JP4553618B2 - Optical fiber - Google Patents

Description

  The present invention relates to an optical fiber, and more specifically, by designing the refractive index, structure, and material of a tellurite fiber, light having a zero dispersion wavelength in an optical communication wavelength band of 1.4 to 1.7 μm. Related to fiber.

  In recent years, with the explosive increase in communication demand due to the rapid spread of the Internet and the demand for cost reduction of optical communication systems, signal light of multiple different wavelengths is multiplexed and transmitted on one optical fiber. Wavelength division multiplexing (WDM) transmission systems have been developed and are becoming increasingly popular. Development of devices such as a wavelength conversion element, a high-speed switch, a supercontinuum light source, and the like is eagerly desired in order to increase the scale of a WDM transmission network with good cost performance and to make it flexible and highly functional.

  As a method for realizing such a device, a nonlinear optical device using a nonlinear optical effect of an optical fiber has been actively studied. In a conventional quartz fiber, in order to realize high nonlinearity, a high refractive index difference of 2% or more is set by adding germanium to the core and adding fluorine to the clad. In order to make the nonlinear effect appear efficiently in the optical communication wavelength band, the zero dispersion wavelength must be in the 1.4 to 1.7 μm band so as to satisfy the phase matching condition. However, in the case of quartz fiber, the zero dispersion wavelength due to material dispersion is 1.3 μm, and it is difficult to shift the dispersion greatly by additives, so the zero dispersion is shifted to 1.5 μm by various refractive index profiles. (For example, refer nonpatent literature 1).

  In addition, in most conventional nonlinear optical devices using fibers mainly composed of quartz, the fiber length is several hundreds of meters or more in order to ensure the interaction length necessary for the nonlinear optical effect. Therefore, it is desired to realize a highly efficient and compact nonlinear device using an optical material having high nonlinearity.

On the other hand, fibers using tellurite glass have been applied to Er ³⁺ doped fiber amplifiers and Raman amplifiers so far and have achieved wideband amplification (see Non-Patent Documents 2 and 3). Tellurite glass has a non-linear optical effect that is 10 times greater than that of quartz glass, and at the same time realizes a low-loss fiber of 20 dB / km when applied to a Raman amplifier. Therefore, if the tellurite fiber can be applied as a nonlinear device, an unprecedented compact and highly efficient device can be expected.

Shojiro Kawakami, Kazuo Shiraishi, Shoji Ohashi, “Optical Fiber and Fiber Type Device”, Baifukan, p. 97 A.Mori, et al., “1.5μm Broadband Amplification by Tellurite-Based EDFAs”, PD1, OFC1997 A. Mori, et al., “Ultra-wideband tellurite-Based Raman fiber amplifier”, Electronics Letter vol.37, No.24, pp.1442-1443, 2001 Takayoshi Ohkoshi, “Optical Fiber”, Ohmsha, p. 214 Gorachand Ghosh, “Sellmeier Coefficients and Chromatic Dispersiond for Some Tellurite Glasses”, J. Am. Soc., 78 (10) 2828-30, 1995

  In order to make a nonlinear effect appear efficiently in an optical communication wavelength band in a nonlinear optical device, the zero-dispersion wavelength must be in the 1.4 to 1.7 μm band so as to satisfy the phase matching condition. In the case of the tellurite fiber, the material dispersion has a large negative dispersion in the 1.4 to 1.7 μm band, and the zero dispersion wavelength is located on the long wavelength side exceeding 2 μm.

  As long as a uniform core is used in the conventional quartz fiber, the zero dispersion wavelength is shifted from the material dispersion of 1.3 μm to the longer wavelength side by the waveguide dispersion. On the other hand, by using a W-type refractive index profile, the zero dispersion wavelength can be shifted from the material dispersion of 1.3 μm to the short wavelength side (for example, see Non-Patent Document 4). The 1.3 to 1.7 μm wavelength band is generally used in optical communication systems because of its low light transmission loss. The W-type refractive index profile has been studied as a structure having low dispersion and flat dispersion characteristics in this wavelength band.

  However, there is a problem that the zero-dispersion wavelength cannot be shifted to the short wavelength side only by applying the W-type refractive index profile applied to the silica fiber to the tellurite fiber.

  The present invention has been made in view of such problems. The object of the present invention is to shift the zero-dispersion wavelength to a communication wavelength band of 1.4 to 1.7 μm and use tellurite glass. The object is to provide a low-loss and high-efficiency optical fiber.

The present invention, in order to achieve the above object, the invention according to claim 1, an optical fiber having a core of tellurite glass ing, and a cladding wherein the core is inserted into the The clad has a first clad in which the core is inserted, and a second clad having a refractive index higher than the refractive index of the first clad, and the first clad is inserted , tellurite glass _has a composition consisting of _{TeO 2 -LO-M 2 O-} Q 2 O 3, the glass of the first _{cladding, B 2 O 3 -LO-M} 2 O-Q 2 O 3 -P ₂ O ₅ having a composition consisting -GeO _2, glass of the second cladding _has a composition consisting of _{TeO 2 -LO-M 2 O-} Q 2 O 3 -P 2 O 5 -GeO 2, wherein L is at least one of Zn and Ba, and M is i, Na, and the K, Rb, at least one or more of the Cs, Q is a B, Bi, La, Al, at least one or more of Lu, the zero dispersion wavelength 1.4~1.7μm band The relative refractive index difference between the core and the first cladding and the relative refractive index between the first cladding and the second cladding are set so that

The invention of claim 2 is an optical fiber having a core of tellurite glass ing, and a cladding wherein the core is inserted into the cladding, the relative refractive index difference between the core 10% The first clad in which the core is inserted has a refractive index higher than the refractive index of the first clad, and the relative refractive index difference between the first clad and the first clad is 5% or more, The core tellurite glass has a composition made of TeO ₂ -LO-M ₂ O-Q ₂ O ₃ , and the first clad glass has the following composition: B ₂ O ₃ —LO—M ₂ O—Q ₂ O ₃ —P ₂ O ₅ —GeO ₂ has a composition, and the second cladding glass is made of TeO ₂ —LO—M ₂ O—Q ₂ O. ₃ -P ₂ O ₅ having a composition consisting -GeO _2, where, L is n is at least one of Ba, M is at least one of Li, Na, K, Rb, and Cs, and Q is at least one of B, Bi, La, Al, and Lu. characterized in that there.

According to a third aspect of the present invention, in the tellurite glass according to the first or second aspect , Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Pm ³⁺ , Sm ³⁺ , Eu ³⁺ , Tb ³⁺ , Dy ³⁺ , It is characterized in that at least one of Ho ³⁺ , Er ³⁺ , Tm ³⁺ and Yb ³⁺ is added.

  As described above, according to the present invention, a tellurite fiber having a nonlinear optical effect that is 10 times or more larger than that of quartz glass is used to reduce the optical communication wavelength band from 1.4 to 1.7 μm. Since the dispersion wavelength can be shifted, it is possible to provide an optical fiber which is a compact and highly efficient nonlinear device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The glass mainly composed of TeO ₂ has a refractive index n _D of about 2, and at the same time, the material wavelength dispersion has a large negative dispersion in the 1.2 to 1.7 μm band, and the zero dispersion wavelength exceeds 2 μm. Located on the long wavelength side (see, for example, Non-Patent Document 5). Therefore, if a fiber having a step index type core / cladding refractive index profile is produced using tellurite glass, it cannot be greatly changed from the characteristics of material wavelength dispersion.

  The first embodiment according to the present invention controls the dispersion value of the tellurite fiber by appropriately selecting the composition of the tellurite glass. The tellurite fiber has a refractive index higher than the refractive index of the first cladding having a relative refractive index difference of 10% or more with respect to the core, and a relative refractive index difference with the first cladding of 5% or higher. A W-type refractive index profile consisting of the second clad. The relative refractive index difference between the core and the clad of an optical fiber that is generally used is 4% or less. Therefore, even if a W-type refractive index profile is configured, a sufficient dispersion shift cannot be obtained.

  FIG. 1 shows a refractive index profile of an optical fiber according to the first embodiment of the present invention. This is a W-type refractive index profile in which the refractive index nD of the core 11 is 2.10, the refractive index nD of the first cladding 12 is 1.47, and the refractive index nD of the second cladding 13 is 1.785. The relative refractive index difference Δn = 30% between the core and the first cladding, and the relative refractive index difference Δn = 15% between the core and the second cladding. FIG. 2 shows the calculation result of the zero dispersion wavelength of the optical fiber according to the first embodiment. When the core radius R = 0.56 μm, zero dispersion is realized in the 1.55 μm band.

In the second embodiment according to the present invention, by appropriately selecting the composition of tellurite glass, a fiber that is sufficiently thermally stable with respect to fiber processing, has a high nonlinear constant, and has a low loss is manufactured. . The tellurite glass has a composition composed of TeO ₂ —LO—M ₂ O—Q ₂ O ₃ , where L is at least one of Zn and Ba, and M is Li, Na, K, At least one of Rb and Cs, and Q is at least one of B, Bi, La, Al, and Lu. The composition ratio is
40 <TeO ₂ <90 (mol%)
5 <LO <30 (mol%)
3 <M ₂ O <40 (mol%)
0 <Q ₂ O ₃ <20 (mol%)
It is desirable to be in the range.

In the third embodiment of the present invention, the core glass has the composition of the second embodiment, and the clad glass has a composition made of R-LO-M ₂ O—Q ₂ O ₃ . Specifically, in the first cladding, R is B ₂ O ₃ , P ₂ O ₅ or GeO ₂ , L is at least one of Zn and Ba, and M is Li, Na, K, Rb. , Cs, and Q is at least one of B, Bi, La, Al, and Lu. The composition ratio is
40 <B ₂ O ₃ + P ₂ O ₅ + GeO ₂ <90 (mol%)
5 <LO <30 (mol%)
3 <M ₂ O <40 (mol%)
0 <Q ₂ O ₃ <20 (mol%)
It is desirable to be in the range. In the second cladding, R is TeO ₂ , P ₂ O ₅ or GeO ₂ , L is at least one of Zn and Ba, and M is at least one of Li, Na, K, Rb, and Cs. As described above, Q is at least one of B, Bi, La, Al, and Lu. The composition ratio is
40 <TeO ₂ + P ₂ O ₅ + GeO ₂ <90 (mol%)
5 <LO <30 (mol%)
3 <M ₂ O <40 (mol%)
0 <Q ₂ O ₃ <20 (mol%)
It is desirable to be in the range.

As a fourth embodiment according to the present invention, Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Pm ³⁺ , Sm ³⁺ , Eu ³⁺ , Tb ³⁺ , Dy ³⁺ , Ho ³⁺ , Er ³⁺ , Tm are used as the rare earth ions in the tellurite glass material. By adding at least one of ³⁺ and Yb ³⁺ , characteristics such as a nonlinear amplification and a filtering effect due to absorption and absorption can be provided.

  Hereinafter, specific examples of optical fibers according to embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
An example of glass composition (in mol%) used for tellurite fiber according to an embodiment of the present invention, thermal stability (Tx−Tg: ° C.), and refractive index (n _D ) of each glass composition The relative refractive index difference between the core and the first cladding and the relative refractive index difference between the core and the second cladding (n +:% / n −:%), the core radius, and the first cladding radius (R: μm / R ′: Table 1 shows the measured test results for (μm).

  Next, a method for manufacturing the tellurite fiber will be described. First, glass materials for the core (and the first clad) are mixed in a glove box filled with nitrogen gas and melted at 700 to 1200 ° C. in an oxygen atmosphere using a gold or platinum crucible. A glass base material of the core and the first clad is produced by a suction casting method in which a melt is poured in the order of the first clad glass and the core glass into a mold preheated to 250 to 500 ° C. Similarly, the glass material of the second clad is melted and poured into a cylindrical mold preheated to 250 to 500 ° C., and then rotated at a high speed while holding the mold horizontally, A cylindrical jacket tube is produced.

  The core and the first cladding glass base material are inserted into the jacket tube, and drawing and drawing are performed. In drawing and drawing, since reheating is required, thermal stability is an important factor for realizing a fiber with low loss and high strength. In general, tellurite glass is stretched and drawn at a temperature 30 to 80 ° C. higher than the glass transition temperature Tg, so that the thermal stability = (crystallization temperature Tx) − (glass transition temperature Tg) is 100 ° C. It is desirable that there be more. In the glass composition of Table 1, the thermal stability Tx-Tg is 140 ° C. or higher, respectively, and the thermal stability is sufficient.

  A tellurite fiber is prepared according to the composition of Table 1 [Example 1]. The radius R of the core is 0.57 μm, the radius of the first cladding is 1.2 μm, and the MFD (Mode Field Diameter) is 2.2 μm. The loss of the fiber is 35 dB / km at 1.55 μm, and the zero dispersion wavelength is 1.57 μm.

  FIG. 3 shows a wavelength converter using the tellurite fiber according to the first example. The wavelength converter includes light sources 301 to 332 that output 32 WDM signals at 100 GHz intervals in a wavelength band of 1530 to 1560 nm, and a light source 333 that outputs excitation light of 1565 nm. Further, an AWG (Arrayed Waveguide Grating) 341 that combines the outputs of the light sources 301 to 332, an optical coupler 342 that combines the combined WDM signal light Es and the excitation light Ep, and a first embodiment having a length of 50 m. The tellurite fiber 343 is provided. With such a configuration, the wavelength conversion device collectively converts the wavelengths of the 32 WDM signals Es and outputs the converted light Ec.

  FIG. 4 shows the output spectrum of the wavelength converter. For a power of 50 mW of the excitation light Ep, the conversion efficiency is -15 dB, and the wavelength batch conversion with a bandwidth of 70 nm can be performed.

(Example 2)
A tellurite fiber is produced by the same production method as in Example 1 and with the composition shown in Table 1 [Example 2]. The radius of the core R = 0.57 μm, the radius of the first cladding is 1.2 μm, and the MFD is 2.2 μm. The loss of the fiber is 30 dB / km at 1.2 μm, and the zero dispersion wavelength is 1.56 μm.

  Using the tellurite fiber of Example 2, a wavelength converter having the same configuration as that of FIG. 3 is manufactured. As light sources, light sources 301 to 332 that output 32 WDM signals at intervals of 100 GHz in a wavelength band of 1530 to 1560 nm and light sources 333 that output 1480 nm excitation light and 1565 nm excitation light are used. Using the tellurite fiber 343 according to the second example having a length of 15 m, signal amplification is performed simultaneously with wavelength amplification. The conversion efficiency is 5 dB and the wavelength batch conversion with a bandwidth of 70 nm can be performed for the power of 1480 nm excitation light of 50 mW and the power of 1565 nm excitation light of 50 mW.

  When 15 m of the tellurite fiber of Example 2 is applied to a nonlinear fiber loop mirror described later with reference to FIG. 10, the signal light is generated by a gate light power of 10 mW with respect to 80 GHz, 8 ps highly modulated signal light. Can be switched.

(Example 3)
A tellurite fiber is produced by the same production method as in Example 1 and with the composition shown in Table 1 [Example 3]. The radius of the core R = 0.58 μm, the radius of the first cladding is 1.3 μm, and the MFD is 2.3 μm. The loss of the fiber is 38 dB / km at 1.5 μm, and the zero dispersion wavelength is 1.55 μm.

  Pulse excitation light having a wavelength of 1.55 μm, a pulse width of 0.5 ps, and a peak power of 30 W is incident on a 150 m long tellurite fiber. As shown in FIG. 5, the tellurite fiber of Example 3 outputs supercontinuum light over a 1.7 μm band (0.7 to 2.4 μmm).

Example 4
A tellurite fiber is produced by the same production method as in Example 1 and with the composition shown in Table 1 [Example 4]. The radius of the core R = 0.60 μm, the radius of the first cladding is 1.5 μm, and the MFD is 2.5 μm. The loss of the fiber is 32 dB / km at 1.5 μm, and the zero dispersion wavelength is 1.50 μm.

  Pulse excitation light having a wavelength of 1.55 μm, a pulse width of 0.5 ps, and a peak power of 30 W is incident on a 50 m long tellurite fiber. As the pulse undergoes the soliton effect, a “soliton self-phase shift” is observed in which the pulse spectrum shifts to the longer wavelength side as it propagates through the fiber.

  FIG. 6 shows a wavelength tunable pulse light source using the tellurite fiber according to the fourth embodiment. This is a variable wavelength pulse light source that utilizes the effect of changing the amount of spectral shift by changing the peak power of the incident pulse. The variable wavelength pulse light source is formed by cascading an optical amplifier 902, a tellurite fiber 903 according to a fourth embodiment having a length of 50 m, and a programmable PLC multiplexer / demultiplexer 904 to a pulse light source 901 modulated at 10 GHz.

  Further, an optical amplifier 905 and a tellurite fiber 906 according to the fourth embodiment having a length of 50 m are cascade-connected to the output of the programmable PLC multiplexer / demultiplexer 904. With such a configuration, the wavelength variable pulse light source has a channel rate of 10 to 100 Gbit / s and a wavelength variable range of 150 nm (1550 to 1700 nm).

(Example 5)
A tellurite fiber is produced by the same manufacturing method as in Example 1 with the composition shown in Table 1 [Example 5]. The radius of the core R = 0.55 μm, the radius of the first cladding is 1.3 μm, and the MFD is 2.2 μm. The loss of the fiber is 28 dB / km at 1.5 μm, and the zero dispersion wavelength is 1.56 μm.

  FIG. 7 shows a parametric optical amplifier using the tellurite fiber according to the fifth embodiment. In the parametric optical amplifier, an isolator 1302, a tellurite fiber 1303 according to the fifth embodiment having a length of 150 m, and an optical coupler 1304 are connected in cascade to a variable wavelength light source 1301. An output of a light source having a wavelength of 1560 nm and a pumping light power of 1.5 W is incident on the optical coupler 1304 from behind via an EDFA amplifier 1306.

  FIG. 8 shows the output spectrum of the parametric optical amplifier. This is a result of wavelength scan measurement using −30 dBm signal light, and gain of 20 dB or more was obtained in a 120 nm wavelength band ranging from 1500 to 1620 nm.

(Example 6)
A tellurite fiber is produced by the same production method as in Example 1 and with the composition shown in Table 1 [Example 6]. The radius of the core R = 0.58 μm, the radius of the first cladding is 1.4 μm, and the MFD is 2.4 μm. The loss of the fiber is 33 dB / km at 1.5 μm, and the zero dispersion wavelength is 1.56 μm.

  FIG. 9 shows an optical Kerr shutter experimental system using the tellurite fiber according to the sixth embodiment. The optical Kerr shutter experimental system includes a DFB-LD 1701 that outputs control light having a wavelength of 1552 nm, a DFB-LD 1702 that outputs signal light having a wavelength of 1535 nm, and an Er-doped fiber amplifier 1703 that amplifies the control light. The signal light is input to a 10 m long tellurite fiber 1704 so that the polarization directions form an angle of 45 degrees. Signal light is branched from the output of the tellurite fiber 1704 and input to the streak camera 1706 via the polarizer 1705.

  With such a configuration, when no control light is incident, the polarization of the signal light propagates through the tellurite fiber 1704 in a certain direction and is blocked by the polarizer 1705. On the other hand, when the control light is incident, the polarization component of the signal light changes due to the nonlinear refractive index effect of the tellurite fiber 1704 and is transmitted through the polarizer 1705. In this way, a signal light pulse having a width of 8 ps can be switched.

(Example 7)
A tellurite fiber is produced by the same production method as in Example 1 and with the composition shown in Table 1 [Example 7]. The radius of the core R = 0.60 μm, the radius of the first cladding is 1.4 μm, and the MFD is 2.5 μm. The loss of the fiber is 37 dB / km at 1.5 μm, and the zero dispersion wavelength is 1.56 μm.

  FIG. 10 shows a nonlinear fiber loop mirror using the tellurite fiber according to the seventh embodiment. In the nonlinear fiber loop mirror, an optical coupler 1901 that inputs gate light, a tellurite fiber 1902 having a length of 15 m, an optical coupler 1903 that outputs gate light, and an optical coupler 1904 that inputs and outputs signal light are cascade-connected. Loop.

  The signal light is branched into two by the optical coupler 1904 and propagates through the tellurite fiber 1902 in the forward direction and the reverse direction. The signals are input to the optical coupler 1904 again, interfere with each other, and are output. At this time, the gate light input from the optical coupler 1901 is switched by controlling the phase change of the signal light in the tellurite fiber 1902. With the gate light power of 200 mW, switching of 80 GHz, 8 ps highly modulated signal light can be performed.

(Example 8)
A tellurite fiber is produced by the same production method as in Example 1 and with the composition shown in Table 1 [Example 8]. The radius of the core R = 0.55 μm, the radius of the first cladding is 1.6 μm, and the MFD is 2.5 μm. The loss of the fiber is 30 dB / km at 1.2 μm, and the zero dispersion wavelength is 1.55 μm.

  FIG. 11 shows a clock recovery apparatus according to an embodiment of the present invention. The transmitter 2001 of the WDM transmission system outputs a 40 Gb / s WDM signal. The clock recovery device 2003 receives the one-wavelength signal selected by the wavelength selection filter 2002 by the clock recovery unit 2301 and extracts the RF clock. The extracted clock is reproduced as an optical pulse by a mode-locked fiber laser, amplified by an EDFA 2302, and incident on a tellurite fiber 2303 having a length of 30 m. Supercontinuum light generated in the tellurite fiber 2303 over a 100 nm band of 1.5 to 1.6 μm is input to the AWG 2304. Filtering by the AWG 2304 makes it possible to regenerate the clock pulses for the channels wavelength-multiplexed by the single channel clock recovery.

  An arbitrary one-channel clock pulse is incident on a non-linear loop mirror 2004 using a 50 m long tellurite fiber. The corresponding channel of the WDM signal is input to the nonlinear loop mirror 2004 as the gate light, and optical 3R reproduction for restoring the deteriorated signal quality can be realized.

  In the above embodiments, tellurite glass, phosphate glass, and the like are exemplified as the composition of the optical fiber, but the present invention is not limited to these. The optical device using the optical fiber of the present embodiment is an optical device that uses the optical fiber of the present embodiment as a highly nonlinear fiber, and is not limited to the above-described examples.

  The optical fiber of the present invention is effective in promoting high performance, large capacity, and low price in an optical communication system, and as a result, can greatly contribute to the advancement of services and economics using these systems. .

It is a figure which shows the refractive index profile of the optical fiber concerning the 1st Embodiment of this invention. It is a figure which shows the calculation result of the zero dispersion wavelength of the optical fiber concerning 1st Embodiment. It is a block diagram which shows the wavelength converter concerning one Embodiment of this invention. It is a figure which shows the output spectrum of a wavelength converter. It is a figure which shows the spectrum of the generated super continuum light. It is a block diagram which shows the wavelength variable pulse light source concerning one Embodiment of this invention. It is a block diagram which shows the parametric optical amplifier concerning one Embodiment of this invention. It is a figure which shows the output spectrum of a parametric optical amplifier. It is a block diagram which shows the optical Kerr shutter experimental system concerning one Embodiment of this invention. It is a block diagram which shows the nonlinear fiber loop mirror concerning one Embodiment of this invention. It is a block diagram which shows the clock reproduction apparatus concerning one Embodiment of this invention.

Explanation of symbols

11 Core 12 First clad 13 Second clad

Claims (3)

A core ing of tellurite glass, an optical fiber having a cladding said core is interpolated,
The clad has a first clad in which the core is inserted, and a second clad having a refractive index higher than the refractive index of the first clad, and the first clad is inserted,
Tellurite glass of the core _has a composition consisting of _{TeO 2 -LO-M 2 O-} Q 2 O 3,
Glass of the first _{cladding, B 2 O 3 -LO-M} 2 O-Q 2 O 3 -P 2 O 5 -GeO having a composition consisting of _2,
Glass of the second cladding _has a composition consisting of _{TeO 2 -LO-M 2 O-} Q 2 O 3 -P 2 O 5 -GeO 2,
Here, L is at least one of Zn and Ba, M is at least one of Li, Na, K, Rb, and Cs, and Q is B, Bi, La, Al, and Lu. At least one kind,
The relative refractive index difference between the core and the first cladding and the relative refractive index between the first cladding and the second cladding are set so that the zero dispersion wavelength is in a 1.4 to 1.7 μm band. Characteristic optical fiber. A core ing of tellurite glass, an optical fiber having a cladding said core is interpolated,
The cladding is
A relative refractive index difference with respect to the core is 10% or more, and a first cladding in which the core is inserted;
A refractive index higher than the refractive index of the first cladding, a relative refractive index difference with the first cladding is 5% or more, and a second cladding in which the first cladding is inserted ,
Tellurite glass of the core _has a composition consisting of _{TeO 2 -LO-M 2 O-} Q 2 O 3,
Glass of the first _{cladding, B 2 O 3 -LO-M} 2 O-Q 2 O 3 -P 2 O 5 -GeO having a composition consisting of _2,
Glass of the second cladding _has a composition consisting of _{TeO 2 -LO-M 2 O-} Q 2 O 3 -P 2 O 5 -GeO 2,
Here, L is at least one of Zn and Ba, M is at least one of Li, Na, K, Rb, and Cs, and Q is B, Bi, La, Al, and Lu. An optical fiber comprising at least one kind . In the tellurite glass, at least one of Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Pm ³⁺ , Sm ³⁺ , Eu ³⁺ , Tb ³⁺ , Dy ³⁺ , Ho ³⁺ , Er ³⁺ , Tm ³⁺ and Yb ³⁺ is added as a rare earth ion. the optical fiber according to claim 1 or 2, characterized in that it is.

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