KR101713679B1 - All-optical fiber isolator using optical fiber incorporated with Quantum dots - Google Patents

Abstract

An optical isolator comprising an optical fiber serving as an optical waveguide for propagating incident light, a polarizer for polarizing the incident light, and a Faraday rotator for rotating the polarization plane polarized in the polarizer by 45 degrees, Optical element exhibiting a magnetooptical effect enough to be used as an optical isolator at a visible light wavelength by containing quantum dots in the inner cladding layer and / or the inner cladding layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an all-optical fiber isolator using an optical fiber including a quantum dot,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator, and more particularly, to a full optical fiber isolator improved in magneto-optical effect.

Optical isolators, which are irreversible devices that allow only one direction of propagation, have received much attention due to their use in high output fiber lasers, optical amplifiers and high speed fiber optic communication devices to block back reflection of undesired light and unwanted propagation of light .

When the linearly polarized light passes through the magneto-optical medium under the magnetic field and rotates through 45 占 of the plane of polarization, and then returns to the magneto-optical medium, the light-inverted- .

The most common isolators are optical isolators that require large optical devices such as birefringent plates and special launch lenses that require precise alignment and careful handling. Recently, all fiber optic isolators are attracting much attention because of their low insertion loss, high reflection characteristics, and high isolation, and thus are being used for optical laser systems and fiber optic amplifiers. In particular, high power Yb-doped fiber laser (pulsed) systems operating at 660 nm (multi-kW output levels) have been developed for industrial and biomedical applications.

However, all fiber optic isolators operating at a wavelength of 660 nm have not yet been developed. This is mainly due to the low sensitivity of the silica glass fibers, which is due to the low self-optical sensitivity of silica fibers at visible wavelengths (-0.64 rad / Tm at the 1550 nm of the Verdet constant and -0.22 rad / Tm at 1310 nm) .

Although specialized optical fibers, such as annealed fibers, twisted fibers, and flint fibers, have been proposed to reduce the linear birefringence of the fibers to increase the magneto-optical sensitivity, complex manufacturing processes, high slicing losses, and high cost still remain problems.

To solve these problems, phosphate or borosilicate glass fibers incorporating Tb-ions with high Verde constants have been reported, wherein a rod-in-tube technique is used.

However, the propagation loss of the fibers was found to be much greater than the propagation loss of silica glass fibers.

In order to solve the problems of the prior art described above, it is an object of the present invention to provide a pre-optical fiber isolator having an improved magneto-optical effect.

It is an object of the present invention to provide an optical isolator including an optical fiber serving as an optical waveguide for propagating incident light, a polarizer for polarizing the incident light, and a Faraday rotator for rotating the polarized plane polarized by 45 °, The optical fiber has at least one selected from the group consisting of a compound semiconductor, a rare earth element, a paramagnetic material, a semi-magnetic material, a magneto-optical glass, and a magneto-optical single crystal in a core layer of the optical fiber and exhibits a magnetooptical effect enough to be used as an optical isolator at a visible light wavelength It is accomplished by the whole fiber optic isolator.

It is another object of the present invention to provide a cladding layer or an inner cladding layer, wherein the optical fiber includes a compound semiconductor, a rare earth element, a paramagnetic material, a semi-magnetic material, a magneto- A single crystal, and at least one selected from the group consisting of a single crystal, and exhibits a magnetooptical effect enough to be used as an optical isolator at a visible light wavelength.

Here, preferably, the compound semiconductor is PbSe, PbS, PbTe, CdMnTe, CdMnTe, ZnMnTe, MnGeAs _2, MnGeP _2, CdMnSe, CdSe, ZnSe, ZnXO (X = Co, Mn), As ₂ S _2, Bi ₁₂ SiO, Y ₃ Fe ₅ O _12, ZnO or CdS quantum dots, the rare earth elements are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu quantum dot, wherein The paramagnetic material may be Fe, Ni, Co, Cr, Mn, Pt, Al, or Ti quantum dots, the semi-magnetic material may be Bi, Sb, P, Au, Ag, Hg, Cu, or Pb quantum dots, A quantum dot or a fine powder of FR-7, MOS-4, MOS-10, Tb-10, Tb-12 or Tb-15 glass, and the photonic single crystal is made of TGG (Terbium Gallium Garnet) crystal or YIG (Yttrium Iron Garnet) A quantum dot of crystals or a fine powder.

Preferably, the compound semiconductor is a Cd _{0 .5} Mn _{0 .5} Te quantum dot.

Preferably, the visible light wavelength is 660 nm.

Preferably, the Faraday effect exhibiting a magnetooptical effect to the extent that it is used as an optical isolator at the visible light wavelength has a Verde constant of 3.5 to 5.5 radT ^-1 m ^-1 at a wavelength of 660 nm.

The present invention increases the magneto-optical effect by including quantum dots in the optical fiber used in the entire optical fiber isolator, so that even if a weak magnetic field is applied to the Faraday rotator or a magnetic field is applied to the optical fiber for a short length, sufficient Faraday effect is exhibited, ≪ / RTI > In addition, the light in the visible light wavelength range can provide a sufficient Faraday effect in various wavelength ranges including the wavelength of 660 nm required for the biomedical application even in the optical fiber core which is a glass component in which the Faraday effect does not occur well.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an experimental apparatus for measuring the magneto-optical properties of a fiber-optic isolator to which a CdSe quantum dot doped optical fiber according to the present invention is applied.
FIG. 2 is a schematic view illustrating a structure of a pre-optical fiber isolator according to the present invention.
3 is a graph showing a change in Faraday rotation angle of an optical fiber doped with CdSe quantum dots in a magnetic field change according to the present invention.
4 is a graph showing a change in the normalized output of the CdSe quantum dot doped optical fiber according to the Faraday rotation angle according to the present invention.
FIG. 5 is a graph showing changes in optical isolation of a CdSe quantum dot doped optical fiber when the applied magnetic field according to the present invention changes. FIG.
Figure 6 is a Cd _{0 .5 0 .5} Mn graph the Faraday rotation angle of Te, CdSe, the optical fiber-containing Co, Mn and showing the value measured at 660nm in accordance with the present invention.

All terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

The present invention provides an all-optical fiber isolator having an enhanced magneto-optic effect (a Faraday effect or a Zeeman effect).

An optical isolator for allowing light to flow only in one direction generally comprises an optical fiber serving as an optical waveguide for propagating incident light, a polarizer for polarizing the incident light, and a Faraday rotator for rotating the polarization plane polarized in the polarizer by 45 have.

However, since it is necessary to increase the magneto-optical effect more in order to use the wavelength of the visible light band as described above, the present invention solves the problem by including quantum dots in the core layer and / or the cladding layer or the inner cladding layer of the optical fiber Furthermore, by increasing the magneto-optic effect, the intensity of the magnetic field in the Faraday rotator can be lowered and the range of applying the magnetic field can be reduced.

Herein, the inner cladding layer is composed of the inner cladding layer, the trench layer, and the outer cladding layer, which is described in the prior patent of the present inventor, " Patent Publication No. 2011-0134869, entitled " The present invention can be applied to an optical fiber including a core layer and a cladding layer, which is a general optical fiber structure. However, the core layer and / or the core layer of the optical fiber structure shown in the above- It may be applied only to the inner cladding layer.

Here, the quantum dot may be at least one quantum dot selected from the group consisting of a compound semiconductor, a rare earth element, a paramagnetic material, a semi-magnetic material, a magneto-optical glass, and a magneto-optical single crystal.

Preferably, the compound semiconductor is PbSe, PbS, PbTe, CdMnTe, CdMnTe, ZnMnTe, MnGeAs _2, MnGeP _2, CdMnSe, CdSe, ZnSe, ZnXO (X = Co, Mn), As ₂ S _2, Bi ₁₂ SiO, Y ₃ Fe ₅ O ₁₂ , ZnO, and CdS quantum dots.

Preferably, the rare earth element is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu quantum dots.

Preferably, the paramagnetic material is Fe, Ni, Co, Cr, Mn, Pt, Al, and Ti.

Preferably, the semi-magnetic material is Bi, Sb, P, Au, Ag, Hg, Cu, or Pb quantum dots.

Preferably, the magneto-optical glass is a mixture of FR-5 and FR-7 of Schott, Germany, MOS-4 and MOS-10 of MolTech GmbH, Germany, Tb-12, and Tb-15 of Foctek Photonics Inc., China), and the magneto-optical glass is pulverized and contained in the core and / or cladding layer or inner cladding layer of the optical fiber in quantum dots or very fine powder state .

Here, the magneto-optical glass means a glass whose optical characteristics are changed by a change in applied magnetic field produced by adding a rare earth element such as Tb, Y, Eu to the borosilicate glass composition.

Preferably, the magneto-optic single crystal may be added to the core and / or cladding layer or the inner cladding layer of the optical fiber in a state of quantum dots or very fine powder by pulverization. These magneto-optic single crystals are commonly referred to as chemical components, and TGG (Terbium Gallium Garnet) crystals and YIG (Yttrium Iron Garnet) crystals are the most representative.

FIG. 2 shows one embodiment of various embodiments of the prior art optical fiber isolator to which the optical fiber according to the present invention is applied. Fig. 2 has a symmetrical structure, and symmetrical opposite parts that do not denote the same parts have the same structure. Here, the Faraday rotator 201 may be a permanent magnet or a solenoid, but is not limited thereto. The optical fiber connected within the Faraday rotator 201 and from the Faraday rotator 201 to the junction 205 is an optical fiber 202 doped with a quantum dot. The optical fiber connected in the linear polarizer 204 and in the linear polarizer 204 to the junction 205 is a polarization maintaining optical fiber 203. The optical fiber connected from the connector 207 to the junction 205 may be a single-mode optical fiber or a multi-mode optical fiber. The optical fiber 201, the linear polarizer 204, and the connector 207 are provided to constitute a single optical fiber isolator 200.

The present inventors have been able to induce a high Faraday effect by doping a CdSe quantum dot or a Cd _{0 .5} Mn _{0 .5} Te quantum dot in a core layer and / or a cladding layer or an inner cladding layer of an optical fiber, Will be described in detail with reference to the accompanying drawings. Embodiments of the present invention will be described in order to facilitate those skilled in the art to which the present invention belongs. As will be readily understood by one of ordinary skill in the art, the following embodiments may be modified in various ways within the scope and spirit of the present invention. Wherever possible, the same or similar parts are denoted using the same reference numerals in the drawings.

[Example 1]

On fiber optics CdSe The quantum dot Doped  All optical fiber Isolator  Manufacturing and Performance

The optical fiber preform doped with CdSe quantum dots was fabricated by Modified Chemical Vapor Deposition (MCVD). A toluene solution containing CdSe quantum dots (Sigma-Aldrich: Lumidot CdSe QDs in toluene, peak absorption ~ 650 nm, 7.5 mg in 1.5 ml solution) was applied to a core layer of alumino-germano- silica glass laminated on a silica glass tube And doped at room temperature by a solution doping process. To reduce the evaporation of the dopants that may occur during the modified chemical vapor deposition process, a soaked tube is dried after the solution doping process and then an additional glass layer is deposited. The tube is dried, sintered, partially shrunk and sealed with a bar base. Finally, the base material was drawn at 2150 DEG C into a fiber having an outer diameter of 125 mu m using a drawing device. The core diameter and cut-off wavelength of the fabricated fibers are 5.4 탆 and 560 nm, respectively. The absorption coefficient of the optical fiber was about 0.003 m-1 at 660 nm as measured by the cut-back method. The Verdet constant of the CdSe quantum dot doped fiber was measured to be 5.3 rad / Tm at 633 nm.

FIG. 1 shows an experimental apparatus for measuring the optical properties of the CdSe quantum dot-doped optical fiber 108 manufactured by the above method. The Faraday rotation angle of the CdSe quantum dot doped optical fiber was measured with a polarimeter (PA510, Thorlabs, USA) using a 660 nm laser diode 101 and a linear polarizer 107 as a light source under the magnetic field supplied by the Faraday rotator 110 . Here, the output of the laser diode 101 is 1.1 mV, and the output light spectrum reflected by the reflection mirror is monitored by an optical spectrum analyzer 102 (OSA, resolution: 1 nm). The CdSe quantum dope optical fiber 108 was single mode at a wavelength of 660 nm and the fiber type linear polarizer 107 (operating at 660 nm) was sliced directly into the fiber.

Figure 3 shows the Faraday rotation angle at 660 nm as a function of the magnetic field. During the measurement, the CdSe quantum dot doped optical fiber 108 was wound around the Faraday rotator 110 to increase the effective length of the fiber, which is the total length of the optical fiber under the same orientation as the magnetic field. The Faraday rotation angle of the quantum dot-doped optical fiber 108 of CdSe increases linearly as shown in FIG. 3 as the current of the Faraday rotator 110 composed of the solenoid is changed to increase the applied magnetic field. When a magnetic field of 0.1 T was applied to an effective length of 183 cm of fiber, the Faraday rotation angle reached 45 °. This result shows that a full fiber optic isolator that blocks reflected light at 660 nm is possible because the polarization angle of the 90 ° rotation of the back-reflected light is expected to be due to the non-reversible nature of the Faraday effect.

Since the light is reflected directly backwards, the Faraday rotation is additive due to the irreversible nature of the Faraday effect. Measurement of the actual reflected power at the input side with changes in the magnetic field strength will only provide the idea of isolation provided by the fiber optic device. This experiment was performed using a reflective mirror 111 that reflected 660 nm excitation light from a CdSe quantum dot and the back reflection power was measured using a 3 dB coupler 104 (660 nm) as shown in FIG. Fig. 4 shows the variation of the normalized output power (reflected power) of the fiber with the Faraday rotation angle measured when the magnetic field changes from 0 to 0.16T. The normalization was made with output power without magnetic field. The normalized output power was found to decrease with increasing Faraday rotation angle and no output power was detected at an angle of 90 °, indicating good isolation properties. When the Faraday rotation angle exceeds 90 degrees, the output power increases again because the polarization state begins to return to its original state. The reflected optical power can be simply described by Malus' law.

[Formula 1]

I = I ₀ cos ² & thetas;

In the above Equation 1, I and I ₀ are the power of the reflected optical signal (rear ratio) incident light source (forward ratio), respectively, and? Is the Faraday rotation angle. Note that attenuation factors such as optical power bending, coupling, splicing, and return loss are neglected in the equation. As shown in Fig. 4, the obtained output data was combined with a loose curve and matched well with a small deviation error. The optical isolation of the CdSe quantum dot doped optical fiber 108 with respect to the applied magnetic field is shown in FIG. The maximum separation was about 14 dB at 0.1 T, which increased as the magnetic field increased from 0 to 0.1 T. When the magnetic field is greater than 0.1 T, the isolation has decreased due to the fact that the polarization state returns to its original input state.

The discrepancy between the experimental results in Figures 4 and 5 and Malus's law is due to the linear birefringence of the optical fiber due to bending as the optical fiber is wound on the Faraday rotator 110 to increase the effective length. To improve the precision and performance of the entire fiber optic isolator, the linear birefringence must be minimized along the fiber. This can be accomplished using a high specific Verde constant fiber, so that fibers of short length sufficient to be straight at a fixed length without twisting or bending the optical fiber can be used to induce very high cyclic birefringence on the optical fiber. Table 1 summarizes the experimental parameters of all fiber optic isolators using CdSe Qdoped optical fiber for the applied field changes. This full fiber optic isolator can be applied to a variety of optical fibers, such as optical switches, optical modulators, non-reversible elements in the scope of the laser oscilloscope, optical circulators, and optical sensors.

Experimental parameters of all fiber optic isolators using CdSe quantum dots doped fiber according to the change of magnetic field are shown in Table 1 below.

Solenoid current [A]

Magnetic field [T]
Faraday rotation angle [θ]
Output [dBm / nW]
Normalized output
Isolation [dB] 0 0 0 -50.67 / 8.56 1,000 0 10 0.037 27.8 -51.99 / 6.31 0.737 1.32 20 0.072 53.8 -54.44 / 3.59 0.420 3.77 30 0.107 81.8 -60.22 / 0.95 0.111 9.55 35 0.124 95.0 -64.64 / 0.04 0.034 13.97 40 0.145 107.8 -59.54 / 1.11 0.130 8.87 45 0.160 120.0 -57.02 / 1.98 0.232 6.34

[Example 2]

CD _{0 .5} Mn _{0 .5} Te The quantum dot  Magneto-optical properties of optical fibers

Cd _{0 .5} Mn _{0 .5} the optical fiber preform is Te-containing quantum dots was fabricated by the modified chemical vapor deposition (MCVD). A porous core layer was formed at 1650 ° C using SiCl ₄ and GeCl ₄ in a silica glass tube. After partial sintering, 0.475 g (0.1 M) of nitric acid was added to 5 ml of nitric acid (Junsei Chem., 70% Mn _{0 .5 0 .5} Cd Te powder (International Crystal Lab.) to infiltrate the mixed solution on a porous core layer Cd _{0 .5 0 .5} Mn were fabricated is a Te-containing quantum dot optical fiber preform, thus making the optical fiber The base material was drawn to the optical fiber at 2000 ° C or less. After passing the optical fiber through the center of the solenoid (Walker LDJ, 3.0-28-1500DC), the magneto-optical characteristics of the magnetic field were measured using a laser diode (LD) light source with a wavelength of 660 nm and a polarimeter (THORLABs, PA-510) Respectively.

In order to confirm the influence of Mn ions confirmed to exist together in the optical fiber core, Mn ion doped optical fibers were prepared and compared. _{0 .5 0 .5} Mn and Cd were compared to evaluate the Faraday rotation properties of the Te-containing quantum dot optical fiber, with a cobalt (Co) ion-doped optical fiber with the addition of a CdSe quantum dot optical fiber manufactured in the lab and normal single mode fiber. As a result of measuring the magnetooptical characteristics of each optical fiber through a polarimeter by applying a magnetic field parallel to the optical fiber through an increase in the solenoid current value, as shown in FIG. 6, the Faraday rotation angle linearly increased as the magnetic field increased, _{0 .5 0 .5} Cd Mn case of the Te-containing quantum dot optical fiber was under the same magnetic field when the absolute value exhibited about 1.5 times and 6 times higher than the Faraday rotation angle of the optical fiber containing the Co ions and Mn ions, than CdSe-containing fiber 1.5 times larger than SMF and about 2 times larger than SMF. Mn doped Cd _{0 .5} Mn _{0 .5} Te quantum dots were higher than Mn ions in the increase of Faraday rotation of the optical fiber containing Cd _{0 .5} Mn _{0 .5} Te quantum dots _. , Which is due to the Zeeman effect of Cd _{0 .5} Mn _{0 .5} Te quantum dots. Obtained using the Faraday rotation angle measured Cd _0.5 Mn _0.5 Te quantum dots, Co ions or Verde constant of the optical fiber SMF and Mn ions are contained and are respectively 5.12, 3.54, -1.04 at 660 nm wavelength of 2.77 radT ^-1 m ^{- 1} .

The following Table 1 shows the magneto-optical properties of the optical fiber containing the Cd _{0 .5} Mn _{0 .5} Te quantum dot, Co ion or Mn ion.

Effective length (m)

Magnetic field (T)
The rotation angle?
Verde constant (rad ^-1 m ^-1 ) Mn _{0 .5 0 .5} Cd Te-doped fiber 0.7 0.142 29.18 5.12 Co-doped fiber 0.7 0.142 20.18 3.54 CdSe doped fiber 0.7 0.142 20.28 3.56 Mn doped fiber 0.7 0.142 -5.93 -1.04 SMF 0.7 0.142 15.82 2.77

While the illustrative embodiments of the present invention have been shown and described, various modifications and alternative embodiments may be made by those skilled in the art. Such variations and other embodiments will be considered and included in the appended claims, all without departing from the true spirit and scope of the invention.

100: Optical property measuring device of all optical fiber isolate
101: Laser diode
102: Optical spectrum analyzer
103: Single mode optical fiber
104: coupler
105: splicing point
106: polarization maintaining optical fiber (PM fiber)
107: linear polarizer
108: Quantum dot doped optical fiber
109: Fiber optic support
110: Faraday rotator
111: Mirror
200: Exemplary Structure of a Whole Fiber Isolator
201: Faraday rotator
202: Quantum dot doped optical fiber
203: polarization maintaining optical fiber (PM fiber)
204: linear polarizer
205: splicing point
206: Single mode fiber or multimode fiber
207: Connector

Claims (6)

1. An optical isolator comprising an optical fiber serving as an optical waveguide for propagating incident light, a polarizer for polarizing the incident light, and a Faraday rotator for rotating the polarization plane polarized in the polarizer by 45 degrees,
Optical fiber isolator having a quantum dot of Cd _0.5 Mn _0.5 Te, which is a compound semiconductor, in the core layer of the optical fiber and exhibiting magnetooptical effect to the extent that it can be used as an optical isolator at a visible light wavelength. The optical fiber according to claim 1, wherein the optical fiber comprises a cladding layer or an inner cladding layer, and the cladding layer or the inner cladding layer is formed of a compound semiconductor, a rare earth element, a paramagnetic material, Optical effect exhibiting a magnetooptical effect to the extent that it can be used as an optical isolator at a visible light wavelength. The method of claim 2, wherein the compound semiconductor contained in the cladding layer or the inner cladding layer is PbSe, PbS, PbTe, CdMnTe, CdMnTe, ZnMnTe, MnGeAs _2, MnGeP _2, CdMnSe, CdSe, ZnSe, ZnXO (X = Co, Mn _{), As 2 S 2, Bi} 12 SiO, Y 3 Fe 5 O 12, is ZnO or CdS quantum dots, the rare earth elements contained in the cladding layer or the inner cladding layer is La, Ce, Pr, Nd, Pm, Sm, Eu And the paramagnetic material contained in the cladding layer or the inner cladding layer is Fe, Ni, Co, Cr, Mn, Pt, Al, or Ti quantum dots, and Gd, Tb, Dy, Ho, Er, Tm, The magneto-optical glass contained in the cladding layer or the inner cladding layer is selected from the group consisting of Bi, Sb, P, Au, Ag, Hg, Cu or Pb quantum dots. -7, MOS-4, MOS-10, Tb-10, Tb-12 or Tb-15 glass, and the photomagnetic single crystal contained in the cladding layer or the inner cladding layer TGG (Terbium Gallium Garnet) crystal or a YIG (Yttrium Iron Garnet) or quantum dots around the optical fiber isolator, characterized in that a fine powder of the crystal. 3. The pre-optical fiber isolator according to claim 2, wherein the cladding layer or the inner cladding layer contains compound semiconductor Cd _0.5 Mn _0.5 Te quantum dots. The pre-optical fiber isolator according to claim 1 or 2, wherein the visible light wavelength is 660 nm. According to claim 1 or 2, wherein the magnetic Faraday effect showing the optical effect of the degree to be used as an optical isolator in the visible light wavelength is around, it characterized in that Verde constant is 3.5 to 5.5 radT ^-1 m ^-1 at 660nm wavelength Fiber optic isolator.

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