JPH0992914A - Optical fiber ring laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small sized optical fiber ring laser excellent in resonance characteristics. SOLUTION: The resonator of an optical fiber ring laser is formed by using an optical fiber ring 2 in which an optical fiber 3 is formed in a ring type. In the optical fiber ring 2, an Er doped part 11, a polarized wave controller 16, an optical fiber polarizer 19 and an isolator 9 are arranged, and a pumping light incidence part 13 which pumping light for exciting erbium of the Er doped part 11 is made to enter, and the output terminal side 20 which sends forth light are connected with the optical fiber ring 2. In the optical fiber 3 which forms the optical fiber ring 2, non-liner constant increasing material which enlarges the non-liner constant of the optical fiber 3 is introduced into the core of the optical fiber 3 and diffused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber ring laser used, for example, as a light source for optical communication or a synchronous transmission source for optical logic circuits.

[0002]

2. Description of the Related Art In order to construct an ultra high speed optical transmission system,
The use of optical soliton communication is drawing attention, and an optical fiber ring laser is being studied as a source of ultrashort pulses with a pulse width of fs to ps used in this optical soliton communication.

FIG. 1 shows an example of an optical fiber ring laser. In the figure, a single ring type optical fiber ring 2 is formed by the optical fiber 3, and the optical fiber ring 2 forms a resonator. The optical fiber ring 2 is provided with an Er-doped portion 11, a polarization controller 16, an optical fiber type polarizer 19, and an isolator 9 which are erbium-doped fibers obtained by adding erbium ions (Er ³⁺ ) to the core of the optical fiber 3. The optical fiber ring 2 is connected to the pump light incident part 13 via an optical multiplexing / demultiplexing coupler (WDM coupler) 14 and also connected to the output end side 20 via a coupler 15.

In this type of optical fiber ring laser, polarization rotation occurs due to a change in refractive index due to light intensity in the optical fiber 3, that is, so-called non-linear polarization rotation is utilized to extract only a specific polarization. This is a ring laser, and the fiber type polarizer 19 performs a switching action of transmitting strong light polarized by the polarization controller 16 and weakening weak light, so that the intensity is increased each time the light goes around the optical fiber ring 2. This causes modulation switching, which causes pulse oscillation.

Further, FIG. 2 shows another example of the optical fiber ring laser, and the one shown in FIG. 2 has an optical fiber ring 2 in which the optical fiber 3 is formed into a figure 8 ring shape. Is formed. In this optical fiber ring 2, a nonlinear optical amplification loop mirror 5 and a linear loop 6 are 3d.
The nonlinear optical amplification loop mirror 5 is provided with an Er-doped section 11, a polarization controller 16, and an optical multiplexing / demultiplexing coupler 14, which are connected to each other via the B coupler 8. The pump light incident part 13 is connected.
On the other hand, the linear loop 6 is provided with an isolator 9, a polarization controller 16, and a coupler 15, and the coupler 15 is connected to the output end side 20 of the optical fiber ring laser. In the figure, A, B, C, and D respectively represent input / output ports of the 3 dB coupler 8.

Further, as shown in FIG. 2, the optical fiber ring laser having the figure 8 optical fiber ring 2 is
An optical fiber ring laser in which a nonlinear optical loop mirror 4 and a linear amplification loop are connected via a coupler 18 having a branching ratio of α: 1-α is also proposed.

Since the operation of this type of optical fiber ring laser (FIGS. 2 and 3) is well known, its description is omitted.

[0008]

By the way, in the above-mentioned optical fiber ring laser, conventionally, only the study focusing on the ring configuration of the optical fiber ring 2 has been performed, and the optical fiber ring 2 is constructed. Optical fiber 3
Regarding the characteristics of, no consideration was made other than considering dispersion and loss. Therefore, the conventional optical fiber ring laser described above has been formed using, for example, a general silica optical fiber. The nonlinear constant of this silica-based optical fiber is 3.2 × 10 ^-20 m ² / W, or, according to recent measurements, a very small value of 2.7 to 3.0 × 10 ^-2 m ² / W. In order to obtain a large amount of non-linear polarization rotation using such an optical fiber, it is necessary to increase the length of the optical fiber.

Therefore, when an optical fiber ring laser utilizing nonlinear polarization rotation as shown in FIG. 1 is formed by using the silica optical fiber, the nonlinear polarization rotation amount required for the laser is obtained. The length of the optical fiber 3 must be increased, and it is difficult to reduce the size of the optical fiber ring 2. As a result, the optical fiber ring laser is increased in size.

The present invention has been made to solve the above conventional problems, and an object thereof is to provide an optical fiber ring laser which is small in size and excellent in resonance characteristics.

[0011]

Means for Solving the Problems To achieve the above object, the present invention provides means for solving the problems by the following constitution. That is, the present invention is an optical fiber ring laser in which a resonator is formed by using an optical fiber ring in which an optical fiber is formed into a ring shape. In the optical fiber of the optical fiber ring, the nonlinear constant of the optical fiber is increased. It is configured by adding a non-linear constant increasing substance to the core.

As is well known, the non-linear polarization rotation is polarized in a certain direction, assuming that the two orthogonal directions orthogonal to the optical axis of an optical component such as an optical fiber are the x-axis direction and the y-axis direction, respectively. The refractive index in the x-axis direction and the refractive index in the y-axis direction of light are generated by changing depending on the optical electric field strength in the axial direction, which causes birefringence. Specifically, x
The refractive index n _x in the axial direction and the refractive index n _{y in the} y-axis direction can be expressed by the following equations (1) and (2), respectively.

N _x = n _x0 + n _x ′ P (1)

N _y = n _y0 + n _y ′ P (2)

In the equations (1) and (2), P is the power of the light (optical field intensity), and n _x0 and n _y0 are the refractive index in the x-axis direction and the y-axis when there is no nonlinear effect, respectively. And the refractive index in the direction. Further, n _x ′ and n _y ′ are represented by the following equations (3) and (4), respectively, where P _{x is} the optical power in the _x- axis direction and P _y is the optical power in the y-axis direction. It is a thing.

N _x ′ = X {P _x + (2/3) · P _y } (3)

N _y ′ = X {P _y + (2/3) · P _x } (4)

In these equations (3) and (4), X
Is given by the following equation (5).

X = (4π · n ₂ × 10 ⁷ ) / (n · c · Aeff) (5)

In the equation (5), n ₂ is called a non-linear constant or a non-linear refractive index, Aeff is an effective cross-sectional area of the optical fiber, and Aeff ≈π ( a / 2) ² . n is the refractive index, and c is the speed of light.

If the phase shift amount (phase difference) induced when the light propagates L in the longitudinal direction of the optical fiber due to the change in the refractive index is φ, the wavelength of the propagating light is λ,
The following equation (6) can be derived.

[0022] φ = {(2π · L) / λ} · (n y '-n x') = {(2π · L · X) / 3λ} · (P x -P y) = {(8π 2 · L · n ₂ × 10 ⁷ ) / (3λ · n · c · Aeff)} · (P _x −P _y ) ... (6)

As is apparent from the equation (6), when the nonlinear constant is increased, a large amount of phase shift, that is,
A large polarization rotation can be obtained. In the optical fiber ring laser of the present invention, due to the above structure, the optical fiber is added with a non-linear constant increasing substance that increases the non-linear constant of the optical fiber. It is possible to shorten the optical fiber length required to obtain the same amount of polarization rotation as the amount of polarization rotation generated in the fiber ring, making the optical fiber ring smaller and the optical fiber ring laser smaller. The above problems are solved.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals are given to the same parts as those in the conventional example, and the overlapping description will be omitted. The optical fiber laser of the present embodiment example is an optical fiber ring laser having the single ring type optical fiber ring 2 shown in FIG. 1. The characteristic feature of the present embodiment example is that it differs from the conventional example. That is, fine particles of a nonlinear constant increasing substance for increasing the nonlinear constant of the optical fiber 3 are doped (added) into the core and diffused in the optical fiber 3 of the ring.

This nonlinear constant increasing substance is used for the optical fiber 3
Is selected and doped according to the wavelength of the light propagating in the optical fiber. At a wavelength of 560 μm, by adding an inorganic substance such as aluminum (Al) or GaAsP as a nonlinear constant increasing substance, the optical fiber The non-linear constant of 3 can be made about 10 times larger than the non-linear constant of a general silica optical fiber. These A
Inorganic substances such as l can have a large nonlinear constant even at wavelengths of 1.31 μm and 1.55 μm, which have been generally used for optical communication, but instead of these inorganic substances,
A substance having an excellent effect peculiar to a wavelength of 1.31 μm or a wavelength of 1.55 μm may be selectively added as a non-linear constant increasing substance.

The configuration of this embodiment other than the above is as follows.
Since it is the same as the conventional example, the duplicated description will be omitted.

The example of the present embodiment is configured as described above, and the operation of the example of the present embodiment is similar to that of the conventional example. However, in the example of the present embodiment, the optical fiber ring 2 of the optical fiber ring laser is used. The optical fiber 3 forming
Aluminum, which increases the nonlinear constant of the optical fiber 3, is added to the core, which increases the nonlinear constant of the optical fiber 3. Therefore, as is clear from the above formula (6), this optical fiber 3 The amount of phase shift induced when propagating through the optical fiber length L is larger than that of a conventional optical fiber ring laser using an optical fiber having a small nonlinear constant, and thus the amount of nonlinear polarization rotation is increased.

Therefore, the optical fiber length required to obtain the same polarization rotation amount is smaller than that of the conventional optical fiber ring laser using the ordinary optical fiber 3 having a small nonlinear constant.
The optical fiber ring laser of the present embodiment using the optical fiber 3 having a large non-linear constant can be shorter, and the length of the optical fiber 3 forming the optical fiber ring 2 can be extremely shortened. Therefore, it is possible to obtain the same polarization rotation amount as that of the conventional optical fiber ring laser and form an optical fiber ring laser having the same function in a small size by using the short optical fiber 3 in the present embodiment example. It is possible to provide an optical fiber ring laser that is small in size and has excellent resonance characteristics.

The present invention is not limited to the above-mentioned embodiments, but can take various modes. For example,
In the above-described embodiment, an inorganic substance has been taken as an example of the nonlinear constant increasing substance with which the optical fiber 3 is doped, but the nonlinear constant increasing substance has a wavelength of light that propagates through the optical fiber 3 and is emitted from the optical fiber ring laser. In this case, a substance that increases the nonlinear constant at the wavelength may be used, and for example, a semiconductor or an organic substance may be used.

Further, in the above embodiment, the optical fiber 3 is formed by doping the core with a nonlinear constant increasing substance such as aluminum to form the optical fiber ring 2. However, the optical fiber 3 is doped with the nonlinear constant increasing substance. Together with the known polarization fiber, the optical fiber 3
The optical fiber ring 2 may be formed by.

Further, in the above embodiment, the optical fiber ring laser is the optical fiber ring laser having the structure shown in FIG. 1, but the optical fiber ring laser of the present invention is shown in FIGS. So that the optical fiber 3
An optical fiber ring laser may be formed by forming the optical fiber ring 2 having a V shape. As described above, the optical fiber ring laser of the present invention can be an optical fiber ring laser having optical fiber rings of various shapes and sizes, and the optical fiber length is the same as that of the conventional optical fiber ring laser. If so, it is possible to obtain a larger amount of polarization rotation than the conventional one, and conversely, when trying to obtain the same amount of polarization rotation as the conventional optical fiber ring laser, shorten the optical fiber length. Very small fiber optic ring lasers can be formed.

[0032]

According to the present invention, a nonlinear constant increasing substance for increasing the nonlinear constant of the optical fiber is added to the core of the optical fiber forming the optical fiber ring as the resonator of the optical fiber ring laser. Therefore, depending on the nonlinear constant of the optical fiber, the polarization rotation amount (phase shift amount) that increases as the nonlinear constant increases can be made larger than that of the conventional optical fiber ring laser. Therefore, it is possible to shorten the length of the optical fiber required to obtain the same polarization rotation amount as the conventional optical fiber ring laser, and to form a small optical fiber ring using a short optical fiber, An optical fiber ring laser having excellent resonance characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing an example of an optical fiber ring laser.

FIG. 2 is a configuration diagram schematically showing another example of an optical fiber ring laser.

FIG. 3 is a configuration diagram schematically showing still another example of the optical fiber ring laser.

[Explanation of symbols]

 2 Optical fiber ring 3 Optical fiber 9 Isolator 11 Er-doped part 16 Polarization controller 19 Optical fiber type polarizer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor St. Nimura 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. An optical fiber ring laser in which a resonator is formed by using an optical fiber ring in which an optical fiber has a ring shape. In the optical fiber of the optical fiber ring, a non-linearity for increasing a non-linear constant of the optical fiber is used. An optical fiber ring laser in which a constant-increasing substance is added to the core.