Fiber Bragg Grating - FBG String - Concept Classification Application Principle Parameter Process Video Price
Table of Contents:
Ⅰ. What is a Fiber Bragg Grating (FBG)?
A Fiber Bragg Grating is an optical device composed of a series of closely spaced periodic variations. These gratings are inscribed on optical fibers using different methods, creating what we call Fiber Bragg Gratings or FBG Sensors. Among them, gratings with uniform spacing are referred to as Fiber Bragg Gratings (Fiber Bragg Grating), which are the most commonly used FBGs by DCYS's clients.
Ⅱ. Classification of FBG Fiber Bragg Gratings
1. Classification based on fabrication methods:
According to the different engraving methods of fiber bragg gratings, it can be divided into:
UV-written FBG Fiber Bragg Gratings using phase masks,
Direct-written FBG Fiber Bragg Gratings during fiber drawing in the process of fiber optic preforms,
FBG Fiber Bragg Gratings written using femtosecond laser phase masks,
FBG Fiber Bragg Gratings written using femtosecond laser point-by-point inscription , etc.
2. Classification based on the type of optical fiber used:
Fiber Bragg Gratings engraved by DCYS are used various specialty optical fibers offered by DCYS. According to the different kinds of optical fibers, it can be divided into Polyimide Fiber Bragg Gratings (FBGs), Polarization-Maintaining Fiber Bragg Gratings (FBGs) , and Multi-Core Fiber Bragg Gratings (FBGs) etc.
3. Classification based on the number of sensing points:
According to the number of FBGs on the fiber, it can be divided into:
Single-point Fiber Bragg Gratings (as shown in the above image),
Multi-point Fiber Bragg Gratings (FBG strings/arrays, fiber Bragg grating series),
Multi-core Fiber Bragg Gratings, etc.
Image below is an OFSCN® typical multi-point Fiber Bragg Grating (8-point Fiber Bragg Grating string/array).
Spectrum of OFSCN® typical multi-point Fiber Bragg Grating (8-point Fiber Bragg Grating string/array) is below:
4. Classification based on the periodicity of FBGs:
According to the characteristics of the grating pitch on the FBG, it can be divided into:
Uniform Fiber Bragg Gratings with regular spacing,
Long-period Fiber Bragg Gratings,
Phase-shifted Fiber Bragg Gratings,
Sampled Fiber Bragg Gratings,
Chirped Fiber Bragg Gratings, etc.
5. Classification based on reflectivity and transmissivity:
According to the different reflectivity of FBG produced by DCYS, it can be divided into:
Conventional Fiber Bragg Gratings (reflectivity ranging from 30% to 90%).
Weakly reflective Fiber Bragg Gratings (reflectivity less than 30%, even down to parts per million).
High-reflectivity Fiber Bragg Gratings (reflectivity greater than 90%). Transmissivity follows similar concepts.
6. Classification based on operating temperature range:
According to the different operating temperature range of FBG produced by DCYS, it can be divided into:
Standard Fiber Bragg Gratings (operating temperature range from -40°C to above 100°C).
High-temperature resistant Fiber Bragg Gratings (operating temperature greater than 300°C).
Low-temperature resistant Fiber Bragg Gratings (operating temperature lower than -100°C).
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7. Classification based on strain capacity of FBG:
According to the different maximum strain capacity of FBG produced by DCYS, it can be divided into:
Regular Fiber Bragg Gratings (strain capacity less than 10,000 με).
High-strain Fiber Bragg Gratings (strain capacity greater than 10,000 με, typical 30,000 με, and up to 50,000 με).
Fiber Bragg Gratings have many other classification methods, and DCYS can provide customizations for various types of Fiber Bragg Gratings.
Ⅲ. What can Fiber Bragg Grating (FBG) do?
In DCYS, Fiber Bragg Grating (FBG) is primarily used for sensing and measurement. We have numerous patents and rich experience in this field. FBG is sometimes utilized for communication filtering or in various power lasers. DCYS warmly welcomes collaboration in new applications for FBG.
Ⅳ. Relationship between Fiber Bragg Grating and Fiber Bragg Grating Sensor
Due to the inherent fragility of FBG and optical fibers, they cannot be directly used in various engineering projects. Therefore, FBG needs to be protected and functionally encapsulated. The encapsulated FBG, also known as a Fiber Bragg Grating Sensor, includes products like FBG temperature sensors, FBG strain sensors, andother customized FBG sensor. Using different encapsulation techniques, FBG can be manufactured into various types of sensors for optical fiber sensing. Encapsulated FBG sensors can be used for measuring temperature, strain, stress, vibration, displacement, shape, current, magnetic flux, and various other physical quantities. We won't go into further details about the various FBG sensors produced by DCYS.
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Ⅴ. Principle of Using Fiber Bragg Grating for Sensing
Based on the FBG sensing formula "λB = 2neffΛ," the principle of using FBG for optical fiber sensing is as follows:
Ⅵ. Common Fiber Bragg Grating Videos Produced by DCYS
Physical videos showing common Fiber Bragg Grating produced by DCYS:
Ⅶ. Center Wavelength of FBG (Fiber Bragg Grating)
By adjusting the grating pitch (also known as grating period, represented by the mathematical symbol Λ) in the FBG, DCYS can control the center wavelength (represented by the mathematical symbol λ) of the FBG. Theoretically, the center wavelength of FBG can be any value within the transmission band of single-mode or multi-mode optical fibers. However, in practical applications, due to the influence of the light source and optical path in the FBG demodulator, the center wavelength of FBG is often located in the C-band (1525nm to 1565nm) or C+L band (1510nm to 1590nm), and sometimes it may be in the 800nm band or around 1064nm. DCYS can also customize FBGs for other wavelength ranges if there are corresponding demodulation devices.
Ⅷ. Annealing of Fiber Bragg Grating
When FBGs produced by DCYS are used for temperature measurement, they undergo annealing at different temperature levels as required. After annealing, the center wavelength of the FBG becomes more stable at high temperatures when it is packaged into a Fiber Bragg Grating temperature sensor. The annealing process is an internal control technique during the production of Fiber Bragg Grating temperature sensor by the sensor manufacturer. DCYS will perform annealing tailored to your specific working conditions, so customers don't need to worry or communicate separately.
Ⅸ. What is a Chirped Fiber Bragg Grating, and does FBG need chirping?
For any FBG, a series of side peaks (also known as sidelobes) will accompany the main peak in its reflection spectrum. The energy intensity of these sidelobes is much smaller than that of the main peak. However, in some cases where it is impossible to set and adjust the FBG demodulator, the demodulator may fail to distinguish between the sidelobes and the main peak, leading to these sidelobes being incorrectly recognized as part of the signal. Consequently, these sidelobe signals become noise that cannot be separated in the demodulator.
To reduce the energy intensity of these sidelobes further, DCYS typically employs chirping on the FBG during production. Chirping involves modulating the refractive index amplitude of the FBG using specific functions. After chirping, the FBG is called a Chirped Fiber Bragg Grating, and its energy density in the reflection spectrum corresponds to significantly reduced reflectivity.
For some special FBGs, chirping might not be feasible in DCYS. However, our FBG demodulator can filter out these sidelobes through software settings within the system. In such cases, whether FBGs need to be chirped becomes less important.
Ⅹ. Grating Area Length (Measurement Point Length) of Fiber Bragg Grating (FBG), is it better to have a longer or shorter grating area length?
The grating area length of FBG, also known as the measurement point length, determines how close the FBG is to representing a physical point. However, whether a longer or shorter grating area length is better depends on the specific environment in which the FBG sensor is used. In DCYS, the common grating area lengths for FBG are 15 millimeters, 10 millimeters, 8 millimeters, 5 millimeters, 3 millimeters, and 1 millimeter.
Customers can define and adjust the grating area length of FBG customized by DCYS, but different lengths may lead to changes in other parameters. Therefore, it is necessary to discuss with us during the purchase process to strike a balance and make informed choices based on various parameters. DCYS will also provide targeted recommendations based on your specific application environment.
Ⅺ. Fiber Bragg Grating's 3dB Bandwidth (Full Width at Half Maximum or FWHM), is it better to have a narrower or wider 3dB bandwidth?
The 3dB bandwidth of FBG, also known as the Full Width at Half Maximum (FWHM), is the bandwidth occupied by the FBG when the energy density of its main peak decreases to half. In the field of FBG sensors, a smaller 3dB bandwidth is generally better (although it might not be as crucial as you might think) due to limitations in the FBG demodulator .
The 3dB bandwidth of FBG is influenced by other parameters. For FBGs produced by DCYS, the 3dB bandwidth is typically between 0.2nm to 2.0nm (varies with other parameters). Therefore, during the purchase process, it is essential to discuss with us to make balanced decisions based on different parameters. DCYS will provide targeted recommendations based on your specific application environment.
Ⅻ. Fiber Bragg Grating's Side Mode Suppression Ratio (Sidelobe Suppression Rate or SLSR), is it better to have a larger or smaller SLSR?
The Side Mode Suppression Ratio (SLSR) of FBG is a measure of the difference in energy density between the main peak and the sidelobes. In the field of FBG sensors, a larger SLSR is generally better (although it might not be as crucial as you might think). However, in general, an SLSR greater than 12 dB is sufficient for the FBG demodulator's requirements.
The SLSR of FBG is influenced by other parameters. Therefore, during the purchase process, it is necessary to discuss with us to make balanced decisions based on different parameters. DCYS will provide targeted recommendations based on your specific application environment.
XIII. Fiber Bragg Grating's Reflectivity, is it better to have higher or lower reflectivity?
The reflectivity of Fiber Bragg Grating refers to its ability to reflect incident light at the corresponding center wavelength after the superposition of all weak reflection surfaces of the FBG, usually expressed as a percentage.
The optimal reflectivity of FBG depends on the specific application environment and the FBG demodulator used. Therefore, it is not possible to make a general statement whether higher or lower reflectivity is better.
The reflectivity of FBG is influenced by other parameters. Therefore, during the purchase process, it is essential to discuss with us to make balanced decisions based on different parameters. DCYS will provide targeted recommendations based on your specific application environment.
In DCYS, the production of Fiber Bragg Gratings includes conventional FBGs (reflectivity 30% to 90%), weak reflectivity FBGs (reflectivity less than 30%, even reaching parts per million), and high reflectivity FBGs (reflectivity greater than 90%). You can choose according to your specific needs.
XIV. How to Purchase Fiber Bragg Gratings (Key Points for Buying Fiber Bragg Gratings)
DCYS produces a wide range of Fiber Bragg Gratings (FBG) with various applications. These FBGs can be encapsulated in FBG sensors for specific uses or used as bare FBG fibers. When making a purchase, consider the following points based on your requirements:
1. Identify the Physical Quantities to Measure with FBG
For FBGs, it is essential to determine the physical quantities to measure, mainly temperature (for temperature sensing) and strain (for measuring deformation, force, displacement, vibration, acceleration, etc.), as most other physical quantities can be derived from temperature and strain.
2. Determine the Maximum Measuring Range of FBG
For temperature sensing, confirm the temperature range in which the FBG will be used. For strain sensing, determine the maximum strain or deformation that the FBG needs to measure.
3. Specify the Number of Measurement Points for FBG
Decide whether you require single-point or multi-point temperature measurements. For multi-point temperature measurements, specify the number of FBGs needed on a single FBG fiber.
4. Define the Wavelength Range of FBG
The wavelength range of the FBG is mainly determined by the range that your FBG demodulator can test. Common wavelength ranges include C-band (1525nm to 1565nm), C+L band (1510nm to 1590nm), and 800nm band (800nm to 900nm). Other custom wavelength ranges can be discussed.
XV. Fiber Bragg Grating's Price
Once you provide the required parameters, such as the FBG length, physical quantity, measuring range, number of measurement points, wavelength range, and purchase quantity to DCYS, we will be able to calculate the price for you.
XVI. Models, Parameters, and Product Manuals of DCYS's Common FBGs
1. Product Manual for Conventional Fiber Bragg Gratings
Conventional FBGs are written using a UV photomask method, and the fiber used is Polyimide-coated fiber.
2. Product Manual for High-Temperature and Low-Temperature Resistant Fiber Bragg Gratings
High-temperature and low-temperature resistant FBGs are written using a UV photomask method, and the fiber used is Polyimide-coated fiber, which is resistant to high and low temperatures.
3. Product Manual for High-Temperature and Low-Temperature Resistant Femtosecond Fiber Bragg Gratings
High-temperature and low-temperature resistant FBG femtosecond fiber Bragg gratings are written using a femtosecond laser writing method, and the fiber used is Polyimide-coated fiber, which is resistant to high and low temperatures.
4. Product Manual for High-Strength Fiber Bragg Gratings