JPS6096545A - Optical fiber - Google Patents

Abstract

PURPOSE:To produce an optical fiber having little defects in the glass and capable of maintaning the characteristics stably for a long period, by using fluorine as a doping material for the core. CONSTITUTION:An optical fiber having high stability with time can be manufactured by using a quartz glass doped with GeO2 (or P2O5) and fluorine as the core material, and covering the circumference of the core 1 with a clad 2 made of a quartz glass having lower refractive index than the core material. Since the defects of the Si-O-Si bond is filled with the doped fluorine, the intrusion of exterior hydrogen (accordingly the formation of OH groups) is suppressed, and the increase in the loss of the optical fiber with time can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a source fiber that has few defects in the glass and maintains a long-term stable customization.

Optical fibers are usually formed of a core portion with a high refractive index for guiding light, and a cladding portion located outside the core portion and having a lower refractive index than the core portion. ... Germanium oxide (Ge08), phosphorus pentoxide CP105), aluminum oxide (AJ, O,), titanium oxide (T10s) are used as dopants to increase the refractive index in quartz glass.
) etc. are known and are commonly used as doping agents for the core part. As dopants that lower the refractive index, only boron oxide CB, 08) and fluorine CF) are known, and the range of selection is narrow. Due to its characteristics, these dopants that lower the refractive index have traditionally been doped only in the cladding.

Additives that improve the refractive index such as (1; eog I Pjj06) doped into the core have the property of forming bond defects in the glass. It reacts to form OH groups, increasing fiber loss.The reaction is carried out, for example, as shown in the following equation.

Here, dashed lines indicate bonding defects. Since the number of bond defects increases as the amount of dopant added increases, the absorption loss of OHi increases in proportion to the amount of dopant.

The first example of loss increase in GeO2-doped fiber is
As shown in the figure. The white circle shows a single-mode original fiber using only creo2 as the core dopant in a hydrogen gas atmosphere for 200 min.
'O When exposed for 14 hours, there is no loss enhancement, and the loss value is the wavelength λ where the second harmonic absorption of Ge -OH is present.
A value of −1.41 μm was used. When the amount of doping increases and the relative refractive index difference between the core and the cladding increases, the loss (loss) (Juit) increases rapidly.

An example of loss increase in P2O5 doped fiber is shown in the second example.
As shown in the figure. This is a fiber with an outer diameter of 40 μm and a fiber with an outer diameter of 125 μm.
A core wire made of 0 μm silicone resin and nylon with an outer diameter of 0.911I11 is heated to 200°C, and hydrogen scum generated from inside the coating and inside the fiber becomes a 1-IB (1) B bonding defect inside the glass. This is the increase in losses that occurred in response to the increase in losses. Core dopants are GeO□ and P2O.

The sample fiber has a core diameter of 50 μm and a relative refractive index difference of 1
% braided multimode fiber.

The loss values in FIG. 2 are shown at a wavelength λ=1.55 μm where the second harmonic absorption of P-OH exists.

The increase in loss increases in proportion to the molar concentration of P2O5.

As described above, when a dopant that increases the refractive index, such as GeOg or PstOs, is added to the core portion, bonding defects within the glass increase. Gem because bond defects easily react with hydrogen gas to form OH groups.

A fiber having a doped core of 2g05 or the like has the disadvantage that loss increases over time.

In order to eliminate the above-mentioned drawbacks, the present invention relates to an original fiber whose core portion is doped with fluorine to maintain stable characteristics over time. The present invention will be explained in detail below with reference to the drawings.

FIG. 8 shows an embodiment of the present invention.%lt,GeO,.

P, 0. A core portion containing any one of the following types and fluorine, and two portions having a lower refractive index than the core portion. Since the doped fluorine atoms have the effect of pinching defective portions of 5i-0-81 bonds, the original fiber of the present invention has stable characteristics over a long period of time without increasing loss over time.

The following unconventional experiment confirmed that fluorine atoms fill bond defects.

Five sample fibers with different amounts of fluorine doping were used in the experiment. Three of them are graded multi-shaded fibers with a core diameter of 50 μm, a fiber outer diameter of 125 μm, and a relative refractive index difference of 1%. The remaining two fibers are single mode fibers with a core diameter of 8 μm and a relative refractive index difference of 0.8%.

All five fibers are treated with 400 μm diameter Noriyo/rubber.

Table 1 f'-f7) Jti: 11a, e 1.50 -Multimode Fiffer 2 14.8 1.44 0.15 8 16.1 0.76 0.88 Ring-1---Cloudy--- -１翞胛－■搏－慟一------
−−−−−−9−−−Play−−−−−−−−■−■＾−
■-1--Single mode fiber 4 5・〇 - 55,0-0,80 Table 1 shows each element contained in the core of these cores. It was measured. 7 Aino < 1 and 4G small G magnification are not included.

The above five samples 7i1< were prepared as follows. The raw materials for glass are silicon tetrachloride (Si044), germanium tetrachloride (GeCl4), trichloride oxide (P
OCi/8) and silicon tetrafluoride (SiF4) are fed together with oxygen into a starting quartz glass tube heated by an oxyhydrogen burner. Then, glass particles produced by the oxidation reaction are adhered to the back inner wall *f/l to form a glass layer (several μm thick). The refractive index of the preform can be controlled by changing the composition and flow rate over time.
Move the burner along the axial direction of the quartz tube! By repeating the firming operation several dozen times, a glass layer with a refractive index distribution of 1 and 2 was formed. In particular, the fluorine dope 1λ was controlled by changing the flow rate of silicon tetrafluoride sludge.

Taratatsudono first? Then, after producing a core layer, the temperature of the burner was raised to collapse the hollow part (called collapse) to produce a base material for a C fiber. The matrix was melted in a carbon resistance furnace to a temperature of 2 mm to 2,200 mm and drawn into a thread having a thickness of 100 mm to 150 mm to produce the above-mentioned original fiber.

In order to investigate the bonding state of fluorine in the glass, we performed Raman spectroscopy on the sample fiber. The excitation light source includes 51
4. ．． An argon laser oscillating at 5 nm was used.

Figure 4 and Figure 8 and Figure 5 and 700 to L5 of the sample fiber.
00oa Raman spectrum is shown. As shown in Figure 4, by doping fluorine into the fiber, 98Qll
A new peak is observed at f1.

Furthermore, from FIG. 5, a peak is observed at 939 cm-'' even in the original fiber that does not contain Pg05.

Therefore, the Co(7)980cm-'' peak shows Raman scattering due to 5i-F bonds. That is, fluorine combines with silicon to form Si-F bonds.

Generally, when quartz glass is heated in a hydrogen gas atmosphere, the defective portion of the 5i-0 bond in the glass and the hydrogen gas diffused into the glass chemically react to form OH groups. These experimental reports include, for example, Charles M., HartWi.
The Journal of Cthem
icalphysics, VOI, 66, 41,
pp, 227-288.

(1977) and S, P, Failetori, M, Ro.
y paper (Mat, Res, Bull, Vol. 5
, Pp, 885-'190.

1970) etc. Therefore, the temperature of the sample fiber was raised in hydrogen gas, and the relationship between the charge of the generated OH groups and the amount of fluorine doped was determined, and the influence of fluorine on the defective portion was studied. The heating temperature and heating time were 200° C. and 4 hours, respectively, and the pressure was 1 atmosphere.・Figure 6 shows the Raman spectra measured with the fiber of sample 1 before and after heating. After heating, a new scattering peak is generated at 2,200tIrL-1. This peak is a scattering peak due to the vibrational mode of the 5i-H bond. Therefore, by heating, the above equation (1)
It can be seen that the reaction represented by formula (2) occurs and a 5i-11 bond is generated. Similar measurements were performed on the fibers of samples 2 through 5. As a result, it seems that there is a scattering peak like sample 1, but at 2.26 gcm-1
No significant changes were observed within the measurement accuracy.

FIG. 7 shows the relationship between loss enhancement at 1.55 μm measured using fibers of samples 1.2 and 8 and the amount of fluorine dope. As shown in FIG. 2, the increase in loss at 1.55 μm is proportional to the amount of P2O doped, so the vertical axis in FIG. 7 is P, 0. It was normalized by the amount of doping.

It is understood from FIG. 7 that increasing the amount of fluorine doped reduces the amount of OH group formation.

In FIG. 1, the amount of loss increase for a fluorine-doped single mode original fiber is shown by black circles. Fluoride amount is 0.8w
t%. The loss increase is approximately 1/1 compared to an undoped fiber. In order to reduce the loss increase to half of that without doping, the amount of fluorine doped should be 0.15.
Must be at least wt%.

The above results occur because the doped fluorine atoms act to fill Si-- bond defects. Therefore, in a fiber whose core portion is doped with fluorine, there are fewer bond defects, so there is less reaction with hydrogen gas diffused from the outside, and fewer OH groups are generated as a result of the reaction. In this way, a stable fiber is formed with no loss increase over time.

As explained above, since the optical fiber of the present invention has few 5i-00 coupling defects in the core portion that guides the original wave,
It has the advantage of not increasing loss over time and maintaining stable characteristics for a long period of time.

[Brief explanation of drawings]

Figure 1 shows Ge! A diagram showing the relationship between the amount of O, Dawg and the amount of increase in loss, Figure 2 is P, 0. A diagram showing the relationship between doping amount and loss increase amount, FIG. 8 is an example diagram of the original fiber of the present invention,
Figure 4 shows the Raman scattering intensity of a multimode fiber, Figure 5 shows the Raman scattering intensity of a single mode fiber, and Figure 6 shows before and after a heating test in a hydrogen gas atmosphere. FIG. 7 is a diagram showing the Raman scattering intensity, and is a diagram showing the increased charge loss for 0 degrees of fluorine. 1...Core part fully doped with fluorine, 2...Clad part. Patent Applicant Nippon Telegraph and Telephone Public Corporation Representative Patent Attorney Hideto Sugimura Akira Sugimura Patent Attorney Kou Sugimura Figure 1 (1%) Figure 2/'2θ5 JJ (No1 %) Figure 3 Figure 4 πυ F Near / 1500 x sheets (cm) Fig. 5 Fig. 6

Claims (1)

[Scope of Claims] L A core portion that guides light, has a higher refractive index than its surroundings, and is made of quartz glass, and is present around the core portion in close contact with the core portion, and is made of quartz What is claimed is: 1. A source fiber having a cladding portion made of glass, wherein the core portion contains fluorine as a type of doping material. ? An optical fiber according to claim 1, characterized in that the core portion has a fluorine doping content of 0.15 wt% or more.