Balanced Detection Device SPRR Measurement via Optical Switching
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Solution Overview
Problem
Characterizing the performance of balanced detection systems in coherent receivers is challenging due to the inability to measure photocurrents of individual photodiodes without blocking light, especially when photodiodes and optical mixers are integrated and connected using optical fibers.
Innovation Solution
A method and apparatus for measuring the single-port rejection ratio (SPRR) by injecting modulated dual-port and single-port test signals into a balanced detection device, allowing for the calculation of SPRR through differential output current measurements, which quantifies the rejection ratio of the balanced detection system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photocurrents of individual photodiodes are measured without blocking light, then measurement capability is improved, but in integrated coherent receivers with optical fiber connections, light blocking becomes necessary which degrades measurement capability
Solution Approach 1:
The patent introduces an optical switch as an intermediary component that can selectively connect or disconnect optical fibers from photodiodes. This mediator enables the measurement system to control light paths without physically blocking light, allowing photocurrent measurements to be performed by electronically switching optical connections rather than using physical blockers that would degrade measurement capability.
2Reliability
If balanced detection is used to reject common-mode signals, then noise rejection is improved, but the ability to measure individual photodiode photocurrents deteriorates due to differential measurement architecture
Solution Approach 1:
The patent segments the measurement process into separate sequential measurements for each photodiode. By using the optical switch to isolate and measure each photodiode's photocurrent individually in sequence, the system maintains the balanced detection architecture for noise rejection while enabling precise individual photocurrent measurements through temporal separation of measurement operations.
Solution Approach 2:
The patent implements periodic switching of the optical switch to alternately connect different photodiodes to the measurement circuit. This periodic action allows the system to sequentially measure each photodiode's photocurrent while maintaining the balanced detection configuration, achieving both noise rejection and individual measurement capability through time-multiplexed operations.
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
Enables effective characterization of balanced detection systems, providing valuable insights into the performance of coherent receivers by measuring the SPRR, which reflects the rejection of individual optical field powers and interference terms, thus improving the understanding and optimization of balanced detection performance.
Implementation Method 1
The beats between the signal polarization components and the reference field are detected by photodiodes
Implementation Method 2
an optical mixing element coupling light between the input waveguides and the output waveguides
Implementation Method 3
a pair of output waveguides respectively connected to a pair of photodiodes coupled to generate a differential output current
Data Source
AI summary
A method is provided for measuring a factor, called herein the single-port rejection ratio (SPRR), characterizing a balanced detection device. The SPRR is representative of the ratio of the weak differential output current measured under illumination of a single-port of the balanced detection device to the strong measurable differential output current obtained under dual-port illumination. An apparatus for measuring the SPRR is also provided.