Balanced receivers with large bandwidths can be used in intensity-modulated (IM) lightwave systems or in continuous-phase frequency shift-keyed (CPFSK) lightwave systems. In the IM system, they can be used at the receiver to obtain a duobinary encoded signal at the preamplifier output.1 In a coherent CPFSK system, the balanced receiver can improve the receiver sensitivity by 3 dB.2 One can eliminate the local oscillator laser used in the coherent CPFSK system by using a Mach-Zehnder interferometer filter3 and a balanced receiver to incoherently detect the CPFSK signal.4 With data rates in excess of one gigabit per second, both IM and CPFSK lightwave systems will require large bandwidth preamplifiers that have associated problems of high-frequency noise, which increases as frequency squared (f2).2 Most balanced receivers used in current research utilize dual photodiodes followed by a preamplifier. There are several inherent disadvantages to this configuration. One disadvantage is that the resultant capacitance is doubled because of the two antiparallel photodiodes. This leads to a reduction in bandwidth and an increase in high-frequency noise.2 A solution is to separate the photodiodes with their own preamplifier and then sum the signals at the output of the preamplifiers.5 Off-the-shelf discrete components are used to demonstrate the method. A MMIC version of this balanced topology has never been reported and is presented here.

© 1996 Optical Society of America

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