Ion-Implanted Diamond Blade Diced Ridge Waveguides in Pr -YLF—Optical Characterization and Small-Signal Gain Measurement

At a Glance

Metadata	Details
Publication Date	2025-04-30
Journal	Applied Sciences
Authors	O. Al-Taher, Kore Hasse, Sergiy Suntsov, Hiroki Tanaka, Christian Kränkel
Institutions	Helmut Schmidt University, Széchenyi István University
Citations	1
Analysis	Full AI Review Included

Executive Summary

This research successfully demonstrates the fabrication and characterization of high-performance, active ridge waveguides in Praseodymium-doped Lithium Yttrium Fluoride (Pr:YLF) using a hybrid ion implantation and precision dicing technique.

Hybrid Fabrication: Planar waveguides were first created via high-energy Carbon ion (C³⁺) implantation, followed by precision diamond blade dicing to define the ridge geometry, ensuring strong lateral mode confinement.
Ultra-Low Propagation Loss: Achieved propagation losses as low as 0.4 dB/cm for TM polarization in 22 µm wide ridge waveguides, comparable to state-of-the-art methods like fs laser inscription.
High Small-Signal Gain: Demonstrated significant optical amplification under blue pumping, achieving internal gains of 6.5 dB/cm (607 nm, orange) and 5 dB/cm (639 nm, red).
Spectroscopic Integrity: Fluorescence and lifetime measurements confirmed that the ion implantation process did not negatively impact the spectroscopic properties or the upper-level lifetime (50 µs) of the Pr³⁺ ions.
Integrated Laser Potential: The high gain, low loss, and strong confinement make these structures highly promising candidates for developing compact, efficient, watt-level integrated solid-state lasers operating across the visible spectrum.

Technical Specifications

Parameter	Value	Unit	Context
Lowest Propagation Loss	0.4	dB/cm	TM polarization, 22 µm wide ridge
Highest Small-Signal Gain (Orange)	6.5	dB/cm	Signal wavelength 607 nm, TM polarization
Highest Small-Signal Gain (Red)	5	dB/cm	Signal wavelength 639 nm, TM polarization
Pump Wavelength	444	nm	Blue pump source (InGaN diode compatible)
Implanted Ion Species	C³⁺ (Carbon)	N/A	Used for refractive index modification
Implantation Energy	10	MeV	High-energy implantation
Implantation Dose Range	2 x 10¹⁴ to 6 x 10¹⁵	ions/cm²	Range used for planar waveguide formation
Waveguide Upper Level Lifetime	50	µs	³P₀ level lifetime in Pr:YLF
Calculated Ion Penetration Depth	~6.5	µm	Determined via SRIM simulation
Optical Barrier Minimum Depth	6.2	µm	Reconstructed RI profile
Near-Surface RI (Guiding Layer)	1.469	N/A	For both TE and TM polarizations
Ridge Waveguide Dimensions	15	µm	Height
Ridge Waveguide Dimensions	15-25	µm	Width

Key Methodologies

The ridge waveguides were fabricated using a two-step process combining ion implantation for planar guiding and precision dicing for lateral confinement.

Planar Waveguide Formation (Ion Implantation):
- Substrate: Pr:YLF (a-cut) crystals were used.
- Implantation: High-energy Carbon ions (C³⁺) were implanted at 10 MeV.
- Dose: Doses ranged from 2 x 10¹⁴ to 6 x 10¹⁵ ions/cm².
- Mechanism: The ions created a lower refractive index (RI) barrier layer (at ~6.5 µm depth) due to nuclear collisions, forming a planar waveguide structure in the near-surface region.
Thermal Treatment (Annealing):
- Samples were annealed up to 200 °C. Annealing was stopped at this temperature to preserve the amorphous structure and the waveguiding properties, as higher temperatures (250 °C) caused the crystal structure to revert toward its original birefringent state.
Ridge Definition (Precision Dicing):
- Equipment: A Disco DAD322 precision diamond saw was used.
- Blade: A soft resin-bonded blade (Disco G1A853 SD6000 R21B01) with a 200 µm width was employed.
- Dicing Parameters: Blade speed was 25,000 rpm, with a feed speed of 0.2 mm/s.
- Facet Preparation: End facets were prepared using 50 µm deep polishing cuts to minimize chipping and improve coupling efficiency.
Optical Characterization:
- Loss Measurement: Transmission method using a HeNe laser (632.8 nm). Coupling efficiency was estimated via overlap integral calculation.
- Fluorescence/Lifetime: Excited using a tunable continuous-wave frequency-doubled Ti:sapphire laser (444 nm pump). Fluorescence decay was measured using an electro-optic modulator (25 ns trailing edge).
- Gain Measurement: Small-signal gain was measured using a home-built bulk Pr:YLF laser (607 nm and 639 nm) collinearly combined with a 55 mW blue pump beam (TM polarization).

Commercial Applications

The development of low-loss, high-gain integrated active waveguides in Pr:YLF is critical for applications requiring compact, high-power visible light sources.

Integrated Photonics: Core building blocks for miniaturized active optical circuits operating in the visible spectrum.
Visible Solid-State Lasers: Realization of efficient, low-threshold waveguide lasers (green, orange, and red) pumped by readily available blue InGaN laser diodes.
Display and Projection Technology: High-power, high-beam-quality visible sources necessary for advanced laser projection systems and displays.
Biophotonics and Medical Devices: Integrated visible lasers and amplifiers used for spectroscopy, fluorescence imaging, and therapeutic applications requiring specific visible wavelengths.
Metrology and Sensing: Compact, stable visible light sources for high-precision measurement and sensing systems.
Quantum Technology: Potential use in systems requiring specific rare-earth ion transitions for quantum memory or processing, leveraging the preserved spectroscopic properties of Pr³⁺.

View Original Abstract

Planar optical waveguides were fabricated in Pr:YLF crystals by ion implantation. In a further step, ridge waveguides were fabricated using precision diamond dicing. These enable strong light confinement and have propagation losses as low as 0.4 dB/cm. To study the influence of ion implantation on the spectroscopic properties, fluorescence and lifetime measurements were conducted in the ridge waveguides. Under blue pumping, small-signal optical gains of 6.5 dB/cm and 5 dB/cm were demonstrated at wavelengths of 607 nm and 639 nm, respectively. These results make ion-implanted ridge waveguides in Pr:YLF promising candidates for compact integrated lasers in the visible spectral region with high output powers in the watt range.

Tech Support

Original Source

DOI: https://doi.org/10.3390/app15094956

References

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