In this short episode Shahriar takes a detailed look at an Anritsu variable optical attenuator operating in the L- and C-Bands. The mechanical attenuator is defective and provides an opportunity for complete disassembly and examination of the free-space optics, mechanical components and electronics.
The electronics drive a pair of DC motors with potentiometer decoders in feedback along with operational amplifiers and a DAC. This allows the microprocessor to set the exact position of the motors based on calibrated values stored on EPROM. The free-space optics consists of two back-to-back disks with radial metal coatings. Depending on the position of each wheel, the coating limits the transmission of the light through the wheel causing attenuation. The entire housing is hermetically sealed to prevent degradation of the disks.
In this short episode Shahriar takes a close look at an Ist-Rees laser spectrum analyzer. This simple instrument is based on a continuously rotating diffraction mirror to detect various wavelengths. A trigger signal is used to denote the beginning of the scan and the front-panel display shows the current selected wavelength. By aligning the output signal with the trigger signal the wavelength of the input light can be measured.
After the unit teardown, the instrument is used to measure the wavelength of a semiconductor 1310nm laser. The unit is calibrated using this source and is then used to measure the infrared leakage wavelength from a green laser pointer.
In this episode Shahriar investigates a failure of an Agilent 8164A lightwave measurement system. A quick power-on test reveals the main power supply of the unit has failed and has caused catastrophic damage to some of the instrument modules.
After the teardown of the unit the power supply module is examined. Tracing the signal path from the switching transformers shows a pair of damages rectifier diodes. A new component with similar specifications is salvaged from a different power supply. After the installation, the unit can be powered on and detects all the installed modules. Most of the modules are functional, however the main tunable laser module fails alignment. The repair of that component is reserved for another video.
In this episode Shahriar presents the inner workings of an Agilent 86109B optical/electrical DCA-X oscilloscope module. This particular model offers up to 50GHz of electrical bandwidth and an optical input capable of receiving up to 40Gb/s data rates. The differences between a real-time and sub-sampling oscilloscopes are presented with focus on ADC resolution, signal periodicity requirements and input bandwidth. The block diagram of the module as well as a sub-sampling oscilloscope is also presented.
The teardown of the module shows various components such as samplers, O/E conversion block, impulse generator as well as a step-recovery diode driver. I/O interfaces as well as various analog blocks are also shown. Several modules are further disassembled to observe the inner semiconductor designs under the microscope.
In this episode, Shahriar upgrades a Verity visible wavelength monochromator model EP200Mmd to be able to perform automatic scans. The instrument is retrofitted with a stepper motor and a microcontroller which performs wavelength scanning between 225nm to 875nm. The signal from the internal photomultiplier is sampled by the microcontroller and wirelessly sent to the computer. Matlab is used to plot the wavelength response.
The principle operation of a monochromator is thoroughly reviewed starting with the grating mirror behavior. The operation of the photomultiplier is also described. Various mechanical and electronic of the upgraded system is also shown. The presented slides can be found here.
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