Resonance in Link RF Gain by Negative Photocurrent Resistance of Electroabsorption Modulator Under Very High Optical Power

Gain–bandwidth relation of electroabsorption-modulated analogue fibre link: effect of photocurrent resistance

“…As the optical power driving the analogue fibre link has been increased to achieve higher radio-frequency (RF) gain, the operation of the EAM under high optical power has been studied and designs that enable the high-optical-power operation have been suggested. By combining the diluted waveguide that absorbs much reduced optical power per unit length and the modified quantum-well design [6][7][8], an EAM has been demonstrated to handle a very high optical power up to 25 dBm ( 320 mW) [9].Under this very high optical power, however, the analogue fibre link that utilises an EAM has been shown to have saturation in RF gain owing to the photocurrent resistance inherent in the EAM device [9][10][11][12]. The photocurrent resistance R ph is given by (dI ph /dV ) 21 , where I ph is the photocurrent generated in the EAM and V is the reverse bias voltage supplied to the device.…”

“…As a figure of merit that includes both the RF gain and the bandwidth, the gain -bandwidth product (GBW) of the analogue fibre link is examined under very high optical power. The concept of negative photocurrent resistance has been proposed recently to break the limit posed by the saturation due to the photocurrent [11]. The negative photocurrent resistance is caused by blue shift in electroabsorption, which can be induced by, for example, a step barrier inside the conventional quantum well (intrastep quantum well) [7,8].…”

“…Under this very high optical power, however, the analogue fibre link that utilises an EAM has been shown to have saturation in RF gain owing to the photocurrent resistance inherent in the EAM device [9][10][11][12]. The photocurrent resistance R ph is given by (dI ph /dV ) 21 , where I ph is the photocurrent generated in the EAM and V is the reverse bias voltage supplied to the device.…”

“…The photocurrent effect, however, changes the behaviours of both the RF gain and the bandwidth of the analogue fibre link. The general RF gain, G, including the frequency dependence f, is expressed as follows after including the effect of photocurrent [11,12]:…”

“…including the photocurrent resistance [11,13]. When the optical power is increased, C m typically increases owing to the photogenerated charge carriers [13,14], decreasing the bandwidth.…”