An Efficient and Color‐Tunable Solution‐Processed Organic Thin‐Film Laser with a Polymeric Top‐Layer Resonator

Abstract

as a laser resonator, have found a variety of applications in spectroscopy, [5] optical communications, [6] and sensing. [7][8][9][10] DFB lasers can provide narrow single mode emission (linewidth <1 nm) and require only low pump energy for their operation, i.e., they show a low threshold. The resonator is easily integrated into other devices, and it can be implemented with field-effect-transistor geometry, which promises potential for the development of electrically pumped TFOLs. Moreover, DFB lasers can be mechanically flexible, and their production costs are relatively low. DFB gratings are usually fabricated by electron beam lithography, nanoimprint lithography (NIL), or holographic lithography (HL). [11] A particular advantage of the latter is its capability to produce small structures of different dimensionality over a large area (up to a few cm 2 ) in a simple and low-cost manner, which can be exploited to fabricate wavelength-tunable devices on a single chip.So far, different DFB architectures, with gratings fabricated by various methods, have been reported, [1][2][3][4] whereby efforts have been devoted predominantly to lowering the threshold. The lowest values (<1 kW cm −2 ) have been achieved with lasers whose DFB gratings are engraved on conventional inorganic substrates (e.g., glass or SiO 2 ), onto which the active films are deposited (this configuration will henceforth be denoted as standard; Std). Other studies, aimed at improving device integration, reducing device costs, and achieving mechanical flexibility, have focused either on architectures with gratings imprinted directly on the active film, [12][13][14][15][16][17] or on systems wherein both the active material and the resonator, which is generally located below the active film [18][19][20][21][22] and only in few cases on top of it, [23,24] were processed from solution. Unfortunately, the thresholds of these solution-processed lasers are generally high (>8 kW cm −2 ), except for few exceptions. [19] Finally, several strategies have been proposed in order to accomplish wavelength tunability in a single device. [1][2][3][4] For example, by using multiple gratings (e.g. segmented substrates with a stepped grating period), [25] a wedged-shape active film (i.e. with a continuously variable thickness), [26] mechanical stretching, [27] photoisomerizable azo-polymers, [28] or photochromic molecules doped into the active film. [29] Some works have demonstrated electrical-tuning by combining an elastic DFB laser with an electroactive substrate, [30] or by including a layer contaning a Thin film organic lasers represent attractive light sources for numerous applications. Currently, efforts are devoted to the development of low-cost high-performance and color-tunable devices, whereby both the resonator and the active layer should consist of solution-processable organic materials. Herein, solution-processed distributed-feedback lasers are reported with polymeric resonators on top of active films of perylene orange or carbon-bridged oligo(p-phenylenevi...

Carbon‐Bridged p‐Phenylenevinylene Polymer for High‐Performance Solution‐Processed Distributed Feedback Lasers

“…This value is significantly lower than that of previously reported devices based on COPV1 dispersed in PS with gratings engraved on inorganic substrates . Importantly, the threshold obtained for device R Top NS ( 1 ) is around the same than that obtained with the best lasers with a top‐layer resonator architecture based on COPV3, emitting in similar spectral region …”

“…It should simultaneously achieve various characteristics such as high‐quality films with strong photoabsorption (and hence high gain), high photoluminescence quantum yield (PLQY), low waveguide loss, and high photostability. In previous work, it was demonstrated that carbon‐bridged oligo( p ‐phenylenevinylene) dyes (COPV n , with n = 1–6), dispersed in polystyrene (PS), are among the best dyes to be used for DFB lasers emitting at wavelengths that cover a wide range of the visible spectrum (380–600 nm) . Films doped with COPV n , with between 3 and 6 repeat units ( n ), emitting within the 515–585 nm spectral range, exhibited very low amplified spontaneous emission (ASE) and DFB pump intensity thresholds (down to 0.7 kW cm −2 ) and very long operational lifetimes (up to 10 6 pump pulses (pp)).…”

“…Typical state‐of‐the‐art organic DFB lasers have shown pump thresholds of <1 kW cm −2 , traditionally with the gratings engraved into conventional inorganic substrates (e.g., SiO 2 ), onto which the active film is deposited . Efforts aiming at reducing device costs and improving mechanical flexibility have focused on architectures with gratings imprinted directly on the active film (e.g., thermal or solvent imprinting), or devices wherein both the active material and the resonator can be processed from solution (such as UV‐nanoimprint lithography (UV‐NIL)) . Recently, an important landmark was the demonstration of lasers with high efficiency, low threshold, long operational lifetime, and broad wavelength tunability in a single device, thanks to the combination of highly efficient and photostable dyes and a not very common DFB resonator configuration .…”

“…Efforts aiming at reducing device costs and improving mechanical flexibility have focused on architectures with gratings imprinted directly on the active film (e.g., thermal or solvent imprinting), or devices wherein both the active material and the resonator can be processed from solution (such as UV‐nanoimprint lithography (UV‐NIL)) . Recently, an important landmark was the demonstration of lasers with high efficiency, low threshold, long operational lifetime, and broad wavelength tunability in a single device, thanks to the combination of highly efficient and photostable dyes and a not very common DFB resonator configuration . This consisted on a resist layer with the grating engraved by holographic lithography (HL) and deposited on top of an active film of uniform thickness.…”

An Efficient All‐Plastic Organic Waveguide Solid‐State Laser Devices with Distributed Bragg Reflector

“…The slope efficiency of 7.3% was reported for the holographic DFB waveguide laser device with the electroluminescent conjugate polymer of poly[(9,9‐(dihexyl)‐9H‐fluorene‐2,7‐vinylene)‐co‐(1‐methoxy‐4‐(2‐ethylhexyloxy)‐2,5‐phenylene‐vinylene)] (Poly(DH‐PFV‐co‐MEHPPV)) . More recently, the effect of top layer DFB resonator on the laser performances of threshold and slope efficiency were evaluated: the threshold of 1 kW cm −2 (0.1 µJ pulse −1 , 10 µJ cm −2 ) and the slope efficiency of 1.4% were reported …”