The current in the forward bias is known to be more (in `mA`)
than the current in the reverse bias (in ` mu A ` ). What is the reason then to operate
the photodiodes in reverse bias?

Explanation

The photodiode always work under reverse biasing conditions although the current is less. This is because in reverse bias, the width of the depletion layer increases which reduces the capacitance across the junction, thereby increasing response time. The sensitivity of a photodiode is thus very high, a property that is certainly desired.