Optical Receiver Level Detection Without Directional Couplers
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Solution Overview
Problem
Optical receivers for 1550 nm wavelength video portions of FTTP systems have a limited dynamic range, making deployments challenging due to narrow optical input windows, and existing automatic gain control (AGC) solutions are costly and complex, with directional couplers introducing loss and requiring labor-intensive fabrication.
Innovation Solution
A directional detection system using a differential trans-impedance amplifier with two inputs and outputs, where one input is connected to the photodetector anode and the other to the cathode, providing isolated outputs to a signal detector, eliminating the need for directional couplers and enhancing signal detection with higher signal levels and reduced distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a directional coupler is used in the AGC circuit to detect signal levels, then the output level can be sensed and controlled, but the device complexity and manufacturing cost increase due to labor-intensive fabrication
Solution Approach 1:
The patent extracts the directional detection function from the complex directional coupler and implements it using a simplified circuit with a hybrid junction and selective switching. The level detector circuit captures the necessary signal information without requiring the full directional coupler structure, thereby reducing manufacturing complexity while maintaining detection precision
Solution Approach 2:
The patent creates a simplified copy of the directional detection function using readily available components (hybrid junction, switches, resistors) instead of the original directional coupler. This copied function achieves the same signal level sensing capability with significantly reduced fabrication complexity and cost
2Measurement precision
If a directional coupler is used to couple signal to the signal detector, then signal level can be monitored, but signal loss occurs in the RF path
Solution Approach 1:
The patent introduces a hybrid junction as an intermediary device that allows signal level monitoring without directly coupling the detector into the main RF path. The hybrid junction provides isolation between the monitoring path and the through path, enabling accurate signal level measurement while minimizing insertion loss in the primary signal path
Solution Approach 2:
The patent uses a voltage divider network with resistors to create a scaled-down version of the signal for detection purposes. This partial action approach allows sufficient signal level monitoring with minimal impact on the main signal path, reducing the coupling factor needed and thereby reducing signal loss
3Adaptability or versatility
If the optical receiver dynamic range is limited, then the optical input window is narrow making deployments difficult, but increasing dynamic range requires more complex circuitry
Solution Approach 1:
The patent implements automatic gain control (AGC) circuitry that dynamically adjusts the receiver gain based on the detected signal level. This dynamic adaptation allows the receiver to maintain optimal performance across a wide optical dynamic range, effectively increasing adaptability without requiring complex fixed circuitry for each operating condition
Solution Approach 2:
The patent uses the signal level detection circuit to provide feedback to the AGC controller, which then adjusts the receiver gain accordingly. This feedback mechanism enables the system to automatically adapt to varying input signal levels, effectively expanding the usable dynamic range while keeping the circuit design manageable through automated control
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution increases the dynamic range of optical receivers, reduces costs by eliminating labor-intensive directional couplers, and improves signal detection with higher signal levels to the signal detector, allowing for lower-cost op-amps and reduced board space, while maintaining constant RF output levels over varying input conditions.
Implementation Method 1
an optical receiver to demodulate and amplify the signal for use by customer premise terminals
Data Source
AI summary
An apparatus and method for detecting an output power level of an optical receiver, in order to hold output signal levels constant over changing input optical levels. A photodetector detects an optical signal, and a current from the photodetector is applied an amplifier. The amplifier may be either a differential trans-impedance amplifier, or a dual trans-impedance amplifier coupled to a differential output amplifier. An output of the amplifier is applied o a signal detector, wherein an output signal of the signal detector is an indication of an output power level of the optical receiver.