This PDF file contains the front matter associated with SPIE Proceedings Volume 8629, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

This paper outlines the challenges and benefits of applying silicon-based photonic techniques in the 2 to 5 μm midinfrared (MIR) wavelength range for chem.-bio-physical sensing, medical diagnostics, industrial process control, environmental monitoring, secure communications, Ladar, active imaging, and high-speed communications at 2 μm. Onchip passive and active components, mostly waveguided, will enable opto-electronic CMOS or BiCMOS integrated “circuits” for system-on-a-chip applications such as spectroscopy and lab-on-a-chip. Volume manufacture in a silicon foundry is expected to yield low-cost (or even disposable) chips with benefits in size-weight-power and ruggedness. This is “long-wavelength optoelectronic integration on silicon” which we call LIOS. Room temperature operation appears feasible, albeit with performance compromises at 4 to 5 μm. In addition to the electronics layer (which may include RF wireless), a 3-D LIOS chip can include several inter-communicating layers utilizing the photonic, plasmonic, photoniccrystal and opto-electro-mechanical technologies. The LIOS challenge can be met by (1) discovering new physics, (2) employing “new” IV and III-V alloys, (3) scaling-up and modifying telecom components, and (4) applying nonlinearoptical wavelength conversion in some cases. This paper presents proposals for MIR chip spectrometers employing frequency-comb and Ge blackbody sources. Active heterostructures employing Si, Ge, SiGe, GeSn and SiGeSn are key for laser diodes, photodetectors, LEDs, switches, amplifiers, and modulators that provide totally monolithic foundry integration, while numerous III-V semiconductor MIR devices within the InGaAsSb and InGaAsP families offer practical hybrid integration on Si PICs. Interband cascade and quantum cascade lasers on Ge waveguides are important in this context.

Silicon photonics using waveguide- and microresonator-based devices are finding technologically important applications in the field of optofluidics. By integrating microfluidic channels on top of silicon-based planar devices, silicon photonic devices can function as on-chip optical tweezers to manipulate micro/nanoparticles. In this paper, we will highlight our recent progress in the field of optofluidics using silicon nitride devices for on-chip optical manipulation including the experimental demonstrations of: (i) planar optical tweezers using waveguide junctions with and without tapers, (ii) microparticle buffering and dropping on microring resonator devices upon linearly polarized light and (iii) microparticle trapping and assembling on circular microdisk resonators. Such devices can function as basic building blocks for “optical tweezers circuits” in lab-on-chip applications.

In this paper, two recent advances in silicon ring resonator biosensors are presented. First, we address the problem that due to the high index contrast, small deviations from perfect symmetry lift the degeneracy of the normal resonator mode. This severely deteriorates the quality of the output signal. To address this, we discuss an integrated interferometric approach to give access to the unsplit, high-quality normal modes of the microring resonator. Second, we demonstrate how digital microfluidics can be used for effective fluid delivery to nanophotonic microring resonator sensors fully constructed in SOI.

Miniaturized bioanalytical devices find wide applications ranging from blood tests to environmental monitoring. Such devices in the form of hand held personal laboratories can transform point-of-care monitoring provided miniaturization, multianalyte detection and sensitivity issues are successfully resolved. Optical detection in biosensors is superior in many respects to other types of sensing based on alternative signal transduction techniques, especially when both sensitivity and label free detection is sought. The main drawback of optical biosensing transducers relates to the unresolved manufacturability issues encountered when attempting monolithic integration of the light source. If the mature silicon processing technology could be used to monolithically integrate optical components, including light emitting devices, into complete photonic sensors, then the lab on a chip concept would materialize into a robust and affordable way. Here, we describe and demonstrate a bioanalytical device consisting of a monolithic silicon optocoupler properly engineered as a planar interferometric microchip. The optical microchip monolithically integrates silicon light emitting diodes and detectors optically coupled through silicon nitride waveguides designed to form Mach-Zehnder interferometers. Label free detection of proteins is demonstrated down to pM sensitivities.

Optofluidic lasers combine the advantages of microfluidics and laser technology. Unlike traditional lasers, optofluidic lasers obtain the optical feedback from microfluidic channels with gain media (e.g., dyes) inside. Due to the small size of microfluidic channels, optofluidic lasers own the unique capabilities in terms of handling liquid of ρL~ μL volumes. Therefore, there is currently a great deal of interest in adapting optofluidic lasers for compact laser light sources and micro-total-analysis systems. Here, we use two examples to demonstrate the feasibility of using optofluidic lasers to sensitively detect DNA and protein. In the first example, the optofluidic laser is used to detect small conformational change in DNA Holliday junctions. The DNA Holliday junction has four branched double-helical arm structures, each of which is conjugated with Cy3 or Cy5 as the donor/acceptor pair. The conformational changes of the Holliday junction lead to the changes of fluorescence resonance energy transfer (FRET) between the donor and the acceptor. Using the optical feedback provided by the optofluidic laser, we are able to achieve nearly 100% wavelength switching. The FRET signal generated by the optofluidic laser is about 16 times more sensitive to DNA conformational changes than the conventional method. The second example is concerned with a fluorescent proteins laser. Green, yellow, and red optofluidic lasers based on fluorescent proteins are demonstrated, and the lasing threshold of 3 μmCitrine is only 1 μJ/mm². This work will potentially open a door to study protein-protein interactions via the sensitive intra-cavity laser detection method.

Silicon photonics is poised to revolutionize biosensing applications, specifically in medical diagnostics. Optical sensors can be designed to improve clinically-relevant diagnostic assays and be functionalized to capture and detect target biomarkers of interest. There are various approaches to designing these sensors - improving the devices' performance, increasing the interaction of light with the analyte, and matching the characteristics of the biomolecules by using architectures that complement the biosensing application. Using e-beam lithography and standard foundry processes, we have investigated Transverse Magnetic (TM) and Transverse Electric (TE) disk and ring resonators. TM devices hold the potential for higher sensitivity and large-particle sensing capabilities due to the increased penetration distance of light into the analyte. In addition, devices such as slot waveg­guide Bragg grating sensors have shown high sensitivities and high quality factors and may present advantages for specific biosensing applications. These devices have been investigated for wavelengths around λ=1550 nm (conventional wavelength window in fiber-optic communication) and λ=1220 nm, where the water absorption is greatly decreased, offering improved limits of detection. Using reversibly bonded PDMS microfluidic flow cells, the performance and bio-detection capabilities of these devices were characterized. Comparing binding performance across these devices will help validate architectures suitable for biological applications. The most promising sensors for each application will then be identified for further study and development. This paper will discuss the sensors' comparative advantages for different applications in biosensing and provide an outlook for future work in this field.

The giant birefringence of SOI nanowires makes ultra-compact polarization diversity components available for many applications, like polarization-transparent silicon photonics, coherent optical communications, and on-chip quantum photonics. Particularly, the ultrasmall footprint makes these components very attractive for realizing on-chip polarization handling used in the future large-scale photonic integrated circuits, e.g., photonic network on chip. In this paper, a review is given for our ultra-compact polarization diversity components including polarization-beam splitters and polarization rotators.

We present novel deeply etched functional components, fabricated by multi-step patterning in the frame of our 4 μm thick Silicon on Insulator (SOI) platform based on singlemode rib-waveguides and on the previously developed rib-tostrip converter. These novel components include Multi-Mode Interference (MMI) splitters with any desired splitting ratio, wavelength sensitive 50/50 splitters with pre-filtering capability, multi-stage Mach-Zehnder Interferometer (MZI) filters for suppression of Amplified Spontaneous Emission (ASE), and MMI resonator filters. These novel building blocks enable functionalities otherwise not achievable on our SOI platform, and make it possible to integrate optical RAM cell layouts, by resorting to our technology for hybrid integration of Semiconductor Optical Amplifiers (SOAs). Typical SOA-based RAM cell layouts require generic splitting ratios, which are not readily achievable by a single MMI splitter. We present here a novel solution to this problem, which is very compact and versatile and suits perfectly our technology. Another useful functional element when using SOAs is the pass-band filter to suppress ASE. We pursued two complimentary approaches: a suitable interleaved cascaded MZI filter, based on a novel suitably designed MMI coupler with pre-filtering capabilities, and a completely novel MMI resonator concept, to achieve larger free spectral ranges and narrower pass-band response. Simulation and design principles are presented and compared to preliminary experimental functional results, together with scaling rules and predictions of achievable RAM cell densities. When combined with our newly developed ultra-small light-turning concept, these new components are expected to pave the way for high integration density of RAM cells.

The minimum bending radius of optical waveguides is typically the most important parameter that defines the footprint and cost of a photonic integrated circuit. In optical fibers and in planar waveguides with equally large mode fields (~10 μm) the bending radii are typically in the cm-scale. The main advantage of using a high index waveguide core with a thickness below 1 μm is the ability to realise single-mode bends with bending radii of just a few micrometers. In this paper we review the dependence of the minimum bending radius on the size and shape of waveguides with the main emphasis on silicon-on-insulator (SOI) waveguides. Then we present simulation and measurement results from advanced waveguide bends and mirrors that have been integrated with 4-10 μm thick single-mode SOI waveguides. We show that multi-step patterning and novel designs allow the reduction of the bending radius by up to three orders of magnitude while also reducing the bending losses by approximately one order of magnitude when compared to traditional rib waveguide bends on 4 μm SOI. This allows to use the μm-scale SOI waveguides for making almost as compact photonic integrated circuits as those based on sub-μm SOI waveguides.

As the basic building block for photonic device integration, silicon nanophotonic waveguide requires low-loss propagation for high-performance ultra-compact photonic device. We experimentally study SiO₂ grown by two different methods (thermal oxidation and PECVD) as hard masks for Si nano-waveguides fabrication and study their effects on propagation loss. It was found that the denser and smoother quality of thermally grown SiO₂ will increase the etch selectivity of Si and reduce the line-edge roughness transferred to the Si nanowaveguide sidewall, hence giving a lower loss compared to having PECVD SiO₂ hard mask. With thermally grown SiO₂ as hard mask, the Si nano-waveguides loss can have a loss reduction as high as 5.5 times for a 650 nm wide nanowaveguide. Using thermally grown SiO2 as hard mask will allow the Si nano-waveguide to have as low a propagation loss as direct resist mask and enable III-V semiconductor on silicon via bonding for multifunctional photonic system on chip.

Front-end monolithic integration has enabled photonic devices to be fabricated in bulk and thin-SOI CMOS as well as DRAM electronics processes. Utilizing the CMOS generic process model, integration was accomplished on multi-project wafers that were shared by standard electronic customers without requiring in-foundry process changes. Simple die or wafer-level post-processing has enabled low-loss waveguides by the removal of the substrate within photonic regions. The custom-process model of the DRAM industry instead enabled optimization of the photonic device fabrication process and the potential elimination of post-processing requirements. Integrated singlecrystalline silicon waveguide loss of ~3 dB/cm has been achieved within a 45nm thin-SOI CMOS process that is currently used to manufacture microprocessors [1]. A fully monolithic photonic transmitter including a pseudo-random bit sequence (PRBS) generating digital backend was also demonstrated within this process [1]. The constraints of zero-change integration have limited achieved polysilicon waveguide loss to ~50 dB/cm with commercially available bulk CMOS processes [2]. Custom polysilicon deposition and processing conditions available for DRAM integration have also led to the demonstration of ~6 dB/cm loss waveguides suitable for integration within electronics processes utilizing bulk silicon starting substrates [3]. An overview of required process features, device design guidelines and integration methodology tradeoffs will be presented. Relevant device metrics of area and energy efficiency as well as achievable photonic device performance will be presented within the context of monolithic front-end integration within state-ofthe- art electronics processes. Applications of this research towards the implementation of a computer system utilizing photonic interconnect for core-to-memory communication will also be discussed.

Two layer vertical coupling photonic structures can be directly fabricated on a standard SOI wafer using a combination of reactive ion etching (RIE) and proton beam irradiation followed by electrochemical etching. The top layer structures are defined by RIE on the device layer, while the bottom layer structures are defined by proton beam irradiation on the substrate. Light coupling between the structures in the two layers has been demonstrated via vertical coupling waveguides. According to simulations, the coupling efficiency mainly depends on the thickness of the two layer structure and the gap between them. In this process, the thickness of the top layer structures is fixed by the device layer thickness of the SOI wafer, which is typically 200-300 nm. The gap depends on the thickness of the oxide layer of the SOI wafer, and it can be shifted due to the natural bending of the top layer structures. The bottom layer structure thickness can vary due to different energies of proton beam. Furthermore we show the fabrication of tapered bottom waveguides, which are thin at the coupling region for higher coupling efficiency, and thick at the end for easily coupling light from an optical fiber or a focused lens.

The distributed Bragg reflector (DBR) plays a major role in integrated optics. Because of the recent advances of silicon photonics and CMOS electronics in SOI platform, various types of DBR structures are being investigated for integrated optical couplers, filters, (de-)multiplexers, interleavers, Fabry-Perot micro-cavities, laser sources, etc. The first order diffraction gratings in SOI waveguide requires surface relief gratings of period Λ = 225 nm for a DBR response at Λ = 1550 nm. Fabrication of such sub-micron gratings with a uniform period over a length of several mm is really a challenging issue. Here we report the realization of an eleventh order Bragg grating (Λ = 2.6 μm, λ_B ~ 1564 nm, L = 2.62 mm) on the surface of single-mode rib waveguides. The DBRs and waveguide structures were defined by conventional photolithography and subsequent reactive ion etching processes. The waveguide end-facets were polished suitably before they were taken for characterizations using a tunable laser source (tunability 10 pm) in our free-space waveguide coupling set-up. The characterization results of the fabricated DBRs showed a reflectivity R = 88.32% and FWHM = 2.43 nm. Higher reflectivity and narrower grating response can be achieved by further increasing the grating length. The waveguide loss has been increased (~ 0.5 dB/mm) because of the enhanced surface roughness during the RIE process for grating fabrication. It can be reduced if conventional RIE is replaced by ICP RIE.

The availability of low loss waveguide bends in photonic crystal structures makes possible numerous integrated optic devices. The method proposed in this presentation consists of introducing a dielectric shift equivalent to a sheer displacement along a segment of the photonic crystal waveguide and results in a double bent waveguide. The degree of sheer determines the waveguide deflection angle. Theoretical analysis is performed using FDTD and PWM and predicts low loss bends. Experiments are performed in the microwave regime using an array of alumina rods in air over the 2 to 14 GHz range and confirm theoretical predictions.

In this paper we present silicon photonics devices designed for the 3-4μm wavelength region including waveguides, MMIs, ring resonators and Mach-Zehnder interferometers. The devices are based on silicon on insulator (SOI) platform. We show that 400-500 nm high silicon waveguides can have propagation losses as low as ~ 4 dB/cm at 3.8μm. We also demonstrate MMIs with insertion loss of 0.25 dB, high extinction ratio asymmetric Mach-Zehnder interferometers, and SOI ring resonators. This combined with our previous results reported at 3.4μm confirm that SOI is a viable platform for the 3-4 μm region and that low loss mid-infrared passive devices can be realized on it.

The optical properties of a nanoscale silicon slot-waveguide has been rigorously studied by using a full vectorial H-field finite element method (VFEM) based approach and presented in this paper. The variations of effective indices, effective areas, power densities in the slot-region and the confinement factors of the slot waveguide, with both horizontal and vertical slots, are thoroughly investigated for quasi-TM and TE modes. The full vectorial magnetic and electric field profiles, and Poynting vector (S^z) are also presented.

This paper explores issues associated with Photonic Integrated Circuit (PIC) research and development – with an overall goal of initiating a discussion of how PIC technology should develop and eventually be deployed with high impact. Significant research and development programs have focused on PICs for routing and switching, and computer interconnects. Most recently, the application domain of PICs has diversified greatly, and now includes analog signal processing, remote sensing, biological and chemical sensing, neural interfacing, and solar cells. A key feature of PIC technology growth has been the exploitation of high-density fabrication and packaging technology originally developed for the Silicon IC industry. PIC foundry services are emerging – and there has been a natural attempt to ascribe a “Moore’s Law” to PIC scaling. Analogies to Silicon electronic scaling, however, should be used with caution. PIC complexity scaling may be driven more by the ability to access the degrees-of-freedom offered by PIC-based optical domain signal processing, rather than increasing device count. Specific examples of PIC research in chip-scale computer interconnects and integrated micro-concentrators for solar cells are highlighted.

We present our recent work on integrated silicon photonic devices for optical filter and delay applications. A microdisk resonator integrated with interleaved p-n junctions is demonstrated. The resonance can be both blue- and red-shifted by applying a forward current or a negative voltage, respectively. A MZI-nested microring resonator is shown capable of coupling tuning, enabled by a p-i-p junction based thermal heater across the waveguide. We also investigate cascaded self-coupled optical waveguide (SCOW) resonators. Electromagnetically-induced transparency (EIT)-like resonances are generated featuring a narrow lineshape and a high group delay. Finally, we present an athermal lattice filter made up of 10 cascaded Mach-Zehnder interferometer (MZI) units and show that the temperature sensitivity can be considerably reduced.

The insertion of high dielectric rods in the low dielectric region of photonics crystal enables the optical properties to be reconfigurable. We show that for a square array of holes, the inserted rods define the waveguide region, wavelength of operation and functionality of the photonic crystal device (directional coupler presented). Also are examined the modification of the resonator state’s wavelength and field profile when rods are introduced in the central region of two types of quasi-crystals. Based on these results more elaborate reconfigurable devices can be derived.

Electro-optic modulators have been identified as the key drivers for optical communication. With an ongoing miniaturization of photonic circuitries, an outstanding aim is to demonstrate an on-chip, ultra-compact, electro-optic modulator without sacrificing bandwidth and modulation strength. While silicon-based electro-optic modulators have been demonstrated, they require large device footprints of the order of millimeters as a result of weak non-linear electro-optical properties. The modulation strength can be increased by deploying a high-Q resonator, however with the trade-off of significantly sacrificing bandwidth. Furthermore, design challenges and temperature tuning limit the deployment of such resonance-based modulators. Recently, novel materials like Graphene have been investigated for electro-optic modulation applications with a 0.1 dB per micrometer modulation strength, while showing an improvement over pure silicon devices, this design still requires devices lengths of tens of micrometers due to the inefficient overlap between the Graphene layer and the optical mode of the silicon waveguide. Here we experimentally demonstrate an ultra-compact, Silicon-based, electro-optic modulator with a record-high 1dB per micrometer extinction ratio over a wide bandwidth range of 500 nm in ambient conditions. The device is based on a plasmonic Metal-Oxide-Semiconductor (MOS) waveguide, which efficiently concentrates the optical modes’ electric field into a nanometer thin region comprised of an absorption coefficient-tuneable Indium-Tin-Oxide (ITO) layer. The modulation mechanism originates from electrically changing the free carrier concentration of the ITO layer. The seamless integration of such a strong optical beam modulation into an existing silicon-on-insulator platform bears significant potential towards broadband, compact and efficient communication links and circuits.

Silicon-organic hybrid (SOH) devices combine silicon waveguides with a number of specialized materials, ranging from third-order optically-nonlinear molecules to second-order nonlinear polymers and liquid-crystals. Second-order nonlinear materials allow building high-speed and low-voltage electro-optic modulators, which are key components for future silicon-based photonics transceivers. We report on a 90 GHz bandwidth phase modulator, and on a 56 Gbit/s QPSK experiment using an IQ Pockels effect modulator. By using liquid-crystal claddings instead, we show experimentally that phase shifters with record-low power consumption and ultra-low voltage-length product of V_πL = 0.06 Vmm. Secondorder nonlinear materials, moreover, allow creating nonlinear waveguides for sum- or difference-frequency generation, and for lowest-noise optical parametric amplification. These processes are exploited for a large variety of applications, like in the emerging field of on-chip generation of mid-IR wavelengths, where pump powers are significantly smaller compared to equivalent devices using third-order nonlinear materials. In this work, we present the first SOH waveguide design suited for second-order nonlinear processes. We predict for our device an amplification of 14 dB/cm assuming a conservative χ⁽²⁾-nonlinearity of 230 pm/V and a CW pump power as low as 20 dBm.

The silicon optical modulator is a key element in the advancement to meet the continuous demand on larger capacity of data transmission through optical interconnects, where the transmitted signal is required to have very low loss and large bandwidth. We present the experimental results of an all-silicon optical modulator based on carrier depletion in a lateral PIPIN diode. By embedding a p-doped slit in the intrinsic region of the PIN diode, the best compromise between effective index variation and optical loss in the middle of the waveguide is obtained. The PIPIN diode design guarantees a reduction of optical loss because large part of the waveguide is left unintentionally doped. Additionally, self-aligned fabrication was used to have an exact alignment of the active region, and to guarantee maximum modulation efficiency. At 40 Gb/s, the modulator delivered a 6.6 dB extinction ratio, with a 6 dB insertion loss at the operation point.

We have fabricated silicon avalanche photodetectors integrated with silicon-on-insulator straight waveguides as well as ring resonator structures. The photodetectors comprise a p-i-n junction, with photogeneration mediated by the presence of deep-levels. For a 400 μm straight waveguide detector we measure a responsivity of 4.4 A/W at 40 V, and an avalanche multiplication gain of 640. The detectors incorporated with a ring resonator, offer a high sensitivity, wavelength selective detector option suitable for very low power applications, with a responsivity of 20 A/W at 30 V.

Optical modulation is one of the key determinants to the operating speed of a network. In this work, we report an accurate methodology to study high-speed eye diagram from electrical and optical simulation data of individual modulators. The methodology constitutes electrical parameters such as capacitance, conductance and transitioning times to model time response and effective complex refractive index from optical simulations of phase shifter arms and in turn model the phase change and resultant loss induced by each arm. This methodology is suitable for interferometer-based optical devices and has been applied to silicon-based depletion mode modulators at 10-, 40-Gbps.

Reconfigurable optical band interleavers based on interference in coupled racetracks are experimentally investigated. The full reconfigurability, including a "splitter" state, is demonstrated by means of thermal tuning. A novel three components interleaver design is presented.

Low-loss high-speed traveling-wave silicon Mach-Zehnder modulator with reduced series resistance is studied in microwave and optical measurements. Microwave impedance and propagation loss under reverse bias are characterized by S-parameter measurements. Resonant loss due to series inductance-resistance-capacitance coupling limits microwave performances of the traveling-wave modulator. High-speed optical performances are characterized, based on eyediagram measurements in on-off keying at 10-32 Gb/s and constellation and eye-diagram measurements in differential phase-shift keying at 20 Gb/s. Dispersion tolerance in error-free transmission in 10-Gb/s on-off keying and 20-Gb/s differential phase-shift keying is obtained as +/-950 ps/nm and +/-220 ps/nm, respectively by path-penalty measurements. Transmission performance in 10-Gbps on-off keying is comparable with lithium niobate Mach-Zehnder modulator.

Optical modulator devices in silicon have experienced dramatic improvements over the last decade, with data rates demonstrated up to 50Gb/s and ultra-lower power consumption with a few fJ/bit[1]. However a significant need exist for high speed low power devices with a small footprint and broadband characteristics with extinction ratio above 5dB. Here we describe the work within the UK silicon photonics program, which has led to the fabrication and preliminary results of novel nano cavity optical architecture as well as self-aligned pn junction structures embedded in a silicon rib waveguide with an active length in the millimetre range producing high-speed optical phase modulation whilst retaining a high extinction ratio.

Electro-optic (EO) polymer cladding modulators are an option for low-power high-speed optical interconnects on a silicon platform. EO polymers have inherently high switching speeds and have shown 40 Gb/s operation in EO polymer clad ring resonator modulators (RRM). In EO polymer clad RRM, the modulator’s area is small enough to be treated as a lumped capacitor; the capacitance is sufficiently low that the modulation speed is limited by the bandwidth of the resonator. A high Q resonator is needed for low voltage operation, but this can limit the speed and/or require precise control of the resonator’s wavelength, necessitating power consuming heaters to maintain optimal performance over a large temperature range. Mach Zehnder modulators (MZM), on the other hand, are not as sensitive to temperature fluctuations, but typically are relatively long and must employ power consuming terminated travelling wave electrodes. In this paper, a novel MZM design is presented using an EO polymer clad device. In this device, the electrodes are broken into short parallel segments and the waveguide folds around them. The segments of the electrode length are designed to provide good signal integrity up to 20 GHz without termination. The electrodes are driven by a single drive voltage and provide push-pull modulation. Modulators were designed and fabricated using silicon nitride waveguides on bulk silicon wafers and were demonstrated at high speed (20 GHz). A V_πL as low as 1.7 Vcm is measured on initial devices. An optimized device could provide 40 Gb/s performance at 1 V drive voltages, ~100 fF total device capacitance and less than 2 dB optical insertion loss.

Polarization dependencies and dispersions are the two major bottlenecks in waveguide based silicon photonic devices for various applications – especially in DWDM systems. In this paper, we present the design and experimental demonstration of a 2×2 integrated optical MZI that shows both polarization-independent and dispersion-free response over a wide wavelength range (C+L optical band) in SOI platform - for the first time to our knowledge. The entire device footprint (W×L) is ~ 0.8 mm × 5.2 mm; which is comprised of optimally designed single-mode waveguides (for input/output and interferometer arms) and a pair of MMI based 3-dB power splitters. To monitor the wavelength dependent performance, unbalanced arm lengths (L ~ 3037 μm, L+ΔL ~ 3450 μm) were introduced to construct the MZI. The differential arm length (ΔL ~ 412 μm) has been specifically chosen to provide alternate ITU channel transmission peaks at both the output ports alternatively. Accordingly, the fabricated device separates 100 GHz DWDM channel wavelengths alternatively into two output ports and is nearly insensitive to the polarization of the guided light. We have observed a uniform channel extinction of ~ 10 dB (~ 6 dB) at both ports with a 3-dB bandwidth of ~ 110 GHz (~120 GHz) for TM (TE) polarization over the wavelength range of 1520 nm to 1600 nm. The lower extinction for TE polarization is due to its relatively higher bending loss in the longer arm of the MZI. This can be adjusted by introducing identical bends in both the arms.

Free-space beam steering using optical phase arrays are desirable as a means of implementing Light Detection and Ranging (LIDAR) and free-space communication links without the need for moving parts, thus alleviating vulnerabilities due to vibrations and inertial forces. Implementing such an approach in silicon photonic integrated circuits is particularly desirable in order to take advantage of established CMOS processing techniques while reducing both device size and packaging complexity. In this work we demonstrate a free-space diode laser together with beam steering implemented on-chip in a silicon photonic circuit. A waveguide phased array, surface gratings, a hybrid III-V/silicon laser and an array of hybrid III/V silicon amplifiers were fabricated on-chip in order to achieve a fully integrated steerable free-space optical source with no external optical inputs, thus eliminating the need for fiber coupling altogether. The chip was fabricated using a modified version of the hybrid silicon process developed at UCSB, with modifications in order to incorporate diodes within the waveguide layer as well as within the III-V gain layer. Beam steering across a 12° field of view with ±0.3° accuracy and 1.8°x0.6° beam width was achieved, with background peaks suppressed 7 dB relative to the main lobe within the field of view for arbitrarily chosen beam directions.

An on-chip light source plays a determinant role in the realization of integrated photonic chips for optical interconnects technology. Several integration schemes of III/V laser on SOI platform for on-chip laser application have been proposed and demonstrated. However, most of those integration approaches do not provide effective solutions for the following two problems: effective light confinement/amplification in the III/V active region; and efficient light transfer/coupling between silicon and III/V waveguide. In this paper, a novel approach to integrate an ultra-compact Lateral-Current-Injection (LCI) laser on silicon-on-insulator (SOI) platform by direct wafer bonding technique is proposed and designed. The proposed LCI device has an ultra-thin thickness of 270 nm which is ~10 times thinner than the vertical current injection laser bonded on silicon. It has a confinement factor in the active region larger than 40% for 1 μm wide III/V active waveguide, which is the highest among all the other integration schemes proposed so far. An optical vertical interconnect access to transfer light efficiently between III/V and silicon layer is designed. The design of the shortest “Optical Via” of 4 μm which gives ~100% coupling efficiency is presented.

In this work, the optoelectronic properties of silicon light emitting field-effect transistors (LEFETs) have been investigated. The devices have been fabricated with silicon nanocrystals in the gate oxide and a semitransparent polycrystalline silicon gate. We compare the properties of LEFET with a more conventional MOS-LED (two-terminal light-emitting capacitor) with the same active material. The ~45 nm thick gate siliconrich oxide is deposited in a size-controlled multilayer geometry by low pressure chemical vapor deposition using standard microelectronic processes in a CMOS line. The multilayer stack is formed by layers of silicon oxide and silicon rich silicon oxide. The nanocrystal size and the tunneling barrier width are controlled by the thickness of silicon-rich silicon oxide and stochiometric silicon oxide layers, respectively. The silicon nanocrystals have been characterized by means of spectrally and time resolved photoluminescence, high resolution TEM, and x-ray photoelectron spectroscopy. Resistivity of the devices, capacitance, and electroluminescence under direct and pulsed injection current scheme have been studied and here reported. The optical power density and the external quantum efficiency of the LEFETs will be compared with the MOSLED results. This study will help to develop practical optoelectronic and photonic devices via accurate modeling and engineering of charge transport and exciton recombination in silicon nanocrystal arrays.

In this work we present the first experimental demonstration of a novel class of heterogeneously integrated III­ V-on-silicon microlasers. We first show that by coupling a silicon cavity to a III-V wire, the interaction between the propagating mode in the III-V wire and the cavity mode in the silicon resonator results in high, narrow band reflection back into the III-V waveguide, forming a so-called resonant mirror. By combining two such mirrors and providing optical gain in the III-V wire in between these 2 mirrors, laser operation can be realized. We simulate the reflectivity spectrum of such a resonant mirror using 3D FDTD and discuss the results. We also present experimental results of the very first optically pumped heterogeneously integrated resonant mirror laser. The fabricated device measures 55 μm by 2 μm and shows single mode laser emission with a side-mode suppression ratio of 37 dB.

We demonstrate electrically pumped silicon nano-light source at room temperature, having very narrow emission line (<0.5nm) at 1500nm wavelength, by enhancing the electroluminescence (EL) via combination of hydrogen plasma treatment and Purcell effect. The measured output power spectral density is 0.8mW/nm/cm², which is highest ever reported value from any silicon light emitter.

We report the electrical and optical comparison, in continuous wave regime, of two novel classes of silicon photomultipliers (SiPMs) fabricated in planar technology on silicon P-type and N-type substrate respectively. Responsivity measurements have been performed with an incident optical power from tenths of picowatts to hundreds of nanowatts and on a broad spectrum, ranging from ultraviolet to near infrared (340-820 nm). For both classes of investigated SiPMs, responsivity shows flat response versus the optical incident power, when a preset overvoltage and wavelength is applied . More in detail, this linear behavior extends up to about 10 nW for lower overvoltages, while a shrink is observed when the reverse bias voltage increases. With regards to our responsivity measurements, carried out in the abovementioned spectral range, we have found a peak around 669 nm for the N-on-P and a peak at 417 nm for the P-on-N SiPM. A physical explanation of the all experimental results is also provided in the paper.

We observed photonic band-gap disappearance on Bragg-grating wavelength filters with Si photonic-wire waveguides, and studied the physical mechanism with theoretical and numerical analyses. This is a unique phenomenon observed in channel waveguides with very high index-contrast between the waveguide core and cladding materials. The photonic band-gap disappearance was observed in structures where two different optical field distributions of standing wave degenerate.

CMOS-compatible ring-based active devices have attracted significant attention for their ability to confine and manipulate light on a compact SOI platform. Active modulation of a ring resonator is typically achieved by changing the intensity response. As an alternative to intensity modulation, the phase modulation of the ring resonator can be converted into intensity modulation of a Mach-Zehnder interferometer (MZI) by means of a ring-assisted Mach-Zehnder interferometer (RAMZI) structure. We theoretically demonstrate an all-optical single resonance switching using a silicon RAMZI by optically controlling the intracavity loss of the side-coupled silicon ring based on inverse Raman scattering (IRS). The RAMZI structure improves the modulation robustness against fabrication deviations by relaxing the coupling condition for the ring resonator, without compensating the modulation performance. In silicon, the IRS produces optical loss with a bandwidth of 105 GHz at the anti-Stokes wavelength, which blueshifts 15.6 THz from the control light. For our proposed RAMZI structure, the IRS induced loss is spectrally wider than the linewidth of the side-coupled ring, but narrower than the free spectral range (FSR) of the ring, guaranteeing single resonance selectivity. When the control light pulse of 200 ps switches from “off” (zero) to “on” (20pJ), the transmission of the anti-Stokes resonance transfers from 1.7% to 92.3%. The proposed structure provides the potential to multichannel all-optical routers on a CMOS compatible platform.

We demonstrate photonic crystal waveguide true-time-delay lines fabricated on a large area (>2cm × 2cm) silicon nanomembrane transferred onto a glass substrate. The photonic crystal waveguides are designed to provide large time delay values within a short length. 17.1 μm × 10 μm subwavelength grating (SWG) couplers are employed in order to enable efficient light coupling from and to a fiber. Photonic crystal tapers are implemented at the stripphotonic crystal waveguide interfaces to minimize loss and provide larger time delay values. A large group index of ~28.5 is calculated from the measurement data, thus indicating achievability of time delay larger than 58ps per millimeter length of the delay line within a tuning range of 20nm.

Scalable integrated optics platforms based on silicon-on-insulator allow to develop optics and electronics functions on the same chip. Developments in this area are fostered by its potential as an I/O technology that can meet the throughputs demand of future many-core processors. Most of the optical interconnect designs rely on small footprint and high power efficiency microring resonators. They are used to filter out individual channels from a shared bus guide. Second-order microring filters enable denser channel packing by having sharper pass-band to stop-band slopes. Taking advantage of using a single physical ring with clockwise and counter-clockwise propagation, we implement second order filters with lower tuning energy consumption as being more resilient to some fabrication errors. Cascade ability, remote stabilization potential, energy efficiency along with simple design equations on coupling coefficients are described. We design second-order filters with FWHM from 45 GHz to 20 GHz, crosstalk between channels from -40 dB to -20 dB for different channel spacing at a specific FSR, with energy efficiencies of single ring configurations and compatible with silicon-on-insulator (SOI) state of the art platforms.

Silicon microelectronics on unconventional substrates has led to numerous unprecedented applications. Inspired by the great success, it is a natural desire to integrate silicon photonic circuitry on unconventional substrates in the hope of extending the applicability range of silicon photonics to a multitude of novel hybrid silicon photonic devices. However, photonic devices usually have larger dimensions and more complicated morphologies. The transfer method used in electronics cannot be applied directly to transfer photonic devices. Here, we propose a low temperature transfer technique based on adhesive bonding and deep reactive ion etching. A defect-free transfer of 2 cm × 2 cm, 250 nm thick silicon nanomembrane onto a glass slide has been demonstrated. Single mode waveguides and splitters fabricated on the transferred SiNM exhibit comparable results to those fabricated on silicon-on-insulator. With a low process temperature, this method can be easily applied to transfer silicon nanomembranes onto various types of substrates.

Sensitization of erbium through silicon nanocrystals in silicon rich oxide (SRO) host, and the resulting luminescence at 1.54 μm were studied in detail. Silicon nanocrystals (Si-nc) were shown to work as the gateway for energy transfer to erbium atoms. Excitation of silicon nanocrystals by the incident photon flux, and the subsequent transfer of energy to erbium atoms were modeled. Effects of energy back transfer processes through co-operative up conversion and Auger related processes were incorporated. Simulation results show that increase in Si-nc incorporation would correspond to enhanced Er luminescence and a lower threshold level of excitation for population inversion. Effective capture crosssection values for the overall sensitization process were estimated to be in the range of 10^-17/cm² for moderate Si-nc incorporation densities of 10¹⁸/cm³. Strong reductions of capture cross-section values were estimated for higher excitation fluxes. Increase of Er incorporation density in SRO host with constant level of Si-nc density resulted in increases in luminescence estimations, but with reductions in effective capture cross-section values. Results reveal that, Si-nc and Er densities in a SRO system need to be optimized for efficient Er sensitization, and the feasibility of achieving stimulated emission.

In this work we present our theoretical and experimental study on the technique for the fine modification of a silicon integrated microring resonator spectral response. The method involves the local atomic layer deposition of a thin TiO₂ overlayer and is applicable for standard nanophotonic waveguides. The approach is based on the dispersion management due to the specific dispersion properties brought by the thin TiO₂ film deposition. In addition, the technique is able to partially compensate the fabrication imperfections and reduce the propagation losses.