Photodiode Coupling Technology

Photodiode Fiber Coupling 

Our business specializes in optical fiber alignment, offering fiber-coupling and packaging solutions for virtually any photodiode in a TO-can package. We can align various types of optical fibers, including multimode (MM), single-mode (SM), and polarization-maintaining (PM) fibers, to ensure high coupling efficiency in photodiode modules.

Each photodiode module is thoroughly monitored at every production stage to ensure quality and performance. We prioritize cleanliness, ESD safety, and compliance with industry standards. Our designs are rigorously tested according to Telcordia GR-468-CORE specifications to ensure durability and reliability.

Coupling Challenge

Fiber coupling in photodiodes presents the inherent issue of back-reflection, which can affect or damage active components in the optical fiber line. A straight cleave or polish (Figure 1) typically causes a 4% (RL = 16 dB) reflectance at the fiber-air interface (yellow arrow in Figure 1), along with additional reflectance from the photodiode surface (green arrow in Figure 1). This back-reflection can be detrimental, particularly in high-accuracy sensing systems. 

Our RM Technology:

To mitigate back-reflection, we developed our proprietary Refractive-Index Matching (RM) technology (Figure 2). RM technology uses a specialized medium with a refractive index identical to that of the fiber core to fill the gap between the fiber and the photodiode, effectively eliminating Fresnel reflection at the fiber-air interface. Photodiode modules utilizing RM technology demonstrate superior responsivity (e.g., 1.1 A/W for PD4B-80-P10-2G-K-RM) and exhibit very low polarization-dependent loss (PDL). However, there is still a significant reflectance (RL = 20 to 25 dB) from the photodiode surface. Our RM technology is compatible with a wide variety of fiber types and photodetectors.

Our R50 Technology

To further reduce back-reflection, we employ our R50 technology, which involves cleaving or polishing the fiber facet at an angle (Figure 3). This angled approach prevents the reflected beam from re-entering the fiber, significantly improving the return loss to over 50 dB. However, angled polishing can cause polarization-dependent variations in transmittance, particularly with single-mode fibers, due to unequal transmission conditions for TE and TM polarizations. For single-mode fiber applications where polarization varies with mechanical stress or environmental factors, this can lead to random changes in the photodiode signal.

We offer a wide range of photodiodes, including InGaAs and Si photodiodes, designed for various fiber optics applications. Whether you need fiber-coupled solutions with single-mode or multimode fibers, or photodiodes with back-reflection or PDL mitigation, we can deliver high-performance, custom-tailored modules. Explore our datasheets (PDF) for more detailed specifications.

Contact us to discover how our photodiode solutions can enhance your next project in microwave photonics, fiber-optic sensors, or high-speed data transmission or scientific research.