Application

Laser Diode Drivers for LiDAR Applications

LiDAR turns light into distance, and the quality of that distance measurement starts with the current pulse driving the laser diode. Directed Energy has built laser diode drivers for ranging work for more than twenty years, from early laser speed guns for law enforcement through today's 3D imaging and autonomous vehicle programs. The pages below cover the driver features that matter for LiDAR and the measurement problems engineers are solving with them.

Key Product Features

• Open frame constructionOpen frame drivers ship as a bare PCB or a PCB mounted on a heatsink, which lets you place the driver next to the diode and keep the output loop short. That matters in LiDAR because loop inductance is what limits how fast the current edge can rise.
• Enclosed modulesEnclosed versions put the same circuitry inside a shielded housing with defined mounting points and connectors. They cost more board space than an open frame card but they simplify EMI containment and handling in a system that is going to be assembled by more than one person.
• Lab to LaunchThe standard catalog rarely lands exactly on a LiDAR requirement, so Directed Energy runs a Lab to Launch program that starts with off the shelf instruments for the bench and ends with an OEM module built to your parameters. You prototype with a standard product, then move to a custom variant without changing the underlying current source topology.
• Analog and digital controlDrivers are available with analog current setting, digital control, or both, so the same module can be trimmed by a bench supply during characterization and then commanded by a host controller in the product. Benchtop units such as the PCX-7401 add Ethernet, RS232 and USB remote control for automated test.
• Nanosecond pulse edgesShort pulses are what give LiDAR its range resolution, and the driver has to produce them without ringing. The PCO-7111 is specified at 2 ns to 3.5 ns rise and fall with pulse widths of 5 ns to 10 ns, and the PCO-6141 reaches 12 ns edges at up to 60 A.
• Fixed or variable pulse widthsFixed width drivers are simpler and cheaper because the pulse shaping is set at the factory, which suits a volume LiDAR build with one operating point. Variable width parts such as the PCO-6131, specified from under 100 ns to DC, let a research group sweep width and duty cycle while they are still deciding what the operating point should be.
• Current source topology and low inductance layoutThese drivers regulate current, not voltage, so the diode sees a controlled amplitude regardless of how its forward voltage drifts with temperature. The layouts are built to keep output inductance low, since inductance in the output loop directly slows the rising edge and rounds the pulse.

Science and Environmental Measurement

• MappingAirborne and terrestrial LiDAR produce ground models at a density that photogrammetry cannot match, including under tree canopy. Pulse to pulse amplitude stability is what keeps the returns comparable across a survey line, which is a direct requirement on the driver.
• 3D modelingPoint clouds captured from several positions are registered into a single model of a structure, a site or an object. Narrow pulses improve the ability to separate two surfaces that are close together in range.
• Yield forecastingAgricultural LiDAR estimates canopy height, density and biomass across a field, and those numbers feed yield models weeks before harvest. Surveys are repeated through the season, so the instrument has to give the same answer in June that it gave in April.
• Fire and flood modelingFuel load, terrain slope and channel geometry all come out of LiDAR terrain data, and they drive fire spread and flood inundation models. After an event, a repeat survey quantifies what actually changed.
• Pollution modelingAtmospheric LiDAR reads backscatter from aerosols and particulates to profile a plume with altitude. These systems tend to run at high repetition rates and average many shots, which puts a thermal duty cycle requirement on the driver as well as a speed requirement.
• River surveys and water resource managementBathymetric and topographic LiDAR map channel geometry, bank erosion and floodplain extent for water resource planning. Water absorbs strongly at the usual ranging wavelengths, so these systems need every bit of peak optical power the diode can be driven to.

Navigation, Mobility and Energy

• Advanced driver assistance systemsADAS sensors have to resolve a pedestrian from a lamp post at highway speed, which means short pulses, high repetition rates and consistent amplitude. Automotive programs also push the driver into a small thermal envelope, which is where open frame modules mounted directly to a heatsink earn their place.
• Automated guided vehiclesFactory AGVs use LiDAR for both obstacle detection and localization against a known floor plan. Ranges are shorter than automotive, so the design tension moves away from peak power and toward cost, size and reliability over long duty cycles.
• Vehicle speed measurementLaser speed measurement takes a series of range readings and differentiates them, so timing jitter in the emitted pulse converts directly into speed error. Directed Energy supplied drivers into this application before LiDAR became a mainstream term.
• Oil, gas and mineral explorationDifferential absorption LiDAR detects methane and other gases by comparing returns at two wavelengths, one absorbed by the target species and one not. The comparison is only as good as the amplitude repeatability between the two shots, which is a current source specification.
• Wind studies and analysisDoppler LiDAR measures wind speed and direction at hub height for turbine siting and for real time control of an operating turbine. Long coherent averaging times mean the driver runs continuously for hours, so thermal behavior matters as much as pulse shape.

Urban Planning and Infrastructure

• City and land use modelingMunicipal LiDAR builds building footprints, roof geometry and vegetation layers into planning models. Once the base survey exists, later flights are differenced against it to show what has been built and what has been removed.
• Transportation corridor mappingMobile LiDAR mounted on a vehicle captures road surface, signage, clearances and adjacent structures in a single pass, without closing the road. Data rates are high because the platform is moving, which pushes repetition rate up.
• Terrain and contour mappingBare earth models are extracted by classifying ground returns and discarding vegetation and structures. Multiple returns from one pulse are what make that classification possible, and resolving them requires a short, clean pulse.
• Architecture and heritage recordingScanning an existing building produces an as built model that is accurate enough to design against, which is useful when the original drawings are wrong or missing. Interior scans work at close range, so dynamic range in the receiver and control of the emitted amplitude both matter.
• Sewers and tunnelsConfined space scanning captures ovality, joint offsets and deformation along a buried asset. Space and power are both limited on these platforms, which is the case for a compact OEM module rather than a benchtop instrument.
• Floodplain mappingFloodplain delineation depends on vertical accuracy of a few centimeters across large areas, since a small elevation error moves the mapped water line a long way. Consistent pulse timing across a whole survey is what holds that accuracy together.

If a standard driver does not fit the optical, thermal or mechanical envelope of your LiDAR design, that is the normal starting point rather than the end of the conversation. Send the required current amplitude, compliance voltage, pulse width, repetition rate and duty cycle, and an applications engineer will tell you which standard product is closest and what would have to change.