonimic filters

Realization of RC-active filters, as proposed by Sallen and Key, consists of cascade connection of suitable second- and first-order building blocks. The paper presents design tables for two active RC circuits realizing low-pass polyonimic filters. The functions realized are of second to eighth-order low-pass Butterworth, Chebyshev (with 0.1, 0.5, 1, 2 and 3 dB ripple) and Bessel variety. This method uses simple op-amp integrator blocks and can equally be applied to both continuous-time and switch-capacitor filter designs. The advantages of this method are: simple method of designing LP filters from second to eighth order using integrator blocks (e.g. MAX 274 and MAX 275); low sensitivity to component values; low spread in component values; good tuning; can tune parameter f ₁ (cutoff frequency). The disadvantages of this method are: no independent adjustment of the cutoff frequency and the Q-factor; fixed gain of unity.     

A 0.18 μm CMOS transimpedance amplifier with 26 dB dynamic range at 2.5 Gb/s

A new transimpedance amplifier (TIA) for 2.5 Gb/s optical communications fabricated in a standard 0.18 μm CMOS process is presented. The proposed TIA is based on a conventional structure with an inverting voltage amplifier and a feedback resistor, but incorporates a new technique to enhance the input dynamic range and to prevent the TIA from saturation at high input currents. According to electrical characterization the receiver shows an optical sensitivity of −26 dB m for a BER=10⁻¹², assuming a responsivity of 1 A/W, and an optical power dynamic range above 26 dB. The power consumption of the core is only 10.6 mW at a single supply voltage of 1.8 V.     

High-gain mode-adapted semiconductor optical amplifier with12.4-dBm saturation output power at 1550 nm

A mode-adapted semiconductor optical amplifier (SOA) has been fabricated and packaged. At the gain peak, 1500 nm, the fiber to fiber gain was measured to be 32.5 dB. Statistics for eight packaged devices indicate that a fiber-to-fiber gain of 26.3 dB ± 1.3 dB and a saturation output power of 12.4 dBm ± 0.4 dBm are typical at a bias of 500 mA for λ = 1550 nm. Polarization sensitivity at 1550 nm was measured to be 1.1 dB ± 0.4 dB and the transverse electric (TE) polarization state noise figure (NF) was determined to be 7.0 dB ± 0.5 dB. The coupling loss was 1.3 dB ± 0.1 dB per facet. This SOA, with a 1.3-nm filter, was used as an optical preamplifier in a 10-Gb/s return-to-zero (RZ) system testbed with a pseudorandom binary sequence (PRBS) of 2³¹ -1. A 14.5-dB improvement in receiver sensitivity was observed at a bit error rate (BER) of 10^-11     

High-Selectivity Switched-Capacitor Bandpass Filter with Quasi-Continuous Quality Factor Tunability

This paper describes the design and implementation of a second-order switched-capacitor (SC) bandpass (BP) filter with very wide quality factor (Q) programmability range. The filter selectivity is digitally programmed by varying the effective sampling frequency of an SC branch, without modifying any capacitor value. The proposed approach allows a quasi-continuous Q-factor tunability avoiding, in principle, the inherent quantization error associated to any traditional programming technique. Automatic Q-factor tuning is performed by using a scheme based on an amplitude-locking loop approach. Experimental results obtained from a 0.8-m CMOS integrated prototype demonstrate the versatility of the proposed technique for high-Q SC BP filters.     

140Mb/s光接收混合集成AGC主放大模块

本文介绍了140Mb/s光通信系统接收机中所用的AGC主放大模块。此模块采用厚膜电路混合集成形式,将AGC电路、主放大器制作在29.1×13.9mm~2的陶瓷片上,封装在DHM24绝缘子壳内,带宽为200MHz(3dB),增益为50dB,AGC范围大于25dB。在四次群光纤通信系统试验中,接收机灵敏度为-39dBm(误码率10~(-9)),眼图清晰。     

Polarization diversity detection performance of 2.5-Gb/s CPFSKregenerators intended for field use

2.5-Gb/s continuous-phase frequency-shift keying (CPFSK) regenerators are studied in laboratory and field experiments. A polarization diversity receiver is constructed with newly designed automatic gain and automatic frequency controllers. It achieves a sensitivity fluctuation of about 0.5 dB against all input signal polarization states. The automatic gain control is used in the intermediate-frequency circuits of the receiver and stably operates over 15 dB of input signal power variation. The automatic frequency control (AFC) is sufficiently stable to withstand a 30-kHz input signal polarization variation between two orthogonal linear polarization modes. AFC stability is maintained even if the environmental temperature of the laser diode modules fluctuates from 15 to 35 C. The polarization fluctuation in both cases results in only 0.1-dB degradation in receiver sensitivity     

Analysis of different sub-carrier allocation of M-ary QAM-OFDM downlink in RoF system

In this paper, the performance of a 60 GHz radio over fiber (RoF) system with 4/16/64 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) downstream signals is studied. Delivery of 10 Gbit/s M-ary QAM (MQAM) OFDM signals through the 20-km-long single-mode fiber (SMF) is complicated in terms of intensity modulation and direct detection (IM/DD). Using self-homodyne method, the beating of two independent light waves generating the millimeter-wave at the photodetector can be down-converted to baseband in the electrical domain. Meanwhile, three kinds of sub-carrier arrangement schemes are compared and discussed, and the simulation results show that lower peak-to-average power ratio (PAPR) can be obtained adopting the adjacent scheme. At bit error rate (BER) of 10-3, the receiver sensitivity using 4QAM-OFDM sub-carrier signal is almost enhanced by 4 dB and 9 dB compared with those of 16QAM-OFDM signal and 64QAM-OFDM signal.     

SCM/WDM系统中抑制载波的光学单边带调制技术

为了有效抑制SCM/WDM光纤通信系统中的群速度色散和非线性效应,利用SCM/WDM光纤通信系统中信号经过两次调制这一特性,提出了一种在SCM/WDM系统中容易实现的抑制载波的光学单边带调制技术。抑制载波的光学单边带调制信号具有很大的调制深度,即通过抑制载波可以有效的增大了调制深度,进而可以减小调制器的外加电压升高而激发的一系列有害的非线性效应。实测的调制信号的频谱只剩下了半个边频,有效地减小了光信号的频带宽度,从而可以有效地减小群速度色散对信号的劣化。接收机灵敏度的实测图表明,利用文中所述的抑制载波的光学单边带调制技术可以有效地提高接收机的灵敏度达3-5dB。     

Laser diode pumped Er3+-doped fiber amplifier in a 565Mbit/s DPSK coherent transmission experiment

A laser-diode-pumped erbium-doped fiber amplifier, exhibiting 9-dB gain, has been operated as an in-line optical repeater in a 565-Mb/s coherent optical communications system. A sensitivity penalty of 0.4 dB was observed when the amplifier was positioned 35 dB away from the receiver, thus indicating a system improvement of 8.6 dB. By progressively reducing the coupling loss between amplifier and receiver, the noise figure of the contradirectionally pumped amplifier was calculated to be 5.4 dB, a value which is consistent with simple noise theory