# Fbg fiber Bragg grating packaging **URL:** \ **Category:** Official Tech Inquiry & Product Q&A\ **Tags:** fbg-technology, fbg-installation, bare-fbg, fbg-temp-sensor\ **Created:** [October 19, 2026, 8:23am UTC](https://forum.ofscn.net/t/fbg/3067 "2026-10-19T08:23:11Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![wang.ncepu](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/w/97f17d/32.png) [@wang.ncepu](https://forum.ofscn.net/u/wang.ncepu)\ **Post date:** [October 19, 2026, 8:23am UTC](https://forum.ofscn.net/t/fbg/3067/1 "2026-10-19T08:23:11Z")
| Product | [OFSCN® Polyimide Fiber Bragg Gratings / FBG Strings (Bare)](https://www.ofscn.net/fbg-products/polyimide-fbg.html) | | --- | --- | | Fiber/Coating | Polyimide recoated, **non-metallic, electrically insulating** , final diameter approximately **155 μm** | How is this fiber calibrated for temperature? Is it calibrated before leaving the factory? How can it be installed to better isolate stress? ---
**Author:** ![OFSCN\_PS\_Eng](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/839c29/32.png) [@OFSCN\_PS\_Eng](https://forum.ofscn.net/u/OFSCN_PS_Eng)\ **Post date:** [October 19, 2026, 8:23am UTC](https://forum.ofscn.net/t/fbg/3067/2 "2026-10-19T08:23:35Z")
Hello, wang.ncepu, I am happy to answer your two questions about [OFSCN® Polyimide Fiber Bragg Gratings / FBG Strings (Bare)](https://www.ofscn.net/fbg-products/polyimide-fbg.html). ## I. About Temperature Calibration First, we need to distinguish between two concepts: **Bare Fiber Bragg Grating (Bare FBG) is the “sensing element”**, while **a Fiber Bragg Grating temperature sensor is a “finished product that has been packaged and factory calibrated.”** For the polyimide bare grating you selected, the factory provides: - **Room temperature center wavelength** (room temperature wavelength deviation ±0.3nm) - Optical parameters such as wavelength range (default 1525 to 1565nm), grating length (default 10mm), and reflectivity. - Usable temperature range: -200°C to 300°C, usable strain range ≤10000με **It does not come with a “temperature-wavelength” calibration curve or formula for each individual unit.** The reason is that the final wavelength-temperature response of the bare grating largely depends on your subsequent **packaging method, bonding material, installation tension, and substrate structure**. Coefficients calibrated at the factory without installation status often drift after being installed on-site, so the significance of single-piece calibration at the factory is limited. Therefore, there are two practical approaches: 1. **Self-calibration** : After fixing the grating in its final installed state, use a constant temperature bath/high-temperature furnace to increase and decrease the temperature in steps, recording the center wavelength at each point. Finally, fit it to a first-order or second-order polynomial (unit: °C/pm). This is the conventional engineering practice for bare gratings. 2. **Directly select a factory-calibrated packaged temperature sensor** : If you do not wish to perform self-calibration, our finished temperature sensors are calibrated at the factory, such as the [OFSCN® 300°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-300.html). The **factory temperature calibration range is from room temperature to 300°C, and the default temperature-wavelength calibration formula is a second-order polynomial (°C/pm)**, which perfectly matches the upper temperature limit of your bare grating. ![OFSCN 300C FBG Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/890e8bb137088d916b6145a3bd3543febc968fd1.jpeg) ## II. How to Install for “Stress Isolation” Fiber Bragg gratings are **sensitive to both temperature and strain**. The core principle for temperature measurement is: **the grating section (default 10mm) must be in a free, unconstrained state, free from tensile forces at all times**. Specific recommendations: 1. **The installation point must be outside the grating section** : Use clamps or adhesive to fix the fiber on the fiber/sleeve on both sides of the grating section. **The grating section itself must absolutely not be bonded, pressed, or stretched taut**. The grating should retain slight slack after installation. 2. **Avoid applying adhesive to the grating section** : The shrinkage of the adhesive layer during curing will directly apply strain to the grating, which is the most common source of error. 3. **Use a loose-fitting structure** : Place the grating inside a capillary tube/loose tube with a slightly larger inner diameter, fix both ends to the outer jacket, allowing the grating to expand freely within the tube. This is the cleanest way to measure temperature. 4. **Avoid small bend radii and lateral pressure** : Bending and lateral pressure can introduce additional strain. It is recommended to maintain a large bend radius away from the grating section. 5. **Fix the lead-in wires, not the grating section** : Ensure the stress points are on the lead-in wires/protective sheath, preventing stress from transmitting to the grating section. 6. **When the medium has pressure, vibration, or impact, it is recommended to use a packaged sensor directly** : For example, the 300°C/500°C/800°C series sensors use **seamless steel pipe packaging** , where the internal FBG is in a free state, isolating strain structurally. If your site has a **high voltage/strong electromagnetic environment** (the advantage of polyimide coating is non-metallic and electrically insulating), you can also consider all-insulating packaging solutions like the [OFSCN Ceramic-encapsulated Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/fbgs-insulated.html). Another reminder: Regardless of whether it’s a bare grating or a sensor, you will need a fiber Bragg grating demodulator to read the wavelength. If you have your own equipment, please ensure its wavelength range covers 1525 to 1565nm and its resolution meets your temperature measurement accuracy requirements. * * * To provide you with a more suitable recommendation, I would like to reconfirm two key operating conditions: 1. What is your approximate **temperature measurement range**? (The upper limit of the bare grating you selected is 300°C; if it’s higher, other models will be needed.) 2. Is **electrical insulation** required on-site (e.g., for high-voltage equipment, transformers, power cable temperature measurement)? You can click the links above to view detailed technical parameters. If you have specific technical questions, please feel free to discuss them further. ---
**Author:** ![wang.ncepu](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/w/97f17d/32.png) [@wang.ncepu](https://forum.ofscn.net/u/wang.ncepu)\ **Post date:** [October 19, 2026, 8:32am UTC](https://forum.ofscn.net/t/fbg/3067/3 "2026-10-19T08:32:15Z")
**When you mention that the medium has pressure, vibration, or impact, do you recommend using encapsulated sensors directly? What kind of encapsulation is available? Is it non-metallic? Insulated? What is the minimum dimension after encapsulation? Can it be less than 1mm?** ---
**Author:** ![OFSCN\_PS\_Eng](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/839c29/32.png) [@OFSCN\_PS\_Eng](https://forum.ofscn.net/u/OFSCN_PS_Eng)\ **Post date:** [October 19, 2026, 8:32am UTC](https://forum.ofscn.net/t/fbg/3067/4 "2026-10-19T08:32:28Z")
Hello, wang.ncepu, this is a crucial question – **whether the encapsulation material is metallic or non-metallic directly determines if the sensor can be electrically insulated** , and the size is constrained by material and processing. I’ll address your three questions one by one. ## One: Our Encapsulation Types Fall into Three Categories | Encapsulation Type | Material Properties | Electrical Insulation | Typical Products | | --- | --- | --- | --- | | **Seamless Steel Tube Encapsulation** | All Metal | ❌ Not Insulated (Metal tube is conductive) | 100 / 300 / 500 / 800°C Series | | **Ceramic Encapsulation** | Non-metallic | ✅ Fully Insulated | Ceramic Encapsulated Temperature Sensors | | **Insulated (High-Voltage Resistant) Encapsulation** | Non-metallic Composite | ✅ Insulated (High-Voltage Resistant) | 150 Low-Voltage Insulated Type | This means that **“encapsulation” does not necessarily equal “insulation”** : although our most commonly used seamless steel tube encapsulation features a sealed all-metal structure with the internal grating in a free state (good strain isolation effect), the outer tube is steel and conductive itself. If insulation is required, you must choose **ceramic encapsulation** or **insulated encapsulation**. ## Two: How Small Can It Be After Encapsulation? (Key Point) Below are the minimum outer diameters for each model for your reference: | Product | Default Outer Diameter | Minimum Customizable Outer Diameter | Electrical Insulation | | --- | --- | --- | --- | | [OFSCN® 100°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-100.html) | 0.9 mm | **0.6 mm** | ❌ Metallic | | [OFSCN® 300°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-300.html) | 0.9 mm | **0.5 mm** | ❌ Metallic | | [OFSCN® 500°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-350.html) | 0.9 mm | **0.5 mm** | ❌ Metallic | | [OFSCN® 800°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-800.html) | ≤1.1 mm | **0.5 mm** | ❌ Metallic | | [OFSCN 150 Low-Voltage Insulated Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/fbgs-low-voltage.html) | **1.0 mm** | — | ✅ Insulated (High-Voltage Resistant) | | [OFSCN Ceramic-encapsulated Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/fbgs-insulated.html) | 2.0 / 3.0 mm | — | ✅ Fully Insulated | ![OFSCN 150 Low-Voltage Insulated FBG Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/1669dbe3ebe005d54efdd45b3ab089321cea71af.jpeg) ![OFSCN Ceramic-encapsulated FBG Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/f09006a45da58a909a27f5408ac16ee45a64c15a.jpeg) ## Three: Conclusion: Can It Be Less Than 1mm? We need to consider “size” and “insulation” separately: - **To be less than 1 mm — Yes, but only with metallic encapsulation** : The seamless steel tube series can achieve a minimum of **0.5 mm** (300/500/800°C models) or **0.6 mm** (100°C model), which is indeed less than 1 mm. The trade-off is that it is **not insulated**. - **To be insulated — Currently not possible \<1 mm** : The insulated type has a minimum of **1.0 mm** for the 150 model, and ceramic encapsulation starts at **2.0 mm**. - Therefore, there is a **technical trade-off** : currently, **“insulation + outer diameter \<1 mm” cannot be simultaneously satisfied**. If you require both insulation and a smaller size, this would be a deep customization project that can be discussed specifically. > Additional Note: The bare Fiber Bragg Grating (FBG) you initially selected has a diameter of approximately 155 μm (well under 1 mm), and its coating is non-metallic and electrically insulating. However, it lacks encapsulation protection, has weaker resistance to pressure/vibration/impact, and does not come with factory calibration. The key here is whether to compromise between the “slenderness of a bare grating” and the “reliability and calibration of an encapsulated sensor.” * * * To help me narrow down the options further, I’d like to confirm two operating conditions: 1. What is the **temperature range** at the sensor’s location? (This will determine whether to choose the 100/300/500/800°C series or the insulated 150°C model) 2. Is **electrical insulation mandatory** on-site (e.g., inside high-voltage equipment, transformers, or power cables)? Or is resistance to pressure/vibration/impact sufficient? (In that case, metallic encapsulation would suffice, and it can be made very thin.) You can click the links above to view detailed technical parameters. Please feel free to discuss any specific technical questions. Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) ---
**Author:** ![wang.ncepu](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/w/97f17d/32.png) [@wang.ncepu](https://forum.ofscn.net/u/wang.ncepu)\ **Post date:** [October 19, 2026, 8:40am UTC](https://forum.ofscn.net/t/fbg/3067/5 "2026-10-19T08:40:24Z")
| **Products** | **[OFSCN® Polyimide Fiber Bragg Gratings / FBG Strings (Bare)](https://www.ofscn.net/fbg-products/polyimide-fbg.html)** | | --- | --- | | Fiber/Coating | Polyimide recoated, **non-metallic, electrically insulated** , finished diameter approx **155 μm** | Is the fiber material silica? Why is electrical insulation needed in high-pressure interiors, and how does high voltage not affect the wavelength of light? ---
**Author:** ![OFSCN\_PS\_Eng](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/839c29/32.png) [@OFSCN\_PS\_Eng](https://forum.ofscn.net/u/OFSCN_PS_Eng)\ **Post date:** [October 19, 2026, 8:40am UTC](https://forum.ofscn.net/t/fbg/3067/6 "2026-10-19T08:40:51Z")
Hello, wang.ncepu. Both of these questions, one about “materials” and the other about “principles,” are worth clarifying. ## 1. Is the material silica? — Yes [OFSCN® Polyimide Fiber Bragg Gratings / FBG Strings (Bare)](https://www.ofscn.net/fbg-products/polyimide-fbg.html) uses the standard [OFSCN® 300℃ SM Polyimide Optical Fiber](https://www.ofscn.org/optical-fibers/polyimide-coated-sm-300.html), whose structure is roughly: | Layer | Material | Diameter | | --- | --- | --- | | Core | Doped silica glass (silica-based, doped in the core by default, pure silica core customization available) | 9 μm | | Cladding | Quartz glass (silica) | 125 μm | | Coating | Polyimide | 155 μm OD after coating | Therefore: **The optical fiber body (core + cladding) is indeed silica glass**, which is an excellent insulator by itself. The characteristic of being “non-metallic and electrically insulating” relies not only on the glass body but also on the outer **polyimide coating** (also a polymer non-metallic material, approx. 15 μm, bringing the 125 μm cladding to 155 μm). The fiber is drawn from a standard G.652D optical preform. ## 2. Why is “electrical insulation” needed in high-voltage situations? The first part of your statement is actually completely correct: **High voltage does not directly affect the center wavelength of the grating.** Light is transmitted through the optical fiber, and Fiber Bragg Gratings are passive optical devices, inherently immune to electromagnetic interference (EMI) — this is one of the core advantages of fiber optic sensing in high-voltage/strong electromagnetic environments. Therefore, the need for “insulation” **never protects the optical signal, but rather the high-voltage equipment itself and the surrounding medium**. The key is: once a **sensor with a metal enclosure** is placed in a high-voltage field, the problem lies with the conductor, which is “metal”: 1. **The metal body becomes a suspended conductor, distorting the electric field** : Seamless steel pipes and metal joints act as suspended electrodes in a strong electric field, causing the local electric field to become higher and non-uniform. 2. **Initiates corona and partial discharge (PD)**: Areas of electric field distortion are prone to corona discharge and partial discharge. Partial discharge continuously erodes surrounding insulating media (oil, paper, epoxy, gas), being the primary cause of aging in high-voltage insulation. 3. **Risk of tracking and flashover** : Exposed metal surfaces and interfaces between metal and insulators can form tracking paths along the surface, potentially leading to flashover and breakdown in extreme cases. 4. **Ground loops and induced currents** : Metal casings can introduce ground loops or induce circulating currents in alternating magnetic fields, causing additional heating, interference, or even damage to the sensor itself. 5. **Personnel and equipment safety** : Exposed metal sheaths, if energized, pose an electric shock risk upon contact. Conversely, when **non-metallic enclosures (polyimide-coated bare gratings, ceramic enclosures, insulated enclosures)** are placed in a high-voltage field, they act as dielectric materials, do not introduce conductors, do not distort the electric field, and do not cause corona or tracking — this is the real reason why “insulation is required inside high-voltage equipment.” It protects the **insulation system of the electrical equipment** , not the light beam. > In summary: \*\*Optical signals are not afraid of high voltage, but metal enclosures are. \*\* Your intuition (“high voltage doesn’t affect wavelength”) is correct, so the “insulation” requirement is not for the signal but for the equipment being measured. It is precisely because of this that the trade-offs in the table above are valid: for \<1 mm, only metal enclosures are possible (but not insulated); for insulation, the smallest currently available is 1.0 mm for the 150 type. * * * Following this line of thought, I’d like to confirm one operating condition with you to determine which category of need you fall into: Are you intending to **directly embed/bury the grating inside high-voltage electrical equipment** (such as transformers, GIS, cable bodies, generator stators), or are you **just attaching it to the surface of energized equipment to measure the external casing temperature**? These two scenarios have significantly different requirements for “insulation” and “dimensions” — you can click the links above to view detailed technical specifications. If you have specific technical questions, feel free to continue the discussion. ---
**Author:** ![wang.ncepu](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/w/97f17d/32.png) [@wang.ncepu](https://forum.ofscn.net/u/wang.ncepu)\ **Post date:** [October 19, 2026, 8:45am UTC](https://forum.ofscn.net/t/fbg/3067/7 "2026-10-19T08:45:00Z")
So, for this type of fiber optic model I mentioned, if it uses ceramic packaging, would it be completely inflexible? My understanding is that ceramic is like “porcelain” – very hard, cannot deform, and is brittle. Is that correct? ---
**Author:** ![OFSCN\_PS\_Eng](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/839c29/32.png) [@OFSCN\_PS\_Eng](https://forum.ofscn.net/u/OFSCN_PS_Eng)\ **Post date:** [October 19, 2026, 8:45am UTC](https://forum.ofscn.net/t/fbg/3067/8 "2026-10-19T08:45:34Z")
Hello wang.ncepu, your intuition is very natural— **the “hardness” of ceramics is indeed real, but the conclusion that it “cannot bend at all” needs to be examined part by part**. I will break down the structure below. ## I. First, let’s clarify a common misconception: “Ceramic encapsulation” does not cover the entire optical fiber The [OFSCN Ceramic-encapsulated Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/fbgs-insulated.html) does not involve making the entire optical fiber into a piece of ceramic rod. Instead: - **Only the “sensing head” section is encapsulated with a ceramic tube (a fine ceramic capillary tube)**, enclosing the grating area, with a default outer diameter of 2.0 / 3.0 mm. - **The section after the sensing head is a flexible pigtail (lead fiber)**, which can be bent, coiled, and routed like ordinary optical fiber. - The temperature range is -270℃ to 800℃, with a default FC/APC connector (ST, PC/APC available for customization). ![OFSCN Ceramic-encapsulated FBG Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/f09006a45da58a909a27f5408ac16ee45a64c15a.jpeg) Therefore, the accurate statement is: **Ceramic encapsulation makes the “sensing head section” rigid, not that the entire device cannot bend**. ## II. Are your assumptions about ceramics correct? – Half right, half misleading | Your Understanding | |----|----| | Rigid and unformable | ✅ Correct. Industrial ceramics (like alumina, zirconia) are **rigid materials with no plastic deformation zone**. Unlike copper/steel, they cannot be “bent and set”; they will fracture directly when bent to their limit. | | Brittle like “porcelain” | ⚠ Partially correct. The strength and hardness of industrial fine ceramics are far superior to everyday porcelain, but they have **low toughness and poor resistance to impact and point loads (localized squeezing)**. They are indeed at risk of cracking from impacts, drops, or localized squeezing. | | Cannot bend at all | ❌ Not entirely correct. See the next section. | ## III. Key point: The “grating area must not bend” during temperature measurement is not a limitation imposed by the ceramic itself There’s a physical fact you might have overlooked: **whether it’s a bare grating or a ceramic-encapsulated one, the grating area must remain free, straight, and unstressed during temperature measurement**. This is because fiber Bragg gratings are **sensitive to both temperature and strain simultaneously** : - Once the grating area is bent, the bending introduces additional strain, causing the central wavelength to shift towards the longer wavelength. - This shift mixes with the temperature drift, making it **impossible to separate temperature from strain** , thus distorting the temperature measurement accuracy. - Excessive bending also causes bending loss, weakening the reflection peak and reducing the signal-to-noise ratio. Therefore, for your 155 μm [OFSCN® Polyimide Fiber Bragg Gratings / FBG Strings (Bare)](https://www.ofscn.net/fbg-products/polyimide-fbg.html): **the fiber body is flexible and can be bent (within the typical minimum bending radius of optical fibers; loss increases as it approaches the limit), but the requirement that “the 10 mm grating area must be straight, relaxed, and unstressed” is unrelated to the encapsulation material; it’s determined by the principle of temperature measurement.** Ceramic encapsulation, on top of this, additionally ensures: **the sensing head section is completely non-bendable** (as it contains a rigid ceramic tube internally). The benefit is that the grating area is rigidly “locked” in a free state, isolated from external pressure and lateral squeezing. The trade-off is that the sensing head section must be routed as a straight tube. ## IV. So, if your site requires both “insulation” and “bendability,” what are the options? There is essentially a **geometric conflict** here, which can be balanced as follows: | Option | |----|----| | Ceramic encapsulation | ✅ Fully insulated | Non-bendable sensing head (pigtail is still bendable) | 2.0 / 3.0 mm | | [OFSCN 150 Low-Voltage Insulated Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/fbgs-low-voltage.html) | ✅ Insulated (withstand voltage) | Relatively more flexible | 1.0 mm | | Seamless steel pipe encapsulation (100/300/500/800℃ series) | ❌ Metallic conductivity | Rigid tube | 0.9 mm, minimum customizable 0.5 mm | | Polyimide bare grating + DIY insulated loose tube | ✅ (Dielectric entirely non-metallic) | Flexible | 155 μm | If you only need **the sensing head section to be straight while the rest of the routing is free** , ceramic encapsulation is actually perfectly acceptable. Most internal high-voltage temperature measurement points in engineering are installed in a “fixed at a point, short distance, stationary” manner, where a straight tube section is not an issue. ![OFSCN 150 Low-Voltage Insulated FBG Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/1669dbe3ebe005d54efdd45b3ab089321cea71af.jpeg) * * * To determine whether you should choose ceramic or the 150 insulated type, I’d like to confirm two operating conditions: 1. Is your **installation path** such that “the sensing head is fixed at one point, and the pigtail follows a free route,” or “the entire device needs to follow a movable/bending component” (e.g., wound around a coil, routed through a bending pipe)? 2. What is the specific **maximum temperature limit**? (Ceramic type can go up to 800℃, while the 150 insulated type has a limit of 150℃; this difference often directly determines the selection). You can click the links above to view detailed technical parameters. Please feel free to continue the discussion if you have specific technical questions. ---
**Author:** ![wang.ncepu](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/w/97f17d/32.png) [@wang.ncepu](https://forum.ofscn.net/u/wang.ncepu)\ **Post date:** [October 19, 2026, 8:51am UTC](https://forum.ofscn.net/t/fbg/3067/9 "2026-10-19T08:51:14Z")
FBG (Fiber Bragg Grating) sensors are affected by both strain and temperature simultaneously. I noticed that your company also offers FBG fiber optic strain sensors. How are your FBG strain fibers packaged, and how do you isolate them from temperature effects?