JP2991261B2 - Optical waveguide type optical frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type optical frequency converter having high utility in the fields of heterodyne type optical sensors and coherent optical communication.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional optical frequency converter. This optical frequency converter has a basic configuration using a bulk type AO element. In FIG.
18 is an AO element, 19 is a vibrator, and 20 is a high frequency power supply. The elastic wave generated by the vibrator 19 and propagated through the AO element 18 generates a traveling wave type refractive index grating in the AO element 18 by a photoelastic effect. The input light is reflected by the grating, and the frequency is converted at that time. The width of the frequency conversion matches the frequency of the vibrator 19.

As another example of the optical frequency converter, a method utilizing light scattering by sound waves has been reported. For example, Jan of Askouturad and Held E.
Engan reports (Jan Ove Askautrud and Helde
E. Engan; "Fiber-optic frequency shifter with no m
ode change using cascaded acousto-optic interracti
on regions "; OPTICS LETTER, Vol.15, No.11, p649-651,
1990). FIG. 5 shows the basic configuration. In FIG. 5, 2
Reference numeral 1 denotes a single mode fiber, and reference numeral 22 denotes a two-mode fiber that propagates two modes of light, from which resin is stripped so that sound waves can be transmitted. 23 is a vibrator and 24 is an acoustic horn.

The vibration generated by the vibrator 23 is transmitted to the two-mode fiber 22 via the acoustic horn 24,
It becomes a sound wave as micro-bending that travels in the right and left directions on the mode fiber. When a sound wave having both a frequency and a wave number corresponding to an energy difference and a momentum difference between two modes that can propagate through the two-mode fiber 22 is given, the light and the sound wave passing through the two-mode fiber 22 are combined. To higher order mode light. Furthermore, the sound wave recombines with the sound wave traveling in the opposite direction, and only the wave number change cancels out. As a result, it is possible to obtain light in which only the frequency is converted without changing the mode. In this method, highly efficient frequency conversion has been reported.

[0005]

In the method shown in FIG. 4 described above, the frequency conversion width can be freely set, but it is necessary to fix the directions of incident light and reflected light with respect to the AO element 18. On the other hand, in the method shown in FIG. 5, it is necessary to stretch a two-mode fiber 22 that performs AO interaction. Further, it is necessary to fix the position of the acoustic horn 24 transmitting the vibration to the two-mode fiber 22.

For these reasons, in any of the above-described methods, various optical instruments must be fixed and fixed on a surface plate or the like. For this reason, there is a disadvantage that the entire apparatus becomes large. The present invention has been made in view of the above-mentioned conventional technology, and has as its object to provide a small and inexpensive optical frequency converter.

[0007]

According to an embodiment of the present invention to achieve the above object, a quartz glass is deposited on a silicon substrate,
In an optical circuit with a core layer through which light propagates and a cladding layer that confine the light in the core layer, a linear optical waveguide that has a cut portion on the side and that allows light in multiple modes to propagate without the bottom silicon substrate And an optical waveguide connected to both ends of the multi-mode propagating optical waveguide portion and satisfying the single-mode propagation condition, and a vibrator in contact with the multi-mode propagating optical waveguide portion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, 1 is a silicon substrate, 2 is a core layer through which light propagates, 3 is a cladding layer that confines light, and 4 is _LP01.
Single mode optical waveguide that propagates only mode light, 5
Multiple mode optical waveguide for propagating light LP ₀₁ mode and the LP ₁₁ mode, the acoustic horn formed in a wedge shape at 6 and silica glass, 7 vibrator made of PZT element, 8 is a jig for supporting the acoustic horn is there. The material of the core layer 2 is GeO ₂ -P ₂
The material of O ₅ -SiO ₂ and the cladding layer 3 is P ₂ O ₅ -B ₂ O ₃ -S
TiO ₂ , which was deposited and deposited on the silicon substrate 1 so that the relative refractive index became 0.3%.

[0009] Therefore, LP ₀₁ mode of the single-mode optical waveguide 4 for propagating only light cross-section 8 × 8μm, LP ₀₁
The cross section of the plurality mode optical waveguide 5 for propagating light mode and LP ₁₁ mode is set to 13 × 8 [mu] m. After the formation of the two types of waveguides 4 and 5, the silicon substrate 1 of the multi-mode optical waveguide 5 is removed by etching, and both side surfaces of the multi-mode optical waveguide 5 are cut so that sound waves necessary for frequency conversion can also be propagated. To a width of 925 μm. The acoustic horn 6 was made of silica glass, a vibrator 7 was attached to the bottom surface, and was fixed with a jig 8 such that the tip was in contact with the center of the multi-mode optical waveguide 5.

In order to convert the frequency of light propagating through the optical waveguides 4 and 5 with the optical frequency converter having the above configuration, a high-frequency voltage is applied to the vibrator 7 to vibrate the vibrator 7.
The vibration generated by the vibrator 7 is transmitted to the multi-mode optical waveguide 5 through the acoustic horn 6, and propagates through the multi-mode optical waveguide 5 as an elastic wave traveling in both leftward and rightward directions. This elastic wave is accompanied by a change in the refractive index, and causes coupling with light.

At this time, the incident light is first combined with a sound wave traveling in the opposite direction to the light and transits to higher-order mode light, and then combined with the sound wave traveling in the same direction to produce light of the original mode. Transition. Since the traveling directions of the two sound waves are opposite, their momentums almost cancel each other out. Therefore, the mode of light does not change, and light absorbs only the energy of sound waves. For this reason, the light that has passed through the multi-mode optical waveguide 5 has only the mode whose frequency is increased by twice the frequency of the sound wave until then. The frequency generated by the vibrator 7 is 4 MH
At the time of z, the frequency conversion width by the optical waveguide type optical frequency converter was 8 MHz.

Since it is difficult to directly measure the frequency of light with high sensitivity, the operation of the frequency converter was checked using the optical system shown in FIG. In FIG. 2, 10 is a helium-neon laser, 11 is a deflector, 12 is a bulk type frequency converter,
Reference numeral 15 denotes a single mode fiber, 16 denotes an optical waveguide type optical frequency converter according to the present invention, and 17 denotes a detector. First,
The light of a He—Ne laser 10 having a wavelength of 1.543 μm and an output of 10 μW is polarized by a polarizer 11,
MHz frequency conversion is performed to obtain light 13 that has undergone frequency conversion and light 14 that has not undergone frequency conversion. The light 14 not subjected to the frequency conversion is guided to the optical frequency converter 16 according to the present invention by the single mode fiber 15, and the light coming out of the optical frequency converter 16 is combined with the other 80MHz frequency-converted light 13. Waves were caused to interfere and measured by the detector 17.

FIG. 3A shows a measurement result when no high-frequency voltage is applied to the optical frequency converter according to the present invention, and FIG. 3B shows a measurement result when a high-frequency voltage is applied. As is clear from the measurement results, before applying the high-frequency voltage, the bulk type optical frequency converter 12
However, it can be seen that the main peak of the beat is shifted by 8 MHz after the application of the high frequency voltage.

[0014]

As described above in detail with reference to the embodiments, according to the present invention, it is only necessary to supply the power for driving the vibrator to the optical frequency converter formed integrally, so that the optical frequency converter passes through the element. The frequency of the light to be emitted can be converted. Conventionally, the optical axis is required to be adjusted in an optical converter using a combination of individual components, and the stability of the optical axis once assembled is always a problem. However, since the present invention has realized an integrated optical frequency converter, these problems have been solved, and a small and stable optical frequency converter can be realized. Further, in the present invention, since an optical waveguide is used, it can be easily combined with other optical waveguides, so that the optical system can be integrated and miniaturized, and the realization of a more stable optical system is expected.

[Brief description of the drawings]

FIGS. 1A and 1B show a basic configuration of an optical waveguide type optical frequency converter according to an embodiment of the present invention. FIG. 1A is a plan view, FIG. 1B is a side view, and FIG. Is a front view thereof.

FIG. 2 is a basic configuration diagram of an optical system used for confirming the operation of the optical waveguide type optical frequency converter according to the present invention.

FIG. 3A is a graph showing a measurement result when no high-frequency voltage is applied to the optical waveguide type optical frequency converter of the present invention, and FIG. 3B is a graph showing a case where a high-frequency voltage is applied. 6 is a graph showing the measurement results of FIG.

FIG. 4 is a basic configuration diagram of a conventional optical frequency converter using a bulk type AO element.

FIG. 5 is a basic configuration diagram of a conventional optical frequency converter using light scattering by sound waves.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 core layer 3 cladding layer 4 single mode optical waveguide 5 multiple mode optical waveguide 6, 24 acoustic horn 7, 19, 23 vibrator 8 jig 9, 17, 22 high frequency power supply 10 helium / neon laser 11 polarizer 12 Bulk type optical frequency converter 13 Frequency converted light 14 Non-frequency converted light 15, 21 Single mode optical fiber 16 Optical waveguide type optical frequency converter of the present invention 17 Detector 18 AO element 22 2 mode fiber

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Claims (1)

(57) [Claims] 1. An optical circuit comprising: a silica-based glass deposited on a silicon substrate; a core layer through which light propagates; and a clad layer for confining the light in the core layer. A linear optical waveguide portion through which light of a plurality of modes is removed, an optical waveguide satisfying a single mode propagation condition connected to both ends of the multi-mode propagation optical waveguide portion, and the multi-mode propagation optical waveguide portion And a vibrator in contact with the optical waveguide type optical frequency converter.