Skip to main content

Integrated Spectrometers for Spectral Tissue Sensing

Periodic Reporting for period 2 - InSPECT (Integrated Spectrometers for Spectral Tissue Sensing)

Reporting period: 2016-01-01 to 2016-12-31

"Minimally-invasive image-guided procedures are becoming increasingly important in clinical practice. In a variety of procedures physicians lack reliable feedback on the type of tissue at the tip of their interventional device (needle, catheter, probes, etc…) to ensure they are at the right position before effecting the actual diagnosis or treatment. Spectral tissue sensing using compact photonic probes has the promise to be a valuable tool for screening and diagnosing purposes, e.g. for discriminating between healthy and tumorous tissue. Real-time tissue-characterization feedback to the physician during an intervention can significantly improve the outcome of diagnosis and treatment, and ultimately reduces cost of medical treatment. For a widespread adoption of spectral tissue sensing broadband miniature spectrometer devices should be become available at affordable cost, to make it commercially viable for also screening at point of care locations such as physicians’ offices and outpatient centers.

The InSPECT project enables the realization of photonic building blocks for low-cost miniaturized spectral tissue sensing devices. This involves the realization of a miniature broad-band solid-state light source and the realization of a miniature low-cost integrated spectrometer, both operating in the VIS/NIR from 400 to 1700nm. Two spectrometer devices will be developed: (i) a ""microSpectrometer"" based on the miniaturization and monolithic integration of diffractive dispersive elements and VIS+NIR photo-detectors in a small volume (cubic inch) device, and (ii) a ""nanoSpectrometer"", in which the spectrometer function is realized on a photonic integrated circuit (PIC) based on transparent SiO/SiN waveguide technology. For the latter multi-mode to single mode coupling structures will be realized in order to couple the output of a photonic probe to the spectrometer PIC. Ultimately, InSPECT will deliver the key photonics building blocks for low-cost miniature spectrometers, that will drive the widespread adoption of spectral sensing in applications that were not accessible before.
In the different work packages the following progress has been achieved during the first and second year of the project:

- Broad-band all-solid state based light source:
After a first literature study of possible candidates for luminescent materials in the infrared (NIR 700-1000nm and SWIR 1000-1700nm) we came up with a viable solution using luminescent ceramics (based on the (Lu,Gd)3-(Ga,Al)5-O12:Ce3+,Cr3+ system) and luminescent glasses (based on the GeO2:Bi system). VISNIR and SWIR luminescent materials have been further optimized and first studies and experiments have been performed in miniaturizing the light source concept and coupling the light into an optical fiber. Currently the project is aiming at using commercailly available, low cost, high power blue laser diodes, allowing for efficient excitation of the luminescent materials and subsequent fiber coupling. A spectral gap at around 900-1000nm has been identified for which another luminescent material is being synthesized.

- microSpectrometer:
We aim at using a modular approach, incorporating multiple gratings covering several subbands in the VIS-NIR-SWIR spectral range, in combination with two-dimensional VIS-NIR and SWIR sensors. First functional prototypes of the microSpecrometer have been realized and succesfully tested, paving the way for successfull integration and validation halfway 2017. A 2nd concept microSpectrometer has been built using a state-of-the-art commercial SWIR sensor and classical spectrometer layout; though having a larger footprint as specified in the system specifications document, this device has been succesfully functionally tested over the full spectral range.

- nanoSpectrometer:
Creating a broad-band spectrometer on a photonic integrated circuit (PIC) imposes many challenges. The PIC wavelength selective components need to cover the full spectral range from 400-1700 nm, and the PIC's/detectors need to be packaged and connected to the outside world. A system architecture plan and risk analysis document has been drafted/updated, leading to a full nanoSpectrometer system description and interface definitions. First arrayed waveguide gratings (AWGs) have been manufactured and successfully tested covering the VIS, NIR and SWIR spectral range, finally leading to a fully integrated PIC spectrometer solution covering the full 400-1700 nm spectral range of interest. First multimode to single mode conversion devices have been made and successfully tested, connecting the singlemode PIC's to the multimode outside world. Furthermore, a fiber-PIC-detector assembly/packaging process has been worked on and is in place for final device assembly in the 2nd half of 2017.
The technology being developed in InSPECT will ultimately have several societal and economical impacts. On the short term new broadband spectrometer modules like the microSpectrometer and solid state based light sources will become available that can be used e.g. in a healthcare setting for diagnostic purposes. Their compact size and cost effectiveness will allow for a more rapid introduction of new healthcare applications not only in the hospital, but also at the point-of-care setting. On the mid to long term, the realization of the nanoSpectrometer device allows for an ultimate size reduction, paving the way for spectral diagnostics in e.g. in-body implantable devices where size reduction is crucial.
Furthermore we envision the use of compact broadband solid state light sources in spectral sensing and imaging solutions for personal and professoinal health monitoring and minimally invasive healthcare applications.
Recently spectral sensing is also being introduced on the consumer market with low cost, handheld multiple-purpose (e.g. food-quality, drug quality and safety) devices, capable of measuring spectral fingerprints in the NIR spectral region (up to 1 micrometer). InSPECT technology allows to extend the spectral range of these sensing devices also beyond the 1 micrometer silicon cutoff wavelength, where additional important spectral fingerprints can be found and thereby increase the application spectrum.
InSPECT: Realization of compact 400-1700 nm spectrometer and light source