JP5065643B2 - Optical frequency stabilization light source and optical frequency stabilization device - Google Patents

Description

  The present invention relates to an optical frequency stabilized light source that stabilizes an oscillation frequency of laser light, and an optical frequency stabilizing device.

  In an optical wavelength division multiplexing communication system that transmits data of a plurality of different optical frequencies or wavelengths (hereinafter simply referred to as optical frequencies) using a single optical fiber, further increase in communication capacity is required. For this increase in capacity, it is necessary to use more frequency bands, so a light source capable of controlling and stabilizing the oscillation frequency with high accuracy is required.

A semiconductor laser light source is used as the light source. As a method for stabilizing the frequency of the semiconductor laser light source, there is a method using an absorption cell in which a substance having an absorption line spectrum is enclosed (see, for example, Patent Document 1). In this method, converted light obtained by converting the output light from the light source into a frequency in the vicinity of the absorption line spectrum of the substance is generated by the SHG element, transmitted through the absorption cell, and the intensity of the transmitted light is detected. Thus, the semiconductor laser light source is controlled so that the frequency of the converted light matches the peak of the absorption line spectrum.
JP-A-11-145542

  However, in the above method, when the output light is frequency-modulated by controlling the injection current to the semiconductor laser light source, the amplitude (or intensity, hereinafter simply referred to as amplitude) of the output light fluctuates and amplitude modulation (AM modulation) The components are superimposed. Such an amplitude modulation component is also directly superimposed on the light that has been wavelength-converted and passed through the absorption cell, which causes an error when detecting the intensity of the transmitted light after passing through the absorption cell. Further, since the output light is frequency modulated, the optical frequency fluctuates instantaneously.

  Further, the polarization direction of the output light varies due to the variation of the environmental temperature of the semiconductor laser light source. Here, the nonlinear optical element such as the SHG element or the optical phase modulator has optical anisotropy with a specific direction as an optical axis. Therefore, when the polarization direction of the laser light input to the nonlinear optical element varies, the loss and efficiency depending on the polarization direction change, and the amplitude modulation component due to the loss is superimposed on the modulated laser light. Such an amplitude modulation component also becomes an error factor when detecting the intensity of transmitted light after passing through the absorption cell.

  In order to solve the above problems, in the first embodiment of the present invention, a laser light source that outputs laser light, a branch element that branches the laser light, and one of the laser lights branched by the branch element are received. A first light receiving element that outputs an electrical signal corresponding to the intensity of the laser light, and at least one absorption line spectrum of light having a specific optical frequency, disposed on the optical path of the other laser light branched by the branching element A light absorber that encloses a substance, a second light receiving element that receives laser light transmitted through the light absorber and outputs an electrical signal according to the intensity of the laser light, a first light receiving element, and a second light receiving element The difference between the peak of the absorption line spectrum and the optical frequency of the laser beam is detected from the differential amplifier to which the electrical signal output from each light receiving element is input and the electrical signal output from the differential amplifier, and the difference is detected. Make smaller Ku optical frequency-stabilized light source and a stabilizer control unit for controlling the optical frequency of the output laser beam from the laser light source is provided.

  The optical frequency stabilized light source is disposed between the laser light source and the optical element, and is disposed on the output side of the polarizer, the polarizer transmitting a specific polarization direction of the laser light, and the polarizer A phase modulation unit that modulates the phase of the laser beam when the transmitted laser beam is input, and a modulation signal supply unit that supplies a modulation signal to the phase modulation unit; The laser light source detects the difference between the peak of the absorption line spectrum and the frequency of the laser beam from the modulation signal supplied from the modulation signal supply unit to the phase modulation unit and the electrical signal output from the differential amplifier, and reduces the difference. The frequency of the laser beam output from may be controlled.

  The optical frequency stabilized light source is disposed between the laser light source and the optical element, and is disposed on the output side of the polarizer, the polarizer transmitting a specific polarization direction of the laser light, and the polarizer When a transmitted laser beam is input, an SHG wavelength conversion unit that generates second harmonic light from the laser beam, and a frequency modulation signal supply unit that supplies a frequency modulation signal that modulates the frequency of the laser beam output from the laser light source The stabilization control unit detects a difference between the peak of the absorption line spectrum and the optical frequency of the second harmonic light from the frequency modulation signal of the frequency modulation signal supply unit and the electric signal output from the differential amplifier. In order to reduce the difference, the frequency of the laser light output from the laser light source may be controlled.

  In the second embodiment of the present invention, a laser light source that outputs laser light and a substance that is disposed on the optical path of the laser light and has at least one saturated absorption line spectrum of light of a specific optical frequency are enclosed. A light absorber, a half mirror that transmits at least part of the laser light transmitted through the light absorber, and reflects at least another part along the same optical path as the laser light transmitted through the light absorber, and a laser light source An optical element that changes the direction of the laser light reflected by the half mirror and transmitted through the light absorber, and receives the laser light whose direction has been changed by the optical element. A first light receiving element that outputs an electric signal according to the intensity, a second light receiving element that receives the laser light transmitted through the half mirror and outputs an electric signal according to the intensity of the laser light, and a first receiving element. A differential amplifier to which an electric signal output from each of the element and the second light receiving element is input, and an electric signal output from the differential amplifier to detect the absorption of the laser beam in the light absorber There is provided an optical frequency stabilized light source including a stabilization control unit that controls the optical frequency of laser light output from the laser light source.

  The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

  As is apparent from the above description, according to the present invention, even when the intensity and polarization direction of the light source light output from the laser light source fluctuate due to environmental factors such as temperature and the intensity fluctuation component is superimposed on the light source light, By receiving the fluctuation with the second light receiving element, the intensity fluctuation component common to both light receiving elements can be canceled from the intensity of the transmitted light of the gas cell received by the first light receiving element in the differential detector. In addition, when the polarization direction of the light source light varies due to environmental temperature variation, the polarization direction variation can be converted into an intensity variation component by the polarizer, so that the intensity variation component can be similarly cancelled. Therefore, the stabilization control unit can more accurately control the frequency of the light source light output from the laser light source without being affected by the intensity fluctuation component.

  Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.

  FIG. 1 is a block diagram showing a configuration of an optical frequency stabilized light source 11 according to an embodiment of the present invention. As shown in FIG. 1, the optical frequency stabilization light source 11 includes a laser light source 20 and an optical frequency stabilization device 15 that stabilizes the frequency of the laser light source 20.

  The laser light source 20 is supplied with a direct current from the drive circuit 230 of the stabilization control unit 200 and outputs laser light. An example of the semiconductor laser body is a distributed feedback (DFB) semiconductor laser that oscillates in the vicinity of 1.55 μm. Usually, the oscillation frequency of a semiconductor laser can be changed by the laser temperature and the injection current. Laser light output from the laser light source is continuous wave (CW) light, and is hereinafter referred to as “light source light”. The light source light oscillated by the DFB semiconductor laser of the laser light source 20 is divided into output light and monitor light, and the monitor light is subjected to stabilization control of the oscillation frequency in the optical frequency stabilizer 15.

  The optical frequency stabilization device 15 includes a polarizer 30, a phase modulator 40, a non-polarizing beam splitter 50, a gas cell 60, a first light receiving element 70, a second light receiving element 80, a level adjustment circuit 90, A differential amplifier 100, a modulation signal supply unit 110, and a stabilization control unit 200 are provided. The stabilization control unit 200 includes a phase comparator 210, a feedback circuit 220, and a drive circuit 230.

  The polarizer 30 transmits the light source light output from the monitor side of the laser light source 20 and inputs it to the phase modulator 40. The polarizer 30 transmits light in a specific polarization direction in the light source light even when the polarization of the light source light fluctuates. In this case, the polarizer 30 converts the change in the polarization of the light source light into the change in the amplitude of the transmitted light and outputs the converted light.

The phase modulation unit 40 modulates the phase of the light transmitted through the polarizer 30. An example of the phase modulation unit 40 is an LN phase modulator. The LN phase modulator has a crystal of lithium niobate (LiNbO ₃ : LN) having electro-optic characteristics, and electrodes formed to face each other with a waveguide of incident light in the crystal. This electrode is electrically connected to the modulation signal supply unit 110. When a high frequency voltage signal (RF signal) having a frequency fr is input from the modulation signal supply unit 110 to the electrode of the phase modulation unit 40, the phase of the light source light transmitted through the phase modulation unit 40 is modulated, and the light source light is oscillated. Sideband light is generated on the high frequency side and the low frequency side by fr with respect to the frequency. The frequency fr for modulating the phase is set smaller than the absorption line width, and is, for example, 1 MHz to several 100 MHz.

The non-polarizing beam splitter 50 divides the output light of the phase modulation unit 40 evenly so that the ratio of transmitted light to reflected light is approximately 1: 1, and causes the transmitted light to enter the gas cell 60. The gas cell 60 is a transparent cell in which a gas having an absorption line spectrum is enclosed in the vicinity of the oscillation frequency of the light source light output from the laser light source 20. An example of this gas is isotope-substituted acetylene gas (C ₂ H ₂ ).

  The first light receiving element 70 receives light transmitted through the gas cell 60 and outputs an electrical signal having an intensity level corresponding to the amount of received light to the differential amplifier 100. The second light receiving element 80 receives the reflected light reflected by the non-polarizing beam splitter 50 and outputs an electric signal having an intensity level corresponding to the amount of received light to the differential amplifier 100. An example of the first light receiving element 70 and the second light receiving element 80 is an InGaAs / InP photodiode.

  The level adjustment circuit 90 is disposed between the first light receiving element 70 and the differential amplifier 100. The level adjustment circuit 90 is an electric signal input from the first light receiving element 70 to the differential amplifier 100 when the light transmitted through the non-polarizing beam splitter 50 is directly received by the first light receiving element 70 without passing through the gas cell 60. The level of the electric signal from the second light receiving element 80 is the same as the level of the electric signal input to the differential amplifier 100 from the first light receiving element 70 that has received the reflected light of the non-polarizing beam splitter 50. Adjust the intensity level.

  The differential amplifier 100 synthesizes the electric signal input from the first light receiving element 70 and the electric signal input from the second light receiving element 80, amplifies the intensity level difference between these signals, and stabilizes the control unit. It outputs to the phase comparator 210 of 200.

  The phase comparator 210 of the stabilization controller 200 compares the phase of the signal input from the differential amplifier 100 and the phase of the RF signal input from the modulation signal supply unit 110, and compares the phase of the light source light output from the laser light source 20. Whether or not the oscillation frequency matches the absorption line frequency of the isotope-substituted acetylene gas sealed in the gas cell 60, and if not, to what extent from the absorption line frequency to the high frequency side or the low frequency side It is determined whether the frequency interval is shifted. At this time, by setting the RF signal input to the phase comparator 210 to fr or 3fr, a primary differential signal or a tertiary differential signal is obtained. That is, the phase comparator 210 compares the intensities of the light source light, the sideband light, etc. after absorption with the isotope-substituted acetylene gas based on the inputs from the differential amplifier 100 and the modulation signal supply unit 110. Detecting how much the oscillation frequency of the light source light deviates from the absorption line frequency of the isotope-substituted acetylene gas. Further, the phase comparator 210 supplies a signal based on the determination result to the feedback circuit 220. The feedback circuit 220 controls the current supplied from the drive circuit 230 to the DFB semiconductor laser of the laser light source 20 based on the signal from the phase comparator 210. Thereby, the frequency of the light source light output from the laser light source 20 is controlled to coincide with the peak of the specific absorption line spectrum of the isotope-substituted acetylene gas sealed in the gas cell 60.

  In the above embodiment, since the optical frequency stabilization device 15 includes the polarizer 30, the polarization of the light source light input to the phase modulation unit 40 even when the polarization direction of the light source light output from the laser light source 20 varies. The direction can be made constant. Therefore, when the phase modulation unit 40 is arranged together with the polarizer 30, the phase modulation unit 40 can modulate the phase of the light source light without being affected by the fluctuation of the polarization direction. However, the operating point may fluctuate due to temperature fluctuations of the phase modulation unit 40, or the intensity modulation component may be superimposed due to the influence of PDL.

  By providing the polarizer 30, when the polarization direction of the light source light is changed, the change in the polarization direction is converted into an intensity change in the polarizer 30 and is superimposed on the light source light as an amplitude fluctuation component. Further, an amplitude variation component is superimposed on the light source light also due to environmental factors such as temperature. However, in the optical frequency stabilization device 15 of the present embodiment, even when the amplitude fluctuation component is superimposed on the light source light in this way, the light source light is received by the second light receiving element 80, and therefore the amplitude fluctuation component. An electric signal corresponding to an intensity level including is input to the differential amplifier 100. Therefore, in the differential amplifier 100, the amplitude fluctuation component common to both the light receiving elements can be canceled from the electric signal received by the first light receiving element 70. Therefore, the stabilization controller 200 can accurately control the frequency of the light source light output from the laser light source 20 by the peak of the absorption line without being affected by the amplitude fluctuation component.

  FIG. 2 is a block diagram showing a configuration of an optical frequency stabilized light source 12 according to another embodiment of the present invention. In the optical frequency stabilized light source 12 shown in FIG. 2, the same components as those of the optical frequency stabilized light source 11 are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 2, the optical frequency stabilization light source 12 includes a laser light source 20 and an optical frequency stabilization device 16 that stabilizes the frequency of the laser light source 20.

  The optical frequency stabilization device 16 includes a frequency modulation signal supply unit 120 instead of the phase modulation unit 40 in the optical frequency stabilization device 15 shown in FIG. The frequency modulation signal supply unit 120 sends a frequency modulation signal to the drive circuit 230 and frequency modulates the light source light output from the laser light source 20. In this case, the frequency modulation signal supply unit 120 outputs a frequency modulation signal of 10 MHz, for example. Thereby, in the optical frequency stabilization device 16 of the optical frequency stabilization light source 12, the laser light source 20 has a frequency corresponding to the frequency modulation signal with respect to the frequency when the drive circuit 230 does not receive the frequency modulation signal. The light source light, which is frequency-modulated in a time-periodic manner, is output to the high frequency side and the low frequency side by the range.

  The polarizer 30 transmits the light source light output from the monitor side of the laser light source 20 and inputs it to the SHG wavelength converter 45. The polarizer 30 shown in FIG. 2 converts the change in the polarization of the light source light into the change in the amplitude of the transmitted light and outputs the same as the polarizer 30 shown in FIG.

  When the light source light is input, the SHG wavelength conversion unit 45 outputs second harmonic light having an optical frequency twice that of the light source light. The SHG wavelength converter 45 includes, for example, an SHG element that generates second harmonic light with respect to input light, and a separation unit that separates the second harmonic light from the output light of the SHG element and outputs the separated light toward the gas cell 60. Thermistor, Peltier element, temperature control circuit and the like for compensating the operating temperature of the SHG element. As a result, the light output from the SHG wavelength conversion unit 45 has amplitude fluctuation due to polarization fluctuation in addition to frequency modulation due to the frequency modulation signal of the laser light source 20 and frequency fluctuation due to the optical frequency fluctuation of the laser light source 20 itself. Superimposed.

  The non-polarizing beam splitter 50 divides the second harmonic light output from the SHG wavelength conversion unit 45 evenly so that the ratio of transmitted light to reflected light is 1: 1, and the transmitted light is gas cell 60. To enter. The gas cell 60 is filled with a substance whose absorption line spectrum is twice the optical frequency of the light source light targeted for stabilization. An example of this material is the 87 rubidium atom.

  The first light receiving element 70 receives light transmitted through the gas cell 60 and outputs an electrical signal having an intensity level corresponding to the amount of received light to the differential amplifier 100. The second light receiving element 80 receives the reflected light reflected by the non-polarizing beam splitter 50 and outputs an electric signal having an intensity level corresponding to the amount of received light to the differential amplifier 100. An example of the first light receiving element 70 and the second light receiving element 80 is a silicon photodiode.

  The differential amplifier 100 synthesizes the electric signal input from the first light receiving element 70 and the electric signal input from the second light receiving element 80, amplifies the intensity level difference between these signals, and stabilizes the control unit. It outputs to the phase comparator 210 of 200.

  The phase comparator 210 of the stabilization control unit 200 compares the phase of the signal input from the differential amplifier 100 and the frequency modulation signal input from the frequency modulation signal supply unit 120, and determines the laser from the differential signal of the absorption line. Whether the oscillation frequency of the light source light output from the light source 20 matches the optical frequency targeted for stabilization, and if not, which side of the absorption line frequency from the high frequency side or the low frequency side It is determined whether or not the frequency interval is shifted by a certain degree. Further, the phase comparator 210 supplies a signal based on the determination result to the feedback circuit 220. The feedback circuit 220 controls the current supplied from the drive circuit 230 to the DFB semiconductor laser of the laser light source 20 based on the signal from the phase comparator 210. Thereby, the optical frequency of the light source light output from the laser light source 20 is controlled to coincide with the optical frequency targeted for stabilization.

  In the above embodiment, the optical frequency stabilization device 16 includes the polarizer 30 similarly to the optical frequency stabilization device 15, so that even when the polarization direction of the light source light output from the laser light source 20 fluctuates, the phase modulation is performed. The polarization direction of the light source light input to the unit 40 can be made constant. Therefore, when the SHG wavelength conversion unit 45 is arranged together with the polarizer 30, the SHG wavelength conversion unit 45 can generate the second harmonic light from the light source light without being affected by the fluctuation of the polarization direction.

  By providing the polarizer 30, when the polarization direction of the light source light changes, the change in the polarization direction is converted into an intensity change in the polarizer 30 and is superimposed on the light source light as an intensity fluctuation component. Moreover, an intensity fluctuation component is superimposed on the light source light also due to environmental factors such as temperature. However, in the optical frequency stabilization device 16 of the present embodiment, similar to the optical frequency stabilization device 15, this light source light is received by the second light receiving element 80 even when the amplitude fluctuation component is superimposed on the light source light. Therefore, an electrical signal corresponding to the intensity level including the amplitude variation component is input to the differential amplifier 100. Therefore, in the differential amplifier 100, the amplitude fluctuation component common to both the light receiving elements can be canceled from the electric signal received by the first light receiving element 70. Therefore, the stabilization controller 200 can accurately control the optical frequency of the light source light output from the laser light source 20 by the peak of the absorption line without being affected by the intensity fluctuation component.

  FIG. 3 is a block diagram showing a configuration of an optical frequency stabilized light source 13 which is still another embodiment according to the present invention. In the optical frequency stabilized light source 13, the same components as those of the optical frequency stabilized light sources 11 and 12 are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 3, the optical frequency stabilization light source 13 includes a laser light source 20 and an optical frequency stabilization device 17 that stabilizes the optical frequency of the laser light source 20.

  The polarizer 30 transmits the light source light output from the monitor side of the laser light source 20 and inputs it to the SHG wavelength converter 45. In this case, like the polarizer 30 in FIG. 2, the polarizer 30 in FIG. 3 converts the variation in the polarization of the light source light into the variation in the amplitude of the transmitted light and outputs it.

  When the light source light is input, the SHG wavelength conversion unit 45 outputs second harmonic light having an optical frequency twice that of the light source light. Accordingly, the light output from the SHG wavelength conversion unit 45 in FIG. 3 includes the frequency modulation by the frequency modulation signal of the laser light source 20 and the light of the laser light source 20 itself as in the case of the SHG wavelength conversion unit 45 in FIG. In addition to frequency fluctuation due to frequency fluctuation, amplitude fluctuation due to polarization fluctuation is superimposed.

  The polarization beam splitter 55 is disposed on the output side of the SHG wavelength conversion unit 45. The polarization beam splitter 55 has an optical characteristic of transmitting incident light having a specific polarization direction and totally reflecting polarized light whose polarization direction is orthogonal to the incident light, and is output from the SHG wavelength conversion unit 45. The wave light is transmitted, and the transmitted second harmonic light is incident on the quarter-wave plate 65. The quarter-wave plate 65 converts the incident second harmonic light from linearly polarized light into circularly polarized light and makes it incident on the gas cell 60.

  As in the gas cell 60 of the optical frequency stabilization device 16, the gas cell 60 is filled with a substance whose absorption line spectrum is twice the optical frequency of the light source light targeted for stabilization. The half mirror 67 disposed on the output side of the gas cell 60 reflects the half of the second harmonic light that has passed through the gas cell 60 and entered the half mirror 67, transmitted through the gas cell 60, and entered the half mirror 67. The gas cell 60 is again transmitted along the same optical path as the harmonic light. The half mirror 67 transmits the remaining half of the second harmonic light that has passed through the gas cell 60 and entered the half mirror 67.

  Here, if the second harmonic light outputted from the SHG wavelength conversion unit 45 is made to pass through the same optical path in the gas cell 60, the Doppler spread can be removed, so that a saturated absorption phenomenon can be caused.

  The first light receiving element 70 receives the transmitted light that has passed through the half mirror 67 and outputs an electrical signal having an intensity level corresponding to the amount of received light to the differential amplifier 100. Further, the reflected light reflected by the half mirror 67 becomes counterclockwise circularly polarized light and again passes through the gas cell 60 as described above, and then passes through the quarter wavelength plate 65. The quarter-wave plate 65 converts the transmitted light from counterclockwise circularly polarized light to linearly polarized light again, and the polarization direction is perpendicular to the polarization direction of the second harmonic light output from the SHG wavelength conversion unit 45. Become. Therefore, the polarization beam splitter 55 changes the direction by totally reflecting the transmitted light. The second light receiving element 80 receives the reflected light and outputs an electrical signal having an intensity level corresponding to the amount of received light to the differential amplifier 100. An example of the first light receiving element 70 and the second light receiving element 80 is a silicon photodiode.

  The differential amplifier 100 synthesizes the electric signal input from the first light receiving element 70 and the electric signal input from the second light receiving element 80, amplifies the intensity level difference between these signals, and stabilizes the control unit. It outputs to the phase comparator 210 of 200.

  The phase comparator 210 of the stabilization control unit 200 compares the phase of the signal input from the differential amplifier 100 and the frequency modulation signal input from the frequency modulation signal supply unit 120, and the light source output from the laser light source 20. Whether the oscillation frequency of the light matches the optical frequency targeted for stabilization, and if not, how much the frequency interval is shifted from the absorption line frequency to either the high frequency side or the low frequency side It is determined whether it is. Further, the phase comparator 210 supplies a signal based on the determination result to the feedback circuit 220. The feedback circuit 220 controls the current supplied from the drive circuit 230 to the DFB semiconductor laser of the laser light source 20 based on the signal from the phase comparator 210. The drive circuit 230 may control the resonator length or the fiber length in the laser light source 20 instead of controlling the current. Thereby, the optical frequency of the light source light output from the laser light source 20 is controlled to coincide with the optical frequency targeted for stabilization.

  In the above embodiment, the laser light source 20 may include a distributed reflection type (DBR) semiconductor laser or other semiconductor lasers instead of the DFB semiconductor laser, and can be selected according to a required optical frequency. The laser light source 20 is not limited to a semiconductor laser and may be a fiber laser or the like. Further, the modulator disposed in the phase modulation unit 40 is not limited to the LN phase modulator, and a desired phase modulator can be disposed. Further, as the substance to be sealed in the gas cell 60, a desired substance can be selected according to the optical frequency of the light source light and the optical frequency to be stabilized.

  In the optical frequency stabilizing device 17, similarly to the optical frequency stabilizing device 16, even when an amplitude fluctuation component is superimposed on the light source light, the light source light is received by the second light receiving element 80, so that the amplitude thereof is increased. An electric signal corresponding to the intensity level including the fluctuation component is input to the differential amplifier 100. Therefore, in the differential amplifier 100, the amplitude fluctuation component common to both the light receiving elements can be canceled from the electric signal received by the first light receiving element 70. Therefore, the stabilization controller 200 can more accurately control the optical frequency of the light source light output from the laser light source 20 without being affected by the intensity fluctuation component.

  Here, the non-polarizing beam splitter 50 of the said embodiment is one form of the branch element of this invention. The polarization beam splitter 55 is an embodiment of the optical element of the present invention. Moreover, the gas cell 60 is one form of the light absorber of the present invention in which the gas cell 60 encloses a substance having at least one absorption line spectrum of light having a specific optical frequency.

  The optical frequency stabilized light source 11 may include the frequency modulation signal supply unit 120 instead of the modulation signal supply unit 110 and the phase modulation unit 40. In this case, in the optical frequency stabilized light source 11, the frequency modulation signal supply unit 120 sends a modulation signal to the drive circuit 230 to modulate the optical frequency of the laser light. The optical frequency stabilized light source 12 and the optical frequency stabilized light source 13 may include the modulation signal supply unit 110 and the phase modulation unit 40 instead of the frequency modulation signal supply unit 120. In this case, the optical frequency stabilized light source 12 and the optical frequency stabilized light source 13 modulate the phase of the laser beam by the modulation signal supply unit 110 and the phase modulation unit 40.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

It is a block diagram which shows the structure of the optical frequency stabilization light source 11 which is embodiment of this invention. It is a block diagram which shows the structure of the optical frequency stabilization light source 12 which is other embodiment. It is a block diagram which shows the structure of the optical frequency stabilization light source 13 which is other embodiment.

Explanation of symbols

11, 12, 13 Optical frequency stabilization light source, 15, 16, 17 Optical frequency stabilization device, 20 Laser light source, 30 Polarizer, 40 Phase modulator, 45 SHG wavelength converter, 50 Non-polarized beam splitter, 55 Polarized beam Splitter, 60 gas cell, 65 1/4 wavelength plate, 67 half mirror, 70 first light receiving element, 80 second light receiving element, 90 level adjustment circuit, 100 differential amplifier, 110 modulation signal supply unit, 120 frequency modulation signal supply unit , 200, 201 Stabilization control unit, 210 Phase comparator, 220 Feedback circuit, 230 Drive circuit

Claims (8)

A laser light source for outputting laser light;
A branch element for branching the laser beam;
A first light receiving element that is a photodiode that receives one laser beam branched by the branch element and outputs an electrical signal corresponding to the intensity of the laser light;
A light absorber that encloses a substance that is disposed on the optical path of the other laser beam branched by the branch element and has at least one absorption line spectrum of light of a specific optical frequency;
A second light receiving element that is a photodiode that receives the laser light transmitted through the light absorber and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
From the electrical signal output from the differential amplifier, the difference between the peak of the absorption line spectrum and the optical frequency of the laser beam is detected, and the optical frequency of the laser beam output from the laser light source is controlled to reduce the difference. A stabilization control unit ,
A polarizer disposed between the laser light source and the branch element and transmitting a specific polarization direction of the laser light;
A phase modulator arranged on the output side of the polarizer and modulating and outputting the phase of the laser light when the laser light transmitted through the polarizer is input;
A modulation signal supply unit for supplying a modulation signal to the phase modulation unit;
With
The stabilization control unit is configured to detect a difference between a peak of the absorption line spectrum and an optical frequency of the laser light from a modulation signal supplied from the modulation signal supply unit to the phase modulation unit and an electric signal output from the differential amplifier. An optical frequency stabilized light source that controls the optical frequency of the laser light output from the laser light source so as to reduce the difference . A laser light source for outputting laser light;
A branch element for branching the laser beam;
A first light receiving element that is a photodiode that receives one laser beam branched by the branch element and outputs an electrical signal corresponding to the intensity of the laser light;
A light absorber that encloses a substance that is disposed on the optical path of the other laser beam branched by the branch element and has at least one absorption line spectrum of light of a specific optical frequency;
A second light receiving element that is a photodiode that receives the laser light transmitted through the light absorber and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
From the electrical signal output from the differential amplifier, the difference between the peak of the absorption line spectrum and the optical frequency of the laser beam is detected, and the optical frequency of the laser beam output from the laser light source is controlled to reduce the difference. A stabilization control unit ,
A polarizer disposed between the laser light source and the branch element and transmitting a specific polarization direction of the laser light;
An SHG wavelength converter that is arranged on the output side of the polarizer and generates second harmonic light from the laser light when laser light transmitted through the polarizer is input;
A frequency modulation signal supply unit for supplying a frequency modulation signal for modulating the optical frequency of the laser beam output from the laser light source;
With
The stabilization control unit detects a difference between the peak of the absorption line spectrum and the optical frequency of the second harmonic light from the frequency modulation signal of the frequency modulation signal supply unit and the electric signal output from the differential amplifier. An optical frequency stabilized light source that controls the optical frequency of laser light output from the laser light source to reduce the difference . A laser light source for outputting laser light;
A light absorber that encloses a substance that is disposed on the optical path of the laser light and has at least one saturated absorption line spectrum of light of a specific optical frequency;
A half mirror that transmits at least a portion of the laser light transmitted through the light absorber and reflects at least another portion along the same optical path as the laser light transmitted through the light absorber;
An optical element that transmits the laser light from the laser light source and changes the direction of the laser light reflected by the half mirror and transmitted through the light absorber again;
A first light receiving element that is a photodiode that receives the laser light whose direction has been changed by the optical element and outputs an electrical signal corresponding to the intensity of the laser light;
A second light receiving element that is a photodiode that receives the laser light transmitted through the half mirror and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
Said detecting an electrical signal output from the differential amplifier in order to further reduce the absorption of laser light by the light absorber, stabilization control unit for controlling the optical frequency of the laser light output from the laser light source,
A polarizer disposed between the laser light source and the optical element and transmitting a specific polarization direction of the laser light;
A phase modulator arranged on the output side of the polarizer and modulating and outputting the phase of the laser light when the laser light transmitted through the polarizer is input;
A modulation signal supply unit for supplying a modulation signal to the phase modulation unit;
With
The stabilization control unit is configured to detect a difference between a peak of the absorption line spectrum and an optical frequency of the laser light from a modulation signal supplied from the modulation signal supply unit to the phase modulation unit and an electric signal output from the differential amplifier. An optical frequency stabilized light source that controls the optical frequency of the laser light output from the laser light source so as to reduce the difference . A laser light source for outputting laser light;
A light absorber that encloses a substance that is disposed on the optical path of the laser light and has at least one saturated absorption line spectrum of light of a specific optical frequency;
A half mirror that transmits at least a portion of the laser light transmitted through the light absorber and reflects at least another portion along the same optical path as the laser light transmitted through the light absorber;
An optical element that transmits the laser light from the laser light source and changes the direction of the laser light reflected by the half mirror and transmitted through the light absorber again;
A first light receiving element that is a photodiode that receives the laser light whose direction has been changed by the optical element and outputs an electrical signal corresponding to the intensity of the laser light;
A second light receiving element that is a photodiode that receives the laser light transmitted through the half mirror and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
Said detecting an electrical signal output from the differential amplifier in order to further reduce the absorption of laser light by the light absorber, stabilization control unit for controlling the optical frequency of the laser light output from the laser light source,
A polarizer disposed between the laser light source and the optical element and transmitting a specific polarization direction of the laser light;
An SHG wavelength converter that is arranged on the output side of the polarizer and generates second harmonic light from the laser light when laser light transmitted through the polarizer is input;
A frequency modulation signal supply unit for supplying a frequency modulation signal for modulating the optical frequency of the laser beam output from the laser light source;
With
The stabilization control unit detects a difference between the peak of the absorption line spectrum and the optical frequency of the second harmonic light from the frequency modulation signal of the frequency modulation signal supply unit and the electric signal output from the differential amplifier. An optical frequency stabilized light source that controls the optical frequency of laser light output from the laser light source to reduce the difference . A branching element for branching the laser beam output from the laser light source;
A first light receiving element that is a photodiode that receives one laser beam branched by the branch element and outputs an electrical signal corresponding to the intensity of the laser light;
A light absorber that encloses a substance that is disposed on the optical path of the other laser beam branched by the branch element and has at least one absorption line spectrum of light of a specific optical frequency;
A second light receiving element that is a photodiode that receives the laser light transmitted through the light absorber and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
A stable control for detecting the difference between the absorption line spectrum and the optical frequency of the laser light from the electrical signal output from the differential amplifier and controlling the optical frequency of the laser light output from the laser light source in order to reduce the difference. Control unit ,
A polarizer disposed between the laser light source and the branch element and transmitting a specific polarization direction of the laser light;
A phase modulator arranged on the output side of the polarizer and modulating and outputting the phase of the laser light when the laser light transmitted through the polarizer is input;
A modulation signal supply unit for supplying a modulation signal to the phase modulation unit;
With
The stabilization control unit is configured to detect a difference between a peak of the absorption line spectrum and an optical frequency of the laser light from a modulation signal supplied from the modulation signal supply unit to the phase modulation unit and an electric signal output from the differential amplifier. An optical frequency stabilizing device that detects an optical frequency and controls an optical frequency of laser light output from the laser light source so as to reduce the difference . A branching element for branching the laser beam output from the laser light source;
A first light receiving element that is a photodiode that receives one laser beam branched by the branch element and outputs an electrical signal corresponding to the intensity of the laser light;
A light absorber that encloses a substance that is disposed on the optical path of the other laser beam branched by the branch element and has at least one absorption line spectrum of light of a specific optical frequency;
A second light receiving element that is a photodiode that receives the laser light transmitted through the light absorber and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
A stable control for detecting the difference between the absorption line spectrum and the optical frequency of the laser light from the electrical signal output from the differential amplifier and controlling the optical frequency of the laser light output from the laser light source in order to reduce the difference. Control unit ,
A polarizer disposed between the laser light source and the branch element and transmitting a specific polarization direction of the laser light;
An SHG wavelength converter that is arranged on the output side of the polarizer and generates second harmonic light from the laser light when laser light transmitted through the polarizer is input;
A frequency modulation signal supply unit for supplying a frequency modulation signal for modulating the optical frequency of the laser beam output from the laser light source;
With
The stabilization control unit detects a difference between the peak of the absorption line spectrum and the optical frequency of the second harmonic light from the frequency modulation signal of the frequency modulation signal supply unit and the electric signal output from the differential amplifier. An optical frequency stabilizing device that controls the optical frequency of the laser light output from the laser light source in order to reduce the difference . A light absorber that encloses a substance that is disposed on an optical path of laser light output from a laser light source and has at least one saturated absorption line spectrum of light having a specific optical frequency;
A half mirror that transmits at least a portion of the laser light transmitted through the light absorber and reflects at least another portion along the same optical path as the laser light transmitted through the light absorber;
An optical element that transmits the laser light from the laser light source and changes the direction of the laser light reflected by the half mirror and transmitted through the light absorber again;
A first light receiving element that is a photodiode that receives the laser light whose direction has been changed by the optical element and outputs an electrical signal corresponding to the intensity of the laser light;
A second light receiving element that is a photodiode that receives the laser light transmitted through the half mirror and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
Said detecting an electrical signal output from the differential amplifier in order to further reduce the absorption of laser light by the light absorber, stabilization control unit for controlling the optical frequency of the laser light output from the laser light source,
A polarizer disposed between the laser light source and the optical element and transmitting a specific polarization direction of the laser light;
A phase modulator arranged on the output side of the polarizer and modulating and outputting the phase of the laser light when the laser light transmitted through the polarizer is input;
A modulation signal supply unit for supplying a modulation signal to the phase modulation unit;
With
The stabilization control unit is configured to detect a difference between a peak of the absorption line spectrum and an optical frequency of the laser light from a modulation signal supplied from the modulation signal supply unit to the phase modulation unit and an electric signal output from the differential amplifier. An optical frequency stabilizing device that detects an optical frequency and controls an optical frequency of laser light output from the laser light source so as to reduce the difference . A light absorber that encloses a substance that is disposed on an optical path of laser light output from a laser light source and has at least one saturated absorption line spectrum of light having a specific optical frequency;
A half mirror that transmits at least a portion of the laser light transmitted through the light absorber and reflects at least another portion along the same optical path as the laser light transmitted through the light absorber;
An optical element that transmits the laser light from the laser light source and changes the direction of the laser light reflected by the half mirror and transmitted through the light absorber again;
A first light receiving element that is a photodiode that receives the laser light whose direction has been changed by the optical element and outputs an electrical signal corresponding to the intensity of the laser light;
A second light receiving element that is a photodiode that receives the laser light transmitted through the half mirror and outputs an electrical signal corresponding to the intensity of the laser light;
A differential amplifier electrical signal is input respectively output from the first Ichi受 optical element and the second light receiving element,
Said detecting an electrical signal output from the differential amplifier in order to further reduce the absorption of laser light by the light absorber, stabilization control unit for controlling the optical frequency of the laser light output from the laser light source,
A polarizer disposed between the laser light source and the optical element and transmitting a specific polarization direction of the laser light;
An SHG wavelength converter that is arranged on the output side of the polarizer and generates second harmonic light from the laser light when laser light transmitted through the polarizer is input;
A frequency modulation signal supply unit for supplying a frequency modulation signal for modulating the optical frequency of the laser beam output from the laser light source;
With
The stabilization control unit detects a difference between the peak of the absorption line spectrum and the optical frequency of the second harmonic light from the frequency modulation signal of the frequency modulation signal supply unit and the electric signal output from the differential amplifier. An optical frequency stabilizing device that controls the optical frequency of the laser light output from the laser light source in order to reduce the difference .

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