Wei Liang

Bio: Wei Liang is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Laser & Semiconductor laser theory. The author has an hindex of 13, co-authored 25 publications receiving 984 citations.

Highly sensitive fiber Bragg grating refractive index sensors

Abstract: We combine fiber Bragg grating (FBG) technology with a wet chemical etch-erosion procedure and demonstrate two types of refractive index sensors using single-mode optical fibers. The first index sensor device is an etch-eroded single FBG with a radius of 3 μm, which is used to measure the indices of four different liquids. The second index sensor device is an etch-eroded fiber Fabry-Perot interferometer (FFPI) with a radius of ~1.5 μm and is used to measure the refractive indices of isopropyl alcohol solutions of different concentrations. Due to its narrower resonance spectral feature, the FFPI sensor has a higher sensitivity than the FBG sensor and can detect an index variation of 1.4 X 10(-5). Since we can measure the reflection signal, these two types of sensors can be fabricated at the end of a fiber and used as point sensors.

Transmission characteristics of a Fabry-Perot etalon-microtoroid resonator coupled system.

Abstract: The transmission spectra of a Fabry-Perot etalon coupled to a microtoroid resonator are studied theoretically and experimentally. The resonance line shapes depend strongly on the resonance wavelength detuning and coupling strength between the two resonators. A wide variety of line shapes, ranging from a single to triple peaks, symmetric to asymmetric Fano-like peaks, and notches were predicted and observed experimentally. The capability to modify the spectral line shapes by tuning the coupling between or losses of two resonators may find applications in optical filtering, switching, sensing, and dispersion engineering.

Coherent beam combining with multilevel optical phase-locked loops

Abstract: Coherent beam combining (CBC) technology holds the promise of enabling laser systems with very high power and near-ideal beam quality. We propose and demonstrate a novel servo system composed of multilevel optical phase lock loops. This servo system is based on entirely electronic components and consequently can be considerably more compact and less expensive compared to servo systems made of optical phase/frequency shifters. We have also characterized the noise of a 1064 nm Yb-doped fiber amplifier to determine its effect on the CBC and studied theoretically the efficiency of combining a large array of beams with the filled-aperture implementation. In a proof-of-concept experiment we have combined two 100 mW 1064 nm semiconductor lasers with an efficiency of 94%.

Coherent combining of the output of two semiconductor lasers using optical phase-lock loops

Abstract: We have experimentally demonstrated current-injection optical phase-lock loops (OPLLs) based on commercial single-section semiconductor distributed-feedback (DFB) lasers. Using two parallel OPLLs, we have obtained 87% efficient coherent power combining of the two DFB lasers. The rms differential phase error between the two lasers is about 30°.

Coherent Power Combination of Semiconductor Lasers Using Optical Phase-Lock Loops

Abstract: Heterodyne optical phase-lock loops (OPLLs) enable the precise electronic control over the frequency and phase of a semiconductor laser (SCL) locked to a ldquomasterrdquo reference laser. One of the more interesting applications of OPLLs is the creation of coherent arrays by locking a number of ldquoslaverdquo SCLs to a common master laser. In this paper, we demonstrate the coherent power combination of various high-power semiconductor lasers using OPLLs in both the filled-aperture and tiled-aperture configurations. We further demonstrate the electronic control over the phase of each individual SCL using a voltage-controlled oscillator. It is feasible to combine a large number of SCLs using this approach, leading to compact, efficient, and cost-effective high-power and high-radiance optical sources.

Developing optofluidic technology through the fusion of microfluidics and optics

Abstract: We describe devices in which optics and fluidics are used synergistically to synthesize novel functionalities. Fluidic replacement or modification leads to reconfigurable optical systems, whereas the implementation of optics through the microfluidic toolkit gives highly compact and integrated devices. We categorize optofluidics according to three broad categories of interactions: fluid–solid interfaces, purely fluidic interfaces and colloidal suspensions. We describe examples of optofluidic devices in each category.

Integrated optofluidics: A new river of light

Abstract: The realization of miniaturized optofluidic platforms offers potential for achieving more functional and more compact devices. Such integrated systems bring fluid and light together and exploit their microscale interaction for a large variety of applications. The high sensitivity of compact microphotonic devices can generate effective microfluidic sensors, with integration capabilities. By turning the technology around, the exploitation of fluid properties holds the promise of highly flexible, tunable or reconfigurable microphotonic devices. We overview some of the exciting developments so far.