High index contrast photonic platforms for on-chip Raman spectroscopy

Raza, Ali; Clemmen, Stéphane; Wuytens, Pieter; Goede, Michiel de; Tong, Amy S. K.; Thomas, Nicolas Le; Liu, Chengyu; Suntivich, Jin; Skirtach, André G.; García-Blanco, Sonia M.; Blumenthal, Daniel J.; Wilkinson, James S.; Baets, Roel

doi:10.1364/oe.27.023067

Cited by 46 publications

(55 citation statements)

References 38 publications

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“…Thus, the calculated coupling efficiency (i.e., mode overlap calculation using the Lumerical MODE solutions software) was used for the normalization of the results. The normalization was followed by amplitude scaling based on the saturation length of the waveguides [39]. Although the length of all waveguides is equal (∼1.4 cm), the effective waveguide length for WGR can be different due to the different propagation loss of the waveguides.…”

Section: Resultsmentioning

confidence: 99%

“…where ρ is the molecular density, σ is the Raman cross-section of the molecule, η is the Raman conversion efficiency, γ in and γ out are the in-and out-coupling losses, α is the propagation loss of the waveguide [39]. In Eq.…”

Section: Resultsmentioning

confidence: 99%

“…Evans et al studied WGR in titanium oxide (TiO 2 ) waveguides [38]. Raza et al compared four high refractive index contrast materials typically used in integrated photonics, namely aluminum oxide (Al 2 O 3 ), silicon nitride (Si 3 N 4 ), titanium oxide (TiO 2 ) and tantalum oxide (Ta 2 O 5 ) [39]. In their study, the relatively low refractive index contrast of Al 2 O 3 led to poor Raman coupling efficiency, while the elevated background and high propagation losses of TiO 2 led to poor SNR.…”

Section: Introductionmentioning

confidence: 99%

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Study on multiple waveguide platforms for waveguide integrated Raman spectroscopy

et al. 2020

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Waveguide Raman spectroscopy uses the evanescent field outside a waveguide to probe the analyte on the surface of the chip, permitting to selectively study thin films or nanostructures on top of the waveguide while benefiting from the long iteration path of the excitation with the analyte. Both the polarization of the excitation mode as well as the refractive index contrast of the waveguide platform play an important role in the Raman excitation process as well as the coupling efficiency of the generated Raman signal back into the waveguide. In this article, we characterize three waveguide platforms of different refractive index contrasts for waveguide Raman, namely Al 2 O 3 , Si 3 N 4 and TiO 2 on SiO 2. Toluene was used as a test analyte. Both background and analyte were measured for quasi-transverse electric (quasi-TE) and quasitransverse magnetic (quasi-TM) modes. TM modes generate less background than TE modes due to less confinement of the mode in the waveguide core materials. A combination of Si 3 N 4 and quasi-TM polarization led to the highest SNR in this study.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study on multiple waveguide platforms for waveguide integrated Raman spectroscopy

et al. 2020

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“…In recent years, the silicon nitride (Si 3 N 4 ) platform was developed, which enables waveguide-based excitation and collection of Raman [19,20,21,22] and SERS spectra [23,24,25,26,27,28,29,30,31]. Despite the continuous improvement in the performance of the waveguide-based SERS platforms, they are limited by the background signal of the Si 3 N 4 [32,33]. Currently, free-space SERS substrates still slightly outperform waveguide-based SERS platforms [34].…”

Section: Introductionmentioning

confidence: 99%

Waveguide-based surface-enhanced Raman spectroscopy detection of protease activity using non-natural aromatic amino acids

Turk

Raza

Wuytens

et al. 2020

Biomed. Opt. Express

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Surface enhanced Raman spectroscopy (SERS) is a selective and sensitive technique, which allows for the detection of protease activity by monitoring the cleavage of peptide substrates. Commonly used free-space based SERS substrates, however, require the use of bulky and expensive instrumentation, limiting their use to laboratory environments. An integrated photonics approach aims to implement various free-space optical components to a reliable, mass-reproducible and cheap photonic chip. We here demonstrate integrated SERS detection of trypsin activity using a nanoplasmonic slot waveguide as a waveguide-based SERS substrate. Despite the continuously improving SERS performance of the waveguide-based SERS substrates, they currently still do not reach the SERS enhancements of free-space substrates. To mitigate this, we developed an improved peptide substrate in which we incorporated the non-natural aromatic amino acid 4-cyano-phenylalanine, which provides a high intrinsic SERS signal. The use of non-natural aromatics is expected to extend the possibilities for multiplexing measurements, where the activity of several proteases can be detected simultaneously.

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“…The spectrum of this background being itself a function of the mode shape, it depends slightly on the optical cladding (analyte) and therefore cannot be known perfectly for an unknown analyte. Moreover, the shot-noise associated with this background cannot be subtracted and constitute the greatest limiting factor to the signal-to-noise ratio [18]. The impact of this background is therefore detrimental [18]- [20], and its reduction has a high impact on the future prospects of on-chip Raman sensing.…”

Section: Introductionmentioning

confidence: 99%

Surface-Enhanced Raman Spectroscopy Based on Plasmonic Slot Waveguides With Free-Space Oblique Illumination

Zhao

Raza

et al. 2020

IEEE J. Quantum Electron.

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We report a novel on-chip approach for surfaceenhanced Raman spectroscopy (SERS) using a plasmonic slot waveguide. The Raman signal is excited via free-space excitation and is collected by the waveguide. A significant improvement of the signal-to-background-ratio (SBR), as compared to the case of back-scattered Raman spectroscopy with waveguide-mode excitation, is demonstrated using a silicon nitride plasmonic slot waveguide with a 7-mm access waveguide. The flexible adjustment of the incident angle in free space and modification of waveguide geometry enables the further optimization of the pump-to-Stokes conversion efficiency. The combination of high SBR and long access waveguide allows the integration with additional photonics devices (sources, filters, spectrometers) on the same chip.

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High index contrast photonic platforms for on-chip Raman spectroscopy

Cited by 46 publications

References 38 publications

Study on multiple waveguide platforms for waveguide integrated Raman spectroscopy

Study on multiple waveguide platforms for waveguide integrated Raman spectroscopy

Waveguide-based surface-enhanced Raman spectroscopy detection of protease activity using non-natural aromatic amino acids

Surface-Enhanced Raman Spectroscopy Based on Plasmonic Slot Waveguides With Free-Space Oblique Illumination

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