JPS63172107A - Optical coupler - Google Patents

Abstract

PURPOSE:To facilitate the position adjustment by providing a first optical system which converts the light emitted from a light source to a slowly converging light beam and a second optical system which is fixed to the end face of optical parts to be optically coupled and approximately condenses the light beam from the first optical system on the end face of optical parts. CONSTITUTION:The diverging light emitted from a semiconductor laser LD is converted to the slowly converging light beam by a first lens system (group) L1 and is condensed on the end face of an optical fiber 1 by a GRIN lens (a second optical system) L2 fixed to the incidence end face of the optical fiber 1 by adhesion and is made incident on this end face. There is enough space to arranged optical parts 10 between the first lens L1 and the second lens L2. A displacement extent DELTAx' of the beam spot on the end face of the optical fiber 1 is expressed with DELTAx'=betaDELTAx where DELTAx is the displacement extent of the light beam, and the displacement extent of the beam spot is beta-number of times as large as that of the light beam. Thus, position adjustment is very facilitated when the position of the light beam spot on the end face of the optical fiber 1 is adjusted by 1mum.

Description

[Detailed Description of the Invention] Summary of the Invention To describe an example of a case where the light source is a laser diode (LD) and the optical component into which the light from the light source enters is an optical fiber, the LD output light is transmitted through the first lens. The light beam is converted into a gently converging light beam, and is focused onto the end face of the optical fiber by a second GRIN (gradient refractive index) lens with a pitch of about 0.23 fixed to the optical fiber. High coupling efficiency and large one-position deviation tolerance. Since the distance between the lenses can be increased, it becomes possible to insert other optical components between the lenses.

BACKGROUND OF THE INVENTION TECHNICAL FIELD This invention relates to an optical coupling bag for making a light beam from a light source enter a predetermined position of an optical component, and in particular for making the emitted light of a semiconductor laser (laser diode: LD) enter an optical fiber. This invention relates to an optical coupling device.

Prior art and its problems Conventional optical systems for inputting light emitted from a semiconductor laser into an optical fiber are shown in FIGS. 4 to 6.

The one shown in FIG. 4 is a big tail type in which a semiconductor laser LD and an optical fiber 1 are directly coupled.

5 and 6 utilize a semiconductor laser nozzle cage with a built-in ball lens. In FIG. 5, the emitted light from the semiconductor laser LD is focused by the ball lens 2 and enters the end face of the optical fiber 1. In FIG. In the device shown in FIG. 6, the emitted light from a semiconductor laser LD is first collimated by a ball lens 2, and this collimated light is focused by a graded refractive index (GRIN) lens 3 and made to enter the end face of an optical fiber 1. It is something. In this way, the ball is placed directly near the semiconductor laser chip.
In order to place the lens, it is necessary to perform special processing on the semiconductor laser package.

On the other hand, when the semiconductor laser and the optical fiber are used as part of an optical measurement device, an optical isolator is provided between the semiconductor laser and the optical fiber.

Optical components such as beam splitters, polarizers, and wave plates are often inserted. The optical coupler shown in FIGS. 4 and 5 cannot be used at all for such applications. Even in the structure shown in FIG. 6, the distance between the ball lens 2 and the GRIN lens 3 is usually about the same distance as a loss, which is insufficient.

For such applications, a semiconductor laser without a built-in ball lens is used, and an optical system as shown in FIG. 7 is assembled. In this figure, the emitted light from the semiconductor laser LD is converted into a parallel light beam with a diameter of about 3 mm by the lens 5, reaches the lens 6 through the optical component 10 as described above, is condensed by the lens 6, and is connected to the optical fiber 1. incident on .

In such an optical system, if a single mode optical fiber is used as the optical fiber 1, the beam spot diameter of the single mode optical fiber (approximately 6μ in diameter)
11) Lens 6 and optical fiber 1 with the positional accuracy determined by
It is necessary to adjust the position of the This positional accuracy is approximately ±1- in a plane perpendicular to the optical axis. Therefore, lens 6
Furthermore, it is extremely difficult to adjust the position of the tip fiber 1, and there is also the problem that the lens 6 and the optical fiber 1 become misaligned due to temperature changes or changes over time, resulting in deterioration of optical coupling efficiency.

The above position adjustment is performed as follows.

The semiconductor laser LD and lens 5 are fixed.

Then, both the lens 6 and the optical fiber 1 must be moved independently so that the focused light beam is just incident on the end face of the optical fiber 1.

When the lens 6 is moved in a plane perpendicular to the optical axis, the focused light beam spot also moves by the same amount. Therefore, the positions of both the lens 6 and the optical fiber 1 must be adjusted with the above-mentioned accuracy of ±1 μm. It can be seen that position adjustment is very difficult.

Summary of the Invention Purpose of the Invention The object of the present invention is to provide an optical coupling device that can provide a large distance between a light source and an optical fiber (optical component) to the extent that an optical component can be placed therein, and can easily adjust one position. shall be.

Arrangement of the Invention 1 Operation and Effect The optical coupling device according to the present invention includes a first optical system that converts diverging light from a light source into a slowly converging light beam;
and a second optical fiber fixed to the end face of the optical fiber (optical component) to be optically coupled, and condensing the light beam from the first optical system substantially at the end face of the optical fiber (optical component).
It is characterized by being equipped with an optical system.

According to this invention, the light emitted from the light source is converted into a light beam that slowly converges by the first optical system, so the distance between the first optical system and the second optical system is increased (for example, (on the order of tens of signals or more), and therefore a light beam or splitter as needed during this time.

Optical components such as polarizing plates, wavelength plates, and optical isolators can be arranged. The second optical system is fixed to an optical fiber (optical component). therefore.

It is possible to move the second optical system and the optical fiber (optical component) together. Also, since the slowly converging light beam is focused by the second optical system, the relative displacement between the second optical system and optical fiber (optical component) and the slowly converging light beam is , it appears in a reduced size on the fish gathering surface. This makes it extremely easy to adjust the positions of the second optical system and the optical fiber (optical component). Furthermore, stable optical coupling can be achieved over a wide temperature range and over a long period of time. Furthermore, it is also possible to use a normal semiconductor laser without a built-in ball lens as a light source.

Description of examples FIG. 1 shows an embodiment of the invention.

The diffused light emitted from the semiconductor laser LD is converted into a gently converging light beam by the first lens system (group) LL, and then the GRIN lens (second optical system) The light is focused on the end face of the optical fiber 1 by L2 and enters the end face of the optical fiber 1. first lens L
A sufficient space is provided between the lens L1 and the second lens L2 in which the optical component 10 can be placed.

As a specific configuration example, an aspheric single lens, a spherical combination lens, etc. can be applied to the first lens system (group) Ll. The second lens system (group) L2 needs to be fixed to the optical fiber, so a GRIN lens is convenient, but other lenses can also be used.

The parameter relationships of the optical system shown in FIG. 1 will be explained with reference to FIG. 2. The signs of distance and angle shall follow the rules of ordinary geometric optics. Further, the focal lengths of the lens systems L and L are respectively f and f.

Figure 2 shows the angle u formed between the semiconductor laser LD and the optical axis.
It shows the optical path of the light beam emitted at (ut<O) until it intersects the optical axis at the end face position of the optical fiber at an angle u2'(u'>O). Angle U is the angle at which the light beam intersects the optical axis in the absence of lens system L2.

If α-u/u and β-u/u' are set here, the positional relationship between the semiconductor laser LD, the lens system, and the end face of the L2° optical fiber is as follows.

Distance from the first lens system L1 to the semiconductor laser LD s - f s (1+α) ... (
1) Distance from the second lens system L2 to the end face of the optical fiber s2' - f2 (1-β) - (2
) Distance from the first lens system L to the second lens system L2 d −f [(1/α) +1] f2[(1/β
)-1] ...(3) The relationship between α and β is from the above definition.

α−(u'/u1)β...
(4). The range of β is approximately 0.1 to 0.3.

The angle u1 is the spread angle of the light emitted from the semiconductor laser LD (the angle at which the light intensity becomes 1/e2 of the light intensity on the optical axis), and the angle U'
When is taken as the optimum incident angle to the optical fiber (the convergence angle of the Gaussian beam that yields the maximum incident light rate), this optical system can couple the semiconductor laser LD and the optical fiber with maximum efficiency.

In general, the spread angle of emitted light from a semiconductor laser is different in the direction perpendicular to and parallel to the active layer. It is considered appropriate to take the average value of the vertical and parallel floor angles as the angle u1.

When pursuing the maximum incident light rate, it is necessary to experimentally determine the optimal value for the spread angle. Furthermore, when the numerical aperture of the first lens system L1 is small and only a part of the emitted light from the semiconductor laser or LD enters the lens system L1, it is possible to set the angle determined by the dynamic aperture of the lens system L1 to ul. preferable.

Numerical examples of each optical parameter in the above optical system are shown.

for example.

f　,　-4.5mm f　2-　1.9mm u 1 = -17' u2'-5゜ shall be.

GRI of 0.23 pitch as second lens system L2
If you use an N lens (0.25 pitch GRIN lens focuses parallel light), the value of β will be approximately 0.13, so use the above equations (1) 2 to 4 and use the above numerical values. Substituting , we get the following value.

β-0,13 a = O, t) 3g2 S 1-4.67w 52' 1.65 mm d, = 109 mm It should be noted that the inter-lens distance d can be as large as about 100 mm. With such a distance between the lenses, it is possible to fully insert optical components 10 such as an optical isolator and a beam splitter, so that it can be applied to applications such as optical measurement.

When the optical component IO is inserted, it is necessary to correct the distance d1 by the amount of the optical path change caused by the refractive index of the optical component IO.

The ability of the above-mentioned optical system to expand the allowable displacement of the optical fiber 1 will be explained below. Since the second lens system L2 and the optical fiber 1 are fixed with adhesive, there will be no positional deviation between the two, so what should be considered as 9th contact is due to the relative positional deviation between the lens system L2 and the slowly converging light beam. be.

FIG. 3 shows how the light beam is displaced parallel to the direction perpendicular to the optical axis with respect to the lens system L2. The light beam before displacement is shown by a chain line, and the light beam after displacement is shown by a broken line. The same is true even if it is assumed that the lens system L2 is displaced with respect to the light beam.

The displacement amount ΔX' of the beam spot on the end face of the optical fiber 1 with respect to the displacement amount ΔX of the light beam is Δx' =
[(f-s')/f2]ΔX-βΔx=
15), and it can be seen that the displacement amount is β times smaller. This also applies when the lens system L1 and the optical fiber 1 are relatively displaced.

Therefore, compared to the conventional optical system shown in FIG.
In the optical system shown in the figure (or figure 2), the tolerance for positional deviation due to temperature changes, secular changes, etc. increases by 1/β times,
The adjustment resolution is also increased by 1/β. For example, in the optical system shown in Figure 7, the positional deviation tolerance (adjustment resolution) of the optical fiber is set to 1μ.
In the optical system shown in FIG. 1, if β-0,1 is assumed, the nine positional deviation tolerance ff1 (adjustment resolution) is 10 μl. That is, when adjusting the light beam spot position on the end face of the optical fiber 1 by 1μ11, the lens system L
2 (and optical fiber 1) may be moved by 10 μm. It will be understood that position adjustment becomes extremely easy.

As described above, according to the above optical system, the spread angle u1
Since the emitted light beam of the semiconductor laser LD is converted into a beam having an optimum convergence angle U' to the optical fiber at the input end face of the optical fiber, the coupling efficiency is increased.

In addition, since the optical fiber is fixed to the lens system L2 in such a way that its end face is located at a position slightly closer to the lens system L2 than the focal position of the second lens system L2, the permissible deviation of one position is increased, and temperature changes 6. The adjustment resolution is increased, allowing the coupling efficiency to be maintained stably even against changes over time.

Furthermore, the distance between lens system L and L2 can be increased. Therefore, the optical component 10 can be inserted as necessary.

Since special processing such as installing a ball lens in the vicinity of the semiconductor laser chip is not required, an inexpensive commercially available semiconductor laser in a normal package can be used, and the first effect is achieved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a principle explanatory diagram for quantitatively explaining each optical parameter, and FIG. 3 is an explanatory diagram of positional deviation magnification. . FIGS. 4 to 7 are schematic configuration diagrams showing conventional examples, respectively. LD...Semiconductor laser (light source). Ll...first lens system (first optical system). L2... second lens system (second optical system). 1... Optical fiber (optical component to be optically coupled). that's all

Claims (2)

[Claims] (1) A first optical system that converts diverging light from a light source into a gently converging light beam, and a light beam from the first optical system that is fixed to the end face of the optical component to be optically coupled. an optical coupling device comprising: a second optical system that substantially focuses the light on the end face of the optical component; (2) the optical component is an optical fiber, and the second optical system is fixed to one end surface of the optical fiber;
An optical coupling device according to claim (1).