Waveguide transmission
We have seen that some waveguides exhibit variable and increasing back reflection of single wavelength illumination over time, limiting their effectiveness and reliability. We have developed approaches to improve the transmission of these waveguides. We have found that by modulating the illumination wavelength over a small wavelength range we can reduce or eliminate this back reflection from the waveguide. In addition, we describe the writing and erasing of gratings within SiON waveguides by forming standing waves. Methods, systems, instruments, and devices are described that provide improved transmission of light through such waveguides.
1. A method for improving light transmission through a chip comprising at least one waveguide comprising:
providing a chip comprising at least one waveguide; and
providing to the waveguide on the chip illumination light from a laser, wherein the wavelength of the illumination provided by the laser is modulated over time within a range of wavelengths, wherein the range of wavelength modulation is less than 1 nm, whereby the waveguide exhibits less back reflection than when the laser wavelength is not modulated.
2. The method of claim 1 wherein the laser wavelength is between about 500 nm and about 650 nm.
3. The method of claim 1 wherein the range of wavelength modulation is less than 500 picometers.
4. The method of claim 1 wherein the range of wavelength modulation is less than 250 picometers.
5. The method of claim 1 wherein the frequency of wavelength modulation is less than about 1 Hz.
6. The method of claim 1 wherein the frequency of wavelength modulation is less than about 0.1 Hz.
7. The method of claim 1 wherein the wavelength modulation is carried out by cycling the laser through more than two different wavelengths.
8. The method of claim 1 wherein the wavelength modulation is carried out by cycling the laser through 3 to 30 different wavelengths.
9. The method of claim 1 wherein the wavelength modulation is carried out by randomly addressing wavelengths within the range of wavelength modulation.
10. The method of claim 1 wherein the wavelength modulation is carried out by monitoring a back reflection level and changing the laser wavelength if the back reflection level exceeds a threshold level.
11. The method of claim 10 wherein the threshold level is between 0.1% and 2% of the intensity of complete back reflection.
12. The method of claim 10 wherein the back reflection level is determined by measuring a drop in forward transmission.
13. The method of claim 1 wherein the waveguide comprises a SiON core.
14. The method of claim 1 wherein the waveguide comprises a core that is surrounded by silicon dioxide.
15. The method of claim 1 wherein the chip comprises a detector.
16. The method of claim 15 wherein the detector comprises a CMOS detector.
17. The method of claim 1 wherein the waveguides provide illumination to nanoscale wells on the chip comprising fluorescent species.
18. The method of claim 1 wherein the chip comprises a semiconductor chip.