TWI402548B - Fiber system having multi mode fiber amplifier and single mode fiber and the wide band coupling method thereof - Google Patents

Description

Optical fiber system with multimode fiber amplifier and single mode fiber and wide frequency coupling method thereof

The present invention relates to a fiber optic system and a light coupling method thereof, and more particularly to a fiber optic system having a multimode fiber amplifier and a single mode fiber and a wide frequency coupling method thereof.

At present, in the coupling method of a multimode fiber to a single mode fiber, a lens combination is mainly used, as exemplified below. A hybrid optical fiber lens and a ball lens are disclosed in the Republic of China Patent Publication No. 00521169. A gradient refracting rod lens is disclosed in the Republic of China Patent Publication No. 200300215, and a multi-lens device is disclosed in the Republic of China Patent No. I230812. The above three conventional methods can be used to reduce the mismatch between the modal modes of the multimode fiber and the single mode fiber, thereby increasing the coupling efficiency. However, the disadvantage of these conventional methods is that more components are needed, which increases the difficulty of alignment and assembly of the components, and can only be used for coupling light at a single wavelength, and is not suitable for broadband multimode fiber amplifiers. Coupled light.

Therefore, it is necessary to provide an innovative and progressive fiber system with multimode fiber amplifiers and single mode fibers and a wide frequency coupling method to solve the above problems.

The present invention provides a broadband frequency coupling method for a fiber system having a multimode fiber amplifier and a single mode fiber, comprising the steps of: (a) providing a first single mode fiber and a second single mode fiber, the first single mode The optical fiber has a first Mode Field Diameter (MFD), and the second single mode fiber has a second mode field diameter; (b) providing a multimode fiber amplifier having a third mode field diameter, a third core, an input, and an output, the third core having a third core diameter, wherein the third core diameter of the multimode fiber amplifier is determined by a first mode field diameter of the first single mode fiber such that a third mode field diameter of the multimode fiber amplifier is The first mode fiber has a first mode field having the same diameter; (c) one end of the first single mode fiber is abutted to the input end of the multimode fiber amplifier, and one end of the second single mode fiber is adjacent to the An output of the multimode fiber amplifier; and (d) providing a pumping light to the multimode fiber amplifier such that the multimode fiber amplifier receives light from the first single mode fiber and amplifies the output to the second Single mode fiber.

The present invention further provides a fiber optic system having a multimode fiber amplifier and a single mode fiber, comprising a first single mode fiber, a second single mode fiber, and a multimode fiber amplifier. The first single mode fiber has a first mode field diameter. The second single mode fiber has a second mode field diameter. The multimode fiber amplifier has a third mode field diameter, a third core, an input end and an output end, the third core having a third core diameter, wherein the third fiber of the multimode fiber amplifier The core diameter is determined by the first mode field diameter of the first single mode fiber such that the third mode field diameter of the multimode fiber amplifier is the same as the first mode field diameter of the first single mode fiber, the first One end of the single mode fiber is immediately adjacent to the input of the multimode fiber amplifier, and one end of the second single mode fiber is adjacent to the output of the multimode fiber amplifier.

The invention adjusts the third core diameter of the multimode fiber amplifier so as to achieve modal matching with the first single mode fiber and the second single mode fiber. And improve the coupling efficiency. Thereby, the insertion loss (Insertion Loss) of the multimode fiber amplifier can be reduced, thereby increasing the gain of the multimode fiber amplifier. Furthermore, the method of the invention is simple, highly reproducible and low in cost.

Referring to Figure 1, there is shown a schematic diagram of a fiber optic system having a multimode fiber amplifier and a single mode fiber of the present invention. The fiber optic system 1 includes a first single mode fiber 11 , a second single mode fiber 12 , and a multimode fiber amplifier 13 . The first single mode fiber 11 has a first mode field diameter, a first core 111, a first end 112 and a second end 113. The first core 111 has a first core diameter. The second single mode fiber 12 has a second mode field diameter and a second core 121 having a second core diameter. The first core diameter and the second core diameter are physical diameters, which can be measured by measurement; the first mode field diameter and the second mode field diameter are calculated by calculation. In this embodiment, the diameter of the first core is the same as the diameter of the second core, which is 8 micrometers (μm); the diameter of the first mode field is the same as the diameter of the second mode field, and each is 10 micrometers (μm). ).

The multimode fiber amplifier 13 is preferably a multi-mode Cr ⁴⁺ -doped fiber (MMCDF) Optical Amplifier. The multimode fiber amplifier 13 has a third mode field diameter, a third core 131, an input 132, an output 133, and a side 134. The third core 131 has a third core diameter, wherein the third core diameter of the multimode fiber amplifier 13 is determined by the first mode field diameter of the first single mode fiber 11 to make the multimode The third mode field diameter of the fiber amplifier 13 is the same as the first mode field diameter of the first single mode fiber 11. That is, after determining the first mode field diameter of the first single mode fiber 11, the third mode field diameter of the multimode fiber amplifier 13 is the same as the first mode field diameter of the first single mode fiber 11, and is reused. The third mode field diameter of the multimode fiber amplifier 13 derives the third core diameter of the multimode fiber amplifier 13. In this embodiment, the third core diameter of the multimode fiber amplifier 13 is between 12 micrometers (μm) and 19 micrometers (μm), and the third mode field diameter is 10 micrometers (μm).

One end of the first single mode fiber 11 (the second end 113) abuts the input end 132 of the multimode fiber amplifier 13, and one end of the second single mode fiber 12 abuts the output of the multimode fiber amplifier 13 End 133. Preferably, one end of the first single mode fiber 11 (the second end 113) is adhered to the input end 132 of the multimode fiber amplifier 13, and one end of the second single mode fiber 12 is adhered to the multimode fiber. The output 133 of the amplifier 13. The multimode fiber amplifier 13 receives light from the first single mode fiber 11 and amplifies the output to the second single mode fiber 12.

Preferably, the fiber optic system 1 further includes a pumping optical input element for providing a pumping light to the multimode fiber amplifier 13 such that the multimode fiber amplifier 13 has an amplification function. The pump light can enter the multimode fiber amplifier 13 via the side 134 or the input 132 of the multimode fiber amplifier 13. In the present embodiment, the pumping light enters the multimode fiber amplifier 13 via the input 132 of the multimode fiber amplifier 13, the pumping light input component comprising a fiber coupler, a third The mode fiber 15 and a fourth single mode fiber 16. The fiber coupler 14 has an input end 141 and an output end 142. The third single mode fiber 15 and the fourth single mode fiber 16 are both connected to the input end 141 of the fiber coupler 14. The first single mode light The first end 112 of the fiber 11 is coupled to the output 142 of the fiber optic coupler 14. The third single mode fiber 15 is for transmitting a signal light, and the fourth single mode fiber 16 is for transmitting a pump light. The first single mode fiber 11 is used to transmit the coupled signal light and pump light to the multimode fiber amplifier 13. Under normal circumstances, the multimode fiber amplifier 13 absorbs the pump light and amplifies the signal light. The amplified signal light is output to the second single mode fiber 12.

Referring to FIG. 2, the coupling efficiency of the first single mode fiber having a first core diameter of 8 micrometers (μm) and the multimode fiber amplifier having different third core diameters at three different optical wavelengths in the present invention is shown. Figure. Where curve a represents light having a wavelength of 1310 nanometers (nm), curve b represents light having a wavelength of 1450 nanometers (nm), and curve c represents light having a wavelength of 1550 nanometers (nm). As can be seen from the figure, taking curve b as an example, if the wavelength of the incident light is 1450 nanometers (nm), the third fiber core of the multimode fiber amplifier has a maximum coupling angle of 14.5 micrometers (μm). The efficiency is 94.5%; when the third core diameter of the multimode fiber amplifier is 7.0 micrometers (μm), the coupling efficiency decreases to 59.3%.

Referring to FIG. 3a to FIG. 3c, there is shown a schematic diagram of light field distribution inside the optical fiber system in the case of the third core diameter of the multi-mode fiber amplifier of different sizes in the present invention, wherein the left and right sides of each figure are respectively the first The internal light field of the single mode fiber and the second single mode fiber, and the middle region is the internal light field of the multimode fiber amplifier. The third core of the multimode fiber amplifier of Figure 3a has a diameter of 7.0 micrometers (μm), and the third core of the multimode fiber amplifier of Fig. 3b has a diameter of 14.5 micrometers (μm). The multimode fiber amplifier of Fig. 3c The third core has a diameter of 28.0 micrometers (μm). Comparing the above three figures, it can be seen that when the third core of the multimode fiber amplifier has a diameter of 14.5 micrometers (μm) (Fig. 3b), The light field is more consistent with the internal light field of the first single mode fiber and the second single mode fiber, and is close to single-mode excitation.

Referring to FIG. 4, there is shown a coupling efficiency simulation of a first single mode fiber having a first core diameter of 8 micrometers (μm) and a multimode fiber amplifier having a different third core diameter at different wavelengths of light in the present invention. With the actual measurement chart. Wherein curve d represents a simulation curve of a third core diameter of the multimode fiber amplifier of 12 micrometers (μm), and curve e represents a simulation curve of a third core diameter of the multimode fiber amplifier of 19 micrometers (μm), black The dot (•) represents the actual measured value of the third core diameter of the multimode fiber amplifier of 15.5±3.4 micrometers (μm). As can be seen from the figure, the actual measured value is very close to the analog curve, and the third core of the multimode fiber amplifier has a relatively high coupling light at different wavelengths in the range of 15.5±3.4 micrometers (μm). effectiveness.

The invention further relates to a broadband frequency coupling method for a fiber optic system having a multimode fiber amplifier and a single mode fiber, comprising the following steps. First, a first single mode fiber 11 and a second single mode fiber 12 (FIG. 1) are provided. The first single mode fiber 11 has a first mode field diameter, a first core (Core) 111, and a first One end 112 and one second end 113. The first core 111 has a first core diameter. The second single mode fiber 12 has a second mode field diameter and a second core 121 having a second core diameter. In this embodiment, the diameter of the first core is the same as the diameter of the second core, which is 8 micrometers (μm); the diameter of the first mode field is the same as the diameter of the second mode field, and each is 10 micrometers (μm). ).

Next, a multimode fiber amplifier is provided. The multimode fiber amplifier 13 is preferably a multi-mode Cr ⁴⁺ -doped fiber (MMCDF) Optical Amplifier. The multimode fiber amplifier 13 has a third mode field diameter, a third core 131, an input 132, an output 133, and a side 134. The third core 131 has a third core diameter, wherein the third core diameter of the multimode fiber amplifier 13 is determined by the first mode field diameter of the first single mode fiber 11 to make the multimode The third mode field diameter of the fiber amplifier 13 is the same as the first mode field diameter of the first single mode fiber 11. That is, after determining the first mode field diameter of the first single mode fiber 11, since the third mode field diameter of the multimode fiber amplifier 13 is the same as the first mode field diameter of the first single mode fiber 11, The third core diameter of the multimode fiber amplifier 13 is derived using the third mode field diameter of the multimode fiber amplifier 13, and a multimode fiber amplifier 13 having the third core diameter is grown. In this embodiment, the third core diameter of the multimode fiber amplifier 13 is between 12 micrometers (μm) and 19 micrometers (μm), and the third mode field diameter is 10 micrometers (μm).

Next, one end of the first single mode fiber 11 (the second end 113) abuts the input end 132 of the multimode fiber amplifier 13, and one end of the second single mode fiber 12 abuts the multimode fiber amplifier Output 133 of 13. Preferably, one end of the first single mode fiber 11 (the second end 113) is adhered to the input end 132 of the multimode fiber amplifier 13, and one end of the second single mode fiber 12 is adhered to the multimode fiber. The output 133 of the amplifier 13.

Next, a pump light is supplied to the multimode fiber amplifier 13 such that the multimode fiber amplifier 13 receives light from the first single mode fiber 11 and amplifies the output to the second single mode fiber 12. The pump light can enter the multimode fiber via the side 134 of the multimode fiber amplifier 13 or the input terminal 132. Big 13 In the present embodiment, the pumping light enters the multimode fiber amplifier 13 via the input 132 of the multimode fiber amplifier 13, the pumping light input component comprising a fiber coupler, a third The mode fiber 15 and a fourth single mode fiber 16. The fiber coupler 14 has an input end 141 and an output end 142. The third single mode fiber 15 and the fourth single mode fiber 16 are both connected to the input end 141 of the fiber coupler 14. The first end 112 of the first single mode fiber 11 is coupled to the output 142 of the fiber coupler 14. The third single mode fiber 15 is for transmitting a signal light, and the fourth single mode fiber 16 is for transmitting a pump light. The first single mode fiber 11 is used to transmit the coupled signal light and pump light to the multimode fiber amplifier 13. Under normal circumstances, the multimode fiber amplifier 13 absorbs the pump light and amplifies the signal light. The amplified signal light is output to the second single mode fiber 12.

The present invention adjusts the third core diameter of the multimode fiber amplifier 13 to achieve modal matching with the first single mode fiber 11 and the second single mode fiber 12, thereby improving the coupling efficiency. Thereby, the insertion loss (Insertion Loss) of the multimode fiber amplifier 13 can be reduced, thereby increasing the gain of the multimode fiber amplifier 13. Furthermore, the method of the invention is simple, highly reproducible and low in cost.

The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the scope of the present invention. The scope of the invention should be as set forth in the appended claims.

1‧‧‧Fiber optic system

11‧‧‧First single mode fiber

12‧‧‧Second single mode fiber

13‧‧‧Multimode fiber amplifier

14‧‧‧Fiber coupler

15‧‧‧ Third single mode fiber

16‧‧‧fourth single mode fiber

111‧‧‧First core

112‧‧‧ first end

113‧‧‧ second end

121‧‧‧Second core

131‧‧‧ Third core

132‧‧‧ input

133‧‧‧output

134‧‧‧ side

141‧‧‧ input

142‧‧‧ Output

1 shows the light of the present invention having a multimode fiber amplifier and a single mode fiber Schematic diagram of a fiber system; FIG. 2 shows a first single mode fiber having a first core diameter of 8 micrometers (μm) and a multimode fiber amplifier having a different third core diameter at three different optical wavelengths in the present invention. FIG. 3a to FIG. 3c are schematic diagrams showing the light field distribution inside the optical fiber system in the case of the third core diameter of the multimode fiber amplifier of different sizes in the present invention; and FIG. 4 shows the first fiber in the present invention. The coupling efficiency simulation and actual measurement of the first single mode fiber with a core diameter of 8 micrometers (μm) and the multimode fiber amplifier with different third core diameters at different optical wavelengths.

1‧‧‧Fiber optic system

11‧‧‧First single mode fiber

12‧‧‧Second single mode fiber

13‧‧‧Multimode fiber amplifier

14‧‧‧Pump light input components

111‧‧‧First core

121‧‧‧Second core

131‧‧‧ Third core

132‧‧‧ input

133‧‧‧output

Claims (17)

A broadband frequency coupling method for a fiber system having a multimode fiber amplifier and a single mode fiber includes the steps of: (a) providing a first single mode fiber and a second single mode fiber, the first single mode fiber having a first a Mode Field Diameter (MFD) having a second mode field diameter; (b) providing a multimode fiber amplifier having a third mode field diameter, a third core, an input end, and an output end, the third core having a third core diameter, wherein the third core diameter of the multimode fiber amplifier is the first mode of the first single mode fiber The field diameter is determined such that the third mode field diameter of the multimode fiber amplifier is the same as the first mode field diameter of the first single mode fiber; (c) the one end of the first single mode fiber is abutted against the multimode An input end of the fiber amplifier, and one end of the second single mode fiber is abutted to an output of the multimode fiber amplifier; and (d) providing a pumping light to the multimode fiber amplifier, such that the multimode The fiber amplifier receives the light from the first single mode fiber and amplifies the output To the second single mode fiber. The method of claim 1, wherein the first single-mode fiber in the step (a) further has a first core having a first core diameter, the second single-mode fiber Further having a second core having a second core diameter, the first core diameter being the same as the diameter of the second core, and the first mode field diameter and the second mode field diameter the same. The method of claim 2, wherein the first core diameter and the second core diameter are both 8 micrometers (μm), and the first mode field diameter and the second mode field diameter are both 10 micrometers (μm) . The method of claim 1, wherein the third core diameter of the multimode fiber amplifier in the step (b) is between 12 micrometers (μm) and 19 micrometers (μm), and the third mode field diameter is It is 10 micrometers (μm). The method of claim 1, wherein the multimode fiber amplifier in step (b) is chromium doped. The method of claim 1, wherein one end of the first single-mode fiber in the step (c) is adhered to an input end of the multimode fiber amplifier, and one end of the second single-mode fiber is adhered to the multimode fiber amplifier The output. The method of claim 1, wherein the pump light in the step (d) enters the multimode fiber amplifier via an input of the multimode fiber amplifier. The method of claim 7, wherein the first single mode fiber has a first end and a second end, and the second end of the first single mode fiber abuts the input end of the multimode fiber amplifier, the step (d The method includes: providing a fiber coupler, a third single mode fiber, and a fourth single mode fiber, the fiber coupler having an input end and an output end, the third single mode fiber and the fourth single mode An optical fiber is connected to an input end of the fiber coupler, and a first end of the first single mode fiber is connected to an output end of the fiber coupler, wherein the third single mode fiber is used to transmit a signal light, the first The four single mode fiber is used to transmit a pump light, and the first single mode fiber is used to transmit the coupled signal light and the pump light. The method of claim 1, wherein the multimode fiber amplifier in the step (b) There is a further side, and in step (d) the pump light enters the multimode fiber amplifier via the side of the multimode fiber amplifier. An optical fiber system having a multimode fiber amplifier and a single mode fiber, comprising: a first single mode fiber having a first mode field diameter; a second single mode fiber having a second mode field diameter; and a multimode The fiber amplifier has a third mode field diameter, a third core, an input end and an output end, the third core having a third core diameter, wherein the third core diameter of the multimode fiber amplifier Determining a first mode field diameter of the first single mode fiber such that a third mode field diameter of the multimode fiber amplifier is the same as a first mode field diameter of the first single mode fiber, the first mode One end of the optical fiber is in close proximity to the input of the multimode fiber amplifier, and one end of the second single mode fiber is immediately adjacent to the output of the multimode fiber amplifier. The fiber optic system of claim 10, wherein the first single mode fiber further has a first core, the first core has a first core diameter, and the second single mode fiber has a second a core, the second core having a second core diameter, the first core having the same diameter as the second core, and the first mode field diameter being the same as the second mode field diameter. The optical fiber system of claim 11, wherein the first core diameter and the second core diameter are both 8 micrometers (μm), and the first mode field diameter and the second mode field diameter are both 10 micrometers (μm) ). The fiber optic system of claim 10, wherein the third core diameter of the multimode fiber amplifier is between 12 micrometers (μm) and 19 micrometers (μm), and the The three mode field diameter is 10 micrometers (μm). The fiber optic system of claim 10, wherein the multimode fiber amplifier is chromium doped. The optical fiber system of claim 10, wherein one end of the first single mode fiber is adhered to an input end of the multimode fiber amplifier, and one end of the second single mode fiber is adhered to an output end of the multimode fiber amplifier. The fiber optic system of claim 10, further comprising a fiber coupler, a third single mode fiber, and a fourth single mode fiber, the fiber coupler having an input end and an output end, the third single mode fiber And the fourth single mode fiber is connected to the input end of the fiber coupler, the first single mode fiber has a first end and a second end, and the second end of the first single mode fiber abuts the multimode An input end of the optical fiber amplifier, the first end of the first single mode fiber is connected to an output end of the fiber coupler, wherein the third single mode fiber is used for transmitting a signal light, and the fourth single mode fiber is used To transmit a pump light, the first single mode fiber is used to transmit the coupled signal light and pump light. The fiber optic system of claim 10, further comprising a pump optical input component, the multimode fiber amplifier further having a side, the pump optical input component inputting the pump light to the side via the side of the multimode fiber amplifier Mode fiber amplifier.