Teardown and Operation of an Advantest TQ8325 Wavelength Meter

In this episode Shahriar presents the teardown of an Advantest TQ8325 Wavelength Meter. The principle operation of the instrument is explained along with a close up of the free space optics in operation. To verify the functionality of the unit, an infrared laser module is used as a CW coherent source. The impact of the laser diode’s temperature variation on the output wavelength is measured using the wavelength meter.

I’d like to Acknowledge Dr. Jeffery Lee for his consult and expertise on free space optics and fiber optic measurement systems.



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  26. Raymund says:

    Just as Boris said, it would be very interesting to probe the signals coming out of the photodetectors inside the instrument during measurement.

    If my understanding is correct i would guess this be a modulated frequency in the 10KHz range for a single wavelength input.
    This should depend on the input spectrum and the modulation mirror driven by the excenter on the motor.
    By the way, this motor looks like a out of a 3.5″ floppy drive.
    Maybe this was the best they found to achieve the most constant and jitter-free rotation.

    And how and when is the internal Laser used for calibrating?

    Isn’t your laser source a SLED?
    This isn’t a narrow spectrum but a wider spectrum laser source and that would make probing of the internal detector even more interesting.
    Compare it with a narrow spectrum laserpointer or similar.

  27. Boris says:

    Thank you for the very interesting post.
    This device in fact is an example of the Fourier spectrometer for single wavelength measurement. This is just because data processing algorithm in use is looking for the dominant frequency, finds it and recalculates to wavelength. If the broad spectrum source is connected, output signal from the detector would look as superposition of all the frequences present (assuming constant velocity of the mirror, but this is not a point). Fourier transformation of this signal will give the full optical spectrum.
    Funny thing to try is to convert this device to the spectrometer. All what is needed is 3 signals running from the unit to the external PC. They are a) digital signal that indicates mirror moving direction, b) “pulses” from He-Ne laser channel to have instantaneous position of the mirror (are they using separate detector for this?) and c) signal from the main detector.
    All the rest is a good math (AD-conversion, interpolation of readings to be uniformely spaced according to mirror displacement, apodization (I like Hamming window), FT, averaging from multiple scans, graphics).

  28. RicoElectrico says:

    Didn’t you notice that the laser and its HV supply read 1994, not 1985? Also, the digital part has (c) 1989 on it.

  29. enclis says:

    I’m very happy with this teardown, because there is almost no of such a video material.

  30. Yi Yao says:

    It looks like they were expecting lots of rework. The PLL board even has a dedicated section with 100mil holes in a grid like a perf board.

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