Silicon Photonics Applications Research Articles

Realization of all logic gates using hybrid grating structure: An application of silicon photonics

The outcome of present research work divulges all type of logic gates (NOT, AND, OR, XOR, NAND, NOR, XNOR) using two simple silicon grating structures, where plane wave expansion method manipulates to such structure to investigate the transmission characteristics. Output results infers that grating parameter such as number of layers, thickness of odd and even layer, the length of grating odd the proposed structure plays vital role to realize different type of optical logic gates.

Dispersion control of silicon nanophotonic waveguides using sub-wavelength grating metamaterials in near- and mid-IR wavelengths

Controlling the group velocity dispersion of silicon nanophotonic waveguides has been recognized as a key ingredient to enhance the development of various on-chip optical applications. However, the strong wavelength dependence of the dispersion in waveguides implemented on the high index contrast silicon-on-insulator (SOI) platform substantially hinders their wideband operation, which in turn, limits their deployment. In this work, we exploit the potential of non-resonant sub-wavelength grating (SWG) nanostructures to perform a flexible and wideband control of dispersion in SOI waveguides. In particular, we demonstrated that the overall dispersion of the SWG-engineered metamaterial waveguides can be tailored across the transparency window of the SOI platform, keeping easy-to-handle single-etch step manufacturing. The SWG silicon waveguides overcladded by silicon nitride exhibit significant reduction of wavelength dependence of dispersion, yet providing intriguing and customizable synthesis of various attractive dispersion profiles. These include large normal up to low anomalous operation regimes, both of which could make a great promise for plethora of emerging applications in silicon photonics.

Integrated 2D-Graded Index Plasmonic Lens on a Silicon Waveguide for Operation in the Near Infrared Domain.

In this article we address the nanoscale engineering of the effective index of silicon on insulator waveguides by using plasmonic metasurface resonances to realize a graded index lens. We report the design, implementation, and experimental demonstration of this plasmonic metasurface-based graded index lens integrated on a silicon waveguide for operation in the near-infrared domain. The 2D-graded index lens consists of an array of gold cut wires fabricated on the top of a silicon waveguide. These gold cut wires modify locally the effective index of the silicon waveguide and allow the realization of this gradient lens. The reported solution represents a promising alternative to the bulky or multilayered metamaterials approach in the near IR domain. This enabling technology may have found its place in silicon photonic applications by exploiting the plasmonic resonances to control the light at nanoscale.

High-Q photonic resonators and electro-optic coupling using silicon-on-lithium-niobate

Future quantum networks, in which superconducting quantum processors are connected via optical links, will require microwave-to-optical photon converters that preserve entanglement. A doubly-resonant electro-optic modulator (EOM) is a promising platform to realize this conversion. Here, we present our progress towards building such a modulator by demonstrating the optically-resonant half of the device. We demonstrate high quality (Q) factor ring, disk and photonic crystal resonators using a hybrid silicon-on-lithium-niobate material system. Optical Q factors up to 730,000 are achieved, corresponding to propagation loss of 0.8 dB/cm. We also use the electro-optic effect to modulate the resonance frequency of a photonic crystal cavity, achieving a electro-optic modulation coefficient between 1 and 2 pm/V. In addition to quantum technology, we expect that our results will be useful both in traditional silicon photonics applications and in high-sensitivity acousto-optic devices.

Large-FSR Thermally Tunable Double-Ring Filters for WDM Applications in Silicon Photonics

We present the design procedure and experimental results of thermally tunable double ring resonators for integrated wavelength division multiplexing applications. A detailed analytical model specific for double rings is described, and a modified racetrack geometry using Bezier bends is used to reduce bending loss. We demonstrate devices with a free-spectral-range up to 2.4 THz (19 nm) around 1550 nm and nonadjacent channel rejection higher than 35 dB. The experimental results of thermally tunable double ring resonators is also presented with doped silicon integrated heaters, allowing the device to be used as a tunable filter or a switch.

Expanding the Silicon Photonics Portfolio With Silicon Nitride Photonic Integrated Circuits

The high index contrast silicon-on-insulator platform is the dominant CMOS compatible platform for photonic integration. The successful use of silicon photonic chips in optical communication applications has now paved the way for new areas where photonic chips can be applied. It is already emerging as a competing technology for sensing and spectroscopic applications. This increasing range of applications for silicon photonics instigates an interest in exploring new materials, as silicon-on-insulator has some drawbacks for these emerging applications, e.g., silicon is not transparent in the visible wavelength range. Silicon nitride is an alternate material platform. It has moderately high index contrast, and like silicon-on-insulator, it uses CMOS processes to manufacture photonic integrated circuits. In this paper, the advantages and challenges associated with these two material platforms are discussed. The case of dispersive spectrometers, which are widely used in various silicon photonic applications, is presented for these two material platforms.

Optical MUX/DEMUX using 3D photonic crystal structure: A future application of silicon photonics

This paper introduces optical multiplexer and demultiplexer (MUX/DEMUX) using 3-D photonic crystal (3-D PCs) structure around the wavelength of 1310nm. Here 3-D PCs deals with the wavelength of 1306nm–1311nm using photonic bandgap analysis, where bandgap analysis is made by employing planewave expansion (PWE) technique. Simulation result divulges that both nature of background and configuration of structures play a significant role to envisage the design of optical multliplexer and demultiplexer. Again, it is reveled that allowed and disallowed wavelengths depend on structure parameters of 3D photonic crystal with nature of substrate. Aside this, it is found an interesting variation exist between allowed wavelengths with respect to both diameter of air holes and lattice spacing of the structure.

Electroluminescence at 1.3 µm from InAs/GaAs quantum dots monolithically grown on Ge/Si substrate by metal organic chemical vapor deposition

We report the first demonstration of electroluminescence at 1.3 µm from InAs/GaAs quantum dots (QDs) monolithically grown on a Ge/Si substrate by metal organic chemical vapor deposition (MOCVD). High-density coalescence-free InAs/Sb:GaAs QDs emitting at 1.3 µm were obtained on a GaAs/Ge/Si wafer. The post-growth annealing of the GaAs buffer layer shows a significant improvement in the room-temperature (RT) photoluminescence (PL) intensity of QDs grown on a GaAs/Ge/Si wafer, comparable to those QDs grown on a reference GaAs substrate. Together, these results are promising for the realization of a QD laser on a Si substrate by MOCVD for silicon photonics application.

Analysis of silicon waveguide structure for realization of optical MUX/DEMUX circuit: An application of silicon photonics

Structure, operation and simulation of optical multiplexer and demultiplexer using silicon waveguide structure is discussed in this paper. Here silicon waveguide structure is realized by eighty three layers of waveguide in such way that it consists of 42 layer of silicon and 41 layer of air materials in an alternate manner. Here both reflection and absorption losses are considered to realize MUX/DEMUX. Simulation for reflectance is done using plane wave expansion method, where absorption loss is found zero for all wavelengths. Simulation results revealed that number of layers of waveguide, thickness of odd and even layers; structure period and length play an important role to design optical multiplexer and demultiplexer circuit. Present simulation result showed that waveguide having thickness of odd layer (silicon) 1180nm and even layer (air) 200nm, allows wavelength 850nm and reflects wavelength 1310nm and 1550nm. Similarly, structure having thickness, 180nm of odd layer (silicon) and 300nm of even layer allows wavelength 1310nm and reflects to both 850nm and 1550nm. And thickness of 80nm (odd) and 180nm (even) allows 1550nm and reflects both 850nm and 1310nm. Apart from this it is also seen that same waveguide structure having thickness of odd layers, 1nm and even layers, 999nm allows all wavelengths (850nm, 1310nm and 1550nm).

Realization of monochromatic filter using silicon grating structure: An application of silicon photonics

This paper attempts to discuss the realization of monochromatic filter using silicon monoxide-silicon (SiO-Si) grating structure having defect at 18th and 52nd position. Here both absorption and reflection losses are considered to compute reflectance and transmittance. Simulation is made using plane wave expansion method. Simulation result showed that suitable combination of thickness of odd and even layers of above grating structure plays an important role to obtain reflectance and transmittance. It is also revealed that silicon monoxide-silicon grating structure with defect (air) at 18th and 52nd position behaves as monochromatic filter for thickness of even layer, 80nm and thickness of odd layer varies from 40nm to 190nm. Apart from this, it is also observed that for some combination of thickness (t1,t2) grating layers, such as (50nm, 80nm), (60nm, 80nm), (70nm, 80nm), (80nm, 80nm), (90nm, 80nm) (110nm, 80nm), (120nm, 80nm), (130nm, 80nm) grating allows single wavelength only, which can be considered as ideal monochromatic filter. Again simulation studies showed that width of the reflected band gradually increases with the increase of grating length.

Tunable, broadband and high-efficiency Si/Ge hot luminescence with plasmonic nanocavity array

In addition to the massive application in the electronics industry for decades, silicon has been considered as one of the best candidates for the photonics industry. However, a high-efficiency, broadband light source is still a challenge. In this paper, we theoretically propose a Si/Ge based platform consisting of plasmonic nanocavity array to realize the tunable, broadband, and high-efficiency Si/Ge hot luminescence from infrared to visible region with large luminescence enhancement (about 103). It is demonstrated that the large luminescence enhancement is due to the resonance between the intrinsic hot luminescence and the plasmonic nanocavity modes with ultra-small effective mode volumes. And, the size and Ge composition of Si1−xGex nanowire can be tuned to realize the tunable and broadband luminescence. This study gives rise to many applications in silicon photonics, like ultrafast optical communications, sensors, and on-chip spectral measurements.

Heterogeneously Integrated Distributed Feedback Quantum Cascade Lasers on Silicon

Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated diode lasers for wavelengths from 1310 to 2010 nm. Recently, Fabry-Pérot Quantum Cascade Lasers integrated on silicon provided a 4800 nm light source for mid-infrared (MIR) silicon photonic applications. Distributed feedback (DFB) lasers are appealing for many high-sensitivity chemical spectroscopic sensing applications that require a single frequency, narrow-linewidth MIR source. While heterogeneously integrated 1550 nm DFB lasers have been demonstrated by introducing a shallow surface grating on a silicon waveguide within the active region, no mid-infrared DFB laser on silicon has been reported to date. Here we demonstrate quantum cascade DFB lasers heterogeneously integrated with silicon-on-nitride-on-insulator (SONOI) waveguides. These lasers emit over 200 mW of pulsed power at room temperature and operate up to 100 °C. Although the output is not single mode, the DFB grating nonetheless imposes wavelength selectivity with 22 nm of thermal tuning.

Integrated Amorphous Silicon p-i-n Temperature Sensor for CMOS Photonics.

Hydrogenated amorphous silicon (a-Si:H) shows interesting optoelectronic and technological properties that make it suitable for the fabrication of passive and active micro-photonic devices, compatible moreover with standard microelectronic devices on a microchip. A temperature sensor based on a hydrogenated amorphous silicon p-i-n diode integrated in an optical waveguide for silicon photonics applications is presented here. The linear dependence of the voltage drop across the forward-biased diode on temperature, in a range from 30 °C up to 170 °C, has been used for thermal sensing. A high sensitivity of 11.9 mV/°C in the bias current range of 34–40 nA has been measured. The proposed device is particularly suitable for the continuous temperature monitoring of CMOS-compatible photonic integrated circuits, where the behavior of the on-chip active and passive devices are strongly dependent on their operating temperature.

Novel Ring Resonator Combining Strong Field Confinement With High Optical Quality Factor

Slot waveguide ring resonators appear promising candidates for several applications in silicon photonics. Strong field confinement, high device tunability, and low power consumption are beneficial properties compared with strip waveguides. Slot waveguide ring resonators suffer, however, from rather low optical quality factors due to optical losses. This letter proposes and experimentally demonstrates a novel concept based on a partially slotted ring and a strip-to-slot mode converter. An exceptional high quality factor of ${\sim }10^{5}$ has been measured.

(Invited) Bright Light Emitting Silicon/Germanium Nanostructures

Light emission from Si nanostructures has been of great interest for some time now owing to the need for silicon-based light sources for applications in silicon opto-electronics and photonics. Both Si and Ge possess indirect band gaps, which makes them very inefficient light emitters. Band gap engineering employing quantum wells or quantum dots has been proposed as one way to overcome this limitation and Si/Ge or Si/SiGe-alloy thin-multilayer nanostructures grown on Si have been produced on this principle, and although light emission with greatly improved efficiency has been obtained at low temperatures the emission at room temperature is still very weak, because of exciton dissociation. Recent advances in band gap engineering technology have resulted in the development of new systems incorporating one-, two-, and three-dimensionally confined Si-Ge nanostructures that produce bright light in the near infrared. Here, the novel optical properties of three such nanostructures – super unit cells, nanowires, and nanocluster layers – are explored.

(Invited) Bright Light Emitting Silicon/Germanium Nanostructures

Light emission from Si and Ge nanostructures has been of great interest for some time now owing to the need for silicon-based light sources for applications in silicon opto-electronics and photonics. Optical interconnects are required now for on-chip technology as an alternative to metal wires, because of data transmission bottlenecks introduced by their unavoidable delay times, significant signal degradation, problems with power dissipation, and electromagnetic interference. Two major avenues toward optical interconnects on a chip include a hybrid approach with III-V densely packaged optoelectronic components and the all-group-IV approach (mainly Si, Ge and SiGe), where the all major components, e.g., light emitters, modulators, waveguides and photodetectors, are monolithically integrated into the CMOS environment. Both Si and Ge possess indirect band gaps, which makes them very inefficient light emitters. Band gap engineering employing quantum wells, quantum wires or quantum dots has been proposed as one way to overcome this limitation and Si/Ge or Si/SiGe-alloy thin-multilayer quantum well structures grown on Si have been produced on this principle, and although light emission with greatly improved efficiency has been obtained at low temperatures the emission at room temperature is still very weak, because of exciton dissociation. Recently, through employing novel band-gap engineering strategies, we have prepared several different entirely new bright light-emitting Si/Ge nanostructures including one possessing a direct gap. The latter structure is based on constructing a new super unit cell comprised of multiple planar epitaxial layers of Si and Ge grown on (001) Si0.4Ge0.6. Others are based on silicon-germanium layers grown epitaxially on silicon in in such a way as to form multiple layer three-dimensional nanostructures (quantum dots). Lastly, we have developed a simple and efficient electrochemical process that combines galvanic reaction and focused-ion-beam lithography to selectively synthesize gold nanoparticles that are consequently used for the growth of ordered SiGe nanowire arrays with predefined diameter (200 nm) and position. Here we report on the optical properties of such Si/Ge nanostructures, which are found to luminesce efficiently at wavelengths in the important spectral range of 1.1–1.6 μm. This work has been carried out in collaboration with J.-M. Baribeau and N.L. Rowell, National Research Council, Ottawa, Canada; L. Tsybeskov, New Jersey Institute of Technology, Newark, USA; and I. Berbezier, Institut Matériaux Microélectronique Nanosciences de Provence, Marseille, France.

Tailoring the optical constants in single-crystal silicon with embedded silver nanostructures for advanced silicon photonics applications

Plasmonic effects associated with metal nanostructures are expected to hold the key to tailoring light emission/propagation and harvesting solar energy in materials including single crystal silicon which remains the backbone in the microelectronics and photovoltaics industries but unfortunately, lacks many functionalities needed for construction of advanced photonic and optoelectronics devices. Currently, silicon plasmonic structures are practically possible only in the configuration with metal nanoparticles or thin film arrays on a silicon surface. This does not enable one to exploit the full potential of plasmonics for optical engineering in silicon, because the plasmonic effects are dominant over a length of ∼50 nm, and the active device region typically lies below the surface much beyond this range. Here, we report on a novel method for the formation of silver nanoparticles embedded within a silicon crystal through metal gettering from a silver thin film deposited at the surface to nanocavities within the Si created by hydrogen ion implantation. The refractive index of the Ag-nanostructured layer is found to be 3–10% lower or higher than that of silicon for wavelengths below or beyond ∼815–900 nm, respectively. Around this wavelength range, the optical extinction values increase by a factor of 10–100 as opposed to the pure silicon case. Increasing the amount of gettered silver leads to an increased extinction as well as a redshift in wavelength position for the resonance. This resonance is attributed to the surface plasmon excitation of the resultant silver nanoparticles in silicon. Additionally, we show that the profiles for optical constants in silicon can be tailored by varying the position and number of nanocavity layers. Such silicon crystals with embedded metal nanostructures would offer novel functional base structures for applications in silicon photonics, optoelectronics, photovoltaics, and plasmonics.

Narrow band wavelength selective filter using grating assisted single ring resonator

This paper illustrates a filter configuration which uses a single ring resonator of larger radius connected to a grating resonator at its drop port to achieve single wavelength selectivity and switching property with spectral features suitable for on-chip wavelength selection applications. The proposed configuration is expected to find applications in silicon photonics devices such as, on-chip external cavity lasers and multi analytic label-free biosensors. The grating resonator has been designed for a high Q-factor, high transmittivity, and minimum loss so that the wavelength selectivity of the device is improved. The proof-of-concept device has been demonstrated on a Silicon-on-Insulator (SOI) platform through electron beam lithography and Reactive Ion Etching (RIE) process. The transmission spectrum shows narrow band single wavelength selection and switching property with a high Free Spectral Range (FSR) ~60 nm and side band rejection ratio >15 dB.

Determination of the free carrier concentration in atomic-layer doped germanium thin films by infrared spectroscopy

Novel silicon photonics applications requiring heavy n-type doping have recently driven a great deal of interest towards the phosphorous doping of germanium. In this work we report on infrared reflectance spectroscopy measurements of the electron density in heavily n-type doped germanium layers obtained by stacking multiple phosphorous δ-layers. Here, we demonstrate that the conventional Drude model of the electrodynamic response of free carriers in metals can be adapted to describe heavily doped semiconductor thin films. Consequently, the effect of the electron density on the plasma frequency, scattering rate and complex permittivity can be investigated.

Strain dependence of the nonlinear optical properties of strained Si nanoparticles.

We report on the lattice strain dependence of the nonlinear optical (NLO) parameters of strained Si nanoparticles (NPs), which are prepared in a controlled way by a mechanical ball milling process. X-ray diffraction analysis shows that the nature of strain is compressive and is primarily caused by milling-induced lattice dislocations, which is further supported by high-resolution transmission electron microscopy imaging. It is found that the nonlinear refractive index (n₂) and nonlinear absorption coefficient (β) are strongly influenced by the associated lattice strain present in Si NPs. With the increase of lattice strain, the β gradually decreases while n₂ increases slowly. The strain-dependent observed changes in the NLO parameters of Si NPs are found to be advantageous for application purpose, and it is explained on the basis of strain-induced modification in the electronic structure of the highest occupied molecular orbital and lowest unoccupied molecular orbital states of Si NPs. These results demonstrate the potential of strain-dependent enhancement of nonlinearities for silicon photonics applications.