JPH02293801A - Asymmetrical optical fiber coupler - Google Patents

Abstract

PURPOSE:To obtain the bittle-loss coupling degree of a multimode optical fiber and a single mode optical fiber by consisting the above coupler of the single mode optical fiber stretched until the single mode is attained and the single mode optical fiber welded and stretched to the central part of a stretched part and coupling the light of the multimode optical fiber to the single mode optical fiber. CONSTITUTION:The single mode optical fiber 13 is prestretched, by which the mode is converted to the single mode in the stretched part 15 even if any mode is excited in the multimode optical fiber 23 before the stretched part 13. The nearly 100% coupling is obtd. with a little loss by the welding and stretching of this multimode optical fiber 13 and the single mode optical fiber 11. The little loss connection of a semiconductor laser 21 and the single mode optical fiber 24 at a high connection allowance is executed in this way.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to the structure of an optical fiber coupler that converts light from a multimode optical fiber into a single mode optical fiber with high efficiency in communication systems, fiber sensors, etc. It is.

[Problems to be Solved by the Prior Art and the Invention] In optical transmission systems and optical fiber sensors, coupling from a semiconductor laser to an optical fiber is essential, and various methods are currently being proposed and put into practice.

Although it is possible to connect a semiconductor laser and a multimode optical fiber relatively easily and with low loss, in the case of a single mode optical fiber, the connection tolerance is extremely low at lμ even if various improvements are made to the lens. Strictness 0.

Further, although the connection loss from a single mode optical fiber to a multimode optical fiber is small, the connection loss from a multimode optical fiber to a single mode optical fiber is extremely large, exceeding lodB, and there has been no method to reduce this loss.

Under these circumstances, it has been desired to develop a new method for introducing light with low loss from a multimode optical fiber to a single mode optical fiber.

The present invention has been made in consideration of these circumstances, and its purpose is to realize an optical fiber coupler that achieves low-loss coupling between a multimode optical fiber and a single mode optical fiber. There is a particular thing.

[Means for Solving the Problems] The asymmetric optical fiber coupler of the present invention includes a multimode optical fiber that has been stretched until it becomes a single mode, and a fiber that is fused and stretched at the center of the stretched portion of the multimode optical fiber. It is characterized in that it consists of a single mode optical fiber, and the light of the multimode optical fiber is coupled to the single mode optical fiber.

[Function] By pre-stretching the multimode optical fiber, the asymmetric optical fiber coupler of the present invention converts any mode excited in the multimode optical fiber before the stretching section into a single mode at the stretching section. Convert. By fusing and stretching this multimode optical fiber and single mode optical fiber, nearly 100% coupling is obtained with low loss.

This realizes a low-loss, high-tolerance connection method between a semiconductor laser and a single-mode optical fiber. Furthermore, in optical fiber communication, it becomes possible to transmit and receive optical signals with low loss from a single mode optical fiber to a multimode optical fiber, and from a multimode optical fiber to a single mode optical fiber.

[Example〕 Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1(a) is a configuration diagram during production, and FIG. 1(b) is a configuration diagram after production.

In these figures, 11 is a single mode optical fiber;
2 is the core of a single mode optical fiber, 13 is a multimode optical fiber, l4 is the core of the multimode optical fiber, 15 is a stretched part, l6 is a fusion/stretched part, 17 is incident light, and l8 is output light. . The optical fiber parameters used are: relative refractive index Δ=0.6% and core diameter 30 μm for multimode optical fiber 13.
1 Clad diameter 150μ skin. Single mode optical fiber II
So, the relative refractive index is Δ-0.3%, the core diameter is 8μl1, and the cladding diameter is 125μ! It is.

To realize the present invention, first, as shown in FIG. 1(a), a multimode optical fiber 13 is stretched until the core diameter becomes a single mode condition. Here, the outer diameter of the stretched portion 15 was stretched to 30 μl. A semiconductor laser with a wavelength of 1.3 μm was introduced into the multimode optical fiber 13 during stretching, and the optical output was measured, and the fluctuation in the optical output was within 5%.

Next, the stretched multi-mode optical fiber 13 and single-mode optical fiber 11 are set in a fusion-stretching device, and as shown in FIG.
), the multimode optical fiber l3 is connected to the stretching part l5.
and single mode optical fiber ll are fused and drawn. Multimode optical fiber l3 to single mode optical fiber 1 during stretching
Measure the laser beam 18 of the wavelength 1.3μ blade coupled to K,
The manufactured optical fiber coupler is fixed to the substrate at the coupling length that provides the maximum coupling, and then stored in a case. The characteristics of the fabricated optical fiber coupler are a coupling degree of 92%, an excess loss of 0.5 dB,
Also, even if the ambient temperature changes from -10℃ to 80℃, the IOC
Even when subjected to an impact of 1%, the degree of bonding varied within 1%.

The low loss change from multimode to single mode can be explained as follows.

By stretching a multimode optical fiber, the higher-order modes are gradually converted to lower-order modes and finally to the fundamental mode. That is, although multiple modes are converted to a single mode, the propagation constant of light propagating through the stretching section 15 and the propagation constant of the original single mode optical fiber 11 are quite different. However, when optical fibers with asymmetric cores are fused and stretched, the core becomes even smaller and the propagation constant approaches the refractive index of the cladding and becomes the same value. As a result, nearly 100% coupling occurs, and if the core shapes do not change between the asymmetric cores, almost no optical coupling should occur.

A specific application example of this asymmetric fiber coupler is shown in FIG. Here, 2I is a semiconductor laser, 22 is a lens, 2
3 is a multimode optical fiber, 24' is a single mode optical fiber, and 25 is a fiber coupler. The length of the case of the fabricated asymmetric optical fiber coupler is 6 lv, and the length of the optical fiber at both ends is locx. The degree of coupling between the semiconductor laser 2l and the multimode optical fiber 23 is 1.5 dB.Therefore, including the loss of the asymmetric optical fiber coupler, the coupling to the single mode optical fiber 24 is 2.2 dB. Ta.

Next, FIG. 3 shows the change in coupling loss when the multimode optical fiber 23 is moved in a direction perpendicular to the central axis of the multimode optical fiber 23.

In the figure, (a) shows the characteristics when the semiconductor laser is directly coupled to a single mode optical fiber without going through an asymmetric optical fiber coupler, and (b) shows the characteristics when the semiconductor laser is connected through an asymmetric optical fiber coupler. In the conventional method (2L), the allowable movement m of the optical fiber with IdB deterioration is 1 μl, but in the method (b) of the present invention, the allowable movement amount of the optical fiber is significantly improved to 6 μs.

[Effects of the Invention] As explained hereafter, in the present invention, by pre-stretching a multimode optical fiber, no matter what mode is excited in the multimode optical fiber before the stretching section, it becomes a single one at the stretching section. - Furthermore, by fusion and stretching with a single mode optical fiber, nearly 100% coupling with low loss can be obtained. High connection methods can be achieved.

Furthermore, in optical fiber communication, it becomes possible to transmit and receive optical signals with low loss from a single mode optical fiber to a multimode optical fiber, and from a multimode optical fiber to a single mode optical fiber.

[Brief explanation of drawings]

FIG. 1(a) is a block diagram of the asymmetric optical fiber coupler of the present invention during manufacture, FIG. 1(b) is a block diagram of the asymmetric optical fiber coupler of the present invention after manufacture, and FIG. 2 is a block diagram of the asymmetric optical fiber coupler of the present invention A diagram showing an example in which a fiber coupler is applied to a connection between a semiconductor laser and an optical fiber, and FIG. 3 is a diagram showing a change in coupling loss. 1l...Single mode optical fiber, i2...Core of single mode optical fiber, 3...Multimode optical fiber, 4.Core of multimode optical fiber, 5...Stretching part, 16...Fusion Arrival/extension section, 7...
Incident light, 18... Outgoing light, l... Semiconductor laser,
22... Lens, 3... Multimode optical fiber, 4... Single mode optical fiber, 5... Optical fiber coupler of the present invention. Figure 2 Figure 3 Eye high Ω misalignment (μm)

Claims (1)

[Claims] Consisting of a multimode optical fiber stretched until it becomes a single mode, and a single mode optical fiber fused and stretched at the center of the stretched portion of the multimode optical fiber, the multimode optical fiber is An asymmetric optical fiber coupler, characterized in that it couples light from an optical fiber to the single mode optical fiber.