Optical Transmitter Modulator for Quantum Key Distribution
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Solution Overview
Problem
Current quantum key distribution (QKD) systems face challenges in increasing key sharing rate and maintaining stable interference characteristics due to the need for precise optical path differences in one-way QKD systems, which are difficult to achieve with existing modulators and interferometers, especially in high-speed transmission systems.
Innovation Solution
An optical transmitter configuration using a composite modulator with three optical modulators - a first modulator for intensity or phase modulation, a second and third modulator in series for phase modulation, and a combining section to generate output pulses with three intensity values and four phase values, allowing for efficient modulation and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple optical modulators are used to achieve three intensity values and four phase values, then modulation capability is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent combines multiple modulation functions (intensity modulation and phase modulation) into a single optical modulator by utilizing the interference characteristics of a Mach-Zehnder interferometer. The modulator uses two input optical pulses with different phases that interfere constructively or destructively at the output, enabling both intensity and phase control through a unified device structure rather than separate modulators for each function.
Solution Approach 2:
The optical modulator is designed to perform multiple functions simultaneously - it can generate three distinct intensity values (0, 1/2, 1) and four distinct phase values (0, π/2, π, 3π/2) using the same device. The modulator accepts control signals that selectively activate different modulation modes, making it a universal component that replaces what would traditionally require multiple specialized modulators.
2Adaptability or versatility
If multiple optical modulators are used to achieve three intensity values and four phase values, then modulation capability is improved, but power consumption increases
Solution Approach 1:
The patent combines multiple modulation functions (intensity modulation and phase modulation) into a single optical modulator by utilizing the interference characteristics of a Mach-Zehnder interferometer. The modulator uses two input optical pulses with different phases that interfere constructively or destructively at the output, enabling both intensity and phase control through a unified device structure rather than separate modulators for each function.
Solution Approach 2:
The optical modulator is designed to perform multiple functions simultaneously - it can generate three distinct intensity values (0, 1/2, 1) and four distinct phase values (0, π/2, π, 3π/2) using the same device. The modulator accepts control signals that selectively activate different modulation modes, making it a universal component that replaces what would traditionally require multiple specialized modulators.
3Reliability
If precise optical path differences are maintained in interferometers, then interference characteristics are stabilized, but device complexity and control difficulty increase
Solution Approach 1:
The patent segments the optical path into two separate input pulses that are generated with predetermined phase differences. Instead of maintaining a single precise optical path difference in a traditional interferometer, the system divides the optical signal into two branches with controlled phase relationships, making the phase control more manageable and less sensitive to environmental disturbances.
Solution Approach 2:
The system pre-establishes the phase relationships between the two input pulses before they enter the modulator. The double-pulse generator creates pulses with predetermined phase differences, and the modulator is biased at a predetermined operating point. This preliminary setup simplifies the control requirements during operation, as the system only needs to apply small modulation signals rather than continuously adjusting large optical path differences.
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 configuration enables efficient modulation with reduced modulator count, improving power efficiency and versatility, while preventing security reductions due to wavelength deviations among light sources, and supporting both quantum cryptographic schemes A and B.
Implementation Method 1
a phase modulator for phase-modulating the optical pulses
Implementation Method 2
an intensity modulator for intensity-modulating the optical pulses
Implementation Method 3
Alice and Bob organize an optical interferometer
Data Source
AI summary
An optical transmitter which modulates the phases and intensities of double pulses and then transmits them, includes a branching section which branches each of the input double pulses to first and second paths, a first optical modulator placed in the first path, second and third optical modulators placed in series in the second path, and a combining section which combines the double pulses having traveled through the first path with the double pulses having traveled through the second path to output double pulses. A control section controls such that each of the first and second optical modulators performs any one of relative intensity modulation and relative phase modulation on the double pulses passing through, and the third optical modulator performs relative phase modulation on the double pulses passing through.