In the last decade, coherent narrow linewidth optical system technology has contributed to reaching a new generation called high-speed optical communication. This technology has improved the transmission capacity of long-haul fiber optic transmission systems. State of the art in the market is a bit rate up to 100 Gbps per channel, where in one fiber optic can be traversed by 80 channels or 8 TB per fiber. The main key of the high-speed transmission is narrowing the laser linewidth which will increase the laser coherency. Some techniques have been proposed before such as the use of quantum well structure, distributed feedback braggers and application of external cavity resonators that have been able to narrow semiconductor linewidth lasers. In this paper we make a theoretical analysis to attempt for narrowing the linewidth semiconductor laser with laser current injection control. We intend the application of narrowing linewidth technique for the free-space optical communications in the case of visible light communication where the demand of laser source with narrower linewidth of signal is one of the key to improve the performance. The analysis is performed based on Schawlow-Townes equation. We prove that increasing the current injection twice causes linewidth constriction twice. The analysis and simulations are performed using Optiwave software.
This paper presents key properties and examples of applications of resonant leaky-mode biosensors operating in the subwavelength regime. The main resonance features observed under variation of input wavelength and angle are discussed. The dependence of the resonance lineshape on element design parameters is highlighted. The surface-localized power concentration at resonance is described along with the standing-wave pattern of the leaky modes obtained at normal incidence. An example fabrication process involving holographic patterning, etching, and deposition of high-index material is provided. The fabricated elements resonate well with good agreement between experiment and theory found. As examples of practical applications, experimental results on detection of proteins and bacteria are given. The tag-free resonant sensor technology demonstrated may be feasible for use in fields such as in medical diagnostics, drug development, environmental monitoring, and homeland security.
Optical sensor technology based on subwavelength periodic waveguides is applied for tag-free, high-resolution biomedical and chemical detection. Measured resonance wavelength shifts of 6.4 nm for chemically attached Bovine Serum Albumin agree well with theory for a sensor tested in air. Reflection peak efficiencies of 90% are measured, and do not degrade upon biolayer attachment. Phase detection methods are investigated to enhance sensor sensitivity and resolution. Direct measurement of the resonant phase response is reported for the first time using ellipsometric measurement techniques.
The chief properties and possible applications of periodic waveguides and their leaky modes are presented in this paper. After summarizing the basic physics of the guided-mode resonance, computed leaky-mode field patterns are provided to illustrate their structure and the high local focal field enhancement obtainable. An example fabricated bandstop filter is found to exhibit 90% efficiency, 1 nm linewidth, and low sidebands. Computed spectra for a single-layer bandpass filter operating at 1.55 μm wavelength yield low sidebands, extending 100 nm, and an angular aperture of ~1.7°. Resonant vertical-cavity surface-emitting lasers (VCSEL) are presented in which multilayer Bragg-stack mirrors are replaced with leaky-mode resonance layers. The use of guided-mode resonance mirrors provides optical power flow across and laterally along the laser active region. The round-trip gain is thereby increased resulting in high laser efficiency and relaxed mirror reflectivity constraints. As the GMR mirror achieves high reflectivity at resonance, the laser wavelength is locked at the resonance wavelength principally defined by the period. Example resonant VCSEL embodiments are shown along with their computed characteristics. Resonant biosensors are addressed last. The high parametric sensitivity of the guided-mode resonance effect, a potential limitation in filter applications, can be exploited for sensors as illustrated by several examples.
Conference Committee Involvement (1)
Third International Seminar on Photonics, Optics, and Its Applications (ISPhOA 2018)