Avalanche Photodiode Detector Research Articles

Temperature stability of transit time delay for a single-mode fibre in a loose tube cable

The effect of temperature on the transit-time delay of a loose-tube-type single-mode optical-fiber cable is investigated experimentally. A 1058-m length of cable was placed loosely coiled in an oven and used to connect a 820-nm single-mode laser diode to a high-speed avalanche-photodiode detector feeding a vector voltmeter; the signal was provided by a high-stability frequency-synthesized generator. Measurements were made every 2 C from -50 to 60 C and compared to those obtained with a 200-m lacquered bare fiber. The phase change of both fibers varied with temperature at a positive slope of 6-7 ppm/C. This value is significantly better than those reported for other cable types, suggesting the application of loose-fiber cables to long-haul gigabit digital transmissions or precision time-base distribution for VLBI.

Detectors For The 1.1 To 1.6 µm Wavelength Region

The current state of the art of photodetectors, both PIN and avalanche, for 1.1 to 1.6 um operation is reviewed. The devices are compared as components of optical receivers using several different types of amplifiers. GalnAsP/InP PIN and avalanche photodiode (APD) detectors are shown to be clearly superior to Ge devices with respect to dark current and other sources of noise. Receivers with performance within a few dB of the quantum limit appear to be possible with current technology.

Gallium arsenide electroabsorption avalanche photodiode waveguide detectors

Gallium arsenide electroabsorption avalanche photodiode (EAP) detectors have been fabricated in n - n(+) GaAs waveguides. Since these EAP detectors respond to wavelengths beyond the normal absorption edge of GaAs, due to the Franz-Keldysh effect, they have been used to detect the below band gap radiation from GaAs lasers and the 1.06-mum radiation from Nd:YAG lasers. The measured absorption and responsivity at these wavelengths suggest a number of applications. These EAP devices have been used to detect analog signals with a distortion less than 6%. Methods for utilizing them in time- and frequency-demultiplexing applications are also described.

GaInAsP/InP avalanche photodiodes

Avalanche photodiodes for detection at 0.9–1.2 μm have been successfully fabricated in epitaxial layers of GaInAsP on InP substrates. Uniform avalanche gains in excess of 12, rise times of 150 psec or less, and low-bias quantum efficiencies of 45% have been measured.

Tactical Optical Communications Set

The replacement of currently employed 26-pair and 27-pair cables within tactical communications Command Posts and data processing facilities has long been a goal of Army communications personnel. The use of optical atmospheric and fiber optic links offers advantages in cost, mobility, size, and security over current cable systems. The AN/TVC-4 is an advanced development model of a tactical optical communications set. It utilizes a GaAs laser diode source and an avalanche photodiode detector to provide full duplex data and voice transmission. Maximum data rate is 200 kilobits/sec with a close-confinement, single heterostructure laser diode and 5 megabits/sec with a Large Optical Cavity (LOC) laser diode. The system is designed to maintain a 10-6 probability of error (Pe) at a 3-km range under conditions of 10 dB/km atmospheric attenuation. The complete transceiver, less battery pack, is housed in a rugged 7 X 7 X 7.5 in. package which has undergone temperature, shock, vibration and humidity qualification testing. System design, component selection and performance analysis are described in detail and the results of field tests are presented.

Stabilization of the operating point of an avalanche photodetector

The reverse breakdown voltage of an avalanche photodiode detector depends on the temperature of the diode. To operate at maximum signal sensitivity the diode must be biased just below this avalanche breakdown voltage. The diode output noise rises sharply at breakdown, so the bias voltage requires critical adjustment to obtain the maximum signal-to-noise ratio. The paper describes how the diode output noise can be used to adjust the applied bias voltage automatically, to compensate for changes in diode temperature.