Optical Modulator Surface Structure for Over-Etching Control
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Solution Overview
Problem
Existing optical modulators face issues with over-etching of electrode underlayers, leading to increased drive voltage and electrode peeling, particularly in high bandwidth-coherent driver modulators with reduced electrode intervals and thicknesses.
Innovation Solution
The optical modulator features a substrate with an uneven surface portion that guides the etching direction, suppressing over-etching by forming protruding portions parallel to the electrode underlayer, maintaining a predetermined range and dimensions to prevent electrode separation and voltage increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the electrode underlayer is thinly formed to suppress light absorption, then light absorption is reduced, but over-etching is likely to progress
Solution Approach 1:
The electrode underlayer is designed with non-uniform thickness: a thin portion (5-20 nm) beneath the electrode to reduce light absorption, and a thick portion (50-200 nm) at the peripheral region to prevent over-etching. This local quality variation allows simultaneous optimization of optical performance and etching resistance.
2Power
If the electrode interval is reduced to reduce drive voltage, then drive voltage is reduced, but over-etching widens the substantial distance between optical waveguide and electrode
Solution Approach 1:
The thick peripheral portion of the electrode underlayer is formed in advance to counteract the capillary action that causes over-etching during the etching process. This preliminary anti-action prevents the etching solution from excessively removing the underlayer material, thereby maintaining the designed electrode interval and position accuracy even when electrodes are closely spaced.
3Ease of manufacture
If the electrode underlayer is over-etched, then over-etching progresses by several μm, but drive voltage significantly increases
Solution Approach 1:
The thick peripheral portion of the electrode underlayer is formed as a preliminary protective structure before the etching process. This preliminary action ensures that even if etching progresses, the thick portion prevents excessive removal, maintaining the electrode interval within design specifications and keeping drive voltage at acceptable levels.
4Manufacturing precision
If the electrode underlayer is over-etched, then grounding area of the electrode is reduced, but electrode peeling occurs
Solution Approach 1:
The electrode underlayer exhibits local quality variation with a thick peripheral portion providing enhanced bonding area and mechanical strength, while the thin central portion optimizes optical properties. This structural differentiation prevents electrode peeling by ensuring sufficient grounding area in the peripheral region.
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 design effectively prevents over-etching and electrode peeling, stabilizing the electrode structure and reducing drive voltage, thereby enhancing the performance and reliability of optical modulators.
Implementation Method 1
when the electrode underlayer is etched, as shown in FIG. 2, there is a problem in that the electrode underlayer 3 becomes an over-etching portion 30 due to a capillary action
Implementation Method 2
an optical waveguide is formed on a substrate of lithium niobate (LN) or the like having an electro-optic effect, and an electrode that applies an electric field to the optical waveguide is formed on the substrate
Data Source
AI summary
An object of the present invention is to provide an optical modulator that suppresses progressing of over-etching and prevents an increase in a drive voltage and electrode peeling. The optical modulator of the present invention includes a substrate 1 on which an optical waveguide 10 is formed, an electrode 2 disposed close to the optical waveguide on the substrate, and an electrode underlayer 3 formed between the substrate 1 and the electrode 2. A surface side of the substrate 1 has an uneven portion 5 in a predetermined range S2 entering an inside of the electrode from an end portion of the electrode 2 close to the optical waveguide when the substrate is viewed in a plan view.