Abstract A method of maximizing the signal-to-noise (S/N) ratio or a direct-detecting optical pulse receiver for an input pulse having a well-defined duration and receiver apparatus derived therefrom. The S/N ratio is defined as the ratio of the signal output peak instantaneous power to the noise output mean power. The optical receiver comprises an optical detector with fast-response, highsensitivity characteristics followed by a cascade arrangement of amplifiers, two RC dividing networks, one low pass and the other high pass and an amplitude detector. The noise sources comprise the quantum noise generated within the input light-sensitive device and the thermal noise generated within the input load resistor of the device. The dividing networks form a bandpass filter which is designed to maximize the S/N ratio. As a result, the time constants of the filters turn out to be substantially equal and the output load resistance of the detector is set as high as is practical. The method achieves a S/N ratio approaching that obtainable with an ideal matched filter for small values of the input pulse width (to), e.g., of the order of 10 nanoseconds. The S/N ratio improvement over prior art receivers is in the order of 20 db. The receiver is especially effective when to is less than 1 microsecond.
A method for constructing a direct detecting optical pulse receiver having an optical detector with a load resistance R1, a junction capacitance plus shunt capacitance C1, and a time constant Alpha equal to R1 C1, a high-pass filter with a time instant Beta and a low-pass filter with a time constant gamma , said high-pass and low-pass filters being connected in cascade to the output of said optical detector, comprising the steps of: setting said resistance R1 to a value which makes the term (R1/IIoe''R1 + 2kT) substantially equal to 1/Ioe'', where Io is the D.C. current of the detector, e'' is the charge on the electron, k is Boltzmann''s constant and T is the temperature of the detector; setting the time constants Beta and gamma equal to each other at a value which substantially maximizes the relationship:
Claim 2
Independent Claim
138 words
A method for constructing a direct detecting optical pulse receiver having an optical detector with a load resistance R1, a junction capacitance plus shunt capacitance C1, and a time constant Alpha equal to R1 C1, a high-pass filter with a time instant Beta and a low-pass filter with a time constant gamma , said high-pass and low-pass filters being connected in cascade to the output of said optical detector, comprising the steps of: setting said resistance R1 to a value which makes the term (R1/IIoe''R1 + 2kT) substantially equal to 1/Ioe'', where Io is the D.C. current of the detector, e'' is the charge on the electron, k is Boltzmann''s constant and T is the temperature of the detector; setting the time constants Beta and gamma equal to each other at a value which substantially maximizes the relationship: