Introduction
The field of nanophotonics, which describes the integration of nanotechnology with photonic devices, has promoted the research and development of fiber optic nanophotonic devices. Researchers have found that the incorporation of nanoparticles into optical fibers has allowed for advantageous features, such as improved refractive index and an ability to manipulate light, to be incorporated into novel communications, sensing, computation, biological and chemistry devices.
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Silicon Nanoparticles in Fiber Optics Devices
The Raman scattering effect describes that way in which light interacts with a given material to produce wavelengths of a specific length as a result of the interaction between the light and the molecules of the object of interest. More specifically, the light will increase the energy of the molecules of an object to match its vibration properties, thereby allowing the molecule to re-emit photons that have a smaller amount of energy as compared to the incident photon. The energy of this smaller photon will produce a longer wavelength and red color, which concludes the Raman effect.
The Raman effect is a principal tool used in the fiber optic telecommunication industry, as the longer wavelengths that are produced following this method are capable of travelling through long stretches of glass fiber1. In doing so, light is able to be transferred from a strong pump beam to a weaker data beam. A recent study conducted by researchers from the Moscow Institute of Physics and Technology (MIPT), ITMO University and the Australian National University have utilized silicon nanoparticles to induce this Raman effect.
In their work, the researchers found that silicon nanoparticles reveal an exceptionally large refractive index, a property that determines the amount of light capable of penetrating through a given object. In fact, the refractive index of the silicon nanospheres used in this study allowed for the magnetic dipole resonance to be as much as 300 nanometers (nm) longer than when other metallic nanoparticles were used1. When the Raman effect was investigated using these nanoparticles, the researchers found that the Raman emission intensity of these particles was 100 times greater than when non-resonant particles were used. The researchers of this study are hopeful that the application of silicon nanoparticles in future fiber optic devices will improve the ability to transmit data over large distances.
Nanoparticle Coatings
A wide variety of both nanoparticle coatings and nanostructured thin films have been applied to fiber optic devices that have been utilized during the development of novel sensor technologies. The integration of these two technologies have proven advantageous in improving the ability of these new sensors to monitor the following parameters:
- Gas detection
- pH levels
- Temperature
- Humidity
- Ions
- Biomolecules
- Sensitivity
- Dynamic range
- Robustness
- Overall lifetime of devices
Additionally, researchers have found that the unique properties of the applied nanoparticle coatings can also provide additional properties to newly developed devices. For example, the application of silver nanoparticle coatings can improve the antibacterial behaviors associated with the enhanced device.
These device improvements occur as a result of embedding sensitive materials into the coatings or thin films. Therefore, when light penetrates through the optic fiber sensor, specific interactions can occur between the external medium present within the core of the device and the evanescent field that is used to guide the light. Depending upon the specific properties associated with the nanocoating will determine the changes that will occur during this interaction. One of the most commonly used nanostructured coatings in fiber optic devices is the cladding-removed optical fiber (CROF)2 that offers devices an improved sensitivity and a number of other sensing values, some of which include the ability to detect humidity levels and the presence of numerous chemicals including ethanol, ammonia, methanol and several others.
References
1. “Silicon Nanoparticles could a boon for Fiber Optic Telecommunications” – IEEE Spectrum
2. Urrutia, A., Goicoechea, J., & Arregui, F. J. (2015). Optical Fiber Sensors Based on Nanoparticle-Embedded Coatings. Journal of Sensors. DOI: 10.1155/2015/805053.
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