# Why is lower loss better?

**URL:** <https://forum.ofscn.net/t/why-is-lower-loss-better/2907>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [September 22, 2026, 11:49am UTC](https://forum.ofscn.net/t/why-is-lower-loss-better/2907 "2026-09-22T11:49:27Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\
**Post date:** [September 22, 2026, 11:49am UTC](https://forum.ofscn.net/t/why-is-lower-loss-better/2907/1 "2026-09-22T11:49:27Z")

</div>

Would excessive loss make the demodulator unable to “see” the sensor’s signal?

---

<div class="post-metadata">

**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [September 22, 2026, 11:53am UTC](https://forum.ofscn.net/t/why-is-lower-loss-better/2907/2 "2026-09-22T11:53:13Z")

</div>

\*\*Yes, excessive optical loss in a fiber optic link will directly cause the Fiber Bragg Grating (FBG) interrogator to fail in recognizing and capturing the reflected signal, leading to phenomena such as “peak loss” or a complete absence of signal. \*\*

From the perspective of optical physics principles and instrument signal detection mechanisms, this is primarily determined by the following physical factors:

* * *

### 1. Optical Power Budget and Interrogator Sensitivity Limit (Noise Floor)

In fiber Bragg grating sensing systems, the interrogator’s internal structure typically consists of a broadband light source (or swept-frequency laser source) and a high-sensitivity optoelectronic detection system (such as a photodiode (PD) or spectral detection array).

An interrogator has a fixed **Dynamic Range** and a \*\*Minimum Detectable Optical Power Sensitivity (Sensitivity Limit, P\_{\min}) \*\*:

- Transmitted light travels through the fiber link to the FBG sensor;
- The FBG sensor reflects a narrow-band light at its center wavelength based on its center wavelength and reflectivity (e.g., standard FBG reflectivity is about 70\%, low-reflectivity gratings are about 20\%, etc.);
- The reflected light travels back through the fiber link to the interrogator’s receiving end.

If the one-way loss in the fiber link is \alpha\_{\text{loss}}\ \text{dB}, the round-trip bidirectional loss is 2 \times \alpha\_{\text{loss}}\ \text{dB}. When the total attenuation is too high, causing the peak power of the reflected light returning to the receiving end to fall below the interrogator’s noise floor or minimum detection threshold, the photodetector will be unable to extract a valid signal from the background electrical noise.

* * *

### 2. Signal-to-Noise Ratio (SNR) Degradation and Peak-Finding Algorithm Failure

Fiber Bragg grating interrogators use specific digital signal processing algorithms (such as the centroid method, Gaussian fitting algorithm, etc.) to calculate the center wavelength of the reflection spectrum. The stable operation of these algorithms relies on sufficient **Signal-to-Noise Ratio (SNR)** and **Side-Mode Suppression Ratio (SMSR, typically requiring \ge 15\ \text{dB})**:

- **Excessive Loss Submerges Peak Shape** : When optical loss causes the amplitude of the reflection peak to approach the noise level, the SNR deteriorates severely, making it impossible for the interrogator to distinguish the real reflection peak from system white noise or shot noise.
- **Data Jitter and Lost Points** : Under critical loss conditions, the interrogator may frequently lose track of the peak, resulting in data stream interruptions, drastic jumps, or channel alarms.

* * *

### 3. Common Engineering Factors Causing Excessive Loss

In fiber optic cabling and sensor network construction, typical physical reasons for exceeding signal loss limits include:

- **Connector End-Face Contamination or Physical Damage** : Dust, scratches, or misalignment on the end-face of fiber optic connectors (e.g., FC/APC) can introduce insertion loss and backscatter ranging from several dB to tens of dB;
- **Fiber Macro- and Micro-bending Loss** : When the bending radius of the fiber is less than the critical bending radius, the total internal reflection condition is compromised, leading to significant increases in cladding leakage modes;
- **Poor Splicing Quality** : Mode mismatch, axial misalignment, or poor fusion splicing;
- **Accumulated Transmission Distance and Splice Points** : Intrinsic Rayleigh scattering over long-distance fiber transmission and the cumulative loss from multiple in-line passive devices.

* * *

### Official Product and Technical Parameter Reference

When constructing a fiber Bragg grating sensing network, it is advisable to select interrogator equipment with good optical power linearity and dynamic range, and to control the power attenuation budget for the entire optical path.

- [OFSCN® Fiber Bragg Grating Interrogator](https://www.ofscn.net/fbg-products/analyzer.html)
  - Wavelength Range: Default 1525 \sim 1565\ \text{nm} or 1528 \sim 1568\ \text{nm} (customizable)
  - Wavelength Resolution: Default 1\ \text{pm} or 0.1\ \text{pm}
  - Sampling Frequency: 1\ \text{Hz} \sim 100\ \text{Hz}

 ![OFSCN® Fiber Bragg Grating Interrogator](https://forum.ofscn.net/uploads/default/original/1X/8ecc1c112d2015cbc63afa6d42b87517befb2f87.jpeg)  
 ![OFSCN® Fiber Bragg Grating Interrogator](https://forum.ofscn.net/uploads/default/original/1X/248718a63e2aa4cf7db24ad7a4df5ace79c95a05.jpeg)