Paul Lambeck

Remote opto-chemical sensing with extreme sensitivity: design, fabrication and performance of a pigtailed integrated optical phase-modulated Mach–Zehnder interferometer system

This paper describes the design, fabrication and testing of a pigtailed integrated optical (IO) phase-modulated Mach–Zehnder interferometer (MZI) including both the optical chip and the electronics. The optical chip is realised in SiON technology. The IO components (the sensing function, the straight waveguiding channels, the phase modulator, the polariser, the splitter, the combiner and the fibre-to-chip connection unit) are individually optimised and interconnected by using transversal adiabatic tapers. To obtain a high waveguide evanescent field sensitivity, the sensor is designed for — but not limited to — a wavelength of 632.8 nm. The integrated MZI is actively phase-modulated by virtue of the electro-optic effect of the incorporated material zinc oxide (ZnO). The electro-optical voltage–length product Vπ is 16 V cm at frequencies above 10 Hz. The polariser is a distributed function, that effectively filters TM-polarised light (TE/TM polarising ratio >30 dB). The fibre pigtail, affording remote optical sensing, is based on a cheap, easy-to-use fibre-to-chip connection with a typical coupling efficiency of 50%, while the device throughput (“insertion loss”) is −20 dB. The drive- and demodulation electronics enable a phase resolution 5×10−5×2π, corresponding to a refractive index resolution of 2×10−8. The sensing system as has been realised up to now shows a phase resolution of 1×10−4×2π, its long-term stability (hours) being ≤3×10−4×2π. This corresponds to a refractive index resolution of 5×10−8, and a long-term stability of 10−7.

Integrated optical sensors for the chemical domain

During the last decade there has been a rapidly growing interest in integrated optical (IO) sensors, expecially because many of them principally allow for sensitive, real time, label-free-on-site measurements of the concentration of (bio-)chemical species. This review aims at giving an overview of the most relevant developments in this area. After a general introduction into the field of IO sensors for the chemical domain, relevant aspects of integrated optics and chemical sensing are presented in short. A large variety of IO sensing platforms are introduced and discussed: interferometers, resonators, coupling-based devices such as grating couplers and surface plasmon resonance based sensors and finally a new class of sensors based on chemically induced field profile changes. Strong and weak points of principle and of configuration based on these principles are indicated and the main performance data of the IO sensing platforms, especially the obtained resolution, are indicated. Best resolutions of the chemically induced refractive indices on the order of magnitude

Plasma enhanced chemical vapor deposition silicon oxynitride optimized for application in integrated optics

10^{-6}-10^{-8}RIU

Silicon Oxynitride A Versatile Material for Integrated Optics Applications

can be obtained, corresponding to a resolution of

Realization of a multichannel integrated Young interferometer chemical sensor

10^{-3}-10^{-5}

Integrated opto-chemical sensors

nm in the chemically induced growth of layer thickness of chemo-optical transducer materials. Depending on the anlalyte and the type of transduction layer chemical concentrations down to some ppb or some pg

Theory and modelling of optical waveguide sensors utilising surface plasmon resonance

ml^{-1}

Optimization of a chemo-optical surface plasmon resonance based sensor

can be determined. Several IO sensing systems are commercially available. Extension of individual sensors to sensor arrays is treated and finally an outlook for the future is given.

Quasi-one-dimensional photonic crystal as a compact building-block for refractometric optical sensors

Silicon Oxynitride (SiON) layers are grown from SiH4/N2, NH3 and N2O by Plasma Enhanced Chemical Vapor Deposition (PECVD). The process is optimized with respect to deposition of layers with excellent uniformity in the layer thickness (δd<1%), high homogeneity of the refractive index (Δn=2–7×10−4) and good reproducibility of the layer parameters. The optical losses of slab-type waveguides is determined to be as low as 0.2 dB/cm at 632.8 nm wavelength. Due to absorption of N–H and Si–H vibrational overtones, the optical losses in the third telecommunication window, around 1550 nm, is increased to about 2 dB/cm for low index layers. By an anneal step, however, the hydrogen content of the films can be reduced as is confirmed by IR-spectroscopy and the optical losses decrease to below 0.2 dB/cm. Based on the optimized PECVD SiON technology, a layer structure fulfilling the strong requirements of telecommunication devices, is designed for operation at 1550 nm wavelength. This structure, consisting of a SiON core layer (n=1.4857) surrounded by thick oxide cladding layers (n=1.4637), has the potential for realization of channel waveguides allowing for low-loss bends with a small bending radius and high fiber-to-chip coupling efficiency.

Sensitivity enhancement in evanescent optical waveguide sensors

Silicon oxynitride is a very attractive material for integrated optics application, because of its excellent optical properties (~e.g. optical loss below 0.2 dB/cm!, the large refractive index range ~between 1.45 for silicon oxide and 2.0 for silicon nitride), and last but not least, the availability of reliable, low-cost fabrication technologies. Since good uniformity and reproducibility of the layers is extremely important for integrated optics applications, we have optimized the plasma-enhanced chemical vapor deposition and low-pressure chemical vapor deposition technologies of silicon oxynitride with respect to these requirements. Over a 50x50 mm area on a 3 inch wafer, an inhomogeneity of the refractive index of Dn<5E-3 and a nonuniformity of the layer thickness of < 1% can be obtained. Furthermore, new challenges such as the conditioning of the reactor, in order to guarantee process reproducibility in the same order of magnitude, are discussed. The high optical loss of silicon oxynitride in the third telecommunication window (wavelength range 1530-1605 nm), which is caused by the overtones of the Si-H and N-H bonds, was decreased by thermal treatment. Silicon oxynitride waveguides having a refractive index of 1.48 and an optical loss below 0.2 dB/cm (at 1550 nm) were realized.