JPH04113469U - Semiconductor laser frequency stabilization device - Google Patents

Abstract

(57) [Summary] [Purpose] A small, stable and highly reliable semiconductor laser.
Realize the frequency stabilization device. [Structure] A semiconductor laser chip 3 and a photodiode 4 are arranged in a sealed container 1 filled with a standard gas 2, and after the light emitted from the semiconductor laser chip 3 passes through the standard gas 2, the photodiode is The light is received by the diode 4, and the control circuit 9 controls the oscillation frequency of the semiconductor laser chip 3 to match the absorption line of the standard gas 2 based on the output from the photodiode 4.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention is a semiconductor device used in the fields of coherent optical communications and coherent optical measuring instruments. This invention relates to improvements in conductor laser frequency stabilization devices.

0002

[Conventional technology]

Traditionally, semiconductor laser frequency stabilization equipment uses a glass to absorb part of the laser light. The semiconductor laser is stabilized by applying negative feedback to match the absorption line. There is something to do.

0003

[Problem that the idea aims to solve]

However, in such devices, the semiconductor laser and absorption cell are constructed separately. Therefore, extra optical systems such as beam splitters and lenses are required, and the size is also large. The distance between the semiconductor laser and the photodiode is large, so alignment is difficult. It is also difficult to maintain, and there are problems with reliability. This invention was developed to solve the above problems, and is a compact and stable device. The purpose of this research is to realize a highly reliable semiconductor laser frequency stabilization device.

0004

[Means to solve the problem]

This invention is a semiconductor laser that controls the oscillation frequency of a semiconductor laser to the absorption line of atoms or molecules. This device is related to a body laser frequency stabilization device, and its feature is that it is a sealed container. a semiconductor laser chip disposed in the container, and a semiconductor laser chip sealed in the container. A standard gas that absorbs the light emitted from the semiconductor laser chip at the absorption line frequency. , a photodiode disposed in the container and receiving light that has passed through the standard gas; and the output of the semiconductor laser chip based on the output from the photodiode. and a control circuit for controlling the vibration frequency to the absorption line of the standard gas.

[0005]

[Effect] A semiconductor laser chip, photodiode, and standard gas are integrated in a sealed container. Because of this, there is no need for extra optical systems such as beam splitters or lenses, and the size is small. This makes alignment easier and improves reliability.

[0006]

【Example】

The present invention will be explained in detail below using the drawings. FIG. 1 is a cross-sectional view showing an embodiment of a semiconductor laser frequency stabilizing device according to the present invention. It is a diagram.

In the figure, 11 is a substrate, 12 is a cap fixed to the substrate 11, and the package 1 consisting of the substrate 11 and the cap 12 constitutes a container having a sealed space inside. 2 is a standard gas sealed in the package 1, 3 is a semiconductor laser chip fixed to the substrate 11, and 4 is a photodiode fixed to the substrate 11 to receive the light emitted from the semiconductor laser chip 3. 5 is a lens fixed to a hole in the cap 12. Terminals 6 and 7 take out the electrodes of the photodiode 4 and semiconductor laser chip 3 to the outside, respectively, and 8 is a ground terminal, both of which are fixed to the substrate 11. 9 is a control circuit which inputs the signal from the terminal 6 and applies its output to the terminal 7. For example, when the oscillation frequency band of the semiconductor laser chip 3 is 1.5 μm, the standard gas 2 may be C ₂ H ₂ (acetylene), HCN (hydrogen cyanide), or NH ₃ (ammonia), which have absorption lines corresponding to this. ) etc.

[0008] The operation of the apparatus of FIG. 1 will now be described. One of the lights emitted from the semiconductor laser chip 3 In this case, a specific frequency is generated by the absorption line of the standard gas 2 while it travels through the space inside the package 1. After being absorbed by the number, the light enters the photodiode 4. The control circuit 9 is a photo die The current of the semiconductor laser chip 3 is controlled in accordance with the output of the ode 4, and the semiconductor laser The oscillation frequency of the chip 3 is controlled to the absorption frequency of the standard gas. semiconductor laser chip The other part of the light emitted from the lens 3 is converted into parallel light by the lens 5 and taken out to the outside.

FIG. 2 is a characteristic curve diagram showing the change in the output P of the photodiode 4 when the current of the semiconductor laser chip 3 is changed via the terminal 7 and the laser frequency f is swept. The control circuit 9 controls the oscillation frequency of the semiconductor laser chip 3 to be at the center A (frequency f ₁ ) of the absorption line in FIG. 2 or at the bottom of the absorption line (frequency f ₂ ).

FIG. 3 is a block diagram showing an example of the configuration of the control circuit 9 for controlling the oscillation frequency of the semiconductor laser chip 3 to the absorption center f ₁ . In the control circuit 9a, the output of the photodiode 4 is synchronously detected by a lock-in amplifier 91 using the output of the oscillator 92 as a reference signal. The PI control circuit 93 controls the current of the semiconductor laser chip 3 so that the output of the lock-in amplifier 91 is constant. The output of the PI control circuit 93 is added to the oscillation output of the oscillator 92 in an adder circuit 94 and output from the laser drive circuit 95. The output frequency of the semiconductor laser chip 3 is current-modulated by the output of the oscillator 92.

FIG. 4 is a block diagram showing an example of the configuration of the control circuit 9 for controlling the oscillation frequency of the semiconductor laser chip 3 to the absorption shoulder f ₂ . In the control circuit 9b, the output from the photodiode 4 is compared with the output of the reference voltage source 97 in the subtraction circuit 96, and the difference is input to the PI control circuit 93. The output 93 of the PI control circuit is applied to the semiconductor laser chip 3 via a laser drive circuit 95. The PI control circuit 93 controls the output of the photodiode 4 to be equal to the output of the reference voltage source 97. The output of the reference voltage source 97 is set to a voltage corresponding to the absorption peak.

[0012] According to the semiconductor laser frequency stabilizing device having such a configuration, the standard gas is sealed in the package containing the semiconductor laser chip and the photodiode, so the configuration is simple. It becomes small. Normally, a dry gas such as _N2 is placed inside the semiconductor laser package to prevent the semiconductor laser chip from deteriorating due to moisture, so even if standard gas is used instead, the number of steps will increase. Nor. Further, although the frequency of a normal semiconductor laser fluctuates depending on temperature and current, according to the above embodiment, the oscillation frequency is controlled to the absorption line of the standard gas, so a quantum standard with a stable frequency can be realized.

In the above embodiment, the amount of absorption is increased by arranging the second lens on the side of the semiconductor laser chip 3 facing the photodiode 4 to extend the optical path within the standard gas. can be done. In addition, the standard gas is not limited to the 1.5 μm band, but any arbitrary gas such as Rb gas for the 0.78 μm band, Cs gas for the 0.85 μm band, and NH ₃ or CH ₃ OH for the 1.3 μm band can be used. can. Further, as the sealed container, a package for a semiconductor laser may be used as is, or any other suitable container may be used.

[0014]

[Effect of the idea]

As described above, according to the present invention, a highly reliable semiconductor with small size and stable operation can be realized. A laser frequency stabilizing device can be realized with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an embodiment of a semiconductor laser frequency stabilizing device according to the present invention.

FIG. 2 is a characteristic curve diagram showing the absorption characteristics of a standard gas.

FIG. 3 is a block diagram showing an example of the configuration of the control circuit 9 in FIG. 1;

4 is a block diagram showing another example of the configuration of the control circuit 9 in FIG. 1. FIG.

[Explanation of symbols]

1 container 2 Standard gas 3 Semiconductor laser chip 4 Photodiode 9 Control circuit

Claims (1)

[Scope of utility model registration request] Claim 1: A semiconductor laser frequency stabilization device for controlling the oscillation frequency of a semiconductor laser to an atomic or molecular absorption line, comprising: a sealed container; and a semiconductor laser chip disposed within the container. a standard gas sealed in the container that absorbs the light emitted from the semiconductor laser chip at an absorption line frequency; and a photodiode disposed in the container that receives the light that has passed through the standard gas. - a control circuit for controlling the oscillation frequency of the semiconductor laser chip to the absorption line of the standard gas based on the output from the photodiode. conversion device.