Research on Dispersion Compensation of 40 GB/s Optical Duo-Binary Coded Transmission System

A 40 Gb/s high speed optical transmission system is designed, and the different dispersion compensation schemes are adopted to realize the transmission of the optical duo-binary (ODB) signals over 120 km optical fiber. Optical duo-binary signals are generated by using a precoder, two low- pass filters (LPF) and one mach-zehnder modulator (MZM). Through combination of dispersion compensation fiber (DCF) and single mode fiber (SMF) in the transmission link, four different dispersion compensation schemes (pre-compensation, post-compensation and hybrid compensation (pre+ post) and hybrid compensation (post+ pre)) were compared. Analyzing Q factor, BER, eye diagrams and receiver sensitivity in several dispersion compensation schemes, the simulation results are: the cut-off frequency of LPF affects the transmission performance, and the hybrid compensation (post+ pre) scheme is the optimal dispersion compensation method.

A Full-Duplex PON with Hybrid 64/16/4QAM OFDM Downlink and Hybrid 16/8/QPSK OFDM Uplink

In the context of next-generation optical access networks beyond 10 G, for high SE and flexible dynamic bandwidth allocation (DBA), the scheme of hybrid 64/16/4QAM-OFDM signal for downlink transmission and hybrid 16/8/QPSK-OFDM signal for uplink transmission is successfully proposed and experimentally presented in a full-duplex PON based on OFDM system. Here, for the uplink, in order to unit management of the optical line terminal (OLT) and reduce cost, the optical source functioned as the optical subcarrier at optical network units (ONUs) is from OLT in the central station. Moreover, there is an external cavity laser (ECL) with center frequency of 193.2 THz not only employed as optical modulated signal but also acted as LO signal. Our simulation results show that bit error ratio (BER) under hardware detection forward error correction has been successfully gained after 20 km of SSMF transmission. It is observed that the receiver sensitivity of multilevel PSK (M-PSK) is obviously larger than that of the M-QAM in this measurement scheme.

PAPR Influence Analysis in 8QAM-OFDM Optical Access Systems

In this article, the peak to average power ratio (PAPR) performance of 8 quadrature amplitude modulation-orthogonal frequency division multiplexing (8QAM-OFDM) optical signals has been researched in broadband optical access system. The complementary cumulative distribution functions (CCDFs) are analyzed of two different 8QAM-OFDMsignals with 16, 32, 64, 128, 256, 512 sub- carriers by simulation. The simulation results show that, with the increase of the number of subcarrier, the PAPR value becomes higher. When the numbers of subcarrier are16 and 512, the PAPR of 8QAM-OFDM optical signals are smaller than 5.2 dB and 5.3 dB respectively. Hence, the number of sub-carriers should be chosen according to practical application.

A 16PSK-OFDM-FSO Communication System under Complex Weather Conditions

Free Space Optical (FSO) communication is one of the most promising access methods. But, the different weather conditions will affect the transceiver performance. In this paper, we build a FSO communication system with 16-ary phase shift key-orthogonal frequency division multiplexing (16PSK-OFDM) downstream signals. We analyze the transmission performance of 16PSK-OFDM optical signals under five different weather conditions (sunny, light rain, moderate rain, snow, and fog). The optical spectral diagrams, constellation diagrams, and bit error rate (BER) of the received signals are simulation measured and analyzed. The results show that the constellation diagram under sunny condition is clear, and the value of BER is about 10?4.2 after 16PSK-OFDM optical signals pass through 500 m FSO link. Note that, the constellation points are dispersed under the other weather conditions.

Application Research on Two Types of 8QAM-OFDM Optical Access Signals

In this paper, the downstream transmission performance of two types of 8QAM-OFDM optical signals in broadband optical access system has been analyzed. After modulation and coding, two types of 10 Gbit/s 8QAM-OFDM optical access signals are downstream transmitted over 1 km, 10 km, 20 km and 40 km single mode fibers (SMFs) and received successfully. Different transmission distances impact on the bit error rate (BER) of the received signal is analyzed by simulation, while the signal to noise ratio (SNR) is 20 dB. The results show that, while the transmission distance is shorter than 10 km, the BER values of two types of 8QAM-OFDM optical signals are smaller than 10?10. As the above optical access signals are transmitted over 40 km SMF, the BER value of the first type of 8QAM-OFDM signals is bigger than 10?6, and the BER of the other type of 8QAM-OFDM signals is smaller than 10?6.

Optical 64QAM-OFDM Transmission Systems with Different Sub-Carriers

In this paper, the transceiver performance of optical 64QAM-OFDM signals with different sub-car- riers is studied. Firstly, we build a 40Gbit/s optical coherent 64QAM-OFDM transmission system. 64QAM-OFDM optical signals with 16, 32, 64, 64, 128, 256 and 512 sub-carriers are transmitted over 100 km single mode fiber (SMF). Then, the optical spectrum diagrams before and after transmission, the bit error rate (BER) and constellation diagrams of received signals were compared. The simulation results show that, with the number of sub-carriers increasing, the value of PAPR will gradually increase and the quality of the received optical signals will deteriorate. Moreover, with the number of sub-carriers increasing, the computational complexity will increase when digital signal processing (DSP) is used. Therefore, we should choose the optimal number of sub-carriers, and the PAPR influence and BER are also considered for achieving effective transmission.

4-Pulsed Amplitude Modulation Optical Downlink Signals Reception in Optical Access Systems Using Different Bandwidth Optical Bessel Filter

A novel scheme which can realize high-speed optical signals transmission and reception by using 4-pulsed amplitude modulation (4-PAM) and demodulation in 10 Gb/s passive optical access systems with different bandwidth optical Bessel filter (OBF) is introduced. In this scheme, a PAM sequence generator module, an M-ary pulse generator module and one Mach-Zehnder intensity Modulator (MZM) are employed for generating the 10 Gb/s optical 4-PAM signals. And then, the generated optical 4-PAM signal achieves transmission over 20 km single mode fiber (SMF) for downstream (DS) access links application. Finally, the optical 4-PAM signal after transmission is directly detected and demodulated. We measure time-domain sequential waveform curves, optical spectrum curves, and eye-diagrams, and analyze the receiver sensitivity of 10 Gb/s 4-PAM signals before and after transmission. The received performance of the optical 4-PAM signals after transmission over 20 km single mode fiber (SMF) with different bandwidth OBF has also been analyzed.

Study on 4PAM Radio over Fiber System Using Self-Mixing Technique

In this paper, a simplified optical millimeter-wave generated by two optical sidebands beating together in a 60 GHz radio over fiber (RoF) system with 10 Gbit/s 4-pulse amplitude modulation (4 PAM) transmission signal is proposed and simulated. 10 Gbit/s electrical 4 PAM signals modulated are conveyed over the length of 40 km standard single mode fiber (SMF) and recovered via the self-mixing technique after detecting directly at the receiver. Graphs of time-domain wave, frequency-domain and optical spectrum are measured out in different period, and the comparison of error vector magnitude curves of NRZ and 4 PAM signals under the different length of fiber is accomplished. The capacity of 4 PAM modulation is higher, though NRZ performs better than 4 PAM selected in RoF system within 80 km of fiber length as shown in the simulation results.

DP-DQPSK Optical Access System Integrated with Fiber and Free-Space Downlink for High Spectral Efficiency Application

In this letter, we present the generation, the balanced detection, and the transmission performance evaluation of dual polarization differential quadrature phase shift keying (DP-DQPSK) signals in optical access system integrated with fiber and free-space downlink. Polarization-multip- lexed (POLMUX) technique is introduced in the system for high spectral efficiency access utilization. 10 Gb/s DP-DQPSK downlink signals are successfully transmitted over 50 km SMF-28 and a 800 m wireless optical channel under the bad weather condition, such as fog and haze. The results show that the potentiality of DP-DQPSK optical access system is integrated with fiber and free- space downlink for providing flexible user access with high bandwidth efficiency.

FSK Modulation Scheme for High-Speed Optical Transmission

In this paper,we describe the generation,detection,and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers,one Mach-Zehnder modulator (MZM),and one Mach-Zehnder delay interferometer (MZDI).An RZ-FSK signal is generated by cascading a dual-arm MZM,which is driven by a sinusoidal voltage at half the bit rate.Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection.We perform numerical simulation on two types of frequency modulation schemes using MZM or PM,and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal.In the proposed scheme,a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK),under varying dispersion management.The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed.We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal.The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed.We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF),under the post-compensation management scheme.Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying),it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate.It can also be used in orthogonal label-switching as the modulation format for the payload or the label.As an example,we propose a simple orthogonal optical label switching technique based on 40 Gb/s FSK payload and 2.5 Gb/s intensity modulated (IM) label.

A novel odor stimulation system in freely moving,behaving animals

Precise and reliable presentation of odorants to animals is crucial for olfactory studies.Although odor stimulation systems in anesthetized or awake,head-fixed animals are well established,temporally precise odor presentation in awake,freely moving animals remains a challenge.Here,we describe a new odor stimulation system which presents odors directly to the nostrils of freely moving mice.The system comprises 3 modules:an odor-delivery module,an odor-generation module,and a control module.The new system is precise and temporally reliable,and odor stimulation can be triggered by specific sniffing phases or other events.Moreover,the system can be combined with neural recordings,such as electrophysiology,and olfactory behavioral tests to investigate how neurons in the brain represent odor information during individual olfactory behaviors.This innovative odor stimulation system may replace traditional stimulation systems:It will enable precise odor presentation in a wide range of olfactory studies in freely moving animals.