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Mode-division multiplexing (MDM), which allows different guided modes of a few-mode fiber to carry different signals, is a new technology being actively pursued worldwide to increase the signal-carrying capacity of a fiber. For the development of the MDM technology, many mode-controlling devices are needed, such as mode converters, mode (de)multiplexers, mode filters, and mode-selective switches. Among the various technologies available for the implementation of such devices, the polymer waveguide technology offers many distinct advantages. This paper presents a review of polymer waveguide devices for MDM applications, which include grating-based mode converters, 3D mode (de)multiplexers, graphene-based mode filters, and thermo-optic mode-selective switches.

As the link capacity increases dramatically, it is also becoming more and more important to develop smart photonic networks-on-chip so that the bandwidth/channels can be utilized optimally and flexibly. One of the keys for realizing smart (reconfigurable) photonic networks is reconfigurable photonic integrated devices and circuits. As silicon has a large thermo-optic (TO) coefficient as well as a high heat conductivity, it is promising to realize efficient thermallyreconfigurable silicon photonic integrated devices and circuits with simple fabrication processes. This paper gives a review of our recent work on reconfigurable photonic integrated devices and circuits on silicon, including: (1) tunable microring-resonator (MRR)-based optical filters; (2) ultra-broadband optical switches; (3) monolithically-integrated reconfigurable optical add-drop multiplexers (ROADMs) for wavelength-division-multiplexing (WDM), mode-divisionmultiplexing (MDM), as well as hybrid WDM-MDM systems.

A plasmonic integrated circuit configuration comprising plasmonic and electronic components is presented and the feasibility for high-speed signal processing applications is discussed. In integrated circuits, plasmonic signals transmit data at high transfer rates with light velocity. Plasmonic and electronic components such as wavelength-divisionmultiplexing (WDM) networks comprising metal wires, plasmonic multiplexers/demultiplexers, and crossing metal wires are connected via plasmonic waveguides on the nanometer or micrometer scales. To merge plasmonic and electronic components, several types of plasmonic components were developed. To ensure that the plasmonic components could be easily fabricated and monolithically integrated onto a silicon substrate using silicon complementary metal-oxide-semiconductor (CMOS)-compatible processes, the components were fabricated on a Si substrate and made from silicon, silicon oxides, and metal; no other materials were used in the fabrication. The plasmonic components operated in the 1300- and 1550-nm-wavelength bands, which are typically employed in optical fiber communication systems. The plasmonic logic circuits were formed by patterning a silicon oxide film on a metal film, and the operation as a half adder was confirmed. The computed plasmonic signals can propagate through the plasmonic WDM networks and be connected to electronic integrated circuits at high data-transfer rates.

We present a readout circuit for 1 × 64 Nb5N6 microbolometer array detector. The intrinsic average responsivity of the detectors in the array is 650 V/W, and the corresponding noise equivalent power (NEP) is 17 pW/√Hz. Due to the low noise of the detector, we design a low noise readout circuit with 64 channels. The readout integrated circuit (ROIC) is fabricated under CMOS process with 0.18μm design rule, which has built-in bias and adjustable numerical-controlled output current. Differential structure is used for each pixel to boost capacity of resisting disturbance. A multiplexer and the second stage amplifier is followed after the ROIC. It is shown that the ROIC achieves an average gain of ~47dB and a voltage noise spectral density of ~9.34nV/√Hz at 10KHz. The performance of this readout circuit nearly fulfills the requirements for THz array detector. This readout circuit is fit for the detector, which indicates a good way to develop efficient and low-cost THz detector system.

31st International Congress on High-Speed Imaging and Photonics, ICHSIP-31, Osaka, Japan, 7 Nov 2016 - 10 Nov 2016; Proceedings of SPIE 10328, 1032805 (2017). doi:10.1117/12.2269153, AGIPD is a hybrid pixel detector developed by DESY, PSI, and the Universities of Bonn and Hamburg. It is targeted for use at the European XFEL, a source with unique properties: a train of up to 2700 pulses is repeated at 10 Hz rate. The pulses inside a train are ≤100fs long and separated by 220 ns, containing up to 10E12 photons of 12.4 keV each. The readout ASICs with 64 x 64 pixels each have to cope with these properties: Single photon sensitivity and a dynamic range up to ⪆10E4 photons/pixel in the same image as well as storage for as many as possible images of a pulse train for delayed readout, prior to the next train. The high impinging photon flux also requires a very radiation hard design of sensor and ASIC, which uses 130 nm CMOS technology and radiation tolerant techniques. The signal path inside a pixel of the ASIC consists of a charge sensitive preamplifier with 3 individual gains, adaptively selected by a subsequent discriminator. The preamp also feeds to a correlated double sampling stage, which writes to an analogue memory to record 352 frames. It is random-access, so it can be used most efficiently by overwriting bad or empty images. Encoded gain information is stored to a similar memory. Readout of these memories is via a common charge sensitive amplifier in each pixel, and multiplexers on four differential ports. Operation of the ASIC is controlled via a command interface, using 3 LVDS lines. It also serves to configure the chip’s operational parameters and timings. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only., Published by SPIE, Bellingham, Wash.

Recently, mode-division multiplexing (MDM) has been investigated in transmission systems and optical access networks for capacity enhancement. In this paper, recent progress in MDM optical passive networks (PON) enabled by low-modal crosstalk few-mode fibers (FMFs) and optical components is reviewed. All-fiber mode multiplexer/demultiplexers (MUX/DeMUX) composed of mode-selective couplers (MSCs) are introduced to simultaneously multiplex or demultiplex multiple modes. Few-mode circulators (FMCs) are employed to realize bidirectional MDM-PON transmission. Direct detection without complex multiple-input-multiple-output (MIMO) digital signal processing (DSP) is applied. Moreover, multidimensional PONs by cascading MDM optical distribution network (ODN) with conventional time-division multiplexing (TDM) and wavelength-division multiplexing (WDM) ODNs are proposed and experimentally demonstrated.

All-fiber mode selective coupler (MSC) is comprised of a few mode fiber (FMF) and a single mode fiber (SMF), coupling the LP 01 mode of the SMF to a specific higher-order mode (HOM) of the FMF. In order to achieve high coupling ratio and low insertion loss, phase-matching condition between the LP 01 mode of SMF arm and the HOM of FMF arm should be satisfied. A polished-type MSC is made by getting their cores into intimate contact. Prism coupling with a polished coupler block can measure the effective refractive index of the mode accurately. We propose and demonstrate three kinds of allfiber mode multiplexer that is composed of consecutive MSCs. 4-mode multiplexer can multiplex 4 modes of LP 01 , LP 11 , LP 21 , and LP 02 by cascading LP 11 , LP 21 , and LP 02 MSCs. It is used for MDM transmission of three modes with 120 Gb/s DP-QPSK signals. In order to enhance the signal transmission performance by receiving degenerate LP modes simultaneously, a mode multiplexer to utilize two-fold degenerate LP 11 modes is proposed. It is composed of two consecutive LP 11 MSCs that allows the multiplexing of LP01 mode and two orthogonal LP 11 modes. We demonstrates WDM transmission of 30 wavelength channels with 33.3 GHz spacing, each carrying 3 modes, over 560 km of FMF. 6- mode multiplexer can multiplex 6 modes of LP 01 , LP 11a , LP 11b , LP 21a , LP 21b , LP 02 modes. We demonstrated WDM-MDM transmission with the all-fiber 6-mode multiplexer. In this paper, the manufacturing method and the recent advancements of the all-fiber mode multiplexer based on the MSCs are reviewed. Long-distance mode division multiplexing (MDM) optical signal transmissions with the all-fiber mode multiplexer are experimentally demonstrated.

The Asymmetric Directional Coupler (ADC) based on SOI (Silicon-on-Insulator) technology converts and couples the fundamental mode to the first higher order mode. The ADC is designed to achieve phase-matching condition, which is accomplished when both propagation constants are equal in each waveguide arm. Devices are fabricated in a SOI wafer with a 220 nm thick silicon layer. The refractive indexes of Si and SiO 2 are n Si =3.47 and n Si02 =1.46 respectively. The access waveguides (W 1 =0.45 μm) have been designed to propagate just the fundamental mode, TE 0 . The optimum width for the second waveguide was chosen to achieve the phase-matching condition for the TE 1 mode, which corresponds to W 2 =0.962 μm. The coupling to the input and output waveguides is achieved through grating couplers. The input grating coupler will need to couple the LP 01 mode from the SSMF (Standard Single-Mode Fiber) to the TE 0 mode in the SOI waveguide; thus a typical design for a SOI coupler can be used. However, the output coupler must simultaneously couple the TE 0 and TE 1 modes in the SOI wide waveguide to the LP 01 and LP 11 modes in the FMF (Few-Mode Fiber). Input gratings are designed to have an area of 12x12 μm 2 and a period of Λ=610 nm in order to maximize the optical power coupled between the fiber and the waveguide for an incident angle of 10 degrees. Output gratings are designed with the same period but distinct area (12.5x12.5 μm 2 ) to correctly couple the LP 01 and LP 11 modes in the FMF.

A hybrid multiplexer (HMUX) for wavelength/mode-division (WDM/MDM) based on photonic crystals (PCs) is proposed. The device can realize TE0 and TE1 modes multiplexing at wavelengths of 1550nm and 1570nm. According to quasi phase matching, a structure with an asymmetrical parallel waveguide (APW) was used to achieve mode conversion. The transmittance of the TE0 mode at wavelengths of 1550nm and 1570nm are 98.4% and 96.3%, the corresponding insertion loss are 0.07dB and 0.16dB respectively. The crosstalk of the TE0 mode at wavelengths of 1550nm and 1570nm are -27.66dB and -27.32dB respectively. The transmittance of the TE1 mode at wavelengths of 1550nm and 1570nm are 95.8% and 93.9%, the corresponding insertion loss are 0.19dB and 0.27dB respectively. The crosstalk of the TE1 mode at wavelengths of 1550nm and 1570nm are -38.73dB and -38.9dB respectively. The PC-based HMUX has great performance, and it will have great application potential in future ultrahigh-speed and large-capacity communication systems.

The coupling in a directional coupler (DC) has attracted lots of attention as a basic block for photonic integrated circuits. Most of previous work was focused on symmetric DCs consisting of two identical optical waveguides. In this case light power can be transferred from one waveguide to the other one completely when choosing the length L of the coupling region appropriately. Recently, an asymmetric DC (ADC) consisting of non-identical waveguides in the coupling region has been attracting more and more attention because of the versatility for various useful applications. ADCs can be formed by combining two ore more waveguides with different dimensions, shapes as well as bending radii for the core regions. In particular, silicon nanophotonics developed in the recent years provides a very good platform to make ADCs very useful and interesting. In this paper, we give a review for recent progresses of versatile ADCs on silicon, including the following three parts: (1) ADCs for power splitter used in microring resonators and Mach-Zehnder interferometers; (2) ADCs for realizing ultracompact and broadband PBSs; (3) ADCs for realizing mode (de)multiplexers.

The spectral noise characteristic and relative intensity noise of an all fibre Sagnac interferometer system consisting of a 980nm pump source at 130mW maximum output power, a 980/1550nm wavelength division multiplexer, a 10m-piece of Erbium-doped fibre, a fibre Bragg grating (FBG) centered at 1.548um, an optical circulator at 1550nm and a 50/50 fibre coupler, were measured with an optical spectrum analyzer (OSA) for fine tuning for a range of temperature between 5 and 180 degrees Celsius in step of 1 degree Celsius. At the probing end, a high-bi piece of fibre and a Peltier were employed for temperature variation of the system. Spectral and temperature response of the noise reduction due to temperature variation was performed remotely using and Arduino micro-controller and a DS18B20 digital sensor, into a local area network. Full optical and thermal characterization of the system will be included in the presentation.

In this paper we present a tandem UV/VIS/ NIR wavelength selector based on a multilayer a-SiC:H optical filter that requires appropriate ultraviolet steady states optical switches to select the desired wavelengths in the ultraviolet/visible/infrared spectral ranges. Five ultra-light communication channels are transmitted together, each one with a specific bit sequence. Results show that the background side and intensity works as a selector in the infrared, visible and ultra violet light regions, shifting the sensor sensitivity. This nonlinearity allows the identification and decoding of the different input channels. This concept is extended to implement a 1 by 5 wavelength division multiplexer with channel separation in the visible range and a transmission capability of 30 Kbps. The relationship between the optical inputs and the output signal is established and an algorithm to decode the MUX signal presented.

In this project we present a microfluidic platform with in-channel micro-electrodes for in situ screening of bio/chemical samples through a lab-on-chip system. We used a novel method to incorporate electrochemical sensors array (16x20) connected to a PCB, which opens the way for imaging applications. A 200 μm height microfluidic channel was bonded to electrochemical sensors. The micro-channel contains 3 inlets used to introduce phosphate buffer saline (PBS), ferrocynide and neurotransmitters. The flow rate was controlled through automated micro-pumps. A multiplexer was used to scan electrodes and perform individual cyclic voltammograms by a custom potentiostat. The behavior of the system was linear in terms of variation of current versus concentration. It was used to detect the neurotransmitters serotonin, dopamine and glutamate.

A highly selective plasmonic demultiplexer based on a plasmonic slot waveguide platform is proposed. The structure is optimized as an add drop multiplexer/demultiplexer. The optimal design is targeting minimum FWHM. The device is optimal quad multiplexer/demultiplexer has FWHM of 9.8 nm for each channel with a high output transmission near the 1550 nm. The proposed structure is simple, can be easily fabricated. Extended optimization was performed that enabled the multiplexed signal to have FWHM of 8.16 nm with peak power of 30 % near the 1300 nm. The structure can be utilized for double channel multiplexing applications and more by doing the needed optimization for such high scalability.

In the mid-infrared (Mid-IR), arrays of distributed feedback Quantum Cascade Lasers (QCL) have been developed as a serious alternative to obtain extended wavelength operation range of laser-based gas sensing systems. Narrow-linewidth, single mode operation and wide tunability are then gathered together on a single chip with high compactness and intrinsic stability. In order to benefit from this extended wavelength range in a single output beam we have developed a platform for InP-based photonics. After the validation of all required building blocks such as straight waveguides, adiabatic couplers between active and passive waveguides, and echelle grating multiplexers, we are tackling the integration into a single monolithic device. We present the design, fabrication and performances of a tunable source, fully monolithic based on the echelle grating approach. Advantages are design flexibility, relatively simple processing and the need for one single epitaxial growth for the entire structure. The evanescent coupler has been designed to transfer all light adiabatically from the active region to a low loss passive waveguide, while taking advantage of the high gain available in the quantum wells. The multiplexer is based on an etched diffraction grating, covering the whole range of the 30 lasers of the array while keeping a very compact size. These results show the first realization of a monolithic widely tunable source in the Mid-IR and would therefore benefit to the development of fully integrated spectroscopic sensor systems.

Nanostructure is an effective solution for realizing optoelectronic devices with compact size and high performances simultaneously. This paper reports our research progress on integrated nanophotonic devices for optical interconnections. We proposed a parent-sub micro ring structure for optical add-drop multiplexer (OADM) with compact footprint, large free spectral range, and uniform channel spacing. All eight channels can be multiplexed and de-multiplexed with 2.6 dB drop loss, 0.36 nm bandwidth (>40 GHz), -20 dB channel crosstalk, and high thermal tuning efficiency of 0.15 nm/mW. A novel principle of optical switch was proposed and demonstrated based on the coupling of the defect modes in photonic crystal waveguide. Switching functionality with bandwidth up to 24 nm and extinction ratio in excess of 15 dB over the entire bandwidth was achieved, while the footprint was only 8 μm×17.6 μm. We proposed an optical orbital angular momentum (OAM) coding and decoding method to increase the data-carrying capacity of wireless optical interconnect. An integrated OAM emitter, where the topological charge can be continuously varied from -4 to 4 was realized. Also we studied ultrafast modulated nLED as the integrated light source for optical interconnections using a nanobeam cavity with stagger holes.

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.

Multi-Plane Light Conversion enables novel beam shaping devices, including spatial multiplexers. After a presentation of the achievable performances of these spatial multiplexers, which can combine 10 spatial modes with cross-talk below -22 dB and insertion loss below 4 dB, we review the performances of Multi-Plane Light Con-version in multiple application cases. These application cases include mode-multiplexed optical amplification, high-power beam shaping and combining and LAN fiber capacity upgrade.

We present three main material platforms: SOI, suspended Si and Ge on Si. We report low loss SOI waveguides (rib, strip, slot) with losses of ~1dB/cm. We also show efficient modulators and detectors realized in SOI, as well as filters and multiplexers. To extend transparency of SOI waveguides, bottom oxide cladding can be removed. We have fabricated low loss passive devices in a suspended platform that employ subwavelength gratings. Ge on Si material can have larger transparency range than suspended Si. We have designed passive devices in this platform, demonstrated all optical modulation and carried out two photon absorption measurements. We have also investigated theoretically free carrier optical modulation in Ge.

This paper proposed a calibration scheme of optical path correlator(OPC) for optical coherence domain polarimeter (OCDP), the calibration scheme employs a dual Mach-Zehnder interferometers multiplexing one OPC by dual wavelength wave division multiplexer, one interferometer as target interferometer is used to sensing measurement, another interferometer with 3×3 coupler as reference interferometer is used for OPC scan speed and positon calibration to improve the target interferometer signal-to-noise ratio(SNR) and interference envelope positioning accuracy, this calibration scheme is used OCDP to measure polarization crosstalk, the experimental results show that SNR is achieved 95dB and the polarization crosstalk position accuracy is achieved submicron.

Scientists have recently discovered that the ageing process of optical elements is faster than it was originally anticipated. It is mostly due to the multiple increases of the optical power in optical components, the introduction of wavelength division multiplexers and, overall, the increased flow of traffic in optical communications. This article examines the ageing process of optical couplers and it focuses on their performance parameters. It describes the measurement procedure followed by the evaluation of the measurement results. To accelerate the ageing process, gamma irradiation from 60 Co was used. The results of the measurements of the optical coupler with one input and eight outputs (1:8) were summarized. The results gained by measuring of the optical coupler with one input and four outputs (1:4) as well as of the optical couplers with one input and two outputs (1:2) with different split ratios were also processed. The optical powers were measured on the input and the outputs of each branch of each optical coupler at the wavelengths of 1310 nm and 1550 nm. The parameters of the optical couplers were subsequently calculated according to the appropriate formulas. These parameters were the insertion loss of the individual branches, split ratio, total losses, homogeneity of the losses and directionalities alias cross-talk between the individual output branches. The gathered data were summarized before and after the first irradiation when the configuration of the couplers was 1:8 and 1:4. The data were summarized after the third irradiation when the configuration of the couplers was 1:2.

With the development of optical fiber communication, dense wavelength division multiplexing (DWDM) system is important for the rapid management of multi-wavelength in the core node of the optical transmission network. In this paper, a reconfigurable optical add-drop multiplexer (ROADM) based on the tunable Fabry-Perot (F-P) array is proposed. An optical switch with high isolation and low crosstalk is designed by using the characteristics of filtering and tuning for the F-P array. The principle, structure, and function of the tunable F-P array are introduced. The characteristics of filtering and tuning for the F-P filter are also calculated, and the factor for the isolation, crosstalk, response time and insertion loss are analyzed. A single physical channel ROADM with 16 signal channels, which operates in C-band, is designed and optimized by simulation.

In recent years, reconfigurable optical add drop multiplexers (ROADM) and multiple-dimensions optical cross-connection (OXC), as the essential devices of next-generation dynamic optical networks, have been attracted great interests by research institutions and relevant industry. 1×N Wavelength selective switches (WSSs) are one of the key components in current and next generation ROADM. Currently, WSS primarily rely on micro-electromechanical systems (MEMS) and liquid crystal on silicon spatial light modulators (LCOS-SLM) switches. LCOS-based WSSs have several advantages, including flexible spectrum coverage, adaptive alignment, and robustness. Based on a novel 2-f optical structure, we therefore propose 1×32 WSS system including a 1×32 fiber-coupling lenslet arrays, a collimating lens, a transmission grating, a cylindrical lens and a LCOS-SLM. By uploading the optimized phased holograms on the LCOS, we have successfully switched input signal with arbitrary wavelength in C-band into any output port. The output channel spacing can be adjusted flexibly and each port switches independently. Experimental results demonstrate the insertion loss is around 5~10dB and the switch crosstalk at 1550nm is -35dB. The 3dB-bandwidth of signal@100G is 40G.The research has established the theory and experiment foundation for the development of M×N WSS in future.

Hybrid photonic integration allows individual components to be developed at their best-suited material platforms without sacrificing the overall performance. In the past few years a polymer-enabled hybrid integration platform has been established, comprising 1) EO polymers for constructing low-complexity and low-cost Mach-Zehnder modulators (MZMs) with extremely high modulation bandwidth; 2) InP components for light sources, detectors, and high-speed electronics including MUX drivers and DEMUX circuits; 3) Ceramic (AIN) RF board that links the electronic signals within the package. On this platform, advanced optoelectronic modules have been demonstrated, including serial 100 Gb/s [1] and 2x100 Gb/s [2] optical transmitters, but also 400 Gb/s optoelectronic interfaces for intra-data center networks [3]. To expand the device functionalities to an unprecedented level and at the same time improve the integration compatibility with diversified active / passive photonic components, we have added a passive polymer-based photonic board (polyboard) as the 4th material system. This passive polyboard allows for low-cost fabrication of single-mode waveguide networks, enables fast and convenient integration of various thin-film elements (TFEs) to control the light polarization, and provides efficient thermo-optic elements (TOEs) for wavelength tuning, light amplitude regulation and light-path switching.

Advanced multiplexing technologies including wavelength-division-multiplexing (WDM), polarization-division multiplexing (PDM), and mode-division multiplexing (MDM) have been utilized as a cost-effective solution to enhance the capacity of an optical-interconnect link. The on-chip (de)multiplexers, including WDM filters, PDM devices, and MDM devices, are the most important key components in a multi-channel multiplexed optical interconnect system. Hybrid (de)multiplexer to enable various multiplexing technologies simultaneously are becoming more and more important to achieve many channels. In this paper we give a review for our recent work on silicon photonic integrated devices for realizing multi-channel multiplexed on-chip optical interconnects.

The main goal of this study was to develop and validate the performance of a miniature and portable data acquisition (DAQ) system designed for interrogating carbon nanotube (CNT)-based thin films for real-time spatial structural sensing and damage detection. Previous research demonstrated that the electrical properties of CNT-based thin film strain sensors were linearly correlated with applied strains. When coupled with an electrical impedance tomography (EIT) algorithm, the detection and localization of damage was possible. In short, EIT required that the film or “sensing skin” be interrogated along its boundaries. Electrical current was injected across a pair of boundary electrodes, and voltage was simultaneously recorded along the remaining electrode pairs. This was performed multiple times to obtain a large dataset needed for solving the EIT spatial conductivity mapping inverse problem. However, one of the main limitations of this technique was the large amount of time required for data acquisition. In order to facilitate the adoption of this technology and for field implementation purposes, a miniature DAQ that could interrogate these CNT-based sensing skins at high sampling rates was designed and tested. The prototype DAQ featured a Howland current source that could generate stable and controlled direct current. Measurement of boundary electrode voltages and the switching of the input, output, and measurement channels were achieved using multiplexer units. The DAQ prototype was fabricated on a two-layer printed circuit board, and it was designed for integration with a prototype wireless sensing system, which is the next phase of this research.

Processing ultra-fast optical signals without optical/electronic conversion is in demand and time-to-space conversion has been proposed as an effective solution. We have designed and fabricated an arrayed-waveguide grating (AWG) based optical spectrum control circuit (OSCC) using silica planar lightwave circuit (PLC) technology. This device is composed of an AWG, tunable phase shifters and a mirror. The principle of signal processing is to spatially decompose the signal’s frequency components by using the AWG. Then, the phase of each frequency component is controlled by the tunable phase shifters. Finally, the light is reflected back to the AWG by the mirror and synthesized. Amplitude of each frequency component can be controlled by distributing the power to high diffraction order light. The spectral controlling range of the OSCC is 100 GHz and its resolution is 1.67 GHz. This paper describes equipping the OSCC with optical coded division multiplex (OCDM) encoder/decoder functionality. The encoding principle is to apply certain phase patterns to the signal’s frequency components and intentionally disperse the signal. The decoding principle is also to apply certain phase patterns to the frequency components at the receiving side. If the applied phase pattern compensates the intentional dispersion, the waveform is regenerated, but if the pattern is not appropriate, the waveform remains dispersed. We also propose an arbitrary filter function by exploiting the OSCC’s amplitude and phase control attributes. For example, a filtered optical signal transmitted through multiple optical nodes that use the wavelength multiplexer/demultiplexer can be equalized.

We have demonstrated a bidirectional wavelength division (de)multiplexer (WDM) on the silicon-on-insulator platform. An excellent match of the peak transmission wavelength of each channel between the two AMMIs was achieved. This type of device is ideal for integrated optical transceivers where the transmission wavelengths are required to match with the receiving wavelengths. The device also benefits from simple fabrication (as only a single lithography and etching step is required), improved convenience for the transceiver layout design, a reduction in tuning power and circuitry, and efficient use of layout space.

In this paper, we communicate on the design, fabrication, and testing of optical modulators for Silicon-based photonic integrated circuits (Si-PICs) in the O-band (1.31 μm), targeting the 100GBASE-LR4 norm (4 wavelengths at 25 Gbit/s). The modulators have been conceived to be later coupled with hybrid-III-V/Si lasers as well as echelle grating multiplexer, to create a hetero-integrated optical transmitter on a silicon-on-insulator (SOI) platform. The devices are based on a Mach-Zehnder Interferometer (MZI) architecture, where a p-n junction is implanted to provide optical modulation through carrier depletion. A detailed study focusing on the best doping scheme for the junction, aimed at optimizing the overall transmitter performance and power-efficiency is presented. In detail, the trade-off between low optical losses and high modulation efficiency is tackled, with a targeted CMOS-compatible voltage drive of 2.5 V. Process simulations of the junction are realized for the doping profile optimization. Modulators of different lengths are also investigated to study the compromise between extinction ratio, insertion losses and bandwidth. Furthermore, coplanar-strip (SGS) travelling-wave electrodes are designed to maximize the bandwidth, to reach the targeted bit rate of 25 Gbit/s. Measurements show modulation efficiencies up to 19 °/mm (or 2.4 V.cm) for a 2.5 V input voltage, with doping-related losses below 1 dB/mm, in line with theoretical estimates, and well-suited to enhance the Si-PIC transmission and power-efficiency. Finally, an electro-optical (EO) bandwidth at 1.25 V bias is measured above 28 GHz.

In this communication, we report about the design, fabrication, and testing of echelle grating (de-)multiplexers for the 100GBASE-LR4 norm and other passive architectures such as vertical fiber-couplers and slow-wave waveguides in the O-band (1.31-μm) for Silicon-based photonic integrated circuits (Si-PICs). In detail, two-point stigmatic 20th-order echelle gratings (TPSGs) on the 300-nm-thick SOI platform designed for 4x800-GHz-spaced wavelength division multiplexing featuring extremely low crosstalk (< -30 dB), precise channel spacing and optimized average insertion losses (~ 3 dB) are presented. Distributed Bragg reflectors (DBRs) are used to improve the grating facets reflectivity, while multi-mode interferometers (MMIs) are used in optimized perfectly-chirped echelle gratings (PCGs) for pass-band flattening. Moreover, 200-mm CMOS pilot lines processing tools including VISTEC variable-shape e-beam lithography are employed for the fabrication. In addition, wafer-level statistics of the multiplexers clearly shows the echelle grating to be inherently fabrication-insensitive to processing drifts, resulting in a minimized dispersion of the multiplexer performances over the wafer. In particular, the echelle grating spectral response remains stable over the wafer in terms of crosstalk, channel spacing and bandwidth, with the wavelength dispersion of the filter comb being limited to just 0.8 nm, thus highlighting the intrinsic robustness of design, fab pathways as well as the reliability of modeling tools. As well as that, apodized one-dimensional vertical fiber couplers, optimized multi-mode interferometers (MMIs) and extremely low-losses slow-light waveguides are demonstrated and discussed. The adiabatic apodization of such 1-D gratings is capable to provide band-edge group indices ng as high as 30 with propagation losses equivalent to the indexlike propagation regime.

We propose a 650/1550nm wavelength Mux/DeMux for SS-OCT system based on silica-on-silicon (SoS), in which mixing red/infrared lightbeams can be fully separated at low insert loss through special cascaded multimode interference (MMI) structure. Each independent lightbeam is entered into its respective channel by selecting proper width and length of the MMI. By using of Finite Difference Beam Propagation Method (FD-BPM), the Mux/DeMux is optimally designed in size of 1×0.1cm2, working at 650nm and 1550nm simultaneously. The results show the degrees of separation between two lightwaves are super high, loss of infrared light is less than 0.5dB and 1dB, and its output power stability is less than 0.25dB and 0.8dB, in 1510nm -1570nm and in 1500nm -1600nm, respectively. The Mux/DeMux can be used in SS-OCT PIC based on SoS.

As the bit rates of routed data streams exceed the throughput of single wavelength-division multiplexing channels, spectral and spatial traffic aggregation become essential for optical network scaling. These aggregation techniques reduce network routing complexity by increasing spectral efficiency to decrease the number of fibers, and by increasing switching granularity to decrease the number of switching components. Spectral aggregation yields a modest decrease in the number of fibers but a substantial decrease in the number of switching components. Spatial aggregation yields a substantial decrease in both the number of fibers and the number of switching components. To quantify routing complexity reduction, we analyze the number of multi-cast and wavelength-selective switches required in a colorless, directionless and contentionless reconfigurable optical add-drop multiplexer architecture. Traffic aggregation has two potential drawbacks: reduced routing power and increased switching component size.

A multicore fiber (MCF)-based mode multiplexer/demultiplexer (MUX/DEMUX) that can overcome the alignment issue of the fiber-based mode MUX/DEMUX is proposed. Design concept and fabrication results of the MCF-based mode MUX/DEMUX for two-spatial-mode operation (LP 01 and LP 11 ) (2M-MUX/DEMUX) and for three-spatial-mode operation (LP 01 , LP 11a , and LP 11b ) (3M-MUX/DEMUX) are presented. The fabricated 2M-MUX/DEMUXes for C-band or L-band, using the same MCF with different elongation ratios demonstrate a coupling efficiency of greater than 90% over each band. Finally, a 3M-MUX/DEMUX with a fan-in/fan-out device is presented. The selective excitation of LP 01 , LP 11a , and LP 11b modes depending on input ports is experimentally demonstrated.

We demonstrate an integrated-optic device for multiplexing an OFDM signal based on optical IFFT. The silica waveguide-based multiplexer is composed of four inputs followed by mutually connected directional couplers, an array of delay lines, and a combiner. Four signals modulated with different sequences of data are fed into the multiplexer, and an optical OFDM signal is generated through the IFFT process directly in the optical domain. We report the configuration, operating principle, and experimental results to indicate that the multiplexer operates properly. We successfully generated 40 and 80 Gbit/s OFDM signals with the multiplexer.

We report a six mode spatial multiplexer with high efficiency and high mode selectivity, based on the technique of Multi-Plane Light Conversion (MPLC). Using this mode selective multiplexer, we demonstrate a total insertion loss in a six-mode fiber below 5 dB and a mode-to-mode selectivity greater than 20 dB over a broad wavelength range from 1530 to 1565 nm. Furthermore, this device can address any spatial mode profile of any few-mode fiber with high fidelity. This mode-multiplexer proves to be fully compatible with a wavelength- and space-division multiplexed optical transmission line.

Laser communication with both high photon information efficiency (many bits/detected-photon) and high spectral efficiency (many bits/sec-Hz) is impossible with a single spatial-mode free-space link. Achieving these high efficiencies in the same system requires operation with 10's to 1000's of high-transmissivity spatial modes. Such systems will likely be restricted to 1 to 10 km line-of-sight terrestrial paths on which turbulence-induced cross talk will be encountered. In this paper we propose a cross-talk simulator for multiple spatial-mode free-space optical communication that could provide valuable information about the relevant merits of different mode sets when they are employed in conjunction with real modal multiplexers and demultiplexers.

Spatial domain multiplexing (SDM) is a system that allows multiple channels of light to traverse a single fiber, utilizing separate spatial regions inside the carrier fiber, thereby applying a new degree of photon freedom for optical fiber communications. These channels follow a helical pattern, the screen projection of which is viewable as concentric rings at the output end of the system. The MIMO nature of the SDM system implies that a typical pin-diode or APD will be unable to distinguish between these channels, as the diode will interpret the combination of the SDM signals from all channels as a single signal. As such, spatial de-multiplexing methods must be introduced to properly detect the SDM based MIMO signals. One such method utilizes a fiber consisting of multiple, concentric, hollow core fibers to route each channel independently and thereby de-mux the signals into separate fibers or detectors. These de-mux fibers consist of hollow core cylindrical structures with beveled edges on one side that gradually taper to route the circular, ring type, output energy patterns into a spot with the highest possible efficiency. This paper analyzes the beveled edge by varying its length and analyzing the total output power for each predetermined length allowing us to simulate ideal bevel length to minimize both system losses as well as total de-mux footprint. OptiBPM simulation engine is employed for these analyses.

A novel controllable wavelength-selective coupling photonic crystal fiber (PCF) has been proposed. This coupler allows highly accurate control of the filtering wavelength. The different wavelengths can be selected by controlling the bending radius of the fiber. Coupling characteristics of novel controllable wavelength-selective coupling PCF are evaluated by using a vector finite element method and their application to a multiplexer demultiplexer based on the novel coupler is investigated. When the fiber length is 4741μm, the bending radius of PCF couplers for 1.48/1.55μm, 1.3/1.55μm, 0.98/1.55μm, and 0.85/1.55μm is calculated, respectively and the beam propagation analysis is performed. Different from the traditional wavelength-selective coupling PCF, the dual-core PCF is bent and it can realize the separation of multiple wavelengths.

We are developing transition-edge sensor (TES)-based microcalorimeters for the X-ray Integral Field Unit (XIFU) of the future European X-Ray Observatory Athena. The microcalorimeters are based on TiAu TESs coupled to 250{\mu}m squared, AuBi absorbers. We designed and fabricated devices with different contact geometries between the absorber and the TES to optimise the detector performance and with different wiring topology to mitigate the self-magnetic field. The design is tailored to optimise the performance under Frequency Domain Multiplexing. In this paper we review the main design feature of the pixels array and we report on the performance of the 18 channels, 2-5MHz frequency domain multiplexer that will be used to characterised the detector array., Comment: 9 pages, 8 figures

We have demonstrated a kilopixel, filled, infrared bolometer array for the balloon-borne Primordial Inflation Polarization Explorer (PIPER). The array consists of three individual components assembled into a single working unit: 1) a transition-edge-sensor bolometer array with background-limited sensitivity, 2) a quarter–wavelength backshort grid, and 3) an integrated Superconducting Quantum Interference Device (SQUID) multiplexer (MUX) readout. The detector array is a filled, square–grid of suspended, one-micron thick silicon bolometers with superconducting sensors. The Backshort–Under–Grid (BUG) is a separately fabricated component serving as a backshort to each pixel in the array. The backshorts are positioned in the cavities created behind each detector by the back–etched well. The spacing of the backshort beneath the detector grid can be set from ~30-300_microns by independently adjusting process parameters during fabrication. Kilopixel arrays are directly indium–bump–bonded to a 32x40 SQUID multiplexer circuit. The array architecture is suitable for a wide range of wavelengths and applications. Detector design specific to the PIPER instrument, fabrication overview, and assembly technologies will be discussed.

In some optical systems in which a large field of view (and hence a large detector) is required, it is the detector which drives the total system cost. We propose a concept, and demonstrate an optical system, for an astronomical multiplexer. The instrument projects different portions of the telescope focal plane into a single (possibly) small detector without changing the original plate scale of the image. The resulting image is a superposition of the different portions of the field of view. Since in most cases astronomical images are sparse, photometric measurements can be done directly on the combined images for most objects in the field. We discuss an outline of the concept of multiplexing, in terms of its signal-to-noise properties, and multiplexed image reconstruction algorithm. Furthermore, we present an optical design for an astronomical multiplexer we recently constructed along with some first light images.

We developed a new readout system for the near-infrared detector VIRGO-2K (2kx2k HgCdTe array) installed in the optical-infrared simultaneous camera, HONIR, for the 1.5 m Kanata telescope at Higashi-Hiroshima observatory. The main goal of this development is to read out one frame within ~ 1 second through 16 output readout mode of the detector, in order to reduce the overhead time per exposure. The system is based on a CCD controller, Kiso Array Controller (KAC). We redesigned the analog part of KAC to fit VIRGO-2K. We employed a fully differential input circuit and a third order Bessel low-pass filter for noise reduction and a constant current system to improve the linearity of the detector. We set the cutoff frequency of the Bessel low-pass filter at the readout clock rate (120 kHz). We also set the constant current at 200 μA according to the data sheet of VIRGO-2K. We tested the new readout system at room temperature and confirmed that the low-pass filter works well as designed. The fluctuation of the current level of the constant current system is less than 2% for the typical output voltage range of VIRGO-2K (3.2-4.4 V). We measured the readout noise caused by the new readout system (connected to cooled multiplexer) and found that it is 30-40 μV rms, being comparable to or slightly higher than the typical readout noise of VIRGO-2K, ∼ 37 μV rms.

With this paper we investigate the system-level performance of VCSELs, parameterized with true experimental LI-VI data and dynamic characteristics of state-of-the-art VCSELs with 3 dB modulation bandwidth at 15 GHz, and propose their deployment as high-speed multi-level optical sources in a mid-range active optical cable (AOC) model for performance prediction of a rack-to-rack interconnection. The AOC architecture combines a 6-element 1550 nm VCSEL array, each directly modulated with 40 Gbaud PAM-4 data, with a wavelength division multiplexer (WDM), in order to implement a parallel link with aggregate traffic of 0.48 Tb/s. Transmission reach exceeded 300 m by deploying a two-tap feed forward equalizer filter at the electrical VCSEL driver. Bit Error Rate (BER) measurements and analysis were carried out in MATLAB. In practice, the thermal behavior and basic operational characteristics of the VCSELs fabricated by the Technische Universitat Munchen (TUM) were used to study the thermal performance and operational range of the complete AOC model. The VCSELs were initially operated at 20°C and BER measurements showed power penalties of 1.7 dB and 3.5 dB at 300 m and 500 m of transmission distance respectively for all 6 data channels. System performance was also investigated for elevated operating temperatures of the VCSEL module and the additional system degradation and BER penalties introduced by operation at 50°C and 65°C were also investigated for transmission distances of 300 m and 500 m.

The article explores multiplexers (MUX) and demultiplexers (DEMUX) based on the angular dispersion effect. The article presents calculation of the reflective prism based on MUX-DEMUX CWDM built under the Littrow scheme, as well as the requirements to its optical elements.

Submicron silicon-on-insulator (SOI) optical waveguides, which has ultra-high index contrast and ultra-small cross section, provide a very promising way to realize nano-photonic integrated circuits (PICs) with high integration density. Mode conversion and coupling play an important role for realizing various functionality elements. In this paper, a review is given for our recent work including the following parts. First, we discuss the polarizationdependent mode conversion happening in an adiabatic submicron SOI optical waveguide tapers and the application to realize polarization rotation with simple fabrication processes. Second, the mode coupling/conversion in an asymmetrical directional coupler (ADC) is summarized. The application for ADCs includes the realization of ultrasmall polarization-beam splitters (PBS) as well as ultra-compact broadband mode multiplexers (which is very important to enable ultra-high speed optical interconnects with a multimode optical waveguide).

In this paper we will discuss recent results in our work on Silicon Photonics. This will include active and passive devices for a range of applications. Specifically we will include work on modulators and drivers, deposited waveguides, multiplexers, device integration and Mid IR silicon photonics. These devices and technologies are important both for established applications such as integrated transceivers for short reach interconnect, as well as emerging applications such as disposable sensors and mass market photonics.

In this work we introduce the design, optimization, simulation and experimental characterization results of a 30-to-1 wavelength multiplexer for a Distributed Feedback Quantum Cascade Laser (DFB QCL) laser array operating in the 7- 8.5 μm (mid-long) infrared (IR) range based on an Echelle mirror using a dual Rowland circle grating scheme. This design is proposed in order to achieve a continuous tuning range overcoming the limited tunability of individual QCLs. The design is based on a DFB-QCL array with wavelength spacing of 0.05 μm, aiming to reducing coupling between the slab waveguides to a minimum. We discuss the design parameters such as the order of diffraction, the operation wavelength range in the slab waveguides and the position of both the input and output waveguides are optimized for obtaining higher output power in the overall wavelength range of the multiplexer device than in a single Rowland circle grating scheme, providing an improvement in channel transmission. Other design characteristics, such as the structure scalability and reduction in size for these devices are considered and studied, including the input/output waveguide optimization as a function of parameters such as waveguide width, etching depth and wavelength. A systematic process is presented for all steps in the design of these devices, comparing both simulated and experimental results, placing them as suitable options when compared to other IR multiplexer schemes in terms of size and transmission.

We report details of an experimental demonstration involving a 15 meter pointed indoor optical wireless link in the 1550-nm wavelength range, that is comprised of a uni-directional Cable Television (CATV) signal and a bi-directional link comprised of two 10 Gbps data links. Four port wavelength division mux-demuxes have been used on both ends of the link. The CATV transmission system is connected to port 1 of the mux-demux. CATV signal consists of both analog and digital parts, and its bandwidth is 1 GHz. The laser is directly modulated by the CATV signal, and at the receiver end, the optical signal is demodulated and fed to a TV. Port 2 of the mux-demux is left unused. Ports 3 and 4 are used for the 10 Gbps links. A bit error rate tester has been used to generate the 10 Gbps signals that are converted to optical wavelengths by enhanced Small Form Factor Pluggable (SFP+) modules at both ends of the setup. Collimators are used at both ends to transmit the combined optical signal that is the output of the mux and to receive the optical signal by focusing it onto a single-mode fiber as the input of the demux. We present results on the CATV portion of the setup and the bit-error-rate performance of the two 10 Gbps links. This experiment shows the feasibility of using pointed optical links in datacenters as secondary links to alleviate the loads of highly utilized wired connections and improve the overall throughput performance of datacenters.

A flexible and efficient channel bandwidth assignment is highly required for next optical generation networks. Among various techniques to enhance the wavelength routing capability, wavelength conversion plays an important role on improving network reconfigurability. In this paper, we experimentally demonstrate a sub-band wavelength conversion of a wide-band optical orthogonal frequency-division multiplexing (OFDM) signal based on four-wave mixing (FWM) using high-nonlinear fiber (HNLF) to solve the spectrum conflicts in the flexible coherent optical OFDM (CO-OFDM) networks. Combining with the wavelength selective switch (WSS) in a reconfigurable optical add/drop multiplexer (ROADM), some spectrum-overlapped sub-bands are successfully relocated to ‘seamlessly’ form a new wide-band signal, which efficiently eliminates the spectrum conflicts, and achieves a good spectral efficiency.

Space-division multiplexing (SDM) systems transmit over multiple spatial-paths to increase capacity or photon efficiency. In these links, coupling between the spatial paths scramble each input signal across all the output channels. This scrambling is described by a N × M frequency dependent transfer matrix which can be undone using multiple-input multiple-output processing. Using a swept-wavelength interferometer with spatial diversity, we can completely characterize the amplitude and phase transmission between each input and output across the entire C-band in a single 100-ms scan. Matrix eigenanalysis of the transfer matrix enables extraction of the system's insertion loss, mode-dependent loss, and the principle-states of polarization. Results will include transfer matrix measurements of few-mode fibers, coupled-core fibers, photonic lantern spatial-multiplexers, and SDM compatible wavelength routing components such as a wavelength selective switch.