Primary Study On Organic Photonic Crystal Distributed Feedback Lasers

The times we are living is the information era, and it is a semiconductor era in some sense, either. The emergence of semiconductor brought Large-Scale Integration, computers, Infobahn, and so on, which are closely linked our daily life in modern times. Almost all semiconductor devices are focusing on how to use and control electronic movement in which an electron is the decision. The integration limit in the future can be seen which is decided by the electronic characteristics. But photon has advantages that electronics does not have: speed-up, no interaction, etc. Therefore, photonic will act the leading role in the next generation of devices.Photon crystals are put forward in 1987 as a new concept and new material. One notable feature of this material is that photonic movement can be controlled as people expect. Because of its unique characteristics, high-performance optical devices which have new theories or can not be produced previously can now be produced using photonic crystals.Along with the emergence of photonic crystal, in recent years, a new- style laser: photonic crystal laser has appeared,which introduced photonic crystal structure into semiconductor laser. Photonic crystal can control the propagation of light in laser devices, which improves the feedback in lasers. The characteristic of photonic crystal determines the unique property of photonic crystal laser. The photonic band gap can restrain the spontaneous radiation of laser, so the photonic crystal laser has low threshold. Furthermore, the photonic crystal laser has the property of little volume and easy to couple with fiber. The photonic crystal laser will have important and extensive applications in optical communication domain in the future.In this thesis the optical pumping organic photonic crystal distributed- feedback laser devices have been designed, fabricated, and characterized by combining computational simulate with test analysis, and the parameters of the device was optimized. This makes a favorable basis on both theory and experiment to design and fabricate the electrical pumping organic photonic crystal distributed feedback laser in the future.The structure of the organic photonic crystal distributed feedback laser device we designed is described as follow. First, a layer of SiO2 with thickness about 40 nm was grown on Si slab as the substrate of the device, and a layer of high-index material Si3N4 was deposited on the SiO2 surface. Then a periodic pattern was etched in the higher-index material to create the photonic crystal .It's lattice constant is 400 nm, the radius is about 140 nm, the etching deepness equaled to the thickness of high-index material. Finally, an organic gain material was deposited on top of the photonic crystal, completely filling the holes of the photonic crystal. This structure increased the index contrast between the photonic crystal layer and the organic material. This results in stronger mode coupling, leading to enhanced feedback and hence to smaller devices.The process of designing, fabricating and characterizing the organic photonic crystal DFB laser is comprised of several parts as follow,1. In the respect of the theory computation .First of all, we introduce the concept of waveguide, and calculated the effective index of the waveguide structure. The effective index of waveguide vs. the thickness of the waveguide was portrayed by the matlab software. We got the scale of effect thickness to high-index material approximatively. Secondly, we adopted the Finite Difference Time Domain Method (FDTD)to compute the band structures of the photonic crystal slab, and the numerical method was implemented by the MIT Photonic Bands (MPB) software. 16 plane waves per unit cell length were used to get the band diagram. We could calculate the lasing range of the photonic crystal slab by assuming the lattice constant .Then we could make sure of the organic small molecule material to provide the optical gain.2. In the respect of fabricating the device. The Si3N4 photonic crystal slabs with SiO2 as the substrate are prepared outside .In our super-clean laboratory, first of all, the surface of photonic crystal slabs need preconditioning, in order to make sure that the surface is clean enough .Then we adopt SD400 multi-origin controlled organic molecular vapor deposition system, then the organic molecular was vaporized onto the surface of photonic crystal. Finally, we got the organic photonic crystal DFB lasers with different organic gain layer thickness as expectation.3. In the respect of characterizing the device,we used He-Cd laser and BP150 grating spectrometer to characterize the lasing properties of the devices. Combining with our experiment condition, the He-Cd ultraviolet (UV) CW laser with 325 nm wavelength was adopted as the optical pumping source. We have measured the photoluminescence spectrums corresponding different thickness of organic gain layer. As a result, the emitting peaks appear red shift as the increase of the thickness of organic gain layer, we found that lasing occurs probably at a wavelength of 680 nm, as we expect in simulation. When the thickness of organic gain layer is 450 nm, the lasing effect is the best, the laser wavelength is 682.2 nm and the Full Wave at Half Maximum (FWHM) of emit peak is only 0.6 nm. As changing the power of the optical pumping, the output lasing intensity is varying accordingly. Then we measure that the different emit light power correspond to the different density of pump light power, the lasing threshold curve can be portrayed. The lasing threshold is lowest when the thickness of organic gain layer is 450 nm, and it is just 0.5kW/cm2. At the same time, we measure the of laser radiation angle to the laser structure which has the thickness of organic gain layer as 450nm, and the smallest angle is about 4。.In sum, the organic photonic crystal DFB lasers have been designed, fabricated, and characterized in this thesis. As we did the three aspect jobs that introduced above, the design of the device structure had been optimized, and the detailed structure parameters of the device were supported. Through our long-playing examination explore, we form a consummate system of fabrication techniques and testing instrument, which will establish the foundation of theory and experiment to develop electrical pumping organic photonic crystal DFB laser in the future.