Long-span optical FSK heterodyne single-filter detection transmission experiment using a phase-tunable DFB laser diode

High receiver sensitivity (?51.9 dBm) and long span (243 km) transmission expriments have been achieved with a 140 Mbit/s optical FSK heterodyne single-filter detection system, using a phase-tunable DFB laser diode as a transmitter. This has enabled direct FSK modulation without waveform distortion. Also, a 280 Mbit/s 204 km transmission experiment has been carried out successfully.     

Over 300 km transmission experiment on an optical FSK heterodyne dual filter detection system

An optical FSK heterodyne dual filter detection system has been developed for the first time at 34 Mbit/s bit rate with a high receiver sensitivity of -61.4 dBm. A 66.9 dB large span loss margin has been achieved with high transmitted power and high receiver sensitivity. As a result, a 301 km transmission experiment has been performed.     

1.4 Gbit/s optical DPSK heterodyne transmission system experiment

The authors report the performance of a 1.4 Gbit/s differential phase shift keying (DPSK) coherent fibre system experiment using a balanced receiver. They show that the detection sensitivity as a function of local oscillator power follows the same functional dependence as the theoretical prediction     

Analogue video transmission over cabled monomode fibre using optical frequency modulation with heterodyne detection

The design and receiver sensitivity of a heterodyne detection system using analogue optical frequency modulation is examined for the transmission of a single baseband colour video signal. After transmission over 30 km of cabled monomode fibre, receiver sensitivity was measured to be ?70.3 dBm for a 53 dB unified weighted video SNR.     

Optical heterodyne detection

Optical heterodyne detection presents some difficult problems, but for certain applications it offers considerable advantage over the more conventional detection methods. Some of these advantages and problems, and how they are affected by the transmission medium involved, are discussed in this article. Experimental evidence has shown that although heterodyne reception is not desirable at the end of long atmospheric transmission paths, it is entirely feasible for long paths that are enclosed to isolate them from atmospheric disturbances.     

Infrared heterodyne detection

Heterodyne experiments have been performed in the middle infrared region of the electromagnetic spectrum using the CO2laser as a radiation source. Theoretically optimum operation has been achieved at kHz heterodyne frequencies using photoconductive Ge:Cu detectors operated at 4°K, and at kHz and MHz frequencies using Pb1-xSnxSe photovoltaic detectors at 77°K. In accordance with the theory, the minimum detectable power observed is a factor of 2/η greater than the theoretically perfect quantum counter, hvΔf. The coefficient 2/η varies from 5 to 25 for the detectors investigated in this study. A comparison is made between photoconductive and photodiode detectors for heterodyne use in the infrared, and it is concluded that both are useful. Heterodyne detection at 10.6 µm is expected to be useful for communications applications, infrared radar, and heterodyne spectroscopy. It has particular significance because of the high radiation power available from the CO2laser, and because of the 8 to 14 µm atmospheric window.     

Biphase linecoding in optical FSK heterodyne transmission experiment, without sensitivity degradation compared to NRZ

A biphase linecoding scheme was used in a 140 Mbit/s optical FSK transmission experiment. Owing to the analogue decoding, only 0.3 dB sensitivity penalty was observed, compared to NRZ. A sensitivity of -54 dBm was achieved.<>     

116 photons/bit in a 565 Mbit/s optical DPSK heterodyne transmission experiment

A 565 Mbit/s DPSK heterodyne experiment is presented. A sensitivity of -50.0 dBm at the receiver input was achieved, which is the best reported value for this data rate. The experimental data match the theory within 1.4 dB.<>     

Over 1000 km FSK heterodyne transmission system experiment usingerbium-doped optical fiber amplifiers and conventional single-modefibers

The influence of spontaneous emission noise on coherent transmission systems using multistage erbium-doped optical fiber amplifiers is experimentally examined. A frequency-shift keying (FSK) heterodyne transmission experiment was successfully performed at 560 Mb/s through 1028 km of fiber using ten cascaded fiber amplifiers and conventional single-mode fibers with a zero dispersion wavelength of around 1.3 μm. In the experiment, no transmission penalty due to accumulated spontaneous emission noise or to fiber chromatic dispersion was observed     

1 Gbit/s optical FSK heterodyne transmission experiment over 100 km of single-mode fibre

A 1 Gbit/s optical FSK modulation/heterodyne detection transmission experiment has been conducted at a wavelength of 1497 nm. The receiver sensitivity is ?37dBm and no degradation is observed after transmission through 100 km of single-mode fibre.     

立体声数字音频信号光纤传输实验系统的设计

选用非编程芯片设计了一种立体声数字音频信号光纤传输实验系统。系统由信号发送端机、光纤传输链路、信号接收端机组成,并利用2个不同波长的光信号作为载波分别传输左右声道的音频信号。仿真结果表明,系统可实现立体声音频信号的稳定传输。系统的全非编程芯片设计结构,使其各部分电路功能明确和易于更换,适合用于实验教学演示,能让学生更直观地理解数据如何组帧、传输等过程,具有较强的应用价值。     

100 Mbit/s ASK heterodyne detection experiment using 1.3 ?m DFB-laser diodes

By utilising 1.3 ?m-wavelength DFB-laser diodes and an LiNbO3 waveguide modulator, receiver sensitivity improvement as much as 10 dB over direct detection has been realised stably in a 100 Mbit/s ASK optical heterodyne detection 30 km transmission experiment.     

Fibre-optic based confocal scanning microscopy with semiconductor laser excitation and detection

A compact novel form of confocal scanning microscope using a semiconductor laser is described. Confocal operation is ensured by the use of a single mode optical fibre for both launching the light into the microscope and collecting the signal from the object. The collected light is allowed to reenter the laser and the image is detected as a modulation on the signal from the laser power monitor diode.<>     

Video transmission over cabled monomode fibre at 1.523 ?m using PFM with 2-PSK heterodyne detection

625-line colour video transmission over 61 km of cabled monomode fibre at 1.523 ?m is reported. PFM with 2-PSK heterodyne detection gives a receiver sensitivity of ?53.4 dBm at 50 dB video SNR, which is 5.2 dB from the shot noise limit and 8.4 dB better than direct detection. Alternative modulation configurations are discussed.     

200 Mbit/s DPSK heterodyne transmission experiment using colour centre lasers at 2.55 mu m

A 200 Mbit/s DPSK heterodyne transmission experiment has been performed using colour centre lasers operating at 2.55 mu m wavelength for the first time. The minimum received power was 14 dB better than with the previously reported 400 Mbit/s IM-DD system.<>     

Quantum noise in heterodyne detection

A fully quantum mechanical theory of diode mixers which includes quantization of the external circuit is presented. We find that Tucker's theory for SIS mixer conversion efficiencies is correct, but that his expression for the measurement noise must be augmented by an amount corresponding to half a photon at every frequency to which the mixer responds. Noise in high quality SIS mixers is shown to be accurately described by the conceptually simpler photodiode mixer noise theory. The radiation coupling efficiency term, η, which appears in photodiode theory turns out to be the coupling efficiency between the signal source admittance and the admittance which the SIS presents to the LO. Our theory reduces to Caves' quantum linear amplifier formalism, and therefore predicts measurement noises bounded by the quantum lower limit ofhv/k_{B}. Predictions of performance versus frequency for SIS's are made. We predict that NbN SIS's will behave as nearly ideal photodiodes for frequencies as high as 3000 GHz.     

A 10 Gb/s optical heterodyne detection experiment using a 23 GHzbandwidth balanced receiver

A balanced receiver for multigigabit-per-second coherent optical transmission systems is described. A balanced optical receiver with a frequency bandwidth of 23 GHz is achieved by connecting an InGaAs twin-p-i-n photodiode to a 0.5-30.0 GHz GaAs monolithic distributed amplifier fabricated with a soldier bump flip-chip interconnection technique. An experiment which demonstrated that this receiver has the potential for use in 10-Gb/s optical CPFSK (continuous-phase frequency shift keying) heterodyne detection systems was conducted     

A 2-Gbit/s optical FSK heterodyne transmission experiment using a 1520-nm DFB laser transmitter

Optical FSK transmission at 2 Gbit/s using a directly modulated DFB laser at 1520-nm wavelength is reported. A receiver sensitivity ofbar{P} = -36.7dBm (etabar{P} = -39.2dBm) at 10^-9BER was achieved for transmission over 101 km of single-mode fiber with no additional penalty attributable to the fiber. The effect of the nonlinear phase of the transmitter FM response, and the system performance for discriminator demodulation, including the impact of laser phase noise, is analyzed and compared with experimental results.