Semiconductor External Cavity Laser with Integrated Planar Waveguide Bragg Grating
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Solution Overview
Problem
Existing external cavity lasers struggle to simultaneously achieve wide bandwidth frequency modulation, uniform amplitude and phase response, narrow linewidth, and ultra-low frequency noise, especially in the frequency range where phase delay becomes significant, limiting their application in demanding technologies like distributed interferometric sensing and optical frequency metrology.
Innovation Solution
A semiconductor external cavity laser with an integrated wide bandwidth intracavity frequency modulation section, utilizing a silica-on-silicon planar lightwave circuit and a high-reflection coated lithium niobate phase tuning section, which applies an AC-voltage signal to modulate the refractive index and achieve frequency modulation without thermal-induced phase delay, maintaining narrow linewidth and low frequency noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If direct bias current modulation is applied to the gain chip for frequency modulation, then frequency modulation is achieved, but large phase delay occurs due to thermal time constants
Solution Approach 1:
The patent extracts the frequency modulation function from the gain chip and relocates it to a separate lithium niobate waveguide section with integrated Bragg grating. This separation allows the gain chip to focus on light amplification while the dedicated FM section handles frequency modulation without thermal interference, eliminating the phase delay problem caused by thermal time constants in the gain chip.
Solution Approach 2:
The patent introduces an acoustic wave as an intermediary to achieve frequency modulation. The acousto-optic transducer generates acoustic waves that interact with the optical field in the lithium niobate waveguide, providing a thermal-free mechanism for frequency modulation that avoids the phase delay inherent in direct electrical or thermal modulation of the gain chip.
2Reliability
If the grating section is separated from the modulated section, then narrow linewidth and low frequency noise are achieved, but device complexity increases
Solution Approach 1:
The patent merges the grating section and the frequency modulation section into a single integrated lithium niobate waveguide structure. The Bragg grating is formed directly in the lithium niobate waveguide that also contains the acousto-optic modulation region, allowing both functions to coexist in one component. This integration maintains the noise performance benefits of separation while eliminating the complexity of physically separate components and their interconnections.
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 extends frequency modulation over a wide bandwidth with negligible phase delay, maintaining the performance of PLANEX-type lasers, achieving uniform frequency response and low noise, suitable for advanced applications requiring high precision.
Implementation Method 1
applies an AC-voltage signal to modulate the refractive index and achieve frequency modulation without thermal-induced phase delay
Implementation Method 2
integrated planar waveguide bragg grating
Data Source
AI summary
The present disclosure describes semiconductor external cavity laser with wide bandwidth frequency modulation capabilities. The laser is preferably packaged in a standard form-factor package, such as a 14-pin butterfly package. The front end of the cavity comprises an integrated planar circuit (e.g., silica-on-silicon planar lightwave circuit with Bragg gratings), and the “back facet” of the laser is implemented as a high-reflection (HR) coated LiNbO3 phase tuning section in the double pass configuration. AC-voltage signal applied to the electrodes of phase tuning section modulates a refractive index of the propagating TE-polarization mode of external cavity and produces frequency modulation. Such frequency modulation is not associated with any thermal behavior of the gain element included in the external cavity laser, and has a negligible phase delay over a wide bandwidth.