On-Chip Spectrometer Breakthrough: Thin-Film Lithium Niobate Enables Picometer Resolution at 100Hz Scanning

Spectrometers: Indispensable Analytical Tools

Spectrometers serve as critical instruments for material characterization, laser testing, and chemical analysis. However, conventional benchtop systems face significant limitations in size, cost, and portability.

Research Breakthrough

A team led by Prof. Liu Liu at Zhejiang University has developed a revolutionary on-chip spectrometer using thin-film lithium niobate (TFLN) technology. Key achievements:

• 1 pm resolution (sparse spectra) / 6 pm resolution (5 nm continuous scan)
• 100 Hz scanning speed
• Single-control architecture: Only 1 logic circuit + 1 detector required
• Spiral waveguide design: Multimode waveguide gratings (MWGs) form resonant cavities for precision filtering

Background: Limitations of Traditional Spectrometers

1. Size & Portability:

   • Bulky designs (e.g., Yokogawa AQ6370 series: 600–2600 nm range, 50–100 pm resolution) require dedicated lab space.
   • Cost: 20,000–30,000 per unit, prohibitive for budget-limited users.

2. Manufacturing Challenges:

   • Complex assembly limits production scalability.

Solution: On-chip integration to miniaturize spectrometers while reducing cost and power consumption.

Technical Innovation: The "Laser-Sharp Blade"

The core innovation lies in the MWG-based resonant cavity:

1. Light Processing Mechanism:

   • A TE₀ mode undergoes Bragg reflection at each grating pair.
   • Asymmetric grating design converts TE₀ → TE₁ mode, enhancing wavelength selectivity (like "sharpening a blade").
   • Repeated reflections narrow the linewidth (Δλ ≈ 1 pm).

2. Fabrication:

   • 400 nm TFLN device layer + 900 nm SiNₓ cladding + 300 nm Au electrodes.
   • 13.8 cm spiral waveguide with 60 gratings per 6 mm segment.
   • Bending radii: 60–200 μm (minimizing loss).

Performance Validation

1. Spectral Reconstruction:
   • Achieved 1 pm resolution (discrete lines) and 5 nm operational bandwidth.
2. Efficiency:
   • Single photodetector (PD) + reconfigurable voltage sampling reduce power consumption.
3. Applications:
   • High-precision gas detection (pm-level resolution).
   • Remote sensing (low-power operation at 100 Hz scanning).

Significance & Future Outlook

This TFLN-based spectrometer demonstrates:
✅ Smallest footprint for integrated spectrometers.
✅ Industry-leading resolution (competing with $30k benchtop systems).
✅ Scalable fabrication via CMOS-compatible processes.

Potential Impact:

• Lab-on-a-chip diagnostics
• Portable environmental monitoring
• Space-constrained industrial inspection

The work was published in [Journal Name] (DOI: XX.XXXX/XX.XXXXXX).

Technical Terms Glossary

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