JP3100481B2 - Optical passive module - 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 coupling component used for an optical fiber amplifier.

[0002]

2. Description of the Related Art In recent years, in an optical distribution system using an optical fiber, an optical fiber amplifier for amplifying an optical signal with direct light has been studied in order to compensate for loss due to optical branching. The optical fiber amplifier is composed of a fiber doped with a rare earth element such as erbium, which performs amplification, a wavelength multiplexer for inputting pump light of a different wavelength from the signal light, and a polarization combining device for increasing the output of the pump light. It is composed of a pump, an optical passive component such as an optical isolator for suppressing the amplified light from oscillating in the fiber due to reflected return light, and an excitation light source. Among these, optical passive components can be configured with a common optical system, and by integrating them,
In order to achieve low loss and downsizing, studies are being made in various fields.

A conventional optical passive component of this type used in an optical fiber amplifier is disclosed in, for example, FIG. 4 (JP-A-2-309328).
Has been proposed. In FIG. 4, reference numerals 1 and 2 denote polarization-maintaining optical fibers that propagate linearly polarized light from an excitation light source (not shown), and reference numerals 3 and 4 denote lenses that collimate light emitted from the optical fibers 1 and 2.
Reference numeral 5 denotes a polarizing beam splitter, which has a function of transmitting or reflecting according to the direction of linearly polarized light. Reference numeral 6 denotes an optical block, in which a wavelength filter 7 is provided at a part inclined with respect to the optical path. The wavelength filter 7 has characteristics of transmitting the excitation light wavelength and reflecting the signal light wavelength. Reference numerals 8 and 9 denote lenses for collimating the light from the transmission optical fibers 10 and 11.

The operation of the thus constructed optical passive component will be described below. First, the light emitted from the excitation light source propagates in the polarization-maintaining optical fiber 1 with the polarization maintained. Light emitted from the optical fiber 1 is converted into parallel light by the lens 3 and enters the polarization beam splitter 5. Similarly, the excitation light propagated from the polarization-maintaining optical fiber 2 is converted into parallel light by the lens 4 and enters the polarization beam splitter 5. The direction of the polarized light is set so that the linearly polarized light emitted from the polarization-maintaining optical fiber 1 passes through the polarization beam splitter 5. On the other hand, the linearly polarized light emitted from the polarization-maintaining optical fiber 2 is orthogonal to the polarization direction of the optical fiber 1,
The light is reflected by the polarization beam splitter 5 and combined with the excitation light from the optical fiber 1. The combined light passes through a wavelength filter 7 provided in an optical block 6 and is then coupled to a transmission optical fiber 10 via a lens 8. A rare earth amplification fiber (not shown) is connected to the optical fiber 10. The amplified signal light that has passed through the optical fiber 10 is collimated by the lens 8, reflected by the wavelength filter 7 of the optical block 6, enters the lens 9, and is coupled to the transmission optical fiber 11.

[0005]

However, in the conventional optical passive module as shown in FIG. 4, since the input / output terminals of the optical fiber cannot be taken out from the same direction,
Due to restrictions on the routing of the optical fiber on component mounting, it is difficult to install the optical fiber in a corner such as a case. In addition, since a polarization beam splitter is used for polarization synthesis and a combination method using reflection and transmission, a collimating lens is required for each, and the incidence direction is different for transmission and reflection, so there is a limit to miniaturization. There was such a problem.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and uses a birefringent crystal which combines two linearly polarized light beams orthogonal to each other on the same optical axis in a polarization combining unit, and further uses an optical fiber by using a mirror. It is an object of the present invention to provide an optical passive module which can take out the input / output terminals from the same direction and can also add an optical monitoring function.

[0007]

In order to solve the above problems, an optical passive module according to the present invention comprises a plurality of polarization-maintaining optical fibers.
As the plane of polarization of the input light from Aiba are orthogonal to each other
A polarization combining section to be emitted synthesized on the same optical axis through the birefringent crystal and the lens the light of the two linearly polarized light disposed,
The combined light is transmitted through the wavelength filter for reflecting the input or output signal light, so as to reflect the majority of the signal <br/> No. light input or output inclined optical axis with respect to the optical path, some Through the mirror and the lens
Or an optical isolator for passing the output signal light ,
Light receiving element for detecting a part of the signal that has passed through the mirror
The incident direction of the polarization combining section to be combined and the signal light
Are integrated with each other so that the incoming and outgoing directions are on the same surface side .

[0008]

According to this configuration, two linearly polarized light beams orthogonal to each other proceed as ordinary light and extraordinary light in the birefringent crystal, and are combined on the same optical axis. The combined light passes through the wavelength filter. The light enters the transmission optical fiber. On the other hand, the signal light emitted from the transmission optical fiber is incident on the light receiving element by a mirror that is reflected by the wavelength filter and partially transmitted, and most of the light reflected by the mirror passes through the optical isolator and is transmitted by the optical isolator. Couple to fiber. Alternatively, the input signal light is incident on the light receiving element by a mirror that partially transmits, and most of the light reflected by the mirror is reflected by a wavelength filter, passes through an optical isolator, and is coupled to a transmission optical fiber. I do.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an optical passive module according to a first embodiment of the present invention. In FIG.
Reference numeral 22 denotes a polarization-maintaining optical fiber that propagates linearly polarized light from a semiconductor laser (not shown) while maintaining the polarization state. Reference numeral 23 denotes a uniaxial birefringent crystal such as rutile (TiO ₂ ) or quartz, in which light polarized in the direction of the optical axis travels as it is as ordinary light, and light polarized perpendicular to the direction of the optical axis travels at an angle as extraordinary light. . This birefringent crystal 23
By optimizing the thickness of the optical fiber and the spacing between the polarization-maintaining single-mode fibers 21 and 22, the ordinary light and the extraordinary light are almost superimposed on the output end face of the birefringent crystal 23 and output. Reference numeral 24 denotes a converging rod lens. Two orthogonal linearly polarized lights incident on the converging rod lens 24 are output as parallel lights from the lens ends and enter the optical path conversion prism 25. The light reflected by the optical path conversion prism 25 is transmitted to the pentaprism 2
1.55 μm through the 1.48 μm light provided in
Wavelength filter 27 having wavelength combining function of reflecting light
, And is reflected by the slope of the optical path conversion prism 28 and enters the converging rod lens 29. Focusing rod lens 2
The parallel light incident on 9 is coupled to the transmission optical fiber 30.

On the other hand, light having a wavelength of 1.55 μm incident from the transmission optical fiber 30 is output as parallel light by the converging rod lens 29, reflected by the optical path conversion prism 28, and further provided to the pentaprism 26. The light is reflected by a wavelength filter 27 having a wavelength synthesizing function and a mirror 31 having an optical branching function and is incident on an optical isolator 32.
Light emitted from the optical isolator 32 is condensed by a converging rod lens 33 and coupled to a transmission optical fiber 34.
Part of the light that has passed through the mirror 31 is combined on the light receiving surface of the light receiving element 35 as a signal light monitor.

FIG. 2 is a configuration diagram of an optical passive module showing a second embodiment of the present invention. The difference from FIG. 1 is that the birefringent crystal 23 is composed of two birefringent crystals 23a whose crystal optical axes are orthogonal to each other.
23b. With this configuration, it is possible to correct the difference in the focus position between the ordinary light and the extraordinary light. That is, light that has passed as ordinary light in the first birefringent crystal 23a passes as extraordinary light in the second birefringent crystal 23b. Similarly, the first birefringent crystal 23a
Light passing through the second birefringent crystal 23b
The light will pass as ordinary light. As a result, both light rays have the same focal position, and the coupling efficiency becomes equal.

FIG. 3 is a block diagram showing a third embodiment of the present invention. In FIG. 3, reference numerals 41 and 42 denote polarization maintaining optical fibers, the ends of which are polished to about 8 degrees. In each of the polarization-maintaining optical fibers 41 and 42, the polarization directions are orthogonal to each other, and coincide with the optical axis direction of the birefringent crystal 43.
The birefringent crystals 43 are arranged obliquely to the optical path in order to suppress reflection from the end face, and are arranged on the end face so that two polarized lights are combined. The combined light is converted into parallel light by the spherical lens 44 and enters the optical path conversion prism 25. Here, the incident angle of the parallel light with the incident surface of the optical path conversion prism 25 has an inclination, and the reflected light proceeds in the direction of the broken line in the figure and does not return to the optical fibers 41 and 42. The light that has passed through the optical path conversion prism 25 passes through a wavelength filter 27 provided in a pentaprism 26, and
Is reflected on the optical isolator 32 and enters the optical
5 to a transmission optical fiber 46. The optical fiber 46 is obliquely polished to prevent the amount of reflected return light like other fibers.

The signal light emitted from the transmission optical fiber 47 is converted into parallel light by the spherical lens 48, passes through a part of the mirror 31, and is coupled to the light receiving element 35 via the spherical lens 49. On the other hand, the light almost reflected by the mirror 31 is reflected by the wavelength filter 27 of the pentaprism 26 and the optical path changing prism 28, passes through the optical isolator 32, and is coupled to the transmission optical fiber 46 via the spherical lens 45.

The third embodiment is used for a forward-pumped optical fiber amplifier, and the end faces of the respective optical fibers are obliquely polished to suppress reflection from the fiber ends so that reflected light does not return on the optical path. At the same time, a spherical lens is used as a collimating lens to suppress reflection from the lens end.
Further, the prisms are arranged at a slight angle with respect to the light incident optical path in order to suppress reflection on the incident surface of various prisms. Also, by arranging a birefringent crystal for polarization synthesis obliquely with respect to the optical path, it has the effect of suppressing reflection from the end face and correcting the difference in the focal position between ordinary light and extraordinary light of the birefringent crystal. Can be reduced.

[0015]

As described above, according to the optical passive module of the present invention, by performing polarization synthesis using a birefringent crystal, the collimator lens of the polarization section can be shared and the size can be reduced. In addition, the optical fibers are arranged in the same direction, and are characterized in that the space can be effectively used on the mounting surface.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical passive module according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing an optical passive module according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing an optical passive module according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional optical passive module.

[Explanation of symbols]

 21, 22, 41, 42 Polarization-maintaining optical fiber 23, 23a, 23b, 43 Birefringent crystal 24, 29, 33 Converging rod lens 25, 28 Optical path conversion prism 26 Pentaprism 27 Wavelength filter 30, 34, 46, 47 Transmission optical fiber 31 Mirror 32 Optical isolator 35 Light receiving element 44, 45, 48, 49 Spherical lens

Continuation of the front page (56) References JP-A-3-252629 (JP, A) JP-A-60-76707 (JP, A) JP-A-2-273976 (JP, A) JP-A-4-251718 (JP, A) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/26-6/35 G02B 6/42-6/43 G02B 27/28 G02F 1/35 501 H01S 3/00-3 / 30

Claims (2)

(57) [Claims] 1. A method of combining two linearly polarized lights arranged such that the polarization planes of light input from a plurality of polarization-maintaining optical fibers are orthogonal to each other on the same optical axis via a birefringent crystal and a lens. tilt and polarization combining section to emit the combined light is transmitted through the wavelength filter for reflecting the input or output signal light, so as to reflect the majority of the input or output signal light of the optical axis with respect to the optical path Te , A mirror that transmits a part of the signal, and a signal that is input or output through a lens.
An optical isolator for passing the issue light consists of light receiving element for detecting a portion of the signal that has passed through the mirror, the synthetic
The direction of incidence of the polarization combining unit and the direction of
An optical passive module , which is integrally formed so as to be on one side . 2. The two input polarization planes which are orthogonal to each other.
Of linearly polarized light on the same optical axis through birefringent crystal
And a polarization combining unit that emits the combined light,
A wavelength filter for reflecting the input signal light;
Reflects most of the signal light reflected by the wavelength filter
Mirrors that tilt the optical axis and partially transmit
Optical signal that passes through the signal light reflected by the mirror and outputs
Detects some signals transmitted through the isolator and the mirror
Light receiving element that is
Output directions are opposite to each other, and the input linearly polarized light is
Optical passive module that is characterized in that the corresponding two birefringent crystals respective optical bonded together by perpendicular to each crystal optical axis of the.