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Traditional distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers typically have commonly employed buried gratings as frequency-selective optical feedback mechanisms. However, the fabrication of such gratings often requires regrowth processes, which introduce significant technical challenges, particularly for material systems such as GaAs and GaSb. While metal gratings have been implemented in GaSb-based lasers, they incur additional absorption losses, thereby constraining the device's efficiency and achievable output power. Herein, we introduce a laterally coupled dielectric Bragg grating structure, which enables highly controllable, deterministic, and stable coupling between the grating and the optical mode. Our device demonstrates a continuous-wave output power of 47.02 mW at room temperature, exhibiting stable single-mode operation from 300 to 1000 mA and a maximum side mode suppression ratio of 46.7 dB. These results underscore the innovative lateral coupled dielectric grating as a feasible and technologically superior approach for fabricating DFB and DBR lasers, which hold universal applicability across different material platforms and wavelength bands. [ABSTRACT FROM AUTHOR]

Feedback-insensitive Quantum Dot (QD) comb lasers hold significant promise for integrated dense wavelength division multiplexing photonic systems due to their ability to generate multiple wavelengths and operate without bulky isolators, facilitating the development of high-density and large-scale photonic integrated circuits. In this study, we investigated the optical feedback (OFB) influence of the InAs/GaAs QD comb laser from various perspectives. Our findings reveal that the comb laser exhibits a stable locking region with consistent optical spectra across a range of OFB strengths (−45 to −10 dB). Furthermore, under a high OFB strength of −10 dB, there is a notable 40 dB suppression of relative intensity noise in the low-frequency range (below 1 GHz). Transmission experiments demonstrate clear eye openings at 25 Gbps using a bit pattern of 231-1 pseudorandom binary sequence. Remarkably, the bit error rates decrease by five orders of magnitude under −10 dB OFB. These results indicate the ultra-robustness of 100 GHz grid QD comb laser, which exhibits great transmission enhancement under a strong OFB of −10 dB. [ABSTRACT FROM AUTHOR]

The measurement and control of mechanical resonators are critical for cavity magnomechanics, which has emerged as an important frontier for hybrid quantum systems based on magnonics. Traditional microwave-based measurements require handling high-frequency signals and cannot achieve field distribution detection. Here, we demonstrate a method for optically measuring and manipulating a ferromagnetic mechanical resonator. This technique allows for direct observation of the response and field distribution of mechanical oscillations during magnomechanically induced transparency/absorption processes, confirming that the mechanical mode S 1 , 2 is coupled with the magnon. The optical measurement not only serves to validate the magnomechanical coupling theory but also reduces the necessity for high-frequency measurements. Furthermore, we utilize the instantaneously measured results to implement feedback control of the self-oscillating mechanical resonator to overcome the dynamical back-action limit, achieving a threefold enhancement of phonon lasing amplitude. This feedback control lays the foundation for the study of quantum cavity magnomechanics, such as the feedback cooling of a magnomechanical resonator. [ABSTRACT FROM AUTHOR]

A method for generating bandwidth-enhanced chaotic laser with time-delay signature suppression by a microring resonator is proposed and demonstrated experimentally. Through multiple beam interference effect and nonlinear effect within a microring resonator, chaotic laser generated by conventional optical feedback is optimized. A chaotic laser with the standard bandwidth of 26.5 GHz, the spectrum flatness of ±1.5 dB, and the time-delay signature value of 0.09 is obtained. The influence of the injection power and the frequency detuning on the optimized characteristics of chaotic laser are analyzed. The results show that chaotic laser with the standard bandwidth above 20 GHz and the spectrum flatness below ±3.5 dB can be achieved simultaneously in wide operating parameter regions. Furthermore, the effect of the radius of a microring resonator on the characteristics of the chaotic laser is investigated. The results show that a microring resonator can realize the performance optimization of chaotic laser. Due to the decreased loss, the time-delay signature suppression is better as the radius of a microring resonator increases. This scheme is simple and integration-compatible, which contributes to the development of an integrated, time-delay signature suppressed and broadband chaotic laser sources. [ABSTRACT FROM AUTHOR]

The authors report incoherent random laser action in systems where the optical feedback is provided by multiple scattering generated by different classes of silver nanoparticles in the colloidal state, having plasmon resonances at different frequencies. They found improved performance of triangular silver nanoplates as compared to nanospheres, with a threshold as low as 1 mJ/cm2 and a 5 times lower optimal silver concentration, due to plasmonic enhancement effects and tuning of the plasmon resonance. The nanoparticles were also tested for stability against illumination by the pump laser, as the onset of pulsed laser melting is comparable to random laser threshold in terms of pump fluence, severely limiting the range of operation of nanoparticles with main plasmon resonance close to the pump wavelength. The optimal approach to choose plasmonic nanoparticles for random lasing must, therefore, take the stability aspect into serious consideration as well as the plasmonic enhancement of random lasing. [ABSTRACT FROM AUTHOR]

As a new type of semiconductor laser, photonic crystal surface-emitting lasers (PCSELs) feature large-area single-mode surface emission with high power and high beam quality. The unique features of single-mode lasing over a large area active region are implemented by the in-plane optical feedback from two-dimensional (2D) photonic crystal cavities. In larger PCSEL cavities, the lasing gain threshold becomes similar for the fundamental and high-order modes, which degrades single-mode operation. Here, we investigate the impact of carrier injection on PCSEL modes by controlling the injection area and the gain mode interaction. Optical and electrical simulations are carried out to calculate the gain mode overlapping factor for different p electrode designs. We fabricated 250 × 250 µm2 photonic crystal cavities with different p electrode sizes for injection area control. The PCSEL device characterization results show that devices with an electrode size to cavity side length ratio of 0.6 have the maximum slope efficiency and a lower lasing threshold with a single lobe beam profile. Such selective carrier injection can also provide gain-guided resonance in the PCSEL cavities and enhance optical gain in the fundamental mode while suppressing gain in the high-order modes. [ABSTRACT FROM AUTHOR]

An external-cavity laser with resonant optical feedback is a common and mature method to achieve narrow linewidth lasers. Since the proposal of optical feedback in 1964, a series of studies on resonant optical feedback have been reported. Although longer feedback length leads to narrower linewidth, it also introduces coupling of environmental noise and causes instability in the laser cavity, which is detrimental to high-speed tuning of the laser wavelength. With such a challenge, current research on resonant optical feedback primarily focuses on the static results of laser linewidth compression. In order to obtain narrow linewidth high-speed tuned external-cavity lasers, further research on the laser dynamics is required to obtain dynamic tuning of narrow linewidth external-cavity lasers. In this work, we construct an external-cavity laser based on resonant optical feedback, and utilize a coherent detection method to measure the dynamic process of laser linewidth compression and wavelength tuning. Based on resonant optical feedback from the external cavity, the linewidth of the main-cavity laser can be compressed from near 100 kHz to the 100 Hz level, with the frequency noise compressed from the order of 104 to the 102 Hz2/Hz level. Since the wavelength switching process includes frequency shift process, linewidth compression process, and frequency stabilization process, etc., we first conduct a research on laser linewidth compression dynamics. In the results of linewidth compression dynamics, we discover that using a shorter fiber ring results in shorter linewidth compression time, which is advantageous for laser dynamic tuning. We subsequently carry out the laser wavelength switching process with a main-cavity switching time in milliseconds. In the wavelength switching process, while undergoing the frequency shift process of fast tuning transient laser frequency, the laser first undergoes the linewidth broadening process, then enters the main-cavity laser frequency stabilization process and undergoes the linewidth compression process at the same time. The experimental results show that the 100 m feedback fiber ring will not significantly increase the external-cavity laser wavelength switching time under the condition that linewidth compression is faster than main-cavity laser switching, while a longer fiber ring will introduce a strong noise. Our work experimentally demonstrates that shorter feedback ring lengths lead to faster compression, which provides valuable insights for the development of high-speed and high-precision tunable narrow linewidth external-cavity lasers. [ABSTRACT FROM AUTHOR]

Nonlinear dynamics at mid-infrared wavelength is of interest for various applications but has been mainly limited to quantum cascade lasers so far. In this article, we show that interband cascade lasers can generate complex optical chaos with bandwidth in the GHz range and this outperforms the performances of quantum cascade laser chaos. The chaos nature of our signal is confirmed by a thorough time-series analysis. Modeling of the semiconductor laser under short-cavity external optical feedback allows confirming the high bias chaos operation that we observe experimentally. These results pave the way for applications at mid-infrared wavelength, such as private free-space communication. [ABSTRACT FROM AUTHOR]

The development of a 1.65 µm cavity ringdown methane spectrometer for methane isotope analysis is reported. In order to reduce the laser linewidth, simple optical feedback with an 11 m external fiber cavity using a retroreflector was implemented and it improved the sensitivity. The detection limit at the ppt level for both 12CH4 and 13CH4 concentrations at 100 Torr gas pressure was evaluated from the Allan–Werle plot calculated from the dataset obtained at the fixed laser frequency. In contrast, the detection limit estimated from the baseline noise on the absorption spectrum was a few ppb for both methane isotopologues due to the periodic background oscillations that remained even after baseline correction. The system demonstrated the direct measurement of ambient methane in atmospheric room air, and the estimated 13CH4 ratio as well as the methane concentration were in good agreement with the reference values of ambient air. [ABSTRACT FROM AUTHOR]

Time-delayed optical feedback is known to trigger a wide variety of complex dynamical behavior in semiconductor lasers. Adding a second optical feedback loop is naturally expected to further increase the complexity of the system and its dynamics, but due to interference between the two feedback arms, it was also quickly identified as a way to improve the laser stability. While these two aspects have already been investigated, the influence of the feedback phases, i.e., sub-wavelength changes in the mirror positions, on the laser behavior still remains to be thoroughly studied, despite indications that this parameter could have a significant impact. Here, we analyze the effect of the feedback phase on the laser stability in a dual-feedback configuration. We show an increased sensitivity of the laser system to feedback phase changes when two-feedback loops are present and clarify the interplay between the frequency shift induced by the feedback and the interferometric effect between the two feedback arms. [ABSTRACT FROM AUTHOR]

Mid-infrared laser absorption spectroscopy utilizing a high-finesse optical cavity enables high precision trace analysis of gas molecules. In particular, optical detection of radiocarbon (14C) based on cavity ringdown spectroscopy using a quantum cascade laser (QCL) is gaining attention as an alternative to accelerator mass spectrometry. This paper reports a compact-packaged narrow-linewidth QCL system utilizing resonant optical feedback from an external V-shaped cavity. Based on frequency noise analysis, the derived laser linewidth is 44 kHz for 100 μs integration time with the capability to perform seamless frequency scanning around 10 GHz. We installed this laser system within a table-top cavity ringdown spectrometer for 14CO2. A single-shot detection limit of 1.2 × 10−9 cm−1 Hz−1/2 leading to a detectable abundance evaluated from a noise analysis of 0.2 in fraction modern 14C for a 10-s averaging time was achieved. This capability of rapid analysis for 14CO2 is suitable for various applications requiring trace 14C analysis. [ABSTRACT FROM AUTHOR]

Common-signal-induced synchronization of semiconductor lasers with optical feedback inspired a promising physical-layer key distribution with information-theoretic security and potential in high rate. A significant challenge is the requirement to shorten the synchronization recovery time for increasing the key rate without sacrificing the operation parameter space for security. Here, open-loop synchronization of wavelength-tunable multi-section distributed Bragg reflector lasers is proposed as a solution for physical-layer key distribution. Experiments show that the synchronization is sensitive to two operation parameters, i.e., currents of grating section and phase section. Furthermore, fast wavelength-shift keying synchronization can be achieved by direct modulation on one of the two currents. The synchronization recovery time is shortened by one order of magnitude compared to close-loop synchronization. An experimental implementation is demonstrated with a final key rate of 5.98 Mbit/s over 160 km optical fiber distance. It is thus believed that fast-tunable multi-section semiconductor lasers open a new avenue for a high-rate physical-layer key distribution using laser synchronization. [ABSTRACT FROM AUTHOR]

This document is a summary of a special topical collection in the journal APL Photonics on the advancements and applications of optical frequency combs. Optical frequency combs are a technology that combines ultrafast laser technology and single frequency laser stabilization techniques to generate stable optical and microwave signals for high-resolution time and frequency applications. The collection includes articles on various topics such as laser ranging, terahertz photonics, molecular referencing, optical communications, and space-based time/frequency dissemination. The articles highlight the impact and innovation that frequency comb technology brings to each field. The collection demonstrates the transformative potential of optical frequency combs and the ongoing research to further expand their applications. [Extracted from the article]

Semiconductor lasers with optical feedback are stochastic nonlinear systems that can display complex dynamics and abrupt changes when their operation conditions change. Even very small changes can lead to large variations in the spatial and spectral properties of the laser emission. This makes a semiconductor laser with feedback an ideal system for conducting controlled experiments to test data analysis tools to detect and characterize transitions. Here, we identify feedback-induced transitions by analyzing speckle patterns that are generated after the laser light propagates in an optical fiber. Speckle patterns result from the interference of multiple modes, and their statistical properties are understood, but a direct mathematical model does not exist. Here we show the versatility of the correlation length and the permutation entropy as measures for characterizing speckle patterns. Combining entropy and correlation analysis with speckle contrast analysis, we uncover changes that occur when the laser current increases from below to well above the threshold, which unveils the effects of optical feedback on the coherence of the laser emission. [ABSTRACT FROM AUTHOR]

We study theoretically the mechanisms of square wave formation of a vertically emitting micro-cavity operated in the Gires–Tournois regime that contains a Kerr medium and that is subjected to strong time-delayed optical feedback and detuned optical injection. We show that in the limit of large delay, square wave solutions of the time-delayed system can be treated as relative homoclinic solutions of an equation with an advanced argument. Based on this, we use concepts of classical homoclinic bifurcation theory to study different types of square wave solutions. In particular, we unveil the mechanisms behind the collapsed snaking scenario of square waves and explain the formation of complex-shaped multistable square wave solutions through a Bykov T-point. Finally, we relate the position of the T-point to the position of the Maxwell point in the original time-delayed system. [ABSTRACT FROM AUTHOR]

This study investigates the interaction between frequency combs and optical feedback effects in Quantum Cascade Lasers (QCLs). The theoretical analysis reveals new phenomena arising from the interplay between comb generation and feedback. By considering the bias current corresponding to free-running single mode emission, the introduction of optical feedback can trigger the generation of frequency combs, including both fundamental and harmonic combs. This presents opportunities to extend the comb region and generate harmonic frequency combs with different orders through optimization of external cavity parameters, such as losses and length. Furthermore, this study demonstrates that optical feedback can selectively tune the harmonic order of a pre-existing free-running comb by adjusting the external cavity length, particularly for feedback ratios around 1%, which are readily achievable in experimental setups. Under strong feedback conditions (Acket parameter C > 4.6), mixed states emerge, displaying the features of both laser and external cavity dynamics. While this study is predominantly centered on terahertz QCLs, we have also confirmed that the described phenomena occur when utilizing mid-infrared QCL parameters. This work establishes a connection between comb technology and the utilization of optical feedback, providing new avenues for exploration and advancement in the field. In fact, the novel reported phenomena open a pathway toward new methodologies across various domains, such as the design of tunable comb sources, hyperspectral imaging, multi-mode coherent sensing, and multi-channel communication. [ABSTRACT FROM AUTHOR]

We model dynamics of a quantum dot based micropillar laser array subject to the time-delayed optical feedback. The global coupling provided by the feedback generates a rich set of various instabilities including chaotic regimes with strong time-delay signature in the autocorrelation function. We demonstrate that the dispersion of the array coupling phases leads to effective suppression of the time-delay signature due to the dispersion of the system's internal timescales. We find that the transition to the complete suppression of the time-delay signature appears via a chimera state where highly correlated and non-correlated laser outputs coexist. The degree of correlation in the chimera state depends on the coupling phase dispersion. [ABSTRACT FROM AUTHOR]

In this work, we propose to employ strong optical feedback to narrow the spectral linewidth of quantum cascade lasers without using any phase control. Rate equation analysis demonstrates that optical feedback beyond a certain level always reduces the laser linewidth for any feedback phase. It is also found that the linewidth becomes less sensitive to the feedback phase for higher feedback strength. Simulations show that optical feedback with a feedback ratio of −10 dB can suppress the laser linewidth by about two orders of magnitude. This is in contrast to near-infrared laser diodes, which can be easily destabilized by strong feedback. [ABSTRACT FROM AUTHOR]

This article discusses the phenomenon of different colors displayed by a circular polarizing filter (CPL) when placed on different surfaces. The CPL is composed of a linear polarizer (LP) and a quarter-wave plate (QWP), and the principles of polarization can be used to explain the phenomenon. The article explains the process of light propagation and polarization states when the CPL is placed on a steel breadboard and a piece of paper. The article also discusses the wavelength dependence of the QWP and how it affects the colors observed. The phenomenon is further explored by analyzing the CPL on different reflective surfaces such as aluminum mirror and copper. The article concludes by highlighting the educational value of this phenomenon for teaching about polarization. [Extracted from the article]

This paper presents a self-coherent optical feedback system that achieves resonance between the external cavity mode and the relaxation oscillation frequency of distributed feedback (DFB) laser and the repetition frequency of Fabry–Perot (FP) laser, all in an effort to achieve optical feedback self-locking. Results using this system show that for FP lasers, feedback is able to reduce the 3 dB radio frequency linewidth from 2 MHz to 600 kHz. In the case of DFB lasers, an electric frequency comb with an external cavity repetition rate of 17.25 MHz is achieved. This research presents a significant step toward the improvement of the performance of quantum dot lasers in optical communication systems. [ABSTRACT FROM AUTHOR]

In various optical feedback cavity-enhanced spectroscopies (OF-CESs) based on absorption or scattering, conventional phase-locking methods are constrained by their ability to handle only minor phase deviations. This limitation is due to the source of an error signal for phase adjustment. This paper introduces a robust approach for phase-locking, which combines the shape and intensity of cavity transmission profiles to identify phase deviations. The advantage of this combination is that it can always generate a suitable error signal, irrespective of the phase's position in the entire 2π period. The outstanding performance of the corresponding servo loop under severe airflow shocks demonstrates that our approach significantly increases the feasibility of applying various OF-CES setups for real-time, in situ gas detection in harsh environments. [ABSTRACT FROM AUTHOR]

In this paper, we study the dynamics of a vertically emitting micro-cavity operated in the Gires–Tournois regime that contains a semiconductor quantum-well and that is subjected to strong time-delayed optical feedback and detuned optical injection. Using a first principle time-delay model for the optical response, we disclose sets of multistable dark and bright temporal localized states coexisting on their respective bistable homogeneous backgrounds. In the case of anti-resonant optical feedback, we identify square-waves with a period of twice the round-trip in the external cavity. Finally, we perform a multiple time scale analysis in the good cavity limit. The resulting normal form is in good agreement with the original time-delayed model. [ABSTRACT FROM AUTHOR]

Photonic reservoir computing (PRC) is a special hardware recurrent neural network, which is featured with fast training speed and low training cost. This work shows a wavelength-multiplexing PRC architecture, taking advantage of the numerous longitudinal modes in a Fabry–Perot (FP) semiconductor laser. These modes construct connected physical neurons in parallel, while an optical feedback loop provides interactive virtual neurons in series. We experimentally demonstrate a four-channel wavelength-multiplexing PRC architecture with a total of 80 neurons. The clock rate of the multiplexing PRC reaches as high as 1.0 GHz, which is four times higher than that of the single-channel case. In addition, it is proved that the multiplexing PRC exhibits a superior performance on the task of signal equalization in an optical fiber communication link. This improved performance is owing to the rich neuron interconnections both in parallel and in series. In particular, this scheme is highly scalable owing to the rich mode resources in FP lasers. [ABSTRACT FROM AUTHOR]

The recent development of perovskite-based lasers showcased the outstanding optical properties of the material such as high absorption coefficient and high quantum yield. The lasers were demonstrated in the form of nanowires and nanoplates, which are difficult to be integrated on a chip in the form of high-density arrays due to the difficulties in positioning them on the chip. The solution to this problem should be to use the well-known lithography process in the fabrication process of the lasers. In this work, we demonstrate several perovskite-based plasmonic lasers that were fabricated by using the lithographic in-mold patterning method that relies on the electron beam lithography process. The lasers utilized CsPbBr3 perovskite nanocrystals as the gain material and plasmonic distributed Bragg reflector grating structure as the optical feedback provider to achieve a low lasing threshold of 42.5 μJ/cm2 with a linewidth of 0.6 nm (FWHM) at room temperature. The use of the lithographic process in the fabrication of the lasers makes it possible to fabricate and integrate them on a chip in a relatively high-density manner, so that they can be used extensively in quantum optics and on-chip integrated photonics applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel near field transducer (NFT) design concept for heat assisted recording. In this design, metal bars separated by thin dielectric are used to form a resonance plasmonic grating with distributed feedback (DFB). The motivation for such structure design is the use of dielectric separation for enhancing the material stability at elevated temperature so that best materials can be used without compromising much needed plasmonic properties. COMSOL Multiphysics software is used to simulate the plasmonic excitation and propagate to provide a detailed performance analysis on novel NFT with a nanocomposite structure to create distributed optical feedback (DFB) for maintaining the plasmonic resonance. The NFT is composed of an array of Au rectangular gratings separated by a constant gap, with each grating component embedded in the dielectric medium. It is shown that the grating based NFT could have the same NFT efficiency compared with a solid piece of Au NFT of the same geometric dimensions. [ABSTRACT FROM AUTHOR]

We numerically investigate the influence of an integrated filtered optical feedback on the behavior of a semiconductor ring laser subject to external optical injection. The optical injection is spectrally directed at one of the non-lasing longitudinal modes of the laser. This so-called side-mode injection can cause wavelength switching, directional switching, and changes in the dynamical regime of the semiconductor ring laser. Such changes are often unwanted as they can affect the stability and the performance of the semiconductor ring laser. We investigate to what extent these undesired effects can be avoided by stabilizing the laser using on-chip filtered feedback. A two-directional mode model is used to investigate the dynamical behavior of the semiconductor ring laser under the simultaneous effect of the external optical injection and the integrated feedback. The results show that on-chip filtered optical feedback can be used to reduce the sensitivity of the semiconductor ring laser to external optical injection. [ABSTRACT FROM AUTHOR]

This work describes an experimental method for measuring the speed of light in air. It uses optical feedback from a visible picosecond diode laser operated below the threshold and a voltage-controlled oscillator to determine the time required for a pulse to travel a known distance. The experimental setup is compact, fitting into a space of 1 × 0.5 m2, and at the same time, can determine the speed of light with an uncertainty of 0.03%. The method does not require fast detectors or oscilloscopes. [ABSTRACT FROM AUTHOR]

Line intensities for carbon dioxide are measured with a novel spectroscopic approach, assisted by an optical frequency comb synthesizer for frequency calibration purposes. The main feature of the spectrometer consists in the exploitation of optical feedback from a V-shaped high-finesse optical resonator to effectively narrow a distributed feedback diode laser at the wavelength of 2 μm. Lasergas interaction takes place inside an isothermal cell, which is placed on the transmission from the cavity. High quality, self-calibrated, absorption spectra are observed in pure CO2 samples at different gas pressures, in coincidence with three lines of the R-branch of the ν1 + 2ν2 + ν3 band. Line intensities are determined using a global fitting approach in which a manifold of spectra are simultaneously analyzed across the range of pressures between 5 and 100 Torr, sharing a restricted number of unknown parameters. Various sources of uncertainty have been identified and carefully quantified, thus leading to an overall uncertainty ranging between 0.17% and 0.23%. The measured values are in a very good agreement with recent ab initio predictions. [ABSTRACT FROM AUTHOR]

Artificial intelligent skins hold the potential to revolutionize artificial intelligence, health monitoring, soft robotics, biomedicine, flexible, and wearable electronics. Present artificial skins can be characterized into electronic skins (e-skins) that convert external stimuli into electrical signals and photonic skins (p-skins) that convert deformations into intuitive optical feedback. Merging both electronic and photonic functions in a single skin is highly desirable, but challenging and remains yet unexplored. We report herein a brand-new type of artificial intelligent skin, an optoelectronic skin (o-skin), which combines the advantages of both e-skins and p-skins in a single skin device based on one-dimensional photonic crystal-based hydrogels. Taking advantage of its anisotropic characteristics, the resulting o-skin can easily distinguish vector stimuli such as stress type and movement direction to meet the needs of multi-dimensional perception. Furthermore, the o-skin also demonstrates advanced functions such as full-color displays and intelligent response to the environment in the form of self-adaptive camouflage. This work represents a substantial advance in using the molecular engineering strategy to achieve artificial intelligent skins with multiple anisotropic responses that can be integrated on the skin of a soft body to endow superior functions, just like the natural organisms that inspire us. [ABSTRACT FROM AUTHOR]

Interband cascade lasers are power-efficient mid-infrared laser sources which usually exhibit a spectral linewidth of hundreds of kHz. However, narrower linewidth lasers are more desirable for high-resolution molecular spectroscopy applications. This work narrows the spectral linewidth of an interband cascade laser from about 530 kHz down to about 30 kHz by applying optical feedback from an external mirror. In contrast to common laser diodes, the linewidth reduction of interband cascade lasers does not require any feedback phase control, which significantly simplifies the experimental configuration, and hence, is highly favorable for practical applications. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the effect of optical feedback on the dynamics of a passively mode-locked ring laser operating in the regime of temporal localized structures. This laser system is modeled by a set of delay differential equations, which include delay terms associated with the laser cavity and the feedback loop. Using a combination of direct numerical simulations and path-continuation techniques, we show that the feedback loop creates echoes of the main pulse whose position and size strongly depend on the feedback parameters. We demonstrate that in the long-cavity regime, these echoes can successively replace the main pulses, which defines their lifetime. This pulse instability mechanism originates from a global bifurcation of the saddle-node infinite-period type. In addition, we show that, under the influence of noise, the stable pulses exhibit forms of a behavior characteristic of excitable systems. Furthermore, for the harmonic solutions consisting of multiple equispaced pulses per round-trip, we show that if the location of the pulses coincides with the echo of another, the range of stability of these solutions is increased. Finally, it is shown that around these resonances, branches of different solutions are connected by period-doubling bifurcations. [ABSTRACT FROM AUTHOR]

An experiment for measuring the speed of light by measuring the distance between regularly generated optical pulses is described. The experiment utilizes optical feedback from a visible picosecond diode laser to accurately determine the distance between two successive laser pulses. The required setup is compact, and it does not implement either a fast detector or an oscilloscope. This experiment is suitable for an undergraduate physics instructional laboratory course or as an independent student project. [ABSTRACT FROM AUTHOR]

This research reports a theoretical investigation on the role of filtered optical feedback (FOF) in the quantum dot light emitting diode (QD-LED). The underlying dynamics is affected by a sidle node, which returns to an elliptical shape when the wetting layer (WL) is neglected. Both filter width and time delay change the appearance of different dynamics (chaotic and mixed mode oscillations, MMOs). The results agree with the experimental observations. Here, the fixed point analysis for QDs was done for the first time. For QD-LED with FOF, the system transits from the coherence collapse case in conventional optical feedback to a coherent case with a filtered mode in FOF. It was found that the WL washes out the modes which is an unexpected result. This may attributed to the longer capture time of WL compared with that between QD states. Thus, WL reduces the chaotic behavior. [ABSTRACT FROM AUTHOR]

Nonlinear spatiotemporal systems are the basis for countless physical phenomena in such diverse fields as ecology, optics, electronics, and neuroscience. The canonical approach to unify models originating from different fields is the normal form description, which determines the generic dynamical aspects and different bifurcation scenarios. Realizing different types of dynamical systems via one experimental platform that enables continuous transition between normal forms through tuning accessible system parameters is, therefore, highly relevant. Here, we show that a transmissive, optically addressed spatial light modulator under coherent optical illumination and optical feedback coupling allows tuning between pitchfork, transcritical, and saddle-node bifurcations of steady states. We demonstrate this by analytically deriving the system's dynamical equations in correspondence to the normal forms of the associated bifurcations and confirm these results via extensive numerical simulations. Our model describes a nematic liquid crystal device using nano-dimensional dichalcogenide (a-As 2 S 3) glassy thin films as photo sensors and alignment layers, and we use device parameters obtained from experimental characterization. Optical coupling, for example, using diffraction, holography, or integrated unitary maps allows implementing a variety of system topologies of technological relevance for neural networks and potentially Ising or XY-Hamiltonian models with ultralow energy consumption. [ABSTRACT FROM AUTHOR]

In spite of its importance for the evaluation of the Earth radiative budget, thus for climate change, very few measurements of the water vapor continuum are available in the near infrared atmospheric windows especially at temperature conditions relevant for our atmosphere. In addition, as a result of the difficulty to measure weak broadband absorption signals, the few available measurements show large disagreements. We report here accurate measurements of the water vapor self-continuum absorption in the 2.1 μm window by Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) for two spectral points located at the low energy edge and at the center of the 2.1 μm transparency window, at 4302 and 4723 cm-1, respectively. Self-continuum cross sections, CS, were retrieved with a few % relative uncertainty, from the quadratic dependence of the spectrum base line level measured as a function of water vapor pressure, between 0 and 16 Torr. At 296 K, the CS value at 4302 cm-1 is found 40% higher than predicted by the MT_CKD V2.5 model, while at 4723 cm-1, our value is 5 times larger than the MT_CKD value. On the other hand, these OF-CEAS CS values are significantly smaller than recent measurements by Fourier transform spectroscopy at room temperature. The temperature dependence of the self-continuum cross sections was also investigated for temperatures between 296 K and 323 K (23-50 °C). The derived temperature variation is found to be similar to that derived from previous Fourier transform spectrometer (FTS) measurements performed at higher temperatures, between 350 K and 472 K. The whole set of measurements spanning the 296-472 K temperature range follows a simple exponential law in 1/T with a slope close to the dissociation energy of the water dimer, D0 ≈ 1100 cm-1. [ABSTRACT FROM AUTHOR]

Doppler-free saturated-absorption Lamb dips were measured on weak rovibrational lines of 12C16O2 between 6189 and 6215 cm-1 at sub-Pa pressures using optical feedback frequency stabilized cavity ring-down spectroscopy. By referencing the laser source to an optical frequency comb, transition frequencies for ten lines of the 30013 ← 00001 band P-branch and two lines of the 31113 ← 01101 hot band R-branch were determined with an accuracy of a few parts in 1011. Involving rotational quantum numbers up to 42, the data were used for improving the upper level spectroscopic constants. These results provide a highly accurate reference frequency grid over the spectral interval from 1599 to 1616 nm. [ABSTRACT FROM AUTHOR]

The phenomenon of self-pulsation (SP) in terahertz (THz) quantum cascade lasers (QCLs) due to optical feedback was reported recently. In this Letter, we propose a THz imaging modality using the SP phenomenon in a THz QCL. We explore the theoretical oscillation properties of the SP scheme and demonstrate its suitability to perform imaging experimentally. The SP imaging scheme operates in self-detection mode, eliminating the need for an external detector. Moreover, the scheme requires only a fixed current, meaning that one can avoid many of the pitfalls associated with high temperature operation of THz QCLs, including frequency chirp and mode hops caused by sweeping the laser current. This also means that one is free to locate the operating point at the maximum power, to produce the desired beam profile or for highest spectral purity, depending on the application. The SP imaging modality proposed in this work can be translated directly to high operating temperature THz QCLs. [ABSTRACT FROM AUTHOR]

We demonstrate the use of three kinds of flexible digital servos for the stabilization of the optical fiber link, the interferometer temperature, and the polarization of the transmitted light at the remote site, respectively. The main fiber noise cancellation digital servo provides a large phase detection range (∼210π radians), automatic relock function, and low cycle-slip rate over a 62 km field-deployed fiber link achieved by utilizing a feedback optical actuator of an acousto-optic modulator fed by a voltage-controlled oscillator. The temperature control and polarization control digital servos enable that the temperature of the interferometer can be stabilized at a stability of 0.01 K and the data uptime is enhanced from 85.5% to 99.9% by implementing the polarization controller. The results demonstrate that the performance of the three digital servos is sufficient for high-precision optical frequency transfer applications and indicates comparable performance to existing analog optical frequency control systems. The full digital controlled optical frequency transfer method demonstrated here provides guidance for the development of a low-cost, low-complexity, and high-reliability optical frequency transfer system. [ABSTRACT FROM AUTHOR]

We consider the Yamada model for an excitable or self-pulsating laser with saturable absorber and study the effects of delayed optical self-feedback in the excitable case. More specifically, we are concerned with the generation of stable periodic pulse trains via repeated self-excitation after passage through the delayed feedback loop and their bifurcations. We show that onset and termination of such pulse trains correspond to the simultaneous bifurcation of countably many fold periodic orbits with infinite period in this delay differential equation. We employ numerical continuation and the concept of reappearance of periodic solutions to show that these bifurcations coincide with codimension-two points along families of connecting orbits and fold periodic orbits in a related advanced differential equation. These points include heteroclinic connections between steady states and homoclinic bifurcations with non-hyperbolic equilibria. Tracking these codimension-two points in parameter space reveals the critical parameter values for the existence of periodic pulse trains. We use the recently developed theory of temporal dissipative solitons to infer necessary conditions for the stability of such pulse trains. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the possibility to process two tasks in parallel with a photonic reservoir computer based on a vertical-cavity surface-emitting laser (VCSEL) as a physical node with time-delay optical feedback. The two tasks are injected optically by exploiting the polarization dynamics of the VCSEL. We test our reservoir with the very demanding task of nonlinear optical channel equalization as an illustration of the performance of the system and show the recover of two signals simultaneously with an error rate of 0.3% (3%) for a 25 km-fiber distortion (50 km-fiber distortion) at a processing speed of 51.3 Mb/s. [ABSTRACT FROM AUTHOR]

Speckle is a wave interference phenomenon that has been studied in various fields, including optics, hydrodynamics, and acoustics. Speckle patterns contain spectral information of the interfering waves and of the scattering medium that generates the pattern. Here, we study experimentally the speckle patterns generated by the light emitted by two types of semiconductor lasers: conventional laser diodes, where we induce low-coherence emission by optical feedback or by pump current modulation, and coupled nanolasers. In both cases, we analyze the intensity statistics of the respective speckle patterns to inspect the degree of coherence of the light. We show that the speckle analysis provides a non-spectral way to assess the coherence of semiconductor laser light. [ABSTRACT FROM AUTHOR]

The time-delayed Adler equation is the simplest model for an injected semiconductor laser with coherent injection and optical feedback. It is, however, able to reproduce the existence of topological localized structures (LSs) and their rich interactions. In this paper, we perform the first extended bifurcation analysis of this model and we explore the mechanisms by which LSs emerge. We also derive the effective equations governing the motion of distant LSs and we stress how the lack of parity in time-delayed systems leads to exotic, non-reciprocal, interactions between topological localized states. [ABSTRACT FROM AUTHOR]

We experimentally realize the finite-rate isothermal process of a Brownian particle in a breathing harmonic potential. For the compression process, finite-rate equilibration can be achieved by increasing and then decreasing the stiffness of the potential to the final stiffness according to the shortcuts-to-isothermal (ScI) protocol. On the other hand, the realization of the ScI expansion is experimentally impossible with optical tweezers due to the requirement of a negative stiffness. Here, we propose a simple and elegant method to resolve this problem and demonstrate the ScI expansion by using the optical feedback trap capable of creating an arbitrary spatiotemporal potential even with a negative stiffness. In addition, we check the thermodynamic energetics such as work, heat, and internal energy, which indeed obey stochastic thermodynamics. Our method provides the possibility of a Brownian heat engine with maximum efficiency but non-vanishing power. [ABSTRACT FROM AUTHOR]

This work investigates the performance of 1.3-μm quantum dot lasers epitaxially grown on silicon under optical feedback sensitivity with different temperature and doping profiles. Experiments show that these quantum dot lasers exhibit a very high degree of resistance to both incoherent and coherent optical feedbacks. 10 Gbps penalty-free transmissions are also unveiled under external modulation and at different temperatures. The paper draws attention on quantum dot lasers with p-doping that exhibit a better thermal resistance, a lower linewidth enhancement factor, a higher critical feedback level, and a better spectral stability with less intensity noise. Together, these properties make epitaxial quantum dot lasers with p-doping more promising for isolator-free and Peltier-free applications, which are meaningful for future high-speed photonic integrated circuits. [ABSTRACT FROM AUTHOR]

The properties of self-mixing interference in terahertz distributed feedback quantum cascade lasers (THz DFB-QCLs) were studied by coupled wave theory and the multimode rate equation method. Under weak self-mixing optical feedback, the response behaviors of the DFB-QCLs are similar to those of Fabry–Pérot lasers and can be described by the Lang–Kobayashi equations with a modified feedback parameter. The amplitudes of the self-mixing power and frequency signals decrease with the increasing DFB coupling factor. Under strong feedback, new side modes arise, which broaden the laser linewidth. The number of side modes decreases with the increasing DFB coupling factor. The simulation also demonstrates that the maximum power mode of a THz DFB-QCL under strong self-mixing feedback is the minimum linewidth mode. These results support the development of self-mixing interferometers based on DFB-QCLs. [ABSTRACT FROM AUTHOR]

The motion control of a levitated nanoparticle plays a central role in optical levitation for fundamental studies and practical applications. Here, we presented digital parametric feedback cooling based on square wave modulation by switching trapping laser intensity between two levels. The effects of the modulation depth and modulation signal phase on the cooling result were investigated in detail. Using such a digital parametric feedback method, the center-of-mass temperature of all three motional degrees of freedom can be cooled to dozens of millikelvin. The flexibility and agility of the digital feedback control pave the way for a variety of motion control modes. [ABSTRACT FROM AUTHOR]

This work investigates the effect of the polarization anisotropy on the linewidth enhancement factor and the reflection sensitivity of InAs/InP quantum dash semiconductor lasers. The results show that the small linewidth enhancement factor and high stability against external optical feedback are obtained for nanostructures oriented perpendicular to the cavity axis as opposed to those oriented parallel to the cavity axis. Effective simulations on the critical feedback level of these two lasers are also in agreement with experimental results. Such anisotropy is attributed to the polarization dependence of the transition matrix element in these quantum nanostructures. [ABSTRACT FROM AUTHOR]