JP3251330B2 - Optical module for optical amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module for an optical amplifier using an optical fiber doped with a rare earth element such as erbium.

Recently, research on optical amplifiers capable of directly amplifying optical signals has been actively conducted, and among them, rare earth elements (E
Optical amplifiers that combine an optical fiber doped with (r, Nb, Yb, etc.) and pumping light have attracted attention.

[0003] This optical amplifier has no polarization dependence,
It has excellent features such as low noise and low coupling loss with the optical fiber transmission line. It is expected to enable a dramatic increase in the transmission repeater distance in an optical fiber transmission system and distribution of optical signals to a large number. I have.

In order to realize such an optical amplifier,
An optical circuit including at least a demultiplexer for demultiplexing the signal light and the pump light, a coupler for extracting the monitor light, and the like is required, and an optical circuit disposed in front of the erbium-doped optical fiber and an optical circuit disposed in the rear. There is a demand for an optical module for an optical amplifier that combines the above with a compact.

[0005]

2. Description of the Related Art Conventionally, a front optical module is independently disposed in front of an erbium-doped optical fiber, and a rear optical module is independently disposed behind the erbium-doped optical fiber. Each optical module is provided with an individual optical device such as a duplexer and a coupler. It is configured to be mounted on a substrate.

As an optical device, an optical film 4 such as a demultiplexing film or a coupler film is deposited on the slope of one of the right-angle prisms 3 as shown in FIG. 5 is employed.

Since the optical film of such an optical device is sandwiched between right-angle prisms, it is called a short-circuit configuration, and the optical path configuration can be simplified.

[0008]

As described above, since the conventional optical module for an optical amplifier uses an optical device such as a cube-shaped beam splitter using an optical film having a short structure, the excitation light output is reduced. In addition, when the signal light output becomes high power, the optical adhesive, which is an organic substance, is deteriorated and damaged by light energy, and the reliability of the optical device is deteriorated.

Further, conventionally, since the front optical module and the rear optical module are configured by individually mounting the cube-shaped optical devices on the substrate, there is a problem that the mounting area increases and the insertion loss increases.

However, if a large number of open films are simply deposited on independent glass substrates and these glass substrates are individually fixed to a substrate or a housing, it is difficult to precisely control the mutual positions and angles of the glass substrates. In addition, there has been a problem that the angle deviation caused by the temperature, aging, and the like of each glass substrate is added by the number of reflections, and the stability of the optical path is low.

Further, conventionally, since the front optical module and the rear optical module are independent of each other, the space occupied by the optical module is increased, which is a factor that hinders downsizing of the optical amplifier.

The present invention has been made in view of such a point, and an object of the present invention is to provide an optical circuit in front of a rare-earth-doped optical fiber and an optical circuit in the rear using a variety of optical films having an open configuration. And an optical module for an optical amplifier, wherein the optical module is integrated in the same housing.

[0013]

In order to solve the above-mentioned problems, the present invention provides various open optical films such as a demultiplexing film, a coupler film, and a polarization separation film on the surfaces of a first and a second parallel flat glass substrate. In this case, the optical functions are integrated and integrated by adopting an optical path configuration that reflects or refracts light on the surface of the glass substrate and in the substrate.

Further, an optical circuit in front of the rare-earth-doped optical fiber and an optical circuit in the rear of the rare-earth-doped optical fiber with respect to the propagation direction of the signal light are integrated into one housing to form a compact optical module.

Further, the optical circuit of the optical amplifier has various configurations according to the purpose of use of the optical amplifier. In order to integrate the optical circuit into a smaller and more efficient optical path, an optical film, an isolator and the like are used. Optimize the array configuration.

[0016]

According to the present invention, since the functions of various optical devices are integrated by an open optical film partially deposited on a glass substrate, the device is deteriorated by the high power of the excitation light and the signal light as in the prior art. Thus, a compact and highly reliable optical module for an optical amplifier can be provided.

Further, since the front optical circuit and the rear optical circuit are integrated in the same housing, the miniaturization of the optical module can be further promoted.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. Referring first to FIG. 2, there is shown a block diagram of an optical amplifier to which the optical module of the present invention is applied. Numeral 10 denotes E doped with erbium (Er) in the core.
an r-doped optical fiber;
A front optical circuit 12 is provided in front of the front panel, and a rear optical circuit 26 is provided in the rear.

The forward optical circuit 12 includes an optical coupler 14, an optical isolator 16, a duplexer 18, and a photodiode 20.
And a polarization coupler 24. The photodiode 20 detects the signal light branched by the coupler 14 and monitors the signal light.

The rear optical circuit 26 includes a demultiplexer 28, an optical isolator 30, an optical coupler 32, and a photodiode 3.
4 and 36 and a polarization coupler 40. The photodiode 34 detects the signal light branched by the optical coupler 32 and performs feedback control by an APC circuit (not shown) so that the amplified signal light power becomes constant.

When the connector connected to the optical fiber on the output side is disengaged, the photodiode 36 reflects and returns the signal light. Is detected, the drive current of the excitation laser diodes 22a, 22b, 38a, 38b is reduced to stop the optical amplifier, thereby ensuring safety.

The P-polarized pump light emitted from the pump laser diode 22a and the laser diode 22
The S-polarized excitation light emitted from b is synthesized by the polarization coupler 24, reflected by the demultiplexer 18 and input to the Er-doped optical fiber 10, and changes the Er ions in the doped optical fiber 10 to a high energy level. To excite.

Similarly, the P-polarized excitation light emitted from the excitation laser diode 38a and the laser diode 38
The S-polarized excitation light emitted from b is synthesized by the polarization coupler 40, reflected by the demultiplexer 28, and input from the rear into the Er-doped optical fiber 10, and excites Er ions to a high energy level.

In such a state, the optical coupler 1
4. When signal light having a wavelength of, for example, 1.55 μm is input through the optical isolator 16 and the demultiplexer 18, stimulated emission of light having the same wavelength as the signal light occurs, and the signal light gradually moves along the Er-doped optical fiber 10. Amplified.

The amplified signal light passes through the demultiplexer 28, the optical isolator 30, and the optical coupler 32 and is sent out to the optical fiber transmission line. The signal light split by the optical coupler 32 is detected by the photodiode 34 and feedback-controlled by an APC circuit (not shown) so that the amplified signal light power becomes constant.

In addition, the drive circuit of the LDs 22a, 22b, 38a, 38b is turned on / off according to the input of the signal light by the output of the photodiode 20. Next, an embodiment of the optical module of the present invention will be described in detail with reference to FIG. Components that are substantially the same as the components shown in the block diagram of FIG. 2 will be described with the same reference numerals.

Eight lens assemblies 44, 46, 48 , 52, 76, 78, 80, 82 for converting the light beam emitted from the optical fiber into a collimated beam are provided in the housing 42.
And three photodiodes 20, 34, and 36.

The lens assembly 44 is connected to the input side of the Er-doped optical fiber 10, and the lens assembly 46 is connected to the output side. The lens assembly 48 is connected to the input side optical fiber 50 and functions as an input port of the optical module, and the lens assembly 52 is connected to the output side optical fiber 54 and functions as an output port of the optical module. The end of the output side optical fiber 54 is connected to the optical connector 5.
6 is connected.

The lens assembly 76 is connected to a forward-pumping laser diode 22a that outputs P-polarized light by a polarization-maintaining fiber 86, and the lens assembly 78 is connected to a forward-pumping laser diode 22b that outputs S-polarized light by a polarization-maintaining fiber 88. It is connected.

On the other hand, the lens assembly 80 is connected to the backward pumping laser diode 38a for outputting P-polarized light by the polarization maintaining fiber 90, and the lens assembly 82 is connected to the backward pumping laser diode for outputting S-polarized light by the polarization maintaining fiber 92. 38b.

Inside the housing 42, a coupler prism 58 for splitting the signal light and an excitation prism 64 for combining the excitation light with the signal light have a predetermined angle with respect to the signal light path, for example, 45 degrees.
° It is arranged at an angle.

The coupler prism 58 is made of a parallel flat glass 6.
The coupler film 62 is formed by evaporating a coupler film 62 on one surface 60a and an anti-reflection film on the other surface 60b. The coupler film 62 is a polarization-independent coupler film using a high refractive material.

The excitation prism 64 is a parallel plate glass 66
A demultiplexing film 68 is deposited on one surface 66a of the
b, a first polarization separation film 70 and a second polarization separation film 72 are deposited, and a non-reflection film is deposited on the remaining surface.

An optical isolator 16 is inserted on the optical path of the input signal light between the coupler prism 58 and the excitation prism 64, and the optical isolator 3 is inserted on the optical path of the output signal light.
0 is inserted. These optical isolators 16, 3
Reference numeral 0 denotes a taper-tilt type optical isolator as described in, for example, Japanese Patent Publication No. 61-58809.

Further, on the optical path of the output signal light between the optical isolator 30 and the coupler prism 58, a wavelength of 1.5
A narrow-band bandpass filter 74 that transmits only 5 μm signal light is inserted.

Therefore, the wavelength 1.
The 48 μm S-polarized excitation light transmits through the non-reflection film, is reflected by the demultiplexing film 68, enters the first polarization separation film 70, and is reflected again.

On the other hand, the wavelength 1.4 emitted from the LD 22a is 1.4.
The 8 μm P-polarized excitation light transmits through the first polarization separation film 70, is combined with S-polarized light, and enters the demultiplexing film 68. The synthesized excitation light is reflected by the demultiplexing film 68 and input from the front into the Er-doped optical fiber 10 via the lens assembly 44, and excites the Er ions to a high energy level.

The wavelength emitted from the LD 38b is 1.48 μm.
The S-polarized excitation light passes through the non-reflection film, is reflected by the demultiplexing film 68, enters the second polarization separation film 72, and is reflected again.

On the other hand, the wavelength 1.4 emitted from the LD 38a is 1.4.
The 8 μm P-polarized excitation light passes through the second polarization separation film 72, is combined with S-polarized light, and enters the demultiplexing film 68. The combined excitation light is reflected by the demultiplexing film 68 and is incident on the Er-doped optical fiber 10 from the rear through the lens assembly 46 to excite the Er ions to a high energy level.

The signal light from the input optical fiber 50 is incident on the optical module via the lens assembly 48, and the coupler prism 58, the optical isolator 16, and the excitation prism 6
4 and input to the Er-doped optical fiber 10 via the lens assembly 44.

Since Er ions are excited to a high energy level, when signal light having a wavelength of 1.55 μm is input to the Er-doped optical fiber 10, light having the same wavelength as the signal light is stimulated and emitted, Is gradually amplified along the doped optical fiber 10.

A part of the input signal light is reflected and branched by the coupler film 62 of the coupler prism 58, and the photodiode 2
0 is detected. L by the output of the photodiode 20
The drive circuits of D22a, 22b, 38a, 38b are on / off controlled.

The signal light amplified by the Er-doped optical fiber 10 is converted into a collimated beam by a lens assembly 46 fixed to the housing 42, and passes through an anti-reflection film and a demultiplexing film 68 formed on the surface of the branch coupler 64. Then, the light passes through the polarization-independent optical isolator 30 and the narrow band-pass filter 74 that transmits only the signal light, and enters the coupler prism 58.

A part of the signal light is reflected and branched by the coupler film 62 of the coupler prism 58 to the photodiode 34, and an AP (not shown) is set so that the signal light power after amplification becomes a constant value.
Feedback control is performed by the C circuit. Most of the signal light passes through the coupler film 62 and is coupled to the output optical fiber 54 via the lens assembly 52.

When the optical connector 56 connected to the tip of the output side optical fiber 54 is disengaged, the signal light is reflected and returns to the amplifier. The reflected feedback light is transmitted from the lens assembly 52 to the coupler prism 58. The incident light is partially reflected by the coupler film 62 and detected by the photodiode 36. When the reflected feedback light is detected by the photodiode 36, the drive current of the pumping LDs 22a, 22b, 38a, 38b is reduced to stop the optical amplifier, thereby ensuring safety.

In the above-described embodiment, the demultiplexing film 68 is vapor-deposited on one surface 66a of the excitation prism 64, and the LD 22b,
Although the excitation light from 38b is reflected, the reflection loss is slightly generated in the demultiplexing film. Therefore, the reflection loss may be reduced by masking this portion and partially depositing the total reflection film.

According to this embodiment, the front optical circuit and the rear optical circuit each having two excitation LDs can be housed in the same housing by using two prisms.
The size and the performance of the optical amplifier can be reduced.

Referring to FIG. 4, another configuration of the coupler prism is shown. The coupler prism 58 'is composed of a parallel plate-like glass substrate 60 as in the above-described embodiment. A coupler film 62' having a first branching ratio is deposited on one surface 60a, and the remaining surface has no reflection. A film has been deposited. A coupler film 94 having a second branching ratio is deposited on the other surface 60b of the glass substrate 60, and an anti-reflection film is deposited on the remaining surface.

In this embodiment, a part of the amplified signal light is reflected by the coupler film 62 'of the coupler prism 58'.
A part thereof is further reflected by the coupler film 94 and propagates in the direction of arrow A. The signal light monitoring photodiode 34 shown in FIG. 3 is attached at a position where the signal light propagating in the direction of arrow A is detected.

On the other hand, most of the signal light reflected and branched by the coupler film 62 'passes through the coupler film 94 and propagates in the direction of arrow B. By incorporating this signal light into the optical monitor,
The signal light waveform can be observed.

[0051]

Since the present invention is configured as described in detail above, the optical circuit of the optical amplifier can be reduced in size and high stability with low loss, and the miniaturization and high performance of the optical amplifier can be realized. Also,
The front and rear optical circuits are housed in the same housing by using a coupler prism and an excitation prism in which an optical film with an open configuration is deposited on a glass substrate, so that the optical module for an optical amplifier can be reduced in size and cost. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a short configuration and an open configuration of an optical film.

FIG. 2 is a block diagram of an optical amplifier to which the present invention is applied.

FIG. 3 is a plan view of the embodiment of the present invention.

FIG. 4 is a diagram showing another configuration of the coupler prism.

[Explanation of symbols]

10 Er-doped optical fiber 16, 30 Optical isolator 22a, 22b, 38a, 38b Laser diode 20, 34, 36 Photodiode 42 Housing 44, 46, 48, 52, 76, 78, 80, 82 Lens assembly 58 Coupler prism 62 Coupler film 64 Excitation prism 68 Demultiplexing film 70, 72 Polarization separating film 74 Band pass filter

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Teruhiro Kubo 2-1 Kitaichijo Nishi, Chuo-ku, Sapporo-shi, Hokkaido Fujitsu Hokkaido Digital Technology Co., Ltd. In-house Corporation (58) Field surveyed (Int.Cl. ⁷⁾ H01S 3/10 H01S 3/06-3/07 H01S 3/0941 G02F 1/35

Claims (8)

(57) [Claims] An optical module for an optical amplifier, comprising an optical circuit in front of a rare-earth-doped optical fiber and an optical circuit behind it in a signal light propagation direction in a common housing, wherein the housing has the rare-earth-doped optical fiber. A first input port and a first output port to which an input end and an output end of the optical fiber are respectively connected, a second input port to which an input optical fiber is connected,
A second output port to which an output optical fiber is connected; and a third input port to which excitation light from the first excitation light source is introduced, wherein a first coupler film is formed on one surface of the first parallel flat glass. The coupler prism and the excitation prism having a demultiplexing film formed on one surface of the second parallel flat glass are disposed in the housing at an angle with respect to the optical path of the signal light, respectively . First and second light receiving elements that respectively receive the input-side signal light and the output-side signal light reflected and branched by the coupler film are attached to a housing, and the excitation light from the first excitation light source is divided into Reflected by the wave film
Introduced into one of the first input port and the first output port
An optical module for an optical amplifier. 2. A housing according to claim 1, wherein a fourth input port into which the excitation light from the second excitation light source is introduced is provided in the housing, and the excitation light from the first excitation light source is reflected by the demultiplexing film to form the first input light. A first pumping port and a first output port, wherein the pumping light from the second pumping light source is reflected by the demultiplexing film and input to the other of the first input port and the first output port. The optical module for an optical amplifier according to claim 1, wherein: And a fifth input port through which excitation light from a third excitation light source is introduced, and a sixth input port through which excitation light from a fourth excitation light source is introduced, wherein the second input port is provided in the housing. A first polarization splitting film for synthesizing the excitation light from the first and third excitation light sources and a second polarization splitting film for synthesizing the excitation light from the second and fourth excitation light sources on the other surface of the parallel plate glass. The optical module for an optical amplifier according to claim 2 , wherein the optical module is formed. 4. A housing according to claim 1, further comprising: a third light receiving element mounted on the housing for reflecting and detecting the reflected return light caused by the optical connector connected to the output fiber, which is disengaged, by the first coupler film. The optical module for an optical amplifier according to claim 1. 5. A second coupler film is formed on the other surface of the first parallel plate glass, and a part of the signal light amplified by the rare-earth doped optical fiber is reflected by the first coupler film, and The second light receiving element is mounted at a position for receiving a part of the signal light reflected by the second coupler film, and is connectable to an optical monitor at a position where the signal light transmitted through the second coupler film is output. 5. The optical module for an optical amplifier according to claim 1, wherein three output ports are provided. 6. A first polarization-independent optical isolator that allows passage of signal light only from the second input port to the first input port, between the coupler prism and the excitation prism. 6. The optical amplifier according to claim 1, further comprising a second polarization-independent optical isolator that allows passage of signal light only from one output port to the second output port. Optical module. 7. The method according to claim 1, wherein a narrow band-pass filter that transmits only signal light is inserted between the second polarization-independent optical isolator and the coupler prism. An optical module for an optical amplifier according to the above. 8. The optical module for an optical amplifier according to claim 5, wherein said first and second coupler films are polarization-independent coupler films formed of a high refractive index material.