JPS6327073A - Led stabilized light source - Google Patents

Abstract

PURPOSE:To obtain a stable optical output in high accuracy by using an LED having two outputs of forward light and rearward light as a light source, and forming a feedback loop. CONSTITUTION: An LED 1 is driven by a driving circuit 2. The LED 1 generates two optical outputs of a forward light and a rearward light. The forward light is led through an optical fiber 6 and the rearward light is led through an optical fiber 7 to an optical coupler 8. The coupled light is led by an optical fiber 9 to an optical branch 10, and branched to optical fibers 11, 12. The light branched to the fiber 11 is externally led as an output light, and the light branched to the fiber 12 is led to a PD 3. After the output signal of the PD 3 is amplified by a preamplifier 4, the signal is fed to a comparator 5, which compares it with a reference voltage. The circuit 2 is controlled by the output of the comparator 5 to vary the driving current of the LED 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use The present invention is used for loss measurement and adjustment of optical fibers and optical components. 2. Description of the Prior Art Regarding Stabilized Light Sources Using LEDs (Light Emitting Diodes) with High Output and High Stability Conventionally, stabilization of light sources using LEDs has been carried out by a feedforward method. However, the feedforward method has disadvantages in that it takes time for the optical output to stabilize immediately after power is turned on, and that it is difficult to follow sudden changes in ambient temperature.

On the other hand, in an LD (laser diode) having two optical outputs, forward light and back light, the back light of the two optical outputs is monitored and fed back to stabilize the optical output.

Therefore, similarly in the case of an LED having two optical outputs, forward light and back light, it is possible to stabilize the optical output by monitoring the back light of the two light outputs and applying feedback. That is, as shown in FIG. 2, the LED 1 is driven by a drive circuit 2, its forward light is outputted to the outside as optical output, and the back light is guided to an FD (photodiode) 3.The output signal of this PO2 is sent to a preamplifier. 4 and then sent to comparator 5 for comparison with the reference voltage.
The drive circuit 2 is controlled with an output according to the comparison result. The idea is to stabilize the LED l by using such feedback looseness.

Problems to be Solved by the Invention However, in the feedback loop shown in FIG. Because the ratio of light to backlight fluctuates, even if you monitor the backlight and apply feedback to stabilize it,
This only stabilizes the back light and does not lead to direct stabilization of the forward light output as optical output. Therefore, it is difficult to stabilize the optical output with high precision.

In order to avoid this, it is possible to stabilize the optical output by feeding back part of the forward light, but in that case, 2
Since back light is not used at all among the two optical outputs, the efficiency is poor and high optical output cannot be obtained.

The purpose of this invention is to stabilize the light output as optical output with high accuracy and improve the output of a light source using an LED having two optical outputs, forward light and back light. do.

Means for Solving the Problems The LED stabilized light source according to the present invention includes an LED having two light outputs, a forward light and a back light, and a length that makes the two light outputs of the LED incoherent. an optical coupler that couples the lights with an optical path difference of A feedback loop is provided.

Operation Since the output light of the LED has incoherence, the two optical outputs of the forward light and the back light of the LED can be combined by the optical coupler without mutually interfering with each other. This combined light is split by the optical splitter, and one of the split lights is fed back to the LED drive circuit, so that the above-mentioned combined light is stabilized. Therefore, it was decided that the other light branched by the optical splitter would be stabilized.

By outputting this other branched light to the outside,
The optical output output to the outside can be stabilized. Further, since the light obtained by combining the forward light and the back light is branched and output to the outside, the optical output becomes higher by the amount of the combined back light compared to the case where a part of the forward light is fed back.

Embodiment In FIG. 1, the LEDI is driven by a driving circuit 2. In FIG. This LEDI generates two optical outputs, a forward light and a bar 2 output, and the forward light is guided through the optical fiber 6 and the back light is guided through the optical fiber 7 to the optical coupler 8.

Generally, light output from an LED is non-polarized and incoherent. Therefore, optical fiber 6.7
By providing a difference in the length of the optical path between the two to the extent that coherence is lost, these can be combined without interfering with each other. In the case of LED light, the coherent length is short, so this optical path difference of about several cm is sufficient. The light thus combined is guided by optical fiber 9 to optical splitter 10 and branched into optical fibers 11 and 12. optical fiber 1
The light branched to the optical fiber 1 side is outputted to the outside, while the light branched to the optical fiber 12 polarization is guided to PO2.

The output signal of PO2 is amplified by a preamplifier 4 and then sent to a comparator 5, where it is compared with a reference voltage. The drive circuit 2 uses the output of the comparator 5 as a result of the comparison.
is controlled, and the driving li current of the LEDI is changed.

A feedback loop is thus formed.

Therefore, this feedback loop allows LE
The light that is the sum of the forward light and the back light of the DI is stabilized, and a part of it becomes the light that is output to the outside, so that the light that is output to the outside can be stabilized with high precision.

In addition, the output light is the light that once combines the forward light and the back light and then removes a part of it as light for feedback, so the output light is not only the forward light but also the back light. Compared to the case where part of the light is fed back, the optical output is increased by the amount of back light.

Note that various optical paths other than optical fibers can be considered for guiding the forward light and back light of LEDI to the optical coupler with a predetermined optical path difference, but optical fibers seem to be advantageous in terms of simplicity of the optical system and loss. .

Effects of the Invention According to the present invention, when an LED having two optical outputs, forward light and back light, is used as a light source, it is possible to stabilize the light output as the first output with high precision and increase the output. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional example. 1...2 light output type LED 2...Drive circuit 3...
・PD 4...Preamplifier 5...
comparator

Claims (1)

[Claims] (1) An LED having two optical outputs, forward light and back light, an optical coupler that couples the two optical outputs of the LED with an optical path difference long enough to lose coherence; An LED stabilized light source comprising: an optical splitter that branches the split light; a light receiver that receives one of the branched lights; and a feedback loop that feeds back the output of the light receiver to the LED drive circuit.