This PDF file contains the front matter associated with SPIE Proceedings Volume 9751, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

This paper discusses some of the remaining challenges for silicon photonics, and how we at Southampton University have approached some of them. Despite phenomenal advances in the field of Silicon Photonics, there are a number of areas that still require development. For short to medium reach applications, there is a need to improve the power consumption of photonic circuits such that inter-chip, and perhaps intra-chip applications are viable. This means that yet smaller devices are required as well as thermally stable devices, and multiple wavelength channels. In turn this demands smaller, more efficient modulators, athermal circuits, and improved wavelength division multiplexers. The debate continues as to whether on-chip lasers are necessary for all applications, but an efficient low cost laser would benefit many applications. Multi-layer photonics offers the possibility of increasing the complexity and effectiveness of a given area of chip real estate, but it is a demanding challenge. Low cost packaging (in particular, passive alignment of fibre to waveguide), and effective wafer scale testing strategies, are also essential for mass market applications. Whilst solutions to these challenges would enhance most applications, a derivative technology is emerging, that of Mid Infra-Red (MIR) silicon photonics. This field will build on existing developments, but will require key enhancements to facilitate functionality at longer wavelengths. In common with mainstream silicon photonics, significant developments have been made, but there is still much left to do. Here we summarise some of our recent work towards wafer scale testing, passive alignment, multiplexing, and MIR silicon photonics technology.

Electronic circuit designers commonly start their design process with a schematic, namely an abstract representation of the physical circuit. In integrated photonics on the other hand, it is very common for the design to begin at the physical component level. In order to build large integrated photonic systems, it is crucial to design using a schematic-driven approach. This includes simulations based on schematics, schematic-driven layout, layout versus schematic verification, and post-layout simulations. This paper describes such a design framework implemented using Mentor Graphics and Lumerical Solutions design tools. In addition, we describe challenges in silicon photonics related to manufacturing, and how these can be taken into account in simulations and how these impact circuit performance.

This submission describes the operational principles of silicon-based Micro Ring resonators (MRRs) for use in optical communication using OOK, particularly with regard to WDM. The importance of accurate device modeling is emphasized. Experimental results are provided for Si MRRs fabricated to provide high extinction ratio and low-insertion loss suitable for operation at a 10Gbps transfer rate.

Nanoantenna is used for coupling free space radiation to subwavelength plasmonic waveguide. We provide a theoretical design of ultra-compact dipole nanoantennas --- Yagi-Uda antenna with a reflector in telecom range and experimentally demonstrate efficient optical coupling between lensed fiber and plasmonic slot waveguide by utilizing our designed nanoantenna. We also prove that the couple-in efficiency of 8% from the lensed fiber does not equal to the couple-out efficiency of 50% from the plasmonic slot waveguide using the same nanoantenna design, which is different than many published and experimental results. We also study the relationship between couple in efficiency and the incident light spot size, which is experimentally characterized.

We propose a compact polarization diversity optical circuit using silica waveguides and photonic crystal waveplates. By setting these circuits at the front and rear of the silicon optical devices, the polarization dependence of the silicon devices can be suppressed. Photonic crystals can be produced artificially using nanolithography, so that the retardation and orientation of the photonic crystal waveplate can be locally varied on a single chip. This enables to dramatically reduce the size of the polarization diversity circuit, which consists of a 1x2 multimode interference (MMI) coupler, two arm waveguides with quarter-waveplates (QWPs), a 2x2 MMI coupler, and output waveguides with half-waveplates (HWPs). The input light, including the transverse electric (TE) and transverse magnetic (TM) modes, is split by the 1x2 MMI coupler. The optical axes of the two QWPs, spaced 125 μm apart, are set to be orthogonal to each other, so that the phases of the TE modes in the two arm waveguides differ by 90 degrees, and those of the TM modes differ by -90 degrees. The TE mode and the TM mode are separated at the outputs of the 2x2 MMI coupler, and the polarization of the light at one of the outputs is aligned to that at the other output by the HWP. In this paper, we designed a 4x8 polarization diversity circuit for a 4x4 silicon optical switch.

Broadband antireflection coatings are commonly required in many silicon or III-V compound semiconductor based optoelectronic devices such as solar cells, photodetectors, and image sensors so as to enhance light conversion efficiency. Conventional approach using a single-layer antireflection coating is simple and commonly used in industry but it has a limited working bandwidth. To achieve broadband or even omni-directional characteristics, structures using thick graded refractive index (GRIN) multilayers or nanostructured surfaces which have equivalent graded refractive index profile have been proposed and demonstrated. In this paper, we will show our development of broadband antireflection for high index substrate using SiN_x/SiO₂ via inductively coupled plasma chemical vapour deposition (ICPCVD). Global optimization of thin-film broadband antireflection coating using adaptive simulated annealing is presented. Unlike the conventional optical coating design which uses the refractive index of available materials, the optimization approach used here decides the optimal values of the refractive index as well as the thickness of each layer. The first thin-film material optimization is carried out on the ICP-CVD machine operating at low temperature of 250°C by tuning the SiH₄/N₂ gas ratio. The demonstrated double layer antireflection thin film reduces the average reflectance of Si surface from ~32% to ~3.17% at normal incidence for wavelength range from 400 to 1100 nm. This optical thin-film design and material development can be extended to optical wavelength filters and integrated micro-GRIN devices.

Integration of photonic components on the same photonic wafer permits future optical communication systems to be dense and advanced performance. This enables very fast information handling between photonic active components interconnected through passive optical low loss channels. We demonstrate the UV-Laser based Quantum Well Intermixing (QWI) procedure to engineer the band-gap of compressively strained InGaAsP/InP Quantum Well (QW) laser material. We achieved around 135nm of blue-shift by simply applying excimer laser (λ= 248nm). The under observation laser processed material also exhibits higher photoluminescence (PL) intensity. Encouraging experimental results indicate that this simple technique has the potential to produce photonic integrated devices and circuits.

We report a low-temperature (220°C) covalent bonding of InP-based epitaxy substrate to silicon substrate through a thin thermal oxide interlayer of around 20 nm. Our SiO₂ interlayer is grown only on the silicon substrate, which avoids the challenge in obtaining high quality SiO₂ film on III-V substrate. The 20 nm thin oxide is proved to be sufficient as the outgassing medium during the bonding process. It is found that the bonding has minimal effect on the transferred epitaxy layer. This is evident from the X-ray Diffraction and room temperature photoluminescence (PL) characterizations of the III-V sample before (as-grown) and after bonding, where no significant peak shifting or broadening is observed. The high resolution Transmission Electron Micrograph (HR-TEM) also reveals almost zero-defect atomic bonding between III-V and thermal oxide on silicon.

At the dawning of the exaflop era, High Performance Computers are foreseen to exploit integrated all-optical elements, to overcome the speed limitations imposed by electronic counterparts. Drawing from the well-known Memory Wall limitation, imposing a performance gap between processor and memory speeds, research has focused on developing ultra-fast latching devices and all-optical memory elements capable of delivering buffering and switching functionalities at unprecedented bit-rates. Following the master-slave configuration of electronic Flip-Flops, coupled SOA-MZI based switches have been theoretically investigated to exceed 40 Gb/s operation, provided a short coupling waveguide. However, this flip-flop architecture has been only hybridly integrated with silica-on-silicon integration technology exhibiting a total footprint of 45x12 mm2 and intra-Flip-Flop coupling waveguide of 2.5cm, limited at 5 Gb/s operation. Monolithic integration offers the possibility to fabricate multiple active and passive photonic components on a single chip at a close proximity towards, bearing promises for fast all-optical memories. Here, we present for the first time a monolithically integrated all-optical SR Flip-Flop with coupled master-slave SOA-MZI switches. The photonic chip is integrated on a 6x2 mm2 die as a part of a multi-project wafer run using library based components of a generic InP platform, fiber-pigtailed and fully packaged on a temperature controlled ceramic submount module with electrical contacts. The intra Flip-Flop coupling waveguide is 5 mm long, reducing the total footprint by two orders of magnitude. Successful flip flop functionality is evaluated at 10 Gb/s with clear open eye diagram, achieving error free operation with a power penalty of 4dB.

A small footprint, low power, cost effective single mode fiber coupled broadband light source and spectrometer is presented. It is based on Super Luminescent Diode (SLED) devices and a compact design enables coverage of the 1250 nm-1750 nm region with a total optical power of 50 mW at the output of the fiber. This Broad Spectrum Tunable Super Luminescent (BeST-SLED^TM) light source can operate at temperatures ranging from -40°C to 60°C, and resides in a custom designed 26-pin package. The fiber is a polarization maintaining fiber with a FC/APC connector at the output. Three variations of the BeST-SLED^TM were developed, BEST-SLED™ Bands, BeST-SLED^TM Tunable and BeST-SLED^TM FTNIR. In the Bands version six SLEDs were packaged allowing for one SLED on at a time or any combination of the SLEDs on. In the Tunable version an Acoustic Optical Tunable Filter (AOTF) was integrated into the package allowing the user to select one wavelength at a time to pass into the fiber with resolution of ~1 nm @1550nm. In the FTNIR version, a Silicon Photonic based interferometer (the Nano-Spec^TM) was integrated into the package for a Fourier Transform Near Infrared based Spectrometer and light source. The BeST-SLED^TM is being used in process control applications such as steam quality measurements, oil in water, gas composition and air quality monitoring.

The characteristics of integrated lasers consisting of a Fabry-Pérot (FP) cavity with one side connected to a whisperinggallery mode (WGM) microcavity are reported, in which the WGM microcavity acts as a resonant reflector for the FP cavity with its reflectivity capable of being modulated. The mode coupling between the WGM and FP mode would clamp the lasing mode around the wavelength of the WGM and suppress additional side modes. Single mode lasing with the side mode suppression ratio higher than 40 dB is realized for an integrated laser with the FP cavity directly connecting to one vertex of a square microcavity. The wavelength tunability is further demonstrated by varying the bias currents into the square cavity and the FP cavity regions. In addition to the lasing characteristics of single mode operation, we also report the high speed modulation characteristics of the integrated laser.

Monolithic mode-locked semiconductor lasers are attractive sources of short optical pulses with advantages over more conventional sources in compactness, robustness, performance stability, power consumption, and cost savings. The use of quantum well intermixing (QWI) to integrate passive sections and surface etched distributed Bragg reflectors (DBR) into monolithic laser cavity will be described. The performance of the devices will be presented.

We demonstrate electrically-pumped III-V quantum-well lasers bonded on SiO₂ with a metal-coated etched-mirror. The metal-coated etched-mirror allow the lasers to be used as on-chip laser, but our process design make sure that it requires no additional fabrication step to fabricate the metal-coated etched mirror. The bonded III-V on SiO₂ also permits tight laser mode confinement in the active region due to high index contrast between III-V and SiO₂. Moreover, it promises a flexible choice of host substrate, in which the silicon substrate could also be replaced with other materials. The laser devices demonstrated have the lowest threshold of 50 mA, a maximum output power of 9 mW and a differential quantum efficiency of 27.6%.

A novel inverted quantum dot structure is presented, which consists of an InGaAs quantum well that has been periodically perforated and then filled with the higher bandgap GaAs barrier material. This structure exhibits a unique quantized energy structure something like a planar atomic bond structure and formation of allowed and forbidden energy bands instead of highly localized, fully discrete states. We describe the growth, processing and characteristics of inverted quantum dot structures and outline interesting and potentially important effects arising from the introduction of nanoscale features (<50 nm) in the active medium.

We present a new approach based on the integration of the functions of a high-efficiency current switch and a laser emitter into a single heterostructure as elements of time-of-flight (TOF) systems. The approach being developed employs the effect of an electrical bistability, which occurs in the general case in thyristor structures. We report recent results obtained in a study of the dynamic electrical and optical characteristics of the pulsed sources we developed. An effective generation of 2- to 100-ns laser pulses at a wavelength of 905 nm is demonstrated. The possibility of generating laser pulses shorter than 1 ns is considered. The maximum peak power reached values of 7 and 50 W for 10- and 100-ns pulses, respectively.

We report our progress towards actively stabilized silicon microring switch arrays for optical interconnects using our recently proposed slope-detection method. The stabilization scheme utilizes an in-resonator all-silicon photomonitor that detects the detuning of the microring resonance wavelength from a carrier wavelength at 1550 nm. The photomonitor utilizes linear sub-bandgap surface-state absorption (SSA) on the unpassivated air-silicon waveguide interfaces. Our experiments demonstrate SSA-based photomonitors with a cavity-enhanced responsivity of ~ 1.9- 2.3 mA/W upon a bias voltage of -1 V. We demonstrate actively stablized 2-by-2 microring switch fabrics with intensity variations of ~1 dB over a temperature modulation of ~7 °C among the four transmission channels.

The development of silicon – based photonic components and systems has advanced tremendously over the last decade, largely for applications in optical interconnects. The role of silicon - based platforms for both linear and nonlinear optics remains highly pertinent because of their ability to be integrated with CMOS – based electronics. In this paper, we present recent research progress pertaining to ultrafast optical signal processing on silicon – based platforms. Advances in on – chip multiplexing strategies with the potential for meeting 200GHz dense wavelength division multiplexing standards across the C – and L – bands will be discussed. In addition, the development of a silicon – based nonlinear optics platform with high nonlinear figures of merit will be presented. Nonlinear optical devices fabricated from the developed platform possess nonlinear parameters 500 times larger than that in silicon nitride waveguides, while possessing negligible nonlinear losses at 1.55μm. Ultra – broadband, low power nonlinear wavelength generation using these devices, as well as their potential for realizing advanced light sources for optical interconnect – based applications will be presented.

Silicon photonics is a scalable, cost-effective technology for the production of photonic integrated circuits (PICs). The emergence of silicon photonics as a dominant technology for PICs is largely because it leverages decades of investment in design and fabrication technologies for electronic integrated circuits. However, the lithography requirements for photonic and electronic components are importantly different: geometries are generally curved; sidewall roughness is critically important; and, while the feature sizes are generally much larger, photonic device performance can be extraordinarily sensitive to the precise final geometry. For example, rounding of 90 degree corners in y-branches or multimode interferometers can have a dramatic impact on performance. The use of optical proximity correction (OPC) can greatly reduce these problems but does not eliminate them altogether. The designer is therefore faced with the problem of potentially optimizing a component using highly accurate numerical simulations that cannot be manufactured to the desired geometry, leading to a discrepancy between desired and actual performance. To solve this problem, we present a method for designing and optimizing photonic components that are lithography friendly so that the simulated geometry can be readily manufactured. As an example, we consider the case of waveguide Bragg gratings which are particularly challenging to manufacture by lithography.

A novel integrated Mach-Zehnder modulator (MZM) bias controller based on eye-amplitude monitoring is demonstrated in IHP’s 0.25-μm BiCMOS technology. The bias controller monitors the MZM output light, automatically moves the MZM bias voltage to the optimal value that produces the largest eye amplitude, and maintains it there even if the MZM transfer characteristics change due to thermal drift. The controller is based on the feedback loop consisting of Si photodetector, trans-impedance amplifier, rectifier, square amplifier, track-and-hold circuit, comparator, polarity changer, and charge-pump, all of which are monolithically integrated. The area of the controller is 0.083-mm² and it consumes 92.5-mW. Our bias controller shows successful operation for a commercially-available 850-nm LiNbO₃ MZM modulated with 3-Gbps PRBS data by maintaining a very clean eye for at least 30 minutes. Without the controller, the eye for the same MZM modulation becomes completely closed due to thermal drift. The data rate is limited by the Si PD integrated in the controller not by the controller architecture. Since our controller is based on the Si BiCMOS technology which can also provide integrated Si photonics devices on the same Si, it has a great potential for realizing a Si MZM with an integrated bias controller, which should fully demonstrate the advantage of electronic-photonic integrated circuit technology.

We present a design approach for compact reconfigurable phased-array wavelength-division multiplexing (WDM) devices with N access waveguides (WGs) based on multimode interference (MMI) couplers. The proposed devices comprise two MMI couplers which are employed as power splitters and combiners, respectively, linked by an array of N single-mode WGs. First, passive devices are explored. Taking advantage of the transfer phases between the access ports of the MMI couplers, we derive very simple phase relations between the arms that provide wavelength dispersion at the output plane of the devices. When the effective refractive index of the WGs is modulated with the proper relative optical phase difference, each wavelength component can switch paths between the preset output channel and the remaining output WGs. Moreover, very simple phase relations between the modulated WGs that enable the reconfiguration of the output channel distribution when the appropriated coupling lengths of the MMI couplers are chosen are also derived. In this way, a very compact expression to calculate the channel assignment of the devices as a function of the applied phase shift is derived for the general case of N access WGs. Finally, the experimental results corresponding to an acoustically driven phased-array WDM device with five access WGs fabricated on (Al,Ga)As are shown.

A method for fabricating filters for fiber optic sensors is presented. The interference filter's construction is laid on it's side to allow for the use of air as the low refractive index material. Bandpass filters tuned to the absorption line of a trace gas can then be used as a sensitive means of detecting gas concentration. Complex filter designs can be fabricated in a single patterned layer. A CO₂/CH₄ gas sensor is presented as a design example.

Compact optical systems generally form the backbone of integrated optoelectronic microsystems. Miniaturization as well as integration requirements result in system configurations with folded optical axis such as in planar integrated freespace optics. For optimum performance in such systems geometries, the surface profiles of the corresponding optical elements deviate from classical spherical or aspherical shapes. Optimized plane-symmetric or freeform optical elements are required instead. We discuss design, fabrication and characterization of freeform optical elements for the integration of optical microsystems. The systems performance is demonstrated for imaging as well as sensor applications.

Micro-optical sensors based on optical waveguides are widely used to measure temperature, force and strain but also to detect biological and chemical substances such as explosives or toxins. While optical micro-sensors based on silicon technology require complex and expensive process technologies, a new generation of sensors based completely on polymers offer advantages especially in terms of low-cost and fast production techniques. We have developed a process to integrate micro-optical components such as embedded waveguides and optical interconnects into polymer foils with a thickness well below one millimeter. To enable high throughput production, we employ hot embossing technology, which is capable of reel-to-reel fabrication with a surface roughness in the optical range. For the waveguide fabrication, we used the thermoplastic polymethylmethacrylate (PMMA) as cladding and several optical adhesives as core materials. The waveguides are characterized with respect to refractive indices and propagation losses. We achieved propagation losses are as low as 0.3 dB/cm. Furthermore, we demonstrate coupling structures and their fabrication especially suited to integrate various light sources such as vertical-cavity surface-emitting lasers (VCSEL) and organic light emitting diodes (OLED) into thin polymer foils. Also, we present a concept of an all-polymer and waveguide based deformation sensor based on intensity modulation, which can be fabricated by utilizing our process. For future application, we aim at a low-cost and high-throughput reel-to-reel production process enabling the fabrication of large sensor arrays or disposable single-use sensing structures, which will open optical sensing to a large variety of application fields ranging from medical diagnosis to automotive sensing.

Lock-in amplifier (LIA) has been proposed as a detection technique for optical sensors because it can measure low signal in high noise level. LIA uses synchronous method, so the input signal frequency is locked to a reference frequency that is used to carry out the measurements. Generally, input signal frequency of LIA used in optical sensors is determined by modulation frequency of optical signal. It is important to understand the noise characteristics of the trans-impedance amplifier (TIA) to determine the modulation frequency. The TIA has a frequency range in which noise is minimized by the capacitance of photo diode (PD) and the passive component of TIA feedback network. When the modulation frequency is determined in this range, it is possible to design a robust system to noise. In this paper, we propose a method for the determination of optical signal modulation frequency selection by using the noise characteristics of TIA. Frequency response of noise in TIA is measured by spectrum analyzer and minimum noise region is confirmed. The LIA and TIA circuit have been designed as a hybrid circuit. The optical sensor is modeled by the laser diode (LD) and photo diode (PD) and the modulation frequency was used as the input to the signal generator. The experiments were performed to compare the signal to noise ratio (SNR) of the minimum noise region and the others. The results clearly show that the SNR is enhanced in the minimum noise region of TIA.

Counting the number of people is still an important task in social security applications, and a few methods based on video surveillance have been proposed in recent years. In this paper, we design a novel optical sensing system to directly acquire the depth map of the scene from one light-field camera. The light-field sensing system can count the number of people crossing the passageway, and record the direction and intensity of rays at a snapshot without any assistant light devices. Depth maps are extracted from the raw light-ray sensing data. Our smart sensing system is equipped with a passive imaging sensor, which is able to naturally discern the depth difference between the head and shoulders for each person. Then a human model is built. Through detecting the human model from light-field images, the number of people passing the scene can be counted rapidly. We verify the feasibility of the sensing system as well as the accuracy by capturing real-world scenes passing single and multiple people under natural illumination.

Currently, photonic mixing device (PMD) cameras undergo a great deal of attention. They allow simultaneous recordings of amplitude and distance images with one shot. This opens up new application possibilities like drivers’ assistance in vehicles or gesture control in the multimedia sector. Unfortunately, PMD cameras reach only low spatial resolution. Wherein the pixel resolution for state-of-the-art indoor cameras ranging about VGA resolution, they are even lower for outdoor applications. This limits the possibilities for object recognition. From two-dimensional (2D) imaging there are already methods known for increasing spatial resolution virtually. It means resolution enhancement without changing physically given sensor specifications like pixel dimension or sensor size. In this context, often referred as superresolution (SR). This work compares four well-known geometric SR algorithms from 2D imaging adapted to PMD imaging. Resolution enhancement and quality of the SR results are evaluated objectively by measuring the spatial frequency response (SFR) and investigating the noise performance in amplitude and distance images. Based on these results, SR algorithms for possible measurement tasks in metrological or photographic applications are proposed.

Position-sensitive photomultiplier tubes (PSPMTs) in array are used as gamma ray position detector. Each PMT converts the light of wide spectrum range (100 nm ~ 2500 nm) to electrical signal with amplification. Because detection system size is determined by the number of output channels in the PSPMTs, resistive network has been used for reducing the number of output channels. The photo-generated current is distributed to the four output current pulses according to a ratio by resistance values of resistive network. The detected positions are estimated by the peak value of the distributed current pulses. However, due to parasitic capacitance of PSPMTs in parallel with resistor in the resistive network, the time constants should be considered. When the duration of current pulse is not long enough, peak value of distributed pulses is reduced and detected position error is increased. In this paper, we analyzed the detected position error in the resistive network and variation of time constant according to the input position of the PSPMTs.

Conversely to the continuous wave indirect time-of-flight (CW-iToF) imaging scheme, pulsed modulation ToF (PM-iToF) imaging is a promising depth measurement technique for operation at high ambient illumination. It is known that non-linearity and finite charge-transfer speed impact trueness and precision of ToF systems.^1–3 As pulses are no Eigenfunctions to the shutter system, this issue is especially pronounced in pulsed modulation.^{2, 3} Despite these effects, it is possible to find analytical expressions founded on physical observations that map scenery parameters such as depth information, reflectance and ambient light level to sensor output.^{3, 4} In the application, the inverse of this map has to be evaluated. In PM-iToF, an inverse function cannot be yielded in a direct manner, as models proposed in the literature were transcendental.^{3, 4} For a limited range an approximating linearization can be performed to yield depth information.⁵ To extend the usable range, recently, an alternative approach that indirectly approximates the inverse function was presented.⁶ This method was founded on 1D doping concentration profiles, which, however, are typically not made available to end users. Also, limitations of the 1D approximation as well as stability are yet to be explored. This work presents a calibration methodology that copes with detector insufficiencies such as finite charge transfer speed. Contrarily to the state of the art, no prior knowledge on details of the underlying devices is required. The work covers measurement setup, a benchmark of various calibration schemes and deals with issues such as overfitting or defect pixels.

In the last decade significant progress has been made on optical non-contact time-of-flight (ToF) based ranging techniques. Direct implementations based on time-correlated single photon counting (TCSPC-dToF), coincidence detection (CD-TCSPC-dToF) as well as multiple indirect realizations based on e.g. single-photon synchronous detection (SPSD-iToF), continuous-wave modulation (CW-iToF) or pulse modulation (PM-iToF) have been presented. All those modulation/demodulation techniques can be employed in scanning (scanning LIDAR) as well as non-scanning (Flash-LIDAR) schemes. Many parameters impact key performance metrics such as depth measurement precision or angular resolution. Unfortunately, publications or datasheets rarely quote all relevant parameters. Thus, benchmarking between different approaches based on published metrics is cumbersome. The authors believe that such a benchmark would have to be founded on modeling in order to ensure fair comparison. This work presents an overview over the most common ToF based depth measurement approaches, how these can be modeled and how they compare.

We propose a new hybrid 3D light detection and ranging (LIDAR) system, which measures a scene with 1280 x 600 pixels at a refresh rate of 60fps. The emitted pulses of each pixel are modulated by direct sequence optical code division multiple access (DS-OCDMA) techniques. The modulated pulses include a unique device identification number, the pixel position in the line, and a checksum. The LIDAR emits the modulated pulses periodically without waiting to receive returning light at the detector. When all the pixels are completely through the process, the travel time, amplitude, width, and speed are used by the pixel-by-pixel scanning LIDAR imager to generate point cloud data as the measured results. We programmed the entire hybrid 3D LIDAR operation in a simulator to observe the functionality accomplished by our proposed model.

We propose a compactly integrated transverse-magnetic (TM)-pass polarizer based on rectangular-shape onedimensional photonic-crystal silicon waveguide with an extremely high polarization extinction ratio of >30 dB and low insertion loss (~1 dB) over a broad wavelength range of 210 nm from 1,460 nm to 1,670 nm. The polarizer has been numerically simulated using three-dimensional finite-difference time-domain (3D FDTD) method. The optimum length of the proposed TM-pass polarizer is about 4 μm. At the 1,550 nm wavelength, the simulated polarization extinction ratio of the polarizer is 36 dB, and its corresponding insertion loss is about 1 dB.

Picosecond pulsed laser source have applications in areas such as optical communications, biomedical imaging and supercontinuum generation. Direct modulation of a laser diode with ultrashort current pulses offers a compact and efficient approach to generate picosecond laser pulses. A fully integrated complementary metaloxide- semiconductor (CMOS) driver circuit is designed and applied to operate a 4 GHz distributed feedback laser (DFB). The CMOS driver circuit combines sub-circuits including a voltage-controlled ring oscillator, a voltagecontrolled delay line, an exclusive-or (XOR) circuit and a current source circuit. Ultrashort current pulses are generated by the XOR circuit when the delayed square wave is XOR’ed with the original square wave from the on-chip oscillator. Circuit post-layout simulation shows that output current pulses injected into an equivalent circuit load of the laser have a pulse full width at half maximum (FWHM) of 200 ps, a peak current of 80 mA and a repetition rate of 5.8 MHz. This driver circuit is designed in a 0.13 μm CMOS process and taped out on a 0.3 mm² chip area. This CMOS chip is packaged and interconnected with the laser diode on a printed circuit board (PCB). The optical output waveform from the laser source is captured by a 5 GHz bandwidth photodiode and an 8 GHz bandwidth oscilloscope. Measured results show that the proposed laser source can output light pulses with a pulse FWHM of 151 ps, a peak power of 6.4 mW (55 mA laser peak forward current) and a repetition rate of 5.3 MHz.