Showing papers on "Insertion loss published in 2014"

Mode-selective photonic lanterns for space-division multiplexing

Abstract: We demonstrate a 3x1 fiber-based photonic lantern spatial-multiplexer with mode-selectivity greater than 6 dB and transmission loss of less than 0.3 dB. The total insertion loss of the mode-selective multiplexers when coupled to a graded-index few-mode fiber was < 2 dB. These mode multiplexers showed mode-dependent loss below 0.5 dB. To our knowledge these are the lowest insertion and mode-dependent loss devices, which are also fully compatible with conventional few-mode fiber technology and broadband operation.

Frequency-Selective Rasorber Based on Square-Loop and Cross-Dipole Arrays

Abstract: A novel design of a transmission window within the absorption band of a circuit analog absorber, named as frequency-selective rasorber (FSR), is presented. Based on an equivalent circuit model, the conditions are formulated to produce a passband with small insertion loss and to reduce the reflection at frequencies below and above the passband in the meanwhile. Simple design guidelines of our proposed FSR are then developed. With loaded lumped elements, the arrays of square-loop and cross-dipole are combined to realize its implementation. It is shown through measurements that an insertion loss of 0.68 dB can be obtained at 4.42 GHz and the fractional bandwidth for at least 10 dB reflection reduction within the lower and upper frequency bands is 92.3% under the normal incidence. A good agreement between simulated and measured results validates our design.

A Non-Reciprocal Component with Distributedly Modulated Capacitors

Abstract: The concept of distributedly modulated capacitors (DMC) is proposed as a form of time-varying transmission-line structure offering nonreciprocal propagation and coupling characteristics. The nonreciprocity is achieved by taking advantage of the additional dimension of time-variance in the transmission-line property. The complete theory, based on: 1) the distributed parametric effect on a time-varying transmission line and 2) the distributed capacitive mixers, is presented with emphasis on the theoretical bounds of the isolation and insertion performances of DMC. Simulations are carried out and a prototype consisting of double-balanced varactor diodes on microstrip lines is implemented on a Rogers board. The measured results agree well with the theoretical derivations and the simulation results. It is thus confirmed that the DMC has great potential of being a circulator device with broadband, minimum insertion loss, and synthesizable isolation characteristics. It can be integrated into an RF system front-end that allows transmission and reception of signals at the same time and the same frequency.

Efficient, compact and low loss thermo-optic phase shifter in silicon

Abstract: We design a resistive heater optimized for efficient and low-loss optical phase modulation in a silicon-on-insulator (SOI) waveguide and characterize the fabricated devices. Modulation is achieved by flowing current perpendicular to a new ridge waveguide geometry. The resistance profile is engineered using different dopant concentrations to obtain localized heat generation and maximize the overlap between the optical mode and the high temperature regions of the structure, while simultaneously minimizing optical loss due to free-carrier absorption. A 61.6 μm long phase shifter was fabricated in a CMOS process with oxide cladding and two metal layers. The device features a phase-shifting efficiency of 24.77 ± 0.43 mW/π and a −3 dB modulation bandwidth of 130.0 ± 5.59 kHz; the insertion loss measured for 21 devices across an 8-inch wafer was only 0.23 ± 0.13 dB. Considering the prospect of densely integrated photonic circuits, we also quantify the separation necessary to isolate thermo-optic devices in the standard 220 nm SOI platform.

Wideband 3D Frequency Selective Rasorber

Abstract: This communication presents a 3D frequency selective rasorber (FSR) with bandpass filtering response and wideband absorption characteristics. By loading an array of lumped resistors at one side of a microstrip-line based bandpass frequency selective structure (FSS), multiple resonators, including lossy resonators, are constructed. The bandpass performance with high selectivity is provided by resonators in the substrate region of the microstrip line. The absorption characteristic is obtained by the lossy resonators at the resistor-loaded side of the air region. All reflected waves at the resistor-loaded side can be effectively absorbed by appropriately choosing the resistance value. Physical mechanism of the FSR is analyzed with the aid of an equivalent circuit model and current distributions. As an example, a prototype of the designed FSR is fabricated and tested. Experimental results show that the insertion loss at the center frequency is 2.4 dB and a bandwidth of 114% for the absorption better than 10 dB in the upper rejection band is achieved under the normal incidence.

A low-cost microwave rotary joint

Abstract: A simple and cheap coaxial microwave rotary joint covering frequencies from 1 to 21 GHz is described Measured typical insertion loss is 07 dB, return loss stays better than 10 dB and the rotating torque requirement is 26 mNm Maximum variation of attenuation as a function of rotating angle is 05 dB Operation up to 37 GHz has been tried with loss values around 2 dB, typical

Topology optimized mode conversion in a photonic crystal waveguide fabricated in silicon-on-insulator material.

Abstract: We have designed and for the first time experimentally verified a topology optimized mode converter with a footprint of ~6.3 μm × ~3.6 μm which converts the fundamental even mode to the higher order odd mode of a dispersion engineered photonic crystal waveguide. 2D and 3D topology optimization is utilized and both schemes result in designs theoretically showing an extinction ratio larger than 21 dB. The 3D optimized design has an experimentally estimated insertion loss lower than ~2 dB in an ~43 nm bandwidth. The mode conversion is experimentally confirmed in this wavelength range by recording mode profiles using vertical grating couplers and an infrared camera. The experimentally determined extinction ratio is > 12 dB and is believed to be limited by the spatial resolution of our setup.

Comparison of AWGs and Echelle gratings for wavelength division multiplexing on silicon-on-insulator

Abstract: We compare the performance (insertion loss and crosstalk) of silicon-based arrayed waveguide gratings (AWGs) and echelle gratings for different channel spacings. For high-resolution de/multiplexer (DWDM) applications, AWGs are the better choice, whereas echelle gratings perform well for low-resolution de/multiplexer (CWDM) applications. Alternatively, for low-resolution de/multiplexer applications, the conventional box-shaped silicon AWG can be modified by an S-shaped AWG. We report crosstalk as low as -27 dB for regular AWGs, whereas in the S-shaped AWGs, the crosstalk is better than -19 dB, with an insertion loss below -2 dB. The crosstalk of the echelle gratings varies between -19 and -23 dB, with insertion loss below -2 dB.

Graphene based low insertion loss electro-absorption modulator on SOI waveguide

Abstract: Graphene is considered a promising material for broadband opto-electronics because of its linear and gapless band structure. Its optical conductivity can be significantly tuned electrostatically by shifting the Fermi level. Using mentioned property, we experimentally demonstrate a graphene based electro-absorption modulator with very low insertion loss. The device is realized on a silicon on insulator (SOI) waveguide operating at 1550 nm wavelength. The modulator shows a modulation depth of 16 dB and an insertion loss of 3.3 dB, surpassing GeSi and previous graphene based absorption modulators and being comparable to silicon Mach-Zehnder interferometer based modulators.

Low-Loss Silicon Nitride AWG Demultiplexer Heterogeneously Integrated With Hybrid III–V/Silicon Photodetectors

Abstract: A unique and novel platform that combines III-V and silicon photonic components with ultra-low loss silicon nitride waveguides for monolithic integration of novel photonic circuits is presented. Successful (proof-of-principle) integration of eight hybrid III-V/silicon photodetectors and an arrayed waveguide grating is shown. The InGaAs photodiodes in this platform had average fiber-coupled responsivity of 0.36 A/W at 1550 nm, 30 GHz electrical bandwidth, and operated up to 50 Gb/s. The AWG had an insertion loss of 0.85 dB and adjacent-channel cross-talk less than -38 dB.

Efficient, Compact and Low Loss Thermo-Optic Phase Shifter in Silicon

Abstract: We design a resistive heater optimized for efficient and low-loss optical phase modulation in a silicon-on-insulator (SOI) waveguide and characterize the fabricated devices. Modulation is achieved by flowing current perpendicular to a new ridge waveguide geometry. The resistance profile is engineered using different dopant concentrations to obtain localized heat generation and maximize the overlap between the optical mode and the high temperature regions, while simultaneously minimizing optical loss due to free-carrier absorption. A 61.6 micrometer-long phase shifter was fabricated in a CMOS process with oxide cladding and two metal layers. The device features a phase-shifting efficiency of 24.77 +/- 0.43 mW/pi and a -3 dB modulation bandwidth of 130.0 +/- 5.59 kHz. The insertion loss measured for 21 devices across an 8-inch wafer was only 0.23 +/- 0.13 dB. Considering the prospect of densely integrated photonic circuits, we also quantify the separation necessary to isolate thermo-optic devices in the standard 220 nm SOI platform.

λ-Size ITO and Graphene-Based Electro-Optic Modulators on SOI

Abstract: One of the key devices that convert electronic signals into high bit-rate photonic data is the electro-optic modulator (EOM). Its on-chip design plays an important role for the integration of electronic and photonic devices for various types of applications including photonic computing and telecommunication. Recently, indium tin oxide (ITO) and graphene have attracted significant attention primarily due to their extraordinary electro-optic properties for the design of ultra-compact EOMs to handle bandwidth and modulation strength trade-off. Here we show design details of a high-performance ITO-EOM in a plasmonic silicon-on-insulator hybrid structure. Results show that ITO is capable of changing its extinction coefficient by a factor of 136 leading to 3 λ-short devices with an extinction ratio of about 1dB/μm. Further numerical device optimizations demonstrate the feasibility for an extinction ratio and on-chip insertion loss of about 6 dB/μm and 0.25 dB, respectively, for a sub-wavelength compact (0.78 λ) EOM design using ITO. Utilizing graphene as an active switching material in a similar ultra-compact plasmonic hybrid EOM design yields enhanced light-matter interaction, in which extinction-ratio is 9 times larger than the insertion-loss for a 0.78 λ short device. Both ITO and graphene EOMs are capable of broadband operations (>500 nm) since no resonator is deployed.

Mid-infrared integrated waveguide modulators based on silicon-on-lithium-niobate photonics

Abstract: Heterogeneous integration techniques, such as direct bonding, have enabled solutions to many problems facing integrated photonics. In particular, the relatively new field of mid-infrared (mid-IR) integrated photonics has been hindered by the availability of functional, transparent substrates in this wavelength range. The key to achieving compact, high-performance optical modulation and frequency conversion is the monolithic integration of silicon photonics with a material with high second-order nonlinear susceptibility. By transferring large areas of thin, monocrystalline silicon to bulk lithium niobate (LiNbO3) substrates, the first silicon-based platform to exploit the Pockels or linear electro-optic effect in the mid-IR range is achieved. Integrated Mach–Zehnder interferometer modulators with an extinction ratio of ∼8 dB, a half-wave voltage-length product of 26 V·cm, and an on-chip insertion loss of 3.3 dB are demonstrated at a wavelength of 3.39 μm. Ultrathin optical waveguides fabricated and characterized on this platform exhibit a low transverse electric mode linear propagation loss of 2.5 dB/cm. Future capabilities such as wideband difference frequency generation for integrated mid-IR sources are envisioned for the demonstrated silicon-on-lithium-niobate platform.

Wideband Four-Way Out-of-Phase Slotline Power Dividers

Abstract: Two new wideband four-way out-of-phase slotline power dividers are proposed in this paper. The half-wavelength slotlines are employed to construct the presented compact power dividers. Based on the proposed power-dividing circuit, a four-way power divider is implemented with compact size and simple structure. To obtain high isolation among the four output ports and good output impedance matching, another four-way out-of-phase slotline power divider with improved isolation performance is designed by introducing an air-bridge resistor and two slotlines with isolation resistors. The simulated and measured results of the proposed power dividers demonstrate reasonable performance of impedance matching, insertion loss, amplitude balancing, and isolation among the output ports.

New Wideband Transition From Microstrip Line to Substrate Integrated Waveguide

Abstract: A new wideband transition from microstrip line to substrate integrated waveguide (SIW) is introduced. Unlike most transitions that show reduced return loss over significant parts of a regular waveguide band, the presented configuration achieves return losses better than 30 dB in standard waveguide frequency bands from X to E. The new aspect of this transition is the addition of two vias to the widely used microstrip taper transition. Moreover, the influence of the substrate height is demonstrated. The results in each frequency band are compared with the data for the regular microstrip taper alone. A design formula for the placement of the vias and taper dimensions is presented and demonstrated to provide excellent results. The structures are simulated and optimized with CST Microwave Studio. Measurements performed on a Ku-band back-to-back prototype transition demonstrate a minimum return loss of 26.05 dB and maximum insertion loss of 0.821 dB over the entire Ku-band, thus validating the design approach.

Polarization rotator-splitters and controllers in a Si3N4-on-SOI integrated photonics platform.

Abstract: We demonstrate novel polarization management devices in a custom-designed silicon nitride (Si(3)N(4)) on silicon-on-insulator (SOI) integrated photonics platform. In the platform, Si(3)N(4) waveguides are defined atop silicon waveguides. A broadband polarization rotator-splitter using a TM0-TE1 mode converter in a composite Si(3)N(4)-silicon waveguide is demonstrated. The polarization crosstalk, insertion loss, and polarization dependent loss are less than -19 dB, 1.5 dB, and 1.0 dB, respectively, over a bandwidth of 80 nm. A polarization controller composed of polarization rotator-splitters, multimode interference couplers, and thin film heaters is also demonstrated.

On the Analysis and Design of Low-Loss Single-Pole Double-Throw W-Band Switches Utilizing Saturated SiGe HBTs

Abstract: This paper describes the analysis and design of saturated silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) switches for millimeter-wave applications. A switch optimization procedure is developed based on detailed theoretical analysis and is then used to design multiple switch variants. The switches utilize IBM's 90-nm 9HP technology, which features SiGe HBTs with peak f T/ fmax of 300/350 GHz. Using a reverse-saturated configuration, a single-pole double-throw switch with a measured insertion loss of 1.05 dB and isolation of 22 dB is achieved at 94 GHz after de-embedding pad losses. The switch draws 5.2 mA from a 1.1-V supply, limiting power consumption to less than 6 mW. The switching speed is analyzed and the simulated turn-on and turn-off times are found to be less than 200 ps. A technique is also introduced to significantly increase the power-handling capabilities of saturated SiGe switches up to an input-referred 1-dB compression point of 22 dBm. Finally, the impact of RF stress on this novel configuration is investigated and initial measurements over a 48-h period show little performance degradation. These results demonstrate that SiGe-based switches may provide significant benefits to millimeter-wave systems.

Tunable CMOS Integrated Duplexer With Antenna Impedance Tracking and High Isolation in the Transmit and Receive Bands

Abstract: A hybrid transformer-based integrated tunable duplexer is demonstrated. High isolation between the transmit and receive ports is achieved through electrical balance between the antenna and balance network impedances. A novel high-power-tolerant balance network, which can be tuned at both the transmit and receive frequencies, allows high isolation in both the transmit and receive bands even under realistic antenna impedance frequency dependence. To maintain high isolation despite antenna impedance variation, a feedback loop is employed to measure the transmitter leakage and correct the impedance of the balance network. An isolation > 50 dB in the transmit and receive bands with an antenna voltage standing-wave ratio within 2:1 was achieved. The duplexer, along with a cascaded direct-conversion receiver, achieves a noise figure of 5.3 dB, a conversion gain of 45 dB, and consumes 51 mW of power. The insertion loss in the transmit path was less than 3.8 dB. Implemented in a 65-nm CMOS process, the chip occupies an active area of 2.2 mm 2 .

CMOS-compatible highly efficient polarization splitter and rotator based on a double-etched directional coupler.

Abstract: We present a highly efficient polarization splitter and rotator (PSR), fabricated using 248 nm deep ultraviolet lithography on a silicon-on-insulator substrate. The PSR is based on a double-etched directional coupler with a length of 27 µm. The fabricated PSR yields a TM-to-TE conversion loss better than 0.5 dB and TE insertion loss better than 0.3 dB, with an ultra-low crosstalk (−20 dB) in the wavelength regime 1540-1570 nm.

Ultrafast all-optical modulation with hyperbolic metamaterial integrated in Si photonic circuitry.

Abstract: The integration of optical metamaterials within silicon integrated photonic circuitry bears significantly potential in the design of low-power, nanoscale footprint, all-optical functionalities. We propose a novel concept and provide detailed analysis of an on-chip ultrafast all-optical modulator based on an hyperbolic metamaterial integrated in a silicon waveguide. The anisotropic metamaterial based on gold nanorods is placed on top of the silicon waveguide to form a modulator with a 300x440x600 nm(3) footprint. For the operating wavelength of 1.5 μm, the optimized geometry of the device has insertion loss of about 5 dB and a modulation depth of 35% with a sub-ps switching rate. The switching energy estimated from nonlinear transient dynamic numerical simulations is 3.7 pJ/bit when the transmission is controlled optically at a wavelength of 532 nm, resonant with the transverse plasmonic mode of the metamaterial. The switching mechanism is based on the control of the hybridization of eigenmodes in the metamaterial slab and the Si waveguide.

Low-loss and low-crosstalk 8 × 8 silicon nanowire AWG routers fabricated with CMOS technology

Abstract: Low-loss and low-crosstalk 8 × 8 arrayed waveguide grating (AWG) routers based on silicon nanowire waveguides are reported. A comparative study of the measurement results of the 3.2 nm-channel-spacing AWGs with three different designs is performed to evaluate the effect of each optimal technique, showing that a comprehensive optimization technique is more effective to improve the device performance than a single optimization. Based on the comprehensive optimal design, we further design and experimentally demonstrate a new 8-channel 0.8 nm-channel-spacing silicon AWG router for dense wavelength division multiplexing (DWDM) application with 130 nm CMOS technology. The AWG router with a channel spacing of 3.2 nm (resp. 0.8 nm) exhibits low insertion loss of 2.32 dB (resp. 2.92 dB) and low crosstalk of -20.5~-24.5 dB (resp. -16.9~-17.8 dB). In addition, sophisticated measurements are presented including all-input transmission testing and high-speed WDM system demonstrations for these routers. The functionality of the Si nanowire AWG as a router is characterized and a good cyclic rotation property is demonstrated. Moreover, we test the optical eye diagrams and bit-error-rates (BER) of the de-multiplexed signal when the multi-wavelength high-speed signals are launched into the AWG routers in a system experiment. Clear optical eye diagrams and low power penalty from the system point of view are achieved thanks to the low crosstalk of the AWG devices.

Highly Linear, Broadband Optical Modulator Based on Electro-optic Polymer

Abstract: In this paper, we present the design, fabrication and characterization of a traveling wave directional coupler modulator based on electro-optic polymer, which is able to provide both high linearity and broad bandwidth. The high linearity is realized by introducing domain-inversion technique in the two-domain directional coupler. A travelling wave electrode is designed to function with bandwidth-length product of 302GHz cm, by achieving low microwave loss, excellent impedance matching and velocity matching, as well as smooth electric field profile transformation. The 3-dB bandwidth of the device is measured to be 10GHz. The spurious free dynamic range of about 110dB Hz^(2/3) is measured over the modulation frequency range 2-8GHz. To the best of our knowledge, such high linearity is first measured at the frequency up to 8GHz. In addition, a 1-to-2 multi-mode interference 3dB-splitter, a photobleached refractive index taper and a quasi-vertical taper are used to reduce the optical insertion loss of the device.

Compact Balanced-to-Balanced Microstrip Diplexer With High Isolation and Common-Mode Suppression

Abstract: In this letter, a compact balanced-to-balanced microstrip diplexer with high isolation and common-mode (CM) suppression is proposed for wireless local area networks (WLAN) and worldwide interoperability for microwave access (WiMAX) applications simultaneously. The proposed diplexer is designed via the combination of two balanced bandpass filters (BPF) without extra junction matching network. Both BPFs are composed of uniform impedance resonators (UIR) and short- ended microstrip parallel-coupling feedlines. Finally, the proposed diplexer is fabricated and measured. The measured differential-mode (DM) isolation in the two passbands is more than 33 dB. While for the CM signal, the insertion loss is below 30 dB in the two operation bands. The simulated and measured results exhibit a satisfactory agreement to validate the proposed configuration. The diplexer size is only 0.26λg ×0.38λg, where λg is the guided wavelength at 2.45 GHz.

Tunable wideband microwave photonic phase shifter using on-chip stimulated Brillouin scattering

Abstract: We present the first microwave photonic phase shifter using stimulated Brillouin scattering (SBS) on-chip. The unique ability of SBS to generate both narrowband gain and loss resonances allows us to achieve low ±1.5 dB amplitude fluctuations, which is a record for integrated devices, along with 240° continuously tunable phase shift. Contrary to previous SBS-based approaches, the phase shift tuning mechanism relies on tuning the power, not the frequency, of two SBS pumps, making it more suited to on-chip implementations. We finally demonstrate that SBS pump depletion leads to amplitude response fluctuations, as well as increasing the insertion loss of the phase shifter. Advantageously, shorter integrated platforms possess higher pump depletion thresholds compared to long fibers, thus offering greater potential for reducing the insertion loss.

Fabrication tolerant and broadband polarization splitter and rotator based on a taper-etched directional coupler.

Abstract: We propose a fabrication tolerant polarization splitter and rotator (PSR) on the silicon-on-insulator platform based on the mode-coupling mechanism. The PSR consists of a silicon wire waveguide coupled to a taper-etched waveguide. Compared to previously reported PSRs based on directional couplers which are sensitive to fabrication variations, the partially etched taper structure can compensate for fabrication inaccuracies. In addition, the taper-etched geometry breaks both the horizontal and vertical symmetries of the waveguide, introducing an additional degree of design freedom to accommodate different upper cladding layers. The proposed PSR can be readily integrated in a planar waveguide circuit using e.g. SiO2 cladding, making it compatible with typical metal back-end-of-line processes. Our simulation results show that the PSR has a low TM-to-TE polarization conversion loss of −0.09 dB in the C-band (or a conversion efficiency of 98%). A low TE-to-TE through insertion loss (−0.07 dB) and a very low polarization crosstalk (−30 dB) over a wide wavelength range exceeding 160 nm with a large fabrication tolerance (>50 nm) are numerically demonstrated.

Design of an ultra-compact electro-absorption modulator comprised of a deposited TiN/HfO₂/ITO/Cu stack for CMOS backend integration.

Abstract: An ultra-compact electro-absorption (EA) modulator operating around 1.55-μm telecom wavelengths is proposed and theoretically investigated. The modulator is comprised of a stack of TiN/HfO2

Synthesis Model and Design of a Common-Mode Bandstop Filter (CM-BSF) With an All-Pass Characteristic for High-Speed Differential Signals

Abstract: A new common-mode bandstop filter (CM-BSF) with an all-pass performance (from dc to 9 GHz) for differential signals is proposed by using a C-shaped patterned ground structure (PGS) with meandered signal lines on a two-layer printed circuit board (PCB). This technique can successfully generate two close transmission zeros in common-mode within the frequencies of concern. A corresponding equivalent circuit model is established to predict the filter behaviors, and a formula for common-mode transmission zeros is derived based on the circuit model. Next, a design method is developed and a synthesis procedure is proposed. According to the procedure, a wideband CM-BSF is synthesized and fabricated on a two-layer PCB. In addition, the simulation and experiment results are demonstrated to verify the technique and show excellent performance of the proposed CM-BSF. It is shown that common-mode noise can be suppressed over 10 dB from 1.9 to 8.9 GHz with 130% fractional bandwidth (FBW) while the insertion loss of differential-mode can be kept less than 3 dB from dc to 9 GHz. The electrical size is only 0.21 λ g ×0.21 λ g , where λ g is the wavelength of the stopband central frequency. To sum up, the proposed CM-BSF has merits of low cost (two layer), a simple geometric structure, a compact size, and a large common-mode FBW. Most importantly, the filter can keep good signal integrity of the digital differential signals due to its all-pass characteristic.

Silicon optical diode based on cascaded photonic crystal cavities

Abstract: An all-silicon passive optical diode based on optical nonlinearity in cascaded photonic crystal (PhC) L3 cavities is proposed and demonstrated. A nonreciprocal transmission ratio (NTR) of 30.8 dB and insertion loss of 8.3 dB are realized in the device. The device has a relatively broad 17 dB operation bandwidth of 0.08 nm, and at least 16 dB of NTR is achieved when input power varies between −6.25 and −2.95 dBm. A nonlinear couple mode model for cascaded PhC cavities is established to analyze the behavior of the device, and numerical simulation results are in good agreement with the experiment results.