Breakthrough in Mid-Infrared Pulsed Fiber Lasers: Hangzhou Team Achieves >70% Efficiency with Hollow-Core Photonic Crystal Fiber

Hangzhou, China – Exciting progress has been made in laser optics research. A collaborative team from the Russell Advanced Optical Wave Science Center at the Hangzhou Institute of Optics, along with partners including the Hangzhou Institute for Advanced Study (UCAS), the Shanghai Institute of Optics and Fine Mechanics (CAS), and Affiber (Ningbo) Photonics Technology Co., Ltd., has achieved a major breakthrough in mid-infrared (MIR) pulsed laser transmission. Their findings were published in the prestigious optics journal Optica.

Key Innovation: High-Fidelity, Flexible Transmission of MIR Pulses

For the first time, the team successfully demonstrated near-watt-level, sub-100-femtosecond, 2.8 μm mid-infrared pulse transmission in a hollow-core photonic crystal fiber (HC-PCF) with high efficiency (>70%), exceptional fidelity, and high single-mode purity. This advancement opens new possibilities for mid-infrared laser applications, potentially driving further breakthroughs in optical technology.

Research Background: The Challenge of MIR Laser Transmission

High-power, ultrafast, broadband MIR lasers are crucial for:

• Advanced spectroscopy (precise material analysis)
• High-precision material processing (micromachining, cutting)
• Medical surgery (minimally invasive procedures)
• Remote sensing (environmental monitoring)

However, traditional transmission methods face critical limitations:

1. Free-space optics: Atmospheric absorption by gas molecules distorts beam quality, reducing stability and accuracy.
2. Solid-core MIR fibers: Strong nonlinear effects cause severe temporal splitting and spectral red-shifting, degrading pulse fidelity.

These issues have restricted the practical deployment of high-power MIR ultrafast lasers in precision-demanding fields.

Solution: Hollow-Core Photonic Crystal Fiber (HC-PCF)

To overcome these challenges, the team developed a custom single-ring, 8-cell HC-PCF (5 m length) with:

• Low transmission loss
• Minimal nonlinearity accumulation
• Rapid vacuum compatibility

Results:

• **>70% overall transmission efficiency**
• Near-identical spectral shape (high fidelity)
• Pulse broadening from 117 fs to 404 fs (due to slight waveguide dispersion: -2.04 fs²/mm @ 2.8 μm)

Dispersion Compensation:
Using Ge and ZnSe (positive dispersion materials), the team compensated for negative dispersion from the HC-PCF, lenses, and gas cell windows. The final output achieved:

• 98 fs pulse width (close to transform-limited 96 fs)
• 170 kW peak power
• **>95% single-mode energy purity**

Comparative Validation: HC-PCF vs. Conventional Methods

The team conducted side-by-side tests against:

1. Free-space optics (atmospheric distortion issues)
2. Solid-core fluoride fibers (severe nonlinear effects)

Key Findings:
✅ HC-PCF outperformed both, maintaining pulse integrity without temporal splitting or spectral distortion.
✅ Proven suitability for high-peak-power MIR ultrafast lasers—critical for spectroscopy, infrared countermeasures, and remote sensing.

Future Implications

This work establishes a reliable, high-performance MIR laser delivery platform, enabling:
🔹 Sharper spectroscopy (e.g., molecular fingerprinting)
🔹 More precise laser machining
🔹 Enhanced medical and defense applications

With further refinement, HC-PCF-based systems could revolutionize ultrafast MIR laser deployment across industries.

Publication: Optica [DOI: XXXX]
Collaborators: Hangzhou Institute of Optics, UCAS, SIOM-CAS, Affiber Photonics

(Note: Adjust institution/company names if official English variants differ.)

Key Technical Terms:

• 空芯光子晶体光纤 → Hollow-core photonic crystal fiber (HC-PCF)
• 飞秒脉冲 → Femtosecond (fs) pulses
• 非线性积累 → Nonlinearity accumulation
• 色散补偿 → Dispersion compensation
• 单模纯度 → Single-mode purity
• 光谱红移 → Spectral red-shifting

Let me know if you'd like any refinements!