Dual-wavelength vertical external-cavity surface-emitting laser - strict growth control and scalable design
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-01-27 |
| Journal | Applied Physics B |
| Authors | A. Jasik, Adam K. SokĂłĆ, Artur Broda, Iwona Sankowska, Anna WĂłjcik-JedliĆska |
| Institutions | Institute of Electron Technology, Lodz University of Technology |
| Citations | 10 |
| Analysis | Full AI Review Included |
DW VECSEL Technical Review & Thermal Management Solutions
Section titled âDW VECSEL Technical Review & Thermal Management Solutionsâ6CCVD Reference Document: Dual-Wavelength Vertical External-Cavity Surface-Emitting Laser (DW VECSEL)
This document analyzes the research detailing a simplified, highly controllable dual-wavelength VECSEL design, emphasizing the critical role of Single Crystal Diamond (SCD) for achieving high-power continuous-wave (CW) operation.
Executive Summary
Section titled âExecutive SummaryâThis research presents a highly scalable dual-wavelength VECSEL architecture suitable for applications requiring high-power, co-axial, two-color beams, such as difference-frequency generation (DFG) for mid-IR sources.
- Simplified Architecture: The DW VECSEL utilizes a simple two-section gain region without requiring complex internal optical filters or highly volatile indium source control.
- Dual-Wavelength Emission: Achieved simultaneous, co-axial lasing at $\lambda$s = 991 nm and $\lambda$l = 1038 nm, with comparable threshold pumping power for both wavelengths.
- High Power Operation: Combined CW output power reached 1.79 W, demonstrating high efficiency and thermal stability.
- Thermal Management Requirement: The high output power was only achievable in CW mode after the structure was bonded to a 300 ”m thick Single Crystal Diamond (SCD) heat spreader.
- Precision Manufacturing: Successful operation depended on strict growth rate control (better than 1%) to maintain epitaxial layer thickness accuracy within 0.5% of the theoretical design.
- Scalability Demonstrated: The design was successfully scaled by thinning the epitaxial layers (3% and 6% reductions), demonstrating spectral tuning across a range from 928/977 nm to 988/1038 nm.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points define the performance and dimensional requirements of the DW VECSEL structure:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Combined CW Output Power (Max) | 1.79 | W | Achieved with diamond heat spreader |
| Lasing Wavelength ($\lambda$s) | 991 | nm | Short wavelength (unscaled) |
| Lasing Wavelength ($\lambda$l) | 1038 | nm | Long wavelength (unscaled) |
| Maximum Pump Power (Pin) | 25 | W | Used for maximum CW output |
| Required Layer Thickness Accuracy | 0.5 | % | Limit for successful MBE QW placement |
| Heat Spreader Material | SCD | N/A | Single Crystal Diamond (crucial for CW) |
| Heat Spreader Thickness | 300 | ”m | Bonded structure dimension |
| CW Pump Spot Diameter | 200 | ”m | Used on diamond-bonded chip |
| Operating Temperature (Heat Sink) | -4 to +10 | °C | Required cooling range |
| Epitaxial Chip Dimensions | 3 x 3 | mm2 | Cleaved laser chip size |
| Short QW Composition (InGaAs) | In0.18Ga0.82As | N/A | Short-wavelength emitter |
| Deep QW Composition (InGaAs) | In0.23Ga0.77As | N/A | Long-wavelength emitter |
Key Methodologies
Section titled âKey MethodologiesâThe successful fabrication relied on rigorous control over the III-V epitaxial growth process, especially concerning material thickness and composition, paired with advanced thermal modeling.
- Material Growth: Structures were grown using Molecular Beam Epitaxy (MBE) on a Riber 32P reactor utilizing standard Knudsen cells (Group III) and a valved cracking cell (Arsenic).
- Thermal Modeling: A 3-dimensional heat transfer model utilizing the Finite Element Method (FEM) was employed to determine the exact temperature distribution and optimize the QW arrangement for carrier transport analysis.
- Growth Control and Validation:
- In Situ: Growth rate was controlled using Reflection High-Energy Electron Diffraction (RHEED) oscillations.
- Ex Situ: High-Resolution X-ray Diffractometry (HR XRD) was used to verify layer thicknesses. This confirmed the need for strict layer thickness calibration due to observed flux instability (e.g., AlAs layers showed deviation up to 7.1% for thin layers).
- Active Region Design: The gain region was divided into two sections (three pairs of shallow QWs and six single deep QWs) separated by a wide-bandgap (30 nm) AlAs blocking layer to control independent carrier pumping and prevent interaction between the fields.
- Thermal Integration: Cleaved $3 \times 3$ mm2 chips were bonded to a 300 ”m thick Single Crystal Diamond heat spreader within a copper holder using thermoconductive paste to enable high-power CW operation.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the materials necessary to replicate, optimize, and scale the high-performance VECSELs described in this research, specializing in precision diamond thermal management.
Applicable Materials
Section titled âApplicable MaterialsâThe high combined output power (1.79 W at 25 W pumping) required the use of a diamond heat spreaderâa core 6CCVD product. We recommend the following material for VECSEL applications:
| 6CCVD Material | Specification Match | Rationale |
|---|---|---|
| Thermal Grade Single Crystal Diamond (SCD) | Thickness: 300 ”m (or custom $0.1$ ”m - $500$ ”m) | Essential for high-power CW operation, providing superior thermal conductivity necessary to dissipate heat generated by 25 W optical pumping. |
| Optical Grade SCD | Polishing: Ra < 1 nm | Surface quality matching is crucial for minimizing optical scattering losses and achieving high-quality wafer bonding (e.g., fusion bonding or solder-based methods). |
Customization Potential
Section titled âCustomization PotentialâThis research required small-area diamond bonding (the chip size was $3 \times 3$ mm2) and precise thickness control (300 ”m). 6CCVD exceeds these requirements.
- Precision Dimensions: While the research used a small $3 \times 3$ mm2$ chip, 6CCVD routinely provides custom laser-cutting services to fabricate diamond heat spreaders in arbitrary shapes and sizes, ensuring optimal fit and minimal waste for delicate III-V chips.
- Polishing Excellence: 6CCVD guarantees ultra-smooth polishing down to Ra < 1 nm for SCD, which is vital for the thermal and optical interface between the epitaxy and the heat spreader in high-power VECSELs.
- Metalization Services: Although the bonding technique was not explicitly defined, VECSEL bonding often requires metal layers (e.g., Ti/Pt/Au or AuSn solder interfaces). 6CCVD offers in-house, custom thin-film metalization services (Au, Pt, Pd, Ti, W, Cu), allowing the integration engineer to specify the exact metallization scheme needed for robust thermal bonding.
Engineering Support
Section titled âEngineering SupportâThe paper highlights the extreme sensitivity of VECSEL performance to thermal parameters and epitaxial layer thickness. 6CCVDâs in-house PhD team provides expert guidance to mitigate these challenges.
- Thermal Design Optimization: Our engineers can assist customers by determining the optimal diamond thickness, crystal orientation, and mounting preparation to maximize heat spreading capacity for similar High-Power Optically Pumped Semiconductor projects.
- Material Selection: We help select the optimal material gradeâwhether high-purity SCD for highest thermal conductivity or customized Boron-Doped Diamond (BDD) films for integrated electrical componentsâensuring material properties perfectly match application requirements.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
This paper reports on the design and fabrication of a dual-wavelength vertical external-cavity surface-emitting laser. Grown by molecular beam epitaxy, the laser structures have a relatively simple active region divided into two sections, between which there is no optical filter. Comparable threshold power was achieved for both wavelengths. The growth rate was controlled precisely by growing AlAs/GaAs superlattices with different period thicknesses and testing them with high-resolution X-ray diffractometry. The simultaneous emission of two wavelengths was detected in setup without a heat spreader, one of 991 nm and the other of 1038 nm. After diamond heat spreader was bonded, both wavelengths lased in continuous-wave mode with the combined output power of 1.79 W. The design scalability allowed us to obtain two further structures with layers thinned by about 3 % in the first and by about 6 % in the second, operating at 958/1011 and 928/977 nm, respectively.