43 Gbit/s x 54 ch Transmission with Dense 75 GHz Channel Spacing in NRZ Modulation Scheme

We demonstrated 2.16-Tbit/s (43 Gbit/s x 54 ch) WDM transmission over 600 km of standard single-mode fiber with high spectral efficiency 0.53 bit/s/Hz using optimized optical mux/demux filters for 75-GHz channel spacing in a simple NRZ modulation scheme.     

Quantum key distribution in an optical fiber at distances of up to 200 km and a bit rate of 180 bit/s

An experimental demonstration of a subcarrier-wave quantum cryptography system with superconducting single-photon detectors (SSPDs) that distributes a secure key in a single-mode fiber at distance of 25 km with a bit rate of 800 kbit/s, a distance of 100 km with a bit rate of 19 kbit/s, and a distance of 200 km with a bit rate of 0.18 kbit/s is described.     

Simulation Results for DWDM Systems with Ultra-High Capacity

We present stimulation results for DWDM systems with an ultra-high capacity up to 1.28 Tbit/s and spectral efficiency approaching 0.4 bit/s/Hz. The impact of signal-to-noise ratio (SNR) on parameters such as channel spacing, length of fiber, dispersion, and number of channels has been investigated and the results obtained have been explained on the basis of fiber nonlinear effects. It has been shown that with an increase in channel spacing, the SNR increases to the maximum optimum value and then decreases to a steady value. With an increase in number of channels, the SNR decreases for small wavelength spacing. For large wavelength spacing, it becomes independent of the number of channels. Keeping channel spacing constant, the SNR decreases with an increase in the length of the fiber. The SNR also improves with a small increase in dispersion of the fiber. Further, it is observed that, with increase in length over dispersion-shifted fiber, the received power decreases and the bit error rate increases.     

Simulation Results for DWDM Systems with Ultra-High Capacity

We present stimulation results for DWDM systems with an ultra-high capacity up to 1.28 Tbit/s and spectral efficiency approaching 0.4 bit/s/Hz. The impact of signal-to-noise ratio (SNR) on parameters such as channel spacing, length of fiber, dispersion, and number of channels has been investigated and the results obtained have been explained on the basis of fiber nonlinear effects. It has been shown that with an increase in channel spacing, the SNR increases to the maximum optimum value and then decreases to a steady value. With an increase in number of channels, the SNR decreases for small wavelength spacing. For large wavelength spacing, it becomes independent of the number of channels. Keeping channel spacing constant, the SNR decreases with an increase in the length of the fiber. The SNR also improves with a small increase in dispersion of the fiber. Further, it is observed that, with increase in length over dispersion-shifted fiber, the received power decreases and the bit error rate increases.     

Minimization of Cross-Gain Saturation in Wavelength Division Multiplexing by Optimizing Differential Gain in Semiconductor Optical Amplifiers

We successfully simulated the 10 × 40 Gbit/s soliton RZ-DPSK WDM signals over 1050 km with spectral efficiency approaching 0.4 bit/s/Hz using semiconductor optical amplifiers (SOAs) as in-line amplifier. The cross-gain saturation of SOA can be minimized by settling crosstalk at a lower level by decreasing the differential gain. This decrease in differential gain is in such a way that we get nil power penalty. The maximum transmission distance of 1050 km is possible with differential gain 210 atto cm² of SOA.

The impact of amplification factor, ASE noise power, crosstalk, quality factor and bit error rate for different differential gain has been investigated. It has been shown that with the increase in differential gain of SOA, the transmission distance goes on decreasing. At high value of differential gain 2.5 × 10^-16 cm² for the transmission distance 1050 km, all channels produce inter channel crosstalk with bit error rate greater than 10^-6. But for lower differential gain 190 atto cm², the quality of all channel increases at the cost of large power penalty.

With slight increase in differential gain 200 atto cm², the maximum transmission distance observed is 4550 km with quality of received signal more than 15 dB and having nil power penalty. We observed clear eye diagrams and optical power spectra for received signal with transmission distance 1050 km and 4550 km using soliton RZ-DPSK system. The bit error rate for all channels increase more than 10^-10 with the increase in launched input power that is due to power saturation.     

Optical heterodyne transmission system with 565 Mbit/s DPSK modulation showing a receiver sensitivity of -53.3 dBm

A 565 Mbit/s DPSK heterodyne optical transmission system is discussed. A narrow linewidth external cavity laser is used as a transmitter laser. A bit error rate of 10^-9 is achieved with a detected power of -53.3 dBm or 55 photoelectrons per bit.     

2.87-Gb/s random bit generation based on bandwidth-enhanced chaotic laser

We experimentally demonstrate a fast random bit generator (RBG) based on bandwidth-enhanced chaotic laser from an optical feedback laser diode with optical injection.The bandwidth-enhanced chaotic signal is sampled and converted to a binary sequence in real time without the need of programming for off-line processing.Multi-rate bit sequences,with the fastest rate of up to 2.87 Gb/s,are obtained with verified randomness.     

基于互注入半导体激光器的混沌输出产生17.5 Gbit/s随机码

采用两个借助光纤连接的相互注入半导体激光器,实验获取了10 GHz超宽带混沌种子信号.通过8-bit模数转换器将混沌信号转换为二进制数据流,并进行进一步的逻辑异或处理和舍弃最高有效位操作,最终获得了能顺利通过美国国家标准与技术研究院(National Institute of Standard and Technology,简记为NIST)800-22标准测试以及Diehard测试,速率达17.5 Gbit/s的高速随机码. 关键词： 随机码 混沌激光 互注入半导体激光器     

Message encoding-decoding at 2.5 Gbits/s through synchronization of chaotic pulsing semiconductor lasers

Chaotic optical communication with fast chaotic pulsing semiconductor lasers is experimentally demonstrated. Both a pulse stream at a 500-MHz repetition rate and a pseudorandom bit sequence at a 2.5-Gbit/s bit rate are successfully transmitted. The quality of synchronization in a chaos-modulation scheme is examined. The quality of message recovery is correlated to the quality of chaos synchronization.     

基于混沌激光产生1 Gbit/s的随机数

利用光反馈半导体激光器产生的混沌激光作为随机数发生器的物理熵源,通过8位 ADC将熵源信息转化为二进制码,并经后续差分运算处理改善其随机性,最终获得了1 Gbit/s的随机数.所产生的随机数通过了NIST Special Publication 800-22的全部测试项. 关键词： 混沌激光 随机数发生器 半导体激光器 模数转换     

Entropic analysis of the information rate density of broadband active fiber-optic communication links

The maximum transfer rate characteristics of broadband active fiber-optic communication links are considered within the model of filling numbers. It is established that, for active information transmission systems, in contrast to passive ones, not only the parameters of the line itself are significant but also the input signal-to-noise ratio. It is shown that the classical approach underestimates considerably the value of the maximum information rate density of erbium fiber amplifiers. In lengthy communication links with erbium amplifiers, the value of the information rate density may reach ～12–15 (bit/s)/Hz, which is more than one order of magnitude higher than the values achieved currently.     

20-Gb/s and Higher Bit Rate Optical Wavelength Conversion for RZ-DPSK Signal Based on Four-Wave Mixing in Semiconductor Optical Amplifier

We investigate 20 Gb/s wavelength conversion for return-to-zero differential phase-shift keying (RZ-DPSK) signal using four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). We show that the 10-Gb/s RZ-DPSK signal-to-pump ratio increases up to -0.286 dB with Q factor improvement of 1.663 dB for increasing the cascadeability of optical networks. The effect of variation in bandwidth for an ideal dual-arm Mach-Zehnder interferometer (MZI) is illustrated. For different bit rates, the converted power signal is investigated with increase in signal input power. We show that the quality of converted signal is best before the saturation of SOA. The dependence of four-wave mixing (FWM) efficiency and converted signal power with signal input power is also studied, and it is found that FWM efficiency decreases with increase in signal input power.

The impact of signal-to-pump power ratio, unsaturated amplifier gain, and pump power is further optimized with minimum Q factor penalty for 10-Gb/s and 20-Gb/s bit rate. We show that converted signal power increases up to power saturation level and then starts decreasing. We also show that with higher bit rate, we have a wide range of choices for pump power signal. We further investigate the quality of converted signal at 10 Gb/s, which shows an improvement over signal input power. Finally, the increase in transmission distance after wavelength conversion is investigated.     

320 Gbit/s wavelength conversion using four-wave mixing in quantum-dot semiconductor optical amplifiers

In this study, we demonstrate error-free all-optical wavelength conversion of ultrahigh-speed intensity modulated signals by means of four-wave mixing in a quantum-dot semiconductor optical amplifier. Error-free performance at a bit rate of 320 Gbit/s is measured for the extracted 40 Gbit/s tributaries with a 3.4 dB average power penalty to the original signal.     

A 729 nm laser with ultra-narrow linewidth for probing 4S1/2-3D5/2 clock transition of Ca

A Coherent Inc. Ti:sapphire laser MBR-110 is locked to a temperature-controlled high finesse Fabry-Perot cavity supported on an isolated platform. The linewidth is measured by locking the laser to another similar super-cavity at the same time and the heterodyne beatnote between two laser beams that locked to different cavities determines the linewidth. The result shows that the laser's linewidth is suppressed to be 41 Hz. The long-term drift is measured with a femtosecond comb and determined to be ~ 0.1 Hz/s. This laser is used to probe the 4S_1/2-3D_5/2 clock transition of a single ⁴⁰Ca⁺ ion. The Zeeman components of the clock transition with a linewidth of 160 Hz have been observed.     

Spectral efficiency analysis of OCDMA systems

We discuss several kinds of code schemes and analyze their spectral efficiency, code utilizing efficiency, and the maximal spectral efficiency. Error correction coding is used to increase the spectral efficiency, and it can avoid the spectral decrease with the increase of the length. The extended primer code （EPC） has the highest spectral efficiency in the unipolar code system. The bipolar code system has larger spectral efficiency than unipolar code system, but has lower code utilizing efficiency and the maximal spectral efficiency. From the numerical results, we can see that the spectral efficiency increases by 0.025 （b/s）/Hz when the bit error rate （BER） increases from 10^-9 to 10^-7.     

Numerical investigation on buffer performance based on acoustic excitation by stimulated Brillouin scattering in an As2Se3 fiber

Buffer performance of a 2.5 Gb/s bit stream with non-return-to-zero format is investigated based on acoustic excitation by stimulated Brillouin scattering in an As₂Se₃ fiber. The storage process and the retrieval process of the bit stream are separately controlled by a “Write” pulse and a “Read” pulse. The research results show that the output signal-to-noise ratio and the readout efficiency of the buffer are agreeable, and the pulse distortion is low, if both the “Write” and the “Read” pulses are with high enough peak power and spectrum wider than that of the signal pulse. Buffering of a consecutive 10-bit-long 2.5 Gb/s NRZ bit stream has also been demonstrated in the As₂Se₃ fiber with length of only 0.5 m. The storage of a long bit stream, such as the data packet containing about 1000 bits in the telecommunications, is limited by the high loss in the As₂Se₃ fiber. However, the development of the special optical fiber with high Brillouin gain coefficient, long acoustic lifetime and low loss can make this technology applicable for all-optical buffering in high speed optical networks.     

An optical OFDM multiplexer and 16 × 10 Gb/s OOFDM system using serrodyne optical frequency translation based on LiNbO3 phase modulator

This paper proposes an all-optical orthogonal frequency division multiplexing (OFDM) multiplexer based on sawtooth wave driving LiNbO₃ phase modulators by using serrodyne optical frequency translation. This multiplexer has high integration ability. The designing concept and implementation method have been discussed. A 16 × 10 Gb/s optical OFDM system is designed based on this multiplexer. Transmission characteristics, including tolerances of polarization mode dispersion (PMD) and nonlinear impairments have been studied numerically. Simulations show that the PMD tolerance is about 42 ps. The spectral efficiency reaches 1 bit/s/Hz with binary modulation format.     

An improved channel estimation method for a WDM transmission system derived from the CO-OFDM with PDM 64-QAM

In this study, firstly we presented a wavelength division multiplexed (WDM) transmission system derived from the coherent optical orthogonal frequency division multiplexing (CO-OFDM) with polarization division multiplexing (PDM) and 64 order quadrature amplitude modulation (QAM). We then proposed an improved channel estimation method based on discrete Fourier transform for the system to further improve the performance of the WDM transmission system. Under the experimental conditions employed, the principle and the spectral efficiency of the system, including a proposed algorithm to improve its performance (e.g. the robustness of the transmission impairments of the system) were studied. The simulations results demonstrated that our method improved the system efficient significantly. The system signal at 24 Tb/s can achieve a spectral efficiency of 12.5 bit/s/Hz up to a distance of 2000 km.     

20-Gb/s and Higher Bit Rate Optical Wavelength Conversion for RZ-DPSK Signal Based on Four-Wave Mixing in Semiconductor Optical Amplifier

Abstract

We investigate 20 Gb/s wavelength conversion for return-to-zero differential phase-shift keying (RZ-DPSK) signal using four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). We show that the 10-Gb/s RZ-DPSK signal-to-pump ratio increases up to ?0.286 dB with Q factor improvement of 1.663 dB for increasing the cascadeability of optical networks. The effect of variation in bandwidth for an ideal dual-arm Mach-Zehnder interferometer (MZI) is illustrated. For different bit rates, the converted power signal is investigated with increase in signal input power. We show that the quality of converted signal is best before the saturation of SOA. The dependence of four-wave mixing (FWM) efficiency and converted signal power with signal input power is also studied, and it is found that FWM efficiency decreases with increase in signal input power.

The impact of signal-to–pump power ratio, unsaturated amplifier gain, and pump power is further optimized with minimum Q factor penalty for 10-Gb/s and 20-Gb/s bit rate. We show that converted signal power increases up to power saturation level and then starts decreasing. We also show that with higher bit rate, we have a wide range of choices for pump power signal. We further investigate the quality of converted signal at 10 Gb/s, which shows an improvement over signal input power. Finally, the increase in transmission distance after wavelength conversion is investigated.     

Directly modulated DBR lasers for long-haul transmission at 1.7 Gbit/s

We demonstrate 1.7 Gbit/s transmission through 257 km of conventional fiber using directly modulated distributed-Bragg reflector (DBR) lasers and fiber amplifiers. This experiment resulted in a record bit rate distance product of 437 km Gb/s for direct modulation at rates between 1 and 3 Gbit/s. This paper has been accepted for presentation at OFC '92.