Harmonic Frequency Conversion Module Polarizer Noise Reduction
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Solution Overview
Problem
Harmonic frequency conversion modules using polarization maintaining (PM) fiber optical links suffer from power fluctuations and noise due to polarization distortions caused by temperature sensitivity, external stresses, and misalignment, which affect the quality of the output light and introduce interference noise.
Innovation Solution
Incorporating one or more polarizers in the PM fiber optical link, particularly after significant polarization distortion points, to stabilize the output power and reduce noise by removing parasitic polarization modes and controlling the polarization extinction ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polarization maintaining (PM) fiber optical links are used to transmit polarized light to non-linear crystals, then the polarization sensitivity of the crystal is satisfied, but power fluctuation and noise are introduced in the output
Solution Approach 1:
A polarizer is introduced as an intermediary element in the PM fiber optical link, positioned after polarization distortion points. This polarizer acts as a mediator that selectively transmits only the desired linear polarization mode while blocking the parasitic orthogonal polarization mode, thereby eliminating the source of power fluctuation and noise without compromising the polarization sensitivity required by the non-linear crystal
Solution Approach 2:
The harmful parasitic polarization mode is extracted and removed from the optical signal by using a polarizer. The polarizer separates the desired polarization mode from the unwanted orthogonal mode, allowing the system to maintain only the useful polarization component and eliminate the harmful one that causes instability and noise
2Device complexity
If PM fiber is used with temperature sensitivity and external stresses, then the system is compact and integrated, but polarization quality deteriorates due to birefringence changes
Solution Approach 1:
Polarizers are strategically placed at predetermined locations within the PM fiber optical link, specifically after significant polarization distortion points. This preliminary action ensures that polarization quality is restored before the light reaches subsequent sensitive components, compensating for the effects of temperature sensitivity and external stresses that occur throughout the integrated system
Solution Approach 2:
Rather than attempting to maintain uniform polarization quality throughout the entire PM fiber link, polarizers are placed at specific local positions where polarization distortion accumulates to critical levels. This localized correction approach maintains system integration while restoring polarization quality at critical points without requiring complete system redesign
3Adaptability or versatility
If multiple polarization distortion points exist in the PM fiber link, then the system integrates multiple functional elements, but interference noise increases due to parasitic polarization modes
Solution Approach 1:
The PM fiber optical link is segmented into sections by strategically placing polarizers after significant polarization distortion points. Each polarizer segment resets the polarization state, creating independent sections that prevent the accumulation and interaction of parasitic polarization modes from multiple functional elements, thereby reducing interference noise while maintaining system versatility
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
The solution effectively minimizes power fluctuations and noise in the frequency converted light, making the output more stable and less dependent on external conditions, with significant improvements observed even with a single polarizer and further enhancements with multiple polarizers.
Implementation Method 1
PM fibers are used for transmitting polarized light. But their transmission is high for both polarizations, therefore polarization quality of the output light depends on: a) polarization quality of incoming light, b) quality of alignment of input and all intermediate elements.
Implementation Method 2
If the incoming polarization is easy to control, quality of alignment is often limited. If it is non-ideal, inevitably two orthogonal polarization modes with different propagation speeds are created in the PM fiber.
Implementation Method 3
Second harmonic generation is a commonly practiced technique for obtaining coherent light at short wavelengths from long wavelength laser sources. It is a non-linear process where an optical beam, called the pump beam, interacts with an optically non-linear medium, in the case of second harmonic generation, to generate a second harmonic beam, where the frequency of the second harmonic beam is twice the frequency of the pump beam.
Data Source
AI summary
A harmonic frequency conversion module is disclosed including a polarization maintaining (PM) fiber optical link for providing an output stabilized from power fluctuation by the inclusion of one or more polarizers in the PM fiber optical link. Removing polarization distortions removes noise which has a significant negative effect on the output of harmonic frequency conversion elements. It has been found that the noise in frequency converted light has additional components, caused by mode interaction during conversion. In accordance with the present invention, we are able to remove the spikes in this noise, making it more stable and less dependent on external conditions. If the PM optical fiber route consists of multiple elements creating polarization distortions, a polarizer should be inserted between the most distorting element and the output of the fiber system. If many elements contribute to polarization distortions, several polarizers can be inserted into the system.