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  • Writer's pictureShimry Haviv

LED & Photodiode Based Spectrometry

Transitioning from Traditional Spectrometry to Cost-Effective LED & Photodiode Based Systems

Traditional Spectrometry

Spectrometry has seen remarkable advancements over the years, playing an important role in various industries, from environmental monitoring to biomedical research. It provides valuable insights into the composition and characteristics of materials. However, traditional spectrometric systems face significant challenges. They often rely on broad light sources that are expensive and large. There's also a constant trade-off between resolution and spectral range, making it hard to achieve optimal performance for diverse applications. Additionally, many applications only require specific parameters rather than a full spectrometer performance and range.

Traditional Spectrometer - Life Science Application
Traditional Spectrometer Example - Life Science Application

Cost-Effective Spectrometry

A promising approach to creating cost-effective spectrometric devices is using a LED & Photodiode Based Spectrometry, where a set of LEDs tailored to the desired wavelength region and one or more photodiodes (PDs) are used for detection. This method can even be useful for consumer applications requiring miniaturization and low-cost devices. Instead of detecting the spectral signature spatially over a CCD or CMOS array, this method uses the time domain, with LEDs operating in a known sequence. By leveraging the efficiency and versatility of LEDs combined with sensitive photodiodes, we can address many limitations of traditional spectrometry while significantly reducing costs.

This transition to LEDs & PDs systems has the potential to revolutionize the field by offering several key advantages:

Reduced Cost

Broadband light sources, like tungsten lamps, are expensive and require ongoing maintenance. LEDs, on the other hand, are significantly cheaper, have lower power consumption, and boast longer lifespans.

Targeted Wavelength Selection 

With LED technology, we have the flexibility to precisely select and control the wavelengths emitted, allowing for tailored spectral analysis to suit specific applications.

Compact Footprint

Simpler configurations utilizing LEDs and photodiodes enable the development of smaller, more portable spectrometers, ideal for field applications.

Modern Compact Spectrometric Device
Spectral concept illustration

LED & Photodiode Based Spectrometer for Startups

Recently, we started working with a startup with a promising technology that asked us to develop a PoC of their LEDs + PDs spectrometric device for material detection in blood. The project included lab experiments, simulating several concepts and performance evaluation, and designing the PoC of the chosen concept. In this case, the efficiency of the optical system in both the illumination path and the collection path was highly important to achieving sufficient SnR. Another important care that was taken in the design, is the prevention of background noise and stray light, since the desired signal is very low compared to the total output signal.   

Understanding the specific use case along with the system limitations is especially important when designing such a cost-effective device, where there is an inherent trade-off between many parameters and "the blanket is short".

Virtual Prototype of Spectrometric Device in LightTools
Virtual Prototype of Spectrometric Device in LightTools

To further discuss the general subject, here are some general design considerations that we learned throughout this project:

Design Considerations for LEDs & PDs Based Systems

While LEDs & PDs based systems offer exciting possibilities, careful consideration needs to be given to several design aspects:

Optimizing LED Selection

Choosing the right LEDs is crucial. They need to perfectly match the specific absorption bands of interest within the target material. Here are some factors to consider when selecting LEDs:

  • Center Wavelength: The center wavelength of the LED emission spectrum should closely match the absorption peak of the target analyte within the material. A good match ensures maximum light absorption by the analyte, leading to a stronger detection ability.

  • Spectral Bandwidth: The spectral bandwidth of the LED, or the range of wavelengths it emits, should be narrow. A narrow bandwidth minimizes interference from other wavelengths, improving measurement accuracy.

  • Output Power: The LED's output power should be sufficient to generate a strong signal after passing through the sample. However, overly high power can introduce noise into the system. Finding the optimal balance is key.

  • Temperature Dependency: Consider how LED output changes with temperature for consistent measurements.

Illustration of Different Absorption Spectrum of Different Materials
Illustration of Different Absorption Spectrum of Different Materials

Noise Analysis and Mitigation 

LEDs can introduce noise into the system due to factors like inherent fluctuations in light output and shot noise from the photodiode. Optimizing the signal-to-noise ratio becomes paramount for accurate measurements. Here are some techniques to mitigate noise:

  • Shielding: Proper shielding of the detector and electronics helps to minimize electromagnetic interference.

  • Signal Averaging: Averaging multiple signal measurements can help to reduce random noise.

  • Lock-in Amplifier: For situations with strong periodic noise, a lock-in amplifier can be used to synchronize the measurement with the modulation frequency of the LED, effectively filtering out noise at other frequencies.

Illustration of Electro-Optic Evaluation &Testing Setup
Illustration of Electro-Optic Evaluation &Testing Setup

Defining Accuracy, Precision, and Limit of Detection 

Determining the desired accuracy and precision for the device's performance and defining the target parameters of the optical performance is critical. The minimum detectable concentration of the target analyte is also crucial for various applications. The accuracy, precision, and limit of detection are influenced by several factors, including the signal-to-noise ratio, and the absorption cross-section of the target analyte. By carefully optimizing the design, the limit of detection of LEDs & PDs based systems can be improved for specific use cases.

Application-Specific Design: Unlocking the Full Potential

The true power of LEDs & PDs based systems lies in their customizability. By designing a system specifically for a well-defined use case, we can achieve significant advantages:

  • Targeted Wavelength Selection: We can choose LEDs that perfectly match the material's absorption profile, maximizing sensitivity for the target analyte.

  • Noise Reduction Techniques: Advanced photodiode circuitry and signal processing techniques can be employed to minimize noise and improve data quality.

  • Simplified Design: By focusing on the critical features needed for the specific application, we can reduce complexity and keep costs down.

This application-specific approach unlocks a new generation of affordable, user-friendly spectrometric systems. These advancements empower researchers, field personnel, and anyone requiring on-site spectral analysis with a powerful and accessible tool.

Illustration of Application-Specific Spectrometric Devices in Life Sciences Application
Illustration of Application-Specific Spectrometric Devices in Life Sciences Application

Optical Spectrometry Engineering

At Joya Team, we are at the forefront of developing customized spectrometers using cost-effective LED and photodiode-based systems. The applications through different markets such as food and drug detection, water, health, medical and many others, are limitless.

Our expertise in optical engineering, optical design, and photonics allows us to innovate in the field of spectrometry.

We specialize in non-imaging design, optical prototyping, and optical system engineering as parts of our services portfolio to create advanced, customized spectrometric solutions and also create tailored solutions for various consumer applications.

We invite companies looking to enhance their products with cutting-edge spectrometry to explore our services.

Contact us today to discuss how we can transform your ideas into reality.

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