JPH0710002B2 - LED stabilized light source - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an LED stabilized light source suitable for use in measuring or adjusting an optical fiber or an optical component, which has a stable light output and a good wavelength characteristic.

[Prior art]

Since the light output of an LED changes depending on its temperature, it has been conventionally practiced to measure the temperature with an element such as a thermistor and control the drive circuit accordingly to stabilize the light output. In addition, a method of keeping the temperature of the LED element itself constant is also used.

[Problems to be Solved by the Invention]

However, in the former case, it takes several tens of minutes until the optical output stabilizes, and there is no compensation for the wavelength characteristic. In the latter case, if the temperature of the LED element itself is kept constant, the light output and the wavelength characteristic are stable. But,
It takes several tens of minutes to stabilize, and the device is complicated and costly. In these two methods, an external wavelength filter is often used to narrow the wavelength width. However,
In the former method, the wavelength is not compensated, so that the stability of the optical output changes when the half width of the wavelength filter changes. Therefore, in this case, adjustment is required for each half-value width of the wavelength filter used. Also, since the temperature characteristics differ for each LED used, it is necessary to adjust accordingly. Further, when a wavelength filter is built in, there is also a problem that the compensation range must be widened. It is an object of the present invention to provide an LED stabilized light source which has a simple structure and can stabilize the light output and wavelength characteristics at low cost.

[Means for solving problems]

An LED stabilizing light source according to the present invention includes an LED, a drive circuit for driving the LED, a wavelength filter into which the light of the LED is incident, and an output light of the wavelength filter, which is one of the branched lights. Is output to the outside, a photoreceiver for receiving the other of the split lights, an output signal of the photoreceiver is compared with a reference signal, and an output according to a deviation between them is fed back to the drive circuit. And a feedback loop that performs feedback control so that the output signal of the photodetector matches the reference signal by changing the magnitude of the optical output of the LED.

[Action]

The wavelength of the LED light is limited by the wavelength filter, and the LED light of a certain wavelength range enters the optical branching device, and the light of this specific wavelength range is branched. Then, this branched light is converted into an electric signal, and this signal and the reference signal are compared.
It is fed back to the LED drive circuit. That is, control is performed such that the signal corresponding to the branched light is focused so as to match the reference signal. In this way, since the adjustment of the LED drive circuit, that is, the adjustment of the LED drive current is performed by the feedback control, the response characteristics with respect to the optical power from the LED are good, and a quick response can be achieved. Further, since the LED light power is adjusted by changing the LED drive current, the wavelength characteristic of the LED light does not change due to this adjustment. When the emission spectrum of the LED changes, the light power that has passed through the wavelength filter changes even with the same light emission power, so the LED drive current changes due to the above feedback control, and the light emission power also changes. Is controlled to be constant. Therefore, when the emission spectrum of the LED changes in this way, it is not possible to keep the wavelength characteristics of the light that has passed through the wavelength filter constant in the strict sense, but it is necessary to adjust the characteristics of the wavelength filter with respect to the emission spectrum of the LED. By doing so, it is possible to suppress the deviation of the wavelength characteristics within a range where there is practically no problem, and this point is originally outside the scope of the present invention, and it is possible to control the temperature separately.
It can be said that there is no choice but to stabilize the LED emission spectrum itself.

【Example】

In FIG. 1, the LED emits light by receiving a drive current from the drive circuit 2. This light is made incident on the optical branching device 4 through the wavelength filter 3. One of the branched lights is output to the outside, the other is incident on a PD (photodiode; light receiving element) 5, and its output is sent to a comparator 7 via a preamplifier 6. The comparator 7 compares the output of the PD 5 sent via the preamplifier 6 with the reference voltage, and feeds back an output according to the comparison result to the drive circuit 2. This sent it through the preamplifier 6.
The control that makes the output of PD5 match the reference voltage, that is,
Feedback control is performed so that the light branched by the optical branching device 4 after being wavelength-limited by the wavelength filter 3 becomes constant. That is, when the output voltage of the preamplifier 6 matches the reference voltage, a certain output is generated from the comparator 7 and a certain driving current is given from the driving circuit 2 to the LED1, and a predetermined light output is generated from the LED1. If the output voltage of the preamplifier 6 is larger than the reference voltage, the output of the comparator 7 becomes smaller than the above, the driving current of the LED 1 becomes small, and the light output becomes small. As described above, the output voltage of the preamplifier 6 matches the reference voltage. It stabilizes in the condition. When the output voltage of the preamplifier 6 is smaller than the reference voltage, the output of the comparator 7 becomes large, the driving current of the LED 1 becomes large, and the optical output thereof becomes large, and the output voltage of the preamplifier 6 matches the reference voltage as described above. It stabilizes in the condition. In this way, since the ratio of the light output to the outside and the light incident on the PD 5 is constant regardless of the half-width of the wavelength filter 3, the light output to the outside has stable output and wavelength characteristics. Will be things. That is, when the passing wavelength characteristic of the wavelength filter 3 is as shown by the curve B in FIG.
It is assumed that the emission wavelength characteristic of moves according to temperature as shown by curves A1 and A2. Then, the spectrum of the light that has passed through the wavelength filter 3 is as shown in FIG.
In case of, it becomes smaller than B as shown in Fig. By the optical branching device 4, a certain proportion of the light of the spectrum such as b and c is
Since it is guided to PD5 and used for feedback control, when the wavelength shifts like A2, the driving current of LED1 is increased to increase the light output like A2 'in order to increase the small output like C. As a result, the output like Ha is made as large as B. Even if the emission wavelength characteristic of the LED 1 changes in this way, light having the same light output and wavelength characteristic as when there is no such change is emitted to the outside. Since the stabilizing action of such optical output and wavelength characteristics is based on the feedback control, it is stabilized immediately after the power is turned on. The wavelength stability is improved as the wavelength filter 3 having a narrower half width is used. For example, if the wavelength characteristic of the wavelength filter 3 is as shown by the curve B in FIG. 3A and the half value width is not so narrow with respect to the emission spectrum of the LED 1, the emission wavelength is A1 in FIG. To A2
As a result, when the feedback control results in A2 ', the spectrum of the light passing through the filter 3 is as shown in Fig. 3B for A1, whereas it is shown in Fig. 3B for A2'. As described above, a phenomenon in which the center wavelength is slightly deviated is observed, but such wavelength shift can be avoided by using a wavelength filter 3 having a narrow half-width of the wavelength characteristic. Usually, the full width at half maximum of the LED spectrum is long wavelength (1.3 μm, 1.
If it is limited to 55 μm band LED, it is about 100 nm to 150 nm. Further, the emission wavelength change of the LED is about 50 nm for the large one and about 15 nm for the small one in the temperature range of −10 ° C. to 50 ° C.
Therefore, a wavelength filter with a half width of about 20 nm will be used. In fact, when a 1.3 μm band LED was used as the LED 1 in the above example and the filter 3 having a half width of 20 nm was incorporated, the wavelength shift was 1 nm or less in the temperature range of −10 ° C. to 50 ° C. In this way, adjustment of the characteristics of the wavelength filter 3 with respect to the emission spectrum of the LED 1 can be sufficiently dealt with in practice, but originally, regarding the deviation of the wavelength characteristics of the light that has passed through the wavelength filter 3, the temperature of the LED 1 is controlled by temperature control. It can be said that it is desirable to deal with it by stabilizing it. Here, depending on the feedback loop in which the power of the light output to the outside through the wavelength filter 3 is stabilized by the feedback control with respect to the LED drive current, the wavelength characteristics of the light output to the outside via the wavelength filter 3 will not change at all. It seems that we should pay attention to the points that cannot be done. That is, the power of light in a specific wavelength range that is output to the outside through the wavelength filter 3 is stabilized, and the wavelength characteristics of the light output to the outside may vary depending on the feedback control for stabilization. It cannot be changed further.

【The invention's effect】

According to the present invention, after the light from the LED is passed through the wavelength filter, it is branched by the optical branching device and converted into an electric signal, which is compared with the reference signal and feedback-controlled to the LED drive circuit. It is possible to output light with stable wavelength characteristics as well as output power. Moreover, since the LED drive current is varied by feedback control, the response characteristics are good, and stable light output can be obtained immediately after power is turned on. Therefore, at a low cost with a simple configuration,
The light output of the LED can be stabilized against changes in ambient temperature and the passage of time.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG.
B and C and FIG. 3B, B and C are graphs showing wavelength spectra. 1 ... LED, 2 ... driving circuit, 3 ... wavelength filter, 4
...... Optical branching device, 5 ... PD, 6 ... Preamplifier, 7 ... Comparator.

Claims (1)

[Claims] 1. An LED, a drive circuit for driving the LED, a wavelength filter into which the light of the LED is incident, an output light of the wavelength filter, and one of the branched lights is output to the outside. Optical branching device, a light receiving device for receiving the other of the branched light, an output signal of the light receiving device is compared with a reference signal, and an output corresponding to the deviation thereof is fed back to the drive circuit to output the light of the LED. An LED-stabilized light source having a feedback loop that performs feedback control such that the output signal of the photodetector matches the reference signal by changing the magnitude of the output.