Tunable Semiconductor Laser with Grounded Passive Section
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Solution Overview
Problem
Monolithically integrated semiconductor lasers with short cavities face challenges in achieving narrow linewidths due to the requirement for short DBR sections, leading to significant linewidths dominated by photon population and round trip time, which affects side mode suppression and transmission stability.
Innovation Solution
Incorporating a grounded passive section with a p-i-n doped epitaxial structure between the DBR sections, which is not electrically drivable, to increase the laser cavity optical path length and reduce linewidth/phase noise, while maintaining single longitudinal mode operation and side mode suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DBR sections are made shorter to reduce cavity length, then side mode suppression is improved, but linewidth increases due to reduced round trip time
Solution Approach 1:
The cavity is segmented such that the passive section is excluded from the effective optical path length used in linewidth calculations. While photons physically traverse the passive section, its electrical isolation properties allow it to be treated as if it were not part of the resonant cavity, effectively reducing the round trip time without compromising SMSR.
Solution Approach 2:
The electrical characteristics of the passive section are changed to create a region that is optically transparent but electrically isolated. By modifying the doping profile and electrical contact structure of the passive section, it becomes electrically inert while remaining optically transparent, changing the parameter of electrical conductivity without affecting optical transmission.
2Ease of manufacture
If electrical isolation regions are minimized to reduce device complexity, then manufacturing is simplified, but electrical interference increases between control electrodes
Solution Approach 1:
The electrical isolation function is extracted from the traditional narrow isolation region and relocated to a dedicated passive section. This passive section is specifically designed to provide electrical isolation between adjacent laser sections while being optically transparent, separating the electrical isolation function from the optical cavity structure and allowing minimal physical isolation regions.
Solution Approach 2:
The passive section serves as an intermediary region that provides electrical isolation between control electrodes without requiring large physical separation. This intermediary structure allows adjacent active sections to be positioned close together for compact design while the passive section blocks electrical interference, mediating between the competing requirements of compactness and electrical isolation.
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 grounded passive section reduces linewidth/phase noise and shot noise contributions, enhancing the stability and performance of the laser by increasing the round-trip time for photons and maintaining high side mode suppression ratios.
Implementation Method 1
The DBRs are provided by gratings within the optical waveguide of the laser, and are tuned to control the lasing wavelength of the laser cavity
Implementation Method 2
a gain section and a phase control section on a common waveguide
Data Source
Figure 1A
Figure 1B~1C
Figure 1D
AI summary
A monolithically integrated, tunable semiconductor laser with an optical waveguide, comprising a laser chip having epitaxial layers on a substrate and having first and second reflectors bounding an optical gain section and a passive section, wherein at least one of the reflectors is a distributed Bragg reflector section comprising a grating and configured to have a tunable reflection spectrum, wherein the laser is provided with a common earth electrode that is configured to be electrically grounded in use, wherein control electrodes are provided on the optical waveguide in at least the optical gain section and the at least one distributed Bragg reflector section, wherein the passive section is provided with a passive section electrode that electrically contacts the opposite side of the optical waveguide from the substrate, the passive section is configured not to be drivable by an electrical control signal, and no grating is present within the passive section, and wherein the passive section is a grounded passive section in which the passive section electrode is configured to be electrically grounded in use and electrically contacts the passive section, and wherein the passive section electrode and the common earth electrode electrically contact opposite sides of the optical waveguide.