Undoped Waveguide in Semiconductor Optical Modulator
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing semiconductor optical modulation devices face challenges in high-speed operation due to parasitic capacitance and pile-up phenomena caused by window structures, which hinder efficient optical feedback reduction and lead to deteriorated transmission properties.
Innovation Solution
A novel window structure is introduced, where an undoped optical waveguide with a refractive index similar to the optical absorption region is used between the optical absorption region and the window structure, reducing parasitic capacitance and pile-up effects, and allowing for efficient high-speed modulation without requiring high fabrication accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a window structure with impurity doping is formed to reduce optical feedback, then the reflectance is decreased, but parasitic capacitance increases causing deteriorated high-speed response
Solution Approach 1:
An undoped optical waveguide layer is introduced as an intermediary between the window structure and the optical absorption region. This intermediate layer has a refractive index similar to the optical absorption region, providing optical continuity while electrically isolating the doped window structure from the modulation region, thereby preventing parasitic capacitance formation without compromising optical feedback reduction
Solution Approach 2:
The patent applies different doping conditions to different regions: the window structure is heavily doped to reduce reflectance, while the optical waveguide layer connecting it to the optical absorption region is kept undoped. This local differentiation of electrical properties allows each region to fulfill its specific function without adverse effects on the other
2Reliability
If impurity doping is applied in the window structure to provide opposite polarity conductivity, then electrical conductivity is improved, but a pn junction is formed increasing parasitic capacitance
Solution Approach 1:
The structure is segmented into distinct functional zones with different electrical characteristics: a doped window structure for electrical conductivity and reflectance control, separated from the undoped optical absorption region by an undoped optical waveguide layer. This segmentation prevents the formation of a continuous pn junction while maintaining local electrical properties where needed
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 novel window structure effectively suppresses the increase in parasitic capacitance and pile-up phenomena, enhancing the high-speed response property and production yield of semiconductor optical modulation devices, suitable for high-speed modulation applications like 40 Gbps transmission.
Implementation Method 1
an undoped optical waveguide with a refractive index similar to the optical absorption region is used between the optical absorption region and the window structure
Implementation Method 2
extending the distribution shape of an optical intensity from the top end of a waveguide structure of the optical absorption region to the light emitting edge and decreasing re-coupling of a light reflected at the light emitting edge to the optical waveguide structure
Implementation Method 3
semiconductor electro adsorption (EA) modulation device utilizing the electro absorption effect has an excellent property in view of the reduced size, less power consumption
Data Source
AI summary
A low reflective window structure in an existent electro-absorption optical modulator involves a trading off problem between the increase in the parasitic capacitance and the pile-up. This is because the capacitance density of the pn junction in the window structure is higher compared with the pin junction as the optical absorption region, and the application of electric field to the optical absorption region becomes insufficient in a case of receding the electrode structure from the junction between the optical absorption region and the window structure making it difficult to discharge photo-carriers generated in the optical absorption region. An undope waveguide structure comprising a structure having such compositional wavelength and a film thickness that the compositional wavelength for each of multi-layers constituting the waveguide structure is sufficiently shorter than that of the signal light and the average refractive index is about identical with that in the optical absorption region may be disposed. In a case of forming the electrode structure so as to overlap the junction boundary between the optical absorption region and the undope waveguide, and do not extend on the joined boundary between the undope waveguide and the window structure, increase in the parasitic capacitance due to the pn junction of the window structure and pile up can be suppressed simultaneously.