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A perfect lens with unlimited resolution has always posed a challenge to both theoretical and experimental physicists. Recent developments in optical meta-materials promise an attractive approach towards perfect lenses using negative refraction to overcome the diffraction limit, improving resolution. However, those artificially engineered meta-materials usually company by high losses from metals and are extremely difficult to fabricate. An alternative proposal using negative refraction by four-wave mixing has attracted much interests recently, though most of existing experiments still require metals and none of them has been implemented for an optical lens. Here we experimentally demonstrate a metal-free flat lens for the first time using negative refraction by degenerate four-wave mixing with a thin glass slide. We realize optical lensing effect utilizing a nonlinear refraction law, which may have potential applications in microscopy.Flat lenses using negative refraction create a new avenue for novel optical imaging applications, attracting intense interests from optics, microwave and even acoustic communities [1][2][3][4][5][6][7]. Unlike traditional optical lenses, a flat lens which can bend incoming waves at negative angles opposed to those within normal refraction regime [1][2][3] can form an image much more sharply thanks to its ability to negatively refract waves at all-angle including the evanescent ones, making itself a "perfect lens" to overcome the diffraction limit [2,6]. Such lenses have been realized in many formats ranging from optics, microwave to acoustic, including photonic crystals [7], metal thin film [6], meta-material [5, 9-12], etc. However, most of them suffer from high losses in association with metallic materials, which are the key elements bringing in negative permittivity and artificial permeability. Secondly, fabrications of such nano/micro structures raise additional obstacle for their practical applications. In nonlinear optics, alternative approaches to achieve negative refraction have been proposed including phase conjugation, time reversal and four wave mixing (4WM) [3,13,14]. In contrast to those artificially engineered methods i.e. meta-materials and photonic crystals, which create spatial dispersion for negative refraction using linear composition of different materials, nonlinear optics explores nonlinear wave mixings with angle matching schemes to fulfill the requirements for negative refraction. Principally, only a thin flat nonlinear slab is required. Up to now, such negative refractions using wave mixing have been realized in some thin films with high nonlinearity such as metal and graphite thin film [15][16][17]. However, in these experiments due to their low nonlinear conversion efficiencies or materials' optical transparency, none of them has been implemented for imaging purpose.In this letter, we experimentally demonstrate a metal-free flat lens using negative refraction by degenerate four-wave mixing with a simple thin glass slide. Within glass slides containing thi...

A simple optical lens plays an important role for exploring the microscopic world in science and technology by refracting light with tailored spatially varying refractive indices. Recent advancements in nanotechnology enable novel lenses, such as, superlens and hyperlens, with sub-wavelength resolution capabilities by specially designed materials’ refractive indices with meta-materials and transformation optics. However, these artificially nano- or micro-engineered lenses usually suffer high losses from metals and are highly demanding in fabrication. Here, we experimentally demonstrate, for the first time, a nonlinear dielectric magnifying lens using negative refraction by degenerate four-wave mixing in a plano-concave glass slide, obtaining magnified images. Moreover, we transform a nonlinear flat lens into a magnifying lens by introducing transformation optics into the nonlinear regime, achieving an all-optical controllable lensing effect through nonlinear wave mixing, which may have many potential applications in microscopy and imaging science.

With the rapid progress in fiber technologies, femtosecond fiber lasers, which are compact, cost-effective and stable, have been developed and are commercially available. Studies of optical parametric oscillators (OPOs) pumped by this type of laser are demanding. Here we report a femtosecond optical parametric oscillator (OPO) at 79.6 MHz repetition rate based on MgO-doped periodically poled LiNbO 3 (MgO:PPLN), synchronously pumped by the integrated second harmonic radiation of a femtosecond fiber laser at 532 nm. The signal delivered by the single resonant OPO is continuously tunable from 757 to 797 nm by tuning the crystal temperature in a poling period of µ 7.7 m. The output signal shows good beam quality in TEM 00 mode profile with pulse duration of 206 fs at 771 nm. Maximum output signal power of 71 mW is obtained for a pump power of 763 mW and a low pumping threshold of 210 mW is measured. Moreover, grating tuning and cavity length tuning of the signal wavelength are also investigated.

Whispering-gallery-mode (WGM) microcavities strongly enhance nonlinear optical processes like optical frequency comb, Raman scattering and optomechanics, which nowadays enable cutting-edge applications in microwave synthesis, optical sensing spectroscopy, and integrated photonics. Yet, tunability of their resonances, mostly via coarse and complicated mechanism through temperature, electrical or mechanical means, still poses a major challenge for precision applications as above. Here we introduce a new passive scheme to finely tune resonances of WGMs atMHz precision with an external probe. Such probe remotely transfers heat through a gap from an optical microcavity, effectively tuning its resonances by thermal-optic nonlinearity. Moreover, we explore this unique technique in microcavity nonlinear optics, demonstrating the generation of a tunable optical frequency comb and backward stimulated Brillouin scattering with variable beating frequencies.This new technique addresses the core problem of WGM microcavity's fine-tuning, paving the way for important applications like spectroscopy and frequency synthesis.Whispering-gallery-mode (WGM) micro-cavities have been intensively investigated in a wide range of areas for both fundamental physics and practical applications. The ultra-high quality (Q) factors and ultra-small mode volumes make WGM micro-cavities ideal platforms for ultra-sensitive optical sensing, strongly enhanced nonlinear optics, cavity QED, optomechanics, and micro-scale optical frequency comb [1][2][3][4][5]. However, one major obstacle halting the practical implementations in these applications is the lack of tunability for fixed microstructures unlike their bigger-scale opponents, i.e. Fabry-Pérot cavities. For example, WGMs have to be finely tuned to closely match with atomic lines in cavity QED [6]; dual-comb spectroscopy requires precision scanning of optical comb lines [7]; tunable microwave generation from SBS enabled sources also poses a great demand for tunability [8]. Previously, various approaches have been demonstrated to tune WGM resonances mainly through thermal, mechanical, electrical and optical

Negative refraction has attracted much interest for its promising capability in imaging applications. Such an effect can be implemented by negative index metamaterials, however, which are usually accompanied by high loss and demanding fabrication processes. Recently, alternative nonlinear approaches like phase conjugation and four wave mixing have shown advantages of low-loss and easy-to-implement, but associated problems like narrow accepting angles can still halt their practical applications. Here we demonstrate theoretically and experimentally a new scheme to realize negative refraction by nonlinear difference frequency generation with wide tunability, where a thin BBO slice serves as a negative refraction layer bending the input signal beam to the idler beam at a negative angle. Furthermore, we realize optical focusing effect using such nonlinear negative refraction, which may enable many potential applications in imaging science. © 2015 Optical Society of America OCIS codes : (190.4223) Nonlinear wave mixing, (180.4315) Nonlinear microscopy, (120.5710) Refraction, (160.4330 Negative refraction (NR) bending light in a reversed manner as opposed to the normal refraction has continuously attracted growing interests from many fields including optics, acoustics and microwaves [1][2][3][4][5][6][7][8], for its promising applications in imaging, cloaking, sensing [9][10][11][12][13][14]. Such a phenomenon has been realized in many formats including photonic crystals [8], metal thin films [10], meta-materials [3-7, 11], while high losses especially in optical regime from metallic materials: the key elements enabling NR, and the demanding technologies to fabricate these nano/micro structures, strongly limit NR's practical applications. Alternatively, an effective NR has been proposed in nonlinear optics by using nonlinear optical processes such as phase conjugation, time reversal and four wave mixing (4WM) in order to achieve effective NR between incident waves and nonlinear generated ones. For example, NR has been demonstrated with signal beams and 4WM beams in a 4WM scheme with thin 3rd order nonlinear slab such as metal, graphite thin film and glass [15][16][17][18][19]. Furthermore, one revolutionary imaging technique with potentials to achieve superresolution microscopy has been realized by exploring the phase matching conditions during 4WMs in Ref. [20][21]. However, in these nonlinear NRs, some minor problems such as narrow phase matching angle may still hold off their applications in imaging.In this letter, we propose and experimentally demonstrate a new way to achieve NR based on nonlinear difference frequency generation (DFG). With a thin slice of BBO crystal containing second-order nonlinearity, an infrared signal beam interacts with the pump beam nonlinearly through DFG process to give rise to the visible idler beam which is negatively refracted with respect to the signal to fulfill the phase matching. These negatively refracted idler beams can focus and form the image of the object illuminated by t...

Coherent excitation of phonons by optical waves, one of the most important channels for light-matter interactions, provides a promising route for optical manipulation of microscopic acoustic phonons for quantum opto-mechanic and phononic devices. Prior research, such as stimulated Brillouin scattering (SBS) in fibers, mainly emphasized phonon amplitude modulation; however, coherent phase control of these phonons has not yet been well explored.Here we experimentally demonstrate a new mechanism to coherently control acoustic phonon phases by a seeded SBS scheme in an optical fiber. Interference between acoustic phonons enables either nearly total transmission or enhanced reflection of optical waves, effectively controlled by phase modulation. This new technique addresses the crucial problem of phase-controlled phonon generation, paving the way for important applications in quantum opto-mechanic and phononic devices.

Compared with LCD and OLED, micro/mini LED display has been proved to be more suitable for tiled display. For tiled display, tiled seams visibility is one of the critical concerns. To achieve seamless tiled display, several aspects have to be carefully handled, such as panel border design, process realization, and encapsulation method and so on. This article discusses these related technical solutions for seamless tiled display.