Integration Of Optical Components Research Articles

Avoiding lateral mode leakage in thin film lithium niobate waveguides for the generation of spectrally pure photons at telecom wavelengths

Photonic integrated optical components, notably straight waveguides, serve as pivotal elements for on-chip generation and manipulation of quantum states of light. In this work, we focus on optimizing waveguides based on lithium niobate on insulator (LNOI) to generate photon pairs at telecom wavelengths using spontaneous parametric down-conversion (SPDC). Specifically, we investigate lateral leakage for all possible SPDC processes involving type 0, type I, and type II phase matching conditions in an X-cut lithium niobate waveguide and provide a recipe to avoid leakage loss for the interacting photons. Furthermore, focusing on type II phase matching, we engineer the waveguide in the single-mode regime such that it also satisfies group index matching for generating spectrally pure single photons with high purity (99.33%). We also address fabrication imperfections of the optimized design and find that the spectral purity of the generated photons is robust to fabrication errors. This work offers guidance for the suitable selection of morphological parameters to obtain lossless, single-mode LNOI waveguides for building linear optical circuits and photon pair generation at telecom wavelengths using desired phase-matching conditions.

Microscale Diffractive Lenses Integrated into Microfluidic Devices for Size-Selective Optical Trapping of Particles.

Integration of optical components into microfluidic devices can enhance particle manipulations, separations, and analyses. We present a method to fabricate microscale diffractive lenses composed of aperiodically spaced concentric rings milled into a thin metal film to precisely position optical tweezers within microfluidic channels. Integrated thin-film microlenses perform the laser focusing required to generate sufficient optical forces to trap particles without significant off-device beam manipulation. Moreover, the ability to trap particles with unfocused laser light allows multiple optical traps to be powered simultaneously by a single input laser. We have optically trapped polystyrene particles with diameters of 0.5, 1, 2, and 4 μm over microlenses fabricated in chromium and gold films. Optical forces generated by these microlenses captured particles traveling at fluid velocities up to 64 μm/s. Quantitative trapping experiments with particles in microfluidic flow demonstrate size-based differential trapping of neutrally buoyant particles where larger particles required a stronger trapping force. The optical forces on these particles are identical to traditional optical traps, but the addition of a continuous viscous drag force from the microfluidic flow introduces tunable size selectivity across a range of laser powers and fluid velocities.

132 W 132 μJ Femtosecond Pulses from a Coherently Combined System of Two Rod-Type Photonic Crystal Fibers

A coherent beam combination has the potential to revolutionize high-peak-power laser systems. However, achieving a high-average-power ultrashort pulse is difficult due to the accumulation of a nonlinear phase and gain narrowing. In this article, we demonstrate a coherent beam combination system that does not require pulse shaping or a spectral modulator. By optimizing the gain of each amplifier and using highly integrated optical components, we reduce the limitations caused by the accumulation of a nonlinear phase and gain narrowing. In our study, we used a polarization beam splitter to combine the pulses from two rod-type photonic crystal fibers (PCFs) in a Mach–Zehnder-type interferometer. A piezo-mounted mirror controlled with a Hänsch–Couillaud polarization detecting system was used to stabilize active phase locking. The system produces 165 W with a 91.6% combining efficiency compared to 90 W per amplifier. Compressed pulses with an energy of 132 µJ and Gaussian fitting pulse duration of 330 fs were achieved.

Photon-Trapping Microstructure for InGaAs/Si Avalanche Photodiodes Operating at 1.31 μm.

With the rapid development of photo-communication technologies, avalanche photodiode (APD) will play an increasingly important role in the future due to its high quantum efficiency, low power consumption, and small size. The monolithic integration of optical components and signal processing electronics on silicon substrate chips is crucial to driving cost reduction and performance improvement; thus, the technical research on InGaAs/Si APD is of great significance. This work is the first to demonstrate the use of a photon-trapping (PT) structure to improve the performance of the InGaAs/Si APD based on an SOI substrate, which exhibits very high absorption efficiency at 1310 nm wavelength while the thickness of the absorption layer is kept at 800 nm. Based on the optical and electrical simulations, an optimized InGaAs/Si PT-APD is proposed, which exhibits a better performance and a higher responsivity compared to the original InGaAs/Si APD.

Effects of the hardness and roughness on the plastic deformation properties of electroplated gold bumps during thermocompression bonding

Within the scope of this work, an optimization approach of existing investigations on electroplated hard gold contacts is to be developed, which have an initial Vickers hardness of 103 HV. These investigations envisage the height-controlled bonding of structures in the multichip integration of optical components. The investigations relate to the influence of material hardness and roughness on the plastic deformation behaviour during bond formation by thermocompression bonding (TCB). Furthermore, pre-treatments such as mechanical surface planarization and chemical surface activation using atmospheric pressure plasma are employed prior to the bonding process to enable the reduction of the bonding parameters pressure and temperature and consequently contribute to control the plastic deformation during thermocompression and reduce the typical plastic deformation range of 30 % to a deformation range below 5 %. The previous investigations were performed on gold contacts, which have been thermally annealed prior to the bonding process and resulted in a plastic deformation range up to 30 %. With the new approach, i.e. throughout the material hardening and altering the surface condition, a plastic deformation range below 3 % was successfully obtained. The attainable bonding temperatures and bonding pressures were between 190 °C–250 °C and 145 MPa–230 MPa, respectively. The bonding time varied between 30 s and 60 s.

Super‐Mossian Dielectrics for Nanophotonics

AbstractHigh refractive index dielectrics enable nanoscale integration of optical components with practically no absorption loss. Hence, high index dielectrics are promising for many emerging applications in nanophotonics. However, the lack of a complete library of high index dielectric materials poses a significant challenge to understanding the full potential for dielectric nanophotonics. Currently, it is assumed that the absorption edge and the sub‐bandgap refractive index of a semiconductor exhibit a rigid trade‐off, popularly known as the Moss rule. Thus, the Moss rule appears to set an upper limit on the refractive index of a dielectric for a given operating wavelength. However, there are many dielectric materials that surpass the Moss rule, referred to here as super‐Mossian dielectrics. Here, the general features of super‐Mossian dielectrics and their physical origin are discussed to facilitate the search for high index dielectrics. As an example, iron pyrite, an outstanding super‐Mossian material with index nearly 40% higher than the Moss rule prediction, is developed. The local dielectric resonances in iron pyrite nanoresonators are experimentally observed, and the impact of super‐Mossian materials on nanophotonics is demonstrated.

On the Study of Advanced Nanostructured Semiconductor-Based Metamaterial

Tunable metamaterials belonging to the class of different reconfigurable optical devices have proved to be an excellent candidate for dynamic and efficient light control. However, due to the consistent optical response of metals, there are some limitations aiming to directly engineer electromagnetic resonances of widespread metal-based composites. The former is accomplished by altering the features or structures of substrates around the resonant unit cells only. In this regard, the adjusting of metallic composites has considerably weak performance. Herein, we make a step forward by providing deep insight into a direct tuning approach for semiconductor-based composites. The resonance behavior of their properties can be dramatically affected by manipulating the distribution of free carriers in unit cells under an applied voltage. The mentioned approach has been demonstrated in the case of semiconductor metamaterials by comparing the enhanced propagation of surface plasmon polaritons with a conventional semiconductor/air case. Theoretically, the presented approach provides a fertile ground to simplify the configuration of engineerable composites and provides a fertile ground for applications in ultrathin, linearly tunable, and on-chip integrated optical components. These include reconfigurable ultrathin lenses, nanoscale spatial light modulators, and optical cavities with switchable resonance modes.

Nonlinear coupling and modulation of the guided modes in photorefractive slab waveguide

Owing to its excellent electro-optic, ferroelectric and nonlinear optical properties, photorefractive crystal (PRC) provides a versatile platform for developing nonlinear waveguides, which has a great potential in integrated optics components. In this paper, we theoretically study nonlinear coupling of optical guided modes in photorefractive waveguides by the spatial-partition fast Fourier transform beam propagation method (SP FFT-BPM). The modulation of applied external electrical field on the guided modes is investigated, and demonstrated as a new method to modulate the guided modes without artificially refabricating physical configuration or structure of the waveguide.

Achromatic photonic tricouplers for application in nulling interferometry.

Integrated-optic components are being increasingly used in astrophysics, mainly where accuracy and precision are paramount. One such emerging technology is nulling interferometry that targets high contrast and high angular resolution. Two of the most critical limitations encountered by nullers are rapid phase fluctuations in the incoming light causing instability in the interference and chromaticity of the directional couplers that prevent a deep broadband interferometric null. We explore the use of a tricoupler designed by ultrafast laser inscription that solves both issues. Simulations of a tricoupler, incorporated into a nuller, result in an order of a magnitude improvement in null depth.

High-efficiency edge-coupling based on lithium niobate on an insulator wire waveguide.

Edge-coupling on single-crystal thin-film lithium niobate on insulator (LNOI) was systematically studied in this paper. An inverse taper-shaped spot-size converter (SSC) to convert the mode field from the laser chip to a nanoscale LNOI waveguide was adopted to improve the coupling efficiency. Structure of the edge coupler was fully investigated and optimized by using the eigenmode expansion method. The single-mode conditions of the LNOI waveguide for three common communication bands were taken into consideration. Further, the length and tip width of the inverse taper, the cross-section dimensions of SiON waveguide, and the sidewall angle were investigated with respect to coupling efficiency. As a result, the maximum coupling efficiency from an edge coupler to laser chip can reach 54%, 48%, and 58% at 1550, 1310, and 850 nm in Z-cut LNOI for quasi-TM mode, respectively. This proposed work gives a better understanding of the function of the edge coupler based on LNOI material and provides an appropriate method for the design of an edge coupler with high efficiency, which could benefit the further application of high-density monolithic integrated optical components.

Photonic integrated quantum key distribution receiver for multiple users

Integrated photonics has the advantages of miniaturization, low cost, and CMOS compatibility, and it provides a stable, highly integrated, and practical platform for quantum key distribution (QKD). While photonic integration of optical components has greatly reduced the overall cost of QKD systems, single-photon detectors (SPDs) have become the most expensive part of a practical QKD system. In order to circumvent this obstacle and make full use of SPDs, we have designed and fabricated a QKD receiver chip for multiple users. Our chip is based on a time-division multiplexing technique and makes use of a single set of SPDs to support up to four users' QKD. Our proof-of-principle chip-based QKD system is capable of producing an average secret key rate of 13.68 kbps for four users with a quantum bit error rate (QBER) as low as 0.51% over a simulated distance of 20 km in fiber. Our result clearly demonstrates the feasibility of multiplexing SPDs for setting QKD channels with different users using photonic integrated chip and may find applications in the commercialization of quantum communication technology.

Research progress of analogical gravitation on optical metamaterial chips

Optical metamaterial is a kind of artificially designed microstructured material. Its occurrence breaks the localization of traditional material design thinking and provides a new paradigm for artificially controlling electromagnetic waves on a micro-nano scale, especially realizes optical properties beyond conventional materials in nature. Furthermore, metamaterial has the ability to couple electromagnetic waves into the sub-wavelength regime, meeting the high-speed development of modern science and technology, which puts forward new requirements for high performance, miniaturization and integration of optical components. Therefore, optical chips based on metamaterials bring many encouraging applications such as in perfect imaging that breaks through the diffraction limit, multifunctional integrated optics, etc. In addition, metamaterial photonic chips can also simulate some phenomena in general relativity, especially exploring some phenomena that have not been experimentally proven. This review paper briefly introduces the study of analogical gravitation based on different kinds of photonic chips on the basis of metamaterials. In the end, there present the summary and outlook about the current development, advantages and challenges of this field.

Direct-tuning methods for semiconductor metamaterials

Among various tunable optical devices, tunable metamaterials have exhibited their excellent ability to dynamically manipulate lights in an efficient manner. However, for unchangeable optical properties of metals, electromagnetic resonances of popular metallic metamaterials are usually tuned indirectly by varying the properties or structures of substrates around the resonant unit cells, and the tuning of metallic metamaterials has significantly low efficiency. In this paper, a direct-tuning method for semiconductor metamaterials is proposed. The resonance strength and resonance frequencies of the metamaterials can be significantly tuned by controlling free carriers’ distributions in unit cells under an applied voltage. This direct-tuning method has been verified in both two-dimensional and three-dimensional semiconductor metamaterials. In principle, the method allows for simplifying the structure of tunable metamaterials and opens the path to applications in ultrathin, linearly-tunable, and on-chip integrated optical components (e.g., tunable ultrathin lenses, nanoscale spatial light modulators and optical cavities with resonance modes switchable).

Characterization of heterogeneous InP-on-Si optical modulators operating between 77 K and room temperature

Heterogeneous integration of InP modulators on a silicon photonic platform, fabricated by bonding III–V wafer on patterned silicon waveguides, are proved to work between 77 K and 295 K. The performance of modulators based on the Franz-Keldysh effect (bulk) and the quantum confined Stark effect (quantum-well) is investigated for wavelengths ranging within 1460 nm–1580 nm. The bulk modulator is preferred when operating over a wide range of temperatures. The demonstration of such integrated optical components at low temperatures is especially attractive for applications that demand massive data communication between cryogenic and room temperatures requiring photonic interconnect, as well as applications with extreme environmental conditions, such as outer space exploration.

Simulation and Analysis of Telescopic Photonic Beam Combiner for Stellar Interferometry in Labview

The optical methods are the sensitive and subtle techniques of conducting optical investigations without any physical contact. They are both accurate and fast at the same time which provides an ease of having multiple observations. The need of optical interferometry has been increased at a very quick pace due to its high range of applications, from surface testing to locating of extra-solar planets in the universe. Optical Interferometry is a process or technique of combining light from various telescopes for calculating the angular resolution. The technique of optical interferometry helps astronomers for achieving a high angular resolution, that is not possible with the conventional telescopes. Optical approaches are the best approaches for non-contact evaluations, and these are accurate and fast. Due to optical nature of the interferometry, this process is used in various fields, and today it has become one of the important areas of research. Integrated Optics (IO) beam combiners are an efficient and compact technology to combine light interferometrically collected by multiple telescopes. IO beam combiner is based on the modal filtering properties of waveguides or fibers, and it improves thermo-mechanical stability, because of the characteristic rigidity of IO component substrate. Other advantages of this technology are miniaturization and non-existence of alignment needs. Several IO beam combiners are being proposed and tested nowadays. The purpose of this paper is to investigate different techniques used to develop interferometric instrument from previous researches and to simulate the technique suggested by Ermann in Labview.

Revolving and spinning of optical patterns by two coaxial spiraling elliptic beams in nonlocal nonlinear media.

Rotating patterns can be produced by two coaxial spiraling elliptic beams in nonlocal nonlinear media. The two constituent beams carry the orbital angular momentum (OAM), which has the same or opposite signs. The resultant patterns exhibit revolving and spinning rotations similar to the Sun-Earth system. The revolving-typed rotation comes of the overall OAM, while the spinning-typed rotation results from the respective OAM of the constituent beam. A kind of soliton patterns can stably exist, for which a vortex is nested centrally in the rotating square-shaped optical envelope and four peaks appear at four corners. The centrally nested vortex splits into two single vortex for r≠1, with r being the power ratio between the two constituent beams. The two single vortexes align vertically for r<1 and horizontally for r>1, and their spacing increases with |r-1|. The theoretical results give a possibility of the transforming from cross-phase-typed OAM into the helical-phase-typed OAM, which may find potential applications in beam shaping and controlling. In addition, the square optical envelope may exhibit advantages in the integration of optical components.

Low-index-contrast waveguide bend based on truncated Eaton lens implemented by graded photonic crystals

Low-index contrast waveguides such as silica waveguides are indispensable part of passive integrated optical components. Reducing the bending radius of silica waveguides with low bend loss is vital in miniaturizing silica planar lightwave circuits. The Eaton lens is a gradient index lens that can bend parallel light rays by 90{\deg}, 180{\deg}, or 360{\deg}. We present a low-loss and compact 90{\deg} waveguide bend with a radius of 9 $\mu$m designed by truncating the Eaton lens. The performance of the designed bend, implemented by graded photonic crystal, was evaluated by full-wave two-dimensional finite element method. The average bend loss in the C-band is 0.9dB while the average bend loss for the wavelength range of 1260-1675nm is 1.05dB. The proposed design strategy can be applied to other low-index contrast waveguides.

One-Dimensional Programmable Polymeric Microfiber Waveguide with Optically Reconfigurable Photonic Functions.

Programmable materials and reconfigurable photonic components, which can change their physicochemical properties and functionalities upon external stimuli, are a major topic of interest in modern science. However, most conventional reconfigurable photonic components rely heavily on mechanical deformation, restricting their application. Herein, a novel strategy based on a dynamically tunable fluorescence resonance energy transfer process to design and fabricate programmable fluorescent micropatterns within single polymer microfiber is proposed. A set of reconfigurable photonic components (including optical switchable waveguide systems, photonic analogies of diodes and transistors, as well as one-dimensional (1D) optical encoding) can be achieved within a single polymeric waveguide microfiber straightforwardly, in which such photonic components can be written, erased, and rewritten as 1D binary patterns with tailored external optical stimuli. These results might be of great fundamental value for the rational design of novel reconfigurable photonic devices with numerous potential applications in highly integrated optical communication components and optical computing devices.

Modal analysis using photonic lanterns coupled to arrays of waveguides.

We present a new concept of an integrated optics component capable of measuring the complex amplitudes of the modes at the tip of a multimode waveguide. The device uses a photonic lantern to split the optical power carried by an N-modes waveguide among a collection of single-mode waveguides that excite a periodic array of at least N2single-mode evanescently-coupled waveguides. The power detected at each output of the array is a linear combination of the products of the modal amplitudes-a relation that can, under suitable conditions, be inverted allowing the derivation of the amplitudes and relative phases of the modal mixture at the input. The expected performance of the device is discussed and its application to the real-time measurement of modal instability in high power fiber lasers is proposed.

Hybrid Organic-Inorganic photoresists, a promising class of materials for Optofluidic integration

Through the efforts to fuse planar optics and microfluidics in order to produce dye lasers, biosensors, trapping and cell sorting device, we can notice the rising interest in optofluidics since early and mid 2000's. However mass production of these devices heavily relies on fast and easy patterning of the constituent material. PDMS, being one of these materials, gained an added value because of its elasticity, hydrophobicity and permeability to gaz. Nonetheless, these specifications are not convenient for all types of applications. The growing capability to use Hybrid Organic-Inorganic materials for the fabrication of integrated optics components and microfluidic channels is what makes this class of materials an ideal candidate for this integration. This work aims to implement, on the same chip, an optical and a microfluidic layer using Sol-Gel processing of Organic-Inorganic materials. The interest in this vertical integration arises from the need to manipulate the fluid in the microchannels using evanescent field optical pressure.