MZI Control Circuit Using Reference Light to Eliminate Pilot Tone Noise
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Solution Overview
Problem
Existing MZI control technologies require intentionally varying a single or multiple bias voltages from their optimum points, leading to noise in the output light due to pilot tones, which degrades signal quality in high-speed transmission systems.
Innovation Solution
A control circuit that adjusts the bias of an optical circuit with a single or multiple MZIs by using reference lights of different wavelengths to monitor and correct the optical path difference, eliminating the need for pilot tones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pilot tones are added to monitor bias conditions, then monitoring sensitivity is improved, but noise is introduced that degrades signal quality
Solution Approach 1:
The patent introduces reference light with a different wavelength as an intermediary to monitor the optical path difference. Instead of adding pilot tones to the signal wavelength, a separate reference wavelength is used that passes through the same MZI, allowing indirect measurement of bias conditions without contaminating the signal light with noise.
Solution Approach 2:
The patent separates the monitoring function from the signal transmission by using a different wavelength for reference light. This segmentation allows the monitoring function to be performed independently without introducing noise into the signal band, resolving the contradiction between monitoring sensitivity and signal quality.
2Manufacturing precision
If multiple bias voltages are adjusted to maintain optimal performance, then optical path difference control is improved, but system complexity increases
Solution Approach 1:
The patent implements a feedback control system where the intensities of reference light and signal light are monitored and used to automatically adjust the bias voltage. The controller receives intensity information and adjusts the bias to maintain optimal optical path difference, eliminating the need for complex manual adjustment of multiple voltages while maintaining precise control.
Solution Approach 2:
The system performs self-adjustment by using the light intensities themselves as the control signal. The same light that passes through the MZI provides the feedback information needed to adjust the bias, making the system self-regulating without requiring external complex control mechanisms.
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 improves the quality of the output from the optical circuit without adding noise, enhancing sensitivity for monitoring bias conditions and reducing signal quality degradation.
Implementation Method 1
An optical splitter circuit 2 branches the input light input to the optical input port 1 into two
Implementation Method 2
For this fine adjustment, a Pockels effect or thermal expansion of an optical waveguide by a heater can be used
Implementation Method 3
For this fine adjustment, a Pockels effect or thermal expansion of an optical waveguide by a heater can be used
Implementation Method 4
An optical multiplexing circuit 6 multiplexes the light propagated through the first optical waveguide 3 and the light propagated through the second optical waveguide 4
Implementation Method 5
An optical circuit including a Mach-Zehnder interferometer (MZI) or a composite of MZIs is widely used as an optical filter or an optical modulator having periodicity
Data Source
AI summary
A control circuit controls at least one optical path difference among optical path differences of two optical paths included in a single MZI or each of a plurality of the MZIs included in an optical circuit. The control circuit includes a reference light generation unit, a reference light input unit, an optical power monitor unit, and a controller. The reference light generation unit generates reference light respectively having N types (N is a natural number) of wavelengths different from the wavelength λ of input light input to the optical circuit in parallel or in a time division manner. A reference light input unit inputs the reference light to the optical circuit. The optical power monitor unit monitors a light intensity of propagated input light which is input light that has propagated through the optical circuit, and a light intensity of propagated reference light which is reference light that has propagated through the optical circuit, or a light intensity of light obtained by multiplexing the propagated input light and the propagated reference light. The controller performs control to correct the optical path difference on the basis of the light intensity of the propagated input light and the light intensities of N types of propagated reference light, which are obtained using the monitoring result.