HSAAI ACTIVE IMAGER
HSAAI Active Imaging
The above figure shows a complete, solid-state, HSAAI system consisting of two CMOS chips, a laser diode, two lenses, and a power supply.
– One of the CMOS chips is a heterodyne receiver described later.
– The other CMOS chip spectrally filters laser diode light using race-track resonators and radiates that light using an array of Bragg Gratings.
– The receiver and illuminator could be combined on one chip, but that would add development risk and degrade producibility.The laser diode is a continuous wave (CW), low peak power device.
The combination of CMOS photonics and CW diode emitter results in a small, light weight, power efficient, inexpensive, and great performance active imager.
HSAAI provides all weather imaging plus range to objects in the field of view.
– In the above figure, the scene is visible even in heavy fog because the HSAAI gating rejects backscatter from nearby atmosphere.
– The color-coded image is one way to display range-to-pixel.
– Unlike most active imagers, HSAAI images over very long range gates.
– In any weather, range gate covers more than half the maximum range.
Active Imaging Concept
- The above picture illustrates the benefit of long range gates.
- HSAAI uses many illuminator pulses to form a single video frame of imagery, so the illumination versus range can be tailored, and the whole scene is visible.
Also, there is no speckle; this is incoherent imagery. - The following picture shows a few of many potential uses of HSAAI.
– HSAAI is small enough and reliable enough that several can be used for automated driving or obstacle avoidance.
– HSAAI is small enough and fast enough to use for end-game target tracking. - HSAAI has the range performance needed for long range target acquisition.
- HSAAI is small enough and can be cheap enough to sell a rancher’s and farmer’s flashlight to look for stay horses or cattle at night.
- HSAAI ranging is fast enough and accurate enough for ordnance tracking.
HSAAI System Architecture
- A concept for the HSAAI receiver is illustrated in the following picture.
- Local oscillator light is derived from the illuminator light by ring or racetrack resonators and distributed to the light collection sites (LCS).
- Each LCS collects scene light via a coupler and polarization diversifier.
- The scene light is combined with local oscillator light in a waveguide and coupled to a fast, probably Germanium, photo diode.
- The photo diode output is rectified using a MOMS diode and integrated.
HSAAI Heterodyning
HSAAI Heterodyning
HSAAI does not implement traditional heterodyningThe HSAAI concept is simple: A multiplication in time is a convolution is frequency.
– The illuminator signal is translated to the 45 to 60 GHz frequency bandwidth of available Germanium photo detectors.
– The signal is rectified with a MOMS diode and integratedHowever, a 0.1 to 0.3 nanometer illuminator spectral bandwidth at 1.3 microns wavelength results in a heterodyne signal that is basically noise.
– That result is reflected in range performance calculations by summing the square root of photon counts.HSAAI heterodyning is implemented because
– It provides immunity from the effect of even direct sunlight. It provides better range performance than direct detection. It enables long range gates despite ambient illumination and high photo detector dark current.It is true that HSAAI heterodyning will not work for most heterodyne applications, but it does work for HSAAI.