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We describe the performance of high bandwidth-density silicon photonic based integrated circuits (SiPh ICs) that enable the first fully functional photonic engine (PE) module co-packaged with an Ethernet switch. We demonstrate the 1.6 Tbps SiPh transmitter (Tx) IC that integrates on-die all the lasers, micro ring modulators, monitor photodetectors, spot size converters, and V-grooves that are needed to support sixteen 106.25 Gbps PAM4 optical transmit channels. This SiPh Tx, together with discrete receiver (Rx) SiPh ICs, enabled an 800 Gbps PE. The PE is designed to allow up to sixteen modules to be co-packaged around a high-bandwidth switch ASIC. The PE test results described in this article were obtained using sixteen 53.125 Gbps electrical channels that were multiplexed to drive eight simultaneously operating 106.25 Gbps optical channels. We report DR4 IEEE standards compliant high-speed optical eye performance as well as full link operation. Post-FEC error-free operation over temperature and over extended time duration is demonstrated on all channels.

Data center IP traffic is doubling every 2.5 years, driving the need to scale connectivity bandwidth on a similar cadence. At higher data rates the electrical link reach shrinks but energy efficiency does not improve significantly. Co-packaging optics close to ASICs enables data throughput scaling by reducing the SERDES power and hence overall power due to shorter electrical channels. Despite the advantages, co-packaging optics next to electronics can be challenging. This paper reviews Intel’s advancements in demonstrating industry’s first fully operational Silicon Photonic integrated circuit co-packaged with switch ASICs, describing in detail component level, integrated photonic integrated circuit (PIC) level, and transceiver module level design and performance.

We demonstrate a silicon micro-ring modulator supporting 128 Gb/s NRZ modulation with SNR=5.2, ER=3.8dB, 0.8 Vpp drive swing, and 5.3 fJ/bit power consumption. We have also achieved 192 Gb/s PAM-4 modulation with TDECQ of 2.5dB.

We present performance of 1.6 Tbps silicon photonic integrated circuits (SiPICs) and their key device components. These high bandwidth density SiPICs enabled fully functional photonic engines (PEs) that can be co-packaged with Ethernet switches and demonstrated IEEE standards compliant interop-link with 400 Gbps DR4 modules.

We demonstrate 1.6Tbps Silicon Photonic Integrated Circuit (SiPIC) meeting co-packaged optics requirements for network switch applications. The SiPIC has sixteen 106Gbps PAM4 optical channels, including lasers, modulators and V-grooves. Post-FEC error-free operation over temperature is demonstrated.

We demonstrate a III-V/silicon hybrid external cavity laser with a tuning range larger than 60 nm at the C-band on a silicon-on-insulator platform. A III-V semiconductor gain chip is hybridized into the silicon chip by edge-coupling the silicon chip through a Si3N4 spot size converter. The demonstrated packaging method requires only passive alignment and is thus suitable for high-volume production. The laser has a largest output power of 11 mW with a maximum wall-plug efficiency of 4.2%, tunability of 60 nm (more than covering the C-band), and a side-mode suppression ratio of 55 dB (>46 dB across the C-band). The lowest measured linewidth is 37 kHz ( 250 Gb/s coherent optical transmission using a silicon micro-ring-based tunable laser.

We demonstrate an all-silicon-photonic coherent link, including a hybrid tunable laser with 45dB SMSR, and

We have investigated the correlated surface electronic and optical properties of [0001]-oriented epitaxial InN nanowires grown directly on silicon. By dramatically improving the epitaxial growth process, we have achieved, for the first time, intrinsic InN both within the bulk and at nonpolar InN surfaces. The near-surface Fermi-level was measured to be ∼0.55 eV above the valence band maximum for undoped InN nanowires, suggesting the absence of surface electron accumulation and Fermi-level pinning. This result is in direct contrast to the problematic degenerate two-dimensional electron gas universally observed on grown surfaces of n-type degenerate InN. We have further demonstrated that the surface charge properties of InN nanowires, including the formation of two-dimensional electron gas and the optical emission characteristics can be precisely tuned through controlled n-type doping. At relatively high doping levels in this study, the near-surface Fermi-level was found to be pinned at ∼0.95-1.3 eV above the valence band maximum. Through these trends, well captured by the effective mass and ab initio materials modeling, we have unambiguously identified the definitive role of surface doping in tuning the surface charge properties of InN.

Full-color, catalyst-free InGaN/GaN dot-in-a-wire light-emitting diodes (LEDs) were monolithically grown on Si(111) by molecular beam epitaxy, with the emission characteristics controlled by the dot properties in a single epitaxial growth step. With the use of p-type modulation doping in the dot-in-a-wire heterostructures, we have demonstrated the most efficient phosphor-free white LEDs ever reported, which exhibit an internal quantum efficiency of ∼56.8%, nearly unaltered CIE chromaticity coordinates with increasing injection current, and virtually zero efficiency droop at current densities up to ∼640 A/cm(2). The remarkable performance is attributed to the superior three-dimensional carrier confinement provided by the electronically coupled dot-in-a-wire heterostructures, the nearly defect- and strain-free GaN nanowires, and the significantly enhanced hole transport due to the p-type modulation doping.

The thermal dynamic behaviors of terahertz quantum cascade lasers are investigated using a spectrally matching terahertz quantum-well photodetector. The THz output power of a lasing device under a pulse excitation is found to decrease with time, which is attributed to the increase of active-region temperature. The measurements show that the duration of output lasing pulse ranges from a few microseconds up to 77 ?s, depending on device bias and heat-sink temperature. A theoretical analysis based on a two-dimensional heat diffusion model is presented. The model calculates lasing quenching time based on an ?average active-region temperature? criterion as well as a ?reserve of gain? criterion. The best fit for quenching time is found when the vertical thermal conductivity in the quantum well region is two orders of magnitude lower than that of substrate. The measured lasing quenching time is in very good agreement with theoretical modeling calculated using both criteria.

This paper investigates the heat conduction behavior of a terahertz (THz) quantum-cascade laser (QCL) active region by measuring its temperature using in-situ microprobe band-to-band photoluminescence (PL) technique. The heat resistance of different regions in QCL structure is derived from the temperature measurement. Experimental results show that thinning the substrate from 300 mum thick to 140 mum lowers thermal resistance of the device by 21%, which helps achieving continuous-wave operation. A thermodynamic differential equation was numerically solved and the temperature profiles and thermal behavior of various regions within actively biased QCL devices under various conditions were obtained. The simulation confirms the measured results that the substrate accounts for 59% of the total device thermal resistance.

Far-fleld beam pattern measurement results of in-house fabricated 1mm long THz QCLs with ridge widths of 30"m and 100"m are presented. Both devices show difiractive-like beam patterns in the elevation direction (perpendicular to semiconductor heterojunction plane). In the in-plane direction (parallel to semiconductor heterojunction plane), the device with a wider ridge width (100"m) shows a quasi-Gaussian-like beam proflle. A radio-frequency (RF) design simulator (HFSS) is deployed to simulate far-fleld beam pattern of the QCL devices. The simulation results are in good agreement with the experimental results.

In this article we discuss the impact of channel length scaling on the above threshold current characteristics of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs). MEDICI simulation results of the interface surface potential show a lowering of the potential barrier for shorter channel lengths. This suggests a decrease in threshold voltage and increase in subthreshold slope with drain voltage particularly in submicron channel lengths, causing a nonsaturating output current. Simulation results of the above threshold current-voltage characteristics for short channel TFTs corroborate with measurement data of fabricated devices.

This article reports the design of vertical thin film transistors (VTFTs) in hydrogenated amorphous silicon (a-Si:H) technology. This transistor structure offers an elegant method of defining the channel length in nanoscale dimensions by means of dielectric film thickness. In addition, the device area of the vertical TFT structure is less than ∼1∕3 that of the ubiquitous lateral TFT structure. We study the deposition mechanisms to gain insight into the fabrication of VTFTs from a conceptual standpoint. The a-Si:H VTFT reported here advances current state of the art, by demonstrating the first 100nm channel length VTFT with an on/off current ratio of 108, threshold voltage of 2.8V, and a subthreshold slope of 0.8V∕decade. This is the shortest and truly vertical channel a-Si:H TFT reported, hitherto. We propose an application of a-Si:H VTFTs in high-resolution flat-panel electronics with TFT size independent fill factor, promising immense benefits in medical x-ray imaging.

Based on the mathematical similarity of the Schrodinger and Helmholtz equations, the tight-binding method has been employed for solving optical waveguide problems, in a manner similar to the methods commonly used in solid-state physics. The solutions (TE mode electric field waveforms and propagation constants) of a single dielectric slab waveguide are considered to be known, and tight-binding is used to compute the propagation constants of several multi-waveguide structures. Analytical solutions are derived for linear and circular arrays of adjacent waveguides. The problem of two similar adjacent waveguides is treated in detail for two cases of similar and different propagation constants of the two waveguides. For this case, the proposed method is verified using the beam propagation method (BPM). Optical band formation and effect of introducing defects is also illustrated by further examples.

Using a model reduction method, a formula for the ideality factor of a pn junction as a function of the diffusion and generation terms of its reverse current is derived. Using this formula a method for separate computation of these two currents for a pn junction is presented. The validity of the method is investigated using computer simulations for an assumed diode with known ideality factor and total leakage current. Experimental results for two commercially available diodes validate the proposed technique.

We report planar integration of tapered terahertz (THz) frequency quantum cascade lasers (QCLs) with metasurface waveguides that are designed to be spoof surface plasmon (SSP) out-couplers by introducing periodically arranged SSP scatterers. The resulting surface-emitting THz beam profile is highly collimated with a divergence as narrow as ~4° × 10°, which indicates a good waveguiding property of the metasurface waveguide. In addition, the low background THz power implies a high coupling efficiency for the THz radiation from the laser cavity to the metasurface structure. Furthermore, since all the structures are in-plane, this scheme provides a promising platform where well-established surface plasmon/metasurface techniques can be employed to engineer the emitted beam of THz QCLs controllably and flexibly. More importantly, an integrated active THz photonic circuit for sensing and communication applications could be constructed by incorporating other optoelectronic devices such as Schottky diode THz mixers, and graphene modulators and photodetectors. Published version

Advanced data centers require high throughput I/O processing for servers and storage devices connectivity. Silicon photonics technology offering low-cost, low-power, and high-performance is a promising solution for interconnection applications. In this talk, we will review the latest progress of the highly integrated Silicon photonics devices for 4×25 Gb/s active optical cables and transceivers. This includes hybrid lasers, WDM multiplexers, electro-absorption modulators, and germanium detectors.

This paper reports an experimental study of the effects of different metal claddings on the performance of terahertz quantum cascade lasers. The experimental results show that by using a metal cladding made of Ta/Cu/Au to replace that of Pd/Ge/Ti/Pt/Au, the maximum lasing temperature of the devices is increased from 132 to 172 K, and the threshold current density of the devices at 10 K can be reduced from 0.74 to 0.68 kA cm−2. The improvement of the device performance is attributed to lower optical losses associated with the metal cladding layers. The different effects of the metal contacts on device optical properties and electrical properties are also discussed.

A rate equation model is presented to analyze the performance of terahertz quantum cascade lasers based on consecutive phonon-photon-phonon emissions. Devices lased up to 128.5, 138, and 144 K at 2.5, 3.2 and 2.6 THz, respectively. © Optical Society of America., CLEO: QELS_Fundamental Science, CLEO:QELS FS 2013, 9 June 2013 through 14 June 2013, San Jose, CA

We designed and demonstrated a terahertz quantum cascade laser based on indirect pump injection to the upper lasing state and phonon scattering extraction from the lower lasing state. By employing a rate equation formalism and a genetic algorithm, an optimized active region design with four-well GaAs/Al0.25Ga0.75As cascade module was obtained and epitaxially grown. A figure of merit which is defined as the ratio of modal gain versus injection current was maximized at 150 K. A fabricated device with a Au metal-metal waveguide and a top n(+) GaAs contact layer lased at 2.4 THz up to 128.5 K, while another one without the top n(+) GaAs lased up to 152.5 K (1.3 (h) over bar omega/k(B)). The experimental results have been analyzed with rate equation and nonequilibrium Green's function models. A high population inversion is achieved at high temperature using a small oscillator strength of 0.28, while its combination with the low injection coupling strength of 0.85 meV results in a low current. The carefully engineered wavefunctions enhance the quantum efficiency of the device and therefore improve the output optical power even with an unusually low injection coupling strength. (C) 2013 AIP Publishing LLC.

We experimentally investigated the effect of oscillator strength (radiative transition diagonality) on the performance of resonant phonon-based terahertz quantum cascade lasers that have been optimized using a simplified density matrix formalism. Our results show that the maximum lasing temperature (Tmax) is roughly independent of laser transition diagonality within the lasing frequency range of the devices under test (3.2‐3.7THz) when cavity loss is kept low. Furthermore, the threshold current can be lowered by employing more diagonal transition designs, which can effectively suppress parasitic leakage caused by intermediate resonance between the injection and the downstream extraction levels. Nevertheless, the current carrying capacity through the designed lasing channel in more diagonal designs may sacrifice even more, leading to electrical instability and, potentially, complete inhibition of the device’s lasing operation. We propose a hypothesis based on electric-field domain formation and competition/switching of different current-carrying channels to explain observed electrical instability in devices with lower oscillator strengths. The study indicates that not only should designers maximize Tmax during device optimization but also they should always consider the risk of electrical instability in device operation. V C 2013 American

We measured the lattice and subband electronic temperatures of terahertz quantum cascade devices based on the optical phonon-scattering assisted active region scheme. While the electronic temperature of the injector state (j = 4) significantly increases by Delta T = T-e(4) - T-L similar to 40 K, in analogy with the reported values in resonant phonon scheme (Delta T similar to 70-110 K), both the laser levels (j = 2,3) remain much colder with respect to the latter (by a factor of 3-5) and share the same electronic temperature of the ground level (j = 1). The electronic population ratio n(2)/n(1) shows that the optical phonon scattering efficiently depopulates the lower laser level (j = 2) up to an electronic temperature T-e similar to 180 K.

We report on the experimental measurement of active region lattice (T L) and electronic temperatures (T e) in terahertz quantum cascade devices based on the phonon-photon-phonon scheme, by means of microprobe band-to-band photoluminescence spectroscopy. Three mesa devices, differing for doping region and number of quantum wells composing the active region, have been investigated. With device on, under band alignment for lasing condition, we measured a difference (Te - TL) ∼ 40 K much smaller than the typical value (Te - TL ∼ 100 K) reported for resonantphonon THz QCLs. © 2013 SPIE., Quantum Sensing and Nanophotonic Devices X, February 3-7, 2013, San Francisco, CA, USA, Series: Proceedings of SPIE

A new temperature performance record of 199.5 K for terahertz quantum cascade lasers is achieved by optimizing the lasing transition oscillator strength of the resonant phonon based three-well design. The optimum oscillator strength of 0.58 was found to be larger than that of the previous record (0.41) by Kumar et al. [Appl. Phys. Lett. 94, 131105 (2009)]. The choice of tunneling barrier thicknesses was determined with a simplified density matrix model, which converged towards higher tunneling coupling strengths than previously explored and nearly perfect alignment of the states across the injection and extraction barriers at the design electric field. At 8 K, the device showed a threshold current density of 1 kA/cm2, with a peak output power of ∼ 38 mW, and lasing frequency blue-shifting from 2.6 THz to 2.85 THz with increasing bias. The wavelength blue-shifted to 3.22 THz closer to the maximum operating temperature of 199.5 K, which corresponds to ∼ 1.28¯hω/κB. The voltage dependence of laser frequency is related to the Stark effect of two intersubband transitions and is compared with the simulated gain spectra obtained by a Monte Carlo approach.

Vertically aligned InGaN/GaN nanorod light emitting diode (LED) arrays were created from planar LED structures using a new top-down fabrication technique consisting of a plasma etch followed by an anisotropic wet etch. The wet etch results in straight, smooth, well-faceted nanorods with controllable diameters and removes the plasma etch damage. 94% of the nanorod LEDs are dislocation-free and a reduced quantum confined Stark effect is observed due to reduced piezoelectric fields. Despite these advantages, the IQE of the nanorod LEDs measured by photoluminescence is comparable to the planar LED, perhaps due to inefficient thermal transport and enhanced nonradiative surface recombination.

A novel terahertz quantum cascade laser, based on consecutive phonon-photon-phonon emissions, is proposed. The design procedure used a density matrix based figure-of-merit and a generic algorithm approach; the fabricated device lased up to 138 K. © 2012 OSA., 2012 Conference on Lasers and Electro-Optics, CLEO 2012, 6 May 2012 through 11 May 2012, San Jose, CA

We report on the achievement of a new class of nanowire light emitting diodes (LEDs), incorporating InGaN/GaN dot-in-a-wire nanoscale heterostructures grown directly on Si(111) substrates. Strong emission across nearly the entire visible wavelength range can be realized by varying the dot composition. Moreover, we have demonstrated phosphor-free white LEDs by controlling the indium content in the dots in a single epitaxial growth step. Such devices can exhibit relatively high internal quantum efficiency (>20%) and no apparent efficiency droop for current densities up to ~ 200?A?cm ? 2.

We report on the achievement of a record high internal quantum efficiency in InGaN/GaN dot-in-a-wire light emitting diodes by significantly reducing the electron overflow and enhancing the hole transport in the device active regions.

International audience; We report on the resonant detection of a 3.1 THz radiation produced by a quantum cascade laser using a 250 nm gate length GaAs/AlGaAs field effect transistor at liquid nitrogen temperature. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is enhanced by increasing the drain current and driving the transistor into saturation regime. These results clearly show that plasma wave nanometer-size transistors can be used as detectors in all-solid-state terahertz systems where quantum cascade lasers act as sources.

The density matrix based model is employed to design number of THz quantum cascade lasers with various laser transition oscillator strengths. The optimum oscillator strength varies between 0.35 and 0.47. Experimental results verify the theoretical predictions. © 2011 OSA., 2011 Conference on Lasers and Electro-Optics, CLEO 2011, 1 May 2011 through 6 May 2011, Baltimore, MD

A simplified density-matrix model describing the population and coherence terms of four states in a resonant phonon scattering based terahertz quantum cascade laser is presented. Despite its obvious limitations and with two phenomenological terms---called the pure dephasing time constants in tunneling and intersubband transition---the model agrees reasonably well with experimental data. We demonstrate the importance of a tunneling leakage channel from the upper lasing state to the excited state of the downstream phonon well. In addition, we identify an indirect coupling between nonadjacent injector and extractor states. The analytical expression of the gain spectrum demonstrates the strong broadening effect of the injection and extraction couplings. The gain is decomposed into three terms: a linear gain and two nonlinear components related to stimulated anti-Stokes scattering processes. The nonlinear gain is not negligible at high temperature. Under certain approximations, analytical forms of population and coherence terms are derived. This model is well suited for structures with only a few states involved. This model can simplify the optimization process for new laser designs; it is also convenient for experimentalists to adopt.

The design and fabrication of a bi-modal semi-insulating surface-plasmon waveguide for a quantum cascade laser emitting at 3.75 THz is presented. Different transverse modes are excited under different electric current injection due to their different overlapping with the laterally nonuniform gain profile in the active region. HFSS and COMSOL program are used to simulate the near/far field and waveguide loss for various waveguide structures, respectively. It is found that a 150 µm wide surface-plasmon waveguide allows either co-excitation or selective excitation of the first two transverse modes. The total optical loss (i.e., the combination of waveguide and mirror loss) is found below 20 cm−1. An electrically controllable dynamic beam pattern steering is predicted. The near field and far field measurements of a fabricated quantum cascade laser device confirm the theoretical results. The dynamic switching of far-field beam pattern by an angle of 25° is observed when the injected current density changes from 1.9 kA/cm2 to 2.3 kA/cm2.

We report a hybrid organic-inorganic optical upconverter with an embedded metal mirror. The device was fabricated through direct tandem integration of an organic light emitting diode (OLED) with an inorganic InGaAs/InP photodetector, converting 1.5 μm infrared light to visible light. It was found that the device with an embedded mirror exhibited a low turn-on voltage (∼3.2 V) and an enhanced efficiency. The ratio of photocurrent-induced with an input power density of 0.67 mW/mm2 versus dark-current-induced visible light was over 500 at a device bias of 6 V at room temperature. The results show that the embedded mirror at the inorganic-organic interface plays a vital role in the performance enhancement of a hybrid upconverter. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The active region temperature of THz quantum cascade lasers during continuous-wave operation was measured using interband photoluminescence technique. The active region was found to be ~40 K above heat sink temperature at maximum THz power output.

The optical performance of top-down etched InGaN/GaN nanorod light emitting diodes (LEDs) was studied using temperature variable photoluminescence spectroscopy with a 405 nm pump laser. Efficiency droop is measured from such nanorod structures, which is further enhanced with decreasing temperature. Through detailed rate equation analysis of the temperature-dependent carrier distribution and modeling of the quantum efficiency, this unique phenomenon can be largely explained by the interplay and dynamics between carrier radiative recombination in localized states and nonradiative recombination via surface states/defects.

In this work, photoluminescence and micro-Raman scattering experiments were performed on undoped InN nanowires. It was found that, besides the main photoluminescence peak, a clear phonon sideband emission peak, with an extremely narrow linewidth ~9 meV, was measured. The phonon spectrum revealed by micro-Raman scattering indicates only uncoupled LO phonons are involved in such phonon sideband emission. The clearly resolved phonon sideband emission peak with a narrow linewidth, together with the uncoupled LO phonon modes, suggests the superior quality of the presented InN nanowires, i.e., extremely low residual electron density and the absence of surface electron accumulation, which is consistent with the physical properties of intrinsic InN nanowires as in the previous studies. The detailed phonon sideband properties are also discussed in the text.

We report the design and characterization of external-cavity DBR lasers built with a III-V-semiconductor reflective-SOA with spot-size converter edge-coupled to SOI waveguides containing Bragg grating mirrors. The un-cooled lasers have wall-plug-efficiencies of up to 9.5% at powers of 6 mW. The lasers are suitable for making power efficient, hybrid WDM transmitters in a CMOS-compatible SOI optical platform.

We report on the achievement of, for the first time, InN/InGaN core/shell nanowire heterostructures, which are grown directly on Si(111) substrates by plasma-assisted molecular beam epitaxy. The crystalline quality of the heterostructures is confirmed by transmission electron microscopy, and the elemental mapping through energy dispersive x-ray spectrometry further reveals the presence of an InGaN shell covering the sidewall and top regions of the InN core. The optical characterizations reveal two emission peaks centered at ∼1685 nm and 1845 nm at 5 K, which are related to the emission from the InGaN shell and InN core, respectively. The InN/InGaN core/shell nanoscale heterostructures exhibit a very high internal quantum efficiency of ∼62% at room temperature, which is attributed to the strong carrier confinement provided by the InGaN shell as well as the nearly intrinsic InN core.

The design and fabrication of a high power THz quantum cascade laser (QCL), with electrically controllable transverse mode is presented. The switching of the beam pattern results in dynamic beam switching using a symmetric side current injection scheme. The angular-resolved L-I curves measurements, near-field and far-field patterns and angular-resolved lasing spectra are presented. The measurement results confirm that the quasi-TM(01) transverse mode lases first and dominates the lasing operation at lower current injection, while the quasi-TM(00) mode lases at a higher threshold current density and becomes dominant at high current injection. The near-field and far-field measurements confirm that the lasing THz beam is maneuvered by 25 degrees in emission angle, when the current density changes from 1.9 kA/cm(2) to 2.3 kA/cm(2). A two-dimension (2D) current and mode calculation provides a simple model to explain the behavior of each mode under different bias conditions.

We report a hybrid organic-inorganic optical upconverter with an embedded mirror, which converts 1.5μm infrared light to visible light. The device was fabricated through direct tandem integration of an organic light-emitting diode with an inorganic InGaAs∕InP photodetector. It was found that the device with an embedded mirror exhibited a low turn-on voltage (∼3.2V) and an enhanced efficiency. The ratio of photocurrent-induced light with an input power density of 0.67mW∕mm2 versus dark-current-induced visible light was over 500 at a device bias of 6V at room temperature. The results show that the embedded mirror at the inorganic-organic interface plays a vital role in the performance enhancement of a hybrid upconverter.