Si-based receivers for optical data links

We present results for Ge_xSi_1-x waveguide pin detectors grown by rapid thermal chemical vapor deposition (RTCVD). Detectors with multiple Ge_0.29Si_0.71 absorption layers show an internal quantum efficiency of 33% at λ=1.3 μm with a dark current of 27 pA/μm². The external quantum efficiency is limited to 7% by the fiber-to-waveguide coupling efficiency. The output eye diagram for a hybrid λ=1.3 μm silicon receiver at 500 Mb/s is demonstrated. Prospects of a silicon-based optoelectronic receiver array technology are discussed     

Coherent homodyne optical communication receivers withphotorefractive optical beam combiners

The principles of operation and the results of performance measurements are reported of a new type of coherent optical receiver that used a dynamic volume index of refraction grating formed inside a photorefractive material to coherently combine signal and local oscillator light prior to photodetection. Because the refractive index grating is formed by the interference pattern generated where mutually coherent optical beams overlap, the receiver can automatically adjust to changes in angle of arrival or optical wavefront profiles which occur on time scales longer than the grating formation time. The grating appears stationary to high-speed phase modulation imposed on the signal beam and coherently diffracts local oscillator light into the signal beam direction. Performance measurements are reported for a prototype system that used two independent Nd:YAG lasers at 1.064 μm, an iron-doped indium phosphide photorefractive crystal, and a four-slot phase modulation signal format. A receiver BER of 10^-6 was obtained at received signal powers that corresponded to an average of 70 detected signal photons per bit at a source data rate of 50 Mb/s, 130 detected signal photons/bit at 220 Mb/s, and about 400 detected signal photons/bit at a 325 Mb/s source data rate. Quantum-limited operation corresponds to an average of six detected signal photons per transmitted information bit for this signal format     

Optimization of linear receivers for data communication signals

The optimization of receivers constrained to consist of a (linear) filter and level slicer is considered for general data communication signals in additive white Gaussian noise. Special consideration is given to the two limiting cases of arbitrarily low and high signal-to-noise ratios (SNRs). The low-SNR case results in an average matched filter receiver; the high-SNR filter is shown to be the solution to a specific nonlinear mathematical problem with a simple geometric interpretation. An efficient algorithm is developed to solve the problem. The results are illustrated for a duobinary minimum-shift-keyed signal observed over an interval of three-symbol-period duration     

Novel noise measurement setup with high dynamic range for optical receivers

A novel method is proposed, and verified experimentally, for wideband noise measurements with high dynamic range on optical receiver front ends. A synthetic white noise source, based on delayed selfhomodyne mixing, is calibrated with a weak shot noise source. The receiver noise is reconstructed from the calibrated synthetic noise source by ratio measurements.<>     

Wideband frequency-response measurement of optical receivers usingoptical heterodyne detection

Measurements have been carried out using 1.3-μm distributed-feedback laser diodes (DFB-LDs). The frequency difference of the LDs is continuously varied with temperature changes of a few degrees and the spectral linewidth of one of the LDs is narrowed by optical feedback using a grating. Wideband, highly sensitive measurement has been achieved for a p-i-n photodiode and a Ge avalanche photodiode from DC to 20 GHz. The result is compared with that of the pulse spectrum analysis (PSA) method. Although the finite pulsewidth in the PSA method causes roll-off in the frequency response, the optical heterodyne method has the advantage for very wideband frequency response measurement. The S/N ratio in the optical heterodyne method can be made as high (~40 dB) as that of the PSA method by narrowing the spectral linewidth of DFB-LDs     

The tradeoff between noise,data rate,and power consumption of transimpedance amplifiers for optical receivers

Analog Integrated Circuits and Signal Processing - The inverter-based shunt-feedback transimpedance amplifier (TIA) has become an essential building block for high-speed receivers for optical...     

Noncoherent data transition tracking loops for symbol synchronization in digital communication receivers

Starting with the maximum a posteriori (MAP)estimation approach, this paper derives the optimum (in the MAP estimation sense) means for performing symbol-timing recovery in the absence of carrier-phase information (i.e., prior to carrier-phase recovery). Specifically, we examine the necessary modification of a well-known form of coherent symbol synchronizer,namely, the data transition tracking loop (DTTL), to allow its operation in the absence of carrier-phase information, i.e., as a so-called noncoherent symbol sync loop. By employing such a noncoherent scheme, one can eliminate the need for iteration between the carrier and symbol sync functions,as typically takes place in receivers that more commonly perform carrier tracking and acquisition prior to symbol timing. The performance of both the linear and nonlinear versions of this noncoherent DTTL is obtained by a combination of analysis and simulation, and compared with that of the corresponding coherent DTTLs.     

Optical receivers for lightwave communication systems

As long-wavelength optical telecommunications systems are now being installed in countries throughout the world, this is an opportune time to review the successful developments in detectors and receivers for this application. We given prominence to receivers using p-i-n and avalanche photodiodes, describing in some detail the principles of their operation as well as the details of their development. However, we also consider bipolar phototransistors, photoconductive detectors, and the receiver requirements for coherent optical systems, concluding with a broad comparison of the various receiver designs.     

Optical receivers for lightwave communication systems

As long-wavelength optical telecommunications systems are now being installed in countries throughout the world, this is an opportune time to review the successful developments in detectors and receivers for this application. We given prominence to receivers using p-i-n and avalanche photodiodes, describing in some detail the principles of their operation as well as the details of their development. However, we also consider bipolar phototransistors, photoconductive detectors, and the receiver requirements for coherent optical systems, concluding with a broad comparison of the Various receiver designs.     

New automatic-gain-control system for optical receivers

A device using liquid crystals can be readily inserted in existing optical communications to simplify receiver circuitry, allow planning flexibility and simplify maintenance.     

长途通信光缆的障碍分析与维护

光缆已是铁通公司的一种重要的通信传输媒体.为了保障通信的安全,避免通信业务受到伤害,就必须做好光缆线路的管理和维护,因此,有必要了解各种光缆障碍现象、发生的原因,以及解决的办法,以便我们及时处理故障,保证通信的安全.     

High performance receivers for optical communications

The principles underlying optical detection are reviewed and the practical realisation of devices and receivers for digital optical communications is discussed. Some emphasis is placed on the advanced receiver signal processing techniques-both electronic and optoelectronic-that are now coming forward to provide a performance approaching the fundamental limits imposed by quantum mechanical considerations     

Transformer-tuned front-ends for heterodyne optical receivers

We present measured noise spectra for heterodyne optical receivers with front-end tuning based on a T-equivalent circuit of transformer coupling. A noise spectral density below 6pA/?(Hz) over a 1-3 GHz bandwidth is demon-strated, even with parasitic capacitances totalling 2 pF.     

Exact evaluation of laser linewidth requirements for optical PSKhomodyne communication systems with balanced PLL receivers

The power penalty induced by imperfect phase recovery in PSK homodyne communication systems with balanced phase-locked loop receivers are exactly evaluated. Optimum phase deviations between the mark-state and the space-state bits are used in this study. This study for the first time shows the imperfect-phase-recovery-induced power penalty as a function of laser linewidth with optimum phase deviations considered. It can be estimated from the theoretical result that an optimal balanced PLL receiver requires the laser linewidth as Δν⩽1.15×10^-6× (bit rate) in contrast to the previous reported one Δν⩽5.88×10^-6× (bit rate). We also point out here that the previously reported laser linewidth requirement was wrongly estimated     

Method of calculating minimum distance for suboptimum receivers

A method of calculating the minimum distance for suboptimum receivers is presented. The amount of computation required to calculate the minimum distance by this method is significantly less than by the method used previously. If the value of a parameter is well chosen the results are the same in both methods.     

基于合成光学相干函数的长距离分布式传感技术

研究了基于合成光学相干函数的长距离分布式光纤传感系统,阐述了系统工作原理,测量了10.225km光纤末端6个连续反射点,空间分辨率达到了2.20m,并验证了反射光解调信号强度与回波损耗的对应关系.     

Tuned front-end design for heterodyne optical receivers

A theoretical analysis of the noise performance of optical receivers with front-end tuning, suitable for wideband coherent systems, is presented. An algorithm for choosing the values of the tuning components in the front end so as to minimize the thermal noise output power has been developed. This theory is applied to the well-known simple parallel and serial tuning configurations and also to three more advanced designs. It is shown that any tuning is better than none in the wide-bandwidth designs considered and that the more advanced designs yield up to 12-dB reduction in thermal noise power. Two of the designs can be implemented with discrete components and should yield shot-noise-limited detection with 50-100 μW of local oscillator power in receivers with 5-GHz bandwidth. The practical problem of equalizing the front-end response is considered, and it is shown that good performance can be expected using realizable components     

Area-efficient CMOS transimpedance amplifier for optical receivers

In this letter, a broadband area-efficient transimpedance amplifier (TIA) for optical receivers is designed using a standard 0.18 μm CMOS technology. A new shunt–shunt peaking technique is used at the input transimpedance stage, which is followed by a gain stage and a capacitive degeneration stage. The amplifier achieves a wide bandwidth with only one inductor; hence a smaller silicon area is maintained. The proposed TIA has a measured transimpedance gain of 50 dB Ohm and a −3 dB bandwidth of 6.5 GHz for 0.25 pF input photodiode capacitance. It consumes DC power of 14 mW from a 1.8 V supply voltage and occupies only 0.09 mm² silicon area.     

单片机矩阵大面积测温及远程通讯系统

文中给出了一种利用矩阵结构进行多点测温的方法，它能充分利用计算硬件资源，降低系统成本，扩展了单片机在大面积多点测量领域里的应用，系统设计有效了克服通迅中信号的碰撞问题和传输错误，具有可靠性高，抗干扰性能等优点。