No abstract

No abstract

No abstract

No abstract

ABSTRACEIn the detection of modulated light in fiberoptic links, PIN photodiodes play an important role. These devices are essentially junction devices. Under proper biasing conditions, the junction capacitance of these devices can be changed by light illumination. This paper reports the results of tuning and frequency modulation experiments with a 24.5GHz HEMT oscillator configured with a PIN photodiode as the tuning element. In addiion to microwave applications of the PIN photodiode, the optical perfomance of the PIN photodiode was also investigated. Experimental results supported the detection of a frequency reference at 8.230GHz and a pulsed modulated IF at 4.399 GHz. By this procedure, we were able to simultaneously synchronize the HEMT oscillator, amplify the IF, and mix the IF with HEMT oscillation frequency. INTRODUCIIONOptoelectronic devices are an integral part of many high-speed fiber optac networks. Most of the optoelectronic devices are based on the p-n junction, and among them semiconductor laser diodes and PIN photodiode are commonly used in many integrated optoelectronic subsystems. In fact optoelectronic integrated technology (OEIC) has reached a level of maturity.Nowadays where the integration of PIN photodiodes with FET amplifiers is routinely performed. In such a configuration the photoconductive characteristic of the p-n junction is used, where the modulated photons are absorbed in the depletion region (i region) of the device. However, p-n junctions manifest other circuit characteristics such as capacitance modulation, as prominently experienced in varactor diodes. Because the characteristics of PIN photodiodes do not differ from those of microwave p-n junction based switches and modulators, these optical devices could also exhibit changes in junction capacitance as a function of biasing. This change in capacitance can be exploited in a similar fashion as are varactor diodes when used in a number of microwave applications. Of particular interest is frequency tuning and modulation of oscillators (1).Conversely, under appropriate biasing conditions the PIN diode's junction capacitance can be controlled by light, resulting in phase shifting(2) and switching(3) depending on whether capacitive or conductive change of the device is employed. The light dependent capacitance and conductance of the PIN diode is linked to light modulation of the depletion width in the intrinsic layer, which is very sensitive at bias voltages close to zero biasing (2). The same performance can also be expected out of PIN photodiodes, when they are reverse-biased well below the punch-through voltage.On the other hand, when the PIN photodiode is integrated with FET as an optical receiver, the FET can behave not only as amplifier but also as a nonlinear oscillator and mixer. The double duty features of PIN photodiode and FET makes them useful in optical interfaces with electronic circuits. These features are investigated in this paper.