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.     

Very-high-rank avalanche diode frequency multiplier

Recent experimental observations on silicon avalanche diode multipliers operated at about 35-GHz output frequency are presented. High-rank (up to 35) frequency multiplication is achieved with output power over 250 mW and conversion loss of 13 dB. The possibility of frequency multiplication by any integer n ranging from 8 to 35 with the same diode and without any idler circuit is pointed out. It is concluded that any output frequency can be selected between 28 and 39 GHz by varying the input frequency and the circuit tuning.     

Analog avalanche diode frequency division

The potential interest of analog, avalanche diode frequency dividers is demonstrated. Their fundamental operating principle relies on the use of an idler signal. Experiments performed on avalanche diode frequency dividers with division ratios of 2, 3, and 4 in the centimeter-wave range have pointed out the possibility of wide instantaneous bandwidth and interesting RF conversion efficiencies     

Characterization of avalanche diode TRAPATT oscillators

The characteristics of a coaxial avalanche diode oscillator circuit are calculated and compared with experimental results. The circuit admittance, as seen at the diode terminals, is calculated in the frequency domain for "optimally tuned" experimental conditions. The impulse response function of the circuit, as obtained from the transformed admittance, is used to obtain time-evolution solutions of the avalanche diode circuit system. The impulse response is more general than the previously employed differential equation characterization of a lumped element equivalent circuit. The simulation presented of the high-efficiency mode of oscillation allowed no adjustable parameters and is in excellent agreement with experiment. The simulation verifies the original TRAPATT [1] explanation for the high-efficiency mode of oscillation.     

Power amplification using an avalanche diode

A silicon avalanche diode operating in the high-power highefficiency mode of oscillation has been used as a reflection amplifier at frequencies below the oscillation frequency. Saturated power-output levels in excess of 7 W peak have been obtained with 6dB gain at 767 MHz.     

Injection-locked avalanche diode oscillator FM receiver

An injection-locked-oscillator FM receiver has been built in X-band waveguide using an avalanche diode oscillator. Measurements of the output voltage as a function of peak frequency deviation of the input signal were made and compared with theoretical values. Good agreement between theoretical and measured performance indicates that the avalanche diode is adequately described by the van der Pol model and that linear broad-band performance can be expected of the receiver.     

Computing the performance of optical receivers with avalanche diodedetectors

A method is described for exactly computing the probability distribution of the sum of the output of an avalanche diode and Gaussian noise using the Personick-McIntyre model of the random electron multiplication in the diode. A saddlepoint approximation is also presented. Both are incorporated in an optimization procedure for efficiently calculating the minimum input signal strength and the decision level that are needed to attain a preassigned error probability when the diode is embodied in a binary optical communication receiver     

Small-signal analysis of the Read avalanche diode

A small-signal analysis is made on the Read-type avalanche transit time diode in which both holes and electrons and differing ionization rates for holes and electrons are considered in a silicon diode. The avalanche region is assumed to be an unsymmetric abrupt junction in which the ionization coefficients vary with the distance through their exponential dependence on the field in the avalanche region. Solutions for the ionization integral are given in the dc case. The time-varying terms are introduced as small-signal perturbations on the dc case and solutions for the ionization integral are again obtained and expressed as a Fourier series. The coefficients of the series appear in the expressions for the admittance. This approach provides simple analytical solutions for the Read diode admittance. Also, direct evaluation of the Fourier coefficients is given in terms of the diode's breakdown voltage and other known parameters. An equivalent circuit for the Read diode is developed. Over a substantial frequency but for small transit angles of the drift region, it consists of a frequency independent negative conductance, inductance, and capacitance. The diode's spreading resistance is in series with these parallel elements. The circuit agrees with the measurements of Josenhans and Misawa. On the basis of the small-signal avalanche analysis the ultimate oscillator efficiency is estimated to be about 26 percent.     

Sensitivity penalty calculation for burst-mode receivers using avalanche photodiodes

This paper presents the sensitivity penalty for burst-mode receivers using avalanche photodiodes. The analysis takes into account detailed avalanche photodiode statistics, additive Gaussian noise, intersymbol interference and dc offsets in the receiver channel. The penalty has been calculated via comparison of bit-error rates (BERs), obtained using numerical integration, both in continuous- and burst-mode operation. Sensitivity penalties for burst-mode operation as a function of the mean avalanche gain are presented. The Gaussian approximation systematically underestimates the burst-mode penalty. It is shown that the penalty depends upon both the type of avalanche photodiode (APD) and the required BER. Optimum avalanche gains maximizing the sensitivity of the receiver are given. The influence of dc-offsets upon the sensitivity is studied. Furthermore, it is shown that the impulse response of the filters used to extract the decision threshold profoundly impacts the receiver performance. Finally, some important guidelines for the design of high sensitivity and wide dynamic range burst-mode receivers are given.     

A potentially low-noise avalanche diode microwave amplifier

A sequence of AlGaAs, GaAs heterojunctions can be used to generate a series of potential steps that are just large enough to accelerate conduction-band electrons to energies above the impact-ionization threshold while valence-band holes do not obtain this much energy. The smaller difference in the valence-band heterojunction discontinuity and the higher scattering rate for holes than conduction-band electrons are shown to suppress the initiation of impact ionization by valence-band holes in this structure. The resulting transit-time device is predicted to be a relatively low-noise amplifier or oscillator that can be used in the microwave region and will be insensitive to small fluctuations in the power supply voltage.     

Double epitaxy improves single-photon avalanche diode performance

A new single-proton avalanche diode (SPAD) with double-epitaxial silicon structure is presented. The device has a time response with short diffusion tail (270 ps time-constant), high resolution (45 ps FWHM, full-width at half maximum of the peak) and low noise, i.e. low-dark-count rate.<>     

TRAPATT oscillations in a p-i-n avalanche diode

The characteristics of TRAPATT oscillations in a p-in diode are discussed and an approximate semi-analytical solution for the diode voltage waveform is derived when the diode current is a square wave. It is shown that a traveling avalanche zone is not necessary to generate a dense "trapped" plasma and that the boundary conditions prevent the trapped plasma from completely filling the depletion layer. Typical voltage waveforms and corresponding diode power, efficiency, and impedance at the fundamental and higher harmonics are presented. When the diode current is a square wave the diode does not necessarily exhibit a negative resistance at all higher harmonics. A computer program for TRAPATT oscillations in a p-i-n diode is described. Its running time is two or three orders of magnitude less than more exact time domain computer analyses. Typical results of diode power, dc to RF conversion efficiency, and required circuit impedances are presented for several different current waveforms which are composed of up to the seventh harmonic of a square wave and the first two harmonics of a half-wave sine wave. It is shown that high-efficiency oscillations are possible with diode currents composed of only the fundamental and one harmonic.     

Microwave Si avalanche diode with nearly-abrupt-type junction

Microwave Si avalanche diodes with a nearly-abupt-type junction have been made. The maximum output power so far obtained in CW operation is 1.1 watts at 12 GHz with an efficiency of 7.7 percent. The maximum efficiency observed is 8.0 percent. The improved performance over the previously reportedp nu nstructure, for which the best result was 250 mW at 12 GHz with an efficiency of 2.8 percent results from a reduction in length of the avalanche region in the abrupt junction. In the previously reportedp nu ndiode the efficiency is still sharply increasing at the burnout point, while in the present diode the efficiency is nearly saturated at the burn-out point. The advantages and disadvantages of using different polarity of the diode (p on n or n on p) and different material (Ge) are given. Small-signal theory was used to analyze device operation.     

GaAs double-drift avalanche diode from vapour-phase epitaxy

p-type doping of GaAs grown by a vapour-epitaxy technique is accomplished in the range of 1015 cm?3 using a Zn source in a controlled-temperature zone, n-type doping is accomplished by admitting a controlled admixture of SnCl4 and AsCl3 into the system. Diodes were fabricated from a p?n?n+ substrate wafer and operated in an I?C TRAPATT mode in a compact circuit. TRAPATT action yields a spiky current waveform useful as a pulse generator.     

Low-noise operation of CW GaAs avalanche diode oscillators

Previous pulsed low-noise measurements of avalanche oscillators have now been extended to CW devices having GaAs vapor-grown p-n junctions. The best AM noise-to-signal ratio observed was -140 dB, which is about 15 dB better than previously measured for GaAs avalanche diode oscillators.     

Injected signal characteristics of high-power avalanche diode oscillators

Efficient injection locking results and other injected signal characteristics of high-power avalanche diode oscillators are presented. An injection locking figure of merit as high as 0.145 has been obtained.     

Bit-error rates for optical receivers using avalanche photodiodeswith dead space

Bit-error rates are computed for an on-off keying optical communication system using avalanche photodiodes (APDs). We use a model for the APD that includes dead space and the finite response time. Dead space is the minimum distance that a newly generated carrier must travel in order to acquire sufficient energy to become capable of causing an impact ionization in the multiplication region of the APD. The detector's finite impulse response and its randomness are important for high data-rate systems. Using an exact analysis, we show that the presence of dead space enhances the performance at relatively low data rates. Using a Gaussian approximation technique with the exact mean and variance, we demonstrate that dead space degrades the performance at-high data rates since it is responsible for longer tails in the impulse response function of the APD, which in turn increases the effect of intersymbol interference     

Computation of bit-error probabilities for optical receivers using thin avalanche photodiodes

The large-deviation-based asymptotic-analysis and importance-sampling methods for computing bit-error probabilities for avalanche-photodiode (APD) based optical receivers, developed by Letaief and Sadowsky [IEEE Trans. Inform. Theory, vol. 38, pp. 1162-1169, 1992], are extended to include the effect of dead space, which is significant in high-speed APDs with thin multiplication regions. It is shown that the receiver's bit-error probability is reduced as the magnitude of dead space increases relative to the APD's multiplication-region width. The calculated error probabilities and receiver sensitivities are also compared with those obtained from the Chernoff bound.     

Noise theory for the read type avalanche diode

An analysis is presented for the noise current spectrum of an avalanche diode under assumed conditions of ideal uniform avalanche behavior in a zone which is thin compared with the total high-field depletion zone. The result is applied to the Read diode amplifier. For a typical set of operating parameters, the theory predicts a noise figure on the order of 40 dB. Depending upon particular device parameters, lower noise figures may be possible.     

Composite avalanche diode structures for increased power capability

The possibility of operating several avalanche oscillator wafers in parallel to obtain higher power and/or higher efficiency CW operation is explored analytically and experimentally. Experiments show that over a wide range the efficiency is roughly proportional to the power density in the semiconductor. The power densities required for good efficiency are very high and cannot be achieved in large area junctions without an excessive temperature rise caused by the thermal spreading resistance of the heat-sink material. The scheme delineated herein considers small area wafers spaced sufficiently close electrically that they operate as a single avalanche oscillator whereas their physical separation permits essentially independent heat sinking. It has been found that, as expected, the efficiency for CW operation improves approximately inversely with the diode diameter whereas the power capability for a given size wafer increases directly with the number of such wafers employed. The relative merits of mounting diodes on copper and on diamond are discussed. Experimental work indicates that the present approach is capable of producing 10 to 15 watts CW at 14 GHz in a single oscillator with available silicon diodes.