Resonant p-i-n-FET receivers for lightwave subcarrier systems

A theoretical and experimental analysis of narrowband resonant direct-detection p-i-n-FET receivers for subcarrier multiple-access networks is described. It is shown how a small inductance can be used to optimize the coupling between the p-i-n and FET, over a range of microwave subcarrier frequencies, minimizing the frequency-dependent thermal noise and leaving shot-noise as the ultimate limitation. Shot-noise then establishes a fixed ratio of the total usable bandwidth to the minimum received power per channel, which for the binary FSK system considered is 6.1 GHz/μmW. A resonant p-i-n-FET receiver, designed to provide maximum sensitivity between 2.5 and 5.0 GHz, has been constructed. The measured signal-to-noise ratio is in excellent agreement with that predicted by the noise analysis     

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     

Mode-partition noise in microwave subcarrier transmission systems

A simple model describing the change in mode-partition noise as a function of modulating frequency, modulation depth, and dispersion in a microwave SCM, fiber optic transmission system is presented with experimental verification. The effects of temperature on laser intensity and mode-partition noise are also explored. Longitudinal mode distribution associated with low and high noise levels are identified     

Semiconductor optical amplifier for wavelength conversion in subcarrier multiplexed systems

The fabrication and performance of a InGaAsP-InP semiconductor optical amplifier for wavelength conversion in subcarrier multiplexed system is described. The amplifier is of the buried facet design and has polarization and reflectivity gain ripple of less than 1 dB. Using subcarrier multiplexing, multiple 50-Mb/s data streams at a wavelength of 1.553 /spl mu/m are infected into the amplifier. The gain nonlinearity of the amplifier transfers the data to a different wavelength of light simultaneously injected into the amplifier. Error free retrieval of subcarrier multiplexed data has been demonstrated for the wavelength converted output. The small signal bandwidth of the wavelength conversion process is 5 GHz. Calculation suggests that higher bandwidth is feasible at higher input powers at the expense of lower modulation transfer during wavelength conversion.     

Crosstalk due to optical demultiplexing in subcarrier multiplexed systems

We report an in-depth investigation of the inter-modulation crosstalk in subcarrier multiplexing (SCM) systems with optical demultiplexing (ODeMux). Both theoretical derivations and numerical simulations show that the crosstalk in ODeMux systems mainly comes from the nonlinear mixing of the baseband and subcarrier modulations inside the signal channels. Several key parameters are then studied to estimate their effects on the magnitude of the crosstalk. As a result, performance optimization strategies are proposed for ODeMux SCM systems. In order to further enhance the transmission performance of ODeMux SCM systems, we discuss two techniques to suppress the inter-modulation crosstalk and analyze their effectiveness with numerical simulations.     

Optical interference in subcarrier multiplexed systems withmultiple optical carriers

It is shown that, when multiple optical carriers are used in a subcarrier multiplexing system, optical interference noise limits the system bandwidth or the number of available channels. Results of a statistical analysis are presented for a system with multilongitudinal mode semiconductor lasers. The results of the statistical calculations indicate that, when one channel per optical source is transmitted, then the system will be limited to only 16 video-quality channels. However, this number can be increased carefully by choosing and maintaining separate wavelengths for the lasers, in order to minimize the interference noise     

Real-time implementation of optical OFDM transmitters and receivers for practical end-to-end optical transmission systems

Real-time optical OFDM transceivers are successfully demonstrated for the first time, which support 1.5 Gbit/s transmission over 500 m 62.5/125 μm multimode fibres in an intensity-modulation and direct-detection system involving a directly modulated DFB laser. The implemented transceivers only use standard commercially available components.     

Lightwave system using microwave subcarrier multiplexing

We present a demonstration of subcarrier multiplexing in a lightwave multiple-access network. Three 44 Mbit/s digital signals are transmitted along a single-mode fibre bus by intensity-modulating two 1.3 ?-wavelength, multimode laser diodes with FSK subcarriers, at frequencics between 3.5 and 4.0 GHz. Intermodulation distotion, generated when two or more subcarriers are transmitted by the same laser, does not degrade the tranmission quality.     

使用微波作为副载波的光纤应力传感器

光纤应力传感器是以光纤传感技术为基础的应变、应力测量系统,具有重要的民用、军用价值。其中有一种能用于大型建筑物形变监测的传统的光纤应力传感器又叫 SOFO。它使用迈克尔逊干涉仪作为信号解调器,因为需要扫描,所以响应时间较长。为了解决这一问题,出现了以微波作为副载波的应力传感器。但是其中使用的光环行器又引入了较大误差,使得系统性能不理想。本文分析了误差原因,并使用耦合器、相位比较器分别替代了环形器、乘法器,取得了良好的实验结果。     

Low-noise receivers for fiber-optic microwave signal transmission

The problem of low-noise reception of high-frequency narrowband modulated optical radiation is discussed. Relatively simple p-i-n diode/FET based optical receiver structures which achieve good narrowband optical sensitivity are proposed. These receivers achieve good gain and noise performance due to a lossless parallel resonance circuit which shunts the input to the detector and FET. Design characteristics are presented for S-band receivers constructed using low-capacitance photodetectors, and GaAs MESFETs. Experimental realizations of these receiver designs, which achieve conversion efficiencies on the order of 250 V/W and optical noise equivalent power of less than 10 pW/√Hz for 0.8-μm radiation, are reported. Scaling rules which should be of use in optimizing the performance of more advanced designs are stated and other types of receiver structures which can be expected to yield high narrowband optical sensitivity are discussed     

A remote supervisory system based on subcarrier overmodulation forsubmarine optical amplifier systems

A supervisory (SV) signal transmission scheme for long haul optical amplifier systems is described. The scheme is based on subcarrier overmodulation of the line signal and features simple configuration; due to the use of EDFA gain modulation, no additive optical components are required in a submarine repeater to transmit a response signal. This paper discusses the subcarrier modulation index and frequency used for the SV signaling, the most significant design parameters. The dependence of the signal-to-noise ratio (SNR) on the modulation index in SV signal transmission is analyzed to clarify the modulation index value required for reliable SV signaling. In addition, the line signal impairment caused by subcarrier overmodulation is also analyzed to show the system's in-service feasibility. The subcarrier frequencies used for command and response signal transmission are discussed from the experimental results on the frequency response of an optical amplifier system and EDFA gain modulation efficiency     

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     

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.     

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.     

Performance comparison of subcarrier multiplexed coherent systems using optical intensity and phase modulators

The performance of subcarrier multiplexed coherent systems is compared theoretically using optical intensity and phase modulators. The results show that a subcarrier multiplexed coherent system with a symmetrical optical intensity modulator can offer a receiver sensitivity improvement as high as 9.1 dB over that with an optical phase modulator.<>     

Optical preamplifiers for subcarrier multiplexed lightwave systems

It is shown that optical preamplifiers used in conjunction with wideband 50 ohm microwave amplifiers make excellent receivers for subcarrier multiplexed lightwave systems.<>     

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     

GLRT receivers for UWB systems

This letter investigates generalized-likelihood-ratio-test (GLRT) detectors for ultra-wideband (UWB) impulse radio systems employing two alternative signaling schemes. One is the so-called transmitted reference method where, in each time frame, a reference pulse is transmitted prior to the data pulse. The other is the differential transmitted reference scheme, wherein the data pulse received in the previous frame is used as a template waveform in the current frame. The two detectors are compared in terms of bit error rate performance.     

Analysis of optical amplifier noise in coherent opticalcommunication systems with optical image rejection receivers

A detailed theoretical analysis of optical amplifier noise in coherent optical communication systems with heterodyne receivers is presented. The analysis quantifies in particular how optical image rejection receiver configurations reduce the influence of optical amplifier noise on system performance. Two types of optical image rejection receivers are investigated: a novel, all-optical configuration and the conventional, microwave-based configuration. The analysis shows that local oscillator-spontaneous emission beat noise (LO-SP), signal-spontaneous emission beat noise (S-SP), and spontaneous-spontaneous beat noise (SP-SP) can all be reduced by 3 dB, thereby doubling the dynamic range of the optical amplifier. A 2.5-dB improvement in dynamic range has been demonstrated experimentally with the all-optical image rejection configuration. The implications of the increased dynamic range thus obtained are also discussed from a systems point of view