Sensing method and sensor system
Sensing Method and Sensor System A sensing method comprises using a vertical cavity surface emitting laser (VCSEL) to oscillate and emit a laser beam. A diaphragm is used to reflect a portion of the laser beam back into the VCSEL. This method can be referred as self mixing interferometry. A current or voltage at the VCSEL is monitored, and is used to sense movement of the diaphragm. This allows a property external to the VCSEL to be sensed without using a photo-detector.
1. A sensing method comprising driving a vertical cavity surface emitting laser (VCSEL) to oscillate and emit a laser beam, using a diaphragm spaced away from a laser beam emitting surface of the VCSEL, the diaphragm having a thickness of 500 nm or less to reflect a portion of the laser beam back into the VCSEL, wherein the diaphragm is supported by a spacer which extends from the laser beam emitting surface of the VCSEL, and monitoring the electrical power drawn by the VCSEL to sense movement of the diaphragm without using a photo-detector.
2. The sensing method of claim 1 , wherein pressure waves such as acoustic waves are sensed by the sensing method.
3. The sensing method of claim 1 , wherein a hole is provided in the diaphragm.
4. The sensing method of claim 1 , wherein the spacer defines a volume between the diaphragm and the VCSEL, wherein the volume is airtight, wherein changes of ambient pressure are sensed by the sensing method.
5. The sensing method of claim 4 , wherein no hole is provided in the diaphragm.
6. The sensing method of claim 1 , wherein a known current is applied to the VCSEL and a voltage at the VCSEL is monitored.
7. The sensing method of claim 1 , wherein a known voltage is applied to the VCSEL and a current at the VCSEL is monitored.
8. The sensing method of claim 1 , wherein a constant current is supplied to the VCSEL from a constant current source, wherein an oscillating signal is supplied to the VCSEL from an oscillator, wherein the oscillation signal adds a modulated current to the constant current, and a lock-in amplifier is used to monitor for movement of the diaphragm at a frequency of the oscillating signal.
9. A sensor system comprising a vertical cavity surface emitting laser (VCSEL) and a diaphragm spaced away from a laser beam emitting surface of the VCSEL, the diaphragm having a thickness of 500 nm or less, wherein the diaphragm is supported by a spacer which extends from the laser beam emitting surface of the VCSEL, wherein the sensor system does not include a photo-detector, and wherein the sensor system further comprises drive and sensing electronics configured to provide a known current to the VCSEL and measure a voltage at the VCSEL or to apply a known voltage to the VCSEL and measure a current provided to the VCSEL, and wherein the sensor system further comprises signal processing electronics configured to receive a signal output from the drive and sensing electronics and to use the signal to monitor movement of the diaphragm.
10. The sensor system of claim 9 , wherein a hole is provided in the diaphragm.
11. The sensor system of claim 10 , wherein the hole has a diameter of at least 1 micron.
12. The sensor system of claim 9 , wherein a separation between the diaphragm and the VCSEL is 100 microns or more.
13. The sensor system of claim 9 , wherein the VCSEL is a bottom emitting VCSEL.
14. The sensor system of claim 9 , wherein the sensing electronics comprises a lock-in amplifier.
15. A sensor system comprising a vertical cavity surface emitting laser (VCSEL) and a diaphragm spaced away from a laser beam emitting surface of the VCSEL, wherein the diaphragm is supported by a spacer which extends from the laser beam emitting surface of the VCSEL, an opening being provided which allows gas to enter a volume between the diaphragm and the VCSEL, wherein the sensor system further comprises drive and sensing electronics configured to provide a known current to the VCSEL and measure a voltage at the VCSEL or to apply a known voltage to the VCSEL and measure a current provided to the VCSEL, and wherein the sensor system further comprises signal processing electronics configured to receive a signal output from the drive and sensing electronics and to use the signal to monitor a change of refractive index of gas in the volume or to monitor a change of reflectivity of the diaphragm.
16. The sensor system of claim 15 , wherein the diaphragm has a thickness of 2 microns or more.
17. The sensor system of claim 1 , wherein the spacer includes a hole.
18. The sensor system of claim 1 , wherein the VCSEL is disposed over an anode and a cathode and is bonded directly to the anode and the cathode.