Light detector having a photodiode with bias control

Claim 2

A light detector for delivering an electrical measurement signal having signal components at a frequency representative of a frequency present in a light beam, having: an avalanche photodiode for receiving the light beam; source means for applying an adjustable bias voltage to said photodiode, whereby a variable measurement current is delivered by said photodiode; a circuit for measuring a mean value of said measurement current and delivering an output signal representative of said mean value; and means responsive to said output signal and controlling said source means for maintaining said mean value at a predetermined set value lower than that for which the current-voltage characteristic of said avalanche photodiode exhibits a bend.

Claim 3

Detector according to claim 1, wherein said converter further comprises voltage adjustment means connected to prevent the output voltage of said converter from lowering beyond a predetermined minimum value by overriding control by said transistor circuit.

Claim 4

A measurement assembly having: a light source delivering a light beam; means for separating said light beam into a first fraction and a second fraction and for directing said second fraction along a path where it is subjected to a physical phenomenon to be studied which modifies the frequency of light in said second fraction, said second fraction having an intensity much lower than that of the first fraction; an avalanche photodiode located to receive both said fractions; electrical source means for applying a bias voltage to said avalanche photodiode and causing a light representative current to pass in said photodiode; a circuit for measuring an average value of said current and delivering an electrical output signal representative of said average value; and means responsive to said output signal and arranged for controlling said source means for maintaining said average value at a predetermined set value lower than the current for which the inverse current-voltage characteristic of said photodiode exhibits a bend.

Claim 5

A measurement assembly having: a light source delivering a light beam; means for separating said light beam into a first fraction and a second fraction and for directing said second fraction along a path where it is subjected to a physical phenomenon to be studied which modifies the frequency of light in said second fraction, said second fraction having an intensity much lower than that of the first fraction; an avalanche photodiode located to receive both said fractions; electrical source means for applying a bias voltage to said avalanche photodiode and causing a light representative current to pass in said photodiode; a circuit for measuring an average value of said current and delivering an electrical output signal representative of said average value; and means responsive to said output signal and arranged for controlling said source means for maintaining said average value at a predetermined set value lower than the current for which the inverse current-voltage characteristic of said photodiode exhibits a bend.

Claim 6

Detector according to claim 1, wherein said means responsive to the output signal of said circuit further comprises limiting means arranged for limiting said bias voltage to a predetermined maximum value.

Claim 7

Detector according to claim 1, wherein said circuit for measuring the mean value has a low pass filter having a cut-off frequency greater than 1 Hertz and in the 1 Hertz order of magnitude.

Claim 8

Detector according to claim 1, wherein said circuit for measuring the mean value comprises an integrating differential amplifier connected to receive an output signal from said photodiode and a reference voltage representing said set value and wherein said means responsive to the output signal of said circuit comprise a DC/DC converter and a transistor circuit having a control input connected to the output of said differential amplifier and an output connected to said converter for controlling said converter.