Illumination device and method for turning on or turning off a first and/or a second laser diode of an illumination device

An optical system for a virtual retinal display, comprising:

• a projector unit including:
• an illumination device including:
• a first laser diode configured to emit a first light beam within a first wavelength range, the first wavelength range changing depending on a temperature of at least one first laser cavity of the first laser diode,
• a second laser diode configured to emit a second light beam within a second wavelength range, the second wavelength range changing depending on a temperature of at least one second laser cavity of the second laser diode,
• a first sensor configured to acquire at least one piece of information concerning a current first wavelength range of the emitted first light beam, and
• a control unit configured to determine the current first wavelength range depending on the information acquired by the first sensor concerning the current first wavelength range, wherein the control unit is configured to turn on the first laser diode at a first point in time, and to turn off the first laser diode at a second point in time following the first point in time, depending on a comparison of a first wavelength value of the determined current first wavelength range with a first wavelength threshold value, and to turn on or leave on the second laser diode, wherein the control unit is configured to select the first wavelength threshold value such that the first light beam emitted by the first laser diode or the second light beam emitted by the second laser diode always lies within a third, constant wavelength range;
• and
• a first controllable deflection unit for the at least a first light beam or the second light beam configured to provide scanning projection of image content;
• and
• a redirecting unit to which the image content can be projected and which is configured to direct the projected image content onto an eye of a user.

A method for turning on or turning off a first laser diode and/or a second laser diode of an illumination device, rein the method comprises the following method steps:

• turning on the first laser diode of the illumination device to emit a first light beam within a first wavelength range at a first point in time using a control unit of the illumination device, wherein the first wavelength range changes depending on a temperature of at least one first laser cavity of the first laser diode;
• turning off the first laser diode at a second point in time following the first point in time using the control unit, depending on a comparison of a first wavelength value of a current first wavelength range, determined by the control unit, of the first light beam emitted by the first laser diode with a first wavelength threshold value;
• and
• turning on or leaving on the second laser diode of the illumination device to emit a second light beam within a second wavelength range (at the second point in time using the control unit, depending on the comparison of the first wavelength value with the first wavelength threshold value;
• wherein the control unit selects the first wavelength threshold value such that the first light beam emitted by the first laser diode or the second light beam emitted by the second laser diode always lies within a third, constant wavelength range.