In recent years, optical fiber couplers have been invented on the basis of optical fibers. In this paper, a 2×2 optical fiber coupler is used as an example to explore the relationship between the phase constant of the important parameter mismatch and the coupling efficiency in the optical fiber coupler, and then it shows that the optical fiber The coupling characteristics of the coupler.
A fiber coupler, also known as a fiber directional coupler, is a passive device that combines multiple optical fibers or a light source and optical fibers to achieve directional transmission of optical power. The principle is to precisely butt the two end faces of the optical fiber, which can ensure that the light energy output by the transmitting fiber can be coupled to the receiving fiber to the greatest extent, and make it intervene in the optical link to minimize the impact on the system. Generally, fiber couplers are classified into single-mode fiber couplers and multi-mode fiber couplers. In terms of application, the single-mode fiber coupler is the most widely used, and the 2×2 fiber coupler is the representative of the single-mode fiber coupler.
In the fiber optic gyroscope, it is used to introduce the light signal from the light source into the interferometer, and transmit the model of the interferometer to the photodetector. The main requirements of fiber optic gyroscopes for fiber couplers are: close to 1:1 splitting ratio; lower loss; higher polarization performance. For polarization-maintaining fiber couplers, low polarization crosstalk is required; for single-mode fiber couplers, low polarization-dependent loss is required.
Compared with the coupler used for optical communication, its main feature is that the fiber optic gyroscope requires the fiber optic coupler to have better temperature stability and higher adaptability to mechanical conditions, especially under large-scale shock conditions, its cantilever The coupling area of the beam structure must guarantee high reliability.
As shown in the figure, the coupling of the fiber coupler is achieved by the evanescent field action between two sufficiently close optical fibers, and is usually fabricated by the fusion taper process. The light wave input from port 1 or 2 passes through the coupling area and is output from ports 3 and 4. Since ports 1 and 3 are two ends of a fiber, when input from port 1, the fiber from the coupling area to port 3 is called the straight-through arm, and the fiber from the coupling area to port 4 is called the coupling arm. The ratio of the output optical power between the straight arm and the coupling arm is called the splitting ratio.
