JP2007226072A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device which can be more easily manufactured and is small and has an electrooptical effect. <P>SOLUTION: An optical fiber (12) has a core (14) and a clad (16). Two electrodes (18, 20) are made to adhere to an outer periphery of the optical fiber (12) so as to interpose the core (14). A voltage source (22) applies DC voltage between the electrodes (18, 20). Both the core (14) and the clad (16) are made of chalcogenide glass, that is, glass containing S, Se or Te. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical device, and more particularly to an optical device that can be used to modulate or adjust optical parameters of light phase, polarization, or intensity.

For adjusting optical parameters such as polarization, phase or intensity, a single crystal waveguide device having an electro-optic effect (Pockels effect) such as LiNbO ₃ or LiTaO ₃ is conventionally used (for example, non-documents). Reference 1).

  On the other hand, since glass is an optical isotropic body and has macroscopic inversion symmetry, it does not exhibit a second-order nonlinear optical effect. However, it has been reported that a second-order nonlinear optical effect is exhibited by a process called polling. For example, an example in which two holes parallel to the core are formed in a silica glass optical fiber and poling is performed with an electrode passing therethrough is known (for example, Non-Patent Document 2).

  As the poling, a method of applying a strong electric field in an ultraviolet irradiation state (ultraviolet light poling), a method of applying a strong electric field at a high temperature (thermal poling), and a method of applying a strong electric field in a high power laser irradiation state (optical poling) Etc. are known.

Non-Patent Document 3 describes that the third-order nonlinearity of glass is involved in the generation of second-order nonlinearity due to poling of the glass material. According to this, the second-order nonlinear component χ ⁽²⁾ generated by applying the electric field E to the silica fiber is
χ ⁽²⁾ = 3χ ⁽³⁾ E
Given in. χ ⁽³⁾ is a third-order nonlinear component of silica glass. Since glass has a third-order nonlinearity even without poling, it exhibits a second-order nonlinear effect only by applying an electric field. However, the second-order nonlinear component χ ⁽²⁾ is very small and not practical.

The second-order nonlinear characteristic is an effect in which the electric polarization of a substance is proportional to the square of the electric field, and brings about a so-called electro-optical effect in which the refractive index n is changed by applying the electric field. Between the electro-optic coefficient r and the second-order nonlinear component χ ⁽²⁾ ,
χ ⁽²⁾ = n ⁴ r / 2
The relationship is established. By utilizing such a second-order nonlinear effect or electro-optic effect, an optical shutter, an optical modulator, an optical path switch, and the like can be realized.
IEEE Journal of Selected Topics i Quantum Electronics, Vol. 6, No. 1, pp. 69-82 (2000) Electronics Lett., Vol. 31, No. 1, pp. 62-63 (1995) Optical Fiber Technology, 5, pp. 232-241 (1999)

  In the case of a single crystal waveguide device, there is a problem that loss is large and connectivity with other optical devices is poor.

An optical device using the second-order nonlinear characteristics of a silica-based optical fiber has low loss and can be easily formed into a fiber shape. However, in order to obtain a large second-order nonlinear characteristic, a high temperature and a strong electric field, for example, an electric field of 5 × 10 ^{3 to} 3 × 10 ⁴ V / cm at 250 ° C. or higher are required. Furthermore, since the obtained second-order nonlinear coefficient is small, a long optical fiber ranging from several meters to several tens of meters must be prepared, which is practically too long.

  Silica-based optical fibers have a low loss in the 2 μm wavelength band and cannot be used in other wavelength bands.

  Under such circumstances, there is a demand for a small optical device that can obtain a second-order nonlinear effect at a lower temperature, has a low loss, can be easily made into a fiber, and is small.

  It is an object of the present invention to provide a novel optical device that satisfies such a desire.

  An optical device according to the present invention includes an optical waveguide having a core and a clad, first and second electrodes sandwiching the core, and a first voltage source that applies a voltage to the first and second electrodes. An optical device is provided, wherein both the core and the clad contain chalcogen.

  According to the present invention, an optical device that can be easily manufactured and has a small electro-optical effect can be realized. Since it is not a crystal, there are few restrictions on arrangement and connection. By using the optical fiber shape, connection with other optical fibers becomes easy. Since it is a transparent material in the far infrared region, it can be used in a wide wavelength range.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a perspective view of one embodiment of the present invention, FIG. 2 shows a side view of this embodiment, and FIG. 3 shows a front view of this embodiment. The optical device 10 according to the present embodiment is composed of a calorogenide optical fiber 12 having a core 14 and a clad 16. In order to apply an electric field to light propagating through the core 14, two electrodes 18 and 20 are bonded to the outer periphery of the optical fiber 12 so as to sandwich the core 14. A voltage source 22 applies a DC voltage between the electrodes 18 and 20. Thereby, an electric field in a direction perpendicular to the optical axis of the optical fiber 12 is applied to the light propagating through the core 14. When the optical device 10 is used as a modulation element that modulates light with an electric signal, the voltage source 22 applies a DC voltage superimposed with the electric signal between the electrodes 18 and 20.

  The chalcogenide glass is generally a glass containing chalcogen, that is, S, Se, or Te, and has a high refractive index. In order to reduce reflection at the end face of the optical fiber 12, non-reflective (AR) films 24 and 26 are coated on both end faces of the optical fiber 16.

In this embodiment, both the core 14 and the clad 16 are made of chalcogenide glass containing As (arsenic) and Se (selenium), and here, As _x Se _y . The optical fiber 12 having such a composition can be manufactured from, for example, As-S-Se. S (sulfur) may be included in the core 14 or the clad 16. The composition ratio of As and Se is adjusted so that the refractive index of the core 14 is higher than the refractive index of the cladding 16, or an appropriate additive is added to the core 14 and / or the cladding 16.

For example, when an optical fiber having a core diameter (Da) of 6 μm, the core 14 is As ₃₉ Se ₆₁ , and the cladding 16 is As _38.25 Se _61.75 , the numerical aperture is 0.18 (relative index difference Δn = 5.74 × 10 ⁻³ ) was obtained. Similarly, when the core diameter (Da) is 6 μm, the core 14 is As ₄₀ S ₅₈ Se ₂ and the cladding 16 is As ₄₀ Se ₆₀ , the numerical aperture is 0.17. In general, As _40−x Se _{60 + x} (where −10 <x <10) can be used as the material of the optical fiber 12 due to the transmission wavelength range and high third-order nonlinearity (electro-optic coefficient). is there.

  In this embodiment, the outer diameter (Db) of the clad is about 160 μm, and the length (L) of the optical device 10 is about 10 cm. Thus, since the overall size is small, polling can be easily performed, and it can be used by being incorporated in a small casing.

By adjusting the mixing ratio of S and Se, the optical fiber 12 becomes transparent in the wavelength range of 6 to 10 μm from the near infrared. For example, As ₄₀ S ₆₀ transmits 6 μm of light, and As ₄₀ Se ₆₀ transmits 10 μm of light. That is, the optical device 10 can be used in a wide wavelength range.

  The optical device 10 according to the present embodiment temporarily develops a second-order nonlinear effect by applying a high electric field at room temperature, and also exhibits an electro-optic effect corresponding to the second-order nonlinear effect. For example, the voltage source 22 applies linearly polarized signal light to the core 14 of the optical fiber 12 in a state where the signal voltage is applied to the DC voltage on which the signal voltage is superimposed between the electrodes 18 and 20. The optical phase of the signal light is modulated by the electro-optic effect corresponding to the electric field between the electrodes 18 and 20.

The optical device 10 can also develop a permanent second-order nonlinear effect by poling at higher temperatures, eg, 200 ° C. or higher. For example, a high-power laser beam is incident on the core 14 of the optical fiber 12 with a high DC voltage applied between the electrodes 18 and 20, or a high-power visible light is incident from the side of the optical fiber 12. There is a method to do. Since the band gap energy of the As ₂ Se ₃ material is about twice the photon energy of the communication wavelength band of 1.55 μm, the absorption is high on the short wavelength side. For this reason, there is no need to use ultraviolet (UV) light as in the case of silica fiber.

  Needless to say, an electrode for applying an electric field may be prepared separately from the electrodes 18 and 20, and the electrodes 18 and 20 may be bonded to the polled optical fiber 12 after poling.

FIG. 4 shows the birefringence characteristics of the prototype optical device 10. The horizontal axis represents the applied voltage, and the vertical axis represents the birefringence phase difference on an arbitrary scale. The core 14 and the cladding 16 is made from the street _{As 40-x Se 60 + x} above. The core diameter (Da) is 6 μm, and the outer diameter (Db) of the clad 16 is 170 μm. The clad 16 has an acrylate coating on the outside, and electrodes 18 and 20 are disposed outside the coating. Since the phase difference changes with the square of the applied electric field, it is considered that the electro-optic coefficient r is generated by the applied electric field. Light superimposed on the optical fiber 12 can be modulated by superimposing a signal on the bias DC voltage.

  In the characteristics shown in FIG. 4, for example, a signal voltage can be superimposed on a DC voltage of 500 V or higher, so that it can be used as an element that modulates the optical phase of incident light.

  For example, by arranging the optical device 10 on one arm of a Mach-Zehnder interferometer and changing the voltage applied between the electrodes 18 and 20, light can be modulated or switched. Optical modulators and optical switches in which a phase modulator is disposed on one arm of a Mach-Zehnder interferometer are known, and the optical device 10 can be used as a phase modulator for such applications.

  Further, by utilizing birefringence, it can be used for optical switching, polarization modulation, conversion of linear polarization / circular polarization, and the like.

  In addition to the As-Se compound, materials that can be used as the core 14 or the clad 16 are generally any one of S, Se, and Te, and any one of As, Ge, Ga, and Sb. It is a compound containing one. Any of these combinations has a low loss above the near infrared and has a large third-order nonlinear component, so that a large second-order nonlinear effect can appear by polling.

_{Specifically, As 40 S 60, As 40} S 50 Se 10, As 40 S 40 Se 20, As 40 S 30 Se 30, As 40 S 20 Se 40, As 40 S 10 Se 50, AS 40 Se 60 is The optical fiber 12 can be used as a constituent material. These are _generally able denoted as _{As 40 S (60-x)} Se x. However. 0 ≦ x ≦ 60.

In the case of an As-S compound, As _40-y S _60-y (where -10 <y <10) can be used.

_{Ge 30 As 10 Se 30 Te 30} , Ge 15 As 35 Se 15 Te 35, Ge 15 As 35 Se 10 Te 40, Ge 15 As 35 Se 50-x Te x is also available.

Ge _0.25 Se _0.75 , Ge _0.25 Se _0.65 Te _0.10 , Ge _0.28 Se _0.60 Te _0.12 , Ge _0.25 Se _0.75-x Te _x , Ge _{0 .28} Se _0.60 Te _0.12 and Ge ₃₃ As ₁₂ Se ₅₅ are also available.

When these available materials generally _expressed, the _{As x Ge y Ga z Sb v} In w S p Se q Te r. However, x, y, z, v, w, p, q, r are
x + y + z + v + w + p + q + r = 100
20 <x + y + z + v + w <55
Meet.

Bi ₂ O ₃ has a third-order nonlinear coefficient χ ⁽³⁾ that is an order of magnitude larger than that of silica-based glass, and is transparent in the far-infrared region. Therefore, Bi ₂ O ₃ can be used as a constituent material of the optical fiber 12.

  Although the embodiment in which the electrodes 18 and 20 are bonded to the optical fiber 12 along the outer shape of the optical fiber 12 has been described, the side surface of the optical fiber 12 is partially flatly polished as shown in the side view of FIG. Alternatively, the optical device 10a may be obtained by bonding the electrodes 18a and 20a to the plane. Although the labor for polishing the side surface of the optical fiber 12 increases, there is an advantage that the electric field applied to the core 14 increases.

  An optical polarization control device can be realized by adding an electrode pair rotated by 45 ° about the optical axis of the optical fiber 12 to the embodiment shown in FIGS. FIG. 6 shows a perspective view of an optical device configured as such.

  In the optical device 10b shown in FIG. 6, the electrodes 30 and 32 are bonded on the outer peripheral surface of the optical fiber 12 with the optical axis of the optical fiber 12 interposed therebetween, and are further displaced in the axial direction of the optical fiber to 36 is bonded on the outer peripheral surface of the optical fiber 12 with the optical axis of the optical fiber 12 in between. The electrodes 34 and 36 are disposed at positions rotated by 45 ° around the optical axis of the optical fiber 12 with respect to the electrodes 30 and 32. A voltage source 38 applies a voltage between the electrodes 30 and 32, and a voltage source 40 applies a voltage between the electrodes 34 and 36. FIG. 6 shows the electric field generated by the electrodes 30 and 32 and the electric field generated by the electrodes 34 and 36. Since the electrode pair composed of the electrodes 34 and 36 is rotated by 45 ° around the optical axis of the optical fiber 12 with respect to the electrode pair composed of the electrodes 30 and 32, the polarization of the incident light is reflected on the Poincare sphere. You can move freely. That is, the optical device 10b can freely adjust the polarization direction of incident light.

  According to the present invention, a Fabry-Perot filter capable of tuning the transmission or reflection frequency can be realized. FIG. 7 shows a front view of the filter. In the optical device 10c shown in FIG. 7 serving as a Fabry-Perot filter, highly reflective films 50 and 52 are used instead of the nonreflective films 24 and 26 of the embodiment shown in FIG. The same components as those in the embodiment shown in FIGS. 1 to 3 are denoted by the same reference numerals.

When the distance between the high reflection films 50 and 52 is L and the effective refractive index of the optical fiber 12 is n, the free spectral range (FSR) of the Fabry-Perot filter is
c / (2nL)
Given in. c is the speed of light.

  By changing the voltage applied between the electrodes 18 and 20, the effective refractive index n of the optical fiber 12 changes. Assuming that the change in the effective refractive index is Δn, the resonance wavelength, that is, the transmission peak wavelength can be tuned within the period of the FSR if ΔnL that is a half wavelength (λ / 2) is obtained.

  Electromagnetic waves can be detected using the optical device 10 shown in FIGS. FIG. 8 shows a schematic configuration diagram of an embodiment of the electromagnetic wave detection device. Here, the optical device 10 having the configuration shown in FIG. 1 is operated as a birefringent medium.

  The probe light source 60 outputs linearly polarized laser light. The probe light output from the laser light source 60 is input to the optical device 10 via the polarizer 62. The polarizer 62 is preferably arranged in a direction rotated by 45 ° with respect to the electric field direction by the electrodes 18 and 20. The probe light output from the optical device 10 enters the light receiver 66 via the analyzer 64. The light receiver 66 outputs an electrical signal having an amplitude corresponding to the intensity of the probe light that has passed through the analyzer 64. The voltage source 22 applies a DC voltage sufficiently high between the electrodes 18 and 20 to cause birefringence to the optical device 10 when the probe light is incident.

  The electromagnetic wave 68 to be measured is interrupted by the chappa 70 and enters the optical fiber 12 from its side surface. The drive circuit 72 drives the chopper 70 to rotate. A drive signal applied from the drive circuit 72 to the chopper 70 is also applied to the lock-in amplifier 74. The lock-in amplifier 74 amplifies the electric signal output from the light receiver 66 in synchronization with the drive signal from the drive circuit 72. The output of the lock-in amplifier 74 is applied to the analysis device 76. The analysis device 76 displays a value indicating the intensity of the electromagnetic wave 68 from the output value of the lock-in amplifier 74 on the screen of the image display device, or prints it out by the printing device.

  In this embodiment, the incidence of the electromagnetic wave 68 changes the birefringence characteristic of the optical fiber 12, and as a result, the polarization direction of the probe light output from the optical device 10 changes. The light quantity of the probe light incident on the light receiver 66 changes due to the change in the polarization direction, and the analysis device 76 measures the intensity of the electromagnetic wave 68 by analyzing the light quantity change of the probe light.

  Electromagnetic waves can also be detected using the optical device 10c shown in FIG. FIG. 9 shows a schematic configuration diagram of an embodiment of an electromagnetic wave detection apparatus using the optical device 10c. Here, the fact that the resonance frequency of the optical device 10c having the configuration shown in FIG. 7 is changed by an electromagnetic wave input from the outside is used.

  The probe light source 80 generates probe light that is linearly polarized laser light. The probe light is input to the optical device 10c in a direction parallel to the electric field direction by the electrodes 18 and 20 or in a polarization direction perpendicular to the electric field direction. The probe light output from the optical device 10 c enters the light receiver 86. The light receiver 86 outputs an electrical signal having an amplitude corresponding to the intensity of the probe light from the optical device 10c. The voltage source 22 applies a sufficiently high DC voltage between the electrodes 18 and 20 to cause an electro-optic effect to the optical device 10c when the probe light is incident.

  The electromagnetic wave 88 to be measured is interrupted by the chappa 90 and enters the optical device 10c from its side surface. A drive circuit 92 drives the chopper 90 to rotate. A drive signal applied from the drive circuit 92 to the chopper 90 is also applied to the synchronization detector 94 as a synchronization signal. The synchronization detection device 94 detects the amplitude of the output signal of the light receiver 86 in synchronization with the synchronization signal from the drive circuit 92. By measuring the relationship between the intensity of the electromagnetic wave 88 and the amplitude of the electric signal output from the light receiver 86 in advance, the intensity of the electromagnetic wave 88 can be measured.

  In this embodiment, the refractive index of the optical fiber 12 is changed by the incidence of the electromagnetic wave 88. As a result, the resonance frequency of the optical device 10c is changed, and the transmittance for the probe light is changed. The change in transmittance changes the amount of probe light incident on the light receiver 86 and changes the amplitude of the output electrical signal of the light receiver 86. After all, in this embodiment, the change in the transmittance of the optical fiber 12 due to the incident electromagnetic wave 88 is measured.

  In the above description, the optical fiber-shaped optical devices 10, 10a, 10b, and 10c can be easily connected to other optical fibers. Of course, it is obvious that the same effect can be obtained even when the shape is not the shape of an optical fiber but the shape of a planar waveguide. Further, since it is not a single crystal, there is no restriction on the shape, and therefore there are few restrictions on arrangement.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a perspective view of one Example of this invention. It is a side view of a present Example. It is a front view of a present Example. It is a characteristic view of a present Example. It is a side view of a modified example. It is a front view of another modified example. It is a front view of the Example which implement | achieves a Fabry-Perot type | mold filter. It is a schematic block diagram of the Example which detects electromagnetic waves. It is a schematic block diagram of another Example which detects electromagnetic waves.

Explanation of symbols

10, 10a, 10b, 10c: Optical device 12: Optical fiber 14: Core 16: Cladding 18, 20: Electrode 18a, 20a: Electrode 22: Voltage source 24, 26: Non-reflective films 30, 32, 34: Electrode 36, 38: Voltage source 50, 52: High reflection film 60: Probe light source 62: Polarizer 64: Analyzer 66: Light receiver 68: Electromagnetic wave 70 to be measured 70: Chupa 72: Drive circuit 74: Lock-in amplifier 76: Analysis device 80 : Probe light source 86: Light receiver 88: Electromagnetic wave 90 to be measured 90: Chupa 92: Drive circuit 94: Synchronous detection device

Claims (7)

An optical waveguide (12) having a core (14) and a cladding (16);
First and second electrodes (18, 20) disposed across the core (14);
First voltage source (22) for applying a voltage to the first and second electrodes (18, 20)
An optical device comprising:
An optical device characterized in that the core (14) and the cladding (16) both contain chalcogen.   The optical device according to claim 1, characterized in that both the core (14) and the cladding (16) further comprise As (arsenic).   Both the core (14) and the clad (16) are made of a compound containing any one of S, Se, and Te and any one of As, Ge, Ga, and Sb. The optical device according to claim 1.   The optical device according to claim 1, wherein the optical waveguide is an optical fiber.   The optical device according to any one of claims 1 to 4, further comprising an antireflective film (24, 26) on both end faces of the optical waveguide.   The optical device according to any one of claims 1 to 4, further comprising a reflection film (50, 52) on both end faces of the optical waveguide.   Further, the third and fourth electrodes (34, 36) for applying an electric field in a direction rotated by a predetermined angle with respect to the first and second electrodes around the optical axis of the waveguide, and the third The optical device according to any one of claims 1 to 6, further comprising a second voltage source (40) for applying a voltage between the first electrode and the fourth electrode.

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