Whispering gallery modes in Microresonators : General info and my research work

Introduction:

Whispering Gallery Mode (WGM) is a captivating optical phenomenon with a rich history that has intrigued scientists and enthusiasts for centuries. This unique phenomenon occurs when waves, whether they are light, acoustic, or electromagnetic, become entrapped within a curved or circular boundary, leading to a remarkable and stable resonance. The term "Whispering Gallery" finds its origins in the mesmerizing acoustical properties observed in domed structures, where even the faintest of whispers can gracefully travel along the curved boundary with minimal loss.

Section 1: General Information about Whispering Gallery Mode

1.What is Whispering Gallery Mode (WGM)?

   Whispering Gallery Mode (WGM) is a fascinating optical phenomenon that occurs when light waves or other waves, such as acoustic or electromagnetic waves, are trapped within a curved or circular boundary. These waves, instead of traveling straight, continuously circumnavigate the boundary due to total internal reflection, creating a unique and stable resonance. The term "Whispering Gallery" originates from the phenomenon observed in domed structures, where whispers or sounds can travel along the curved boundary with minimal loss.

2. Historical Background

   WGM has a rich history and has been observed in various natural and man-made structures for centuries. Notable historical examples include its observation in St. Paul's Cathedral in London, where whispers near the curved dome can be heard clearly at certain points. The phenomenon has also been studied in the context of microcavities, optical resonators, and more, leading to a deeper understanding of wave confinement.

3. Physical Principles of WGM

  Total Internal Reflection: The core principle behind WGM is total internal reflection, where incident waves are confined within a medium due to the total reflection at the boundary. This effect occurs when the incident angle exceeds the critical angle.

   Wave Confinement: WGM results from the wave confinement along the curved boundary, preventing the waves from escaping.

   Resonance Formation: Due to the continuous reflection, resonant modes form within the structure. These modes are characterized by their high quality factor (Q-factor), which indicates the stability and low energy loss associated with these modes.

4. Applications of WGM

   WGM has found a wide range of applications in various fields, including:

    Optics: In the field of optics, WGM resonators are used in laser technology, high-resolution spectroscopy, and the development of ultra-sensitive optical sensors.

   Sensing: WGM microcavities are employed in chemical and biological sensing applications, offering high sensitivity to changes in the surrounding environment.

  5. Key Characteristics

   WGM modes are characterized by several key features:

   High Q-factors: These modes have exceptionally high quality factors, which make them ideal for precision measurements and sensing.

   Mode Propagation: The modes of WGM can be categorized into different families, each with distinct characteristics, such as azimuthal and radial modes.

   Applications in Nanophotonics: With the advancement of nanophotonics, WGM microresonators have been extensively explored for their potential in miniaturized photonic devices.

Section 3: References

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