Viewing posts from September, 2017

Shot-Noise Limited Sub-Nanoamp Photoreceiver for Spectroscopy

This is a smaller job for a sensor manufacturer, interesting mostly for the size, weight, and power (SWaP) requirements. It has to be shot noise limited above 500 pA with a 1600 pF photodiode. (This is possible only because the bandwidth is relatively small.)

Doubling the Resolution of Solid Immersion Microscopes: Update

This is a very exciting development, in cooperation with a semiconductor equipment manufacturer. Back in 1989, my colleagues and I started working on a contact-lens microscope for looking into the interior of silicon chips through the back surface. In 1992 I took a picture (shown above) at a numerical aperture of 2.5, with resolution equivalent to NA 3.5 due to a confocal design.

The combination of this with my thesis work on doubling conventional microscope resolution via heterodyne interferometry and digital filtering was going to allow us to take images at an equivalent numerical aperture of 6.4. I never got to build the full scale system.

Now, over 20 years later, I finally get to do it for real. I'm designing and prototyping a microscope to work at NA 6.4, which will have resolution on the order of 15 nm (10%-90% rise). That's pretty cool stuff for a visible-light microscope, and if it works, it should give me bragging rights for a long, long time.

Cascode Enhancement pHEMT Photodiode Preamp

This is pretty small, because it has to be--those are microwave transistors, and will oscillate at the slightest provocation. The axial resistors and TO-92 parts are all for biasing---the actual amplifier is the part between the output coupling cap (the small orange thing in the middle) and the photodiode, which is the white square with the black middle at the right.

Transistor Tester for laser noise canceller

As discussed in medium-gory detail in this paper, laser noise cancellers can let you do shot-noise limited measurements at baseband with lasers that are as much as 70 dB noisier than that.