Multi-gigahertz laser generation based on monolithic ridge waveguide and embedded copper nanoparticles
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | Chinese Optics Letters |
| Authors | Chi Pang, Rang Li, Ziqi Li, Ningning Dong, Jun Wang |
| Institutions | Shanghai Institute of Optics and Fine Mechanics, State Key Laboratory of Crystal Materials |
| Citations | 7 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Achievement: Successful implementation of a monolithic, multi-gigahertz (GHz) pulsed waveguide laser chip utilizing embedded Copper (Cu) nanoparticles (NPs) as the saturable absorber (SA).
- Integration Method: Cu NPs were synthesized directly within the Nd:YAG crystal via Cu+ ion implantation, followed by C4+ ion irradiation and diamond saw dicing to define the ridge waveguide structure.
- Mechanism: Passive mode-locking is achieved through the evanescent field interaction between the waveguide mode and the Cu NPs, which exhibit strong saturable absorption due to the Localized Surface Plasmon Resonance (LSPR) effect.
- Performance Metrics: The device operates at 1 ”m (1064 nm), achieving a high fundamental repetition rate of 7.8 GHz and an ultrashort pulse duration of 24.8 ps.
- Nonlinear Properties: The Cu NP SA demonstrated a saturation intensity (Is) of 12.9 GW/cm2 and a modulation depth of 1.5% when tested with 340 fs pulses at 1030 nm.
- Efficiency and Stability: The laser exhibits a low threshold of 214 mW and excellent mode-locking stability, confirmed by a signal-to-noise ratio up to 47.8 dB.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Gain Medium / Substrate | Nd:Y3Al5O12 | Crystal | Nd:YAG |
| Laser Wavelength | 1064 | nm | Main emission line (Nd3+ 4F3/2 â 4I11/2) |
| Pump Wavelength | 808 | nm | Continuous Wave (CW) excitation |
| Pulse Repetition Rate | 7.8 | GHz | Fundamental mode-locking frequency |
| Pulse Duration | 24.8 | ps | Measured minimum pulse width |
| Laser Threshold | 214 | mW | Launched pump power |
| Maximum Output Power | 58 | mW | At 836 mW launched power |
| Waveguide Loss (TM) | 0.68 | dB | Measured at 1064 nm |
| Saturation Intensity (Is) | 12.9 | GW/cm2 | Measured at 1030 nm (340 fs pulses) |
| Modulation Depth | 1.5 | % | Saturable absorption property |
| Signal-to-Noise Ratio | 47.8 | dB | Mode-locking stability indicator |
| Ridge Waveguide Width | 23.5 | ”m | Fabricated dimension |
| Cu NP Diameter (Mean) | 2.16 | nm | Synthesized nanoparticle size |
| Cu NP Distribution Depth | 50 to 125 | nm | Below the crystal surface |
| LSPR Peak Position | 592 | nm | Measured linear absorption peak |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication and testing process relies on precise ion beam engineering and standard optical characterization techniques:
-
Cu Nanoparticle Synthesis (Ion Implantation):
- Ions: Cu+
- Energy: 100 keV
- Fluence: 1 x 1017 ions/cm2
- Result: Synthesis of Cu NPs (mean diameter 2.16 nm) concentrated near the surface region of the Nd:YAG crystal.
-
Planar Waveguide Formation (Ion Irradiation):
- Ions: C4+
- Energy: 15 MeV
- Fluence: 6 x 1014 ions/cm2
- Result: Creation of a planar optical waveguide layer approximately 10 ”m thick beneath the surface.
-
Ridge Waveguide Fabrication (Dicing):
- Method: Rotating diamond blade slicing.
- Speed: 2000 r/min.
- Result: Parallel air grooves manufactured to define a ridge waveguide width of 23.5 ”m.
-
Structural and Linear Characterization:
- Techniques: Transmission Electron Microscopy (TEM) and High-Resolution TEM (HRTEM) confirmed NP size and distribution.
- LSPR Measurement: Linear optical absorption spectrum measured the LSPR peak at 592 nm, consistent with Mie theory simulation (590 nm).
-
Nonlinear Optical Characterization:
- Technique: Open-aperture (OA) Z-scan system.
- Laser Source: Femtosecond mode-locked laser (1030 nm, 340 fs pulse width, 1 kHz repetition rate).
- Result: Confirmed pronounced saturable absorption, yielding Is = 12.9 GW/cm2.
-
Laser Implementation:
- System: End-face coupling system used to couple the 808 nm pump laser into the monolithic ridge waveguide cavity.
- Mechanism: Mode-locking achieved via evanescent field coupling between the waveguide mode and the embedded Cu NP SA layer.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology, combining integrated waveguides with plasmonic saturable absorbers, is highly relevant for compact, high-speed photonic devices:
- Integrated Optical Circuits: Provides a pathway for realizing fully monolithic, on-chip pulsed laser sources essential for complex integrated photonic systems.
- High-Speed Data Communications: The 7.8 GHz repetition rate is suitable for generating optical clocks and carriers in high-bandwidth fiber optic and free-space communication systems.
- Compact Sensing and Metrology: The small footprint and picosecond pulse generation capability are valuable for integrated time-of-flight sensors, micro-LIDAR, and high-resolution optical coherence tomography (OCT).
- Ultrafast Signal Processing: The device can serve as a compact source for generating high-frequency pulse trains required in all-optical switching and sampling applications.
- Miniaturized Laser Systems: Enables the development of highly compact, robust, and cost-effective pulsed laser modules for portable scientific instruments and industrial tools.
View Original Abstract
Copper (Cu) nanoparticles (NPs) are synthesized under the near-surface region of the Nd:Y3Al5O12 (Nd:YAG) crystal by direct Cu+ ions implantation. Subsequently, the monolithic ridge waveguide with embedded Cu NPs is fabricated by C4+ ions irradiation and diamond saw dicing. The nonlinear optical response of the sample is investigated by the Z-scan technique, and pronounced saturable absorption is observed at the 1030 nm femtosecond laser. Based on the obvious saturable absorption of Cu NPs embedded Nd:YAG crystal, 1 ÎŒm monolithic mode-locked pulsed waveguide laser is implemented by evanescent field interaction between NPs and waveguide modes, reaching the pulse duration of 24.8 ps and repetition rate of 7.8 GHz. The work combines waveguides with NPs, achieving pulsed laser devices based on monolithic waveguide chips.