Post Amplifier Research Articles

A polarization-maintaining pedestal-free femtosecond pulse compressor incorporating an ultrafast dispersion-imbalanced nonlinear optical loop mirror

We report a polarization-maintaining and dispersion-flattened pulse compressor based on a dispersion decreasing fiber (DDF) for compression and a dispersion-imbalanced nonlinear optical loop mirror (DI-NOLM) for pedestal removal. A dispersion management scheme was used in the DI-NOLM to reduce dispersive spreading, which allows efficient switching for ultrashort pulses. Input pulses of 3 ps duration at 10 GHz were compressed to as short as 140 fs with a spectral width of 56 nm, time-bandwidth product of 0.96, and average power of 8.5 mW. This pulsewidth was limited by the higher order dispersion in the DI-NOLM. Using a post filter and a post amplifier, we obtained transform-limited 170 fs pulses at an average power of 100 mW with peak-to-pedestal ratios exceeding 35 dB. The compressor was adjustment-free, which is critical for practical use.

1580-nm band, equally spaced 8 x 10 Gb/s WDM channel transmission over 360 km (3 x 120 km) of dispersion-shifted fiber avoiding FWM impairment

Optically repeated wavelength-division multiplexed (WDM) transmission over dispersion-shifted fibers (DSF's) in the novel 1580-nm wavelength band is reported. WDM systems operating on DSFs are severely impaired by nonlinear crosstalk caused by four-wave mixing (FWM). We avoid this impairment by using novel 1580-nm band instead of the conventional 1550-nm band. Newly developed erbium-doped fiber amplifiers (EDFAs) for 1570-1600-nm wavelength band (gain-shifted EDFAs) are used as pre- and post amplifiers as well as in-line amplifiers. We demonstrate, for the first time, that long in-line amplifier span (120 km, span loss /spl sim/30 dB), high-bit rate (10 Gb/s), optically repeated WDM transmission over a 360 km (3/spl times/120 km) DSF is possible by using 1580-nm band channels without FWM impairment.

Potential of the distributed amplifier as a photo-diode detector amplifier in high bit rate optical communication systems

The theoretical performance of the common source MESFET amplifier and distributed amplifier as a post photodetector amplifier for use in high bit rate optical communication systems are compared. The calculations suggest that a 7dB improvement in the noise level may be obtained from the distributed amplifier in this situation in comparison with the conventional common source amplifier.

Over 350 km CPFSK repeaterless transmission at 2.5 Gbit/s employing high-output power erbium-doped fibre amplifiers

A 351.4 km CPFSK repeaterless transmission at 2.5 Gbit/s is described, which uses a newly developed post amplifier consisting of two erbium-doped fibres. Amplifier output power of +18.8 dBm and a maximum allowable attenuation as high as 63.8 dB in the optical link were achieved.

Broadband cryogenic preamplifiers incorporating GaAs MESFETs for use with low-temperature particle detectors

Two voltage-sensitive preamplifier designs are presented for operation at 1.6 K. Both designs incorporate GaAs MESFETs (Plessy P35-1101). The first design has two stages including a common-source gain stage and a source follower stage. The noise performance, particularly with the low-frequency noise, was found to improve with cooling. The white-noise level at low temperature is 1 nV/Hz1/2, and the low-frequency noise corner occurs at approximately 1 MHz. The voltage gain into 50 Ω is 7.0 dB, with the −3-dB point occuring at 10 MHz. The noise of the first stage was found to dominate the total noise at the output of a low-noise room-temperature post amplifier. The output impedance of the preamplifier is 50 Ω. The second design incorporates one cold FET, dissipating 1 mW, in cascode with a room-temperature bipolar transistor. The noise of this design was found to be approximately equal to that of the two-cold-stage design except for a bulge in the voltage noise centered at 13 MHz due to impedance mismatching of the line to room temperature. The gain of this design is 21 dB, with the −3-dB point at 2 MHz. Cryogenic semiconductor operation is discussed, design parameters of the two preamplifiers are discussed in detail, noise measurements are presented along with a discussion of the different temperature- and bias-dependent noise sources, and an analysis of the signal-to-noise ratio and rise time for the present detection scheme is made.

Very Wide-Band Silicon Bipolar Monolithic Amplifiers

We have developed very wide-band monolithic amplifiers, using an advanced silicon bipolar process called SST-2 which made it possible to lower base resistance and parasitic capacitance. Analog ICs, such as AGC and post amplifiers, for repeater circuits of a high speed optical fiber transmission system were fabricated, and the following excellent characteristics were obtained. (1) The gain and 3 dB down bandwidth of the post amplifier are 15 dB and 1.4 GHz, respectively. (2) The maximum gain, 3 dB down bandwidth and dynamic range of the AGC amplifier are 28 dB, 630 MHz and 30 dB, respectively.

The Nuclear Particle Detection System (NPDS) a proton-alpha particle counter for the Apollo system

The Nuclear Particle Detection System (NPDS) is a charged particle counter designed to measure solar flare protons and alphas incident on the Apollo spacecraft. The instrument detects protons in four differential energy intervals between 10 and 170 MeV, alphas in three differential energy intervals between 42 and 318 MeV. It also integrates all protons with energy ≥ 15 MeV. The instrument consists of two major components: i) the detector telescope and ii) the signal analyzer. The detector telescope employs three solid state detectors and has three charge sensitive preamplifiers in it. The signal analyzer contains primarily six post amplifiers, sixteen level sensors, a logic module, a dc to dc converter and eight ratemeters as outputs. The instrument works in both an E and d E/d x mode to produce a “cusp” in the response curve of each detector to incident protons and alphas. The setting of the level sensors together with the proper range to the front of each detector and the system logic determines the energy intervals of protons and alphas detected. A total of twenty-three instruments have been produced and one will be flown on each Apollo mission starting with Apollo 8. The total system operation is discussed in the paper.

High Stability Multiparametric Modular Circuitry used in the Experiments at the Saclay's Cyclotron

Advent of the small semiconductor detector makes easier complex multiparametric experiments which may include a great number of detectors to provide precise information on location and energy of particles. Such complex systems pose special requirements for reliable, flexible and high performance electronics. A set of modular circuits has been designed for use at the Saclay cyclotron which may be assembled easily for either simple or complex experiments. The following modular and sub-modular circuits are described: (1) charge-sensitive preamplifier module, (2) highly stable gain, low noise, 15 nsec minimum rise time charge-sensitive preamplifier submodule, (3) preamplifier-associated discriminator module, (4) 4-input, low noise, stable, low level linear mixer, (5) low level discriminator to be driven directly from the above preamplifiers, (6) precision, semi-fast high level discriminator, (7) 3-input, highly stable gain, gated linear amplifier with precision, continuously adjustable gain, (8) 4-input, high level linear mixer and biased post amplifier, (9) automatic testing system. The modules are described and the application of the modular system is illustrated in connection with nuclear spectroscopy experiments employing /g=a//g=a/'-scattering.

The Microbarographic Detection of Nuclear Explosions

In order to study the atmospheric pressure perturbations produced by the passages of gravity and acoustic-gravity waves through the atmosphere, a sensitive rate of change instrument (microbarovariograph) has been developed at Lamont. Similar instruments of different design have also been in successful opertion at several other institutions here and abroad. In general, this instrumentation has also proven capable of recording the pressure variations from nuclear explosions in the megaton range for distances which depend on the magnitude and elevation of the initial explosion. The Lamont pressure transducer is a U-tube manometer using a stable liquid plasticizer, dioctyl sebacate, of very low thermal expansion, vapor pressure and creep. One side of the system is connected to a fixed insulated air reservoir or compliant volume. An adjustable leak in parallel controls the long period time constants. Fluctuations of the liquid level in the open end are sensed by a moving coil in a differential transformer whose 60-cycle output is directly proportional in magnitude to the level changes, provided such changes are small. The signal, amplified and demodulated, gives a sensitivity of about 0.030 millibars (30 dynes per cm2) per cm of scale deflection for a stop displacement. A DC post amplifier can give a sensitivity of about 0.001 millibars (1 dyne per cm2) per cm of scale deflection. At the higher sensitivity, special hydraulic filtering procedures must be employed on the transducer in order to reduce atmospheric noise. Broad band recording is best accomplished at the lower sensitivity.