KR19990026180A - Optical isolator composite module and optical amplifier using same - Google Patents

Abstract

It is an object of the present invention to provide an optical isolator composite module in which an optical splitter separating an optical signal entering an input terminal, an optical detector for detecting separated light, a compensator for compensating dispersion due to polarization, and a pumping light source are integrated and combined with an optical isolator. To provide. The optical isolator composite module for achieving the above object comprises a first lens for focusing the signal light of the first frequency incident; A light source for generating and outputting pumping light of a second frequency required to amplify an optical signal from an external special optical fiber; A second lens for focusing the pumping light output from the light source; The optical signal is restricted to flow in only one direction, and the first coating layer is coated on the exit surface to transmit the signal light focused by the first lens and traveling therein, and the pumping focused by the second lens ( An isolator core reflecting light and having a second coating layer applied to the incident surface for reflecting light to reflect a part of the signal light focused by the first lens; A third lens converging the signal light transmitted through the first coating layer and the pumping light reflected from the coating layer; A photo detector positioned in a traveling direction of the partially reflected signal light and configured to detect the partially reflected reflected light to generate a detection signal current according to the magnitude of the detection light; And a fourth lens for focusing the partially reflected signal light. This reduces the number of parts and reduces the number of Splicing Points of the optical fiber.

Description

Optical isolator composite module and optical amplifier using same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier, and more particularly, to an optical isolator composite module in which several optical amplifier component parts are integrated and combined with an optical isolator, and an optical amplifier using such an isolator composite module.

Optical fibers used in optical communication have inherently lower transmission loss and wider bandwidth than other lines such as copper wire and coaxial cable. Nevertheless, transmission loss cannot be ignored at all, so it is necessary to amplify the transmitted optical signal periodically to compensate for the attenuation of the signal. This amplification of the optical signal is performed by a repeater provided in the middle of the line.

In most optical communication systems in use today, repeaters consist of detectors, electrical amplifiers, and semiconductor lasers. In such a repeater, the detector converts the attenuated optical signal into an electrical signal, and the amplifier amplifies the converted electrical signal. The semiconductor laser is driven by the amplified signal to transmit the signal to the next step on the line. However, such a repeater increases the attenuation and has a disadvantage in that the conversion speed of the optical signal into the electrical signal and the conversion speed of the electrical signal into the optical signal are limited due to the bandwidth of the components such as the detector and the amplifier.

Accordingly, pure optical amplifiers that amplify optical signals by themselves have been developed and used. Such an optical amplifier is used not only for optical communication but also for power amplification of a low power light source, compensation for signal splitting in a cable TV network, or shear amplification for an optical detector.

At the moment, the most popular optical amplifiers are Erbium-doped Fiber Amplifiers (EDFAs), which offer greater than 40dB of gain, high output power, and noise in the band around 1.55μm. This is because the noise figure has a low characteristic.

1 is a block diagram of a typical Erbium-doped optical amplifier (EDFA), where FIG. 1A is a forward amplifier and FIG. 1B shows a reverse amplifier.

The forward amplifier of FIG. 1A includes a first lens 10 for focusing input light emitted from a first optical fiber (not shown), a photo detector 11 for detecting the intensity of the input light, and the photo detector 11. The optical separator 12 for coupling the on-line, the first isolator 14 for restricting the optical signal to flow in only one direction, the laser diode 16 for generating the optical signal for pumping, and A coupler 18 for coupling the laser diode 16 to the line and a charge carrier excited by the pumping action of the pumping light are used to generate a laser action to amplify the input optical signal. Erbium-doped fiber (hereinafter referred to as EDF), a second isolator 22 for restricting the optical signal to flow only in the forward direction, a photodetector 24 for detecting the intensity of the output light, and the light For coupling the detector 24 to the track And a second lens 28 for the focusing and the separator 26, and the output light focused light is incident to a second optical fiber (not shown).

In the forward amplifier configured as described above, the EDF 18 is doped with the erbium to the core of the optical fiber by modified chemical vapor deposition (Modified CVD) using a source gas such as erbium trichloride (ErCl3), 1.536 It has an emission wavelength of μm.

On the other hand, the laser diode 16 generates laser light having a wavelength of 1.48 μm or 980 nm and supplies it to the EDF 18. The laser light pumps electrons of erbium to cause distribution inversion, and accordingly, the EDF 18 outputs laser light having a wavelength of 1.536 μm.

The first isolator 14 of the two isolators 14 and 22 is reflected from the input connector (not shown) after the light amplified or spontaneous emission in the EDF 20 is introduced to the input side. It is prevented from dropping the amplification efficiency by flowing back into the EDF (20). In addition, the second isolator 22 prevents an optical signal from being reflected from a connector (not shown) or the like at the output terminal and flowing into the EDF 20.

Meanwhile, the reverse amplifier shown in FIG. 2B has the same structure as the forward amplifier of FIG. 2A except that the pumping laser diode 17 is coupled to the rear end of the EDF 21 by the coupler 19.

In the optical amplifier of FIG. 1, the first lens 10, the optical separator 12, and the isolator 14 are usually manufactured as one composite module.

2 is a view showing a conventional isolator composite module. The isolator composite module 30 includes a first lens 31 for focusing input light emitted from a first optical fiber (not shown), a photo detector 32 for detecting the intensity of the input light, and the photo detector 32. ), An optical separator 34 for coupling on the track, an isolator 36 for restricting the optical signal to flow in only one direction, and a compensator 40 for compensating for dispersion of light output from the isolator 37. do.

The optical separator 34 is implemented using a prism or an optical coating. The optical separator 34 separates a part of an input optical signal and inputs the optical detector 32 to the isolator 36.

The isolator 36 is disclosed in U.S. Patent No. 4,548,478 of Fujitsu, which is made of a material having a birefringence such as calcite, and has a tapered shape of the first birefringent element 37 and the second birefringent element 39. ) And a 45 ° Faraday Rotator (38) inserted between the first birefringent element (37) and the second birefringent element (39).

However, the isolator 36 as described above has a drawback in that dispersion loss occurs due to a difference in refractive index of light, that is, a difference in propagation speed. Accordingly, as disclosed in the European patent application (ATT No. 533,398 A1) of AT < RTI ID = 0.0 > (ATT), < / RTI >

However, such a conventional isolator composite module has a large number of parts and a complicated structure. Accordingly, the insertion loss is a big disadvantage. In addition, as shown in FIG. 2, several places, such as between the optical separator 34 and the photodetector 32, between the optical separator 34 and the isolator 36, and between the isolator 36 and the compensator 40 and the like. In this case, the fiber optics must be spliced. Accordingly, there is a problem that the manufacturing process is complicated and the unit cost of the product is high. On the other hand, polarization loss (Polarization Dependent Loss) has a big disadvantage because the incident light is incident on the optical splitter at an angle of incidence of 45 degrees.

In addition, when the isolator composite module is to be applied to the optical amplifier, in order to amplify the signal light output from the isolator composite module in the EDF, the light emitted from a light source such as a laser diode must be coupled to the path of the signal light. Accordingly, the coupler 18 of FIG. 1 must be used to combine the two optical signals.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, wherein an optical splitter separating an optical signal entering an input terminal, an optical detector for detecting separated light, a compensator for compensating dispersion due to polarization, and a pumping light source are integrated into the optical isolator and It is a technical problem to provide a composite optical isolator composite module.

Another technical problem of the present invention is to provide an optical amplifier using the isolator composite module as described above.

1 is a block diagram of a typical Erbium-doped optical amplifier (EDFA), where FIG. 1A shows a forward amplifier and FIG. 1B shows a reverse amplifier.

2 is a block diagram of a conventional optical isolator composite module.

3 is a view showing the flow of light in the optical isolator composite module according to the present invention.

4 is a perspective perspective view of an isolator core in the optical isolator composite module according to the present invention.

5 is a cross-sectional view showing a path in the case where light travels forward in the isolator core of the optical isolator composite module according to the present invention.

6 is a cross-sectional view showing a path in which light travels backward in an isolator core of the optical isolator composite module according to the present invention.

7 is a perspective view of an optical isolator composite module according to the present invention.

8 is a block diagram of one embodiment of an erbium doped optical amplifier (EDFA) in accordance with the present invention.

The isolator composite module of the present invention for achieving the above technical problem is a first focusing means for focusing the signal light of the first frequency incident; A light source for generating and outputting pumping light of a second frequency required to amplify an optical signal from an external special optical fiber; Second focusing means for focusing the pumping light output from the light source; The optical signal is restricted to flow in only one direction, and the first coating layer is coated on the emission surface to focus the first signal and transmit the signal light traveling therein, and focused by the second focusing means. An isolator core that reflects pumping light; And a third focusing means for focusing the signal light transmitted through the first coating layer and the pumping light reflected from the coating layer.

On the other hand, the optical amplifier of the present invention for achieving the above another technical problem is to block the advancing of the optical signal to eliminate the gain reduction caused by the reflected wave, and the first isolator module for branching and detecting a portion of the signal light; And a special optical fiber for amplifying the signal light signal by induced emission. The first isolator module includes: first focusing means for focusing signal light of an incident first frequency; A light source for generating and outputting pumping light of a second frequency required to amplify an optical signal from an external special optical fiber; Second focusing means for focusing the pumping light output from the light source; The optical signal is restricted to flow in only one direction, and the first coating layer is coated on the emission surface to focus the first signal and transmit the signal light traveling therein, and focused by the second focusing means. An isolator core that reflects pumping light and is coated with a second coating layer for partial reflection on an incident surface thereof to reflect a part of the signal light focused by the first focusing means; Third focusing means for focusing the signal light transmitted through the first coating layer and the pumping light reflected from the coating layer; A photo detector positioned in a traveling direction of the partially reflected signal light and configured to detect the partially reflected reflected light to generate a detection signal current according to the magnitude of the detection light; And a fourth focusing means for focusing the partially reflected signal light.

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

Figure 3 shows an embodiment of an optical isolator composite module according to the present invention.

The optical isolator composite module 50 includes a first lens 51, isolator cores 52, 53, and 54, a photo detector 56 positioned in a direction in which incoming light is reflected, and the photo detector 56. A second lens 57 located at the front end, a laser diode 58 for generating pumping light used for amplifying an optical signal in an erbium-doped optical fiber (not shown), and a third for focusing the pumping light The lens 59 and the fourth lens 60 that focus output light are included.

The isolator core consists of first and second birefringent elements 52, 54 and a Faraday rotor 53 inserted between the first and second birefringent elements 52, 54.

The first birefringent element 52 is an optically anisotropic material, which transmits incident light into two different refractive lights. The optical axis of the crystal is perpendicular to the x-axis direction, and the incident surface 52a of the light has a tapered shape at a predetermined angle φ1 with respect to the exit surface 52b. On the other hand, the incident surface 52a has a partial reflection coating to reflect a part of the light focused by the first lens 51.

The second birefringent element 54 has a shape in which the light exit surface 54b is tapered at a predetermined angle phi 2 with respect to the incident surface 54a. An optical axis exists at a position rotated 45 ° with respect to the optical axis of the first birefringent element 52 in a direction opposite to the rotation direction of the light by the Faraday rotor 53.

The Faraday rotor 53 rotates the birefringent light by 45 °.

FIG. 5 is a cross-sectional view illustrating a path in a case where light travels forward in an isolator core in the isolator composite module according to the present invention, and FIG. 6 is a view in which light is reversed in the isolator core in the isolator composite module according to the present invention. It is sectional drawing which shows the path in case of progress.

In FIG. 5, the path I of light represents a path of light that is a stationary wave Ro in the first birefringent element 52 and an abnormal wave Re in the second birefringent element 54. Path II is a path of light that is an abnormal wave Re 'in the first birefringent element 52 and a stationary wave Ro' in the second birefringent element 54.

As shown in FIG. 5, when the light travels in the forward direction, light that is a normal wave (Ro: Ordinar Ray) in the first birefringent element 52 is an abnormal wave (Re: extra-ordinary) in the second birefringent element 54. Becomes In addition, light that is an abnormal wave Re in the first birefringent element 52 becomes a stationary wave Ro in the second birefringent element 54.

This is because, when light travels from the first birefringent element 52 to the second birefringent element 54, the direction of rotation of the light by the Faraday rotor 53 and the second birefringent element 54 with respect to the first birefringent element 52. This is because the direction of rotation of the optical axis is reversed to each other, so that the light rotates by 90 °, thereby changing the standing wave (Ro) and the abnormal wave (Re).

Meanwhile, in FIG. 6, the path III of light represents a path of light, which is a standing wave Re, in the first birefringent element 52 and the second birefringent element 54, and the path IV represents the first birefringent element 52 and the second. The birefringent element 54 shows a path of light that is an unsteady wave Ro.

As shown in FIG. 6, when the light travels in the reverse direction, the light is rotated by the Faraday rotor so that the light, which is the standing wave Ro in the second birefringent element 54, is also the standing wave Ro in the first birefringent element 52. Becomes In addition, light that is an abnormal wave Re in the second birefringent element 54 is also an abnormal wave Re in the first birefringent element 52.

Therefore, the incident angles θi in the forward direction and the exit angles θi3 and θ ′ i3 in the forward direction are different from the incident surface 52a of the first birefringent element 52. Therefore, light emitted from the first optical fiber and traveling in the forward direction propagates through the isolator core to the second optical fiber, while light traveling in the reverse direction is not incident on the first optical fiber.

In particular, when the light travels in the forward direction, the standing wave Ro and the abnormal wave Re are changed in the first birefringent element 52 and the second birefringent element 54, and thus, the standing wave Ro and the abnormal wave ( The difference in refractive index between the first birefringent element 52 and the second birefringent element 54 which affects the progress of Re is automatically compensated. Therefore, in the isolator module according to the present invention, the spread due to polarization is very small, and a separate compensator is unnecessary.

For a more detailed description of the isolating action of the isolator core as described above, that is, the unidirectional transfer action of light, see Patent Application No. 2393 filed on January 28, 1997, by the applicant of the present invention. And optical amplifiers using the same).

On the other hand, the incident surface 52a of the first birefringent element 52 is partially reflective coated. In addition, the emission surface 54a of the second birefringent element 54 is coated so that almost all of the light that has propagated inside the isolator core is transmitted and almost the light incident from the laser diode 58 is totally reflected.

Hereinafter, the operation of the optical isolator composite module configured as described above will be described in more detail with reference to FIG. 3.

First, the first lens 51 focuses light from a light source or a first optical fiber (not shown) so that the focused light is incident on the incident surface 52a of the isolator core at a predetermined angle. In order to minimize Polarization Dependent Loss, the smaller the angle of incidence is preferable, in this embodiment, it has a value of about 3-12 °.

Since the incident surface 52a of the first birefringent element 52 is partially reflected coated, some of the incident light focused by the first lens 51 is reflected by the incident surface 52a of the first birefringent element 52. And detected by the photodetector 56. Meanwhile, most incident light signals pass through the incident surface 52a and proceed into the first birefringent element 52.

The photo detector 56 detects light reflected from the incident surface 52a of the first birefringent element 52, and may be configured using a photodiode. On the other hand, the second lens 57 increases the detection efficiency by focusing the light reflected from the incident surface 52a of the first birefringent element 52 to the light receiving surface of the photodetector 56.

Meanwhile, the light passing through the incident surface 52a of the first birefringent element 52 and traveling into the first birefringent element 52 passes through the Faraday rotor 53 and the second birefringent element 54 to pass through the fourth lens ( Proceed to 60).

An erbium-doped optical fiber (not shown) is connected to the rear end of the optical isolator composite module 50, and the laser diode 58 generates and outputs pumping light required to amplify the optical signal in the erbium-doped optical fiber. .

The third lens 59 focuses the pumping light output from the laser diode 58 to be incident on the emission surface 54b of the second birefringent element 54.

Since the coating layer 55 is formed on the exit surface 54b of the second birefringent element 54, the pumping light incident on the exit surface 54b of the second birefringent element 54 is almost totally reflected to form the fourth lens ( Proceed to 60).

The coating layer 55 has a thickness and a material thereof so as to perform such a reflective action.

The fourth lens 60 focuses the signal light emitted from the emission surface 54b of the second birefringent element 54 and the pumping light reflected from the emission surface 54b of the second birefringent element 54 to collect a second optical fiber. To be incident (not shown).

7 is a perspective view of an isolator composite module according to the present invention.

As shown in FIG. 7, the isolator composite module according to the present invention may be manufactured by molding in one package. The molded isolator composite module package includes a main body 62 in which an isolator core and the like are sealed, an input terminal 63 into which an input optical signal flows, an output terminal 66 through which an output optical signal flows out, and light detected by an optical diode. A detection signal terminal 64 through which a current varying in magnitude according to the signal flows, and a bias terminal 65 through which a bias current with respect to the laser diode 58 flows.

In the main body, an isolator core, a first lens 51, a photodetector 55 and a second lens 57, a laser diode 58, a third lens 59, and a fourth lens 60 are provided. The relative positions of each other are precisely adjusted and then fixedly placed. Therefore, the parts are relatively incapable of displacement and water or dust does not penetrate into the isolator module.

The light propagates directly between the parts instead of through the fiber, eliminating the need for fiber between the isolator core and the light detector. Moreover, the number of optical fiber connection points which required several places in the conventional apparatus is greatly reduced.

8 is a block diagram of one embodiment of an erbium doped optical amplifier (EDFA) of the present invention.

The optical amplifier 70 uses a first isolator composite module 72 for branching and detecting a part of incident light while restricting the optical signal to flow only in the forward direction, and a charge carrier excited by the pumping action of the pumped light. Erbium-doped optical fiber 74 (EDF) for amplifying an input optical signal by inducing a LASER action, and a second isolator composite module for branching and detecting a part of the amplified signal light while restricting the optical signal to flow only in a forward direction ( 76).

The function or operation of the first isolator composite module 72 is as described above. On the other hand, the second isolator composite module 76 is configured similarly to the first isolator composite module 72, but the laser diode and the third lens are omitted, and the coating layer is not formed on the exit surface of the second birefringent element. Since other components are the same as in the conventional optical amplifier, detailed description thereof will be omitted.

As shown in FIG. 8, the first and second isolator composite modules 72 and 76 limit the light to flow in only one direction, and simultaneously detect the magnitude of the light and output a detection current accordingly.

Meanwhile, the optical amplifier of the present invention is not limited to the above embodiment, and various modifications are possible. For example, in order to improve the characteristic, a plurality of isolator cores may be connected in series.

According to the isolator composite module and the optical amplifier of the present invention as described above, the optical separator for separating the optical signal coming into the input terminal, the optical detector for detecting the separated light and the laser diode for generating pumped light and dispersion due to polarization compensation By integrating and combining the compensator with the isolator, the number of parts is reduced and the structure is simplified. This results in a small insertion loss.

In addition, since each component is fixed by molding in the package and the number of components is reduced, thereby reducing the number of Splicing Points of the optical fiber, the manufacturing process is simplified and thus the unit cost of the product is lowered.

On the other hand, since incident light is incident on the optical splitter at a small angle of incidence, polarization loss (Polarization Dependent Loss) is also reduced. As such, as the optical properties are improved, the reliability of the product is increased.

Claims (14)

First focusing means for focusing signal light of an incident first frequency; A light source for generating and outputting pumping light of a second frequency required to amplify an optical signal from an external special optical fiber; Second focusing means for focusing the pumping light output from the light source; The optical signal is restricted to flow in only one direction, and the first coating layer is coated on the emission surface to focus the first signal and transmit the signal light traveling therein, and focused by the second focusing means. An isolator core that reflects pumping light; And And a third focusing means for converging the signal light transmitted through the first coating layer and the pumping light reflected from the coating layer. The optical isolator composite module according to claim 1, wherein said first focusing means, said light source, said second focusing means, said isolator core and said third focusing means are sealed in one package. The method of claim 1, The incident surface of the isolator core is coated with a second coating layer for partial reflection to reflect a part of the signal light focused by the first focusing means, A photo detector positioned in a traveling direction of the partially reflected signal light and configured to detect the partially reflected reflected light to generate a detection signal current according to the magnitude of the detection light; And And a fourth focusing means for focusing the partially reflected signal light. 4. The optical isolator composite module according to claim 3, wherein the signal light focused by the first focusing means is incident on the incident surface of the isolator core at an incident angle of 3 to 12 degrees. The method of claim 3 wherein the isolator core is A first birefringent element having a tapered shape at an incident surface at a first predetermined angle with respect to the exit surface, and having a second coating layer coated on the incident surface; A Faraday rotator for rotating the polarized light emitted from the first birefringent element by 45 °, The emission surface has a tapered shape at a second predetermined angle with respect to the incident surface, and the optical axis exists at a position rotated in a direction opposite to the rotation direction of the light by the Faraday rotor with respect to the optical axis of the first birefringent element. And a second birefringent element having a first coating layer coated on an exit surface thereof. The method of claim 5, wherein the first focusing means, the light source, the second focusing means, the isolator core, the third focusing means, the photo detector and the fourth focusing means are sealed in one package. An optical isolator composite module. A first isolator module which cuts off a reverse direction of the optical signal to eliminate a gain reduction phenomenon caused by the reflected wave and detects a part of the signal light by branching; And In the optical amplifier comprising a; special optical fiber for amplifying the signal light signal by inductive emission, wherein the first isolator module First focusing means for focusing signal light of an incident first frequency; A light source for generating and outputting pumping light of a second frequency required to amplify an optical signal from an external special optical fiber; Second focusing means for focusing the pumping light output from the light source; The optical signal is restricted to flow in only one direction, and the first coating layer is coated on the emission surface to focus the first signal and transmit the signal light traveling therein, and focused by the second focusing means. An isolator core that reflects pumping light and is coated with a second coating layer for partial reflection on an incident surface thereof to reflect a part of the signal light focused by the first focusing means; Third focusing means for focusing the signal light transmitted through the first coating layer and the pumping light reflected from the coating layer; A photo detector positioned in a traveling direction of the partially reflected signal light and configured to detect the partially reflected reflected light to generate a detection signal current according to the magnitude of the detection light; And And a fourth focusing means for focusing the partially reflected signal light. The method of claim 7, wherein the isolator core is A first birefringent element having a tapered shape at an incident surface at a first predetermined angle with respect to the exit surface, and having a second coating layer coated on the incident surface; A Faraday rotator for rotating the polarized light emitted from the first birefringent element by 45 °, The emission surface has a tapered shape at a second predetermined angle with respect to the incident surface, and the optical axis exists at a position rotated in a direction opposite to the rotation direction of the light by the Faraday rotor with respect to the optical axis of the first birefringent element. And a second birefringent element coated with a first coating layer on an exit surface. The method of claim 8, wherein the first focusing means, the light source, the second focusing means, the isolator core, the third focusing means, the photo detector and the fourth focusing means are sealed in one package. An optical isolator composite module. The optical amplifier according to claim 7, wherein the special optical fiber is doped with a rare earth element. The optical amplifier according to claim 10, wherein the special optical fiber is an erbium doped optical fiber. The method of claim 7, wherein And a second isolator module coupled to a rear end of the special optical fiber and blocking a reverse direction of the optical signal due to reflection from the output terminal and branching and detecting a portion of the amplified optical signal. The method of claim 12, wherein the second isolator module Fifth focusing means for focusing signal light of an incident first frequency; A second isolator core restricting the optical signal to flow in only one direction and having a third coating layer applied to the incident surface to reflect a part of the signal light focused by the fifth focusing means; Sixth focusing means for focusing the signal light transmitted through the first coating layer; A second photo detector positioned in a traveling direction of the partially reflected signal light and configured to detect the partially reflected reflected light to generate a detection signal current according to the magnitude of the detection light; And And a seventh focusing means for focusing the partially reflected signal light. The method of claim 13 wherein the second isolator core is A third birefringent element having a tapered shape at an incident surface at a first predetermined angle with respect to the exit surface, and having a third coating layer coated on the incident surface; A second Faraday rotator for rotating the polarization emitted from the third birefringent element by 45 °, The optical axis is formed at a position where the exit surface is tapered at a second predetermined angle with respect to the incident surface, and is rotated in a direction opposite to the rotation direction of the light by the second Faraday rotor with respect to the optical axis of the third birefringent element. And a fourth birefringent element present.