JPS61284711A - Stabilized light source - Google Patents

Abstract

PURPOSE:To stabilize a light output without being affected by the internal variation of a light emitting element by detecting light which varies similarly to light incident on an optical fiber at an output terminal and feeding the detection output back. CONSTITUTION:One of two light beams branched by a half-mirror 2 is incident on the optical fiber at the output terminal and the other is incident on the optical fiber 9 of a photodetector 5. Consequently, the light is incident on the photodetector 5 at invariably the same ratio to the light incident on the optical fiber 4 without the internal variation of a light emitting element 11 and the output of the photodetector 5 corresponds completely to the quantity of light incident on the optical fiber 4 from an adapter 3. For the purpose, the output of the photodetector 5 is compared with a reference voltage by a comparator 11 and a driving circuit 12 is controlled on the basis of the comparison result to provide feedback to the driving current of the light emitting element 1. Consequently, variation in light power incident to the optical fiber 4 at the output terminal is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light source used in optical communications, and more particularly to a stabilized light source whose optical output is stabilized.

BACKGROUND OF THE INVENTION Generally, a light emitting diode, for example, is used as a light emitting element serving as a light source. However, the light emitting state of light emitting elements such as light emitting diodes changes depending on the flowing current, temperature, etc.
In addition, due to aging, it deteriorates and the luminous efficiency decreases, etc.
Its light output is unstable.

Therefore, it is possible to stabilize the optical output, but conventionally stabilization is mainly done by feedforward.
The drawbacks are that it takes time for the optical output to stabilize immediately after the power is turned on, and that it cannot follow sudden changes in ambient temperature.

On the other hand, stabilization by feedback has been known in some areas. That is, as shown in Figure 2,
When outputting the light from the light emitting element 1 to the optical fiber 4 via the adapter 3, a part of the light is branched by an optical splitter consisting of a half mirror 2 and made to enter the light receiver 5. The purpose is to feed back the output to the light emitting element 1 side, thereby stabilizing the light output entering the optical fiber 4. Note that the adapter 3 is connected to the optical fiber 4.
It forms a connector for connecting.

Problems to be Solved by the Invention However, in a light emitting device 1 such as a light emitting diode, 1
The light emitting surface is uneven, and the light emitting part may move on the light emitting surface. When internal changes occur in the light emitting element 1 in this way, in the conventional configuration in which the light is simply split by the half mirror 2, the ratio of the light branched to the light receiver 5 and the light output from the adapter 3 is different. As a result, stabilization by feedback ceases to function, and the optical output fluctuates.

That is, a difference occurs between the fluctuation in the input power at the output end and the fluctuation in the input power at the light receiver 5, and as a result, the fluctuation in the input power at the output end remains even after feedback. For example, if there is a difference between the input power fluctuation at the output end before feedback and the input power fluctuation at the photoreceiver 5 as shown in FIG. Incident power fluctuations at the output end remain.

Therefore, in the conventional light source, even if a feedback technique is used, it is not possible to eliminate the temperature characteristic as shown in FIG. 3C.

This invention provides a stabilized light source that takes into account the internal changes of a single light emitting element, constantly stabilizes the light output even if variations in the light emitting surface occur, and can reduce the temperature characteristics of the output end incident power to almost zero. The purpose is to

Means for Solving the Problems The stabilized light source according to the present invention includes a light emitting element, a light branching device that guides light from the light emitting element to an output end and branches a part of the light, and a light branching device to which the branched light enters. optical fiber,
It consists of a light receiver that receives light sent through this optical fiber, and a feedback loop that feeds back the output of this light receiver to the light emitting element.

One of the two lights split by the working optical splitter is input into an optical fiber at the output end, and the other is input into an optical fiber leading to a light receiver. Therefore, both of the two branched lights will enter the optical fiber, so if there is a fluctuation on the light emitting surface of the light emitting element2, this fluctuation will affect the light entering both optical fibers in the same way. give. As a result, the ratio of the light incident on the optical fiber at the output end and the light incident on the light receiver is always the same, and the stabilizing effect of the optical output due to feedback loose functions fully.

Embodiment In FIG. 1, a light emitting element 1 is made of a light emitting diode, for example, and is driven by a drive circuit 12 to emit light.The light is incident on a half mirror 2 through a lens 6, and is transmitted through this half mirror 2. The light is incident on the optical fiber 4 connected by the adapter 3 via the lens 7. On the other hand, a part of the light reflected by the half mirror 2 enters the optical fiber 9 via the lens 8. This optical fiber 9
The transmitted light is received by the light receiver 5.

The output of the light receiver 5 is sent to the comparator 11 via a light receiving circuit 10 such as a preamplifier and compared with a reference voltage, and the output obtained as a result of the comparison is fed back to the drive circuit 12.

Here, the two lights split by half mirror 2 are
One is input into the optical fiber 4 at the output end, and the other is input into the optical fiber 9 to the light receiver 5. Therefore, both of the two branched lights will enter the optical fiber 4.9, so if there is a fluctuation on the light emitting surface of the light emitting element l,
This variation affects the light incident on both fibers 4.9 in the same way. As a result, despite internal changes in the light emitting element 1, the same proportion of light is always incident on the light receiver 5 relative to the light that is incident on the optical fiber 4.
The output of the light receiver 5 completely corresponds to the amount of light incident on the optical fiber 4 from the adapter 3. Therefore, the output of the light receiver 5 is compared with a reference voltage by a comparator 11, and the drive circuit 12 is controlled based on the comparison result, thereby applying feedback to the drive current of the light emitting element 1. It becomes possible to reduce fluctuations in the optical power incident on the optical fiber 4 to zero. Due to such feedback, the optical output becomes stable within several m5ec immediately after the power is turned on, and the optical output continues to maintain a stable state thereafter.

Note that it is desirable that the optical fiber 9 has the same parameters as the optical fiber 4, such as core diameter and refractive index difference 1 profile. This is because the light incident on the optical fiber 4 and the light incident on the optical fiber 9 can be made more equal. Therefore, the core diameter of 50 pm, which is often used as the optical fiber 4, is
A graded fist index type optical fiber having a clad diameter of 90 pm and a jacket diameter of 125 pm is used as the optical fiber 9.

Effects of the Invention According to the present invention, even if there is an internal change in the light emitting element such as a change in the light emitting surface and this causes a change in the light incident on the optical fiber at the output end, the optical fiber at the output end It is possible to detect light that fluctuates in the same way as the incident light and apply feedback. Therefore, the light output can be stabilized without being affected by internal fluctuations of the light emitting element. As a result, the light output can be stabilized by the feedback loop even when the light emitting element changes over time or due to temperature. Even if the light emitting element deteriorates due to aging and the luminous efficiency deteriorates, this can be compensated for.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the present invention, Figure 2 is a block diagram of a conventional example, and Figures 3 A, B, and C are graphs showing temperature characteristics for pointing out problems in the conventional example. . 1... Light emitting element 2... Half mirror 3...
・Adapter 4.9... Optical fiber 5... Light receiver 6.7.8... Lens 10... Light receiving circuit 11... Comparator 12... Drive circuit

Claims (2)

[Claims] (1) A light emitting element, an optical splitter that guides the light of this light emitting element to an output end and branches a part of the light, an optical fiber into which the branched light is incident, and transmission via this optical fiber. A stabilized light source comprising a light receiver that receives the light emitted from the light, and a feedback loop that feeds back the output of the light receiver to the light emitting element. (2) The stabilized light source according to claim 1, wherein the optical fiber that transmits light to the light receiver is the same type of optical fiber as the optical fiber connected to the output end.