JPH0638271U - Frequency stabilized semiconductor laser light source - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a frequency-stabilized semiconductor laser light source that can accurately control the output frequency at the center of the absorption line and has good short-term stability. [Composition] An output cell of a frequency-stabilized semiconductor laser light source, which is provided with an absorption cell having an absorption line at a specific frequency, stabilizes the frequency by controlling the frequency of the semiconductor laser to the absorption line by a current modulation method. A branching unit that splits the stabilized output light and the two output beams, a first detecting unit that one output beam of the branching unit enters through the absorption cell, an output gain variable, and an output of the other branching unit. Second detection means on which light is incident, a subtractor for subtracting the outputs of the first and second detection means, and first control means for controlling the output frequency of the semiconductor laser based on the output signal of the subtractor. , Second control means for controlling the output gain of the second detection means based on the output signal of the subtractor.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a frequency-stabilized semiconductor laser light source, and more particularly to a frequency-stabilized semiconductor laser light source that compensates an amplitude modulation component.

[0002]

[Prior art]

 In the frequency-stabilized semiconductor laser light source, the injection frequency of the semiconductor laser is modulated to control the output frequency of the semiconductor laser at the center of the absorption line of the standard substance. At this time, the injection current of the semiconductor laser is also subjected to amplitude modulation, and various frequency-stabilized semiconductor laser light sources have been considered in order to remove this amplitude modulation component. FIG. 3 is a block diagram showing a first example of such a conventional frequency-stabilized semiconductor laser light source. In FIG. 3, 1 is a semiconductor laser, 2 is a beam splitter, 3 is an absorption cell filled with a standard substance, 4 is a photodetector, 5 is an oscillator, 6 is a synchronous detection circuit, 7 is a DC voltage source, and 8 and 10 are An adder 9 is a control circuit.

In FIG. 3, the output light of the semiconductor laser 1 is split into two by a beam splitter 2, one of which is output as a stabilized output light and the other of which is incident on an absorption cell 3. The light output transmitted through the absorption cell 3 enters the photodetector 4. The output signal of the photodetector 4 is synchronously detected by the synchronous detection circuit 6 using the output signal of the oscillator 5 as a reference signal, and the output signal of the DC voltage source 7 is added to the output signal of the synchronous detection circuit 6 by the adder 8. . The control circuit 9 outputs a control signal for controlling the output frequency of the semiconductor laser 1 to the absorption line frequency of the absorption cell 5 based on the output signal of the adder 8. Further, the adder circuit 10 modulates the output signal of the control circuit 9 with the output signal of the oscillator 5 and inputs it to the semiconductor laser 1.

In the first conventional example shown in FIG. 3, the output signal of the synchronous detection circuit 6 includes an amplitude modulation signal component corresponding to “a” as shown in FIG. By subtracting the output of the DC voltage source 7 corresponding to the above by the adder 8, a signal as shown in FIG. 4 (B) is obtained. As a result, the control circuit 9 controls the output frequency of the semiconductor laser 1 at the point "B" in FIG.

FIG. 5 is a block diagram showing a second example of a conventional frequency-stabilized semiconductor laser light source. Here, 1 to 6 and 9 to 10 have the same reference numerals as those in FIG. In FIG. 5, reference numeral 11 is an oscillator that outputs an output signal having a frequency tripled in synchronization with the output signal of the oscillator 5.

In the second conventional example shown in FIG. 5, the control circuit 9 controls the output frequency of the semiconductor laser 1 at the zero cross point of the third differential signal of the output signal of the absorption cell 5. As a result, the output frequency of the semiconductor laser 1 is accurately controlled to the center of the absorption line.

Further, FIG. 6 is a configuration block diagram showing a third example of the conventional frequency-stabilized semiconductor laser light source. Here, 1 to 6 and 9 to 10 have the same reference numerals as those in FIG. In FIG. 5, 12 is an adder, 13 is a beam splitter, and 14 is a photodetector.

In the third conventional example shown in FIG. 6, the optical output that has passed through the absorption cell 3 and the optical output that does not pass are detected by separate photodetectors, and the difference between these detection signals is taken. The amplitude modulation component is removed.

[0009]

[Problems to be solved by the device]

 However, in the first and third conventional examples, the amplitude modulation component is subtracted before and after the synchronous detection, but it is not precisely controlled to the center of the absorption line. On the other hand, when the output frequency is controlled at the zero-cross point of the third derivative component as in the second conventional example, although it can be accurately controlled at the center of the absorption line, in order to detect the third derivative, The frequency deviation of the modulation must be increased, and the stabilized output light will be greatly modulated. In addition, the S / N of the third derivative is poor, so the short-term stability does not increase. Therefore, an object of the present invention is to realize a frequency-stabilized semiconductor laser light source capable of accurately controlling the output frequency at the center of the absorption line and having good short-term stability.

[0010]

[Means for Solving the Problems]

 In order to achieve such an object, in the present invention, an absorption cell having an absorption line at a specific frequency is provided, and the frequency stabilization that stabilizes the frequency by controlling the frequency of the semiconductor laser on the absorption line by the current modulation method. In an integrated semiconductor laser light source, a branching unit that branches the output light of the semiconductor laser into a stabilized output light and two output lights, and one output light of the branching unit is incident through the absorption cell. Of the output light of the second detecting means, the output gain of which is variable, and the other output light of the branching means is incident on the output of the second detecting means. A subtractor for subtracting; first control means for controlling an output frequency of the semiconductor laser based on an output signal of the subtractor; and an output gain of the second detecting means for controlling an output signal of the subtractor. Second It is characterized in that a control means.

[0011]

[Action]

 The output frequency of the semiconductor laser is accurately controlled at the center of the absorption line by controlling the gain of the amplitude modulation component amplifier so that it is controlled at the zero-cross point of the third derivative signal of the absorption line.

[0012]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a frequency-stabilized semiconductor laser light source according to the present invention. Here, 1 to 6, 9 to 11, 13, and 14 are denoted by the same reference numerals as those in FIG. 5 or FIG. In FIG. 1, reference numeral 15 is a subtractor, 16 is a synchronous detection circuit, 17 is a control circuit, 18 is an amplifier, and 19 is a variable gain amplifier. Further, the beam splitters 2 and 13 include a branching means 50, the photodetector 4, the amplifier 18 and the photodetector 14, and the variable gain amplifier 19 include detection means 51 and 52, respectively, an oscillator 5, a synchronous detection circuit 6, and a control circuit 9. The adder 10 constitutes the control means 53, and the oscillator 11, the synchronous detection circuit 16 and the control circuit 17 constitute the control means 54, respectively.

In FIG. 1, the output light of the semiconductor laser 1 is split into two by a beam splitter 2, one is output as a stabilized output light, and the other is output to a beam splitter 13 to be further split into two. One is incident on the photodetector 14 and the other is incident on the absorption cell 3. The light output transmitted through the absorption cell 3 enters the photodetector 4.

The output signals of the photodetectors 4 and 14 are amplified by the amplifier 18 and the variable gain amplifier 19 and connected to the subtractor 15, respectively. The output signal of the subtractor 15 is connected to the synchronous detection circuit 6 and the synchronous detection circuit 16, and the output signals of the oscillators 5 and 11 are connected to the synchronous detection circuit 6 and the synchronous detection circuit 16 as reference signals. Further, the output signal of the oscillator 5 is connected to the oscillator 11 for synchronization.

The output signal of the synchronous detection circuit 6 is connected to the control circuit 9, the output signals of the oscillator 5 and the control circuit 9 are connected to the adder 10, and the output signal of the adder 10 is connected to the semiconductor laser 1. On the other hand, the output signal of the synchronous detection circuit 16 is connected to the control circuit 17, and the output signal of the control circuit 17 is connected to the control terminal of the variable gain amplifier 19 as a control signal.

The operation of the embodiment shown in FIG. 1 will be described with reference to FIG. 2A and 2B are characteristic curve diagrams showing frequency characteristics of the synchronous detection circuits 6 and 16. First, when the control signal is not supplied from the control circuit 17 to the variable gain amplifier 19, the output frequency of the semiconductor laser 1 is not accurately controlled to the center of the absorption line due to the influence of the amplitude modulation component. It will be controlled to the point of "a". At this time, the point "a" in FIG. 2 (A) corresponds to the point "b" in FIG. 2 (B), and the point "b" in FIG. 2 (B), which is the center of the absorption line of the absorption cell 3. It means that it is deviated by "e" from the point.

Next, when a control signal is supplied from the control circuit 17 to the variable gain amplifier 19, the control circuit 17 controls the gain of the variable gain amplifier 19 so that the output of the synchronous detection circuit 16 becomes “0”. To do. That is, the output of the controlled variable gain amplifier 19, which is an amplitude modulation component, is subtracted by the subtractor 15 so that the output of the synchronous detection circuit 16 comes to the point "D" in FIG. A) The point of "C" becomes "0V".

As a result, the output frequency of the semiconductor laser 1 is controlled to the zero crossing point of the third derivative signal of the absorption line, that is, the point "d" in FIG. Will be controlled by.

For example, when the band of the control circuit 17 is set to about “1 Hz”, the S / N is bad, but the component above 1 Hz of the output of the synchronous detection circuit 16 that detects the center of the absorption line is removed. The output frequency can be controlled precisely at the center of the absorption line. Further, since the control loop using the third-order differential signal is independent of the control loop for the output frequency, the stabilized output light is not greatly modulated.

Further, for example, if the band of the control loop for setting the output of the synchronous detection circuit 6 to “0”, that is, the control loop for the output frequency is set to about “20 Hz”, the S / N of the output of the synchronous detection circuit 6 is improved. It also improves short-term stability.

It should be noted that acetylene gas, ammonia, etc. can be used as the standard substance sealed in the absorption cell 3, and the frequency-stabilized semiconductor laser light source is configured in various wavelength bands by changing the sealed standard substance. be able to.

Although the amplitude modulation component is removed by the subtracter 15 in the embodiment shown in FIG. 1, it is also possible to remove it by dividing the output of the amplifier 18 by the output of the variable gain amplifier 19.

[0023]

[Effect of device]

 As is clear from the above description, the present invention has the following effects. In the configuration in which the amplitude modulation component is removed before synchronous detection, the output frequency is controlled to the center of the absorption line by controlling the gain of the amplitude modulation component amplifier so that it is controlled at the zero-cross point of the third derivative signal of the absorption line. Since the short-term stability is controlled by the first-order differential signal with good S / N, it is possible to realize a frequency-stabilized semiconductor laser light source with good short-term stability.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of a frequency-stabilized semiconductor laser light source according to the present invention.

FIG. 2 is a characteristic curve diagram showing frequency characteristics of two synchronous detection circuits in FIG.

FIG. 3 is a configuration block diagram showing a first example of a conventional frequency-stabilized semiconductor laser light source.

FIG. 4 is a characteristic curve diagram showing frequency characteristics of the synchronous detection circuit and the adder in FIG.

FIG. 5 is a configuration block diagram showing a second example of a conventional frequency-stabilized semiconductor laser light source.

FIG. 6 is a configuration block diagram showing a third example of a conventional frequency-stabilized semiconductor laser light source.

[Explanation of symbols]

 1 Semiconductor Laser 2,13 Beam Splitter 3 Absorption Cell 4,14 Photo Detector 5,11 Oscillator 6,16 Synchronous Detection Circuit 7 DC Voltage Source 8,10,12 Adder 9,17 Control Circuit 15 Subtractor 18 Amplifier 19 Variable Gain amplifier 50 Branching means 51,52 Detection means 53,54 Control means

Claims (1)

[Scope of utility model registration request] 1. A frequency-stabilized semiconductor laser light source comprising an absorption cell having an absorption line at a specific frequency and stabilizing the frequency by controlling the frequency of the semiconductor laser on the absorption line by a current modulation method. Branching means for branching the output light of the above into a stabilized output light and two output lights, a first detecting means through which one output light of this branching means enters through the absorption cell, and an output gain variable Yes, second detection means on which the other output light of the branch means is incident, a subtractor for subtracting the output of the second detection means from the output of the first detection means, and the output of this subtractor A first control means for controlling the output frequency of the semiconductor laser based on a signal; and a second control means for controlling the output gain of the second detection means based on the output signal of the subtractor. Characteristic lap Number stabilized semiconductor laser light source.