JPH02165116A - Phase control method for semiconductor laser with external fiber resonator - Google Patents

Abstract

PURPOSE:To stably maintain the characteristic of a semiconductor laser, and also, to stably and simply execute the assembly thermally and mechanically by fixing in advance its own optical fiber being an external resonator against the semiconductor laser, and applying pressure to a part of this optical fiber. CONSTITUTION:In a state that an optical fiber 2 is fixed and supported by a fixing member 12 of the lower side, the length is varied by applying an electric field to a piezoelectric element 13, and pressure is applied to the optical fiber 2 by its expanding force. In such a case, magnitude of the electric field applied to the piezoelectric element 13 is adjusted so that desired pressure is applied to the optical fiber 2. When pressure is applied to the optical fiber 2 in such a way, a refractive index in the optical fiber 2 is varied (photoelastic effect). By following it up, the optical path length of the optical fiber 2 is varied, therefore, a phase control of a propagation light can be executed. Therefore, the characteristic of a semiconductor laser 1 can be held stably, and also, the phase control can be executed stably and easily, and thermally and mechanically.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for controlling the phase of light propagating in the resonator in a semiconductor laser having an external optical fiber type optical resonator, the characteristics of the semiconductor laser can be kept stable. In addition, the purpose is to be thermally and mechanically stable and to easily control the phase, and to control the phase of light propagating in the fiber external cavity of a semiconductor laser with a fiber external cavity by applying pressure to the fiber external cavity. Configure it to be controlled by

(Industrial Application Field) The present invention relates to a method for controlling the phase of light propagating in a semiconductor laser having an external optical fiber type optical resonator.

In recent years, measurements and communications using the properties of light as waves have come to be carried out. In such fields of measurement and communication, light sources are used in which an optical resonator is added to the outside of a semiconductor laser to narrow the spectral linewidth. In this case, the phase of the light propagating in the optical resonator needs to be controlled with high precision.

[Conventional technology]

Conventionally, the phase control of light propagating in the optical resonator described above is
This was done as shown in Figure 4. That is, the optical fiber 2 itself, which is a resonator provided outside the semiconductor laser 1, is mechanically moved in the direction of the arrow.
The phase was controlled by changing the resonator length.

[Problem to be solved by the invention]

The conventional phase control method described above has the following problems.

(1) Since the state of optical coupling between the semiconductor laser 1 and the optical fiber 2 changes, the amount of optical feedback changes and the characteristics of the semiconductor laser 1 become unstable.

(11) It is difficult to slightly move the optical fiber 2 with good reproducibility and accuracy.

(iii) difficult to assemble in a thermally and mechanically stable manner;

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to maintain stable characteristics of a semiconductor laser, to make it thermally and mechanically stable, and to easily control the phase.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention.

In the figure, the optical fiber 2 itself, which is an external resonator, is fixed to the semiconductor laser 1.
The phase of propagating light is controlled by applying pressure to a part of the beam.

[For production]

Since an optical fiber is an elastic body, when pressure is applied to it, the refractive index within the optical fiber changes (photoelastic effect), and the optical path length of the optical fiber changes accordingly, which can be used to control the phase of propagating light. becomes possible. This effect will be explained below using specific mathematical formulas.

Here, we will consider a simple model as shown in Figure 2.

In the figure, since the Young's modulus and Poisson's ratio of the core and cladding of the optical fiber 2 are very close, it can be approximately considered to be one layer of dielectric rod. Therefore, the same figure (a
), if we consider that a force is applied to a thin disk from one direction, then the principal stress components near the center σ8, σ
y (kg/mm”) can be expressed by the following formula (Namihira et al., “Effect of Mechanical Pressure on Transmission Characteristics of Optical Fibers,” IEICE Technical Report, 0QE-76-43 (1976)
reference).

σ, = -3r/πa σ, = r/πa ・ ・ ・(1) ・ ・ ・(2) Here, f is the external force per unit length (kg/mm), and a is the radius of the cladding (mm ). Note that since the energy of light is concentrated in the core (center), in such two-dimensional elasticity problems, the value of the elastic constant of the material is unrelated to the stress distribution.

On the other hand, there is the following relationship between the stress σ8, σ and the change in refractive index Δnx, Δn for light polarized in that direction (Tsuji et al., "Photoelastic Experimental Method", Daily Journal Kogyosha (see Kogyosha).

Δn, = c, σ, +C2σx l ・
-(4) Here, CI is the direct photoelastic coefficient, and C2 is the transverse photoelastic coefficient. Note that the directions of the principal stress and the principal refractive index coincide.

By substituting equations (]) and (2) into equations (3) and (4), Δnx −−3c, (f/ia) ten cz(
f/πa) = (f/ga)(-3c+ +Cz)・・(
5) Δny=c+(f/πa) 3C2(f/πa)=(f/Wa)(C1-3C2)---(6) is obtained.

Therefore, when linearly polarized light in the X or Y direction is incident, the round trip optical path length change Δ! 8, ΔN, can be expressed by the following formula.

Δnx = (, e, +C2a, ・ ・
・(3) Δf, = 2Δn, 1 = 2 (f/za) (-3Ci +C2) Q・
(7) Δf, = 2Δn, 1 = 2 (f/πa) (c+ 3 C2) 1.
・・(8) Therefore, the phase shift l-1Δφ8, Δφa in this case is as follows, where λ is the wavelength of light. Δφ8=ΔI1. (2π/λ) = 2 (f/πa) (-3c, +c2) 1× (2
π/λ)・・・・(9) Δφa=Δf, (2π/λ) =2 (f/lt a)(c+ -3cz)
1× (2π/λ)・・・00).

Here, for example, if , equations (9) and 00) are Δφ, =
2(f/πx (125/2) x 1O-3)x(
3x6.7xlO-'-4.11xlO-')X5
xto-'X(2π/ 1.55X 10-')=-
1,38fπ ・ ・ ・(1
0Δφ, =2(f/πX (125/2)
10-')X(-6,7Xl0-6+3 X4.11X
10-')X5 Xl0-"X(2π/ 1.55x
10-')=7.66 fπ
・ ・ ・021.

Therefore, the external force f required to shift the light polarized in the X direction by 2π can be found as f=1.45 (kg/mm) by setting Δφ8=2π in 2〇〇. Further, the external force f required to shift the light polarized in the X direction by 2π can be found as f=0.26 (kg/mm) by setting Δφ = 2π in 2〇2).

From the above, it is clear that the optical fiber 2 weighs several kg (
It can be seen that the phase of propagating light can be shifted by 2π by applying a pressure of (realizable value).

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a configuration diagram showing an embodiment of the present invention.

In the figure, outside the semiconductor laser 1, an optical fiber 2 is disposed as an optical resonator, the negative end surface 2a of which is tapered to a spherical end, and the other end surface 2b of which is provided with a reflective film. Upper and lower fixing members 11 and 12 are arranged between the upper fixing member 11 and the optical fiber 2 as means for applying pressure to a part of the optical fiber 2 in the radial direction. A piezoelectric element 13 made of PZT or the like is provided.

In this embodiment, with the optical fiber 2 fixedly supported by the lower fixing member I2, an electric field is applied to the piezoelectric element 13 to change the length, and pressure is applied to the optical fiber 2 by the elongating force. . At this time, the piezoelectric element 13 is used so that a desired pressure (for example, about several kg) is applied to the optical fiber 2.
Adjust the magnitude of the electric field applied to the By applying pressure to the optical fiber 2 in this manner, the phase of the light propagating in the optical fiber 2 can be easily controlled based on the principle described above.

As described above, according to this embodiment, the optical fiber 2
Since the phase can be controlled while the phase is fixed, it is thermally and mechanically stable and can be easily assembled. Also,
Since the positional relationship between the semiconductor laser 1 and the optical fiber 2 does not change, the optical coupling state also does not change, so that the characteristics of the semiconductor laser 1 can be stably maintained.

Although the fixing members 11, 12 and the piezoelectric element 13 are used in the above embodiment as means for pressurizing the optical fiber, other means may be used to apply pressure.

〔Effect of the invention〕

As explained above, according to the present invention, the characteristics of a semiconductor laser can be maintained stably, it is thermally and mechanically stable, it can be assembled easily, and extremely accurate phase control is possible. do.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the principle of the present invention, Fig. 2 (a) and (b) are diagrams for explaining the present invention in detail, Fig. 3 is a configuration diagram showing an embodiment of the present invention, and Fig. 4 The figure is a block diagram showing a conventional phase control method. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Optical fiber (external resonator), 11.12... Fixing member, 13... Piezoelectric element. 2. Figure 1 shows an example of the twist of the present invention. Figure 3. Hashido (whistle diagram) showing how to beat the next Izuo giant cormorant Rio

Claims (1)

[Claims] A fiber external resonator characterized in that the phase of light propagating in the fiber external resonator (2) of the fiber external resonator-equipped semiconductor laser (1) is controlled by applying pressure to the fiber external resonator. A method for controlling the phase of a semiconductor laser.