Design techniques for subcarrier multiplexed broadcast opticalnetworks

Design techniques which enable the performance of subcarrier multiplexed FM broadcast optical networks to be optimized at the planning stage are described. At the transmitter node, criteria for maximizing the subscriber carrier-to-noise ratio (CNR) are presented. At the subscriber node, it is shown that under the majority of circumstances, the optimum direct detection receiver consists of a low-noise III-V avalanche photodiode and high-impedance front-end preamplifier. Sensitivities approaching -40 dB (1 mW) for 16.5 dB CNR in 36 MHz subscriber bandwidth are predicted for a 60-channel system. Preliminary experimental tests on an optical-feedback subcarrier receiver showed -34 dB (1 mW) sensitivity at 1.55 μm from 16.5 dB CNR in a 36 MHz bandwidth centered on 1.2 GHz with a 12% modulation index single-channel FM test signal     

Coherent transmission of 60 FM-SCM video channels

A fiber-optic 60-channel FM video system using coherent subcarrier multiplexing (SCM) is described. Two receiver implementations were studied. For the 60-channel coherent experiment, a carrier-to-noise ratio of 17 dB and a corresponding signal-to-noise ratio of 56 db was achieved with a detected optical power of -32 dBm and a phase modulation index of β-0.07. This represents a 15.2-dB improvement over a similar 60-channel direct-detection FM-SCM system and a 5.6 dB improvement compared to the performance of the system when a semiconductor optical preamplifier was used     

Wide bandwidth low noise pinFET receiver for high-bit-rate opticalpreamplifier applications

A wide bandwidth low noise pinFET receiver has been fabricated and characterised for optical preamplifier applications. The receiver uses a low capacitance planar pin diode as the photodetector. A bandwidth of 7.08 GHz was measured. The measured input noise current for the receiver front-end is lower than 12 pA/√(f). Using a 1.3 μm DFB laser as the transmitter, at a data rate of 4 Gbit/s, the measured receiver sensitivity is -25.5 dBm with a bit-error-rate of 1×10 ^-9. A set of two of such receivers has also been tested in a 1.3 μm polarisation-insensitive optical preamplifier system experiment. The measured receiver sensitivity, including an optical insertion loss of 1.5 dB, is -29.3 dBm     

Optical preamplifier using optical modulation of amplified spontaneous emission in saturated semiconductor optical amplifier

This paper demonstrates a novel optical preamplifier using optical modulation of amplified spontaneous emission (ASE) emitted from a saturated semiconductor optical amplifier (SOA). Requirements on optical alignments and antireflection coating for SOAs can be relaxed and the elimination of an optical filter gives us a large tolerance of an input light wavelength in the proposed optical preamplifier. A small-signal gain of a fabricated preamplifier was over 13.5 dB for an input power of below -20 dBm. An optical gain bandwidth was over 60 nm. We measured the small-signal response of the optically modulated ASE. The 3 dB bandwidths at SOA bias currents of 200, 300, and 400 mA were 5.8, 12.6, and 16.5 GHz, respectively. We also investigated improvements in receiver sensitivities with the proposed optical preamplifier. Our calculation shows a possibility of 10 dB improvement in receiver sensitivities by using the optical preamplifier at 10 Gb/s. The measured receiver sensitivity was -22.7 dBm at 10 Gb/s with the optical preamplifier, which is corresponding to an improvement of 2.5 dB in the receiver sensitivity. Further improvements of the receiver sensitivity can be expected by optimizing the structure of SOAs for saturating ASE.     

Performance of Multicarrier CDMA Rake System over Rayleigh Fading Channel

Based on the theory of multicarrier (MC) technique and the Rake receiver, a multicarrier DS-CDMA Rake system is proposed, where a data sequence multiplied by a spreading sequence modulates multiple carriers. The receiver provides a Rake for each subcarrier, and the outputs of the Rakes are combined by a maximal-ratio combiner. The average probability of error of the system is derived from an uncorrelated subcarrier and frequency-selective fading channel model. The system performances are evaluated over Rayleigh fading channel with an exponential multipath intensity profile(MIP) and with a rectangular MIP, respectively, when multipath interference is present. It is found that this kind of model has larger superiority in an exponential MIP than in a rectangular MIP.     

Error probability of interleaved MC-CDMA systems with MRC receiver and correlated Nakagami-m fading channels

The performance of an interleaved multicarrier code-division multiple access system with a maximal-ratio combining receiver is studied with the help of the characteristic function of correlated Nakagami-m random variables. Computer simulations are used to demonstrate the accuracy of the analysis. Based on the analytical results, with an exhaustive search of different subcarrier interleaving schemes, the optimal subcarrier interleaver which provides the minimum bit-error rate (BER) can be achieved. Compared to a random interleaver, the optimal subcarrier interleaver offers significant performance improvement.     

A 40-Gb/s preamplifier using AlGaAs/InGaAs HBTs with regrown basecontacts

A preamplifier for 40-Gb/s optical transmission systems incorporating AlGaAs/InGaAs heterojunction bipolar transistors (HBTs) with p⁺ regrown extrinsic base layers is described. The HBTs have a heavily doped regrown p⁺-GaAs layer in the extrinsic base regions and a thin graded InGaAs strained layer for the intrinsic base. Their measured peak f_max is above 200 GHz. The developed preamplifier provides a bandwidth of 38.4 GHz and a transimpedance gain of 41.1 dB Ω. Moreover, the frequency response as an optical receiver has a bandwidth of 32 GHz. These characteristics make the preamplifier suitable for use in a 40-Gb/s optical receiver. These results show that AlGaAs/InGaAs HBTs with p⁺ regrown extrinsic base layers are very promising for use in 40-Gb/s optical transmission systems     

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.<>     

Heterodyne video transmission with differentially encodedquadrature phase shift keying

Heterodyne transmission experiments of multiple video channels using differentially encoded quadrature phase shift keying (QPSK) are described. Combining the QPSK microwave modulation format with the subcarrier multiplexing technique results in a total of 20 video channels at 50 Mb/s being transmitted on 10 microwave subcarriers. Using a differential encoding approach, this system provides good receiver sensitivity and bandwidth efficiency, while maintaining a simple receiver design. No carrier recovery circuit or phase-locked loop is required for demodulation, which greatly reduces the receiver complexity. It is demonstrated that only a standard delay and multiply demodulator are necessary. With optical heterodyne detection, a receiver sensitivity of -37.5 dBm is achieved for the 20 channel system. The extension of this technique to intensity modulated direct detection subcarrier systems along with migration scenarios for digital video and broadband services is discussed     

Optical receiver sensitivity improvement by a semiconductor laser preamplifier

Application of a semiconductor laser as a preamplifier in a p.c.m. i.m. fibre-optic transmission system was studied theoretically and experimentally. Experimental results on equalised baseband noise power and error rate performance are in good agreement with new formulation taking spontaneous emission into account. The semiconductor laser preamplifier is found to substantially enhance optical receiver sensitivity.     

Practical implementation of a highly sensitive receiver using an erbium-doped fiber preamplifier

A practical erbium-doped fiber preamplified direct detection receiver is demonstrated with which receiver input sensitivities of -46.5 dBm at 622 Mb/s and -40.7 dBm at 2.3 Gb/s have been achieved. There is no penalty from the transmission fiber Rayleigh backscattering. The bit error ratio measurements with 2/sup 23/-1 NRZ PRBS (pseudorandom bit sequence) show highly stable characteristics with no apparent error floor, owing to the polarization insensitivity of the preamplifier and to an active locking of the receiver optical filter. The tradeoff between preamplifier and avalanche gain is shown, and the influence of optical filter bandwidth and decision threshold setting is measured.<>     

System performance of optical fibre preamplifier

An optical fibre amplifier has been used as an optical preamplifier for a PIN detector-based receiver. A maximum amplifier gain of 22 dB has been measured and, at this gain with no additional optical filtering, an improvement of 10.5 dB in receiver sensitivity has been achieved.<>     

1.6 Gb/s/pin 4-PAM signaling and circuits for a multidrop bus

A 1.6 Gb/s/pin 4-pulse-amplitude-modulated (PAM) multidrop signaling system has been designed. The motivation for multi-PAM signaling is discussed. The system uses single-ended+reference current-mode signaling with three dc references for maximum bandwidth per pin. A test chip with six I/O pins was fabricated in 0.35-μm CMOS and tested in a 28-Ω evaluation system using on-chip 2¹⁰ pseudorandom bit sequence (PRBS) generator/checkers. Two different 4-PAM transmitter structures were designed and measured. A high-gain windowed integrating input receiver with wide common-mode range was designed in order to improve signal-to-noise ratio when operating with smaller 4-PAM input levels. Gray coding allowed a folded preamplifier architecture to be used in the LSB input receiver to minimize area and power. In-system margins are measured via system voltage and timing shmoos with a master communicating with two slave devices     

Effect of nonuniform laser FM response on the performance ofmultichannel heterodyne FSK systems using optical amplifiers

A theoretical analysis is provided to evaluate the performance of optical frequency division multiplexed systems taking into considerations the combined effect of receiver noise, laser phase noise and nonuniform FM response characteristic of a practical DFB laser. To overcome the effect of nonuniform frequency modulation characteristic of semiconductor lasers, two different linecoding schemes are used for the laser driving signal. The crosstalk penalty due to the combined effect of nonuniform FM response and phase noise of lasers is evaluated. The improvement in receiver sensitivity due to optical preamplifier is also estimated. The computed results show that the performance of the system is highly degraded due to the effect of laser nonuniform fm response and can be reduced substantially by using linecoding. Further, there is considerable improvement in receiver sensitivity due to the use of an optical preamplifier in the absence of phase noise. In the presence of phase noise there is a reduction in receiver sensitivity     

On the performance of multicarrier RAKE systems

In this paper, we integrate the multicarrier signaling technique and the RAKE receiver to design a DS-CDMA system with the capability to increase the data rate, mitigate the effect of correlation among the various subcarriers, and suppress partial-band interference. In the proposed system, a data sequence is serial-to-parallel converted, and multicarrier DS-CDMA is used on each of the parallel data streams. The receiver provides a RAKE for each subcarrier, and the outputs of the RAKEs are combined by a maximal-ratio combiner. We employ a correlated subcarrier and frequency-selective fading channel model to derive the average probability of error of the system and compare the results with those of both a single carrier RAKE system and a multicarrier DS-CDMA system in a frequency selective Rayleigh fading channel with an exponential multipath intensity profile, when multiple access interference and partial-band interference are present     

FM microwave multiplexed broad-band distribution systems using Er3+ fiber amplifiers and preamplifiers

The use of an Er³⁺ fiber preamplifier for microwave multiplexed systems and the use of an inline Er³⁺ amplifier in microwave multiplexed systems for signal distribution are reported. The improvement in receiver sensitivity as a preamplifier, without optical filtering, was 9 dB. No power penalty due to amplified spontaneous emission was found when the amplifier was used in a 30-channel signal distribution system     

Improved sensitivity of 60 video channel FM-SCM receiver with semiconductor optical preamplifier

Reports for the first time on the improvement in receiver sensitivity of a 60 video channel FM-SCM system using a semiconductor optical amplifier as a preamplifier. A receiver sensitivity improvement of 9.6 dB is obtained.<>     

分布光纤拉曼放大器对光通信系统传输性能的改善

考察了后向抽运分布光纤拉曼放大器 (B DFRA)对光通信系统传输性能的改善。分别讨论了B DFRA的两种可能用途 :1)作为第一级预放器与掺铒光纤放大器 (EDFA)及光接收机一同构成接收终端。 2 )在一个有中继的长距离光通信系统中作为各级EDFA的预放器。针对这两种用途分别计算出B DFRA对系统性能的影响 ,并给出选择抽运功率的原则     

Subcarrier multiplexing for high-speed optical transmission

The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RE) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 × 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction     

卫星激光通信中光纤放大器的应用研究

介绍了卫星激光通信的特点,通过计算分析,提出了用于卫星激光通信光发射系统的高功率光纤放大器、用于光接收系统的前置光纤放大器的性能参数。给出了高功率光纤放大器和低噪声前置光纤放大器的实验方案。