Mode volume

About: Mode volume is a research topic. Over the lifetime, 5941 publications have been published within this topic receiving 122954 citations.

All-fiber Mach-Zehnder type interferometers formed in photonic crystal fiber.

Abstract: We propose simple and compact methods for implementing all-fiber interferometers. The interference between the core and the cladding modes of a photonic crystal fiber (PCF) is utilized. To excite the cladding modes from the fundamental core mode of a PCF, a coupling point or region is formed by using two methods. One is fusion splicing two pieces of a PCF with a small lateral offset, and the other is partially collapsing the air-holes in a single piece of PCF. By making another coupling point at a different location along the fiber, the proposed all-PCF interferometer is implemented. The spectral response of the interferometer is investigated mainly in terms of its wavelength spectrum. The spatial frequency of the spectrum was proportional to the physical length of the interferometer and the difference between the modal group indices of involved waveguide modes. For the splicing type interferometer, only a single spatial frequency component was dominantly observed, while the collapsing type was associated with several components at a time. By analyzing the spatial frequency spectrum of the wavelength spectrum, the modal group index differences of the PCF were obtained from 2.83×10-3 to 4.65 ×10-3 . As potential applications of the all-PCF interferometer, strain sensing is experimentally demonstrated and ultra-high temperature sensing is proposed.

Properties of photonic crystal fiber and the effective index model

Abstract: We report on the waveguiding properties of a new type of low-loss optical waveguide. The photonic crystal fiber can be engineered to support only the fundamental guided mode at every wavelength within the transparency window of silica. Experimentally, a robust single mode has been observed over a wavelength range from 337nm to beyond 1550nm (restricted only by available wavelength sources). By studying the number of guided modes for fibers with different parameters and the use of an effective index model we are able to quantify the requirements for monomode operation. The requirements are independent of the scale of the fiber for sufficiently short wavelengths. Further support for the predictions of the effective index model is given by the variation of the spot size with wavelength,

Topological protection of photonic mid-gap defect modes

Abstract: Defect modes in two-dimensional periodic photonic structures have found use in diverse optical devices. For example, photonic crystal cavities confine optical modes to subwavelength volumes and can be used for enhancement of nonlinearity, lasing and cavity quantum electrodynamics. Defect-core photonic crystal fibres allow for supercontinuum generation and endlessly single-mode fibres with large cores. However, these modes are notoriously fragile: small structural change leads to significant detuning of resonance frequency and mode volume. Here, we show that photonic topological crystalline insulator structures can be used to topologically protect the mode frequency at mid-gap and minimize the volume of a photonic defect mode. We experimentally demonstrate this in a femtosecond-laser-written waveguide array by observing the presence of a topological zero mode confined to the corner of the array. The robustness of this mode is guaranteed by a topological invariant that protects zero-dimensional states embedded in a two-dimensional environment—a novel form of topological protection that has not been previously demonstrated. Eigenmodes of photonic crystal defects have now been topologically protected in an experimental demonstration that also shows how to minimize the mode volume.

All-optical switches on a silicon chip realized using photonic crystal nanocavities

Abstract: We demonstrate all-optical switching in the telecommunication band, in silicon photonic crystals at high speed (∼50ps), with extremely low switching energy (a few 100fJ), and high switching contrast (∼10dB). The devices consist of ultrasmall high-quality factor nanocavities connected to input and output waveguides. Switching is induced by a nonlinear refractive-index change caused by the plasma effect of carriers generated by two-photon absorption in silicon. The high-quality factor and small mode volume led to an extraordinarily large reduction in switching energy. The estimated internal switching energy in the nanocavity is as small as a few tens of fJ, indicating that further reduction on the operating energy is possible.

Design of the Microstructured Optical Fiber-based Surface Plasmon Resonance sensors with enhanced microfluidics

Abstract: The concept of a Microstructured Optical Fiber-based Surface Plasmon Resonance sensor with optimized microfluidics is proposed. In such a sensor plasmons on the inner surface of large metallized channels containing analyte can be excited by a fundamental mode of a single mode microstructured fiber. Phase matching between plasmon and a core mode can be enforced by introducing air filled microstructure into the fiber core, thus allowing tuning of the modal refractive index and its matching with that of a plasmon. Integration of large size microfluidic channels for efficient analyte flow together with a single mode waveguide of designable effective refractive index is attractive for the development of integrated highly sensitive MOF-SPR sensors operating at any designable wavelength.