Open loop laser power control for optical navigation devices and optical systems
View Patent ↗A current output of a drive signal, modulated between two current settings, is applied to a laser diode, e.g. VCSEL. The settings are selected such that laser diode's power output meets the average power and peak power limits of the eye safety standards. The drive signal having a duty cycle toggling between the two settings. The duty cycle is selected such that the average and peak power limits are met for the given upper current setting. The drive circuit may include an analog modulator or digital analog converter (DAC) for maintaining the lower and upper current settings. When the drive circuit is implemented as an integrated circuit, the DAC may be incorporated into the IC. The sensitivity of the DAC is selected to maintain the desired lower and upper current settings.
1. A method comprising:
sequencing a laser through a series of current settings;
selecting a minimum current setting and a maximum current setting from the series of current settings;
modulating between the minimum current setting and the maximum current setting at a desired duty cycle to produce a drive signal; and
applying the drive signal to the laser to drive the laser,
wherein a difference between the maximum current setting and the minimum current setting is such that the output power of the laser can be controlled by the drive signal within about 2 percent of a desired output power over temperature.
2. A method, as defined in claim 1 , wherein the output power of the laser is below a select average power limit.
3. A method, as defined in claim 1 , wherein the output power of the laser is below a select peak power limit.
4. A method, as defined in claim 1 , wherein the minimum current setting and the maximum current setting are adjacent current settings.
5. An optical navigation method comprising:
projecting a modulated laser beam at a surface, including:
modulating between a minimum current setting and a maximum current setting at a desired duty cycle to produce a drive signal; and
applying the drive signal to the laser to drive the laser,
wherein a difference between the maximum current setting and the minimum current setting is such that the output power of the laser can be controlled by the drive signal within about 2 percent of a desired output power over temperature;
receiving a reflected signal from the surface, wherein the reflected signal indicates positional data;
repeating the steps of projecting and receiving; and
comparing the reflected signals to determine differences in positional data.
6. An optical navigation method, as defined in claim 5 , wherein the output power of the laser is below a select average power limit.
7. An optical navigation method, as defined in claim 6 , wherein the output power of the laser is below a select peak power limit.
8. An optical navigation method, as defined in claim 6 , wherein the minimum current setting and the maximum current setting are adjacent current settings.