JPH04192823A - Light frequency stabilizing light source - Google Patents

Abstract

PURPOSE:To stabilize the output light frequency in a wide band by inserting a detachable filter into a loop so as to pass through the filter before closing the loop, and detaching the filter after a frequency of a light source is stabilized. CONSTITUTION:When a switch 3 is connected to an A side, an output of an adder 2 appears stepwise in an output side of the switch 3, but since a switch 7 is on the 7D side, and a switch 8 is connected to the 8F side, a step signal passes through a low-pass filter 9, become a slow rise and is applied to an input of an amplifier 4. Accordingly, an output of the amplifier 4 and an output of a light source 5 are both varied slowly, and stabilized, when they become a target stabilized frequency. After the light frequency of the light source 5 is stabilized, the lowpass filter 9 is detached from a loop by connecting the switch 7 to the 7C side and connecting the switch 8 to the 8E side. In such a way, an output optical frequency can be stabilized in a wide band.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical frequency stabilized light source using an optical frequency discriminator having a plurality of peaks or valleys on the frequency axis of the transfer characteristic.

[Prior Art] Next, an optical frequency stabilized light source according to the prior art will be explained with reference to FIG.

In Fig. 3, 1A and 1B are reference voltage sources, 2 is an adder, 3 is a switch, 4 is an amplifier, 5 is a light source, 6A is an optical frequency discriminator, 6B is a compensation circuit, and 1A, 2, 3, 4・5・6A
・6B・2 is a stabilizing loop (hereinafter simply referred to as a loop).

) to form.

The reference voltage source 1A is a voltage source that sets the optical frequency of the light source 5, and the adder 2 uses the output of the compensation circuit 6B and the reference voltage source 1A.
Take out the difference between the output voltage and the output voltage. Switch 3 switches between the output of adder 2 and the reference voltage source 1B. The light source 5 is a light source whose emission frequency changes according to an electrical signal. The compensation circuit 6B compensates for variations in the output of the optical frequency discriminator 6 due to variations in the output power of the light source 5. The reference voltage source 1B is a reference voltage source for setting the optical frequency only when the loop is open.

The optical frequency discriminator 6A converts optical frequency changes into level changes, and is used for devices with periodic transmission characteristics on the frequency axis, such as a Fabry-Perot interference needle, and for some specific types, such as a light absorption cell. It is possible to use a device with a valley in the transfer characteristic at the frequency of . When the frequency of the output of the light source 5 is adjusted to a point where the differential coefficient of the transfer characteristic of the optical frequency discriminator 6A is not 0, the output level changes in accordance with an increase or decrease in frequency.

When the switch 3 in Fig. 3 is connected to the 3A side and the loop is closed, the change in the optical frequency of the light source 5 is passed through the optical frequency discriminator 6A to convert the frequency fluctuation into a level fluctuation, and the level fluctuation By feeding back the light to the light source 5, the output optical frequency can be stabilized to the target frequency.

[Problems to be Solved by the Invention] In order to achieve broadband stabilization in the loop shown in FIG. 3, the response of the loop is often allowed to go too far. In this case, a large ringing in the optical frequency may occur due to the transient response when the switch 3 is connected to the 3A side. At this time, if the optical frequency discriminator 6A has a plurality of peaks or valleys on the frequency axis of the transfer characteristic, the frequency may be erroneously stabilized at a frequency other than the target during the transient response.

Next, the transfer characteristics when a Fabry-Perot interference needle is used in the optical frequency discriminator 6A will be explained with reference to FIG. Fourth
The figure illustrates three peaks and two valleys.

Now, when the switch 3 is connected to the 3B side, the output frequency of the light source 5 is at point P in FIG. 4, and the frequency to be stabilized is at point Q, the output of adder 2 is at point P. A signal corresponding to the frequency difference from to point Q appears. When the switch 3 is set to the 3A side from this state, the output optical frequency of the light source 5 becomes a few bundles at point Q while producing transient ringing.

If the frequency difference between point P and point Q is large, the output frequency may exceed the peak (8 points) of the transfer characteristic during transient ringing. Then, the optical frequency discriminator 6
The polarity of the differential of the transfer characteristic of A is reversed and the loop becomes a positive feedback, so the output frequency changes until the point T, where the output of the optical frequency discriminator 6A becomes the same as the targeted Q point, and stabilizes at the T point. It becomes .

This invention provides optical frequency stabilization in which a detachable filter is inserted into the loop, the light passes through the filter before closing the loop, and the filter is detached after the frequency of the light source is stabilized. The purpose is to provide a light source.

[Means for Solving the Problem] In order to achieve this object, in the first invention, an adder 2 whose first input is the reference voltage source 1A, and an output of the adder 2 and the reference voltage source 1B are switched. switch 3 and switch 3
If the output is input and connected to the 7C side and 8E side, it will be a direct connection, and if it is connected to the 7D side and 8F side, it will be a low pass filter 9.
A switch 7 and a switch 8 are connected in series, an amplifier 4 takes the output of the switch 8 as an input, a light source 5 takes the output of the amplifier 4 as an input, and an optical frequency discrimination device takes a part of the output of the light source 5 as an input. 6A, and a compensation circuit 6B that compensates for fluctuations in the output of the optical frequency discriminator 6A due to fluctuations in the output power of the light source 5. The output of the compensation circuit 6B is used as the second input of the adder 2, and a switch is provided. When 3 is connected to the 3B side and 3A side, the low pass filter 9 is connected in series with the switch 7 and switch 8, and the switch 3 is connected to the adder 2.
After the frequency is stabilized, switch 7 and switch 8 are used to establish direct connection.

In the second invention, an adder 2 whose first input is the reference voltage source 1A, a switch 3 that switches between the output of the adder 2 and the reference voltage source 1B, and an amplifier 4 that amplifies the output of the switch 3.
, a switch 10 that takes the output of the switch 3 as an input, connects it to the LOG side to open it, and connects it to the 10H side to connect the high-pass filter 11 in parallel, a light source 5 that takes the output of the amplifier 4 as an input, and a light source. 5, and a compensation circuit 6B that compensates for variations in the output of the frequency discriminator 6A due to variations in the output power of the light source 5. It is the second input of the adder 2, and when the switch 3 is connected to the reference voltage source 1B side and when connected to the adder 2 side, the high-pass filter 11 is connected in parallel with the switch 1o, and the switch 3 is connected in parallel. After connecting to adder 2 side and stabilizing the frequency, switch 1
Set 0 to open.

Next, the configuration of the optical frequency stabilized light source according to the first invention will be explained with reference to FIG.

7 and 8 in FIG. 1 are switches, 9 is a low-pass filter, and the rest are the same as in FIG. 3.

In Figure 1, switch 7 is connected to the 7D side when the loop is open and when the loop is closed, and switch 8 is connected to the 8F side.
Connect to the side. When the loop is closed and the frequency is stabilized, switch 7 is connected to the 7c side and switch 8 is connected to the 8E side. This allows the characteristics of the loop to be limited only during the transient response.

Next, the configuration of the optical frequency stabilized light source according to the second invention will be explained with reference to FIG. 10 in FIG. 2 is a switch, 11 is a high-pass filter, and the other parts are the same as in FIG. 1.

In Fig. 1, a low-pass filter 9 is connected in series with the loop, but even if a high-pass filter 11 is connected between the loop and the ground as shown in Fig. 2, the same effect as in Fig. 1 can be obtained. Obtainable.

In FIG. 2, the switch 10 is not connected in series with the loop as in FIG. 1, so there is no momentary interruption of the loop.

[Operation] Next, the operation shown in FIG. 1 will be explained. In Figure 1, switch 3
When the switch 7 is connected to 3B, the switch 7 is connected to 7D, and the switch 8 is connected to 8F, the light source 5 generates light at a frequency determined by the reference voltage of the reference power source 1B, the ambient temperature, etc. The adder 2 outputs the difference between the frequency of the light source 5 and the target optical frequency to be stabilized as an error signal.

In order to stabilize the optical frequency of the light source 5, switch 3 is set to 3A.
When connected to the side, the output of the adder 2 appears in a step form on the output side of the switch 3. However, since the switch 7 is on the 7D side and the switch 8 is connected to the 8F [ff, the step signal is a low-frequency signal. The signal passes through the pass filter 9 and is applied to the input of the amplifier 4 as a slow rising signal. Therefore, the output of the amplifier 4 and the output of the light source 5 also change slowly, and become stable when the target stabilization frequency is reached.

After the optical frequency of the light source 5 is stabilized, turn the switch 7 to 7C.
If the switch 8 is connected to the 8E side, the low-pass filter 9 is separated from the loop, and a wideband loop is formed.

Next, the operation of FIG. 2 will be explained. In FIG. 2, the feedback system output of the light [5 is branched into two, passes through a frequency discrimination 116A, and is converted into an electrical signal by a photoelectric converter (not shown). In order to detect only the frequency fluctuation of the light source 5 from the output of the light source 5, the output of the light source 5 is guided to a compensation circuit 6B consisting of a divider, which detects only the fluctuation of the optical frequency, and the adder 2 outputs the reference voltage generated by the reference voltage source 1A. It is compared with the voltage, becomes an error signal, and is amplified by the amplifier 4,
The frequency is stabilized by being fed back to the light source 5.

When closing the loop in Figure 312, connect switch 3 to the B side and connect switch 10 to the 10H side so that the control signal is limited by the high-pass filter 11 (. 3 to the A side, and after the frequency becomes stable, switch 1o to the LOG side.

[Effects of the Invention] According to the present invention, filters with separable low-pass characteristics are connected in series in the loop, or filters with high-pass characteristics are connected in parallel.
Only when the loop is closed can the response of the loop be slowed down to stabilize the frequency.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical frequency stabilized light source according to the first invention, FIG. 2 is a configuration diagram of an optical frequency stabilized light source according to the second invention, and FIG. 3 is a configuration diagram of an optical frequency stabilized light source according to the prior art. 4 are transfer characteristic diagrams when a Fabry-Perot interferometer is used as the frequency discriminator 6A. 1A...Reference voltage source, 1B...Reference voltage source, 2...Adder, 3...Switch, 4...Amplifier, 5...Light source, 6A.
...Optical frequency discriminator, 6B...Compensation circuit, 7...Switch, 8...Switch,
9...Low pass filter, 10...Switch, 11...High pass filter. Agent Patent Attorney Kin Tsukasa Omata Figure 3 Frequency (GHz) Figure 4

Claims (1)

[Claims] 1. An adder (2) having the first reference voltage source (1A) as the first input; and switching between the output of the adder (2) and the second reference voltage source (1B). first switch (3) and first switch (3)
The output of the second switch (7) and the third switch (8) are connected in series, and the output of the third switch (8) is the input. amplifier (4)
, a light source (5) whose input is the output of the amplifier (4), and a light source (
Optical frequency discriminator (6A) that receives part of the output of 5) as input
The optical frequency discriminator (6A
), the output of the compensation circuit (6B) is used as the second input of the adder (2), and the first switch (3) is used as the second input of the adder (2). Reference voltage source (1B)
When connected to the adder (2) side and when connected to the adder (2) side, the low pass filter (9) is connected in series with the second switch (7) and the third switch (8), and the first Optical frequency stabilization characterized in that after the switch (3) is connected to the adder (2) side and the frequency is stabilized, direct communication is established between the second switch (7) and the third switch (8). Light source. 2. An adder (2) whose first input is the first reference voltage source (1A), and a first switch (3) that switches between the output of the adder (2) and the second reference voltage source (1B). ) and the first switch (3)
An amplifier (4) whose input is the output of the first switch (3), and whose input is the output of the first switch (3).When connected to the (10G) side, it is open, and when connected to the (10H) side, the high-pass filter (11) is connected. A second switch (10) for parallel connection, a light source (5) whose input is the output of the amplifier (4), and a light source (
Optical frequency discriminator (6A) that receives part of the output of 5) as input
The optical frequency discriminator (6A
), the output of the compensation circuit (6B) is used as the second input of the adder (2), and the first switch (3) is used as the second input of the adder (2). Reference voltage source (1B)
When connected to the adder (2) side and when connected to the adder (2) side, the second switch (10) is used to turn on the high-pass filter (11).
) are connected in parallel, the first switch 3 is connected to the adder (2) side, and after the frequency is stabilized, the second switch (10) is opened. Light source.