JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 33, NO. 5, MARCH1, 2015 971 InP-Based Active and Passive Components for Communication Systems at 2 μm N. Ye, M. R. Gleeson, M. U. Sadiq, B. Roycroft, C. Robert, H. Yang, H. Zhang, P. E. Morrissey, N. Mac Suibhne, K. Thomas, A. Gocalinska, E. Pelucchi, R. Phelan, B. Kelly, J. O’Carroll, F. H. Peters, F. C. Garcia Gunning, and B. Corbett (Invited Paper) > Abstract—Progress on advanced active and passive photonic components that are required for high-speed optical communi- cations over hollow-core photonic bandgap fiber at wavelengths around 2 μm is described in this paper. Single-frequency lasers capable of operating at 10 Gb/s and covering a wide spectral range are realized. A comparison is made between waveguide and sur- face normal photodiodes with the latter showing good sensitiv- ity up to 15 Gb/s. Passive waveguides, 90° optical hybrids, and arrayed waveguide grating with 100-GHz channel spacing are demonstrated on a large spot-size waveguide platform. Finally, a strong electro-optic effect using the quantum confined Stark ef- fect in strain-balanced multiple quantum wells is demonstrated and used in a Mach–Zehnder modulator capable of operating at 10 Gb/s. Index Terms—Detectors, high bandwidth, lasers, optical com- munications, optical modulators, quantum confined Stark effect (QCSE). I. INTRODUCTION T HERE is an increasing demand for active and passive pho- tonic components relevant for wavelengths around 2 μm. The most long-standing application is in sensing gases, partic- ularly CO 2 , which have absorption features in this waveband [1]. While the absorption cross-sections are not as large when compared to the mid infra-red spectral region, they nevertheless provide sufficient sensitivity for useful detection at the ppm level with a relative ease of use. This market is advancing rapidly with Manuscript received October 6, 2014; revised December 4, 2014; accepted December 12, 2014. Date of publication December 17, 2014; date of current version March 4, 2015. This work was supported in part by the EU FP7-ICT MODE-GAP Project under Grant 258033 and under Science Foundation Ireland CTVR II Project under Grant SFI 10/CE/I1853. N. Ye, M. R. Gleeson, M. U. Sadiq, B. Roycroft, C. Robert, H. Yang, H. Zhang, P. E. Morrissey, K. Thomas, A. Gocalinska, E. Pelucchi, F. H. Peters, F. C. Garcia Gunning, and B. Corbett are with Tyndall National Institute, University College Cork, Cork Ireland (e-mail: nan.ye@tyndall.ie; michael.gleeson@tyndall.ie; muhammad.sadiq@tyndall.ie; brendan.roycroft@ tyndall.ie; cedric.robert@tyndall.ie; hua.yang@tyndall.ie; hongyu.zhang@ tyndall.ie; padraic.morrissey@tyndall.ie; kevin.thomas@tyndall.ie; agnieszka. gocalinska@tyndall.ie; emanuele.pelucchi@tyndall.ie; frank.peters@ tyndall.ie; fatima.gunning@tyndall.ie; brian.corbett@tyndall.ie). N. Mac Suibhne was with Tyndall National Institute, University College Cork, Cork Ireland, and now is with the Aston Institute of Photonic Technolo- gies, School of Engineering and Applied Science, Birmingham B4 7ET, U.K. (e-mail: n.mac-suibhne@aston.ac.uk). R. Phelan, B. Kelly, and J. O’Carroll are with Eblana Photonics, Dublin, Ireland (e-mail: richard.phelan@eblanaphotonics.com; brian.kelly@ eblanaphotonics.com; john.ocarroll@eblanaphotonics.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2014.2383492 increasing environmental regulations and with the growing in- terest in distributed sensing as part of the Internet of Things. The earth’s atmosphere has excellent transmission at 2 μm with the result that the 3-D distribution of CO 2 can be accurately mapped remotely using differential absorption LIDAR systems [2], [3]. Enhanced sensitivity can be achieved by the use of coherent de- tection [4]. Biomedical applications of sensing at 2 μm include breath analysis using the exhaled CO 2 level in order to monitor patients during anesthesia and for the measurement of glucose in the blood stream [5]. Infrared inspection of power devices and solar cells can be done using infrared cameras while astronomy requires low noise avalanche photodiodes in this range. A new spectral band for telecommunications can be opened up around 2 μm when used in conjunction with hollow core photonic bandgap fiber (HC-PBGF). Conventional silica based fibers suffer from high absorption losses of ∼10 dB/km at 2 μm. However, as the fundamental mode in HC-PBGF is primarily guided in air, the loss is limited by surface scattering from the SiO 2 making up the PBGF. The minimum attenuation is ex- pected around 2 μm and can potentially be as low as 0.2 dB/km [6], [7]. The low latency [8] and potential low non-linearity of HC-PBGF make its use very attractive for delay-sensitive appli- cations such as financial transactions. The use of HC-PBGF is enabled by the availability of high quality Thulium doped fiber amplifiers (TDFA) with exceptionally wide (>100 nm) band- widths in this wavelength range [9]. Using these components the first 2 μm communication systems experiments over HC- PBGF have been carried out [10], [11]. Telecommunications at these wavelengths can be further advanced using coherent and phase modulation formats as employed in 1.55 μm band sys- tems. This requires a full range of suitable components for this new wavelength band. In this paper, we describe the development of some of the active and passive components needed. We present the material issues and the performance characteristics of high bandwidth lasers, photodetectors, waveguides, multiplexers and modulators. II. MATERIALS AND LASERS There are a number of material systems that can be used both for individual components and as a platform for device inte- gration. The InP (InAlGaAsP) system is well established for a full range of devices at 1.55 μm and is compatible with the integration of multiple components for photonic integrated cir- 0733-8724 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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