Photon Detector Bias Timing Shift for Weak Light Power Measurement
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Solution Overview
Problem
In quantum key distribution systems, accurately measuring the extinction ratio of optical powers is challenging due to the gated-Geiger-mode operation of photon detectors, which prevents direct measurement of optical power, necessitating separate optical power measurement equipment for timing control of phase modulators.
Innovation Solution
A method and apparatus using a photon detector to measure optical power by shifting the driving timing of the bias voltage, allowing for the counting of photons and indirect measurement of optical power, enabling precise timing control for phase modulators and stable quantum key distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photon detectors are operated in gated-Geiger mode for quantum key distribution, then detection sensitivity is improved, but direct measurement of optical power becomes impossible
Solution Approach 1:
The patent introduces a mediator object (a beam splitter and auxiliary photon detector) that enables optical power measurement without disrupting the primary quantum key distribution detection. The beam splitter divides the optical signal, allowing one path to continue to the main photon detector for QKD while another path directs a portion of the light to an auxiliary detector for power measurement, thus resolving the contradiction between maintaining detection sensitivity and enabling power measurement capability
Solution Approach 2:
The patent creates a copy of the optical signal through the beam splitter, directing a portion of the light to an auxiliary photon detector. This copied signal path enables optical power measurement while the original signal path maintains its quantum key distribution function, allowing both measurement needs to be satisfied simultaneously without compromising detection sensitivity
2Measurement precision
If separate optical power measurement equipment is used for timing control of phase modulators, then measurement capability is improved, but device complexity and system integration increase
Solution Approach 1:
The patent merges the optical power measurement function with the existing quantum key distribution detection system by integrating an auxiliary photon detector and beam splitter into the current optical path. This combination allows the system to perform both quantum key distribution and optical power measurement using a unified apparatus, reducing the need for separate equipment and simplifying system integration while maintaining measurement capability
Solution Approach 2:
The patent enhances the universality of the photon detection system by enabling it to perform multiple functions: quantum key distribution detection, optical power measurement, and timing control for phase modulators. The auxiliary photon detector and beam splitter configuration allow the same optical path to serve both QKD and power measurement purposes, reducing system complexity and improving integration efficiency
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 stable and high-speed quantum key distribution by optimizing the timing of phase modulators, ensuring accurate interference and key generation through precise optical power measurement.
Implementation Method 1
a photon detector for detecting photon arrival of a series of optical pulses
Implementation Method 2
the result of this interference is detected by a photon detector
Data Source
AI summary
A method and apparatus for measuring the optical power of very weak light arriving at a receiver, by using a photon detector, are provided. A photon detector detects the presence or absence of the arrival of a photon in accordance with bias application timing. For a train of optical pulses coming in at an arbitrary timing in respective time slots, the bias application timing is sequentially shifted within the range of a time slot. Each time a shift is made, the number of photons detected is counted by a photon counter. Based on this number of photons, the optical power of the train of the optical pulses is measured.