1832 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 26, NO. 18, SEPTEMBER 15, 2014 Concurrent Dualband Diplexer for Nanoscale Wireless Links Kola Thirupathaiah, Student Member, IEEE, Brijesh Iyer, Student Member, IEEE, Nagendra Prasad Pathak, Member, IEEE, and Vipul Rastogi Abstract—This letter reports the design and full wave analysis of a compact and low-loss filter-based concurrent dualband diplexer for high-density multiband photonic integrated circuits. The proposed diplexer consists of a chamfered T-junction in nanoplasmonic metal–insulator–metal waveguide and two band- pass filters (BPF) inserted in the two output arms. Plasmonic BPF have been designed using stepped width resonator. These filters are concurrently operating at 1427-/1665-nm and 1355-/1595-nm wavelength. The optimized chamfered T-junction has return loss >8 dB, whereas insertion loss of each dualband BPF is <5 dB. Index Terms— Bandpass filter, diplexer, FIT, MIM, MIMSWR. I. I NTRODUCTION T HE future generation communication systems are meant for handling huge data transfer in quick succes- sion, which essentially drives it in subwavelength regime. Simultaneous operation and control of multiple frequency bands of communication systems may prove very useful to fulfill this requirement. Since, plasmonic structures can control or manipulate light at subwavelength range, they have the unique prospective for making miniaturized photonic integrated circuits. Therefore, the design and development of advanced architectures for filtering and multiplexing devices are essential for realization of future communication systems without compromising the size, power consumption and cost of the subsystems. A variety of nano-scale plasmonic waveguide structures had been proposed to implement the photonic integrated circuits e.g. metal-insulator-metal (MIM) waveguide, insulator-metal- insulator (IMI) waveguide, slot waveguide, nanoparticles and nano-wires. Due to its subwavelength nature and highest degree of light detention, MIM structure has been found extremely suitable for such systems [1]. Many MIM wave guide based passive photonic integrated circuits have been investigated and reported such as filters, combiner/splitter, cou- plers and multiplexers/demultiplexer [2]–[10]. But, all these Manuscript received March 26, 2014; revised June 25, 2014; accepted July 3, 2014. Date of publication July 14, 2014; date of current version August 15, 2014. K. Thirupathaiah and V. Rastogi are with the Department of Physics, IIT Roorkee, Roorkee 247667, India (e-mail: kola.jntu@gmail.com; vipulfph@iitr.ac.in). B. Iyer and N. P. Pathak are with the Radio Frequency Integrated Circuits and Systems Laboratory, Department of Electronics and Communication Engi- neering, IIT Roorkee, Roorkee 247667, India (e-mail: bijuiyer@gmail.com; nagppfec@iitr.ac.in). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2014.2337016 Fig. 1. Concept of Nanoscale Wireless Link. circuit elements have been designed for operation at a single band at a time. In a recent publication [11], we have reported the design of a concurrent dualband stepped width resonator which can be used in the design of filters for photonic integrated circuits. This letter is focused on the design and analysis of a concurrent dualband diplexer having capability to simul- taneously multiplex two signals at two different bands. The proposed diplexer have been designed using a broadband plasmonic MIM wave guide based 3-dB T-junction power splitter and two dualband bandpass filters. Section II of this letter describes the application of dualband diplexer in nanoscale wireless broadcasting link, while the full wave analysis and optimization of MIM waveguide based T-junction power splitter has been discussed in section III. Section IV of this letter details the design of dualband band- pass filter using SWR in plasmonic MIM waveguide. The section V of this letter presents the geometry and full wave analysis results of the proposed concurrent dual-band diplexer and the conclusion is described in section VI. II. CONCEPT OF NANOSCALE WIRELESS LINK Concept of single band nanoscale wireless link had been discussed in [12]–[16]. Fig. 1 depicts a multiband nanoscale wireless link in which four different optical bands viz. O, E, L and U have been transmitted wirelessly through free space using quad band dipole antenna. On the receiver side, a receiving antenna captures the radiated signal and directs it to the dualband receivers connected to the two arms of dualband diplexer for further processing. Dualband diplexer plays an important role in miniaturization of this network. The dualband diplexer has been implemented using 1041-1135 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.