Recently, some authors have proposed to add an optical Kerr effect (OKE) while focusing the Gaussian beam (GB) enlightening an optical trap. These authors conclude that the introduction of a nonlinear lensing (NL) is benefit to the optical trapping capacity. The proposed modelling was based on the Gaussian approximation (GA) which assimilates the Kerr lensing effect to a pure lensing effect free from any aberration. In this paper, we evaluate the longitudinal and radial figures of merit of the optical trap based on NL using a diffraction integral taking into account the aberration associated with the OKE. The conclusion is that the GA modelling underestimates (overestimates) the improving of the longitudinal (radial) trapping ability of the optical trap. In summary, what is gained in the longitudinal efficiency of the nonlinear trap is lost in the radial force which decreases, thereby reducing the possibility to keep trapped the particle.

We have considered the negative influence of spherical aberrations (SA) on longitudinal and transversal forces occurring in optical tweezers based on a focused Gaussian beam (GB). We have shown that, for a given power and incident beam width, the replacement of the usual GB by a “rectified” LGp0 (one peak surrounded by p rings having the same sign) improves the longitudinal force by a factor ranging from (p + 1) to (p + 2). The “rectification” of a LGp0 beam is assumed to be done by a binary diffractive optical element which transforms the negative rings into a positive one.

Many laser applications utilise a focused laser beam having a single-lobed intensity profile in the focal plane, ideally with the highest possible on-axis intensity. Conventionally, this is achieved with the lowest-order Laguerre-Gaussian mode (LG(00)), the Gaussian beam, in a tight focusing configuration. However, tight focusing often involves significant spherical aberration due to the high numerical aperture of the systems involved, thus degrading the focal quality. Here, we demonstrate that a high-order radial LG(p0) mode can be tailored to meet and in some instances exceed the performance of the Gaussian. We achieve this by phase rectification of the mode using a simple binary diffractive optic. By way of example, we show that the focusing of a rectified LG(50) beam is almost insensitive to a spherical aberration coefficient of over three wavelengths, in contrast with the usual Gaussian beam for which the intensity of the focal spot is reduced by a factor of two. This work paves the way towards enhanced focal spots using structured light.

Binary diffractive optics have been extensively studied to date as tools for arbitrary laser beam shaping and experimentally implemented with etched transparent optics and spatial light modulators. Here we demonstrate that a simple one-step binary optic is able to enhance the intensity of a focused beam, displaying some counterintuitive focusing anomalies. We explain these effects by considering the optical aberrations in binary diffractive optics and outline how this may be exploited for further improvements in refractive/diffractive combinations for super-resolution microscopy.

We have demonstrated that it is possible to generate a Flat-Top intensity profile in the focal plane of a converging lens when it is illuminated by a high-order radial Laguerre–Gaussian LG10 beam (one peak surrounded by one ring) truncated by a circular aperture.

We experimentally show spontaneous breaking of mirror-symmetry in two evanescently coupled photonic crystal nanocavity-lasers. A transition from a delocalized mode, to two spatially localized states, is observed in the form of a pitchfork bifurcation. Coexistence of these states is demonstrated through short pulse excitation.

Let us consider the family of symmetrical Laguerre-Gaus modes of zero azimuthal order which will be denoted as LG(p0). The later is made up of central lobe surrounded by p concentric rings of light. The fundamental mode LG(00) is a Gaussian beam of width W. The focusing of a LG(p0), beam of power P by a converging lens of focal length f produces a focal spot keeping the LG(p0)-shape and having a central intensity I-0 = 2PW(2) /(lambda f)(2) whatever the value of the radial order p. Many applications of lasers (laser marking, laser ablation,...) seek nowadays for a focal laser spot with the highest as possible intensity. For a given power P, increasing intensity I-0 can be achieved by increasing W and reducing the focal length f. However, this way of doing is in fact limited because the ratio W/f cannot increase indefinitely at the risk of introducing a huge tmncation upon the edge of the lens. In fact, it is possible to produce a single-lobed focal spot with a central intensity of about p times the intensity I-0. This result has been obtained by reshaping (rectification) a LGp, beam thanks to a proper Binary Diffractive Optical Element (BDOE). In addition, forcing a laser cavity to oscillate upon a LG(p0), can improve the power extract due to a mode volume increasing with the mode order p. This could allow envisaging an economy of scale in term of laser pumping power for producing a given intensity I-0. In addition, we have demonstrated that a rectified LG(p0) beam better stand the lens spherical aberration than the usual Gaussian beam.

The interplay between photon tunneling and light-matter interactions in multi-well optical potentials –or photonic molecules (PMs)– is at the heart of many recent developments in quantum and nonlinear optics (see e.g. [1]). A key phenomenon taking place in double well potentials is the spontaneous breaking of the inversion symmetry: a bifurcation from delocalized to localized states in the wells, which are mirror images of each other. Although few theoretical studies have addressed mirror-symmetry breaking in micro and nanophotonic systems [2], no experimental evidence has been reported to date.

We have demonstrated that a simple diaphragm can play the role of a very cheap reconfigurable diffractive optical element allowing the generation of interesting laser beam patterns. For instance, a truncated Laguerre–Gauss LG10 beam (one peak surrounded by one ring) can be transformed in the focal plane of a lens into an optical bottle beam (OBB) which consists to a dark (or minimal intensity) region surrounded by higher intensity light in the three principal directions. Depending on the beam truncation, one can also observe a flat-top intensity profile.

Diffraction of a high-order radial Laguerre-Gauss LG(p0) beam truncated by a circular aperture is considered. In contrast with the truncated usual Gaussian LG(00) beam, which is not Gaussian in the near-field and quasi-Gaussian in the far-field, the truncated LG(p0) beam (for p = 1 to 4) behaves very differently. Depending on the diaphragm size, the radial intensity distribution of a truncated LG(p0) beam in the far-field (focal plane of a lens) can take the shape of (i) a flat-top, (ii) a hollow beam and (iii) one central peak and a ring having the same intensity. In addition, clipping-even weakly-of an LG(p0) beam splits the usual focal point into two.

The observation of symmetry breaking in a coupled nanolaser system could yield new types of switchable devices. Multi-cavity photonic systems, also known as photonic molecules, exhibit multi-well potentials that may prove useful for advanced quantum and nonlinear optics1,2,3,4. A key phenomenon arising in double-well potentials is the spontaneous breaking of inversion symmetry, with a transition to two localized states in the wells, which are mirror images of each other. Although a few theoretical studies have addressed mirror-symmetry breaking in micro- and nanophotonic systems5,6,7, no experimental evidence has been reported to date. Here, we demonstrate spontaneous mirror-symmetry breaking through a pitchfork bifurcation in a photonic molecule composed of two coupled photonic-crystal nanolasers. The coexistence of localized states is shown by switching them with short pulses. This offers exciting prospects for the realization of ultra-compact, integrated, scalable optical flip-flops. Analysis suggests that such symmetry breaking should be possible with a small number of intracavity photons and is thus suitable for quantum correlation devices.

We demonstrate a large tuning of the coupling strength in Photonic Crystal molecules without changing the inter-cavity distance.The key element for the design is the "photonic barrier engineering", where the "potential barrier" is formed by the air-holes in between the two cavities.This consists in changing the hole radius of the central row in the barrier.As a result we show, both numerically and experimentally, that the wavelength splitting in two evanescently-coupled Photonic Crystal L3 cavities (three holes missing in the ΓK direction of the underlying triangular lattice) can be continuously controlled up to 5× the initial value upon ∼ 30% of hole-size modification in the barrier.Moreover, the sign of the splitting can be reversed in such a way that the fundamental mode can be either the symmetric or the anti-symmetric one without altering neither the cavity geometry nor the inter-cavity distance.Coupling sign inversion is explained in the framework of a Fabry-Perot model with underlying propagating Bloch modes in coupled W1 waveguides.

We propose a scheme to achieve controllable self-pulsing operation in a semiconductor photonic-crystal nanolaser. The scheme is based on coupling two asymmetric nanocavities and pumping only one of them. As a result, either periodic or chaotic subnanosecond $Q$-switched pulses can emerge. A coupled-mode approach is used to model the system and study the bifurcation diagram. An experimental realization is proposed on the basis of two evanescently coupled photonic-crystal nanocavities.

We experimentally show that the mode splitting in two-evanescently coupled Photonic Crystal L3 cavities (three holes missing in the ΓK direction of the underlying triangular lattice) can be controlled through barrier engineering. The “potential barrier”s is formed by the air-holes in between the two cavities. By changing the hole radius of the central row in the barrier up to ~30%, the frequency splitting can be strongly reduced. Moreover, the sign of the splitting can be reversed in such a way that the fundamental mode can be either the symmetric or the anti-symmetric one without altering neither the cavity geometry nor the inter-cavity distance.

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We present recent experimental and theoretical results on the nonlinear dynamics of semiconductor micro and nanolasers. Self-pulsing dynamics is encountered both in a compact and monolithic microlaser with intracavity integrated saturable absorber and in photonic crystal nanolasers. We propose a scheme for achieving self-pulsing in nanolasers based on asymmetrically coupled cavities and study theoretically its implementation in a photonic-crystal based system. On the other hand, short pulses with duration as short as 35 ps with multi-GHz repetition rates are found. Short pulses are experimentally evidenced in a micropillar laser with saturable absorber together with excitable dynamics. We evidence the passage between gain-switching and excitability and show optical response with a refractory period less than 250 ps.

We implement the band-folding approach in coupled photonic crystal L3 (three missing holes) nanocavities and demonstrate a dramatic beaming improvement compatible with high-Q operation. Directional laser effect is achieved. In addition, resonant free-space coupling to the symmetric and anti-symmetric hybrid modes of the photonic molecule is shown. We measure the coupling to each mode as a function of the spatial position of the laser spot, which can be used as a technique to probe the symmetry of coupled cavity modes.

We develop a key element in order to implement Photonic Crystal Molecules for a demonstration of spontaneous symmetry breaking: the coupling control. In particular, we numerically show that the mode splitting in two-evanescently coupled Photonic Crystal L3 cavities (three holes missing in the ΓK direction of the underlying triangular lattice) can be controlled through barrier engineering. The potential barrier is formed by the air-holes in between the two cavities. By changing the hole radius of the central row in the barrier up to 30%, the frequency splitting can be strongly reduced. Moreover, the sign of the splitting can be reversed in such a way that the fundamental mode can be either the symmetric or the anti-symmetric one without altering neither the cavity geometry nor the inter-cavity distance.

We present recent experimental and theoretical results on the nonlinear dynamics of semiconductor micro and nano-lasers. First, fast excitable, neuron-like, dynamics is experimentally evidenced in a micropillar laser with intracavity saturable absorber with fast response times in the 200ps range. We study also the refractory time in this system and show the existence of a relative refractory period, analogue to what is found in neurons. Second, we propose a scheme for achieving self-pulsing in nanolasers based on asymmetrically coupled cavities and study theoretically its implementation in a photonic-crystal based system. Short pulses with duration as short as 35ps with multi-GHz repetition rates are found, as well as a region giving rise to a chaotic dynamics. We also predict a parameter region where the self-pulsing bifurcation can lead to ultra-fast excitable dynamics in such a nanolaser.

Nanolasers are promising physical systems as they offer extremely small footprints and may be considered as key ingredients for future high density and high speed optoelectronic circuits. Physically, the small mode and material volumes in play have important consequences on the modulation speed of these lasers. In particular, ultrafast laser operation has been demonstrated in photonic-crystal cavities [1-4], with picosecond response times. However, these short optical pulses have only been triggered by ultrashort pump pulses. Other theoretical studies have demonstrated fast self-oscillatory dynamics in a variety of nonlinear nanocavity systems [5-7], but self-pulsing operation has not been demonstrated so far in nanocavities.