JPH02242237A - Acoustooptical light frequency shifter - Google Patents

Abstract

PURPOSE:To accurately measure the spectral ray width of a semiconductor laser without generating fluctuations in the spectral ray width by forming both ends of 1st, 2nd and 3rd optical fibers respectively diagonally with the side faces of the optical fibers. CONSTITUTION:Both end faces 21a, 21b to 23a, 23b of the 1st 2nd and 3rd optical fibers 21 to 23 are polished respectively diagonally to the side faces of the optical fibers. The reflected light rays from the diagonal end faces 21a, 21b to 23a, 23b of the optical fibers 21 to 23 are no longer passed in the same route as the route of the incident light and the return of the reflected light rays to a light source side is prevented. The diagonal angle theta is about 8 deg.+ or -1 deg. from the perpendicular direction. The optical coupling fails if this angle is larger. The reflected light rays return to the semiconductor laser to be measured if the angle is small. The spectral ray width is accurately measured in this way without generating the fluctuations in the spectral ray width.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an acousto-optic frequency shifter used in a semiconductor laser spectral linewidth measuring device and the like.

2. Description of the Related Art In recent years, optical communications and optical information processing technologies that utilize light have been attracting attention. Among these, optical heterodyne technology, which modulates the frequency of light, is being researched in various fields. In particular, as research and development of narrow-spectrum semiconductor lasers progresses, the delayed self-heterodyne method has been developed as a new technology for measuring the spectral linewidth of semiconductor lasers with high resolution.
The use of acousto-optic optical frequency chic is being investigated.

FIG. 3 shows a system for measuring the spectral linewidth of a semiconductor laser using the delayed self-heterodyne method. The advantage of the delayed self-heterodyne method is that there is no need to vary the delay time, and the spectral distribution of the laser light output can be viewed directly on the cathode ray tube.

As shown in FIG. 3, the optical output of the semiconductor laser 1 is divided into transmitted light and frequency-shifted diffracted light by an acousto-optic frequency shifter 3 to which a high-frequency oscillator 2 is connected.

After the transmitted light is delayed by a delay optical fiber 4, the transmitted light and the diffracted light are frequency-mixed by a coupler 5, and the beat signal is passed through an avalanche photodiode 6 and observed on a spectrum analyzer 7. , the spectral linewidth of the semiconductor laser 1 can be measured. Optical power meter 8 measures the optical power of the beat signal output from coupler 5.

Conventionally, this type of acousto-optic frequency shifter 3 has had a configuration as shown in FIG. In FIG. 2, input terminal 9 is a terminal for inputting ultrasonic excitation energy. The impedance matching unit IO performs impedance matching to efficiently send the ultrasonic energy applied from the input terminal 9 to the ultrasonic excitation transducer 11. The light incident on the first optical fiber 12 from the semiconductor laser 1 is 1
The lens 13 converts the light into parallel light, and the acousto-optic medium 14
is injected into the interior. The second lens 16 is the acousto-optic medium 14
This transmitted light is efficiently coupled to the second optical fiber 15. In addition, the third lens 18
extracts the diffracted light whose frequency has been shifted by the acousto-optic medium 14 through the prism 19, and efficiently couples this diffracted light to the third optical fiber 17.

This prism 19 is for largely separating transmitted light and diffracted light. 1st. second and third optical fibers 1
2, 15.17, both end surfaces 12a and 12b, respectively
.

L5a, 15b, L7a, and 17b were polished perpendicularly to the side surfaces of the respective optical fibers.

Here, when light from a semiconductor laser 1 or the like is made incident on the acousto-optic optical frequency shifter 3, only transmitted light exists when ultrasonic excitation energy is not applied from the input terminal 9, but when ultrasonic excitation energy is input to the input terminal 9, a part of the transmitted light is diffracted by the acousto-optic effect, and diffracted light is generated. The frequency V of this diffracted light is the frequency of the incident light vO
1If the frequency of ultrasonic wave is Va.

V,=Vo±Va (decoding takes either one depending on the direction of light incidence), and one frequency shift is given.

Problems to be Solved by the Invention In the above conventional configuration, the first, second and third
Both end surfaces 12a of the optical fibers 12, 15.17.

12b, 15a, 15b, 17a, 1
7b is polished perpendicularly to the side surface of each optical fiber, so that when measuring the spectral line width of the semiconductor laser 1 using the delayed self-heterodyne method, the reflected light from each end surface is reflected from the semiconductor to be measured. Return to laser l,
There is a problem in that the spectral linewidth of the semiconductor laser 1 fluctuates, making it impossible to measure the spectral linewidth accurately.

The present invention solves the above-mentioned conventional problems, and aims to provide an acousto-optic frequency shifter that can accurately measure the spectral linewidth of a semiconductor laser without causing fluctuations in the spectral linewidth. It is something to do.

Means for Solving the Problems In order to solve the above problems, the acousto-optic frequency shifter of the present invention includes first and second optical fibers that are arranged opposite to each other, and the first and second optical fibers are connected to each other. an acousto-optic element comprising first and second lenses optically coupled, and an ultrasonic excitation transducer in a part of an acousto-optic medium provided between the first and second lenses; a third lens and a third optical fiber that receive a light beam incident from the first optical fiber and diffracted within the acousto-optic element through a prism; Both end surfaces of each of the optical fibers are constructed obliquely with respect to the side surfaces of the respective optical fibers.

Effect: With this configuration, the reflected light from both end faces of the first, second, and third optical fibers does not pass through the same path as the incident light because both end faces are processed diagonally, and one reflected light is This prevents the light from returning to the semiconductor laser to be measured, and thereby the spectral linewidth can be measured with high accuracy without causing fluctuations in the spectral linewidth.

Embodiment One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an acousto-optic frequency shifter according to an embodiment of the present invention, and the same reference numerals are used to denote the same functions and effects as those of the conventional example, and the explanation thereof will be omitted. In FIG. 1, first, second and third optical fibers 21, 22
．． Both end surfaces 21a, 21b of 23.

22a, 22b, 23a, and 23b are polished obliquely to the side surfaces of the respective optical fibers.

With this configuration, the first, second and third optical fibers 2
1, 22. Both oblique end surfaces 21a, 21b of 23,
22a.

The reflected light from 22b, 23a, and 23b no longer passes through the same path as the incident light, and it is possible to prevent the reflected light from returning to the light source side. Here, the oblique angle θ is about 8''±1'' from the vertical direction; if it is larger than this, the optical coupling will not be successful, and if it is smaller than this, the reflected light will return to the semiconductor laser to be measured.

Effects of the Invention As described above, according to the present invention, both end surfaces of the first, second, and third optical fibers are formed obliquely with respect to the side surfaces of the respective optical fibers, so that reflections from both end surfaces of the optical fibers are reduced. The light no longer passes through the same path as the incident light, and when measuring the spectral linewidth of a semiconductor laser using the delayed self-heterodyne method, this reflected light can be prevented from returning to the semiconductor laser under test, and the spectral linewidth will fluctuate. It is possible to measure the spectral linewidth with high precision without causing any interference.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an acousto-optic frequency shifter according to an embodiment of the present invention, Fig. 2 is a block diagram showing a conventional acousto-optic frequency shifter, and Fig. 3 is a spectrum of a semiconductor laser using the delayed self-heterodyning method. FIG. 2 is a configuration diagram showing a line width measurement system. 3... Acousto-optic frequency shifter, 11... Ultrasonic excitation transducer, 13, 16. 18... Lens, 14... Acousto-optic medium, 19... Prism, 2
1, 22.23... Optical fiber, 21a, 21b, 2
2a, 22b, 23a, 23b - both end faces of the optical fiber. Agent Yoshihiro Morimoto Cause 1 Figure 2

Claims (1)

[Claims] 1. first and second optical fibers arranged to face each other, first and second lenses that optically couple the first and second optical fibers, and the first and second lenses an acousto-optic element having an ultrasonic excitation transducer in a part of an acousto-optic medium provided between the acousto-optic element and a prism for transmitting a light beam incident from the first optical fiber and diffracted within the acousto-optic element; a third lens and a third optical fiber, each of which is configured to have both end surfaces of the first, second and third optical fibers obliquely relative to the side surface of each of the optical fibers. Acousto-optic frequency shifter.