Patent Application
20070097350
Disclosed embodiments relate generally to laser based sensing devices. More particularly, disclosed embodiments relate to laser transmitting devices such as the type used in lidar systems. The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Lidar systems are measuring systems that detect and locate objects using the same principles as radar, but using light from a laser. Lidar systems can be used on aircraft, for example, for a number of purposes. One example of a lidar system on an aircraft is an altimeter which uses laser range finding to identify a height of the aircraft above the ground. Another example of a lidar system on an aircraft could include a system which detects air turbulence. Other uses on aircraft are possible, for example including on-ground range finding for purposes of on-ground navigation of aircraft in proximity to airports, etc. Non-aircraft uses of lidar systems are also possible.
One potential problem with some lidar systems relates to the types of lasers used. Frequently, lidar systems use laser sources that are inexpensive and readily available. Many of these lasers emit light in the visible and near infrared wavelengths, which can be an eye hazard if the beam intensity is too high. While the aircraft is moving, the potential eye hazard is reduced, because it is unlikely that a person will have a prolonged exposure. However, while the aircraft is stationary on the ground, the ground crew could be exposed to this hazard. Some potential for eye hazards also exists in situations where an aircraft is flying at low airspeeds and a low altitude, though the risk is not likely to be high.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In accordance with an example embodiment, a laser transmitting system includes a laser source configured to transmit a laser beam at an original transmit intensity. The system also includes a laser intensity adjusting mechanism positioned in the path of the transmitted laser beam. The laser intensity adjusting mechanism is controllable to reduce the intensity of the laser beam from the original transmit intensity. The system also includes a controller coupled to the laser intensity adjusting mechanism. The controller is configured to automatically control the laser intensity adjusting mechanism based upon a safety criteria. Disclosed embodiments also include methods of controlling a laser transmitting system.
The laser transmitting system can be, in some embodiments, a lidar system such as a laser altimeter on board an aircraft. One example of a safety criteria is an altitude of the aircraft on which the laser transmitting system is positioned. Other examples of safety criteria can include identifying whether personnel are in the vicinity of the aircraft, a rate of speed of the aircraft, power level, etc.
As noted above, lidar systems frequently use laser sources that emit light in the visible and near infrared wavelengths, which can be an eye hazard if the beam intensity is too high. On the other hand, if the beam intensity is not high enough at high altitudes, the system performance may suffer. As a non-limiting example, a typical lidar system can range find to the ground when flying below altitudes of approximately 2500 feet. An eye hazard from the laser beam exists at much closer proximity, however, for example beginning at around 42 feet in one example. While the aircraft 100 is moving, the potential eye hazard is reduced because it is extremely unlikely that a person will have a prolonged exposure. However, while the aircraft is stationary on the ground, the ground crew could be exposed to this hazard. The potential eye hazard also exists at low altitudes and airspeeds, for example to an individual who would happen to be observing the aircraft through binoculars. In one example, the eye hazard range would be extended, when a person is viewing the aircraft through binoculars, to around 150 feet. These ranges are provided merely as examples, and those of skill in the art will recognize that the ranges depend on a number of factors, including the power or intensity of the transmitted beam. Disclosed embodiments include use of a power attenuating device or mechanism which adjusts the laser intensity under the control of a control. These embodiments attenuate the transmit beam from its original transmit intensity, reducing the power output to an eye safe level when eye hazards are most severe (low altitudes, on ground, etc).
As shown in
The safety criteria can be a number of different criteria determined in a variety of different manners. For example, the safety criteria can include an altitude of an aircraft 100 on which the laser transmitting system 110 is positioned. In one embodiment, if the laser source is transmitting while the aircraft is above some minimum altitude, 150 feet for example, laser intensity adjusting mechanism 220 is controlled such that there is no attenuation of the transmit intensity or power. In other words, laser beam 222 exiting mechanism 220 has substantially the same power or intensity as laser beam 212 entering mechanism 220. However, when aircraft 100 drops below the minimum altitude, the safety criteria analysis performed by controller 230 identifies this fact and mechanism 220 is controlled accordingly to attenuate the power of the laser beam. This attenuation can be two state in nature (on or off), or it can be over some continuum (discrete or continuously changing), where the lower the aircraft altitude, the greater the attenuation of the transmitted beam. Other safety criteria can include, for example, the detection of personnel in the vicinity of the laser transmitting system, ground speed of the aircraft, airspeed of the aircraft, power level, etc.
In exemplary embodiments, the laser intensity adjusting mechanism 220 includes a variable polarizing attenuator (VPA). Variable polarizing attenuators are commonly available devices which attenuate light under the control of a control signal. Frequently, VPAs are voltage controlled devices. In accordance with disclosed embodiments, a VPA is used in a laser above ground level (LAGL) sensor system or other system under the control of a controller and based on a safety criteria to reduce the eye hazard by switching between high and low intensity states. As described above, for a LAGL sensor, the VPA will allow transmission at high intensity while it is above a defined hazard range, but will switch to one or more low intensity transmission states when it is below the defined hazard range, thereby protecting all ground personnel from the laser hazard.
A VPA implementation of laser intensity adjusting mechanism 220 is illustrated in
When the variable polarization rotator 310 is configured to rotate the beam polarization parallel to the exit polarizer direction 322 as shown in
Referring now to
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
