JPH08179157A - Optical coupling module for optical amplification - Google Patents

Abstract

PURPOSE: To prevent such a problem that components increase in size undesirably because of the need to decrease a tilt angle to suppress polarization dependency since the polarization dependency tends to appear largely with the tilt angle of the polarization beam splitter and to eliminate such a defect that an optical axis moves in parallel to a reference optical axis depending upon the tilt angle when a light beam passes through the respective optical components. CONSTITUTION: The size is reduced by using a low polarization dependency multiplexing and demultiplexing prism 9 and bending the light beam of one side at a right angle to increase the separation of the light beam, the polarization dependency is reduced by suppressing the tilt angle between the optical axis and an optical component, and optical axis deviation is corrected by installing optical components in the same shape symmetrically about a mirror plane, and a pentagonal prism or hexagonal prism 11 for optical demultiplexing which is sectioned in a shape formed out of a slanting surface obtained by cutting one side with a plane at 45 deg. to a prism surface after respective rectangular or square prism surfaces are optically polished and a polarization nondependency type optical isolator 3 are arranged on the same optical axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling module for optical amplification applicable to a wide range of optical fields such as optical communication equipment and optical measuring equipment.

[0002]

2. Description of the Related Art In optical devices used for optical communication equipment and the like, optical transmission technology equipped with an optical amplification system in a long-distance optical communication network has been rapidly developed, and large-capacity signal transmission can be instantly performed all over the world. It is about to be distributed. Almost all the technical difficulties in the early stages have been solved on a laboratory scale, but in consideration of actual mass production, the multiplexing and demultiplexing of pump light sources and the polarization-independent optical isolator arranged between optical fibers When mounting optical passive components such as, the finish degree and shape tolerance of each component are directly reflected in the assembly accuracy and ease of assembly.

On the other hand, in the optical amplification system and the like, cost reduction of the signal beam transmission / reception system is naturally a matter to be implemented, but in the present situation, for example, FIG. 2 (1992 IEICE Spring Conference Lecture No. C- The structure shown in Fig. 262) has been attempted, and since each component constitutes an independent serial optical path, the number of components in the entire system increases, and it is inevitably an economically expensive facility. . For example, in FIG. 2, an in-line non-polarization optical isolator 3 inserted between the optical coupling fibers of the signal input port 1 and the output port 2, an optical multiplexer 4, an optical pumping pump light source 5, 6, a wavelength selection filter 7, a monitor light extraction The non-polarizing beam splitters 8 and the like for use are arranged independently or in a state of being bonded with an adhesive, and not only optical characteristics such as optical coupling efficiency and optical absorption loss, but also manufacturing complexity and the number of parts are reduced. There are still problems with reduction.

A special reflecting film having a different reflectance depending on the wavelength, a polarizing beam splitter, etc. are tilted with respect to the optical axis to combine and separate the rays. Therefore, depending on the tilt angle, the polarization dependence becomes large. Further, in order to suppress the polarization dependence, it is necessary to reduce the inclination angle, which causes a problem that the size of the component becomes large. further,
There is a drawback that the optical axis moves in parallel with the reference optical axis due to the inclination angle when the light ray passes through each optical component.

The applicant of the present application has previously filed Japanese Patent Application No. 5-177296, in which one ridge line portion of a rectangular or square prism is
A pentagonal prism optical prism characterized by a cross-sectional shape consisting of a slanted surface deleted at a plane of 45 °, and one of the two prismatic surfaces facing each other at an angle of 90 ° and facing each other. , And proposed a pentagonal prism optical prism characterized in that a wavelength bandpass filter for multiplexing / demultiplexing composed of a dielectric multilayer film is directly loaded and an inclined surface is composed of a reflecting mirror.

[0006]

SUMMARY OF THE INVENTION The present invention uses a polarization-low dependent type multiplexing / demultiplexing prism, and bends one side light beam at a right angle to increase the separation of the light beam, thereby reducing the size and the optical size. It is intended to reduce the polarization dependence by suppressing the inclination angle between the axis and the optical component.Furthermore, by installing the optical components of the same shape in mirror symmetry, it is possible to correct the optical axis deviation. A rectangular or square prism is optically polished on each side, and a pentagonal prism with a cross-sectional shape consisting of a slanted surface removed by a plane whose one side is 45 ° to the prism surface, or 45 ° even at the diagonal position. It is an optical coupling module for optical amplification, characterized in that one of a hexagonal prism having a cross-sectional shape formed by an inclined surface deleted in a plane and a polarization independent optical isolator are arranged on the same optical axis.

In the pentagonal prism 9'for optical coupling, as shown in FIG. 3B, the surface (a) facing the inclined surface (e) of 45 ° forms a non-reflective film at the wavelength of the excitation light. On the other surface (c), a film that is non-reflective at the signal light wavelength and highly reflective at the pumping light wavelength is formed, adjacent to the 45 ° inclined surface and facing the surface (c). A non-reflective film was formed on the surface (b) to be irradiated at the wavelengths of the excitation light and the signal light.

In the hexagonal prism 9 for optical coupling, as shown in FIG. 3A, the surface (a) facing the inclined surface (e) of 45 ° forms a non-reflective film at the wavelength of the excitation light. On the other surface (c), a film that is non-reflective at the wavelength of the signal light and highly reflective at the wavelength of the pumping light is formed, is adjacent to the 45 ° inclined surface (e), and is On the surface (b) opposed to (1), a non-reflection film was formed at the wavelengths of the excitation light and the signal light.

Then, in the optical coupling module, as shown in FIG.
As shown in (A), the signal light incident through the fiber coupling system is the polarization independent isolator 3 installed in the forward direction.
Is incident on the surface (c) of the hexagonal prism 9 and is coupled with the excitation light. Similarly, the excitation light is incident on the surface (a) of the prism through the fiber coupling system, and the inclined surface (e) of 45 °. At the surface (c), it is totally reflected without polarization dependence, and is combined with the signal light.
We propose a forward-pumped structure that is emitted from (b) and leads from the fiber coupling system to the nonlinear optical amplification fiber.

Further, in the optical coupling module, as shown in FIG.
As shown in (B), the excitation light is incident on the surface (a) of the pentagonal prism 9'through the fiber coupling system, and the inclined surface (e) of 45 °.
At the surface (c) is totally reflected, is coupled with the signal light propagating in the opposite direction, is emitted from the surface (b) and is guided to the nonlinear optical amplification fiber from the fiber coupling system, while the signal light is We propose a backward-pumped structure that leads out to the fiber coupling system through the polarization-independent isolator 3 installed in the forward direction from the surface (b) to the surface (c) of the prism in the reverse direction.

In this optical coupling module, the pentagonal prism or the hexagonal prism used for combining and demultiplexing the signal light and the excitation light has an incident angle and an outgoing angle of each ray of light within 0 to 10 °. , 45 ° It is arranged as a polarization low dependency type prism whose angle is adjusted so that the reflection angle of the reflection surface (e) is a critical angle (−0 to + 0.5 °). It proposes an optical coupling module set within 5 ° with respect to the axis.

Next, in the pentagonal prism 11 'for optical branching, as shown in FIG. 4B, the side surface (g) facing the 45 ° inclined surface (k) is a non-reflective film at the wavelength of the signal light. On the other surface (i), a reflection separation film with a branching ratio of 10% or less at the wavelength of the signal light is formed, which is adjacent to the 45 ° inclined surface (k) and
A pentagonal prism for splitting the monitor signal light, in which a non-reflection film is formed on the surface (h) facing the (i) at the wavelength of the signal light.

In the hexagonal prism 11 for splitting the light, as shown in FIG. 4A, the side surface (g) facing the inclined surface (k) of 45 °.
Forms a non-reflective film at the wavelength of the signal light, and the other surface (i)
On the surface (h) adjacent to the 45 ° inclined surface (k) and facing the surface (i), a reflective separation film with a branching ratio within 10% at the wavelength of the signal light is formed on Is a hexagonal prism for branching the monitor signal light in which a non-reflection film is formed.

In order to make polarization independent, in the optical coupling module for optical coupling, the hexagonal prism 11 for branching the signal light is used as the polarization independent isolator 3 as shown in FIG.
It is arranged between the signal light input port O and the monitor signal light output port U, and the incident angle and the output angle of each light ray are within 0 to 10 °, and the reflection angle of the 45 ° inclined surface (k) is critical. Corner (-0 to
By adjusting the angle so that it is + 0.2 °, total internal reflection is possible without polarization dependence, and formation of a coat film on a 45 ° inclined surface is omitted.

In order to further correct the optical axis shift, in the polarization independent optical coupling optical coupling module, as shown in FIG. 1, the signal light branching pentagonal prism or hexagonal prism 11 is a polarization independent type. Isolator 3 and signal light entrance,
It is arranged between the monitor signal light emission ports and is mirror-symmetrical to the signal light / excitation light coupling / separation prism 9.

In these prisms, since the incident angle of the light beam is 45 ° in the ordinary beam splitter, the energy reflectance of the polarized component (P polarized light, S polarized light) is

[Equation 1] ψ: Refraction angle in the dielectric multilayer film, and as shown in FIG. 5 (A), the reflectance (R) for S wave and P wave
And the transmittance (T) are different. Therefore, the reflectance (R) of both components can be made equal in a narrow wavelength band by inserting an intermediate refractive index layer, but the conditions must be determined by trial and error. However, the incident angle of the light ray is 0 to 0 in FIG.
Within 10 °, the difference between them is small and the film design is easy.
(R) and transmittance (T) are almost equal. FIG. 5 (B) is an enlarged view thereof. On the other hand, if the film is formed on the hexagonal prism, the separated light can be turned by 90 °.

Surfaces of prisms 9 and 9'for optical coupling
The excitation light wavelength and signal light wavelength antireflection coating films of (a) and (b) are generally constructed as follows.

[Table 1]

The excitation light wavelength reflection, the signal light wavelength non-reflection and the wavelength band filter film on the prism surface (c) are generally constructed as follows.

[Table 2]

[0019]

Example 1 Glass prism having a width of 2 mm, a length of 4 mm and a height of 3 mm
(n = 1.5) One side was ground to form a surface at 45 ° with respect to the other prism surface, and a WDM prism 9 loaded with an antireflection film (Table 3) and a wavelength selective bandpass filter (Table 4) was used. Form. This prism has a configuration applicable to Er-doped fiber light amplification with light excitation at a wavelength of 1480 nm. In the optical coupling module for optical amplification incorporating this prism, FIG. 4A functions as a backward pumping signal input optical amplifier, and FIG. 4B functions as a forward pumping signal input optical amplifier.

The following reflecting and non-reflecting films were formed by vacuum deposition on the respective prism surfaces for coupling and separating the signal light and excitation light. Surface (a): Excitation light (wavelength 1480 nm), signal light (wavelength 1550 nm) non-reflective coating Surface (b): Excitation light (wavelength 1480 nm), signal light (wavelength 1550 nm) non-reflective coating Surface (c): Excitation light ( Reflection, signal light (wavelength 1550 nm)
Non-reflection, wavelength selective band filter Coated surface (d): No coating surface (e): No coating surface (f): No coating

The structures of the pumping light wavelength and signal light wavelength non-reflective coating films on the surfaces (a) and (b) are as follows.

[Table 3]

The structure of the pumping light wavelength reflection, the signal light wavelength non-reflection and the wavelength band filter film on the surface (c) is as follows.

[Table 4]

As shown in FIG. 3A, pumping light (wavelength 1480 nm) is introduced from port Q and signal light (wavelength 155 nm) is input from port O.
0 nm) is introduced. The excitation light is reflected twice by the 45 ° inclined surface (e) and the WDM film and is taken into the signal light system. In this case, the arrangement accuracy of the prism is almost unadjusted and parallel to the ports O and P. Further, since the incident light of the port Q is at a right angle to the outgoing light of the port P, the assembly can be easily performed by using the rectangular parallelepiped mount shown in the assembly view of FIG.

As shown in FIG. 3 (B), pumping light (wavelength 1480 nm) is introduced from the port T, and signal light (wavelength 155) is input from the port R.
0 nm) is introduced. The excitation light is reflected twice by the 45 ° inclined surface (e) and the WDM film and is taken into the signal light system. In this case, the arrangement accuracy of the prism is almost unadjusted and parallel to the ports R and S. Further, since the incident light of the port T is at a right angle to the outgoing light of the port S, the assembly can be easily performed by using the rectangular parallelepiped mount 10 shown in the assembly view of FIG. Tables 5 and 6 show the evaluation results.

[0025]

[Table 5]

[0026]

[Table 6]

[0027]

Example 2 A glass prism having a width of 2 mm, a length of 4 mm and a height of 3 mm.
(n = 1.5) Grinding one side to form a surface at 45 ° with respect to the other prism surface, and loading a non-reflective film (Table 3) and wavelength selective bandpass filter (Table 4) into a hexagon for multiplexing The prism 9 is formed.
This prism has a configuration applicable to Er-doped fiber light amplification with light excitation at a wavelength of 1480 nm. Next, the hexagonal prism 11 for splitting the signal light is arranged between the polarization independent isolator 3 and the signal light entrance (port O) and the monitor signal light exit (port U). An optical coupling module for chemical amplification was created. 4A functions as a backward pumping signal input optical amplifier, and FIG. 4B functions as a forward pumping signal input optical amplifier.

On the surface of the prism 11 for splitting the signal light beam, the following branch reflection / non-reflection film is formed by vacuum evaporation. Surface (g): Signal light (wavelength 1550 nm) non-reflective coating Surface (h): Signal light (wavelength 1550 nm) non-reflective coating Surface (i): Signal light (wavelength 1550 nm) branch reflection coating Surface (j): Uncoated surface (k): Uncoated Surface (l): Uncoated

For this optical amplification optical coupling module,
Port O connects to a 1550nm signal fiber optic collimator, Port P connects to an Er fiber collimator, Port Q connects to a 1480nm excitation fiber optic collimator, Port U connects to a signal monitor detector, backward pumped A signal input optical amplifier was formed.

[0030]

According to the present invention, it is possible to prevent the reflected return light of each optical component and to make the polarization independent, to downsize because of the use of the fiber coupling system, and to install the multiplexing / branching prism at the installation angle. The input and output positions do not change unless the is changed, which facilitates assembly and adjustment.

Further, according to the present invention, the polarization-low dependent multiplexing,
Using a demultiplexing prism, one side of the light beam can be bent at a right angle to increase the separation of the light beam, and the size can be reduced.In addition, the tilt angle between the optical axis and the optical component can be suppressed to make it polarization-dependent. It was possible to realize the reduction of the property. Furthermore, by installing optical components of the same shape in mirror symmetry, it was possible to correct the optical axis shift.

[Brief description of drawings]

FIG. 1 is an assembly view of an optical coupling module for optical amplification according to the present invention.

FIG. 2 is a schematic diagram of a conventional optical amplifier.

FIG. 3A is a schematic diagram of a backward pumping type signal input optical amplifier, and FIG. 3B is a schematic diagram of a forward pumping type signal input optical amplifier according to the present invention.

4A and 4B are schematic diagrams of a backward pumping signal input optical amplifier and a forward pumping signal input polarization independent optical amplifier according to the present invention.

FIG. 5 shows polarization dependence of transmittance (T) and reflectance (R) with respect to an incident angle of a dielectric multilayer film in a prism.

[Explanation of symbols]

 1 signal input port 2 signal output port 3 non-polarization optical isolator 4 optical multiplexer 5, 6 pump light source for optical pumping 7 wavelength selection filter 8 non-polarizing beam splitter 9 hexagonal prism for multiplexing 10 rectangular parallelepiped mount 11 hexagonal prism for branching

Claims (10)

[Claims] 1. A pentagonal prism having a cross-sectional shape formed by optically polishing each surface of a rectangular or square prism and removing a slanted surface at one side of which is 45 ° with respect to the prism surface, or further in a diagonal position thereof. Also, an optical coupling module for optical amplification, characterized in that one of a hexagonal prism having a cross-sectional shape formed by an inclined surface removed by a plane forming 45 ° and a polarization-independent optical isolator are arranged on the same optical axis. . 2. The pentagonal prism according to claim 1, wherein a surface (a) facing the inclined surface of 45 ° forms a non-reflective film at the wavelength of the excitation light, and the other surface (c) of the signal light A film that is non-reflective at the wavelength and highly reflective at the wavelength of the excitation light is formed, and the surface (b) adjacent to the inclined surface at 45 ° and facing the surface (c) contains the excitation light and the signal light. A pentagonal prism for optical coupling with a non-reflective film formed at the wavelength. 3. The hexagonal prism according to claim 1, wherein the surface (a) facing the inclined surface (e) of 45 ° forms a non-reflection film at the wavelength of the excitation light, and the other surface (c) is formed. Forms a film that is non-reflective at the wavelength of the signal light and highly reflective at the wavelength of the pumping light, is adjacent to the 45 ° inclined surface (e), and
A hexagonal prism for optical coupling in which a non-reflective film is formed on the surface (b) facing the surface (c) at the wavelengths of the excitation light and the signal light. 4. The optical coupling module according to claim 1, wherein the signal light incident through the fiber coupling system passes through a polarization independent isolator installed in the forward direction, and the surface of the hexagonal prism or pentagonal prism (c ) Is incident on the prism surface (a) and is totally reflected by the 45 ° inclined surface (e) without polarization dependence. A forward-pumped optical coupling module for coupling with the signal light on the surface (c), emitted from the surface (b) together, and leading out to the nonlinear optical amplification fiber from the fiber coupling system. 5. The optical coupling module according to claim 1, wherein the excitation light is incident on the surface (a) of the hexagonal prism or the pentagonal prism through the fiber coupling system and is polarized by the inclined surface (e) of 45 °. Totally reflected without wave dependence, combined with signal light propagating in the opposite direction on surface (c), and emitted from surface (b) together,
From the fiber-coupled system to the nonlinear optical amplification fiber, while the signal light passes through the prism surface (b) to surface (c) in the reverse direction, passes through the polarization-independent isolator installed in the forward direction, and enters the fiber-coupled system. Back-pumped optical coupling module for derivation. 6. The optical coupling module according to claim 1, 4 or 5, wherein the pentagonal prism or hexagonal prism used for multiplexing and demultiplexing the signal light and the excitation light is an incident angle of each light ray on each surface and an emission angle. The angle is within 0 to 10 °, and the angle is adjusted so that the reflection angle of the 45 ° reflecting surface (e) is the critical angle (−0 to + 0.5 °). Furthermore, a polarization-independent isolator is within 5 ° to the optical axis. 7. The pentagonal prism according to claim 1, wherein
The side surface (g) facing the 45 ° inclined surface (k) forms a non-reflection film at the signal light wavelength, and the other surface (i) has a reflection separation film with a branching ratio within 10% at the signal light wavelength. A pentagonal prism for splitting monitor signal light, in which a non-reflective film is formed on the surface (h) adjacent to the 45 ° inclined surface (k) and facing the surface (i) at the wavelength of the signal light. 8. The hexagonal prism according to claim 1, wherein
The side surface (g) facing the 45 ° inclined surface (k) forms a non-reflection film at the signal light wavelength, and the other surface (i) has a reflection separation film with a branching ratio within 10% at the signal light wavelength. A hexagonal prism for splitting the monitor signal light, in which a non-reflective film is formed on the surface (h) adjacent to the 45 ° inclined surface (k) and facing the surface (i) at the signal light wavelength. 9. The optical coupling module for optical coupling according to any one of claims 1, 4, 5 and 6, wherein:
The pentagonal prism or hexagonal prism for splitting the signal light defined in 1. is arranged between the polarization-independent isolator and the signal light entrance port or the signal light exit port, and the incident angle and the exit angle of the light beam on each side surface are 0. Within ~ 10 °, 45 ° inclined surface
An optical coupling module for polarization independent optical coupling in which the reflection angles of (k) and (l) are adjusted to be a critical angle (-0 to + 0.2 °). 10. The optical coupling module for optical coupling according to any one of claims 1, 4, 5, 6 and 9, wherein the signal light branching pentagonal prism or hexagonal prism defined in claim 7 or 8 comprises: Optical axis misalignment correction type optical coupling module, which is arranged between the polarization independent isolator and the signal light incident port and the signal light emission port, and is installed mirror-symmetrically to the prism for coupling and separating the signal light and pumping light. .