JPH09130331A - Optical device for monitoring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the polarization dependency of the branching ratio of a beam for monitor by providing a means which generates a collimated beam, first and second reflection faces, and first and second opto-electric conversion means. SOLUTION: A collimated beam CB is generated between ports 20 and 26 by a lens. A wavelength coupler 36, an optical isolator 38, and reflection faces 40 and 42 are arranged on the collimated lens CB in order from the port 20 toward the power 26. These reflection faces 40 and 42 overlap the collimated beam CB and are arranged at angles to the collimated beam CB. The reflection face 40 reflects a part of light going from the port 20 toward the port 26 and supplies the reflected light to a photo diode 44 for output level monitoring. The reflection face 42 totally reflects a part of light going from the port 26 toward the port 20 and supplies the reflected light to a photo diode 46 for reflected light monitoring.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a monitoring optical device suitable for being applied to an optical amplifier.

In an optical communication system to which optical amplification is applied, such as an optical amplification repeater transmission system, elimination of polarization dependence is an important technical issue. Linear polarization from the laser diode as the transmission light source undergoes various disturbances such as stress application to the fiber and temperature change while propagating in the optical fiber transmission line, and as a result, the polarization state of the signal light input to the optical amplifier is: It changes over time.

In performing gigabit-class ultra-high-speed communication, stable amplification characteristics are required regardless of the polarization state of the signal light. Therefore, the optical amplifier or the optical circuit incorporated in the optical amplifier has no polarization dependence. Or it is required to be extremely small.

[0004]

2. Description of the Related Art Conventionally, a doped fiber doped with a rare earth element such as Er (erbium), a pump light source for outputting a pump light for optically pumping the doped fiber, and a signal light input end or a signal light of the doped fiber. An optical amplifier having an optical coupler connected to an output end and supplying pump light to a doped fiber is known.

In this type of optical amplifier, in order to keep the optical output level constant by performing ALC (automatic level control), a part of the light beam in the forward direction from the input side to the output side of the optical amplifier. Is branched as a monitor beam, and this branched beam is input to the optical / electrical conversion element. The ALC circuit feedback-controls the power of the pump light so that the output level of the photoelectric conversion element becomes constant.

On the other hand, when the optical connector of the output fiber of the optical amplifier is detached during the laying work of the optical fiber transmission line or the maintenance work of the optical amplifier, light having a large power is emitted into the space immediately after being amplified, and the worker's It may be necessary to detect the disconnection of the optical connector because it may harm the body or the like. When the optical connector comes off,
Since Fresnel reflection on the end face of the optical fiber increases,
The disconnection of the optical connector may be monitored by, for example, the reflected light in the reverse direction from the output side of the optical amplifier to the input side.

When the monitor beam is branched, if the branching ratio has polarization dependency, for example, when ALC is performed using the monitor beam, the stability of the optical amplifier deteriorates and the transmission quality deteriorates. Occurs. In a coupler film that is generally used to split a monitor beam, the light incident on the film is split into transmitted light and reflected light, so that the splitting ratio is likely to have polarization dependence and polarization dependence. In order to eliminate the above, it is necessary to design the optical system in a complicated or large size.

Therefore, a main object of the present invention is to provide an optical monitoring device in which the branching ratio of the monitoring beam does not depend on polarization. Other objects of the present invention will become clear from the following description.

[0009]

According to the present invention, means for forming a collimated beam between the first and second excitation ports, and a portion of the collimated beam that overlaps and is inclined with respect to the collimated beam. Placed above the first
A part of the collimated beam is overlapped with the first reflecting surface that reflects a part of the light from the excitation port and outputs the light onto the first optical path, and the tilted surface is inclined with respect to the collimated beam. A second reflecting surface that reflects a part of the light from the second excitation port and outputs the light onto the second optical path, and first and second light provided on the first and second optical paths, respectively. Provided is a monitoring optical device including:

In a preferred embodiment of the present invention, the first and second reflecting surfaces are respectively formed on two adjacent surfaces of a polygonal prism (eg, triangular prism).
The first and second photoelectric conversion elements are arranged on the same side with respect to the collimated beam described above.

In the monitoring optical device of the present invention, a part of the collimated beam is reflected by the reflecting surface, and all of the light hitting the reflecting surface is output on the reflected optical path regardless of polarization, and this Since the light is made incident on the electric conversion element, the polarization dependence unlike the case where the conventional coupler film or the like is used does not occur.

The light reflected by the first reflecting surface is, for example, ALC.
The light reflected by the second reflecting surface is provided to detect that the optical connector on the output side is disconnected. By arranging the first and second opto-electrical conversion elements on the same side with respect to the collimated beam as in the preferred embodiment of the present invention, miniaturization of the device is possible. That is, when the reflected light from the front surface and the back surface of one coupler film is used for monitoring the forward and backward beams, respectively, as in the conventional case, two optical / electrical conversion elements must be arranged on both sides of the collimated beam. However, in the preferred embodiment of the present invention, since the two photoelectric conversion elements can be arranged on the same side with respect to the collimated beam, it is possible to reduce the size of the apparatus. It will be possible.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an optical amplifier showing a first embodiment of the present invention. This optical amplifier is an optical relay provided in the middle of an optical fiber transmission line in an optical communication system (optical communication device) including an optical transmitter, an optical receiver, and an optical fiber transmission line laid between them. Can be applied to vessels. This optical amplifier includes the monitoring optical device of the present invention.

This optical amplifier comprises a doped fiber 2 doped with a rare earth element such as Er, and a pre-stage module 4 and a post-stage module 6 connected to the signal light input end and the signal light output end of the doped fiber 2, respectively. ing. The present invention can be applied to the post-stage module 6 in this embodiment.

The front stage module 4 includes a laser diode 8
Port 1 to which the signal light with wavelength of 1.55 μm is supplied from
0, an optical coupler 12 that splits the signal light supplied to the port 10 into two, a photodiode 14 for input level monitoring to which one branch light is input, an optical isolator 16 that transmits the other branch light, and an optical It has a port 18 for outputting the signal light 4 transmitted through the isolator 16. The port 18 is connected to the signal light input end of the doped fiber 2.

The post-stage module 6 has a port 20 connected to the signal light output end of the doped fiber 2. The wavelength of the signal light is in the 1.55 μm band, and the doped fiber 2
When the dopant is Er, the wavelength of the pump light is set to, for example, the 1.48 μm band. Laser diode 22
The pump light from is supplied to the post-stage module 6 via the port 24. The rear module 6 further has a port 26 for outputting signal light.

The port 26 is connected to the optical connector 30 by an optical fiber 28, and the optical fiber 32 on the output side which is an optical transmission line is connected to the optical connector 34. Optical connector 30
And 34 are detachable from each other, whereby the optical amplifier and the optical fiber transmission line are connected.

A collimated beam CB is provided between the ports 20 and 26 by a lens, which will be described later, which is provided in each of them.
Is formed. Port 2 on the collimated beam CB
A wavelength coupler 36, an optical isolator 38, and reflecting surfaces 40 and 42 are arranged in this order in the direction from 0 to the port 26.

The wavelength coupler 36 supplies the pump light supplied from the port 24 to the doped fiber 2 from the port 20, and supplies the amplified signal light supplied from the port 20 to the optical isolator 38.

The reflecting surfaces 40 and 42 are arranged so as to partially overlap the collimated beam CB and be inclined with respect to the collimated beam CB. The reflecting surface 40 totally reflects a part of the light traveling from the port 20 to the port 26 and supplies the reflected light to the photodiode 44 for output level monitoring. The reflecting surface 42 totally reflects a part of the light traveling from the port 26 to the port 20 and supplies the reflected light to the photodiode 46 for monitoring the reflected light.

A specific method of forming the reflecting surfaces 40 and 42 will be described later. Since total reflection occurs on the reflecting surfaces 40 and 42, the photodiodes 44 and 46 have no polarization dependency. Therefore, for example, when ALC is performed based on the output signal of the photodiode 44, highly accurate control becomes possible.

When the optical connector 34 is connected to the optical connector 30, since the fiber end faces are in close contact with each other, Fresnel reflection hardly occurs and the return loss is 40d.
There is about B, and there is almost no reflected return light. However, when the optical connector 30 and the optical connector 34 are removed for maintenance work or the like, reflected return light is generated due to Fresnel reflection between the fiber end surface and the air, and the return loss is, for example, 14 dB.

The reflected return light can be detected by the photodiode 46 for monitoring the reflected light. When the output level of the photodiode 46 becomes larger than a predetermined value, it is determined that the amplified light is emitted from the optical connector 30 to the space, and the drive current of the laser diode 22 serving as the pump light source is reduced to, for example, Set to 0. This prevents the amplified signal light from being immediately emitted when the optical connector 30 and the optical connector 34 are detached from each other, thereby improving safety in maintenance work and the like.

Next, two examples of conventional monitoring optical devices will be described in order to explain the superiority of the embodiment of the present invention in more detail. 2 and 3 are views showing first and second conventional examples of the monitoring optical device, respectively. 2 and 3 each show a portion corresponding to the latter-stage module 6 in FIG. 1, and the substantially same portions are designated by the same reference numerals.

In the first conventional example shown in FIG. 2, the incident angle is about 45 °.
The coupler film 48 set to
Part of the light traveling from 0 to the port 26 is reflected by the coupler film 48 and input to the photodiode 44 for output level monitoring, and part of the light traveling from the port 26 to the port 20 is reflected by the coupler film 48 and reflected. It is input to the photodiode 46 for optical monitoring.

In this conventional example, port 20 and port 26
Since the coupler film 48 is provided so as to act on all of the collimated beams formed between and, polarization dependency occurs during monitoring by the photodiodes 44 and 46.

In addition, using one coupler film 48,
Since the photodiodes 44 and 46 need to be arranged on the one reflection optical path, respectively, the photodiodes 44 and 46 must be arranged to face each other, and a large printed wiring board 50 is required. The laser diode 22 for pump light is mounted on the printed wiring board 50 by the terminal 52, and the photodiodes 44 and 46 are mounted on the printed wiring board 50 by the terminals 54 and 56, respectively.

In the first embodiment of FIG. 1, since the monitor beam is branched by the total reflection on the reflecting surfaces 40 and 42, the polarization dependence does not occur. An embodiment that enables the use of a small printed wiring board will be described later.

In the second prior art example of FIG. 3, in order to place the photodiodes 44 and 46 on the same side of the module,
A prism 58 for returning the optical path is additionally provided.
In this conventional example, the cost increase and the size increase due to the increase in the number of optical components cannot be avoided.

A second embodiment of the present invention which is particularly suitable for miniaturization will be described with reference to FIG. Reference numeral 60 represents a housing (or substrate) for fixing each optical element, and the sleeve 6 is associated with the ports 20, 24 and 26, respectively.
2, 64 and 66 are fixed to the housing 60 by, for example, laser welding.

In the sleeve 62, a ferrule 68 for supporting the doped fiber 2 and a lens 70 are inserted and fixed at a predetermined interval, and the sleeve 64 is provided for connection with the laser diode 22 for pump light. The ferrule 72 and the lens 74 that support the optical fiber are inserted and fixed at a predetermined interval, and the ferrule 76 and the lens 78 that support the fiber 28 are inserted and fixed at a predetermined interval in the sleeve 66.

The light emitted from the excitation end 2A (excitation port) of the doped fiber 2 is converted into a collimated beam CB by the lens 70, and the collimated beam CB is converted into the lens 7 by the lens 7.
8 by the excitation end 28A of the fiber 28 (excitation port)
Converges. The pump light from the laser diode 22 is collimated by the lens 74, reflected by the wavelength coupler 36, and supplied to the doped fiber 2.

In this embodiment, the reflecting surfaces 40 and 42 are formed on the two surfaces of the triangular prism 80, respectively. The triangular prism 80 is arranged such that the top defined by the reflecting surfaces 40 and 42 overlaps a part of the collimated beam CB.

Thus, a part of the light traveling from the port 20 to the port 26 is totally reflected by the reflecting surface 40 and supplied to the photodiode 44, and a part of the light traveling from the port 26 to the port 20 is totally reflected by the reflecting surface 42. It is reflected and supplied to the photodiode 46.

By forming the reflecting surfaces 40 and 42 on the triangular prism 80, the photodiodes 44 and 46 can be arranged on the same side with respect to the collimated beam CB. As a result, the printed wiring board 50 'on which the laser diode 22 and the photodiodes 44 and 46 are mounted can be downsized.

Two control circuits are mounted on the printed wiring board 50 '. The first control circuit receives the output signal of the photodiode 44 and controls the drive current of the laser diode 22 so that its level becomes constant.

The second control circuit is the photodiode 46.
When the output level becomes higher than a predetermined value, the drive current of the laser diode 22 is controlled so as to reduce the power of the pump light.

The first control circuit is for ALC. The second control circuit detects the Fresnel reflected light at the optical connector 30 when the optical connector 30 is at the free end and prevents the amplified signal light from being emitted from the optical connector 30 into the space. It is a thing.

The cross-sectional area of the collimated beam CB blocked by the prism 30 is preferably 5% or less of the total cross-sectional area of the collimated beam CB. This is because if it is 5% or more, the attenuation of the signal light in this post-stage module becomes large and the S / N deteriorates.

As the reflecting surfaces 40 and 42, a metal film or a dielectric multilayer film can be used. A prism or an optical plate may be arranged so that the total reflection condition is satisfied without using an independent member as the reflecting surface.

In this embodiment, since the reflecting surfaces 40 and 42 are formed on the two surfaces of the triangular prism 80, the reflecting surfaces 40 and 42 overlap the same part of the collimated beam CB. In this case, the monitoring by the reflecting surface 40 acting on the light in the forward direction can be satisfactorily performed, but the reflected return light by the reflecting surface 42 acting in the backward direction may not be satisfactorily monitored.

In such a case, by appropriately setting the length of the fiber 28 connected to the optical connector 30, the reflected return light is returned to a substantially normal Gaussian beam by the round-trip propagation in the fiber 28. And the chipped portion of the reflecting surface 40 is completely corrected in the opposite direction, and
The reflected return light can be well monitored.

FIG. 5 is a configuration diagram of a main part of an optical device showing a third embodiment of the present invention. In this embodiment, a triangular prism 80 'having a right apex angle is used, and reflecting surfaces 40 and 42 are formed on the surfaces sandwiching the apex angle, respectively, so that the forward reflected beam and the backward reflected beam are mutually formed. I try to be parallel.

Then, the photodiode array PDA having at least two light receiving regions is used to receive these two reflected beams. The light receiving region where the forward reflected beam is incident corresponds to the photodiode 44 in the above-described embodiments, and the light receiving region where the backward reflected return light beam is incident corresponds to the photodiode 46.

According to this embodiment, the size of the device can be further reduced as compared with the second embodiment shown in FIG. FIG. 6 is a configuration diagram of a main part of an optical device showing a fourth embodiment of the present invention. In this embodiment, a transparent plate 82 is provided so as to overlap the collimated beam formed between the first and second excitation ports, and one total reflection film 84 having a predetermined area is formed on the transparent plate 82. There is. The monitor beam in the forward direction is reflected by one surface of the total reflection film 84 and is incident on the photodiode 44, and the reflected return light is the total reflection surface 84.
The light is reflected by the other surface and enters the photodiode 46.

In this embodiment, since the two reflecting surfaces are obtained by one total reflection film, the optical device can be easily manufactured. In the embodiment described above, the excitation port is the excitation end of the optical fiber, but the present invention is not limited to this. A light source such as a laser diode can also be used as the excitation port.

[0047]

As described above, according to the present invention,
There is an effect that it is possible to provide a monitoring optical device having no polarization dependency. Further, according to the specific embodiment of the present invention, there is an effect that it is possible to provide a monitoring optical device having no polarization dependency and suitable for miniaturization.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical amplifier showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a first conventional example of a monitoring optical device.

FIG. 3 is a diagram showing a second conventional example of a monitoring optical device.

FIG. 4 is a configuration diagram of a monitoring optical device showing a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a main part of a monitoring optical device showing a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a main part of a monitoring optical device showing a fourth embodiment of the present invention.

[Explanation of symbols]

 2 Doped fiber 20, 24, 26 port 36 Wavelength coupler 38 Optical isolator 40, 42 Reflective surface

Claims (6)

[Claims] 1. A means for forming a collimated beam between first and second excitation ports, and a means for forming a collimated beam overlapping a part of the collimated beam and inclined with respect to the collimated beam, the first excitation A first reflecting surface that reflects a part of the light from the port and outputs it on a first optical path; and a first reflecting surface that overlaps a part of the collimated beam and is inclined with respect to the collimated beam, Second reflecting surface for reflecting a part of the light from the excitation port of the second optical path and outputting the reflected light to the second optical path, and the first and second optical / electrical surfaces provided on the first and second optical paths, respectively. A monitoring optical device including a conversion element. 2. The first and second excitation ports are the excitation ends of the first and second optical fibers, respectively, and the means for forming the collimated beam is the excitation ends of the first and second optical fibers. The optical device for monitoring according to claim 1, further comprising a first lens and a second lens provided to face each other. 3. The first and second reflecting surfaces are respectively formed on two adjacent surfaces of a polygonal prism, and the first and second photoelectric conversion elements are the same for the collimated beam. The optical device for monitoring according to claim 1, which is disposed on the side. 4. A first end to which signal light is supplied and the first end.
A doped fiber doped with a rare earth element having a second end connected to the excitation port, a pump light source for outputting pump light having a wavelength determined according to the wavelength of the signal light and the rare earth element, Light is introduced into the doped fiber at its first and second ends.
The optical device for monitoring according to claim 1, further comprising: a means for supplying from at least one of the ends, and the second excitation port is an excitation end of an optical fiber. 5. The monitoring light according to claim 4, further comprising means for reducing the power of the pump light when the output level of the second optical / electrical conversion element becomes larger than a predetermined value. device. 6. An optical amplifier or optical communication apparatus comprising the monitoring optical device according to claim 1. Description: