Coupled Polymer Microfiber Lasers for Single Mode Operation and Enhanced Refractive Index Sensing

Abstract

220 wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat.deOwing to high quality ( Q ) factor and unique cavity confi guration, whispering gallery cavities (WGCs) have attracted intensive research attentions in diverse fi elds of sciences and technologies such as quantum electrodynamics, optical chaos, optical fi lters, modulators, and lasers. [1][2][3][4][5][6][7][8][9] Recently, WGCs have exhibited promising applications as chemical and biological sensors based on the shifting or splitting of resonance modes. [10][11][12][13][14] This technique is label-free and ultra-sensitive down to the level of nanoparticles, viruses, and even single molecules. [12][13][14] For such sensors, both high Q factor and large free spectral range (FSR) are strongly desirable. However, these two factors are normally confl icting in a single cavity.Recently, investigations on coupled WGCs have demonstrated many interesting phenomena like induced transparency and absorption, slow light, [ 15,16 ] directional and single mode emission, [17][18][19][20][21][22] and enhancement of sensor's sensitivity. [ 23,24 ] Single mode lasing is signifi cant for integrated photonics and on-chip applications. [ 25 ] Traditionally, it has been realized by confi gurations including Fabry-Pé rot (F-P) [ 25 ] and especially distributed feedback (DFB) cavities. [26][27][28] For WGCs, single mode operation can be obtained by reducing the cavity size, [ 29 ] but this method deteriorates laser Q factor. The alternative solution without deteriorating the Q factor is to use coupled WGCs, in which single mode emission is generated through Vernier effect. [ 19,20 ] Coupled WGCs have been explored in microdisks, optofl uidic ring resonators, and silica/glass fi bers. [17][18][19][20][21][22][23][24] Compared to traditional semiconductor and inorganic onedimensional cavities, organic nano/microfi bers possess simpler fabrication and better mechanical fl exibility, thus are attractive for fl exible optoelectronics and nanophotonics. [ 30,31 ] They are also easier to be assembled in arrays or ordered structures, [ 32 ] highly benefi cial for photonic systems, and have successfully employed for logic elements/circuits. [ 33 ] However, nano/ microfi ber lasers, being an important component in integrated photonic devices, have been mostly limited to waveguide effect where two endfaces of the fi ber served as refl ection mirrors. [ 32,[34][35][36][37] Generally, this mechanism has low Q factor because of poor refl ectivity of the endface refl ectors, which hinders it for practical applications, especially in biological sensors. Very recently, we have achieved high Q factor whispering gallery mode (WGM) lasing, inside a circular cross-section of a straight polymer fi ber, with potential application as a sensitive refractive index sensor. [ 38 ] Further investigation of coupled fi ber structures should be important not only for improving the laser and sensor performances, but also for exploring a possibility to integrate with other components, whi...

Single-mode lasing via loss engineering in fiber-taper-coupled polymer bottle microresonators

“…Typically, WGM lasers are usually multimode due to the lack of a mode selection strategy [3,[6][7][8]. Reducing the size of the microcavities is a direct way to realize singlemode lasing, and another possible strategy is to use coupled cavities through the Vernier effect [9][10][11] and the parity-time symmetry effect [12,13].…”

“…Polymers are good hosts for various lasing gain dopants with advantages of easy processing, mechanical flexibility, and low cost. For example, high-quality polymer microfiber resonators are fabricated to generate WGM lasers, with advantages of tunability, singlemode operation, and enhanced refractive index sensing [11,23]. More recently, we used interference light patterns to spatially overlap the intensity profile of a desired WGM and demonstrated single-mode lasing in polymer bottle microresonators [24].…”

Improved Optical Property and Lasing of ZnO Nanowires by Ar Plasma Treatment

“…5a. The non-linear increased intensity is a characteristic of lasing [1,31]. The lasing phenomenon of plasma-treated samples is also based on the reasons mentioned above, after plasma treatment, surface trap states can be removed, and the optical loss has been minimized to achieve population inversion after optical pumping.…”

Low‐Threshold Wavelength‐Switchable Organic Nanowire Lasers Based on Excited‐State Intramolecular Proton Transfer

“…18 nm;S upporting Information, Figure S11) of the gain region. [31] Based on the nanowire microcavity effects (Figure 2c), the Dl % 18 nm can be achieved when the nanowire length decreases to about 2.5 mm. As shown in Figure 3d,asingle-mode lasing around 514 nm, was successfully fulfilled in a2 .2 mml ong nanowire.…”