Optical difference detector and inspection device
AssigneeHamamatsu Photonics K.K.
InventorToshiki YAMADA
Life of this patent
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Abstract
An optical difference detector includes a first APD and a second APD, a first voltage application unit that applies a first bias voltage to the first APD and a second voltage application unit that applies a second bias voltage to the second APD, a differential amplifier that is connected in parallel to the first APD and the second APD and amplifies a difference between a first signal current output from the first APD and a second signal current output from the second APD, and a feedback control unit that controls the second bias voltage so that a low frequency component of a first monitoring current in the first APD and a low frequency component of a second monitoring current in the second APD are equal.
Claims6
A detector, comprising:
- a first avalanche photodiode and a second avalanche photodiode configured to amplify and to output a signal current according to input light;
- a first voltage applicator configured to apply a first bias voltage to the first avalanche photodiode and a second voltage applicator configured to apply a second bias voltage to the second avalanche photodiode;
- a differential amplifier configured to be connected in parallel to the first avalanche photodiode and the second avalanche photodiode and to amplify a difference between a first signal current output from the first avalanche photodiode and a second signal current output from the second avalanche photodiode;
- and
- a feedback controller configured to control at least one of the first bias voltage and the second bias voltage so that a low frequency component of a first monitoring current in the first avalanche photodiode and a low frequency component of a second monitoring current in the second avalanche photodiode are equal,
- wherein the first monitoring current is a first bias current flowing through the first avalanche photodiode due to application of the first bias voltage, and the second monitoring current is a second bias current flowing through the second avalanche photodiode due to application of the second bias voltage.
2-6. (canceled)
Dependencies are inferred from the claim text.