On-chip Light Research Articles

An on-chip hybrid plasmonic light steering concentrator with ∼96% coupling efficiency.

We, for the first time, propose and theoretically study a plasmonic light steering concentrator (PLSC) that is based on a hybrid photonic-plasmonic sandwich structure. In this device, a transverse electric (TE) polarization guided mode supported by a silicon-on-insulator (SOI) waveguide is vertically coupled to a metal-dielectric-metal sandwich structure, while the structure steers the light to a perpendicular metal taper and focuses the light on the apex of the taper with a small radius of 15 nm. Based on the coupled-mode theory, the two supermodes (quasi-TM modes) are clarified to illustrate the coupling mechanism of the device. We numerically obtain over 96% coupling efficiency at the 1500 nm telecommunication wavelength, and the mode width supported by the apex is limited laterally within the range of ∼110 nm, where the field enhancement calculated is found to be more than 107 compared to that of light in the silicon waveguide.

Inclined emitting slotted single-mode laser with 1.7° vertical divergence angle for PIC applications.

In this Letter, a new type of single-mode slotted laser used for an on-chip light source in photonic integrated circuits is proposed. An inclined light beam with a low vertical divergence angle can be directly coupled into the surface grating of the silicon to form an integrated light source. Experimentally, a III-V laser with a 54.6° inclined angle and a vertical divergence angle of 1.7° is achieved by introducing a kind of specially distributed microstructure. The side mode suppression ratio is better than 45dB, and the continuous wave output power reaches 6.5mW at room temperature. We report the inclined emitting microstructured single-mode laser with a low divergence angle for the first time, to the best of our knowledge.

Improving lumen maintenance by nanopore array dispersed quantum dots for on-chip light emitting diodes

The temperature stability of quantum dots (QDs), which is crucial for integrating into high power light-emitting diodes (LEDs) in the on-chip configuration, needs to be further improved. In this letter, we report warm white LEDs, where CdSe/ZnS nanoparticles were incorporated into a porous anodic alumina (PAA) matrix with a chain structure by the self-assembly method. Experiments demonstrate that the QD concentration range in toluene solvent from 1% mg/μl to 1.2% mg/μl in combination with the PAA matrix shows the best luminous property. To verify the reliability of the as-prepared device, a comparison experiment was conducted. It indicates excellent lumen maintenance of the light source and less chromaticity coordinate shift under accelerated life testing conditions. Experiments also prove that optical depreciation was only up to 4.6% of its initial value after the 1500 h aging test at the junction temperature of 76 °C.

Surface Wave Control for Large Arrays of Microwave Kinetic Inductance Detectors

Large ultrasensitive detector arrays are needed for present and future observatories for far infrared, submillimeter wave (THz), and millimeter wave astronomy. With increasing array size, itis increasingly important to control stray radiation inside the detector chips themselves, the surface wave. We demonstrate this effect with focal plane arrays of 880 lens-antenna coupled microwave kinetic inductance detectors (MKIDs). Presented here are near field measurements of the MKID optical response versus the position on the array of a reimaged optical source. We demonstrate that the optical response of a detector in these arrays saturates offpixel at the ~-30-dB level compared to the peak pixel response. The result is that the power detected from a point source at the pixel position is at a similar level to the stray response integrated over the chip area. With such a contribution, it would be impossible to measure extended sources, while the point source sensitivity is degraded due to an increase of the stray loading. However, we show that by incorporating an on-chip stray light absorber, the surface wave contribution is reduced by a factor >10. With the on-chip stray light absorber, the point source response is close to simulations down to the ~ -35-dB level, the simulation based on an ideal Gaussian illumination of the optics. In addition, as a crosscheck, we show that the extended source response of a single pixel in the array with the absorbing grid is in agreement with the integral of the point source measurements.

Negative Landau Damping in Bilayer Graphene.

We theoretically demonstrate that a system formed by two coupled graphene sheets enables a negative damping regime wherein graphene plasmons are pumped by a direct current. This effect is triggered by electrons drifting through one of the graphene sheets and leads to wave instabilities and a spontaneous light emission (spasing) in the midinfrared range. It is shown that there is a deep link between the drift-induced instabilities and wave instabilities in moving media, as both result from the hybridization of oscillators with oppositely signed frequencies. With a thickness of a few nanometers and wide spectral tunability, the proposed structure may find interesting applications in nanophotonic circuitry as an on-chip light source.

Opportunities for visible supercontinuum light generation in integrated diamond waveguides.

We numerically show the advantages of using diamond-on-insulator (DOI) waveguides to design compact supercontinuum (SC) light sources for the visible (VIS) wavelength range. We conclude that the DOI platform is more suitable than silicon nitride waveguides for tailoring the dispersion in such a way that a zero-dispersion wavelength (ZDW) is obtained in the VIS, as is required to achieve efficient VIS SC generation (SCG). After designing a DOI waveguide that features a ZDW at ∼600 nm, we exploit it to numerically obtain a smooth SC ranging from 453nm to 1030nm above the -30 dB point after propagation over 4mm. Our result extends beyond the state-of-the-art shortest VIS wavelengths induced by SCG in integrated waveguides, while using ∼26 times lower input energy and a shorter waveguide length, thus showcasing the potential of the DOI platform for on-chip VIS SC light sources.

Obstacle Recognition Based on Machine Learning for On-Chip LiDAR Sensors in a Cyber-Physical System.

Collision avoidance is an important feature in advanced driver-assistance systems, aimed at providing correct, timely and reliable warnings before an imminent collision (with objects, vehicles, pedestrians, etc.). The obstacle recognition library is designed and implemented to address the design and evaluation of obstacle detection in a transportation cyber-physical system. The library is integrated into a co-simulation framework that is supported on the interaction between SCANeR software and Matlab/Simulink. From the best of the authors’ knowledge, two main contributions are reported in this paper. Firstly, the modelling and simulation of virtual on-chip light detection and ranging sensors in a cyber-physical system, for traffic scenarios, is presented. The cyber-physical system is designed and implemented in SCANeR. Secondly, three specific artificial intelligence-based methods for obstacle recognition libraries are also designed and applied using a sensory information database provided by SCANeR. The computational library has three methods for obstacle detection: a multi-layer perceptron neural network, a self-organization map and a support vector machine. Finally, a comparison among these methods under different weather conditions is presented, with very promising results in terms of accuracy. The best results are achieved using the multi-layer perceptron in sunny and foggy conditions, the support vector machine in rainy conditions and the self-organized map in snowy conditions.

Strong cavity-pseudospin coupling in monolayer transition metal dichalcogenides

Strong coupling between the electronic states of monolayer transition metal dichalcogenides (TMDC) such as MoS$_2$, MoSe$_2$, WS$_2$, or WSe$_2$, and a two-dimensional (2D) photonic cavity gives rise to several exotic effects. The Dirac type Hamiltonian for a 2D gapped semiconductor with large spin-orbit coupling facilitates pure Jaynes-Cummings type coupling in the presence of a single mode electric field. The presence of an additional circularly polarized beam of light gives rise to valley and spin dependent cavity-QED properties. The cavity causes the TMDC monolayer to act as an on-chip coherent light source and a spontaneous spin-oscillator. In addition, a TMDC monolayer in a cavity is a sensitive magnetic field sensor for an in-plane magnetic field.

Quantitative analysis of a III-V tapered horn-shaped metal-clad nano-cavity as an on-chip light source

A horn-shaped metal-clad InGaAsP nano-cavity with sloped sidewalls is proposed as a platform for nanoscale light sources. The nano-cavity’s physical dimensions are 350 × 350 × 350 nm3, and its mode volume is 0.5 (λ0/n)3. In our numerical simulations and quantitative analysis, we have shown that the sloped sidewalls reduce metallic absorption and improve resonant mode confinement; and adjusting their slope from 0 to 16° increased the Q factor from 150 to 900 and laser modulation 3dB bandwidth from 4.3 to 36 GHz. The lasing threshold current was expected to be 35 μA at 16°. In a simulated feasibility study, we demonstrate 60 Gbps modulated laser signal (5 fJ/bit), producing 20 μW output power at the 1.5 μm wavelength with injection current 100 μA, as an implementation of horn-shaped nano-cavity platform to the low power and ultra-fast on-chip nano-laser.

Silicon-on-Insulator Waveguide Devices for Broadband Mid-Infrared Photonics

In this paper, we demonstrate silicon-on-insulator (SOI) channel waveguides with propagation loss and $r$ = 10 $\mu$ $\text{m}$ bends with bending loss as low as 2 dB/cm and 0.02 dB/90 $^{\circ }$ in the broad wavelength range of 3.68–3.88 $\mu$ $\text{m}$ . We also indicate the limitation of SOI waveguide loss in mid-infrared wavelength by analyzing loss mechanisms. Based on this high-performance mid-infrared waveguide, we systematically analyze the coupling efficiency of various directional couplers, which are critical and commonly used building blocks for on-chip light routing and power splitting. By varying coupling length and sweeping wavelength, the performance of directional coupler with various gap separations is meticulously investigated in 3.68–3.88 $\mu$ $\text{m}$ . A experimental database for directional coupler with any power splitting ratio is provided. Our results offer a promising broadband platform for dense wavelength division multiplexing (DWDM) and applications that require precise control of coupling such as racetrack resonator in the mid-infrared region.

On-Chip Narrowband Thermal Emitter for Mid-IR Optical Gas Sensing

Efficient light sources compatible to complementary metal oxide semiconductor (CMOS) technology are key components for low-cost, compact mid-infrared gas sensing systems. In this work we present an on-chip narrowband thermal light source for the mid-infrared wavelength range by combining microelectromechanical system (MEMS) heaters with metamaterial perfect emitter structures. Exhibiting a resonance quality factor of 15.7 at the center wavelength of 3.96 μm and an emissivity of 0.99, the demonstrated emitter is a spectrally narrow and efficient light source. We show temperature-stable (resonance wavelength shift 0.04 nm/°C) and angular-independent emission characteristics up to angles of 50° and provide an equivalent circuit model illustrating the structure’s resonance behavior. Owing to its spectrally tailored, nondispersive emission, additional filter elements in a free-space optical gas sensing setup become obsolete. In a proof-of-concept demonstration of such a filter-free gas sensing system with CO2 ...

Design and analysis of a CMOS-compatible distributed Bragg reflector laser based on highly uniaxial tensile stressed germanium.

We design a CMOS-compatible Distributed Bragg Reflector (DBR) laser based on highly uniaxial tensile stressed germanium. Our design first incorporates three critical elements including high uniaxial tensile stress, low loss optical resonator and heterojunction for electrical injection. A threshold current density of 80 kA/cm2 and an internal quantum efficiency of 8.5% are estimated when the Shockley-Reed-Hall (SRH) lifetime is chosen to be 3 ns. Furthermore, the performance of the DBR laser can be enhanced by improving the crystal quality and carefully designing the p-n junction. The simulation results also indicate that the limitation of the improvement of threshold current density and internal quantum efficiency are 29 kA/cm2 and 19.6%, resulting from the Auger recombination. The influences of strain and n-type doping on the threshold current density and the internal quantum efficiency are discussed. The proposed DBR laser offers a new approach to realize on-chip light source for silicon photonics.

Electrospray deposition of quantum dot-doped Ge23Sb7S70 chalcogenide glass films

The incorporation of quantum dots (QDs) into chalcogenide glass films is attractive for their luminescent properties. Such QD-doped glass structures could serve as a compact, on-chip light source for planar photonic devices. Typical processing methods such as spin coating have limitations of excessive material waste, little control on the pattern of the film and difficulty for scale-up. To overcome these limitations, this study introduces electrospray as a more versatile processing method and has deposited QD-doped chalcogenide glass thin films. The parameters of the electrospray process are prudently chosen to ensure one or none QD is enclosed per liquid droplet. The transmission electron microscopy imaging of resultant films confirm enhanced QD dispersion with reduced aggregations. Absorption and photoluminescence characterization shows the QD-doped chalcogenide glass films prepared by electrospray maintain signature spectra of QDs from the manufacturer.

Microfabricated devices for single objective single plane illumination microscopy (SoSPIM).

Light sheet microscopy is a relatively new form of fluorescence microscopy that has been receiving a lot of attention recently. The strong points of the technique, such as high signal to noise ratio and its reduced photodamage of fluorescently labelled samples, come from its unique feature to illuminate only a thin plane in the sample that coincides with the focal plane of the detection lens. Typically this requires two closely positioned perpendicular objective lenses, one for detection and one for illumination. Apart from the fact that this special configuration of objective lenses is incompatible with standard microscope bodies, it is particularly problematic for high-resolution lenses which typically have a short working distance. To address these issues we developed sample holders with an integrated micromirror to perform single lens light sheet microscopy, also known as single objective single plane illumination microscopy (SoSPIM). The first design is based on a wet-etched silicon substrate, the second on a microfabricated polished polymer plug. We achieved an on-chip light sheet thickness of 2.3 μm (FWHM) at 638 nm with the polymer micromirror and of 1.7 μm (FWHM) at 638 nm with the silicon micromirror, comparable to reported light sheet thicknesses obtained on dedicated light sheet microscopes. A marked contrast improvement was obtained with both sample holders as compared to classic epi-fluorescence microscopy. In order to evaluate whether this technology could be made available on a larger scale, in a next step we evaluated the optical quality of inexpensive replicas from both types of master molds. We found that replicas from the polished polymer based mold have an optical quality close to that of the master component, while replicas from the silicon based mold were of slightly lower but still acceptable quality. The suitability of the replicated polymer based sample holder for single-lens light sheet microscopy was finally demonstrated by imaging breast cancer spheroids.

Efficient Optical Amplification in a Sandwich-Type Active-Passive Polymer Waveguide Containing Perylenediimides

Polymer waveguides doped with luminescent materials serve as a suitable flexible platform for active elements (lasers and amplifiers) in on-chip optical circuits. However, at present, the best parameters (lowest thresholds) achieved with these devices are obtained with the use of the stripe excitation technique in the framework of which external illumination of an active material along the whole length of the waveguide is realized that is not convenient for the waveguide on-chip integration and requires high peak energies due to the large excitation area. In the present work, an elegant method is proposed to overcome this obstacle and provide efficient active material pumping along the whole waveguide length with use of on-chip integration compatible edge-type excitation light injection. This novel type of planar active-passive polymer waveguides includes a thin (50–100 nm) active layer of poly(methyl methacrylate) (PMMA), which is heavily doped with highly luminescent perylenediimide (PDI) molecules, san...

Generic Heterogeneously Integrated III–V Lasers-on-Chip With Metal-Coated Etched-Mirror

In this paper, electrically pumped III–V quantum-well lasers bonded on SiO2 with a metal-coated etched-mirror are reported. There are three key features for the device demonstrated: (i) The metal-coated etched-mirror ensures that the lasers can be used as on-chip light source and provides high reflectance, but requires no additional fabrication steps due to our process design, (ii) the bonded III–V on SiO2 enables high-light confinement in the active region due to high index contrast between III–V and SiO2. Moreover, it promises a flexible choice of host substrate, in which the silicon substrate could also be replaced with other materials, and (iii) the active III–V region is sufficiently close to the SiO2 interlayer, allowing the laser mode to overlap with SiO2. This facilitates effective optical coupling with in-plane passive waveguides, which can be fabricated from thin film of amorphous silicon, silicon nitride or other waveguide materials, to form a subsystem on chip through in-plane integration. The laser devices demonstrated have the lowest threshold of 50 mA, a maximum output power of 9 mW, and a differential quantum efficiency of 27.6%.

Heterogeneous integration of a III-V VCSEL light source for optical fiber sensing.

We propose a fiber Bragg grating (FBG) sensor interrogation system utilizing a III-V vertical cavity surface emitting laser (VCSEL) as the on-chip light source. Binary blazed grating (BBG) for coupling between III-V VCSEL and silicon-on-insulator (SOI) waveguides is demonstrated for interrogation of the FBG sensor. The footprint size of the BBG is only 5.62 μm×5.3 μm, and each BBG coupler period has two subperiods. The diameter of the VCSEL's emitting window is 5 μm, which is slightly smaller than that of the BBG coupler, to be well-matched with the proposed structure. Results show that the coupling efficiency from vertical cavities of the III-V VCSEL to the in-plane waveguides reached as high as 32.6% when coupling the 1550.65 nm light. The heterogeneous integration of the III-V VCSEL and SOI waveguides by BBG plays a fundamental role in inducing a great breakthrough to the miniaturization of an on-chip light source for optical fiber sensing.

Phosphorus implantation into in situ doped Ge-on-Si for high light-emitting efficiency

We investigated the optical, electrical, and structural properties of epitaxially grown Ge-on-Si substrates after phosphorous implantation. Ion implantation increases n-type doping in Ge for an on-chip light source. However, its effects on Ge should be carefully studied as implantation may increase the recombination sites, and possibly reduce light-emitting efficiency. We studied the light-emitting efficiency of implanted Ge using various material characterizations. We found that phosphorous implantation increased the doping concentration of in situ doped Ge-on-Si, which boosted the photoluminescence by 12–30%. It is therefore critical to optimize the post-annealing and implantation doses to increase light-emitting efficiency of Ge.

Low Threshold Light Emission from Reverse-Rib n+ Ge Cavity Made by P Diffusion

Ge laser is expected as a solution for a key issue in electronic-photonic integrations, CMOS compatible on-chip light source. Two important issues remain in Ge laser technologies; the large threshold current (Ith) and the multiple growth of Ge epi-structures to co-integrate Ge devices such as photodetectors, whose pn junction profiles are much different from the Ge lasers. The reported Ith values are larger than those for III-V lasers by two orders of magnitude, and an in-situ heavily n-type doping in Ge prevents to form various pn structures unless the multiple growth with different doping profiles are performed. To solve these issues, the present paper proposes a "reverse-rib" Ge epi-structure in combination with an ex-situ P diffusion for heavily n-type doping, instead of in-situ doping. P-diffused n+-Ge reverse-rib structures first verify a clear threshold behavior of light emission at a low power of optical pumping.

World-smallest fiber-GRIN lens system for optofluidic applications

We have developed a new type of an optical fiber probe which integrates the standard single mode fiber with a gradient index (GRIN) microlens. The system is perfectly suited for optofluidic sensor applications since the diameter of the lens module is exactly the same as the diameter of the optical fiber. Moreover, the performance of the GRIN lens is not degraded by low contrast of the refractive index between of the lens and the fluidic environment. The GRIN lens is made with novel technology of nanostructured optics. Full Text: PDF References M. Woerdemann, C. Alpmann, M. Esseling, C. Denz, Advanced optical trapping by complex beam shaping, Laser Photonics Rev. 7, 839 (2013). CrossRef E. Weber, F. Keplinger, and M. J. Vellekoop, On-Chip Light Modulation Applying Optofluidic Principles, IEEE Sensors Journal 13 4773 (2013). CrossRef F. Hudelist, J. M. Nowosielski, R. Buczynski, A. J. Waddie, M. R. Taghizadeh, Nanostructured elliptical gradient-index microlenses, Optics Letters 35, 130 (2010) CrossRef J. M. Nowosielski, R. Buczynski, F. Hudelist, A. J. Waddie, M. R. Taghizadeh, Nanostructured GRIN microlenses for Gaussian beam focusing, Opt. Comm. 283 1938 (2010). CrossRef A.Sihvola, Electromagnetic Mixing Formulas and Applications (London: The Institution of Electrical Engineers 1999). J. Nowosielski, R. Buczynski, A. J. Waddie, A. Filipkowski, D. Pysz, A. McCarthy, R. Stepien, M. R. Taghizadeh, Large diameter nanostructured gradient index lens, Opt. Ex. 20 11767 (2012). CrossRef R. Stepien, J. Cimek, D. Pysz, I. Kujawa, M. Klimczak, R. Buczynski, Soft glasses for photonic crystal fibers and microstructured optical components, Opt. Eng. 53, 071815 (2014). CrossRef A. Filipkowski, B. Piechal, D. Pysz, R. Stepien, A. Waddie, M. R. Taghizadeh, R. Buczynski, Nanostructured gradient index microaxicons made by a modified stack and draw method, Opt. Lett. 40, 5200-5203 (2015). CrossRef