Application Note: From Bare Die to Module – BRM-6301 Divergence Angle Test Guide for Light Emitters

— One Test Platform for All Packaging Levels, from Divergence Angle to Full Device Characterization

Overview

In optical communications, LiDAR, industrial processing, medical aesthetics, and many other fields, laser diodes (LDs), LEDs, and emerging emitters such as Micro-LEDs serve as light-emitting devices. Their performance directly determines the overall system behavior. Divergence angle – a key parameter that measures the "directivity" of a beam – is often the critical factor affecting system coupling efficiency, collimation design, and beam quality.

However, as shown in Figure 1, light-emitting devices span a broad spectrum of packaging levels – from fragile bare dies, to COS (Chip on Submount) mounted on heat sinks, to TO-packaged devices with lenses, and ultimately to complete modules. Each packaging level imposes different requirements on test systems. Traditional beam profilers can only measure emitters with small far-field divergence angles and are ineffective for large-divergence devices.

This is where BRM-6301 stands out – its defining strength lies in seamless adaptability across virtually all packaging levels, enabling you to standardize testing across different device types on a single platform.

Figure 1: Packaging levels of light-emitting devices – from unpackaged (bare die) to partially packaged (COS) to fully packaged (TO/Butterfly) devices

Brolight's BRM-6301 Divergence Angle Analyzer is an automated test platform purpose-built to address these challenges. Together with the OPTIED Control & Data Platform and a complete product ecosystem including drivers, temperature controllers, spectrometers, optical power meters, and fixtures, we deliver integrated photonics test solutions from device to system level.

This guide starts with the real challenges faced by the industry, explains our solutions, and highlights the significance of divergence angle data for downstream applications.

Part 1: Key Challenges in Photonics Chip and Device Industries

Throughout the entire lifecycle of light-emitting device R&D, pilot production, mass production, and reliability verification, engineers frequently encounter the following challenges:

Challenge 1: Difficulty in Testing Across Different Packaging Levels

Important Note on Array Devices: The BRM-6301 divergence angle analyzer currently does not support batch testing of array-type light-emitting devices (such as VCSEL arrays, Micro-LED arrays, laser bars, etc.). For fine angular characteristic studies of individual chips, it can be configured with a high-precision probe station and microscopic imaging system for single-point testing.

Classified by emission mode and packaging level, BRM-6301 covers the following device categories:

The BRM-6301 Advantage: Whether you are testing edge-emitting or surface-emitting devices, at any packaging level from bare die to Butterfly package, BRM-6301, together with the BRM-67xx series temperature-controlled mounting sockets, delivers a plug-and-play, quick-switch testing experience. One platform, all packaging levels – this is the defining value proposition of BRM-6301.

Challenge 2: Inability to Measure Large-Divergence Devices

Traditional beam profilers rely on CCD or CMOS imaging principles and are limited by sensor size and optical system design. They can typically only measure emitters with small far-field divergence angles. For large-divergence laser diodes (such as some edge-emitting lasers), traditional methods are simply incapable. Figure 2 illustrates the conventional camera-based measurement scheme.

As documented in the literature, a diode laser bar is characterized by two divergence angles: approximately 40° (FWHM) in the fast axis direction and 10° (FWHM) in the slow axis direction. These large, asymmetric divergence angles make efficient optical coupling particularly challenging.

Figure 2: Principle of traditional beam profiler

Challenge 3: Incomplete Testing and Data Silos

In many laboratories, divergence angle is measured with one system, while P-I-V curves (power-current-voltage), threshold current, and wall-plug efficiency (WPE) are measured with another. Data cannot be correlated across systems, making it difficult for researchers to understand how temperature and drive current affect divergence angle from a holistic perspective.

Challenge 4: Lack of Temperature Control, Poor Test Repeatability

Light-emitting device performance is highly temperature-dependent – wavelength drift coefficient is 0.03–0.1 nm/°C, and divergence angle also varies with temperature. Without precise temperature control, test data lack comparability.

Challenge 5: Testing Challenges with Emerging Devices like Micro-LED

With the rapid advancement of display technologies, Micro-LED has gained significant attention as a next-generation display technology. However, the miniaturized nature of Micro-LED presents new testing challenges:

Special Characteristics of Micro-LED Angular Emission Distribution: Studies show that as Micro-LED chip size decreases, the angular emission profile exhibits a distinct double-peak phenomenon, which is more pronounced in blue and green Micro-LEDs than in red Micro-LEDs of the same size. Additionally, red chips inherently have smaller emission angles than blue/green chips, and encapsulation materials further amplify the emission angles of blue/green light, leading to correlated color temperature (CCT) deviations. These characteristics make divergence angle testing an essential requirement for Micro-LED device evaluation.

Testing Method Note: For single Micro-LED chips, the BRM-6301 can be paired with a high-precision probe station and microscopic imaging system for detailed angular characteristic studies.

Part 2: Brolight Integrated Photonics Test Solution

2.1 BRM-6301 Automated Divergence Angle Analyzer

The BRM-6301 is an automated divergence angle analyzer specifically designed for large-divergence laser diodes. Its measurement scheme is shown in Figure 3, addressing the challenge that traditional beam profilers cannot measure large-divergence emitters.

Figure 3: BRM-6301 divergence angle analyzer measurement scheme (Top View & Side View)

Specifications:

Key Capabilities:

• Large-Divergence Measurement: Specifically designed for large-divergence emitters, with no limitation on divergence angle magnitude

• Multi-Packaging-Level Adaptability – the defining differentiator: Flexible configuration with detector and mounting socket options tailored to the emitter's wavelength, power, and packaging level – from bare die to Butterfly package, all on one platform

• Multiple Output Formats: Supports both polar and Cartesian coordinate angle distribution plots, with automatic half-intensity angle data output

• One-Click Report Generation: Automatically compiles measurement data into test report format for easy archiving and customer delivery

• LED Compatible: Also suitable for angular distribution measurement of LEDs

  
  

2.2 Complete Test Ecosystem: Driver, Temperature Controller, and Fixtures Integration

As shown in Figure 4, the BRM-6301 is not an isolated tester but a primary component of Brolight's complete photonics test ecosystem:

Figure 4: Complete LED/LD photonics characterization test ecosystem

2.3 Fixture Adaptation Solutions Across All Packaging Levels

The BRM-6301's ability to adapt to virtually any device packaging level is made possible by the BRM-67xx series temperature-controlled mounting sockets. The table below illustrates the comprehensive coverage:

Key Differentiator: Unlike traditional systems that require complex reconfiguration or custom fixtures for each packaging level, BRM-6301 offers standardized, plug-and-play adaptability – drastically reducing setup time and eliminating measurement inconsistencies across different packaging levels.

Figure 5: Unpackaged (bare die) testing example

2.4 OPTIED Control & Data Platform: The "Central Nervous System" for Instrument Integration

Brolight's OPTIED Control & Data Platform has fully integrated all devices – BRM-6301 divergence angle analyzer, BRM-610X driver controller, BRM-620X temperature controller, BIM-60/66 series spectrometers, and BIM-740x/710x series optical power meters – into a unified ecosystem for instrument control, data acquisition, and correlative analysis. Figure 6 shows a typical OPTIED interface.

Figure 6: OPTIED Control & Data Platform interface

Researchers can easily obtain:

• Divergence angle distribution (polar/Cartesian coordinates) at specific temperatures

• Divergence angle trends as a function of drive current

• P-I-V curve comparisons at different temperatures

• Correlative analysis of divergence angle with threshold current and WPE

• Spectrum-temperature relationship curves: Using BIM-60/66 series spectrometers to analyze wavelength drift coefficients and evaluate device thermal stability

• Optical power-temperature relationship curves: Using BIM-740x/710x series optical power meters to evaluate temperature impact on output power and optimize thermal management design

• One-click export of comprehensive multi-parameter reports

This means: Researchers no longer need to manually export/import data between different software applications. They can directly explore fundamental scientific questions – "How does temperature affect divergence angle?", "How does drive current influence beam quality?", "How does the spectrum drift with temperature?" – all within a single integrated environment.

Part 3: Significance of Divergence Angle Data for Downstream Applications

3.1 Optical Communications – Fiber Coupling Efficiency Optimization

In optical transceiver modules, light emitted from the laser must be efficiently coupled into optical fibers. The divergence angle directly determines the coupling lens design parameters and coupling efficiency.

Typical Users: Optical transceiver module manufacturers, silicon photonics chip design houses

3.2 LiDAR – Far-Field Beam Quality Control

Whether for automotive-grade or industrial-grade LiDAR, beam quality control is an essential consideration. Excessive divergence angle causes far-field spot expansion, reducing optical transmission efficiency, decreasing detection range and resolution, and increasing power consumption.

Typical Users: LiDAR companies, VCSEL chip suppliers

3.3 Laser Pump Sources – Pump Coupling Efficiency Optimization

Semiconductor lasers (LDs) are often used as pump sources for fiber lasers or solid-state lasers. Their divergence angles directly affect the coupling efficiency of pump light into the gain medium.

Typical Users: Fiber laser manufacturers, solid-state laser manufacturers

【Technical Background】Mechanisms of Divergence Angle Impact on Pump Coupling Efficiency

1. Divergence Angle as a Key Factor in Pump Coupling Efficiency

When a semiconductor laser serves as a pump source, the divergence angle of its output beam directly affects the optical coupling efficiency into the pump medium (fiber or laser crystal). For a typical semiconductor laser chip, the large difference between its fast-axis divergence angle (20–60°) and slow-axis divergence angle (6–20°) results in a low proportion of the beam focused into the fiber, which significantly affects optical performance. Studies show that the numerical aperture angle of multi-mode silica fibers is generally less than 40°; beam divergence exceeding this angle cannot be coupled into the fiber.

Typical Data: By optimizing the wedge angle and tip radius of cylindrical lensed fibers, coupling efficiency for mid-infrared LDs can reach over 97% when the mode-field radius of the fiber matches the initial spot size of the laser in the slow-axis direction. Using a graded refractive index (GRIN) lens coupling system, experimental coupling efficiency of 90.8% has been achieved for LD-to-multimode fiber coupling.

2. Impact of Divergence Angle on Solid-State Laser Pumping

In LD end-pumped solid-state lasers, the pump beam divergence angle directly affects the mode matching with the oscillating laser mode. The beam quality parameter (BPP – Beam Parameter Product) is commonly used to evaluate laser diode beam quality, defined as the product of beam waist radius and far-field divergence angle. By optimizing the pump divergence angle, optimal mode matching can be achieved, improving optical-to-optical conversion efficiency.

3. Beam Quality Degradation at High-Power Operation

In high-power operation of broad-area semiconductor lasers, waste heat causes thermal lensing effects that significantly increase the slow-axis far-field divergence angle, leading to severe beam quality degradation and reduced pump coupling efficiency. Research shows that when the working distance offset between the incident beam waist and the fast-axis collimation (FAC) lens increases from 0 μm to 2 μm, the divergence angle of a single emitter after collimation in the fast axis increases from 4.95 mrad to 6.46 mrad. Regular divergence angle testing enables pump source condition monitoring and early warning of performance degradation.

4. Typical Coupling Efficiency Data

3.4 Research and Device Development – Temperature-Divergence Relationship Studies

During the chip design phase, divergence angle is an important indicator for evaluating epitaxial structure and waveguide design. When paired with BIM-60/66 series spectrometers and BIM-740x/710x series optical power meters, the system enables comprehensive evaluation of device temperature characteristics.

Typical Users: Chip design houses, assembly houses, university optoelectronics laboratories

3.5 Micro-LED Display – Angular Characteristics and Color Shift Evaluation

In Micro-LED display technology R&D, angular characteristics are a key parameter affecting display quality.

Application Scenarios:

• Micro-LED Display Module R&D: Evaluate angular emission matching of RGB chips of different sizes

• Post-Mass-Transfer Inspection: Batch-test emission uniformity of transferred chips

• Encapsulation Process Optimization: Evaluate impact of different thickness/materials on emission angle

Typical Users: Micro-LED display chip R&D institutions, panel manufacturers, AR/VR device makers

Testing Method Note: For single Micro-LED chips, the BRM-6301 can be paired with a high-precision probe station and microscopic imaging system for detailed angular characteristic studies.

Part 4: Comparative Advantages Over Traditional Methods

Part 5: Typical Test Workflow Example

Scenario: Test divergence angle of a COS device at 25°C and 60°C, with correlated P-I-V curve analysis

Research Value: Through this workflow, researchers can directly answer fundamental questions such as "By how much does the divergence angle increase when temperature rises by 10°C?" and "How much does the threshold current drift at elevated temperatures?"

Figure 7 shows a measured example of a COS chip.

Figure 7: Partially packaged (COS) device testing example

Part 6: Summary of User Value

For Chip Design Houses

• Verify rationality of epitaxial structure and waveguide design

• Evaluate batch-to-batch consistency

• Provide reliable divergence angle datasheet specifications to downstream customers

For Assembly Houses

• Rapid incoming chip screening

• Evaluate impact of assembly processes on divergence angle

• Provide factory test reports for TO-packaged devices

For Optical Transceiver Module Manufacturers / System Integrators

• Accurately measure divergence angle to optimize coupling optical design

• Evaluate performance differences among suppliers

• Establish incoming inspection standards

For Research Laboratories

• Multi-parameter correlative analysis (temperature, current, divergence angle, efficiency)

• Integrated test platform improves experimental efficiency

• Support custom test sequences for exploratory research

For Micro-LED R&D Institutions

• Evaluate angular matching of RGB chips of different sizes

• Study impact of encapsulation processes on emission angle

• Provide data support for color shift optimization

Comprehensive Light-Emitting Device Performance Parameter Characterization

Commercial LD and LED products are typically characterized by key performance indicators in their datasheets. The Brolight BRM-6301 test platform and supporting ecosystem can completely provide measurement and validation of the following specification parameters:

Customer Value: The Brolight BRM-6301 test platform is not just a "divergence angle analyzer" – it is a complete test solution covering all key performance parameters of light-emitting devices. From P-I-V curves to spectral characteristics, from divergence angle to temperature dependence – all data is uniformly acquired, correlatively analyzed, and can be exported as a single test report in industry-standard format through the OPTIED platform, ready for use in product datasheet compilation or incoming inspection.

Conclusion

The Brolight BRM-6301 Divergence Angle Analyzer, together with the OPTIED Control & Data Platform and the complete driver, temperature controller, and fixture ecosystem, is more than an instrument for divergence angle characterization of light emitters – it is an integrated photonics test platform that combines driver, temperature control, multi-level fixtures, spectral analysis, optical power measurement, and correlative data analysis.

From bare die to module, from single emitters to Micro-LED fine angular studies, from divergence angle to P-I-V curves, from spectrum-temperature to power-temperature relationships – the Brolight test platform delivers comprehensive characterization across the full spectrum of light-emitting devices, helping you truly "see" the full picture of your devices.

References

1. Wang, Z., et al. "High coupling efficiency wedge-shaped cylindrical lensed fiber for the 2 µm band." Applied Optics, Vol. 64, Issue 15, pp. 4265-4270 (2025).

2. Ma, Z., et al. "Coupling efficiency of laser diode to multimode fiber by graded refractive index lens." Optical Fiber Technology, Vol. 83, 103689 (2024).

3. "Power Enhancement and Spot Homogenization Design for Arrayed Semiconductor Lasers." Micromachines, Vol. 15, Issue 6, 744 (2024). National Institutes of Health (NIH/PMC).

4. Gao, Q., Wang, W., Pang, Y. "Diode-laser transversal pumped coupling technology." Proceedings of SPIE, Vol. 4915, pp. 346-349 (2002).

5. Zhang, H., et al. "The SMILE Effect in the Beam Propagation Direction Affects the Beam Shaping of a Semiconductor Laser Bar Array." Photonics, Vol. 11, Issue 2, 161 (2024). MDPI.

About Brolight

Brolight, a brand under A&P Instrument, was established in 2012 and is headquartered in Hangzhou, China. As a national high-tech enterprise specializing in the R&D, manufacturing, and sales of scientific educational instruments and photonics instruments, Brolight holds ISO9001:2015 quality management system certification. Leveraging over 40 years of deep expertise in the photonics industry accumulated by its parent company, Brolight is committed to delivering high-quality photonics testing solutions to research and industrial users worldwide.

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