Application Note: Accurate Divergence Angle Measurement, Full LD Performance Characterization: Brolight BRM‑6301 Laser Diode Divergence Angle Analyzer All-in-One Test Solution

Preface

In a wide range of fields like optical communications, LiDAR, industrial processing, medical aesthetics, and beyond — the laser diode (LD) serves as the core light-emitting device, and its performance directly determines the whole system performance. Among all critical parameters, the divergence angle — a key metric that characterizes beam "directivity" — is often the decisive factor affecting coupling efficiency, collimation design, and key index of beam quality.

However, as shown in Figure 1, laser devices vary widely in form—from bare dies and COS (Chip on Submount) , to TO‑packaged devices with lenses. Each form factor places different demands on the test system. Traditional beam profilers are only suitable for LDs with small far‑field divergence angles and cannot handle large divergence devices.

Figure 1: Configurations of light-emitting devices

BRM-6301 Laser Diode Divergence Angle Analyzer from Brolight is an automated testing system specifically designed to address this challenge. Paired with the OPTIED software and a comprehensive product system including drivers, temperature controllers, spectrometers, optical power meters, and fixtures, it provides customers with an integrated optoelectronic testing solution—from individual devices to complete systems.

This article begins with the real pain points faced by the industry, then elaborates on our solutions and the significance of divergence angle data for subsequent applications.

The Real Pain Points in the Optoelectronic Chip and Device Industry

Throughout the entire progress of laser devices—from R&D and pilot production to mass production and reliability verification—engineers frequently encounter the following challenges:

Difficulty in unifying tests for different device types

Note on Array Devices: BRM-6301 Laser Diode Divergence Angle Analyzer divergence angle tester currently does not support batch testing for array-type light-emitting devices (such as VCSEL arrays, Micro-LED arrays, laser bar arrays, etc.). For fin angular characteristic studies on individual chips, single-point testing can be performed by integrating the system with a high-precision probe station and a microscopic imaging system.

Classified by emission mode and packaging level, BRM-6301 Laser Diode Divergence Angle Analyzer covers the following device categories:

BRM-6301 Laser Diode Divergence Angle Analyzer 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.

 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.

Figure 2: Principle of traditional beam profiler

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.

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.

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 Laser Diode Divergence Angle Analyzer can be paired with a high-precision probe station and microscopic imaging system for detailed angular characteristic studies.

Brolight Integrated Photonics Test Solution

BRM-6301 Laser Diode Divergence Angle Analyzer

BRM-6301 Laser Diode Divergence Angle Analyzer 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

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

As shown in Figure 4, the BRM-6301 Laser Diode Divergence Angle Analyzer 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

Fixture Adaptation Solutions Across All Packaging Levels

Figure 5: Unpackaged (bare die) testing example

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.

Significance of Divergence Angle Data for Downstream Applications

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

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

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

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). 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 divergence angle of the laser diode (LD) perpendicular to the junction plane from 30° to 3–5°, the coupling efficiency with a 200 μm core-diameter fiber can reach over 90%. Accurate measurement of the divergence angle is a prerequisite for optimizing the design of the coupling optical path and improving pump efficiency.

Impact of Divergence Angle on Solid-State Laser Pumping

In LD end-pumped solid-state lasers, the divergence angle of the pump light directly affects the degree of mode matching with the oscillating laser. By optimizing the divergence angle of the pump light, optimal mode matching can be achieved, thereby improving the optical-to-optical conversion efficiency.

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. Regular divergence angle testing enables pump source condition monitoring and early warning of performance degradation.

Typical Coupling Efficiency Data

Sources: Academic journals including Infrared and Laser Engineering, Chinese Journal of Lasers, High Power Laser and Particle Beams, as well as publicly available literature from research institutions such as the Institute of Semiconductors, Chinese Academy of Sciences, and the China Academy of Engineering Physics (CAEP).

Research on the Temperature-Divergence Angle Relationship in Device Development

In the laser diode chip design stage, the divergence angle is a key parameter for assessing epitaxial layer quality and waveguide architecture. Combined with the BIM-60/66 series spectrometers and BIM-740x/710x series power meters, a thorough evaluation of the device's temperature-dependent performance can be achieved.

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

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.

Comparative Advantages Over Traditional Methods

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

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

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: 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.

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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• Website: www.ibrolight.com

• Tel: +86-153 3689 0307

• Email: info@ibrolight.com