Guangwei Yuan

Label-free silicon photonic biosensor system with integrated detector array

An integrated, inexpensive, label-free photonic waveguide biosensor system with multi-analyte capability has been implemented on a silicon photonics integrated circuit from a commercial CMOS line and tested with nanofilms. The local evanescent array coupled (LEAC) biosensor is based on a new physical phenomenon that is fundamentally different from the mechanisms of other evanescent field sensors. Increased local refractive index at the waveguides upper surface due to the formation of a biological nanofilm causes local modulation of the evanescent field coupled into an array of photodetectors buried under the waveguide. The planar optical waveguide biosensor system exhibits sensitivity of 20%/nm photocurrent modulation in response to adsorbed bovine serum albumin (BSA) layers less than 3 nm thick. In addition to response to BSA, an experiment with patterned photoresist as well as beam propagation method simulations support the evanescent field shift principle. The sensing mechanism enables the integration of all optical and electronic components for a multi-analyte biosensor system on a chip.

Evanescent field response to immunoassay layer thickness on planar waveguides.

The response of a compact photonic immunoassay biosensor based on a planar waveguide to variation in antigen (C-reactive protein) concentration as well as waveguide ridge height has been investigated. Near-field scanning optical microscope measurements indicate 1.7%nm and 3.3%nm top surface optical intensity modulation due to changes in effective adlayer thickness on waveguides with 16.5 and 10 nm ridge heights, respectively. Beam propagation method simulations are in good agreement with the experimental sensitivities as well as the observation of leaky mode interference both within and after the adlayer region.

Characterization of CMOS compatible waveguide-coupled leaky-mode photodetectors

Near-field scanning optical microscopy has been employed for the first time to analyze integrated photodetectors. Waveguide-coupled leaky-mode polysilicon metal-semiconductor-metal photodiodes fabricated in commercial complementary metal-oxide-semiconductor technology for on-chip optical interconnects exhibit a measured effective absorption coefficient of 0.67 dB/mum allowing a 10-mum-long detector to absorb 83% of the light in the waveguide with an estimated responsivity of 0.35 A/W at 654 nm. The measured effective absorption coefficient is in good agreement with effective index mode overlap calculations

Geometry Dependence of CMOS-Compatible, Polysilicon, Leaky-Mode Photodetectors

Complementary metal-oxide-semiconductor-compatible metal-semiconductor-metal polysilicon photodiodes fabricated in a commercial 0.35-mum technology offer estimated responsivities of up to 0.35 A/W at 654 nm. An effective absorption coefficient of 0.63 dB/mum was extracted from responsivities for 5- to 10-mum-long waveguide-coupled detectors. Increasing responsivity at smaller contact spacing indicated a two-part photocurrent response, with secondary photocurrent dominating at small contact spacings and high electric fields

Fully CMOS-Compatible On-Chip Optical Clock Distribution and Recovery

Clock distribution in the multi-gigahertz range is getting increasingly difficult due to more stringent requirements for skew and jitter on one hand and the deteriorating supply voltage integrity and process variation on the other hand. Global clock network, especially in nanometer CMOS designs with ever increasing die sizes, has become a prominent performance limiter. A potential alternative to traditional interconnect technology for achieving clock distribution beyond 10 GHz while maintaining required skew and jitter budgets is using on-chip optical interconnects. A practical on-chip optical clocking system must be CMOS compatible in order to provide attractive cost effectiveness for system level integration and ease of manufacturing. This paper presents the design of a fully CMOS compatible optical clock distribution and recovery system in a 3.3 V, 0.35-μm CMOS process. Experimental results from the test chip prove the feasibility of providing optical-electrical interface in devices and circuits in a fully CMOS compatible manufacturing environment. Although the test chips were designed in a mature CMOS process technology and the measured performance is low, the test chips demonstrated the feasibility of on-chip optoelectronic integration with fully CMOS compatible process. On-chip optical clock distribution is one of the natural applications of fully CMOS compatible on-chip optical interconnect technology.

Response of Local Evanescent Array-Coupled Biosensors to Organic Nanofilms

A label-free planar optical waveguide immunosensor that operates on the novel principle of local evanescent field shift is demonstrated in this paper. Increased local refractive index at the waveguides upper surface due to the formation of an organic adlayer shifts the evanescent field distribution up, and hence, changes the light intensity both above and below the waveguide structure. Beam propagation simulations show increased modulation ratio sensitivity to adlayer thickness with increasing detection distance below the waveguide. The local nature of detection allows sensors to be implemented in array formats on a single waveguide for multiple-analyte sensing. Both near-field scanning optical microscopy and integrated buried detector arrays are employed to study the response to patterned organic nanofilms including immunocomplexes, photoresist, and adsorbed bovine serum albumin (BSA) layers. Buried polysilicon detector arrays integrated with silicon nitride waveguides in a commercial CMOS process exhibit a 15% photocurrent modulation ratio response to an approximately 1-nm-thick adsorbed film of BSA. CMOS compatibility enables a low-cost sensor system on a chip. Temperature dependence measurements show that sensor has a 0.3%/degC change in modulation ratio, which is thousands of times less than traditional resonant biosensors.

Novel local evanescent field detection waveguide multianalyte biosensor

A novel waveguide sensor capable of sensing multiple analytes directly and in real time with label-free, local detection has been investigated. Numerical simulations agree with analytical calculations of the sensor sensitivity. The waveguide parameters including detector to core distance, adlayer length, and surface roughness have been extensively analyzed. Initial experimental realization efforts are summarized.

Local evanescent, array coupled (LEAC) biosensor response to low index adlayers

Experiments on planar optical waveguide based local evanescent array coupled biosensors using low-index photoresist and polystyrene nanoparticle adlayers are reported. Near-field scanning optical microscopy measurements are in close agreement with beam propagation method simulations.

Characterization of a 90° waveguide bend using near-field scanning optical microscopy

Multiple modes are directly imaged in a silicon nitride waveguide bend using near-field scanning optical microscopy (NSOM). The observations are in good agreement with modal calculations using conformal index transformation.

Initial demonstration of a local, evanescent, array coupled biosensor concept

A concept for a novel, compact, immunoassay biosensor that can simultaneously sense multiple analytes simultaneously is being investigated. The dielectric planar waveguide sensor relies on modulation of the local evanescent field coupled into an array detector. Proof of concept experiments carried out using near-field scanning optical microscopy (NSOM) on a 17 nm thick pseudo-adlayer demonstrated high sensitivity with an optical SNR of approximately 55:1. The measured results agree with numerical simulations