Wavelength Tunable Light Source With Normalized Ratio Control
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Solution Overview
Problem
Conventional wavelength tunable light sources with wavelength monitor circuits suffer from unsatisfactory accuracy and increased optical loss due to fluctuations in light intensity and unstable wavelength control, primarily because of the dependence on the state of semiconductor optical amplifiers and the need for additional taps that reduce light output.
Innovation Solution
A wavelength tunable light source with a wavelength monitor circuit featuring three photo detectors and a processor that calculates normalized ratios of light received at these detectors to control the electric current, ensuring stable wavelength monitoring with reduced optical loss by using the entire light input for calculation and avoiding additional taps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a wavelength monitor circuit is implemented using a delay interferometer and photodiodes, then wavelength control capability is provided, but measurement precision is insufficient due to light intensity fluctuations from semiconductor optical amplifiers
Solution Approach 1:
The patent implements a feedback control mechanism where the wavelength monitor circuit continuously measures the wavelength and feeds this information back to control the laser diode current, thereby stabilizing the wavelength despite fluctuations in light intensity from semiconductor optical amplifiers
Solution Approach 2:
The patent introduces a delay interferometer as an intermediary component that converts wavelength information into intensity differences between two photodiodes, enabling precise wavelength measurement that is independent of the absolute light intensity level
2Measurement precision
If additional taps are added to the wavelength monitor circuit to compensate for light loss, then measurement capability is improved, but optical loss increases and light output decreases
Solution Approach 1:
The patent designs the wavelength monitor circuit to use the existing light path and components for dual purposes: the main light transmission path and the wavelength monitoring path share common components, eliminating the need for additional taps and reducing overall optical loss
Solution Approach 2:
The patent recovers and utilizes the light that would otherwise be lost in conventional designs by routing it through the delay interferometer for wavelength monitoring, thereby converting what would be waste into useful measurement information
3Quantity of substance
If the coupling ratio of tap-3 is optimized for one wavelength, then light quantity for wavelength monitoring is improved, but wavelength stability deteriorates due to coupling ratio dependence on wavelength
Solution Approach 1:
The patent employs feedback control where the wavelength monitor continuously tracks wavelength deviations and adjusts the laser diode current to compensate, maintaining wavelength stability regardless of coupling ratio variations with wavelength
Solution Approach 2:
The patent makes the wavelength control dynamic by continuously adjusting the laser diode current based on real-time wavelength measurements, allowing the system to adapt to changing conditions and maintain stability across different wavelengths
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 achieves stable and accurate wavelength control with reduced optical loss by normalizing photocurrent ratios from three detectors, ensuring the wavelength remains consistent and minimizing power loss across different wavelengths.
Implementation Method 1
A delay interferometer is used as such a wavelength filter
Implementation Method 2
a wavelength monitor circuit is implemented by combination of a wavelength or spectral filter having a periodic transmission spectrum and a photodiode (PD)
Implementation Method 3
a semiconductor optical amplifier (indicated as 'SOA1') bounce between a resonator filter and the SOA1, light with a specific wavelength is amplified selectively
Data Source
AI summary
A wavelength tunable light source includes a light source, a wavelength monitor circuit configured to receive light emitted from the light source, and a processor that controls the light source based upon an output value of the wavelength monitor circuit, wherein the wavelength monitor circuit has a wavelength filter with a periodic transmission spectrum, and three photo detectors connected to outputs of the wavelength filter, and wherein the processor is configured to calculate a ratio of photo-detection normalized with two of three quantities of light received at the three photo detectors and control electric current input to the light source such that a calculated ratio of photo-detection approaches a target ratio at a designated wavelength.