JPS62194423A - Apparatus for measuring width of laser beam - Google Patents

Abstract

PURPOSE:To simplify and facilitate the adjustment of the system, by inputting beam modulated by an acoustooptical modulator to a detector through a prism while inputting beam not modulated to the detector through a fiber and the prism. CONSTITUTION:The beam incident to an acoustooptical (AO) modulator 1 is divided into beam A being modulated and beam B being not modulated. The beam A modulated is inputted to a detector 7 through prisms 2, 3 while the beam B not modulated is condensed by a lens 5 to pass through a fiber 4 and again condensed by a lens 6 to enter the detector 7 by the prism 3. By mixing beams A, B the width of beam can be measured according to a heterodyne system.

Description

[Detailed Description of the Invention] [Summary] In a delayed self-hetero gain type laser linewidth measuring device, light modulated by an acousto-optic (hereinafter abbreviated as AO) modulator and light not modulated have different emission angles. By using this, an optical system is constructed with a prism and a fiber, making the adjustment of the system simple and easy.

[Industrial application field]

The present invention relates to a laser linewidth measurement device that uses a delayed self-heterogain method to perform simple and easy measurement.

The oscillation frequency of a semiconductor laser, for example in the 1.3 μm band, is approximately 2
00 THz, the linewidth is 10 KHz, i.e. 0 in wavelength
．． 001 people, which is extremely small.

Such a narrow linewidth cannot be measured with a spectrometer, but for convenience a Fabry-Perot interferometer can be used to measure a linewidth of at most 0.05.
It can only measure a person's line width.

On the other hand, according to the self-delayed heterogain method, 10KHz
In other words, a line width of about 0.00001 people can be measured.

In general, semiconductor lasers are required to measure line widths at least below IMHz during coherent optical communication.

[Conventional technology]

FIG. 2 is a configuration diagram of a conventional delayed self-heterodyne laser linewidth measuring device.

In the figure, 21 is the semiconductor laser to be measured, 22 is the AO modulator, 23 is the fiber, and 24.25 is the half mirror 1.
26 is a detector.

As shown in the figure, a conventional optical system is constructed by installing optical devices individually.

The coherent length of the laser is about 0.3 to 300 m, and if a longer fiber 24 is used, the detector 26
The two lights that enter will be different and will not interfere.

When two lights that do not interfere are input into the detector 26, a noise corresponding to the linewidth of a slight standing wave is obtained.

When the energy distribution of light is Lorentzian, the noise can be directly observed as the optical output of the detector 26.

The optical output-energy relationship thus obtained by the detector 26 is Laplace-transformed into an optical output-frequency relationship using a spectrum analyzer, and the half-width of the distribution curve is taken as the linewidth of the laser.

In this case, since the spectrum analyzer has a large noise when the frequency is O, the output of the spectrum analyzer is shifted from the origin to display the optical output-frequency relationship.
The frequency is shifted by a modulator 22.

The AO modulator 22 performs modulation by applying ultrasonic waves.

Using such a heterodyne method using the He〇 modulator 22, the own light is divided into two, one of which is modulated by the AO modulator 22, the other is delayed by the fiber 23, and then the two lights are mixed and detected. It is received in the container 26.

Here, the coherent length refers to the length at which light can be divided into two parts and interfere with each other.

As described above, the delayed self-hetero gain method increases measurement sensitivity, but it is extremely difficult to adjust the optical needle.

That is, since the fiber used is a single mode fiber, even a slight deviation will prevent light from entering the fiber. Since the measurement takes the noise of two lights, the two lights must be strong and must be stronger than other noises, such as white noise.

It is also necessary to match the polarizations of the two lights. If the polarization shifts by 90°, the correlated noise necessary for measurement cannot be obtained.

For this reason, it is desired to simplify measurement using a delayed self-hetero gain method.

[Problem that the invention seeks to solve]

A conventional laser linewidth measuring device using the delayed self-hetero gain method is configured by installing optical devices individually, so it is vulnerable to environmental changes such as temperature changes, and it is difficult to adjust the light and the device.

[Means for solving problems]

The solution to the above problem includes an acousto-optic modulator, a prism, a fiber, and a detector, in which incident light enters the acousto-optic modulator, and light modulated by the acousto-optic modulator passes through the prism. This is achieved by the laser linewidth measuring device according to the invention, which is configured such that the light that is not modulated by the acousto-optic modulator enters the detector via a fiber and the prism. .

(Function) The present invention takes advantage of the fact that the light modulated by the AO modulator and the light that is not modulated have different emission angles, so that one light passes through the prism and the other light passes through the prism and the fiber. An optical system is constructed in which each of the two detectors is received by a detector, making adjustment of the system simple and easy.

〔Example〕

FIG. 1 is a configuration diagram of a laser linewidth measurement device using a delayed self-hetero gain method according to the present invention.

In the figure, 1 is an AO modulator, 2.3 is a prism (beam splitter), 4 is a fiber, 5 and 6 are lenses, and 7
is a detector.

As shown in the figure, the optical system of the present invention is not constructed by installing optical devices individually as in the conventional example, but consists of prisms 2.3.
It is compactly summarized using

Here, the lenses 5 and 6 inserted into the optical path each have the role of condensing light incident on the fiber and condensing light emitted from the fiber onto the prism 3.

Light incident on the AO modulator 1 is divided into modulated light A and unmodulated light B.

The light ^ enters the detector 7 via the prism 2.3.

Light B is focused by a lens 5, passes through a fiber 4, is focused again by a lens 6, and enters a detector 7 through a prism 3.

By mixing light A and light B, line width can be measured using a heterodyne method.

FIG. 3 is a cross-sectional view illustrating the AO modulator.

In the figure, when light with wavelength λ is input to AO modulator 1 and ultrasonic waves are applied thereto, modulated light A with wavelength λ±Δλ is produced.
It is split into unmodulated light B having a wavelength λ.

〔Effect of the invention〕

As described in detail above, in the laser linewidth measuring device using the delayed self-heterodyne method according to the present invention, the optical system can be adjusted simply and easily.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a laser linewidth measuring device using a delayed self-heterodyne method according to the present invention, Fig. 2 is a block diagram of a laser linewidth measuring device using a delayed self-heterodyne method according to a conventional example, and Fig. 3 shows an AO modulator. It is a sectional view for explanation. In the figure, 1 is the modulator, 2.3 is the prism, 4 is the fiber, 5.6 is the lens, 7 is the detector, A is the modulated light, and B is the unmodulated light.

Claims (1)

[Scope of Claims] An acousto-optic modulator, a prism, a fiber, and a detector, wherein incident light enters the acousto-optic modulator, and light modulated by the acousto-optic modulator passes through the prism. enters the detector via
A laser linewidth measurement device characterized in that the light not modulated by the acousto-optical modulator is configured to enter a detector via a fiber and the prism.