Abstract
Waveguide-based photonic sensors provide a unique combination of high sensitivity, compact size and label-free, multiplexed operation. Interferometric configurations furthermore enable a simple, fixed-wavelength read-out making them particularly suitable for low-cost diagnostic and monitoring devices. Their limit of detection, i.e., the lowest analyte concentration that can be reliably observed, mainly depends on the sensors response to small refractive index changes, and the noise in the read-out system. While enhancements in the sensors response have been extensively studied, noise optimization has received much less attention. Here we show that order-of-magnitude enhancements in the limit of detection can be achieved through systematic noise reduction, and demonstrate a limit of detection of ∼ with a silicon nitride sensor operating at telecom wavelengths.
Highlights
Photonic integrated biosensors have been the subject of intense research in the last decade due to their capability to detect small quantities of biochemical substances such as protein biomarkers, DNA or toxins, indicative of the presence of a disease or environmental pollution without time-consuming labeling steps [1,2,3]
The equipment used in the read-out system shown in Figure 2 consists of a Santec WSL-100 laser source, an IPG Photonics erbium doped fiber amplifier (EAD-500C) and the V1550A variable optical attenuator from Thorlabs for the generation of the input light
With the initially dominant mechanical noise dampened, we focus on electrical noise sources, i.e., shot, thermal and quantization noise
Summary
Photonic integrated biosensors have been the subject of intense research in the last decade due to their capability to detect small quantities of biochemical substances such as protein biomarkers, DNA or toxins, indicative of the presence of a disease or environmental pollution without time-consuming labeling steps [1,2,3]. The LOD is given by LOD = 3σ/S in refractive index units, where σ is the system noise, and S is the sensitivity An improvement in both sensitivity and noise will result in enhanced limits of detection. Previous theoretical efforts have shown that interferometric sensors can reject amplitude and phase noise of the laser source, so that detection becomes fundamentally limited by thermal and shot noise, as well as intrinsic waveguiding losses [8]. With the proposed procedure we are able to demonstrate a bulk LOD of 1.4 × 10−8 RIU with a 5 s averaging time, using a balanced MZI with 6 mm long silicon nitride waveguides that exhibit a comparatively low sensitivity Swg ∼ 0.2 RIU/RIU.
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