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OptoProbes PPT
- 1. 1
- 2. Fine light projection tools for deep-brain optogenetic stimulation CLEO 2016 2 Fundamental objectives -> derived technological pathway 1. Deep brain -> Implantable device 1. Minimize brain damage & immune response -> miniature probes. 2. Minimize thermal load -> passive light delivery 2. Projection of complex illumination pattern. • Many densely packed emitting pixels (E-pixels) • Each individually addressed and control 3. Hundreds of E-pixels -> Scalable 4. Affordable technology -> Mass-producible Hippocampus Superficial layers of the brain
- 3. Nano-Photonic Probes – Mechanical Structure 3 Shanks CLEO 2016 3 • Mechanical structure exploits MEMS fabrication technique for Miniaturization. • Dramatic reduction of probe cross-section compared to other technologies. 4 Shanks 18µm 3mm 3mm Emitting pixels 25µm Optical Fiber (125µm dia.) Miniaturization
- 4. Silicon photonics technology – Photonic Circuitry CLEO 2016 4 The visible photonic circuitry is patterned in a thin Si3N4 layer encapsulated by SiO2. Light coupling Light delivery Light Emitters
- 5. Silicon photonics technology – Photonic Circuitry CLEO 2016 5 Light delivery Light Emitters Wavelength Division Multiplexing How to independently drive many illumination points? Light coupling bottleneck
- 6. Solution– Wavelength division multiplexing (WDM) λ1 λ2 λ3 λ4 CLEO 2016 Single Input 1:9 Optical router (AWG) Single fiber delivers multicolor light External hardware can be used to control input light. Illumination points emit different wavelengths 6 Wavelength (nm) 1.0 0.5 RelativeActivity Zhangetal.,Nature Protocols(2010) Optogenetic actuator response curve 100µm λ1 λ2 λ3 λ4 Broadband response curves
- 7. AWG – Array waveguide grating 7 468 470 472 474 476 Power[dB] 2 4 6 8 10 12 λ [nm]
- 8. Complex illumination pattern 8 Light intensity drops very slow ! Independent addressing of many E-pixels Spectral addressing using WDM 200 µm 100𝜇𝑚 Collimated emission patterns (no overlaps between beams) Dense array of E-pixels Photonic Fabrication Techniques
- 9. 100 µm FWHM = 17 µm 200 µm FWHM = 25 µm Beam shape imaging– Fluorescein:Water Solution Concentration = 10µM 470 µm 6.8° CLEO 2016 9 200 µm FWHM = 18 µm 100 µm FWHM = 10 µm Beam shape imaging– Brain Tissue Neuron image: Banker Lab University of Washington neuron
- 10. 10 300 µm Beam shape imaging– Fluorescein:Water Solution FWHM = 30µm Simulation (No scattering) 1000 µm FWHM = 15µm 400 µm Orthogonal cross-section
- 11. Beam shape engineering – Work in progress CLEO 2016 11 285nm θ sin 𝜃 = 𝑛 𝑔𝑟𝑎𝑑𝑖𝑛𝑔 𝑛 𝑆𝑖𝑂2 − 1 𝑛 𝑆𝑖𝑂2 𝜆 Λ 395nm335nm 445nm Period θ =2.2O θ =12O θ =23.5O θ =27.3O Λ • Static in plane (Φ) emission angle control.
- 12. Multi-pixel spectral addressing- Fluorescence Imaging 1600 µm 100µM CLEO 2016 12
- 13. Functional Validation - Electrical Measurements CLEO 2016 13 Single Illumination point Illumination Power < 10μW Tungsten Electrode PROBES CA3 Thy1 Transgenic mice Raster Plot • Reliable excitation of neurons • No photo-bleaching effect PHOTONIC PROBE Laser pulse indicator Obtained @ Deisseroth group, Stanford
- 14. 2-Photon Ca2 imaging Mice co-expressing ChR2 and GCaMP6 14Obtained @ Tolias group, BCM
- 15. Neuron #1 activation 15 Overlay PSTH N1 surface LED Illumination (all 4 neurons)
- 16. Thank you: stay tuned. Trevor FOWLER, Laurent MOREAUX, Eran SEGEV, Derrick CHI, Michael ROUKES, Andrei FARAON, Caltech Team Collaborators: Wesley Sacher , Baylor Collage Andreas Tolias Jacob Raimer Stanford Karl Deisseroth Maisie Lo U. Toronto Joyce Poon
Hinweis der Redaktion
- Hello, and thank you for joining my talk. Today I’m going to talk about our effort to develop fine light projection tools for deep-brain optogenetic stimulation. Such tools should fulfill the following requirements: First we are talking about implantable probes because free –space microscope based methods can only address superficial layers of the brain. These probes should cause minimal brain perturbation, so they should be minimal both in size and in the amount of heat they deliver to the brain. Second in order to project complex illumination pattern they should have many densely packed emitting pixels, and more importantly each of those should be individually addressed and controlled. Finally, We would like to develop a technology which is scalable and mass-producible so we would be able to produce affordable probes to the entire neural community. Our objective is that the technology of visible silicon photonic is the only onethat can address all of those needs.
- The mechanical structure of our probes is made of silicon. As such the entire toolbox of MEMS fabrication techniques can be used to fabricate these probes. This means that there is a lot of flexibility in the design of the shape of these probes, which can be tailored for the specific needs of a specific experiment. Some examples for various possible shapes are shown in those pictures. ….. What’s even more important is the ability to miniaturize these probes. On the left you can see an image comparing the width of the top section of the shanks to the width of a regular single-mode fiber. Multimode fibers are usually even wider than that. On the bottom left you can see a side view of the probe. Using MEMS fabrication techniques we managed to fabricate shanks only 20 um in thickness, through out the length of the shank. The image on the right shows how smaller is this cross-section compared again to a regular optical fiver.
- The photonic circuitry of our probes is patterned in a thin layer of silicon nitride encapsulated by silicon oxide. . We use grating couplers for coupling the light from an optical fiber to the chip. We have waveguides that deliver the light across the chip, and we have another set of grating couplers that function as photonic emitters that project the light out of the probe and into the brain.
- The major problem, however, is how to drive, and individually control each of the multiple illumination points located on this probe. Obviously, driving each of those E-pixels using a dedicated optical fiber is not a scalable solution. Optical communication has solved this problem many years ago by developing all sorts of multiplexing techniques. From those we choose to implement the WDM technique because it is in particular suitable for our needs.
- The reason for that is the following: The response curves of optogenetic actuators usually have rather broad spectrum. Therefore we can use a variety of wavelengths to excite these opsins, and a single optical fiber can couple all those wavelength to the chip. An AWG that is implemented on the chip routes each color to its destination E-pixel, and thus crease a 1:1 mapping between the wavelength of the light and the spatial location where it is emitted. Finally, we can use external hardware like AO filter to switch between different combination of colors and thus control the exact temporal-spatial illumination pattern.
- This slide show few SEM images of the AWG’s we’ve prototyped. These are very compact AWG’s, and integrate one at the base of each shank. The graph on the right shows a typical spectral measurement or our AWG’s. Typical channel spacing is 1nm, and we get about 10dB xtalk ratio.
- In our prototype devices each AWG drives 9 E-pixels. The spacing between these E-pixels was 200um in our first generation, and went down to 100um in the current generation. Our future probes that are planed to be fabricated in photonic foundries will be designed to have pitch smaller than 50um between E-pixels. Such dense array of emitters is possible due to the almost collimated beam shape of the light emitted by the E-pixels. Let me explain why is that important. Consider a probe emitting wide beam shape, which is typically the case when using LEDs as light sources. This would have two drawbacks. First, the intensity of the beam quickly drops. In addition, the illuminated beams patterns overlaps, and thus the illumination generated by adjacent E-pixles is not really independent, even if they are individually controlled. We have to keep the illumination beam really narrow in order to avoid such overlaps.
- This is exactly the case in our photonic probes. The following image shows side view of one of our photonic probes soaked in fluorescein solution. As you can see the probe illuminates highly directional beam almost perpendicular to its surface. The FWHM of the beam is only about 18 200 um away from the probe. This width is about the order of a neural cell body. Scattering of the light in the mouse brain slightly expends the beam, but because this scattering is mostly forward scattering the FWHM beam width is still only 25um at 200 um away from the probe.
- Simulation results, which do not include any scattering shows that the fundamental width of the beam grows to only 30um at a distance of 1mm away from the probe. As you can see in the image above, is stays rather collimated for longer distances as well.
- The in-plane illumination angle of the beam is a design parameter controlled by the period of the grating couplers. These simulation results show that we can change the illumination angleof the beam without any major impact on its divergence angle.
- Going back to multi-pixel light projection, this image shows several E-pixels illuminating simultaneously. These are first generation probes with a pitch of 200um between E-pixels. You can imagine how these can be made much denser without causing overlaps between beams. The movie I’m about to show demonstrate how we address different pixels by manually change the input wavelength to the AWG.
- The first method was direct electrical measurements of the neural activation generated by our probes. The following picture shows the method by which this was done. First a Tungsten electrode was glued on top of the probes. The tip of the electrode was places close to the trajectory of the illumination beam. These coupled probes were implanted into the CA3 brain area of Thy1 transgenic mice. The graph on the right show the raster
- Using this flat packaging we are able to easily get under the microscope objective during in vivo experiments.