Digital Micromirror Device Ladar for High Resolution Imaging
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Solution Overview
Problem
Imaging laser radar (LADAR) focal plane sensors are limited by pixel size and format due to the large amount of circuitry required beneath each pixel, and are restricted to either first pulse or last pulse logic, which hinders the development of high spatial resolution and full temporal bandwidth capabilities, especially for obscured target and foliage penetration applications.
Innovation Solution
A single-pixel camera paradigm utilizing a digital micromirror device (DMD) with an array of mirrors that can be selectively oriented to reflect or not reflect incident light, applying multiple spatial patterns synchronized with laser pulses to reconstruct images of objects at different ranges, allowing for high spatial resolution and full temporal bandwidth imaging without the need for scanning components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional focal plane sensor arrays are used, then imaging capability is provided, but pixel size and format are limited due to large circuitry requirements beneath each pixel
Solution Approach 1:
The patent extracts the spatial encoding function from the focal plane sensor array and relocates it to a digital micromirror device (DMD) positioned in front of a single-pixel detector. This separation allows the detector to be simple while the DMD handles the complex spatial modulation, effectively removing the circuitry burden from each pixel location.
Solution Approach 2:
The DMD acts as an intermediary between the scene and the single-pixel detector. It modulates the reflected light according to programmed spatial patterns before it reaches the detector, enabling a single pixel to capture spatial information that would otherwise require a large sensor array.
2Productivity
If linear mode arrays are used, then detection is provided, but temporal bandwidth is limited to first pulse or last pulse logic
Solution Approach 1:
The system uses periodic pulsed illumination from the laser combined with periodic switching of the DMD mirrors between on and off states. This periodic modulation enables the single-pixel detector to capture temporal information at each pulse, allowing full temporal bandwidth utilization without being restricted to first or last pulse logic.
Solution Approach 2:
The DMD mirrors are pre-programmed with specific on/off patterns before each laser pulse arrives. This preliminary configuration allows the system to encode spatial information in advance, enabling the detector to capture both spatial and temporal data simultaneously during the pulse return window.
3Measurement precision
If Geiger mode arrays are used, then detection statistics can be developed, but many pulses are required
Solution Approach 1:
The patent replaces the Geiger mode photodetector array with a linear mode single-pixel detector combined with computational processing. The DMD's rapid mirror switching and the system's ability to apply multiple spatial patterns compensate for the lower sensitivity of linear mode detection, achieving comparable measurement precision without requiring many repeated pulses.
4Area of stationary object
If single-pixel camera paradigm is used, then high spatial resolution and large format imaging is enabled, but complex spatial pattern application and reconstruction is required
Solution Approach 1:
The DMD mirrors are dynamically switched between on and off states according to programmed spatial patterns at high speeds. This dynamic control allows the system to rapidly apply multiple different spatial encoding patterns, enabling a single pixel to capture information that would otherwise require a large static sensor array.
Solution Approach 2:
The system changes the spatial encoding parameters by applying different DMD mirror patterns for each measurement cycle. By varying the spatial pattern parameters (which mirrors are on or off), the single-pixel detector captures different projections of the scene, which are then computationally reconstructed into high-resolution images.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables high-definition, full temporal bandwidth LADAR with high spatial resolution and the ability to reconstruct images at motion video rates, overcoming the limitations of traditional LADAR systems by using a small format detector array and compressive sampling techniques to achieve efficient image formation.
Implementation Method 1
a digital micro-mirror device oriented to receive laser light reflected from the at least one object and including an array of mirrors each of which may be selectively controlled to be oriented in one of a first direction and a second direction; a detector positioned so that mirrors within the digital micro-mirror device oriented in the first direction reflect incident light onto the detector
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Laser light pulsed to illuminate and reflect from at least one object is received at a digital micro-mirror device including an array of mirrors each of which may be selectively controlled to be oriented to either reflect incident light onto a detector or not. The detector outputs a signal representative of an amount of light sensed. By applying M spatial patterns to the mirrors, each in synchronization with one pulse from the laser, and storing sampled signal values from the detector output at each of K times following a pulse from the laser, the collected information may be used to reconstruct K images each using all M spatial patterns and stored sampled signal values corresponding to a respective one of the K times. Each of the K images corresponds to a different range to the digital micro-mirror device, such that the system may be employed as a range finder.