I. What is insertion Loss?
Insertion Loss refers to the attenuation of signal power caused by the optical characteristics of passive devices (such as reflection, absorption, scattering, etc.) when optical signals pass through them. It is usually expressed in decibels (dB), and the smaller the value, the lower the loss.
For instance, an isolator with an insertion loss of 0.2 dB means that after the optical signal passes through it, the power loss is approximately 4.5%. For a device with an insertion loss of 1 dB, the power loss can be as high as over 20%.
The lower the insertion loss, the smaller the energy loss of the optical signal during transmission, and the higher the transmission efficiency of the system.
Ii. What is Return Loss?
Return Loss refers to the ratio of the reflected light power to the incident light power when an optical signal is reflected at the interface of a passive device, and it is also expressed in decibels (dB). The larger the value, the smaller the reflection and the higher the return loss.
For instance, a device with a return loss of 50 dB means that the reflected light power is only 0.001% of the incident light power, which can almost be ignored.
The higher the return loss, the less reflection of the optical signal at the device interface, and the smaller the signal interference of the system.
Iii. Why are these two Indicators so important?
In optical fiber communication systems, optical signals often need to be used in series through multiple passive components. If the insertion loss of each device is relatively high, the signal will continuously attenuate during transmission, eventually leading to a weak signal at the receiving end and affecting the communication quality. Similarly, if the return loss is low, the reflected light will cause interference in the system, leading to signal distortion, increased noise, and even damage to the laser.
Therefore, low insertion loss and high return loss are the keys to ensuring the efficient and stable operation of optical communication systems.
Iv. Interpretation of Image Content: High-power Bias Maintaining Isolator
Combining the information in the picture, we can see the schematic diagram of a high-power bias maintaining isolator and its parameter annotations:
Insertion loss: usually less than 0.3 dB;
Return loss: greater than 60 dB;
Power capacity: Up to 10 kW;
Polarization preservation: Supports polarization-maintaining fiber (PMF);
Mechanical dimensions: Compact design for easy integration.
These data indicate that this isolator not only has extremely low insertion loss but also extremely high return loss, making it highly suitable for high-power and high-precision optical fiber communication and sensing systems.
V. How to Achieve Low Insertion Loss?
To achieve low insertion loss, the following points need to be met in the design and manufacturing process of passive components:
- High-quality optical materials
High transmittance and low absorption optical materials, such as high-purity quartz glass, are adopted to reduce the absorption and scattering of optical signals within the device.
- Precision optical coating
Coating an anti-reflection film (AR Coating) on the surface of the device can effectively reduce reflection loss and improve the transmittance of optical signals.
- High-precision alignment and packaging
Ensure precise alignment between optical fibers and optical components to reduce coupling losses; At the same time, low-stress packaging technology is adopted to avoid alignment deviation caused by thermal expansion and contraction.
Vi. How to Achieve High Return Loss?
To achieve high return loss, the following aspects need to be addressed:
- Bevel polishing and Angle coupling
Polishing the end face of optical fibers or the surface of optical components at a certain Angle (such as 8°) can effectively reduce vertical reflection and improve return loss.
- High matching refractive index bonding
Use refractive index matching adhesives between optical components to reduce interface reflection.
- Optimize the structural design of the device
If the Faraday rotator in the isolator is combined with the polarizer, it can effectively isolate the reverse light and improve the return loss.
Conclusion: Details determine success or failure
In optical fiber communication systems, passive components, though small, are crucial to the overall situation. Low insertion loss and high return loss not only reflect the performance of the device but also guarantee the stable operation of the entire system.