Optical Positive Feedback Research Articles

Stochastic dynamics of a semiconductor laser with delayed optoelectronic feedback and noise

Semiconductor lasers(SLs), versatile tools in communication, medicine, and scientific research, demand close examination of their dynamic behavior. With their unique geometric forms and diminutive sizes, these lasers possess a heightened sensitivity to noise. In this paper, we delve into time-delay semiconductor laser systems, noise included, honing in on time-delays’ effects on noisy laser equations. Carrier density (N) and laser intensity (I) constitute the core parameters that define the performance of these lasers, and we scrutinize their dynamic trajectories. A cutting-edge method fusing stochastic center manifold theory with the stochastic averaging method enables us to probe the stochastic dynamical attributes of semiconductor laser equations. We uncover that the time-delay parameter (τ 1) produces varied consequences on the laser system’s stability under both positive and negative optical feedback conditions. The negative feedback typically bolsters laser performance, fostering increased stability, whereas the positive counterpart could incite instability. By deftly managing the time-delay parameter, one can fine-tune the dynamic performance of semiconductor lasers, mitigating output power fluctuations and tightening linewidths, thereby augmenting stability and spectral purity. Moreover, in the realm of positive optical feedback scenarios, adroitly modifying the time-delay parameter can quell instability to a degree, paving the way for a novel regulatory approach to optimize laser performance. This lays the groundwork for further enhancement of semiconductor laser performance, as well as curbing the detrimental effects of noise on their operation.

Laser-induced periodic surface structures as optical resonators for organic thin-film distributed feedback lasers

Laser-induced periodic surface structures (LIPSS) have received considerable attention due to their potential for micro-and nanostructuring and surface functionalization of various materials. We present a novel application of LIPSS on a glass substrate as distributed feedback (DFB) laser resonators, capable of providing sufficient positive optical feedback to achieve lasing in thin-film waveguides with organic small molecules as a gain medium. The direct femtosecond micromachining allows for easy variation of the periodicity across a broad range of values, including those required to reach 1st Bragg order DFB operation. We investigate several small molecule organic thin-film systems and observe lasing in strong accordance with the underlying periodicities of all photonic structures involved. These results demonstrate the effectiveness of LIPSS as DFB laser resonators and suggest that they could facilitate the integration of organic thin-film media-based lasers and other photonic devices into various integrated photonic systems.

(Invited) The Evolution of Inorganic Nanocrystals for Bioimaging

The first applications of luminescent nanocrystals to bioimaging were semiconductor quantum dots with optoelectronic properties that largely mirror those of organics and proteins, but with substantially increased stability and brightness that have enabled single molecule and other challenging imaging applications. Building on this success, newer nanocrystals have been engineered with optical properties unlike anything found in traditional probes, including perfect photostability,1,2 anti-Stokes emission a billion-fold more efficient than 2-photon excitation,3 and most recently, photon avalanches hosted within nanostructures.4 Avalanches are steeply nonlinear events in which outsized responses arise from a series of minute inputs. With light, photon avalanching (PA) had been observed only in bulk materials and aggregates, often at cryogenic temperatures, preventing its application to bioimaging. We recently reported the realization of PA at room temperature in sub-30 nm Tm3+-doped NaYF4 upconverting nanoparticles (UCNPs) and demonstrated their use in high-resolution imaging at wavelengths that fall within NIR spectral windows of maximal biological transparency. Avalanching nanoparticles (ANPs) can be pumped by either continuous-wave or pulsed lasers and exhibit all of the defining features of PA: clear excitation power thresholds, exceptionally long rise time at threshold, and a dominant excited-state absorption that is >10,000 times larger than ground-state absorption. Beyond the avalanching threshold, ANP emission scales with up to the 31st power of pump intensity, an extreme nonlinearity caused by the induced positive optical feedback within each nanocrystal. This enables sub-70 nm spatial resolution using only simple scanning confocal microscopy and before any computational data analysis. NaYF4 ANPs with 8-20% Tm3+content can be excited at either 1064 or 1450 nm, with avalanching emission at 800 nm. Pairing the steep nonlinearity of ANPs with existing superresolution techniques and computational methods allows for imaging with higher resolution and at ca. 100-fold lower excitation intensities than is possible with other probes. For application of ANPs to live-cell imaging, we have developed synthetic chemistry-free methods for conjugating engineered antibodies to NP-surface SpyCatcher proteins,5 which bind and spontaneously form covalent isopeptide bonds with cognate SpyTag peptides. This enables controlled and irreversible attachment of antibodies to nanoparticle surfaces, for specific targeting of cell-surface receptors in quantitative live-cell study of their distribution, trafficking, and physiology. Wu, S. et al. Non-blinking and photostable upconverted luminescence from single lanthanide-doped nanocrystals. Proc. Natl. Acad. Sci. 106, 10917–10921 (2009).Fernandez-Bravo, A. et al. Continuous-wave upconverting nanoparticle microlasers. Nat. Nanotechnol. 13, 572–577 (2018).Tian, B. et al. Low irradiance multiphoton imaging with alloyed lanthanide nanocrystals. Nat. Commun. 9, 3082 (2018).Lee, C. et al. Giant nonlinear optical responses from photon-avalanching nanoparticles. Nature 589, 230–235 (2021).Pedroso, C. C. S. et al. Immunotargeting of nanocrystals by SpyCatcher conjugation of engineered antibodies. ACS Nano 15, 18374–18384 (2021). Figure 1

Giant nonlinear optical responses from photon-avalanching nanoparticles.

Avalanche phenomena use steeply nonlinear dynamics to generate disproportionately large responses from small perturbations, and are found in a multitude of events and materials1. Photon avalanching enables technologies such as optical phase-conjugate imaging2, infrared quantum counting3 and efficient upconverted lasing4-6. However, the photon-avalanching mechanism underlying these optical applications has been observed only in bulk materials and aggregates6,7, limiting its utility and impact. Here we report the realization of photon avalanching at room temperature in single nanostructures-small, Tm3+-doped upconverting nanocrystals-and demonstrate their use in super-resolution imaging in near-infrared spectral windows of maximal biological transparency. Avalanching nanoparticles (ANPs) can be pumped by continuous-wave lasers, and exhibit all of the defining features of photon avalanching, including clear excitation-power thresholds, exceptionally long rise time at threshold, and a dominant excited-state absorption that is more than 10,000 times larger than ground-state absorption. Beyond the avalanching threshold, ANP emission scales nonlinearly with the 26th power of the pump intensity, owing to induced positive optical feedback in each nanocrystal. This enables the experimental realization of photon-avalanche single-beam super-resolution imaging7 with sub-70-nanometre spatial resolution, achieved by using only simple scanning confocal microscopy and without any computational analysis. Pairing their steep nonlinearity with existing super-resolution techniques and computational methods8-10, ANPs enable imaging with higher resolution and at excitation intensities about 100 times lower than other probes. The low photon-avalanching threshold and excellent photostability of ANPs also suggest their utility in a diverse array of applications, including sub-wavelength imaging7,11,12 and optical and environmental sensing13-15.

Chromaticity-tunable white random lasing based on a microfluidic channel.

The color and/or chromaticity controllability of random lasing is a key factor to promote practical applications of random lasers as high luminance sources for speckle-free imaging. Here, white coherent random lasing with tunable chromaticity is obtained by using broadband enhancement Au-Ag nanowires as scatterers and the resonance energy transfer process between different dyes in the capillary microfluidic channel. Red, green and blue random lasers are separately fabricated with low thresholds, benefiting from the plasmonic resonance of the nanogaps and/or nanotips with random distribution and sizes within Au-Ag nanowires and positive optical feedback provided by the capillary wall. A white random laser system is then designed through reorganizing the three random lasers. And, the chromaticity of the white random laser is flexibly tunable by adjusting pump power density. In addition, the white random laser has anisotropic spectra due to the coupling role between the lasers. This characteristic is then utilized to obtain different random lasing with different chromaticity over a broad visible range. The results may provide a basis for applying random laser in the field of high brightness illumination, biomedical imaging, and sensors.

Infrared detection and photon energy up-conversion in graphene layer infrared photodetectors integrated with LEDs based on van der Waals heterostructures: Concept, device model, and characteristics

We propose the concept of the infrared detection and photon energy up-conversion in the devices using the integration of the graphene layer infrared detectors (GLIPs) and the light emitting diodes (LEDs) based on van der Waals (vdW) heterostructures. Using the developed device model of the GLIP-LEDs, we calculate their characteristics. The GLIP-LED devices can operate as the detectors of far- and mid infrared radiation (FIR and MIR) with an electrical output or with near-infrared radiation (NIR) or visible radiation (VIR) output. In the latter case, GLIP-LED devices function as the photon energy up-converters of FIR and MIR to NIR or VIR. The operation of GLIP-LED devices is associated with the injection of the electron photocurrent produced due to the interband absorption of the FIR/MIR photons in the GLIP part into the LED emitting NIR/VIR photons. We calculate the GLIP-LED responsivity and up-conversion efficiency as functions the structure parameters and the energies of the incident FIR/MIR photons and the output NIR/VIR photons. The advantages of the GLs in the vdW heterostructures (relatively high photoexcitation rate from and low capture efficiency into GLs) combined with the reabsorption of a fraction of the NIR/FIR photon flux in the GLIP (which can enable an effective photonic feedback) result in the elevated GLIP-LED device responsivity and up-conversion efficiency. The positive optical feedback from the LED section of the device lead to increasing current injection enabling the appearance of the S-type current-voltage characteristic with a greatly enhanced responsivity near the switching point and current filamentation.

Random lasing from Rhodamine 6G doped ethanediol solution based on the cicada wing nanocones

Random lasing from Rhdomaine 6G (Rh6G) doped ethanediol solution based on the cicada wing nanostructures as scatterers has been demonstrated. The optical positive feedback of the random laser is provided by these nanocones on the cicada wing, where the scale of the nanocones and the distance between them is about 150 nm and 200 nm, respectively. Al-coated reflector has been introduced to reduce the loss of the pump energy from the bottom, and moreover lower the laser threshold, which is about 126.0 μJ/pulse. Due to the liquid gain medium, the lifetime of this random laser is longer than conventional random lasers. This random laser shows the potential applications in biological random laser and photonic devices.

Optical nano-structuring in light-sensitive AgCl-Ag waveguide thin films: wavelength effect.

Irradiation of photosensitive thin films results in the nanostructures formation in the interaction area. Here, we investigate how the formation of nanostructures in photosensitive waveguide AgCl thin films, doped by Ag nanoparticles, can be customized by tuning the wavelength of the incident beam. We found, silver nanoparticles are pushed towards the interference pattern minima created by the interference of the incident beam with the excited TEn-modes of the AgCl-Ag waveguide. The interference pattern determines the grating constant of the resulting spontaneous periodic nanostructures. Also, our studies indicate a strong dependence of the shape and size distribution of the formed Ag nano-coalescences on the wavelength of the incident beam. It also influences on the surface coverage of the sample by the formed silver nanoparticles and on period of the self-organized nano-gratings. It is found, exposure time and intensity of the incident light are the most determinant parameters for the quality and finesse of our nanostructures. More intense incident light with shorter exposure time generates more regular nanostructures with smaller nano-coalescences and, produces gratings with higher diffraction efficiency. At constant intensity longer exposure time produces more complete nanostructures because of optical positive feedback. We observed exposure with longer wavelength produces finer gratings.

Co-catalytic Absorption Layers for Controlled Laser-Induced Chemical Vapor Deposition of Carbon Nanotubes

The concept of co-catalytic layer structures for controlled laser-induced chemical vapor deposition of carbon nanotubes is established, in which a thin Ta support layer chemically aids the initial Fe catalyst reduction. This enables a significant reduction in laser power, preventing detrimental positive optical feedback and allowing improved growth control. Systematic study of experimental parameters combined with simple thermostatic modeling establishes general guidelines for the effective design of such catalyst/absorption layer combinations. Local growth of vertically aligned carbon nanotube forests directly on flexible polyimide substrates is demonstrated, opening up new routes for nanodevice design and fabrication.

Development of coherent tunable source in 2–16 μm region using nonlinear frequency mixing processes

A very convenient way to obtain widely tunable source of coherent radiation in the infrared region is through nonlinear frequency mixing processes like second harmonic generation (SHG), difference-frequency mixing (DFM) or optical parametric oscillation (OPO). Using commonly available Nd:YAG laser and its harmonic pumped dye laser radiation as parent beams, we have been able to generate coherent tunable infrared radiation (IR) in 2–16 μm region using different nonlinear crystals by DFM and OPO. We have also generated such IR source in the 4–5 μm region through SHG of CO2 laser in different infrared crystals. In the process we have characterized a large number of nonlinear crystals like different borate group of crystals, KTP, KTA, LiIO3, MgO:LiNbO3, GaSe, AgGaSe2, ZnGeP2, AgGa1−xInxSe2, HgGa2S4 etc. To improve the conversion efficiencies of such frequency conversion processes, we have developed some novel schemes, like multipass configuration (MC) and positive optical feedback (POF). The significance of the obtained results lies in the fact that to get the same conversion in SHG or DFM, one now requires fundamental input radiation with much lower intensity.

“Heterogeneous” versus “homogeneous” nucleation and growth of microcones on titanium surface under UV femtosecond-laser irradiation

Two separate sets of microcones were observed on titanium surface under various ablative 248-nm femtosecond-laser exposures near rough spallation crater edges and in crater centers, respectively. “Heterogeneous” nucleation of microcones occurred on crater edge spikes above the corresponding cumulative spallation thresholds, with their gradual growth proceeding through redeposition of the ablated matter. In contrast, quasi-periodical central microcones emerged through a “homogeneous” nucleation process owing to ablative surface instability, with average cone volume increasing exponentially versus the shot number over the broad fluence range until its stabilization, and logarithmically versus laser fluence at the different shot numbers above the instability threshold fluence of about 30 mJ/cm2. The instability was assigned to a positive optical feedback, resulting from enhanced laser energy deposition and ablation within the inter-cone valleys, as previously suggested and demonstrated by our numerical modeling of near-surface electromagnetic intensity distribution.

Dynamics of vertical-cavity surface-emitting laser subject to optical injection and positive optoelectronic feedback

Based on the spin-flip model (SFM), we theoretically investigate the dynamics of a vertical-cavity surface-emitting laser (VCSEL) subject to optical injection and positive optoelectronic feedback. The results show that under the joint action of positive optoelectronic feedback and optical injection from a master VCSEL (M-VCSEL), two polarization modes of a slave VCSEL (S-VCSEL) will show many dynamic states such as period one, period two, multi-period and chaos, and the evolution routes of these states are different for two polarization modes. Mapping of dynamic region as a function of feedback strength f and injection strength is varied with frequency detuning between M-VCSEL and S-VCSEL (=m-s, where m ands are the free-running frequencies of M-VCSEL and S-VCSEL, respectively). Compared with the case for zero or negative frequency detuning, the region of chaotic state is expanded significantly under positive . For a fixed , the influences of f and on the chaotic bandwidth of S-VCSEL are discussed. Through selecting proper f and , chaotic bandwidth of S-VCSEL can be improved obviously.

Controlling Chaos in a Semiconductor Laser via Weak Optical PositiveFeedback and Modulating Amplitude

Numerical analysis of weak optical positive feedback (OPF)controlling chaos is studied in a semiconductor laser. The physical model ofcontrolling chaos produced via modulating the current of semiconductor laseris presented under the condition of OPF. We find the physical mechanism thatthe nonlinear gain coefficient and linewidth enhancement factor of the laserare affected by OPF so that the dynamical behaviour of the system can beefficiently controlled. Chaos is controlled into a single-periodic state, adual-periodic state, a tri-periodic state, a quadr-periodic state, apenta-periodic state, and the laser emitting powers are increased by OPF insimulations. Lastly, another chaos-control method with modulating theamplitude of the feedback light is presented and numerically simulated tocontrol chaotic laser into multi-periodic states.

Study on the method of controlling chaos in an Er-doped fiber dual-ring laser via external optical injection and shifting optical feedback light

Controlling chaos in an erbium-doped fiber dual-ring laser is studied by injecting an external light and shifting the phase of an optical feedback light. First, the parameters of the externally injected optical signal are adjusted to bring the chaotic laser into a single-period state and a multiperiod state, respectively. In addition, the single-mode locking in a single ring of the laser as well as the dual-mode locking in dual ring of the laser are found. Secondly, the method of optical feedback is used to stabilize chaos by controlling the parameters of the optical devices in an external optical path. We show that the optical negative feedback can stabilize the chaotic laser into a single-period state, while the optical positive feedback can stabilize the chaotic laser into another single-period state and a period-doubling state. Lastly, various dynamical states are produced in the laser by shifting the phase of the optical feedback light.

The performance of the GPSC/MSGC hybrid detector with neon-xenon gas mixtures

The performance for X-ray spectrometry of neon-xenon gas proportional scintillation counters using a CsI-coated microstrip plate in direct contact with the scintillation gas as a VUV photosensor is investigated for different neon-xenon mixtures. At best operation conditions, the detector gain can reach values about 50% higher than those achieved with pure xenon filling. The highest gains and the best energy resolutions are achieved for xenon contents around 40%. However, the achieved energy resolutions are similar to those achieved with pure xenon. As in pure xenon and argon-xenon mixture gas fillings, the detector performance is limited by optical positive feedback resulting from additional scintillation produced in the electron avalanche processes around the MSP anodes. The best energy resolutions are achieved for positive feedback gains in the range of 1.1 to 1.2. The performance achieved with neon-xenon mixtures is inferior to that achieved with argon-xenon mixtures.

The gas proportional scintillation counter/microstrip gas chamber hybrid detector

The gas proportional scintillation counter/microstrip gas chamber (GPSC/MSGC) hybrid detector for X-ray spectrometry is described. The detector uses a CsI-coated microstrip plate placed in direct contact with the gas-filling as the photosensor readout for the GPSC scintillation substituting for the photomultiplier tube (PMT). Usable photosensor maximum gain is limited by optical positive feedback due to the additional scintillation produced in the electron avalanche process at the MSP anodes, in the absence of quenching. A low-photoelectron collection efficiency is achieved in the gas atmosphere, resulting in a scintillation conversion efficiency that is about a factor of 5 lower than that achieved with PMT-based GPSCs. However, energy resolutions of 11% for 5.9keV X-rays are achieved with this detector.

Smart pixel optical sensor based on positive optical feedback.

A smart pixel optical sensor based on positive optical feedback is described and demonstrated. The scheme uses the reflectance of an external scene as part of the positive feedback loop and uses the nonlinear characteristics of a vertical-cavity surface-emitting laser to obtain bistability and hysteresis. As a result, the continuous reflectance variation of the scene is mapped to a digital output with increased noise immunity for each pixel of the array.

Dependence of the performance of CsI-covered microstrip plate VUV photosensors on geometry: experimental results

The behavior of a xenon-filled microstrip gas chamber instrumented with a microstrip plate with eight different microstrip geometries is reported. The best energy resolution achieved for 5.9-keV and for 22.1-keV X-rays was 13.6% and 7.0%, respectively. The same microstrip plate covered with a CsI film was used in place of the photomultiplier tube to detect the vacuum ultraviolet scintillation light produced in a driftless xenon-filled gas proportional scintillation counter. The relative amplitude, energy resolution,. optical positive feedback, and photoelectron extraction efficiency are discussed. The energy resolution obtained for 5.9-keV X-rays was 11.4%, which is better than that achieved with a standard proportional counter, about 13% for argon based proportional counters.

The performance of the GPSC/MSGC hybrid detector with argon-xenon gas mixtures

The performance for X-ray spectrometry of argon-xenon gas proportional scintillation counters (GPSCs) using a CsI-coated microstrip plate in direct contact with the scintillation gas as a vacuum ultraviolet photosensor is investigated for different argon-xenon mixtures. The GPSC/microstrip gas chamber hybrid detectors filled with argon-xenon mixtures present superior performance when compared to those with pure argon and pure xenon fillings. For these mixtures, the signal amplification due to the scintillation processes and the detector energy resolution may achieve values of 15-18 and 11-10%, respectively. The best energy resolutions can be achieved for mixtures with a broad range of xenon concentration, 20-70% Xe, and for lower reduced electric fields in the scintillation region as the xenon concentration is reduced. As in pure argon or pure xenon gas-filling, the detector performance is limited by optical positive feedback resulting from additional scintillation produced in the electron avalanche processes around the microstrip plate anodes. The best energy resolutions are achieved for positive feedback gains of about 1.1.

The gas proportional scintillation counter/microstrip gas chamber hybrid detector with argon filling

We present the results of a study of an argon gas proportional scintillation counter instrumented with a CsI-coated microstrip plate placed in the argon envelope. Although the measured light amplification gain and the photoelectron collection efficiency are 70% and 30–40% higher than those obtained in a similar xenon detector, the charge gain achieved in argon for the avalanches produced by the photoelectrons at the microstrip anodes is a factor of ten lower than in xenon. In both cases, these gains are limited by optical positive feedback. The energy resolution achieved for 5.9 keV X-rays was 14.8% compared to 12% in xenon.