Generation Of Coherent Light Research Articles

Deterministic Assembly of Colloidal Quantum Dots for Multifunctional Integrated Photonics.

Colloidal quantum dots (CQDs) are promising for photonic applications toward lasers, waveguides, and photodetectors. However, integration of high-quality photonic elements into multifunctional devices is still restricted by optical losses stemming from the accumulation of defects and disorder in the solution process. Herein, a platform with a directional Laplace pressure is created for eliminating undesired pinning of liquid fronts in the solution process and boosting ordered assembly of CQDs into designable micro-/nanostructures. The versatility and robustness of this method are demonstrated by deterministic patterning of CQDs with different components and photoluminescence spectra onto various substrates. On the basis of this platform, microring lasers with tunable emission modes, low-loss waveguides, and their coupled structures have been reached for direct on-chip generation and propagation of coherent light. A proof-of-concept demonstration of integrated circuits is also conducted by combining microcavity lasers with waveguides for encoding photonic outputs into information bits.

Hybrid‐Mode‐Family Kerr Optical Parametric Oscillation for Robust Coherent Light Generation on Chip

AbstractOptical parametric oscillation (OPO) using the third‐order nonlinearity () in integrated photonics platforms is an emerging approach for coherent light generation, and has shown great promise in achieving broad spectral coverage with small device footprints and at low pump powers. However, current nanophotonic OPO devices use pump, signal, and idler modes of the same transverse spatial mode family. As a result, such single‐mode‐family OPO (sOPO) is inherently sensitive in dispersion and can be challenging to scalably fabricate and implement. In this work, a novel scheme is proposed using different families of transverse spatial modes for pump, signal, and idler, which is termed as hybrid‐mode‐family OPO (hOPO). The hOPO shows unprecedented robustness in dispersion versus device geometry, pump frequency, and temperature. Moreover, the hOPO is capable of generating a few milliwatts of output signal power with a conversion efficiency of 8 and without competitive processes. This hOPO scheme is an important counterpoint to the existing sOPO approach, and is particularly promising as a robust method to generate coherent on‐chip visible and infrared light sources.

Long-range atomic correlations as a source of coherent light generation.

In this Letter, we give a new, to the best of our knowledge, perspective on the origin of light coherence in lasers. We demonstrate that a coherence appears below the lasing threshold and manifests itself as long-range correlations between polarizations of active medium atoms. These correlations contribute to the formation of a collective state of atomic polarizations and electromagnetic field modes, which interacts more effectively with the active medium and lases when pumping exceeds the lasing threshold. We demonstrate that inhibiting these atomic correlations leads to the destruction of the collective state and suppression of lasing. The obtained results open up new ways to control coherence.

Coherent light wave generation in an incoherently pumped fiber optical parametric oscillator

We present a numerical study on the coherent sideband generation from an incoherently pumped fiber optical parametric oscillator (FOPO). We revisit the fiber dispersion condition in a parametric process that fulfills the convection-induced phase-locking mechanism when pumping incoherently. Particularly, there exist analytical solutions for phase-matching frequencies in a convection-induced phase-locking process when using a parametric gain fiber with two zero dispersion wavelengths. With the optical feedback, we manage to circulate and amplify the convection sideband in a singly resonant FOPO. The autocorrelation shows that the coherence of the oscillating convection sideband can be strongly influenced by the cavity feedback fraction.

High-$Q$ Plasmonic Crystal Laser for Ultra-Sensitive Biomolecule Detection

Plasmonic lasers provide a paradigm-changing approach for the generation of coherent light at the nanoscale. In addition to the usual properties of coherent radiation, the emission of plasmonic lasers can feature high sensitivity to the surrounding environment, which makes this technology attractive for developing high-performance and highly-integrated sensing devices. Here, we investigate a plasmonic laser architecture based on a high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> plasmonic crystal consisting of a periodic arrangement of nanoholes on a thin gold film cladded with an organic-dye-doped glass layer as the gain material. We report an extensive full-wave numerical analysis of the device's lasing performance and its application as a biochemical sensor, showing that the proposed design features excellent figures of merit for surface sensing that in principle can be over an order of magnitude larger than those of previously reported high-performance plasmonic biosensor architectures.

Coherent near-infrared light generation based on self-seeded parametric four-wave mixing in Rb vapor

We demonstrate 1.37 µm coherent near-infrared light generation via self-seeded parametric four-wave mixing (FWM) process in Rb atomic vapor. Two lasers (780 nm and 776 nm) in the co-propagating configuration, drive the Rb atoms from the 5S1/2 ground state to the 5D5/2 excited state. The parametric FWM around the 5P3/2–5D5/2–6P3/2–6S1/2–5P3/2 transition loop is effectively established under phase matching conditions. The generated coherent light wavelength is confirmed using an optical spectrum analyzer, and the output power is investigated with the input laser frequency, power and atomic density. Consequently, a 1.37 µm coherent light with the power of 27 µW and the beam quality of = 1.22 and = 1.25 is obtained. An additional 795 nm laser is introduced to enhance the output power by 1.5 times through velocity-selective optical hyperfine repumping.

Highly efficient THz four-wave mixing in doped silicon

Third-order non-linearities are important because they allow control over light pulses in ubiquitous high-quality centro-symmetric materials like silicon and silica. Degenerate four-wave mixing provides a direct measure of the third-order non-linear sheet susceptibility χ(3)L (where L represents the material thickness) as well as technological possibilities such as optically gated detection and emission of photons. Using picosecond pulses from a free electron laser, we show that silicon doped with P or Bi has a value of χ(3)L in the THz domain that is higher than that reported for any other material in any wavelength band. The immediate implication of our results is the efficient generation of intense coherent THz light via upconversion (also a χ(3) process), and they open the door to exploitation of non-degenerate mixing and optical nonlinearities beyond the perturbative regime.

Nonlinear photonic crystals: from 2D to 3D

Nonlinear photonic crystals are microstructures with quadratic nonlinearity ( χ ( 2 ) ) that have been extensively used for the generation and control of coherent light at new frequencies. Thanks to the recent invention of 3D χ ( 2 ) -nonlinearity engineering techniques using femtosecond laser pulses, studies of intense light interaction with 3D nonlinear photonic crystals are now experimentally feasible. Here we review the latest research advances in nonlinear photonic crystals, focusing especially on the fabrication, characterization, and application of 3D structures. We also discuss the future development of 3D nonlinear photonic crystals with properties and functionalities that are either difficult or virtually impossible to achieve with lower dimensional structures.

Photonic Bound States in the Continuum: From Basics to Applications

AbstractThe introduction of bound states in the continuum (BICs) to photonics has revolutionized the way cavity design and light–matter interactions are thought about in general. BICs can have very high quality factors, even in open structures where access to radiation is permissible. Now, BICs found applications in a large class of areas, including nonlinear enhancement, coherent light generation, sensors, filters, integrated circuits, and many others. In this review, the different types of BICs in photonic systems, as well as their physics and formation mechanisms are briefly overviewed. The rest of the review focuses on the current and emerging applications of photonic BICs and their role in shaping the interaction of light and matter.

Nonlinear Volume Holography: Nonlinear Volume Holography in 3D Nonlinear Photonic Crystals (Laser Photonics Rev. 14(11)/2020)

In article number 2000224 by Yan Sheng and co-workers, nonlinear volume holography is realized by 3D micro-engineering the second-order nonlinear coefficient of a ferroelectric crystal with femtosecond laser pulses. A proof-of-concept nonlinear reconstruction of second harmonic vortex beam is demonstrated. The 3D nonlinear volume holography provides a universal approach for efficient generation of coherent light at new frequencies with predesigned phase and amplitude structures.

Radio-frequency sputtering fabrication of chalcogenide-based Er3+-doped vertical optical cavities for near-infrared operation

Chalcogenide-oxide Bragg reflectors and a 1-D vertical cavity for operation at 1.55 µm were designed and fabricated via radio-frequency sputtering. The Bragg reflectors were made out of repeating layers of Al2O3 and As2Se3, and the cavity was obtained via a Ga5Ge20Sb10S65:Er3+ defect layer. The layers’ properties were assessed via ellipsometry and SEM imaging. Transmission spectroscopy verifies the appearance of a well-defined stop-band centered around 1.5 µm with a very wide bandgap, and extremely low transmission, even with a relatively low layer count. The vertical optical cavity fabrication results in the appearance of a resonance within the band, at a wavelength corresponding to the 4I13/2→4I15/2 transition of erbium. The high transmittance at 808 and 980 nm allows for optical pumping, and thus light amplification and coherent light generation from the cavity. The operation of these devices was investigated, showing coherent light emission at 1.5 µm. The results are encouraging in assessing the viability of this design and these materials for operation in the near-infrared range, providing an important step towards the fabrication of chalcogenide-based optical amplifiers for the near-infrared.

Design of simultaneous multicolor coherent light generation in a single MgO:PPLN bulk crystal

We report on simultaneous sum-frequency mixing and doubling of C-band and ∼ 980 n m laser sources using a single segmented periodically poled lithium niobate (PPLN) crystal in a single-pass configuration. Our theoretical analysis on the spectral outputs show that a proper design of a five-segment single PPLN crystal has potential to generate violet, blue, green, and orange wavelengths by simultaneous sum-frequency and second-harmonic generation processes. Such a design has promising potential for a compact, tunable multicolored laser that can find various applications such as in biomedicine, visible light communications, laser-based color displays, and sensing.

Highly efficient XUV generation via high-order frequency mixing

The efficient generation of the coherent XUV light via frequency conversion of intense laser drivers is a problem of both fundamental and technological importance. Increasing the intensity of the generated high harmonics by raising the intensity of the driving field works only up to a point: at high intensities, rapid ionisation of the medium limits the conversion efficiency. Considering the combined effect of the phase-matching and of the blue shift of the driving field during its propagation in a rapidly ionising medium, we show that the latter can be the dominant limiting mechanism. We introduce a new spatial scale, the blue-shift length, which sets the upper bound for the quadratic intensity growth of the generated harmonics. Moreover, we show that this seemingly fundamental restriction can be overcome by using an additional generating weak mid-IR field. For specific combinations of frequencies of the generating fields, the corresponding high-order frequency-mixing process does not suffer from the blue shift of the drivers and phase mismatch, and thus its efficiency grows quadratically with propagation distance. Our results thus open a new route for highly efficient generation of coherent XUV light.

Widely tunable femtosecond soliton generation in a fiber-feedback optical parametric oscillator

Optical parametric oscillators (OPOs) are uniquely versatile—albeit complex—platforms for the generation of tunable coherent light in difficult-to-access spectral regions. A synchronously pumped χ ( 2 ) femtosecond OPO producing sub-100-fs pulses, by means of optical soliton formation in a single-mode fiber-feedback cavity, is presented for the first time. This approach removes the requirement for active stabilization and bulk dispersion compensation elements associated with traditional OPOs, while reducing the physical footprint by a factor of 3. Transform-limited pulses of 80–120 fs are generated for both normal and anomalous dispersion, while a new type of spectral sideband formation is observed and studied. Experimental results are supported by detailed simulations based on nonlinear pulse propagation theory, which serve to enrich the understanding of femtosecond pulse evolution in OPOs perturbed by strong Kerr nonlinearity. The OPO provides a unique platform for the study of intracavity soliton phenomena across a wide wavelength range.

Design and analysis of dispersion-compensating chalcogenide photonic crystal fiber with high birefringence

The photonic crystal fiber (PCF) with a bunch of air holes enclosing the silica core field has momentous and compelling attributes when compared with the ordinary single-mode fibers. In this work, both the birefringence and dispersion properties of a polarization-maintaining chalcogenide (ChG) photonic crystal fiber are numerically investigated by means of the finite element method. Through simulation, it is found that the birefringence of the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF can reach as high as $$0.03$$ when compared with the conventional fiber that has merely $$5\times {10}^{-4}$$ for wavelengths in the 2–10 $$\upmu \mathrm{m}$$ range. The PCF is designed with zero-dispersion wavelengths for x- and y-polarized modes in the 2–10 $$\upmu \mathrm{m}$$ range. It is also observed that over the entire MIR wavelength range, the GVD remains positive and has a maximum value of 30,000 ps2/nm-km. Hence, the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF plays the dual role of acting as a very good polarization-maintaining fiber due to its very high birefringence and an excellent dispersion-compensating fiber due to its large positive GVD. This $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF serves as a very good candidate for ultra-broadband high bit-rate transmission. Supercontinuum generation is another important application of PCF. Supercontinuum generation is a generation of coherent and broadband light. SC generation in PCFs has several applications in optical coherence tomography (OCT), optical frequency metrology (OFM), pulse compression, and design of ultrafast femtosecond laser pulses.

Milliwatt-threshold visible-telecom optical parametric oscillation using silicon nanophotonics.

The on-chip creation of coherent light at visible wavelengths is crucial to field-level deployment of spectroscopy and metrology systems. Although on-chip lasers have been implemented in specific cases, a general solution that is not restricted by limitations of specific gain media has not been reported. Here, we propose creating visible light from an infrared pump by widely-separated optical parametric oscillation (OPO) using silicon nanophotonics. The OPO creates signal and idler light in the 700 nm and 1300 nm bands, respectively, with a 900 nm pump. It operates at a threshold power of (0.9 ± 0.1) mW, over 50× smaller than other widely-separated microcavity OPO works, which have only been reported in the infrared. This low threshold enables direct pumping without need of an intermediate optical amplifier. We further show how the device design can be modified to generate 780 nm and 1500 nm light with a similar power efficiency. Our nanophotonic OPO shows distinct advantages in power efficiency, operation stability, and device scalability, and is a major advance towards flexible on-chip generation of coherent visible light.

Nonlinear wavefront shaping with optically\xa0induced three-dimensional nonlinear photonic crystals

Generation of coherent light with desirable amplitude and phase profiles throughout the optical spectrum is a key issue in optical technologies. Nonlinear wavefront shaping offers an exceptional way to achieve this goal by converting an incident light beam into the beam (or beams) of different frequency with spatially modulated amplitude and phase. The realization of such frequency conversion and shaping processes critically depends on the matching of phase velocities of interacting waves, for which nonlinear photonic crystals (NPCs) with spatially modulated quadratic nonlinearity have shown great potential. Here, we present the first experimental demonstration of nonlinear wavefront shaping with three-dimensional (3D) NPCs formed by ultrafast-light-induced ferroelectric domain inversion approach. Compared with those previously used low-dimensional structures, 3D NPCs provide all spatial degrees of freedom for the compensation of phase mismatch in nonlinear interactions and thereby constitute an unprecedented system for the generation and control of coherent light at new frequencies.

Strong light–matter coupling and exciton-polariton condensation in lattices of plasmonic nanoparticles [Invited

Arrays of metallic nanoparticles support collective plasmonic resonances known as surface lattice resonances (SLRs). The strong and delocalized electromagnetic fields associated with SLRs provide an excellent platform for experiments within the realm of light–matter interaction. The planar architecture of these arrays also provides a feasible system for coupling to different materials. One of the areas where SLRs have demonstrated their potential is strong light–matter coupling, with possible applications in nonlinear optics, coherent light generation, photochemistry, and optoelectronics. In this perspective, we describe how SLRs are formed in arrays of plasmonic nanoparticles, introduce different materials used for strong coupling with SLRs, discuss some experiments that demonstrate the nonlinear emission of strongly coupled organic molecules with SLRs, and give our vision on future research directions of strongly coupled SLRs with organic molecules.

Generation of coherent mid-IR light by parametric four-wave mixing in alkali vapor.

The parametric four-wave mixing (4WM) process responsible for the generation of coherent blue light in alkali vapors is a self-seeded process which starts by population inversion and amplified spontaneous emission (ASE). Lately, attention has been turned toward frequency up- and down-conversion in alkali vapors, using relatively low pump powers with CW diode lasers. In this Letter, we investigate the interplay between ASE and 4WM in rubidium (Rb) vapors by studying the mid-infrared (mid-IR) radiation emitted in the forward direction at 5.23μm. We show that the ASE can be suppressed by 4WM in the CW regime. Thus, we demonstrate the generation of coherent mid-IR light at 5.23μm in hot Rb vapors via parametric 4WM.

Artificial Second-Order Nonlinear Optics in a Centrosymmetric Optical Material BiVO4: Breaking the Prerequisite for Nonlinear Optical Materials.

Second-order nonlinear optics (NLO) is the foundation of frequency conversion for the generation of coherent light at frequencies where lasers have no emissions or operate poorly. The prerequisite for NLO materials is noncentrosymmetric symmetry that can generate an effectively non-counterbalanced spontaneous electronic polarization. Here, we propose that this material restriction can be broadened by controlling the electron distribution with a local internal electrostatic field (IEF), and we demonstrate artificially created and manipulated second harmonic generation (SHG) in a centrosymmetric optical material, a superimposed Co2+- and Mo6+-doped BiVO4 thin film with 2/m point group symmetry, where a homojunction producing tunable effective polarization is formed. The SHG was characterized and tuned by IEF. This work breaks the structural symmetry constraint on NLO materials. Besides, the phase-matching-like condition was realized for the further improvement of the efficient frequency conversion. Because polarization is also a prerequisite for many other functions besides SHG, we believe that this work should provide some inspiration for the further development of optoelectronic, photonic, and electronic materials.