High Receiver Sensitivity Research Articles

Narrow-gate In/sub 0.53/Ga/sub 0.47/As junction field-effect transistors as tunable resistors for long-wavelength integrated optical receivers

The fabrication of In/sub 0.53/Ga/sub 0.47/As junction field-effect transistors (JFETs) for use as active feedback resistors in integrated transimpedance photoreceivers is described. Transistors using both air-bridge and non-air-bridge technologies are described. Varying the gate-to-source voltage (V/sub GS/) allows the output resistance to be tuned continuously between 3 and 40 k Omega with a drain-to-source shunt capacitance of less than 10 fF. The temperature coefficient of the output resistance is between -5 and -20 Omega / degrees C (for V/sub GS/ less than the pinch-off voltage). The combination of large resistance and low shunt capacitance can result in high receiver sensitivity without sacrificing amplifier dynamic range. The feedback FETs are fabricated adjacent to 1.8- mu m gate JFETs with transconductances of 110 mS/mm and gate-to-source capacitances of 1.3 pF/mm. >

An optical FSK heterodyne dual filter detection system for taking advantage of DFB LD applications

An optimum system configuration for an optical frequency-shift keying (FSK) heterodyne dual-filter detection system with distributed feedback laser diodes (DFB LDs) is investigated, taking into consideration LD phase noise influence. Experimental and theoretical examination show that an IF filter bandwidth greater than 10 times the beat spectral linewidth is necessary to avoid LD phase noise influence. A 301-km long-span transmission experiment has been successfully carried out with an optimum configuration for 34 Mb/s. High receiver sensitivity, -61.8 dBm with more than 10 dB improvement over the direct detection system, has also been achieved. Experimental results at higher bit rates of 140, 200, and 280 Mb/s indicate that a modulation index greater than two is desirable to avoid cross talk between mark and space signals. With sufficient frequency deviations, high receiver sensitivities of -54.7 dBm (140 Mb/s) and -52.5 dBm (200 Mb/s) have been achieved. These represent 9.6- and 9-dB sensitivity improvement, respectively, over direct detection systems. A guide for FSK dual-filter detection system design is derived from the experimental and theoretical results. Potential application regions for a dual-filter detection system with DFB LDs are determined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In/sub 0.53/Ga/sub 0.47/As junction field-effect transistors as tunable feedback resistors for integrated receiver preamplifiers

In/sub 0.53/Ga/sub 0.47/As active feedback junction field-effect transistors (JFETs) for use in integrated transimpedance photoreceivers are discussed. By varying the gate-to-source voltage V/sub GS/, the resistance can be continuously tuned between 3 and 40 k Omega with a drain-to-source capacitance of <10 fF. The temperature coefficient of resistance is between -5 and -20 Omega / degrees C (for V/sub GS/ less than the pinch-off voltage). The combination of large resistance and low capacitance can result in high receiver sensitivity without sacrificing amplifier dynamic range. The feedback FET was fabricated adjacent to 1.8- mu m-gate-length JFETs with transconductances of 110 mS/mm, gate-to-source capacitances of 1.3 pF/mm, and DC amplifier voltage gains of 100. The compatibility of these transistor structures indicates that an integrated preamplifier with dynamically tunable bandwidth can be realized.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power penalty analysis due to polarisation diversity on 1.2 Gbit/s optical DPSK heterodyne transmission

An optical DPSK transmission experiment was performed at a bit rate of 1.2 Gbit/s using a dual-balanced polarisationdiversity receiver. A high receiver sensitivity of less than −42.8 dBm was achieved and the power penalty due to polarisation diversity was analysed.

2 Gbit/s optical CPFSK heterodyne detection transmission experiment using newly developed MQW-DFB laser diodes

The feasibility of newly developed multiple-quantum-well (MQW) DFB LDs as light sources for a high-sensitivity optical CPFSK heterodyne detection system has been confirmed in 2 Gbit/s transmission experiments. An 8 MHz narrow beat linewidth and optimum modulation index resulted in −41.6dBm high receiver sensitivity and 204 km transmission. This sensitivity was only 0.1 dB down from the 2 Gbit/s DPSK experiment result.

Advances in Lightwave Systems Research

Twenty years have passed since the first serious proposal was made to use a glass-fiber waveguide as a telecommunications transmission medium. Since then, vigorous research and development efforts have led to widespread applications of optical-fiber communication throughout the telecommunications industry. Today, lightwave systems research is exploring the vast potential bandwidth of low-loss single-mode fibers for long-haul and local-network applications. Laboratory systems with experimental single-frequency lasers and low-noise avalanche photodiodes have attained multi-gigabit-per-second transmission in single-mode fibers that are well over 100 km long. Coherent technology promises high receiver sensitivity and offers an efficient means for channel selection in a densely packed wavelength-multiplexed system. The first coherent-systems experiments have confirmed theoretical expectations but many challenges lie ahead. Other novel systems for local distribution and networking are also under study. This paper reviews recent research progress in these areas.

Long-distance gigabit-range optical fiber transmission experiments employing DFB-LD's and InGaAs-APD's

High-speed and long-distance transmission characteristics have been examined at 1.2, 2, and 4 Gbit/s, employing mesa structure DFB-DC-PBH LD transmitters and planar InGaAs APD receivers. High receiver sensitivities, -40 dBm at 1.2 Gbit/s, -37.4 dBm at 2 Gbit/s and -32.4 dBm at 4 Gbit/s, have been obtained employing high-speed and low noise InGaAs APD/FET receiver circuits. Long-span transmissions, 1.2-Gbit/s 170-km, 2-Gbit/s 141-km, and 4- Gbit/s 120-km at 1.55 μm, and 4-Gbit/s 74-km at 1.3 μm, have been performed. Power penalties caused by the LD wavelength chirping in the 1.5- μm wavelength region and error rate flooring caused by the LD side-mode oscillation in the 1.3- μm wavelength region are discussed. The transmission length is limited not only by the DFB LD wavelength chirping but also by the two-mode oscillation, which was observed at the pulse leading edge when LD bias current was near the threshold current. From the 1.3 μm wavelength 4-Gbit/s experiment, it was found that the pattern effect of the side-mode oscillation caused the error rate floor, when the LD bias current is set near the threshold current, and that the error rate floor disappeared when the bias current is set slightly above the threshold.

The application of coherent optical techniques to wide-band networks

The successful demonstration of optical heterodyne and homodyne techniques for point to point transmission links has led to an examination of their use in the context of wide-band systems. The high receiver sensitivity and frequency tuning ability potentially provide a means for accessing a significant part of the 50 000-GHz bandwidth provided by single-mode fiber. The possibilities for new network structures based on combinations of space, wavelength, and time switching are presented here, together with the concept of transparent networks which are not dependent on a particular modulation format or information rate.

Multigigabit-per-second avalanche photodiode lightwave receivers

High-speed avalanche photodiodes and high-sensitivity receivers are vital components for future multigigabit-per-second lightwave transmission systems. We review theoretical and experimental performance of high-speed III-V avalanche photodiodes, and also that of multigigabit-per-second lightwave receivers using FET and bi-polar amplifiers. Particular attention is given to APD gain-bandwidth product, and to its effect on high-speed receiver sensitivity. Comparisons between measured receiver sensitivities and calculated performance are presented for bit rates up to 8 Gbit/s.

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.

Frequency-doubling PFM system to prolong the distance of optical fibre TV programme transmission

In the square-wave PFM system for transmission of TV programmes through optical fibres, square-wave PFM pulses are generated at the transmitter with a relatively low centre frequency, whereas double-frequency equal-width narrow pulses are produced in the receiver before the demodulating low-pass filter, at both the rising and falling edges of the transmitted pulses. The use of the frequency-doubling technique in such a system results in narrow transmission bandwidth and high receiver sensitivity, thus prolonging the transmission distance significantly as compared with ordinary PFM. In the experiment, the system is operated at 1.3 μm with multimode fibre having bandwidth 700 MHz km, a laser diode as optical source and a PIN/FET as detector. It can effectively transmit the high-quality broadcast TV programme with accompanying sound channel to a distance of 50.7 km. Experimental results are: receiver sensitivity −40 dB m, weighted SNR for video 59.3 dB, differential gain and differential phase less than 1% and 1°, respectively.

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.

Optical DPSK heterodyne detection experiments using DBR laser diodes with external optical feedback

High receiver sensitivity, with 7 dB improvement over a direct detection system, has been achieved in a 400 Mbit/s optical DPSK heterodyne detection experiment using DBR laser diodes with external optical feedback. The influence of the laser output phase noise was evaluated experimentally in good agreement with theory.

SAGM avalanche photodiode optical receiver for 2 Gbit/s and 4 Gbit/s

A high-sensitivity optical receiver has been designed using an InGaAs avalanche photodetector and a low capacitance (0.63 pF) hybrid GaAs FET preamplifier. Measured receiver sensitivities at 1.51 μm wavelength of −36.6 dBm at 2 Gbit/s and −31.2 dBm at 4 Gbit/s are the best obtained to date at these bit rates.

2-Gb/s sensitivity of a Ga0.47In0.53As photoconductive detector/GaAs field-effect transistor hybrid photoreceiver

We have measured the 2-Gb/s sensitivity of a photoreceiver consisting of a Ga0.47In0.53As photoconductive detector and a GaAs low-noise field-effect transistor. For a bit error rate of 10−9, the photoconductive receiver shows a sensitivity of −28.8 dBm at 2 Gb/s and 1.51 μm. In view of its high receiver sensitivity and simplicity, the Ga0.47In0.53As photoconductive detector may be attractive for applications in high data rate lightwave communication systems, particularly local area networks.

Receiver design for high-speed optical-fiber systems

The technology of optical-fiber systems is advancing rapidly. Parallel to the development of long-haul telecommunication systems in the gigabits per second data rates operating in the long-wavelength region is the wide penetration of optical-fiber systems in local area networks, video trunking and distribution, sensors, etc. These diversified applications impose different and often conflicting constraints on the optical receiver. This paper re-examines the optical receiver design in view of these different requirements, namely, high receiver sensitivity, wide dynamic range, transparent to the operating bit rate, unrestricted data format, and fast acquisition time. Design tradeoffs between conflicting receiver requirements are considered in detail. In particular, the sensitivity of high-capacity long-wavelength transmission systems is emphasized. The state-of-the-art performance of photodetectors and low-noise amplifiers is discussed. We show that dark current of avalanche photodiodes (APD's) is the main factor limiting the sensitivity of long-wavelength optical receivers. In addition, as an example, we report on the design and experimental performance of a hybridized low-noise optical receiver amplifier capable of more than 2-Gbits/s operation. The input noise spectral density achieved is 9 pA/ <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sqrt{Hz}</tex> with a noise corner frequency of 920 MHz, corresponding to an equivalent noise resistance of 120 Ω.

A high-sensitivity correlation receiver for radio interferometry

A high-sensitivity correlation receiver for radio interferometry

1.55 μm optical transmission experiments at 2 Gbit/s using 51.5 km dispersion-free fibre

The high sensitivity of a Ge APD optical receiver, and dispersion-free fibres at a minimum loss wavelength of 1.55 μm, made it possible to achieve 51.5 km optical signal transmission at 2 Gbit/s. The optical receiving level was -31.4 dBm at a 10-9 error rate, and the degradation caused by fibre dispersion was only 0.6 dB. A data-rate repeater-spacing product of 103 (Gbit/s)km was achieved at 1.55 μm.

Broadband high-resolution receivers for the sub-millimetre region

This paper describes the main features of high performance heterodyne receivers for the sub-millimetre frequency range. The great interest in the use of these receivers for scientific observations dictates that high performances in the areas of frequency resolution, sensitivity and tuneability are mandatory. The parallel interest in eventual space application of such receivers due to the high attenuation of the atmosphere to submillimetre waves also motivates technological efforts to minimize the mass and power consumption and maximize the reliability and automation of such systems. The implications of these constraints on hardware choices are examined especially in terms of input mixers, local oscillators and back-end spectrum analysers. Recent technological advances leading to improved performances of these components are described as well as work presently in progress on the realization of a fully automated, high-resolution, high-sensitivity receiver working in the 300–500 GHz band. Details of the applications potential of such systems are discussed with special emphasis on the importance of space-borne heterodyne receiver systems.

The calculation of average error probability in a digital fibre optical communication system

This paper deals with the problem of determining the average error probability in a digital fibre optical communication system, in the presence of message dependent inhomogeneous non-stationary shot noise, additive Gaussian noise and intersymbol interference. A zero-forcing equalization receiver filter is considered. Three techniques for error rate evaluation are compared. The Chernoff bound and the Gram-Charlier series expansion methods are compared to the characteristic function technique. The latter predicts a higher receiver sensitivity.