Intra-step Quantum Research Articles

Design considerations of intra-step SiGeSn/GeSn quantum well electroabsorption modulators

Theoretical investigation of electro-absorption modulators in the mid-infrared range (>∼2 μm) is performed using asymmetric intra-step quantum wells based on Ge1−η1Snη1/Ge1−η2Snη2 heterostructures with SiGeSn outer barriers. After exploring the parameter space of the Sn content difference and width ratio of the intra-layers, a linear and much larger Stark shift is realized, compared to that of a square quantum well, without an increase of the total structure width. A modulator based on an optimized intra-step quantum well structure with a total well width of 12 nm is theoretically predicted to have both a larger peak shift per unit applied field and a larger absorption change than a 12 nm square quantum well device. By analyzing the device performance based on the two figures of merit: (1) absorption change per applied field and (2) absorption change per applied field squared, and taking 10 dB extinction ratio, a 44% higher bandwidth per volt and 46% lower power consumption per bit are achieved in intra-step than in a square well. Although the swing voltage for a square quantum well can be reduced by using a larger on-set applied field and performance could be improved, we found that the intra-step quantum well using zero on-set still retains its advantages when compared to the square quantum well which uses a 0.5 V on-set voltage.

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.

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.

Improvement of saturation optical intensity in electroabsorption modulators with asymmetric intra-step-barrier coupled double strained quantum wells

In this article, the saturation optical intensity in electroabsorption modulators (EAMs) at 1.55 μ m with asymmetric intra-step-barrier coupled double strained quantum well (AICD-SQWs) active region is theoretically investigated and compared with intra-step quantum well (IQW) structure. For this purpose, the two basic escape processes, thermionic emission and tunneling, are considered and the escape times of photogenerated carriers both for the AICD-SQW and the IQW based on the InGaAlAs material system are calculated and compared. From the reduction in escape times, improvement in the saturation optical intensity due to the introduction of the AICD-SQW structure is estimated to be greater than 6 dB at high fields.

Resonance in Link RF Gain by Negative Photocurrent Resistance of Electroabsorption Modulator Under Very High Optical Power

We examine the photocurrent effect in the electroabsorption modulator (EAM) under very high optical power and investigate its implication in the link radio-frequency (RF) gain. After reviewing the effect of the photocurrent in the EAM, using the voltage-source model with the device capacitance included, we demonstrate a possibility that the RF gain can be enhanced by resonance due to the photocurrent if the photocurrent decreases with device bias, exhibiting negative differential resistance. We explore an EAM with intrastep quantum wells showing blueshift to achieve the negative photocurrent resistance and demonstrate a case where an enhancement in the link RF gain is possible.

Monolithic optical gates based on integration of evanescently-coupled uni-traveling-carrier photodiodes and electroabsorption modulators

We report on chip-scale optical gates based on the integration of evanescent waveguide unitraveling-carrier photodiodes (EC-UTC-PDs) and intra-step quantum well electroabsorption modulators (IQW-EAMs) on n-InP substrates. These devices exhibit simultaneously 2.1 GHz and −6.2 dB RF-gain at 21 GHz with a 450 Ω thin-film resistor and a bypass capacitor integrated on a chip.

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]

High-performance electroabsorption modulator

A 100-μm-long electroabsorption modulator monolithically integrated with passive waveguides at the input and output ports is fabricated through ion implantation induced quantum well intermixing, using only a two-step low-pressure metal-organic vapor phase epitaxial process. An InGaAsP/InGaAsP intra-step quantum well is introduced to the active region to improve the modulation properties. In the experiment high modulation speed and high extinction ratio are obtained simultaneously, the electrical-to-optical frequency response (E/O response) without any load termination reaches to 22 GHz, and extinction ration is as high as 16 dB.

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.

Sensitivities of the InGaAs/InGaAsP/InGaAsP Intrastep Quantum Well to Thickness and Composition Variations for Realizing Efficient Electroabsorption Modulators

We examine the sensitivities of the intrastep-quantum-well (IQW) structure with an InGaAs well to the thickness and composition variations. With the layer variations into account, we evaluate the changes in absorption coefficient as a function of electric field and the subsequent transfer functions of the electroabsorption modulator. It is concluded that the examined IQW structure is rather sensitive to the thickness variation but is robust to the composition variation. This work suggests that the thickness control is very important in actually growing the IQW structure to obtain the desired performance with the IQW.

Design of a novel periodic asymmetric intra-step-barrier coupled double strained quantum well electroabsorption modulator at 1.55 μm

A novel structure for electroabsorption modulator at 1.55μm with In(1−x−y)Ga(x)Al(y)As periodic asymmetric intra-step-barrier coupled double strained quantum well (AICD-SQW) is proposed. The intra-step-barrier in the structure provides a high optical saturation power due to delayed red shift. The asymmetric strained well layers reduce the oscillator strength at zero field, and as a result a lower insertion loss is obtained. This is due to the deep separation of electron and heavy hole wave functions. This structure shows that electroabsorption modulator (EAM) 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). In numerical analysis, the exciton equation in momentum space is solved numerically, using Gaussian quadrature method (GQM), to obtain the exciton binding energy and oscillator strength. The asymmetric quantum well structure Hamiltonian is numerically solved by transfer matrix method (TMM), to obtain the electron and hole subband energy levels, taking the strain into account. The electroabsorption coefficient is calculated for different applied electric field for TE input light polarization. The EAM parameters such as extinction ratio, insertion loss, chirp and the figures of merit are calculated and the performances of AICD-SQW are compared with IQW.

High-power electroabsorption modulator for radio over fibre system

An electroabsorption modulator using an intra-step quantum well (IQW) active region is fabricated for a radio over fibre system. The strain-compensated InGaAsP/InGaAsP IQW shows good material quality and improved modulation properties, high extinction ratio efficiency (10 dB V−1) and low capacitance (<0.42 pF), with which high frequency (>15 GHz) can be obtained. High-speed measurement under high-power excitation shows no power saturation up to an excitation power of 21 dBm. To our knowledge, the input optical power is the highest reported for a multi-quantum well EAM without a heat sink.

High-Power Electroabsorption Modulator Using Intrastep QuantumWell

An electroabsorption modulator using the intrastep quantum well (IQW)active region is fabricated for optical network systems. Thestrain-compensated InGaAsP/InGaAsP IQW shows good material qualityand improved modulation properties, high extinction ratio efficiency10 dB/V and low capacitance (<0.42 pF), with which an ultra highfrequency (>15 GHz) can be obtained. High-speed measurementunder high-power excitation shows no power saturation up to excitationpower of 21 dBm. To our knowledge, the input optical power is thehighest reported for multi-quantum well EAMs without heat sinks.

Reduction in Escape Times of Photogenerated Charge Carriers with Asymmetric Intrastep Quantum Wells and Subsequent Improvement in Saturation Optical Intensity

Escape times of photogenerated charge carriers from an InGaAsP intrastep quantum well (IQW) are calculated and compared with those from a conventional quantum well (QW). Since the red shift of the IQW is initiated at a higher electric field, the escape times from the IQW are smaller than those from the conventional QW at given values in modulator transmission. From the reduction in escape times, improvements in the exciton saturation intensity are estimated to be a factor of ∼5 for both high and low modulator-transmission points.

High-Power Intrastep Quantum Well Electroabsorption Modulator Using Single-Sided Large Optical Cavity Waveguide

A novel electroabsorption modulator (EAM) using intrastep quantum wells (IQWs) and a single-sided large optical cavity waveguide is demonstrated to operate at up to 100 mW of input optical power. When the IQW EAM with uncoated facets is tested in an analog fiber link, the radio-frequency link gain reaches -16.1 dB at 100-mW optical power. We have measured a single-octave spurious-free dynamic range (SFDR) of 121 dB/spl middot/Hz/sup 4/5/ and multioctave SFDR of 110 dB/spl middot/Hz/sup 2/3/ for this EAM.