Thermally stable narrow-bandpass filter prepared by reactive ion-assisted sputtering

Area of Science:

• Optical engineering
• Materials science
• Thin film technology

Background:

• Narrow-bandpass (NB) filters are crucial components in optical-fiber communication systems.
• Ensuring the thermal stability and moisture resistance of these filters is essential for reliable performance.
• High-index dielectric materials like Ta2O5 and SiO2 are commonly used in filter fabrication.

Purpose of the Study:

• To investigate the thermal stabilities of three-cavity NB filters.
• To evaluate the moisture resistance and temperature-dependent wavelength shifts of these filters.
• To determine compliance with industry standards for optical communication components.

Main Methods:

• Fabrication of NB filters using reactive ion-assisted bipolar direct-current (dc) magnetron sputtering.
• Utilized tantalum and silicon targets with argon sputtering gas and oxygen reactant.
• Characterized film properties including refractive indices and performed water-immersion tests.
• Measured temperature-dependent wavelength shifts from room temperature to 75 degrees C.

Main Results:

• Achieved refractive indices of 2.1 for Ta2O5 and 1.45 for SiO2 at 1550 nm.
• Demonstrated excellent moisture-resistant properties, indicating high film packing density.
• Observed minimal temperature-dependent wavelength shifts (<3 x 10(-3) nm/°C).
• The total wavelength shift remained below 0.15 nm over a 75°C temperature range.

Conclusions:

• The fabricated NB filters exhibit excellent thermal stability and moisture resistance.
• The filters meet the stringent requirements of Bellcore GR-1209-CORE for optical-fiber communication.
• The sputtering method provides high-quality films suitable for demanding optical applications.