JPS6021033A - Frequency shifter - Google Patents

Abstract

PURPOSE:To expand the volume of information to be processed in optical information processing and optical communication by using acoustooptic elements and arranging a wide band light frequency shifter having fixed output light bearing and output light intensity independently of the shifted quantity of the light frequency. CONSTITUTION:An input light coupling optical element 18 focuses light 22 projected from an input optical fiber 20. When the frequency of ultrasonic wave exciting energy injected from an input terminal 11 is changed, the projecting bearing of diffracted light is also changed. However, the diffracted light is focused on the back focus of an output light coupling optical element 19 by the effect of the element 19 independently of the frequency of the ultrasonic wave exciting energy, so that the diffracted light is guided into an output optical fiber 21. When the coupling loss between the optical element 19 and the output optical fiber 21 is changed by the frequency of the ultrasonic wave exciting energy, the ultrasonic wave energy is controlled to keep the intensity of light taken out from the optical fiber 21 and shifted at its frequency. Consequently, a stable, high-speed and high-band light frequency shifter free from moving parts can be attained.

Description

[Detailed description of the invention] Fields of use of Nikarashichi This is related to the unfired exit 1, an optical frequency a shifter.

Conventional configurations and their problems In recent years, optical communications and optical information processing technologies that utilize light have been attracting attention. Among these, optical heterodyne technology, which performs frequency modulation on the frequency of light, is being researched in various fields.

There are methods to apply frequency modulation to the frequency of light, such as mechanically moving an iJ, diffraction grating, or reflection mirror, and using the Doppler shift of the optical frequency due to the speed of movement, but these methods require high mechanical moving parts. There are many problems in making it practical, such as not only precision being required, but also slow start-up speed. On the other hand, acousto-optic elements that apply light diffraction by ultrasonic traveling waves using acousto-optic effects are seen as promising because they have no mechanically moving parts and can achieve high-speed operation; !
Since the direction of light subjected to single-frequency modulation changes with the modulation frequency, it has never been put to practical use.

FIG. 1 shows a schematic diagram of the acousto-optic effect conventionally used. 1 is an input terminal for ultrasonic excitation energy, and 2 is an impedance matching section for efficiently sending the ultrasonic energy applied from the input terminal 1 to the ultrasonic transmitting transducer 3.

Reference numeral 4 denotes an acousto-optic medium, on which an ultrasonic transmitting transducer 3 is bonded, and optical surfaces 6a and eb through which light enters and exits, and an ultrasonic unnecessary reflection prevention device provided to prevent ultrasonic waves from being reflected in the same path. A surface 7 is provided. The curved line 5 indicates the region where ultrasonic waves that contribute to light diffraction due to the acousto-optic effect exist, that is, the ultrasonic flux.

Now, consider a case where incident light 8 such as a laser beam is incident from the light entrance surface 6a. If the light incidence direction is appropriately selected, only the transmitted light 1o exists when ultrasonic excitation energy is not applied from input terminal 1, but when ultrasonic excitation energy is applied to input terminal 1, only one transmitted light 1o exists. portion is diffracted by the acousto-optic effect, and diffracted light 9 is generated. The frequency v1 of this diffracted light is the frequency of the incident light. , Ili'j l
If the frequency of the K wave is 8, then 1-vo±8 (decoding takes either of the directions of light incidence).

Is it still 1ff? The power level of light is expressed as the angle θ formed by the transmitted light 1o and the diffracted light 9, as follows: θ: λ×■a/μ (λ: wavelength of light μ: sound speed of ultrasonic wave). In practice, the light incident direction is fixed, so after determining the light incident direction that gives a maximum diffraction efficiency of 1 < + at a certain ultrasonic frequency, changing the ultrasonic frequency ■8 will meet the theoretical diffraction condition. However, since both the ultrasonic bundle and the incident light that are actually handled have finite sizes, there is a spread in the direction of the wavefront connection, so even if the ultrasonic frequency va changes, the incident light that satisfies the diffraction condition The component will be diffracted and a diffraction angle likelihood of 9 may exist.

The ultrasonic beam 5 emitted from the ultrasonic transducer 3 and causing optical diffraction reaches the opposing surface 7 of the acousto-optic medium 4 where the ultrasonic transducer 3 is bonded and is reflected. If the sound wave bundle follows the same path as the ultrasound bundle before reflection, the incident light will be re-diffracted by the reflected ultrasound wave, causing two harmful phenomena. Therefore, in order to prevent the ultrasonic flux reflected from the opposing surface of the acousto-optic medium from returning along the same path, the ultrasonic unnecessary reflection surface 7 is designed so that the anti-attraction position of the ultrasonic wave on the ultrasonic unnecessary reflection prevention surface 7 is different. is provided to prevent the incident light 8 from being re-diffracted by reflected ultrasound waves.

Sounds like the above,! ! 5. When using the optical element as an optical frequency shifting device, the power potential of the diffracted and frequency-shifted light changes spatially with the modulation frequency,
This was a practical problem because the output light could not be extracted effectively.

OBJECTS OF THE INVENTION In view of the above drawbacks, the present invention provides a broadband optical frequency shifter that uses an acousto-optic element and has a constant output light direction and output light intensity regardless of the shift amount of the optical layer mantissa. The aim is to dramatically expand the amount of information processed in optical communications.

Structure of the Invention To achieve this goal, the frequency shifter of the present invention includes: an acousto-optic element that shifts the frequency of incident light; an input optical fiber that guides the incident light to an acoustic optical element; an input optical coupling optical element for converging the light guided by the input optical fiber and making it incident on the acousto-optic element; and an output optical node 1 for outputting the frequency-shifted light output from the acousto-optic element. and an output light coupling optical element that guides the frequency-shifted light outputted from the acousto-optic element and whose direction changes depending on the shift frequency to the output optical fiber.

With this configuration, it is possible to realize an optical frequency shifter that has a large frequency shift amount, has stable operation without mechanically moving parts, and is easy to handle.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a schematic structural diagram of an optical frequency shifter in one embodiment of the present invention. In Figure 2, 14
is an acousto-optic medium, for example made of a light-transmitting glass material or a single crystal material. Reference numeral 13 denotes an ultrasonic transducer, which is disposed on the main surface of the acousto-optic medium 14, and is connected to the ultrasonic transducer through an impedance matching section 12.
An input terminal 11 for ultrasonic excitation energy is connected. Reference numeral 17 denotes an ultrasonic anxiety reflection prevention surface, which is disposed at a position facing the main surface of the acousto-optic medium 14 . Reference numeral 16a denotes a light incident surface, which is provided so as to intersect with the principal surface of the acousto-optic medium 14 described in 1- above, and is an input source coupling optical element 18 for converging the light 22 emitted from the input optical fiber 2°.
Incident light 23 is made to enter through. 16b is the light exit surface, j biped r4 - acoustic optical medium 14
The diffracted light d1 diffracted by the acousto-optic effect is emitted from the light exit surface and guided to the output optical fiber 21 via the output light coupling optical element 19. It will be destroyed.

The operation of the optical frequency shifter configured as described above will be explained below.

From the ultrasonic excitation energy input terminal 11, ultra 1
When 61 3-wave excitation 4H energy is applied, the ultrasonic transducer 13 passes through the Innovidance matching unit 12 to convert it into a state that is easily absorbed by the ultrasonic transducer 13, and the ultrasonic transducer 13 transfers it to the acousto-optic medium 14. An ultrasonic beam 15 is emitted into the . The light 22 guided from the input optical fiber 20 is incident here via the input source coupling optical element 18 in an appropriate incident direction. The input light coupling optical element 18 has a role of converging the light 22 emitted from the input optical fiber 20, and is made of a curved lens or a medium whose refractive index changes in a direction perpendicular to the direction in which the light travels.

Now, the light 23i2 incident on the acousto-optic medium 14 is diffracted by the ultrasonic bundle 16, and a portion of the transmitted light 24 is a diffracted light 24 whose frequency is equal to the frequency of the ultrasonic excitation energy by 7 notes.
Output light is emitted from the acousto-optic medium 14 via the light emitting surface 16b, and is made of a curved lens or a medium in which the j+j4)-r ratio changes in the direction perpendicular to the direction in which the light travels. The light is incident on the coupling optical element 19. The output light coupling optical element 19 connects the diffracted light 2 to the output optical fiber 21.
4, and is arranged at a point where the distance from the center point of light diffraction due to the acousto-optic effect to the output light coupling optical element is the same as the focal length of the output light coupling optical element. It is injected through the input terminal 11.

When the frequency of ultrasonic excitation energy changes, the diffracted light 2
Although the output direction of the output light coupling optical element 19 changes, due to the effect of the output light coupling optical element 19, regardless of the frequency of the k1 acoustic wave excitation energy, the diffracted light is transmitted to the output light coupling optical element 19 behind the output light coupling optical element 19. Since the diffracted light is focused at the rear focal point of the diffracted light, the diffracted light is introduced into the output optical fiber 21 disposed at this focusing point. If the coupling loss between the output optical coupling optical element 19 and the output optical fiber 21 changes depending on the frequency of the ultrasonic excitation energy, adjust the ultrasonic excitation energy to increase or decrease the frequency extracted from the output optical fiber 21. It is possible to keep the intensity of the light divided by several knots of θU constant. The remaining ultrasonic bundle that contributed to diffraction, the acousto-optic Q%j, and the ultrasonic unnecessary reflection prevention surface 17 of the rest 14,
Ultrasonic waves are reflected so that they do not follow the same path before and after reflection.
11- Prevents circular diffraction of light due to reflected ultrasonic waves.

Effects of the Invention As described above, according to his own examples, it has become possible to create a stable, high-speed, high-bandwidth optical frequency shifter with no moving parts, which will dramatically increase the amount of information that can be handled when used in optical information processing, optical communications, etc. The practical effects of being able to expand the market are significant.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a conventional acousto-optic element, and FIG. 2 is a schematic diagram of the structure of an optical frequency shifter in an embodiment according to the present invention. 18. Input light coupling optical element, 19...Output light coupling optical element, 20.-Human power optical fiber <-, 21...
- Output optical fiber.

Claims (1)

[Claims] A sound optical element having an ultrasonic excitation transducer as a part of the acousto-optic effect, and a human body attached to the acousto-optic element.
an input optical fiber that guides the light to be transmitted, an input optical coupling optical element that focuses the light guided by the light distribution fiber and enters the acousto-optic element; An output light coupling optical element that focuses and takes out the output (different directions) °C in a constant direction of 1q, and an output optical fiber for deriving the output focused by the output light coupling optical element. frequency shifter.