Sunday, July 12, 2020

Toshiba Announces 200m-range Flash LiDAR Prototype

Toshiba announces a high-resolution, long-range technology for flash LiDAR, probably the next version of one presented at ISSCC 2020. At its heart is Toshiba’s compact, high-efficiency silicon photo-multiplier (SiPM).

In general, SiPM are suitable for long-range measurement as they are highly light sensitive. However, the light-receiving cells composed on SiPM require recovery time after being triggered, and in strong ambient light condition they also need a large number of cells, since they must have reserve cells to react to reflected laser light.

Toshiba’s SiPM applies a transistor circuit that reboots the cells to reduce the recovery time. The cells function more efficiently and fewer are needed, securing a smaller SiPM, as shown in Figure 1. This realizes a higher-resolution SiPM array while maintaining high sensitivity, as shown in Figures 2 and 3.


Field trials with a LiDAR prototype, shown in Figure 4, using commercially available lenses, from wide-angle to telephoto lenses, have demonstrated the system’s effectiveness over a maximum distance of 200m (Figure 5).


5 comments:

  1. In Fig. 4, do they have galvo scanning mirrors on the side that's labeled "Projector"?

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    1. Their PR says:

      "Current LiDAR systems require mechanical components to continuously rotate the laser emitters and their accompanying optical detection devices. Utilizing solid-state LiDAR instead secures numerous operational advantages—and Toshiba’s ground-breaking SiPM innovations are making this possible.

      By removing the need for bulky mechanical components, the technology realizes cost and space savings and enhances operational reliability."

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    2. doesn't seem like a compact solution

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  2. Is this SiPM a SPAD (technology wise) as indicated in Figure 3?

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    1. A SiPM is a silicon photomultiplier, which is simply a SPAD array technology, where groups of SPADs are aggregated together to form a grey scale pixel.

      A SPAD (single photon avalanche diode) is a binary device with 1 bit of dynamic range (photon(s) detected yes/no). If you aggregate a 2x2 array of SPADs together, you get 2.3 bits of dynamic range (0, 1, 2, 3, or 4 photons detected). Similarly a 4x4 array of SPADs gives you about 4 bits of dynamic range.

      The trick with a SiPM is to use analog summation of the outputs of all SPADs in the aggregated array to form a single output, where the pulse height is proportional to the number of detected photons. In general, SiPMs do not digitize the signal at the individual SPAD level.

      To make things more confusing, there is a so-called digital SiPM (dSiPM) that does digitize the signal at the individual SPAD element. Depending on connection this could be simply viewed as a SPAD array or a SPAD array with CCD like binning. Since Toshiba is claiming to incorporate an active recharge circuit, they may very well be using a digital SiPM, since active recharge circuits generally require digitization of the SPAD output.

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