1310 Nm Tm Grating Couplers to Operate Silicon Nitride Ring Resonator Biosensors

Photonic integrated circuits (PICs) fabricated on silicon nitride (SiN) wafers are witnessing a massive implementation because they can provide low-loss waveguides in a broad wavelength range (from the visible to the near infrared) whilst being fabricated in large volumes using standard silicon fabrication processes. One of the most relevant application fields of this technology is biosensing since SiN PICs enable label-free lab-on-a-chip systems for fast and sensitive detection of minute amounts of different biological entities. To this end, resonant structures such as ring resonators (RR) are highly appropriate, but they need suitable interfaces with optical fiber to be tested on-wafer and used in real applications. The interface that satisfies the two previous requirements is the grating coupler (GC). However, experimental evidence of GCs operating at 1310 nm wavelengths for the transverse magnetic (TM) mode, for which RR-based sensors perform better than for the widely employed transverse electric (TE) mode, has not been reported so far. In this work, the operation of fully-etched focusing GCs at 1310 nm wavelengths for the TM mode in a SiN PIC is demonstrated. Experiments show that the fabricated GCs display an ≈40 nm bandwidth and coupling losses around 13 dB per interface. In addition, we show successful biosensing experiments using bovine serum albumin and anti-bovine serum albumin as biological agents in a microfluidic environment. Further engineering for the interface should lead to lower coupling losses, which would pave the way to practical applications of SiN PICs based on RRs operated for the TM mode and at 1310 nm wavelengths.