JPH0740181Y2 - Variable frequency light source using laser frequency characteristic measuring device and nuclear device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for measuring temperature-oscillation frequency characteristics, current-oscillation frequency characteristics, etc. of a semiconductor laser with high accuracy, and a variable frequency light source using the apparatus. It is a thing.

<Prior Art> FIG. 9 is a principle configuration diagram showing a first conventional example of an apparatus for measuring the temperature-oscillation frequency characteristic of a semiconductor laser, which uses a diffraction grating. The temperature of the semiconductor laser 1 to be measured is swept by the temperature control circuit 2. When the output light of the measured laser 1 is incident on the diffraction grating 3 rotating around the rotation center 4, the diffraction angle changes depending on the wavelength.
The temperature-oscillation frequency characteristic of the laser 1 can be measured by observing the incident angle θ of the light when entering the laser 1 and the temperature of the laser 1.

FIG. 10 is a principle configuration diagram showing a second conventional example for measuring the temperature-oscillation frequency characteristic of a semiconductor laser, which uses a Michelson interferometer. The temperature of the measured laser 1 is swept as in FIG. The output light (λ _x ) of the laser to be measured 1 is incident on a Michelson interferometer consisting of half mirrors 6, 7, movable mirrors 8 and mirrors 9, and a photodetector 10 detects interference fringes. By measuring the wavelength value of the laser 1 at each temperature, the temperature-oscillation frequency characteristic of the laser 1 can be measured.

<Problems to be solved by the invention> However, since each of the above-mentioned conventional methods has a mechanically movable part, high-speed response is poor (1 sample / 1 to 2
s). Further, in the case of the method shown in FIG. 9, since the machine accuracy affects the measurement accuracy, it is difficult to improve the accuracy and it is weak against the change with time. In order to improve the accuracy, it is necessary to increase the distance between the diffraction grating 3 and the photodetector 5 in the case of FIG. 9 and to increase the movable distance Δl of the movable mirror 8 in the case of FIG. The problem arises that the system becomes large. Further, in the case of FIG. 10, a reference light source (λ _ref ) is required, which complicates the configuration of the optical system.

The present invention has been made to solve such a problem, and an object thereof is to realize a device capable of measuring the temperature-oscillation frequency characteristic and the current-oscillation frequency characteristic of a semiconductor laser with a simple configuration at high speed and with high accuracy. And It is another object of the present invention to realize a highly accurate variable frequency light source using such a device.

<Means for Solving the Problem> A laser frequency characteristic measuring apparatus according to a first aspect of the present invention is a sweeping means for sweeping a temperature or a current of a semiconductor laser to be measured,
Separation means for separating the output light of the semiconductor laser into two, an absorption cell for making one output light of this separation means incident and absorbing at a specific frequency, and a fabric for making the other output light of the separation means incident. A Perot etalon, a first photodetector for detecting the transmitted light of the absorption cell, a second photodetector for detecting the transmitted light of the Fabry-Perot etalon, and the first and second An arithmetic circuit for calculating an oscillation frequency at each temperature or current of the semiconductor laser to be measured from the output of the photodetector and the sweep signal of the sweep means is provided.

A second variable frequency light source according to the present invention is a semiconductor laser,
A sweeping means for sweeping the temperature of the semiconductor laser, a separating means for separating the output light of the semiconductor laser into two, and a standard substance which absorbs one output light of the separating means and absorbs at a specific frequency are enclosed. The absorption cell, the Fabry-Perot etalon that enters the other output light of the separating means, the first photodetector that detects the transmitted light of the absorption cell, and the transmitted light of the Fabry-Perot etalon. A second photodetector for detecting, an arithmetic circuit for calculating the oscillation frequency of the semiconductor laser from the outputs of the first and second photodetectors and the sweep signal of the sweep means, and an absorption line of the absorption cell. Alternatively, the transmission line of the Fabry-Perot etalon is provided with control means for controlling the oscillation frequency of the semiconductor laser.

<Operation> The frequency of the output light of the semiconductor laser swept by temperature or current is the peak position of the transmitted light of the absorption cell and the
Absolute value is calibrated by the number of peaks of the transmitted light of the Perot etalon.

<Example> The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration block diagram showing an embodiment of a laser frequency characteristic measuring apparatus according to the present invention. Reference numeral 11 is a semiconductor laser to be measured, 13 is a constant temperature bath containing the measured laser 11, 12 is a constant temperature bath.
13 is a temperature control circuit for controlling the temperature, 15 is a temperature control circuit 12
Reference numeral 16 is a sweep quote oscillator for adding a sweep signal to the temperature setting input via the adding means 14, and 16 is a constant current source for driving the laser 11 under measurement with a constant injection current. Reference numeral 17 is a collimating lens that collimates the output light of the laser 11 to be measured, 18 is a first beam splitter that splits the output light of the lens 17 into two, and 19 is a specific beam that enters the transmitted light of the beam splitter 18. Absorption cell encapsulating a substance that absorbs at a wavelength, 20 is a Fabry-Perot etalon that receives the reflected light of the beam splitter 18, 21 and 22
Absorption cell 19, Fabry-Perot Etalon 20 respectively
First and second photodetectors for detecting transmitted light of
2 is an arithmetic circuit for calculating the oscillation frequency of the laser under test 11 at each temperature from the outputs of the photodetectors 21, 22 and the sweep oscillator 15. The arithmetic circuit 23 can be composed of, for example, a microprocessor. The constant temperature chamber 13, the temperature control circuit 12, the adding means 14, and the sweeping reference oscillator 15 constitute a sweeping means for sweeping the temperature of the semiconductor laser 11 to be measured.

Next, the operation of the apparatus having the above configuration will be described. The measured laser 11 is driven by a constant current source 16 at a constant current. When a 1,5 μm band DFB laser is used as the laser to be measured 11, the oscillation frequency shifts at about 12.5 GHz / ° C. (100 pm / ° C.) with respect to temperature changes. If acetylene is used as the encapsulating material of the absorption cell 19, the absorption line in the 1.536 to 1.54 μm band is as shown in FIG. Also Fabry Perot
Assuming that the FSR (transmission peak interval) of the etalon 20 is 100 MHz and the temperature sweep of the measured laser 11 is performed from 10 ° C to 40 ° C in 100 s, the transmission power of the Fabry-Perot etalon 20 is
The relationship between the transmission power of the absorption cell 19 and the temperature sweep signal is as shown in FIGS. 3 (A) (B) (C). FIG. 3 shows an enlarged view within the dotted line in FIG. Absorption line frequency is known absolute value is measured with high accuracy, P19 and P21, the frequency difference of the absorption line of P21 and P23, respectively about 171GHz, so 174GHz, t ₁
The number of transmitted etalon signals between 〜 t ₂ is 171 GHz / 100 MHz ≈ 1
710 lines, 1740 lines between t ₂ and t ₃ . That is, since the frequency intervals of the absorption lines are different, the absorption lines can be identified by the number of etalon transmission signals. As shown in FIG. 4, if the number of etalon transmission signals from each absorption line is N, then N
The actual oscillation frequency ν (N) is ν (N) = ν ₁ + 100 · N (1) Here, ν ₁ (THz) is the oscillation frequency of each absorption line. If the temperature at the N-th time is T (N), then ν (N)
The temperature-oscillation frequency characteristic of the laser to be measured as shown in FIG. 5 can be accurately obtained from the arithmetic unit 23 from T and N (N). The frequency resolution is determined by the etalon's FSR, which in this case is 100 MHz. When acetylene is used as the absorbing material as in the above example, 1.53 to 1.545
It is possible to measure the measured laser in the μm band. For the laser to be measured in other wavelength bands, molecules having absorption lines in those wavelength bands are used as the absorbing substance. Further, the current-frequency characteristic can be obtained by measuring the temperature-oscillation frequency characteristic using the drive current of the laser to be measured as a parameter.

According to the laser frequency characteristic measuring device having such a configuration,
Since there are no mechanical moving parts, high-speed measurement is possible and it is resistant to changes over time.

Further, as compared with the case of FIG. 10 of the conventional example, since the frequency reference light source is not necessary, the structure becomes simple.

In addition, the molecular absorption line and the etalon FS with the accurate frequency absolute value
Since the wavelength value is measured with R, the measured value is highly accurate. Therefore, there is no need for calibration.

Although the temperature is swept with the driving current of the laser under measurement being constant in the above example, if an absorbing substance with a small absorption line interval is used, the driving current is swept (6G
It is also possible to measure current-frequency characteristics.

FIG. 6 is a block diagram showing a modified example of the apparatus shown in FIG. 1 for controlling the output power of the laser to be measured constant. Unlike the case of FIG. 1, instead of driving the measured laser 11 with a constant current, the output power of the power control circuit 24 is kept constant by using the output of the monitoring photodiode in the measured laser. As a result, the temperature-oscillation frequency characteristic can be measured without changing the output power even if the temperature of the laser to be measured is changed. Depending on the absorption substance, the absorption waveform and frequency change depending on the incident light intensity, such as saturation when the incident power increases and the absorption waveform changes. However, the effect can be eliminated. Further, in practice, semiconductor lasers are often used with stabilized power.

FIG. 7 is a block diagram showing the configuration of an embodiment of the variable frequency light source according to the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof is omitted. Reference numeral 11a is a semiconductor laser that serves as a light source of the variable frequency light source device, and 25 is a second beam splitter that splits the output light of the semiconductor laser 11a through a collimator lens 17 and splits it into two beams, the transmitted light of which is the first beam. The light that enters the splitter 18 and is reflected by it becomes the variable frequency output light of this device. 26 is the Fabry-Perot etalon 20.
A frequency control circuit for controlling the output frequency of the semiconductor laser 11a to an arbitrary transmission frequency of 27, a switch for switching the frequency sweep mode and the frequency control mode of the semiconductor laser 11a,
28 is an adding means for adding the output of the switch 27 to the output of the constant current source 16, the output of which is applied to the injection current of the semiconductor laser 11a, and 29 is the voltage connected between the sweep oscillator 15 and the adding means 14. The hold circuit has an update mode in which the output of the sweep oscillator 15 is output as it is and a hold mode in which the output of the sweep oscillator 15 is held.

Two modes of operation of such a variable frequency light source are described below.

(B) Oscillation frequency sweep mode Switch 27 is turned off and voltage hold circuit 29 is in update mode. In this case, the frequency sweep light is output from the beam splitter 25. At the same time, the frequency of the output light is calculated by the arithmetic circuit 23 in the same manner as in the case of FIG. 1, and the display thereof is performed. That is, the number N of etalon transmission signals can be counted and the laser oscillation frequency during the sweep can be accurately measured by using the equation (1).

(B) Oscillation frequency control mode In the oscillation frequency sweep mode of (a), when the laser oscillation frequency is on the Nth etalon transmission line, the switch 27 is turned on and the voltage hold circuit 29 is set to the hold mode to change the temperature of the semiconductor laser 11a. Keep constant. As a result, the laser oscillation frequency is controlled to be constant on the Nth etalon transmission line. The resolution of the laser oscillation frequency that can be taken in this mode is the FSR of the Fabry-Perot Etalon 20 (100 MHz in this case).
z). That is, output light having a constant frequency can be obtained stepwise at each FSR interval. It is also possible to perform stepwise sweeping in combination with (a).

According to the mode (a), the variable frequency light and the frequency value thereof can be used to detect the spectrum of the substance, measure the characteristics of the optical filter, and the like. Further, according to the (b) mode, it is possible to measure the characteristics of the laser light to be measured and the like by taking a beat with the output light having a constant frequency.

According to the variable frequency light source having such a configuration, since the absorption line of the substance and the FSR of the etalon are used as the scale of the laser oscillation frequency, the oscillation frequency can be grasped with high accuracy.

Moreover, since there is no mechanically movable part, the oscillation frequency can be swept with high accuracy and is resistant to changes over time.

The absorbing substance is not limited to acetylene, and any substance having a plurality of absorption lines such as ammonia and hydrogen cyanide arranged at different frequency intervals can be used.

Further, the outputs of the photodetectors 21 and 22 may be output as marker signals to the outside at the same time as the output light. The marker signal can be used to calibrate on the display.

FIG. 8 is a configuration block diagram showing a modification of the apparatus shown in FIG. The difference from FIG. 7 is that the photodetector 22 and the frequency control circuit 26
The changeover switch 30 is connected between the semiconductor laser 11 and the semiconductor laser 11 in the (b) mode by connecting the output of the photodetector 21 to the frequency control circuit 26 by the switch 30.
The oscillation frequency of a can be locked to the absorption line of the standard substance of the absorption cell 19. With this configuration,
In the (b) mode, output light with a stable absolute frequency can be obtained.

<Effects of the Invention> As described above, according to the present invention, a laser frequency characteristic measuring device capable of measuring the temperature-oscillation frequency characteristic and the current-oscillation frequency characteristic of a semiconductor laser with high speed and high accuracy is realized with a simple configuration. be able to. Further, it is possible to realize a highly reliable variable frequency light source with a simple structure by using the above-mentioned device, with a high oscillation frequency.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a laser frequency characteristic measuring apparatus according to the present invention, FIG. 2 is a characteristic curve diagram showing absorption characteristics of an absorption cell, and FIGS. 3 and 4 are apparatus shown in FIG. FIG. 5 is a diagram showing the temperature-wavelength characteristics of the laser to be measured measured by the apparatus shown in FIG. 1, and FIG.
FIG. 7 is a structural block diagram showing a modified example of the device shown in FIG. 7, FIG. 7 is a structural block diagram showing an embodiment of a variable frequency light source according to the present invention, and FIG. 8 is a structural block diagram showing a modified example of the device shown in FIG. 9 and 10 are structural principle diagrams showing a conventional laser frequency characteristic measuring apparatus. 11 ... Semiconductor laser to be measured, 15 ... Sweeping means, 18 ... Separation means, 19 ... Absorption cell, 20 ... Fabry-Perot etalon, 21 ... First photodetector, 22 ... Second Photodetector, 23 ... Arithmetic circuit, 26 ... Frequency control circuit, 27 ... Switch, 29 ... Voltage hold circuit, 30 ... Changeover switch.

Claims (2)

[Scope of utility model registration request] 1. A sweeping means for sweeping a temperature or a current of a semiconductor laser to be measured, a separating means for separating the output light of the semiconductor laser into two, and an output light of one of the separating means is incident to a specific frequency. An absorption cell that causes absorption, a Fabry-Perot etalon that inputs the other output light of the separation means, a first photodetector that detects the transmitted light of the absorption cell, and a transmission of the Fabry-Perot etalon A second photodetector for detecting light, and a calculation for calculating the oscillation frequency at each temperature or current of the semiconductor laser to be measured from the outputs of the first and second photodetectors and the sweep signal of the sweep means. And a laser frequency characteristic measuring device. 2. A semiconductor laser, a sweeping means for sweeping the temperature of the semiconductor laser, and an output light of the semiconductor laser.
Separation means for separating, an absorption cell enclosing a standard substance which receives output light from one of the separation means and absorbs light at a specific frequency, and a Fabry-Perot etalon that receives output light from the other of the separation means. A first photodetector for detecting the transmitted light of the absorption cell, and the Fabry-Perot
A first photodetector for detecting the transmitted light of the etalon; an arithmetic circuit for computing the oscillation frequency of the semiconductor laser from the outputs of the first and second photodetectors and the sweep signal of the sweep means; A variable wavelength light source comprising: an absorption line of an absorption cell or a transmission line of the Fabry-Perot etalon; and control means for controlling the oscillation frequency of the semiconductor laser.