Optical Modulation Signal Generating Device Using Frequency Filter
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Solution Overview
Problem
Current optical modulation systems face challenges in achieving high-speed modulation and long-distance transmission due to frequency fluctuations in optical signals, which degrade the signal quality when propagated through optical fibers, particularly in direct modulation systems and electroabsorption modulators, and are limited by the size and integration issues of phase modulation type modulators like LN modulators.
Innovation Solution
An optical modulation signal generating device that converts frequency modulation into intensity modulation using a frequency filter, specifically employing a semiconductor optical amplifier and an optical source with a wavelength selective filter, phase adjusting region, and active layer to generate an optical signal with minimal frequency fluctuation, utilizing filters like etalon, Mach-Zehnder interferometer, or lattice type filters to restrict frequency fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If direct modulation of laser is used, then control is simple, but frequency fluctuation occurs causing signal degradation after optical fiber propagation
Solution Approach 1:
The invention separates the modulation function into two independent parts: frequency modulation (which does not cause signal degradation) and intensity modulation (which provides the actual signal). The frequency modulator and intensity modulator are separate modules that work in sequence, allowing each to be optimized independently while avoiding the frequency fluctuation problems of direct modulation.
Solution Approach 2:
The invention introduces an intermediary frequency modulation stage before the intensity modulation stage. This intermediate frequency modulation converts the electrical signal to frequency variations, which are then converted to intensity variations by the second modulator. This intermediary step eliminates the direct frequency-to-intensity conversion that causes frequency fluctuation problems.
2Ease of manufacture
If electroabsorption modulator is used, then integration with DFB-LD is easy, but frequency fluctuation occurs at signal rising and falling edges
Solution Approach 1:
The invention divides the modulation process into two separate modulation stages performed by different modulators. The first modulator (frequency modulator) handles the initial modulation without causing frequency fluctuation, and the second modulator (intensity modulator) handles the final intensity conversion. This segmentation eliminates the frequency fluctuation problem that occurs in electroabsorption modulators during signal transitions.
3Reliability
If phase modulation type modulator is used, then frequency fluctuation is restricted, but element size is large and integration is difficult
Solution Approach 1:
The invention uses a semiconductor optical amplifier that copies the frequency modulated signal and converts it to intensity modulated signal through its gain characteristics. This copying mechanism allows the system to achieve frequency stability without requiring large physical elements, as the semiconductor optical amplifier can be miniaturized while maintaining the frequency modulation functionality.
Solution Approach 2:
The invention changes the operating parameters of the semiconductor optical amplifier to achieve frequency modulation functionality. By controlling the injection current and operating point of the semiconductor optical amplifier, the system achieves frequency modulation with minimal frequency fluctuation while maintaining a compact form factor suitable for integration.
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 approach enables high-speed modulation and long-distance transmission by minimizing frequency fluctuations, maintaining signal quality even after propagation through 50 km of optical fiber, thereby overcoming the limitations of existing systems.
Implementation Method 1
generates a phase difference between the respective branch lights of the two optical paths by a change of a refractive index due to electric field impression
Implementation Method 2
In a case of a quantum well structure, a quantum-confined Stark effect (QCSE) is generally used
Implementation Method 3
in a case of a bulk structure, a Franz-Keldysh effect is generally used
Implementation Method 4
a frequency filter for converting the frequency modulation component of the optical signal into an intensity modulation component and a frequency modulation component
Implementation Method 5
employing filters like etalon, Mach-Zehnder interferometer, or lattice type filters to restrict frequency fluctuations
Implementation Method 6
a semiconductor optical amplifier and an optical source with a wavelength selective filter, phase adjusting region, and active layer to generate an optical signal with minimal frequency fluctuation
Data Source
AI summary
There is provided an optical modulation signal generating device in which an operation speed is not limited by a relaxation oscillation frequency of a laser, and high-speed modulation and long-distance transmission can be performed. The optical modulation signal generating device converts a signal from a signal source into an optical signal and outputs the optical signal to a transmission medium having frequency dispersion. The optical modulation signal generating device includes an optical source (102) for performing frequency modulation by the signal from the signal source to generate an optical signal having only a frequency modulation component, and a frequency filter (103) for converting the frequency modulation component of the optical signal into an intensity modulation component and a frequency modulation component.