Introduction to Core Selection Parameters for Lasers

Some optoelectronics researchers often find themselves stumped when it comes to selecting the right laser for their projects—after all, lasers come with a wide array of parameters, leaving many unsure about which ones to prioritize. Drawing on Jibulight's extensive experience in both fundamental optoelectronic research and product development, we’re here to provide a detailed guide to the core parameters of laser technology, helping you quickly grasp how these features influence a laser’s performance. 

1. Material Technology 

Manufactured using different material processes as shown in the table below: 

Semiconductor lasers have become the mainstream choice thanks to their high efficiency, compact size, low cost, and versatile applications—key reasons include: 

(1) High Efficiency and Low Energy Consumption: 

Semiconductor lasers boast an electro-optical conversion efficiency of 30% to 50%, significantly higher than that of CO₂ lasers (10%) and solid-state lasers (1% to 20%). Additionally, their compact size—just 1/10 to 1/100th the volume of conventional lasers—makes them ideal for integration into automated systems. 

(2) Diverse Application Scenarios 

a. Industrial Processing: Covers applications such as soldering, cutting, and marking, with high-precision control ranging from micro-solder joints (0.1 mm) to larger pads. 

b. Medical & Healthcare: Used in photon-based medical treatments such as myopia correction and skin beauty procedures, its wavelength closely matches the absorption characteristics of the materials involved. 

c. Optical Communication: Achieving precise signal modulation in fiber-optic transmission to support high-speed data communication. 

(3) Accelerating Technology Iteration Through Domestic Production 

Domestic manufacturers have achieved mass production of products spanning a power range from 25W to 500W by mastering core technologies such as quantum well technology, and have expanded into specialized wavelength bands like blue and green light, further strengthening their market competitiveness. 

2. Laser Wavelength 

Based on the wavelength range, efficiency, stability, and application direction outlined in Point 1, we can roughly determine the material and manufacturing process suitable for selecting the laser. Once the general laser type has been identified, further refinement of the laser’s wavelength is required to meet the specific output wavelength demands of the project. Commonly used laser wavelengths include 850 nm, 905 nm, 1064 nm, 1310 nm, 1550 nm, 1653 nm, 2000 nm, as well as tunable-wavelength lasers. To precisely verify the laser’s exact wavelength, we can use a spectroscopic analyzer, as shown in the figure below. 

3. Output Optical Power 

Output optical power refers to the energy of light radiation emitted by the laser per unit time, used to measure the intensity of the light source. Specifically, it indicates the range of optical power that the laser can produce during operation—since the driving current must reach a certain threshold to generate light, there is typically a minimum and maximum output power. It’s important to note the distinction between average optical power and peak optical power: 

Average optical power: Typically measured in watts (W), this represents the energy continuously output by the laser. 

Peak/Pulse Optical Power: Refers to the maximum power instantly reached by a laser pulse (measured in kilowatts, kW), commonly used for pulsed lasers. 

4. Bandwidth/Response Speed 

Generally refers to modulation bandwidth: This is the maximum transmission rate of a digital signal or the highest bandwidth of an analog signal, used to measure the signal-processing capability of optoelectronic devices. For analog signals, bandwidth is also known as frequency bandwidth, measured in Hertz (Hz). In contrast, for digital signals, bandwidth represents the amount of data that can be transmitted over a link within a given unit of time. The relationship between a laser's bandwidth and its response speed is similar to that of the photodetector we discussed earlier—response time (τr) remains a key indicator of how quickly the laser can react. Meanwhile, the 3dB bandwidth, as a frequency-domain metric, is closely linked to the response time in terms of the laser's speed of response. Roughly speaking, the relationship between the optical laser bandwidth BW and its response time Tr can be approximated by the following formula: 

Tr = 0.35 / BW. 

5. Line Width 

The wavelength accuracy of a tunable laser refers to the stability and precision of its output wavelength, typically measured in picometers (pm). Accuracy can vary significantly across different models: - **Standard tunable lasers** usually achieve a wavelength accuracy of around ±30 pm. For instance, one particular model delivers ±30 pm precision across the 1260–1680 nm range. - **High-precision tunable lasers**, on the other hand, can meet even stricter standards—some products boast accuracies as tight as ±20 pm. However, such detailed specifications often come from a single, less authoritative source. Wavelength accuracy is influenced by factors like filters, mechanical tuning mechanisms, and temperature control systems. To maintain high precision, advanced devices rely on sophisticated manufacturing techniques and robust closed-loop feedback systems. 

6. Side-mode suppression ratio (SMSR) 

The Side Mode Suppression Ratio (SMSR) is a critical metric for evaluating the performance of laser longitudinal modes, defined as the ratio of the main mode’s intensity to the maximum intensity of the side modes. This parameter plays a key role in fields such as optical communications, laser design, and wavelength-division multiplexing systems—where a higher SMSR value indicates greater single-mode stability in the laser. To measure the SMSR, a spectrum analyzer is used to determine the power difference between the dominant longitudinal mode and the most prominent side mode under full modulation conditions. For instance, consider a particular laser: if the main mode has a power of 1.03 dBm and the strongest side mode reaches -49.169 dBm, the laser’s Side Mode Suppression Ratio would be calculated as 1.03 dBm – (-49.169 dBm) = 47.203 dB. 

7. Noise Intensity 

Laser noise refers to the fluctuations in both frequency and intensity of the laser's output light, primarily manifesting as frequency noise (or phase noise) and intensity noise. These characteristics directly impact the performance of high-precision optical systems. 

8. Power Stability 

Laser stability refers to the steadiness of a fixed output optical power—the ability of the output light characteristics to remain stable over time. It is typically evaluated by assessing how well the laser recovers its original equilibrium state after repeated on-off cycles or exposure to external environmental disturbances, as well as by examining the long-term stability of the output light. Average optical power stability is primarily measured using a power meter: the meter’s detector is directly connected to one end of the optical fiber, allowing real-time monitoring of the output power. For peak/pulse optical power stability, the pulsed light signal is first mixed via beat frequency detection, and then the stability is calculated based on the amplitude fluctuations within the pulse waveform. 

9. Optical Isolation 

The optical isolation of a laser refers to the isolation capability of the isolator within the laser, specifically how effectively it suppresses the impact of back-reflected light on the laser's performance. At its core, this function prevents reflected light from disrupting the laser's operational stability, ensuring that the laser output signal travels unidirectionally. This critical role is enabled by an internal optical isolator based on the Faraday effect. Isolation, measured in decibels (dB), quantifies the ability to block back-reflected light—where a higher numerical value indicates better isolation performance—and ultimately helps maintain system stability by eliminating unwanted reflections. 

10. Polarization Extinction Ratio 

The Polarization Extinction Ratio (PER) of a laser is a key metric for evaluating the performance of laser polarization devices, representing the ratio of power between two orthogonal polarization components in polarized light, expressed in decibels (dB). National Standard GB/T 11297.3-2002 specifies a test method: place the crystal under test within an orthogonal polarizing system, rotate the sample, and measure the ratio of the maximum to the minimum transmitted light intensity. 

11. Tuning Step 

The tuning step of a tunable laser refers to the ability of a tunable laser to achieve continuous or discrete changes in its output wavelength by gradually adjusting the resonator parameters of the laser—such as refractive index, cavity length, driving current, temperature, and more. At the heart of this process is the ability to alter the resonant conditions, enabling the laser to emit light at different wavelengths or frequencies. This tuning capability allows the laser to sequentially output light at various wavelengths over time, making it particularly valuable for applications like wavelength-division multiplexing, as well as in spectral scanning and absorption line monitoring. 

12. Wavelength Accuracy 

The wavelength accuracy of a tunable laser refers to the stability and precision of its output wavelength, typically measured in picometers (pm). Accuracy can vary significantly across different models: - **Standard tunable lasers** usually achieve a wavelength accuracy of around ±30 pm. For instance, one particular model delivers ±30 pm precision across the 1260–1680 nm range. - **High-precision tunable lasers**, on the other hand, can meet even stricter standards—some products boast accuracies as tight as ±20 pm. However, such detailed specifications often come from a single, less authoritative source. Wavelength accuracy is influenced by factors like filters, mechanical tuning mechanisms, and temperature control systems. To maintain high precision, advanced devices rely on sophisticated manufacturing techniques and robust closed-loop feedback systems. 

13. Input Method: 

The directly modulated laser is similar to a photodetector, with common input options including SMA and BNC connectors. While both interfaces are widely used across various applications, the SMA connector is smaller and easier to integrate into products. However, the SMA connector has a shorter mating life compared to the BNC, though the BNC offers greater convenience for quick connections. That’s why most photodetectors used in laboratory research and experiments typically feature BNC inputs. Since Jibulight’s directly modulated lasers are primarily designed for system integration, they come standard with SMA inputs—but each model can be customized to meet specific customer requirements for either SMA or BNC inputs. 

14. Output Method 

Common light-output methods include FC output with fiber flanges fixed to the housing’s sheet metal, APC-coupled fiber lead outputs, or even free-space optical coupling. Depending on your specific needs, you can choose between free-space input or fiber-coupled input options. While fiber-flange input avoids the highly challenging task of precise optical alignment, it comes with limitations—such as a fixed beam spot size determined by the fiber—and lacks adjustability. Additionally, fiber transmission inherently involves some optical power loss and is significantly affected by temperature changes. On the other hand, free-space optical coupling eliminates the need for fibers as a transmission medium altogether, preventing power losses while offering flexibility to fine-tune both light power and beam spot size. The Electric Optical Alignment Micro-Manipulator, independently developed and manufactured by Jumu Guangyan, is designed to effortlessly address the challenges associated with achieving accurate beam spot alignment in various applications. If you’re interested in learning more about this innovative product or would like to explore purchasing options, please follow our WeChat official account: Jumu Guangdian Research Assistant, where you can easily access detailed product information and procurement resources. 

Summary: 

This article outlines the many critical parameters of lasers, as selecting and properly utilizing these parameters is essential for the laser's effective application. By gaining a deep understanding of these parameters and applying them wisely, you can better design and optimize optoelectronic lasers, ultimately enhancing the performance and stability of the entire optoelectronic system.