21 research outputs found
Practical Theory of Spectral Evolution in an Organic Laser Diode
No full textThe spectrum of the light emitted by a microcavity OLED is strongly time dependent on the nanosecond timescale after switch-on of the pump mechanism. This is one reason why convincing confirmation of laser operation in such device is difficult. The simple theory here presented is helpful in interpreting observed light-emission behavior. One important finding is that the occurrence in the optical spectrum of a narrow Lorentzian on top of a spontaneousemission pedestal is no guarantee for observed laser operation. Another finding is that reabsorption by the singlet excitons leads to the highest gain when the cavity is detuned to the red side of the emission spectrum. This is confirmed by experimental observations on an optically pumped organic laser diode
2.85-Gb/s Organic Light Communication With a 459-MHz Micro-OLED
No full textWe present a broadband free space light communication system using high-speed organic light emitting diodes (OLEDs) as transmitters. Firstly, we report the design and bandwidth measurements of micro-OLEDs with active area of 40 × 40μm2. For this OLED, a cut-off frequency up to 459 MHz is observed. Secondly, by applying Direct Current Optical Orthogonal Frequency Division Multiplexing (DCO-OFDM) with adaptive bit and energy loading techniques, a data rate of 2.85 Gb/s is achieved. The increase of bandwidth and throughput reported in the current work are attributed to the improvements at the material, device and transmission levels. At the material level, a low work function Calcium cathode and ALD encapsulation of OLED is considered. At the device level, the active area is reduced in size and the OLEDs thickness is optimized. At the transmission level, parameters such as bias voltage, modulation amplitude and clipping have been fine-tuned to obtain high data rate
Ultra-short optical pulse generation and laser perspective in an Alq3 based micro OLED
No full textWe report experimental and theoretical investigations with high-speed µ-OLEDs and demonstrate promising optical pulse responses as short as 400 ps using Alq3. These observations indicate that high-speed µ-OLEDs can be used for light communication in the GHz regime. The measurements are for in-house fabricated µ-OLEDs without cavity and size of 100 µm x 100 µm. With a validated model for an electrically pumped OLED, we simulate the generation of ultra-short optical pulses. The model includes Stoke-shifted reabsorption and field-enhanced Langevin recombination rate. For the Alq3 system we compare the results with the above-mentioned measurements. The good agreement between the measurement and the simulation is the basis for further study of the prospects for ultra-short dynamics and organic laser diode operation on the ps time scale.</p
OLED-pumped Organic Laser
No full textWe report a numerical investigation of the recently proposed (Nature 621, 2023, 746) high-speed μ-OLED optically pumped organic laser and confirm that in this configuration the threshold for quasi-CW lasing is much easier reached than in case of a direct-electrically pumped organic laser diode. With a new model for the electrically biased OLED, we simulate the generation of pulsed and quasi-CW light. This light is fed into the organic laser where it optically pumps the emitting organic medium The model is voltage-driven and includes field-enhanced Langevin recombination in the OLED, Stoke-shifted reabsorption in both the OLED and organic laser, with an optical cavity in the latter. We numerically demonstrate 3.5 kA/cm2 laser threshold current density, 1 GHz modulation and conjecture the capability of Gb/s data transmission with this device.</p
High-speed OLED bandwidth optimisation method based on Relative Intensity Noise measurements
No full textInternational audienceIn the context of visible light communication, we present a heuristic approach to optimize the bandwidth of organic light-emitting diodes. Our approach utilizes a vector network analyzer and an optoelectronic loop to directly and rapidly visualize the effects of stack modifications on the optical bandwidth of high-speed OLEDs. This technique is applied for the first time to conduct systematic heuristic studies on OLED bandwidth and to identify relevant parameters such as OLED capacitance, serial resistance, emission layer thickness, and active area. More precisely, we utilize high-speed OLEDs based on coplanar wave guided electrodes, and demonstrate that reducing the active area of OLEDs from 500 x 500 μm² to 200 x 200 μm² and further to 100 x 100 μm² increases the bandwidth from 49 MHz to 91 MHz and above 200 MHz, respectively. Moreover, and counter intuitively, the bandwidth is increased when the hole blocking layer is removed from the organic heterostructure
Simple Theory of Spectral Evolution in an Organic Laser Diode
No full textSubmission for "60 years of organic semiconductor photophysics: a special issue in honor of Dr. Martin Pope" from Organic ElectronicsThe spectrum of the light emitted by a microcavity OLED is strongly time dependent on the nanosecond timescale after switch-on of the pump mechanism. This is one reason why convincing confirmation of laser operation in such device is difficult. The simple theory here presented is helpful in interpreting observed light-emission behavior. One important finding is that the occurrence in the optical spectrum of a narrow Lorentzian on top of a spontaneousemission pedestal is no guarantee for observed laser operation. Another finding is that reabsorbtion by the singlet excitons leads to the highest gain when the cavity is detuned to the red side of the emission spectrum. This is confirmed by experimental observations on an optically pumped organic laser diode
Multiscale Fabrication Process Optimization of DFB Cavities for Organic Laser Diodes
No full textIn the context of the quest for the Organic Laser Diode, we present the multiscale fabrication process optimization of mixed-order distributed-feedback micro-cavities integrated in nanosecond-short electrical pulse-ready organic light-emitting diodes (OLEDs). We combine ultra-short pulsed electrical excitation and laser micro-cavities. This requires the integration of a highly resolved DFB micro-cavity with an OLED stack and with microwave electrodes. In a second challenge, we tune the cavity resonance precisely to the electroluminescence peak of the organic laser gain medium. This requires precise micro-cavity fabrication performed using e-beam lithography to pattern gratings with a precision in the nanometer scale. Optimal DFB micro-cavities are obtained with 300 nm thick hydrogen silsesquioxane negative-tone e-beam resist on 50 nm thin indium tin oxide anode exposed with a charge quantity per area (i.e., dose) of 620 µC/cm2, developed over 40 min in tetramethylammonium hydroxide diluted in water. We show that the integration of the DFB micro-cavity does not hinder the pulsed electrical operability of the device, which exhibits a peak current density as high as 14 kA/cm2
Rate Equation Theory for Organic Diode Laser and Experimental Validation with Microcavity OLED
No full textWe present a new model for an organic laser diode based on rate equations for polarons, singlet and triplet excitons, both in host and dopant molecules, and photon densities. The model is validated by comparing calculated optical responses with measurements on high-speed low-Q OLEDS under pulsed nanosecond electrical excitation. The model confirms the threshold-current density of ~500A/cm2 observed in the recent first experiment with indication of lasing in an OLED with DFB-grating in the group of Adachi [1], if the Q-factor ~20K and no residual absorption occurs
Design, Fabrication and Validation of Mixed Order Distributed Feed-Back Organic Diode Laser Cavity
No full textIn the context of the quest for the organic laser diode, we address a key challenge to design and fabricate high-quality factor cavities compatible with electrical excitation of organic semiconductors. More precisely, we present the design of DFB micro-cavities for integration in organic laser diodes and their validation under optical pumping. To design high-quality factor mixed-order DFB micro-cavities, we consider the half- and quarter-wavelength multilayered system and use the optical waveguide analysis to quantify the effective indices of the high and low indices, and the matrix transfer method to calculate the reflectances. Matrices of DFB micro-cavities made from different doses and different grating periods were fabricated. We then identified those showing laser emission under optical pumping as an indication of optimal matching of their resonance wavelength with respect to the electroluminescence peak of the organic gain material. Potential applications of organic laser diodes deal with light communication, spectroscopy, sensors, and other applications where heterogenous integration is important
Organic Diode Laser Dynamics: Rate-Equation Model, Reabsorption, Validation and Threshold Predictions
No full textWe present and analyze a simple model based on six rate equations for an electrically pumped organic diode laser. The model applies to organic host-guest systems and includes Stoke-shifted reabsorption in a self-consistent manner. With the validated model for the Alq3:DCM host-guest system, we predict the threshold for short-pulse laser operation. We predict laser operation characterized by damped relaxation oscillations in the GHz regime and several orders of magnitude linewidth narrowing. Prospect for CW steady-state laser operation is discussed
