(edfa-optical-setup)=

# Optical setup

## Before connecting

- Use **high-quality APC connectors** everywhere.
  Back-reflections must be as low as possible because the amplifiers work bidirectionally on one fiber.
- Clean all connectors.

## Balancing the two directions

Compensate for any difference in insertion loss between the two directions with **fixed attenuators**, so that the input powers at both sides of the amplifier are equal, ideally within **±1 dB**.

## Choosing input power

The amplifier can deliver +13 dBm (C-band) and +10 dBm (L-band), but we recommend lower levels, especially when coherent data channels share the fiber.

Working near the optimal-gain point, ignoring external filter loss:

- Prepare an input level of about **−22 to −23 dBm** at the amplifier.
- Expected gain is about **23 dB (C-band)** and **22 dB (L-band)**, giving about **0 to +1 dBm** at the output.

> **Worked example (illustrative).**
> The incoming signal at the WEST port is −12 dBm.
> To reach −22.5 dBm, insert a **10.5 dB** attenuator (use 10 dB plus 0.5 dB or the nearest available value).
> With 23 dB gain, the output at the EAST port is about +0.5 dBm.
> Verify the same on the reverse direction.