Silicon-based optoelectronic heterogeneous integration for optical interconnection

The performance of optical interconnection has improved dramatically in recent years.Silicon-based optoelectronic heterogeneous integration is the key enabler to achieve high performance optical interconnection,which not only provides the optical gain which is absent from native Si substrates and enables complete photonic functionalities on chip,but also improves the system performance through advanced heterogeneous integrated packaging.This paper reviews recent progress of silicon-based optoelectronic heterogeneous integration in high performance optical interconnection.The research status,development trend and application of ultra-low loss optical waveguides,high-speed detectors,high-speed modulators,lasers and 2D,2.5D,3D and monolithic integration are focused on.

Sixteen-element Ge-on-SOI PIN photo-detector arrays for parallel optical interconnects

We describe the structure and testing of one-dimensional array parallel-optics photo-detectors with 16 photodiodes of which each diode operates up to 8 Gb/s. The single element is vertical and top illuminated 30μm-diameter silicon on insulator （Ge-on-SOI） PIN photodetector. High-quality Ge absorption layer is epitaxially grown on SO1 substrate by the ultra-high vacuum chemical vapor deposition （UHV-CVD）. The photodiode exhibits a good responsivity of 0.20 A/W at a wavelength of 1550 nm. The dark current is as low as 0.36/aA at a reverse bias of 1 V, and the corresponding current density is about 51 mA/cm2. The detector with a diameter of 30 t.trn is measured at an incident light of 1.55 μm and 0.5 mW, and the 3-dB bandwidth is 7.39 GHz without bias and 13.9 GHz at a reverse bias of 3 V. The 16 devices show a good consistency.

A Single Mode Hybrid Ⅲ-Ⅴ/Silicon On-Chip Laser Based on Flip-Chip Bonding Technology for Optical Interconnection

A single mode hybrid Ⅲ-Ⅴ/silicon on-chip laser based on the flip-chip bonding technology for on-chip optical interconnection is demonstrated. A single mode Fabry-Perot laser structure with micro-structures on an InP ridge waveguide is designed and fabricated on an InP/AIGaInAs multiple quantum well epitaxial layer structure wafer by using i-line lithography. Then, a silicon waveguide platform including a laser mounting stage is designed and fabricated on a silicon-on-insulator substrate. The single mode laser is flip-chip bonded on the laser mounting stage. The lasing light is butt-coupling to the silicon waveguide. The laser power output from a silicon waveguide is 1.3roW, and the threshold is 37mA at room temperature and continuous wave operation.

MSONoC: a non-blocking optical interconnection network for inter cluster communication

Electric router is widely used for multi-core system to interconnect each other. However, with the increasing number of processor cores, the probability of communication conflict between processor cores increases, and the data delay increases dramatically. With the advent of optical router, the traditional electrical interconnection mode has changed to optical interconnection mode. In the packet switched optical interconnection network, the data communication mechanism consists of 3 processes: link establishment, data transmission and link termination, but the circuit-switched data transmission method greatly limits the utilization of resources. The number of micro-ring resonators in the on-chip large-scale optical interconnect network is an important parameter affecting the insertion loss. The proposed λ-route, GWOR, Crossbar structure has a large overall network insertion loss due to the use of many micro-ring resonators. How to use the least micro-ring resonator to realize non-blocking communication between multiple cores has been a research hotspot. In order to improve bandwidth and reduce access latency, an optical interconnection structure called multilevel switching optical network on chip(MSONoC) is proposed in this paper. The broadband micro-ring resonators(BMRs) are employed to reduce the number of micro-ring resonators(MRs) in the network, and the structure can provide the service of non-blocking point to point communication with the wavelength division multiplexing(WDM) technology. The results show that compared to λ-route, GWOR, Crossbar and the new topology structure, the number of micro-ring resonators of MSONoC are reduced by 95.5%, 95.5%, 87.5%, and 60% respectively. The insertion loss of the minimum link of new topology, mesh and MSONoC structure is 0.73 dB, 0.725 dB and 0.38 dB.

Adaptive and Intelligent Digital Signal Processing for Improved Optical Interconnection

In recent years, explosively increasing data traffic has been boosting the con?tinuous demand of high speed optical interconnection inside or among data centers, high performance computers and even consumer electronics. To pursue the improved intercon?nection performance of capacity, energy efficiency and simplicity, effective approaches are demonstrated including particularly advanced digital signal processing (DSP) meth?ods. In this paper, we present a review about the enabling adaptive DSP methods for opti?cal interconnection applications, and a detailed summary of our recent and ongoing works in this field. In brief, our works focus on dealing with the specific issues for short-reach interconnection scenarios with adaptive operation, including signal-to-noise-ratio (SNR) limitation, level nonlinearity distortion, energy efficiency consideration and the de?cision precision.

Tailoring light on three-dimensional photonic chips: a platform for versatile OAM mode optical interconnects

Explosive growth in demand for data traffic has prompted exploration of the spatial dimension of lightwaves, which provides a degree of freedom to expand data transmission capacity. Various techniques basedon bulky optical devices have been proposed to tailor light waves in the spatial dimension. However, theirinherent large size, extra loss, and precise alignment requirements make these techniques relativelydifficult to implement in a compact and flexible way. In contrast, three-dimensional (3D) photonic chips withcompact size and low loss provide a promising miniaturized candidate for tailoring light in the spatialdimension. Significantly, they are attractive for chip-assisted short-distance spatial mode optical interconnectsthat are challenging to bulky optics. Here, we propose and fabricate femtosecond laser-inscribed 3D photonicchips to tailor orbital angular momentum (OAM) modes in the spatial dimension. Various functions on theplatform of 3D photonic chips are experimentally demonstrated, including the generation, (de)multiplexing,and exchange of OAM modes. Moreover, chip-chip and chip–fiber–chip short-distance optical interconnectsusing OAM modes are demonstrated in the experiment with favorable performance. This work paves the wayto flexibly tailor light waves on 3D photonic chips and offers a compact solution for versatile opticalinterconnects and other emerging applications with spatial modes.

10 Gb/s free space optical interconnect with broadcasting capability enabled by a silicon integrated optical phased array

We have proposed and experimentally demonstrated a reconfigurable free space optical interconnect with broadcasting capability based on an eight-channel silicon integrated optical phased array.By using the silicon integrated beam steering and broadcasting device,10 Gb/s on-off keying data is transmitted over 15 cm in free space for up to three receivers located in three different cards.The experimental results show that the optical phased array can be used with broadcasting capability provided to multi-receivers in the card to card optical interconnects,which can significantly reduce device size,system complexity,and total costs.

A pair of integrated optoelectronic transceiving chips for optical interconnects

In this Letter, a pair of integrated optoelectronic transceiving chips is proposed. They are constructed by integrating a vertical cavity surface emitting laser unit above a positive-intrinsic-negative photodetector unit. One of the transceiving chips emits light at the wavelength of 848.1 nm with a threshold current of 0.8 mA and a slope efficiency of 0.81 W/A. It receives light between 801 and 814 nm with a quantum efficiency of higher than 70%. On its counterpart, the other one of the transceiving chips emits light at the wavelength of 805.3 nm with a threshold current of 1.1 mA and a slope efficiency of 0.86 W/A. It receives light between 838 and 855 nm with a quantum efficiency of higher than 70%. The proposed pair of integrated optoelectronic transceiving chips can work full-duplex with each other, and they can be applied to single fiber bidirectional optical interconnects.

A scheme of optical interconnection for super high speed parallel computer

An optical cross connection network which adopts coarse wavelength division multiplexing (CWDM) and data packet is introduced. It can be used to realize communication between multi-CPU and multi-MEM in parallel computing system. It provides an effective way to upgrade the capability of parallel computer by combining optical wavelength division multiplexing (WDM) and data packet switching technology. CWDM used in network construction, optical cross connection (OXC) based on optical switch arrays, and data packet format used in network construction were analyzed. We have also done the optimizing analysis of the number of optical switches needed in different scales of network in this paper. The architecture of the optical interconnection for 8 wavelength channels and 128 bits parallel transmission has been researched. Finally, a parallel transmission system with 4 nodes, 8 channels per node, has been designed.

An approach to the optical interconnect made in standard CMOS process

A standard CMOS optical interconnect is proposed, including an octagonal-annular emitter, a field oxide, metal 1-PSG/BPSG-metal 2 dual waveguide, and an ultra high-sensitivity optical receiver integrated with a fingered P＋/N-well/P-sub dual photodiode detector. The optical interconnect is implemented in a Chartered 3.3-V 0.35-μm standard analog CMOS process with two schemes for the research of the substrate noise coupling effect on the optical interconnect performance： with or without a GND-guardring around the emitter. The experiment results show that the optical interconnect can work at 100 kHz, and it is feasible to implement optical interconnects in standard CMOS processes.

Ultra-compact silicon-arrayed waveguide grating routers for optical interconnect systems

We present compact silicon-arrayed waveguide grating routers （AWGRs） with three different channel spacings of 20, 6.4, and 3.2 nm for optical interconnect systems. The AWGR with the 20 nm channel spacing shows a low loss of 2.5 dB and a low crosstalk of -20 dB and has a footprint of only 0.27 mm× 0.19 mm. The AWGR with the channel spacing of 6.4 nm has loss ranging from 3 to 8 dB, and the crosstalk is -18 dB. As for the 3.2 nm channel spacing, the loss is about 4 dB, and the crosstalk is -12 dB.

Power-aware transceiver design for half-duplex bidirectional chip-to-chip optical interconnects

A power-aware transceiver for half-duplex bidirectional chip-to-chip optical interconnects has been designed and fabricated in a 0.13 μm complementary metal-oxide-semiconductor （CMOS） technology. The transceiver can detect the presence and absence of received signals and saves 55% power in Rx enabled mode and 45% in Tx enabled mode. The chip occupies an area of 1.034 mm2 and achieves a 3-dB bandwidth of 6 GHz and 7 GHz in Tx and Rx modes, respectively. The disabled outputs for the Tx and Rx modes are isolated with 180 dB and 139 dB, respectively, from the enabled outputs. Clear eye diagrams are obtained at 4.25 Gbps for both the Tx and Rx modes.

LOOKNoC: a low-loss, non-blocking, scalable passive optical interconnect network-on-chip architecture

Low-loss, non-blocking, scalable passive optical interconnect network on-chip(LOOKNoC) structure was proposed based on 2×2 optical exchange switches, using wavelength division multiplexing(WDM)technology to expand to 8×8, 16×16, 32×32, 64×64 passive optical interconnection networks, which can achieve non-blocking communication. The experimental results show that based on the 16×16 optical interconnection network structure, the number of microring resonators(MRs) in LOOKNoC was reduced by 90.9%, 90.9%, 20.0% and 75.0% compared with the generic wavelength-routed optical router(GWOR), λ-router, topology and CrossBar structure. By testing the performance parameters based on the structure of 16×16 by the OMNET++ platform, as the result shows, the average insertion loss of LOOKNoC is 3.0%, 11.6%, 4.8% and 16.7% less than that of GWOR, λ-router, Mesh, and CrossBar structures.

Quasi-vertical tapers for polymer-waveguide-based interboard optical interconnects

A mode transformer based on the quasi-vertical taper is designed to enable high coupling efficiency for interboardlevel optical interconnects involving single-mode polymer waveguides and standard single-mode fibers. A triangular region fabricated above the waveguide is adopted to adiabatically transform the mode from the fiber into the polymer waveguide. The effects of the geometrical parameters of the taper, including width, height, tip width,etc., on the coupling efficiency are numerically investigated. Based on this, a quasi-vertical taper for the polymer rib waveguide system is designed, fabricated, and characterized. Coupling losses of 1.79 0.30 and 2.23 0.31 dB per coupler for the quasi-TM and quasi-TE mode, respectively, are measured across the optical communication C and L bands(1535 to 1610 nm). Low-cost packaging, leading to widespread utilization of polymeric photonicdevices, is envisioned for optical interconnect applications.

Short-Range Optical Wireless Communications for Indoor and Interconnects Applications

Optical wireless communications have been widely studied during the past decade in short-range applications, such as indoor highspeed wireless networks and interconnects in data centers and high-performance computing. In this paper, recent developments in high-speed short-range optical wireless communications are reviewed, including visible light communications （VLCs）, infrared indoor communication systems, and reconfigurable optical interconnects. The general architecture of indoor high-speed optical wireless communications is described, and the advantages and limitations of both visible and infrared based solutions are discussed. The concept of reconfigurable optical interconnects is presented, and key results are summarized. In addition, the challenges and potential future directions of short-range optical wireless communications are discussed.

The 8×10 GHz Receiver Optical Subassembly Based on Silica Hybrid Integration Technology for Data Center Interconnection

An 8×10 GHz receiver optical sub-assembly （ROSA） consisting of an 8-channel arrayed waveguide grating （AWG） and an 8-channel PIN photodetector （PD） array is designed and fabricated based on silica hybrid integration technology. Multimode output waveguides in the silica AWG with 2% refractive index difference are used to obtain fiat-top spectra. The output waveguide facet is polished to 45° bevel to change the light propagation direction into the mesa-type PIN PD, which simplifies the packaging process. The experimentM results show that the single channel I dB bandwidth of AWG ranges from 2.12nm to 3.06nm, the ROSA responsivity ranges from 0.097 A/W to 0.158A/W, and the 3dB bandwidth is up to 11 GHz. It is promising to be applied in the eight-lane WDM transmission system in data center interconnection.

Strict non-blocking four-port optical router for mesh photonic network-on-chip

We report a strict non-blocking four-port optical router that is used for a mesh photonic network-on-chip on a silicon-on-insulator platform.The router consists of eight silicon microring switches that are tuned by the thermo-optic effect.For each tested rousting state,the signal-to-noise ratio of the optical router is larger than 13.8 dB at the working wavelength.The routing functionality of the device is verified.We perform 40 Gbps nonreturn to zero code data transmission on its 12 optical links.Meanwhile,data transmission using wavelength division multiplexing on eight channels in the C band(from 1525 to 1565 nm)has been adopted to increase the communication capacity.The optical router’s average energy efficiency is 25.52 fJ/bit.The rising times(10%to 90%)of the eight optical switch elements are less than 10μs and the falling times(90%-10%)are less than 20μs.

Influence on Multimode Rectangular Optical Waveguide Propagation Loss by Surface Roughness

Optical scattering loss coefficient of muhimode rectangular waveguide is analyzed in this work. First, the effective refrac tive index and the mode field distribution of waveguide modes are obtained using the Marcatili method. The influence on scattering loss coefficient by waveguide surface roughness is then analyzed. Finally, the mode coupling efficiency for the SMFOpticalWaveguide （SOW） structure and MMFOptical Waveguide （MOW） structure are presented. The total scatter ing loss coefficient depends on modes scattering loss coeffi cients and the mode coupling efficiency between fiber and waveguide. The simulation results show that the total scatter ing loss coefficient for the MOW structure is affected more strongly by surface roughness than that for the SOW struc ture. The total scattering loss coefficient of waveguide decreas es from 3.97 x 10^-2 dB/cm to 2.96 x 10^-4 dB/cm for the SOW structure and from 5.24 - 10^-2 dB/cm to 4.7 x 10^-4 dB/ cm for the MOW structure when surface roughness is from 300nm to 20nm and waveguide length is 100cm.

75 GHz germanium waveguide photodetector with 64 Gbps data rates utilizing an inductive-gain-peaking technique

High-performance germanium(Ge)waveguide photodetectors are designed and fabricated utilizing the inductivegain-peaking technique.With the appropriate integrated inductors,the 3-dB bandwidth of photodetectors is significantly improved owing to the inductive-gain-peaking effect without any compromises to the dark current and optical responsivity.Measured 3-dB bandwidth up to 75 GHz is realized and clear open eye diagrams at 64 Gbps are observed.In this work,the relationship between the frequency response and large signal transmission characteristics on the integrated inductors of Ge waveguide photodetectors is investigated,which indicates the high-speed performance of photodetectors using the inductive-gainpeaking technique.