Agilent/Keysight 81551MM Multimode Optical Head

The Agilent/Keysight 81551MM is a Fabry-Perot laser source module engineered for the Agilent 8153A Lightwave Multimeter. This multimode optical head delivers 850 nm ± 10 nm light into 50/125 µm fiber with output power exceeding -2 dBm and spectral bandwidth below 1.5 nm RMS. It has exceptional CW stability: ±0.01 dB short-term (15 minutes, constant temperature) and ±0.06 dB long-term (6 hours, constant temperature).

Technical Specifications

• Central Wavelength: 850 nm ± 10 nm


• Fiber Configuration: Multimode (MM) 50/125 µm


• Spectral Bandwidth: -2 dBm (at 0 dB attenuation)


• Output Attenuation: 0 dB to 4 dB in 0.1 dB steps


• CW Stability (Short-term): ±0.01 dB typical (15 minutes, constant temperature)


• CW Stability (Long-term): ±0.06 dB typical (6 hours, constant temperature)


• Warm-up Time: Long-term stability achieved within one minute of laser enable


• Modulation Modes: Internal digital modulation at 270 Hz, 1 kHz, or 2 kHz (selectable)


• Output Signal Format: Pulse-shaped with 50% duty cycle


• Fiber Cable: 2 m with Diamond HMS-10 connectors

Key Features

• Narrow spectral bandwidth enables precise multimode fiber characterization


• Selectable digital modulation for dynamic signal testing


• Fine-grained attenuation control in 0.1 dB increments


• Rapid warm-up to full CW stability specifications


• Pulse-shaped output suitable for timing and modulation analysis

Compatibility & Integration Designed exclusively for integration with the Agilent 8153A Lightwave Multimeter as part of the Keysight Lightwave Solution Platform. Product status is obsolete; calibration and repair support may remain available through Keysight.