Tunable Silicon Nitride Waveguide Structure via Mechanical Gap Control

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Solution Overview

Problem

Existing silicon nitride waveguides are athermal and difficult to tune using heat, limiting their functionality in interferometric optical devices.

Innovation Solution

Employing a MEMS actuator to adjust the air gap between the waveguide and cladding material, altering the effective refractive index by compressing the cladding to shrink the air gap, thereby tuning the waveguide.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If heat is used to tune silicon waveguides, then wavelength tuning is achieved (0.07 nm/°C), but silicon nitride waveguides show minimal response (0.01 nm/°C) making them athermal and difficult to tune

Engineering Contradiction:

Improvewavelength tuning capabilityVSAvoidtuning effectiveness

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent changes the physical parameter being manipulated from temperature (thermal tuning) to mechanical displacement (actuator-based tuning). By using an actuator to change the gap distance between the waveguide and cladding, the effective refractive index is modified, enabling wavelength tuning in silicon nitride waveguides without relying on thermal effects.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces an actuator as an intermediary component between the control system and the waveguide. This actuator mechanically adjusts the gap between the waveguide and cladding, serving as a mediator that enables tuning functionality in athermal silicon nitride waveguides where direct thermal tuning is ineffective.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If silicon nitride waveguides are used, then fabrication tolerances are relaxed and optical loss is reduced, but wavelength tuning capability is severely limited

Engineering Contradiction:

Improveoptical loss and fabrication toleranceVSAvoidwavelength tuning capability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent makes the previously static waveguide structure dynamic by introducing a movable cladding or adjustable gap mechanism. The actuator enables the gap between the waveguide and cladding to be dynamically adjusted, allowing the silicon nitride waveguide to adapt its effective refractive index and achieve wavelength tuning while maintaining the material's inherent advantages.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the tuning parameter from temperature (which has minimal effect on silicon nitride) to mechanical gap distance. By controlling the actuator to adjust the gap, the effective refractive index is modified, enabling wavelength tuning capability in silicon nitride waveguides without compromising their low loss and relaxed fabrication tolerance characteristics.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If mechanical actuators are used to adjust the air gap, then wavelength tuning is enabled in silicon nitride waveguides, but device complexity increases

Engineering Contradiction:

Improvewavelength tuning capabilityVSAvoidactuator integration

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent extracts the tuning functionality from the waveguide material itself (which is athermal) and places it in a separate mechanical actuator system. This allows the silicon nitride waveguide to maintain its simple, low-loss structure while the actuator provides the necessary tuning capability, separating the guiding function from the tuning function.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The actuator serves as an intermediary that bridges the control system and the waveguide, enabling tuning functionality without requiring modification of the waveguide material or structure. This intermediary approach allows wavelength tuning to be added to silicon nitride waveguides with minimal impact on their inherent advantages.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 tuning of athermal silicon nitride waveguides, achieving wavelength changes comparable to thermal silicon waveguides, enhancing the functionality of interferometric optical devices.

Implementation Method 1

an actuator element configured to move the cladding material relative to the waveguide to vary the gap

Methodology Applied

Scientific EffectMechanical Force: Mechanical Force

Implementation Method 2

a core portion including a waveguide core disposed within a cladding portion... the evanescent field is contained within the waveguide core, the air gap, and a portion of the cladding portion

Methodology Applied

Scientific EffectTotal Internal Reflection: Total Internal Reflection

Implementation Method 3

the evanescent field extends into the air gap and a portion of the cladding portion

Methodology Applied

Scientific EffectEvanescent Field:

Data Source

PatentUS12422624B2Tunable silicon nitride waveguide structure

Publication Date: 2025.09.23 CISCO TECHNOLOGY INC

AI summary

Embodiments herein describe using an actuator to tune a waveguide. In one embodiment, the tunable waveguide includes a gap between the waveguide and cladding. The actuator can compress the cladding to shrink this air, bringing the cladding closer to the waveguide. Doing so changes the effective refractive index of the waveguide. Alternatively or additionally, the actuator can increase the gap.