JP2001290054A - Optical waveguide terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small sized optical waveguide terminal small in an adjusting margin in the direction orthogonal to the optical axis of a lens and small in an occupied space in an assembling process. SOLUTION: The advancing direction of a luminous flux propagating to a second lens is changed by inserting a third lens between a first lens and a second lens, a distance (a height of a light beam) between the light beam and the optical axis in the vicinity of the second lens is lowered, and whereby an eclipse of the luminous flux in the second lens is prevented even if the second lens is not moved in the direction orthogonal to the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a terminal coupled to an optical waveguide, and more particularly to an optical means for coupling an optical output from a laser diode chip to the optical waveguide.

[0002]

2. Description of the Related Art In an optical communication system, a laser diode is generally used as a signal light source. A module that incorporates a laser diode and integrates an optical waveguide that combines light emitted from the laser diode is called an LD module (laser diode module).

FIG. 5 shows an example of an LD module. The LD chip 51 is fixed on a Peltier element 52 provided for temperature adjustment. The light beam emitted from the LD chip 51 is converted into a parallel light beam by the first lens 53,
Capillary 55 which is converged by lens 54 and is an optical waveguide
Is combined with 2 of the first lens 53 and the second lens 54
With the number of lenses, the LD 55 and the capillary 55
Optical system 56 is formed.

[0004]

In the conventional LD module shown in FIG. 5, the position adjustment (centering) of the first lens 53 and the second lens 54 is performed in order to increase the coupling efficiency as much as possible. . However, during the alignment process, L
When the D chip 51 deviates from the optical axis of the first lens 53, the light beam propagates obliquely with respect to the optical axis 57, as shown in FIG.

In this case, the second lens 54 and the capillary 55 are aligned in order to receive the obliquely propagating light beam. However, to receive the obliquely propagating light beam, the second lens 54 has an optical axis. From the first lens 5
The thickness of the coupling optical system including the third lens and the second lens 54 is larger than that in the case where the light beam propagates parallel to the optical axis.

[0006] This is an obstacle when trying to reduce the volume of the coupling optical system inside the LD module. That is, in order to form the coupling optical system in the state as shown in FIG. 6, it is necessary to secure an adjustment margin for moving the second lens 54 in a direction perpendicular to the optical axis. As a result, it is necessary to secure a space for the coupling optical system in accordance with the displacement of the light beam. If you make this space smaller,
Part of the propagating light flux does not enter the second lens 54, causing vignetting and reducing the coupling efficiency.

Conventionally, when it is necessary to insert an optical element such as an optical isolator or a wavelength selection filter between the first lens 53 and the second lens 54, the effective diameter of the optical surface of the optical element must be increased. As a result, it has been difficult to reduce the cost of the inserted optical element.

That is, the present invention has a small adjustment margin in the direction perpendicular to the optical axis of the lens in the assembling process, a small occupied space, and a small-sized optical element capable of effectively inserting an optical element into a coupling optical system. It is an object to provide an optical waveguide terminal.

[0009]

According to the present invention, a third lens is inserted between a first lens and a second lens to change a traveling direction of a light beam propagating to a second lens. Reducing the distance (ray height) of a light ray from the optical axis in the vicinity of the second lens and preventing vignetting of the light beam at the second lens without moving the second lens in a direction perpendicular to the optical axis. The coupling efficiency can be maintained without increasing the thickness of the coupling optical system.

In the optical waveguide terminal of the present invention,
In the vicinity of the third lens, the diameter of the light beam is small because the light beam is converged. Therefore, if an optical element such as an optical isolator is inserted into this portion, the effective diameter can be reduced.

That is, the optical waveguide terminal of the present invention is a first optical waveguide terminal for capturing a light beam from an LD (laser diode) chip.
An optical waveguide terminal including a lens, a second lens for causing a light beam emitted from the first lens to enter a capillary, a holder for fixing the first and second lenses, and the capillary. And a third lens for changing the direction of the light beam between the first lens and the second lens.
A lens is provided, and a convergence position of the light beam emitted from the first lens is provided near the third lens.

Also, in the optical waveguide terminal of the present invention,
In order to provide a function to this terminal, an optical element having no lens function is arranged near the third lens.

Alternatively, an optical isolator is arranged near the third lens.

Alternatively, a wavelength selection filter is arranged near the third lens.

Further, the first lens may be a ball lens (ball lens).

[0016]

According to the propagation path of the light beam from the LD chip side,
The operation of the present invention will be described with reference to FIG. The LD chip 11 is separated from the optical axis 18 of the first lens 13 by δ1. The light beam emitted from the LD chip 11 becomes a convergent light beam after passing through the first lens 13, and the third lens 19 is arranged near the position where the light beam converges.
When the convergence position of the light beam coincides with the principal point of the third lens 19, the third lens does not contribute to the convergence and divergence of the light beam, that is, does not contribute to the imaging position, but has an effect of changing only the propagation direction of the light beam. . When the convergence position of the light beam is slightly deviated from, for example, the front principal point of the third lens 19, the image formation position moves back and forth under the influence of the power of the third lens 19, and the position of the second lens is adjusted accordingly. Adjust it.

The light flux whose traveling direction has been changed by the third lens 19 approaches the optical axis 18 of the first lens as it propagates,
It will reach near the center of the lens 14. Therefore, the light beam can be made incident on the second lens 14 without causing vignetting due to the light beam passing near the periphery of the lens.

Since the height of the light beam becomes low around the third lens 19, if it is necessary to insert an optical element into the terminal, the optical element can be effectively inserted by inserting it around the third lens 19. The diameter can be kept small.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) The first embodiment shown in FIGS.
In the embodiment, the first lens 23 of the coupling optical system is constituted by a ball lens having a focal length of 1 mm, the second lens 24 is constituted by a ball lens having a focal length of 3.2 mm, and the third lens 29 is constituted by a lens having a focal length of 8.1 mm. This is an example. LD chip 2
The light emitted from 1 is coupled to the capillary 25 by this coupling optical system.

FIG. 2 shows the arrangement of the optical elements when the optical axis of the LD chip 21 and the center of the first lens 23 coincide with each other.
FIG. 3 shows the arrangement of the optical elements when the optical axis of the LD chip 21 and the center of the first lens 23 are shifted.

In the case of FIG. 3, due to the characteristics of the ball lens,
Even if the optical axis of the LD chip deviates from its center, the LD chip 2
The light from 1 can be efficiently collected by the ball lens 23. However, the direction of the light beam exiting the ball lens 23 makes a large angle with the optical axis of the coupling optical system. At this time, by arranging the third lens so that the convergence position of the light beam emitted from the first lens coincides with the principal point of the third lens 29, the direction of the light beam directed outward is changed to the second lens. 24
You can turn to the center of.

As a result, the first lens 23 and the second lens 2
High coupling efficiency could be ensured by only a slight adjustment in the direction perpendicular to the optical axis of the fourth and third lenses.

(Embodiment 2) A second embodiment shown in FIG. 4 is a third embodiment of the coupling lens system of the first embodiment.
In this example, an optical isolator 48 including a magnet 44, a first polarizing glass 45, a garnet thick film 46, and a second polarizing glass 47 is inserted in the vicinity of.

The light emitted from the LD chip is the capillary 2
5 and the alignment process during assembly are the first
In the same manner as in the embodiment, the effective diameter of the optical surface of the optical isolator is conventionally required to be about φ1 mm, whereas in the present embodiment, the effective diameter can be reduced to about φ0.5 mm. . As a result, the cost of the garnet thick film and the polarizing glass can be reduced, and the cost of the optical isolator can be reduced.

Also, when a wavelength selection filter is provided instead of the optical isolator, the required effective diameter of the optical surface can be reduced, and the effect of cost reduction is the same.

[0027]

As described above, according to the present invention, even if the volume is small, it is possible to prevent a decrease in the coupling efficiency caused by vignetting by the optical system, and to realize a light guide having a small volume and securing the coupling efficiency. A wave terminal can be provided.

Further, it is possible to use an optical isolator and a wavelength selection filter having a small effective diameter, and it is possible to provide a low-cost optical waveguide terminal.

[Brief description of the drawings]

FIG. 1 is a diagram showing a coupling optical system of an optical waveguide terminal according to the present invention.

FIG. 2 is a diagram showing a case where an optical axis of a laser diode chip and a center of a first lens coincide with each other in the first embodiment of the present invention.

FIG. 3 is a diagram showing a case where the optical axis of the laser diode chip and the center of a first lens are shifted in the first embodiment of the present invention.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a schematic view showing a conventional LD module.

FIG. 6 is a diagram showing an arrangement of optical elements of a coupling optical system when the optical axis of an LD chip and the center of a first lens are shifted in a conventional LD module.

[Explanation of symbols]

 11, 21, 51 LD chip 13, 23, 53 First lens 14, 24, 54 Second lens 15, 25, 55 Capillary 18 Optical axis of first lens 19, 29 Third lens 44 Magnet 45 First polarizing glass Reference Signs List 46 Garnet thick film 47 Second polarizing glass 48 Optical isolator 52 Peltier element 56 Coupling optical system 57 Optical axis of first lens δ1 Displacement of optical axis of LD chip and first lens

Claims (5)

[Claims] A first lens for capturing a light beam from an LD chip (laser diode chip); a second lens for causing the light beam emitted from the first lens to enter a capillary which is an optical waveguide; In an optical waveguide terminal comprising a holder for fixing the first and second lenses and the capillary, the first lens and the second
An optical waveguide terminal, comprising: a third lens for changing a direction of a light beam between the lens and the lens; and a convergence position of the light beam emitted from the first lens is provided near the third lens. 2. The optical waveguide terminal according to claim 1, wherein an optical element having no lens action is arranged near the third lens. 3. The optical waveguide terminal according to claim 2, wherein said optical element is an optical isolator. 4. The optical waveguide terminal according to claim 2, wherein said optical element is a wavelength selection filter. 5. The optical waveguide terminal according to claim 1, wherein said third lens is a ball lens (ball lens).