KR20000074483A - Doping Method of Samarium in Cladding of Fiber Doped Erbium in Core - Google Patents

Abstract

PURPOSE: A method of adding samarium(Sm) into clad of optical fiber with erbium(Er) doped core is provided to improve wide gain band width and gain flatness property demanding for wide width fiber adapted to wavelength division multiplexing(WDM) system of Er doped fiber amplifier(EDFA). CONSTITUTION: The method is characterized in that a clad(2) is doped with Sm-solution comprising 250ml of alcohol, 0.01M of Sm and 0.06M of Al, and a core(1) is doped with Er-solution comprising 250ml of alcohol and 0.1M of Er. The resulting average gain is 15.6dB, and wide band width is about 40nm, ranged from 1530-1570nm

Description

Doping Method of Samarium in Cladding of Fiber Doped Erbium in Core}

The present invention relates to a method of improving the wide gain bandwidth and gain planarization characteristics of an EDF by doping a samarium (Sm) in a clad region of an erbium doped fiber (EDF) in a core. .

In order for erbium-doped fiber (EDF) to be used in a wavelength division multiplexing system or in an optical fiber amplifier, gain characteristics must be uniform for each wavelength. As can be seen from the gain curve of the EDF of FIG. 1, the uniform gain region indicated by the straight line among the entire emission spectrum regions 1530 nm to 1560 nm is about 20 nm. Therefore, in the wavelength division multiplexing method, it is important to secure a larger number of channels by including an uneven gain band of about 10 nm in a uniform gain band in the vicinity of 1530 nm, and various methods have been proposed and related to this. The papers are as follows.

A good combination of samarium-doped and erbium-doped fibers is to obtain gain planarization from Liao (Shien-Kuei Liaw and Yung-Kuang Chen, IEEE PHOTONICS TECHNOLOGY LETTERS. VOL. 8. NO. 7, JULY 1996 Was announced. And Srivastava (AK Srivastava, JL Zyskind, JD Evankow, JW Sulhoff, Y. Sun and MA Mills IEEE PHOTONICS TECHNOLOGy LETTERS.VOL. 8, No. 12, DECEMBER 1997) similarly erbium-doped fiber and samarium This doped fiber was constructed in various combinations in series to obtain gain flattening.

In order to improve the method of flattening the gain and widening the bandwidth by a combination of a conventional samarium-doped optical fiber and an erbium-doped optical fiber, the samarium is applied to the clad region of the optical fiber so that the same effect can be obtained with one optical fiber. By using the absorption spectrum band of samarium, the core is designed to attenuate the peak area of 1530 nm of the erbium-doped optical fiber and to improve this area into a flattened area, thereby broadening gain flattening and bandwidth.

1 is a chart showing the gain spectrum according to the wavelength of a general EDF

2 is a graph showing the absorption spectral curve of samarium (Sm)

3 is a graph showing the absorption spectral curve of Erbium (Er)

4 (a) to (e) is a structure diagram of various optical fibers using samarium proposed in the present invention

5 is a diagram showing the normalized power distribution and the region to which samarium is added in the proposed structure of the pump light and the signal light.

Figure 6 (a) is a chart showing the ASE spectral curve of a typical EDF

(b) is a table showing the ASE spectral curve of Example 1

7 is a diagram showing the optical fiber structure and normalized HE11 mode power distribution of Example 2;

8 is a graph showing the gain characteristics of the optical fiber of Example 2

<Description of Symbols for Major Parts of Drawings>

1: Erbium-doped core 2: Samarium-doped clad

As shown in FIG. 1, which shows a gain characteristic of a typical erbium-doped optical fiber (EDF), the uniform gain bandwidth of the optical fiber is reduced due to the presence of the peak region around 1530 nm. The present invention uses the absorption spectrum of samarium shown in Fig. 2 to make the peak region near 1,530 nm into a uniform gain band. As can be seen in FIG. 2, the light emission peak region around 1,530 nm of erbium can be attenuated by using the absorption characteristic of samarium at around 1,530 nm. In addition, as shown in FIG. 3, samarium shows very little absorption compared to erbium in the vicinity of 980 nm, which is the wavelength of the pump light. Therefore, the use of samarium has little effect on the pump light used for the conventional erbium-doped optical fiber, and thus maintains the existing EDF characteristics. By reducing only the peak region, the gain bandwidth of the erbium-doped optical fiber can be improved. By adding samarium having the above characteristics to the cladding of the erbium-doped optical fiber, the above-mentioned characteristics can be obtained and various possible structures for such optical fibers are shown in FIGS. 4 (a) to (e). The power distribution of the normalized HE11 mode in the optical fiber having a wavelength of 980 nm in the simplest structure in the erbium-doped optical fiber having such a structure and the optical fiber of the 1,530 nm signal which is the wavelength of the peak region is shown in FIG. 5. As shown in FIG. 5, the power of the pump light having the wavelength of 980 nm indicated by the dotted line is mainly distributed in the core region, while the power of the signal having the wavelength of 1,530 nm indicated by the solid line is distributed more significantly in the cladding than the pump light. Therefore, the power of the signal around 1530 nm is absorbed by the cladding of the samarium doped region, and the peak portion is reduced, thereby improving its characteristics. The present invention obtains the above characteristics through a single optical fiber compared to the conventional combination of various combinations of the conventional erbium-doped optical fiber (EDF) and samarium-doped optical fiber (SDF). The complexities of optimization and the loss of connectivity in fiber-to-fiber can be easily improved. In addition, since the weak absorption band of samarium is evenly distributed over the emission band of erbium, the amplified spontaneous emission (ASE) level is also reduced, thereby improving noise characteristics.

Hereinafter, the present invention will be described by the following examples. However, these do not limit the technical scope of the present invention.

<Example 1>

Among the structures proposed in FIGS. 4 (a) to 4 (e), the structure (a) is manufactured by Modified Chemical Vapor Deposition (MCVD) and Solution Soaking. The base material was deposited 9 times at 1,980 ° C with cladding with SiCl4 150 SCCM (Standard Cubic Centimeter per Minute) in a 25 × 19 quartz tube, and then once with porous cladding with SiCl4 150 SCCM at 1,650 ° C, Dome was doped. In order to dope the erbium, the porous core of the quartz tube was deposited three times with GeCl4 150 SCCM and SiCl4 50 SCCM, doped with erbium 0.02M, and then dried, sintered, collapsed, and etched. When the core radius is 1.66 µm, the thickness of the samarium-doped cladding region is 1.92 µm, the refractive index of the core is 1.4717, the refractive index of the cladding is 1.457, and the difference in refractive index between the core and the cladding is expressed as the ratio of the refractive index of the core. (Δ) is a simple stepped refractive index structure that is about 0.01. Meanwhile, the doping method of erbium and samarium in the fabrication process of the optical fiber base material used a solution doping method in which aluminum was added. The reason for using aluminum is that a flatter gain spectrum can be obtained when aluminum is added together with erbium. Furthermore, aluminum plays a role in increasing the concentration of samarium, a rare earth metal, in the optical fiber (Glass Host). The solution composition is Erbium 0.02M, Aluminum 0.30M, Alcohol 250ml, and Cladding is Samarium 0.01M, Aluminum 0.06M, Alcohol 250ml. The reverse ASE spectral curve of the optical fiber manufactured by the above method is shown in FIG. Here, Gap A is the difference between the highest point of 1,530 nm and the lowest point around 1,540 nm, and Gap B is the difference between the highest point of 1,530 nm and the highest point near 1,550 nm. When doping samarium to the cladding as shown in Figure 6 (b), it can be seen that the samarium absorbs significant power. 6 (a) is a graph showing the ASE spectral curve of a typical erbium-doped optical fiber.

<Example 2>

The structure of (b) among the structures proposed in FIGS. 4 (a) to 4 (e) is manufactured by MCVD and Solution Soaking method as in Example 1. The base material is 25 × 19 quartz tube, and the base material manufacturing process is as follows. The cladding SiCl4 150 SCCM was deposited 8 times at 1,950 ° C, then the porous cladding to be doped with samarium at 1,650 ° C was deposited once, the cladding and the core were deposited once, and the porous cores for doping erbium were SiCl4 50 SCCM and GeCl4. Deposit twice with 150 SCCM. In the case of erbium, salineium and erbium were added to the cladding and core, respectively, by solution doping with 250 ml of alcohol, 0.1 M of erbium, 0.8 M of aluminum, and 250 ml of samarium. Doped. The base material was fabricated and inspected, and the cutoff wavelength was 900nm, core radius was 1.73㎛, the refractive index of the core was 1.4707, the refractive index of the cladding was 1.457, the distance between the samarium doped region and the core was 1.42㎛, and the samarium-doped cladding The thickness of the region was 1.32 mu m. FIG. 7 shows normalized power distribution, samarium doped region and erbium doped region in HE11 mode at 980 nm indicated by dotted lines and 1,530 nm indicated by solid lines. The gain characteristic is shown in FIG. The average gain is 15.5dB and the bandwidth is about 40nm from 1530nm to 1570nm, and the difference between the highest gain and the lowest gain in this section is less than 2dB, improving the gain characteristics at 1530nm.

According to the present invention, by adding samarium to the cladding of the optical fiber, a wide bandwidth and gain planarization can be realized as a single optical fiber, thereby enabling many channels in the wavelength division multiplexing (WDM). In addition, since the weak absorption band of samarium is evenly distributed over the light emission band of erbium, the ASE level is reduced, and unlike the conventional combination method, the above characteristics can be realized with only one optical fiber.

Claims (2)

A method of adding samarium to a clad region of an erbium-doped optical fiber in a core, wherein the cladding region of the erbium-doped optical fiber is doped with samarium to implement a wide bandwidth and gain planarization as a single optical fiber. The method of claim 1, wherein when doping samarium in the cladding region, 250 ml of alcohol, 0.01 M of samarium, and 0.06 M of aluminum are solution-doped, and samarium is applied to the clad region of the erbium-doped optical fiber. How to add.