Feifei Yin

60-nm-Wide Tunable Single-Longitudinal-Mode Ytterbium Fiber Laser With Passive Multiple-Ring Cavity

A broadband tunable, single-longitudinal-mode (SLM) ytterbium fiber laser based on a passive multiple-ring cavity (MRC) technique is proposed and demonstrated experimentally for the first time to our knowledge. Two different short ring cavities are inserted into the main ring cavity and serve as wideband mode filters to ensure SLM oscillation. With 1-m ytterbium-doped fiber as the gain medium, the SLM operation is achieved with over 60-nm wavelength tuning range at 100-mW pump power. The laser is very stable with output power of 6 dBm and an optical signal-to-noise ratio of higher than 53 dB in all the 60-nm tuning range.

Code extraction from encoded signal in time-spreading optical code division multiple access.

A vulnerability that allows eavesdroppers to extract the code from the waveform of the noiselike encoded signal of an isolated user in a standard time-spreading optical code division multiple access communication system using bipolar phase code is experimentally demonstrated. The principle is based on fine structure in the encoded signal. Each dip in the waveform corresponds to a transition of the bipolar code. Eavesdroppers can get the code by analyzing the chip numbers between any two transitions; then a decoder identical to the legal users can be fabricated, and they can get the properly decoded signal.

5×200Gbit/s all-optical OFDM transmission using a single optical source and optical Fourier transform real-time detection

An all-optical sampling OFDM scheme using PolMux-DQPSK format with single source is proposed and experimentally demonstrated. 5 × 200 Gb/s AOS-OFDM signal with spectral efficiency of 3.07 bit/s/Hz is successfully transmitted over an 80 km SMF link with real-time detection by optical Fourier transform filters. Furthermore, this scheme can coexist with traditional WDM channels and be a promising technique for seamless upgrade of transmission date rate.

Full-Duplex 60-GHz RoF System With Optical Local Oscillating Carrier Distribution Scheme Based on FWM Effect in SOA

A full-duplex 60-GHz radio-over-fiber (RoF) system using novel optical local oscillating (LO) carrier distribution scheme to reduce the system cost and realize centralized management is proposed and experimentally demonstrated. In the proposed scheme, the optical LO carriers for producing remote electrical LO signals at the base stations (BSs) are generated together with the downlink RoF carriers at the central station (CS) via four-wave-mixing effect in semiconductor optical amplifier, and are then distributed to the BSs along with the downlink RoF signals. By down-converting the 60-GHz-band uplink signal with the remotely produced 60-GHz LO signal and reusing the optical LO carriers as the uplink optical source, only a cost-effective intermediate frequency modulator is required at each BS to transmit the uplink signal, which will dramatically reduce the whole system budget due to a large amount of BSs. Moreover, the operating frequency of each BS can be controlled remotely at the CS end to realize centralized management and convenient reconfiguration. Using the proposed scheme, 622-Mb/s signals for both directions are successfully transmitted over a 20-km single-mode fiber link and a 50-cm wireless channel with less than 0.1- and 0.2-dB power penalty for downlink and uplink, respectively.

100Gb/s PolMux-NRZ-AOS-OFDM transmission system

A novel high speed transmission system using all-optical sampling orthogonal frequency multiplexing (AOS-OFDM) technique is proposed and demonstrated. By utilizing polarization multiplexing (PolMUX) and non-return-to-zero (NRZ) format, the total bit rate is 100 Gb/s with high spectral efficiency of 1.6. In addition, optical cyclic postfixes are inserted to help improve the system performance. The 100 Gb/s PolMux-NRZ-AOS-OFDM signals can pass through 20 km single-mode fiber (SMF) transmission link without any compensation.

DWDM-Based Frequency-Interleaved Optical Distributing System Merging Wired and Wireless Services

A dense wavelength-division-multiplexing (DWDM)-based frequency-interleaved optical distributing system merging wired and wireless services is proposed and experimentally demonstrated. In the proposed scheme, two channels of baseband signals for wired applications and two channels of 62.5-GHz radio-over-fiber signals for wireless applications with a data rate of 1.25 Gb/s share a single 100-GHz DWDM grid to increase the spectral efficiency. The signals are distributed over 40-km single-mode fiber without any compensation and only a power penalty of less than 0.5 dB is observed. Optical demultiplexers based on fiber Bragg gratings are used to select corresponding frequency components at access points.

Broadband tunable optical delay based on real-time Fourier transformation and ramp-type phase modulation

A new tunable optical delay scheme based on real-time Fourier transformation and ramp-type phase modulation is proposed and experimentally demonstrated. A linearly chirped fiber Bragg grating is adopted to implement the real-time Fourier transformation, and tunable delay is realized by changing the ramp-type modulating signals period. Experimental results agree well with the theory. The signal distorts little after the delay, and a 18 ps delay is achieved for a 2-ps-wide optical pulse.

Simple Code Switching Scheme for Security Enhancement of OCDMA Communication System

A simple code switching scheme for security enhancement of an optical code-division multiple-access (OCDMA) communication system is proposed. The scheme avoids the replacement of all the encoders and decoders in the system and all users codes are changed by only tuning the center wavelength of the laser source. Each en/decoder contains multiple codes which are nonoverlapping in the spectrum. The scheme is demonstrated in a proof-of-principle transmission experiment. There are three codes on the encoder and decoder pairs, one 2-D code and two 1-D bipolar gold codes with chip number of 63 and 127, respectively. All three codes are decoded successfully after 12.7-km single-mode fiber link.

All-optical orthogonal frequency multiplexing scheme with cyclic postfix based on fiber Bragg gratings

A novel all-optical orthogonal frequency division multiplexing (AO-OFDM) scheme is proposed and demonstrated. Ultrashort optical pulses are used as samples for optical discrete Fourier transform (DFT) and the inverse DFT process. Different subcarrier channels can be parallelly processed by fiber Bragg gratings. A 20-Gb/s two subcarrier AO-OFDM experiment is carried out with narrowband filtering and optical cyclic postfixes (CP) inserted. Experimental results show that this scheme has good spectral efficiency. Furthermore, the received signals have better eye diagrams and bit error rate performance with the help of CP. This scheme can be used in high-speed optical transmission systems.

Instantaneous frequency measurement by optical filters based on vernier effect

An instantaneous frequency measurement system is proposed based on two optical filter response functions that are utilized to making coarse and fine measurement of unknown RF frequency. The latter response is periodic, which plays a role like a vernier, and the filter is made of FBG. This system employs one intensity modulator, three optical filters and power meters, and powers of single-side signals in three channels are measured. In experiment, 16-GHz range and less than 100-MHz error are successfully achieved for −6-dBm power of RF input.