THORLABS EVOA1550F User Manual page 14

Electronic Variable Optical Attenuators
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Item # EVOA1550F has FC/PC connectors.
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Item # EVOA1550A has FC/APC connectors.
The fiber patch cable and connectors should be cleaned whenever a connection is made. We recommend the
FCC-7020 Fiber Connector Cleaner and the FBC250 Bulkhead Cleaner for fiber tips and bulkheads, respectively.
See Chapter 5, for guidance.
4.4 Wavelength Selection & Calibration
The digital output power display gives the calibrated output power at the wavelength indicated by the selector
knob. The first and second knob positions are for 1310 nm and 1550 nm, while the third position (labeled "USER")
can be calibrated by the user for any wavelength in the 1250 to 1625 nm operating range. The user calibration
trimpot is located on the side utility panel.
To calibrate the USER position on the knob, the following tools are required:
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A single mode laser source at the desired wavelength,
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An accurate power meter for that wavelength,
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Input and output fiber patch cables, and
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A small flathead screwdriver to adjust the trimpot.
Follow these simple steps to calibrate the USER position:
1. Switch the wavelength selector knob to the USER position.
2. Send an optical input into the input bulkhead at the wavelength of interest. We recommend an input
power of a few mW for the best accuracy.
3. Rotate the manual power adjustment knob completely clockwise to set it at minimum attenuation.
4. Attach the power meter to the output fiber patch cable. (Make sure the power meter is set to the correct
wavelength.)
5. Adjust the user calibration trimpot so that the power value on the digital display agrees with the value
shown on the power meter.
6. At this point, we recommend making a note of the user wavelength and placing a piece of tape over the
trimpot to prevent accidental adjustments.
4.5 Attenuation Control
The user can control the attenuation using two analog methods.
The first and simplest method is to rotate the manual power adjustment knob on the front panel (see Figure 2).
This knob provides the full range of attenuation. Rotating it clockwise increases the output power, while rotating
it counterclockwise decreases the output power. The knob has ten full rotations.
The second method is to apply a voltage to the SMA modulation input on the side utility panel (see Figure 4). This
input allows for modulation from DC to 1 kHz. See Section 4.7, Modulation Input & Monitor Output Connections,
for details.
4.6 Digital Output Power Display
The digital output power display uses the signal from the tap output (see Section 4.1) to calculate the calibrated
output power before the tap, in mW, at 1310 nm, 1550 nm, or the user wavelength. The display offers 4.5 digits
Rev. C, December 31, 2024
Chapter 4: Operating Instructions and Details
Page 11