Traveling-wave Electroabsorption Modulators Research Articles

140/180/204-Gbaud OOK Transceiver for Inter- and Intra-Data Center Connectivity

We report on an on – off keying intensity-modulation and direct-detection C-band optical transceiver capable of addressing all datacenter interconnect environments at well beyond 100 Gbaud. For this, the transmitter makes the use of two key InP technologies: a 2:1 double heterojunction bipolar transistor selector multiplexer and a monolithically integrated distributed-feedback laser traveling-wave electro-absorption modulator, both exceeding 100-GHz of 3-dB analog bandwidth. A preamplified 110-GHz PIN photodiode prior to a 100-GHz analog-to-digital converter complete the ultrahigh bandwidth transceiver module; the device under study. In the experimental work, which discriminates between intra- and inter-data center scenarios (dispersion unmanaged 120, 560, and 960 m; and dispersion-managed 10 and 80 km of standard single-mode fiber), we evaluate the bit-error rate evolution against the received optical power at 140, 180, and 204 Gbaud on – off keying for different equalization configurations (adaptive linear filter with and without the help of short-memory sequence estimation) and forward error correction schemes (hard-decision codes with 7% and 20% overhead); drawing conclusions from the observed system-level limitations of the respective environments at this ultrahigh baudrate, as well as from the operation margins and sensitivity metrics. From the demonstration, we highlight three results: successful operation with >6-dB sensitivity margin below the 7% error-correction at 140 Gbaud over the entire 100 m–80 km range with only linear feed-forward equalization. Then, the transmission of a 180-Gbaud on – off keying carrier over 80 km considering 20% error-correction overhead. Finally, a 10-km communication at 204 Gbaud on – off keying with up to 6 dB sensitivity margin, and regular 7% overhead error-correction.

Nonlinearity-aware 200 Gbit/s DMT transmission for C-band short-reach optical interconnects with a single packaged electro-absorption modulated laser.

We experimentally demonstrate the transmission of a 200Gbit/s discrete multitone (DMT) at the soft forward error correction limit in an intensity-modulation direct-detection system with a single C-band packaged distributed feedback laser and traveling-wave electro absorption modulator (DFB-TWEAM), digital-to-analog converter and photodiode. The bit-power loaded DMT signal is transmitted over 1.6km standard single-mode fiber with a net rate of 166.7Gbit/s, achieving an effective electrical spectrum efficiency of 4.93bit/s/Hz. Meanwhile, net rates of 174.2Gbit/s and 179.5Gbit/s are also demonstrated over 0.8km SSMF and in an optical back-to-back case, respectively. The feature of the packaged DFB-TWEAM is presented. The nonlinearity-aware digital signal processing algorithm for channel equalization is mathematically described, which improves the signal-to-noise ratio up to 3.5dB.

Operation of low driving voltage cascaded modulator over non-cascaded modulator for 4 dB extinction ratio at 100 giga bit per second (Gbps)

This paper describes improved results when comparing cascaded traveling wave electro absorption modulator (TWEAM) to non-cascaded TWEAM by simulation. Large signal modeling is used for both types of modulators to achieve 4 and 10dB extinction ratios (ERs) with flat frequency response for applications in short distance as well as long distance optical fiber communication. To obtain 4 and 10dB ERs with 110GHz 3dB bandwidth, a cascaded TWEAM requires 0.4V peak to peak (VP-P) and 1 VP-P input driving voltages respectively. A non-cascaded TWEAM requires about two times the input driving voltage compared to the cascaded modulator to achieve the same values of ER and 3dB bandwidth. Both modulators have been simulated with the same bias and also use the same circuit parameters except for the total active segment lengths (1 and 0.5mm for cascaded and non-cascaded modulator respectively) and microstrip lengths to obtain the same ERs and 3dB bandwidths.

Very low input voltage cascaded travelling wave electroabsorption modulator (CTWEAM) for more than 100 Gbps

This paper presents the large signal modeling and simulation of two segmented travelling wave electroabsorption modulators (TWEAM) as a cascaded TWEAM (CTWEAM) structure. It will be demonstrated that a mushroom shaped mesa structure with low series resistance (0.69Ω-mm) will have 3dB bandwidth more than sufficient for 100Gbps operation. For a CTWEAM device with 990μm active segment length, 1.1V bias voltage and only 0.4V peak-to-peak (Vp–p) modulating voltage has a bandwidth of 110GHz, extinction ratio >4dB and flat frequency response. This device would be an attractive candidate for short distance optical fiber communication as well as long distance telecommunication at 0.4Vp–p and 1Vp–p input RF signal, respectively.

High Performance Hybrid Silicon Evanescent Traveling Wave Electroabsorption Modulators

In this paper, for the rst time, a high performance hybrid silicon evanescent traveling wave electroabsorption modulator based on asymmetric intra-step-barrier coupled double strained quantum wells active layer is introduced which has double steps at III/V mesa structure. Through this active layer, hybrid silicon evanescent traveling wave electroabsorption modulator will be advantages such as very low insertion loss, zero chirp, high extinction ratio, and large Stark shift and better gures of merit as compared with multiquantum well and intra-step quantum well structures. Furthermore, traveling wave electroabsorption modulator with double steps III/V mesa structure results in a wider bandwidth as compared with one-step III/V mesa and mushroom structures. For the modulator with double steps III/V mesa structure with a 200 μm length, the 3 dB bandwidths are obtained as 132 and 52 GHz for 25 and 40 Ω characteristic impedances, respectively.

High-performance traveling-wave electroabsorption modulators utilizing mushroom-type waveguide and periodic transmission line loading

For the first time, periodic loaded electrodes and mushroom-type waveguide are combined to improve the performance of traveling-wave electroabsorption modulators (TWEAMs) based on the asymmetric intra-step-barrier coupled double strained quantum well (AICD-SQW). The electrical modulation response of periodic mushroom-type TWEAM is obtained by using equivalent circuit model, and is compared with simulation result of conventional mushroom-type TWEAM counterpart. The equivalent circuit model simulation results indicate that for the exemplary modulation length of 300 μm, the mushroom-type TWEAM with periodic transmission line loading can achieve much wider bandwidth about 99.7 GHz and 43.1 GHz than the conventional counterpart with about 43 GHz and 33 GHz for 35Ω and 45 Ω terminations, respectively.

Improvement in performance of traveling wave electroabsorption modulator with asymmetric intra-step-barrier coupled double strained quantum wells the active region, segmented transmission-line and mushroom-type waveguide

In this paper, asymmetric intra-step-barrier coupled double strained quantum wells structure (AICD-SQW), segmented transmission-line and mushroom-type waveguide that improve the performance of traveling wave electroabsorption modulators (TWEAM) are presented. The AICD-SQW structure shows that electroabsorption modulator properties such as large change in absorption, high extinction ratio, large Stark shift, very low insertion loss, zero chirp, and higher figures of merit are possible to be achieved simultaneously as compared with intra-step quantum well (IQW). The segmented transmission-line method allows us to design a TWEAM with above 25 Ω impedance and very high bandwidth. Furthermore, increasing the width of p-cladding layer with the same active layer to reduce the resistance in p-i-n mushroom-type waveguide of TWEAM based on AICD-SQW improve the microwave propagation loss and thus the high-speed electro-optical response. For this purpose, the transmission-line microwave properties of TWEAM such as microwave index, microwave loss, and characteristic impedance are obtained for active and passive segments of transmission-line. Then equivalent circuit model elements are extracted. The modulation response of segmented transmission-line mushroom-type TWEAM is obtained by HSPICE simulation and compared to circuit model simulation results of conventional mushroom-type TWEAM counterpart. The analysis results indicate that the segmented transmission-line mushroom-type TWEAM can achieve much wider bandwidth than the conventional mushroom-type TWEAM counterpart, with a small penalty in electro-optic conversion gain due to AICD-SQW structure.

Integrated Optoelectronic Devices on Silicon

ABSTRACTSilicon (Si) has been the dominating material platform of microelectronics over half century. Continuous technological advances in circuit design and manufacturing enable complementary metal-oxide semiconductor (CMOS) chips with increasingly high integration complexity to be fabricated in an unprecedently scale and economical manner. Conventional Si-based planar lightwave circuits (PLCs) has benefited from advanced CMOS technology but only demonstrate passive functionalities in most circumstances due to poor light emission efficiency and weak major electro-optic effects (e.g., Pockels effect, the Kerr effect and the Franz–Keldysh effect) in Si. Recently, a new hybrid III-V-on-Si integration platform has been developed, aiming to bridge the gap between Si and III-V direct-bandgap materials for active Si photonic integrated circuit applications. Since then high-performance lasers, amplifiers, photodetectors and modulators, etc. have been demonstrated. Here we review the most recent progress on hybrid Si lasers and high-speed hybrid Si modulators. The former include distributed feedback (DFB) lasers showing over 10 mW output power and up to 85 oC continuous-wave (cw) operation, compact hybrid microring lasers with cw threshold less than 4 mA and over 3 mW output power, and 4-channel hybrid Si AWG lasers with channel space of 360 GHz. Recently fabricated traveling-wave electro-absorption modulators (EAMs) and Mach-Zehnder interferometer modulators (MZM) on this platform support 50 Gb/s and 40 Gb/s data transmission with over 10 dB extinction ratio, respectively.

50 Gb/s hybrid silicon traveling-wave electroabsorption modulator

We have demonstrated a traveling-wave electroabsorption modulator based on the hybrid silicon platform. For a device with a 100 μm active segment, the small-signal electro/optical response renders a 3 dB bandwidth of around 42 GHz and its modulation efficiency reaches 23 GHz/V. A dynamic extinction ratio of 9.8 dB with a driving voltage swing of only 2 V was demonstrated at a transmission rate of 50 Gb/s. This represents a significant improvement for modulators compatible with integration of silicon-based photonic integrated circuits.

Design study of integrated photonic transmitters for application in Fiber-to-the-Home networks

Different solutions of photonic transmitters based on arrayed waveguide gratings are demonstrated. The basic concepts of realizing integrated multiwavelength lasers with optical modulators are presented and discussed in detail. Full Text: PDF References M. K. Smit, "New focusing and dispersive planar component based on an optical phased array", Electron. Lett. 24(7), 385 (1988). [CrossRef] M.K. Smit, 3rd Int. conference on Optics-photonics Design and Fabrication, 51-52, Tokyo 1, 30 Oct. - 1 Nov. 2002, Optical Society of Japan, 2002. J.H. den Besten, Integration of Multiwavelength Lasers with Fast Electro-Optical Modulators, PhD Thesis, 2004. B.Docter, Deeply-Etched DBR Mirrors for Photonic Integrated Circuits and Tunable Lasers, PhD Thesis, 2009. S. C. Nicholes, M. L. Masanovic, B. Jevremovic, E. Lively, L. A. Coldren, and D. J. Blumenthal, "An 8$,times,$ 8 InP Monolithic Tunable Optical Router (MOTOR) Packet Forwarding Chip", J. Lightwave Techn. 28(4) Feb. (2010). [CrossRef] R.Broeke, A Wavelength Converter Integrated with a Discretely Tunable Laser for Wavelength Division Multiplexing Networks, PhD Thesis, 2003. F.M. Soares, J.H. Baek, N.K. Fontaine, C. Junesand, S. Lourdudoss, K.Y. Liou, R.A. Hamm, W. Wang, B. Patel, W.S. Hobson, J.R. Lothian, S. Vatanapradit, L.A. Gruezke, W.T. Tsang, and S.J.B. Yoo, Optical Fiber Communications Conference, Paper OThS1, 2010. H. Yang, M. Chin, J. Zhou, S. Lee, W. Chen, and H. Zhu, "A traveling-wave electroabsorption modulator with a large optical cavity and intrastep quantum wells", Semicond. Sci. Technol. 23, 105011 (2008). [CrossRef] J.H. den Besten, D. Caprioli, W. Pascher, R. van Dijk, X.J.M. Leijtens, M.K. Smit, "Simulation and design of a 40 GHz Mach?Zehnder modulator on InP", Proceedings of the Symposium on IEEE/LEOS Benelux Chapter, Amsterdam, 2002, pp. 123?126 H.N. Klein, H. Chen, D. Hoffmann, S. Staroske, A.G. Steffan, K.-O. Velthaus, "1.55?m Mach- Zehnder Modulators on InP for Optical 40/80 Gbit/s Transmission Networks", International Conference on Indium Phosphide and Related Materials Conference Proceedings, 171?173, 2006 [CrossRef]

ETDM Transmitter Module for 100-Gb/s Ethernet

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Performance of a packaged distributed-feedback travelling-wave electroabsorption modulator module for data transmission at 100 Gb/s is presented for the first time. Clearly open eye diagrams at 80 Gb/s with an extinction ratio (ER) of 4.9 dB and 100 Gb/s with ER 4.2 dB (limited by measurement setup) are demonstrated together with data transmission over 100-m-long standard single-mode fiber and over dispersion-compensated 10-km fiber link. </para>

Optical and microwave analysis of mushroom-type waveguides for traveling wave electroabsorption modulators based on asymmetric intra-step-barrier coupled double strained quantum wells by full-vectorial method

The finite difference method is exploited for a full-vectorial analysis of mushroom-type waveguides for traveling wave electroabsorption modulators (TWEAM) based on asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQW). In this analysis, the discontinuities of the normal components of the electric field across abrupt dielectric interfaces which are known as the limitations of scalar and semivectorial approximation methods are considered. The optical field distributions in mushroom-type TWEAM based on AICD-SQW and conventional ridge-type TWEAM of the same active region for 1.55 μm operation are presented. The important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and transverse mode confinement factor are calculated. Then, the transmission line microwave properties (microwave index, microwave loss, and characteristic impedance) of TWEAMs are obtained. The modulation response of mushroom-type TWEAM is calculated using circuit model by considering interaction between microwave and optical fields in waveguide and compared with conventional ridge-type TWEAM. It is found that increasing the width of p-cladding layer with the same i-layer to reduce the resistance in p-i-n mushroom-type waveguide of TWEAM based on AICD-SQW can improve the microwave propagation loss and thus the high-speed electro-optical response.

Monolithically Integrated 100 GHz DFB-TWEAM

A monolithically integrated distributed feedback (DFB) laser and traveling-wave electro-absorption modulator (TWEAM) with ges 100 GHz -3 dBe bandwidth suitable for Non-return-to-zero (NRZ) operation with on-off keying (OOK) is presented. The steady-state, small-signal modulation response, microwave reflection, chirp characteristic, and both data operation and transmission were investigated. The DFB-TWEAM was found to be an attractive candidate for future short distance communication in high bitrates systems.

A traveling-wave electroabsorption modulator with a large optical cavity and intrastep quantum wells

This paper reports a novel traveling-wave electroabsorption modulator (TWEAM) with a large optical cavity waveguide and an intrastep quantum well structure designed to achieve a high bandwidth, high saturation power and better fiber-matched optical profile, which is good for high coupling efficiency. The optical mode characteristic shows a great improvement in matching the circular mode of the fiber and the saturation power of 21 dBm, and a 3 dB bandwidth of 23 GHz was achieved for the fabricated TWEAM.

Electroabsorption Modulators Suitable for 100-Gb/s Ethernet

The design of a traveling-wave electroabsorption modulator (TWEAM) has been improved to decrease the drive voltage. The absorption layer was optimized and together with a novel segmentation of microwave design was introduced to increase the active modulator length. The resulting - 3-dBe bandwidth of fabricated devices was estimated to be 99 GHz. Extinction ratios of 10 dB back-to-back and 6.7 dB after transmission over 2.2-km long fiber were measured with an incident drive voltage of only 2 V peak to peak. This TWEAM performance is believed to constitute a new state of the art for modulators suitable for 100-Gb/s Ethernet with on-off keying.

Transmission Line Characterization of Undercut-Ridge Traveling-Wave Electroabsorption Modulators

An experimental analysis of the electrical properties of traveling-wave electroabsorption modulators with undercut waveguides is presented. Modulators of varying ridge widths and amounts of undercut are fabricated and tested to compare characteristic impedance, effective index, microwave loss, and optical bandwidth. We demonstrate effective velocity matching and >40-GHz 3-dB bandwidth for a 400-mum-long device.

Design and optimization of an arbitrarily segmented traveling wave electrode for an ultrahigh speed electroabsorption modulator

The modulation response of an arbitrarily segmented traveling wave electroabsorption modulator (TW-EAM) with a non-periodic electrode layout is analyzed with an effective approach based on the transmission line theory. An optimization method based on a genetic algorithm is used to optimize the segmented electrode with additional capacitive pads for a TW-EAM. Optimized electrode structures are given for 165 μm-length devices under standard 50 Ω RF termination condition and 210 μm-length devices with smaller integrated resistors. Great enhancement of performances in modulation response is achieved as compared to the periodic design reported previously. The simulation with the parameters extracted from measurement results suggests that a 3 dB-bandwidth over 100 GHz could be achieved. The eye diagram from the simulation demonstrates that such devices would be competent for a 100Gb/s optical network.

Widely Tunable Separate Absorption and Modulation Wavelength Converter With Integrated Microwave Termination

A widely tunable wavelength converter utilizing a separate absorption and modulation configuration and only dc bias connections is demonstrated. The device integrates an SG-DBR laser with a traveling-wave electroabsorption modulator and an optically pre-amplified receiver and introduces a simplified bias scheme by the inclusion of passive resistor and capacitor circuit elements. We discuss a the design of these passive elements and their compatibility with fabrication of photonic integrated circuits. The device demonstrates over 12 GHz optical bandwidth and error free 10 Gb/s wavelength conversion is achieved with less than 2.5 dB power penalty over 25 nm of output tuning.

High-Speed OTDM and WDM Networks Using Traveling-Wave Electroabsorption Modulators

We describe the design and performance of a number of elements based on traveling-wave electroabsorption modulators (TW-EAMs) in optical time-division-multiplexing (OTDM) and wavelength-division-multiplexing (WDM) networks. The incorporation of traveling-wave (TW) electrode design into electroabsorption modulators (EAMs) relieves the resistance-capacitance (RC ) bandwidth limitation common to lumped components, enabling higher operation speed without shortening the device. As a result, high-speed operation can be combined with essential modulator characteristics such as modulation efficiency and extinction ratio. While significant modulation bandwidth has been achieved, a lesser known aspect is that the TW electrode also provides an extra dimension for improving and enabling functionalities beyond broadband modulation. This new dimension originates from the distributed effect of the TW design and its interactions with distinctive EAM properties. This paper reviews such developments in recent years with specific applications for optical signal processing in OTDM and WDM networks. The covered functionalities include various optical gating operations for OTDM, regenerative wavelength conversions for WDM, and clock recovery

Development of Packaging Technologies for High-Speed ($≫40$Gb/s) Optical Modules

We developed high-speed optoelectronics packaging technologies for a waveguide photodiode and a traveling wave electro-absorption modulator device for 40-Gb/s digital communication systems. The effects of the device and the packaging designs on the broadband performance were investigated to optimize broadband characteristics. For the receiver, inductive peaking was used for bandwidth control and an internal bias tee was implemented; in addition, two types of preamplifier devices were used to develop high-gain receiver and wide-bandwidth receiver. In the optical-to-electrical response, a 3-dB bandwidth of the high-gain module was about 32 GHz as compared to 42 GHz for the wide-bandwidth module. The clear 40-Gb/s nonreturn-to-zero (NRZ) eye diagrams showed a good system applicability of these modules. In addition, an optimized modulator module showed a 3-dB bandwidth of 38 GHz in the electrical-to-optical response, an electrical return loss of less than 10 dB at up to 26 GHz, an rms jitter of 1.832 ps, and an extinction ratio of 5.38 dB in a 40-Gb/s NRZ eye diagram