A booster optical amplifier sits directly after the transmitter or multiplexer, at the launch point of the fibre span. Its defining requirement is saturated output power — it must put the signal into the fibre at the level the link budget demands. Noise figure is a secondary concern here because the input signal is strong, which naturally suppresses ASE. An in-line amplifier sits mid-span to compensate for accumulated fibre loss; it requires a balanced design where both gain and noise figure matter. A pre-amplifier sits at the receiver end, ahead of the detector. There, the signal has traversed the full link and is weak — ASE competes directly with it, so noise figure is the primary design parameter. The three roles are optimised for power, balance, and sensitivity respectively. Choosing the wrong amplifier type for a given position degrades system performance at the architectural level.

WSL builds custom booster EDFAs from low-power units (e.g. 5 W) through to 200 W or more average power — the highest average powers commercially available. Output is fully tunable from 0 to 100% of rated power, so the amplifier adapts precisely to your link budget rather than forcing the system to work around a fixed catalogue level. For pulsed applications, pulse energies above 10 mJ and peak powers above 100 kW are achievable, configured per project. Most catalogue EDFAs deliver less than 50 W average power, and it is rare to see one above that ceiling. WSL's custom platform removes it entirely — every unit is built to the client's requirement.

The physics is straightforward: amplified spontaneous emission (ASE) is the dominant noise mechanism in an EDFA, and ASE is strongly suppressed when the input signal power is high. At the transmitter end, the booster sees a strong input signal — so ASE is held down naturally, and the noise figure measured at that operating point carries little practical weight. At the receiver end, the pre-amplifier sees a signal that has traversed the full link and suffered fibre attenuation. The input power is low, ASE grows rapidly relative to the signal, and noise figure becomes the critical design axis for preserving OSNR. This does not mean noise figure is irrelevant for a booster — it still contributes to the system OSNR budget across the full link. But it is not the primary design constraint. Saturated output power is, which is why booster EDFAs are optimised around it.

WSL's custom EDFA operates across the full erbium gain window: 1530–1625 nm, covering the C-band (1530–1565 nm) and L-band (1565–1625 nm). The operating band is specified per project — C-band only, L-band only, or dual C+L from a single unit through one cable. For dual-band booster deployments, that single-source delivery eliminates the need for a second amplifier at the transmitter end. One source, one cable, both bands — which simplifies integration and reduces the component count at the transmitter stage.

WSL's custom booster EDFA is air-cooled as standard — no chiller, no coolant loop, no ancillary fluid-handling infrastructure required. For most booster deployments, this is the correct engineering answer: it simplifies transmitter-end integration considerably. Where output power levels or installation environment make air cooling insufficient, water cooling is available as a configured option. The cooling architecture is a system-level decision made at design time. Retrofitting a different cooling approach after the unit is built is costly and often impractical, so the choice should be locked in when the output power and environmental constraints are defined. The flexible model — air as standard, water when needed — means the platform is suited to the full range of booster output requirements without forcing a one-size approach.

Only the erbium physics and the platform are fixed. Everything else is configured per project: operating band (C-band, L-band, or dual C+L); output power (average, peak, and pulse energy, specified to the application); pulse regime (CW, short-pulse such as 100–500 ns, or a custom format); cooling (air or water); delivery cable length and termination; form factor and integration envelope; and control firmware and communication standards. The published specifications represent what WSL has built to date, not the limit of what it builds. Requirements that go beyond them — a different power level, form factor, or environment — are assessed directly with WSL's engineers. Nothing is ruled out in advance. This depth of per-project tailoring is what distinguishes a custom-built EDFA from a catalogue unit selected from a fixed range.

An EDFA amplifies light by passing the signal through an erbium-doped fibre that has been excited by a pump laser, typically at 980 nm. The pump raises erbium ions to a higher energy state. When signal photons in the 1530–1625 nm window travel through the fibre, they trigger stimulated emission — the excited ions release energy as additional photons at the same wavelength, phase, and direction as the signal. The result is all-optical amplification with no optical-to-electrical-to-optical (O-E-O) conversion. In a MOPA (master oscillator power amplifier) architecture — the architecture used in WSL's custom EDFA — a low-power seed oscillator establishes the signal's properties with precision, and successive amplifier stages boost it to the required output level. This staged approach preserves spectral and temporal fidelity while scaling power to the levels a booster application demands.

The 1530–1625 nm operating window is eye-safer than legacy 1064 nm sources, but not unconditionally safe at all power levels. The mechanism is water absorption: the cornea and lens absorb radiation above approximately 1400 nm before it reaches the retina, which is the structure most sensitive to laser damage. This gives the 15xx nm band a significantly higher eye-damage threshold than 1064 nm, where light transmits through to the retina. As rp-photonics.com notes, erbium fibre systems at 1.5 µm are far less dangerous than 1 µm lasers at similar output powers — though at sufficiently high power, corneal damage remains possible. WSL's custom EDFA operates in this eye-safer wavelength range, and reduced-hazard-zone builds are available for applications where a smaller safety perimeter is a system requirement.

WSL's custom EDFA is CE certified and UKCA certified. CE marking confirms that the product meets the safety, health, and environmental protection requirements of the European Economic Area — allowing it to be placed on the EEA market without restriction. UKCA (UK Conformity Assessed) marking is the equivalent conformity mark for the Great Britain market. Holding both certifications means the amplifier is market-ready for deployment across the UK and Europe without additional conformity steps for the buyer.

The starting point is submitting your requirements for a specialist evaluation — not selecting from a catalogue. WSL's engineers assess each requirement directly with the client. To make that first conversation productive, bring the parameters that define your application: required output power (average, and peak power or pulse energy if pulsed); operating band (C-band, L-band, or dual C+L); pulse regime (CW, pulsed, or custom); cooling preference and installation environment; form factor and integration envelope; and control interface and firmware requirements. Requirements that go beyond the published specification are assessed directly — nothing is ruled out before that conversation. Submit your requirements for a specialist evaluation to begin.