JPH0752258B2 - Optical fiber phase modulator - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of an optical fiber phase modulator in which a piezoelectric vibrator is mounted in the middle of an optical fiber.

(Prior Art) FIG. 2 shows an example of a conventional optical fiber phase modulator of this type. An optical fiber 2 is wound around an outer peripheral surface of a cylindrical piezoelectric vibrator 1 a plurality of times and fixed by an adhesive or the like. The piezoelectric vibrator 1 vibrates in the radial direction by the voltage supplied from the drive signal source 3 to the piezoelectric vibrator 1, whereby the optical fiber 2 expands and contracts. The light incident from one end of the optical fiber 2 is phase-modulated based on the change in the optical path length and the refractive index that occur at 1 and is emitted from the other end.

(Problems to be Solved by the Invention) However, in the above device, when the optical fiber 2 is wound around the piezoelectric vibrator 1, it must be performed while applying tension to the optical fiber 2, and a polarization-maintaining optical fiber is used. Sometimes, when the piezoelectric vibrator 1 is wound without considering the birefringent main axis, the crosstalk is deteriorated. Therefore, the birefringent main axis must be parallel or perpendicular to the central axis of the piezoelectric vibrator 1, which is troublesome. There is such a problem, and the displacement of the piezoelectric vibrator 1 is small in terms of shape. Therefore, in order to increase the amount of phase modulation, the voltage of the drive signal source 3 is increased or the winding amount of the optical fiber is increased. Alternatively, it is necessary to use a large-sized piezoelectric vibrator itself, which causes problems such as an increase in load on the drive signal source and an increase in size of the device.

It is an object of the present invention to solve the above problems, to provide an optical fiber phase modulator which is easy to manufacture, can be driven by a low power supply, and is small.

(Means for Solving the Problem) In the present invention, in order to achieve the above object, a plurality of grooves having a width substantially equal to the outer diameter of the optical fiber are formed on the side surface of the laminated piezoelectric vibrator along the vibration direction. We propose an optical fiber phase modulator in which one optical fiber is folded back into each groove and inserted / fixed.

(Operation) According to the present invention, when a driving voltage is supplied to the laminated piezoelectric vibrator, the laminated piezoelectric vibrator vibrates in the vibration direction, that is, along the groove formed on the side surface, whereby the piezoelectric vibrator is inserted and fixed in the plurality of grooves. Another optical fiber is expanded and contracted in the longitudinal direction in all of the plurality of grooves, and the phase of the light passing through the optical fiber is largely modulated by the change in the optical path length and the refractive index.

(Example) FIG. 1 shows a structural example for explaining the principle of the optical fiber phase modulator of the present invention. In the figure, 11 is a laminated piezoelectric vibrator, 12 is an optical fiber, and 13 and 14 are The dummy block, 15 is a drive signal source.

The laminated piezoelectric vibrator 11 is composed of a plurality of plate-shaped piezoelectric elements, six in this case, laminated with electrodes sandwiched therebetween, and fixed to each other. Here, the end face has a size of 8 mm × 8 mm and the entire length. 9m
I am using m. The dummy blocks 13 and 14 are made of an epoxy-based synthetic resin, and have an end surface of the laminated piezoelectric vibrator 11.
Along with the end faces 13a and 14a of the same shape as 11a and 11b, the optical fiber
It has step portions 13b and 14b which are slightly larger than the outer diameter of 12.

The piezoelectric vibrator 11 and the dummy blocks 13 and 14 have their end faces 1
Adhered and fixed at 1a and 13a and 11b and 14b,
Furthermore, on one side surface including the step portions 13b and 14b, the optical fiber is aligned along the vibration direction (here, the same as the voltage application direction).
A groove 16 having a width approximately equal to the outer diameter of the element wire portion 12 and a depth of about half the outer diameter of the optical fiber 12, here, a width of 0.2 mm and a depth of 1 mm is formed by dicing.

Further, the optical fiber 12 is a single-mode optical fiber having a cutoff wavelength of 1.12 μm, and its coating is removed by the same length as the groove 16, and at this time, the exposed wire portion 12a has the groove 16
Piezoelectric resonator 11
Also, they are adhered and fixed to the dummy blocks 13 and 14 with an epoxy adhesive (not shown).

When the respective electrodes of the piezoelectric vibrator 11 and the drive signal source 15 are alternately connected in opposite polarities and a drive voltage is supplied, the piezoelectric vibrator 11 vibrates in the stacking direction, that is, along the groove 16, By this, the wire portion 12a of the optical fiber 12 in the groove 16 expands and contracts,
The change of the optical path length and the refractive index modulates the phase of the light entering the optical fiber 12.

The phase modulator was placed in a Mach-Zehnder interferometer consisting of two 3 dB optical fiber couplers, and the modulation characteristics were measured. As a result, a drive voltage that gives a phase shift of one wavelength at a wavelength of 1.30 μm is about 3 [DC]. V]. Also,
Somewhat as the modulation frequency must be high modulation (driving) voltage but was operable up 10KH _Z. To increase the modulation frequency even further, dummy block 1
It suffices to insert 3 and 14 into the groove of the laminated piezoelectric vibrator 11 without adhering the coating of the optical fiber 12 without removing the coating, and adhere and fix the same. In this case, the width of the groove 16 is set to be approximately the same as the outer diameter of the optical fiber 12 with the coating.

In addition, as described above, when a single-mode optical fiber is used as the optical fiber 12, birefringence may occur due to the influence of lateral pressure when inserting / fixing the laminated piezoelectric vibrator 11, and the polarization is essentially polarized. However, it is difficult to apply to an optical fiber sensor such as an optical fiber gyro.However, in this case, a polarization maintaining optical fiber having a large birefringence in advance inside the optical fiber may be used as the optical fiber 12. When a linearly polarized light was used for the light, and it was incident parallel to the main axis of the polarization of the polarization-maintaining optical fiber and the same test was performed, the same characteristics as when using a single-mode optical fiber were obtained. It was

FIG. 3 shows another structural example for explaining the principle of the optical fiber phase modulator of the present invention. Here, an example in which a plurality of optical fibers are used is shown. That is, 21 is a laminated piezoelectric vibrator, 22, 23, 24, 25 and 26 are optical fibers, 27 and 28 are dummy blocks, and dummy blocks 27 and 28 are bonded to both end surfaces of the laminated piezoelectric vibrator 21. -Fixed, a plurality of, here five grooves 29, 30, 31, 32, 33 are provided on one side surface along the vibration direction by dicing, and the optical fibers 22 to 26 are further provided in the respective grooves 29 to 33. The portions from which the coating is removed are inserted, and the portions having the coating are adhered and fixed to the piezoelectric vibrator 21 and the dummy blocks 27 and 28 with an epoxy adhesive (not shown).

As the laminated piezoelectric vibrator 21, as in the configuration example of FIG. 1, an end face having a size of 8 mm × 8 mm and a length of 9 mm is used, and the optical fibers 22 to 26 are cut off. A 5-core tape type single mode optical fiber having a wavelength of 1.2 μm is used, and the grooves 29 to 33 have a width of 0.15 mm and a depth of 1 mm and are provided in parallel with each other at intervals of 0.5 mm.

When the drive voltage is supplied by alternately connecting the electrodes of the piezoelectric vibrator 21 and the drive signal source 15 described above, the piezoelectric vibrator
21 vibrates along the grooves 29 to 33, which causes the optical fibers 22 to 26 to expand and contract, and the phase of the light entering each of the optical fibers 22 to 26 is similarly modulated by the change in the optical path length and the refractive index. To be done.

Each of the optical fibers 22 to 26 of the phase modulator was put into a Mach-Zehnder interferometer in the same manner as in the configuration example of FIG. 1 and the modulation characteristics were measured. As a result, a driving voltage that gives a phase shift of one wavelength at a wavelength of 1.30 μm is obtained. Was about 3 ± 0.3 [V] at DC. Also in this configuration example, the dummy block 2
The modulation frequency can be increased by not inserting the 7,28 and by directly inserting the optical fibers 22 to 26 into the grooves of the laminated piezoelectric vibrator without removing the coatings and adhering and fixing them. In addition,
Other configurations and operations are similar to those of the configuration example of FIG.

FIG. 4 shows an embodiment of the optical fiber phase modulator of the present invention, which is characterized in that a driving voltage is reduced by folding one optical fiber into a plurality of grooves and inserting / fixing the optical fiber. . That is, in the drawing, 41 is a laminated piezoelectric vibrator, 42 is an optical fiber, 43 and 44 are dummy blocks, and dummy blocks 43 and 44 are adhered and fixed to both end faces of the laminated piezoelectric vibrator 41. A plurality of, in this case, four grooves 45, 46, 47, 48 are provided on one side along the vibration direction by dicing, and the optical fiber 42 is folded back and inserted into each of the grooves 45 to 48 while being covered. , Is bonded and fixed to the piezoelectric vibrator 41 and the dummy blocks 43 and 44 with an epoxy adhesive (not shown).

As the laminated piezoelectric vibrator 41, as in the configuration example of FIG. 1, an end face having a size of 8 mm × 8 mm and a length of 9 mm is used, and the optical fiber 42 has a cutoff wavelength of 1 mm. .
2 μm single mode optical fiber is used, and groove 4
5 to 48 have a width of 0.3 mm and a depth of 1 mm, and are provided in parallel with each other at an interval of 1 mm. The turning radius of the optical fiber 42 can be made sufficiently large by making the extra length portion long.

When the drive voltage is supplied by alternately connecting the electrodes of the piezoelectric vibrator 41 and the drive signal source 15 described above to each other, the piezoelectric vibrator
41 vibrates along the grooves 45 to 48, whereby the optical fiber 42 expands and contracts, and the phase of the light entering the optical fiber 42 is modulated by the change in the optical path length and the refractive index thereof. Modulation is performed in the four parts of one optical fiber 42, and a modulation factor of 4 is obtained (in other words, the drive voltage can be reduced to 1/4).

The phase modulator was put in a Mach-Zehnder interferometer in the same manner as in the configuration example of FIG.
The drive voltage at which a phase shift of one wavelength is obtained at 30 μm is about 0.7 [V] at DC, which is about 1/4 that of the first configuration example.
And was greatly reduced. The other configurations and operations are the first
This is similar to the configuration example in the figure.

(Effects of the Invention) As described above, according to the present invention, since it is configured by simply folding and inserting and fixing one optical fiber in the plurality of grooves formed in the laminated piezoelectric vibrator, As described above, it is not necessary to wind the optical fiber around a cylindrical piezoelectric vibrator while applying tension to the optical fiber, and a laminated piezoelectric vibrator having a large displacement is used and phase modulation is performed in a plurality of portions of one optical fiber. Therefore, there is an advantage that it can be driven at a low voltage, and the entire device can be downsized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example for explaining the principle of the optical fiber phase modulator of the present invention, FIG. 2 is a configuration diagram showing an example of a conventional optical fiber phase modulator, and FIG. 3 is a diagram of the present invention. FIG. 4 is a diagram showing another configuration example for explaining the principle of the optical fiber phase modulator, and FIG. 4 is a configuration diagram showing an embodiment of the optical fiber phase modulator of the present invention. 11,21,41 …… Multilayer piezoelectric vibrator, 12,22 ～ 26,42 …… Optical fiber, 16,29 ～ 33,45 ～ 48 …… Groove.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Junji Watanabe 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Tadao Saito 1-16-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corp. (72) Inventor Shinsuke Matsui 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (56) Reference JP-A-63-180929 (JP, A)

Claims (1)

[Claims] 1. A plurality of grooves having a width substantially equal to the outer diameter of the optical fiber are formed on the side surface of the laminated piezoelectric vibrator along the vibration direction, and one optical fiber is folded back and inserted into each groove.・ An optical fiber phase modulator characterized by being fixed.