Scanning laser microscopy made by CD-ROM OPU

CD-ROM Optical Pickup Unit (OPU) used for homemade scanning laser microscope

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Focus-error signal of an old OPU of a CD-Rom drive used to measure surface roughness. A homemade stepper motor based linear X-Y stage is also created for the base. The signal processing is done with an arduino connected to a PC, running MATLAB to control and visualize measurement results.

Since my university studies I'm amazed at atomic force microscopy (or AFM), how such a well created machine is able to measure in atomic level. As AFM doesn't requires vacuum for the operation, creating one at home would be a great project, I thought.

This project is created to find a way to measure height changes precisely at home, and if I already creating something why not use it as a scanning laser microscope?

The AFM using laser to measure the deflection of the cantilever caused by the measured surface. Creating a similar laser sensor is not impossible, but why design it, when you can hack an already existing device.

Optical disc drives such as the CD-ROM drives use laser light to read or write data from an optical disc. One of the main component is the Optical Pickup Unit (or else OPU), including the laser diode(s) and a photodiode array, which detects the reflected laser beam.

Because of uneven surface of the disc, the laser beam has to be controlled, focused to the information layer, and aim at the track to avoid any data loses. Therefore a control-loop is introduced in the OPU to move the lens to the correct position.

The exact type of OPU what I used for this project is unknown for me but the construction is very familiar to the following SONY OPU.

This organization is called a tree-beam configuration, where photodiodes from A to D is used to create Focus Error (FE) and Center Error (CE),  E and F to create Tracking Error (TE) signals for the control circuit.

These error signals will be used in my project to use the OPU to measure surface roughness of an object.

My final long-term goal is the creation of an AFM, but until than this machine is also can be useful for others. For instance measuring precise machining of surfaces, layers after depositions, and so on.


datasheet of the RF signal processor of the CD-ROM, what I used

application/pdf - 258.36 kB - 04/17/2018 at 13:13


  • 3 × HSI 21F4AB hybrid linear stepper motor
  • 1 × Military prisma assembly XY linear stage
  • 1 × CD-ROM OPU with control circuit

  • Choosing the right OPU

    Roland Varga04/17/2018 at 12:51 0 comments

    When I originally started to working on this project, I sacrificed a lot of CD and DVD drives to find the right OPU. For the better resolution a blue-ray drive would be ideal, but as most modern gears, these are not very well documented. On the other hand old CD-ROM driving ICs have a very detailed datasheets with the pin outs, but as the wavelength is in the 780 nm range, the resolution wont be as good as the blue-ray, or even a DVD-ROM.

    As I started this project only as a proof-of-concept, I decided to use a CD-ROM which build around the SONY CXD3045R digital signal processor and the SONY CXA2581N RF signal processor. I removed all unnecessary hardware components, ( i.e.: all DC motors and rails, and the disc rotatory elements), and I am only using the main board, including the DSP, RF signal processor connected to the OPU itself.

    From the datasheet of the RF processor I was able to identify the necessary signals, and solder some wires to the test points. The digital signal processor will be bypassed, and the error signals from the OPU can be used.

    (Also I found out that the SW pin is responsible for switching the RW and ROM functions, and with this changing the laser output. I will try out is there any differences between the 2 mode )

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makspar wrote 09/05/2018 at 10:25 point

Hello, friend. How is your project going? I study the principle of focusing the laser pick-up.  I have the same CD-ROM. Do you have some information about of this CD-ROM? I found dataseets for ic: CXD3045R, CXA2581N and  M63026FP. You have a scheme this PCB? I disassembled MITSUMI CRMC-FXN01DE with KSS-331A pick-up and obtained some data. I can share them if you want.

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Robert Mateja wrote 04/17/2018 at 16:13 point

That's nice looking linear stage! I have one also ready but with much lower magnification for soldering and inspection optical microscope.Best wishes as this project is very cool.

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Roland Varga wrote 04/18/2018 at 09:28 point

Thank you. It was made from a prism assembly of a military infrared night vision device (according to the ebay description). I found it when I was looking for an affordable linear stage for this project. You can still find some in ebay with "prismen-baugruppe with Ball-Bearing Linear Stage XY Slides Prism" keywords. The theme of the next project log will be the linear stage assembly soon.

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