DFB Laser Phase Section for Precise Wavelength Sweeping
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Solution Overview
Problem
Existing DFB lasers suffer from unpredictable wavelength variations due to random phase conditions caused by imprecise rear facet positioning, leading to non-linear frequency modulation and linewidth degradation, which complicates applications requiring precise wavelength control and sweeping.
Innovation Solution
A DFB laser design with a phase section comprising an optical layer whose refractive index is adjustable through a heating or electrical element, allowing for controlled wavelength tuning and continuous sweeping across the stopband without linewidth degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Bragg grating is arranged in the laser section to select a central wavelength, then wavelength selection capability is improved, but random phase conditions occur due to imprecise rear facet positioning, leading to variable output power and wavelength variations
Solution Approach 1:
The laser cavity is divided into two distinct sections: a laser section containing the active layer and Bragg grating for light generation and wavelength selection, and a separate phase section with an optical layer for phase control. This segmentation isolates the phase control function from the laser emission function, allowing independent optimization of each section and eliminating the coupling between facet positioning errors and phase conditions.
Solution Approach 2:
An optical layer is introduced as an intermediary element between the laser section and the rear facet. This optical layer serves as a mediator that can have its refractive index independently controlled to adjust the phase of reflected light, compensating for random phase conditions without requiring precise mechanical positioning of the rear facet.
2Ease of manufacture
If the rear facet position is not precisely controlled, then manufacturing complexity is reduced, but unpredictable phase shifts occur leading to variable wavelength and power output
Solution Approach 1:
The optical layer acts as an intermediary that decouples the relationship between rear facet position and phase condition. By controlling the refractive index of this intermediate layer, the phase of reflected light can be precisely adjusted regardless of the rear facet's exact position, thereby maintaining wavelength precision while relaxing manufacturing tolerances.
Solution Approach 2:
Instead of controlling the physical position of the rear facet, the invention controls the optical parameter (refractive index) of the optical layer. This parameter change approach allows phase adjustment through material property modification rather than mechanical positioning, simplifying manufacturing while maintaining precision.
3Speed
If current modulation is used to sweep the wavelength, then frequency modulation is achieved, but non-linear frequency modulation and linewidth degradation occur due to random phase conditions
Solution Approach 1:
By separating phase control (in the optical layer) from current modulation (in the active layer), the invention enables linear frequency modulation through direct phase control without the non-linear effects and linewidth degradation caused by random phase conditions in conventional designs.
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
Enables precise control of emitted wavelengths and faster frequency modulation, improving performance in applications like FMCW-LIDAR systems by eliminating parasitic modulation and maintaining linewidth integrity.
Implementation Method 1
When the semiconductor crystal heats up, it expands, its optical index increases
Implementation Method 2
By modulating the current injected into the DFB laser (ΔI), the laser temperature is modulated by the Joule effect
Implementation Method 3
an element in electrical or thermal contact with the optical layer, the element configured, under application of a current or voltage, to change a refractive index of the optical layer
Implementation Method 4
a Bragg grating arranged in said grating layer and configured to reflect light towards said front facet
Implementation Method 5
a substantially planar front facet with an anti-reflective coating
Implementation Method 6
a substantially planar rear facet with a high reflectivity coating
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
According to a first aspect, the present disclosure relates to a distributed feedback (DFB) laser configured to control a wavelength of emitted light from the DFB laser, the DFB laser comprising a planar substrate, a substantially planar front facet with an anti-reflective coating, the front facet substantially perpendicular to the planar substrate, a substantially planar rear facet with a high reflectivity coating, the rear facet substantially perpendicular to the planar substrate, a laser section positioned between the rear facet and the front facet, the laser section comprising: a first ensemble of substantially planar layers configured to produce, with said planar substrate, a first PIN junction, the first ensemble of substantially planar layers comprising: a first top layer substantially parallel to the planar substrate; an active layer substantially parallel to the planar substrate and configured to emit light through the front facet, the active layer arranged between the planar substrate and the first top layer; a grating layer arranged substantially parallel to the active layer, the grating layer arranged between the planar substrate and the first top layer in proximity to the active layer; a Bragg grating arranged in said grating layer and configured to reflect light towards said front facet; and a phase section positioned between the rear facet and the laser section, the phase section comprising: a second ensemble of substantially planar layers comprising: a second top layer substantially parallel to the planar substrate, the second top layer substantially coplanar with the first top layer; an optical layer arranged between the planar substrate and the second top layer, the optical layer substantially coplanar with the active layer and optically coupled with the active layer; a non-grating layer substantially coplanar with the grating layer; and an element in electrical or thermal contact with the optical layer, the element configured, under application of a current or voltage, to change a refractive index of the optical layer so as to change the wavelength of the emitted light.