Thesis

Thesis in action

So I thought I’d take the opportunity to talk a bit about my honours thesis. The contents of my thesis were used for ongoing research so details will remain scarce but the pictures are plentiful. Sufficed to say there were LASERS! Pew! Pew! well almost.

My thesis explored the use of lasers specifically Vertical Cavity Surface Emitting Lasers which could be setup in line arrays or grids for something known as self-mixing. In this process light bounces off a target and is reflected back into the laser cavity causing incredibly small disruptions to the power and efficiency of the lasing cavity. This can be measured by comparing voltage and current going in and a long story short… range finding, fluid flow, medical applications, surface identification and all that other good stuff.

The goal was to miniaturise and modularise an existing design. It should be able to have the laser angle pre-calibrated and be moved easily around the optical bench. Rather than adjusting current carefully via a potentiometer it should be done via a computer terminal which interfaces with NI Labview. The system should have a main bus and should allow daughterboards to be swapped out for different purposes such as changing modulation scheme, changing amplifiers etc.

That’s about all I can say so lets get some pictures

Pictures

Opto Electrical Design

The motherboard was designed to mount directly to an optical breadboard cage mount. The lasers sit on a daughterboard and fire down the centre of the cage. 3 point adjustment screws control the laser alignment.

Motherboard

The motherboard contains powersupplies and primary signal amplifiers. It forms the centre of the bus system and is screwed to a cage plate. All boards in this project are 4 layered with ground and powerplanes in the centre.

Controller board

The daughter board contains an ATEMGA128 microcontroller, serial comms, voltage sensing circuits, current amplifiers, precision voltage references, external modulation circuits and is all controlled via a fancy PWM scheme. Oh and grounded pads are provided to allow shields to be mounted.

Amplifier board

And this tiny board is the back end amplifier. Very configurable.

First light (4 VCSELs)

First light shows 4 VCSELs currently on. The laser daughter board has a configurable pin layout. This daughterboard takes DIP packages. The VCSEL is in the near IR range but the cameras can pick it up quite well.

Laser Test

These cards have a phosphor which is excited by IR light and glows. This allows us to focus the beams and check where the invisible (to the naked eye) lasers are pointing.

Closeup of VCSEL

A closeup view of a VCSEL with 4 lasers enabled. A VCSEL is a vertical cavity and can be ordered in many configurations on a silicon wafer. Here’s a set of 8 cutout and installed onto a DIP package. Bit messy but not bad for a DIY job.

Setup on optical bench

The setup shown with laser, focuser (VCSELs have a 30deg beam divergence) and a wobbulator as a target for the laser. The resulting output can be seen on the oscilloscope at the top of this page.

Outcome

This thesis was awarded a high distinction and won the ITEE school’s best technical demonstration award. The prize was a Tektronix TDS1024 oscilloscope, a prize which I use quite a lot to this day.