Electronic Variable Optical Attenuators
Chapter 4: Operating Instructions & Details
Rev B, September 5, 2017
Page 7
Chapter 4 Operating Instructions & Details
4.1. Overview
This chapter provides deeper details about the EVOA and its operation. To
get started with using the EVOA, refer instead to the Quick Start Guide
(Section 3.4).
The block diagram below (Figure 4) depicts the unit’s basic architecture. The
EVOA is controlled by analog electronics. The front panel provides a power
adjustment knob, a digital output power display, and Power Lock capability.
Figure 4
Basic Architecture of EVOA
Starting from the left of Figure 4: The light in the input fiber is coupled directly
into a MEMS-based variable optical attenuator (VOA), and the attenuated light
is sampled by a low-percentage tap. The tap output is sent into a photodiode
whose signal is used by the digital output power display, the Power Lock
control loop, and the SMA monitor output. The attenuation value can be
controlled by the manual power adjustment knob, the Power Lock control loop,
or the SMA modulation input.
When the power is switched off, the EVOA defaults to a mid-range attenuation
whose value is independent of the knob position.
4.2. Powering & Charging the Unit
The EVOA is powered by an internal rechargeable Li-ion battery which
provides approximately 300 hours of continuous operation on a full charge.
The battery’s internal circuits prevent full discharge after the Low Battery
indicator appears on the display. To charge the unit, use either the 2.1 mm
coaxial power cord that is included with the EVOA, or use a USB mini-B cable
and charger (not included). If the device continues to be used while the Low
Battery indicator is active, it will eventually be shut down by the battery’s safety
circuits.
The 2.1 mm coaxial power cord will provide 1 A of charging current and hence
the fastest charging time. In contrast, the charging current provided by a USB
cable is up to 500 mA, as determined by the power source. For example, some
Monitor
Output
Output
Fiber
Modulation
Input
Input
Fiber
Manual
Control
Digital
Display
Photodiode
Power Lock
Control Loop
Tap
VOA
