Elsevier

Sensors and Actuators B: Chemical

Volume 176, January 2013, Pages 994-1007
Sensors and Actuators B: Chemical

Ultra high sensitivity chemical photonic sensing by Mach–Zehnder interferometer enhanced Vernier-effect

https://doi.org/10.1016/j.snb.2012.10.008Get rights and content

Abstract

In this paper an ultra high sensitivity chemical photonic sensor is proposed, employing a Mach–Zehnder interferometer (MZI)-enhanced Vernier effect. The proposed sensor is demonstrated to reach ultra high overall sensitivity (>1000 μm/RIU) and very low limit of detection (LOD < 10−6 RIU), with a compact, standard SOI chip. Furthermore, two very efficient sensors are designed. The first one is a CO2 sensor for health safety purpose, able to detect gas concentration as low as 5000 ppm. The second one is an ammonia sensor in aqueous solution, able to detect ammonia concentrations down to 2 ppm. The designed sensors are proposed in silicon on insulator (SOI) technology due to its compatibility with standard CMOS technology, but the enhanced Vernier effect could be applied to each technology allowing to simultaneously fabricate ring resonators and MZIs.

Introduction

In the last few years the increasing demand of sensitive and precise detection of biochemical analytes, gases or several other kind of substances has lead great efforts in proposing a large variety of new sensors. Among these, optical sensors have been object of a great interest due to the possibility to achieve high sensitivity, fast response, real-time and multiple measurements by means of typically small and compact devices. In principle, several physical phenomena could be employed for sensing purposes, such as optical absorption [1], fluorescence [2], emission [3] and refractometry [4], to name a few. Due to this wide variety of optical sensing principles, several sensing platforms have been proposed in literature, such as optical fibers [5], photonic crystals [6], microresonators [7], surface plasmon resonances (SPR) [8], gratings [9], and so forth. Furthermore, the consolidated know-how of Silicon On Insulator (SOI) technology allows the integration of active and passive photonic devices, such as optical sources, detectors and waveguides, onto the same substrate, resulting in a further, significant performance improvement. Moreover, SOI technology, as well as other complementary metal oxide semiconductor (CMOS) compatible platforms, allows to fabricate multiple sensors and related read-out electronics on the same chip. Further advantages of the optical integration include miniaturization, robustness, reliability, reduction of production costs, low power consumption, and simplicity in the alignment of the fabricated devices. In this context, evanescent wave refractometer sensors have been demonstrated to exhibit extremely high sensitivity for the detection of biochemical analytes or gas concentration, using real time and label-free schemes. Several integrated optical sensor architectures have been proposed in literature, with the aim to increase the sensitivity as well as to reduce the limit of detection, such as Mach–Zehnder interferometers (MZIs) [10], silicon microring resonators [7], planar waveguide structures [11] and so on. Furthermore, with reference to optical microring resonators, the Vernier effect has been recently demonstrated to be a powerful principle in order to enhance the performance achieved by this kind of devices [12], [13]. In this work, we propose a new photonic sensor architecture, simultaneously exploiting the high sensitivity of MZIs and the architectural improvement due to the Vernier effect. The theoretical modeling of this MZI-enhanced Vernier effect has been developed, giving design guidelines in order to achieve the desired performance. We show how such an innovative sensing scheme could be effectively applied to the detection of health dangerous gases, such as CO2 and ammonia in aqueous solution.

Section snippets

Mach–Zehnder interferometer-enhanced Vernier effect: theoretical modeling

In this section, a theoretical description of the Mach–Zehnder interferometer (MZI) enhanced Vernier effect is developed. The analysis is carried out starting from a brief modeling of the standard Vernier effect, in order to show the most relevant parameters involved in the design. A detailed analysis of the Vernier effect can be also found in [14], [15]. Then, a modeling of the wavelength interrogated Mach–Zehnder interferometer sensor is proposed, highlighting the advantage with respect to

Design of a ultra high sensitivity MZI-enhanced Vernier sensor for CO2 detection

In Section 2 of this paper, the theoretical modeling of the MZI-enhanced Vernier effect has been presented. Here, we have applied the proposed theory to design an ultra high sensitivity sensor for CO2 detection in the near infrared spectral window, around 1550 nm. The carbon dioxide has a very weak absorption strength in such a spectral window [24], so the contribute of gas absorption to the total losses can be reasonably neglected. The CO2 refractive index dispersion has been taken into account

Design of a ultra high sensitivity MZI-enhanced Vernier sensor for NH3 detection

Ammonia (NH3) concentration measurement has become crucial in several scientific and technological areas. According to the European Environment Agency (EEA), ammonia (NH3) is one of the most common of all High Production Volume (HPV) industrial chemicals. Ammonia is widely used in industries such as petrochemical, pulp and paper, fertilizer and the oil industry, to name a few. Furthermore, NH3 has become one of the most employed coolants in large industrial refrigeration systems as a

Conclusions

In this work the advantages of using MZIs in place of ring resonators are theoretically demonstrated for sensing purposes, in terms of both sensitivity and limit of detection. By this way, we have proposed a new concept of photonic sensor architecture, simultaneously exploiting the high sensitivity of MZIs and the architectural improvement due to the well known Vernier effect. A theoretical modeling of this MZI-enhanced Vernier effect has been proposed, highlighting all the main design

Mario La Notte was born in Trani, Italy, on August 1987. He received his Laurea degree (cum laude) in Electronic Engineering in April 2012 from Politecnico di Bari, Italy. He joined Photonics Research Group in January 2012 and his main research interests are silicon on insulator technology, and photonic and optoelectronic integrated circuits for sensing and telecommunications applications. He is coauthor of some papers published in international journals and book chapter.

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    Mario La Notte was born in Trani, Italy, on August 1987. He received his Laurea degree (cum laude) in Electronic Engineering in April 2012 from Politecnico di Bari, Italy. He joined Photonics Research Group in January 2012 and his main research interests are silicon on insulator technology, and photonic and optoelectronic integrated circuits for sensing and telecommunications applications. He is coauthor of some papers published in international journals and book chapter.

    Vittorio M.N. Passaro was born in Bari, Italy, on November 1962. He received the Laurea degree in Electronic Engineering (cum laude) from the University of Bari, Bari, Italy, in 1988, and his Ph.D. degree in Electronic Engineering, curriculum Optoelectronics, from Politecnico di Bari, Italy, in 1992. Since 2000, he joined Politecnico di Bari as an Associate Professor. Since 1988 he has been engaged in several theoretical and experimental aspects of optoelectronic technologies, integrated optics and nanophotonics. He has contributed in dry etching and proton exchange technologies, in particular, on the understanding of the physical–chemical mechanisms occurring during the formation of lithium niobate optical waveguides, and the relationships with their optical properties. Since 2004 he formed the Photonics Research Group at Politecnico di Bari, which is mainly involved in research on Silicon Photonics. He is the author or co-author of more than 270 papers published in international journals and conference proceedings, with more than 1000 cites in specialized literature. He is also the editor of three international books and the coauthor of two international patents. Dr. Passaro is a IEEE Senior Member, an OSA Senior Member and an Associate Member of the National University Consortium of Telecommunications (CNIT).

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