Views: 322 Author: Krystal Publish Time: 2022-10-31 Origin: Site
1. Low-loss optical fiber connection
Two optical fibers often need to be connected to transmit light. For this purpose, the fiber ends must be very close together, the core must be perfectly aligned, and the fiber ends must be fixed to maintain alignment. The mechanical connector is equivalent to a stable optical fiber fixture, which can be temporarily or permanently connected to the optical fiber; Fiber jumpers with connectors are easily connected and disassembled through matching sleeves; Fusion is the most stable connection with the lowest loss, for example, the fusion loss of standard glass fiber can be as low as 0.02 dB.
Although losses are largely dependent on the type and quality of fiber connections, the type of fiber is also an important factor. Multimode FIBER: Low-LOSS connections require the receiving fiber to have an equal or larger core and numerical aperture than the output fiber. If the specifications of the two fibers are different, the loss and the direction of light propagation are related. Because the core of multimode fiber is large, it is generally not difficult to align. Single-mode fiber: The low-loss connection requires that the modes of the two fibers coincide, so the effective mode field and intensity profile should be as identical as possible. The core position should also be accurate, small mode field of the fiber is relatively difficult to correct. The fiber mode has a flat phase, so if there is no angular deviation, the phase is automatically matched. The larger the mode field, the greater the influence of Angle deviation. The loss is independent of the propagation direction.
When you connect any optical fiber, the air gap between the fiber faces should be as small as possible to avoid large Fresnel reflection losses. The air gap width should be much less than a quarter wavelength, and the Fresnel reflection at both ends is cancelled by destructive interference. Of COURSE, WIDER AIR GAPS (INTEGER MULTIPLES OF HALF WAVELENGTH) CAN BE ELIMINATED AS LONG AS THE BEAM DIVERGENCE Angle IS NEGLIGIBLE, BUT STABILITY IS MORE DIFFICULT AT LONG DISTANCES, AND THE TRANSMITTANCE WILL BE WAVELENGTH DEPENDENT. In addition, refractive index matching gels can be used to reduce reflection loss when mechanical connectors are used.
2. Calculation of coupling efficiency of single-mode fiber patch cord
When coupling a free-space beam to a single-mode fiber, the following conditions are required to achieve the highest coupling efficiency:
Gaussian intensity profile
Normal incidence from the fiber end face
The waist is located at the end face of the fiber
The center of the waist is aligned with the core
The beam waist diameter is equal to the fiber mode field diameter
The larger the optical fiber mode field is, the smaller the effect of lateral deviation is, but the greater the effect of Angle deviation is.
3. Preparation of fiber end face
After peeling off the coating layer, the optical fiber can be cut into clean bare optical fiber end faces. The coating is usually removed mechanically, but some use solution. Simple cutting tools include ceramic and ruby blades. Advanced cutting equipment can precisely clamp the fiber, apply adjustable tension or torsion, can be cut flat or diagonal, can cut ordinary fiber can also cut photonic crystal fiber and capillary
If high quality cutting is required, the end face needs to be examined using a microscope. If the conditions are not met, the end face must be cut again. This is especially important for special fiber materials, diameters and types.
Fiber faces sometimes need polishing, such as applications that require very flat or tilted ends. The fiber face can also be coated with a variety of dielectric films to improve performance, such as anti-reflection film or high reflective film.
4 Introduction to optical fiber fusion
Fusion is the most stable way to connect optical fibers with the lowest loss. In addition to fiber fusing machines, users also need a variety of other equipment for stripping, cutting, cleaning, recoating and testing. Main steps of fiber fusion:
Remove the optical fiber coating.
Cut and clean the ends of optical fibers.
Under the microscope, precisely align the ends of the fiber to be fused, leaving only a small gap; Sometimes light sources and power meters may be used to monitor light flux.
Heat and push the fiber to fuse.
Check and verify weld quality.
Use heat shrinkable tubing to protect fusion points.