O-Band Optics: FiberLabs' Next-Generation PDFA and BDFA WDM Signal Amplification

O-band transmission is a foundational technology for high-speed optical communications and data center interconnects. In this post we're looking at FiberLabs' latest flagship amplifiers - the Praseodymium-Doped Fiber Amplifier (PDFA) and Bismuth-Doped Fiber Amplifier (BDFA) - that bring new capacity in O-band WDM signal amplification.

The Rising Importance of O-Band

The wider industry is seeing unprecedented demands for energy-efficient data center interconnects. O-band (1260-1360nm) transmission has become increasingly attractive for these applications due to a fundamental optical property: standard single-mode fiber exhibits zero dispersion in this wavelength region. This characteristic eliminates the need for power-hungry dispersion compensation techniques, making O-band the preferred wavelength range for:

• High-speed Ethernet applications
• Co-packaged optics
• Optical interfaces for AI acceleration
• High-performance computing (HPC) interconnects
• Disaggregated computing architectures

Most of these applications leverage Wavelength Division Multiplexing (WDM) technology in the O-band, with several industry-standard grids established, including CWDM4, LAN-WDM4, LAN-WDM8, and CW-WDM (spanning 18-nm and 36-nm).

Optical Amplification

Until recently, limits to the efficiency of optical amplifiers for the O-band has been a significant bottleneck. While the C-band (1530-1565nm) has benefited from mature Erbium-Doped Fiber Amplifier (EDFA) technology for decades, O-band applications have struggled with limited amplification options.

FiberLabs is tackling these limits with two new fibre amplifiers, one high power PDFA model and one wide wavelength BDFA model.

Praseodymium-Doped Fibre Amplifier (PDFA): Power and Precision

FiberLabs' latest PDFA model (AMP-FL8612-OB-27) represents a significant engineering achievement, delivering:

• Remarkable output power exceeding 27 dBm from a 0 dBm input signal
• Superior performance in the 1285-1325nm wavelength range
• Industry-leading output power specifications surpassing any commercially available O-band fibre amplifier
• Exceptional suitability for LR4 and CW-WDM applications

The PDFA leverages the unique optical properties of praseodymium-doped fluoride glass fibres, carefully engineered to provide optimal gain characteristics in the target wavelength bands. The rare-earth doping profile has been meticulously optimised through years of research to achieve the remarkable output specifications.

Bismuth-Doped Fiber Amplifier (BDFA): Bandwidth and Versatility

The BDFA (AMP-FL8621-OB-19) represents an entirely different approach to O-band amplification, with distinct advantages:

• Broader wavelength bandwidth coverage (1260-1340nm)
• Output power of 19 dBm with a 0 dBm input signal
• Superior gain flatness across multiple channels
• Backward-pumped architecture with 1150nm Yb-fibre laser
• Innovative 99% Fibre Bragg Grating (FBG) design for enhanced gain and reduced noise figure

The BDFA technology stands out for its uniform gain profile across the 1260-1340nm wavelength region, making it particularly well-suited for simultaneous amplification of CWDM4 signals (1271/1291/1311/1331 nm) employed in 400GBASE-LR4 applications, LAN-WDM8(LR8).

BDFA Architecture

The experimental BDFA setup developed by FiberLabs showcases several innovative design elements:

• A 190-meter-long Bismuth-Doped Fibre (BDF) spooled onto a 100mm diameter jig
• Backward pumping configuration using a 1150nm Yb-fibre laser at 2W power
• 99% reflectivity Fibre Bragg Grating (FBG) to recycle residual pump light
• Integrated input and output isolators to prevent parasitic lasing
• Compact design accommodated within a standard 2U rack mount case

In practical tests with CWDM4 signals, the BDFA simultaneously amplified all four channels with more than 10dB gain and less than 3dB gain deviation, demonstrating its excellent suitability for wideband applications.

Head-to-Head Comparison and Application-Specific Performance

FiberLabs conducted extensive comparative testing of both amplifier technologies using two WDM signal patterns:

1. LR8 (0 dBm/ch)
2. CW-WDM (36-nm span, 8+1 channels, 0 dBm/ch)

The results revealed distinct performance characteristics that guide application-specific selection:

BDFA Advantages:

• Higher gain for short wavelength signals within LR8
• Exceptional uniformity across wideband applications
• Ideal for LR8 and CWDM4 transmission scenarios
• Broader overall wavelength coverage
• Less than 3dB gain deviation across channels

PDFA Advantages:

• Superior output power in the 1285-1325nm range
• Exceptional performance with LR4 and CW-WDM signals
• Higher maximum output power ceiling (27dBm vs 19dBm)
• More mature technology with established reliability metrics
• Greater power efficiency in targeted wavelength ranges

Beyond WDM: Expanding Application Horizons

While the primary focus of these amplifiers is WDM signal amplification, their capabilities extend to numerous other applications requiring O-band optical amplification:

• Single-channel transceiver testing and qualification
• Multiphoton microscopy (MPM) for biomedical imaging
• Optical coherence tomography (OCT) for medical diagnostics
• Precision laser processing for manufacturing
• Quantum communication systems
• High-resolution spectroscopy

Technological Significance and Future Outlook

The development of efficient O-band amplifiers represents a pivotal advancement in optical communications technology. As O-band WDM transmissions continue to proliferate in data centers and high-performance computing environments, these amplifiers will play an increasingly critical role in extending reach, improving signal quality, and reducing overall power consumption.

FiberLabs' dual-technology approach with both PDFA and BDFA provides system designers with unprecedented flexibility to optimise their optical networks based on specific wavelength requirements, gain profiles, and power budgets.

Engineering Challenges and Innovation

Creating efficient O-band amplifiers presents several significant engineering challenges:

1. Rare-earth doping profiles: Achieving optimal dopant concentration and distribution in the fibre core requires precise control over the glass manufacturing process.
2. Thermal management: High-power operation necessitates efficient heat dissipation to maintain stability and prevent degradation.
3. Pump laser coupling: Maximising pump power coupling efficiency while minimising insertion losses demands precise optical alignment.
4. Gain flatness: Ensuring uniform amplification across multiple channels requires sophisticated gain flattening techniques.
5. Noise figure optimisation: Minimising amplified spontaneous emission (ASE) noise while maintaining high gain is a delicate balance.

FiberLabs has overcome these challenges through innovative design approaches, proprietary manufacturing techniques, and rigorous testing protocols.

Where to next?

FiberLabs' new flagship PDFA and BDFA models create new opportunities O-band optical amplification. The complementary strengths of these two technologies provide system designers with powerful new tools to address the growing demands of high-speed data transmission.

With the appropriate selection between PDFA and BDFA based on specific WDM grid requirements, optical system engineers can now implement efficient amplification solutions across the entire O-band spectrum, enabling the next generation of high-speed, energy-efficient optical networks.

For detailed technical specifications and to inquire about demonstration hardware, preliminary datasheets for both amplifier models, contact AusOptic for more information.