AUTOMATIC DARK CURRENT COMPENSATION
First Claim
1. A monitoring system receiving a first optical signal tapped from an optical communication channel, comprising:
- an optical coupler combining said first optical signal received on a first input and a second optical signal received on a second input and producing a combined optical signal;
a photodiode detecting said combined optical signal and outputting a first electrical signal;
an analog-to-digital converter receiving said first electrical signal and sampling it to produce a multi-bit second electrical signal;
an electrical signal generator producing a third electrical signal that is repetitive and has a predetermined harmonic characteristic;
a light emitting electrical device receiving said third electrical signal and outputting said second optical signal to said second input in an optical band in which said photodiode is responsive; and
a signal processor receiving said second electrical signal and capable of distinguishing a portion of said second electrical signal according to said predetermined harmonic characteristic.
1 Assignment
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Accused Products
Abstract
A monitoring system useful for monitoring the state of a fiber communication channel in which a portion of the fiber signal is tapped and detected by a photodiode. The dark current of the photodiode and other DC offsets of the system may be compensated by passing a known signal through the photodiode and extracting the component due to the known signal. The known signal may be a locally generated optical signal having a predetermined harmonic signature. Optionally, the fiber signal may be selectively attenuated before being combined with the known signal so only the known signal is detected. The known signal may also be a dark signal induced by selectively attenuating the fiber signal. The system may include a temperature sensor which allows the compensation to be performed against stored temperature dependent compensation values while the fiber signal is not attenuated.
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Citations
18 Claims
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1. A monitoring system receiving a first optical signal tapped from an optical communication channel, comprising:
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an optical coupler combining said first optical signal received on a first input and a second optical signal received on a second input and producing a combined optical signal;
a photodiode detecting said combined optical signal and outputting a first electrical signal;
an analog-to-digital converter receiving said first electrical signal and sampling it to produce a multi-bit second electrical signal;
an electrical signal generator producing a third electrical signal that is repetitive and has a predetermined harmonic characteristic;
a light emitting electrical device receiving said third electrical signal and outputting said second optical signal to said second input in an optical band in which said photodiode is responsive; and
a signal processor receiving said second electrical signal and capable of distinguishing a portion of said second electrical signal according to said predetermined harmonic characteristic. - View Dependent Claims (2, 3, 4)
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5. A monitoring system receiving a first optical signal tapped from an optical communication channel, comprising:
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a signal processor;
a selective optical absorber receiving said first optical signal on an input side, providing a variably attenuated first optical signal on an output side, and controlled by said signal processor to variably attenuate said first optical signal;
a photodiode receiving said variably attenuated first optical signal from said output side and producing a first electrical signal in response thereto; and
an analog-to-digital converter receiving said first electrical signal and sampling it to produce a multi-bit second electrical signal, which is received by said signal processor. - View Dependent Claims (6, 7, 8, 9)
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10. A method of monitoring an optical communications channel, comprising the steps of:
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tapping a fraction of a signal propagating along said optical communications channel to form a first optical signal;
generating a second optical signal with a predetermined harmonic characteristic;
combining said first optical signal with said second optical signal to form a third optical signal;
detecting said third optical signal in a photodiode to form a first electrical signal;
sampling and digitizing said first electrical signal to form a multi-bit second electrical signal; and
extracting a portion of said second electrical signal based upon said predetermined harmonic characteristic. - View Dependent Claims (11, 12, 13)
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14. A method of monitoring an optical communications channel, comprising the steps of:
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tapping a fraction of a signal propagating along said optical communications channel to form a first optical signal;
selectively attenuating said first optical signal according to at least a high attenuation state and a low attenuation state;
detecting said selectively attenuated first optical signal to produce a first electrical signal;
sampling and digitizing said first electrical signal to form a multi-bit second electrical signal;
adjusting values said second electrical signals received while said first optical signal is attenuated according to said low attenuation state in response to at least one value of said second electrical signal received while said first optical signal is attenuated according to said high attenuation state. - View Dependent Claims (15)
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16. A method of monitoring an optical communications channel, comprising the steps of:
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tapping a fraction of a signal propagating along said optical communications channel to form a first optical signal;
passing said first optical signal through a photodiode, a first electrical signal being thereby produced;
determining a dark current produced in said photodiode while said first electrical signal is being produced; and
compensating said first electrical signal for said determined dark current. - View Dependent Claims (17, 18)
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Specification