Thermo-mechanical Tuning of Asymmetric Microsphere Stem Coupling

Solution Overview

Problem

Existing whispering gallery mode (WGM) resonator systems face challenges in achieving tunable coupling mechanisms suitable for miniaturized systems like lab-on-a-chip, as conventional mechanical or piezoelectric positioners are difficult to integrate, and other non-mechanical methods have limitations.

Innovation Solution

A thermo-mechanical coupling method using an asymmetric microsphere stem fabricated with external laser heating and thermal expansion in a single-mode optical fiber, allowing for nanometer-scale tunable coupling with high efficiency and low loss, utilizing a tapered silica fiber to excite high-Q whispering gallery modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If mechanical or piezoelectric nanometer resolution positioners are used to achieve finely tuned coupling, then coupling precision is improved, but device complexity and difficulty of integration into miniaturized systems increases

Engineering Contradiction:

Improvecoupling precisionVSAvoidintegration complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces mechanical positioners and piezoelectric actuators with an all-optical solution using laser-induced thermal expansion. The laser beam heats the fiber, causing thermal expansion that adjusts the coupling distance between the microresonator and fiber, eliminating the need for mechanical moving parts and complex positioning systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the physical state of the fiber by controlling its temperature through laser heating. By varying the laser power, the fiber temperature changes, which causes thermal expansion or contraction, thereby adjusting the coupling parameter (distance between microresonator and fiber) without mechanical movement.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If conventional mechanical positioners are used for coupling control, then coupling adjustment capability is improved, but ease of operation and miniaturization compatibility deteriorates

Engineering Contradiction:

Improvecoupling adjustment capabilityVSAvoidoperational simplicity

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The patent replaces mechanical positioners and piezoelectric actuators with an all-optical solution using laser-induced thermal expansion. The laser beam heats the fiber, causing thermal expansion that adjusts the coupling distance between the microresonator and fiber, eliminating the need for mechanical moving parts and complex positioning systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system uses the laser that is already present in the experimental setup to simultaneously serve two purposes: exciting the microresonator modes and controlling the coupling distance through thermal expansion. This self-service approach eliminates the need for separate positioning systems and simplifies operation.

Inventive Principle:

Principle #25Self-service

3Loss of energy

If tapered silica fiber is used to excite high-Q whispering gallery modes, then coupling efficiency is improved, but system complexity increases

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidsystem complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent changes the physical state of the fiber by controlling its temperature through laser heating. By varying the laser power, the fiber temperature changes, which causes thermal expansion or contraction, thereby adjusting the coupling parameter (distance between microresonator and fiber) without mechanical movement.

Inventive Principle:

Principle #35Parameter changes

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 method enables linear control of coupling distance with laser power, achieving high coupling efficiency and flexibility in coupling regimes, potentially enabling miniaturized and lab-on-a-chip resonator systems, photonic molecule systems, and other nanopositioning applications.

Implementation Method 1

thermo-mechanical effects arising from asymmetric microsphere stem fabrication, external laser heating, and thermal expansion in single mode optical fiber

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

external laser heating

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 3

tapered silica fiber could be used to excite high-Q whispering gallery modes in silica microspheres

Methodology Applied

Scientific EffectEvanescent field coupling: Total Internal Reflection

Data Source

PatentUS10215923B2Nanopositioner and method of making

Publication Date: 2019.02.26 OKINAWA INST OF SCI & TECH SCHOOL

AI summary

A tunable, all-optical, coupling method for a high-Q silica microsphere and an optical waveguide is disclosed. By means of a novel optical nanopositioning method, induced thermal expansion of an asymmetric microsphere stem for laser powers up to 211 mW is observed and used to fine tune the microsphere-waveguide coupling. Microcavity displacements ranging from (0.61±0.13)-(3.49±0.13) μm and nanometer scale sensitivities varying from (2.81±0.08)-(17.08±0.76) nm/mW are obtained. Additionally, an apparent linear dependency of coupling distance on stem laser heating is achieved. Using these methods, coupling can be altered such that the differing and customizable coupling regimes can be achieved.