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Distributed Feedback Lasing from Arbitrary Gain Morphologies

초록/요약

This thesis discusses the use of the organic distributed feedback (DFB) lasers for single mode lasing from arbitrary gain morphologies. Because in the typical DFB laser the use of uniform gain media with the thickness of few hundred itself acts as a resonators to induce and guide DFB modes, which puts the limits on their applications to obtain lasing from irregular shaped gain media, such as dye-staining cells and tissues. Therefore, in the first project, we report a reusable second order Bragg grating template to induce a single mode DFB emission from variety of the states of gain media. The entire DFB structure composes of a slightly thin (25 nm) and disconnected titanium dioxide (TiO2) layer deposited on a one-dimensional (1D) quartz grating surface. The use of optically thick casted and thin coated film, a free-standing thick film and optically active liquid as external gain media yields single mode DFB emission from the same template with reliable performance. Numerical simulations confirms that the thin and disconnected TiO2 grating pattern support and strongly confines DFB mode even under no index difference between superstrate and substrate. Additionally, the template shows high sensitivity and detection limit for refractometric sensing when there is no typical DFB laser waveguide. In the second project we focus on the arbitrary patterning of the photonic components via inkjet printing method to emit and guide light from printed photonic components on a same DFB board (TiO2 deposited DFB board presented in previous section). Inkjet printing is a simple, cost-effective, and environment friendly patterning technique which works beyond the use of heat, UV radiations, and plasma. Therefore, this technique is more suitable for patterning the biomaterials because biofunctionality and bioactivity remains preserved during the patterning process. However, patterning of the biomaterials based soft photonic devices by inkjet printing technology is still challenging because preciseness and uniformity of the device requires to control photons at nanoscale efficiently. This study shows inkjet printing of silk protein photonic components on a single DFB board to emit/guide single mode DFB lasing. A DFB board containing a quartz grating surface coated with a thin TiO2 layer enables coherent feedback of the generated photons from arbitrary silk pattern printed on it. A minimum silk pattern with the diameter of 200 µm can lase under optical pumping. The addition of gold nanoparticles in the silk/dye solution can tune the resonance position to the required wavelength. Furthermore, lasing and waveguiding photonic components can be drawn on a single DFB board to extract the emitted lasing light. The printed components can be restructured by post modification (water-removal and reprinting). In addition, the use of the optically absorptive melanin nanoparticles placed on the printed waveguides can attenuate the propagating lasing signal, which confirms the photonic circuit have potential for the sensing applications. The third project deals with the study of the typical DFB laser with a thin spin-coated gain morphology (optical waveguide) layer onto the quartz grating surface to yield a physically transient and eco-friendly chemosensor. In the organic DFB lasers, quenching the quantum efficiency of the probe dye under multiple optical pumping puts the limit on the life time of the laser. Such laser with short life span can be used for chemosensing applications. Here, we report the usefulness of such organic DFB lasers with short life-time, by spin-coating a solution of natural silk protein and sodium fluorescein probe dye on the reusable quartz grating surface to yield a physically transient, low-cost, and eco-friendly DFB laser chemosensor. The prepared DFB laser shows high sensitivity towards hydrochloric (HCl) acid vapor by attenuating its optical response. The sensitivity of the DFB laser chemosensor depends on the concentration of the HCl acid vapors and the thickness of the silk/dye optical gain layer. Moreover, physically transient DFB laser chemosensor shows its response to HCl vapor 30 time higher than obtained from fluorescence chemosenseor. Additionally, used silk/dye layer can be easily removed by water washing and new laser sample can be prepared by recoating new solution on the quartz grating.

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목차

Chapter 1
Introduction 1
1.1 Lasers 1
1.2 Organic distributed feedback lasers 1
1.2.1 Basics and applications 1
1.2.2 Commercializing and limitation of uses 2
1.2.3 Introducing high refractive index layers on the gain medium 3
1.3 Material patterning for photonic devices 4
1.4 Inkjet printing technology 5
1.4.1 Silk protein inks for printing photonic components 5
1.5 Fluorescent chemosensor and organic lasers 6
1.6 Organization of thesis 7
Chapter 2 8
Methods 8
2.1 Preparation of silk protein solution 8
2.2 Fabrication of quartz grating 8
2.3 Preparation of arbitrary morphologies of optically active gain medium 9
2.3.1 Optically thick and thin gain medium for DFB lasing 9
2.3.2 Preparation of fluidic gain 10
2.3.3 Preparation of arbitrary gain morphology via inkjet printing 10
2.3.4 Preparation of optically thin gain medium for acid vapor sensing 10
2.4 Preparation of HCl acid vapor 11
2.5 Optical measurements 12
2.5.1 Absorbance measurement 12
2.5.2 Optical measurement form arbitrary gain surfaces 12
2.5.3 Optical measurement form inkjet printed gain 12
2.5.4 Optical measurements for acid vapor sensor 12
2.6 Numerical Simulations 13
Chapter 3 14
Single mode distributed feedback lasing from arbitrary gain morphology 14
3.1 Summary 14
3.2 Device schematics and parameters 15
3.3 DFB emission from optically thick gain medium and photon confinement 16
3.3.1 Lasing from optically thick solid gain film 16
3.3.2 Simulated results for photon confinement 19
3.4 DFB emission from liquid gain and operating sensitivity of the device 20
3.4.1 Lasing from liquid gain medium 20
3.4.2 Operating sensitivities of the device 21
3.5 Lasing from optically thin gain film 25
3.6 Lasing from free-standing gain film 26
3.7 Conclusion 27
Chapter 4 29
Lasing from inkjet printed silk-ink on a reusable distributed feedback board 29
4.1 Summary 29
4.2 Inkjet printing gain and its characteristics 30
4.3 Optical properties of inkjet printed silk-ink and its minimum features for lasing 32
4.3.1 Absorption and photoluminescence spectra 32
4.3.2 Single mode DFB emission from printed silk text 33
4.3.3 Effect of grating pitch size and simulated results 34
4.3.4 Estimating the minimum features of patterned gain 36
4.4 Tuning resonance by the addition of gold nanoparticles into the silk-ink 39
4.5 Integrated bio-photonic circuit, its sensing applications and post-modification 41
4.6 Conclusion 45
Chapter 5 46
Physically transient and eco-friendly DFB laser chemosensor for detecting acid vapors prepared by thin and uniform morphology of the gain film 46
5.1 Summary 46
5.2 Working principle and device characteristics 47
5.2.1 Working principle 47
5.2.2 Physical parameters of the device 48
5.2.3 Numerical simulations 49
5.3 Optical characterizations 50
5.4 HCl sensing phenomenon and sensitivity of the device 51
5.4.1 HCl concentration selection and sensing phenomenon 51
5.4.2 Response of the DFB laser towards HCl vapors 53
5.4.3 Sensitivity comparison with fluorescence chemosensor 55
5.5 Gain layer thickness dependent efficiency of the DFB laser chemosensor 56
5.6 Conclusion 60
Chapter 6 61
Future work 61
References 62
List of publications 75

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