JPS6351555B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical frequency sweep type semiconductor laser device that can accurately sweep the optical frequency of a laser beam output by a semiconductor laser in synchronization with a synchronization signal.

[Technical background of the invention]

Recently, optical communication such as optical heterodyne communication using laser light oscillated by a semiconductor laser and optical applied measurement for high-precision measurement have been attracting attention. These optical communications and optical applied measurements effectively utilize the optical frequency of the laser beam, and therefore it is necessary to stably control the optical frequency of the laser beam oscillated by the semiconductor laser.

However, the optical frequency of a semiconductor laser largely depends on its operating temperature and the amount of current injected. Therefore, conventionally, optical frequency stabilization control of semiconductor lasers has been performed, for example, as shown in FIG. That is, the temperature of the semiconductor laser 1 is stabilized by the temperature stabilizing device 2, the oscillation output light of the semiconductor laser 1 in this state is divided into two parts via the beam splitter 3, and one part is guided to the photodetector 4. and the other is guided to a photodetector 6 via an optical resonator 5. Then, the detection outputs of these photodetectors 4 and 6 are extracted via an operational amplifier 7, and thereby the optical frequency and
The voltage-converted output information is fed back to the injection current control device 9 through the integrator 8. Through control by this negative feedback loop, the amount of current injected into the semiconductor laser 1 is varied, and the optical frequency is controlled to be constant and stable.

Conventionally, the optical frequency of a semiconductor laser is generally stabilized in this way, but in the case of the aforementioned optical application measurement, etc., it is desirable to further stably sweep the optical frequency under certain conditions. . In this case, the injection current control device 9 applies a sweep signal as shown in FIG. 2a, thereby varying the amount of current injected into the semiconductor laser 1 and sweeping the oscillation optical frequency.

[Problems with background technology]

However, when the repetition period of the sweep signal is constant, no particular problem occurs, but when the repetition period changes as shown in Figure 2a, the laser oscillation light frequency changes to its average value as shown in Figure 2b. A problem arises in that although the frequency is constant, there is a shift in the sweep frequency range. This is due to feedback control by detecting the average value of the optical frequency of the semiconductor laser 1, and if you try to sweep the frequency irregularly in synchronization with an external synchronization signal, there will be a shift in the sweep start optical frequency. arise.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to synchronize the oscillation output optical frequency of a semiconductor laser with a synchronization signal arbitrarily given from the outside to a predetermined and accurate level. It is an object of the present invention to provide a highly practical optical frequency sweep type semiconductor laser device that can perform sweeping.

[Summary of the invention]

The present invention samples and detects the oscillation optical frequency of the semiconductor laser during non-sweeping of the semiconductor laser, that is, during the period from the end of the sweep to the start of the next sweep, and compares this with a predetermined value to detect the oscillation frequency of the semiconductor laser. By controlling the bias, the oscillation frequency of the semiconductor laser is made constant at the start of the next sweep synchronized with the synchronization signal.

〔Effect of the invention〕

Therefore, according to the present invention, since the bias of the semiconductor laser is controlled during non-sweeping and the oscillation optical frequency is adjusted to be constant, the optical frequency cannot be swept in synchronization with a synchronization signal given arbitrarily from the outside. When doing so, the sweep start optical frequency is always controlled to be stably constant. Therefore, it is possible to always stably and easily sweep the optical frequency, and its practical advantages are great.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic configuration diagram showing a device according to an embodiment of the present invention, and FIGS. 4 a to 4 e are operational waveform diagrams for explaining its operation. In FIG. 3, 11 is a semiconductor laser whose temperature is stabilized by a temperature stabilizing device 12. In FIG. The laser light oscillated and output by the semiconductor laser 11 is received by the optical frequency detection device 13, and its optical frequency is detected. And this optical frequency detection device 13
is designed to generate, for example, a voltage signal corresponding to the detected optical frequency. The optical frequency detection device 13 may be one that detects the optical frequency using an optical resonator, for example, as shown in FIG. It may be one that has been adopted. A voltage signal corresponding to the oscillation output optical frequency of the semiconductor laser 11 detected by the optical frequency detection device 13 is given to a sample and hold circuit (S/H) 14, which will be described later.
The current is applied to the injection current control device 15. The injection current control device 15 variably controls the injection current of the semiconductor laser 11 in response to various control signals to be described later, thereby controlling the injection current of the semiconductor laser 11.
The oscillation light frequency of 1 can be varied.

On the other hand, the synchronous sweep oscillator 16 generates an optical frequency sweep signal in synchronization with a synchronization signal given from the outside, and supplies the sweep signal to the synchronization circuit 17 and the injection current control device 15. . The injection current control device 15 receives this sweep signal and varies the amount of current injected into the semiconductor laser 11, thereby performing a variable sweep of the oscillation light frequency. The synchronous circuit 17 also includes a synchronous sweep oscillator 1
6 and the sweep end signal output from the synchronous sweep oscillator 16.
It generates a hold signal and drives the sample-and-hold circuit 14. As a result, the sample-and-hold circuit 14 can store information about the optical frequency detected by the optical frequency detection device 13 ( voltage) and hold it for the next sweep period.
The comparator 18 is connected to this sample-and-hold circuit 14.
The output signal is compared with a preset voltage value (corresponding to a desired optical frequency) 19, and the comparison result is provided to the injection current control device 15. Inputting the comparison result of the comparator 18, the injection current control device 15 controls the bias of the injection current given to the semiconductor laser 11, so that the optical frequency during non-sweeping is set to a predetermined value given by the voltage value 19. Operates to match optical frequencies.

In this way, the injection current control device 15 monitors and stabilizes the optical frequency according to the information of the optical frequency detected by the optical frequency detection device 13, and also receives the output of the comparator 18 during non-sweeping and controls the semiconductor laser 11. The bias for the semiconductor laser 11 is controlled to keep the optical frequency constant.Furthermore, during sweep initiated by a synchronous signal, the semiconductor laser 11 receives a sweep signal output from the synchronous sweep oscillator 16.
It is designed to sweep the optical frequencies of

According to the device configured in this way,
Now, when a synchronizing signal is input as shown in FIG. 4a, the synchronous sweep oscillator 16 is activated as shown in FIG.
Generate a sweep signal as shown in . This sweep signal is applied to the injection current control device 15, and the oscillation optical frequency of the semiconductor laser 11 is sweep-controlled. Further, the synchronous sweep oscillator 16 generates a sweep end pulse signal as shown in FIG. 4c upon completion of the optical frequency sweep. The synchronization circuit 17, which operates in response to the sweep end pulse signal and the synchronization signal, is constituted by, for example, a flip-flop, and as shown in FIG. A sample signal is generated until the start point.
The interval between the sample signals, which is the sweep period, is used as a hold signal. Therefore, during this sample signal period, the sample and hold circuit 14
The optical frequency information of the semiconductor laser 11 is input to the comparator 8 via the comparator 8, and the semiconductor laser 1 is
1 bias is controlled. As a result, the oscillation frequency of the semiconductor laser 11 is controlled to be constant at the desired frequency at the time when the next sweep is started, as shown in FIG. 4e. Then, based on this constant controlled optical frequency, an optical frequency sweep is performed in response to the sweep signal.

Thus, according to the present device, even if the timing at which the synchronization signal is applied is arbitrary and irregular, the oscillation optical frequency of the semiconductor laser 11 can be swept from a predetermined optical frequency in synchronization with the synchronization signal. Furthermore, by simple control such as sampling the optical frequency of the semiconductor laser 11 during the non-sweep period and adjusting the bias based on this, it is possible to stabilize the oscillation optical frequency at the start of the optical frequency sweep. Furthermore, it is also possible to stably control the optical frequency sweep itself. Therefore,
It can be extremely effective in stabilizing the optical frequency in optical heterodyne communication, and in stabilizing and stabilizing the optical frequency in optical applied measurement. Moreover, since the oscillation optical frequency of the semiconductor laser 11 can be swept stably in synchronization with an arbitrary synchronization signal, its practical advantage is enormous.

Note that the present invention is not limited to the above embodiments. For example, instead of using the optical resonator described above as the optical frequency detection device 13 for detecting the oscillation optical frequency of the semiconductor laser 11, as shown in FIG. The output light of the laser 21 and the output light of the sweep-controlled semiconductor laser 11 may be mixed by the optical mixer 22, and the beat signal light may be detected by the photodetector 23. Then, the frequency component of the beat signal may be extracted via an f/v (frequency/voltage) converter 24 to obtain a voltage signal corresponding to the optical frequency. Further, in the embodiment, the synchronization signal is given from the outside, but it may be generated inside the device. Furthermore, it is of course possible to perform signal processing digitally, and it is possible to perform signal processing using optical frequency sweep functions,
The sample and hold timing can also be set arbitrarily within a range that can stabilize (constant) the optical frequency during non-sweeping. In summary, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of a conventional semiconductor laser optical frequency stabilization device, FIG. 2 a and b are diagrams showing the relationship between the sweep signal and the swept optical frequency in the conventional device, and FIG. 4A to 4E are operational waveform diagrams for explaining the operation of the embodiment device, and FIG. 5 is a diagram showing an example of the configuration of the optical frequency detection device. 11...Semiconductor laser, 12...Temperature stabilization device, 13...Optical frequency detection device, 14...Sample and hold circuit, 15...Injection current control device,
16... Synchronous sweep oscillator, 17... Synchronous circuit, 1
8... Comparator, 19... Reference voltage.

Claims (1)

[Scope of Claims] 1. A semiconductor laser element, means for detecting an optical frequency output by the semiconductor laser element and obtaining an electrical signal corresponding to the optical frequency, and a means for detecting an optical frequency outputted by the semiconductor laser element to obtain an electrical signal corresponding to the optical frequency, a sweep oscillator that sweeps the optical frequency output by the semiconductor laser element by controlling the amount of current injected into the semiconductor laser element; a means for sampling and holding an electrical signal corresponding to the optical frequency in synchronization with the operation of the sweep oscillator; An optical frequency swept semiconductor laser device, comprising means for comparing a sampled and held value with a predetermined reference value and variably controlling the operating bias of the semiconductor laser element according to the comparison result. . 2. The means for obtaining an electrical signal corresponding to the optical frequency output by the semiconductor laser device extracts the laser light output from the semiconductor laser device through a Fabry-Perot resonator, receives this extracted light with a photodetector, and generates a photoelectric signal. The optical frequency swept type semiconductor laser device according to claim 1, which is obtained by converting the optical frequency. 3. A patent claim in which the means for obtaining an electrical signal corresponding to the optical frequency output by the semiconductor laser element is obtained by detecting a beat signal between the laser light output from the semiconductor laser element and a reference light whose optical frequency is known. The optical frequency swept semiconductor laser device according to item 1.