KR100212478B1 - Ling type optical fiber laser using optical fiber roller and double mode optical fiber, and color dispersion compensation method using it - Google Patents

Abstract

The present invention is a method that can more easily implement the difficulties of dispersion compensation when using the conventional dual-mode fiber and two optical fiber mode converters while compensating for the disadvantages of using a distributed transition fiber, and is a powerful mode for a light source to be used in high-speed optical transmission. Optical fiber rotator and dual mode fiber can compensate for color dispersion, which is a major factor of optical pulse expansion, by using optical fiber rotator, dual mode fiber and one mode converter in the resonator to reduce the optical pulse of locked fiber laser to conversion limit The present invention relates to a ring-shaped optical fiber laser using and a dispersion compensation method using the same.

Description

Ring type fiber laser using optical fiber rotator and dual mode optical fiber and chromatic dispersion compensation method using the same

The present invention relates to a method for compensating color dispersion in a resonator using two mode fibers (TMF) for reducing the pulse width of a mode locking fiber laser to be used for ultrafast optical communication systems or ultrafast characteristics measurement of long wavelength optical devices.

Fiber lasers have attracted attention since 1990 due to their applicability in the field of optical communication and fiber optic sensors. In particular, the fiber laser using the erbium-doped fiber has a long wavelength communication band of 1.5 It is possible to oscillate at, and the gain bandwidth is wide as 30 -40nm, so when the pulse is oscillated, ultra short pulse generation in femtosecond (10 ^-15 seconds) is possible. Among the methods for oscillating the laser output in the form of pulse, there are a mode locking method, a Q-switching method, a gain switching method, and the like. Among them, the mode locking method is capable of oscillating the shortest pulse. The pulse width of the optical pulse generated through mode locking or the like is mainly determined by the color dispersion value in the resonator. That is, the color dispersion in the resonator distributes the frequency components in the optical pulses formed in a temporal arrangement so as to correspond to the respective group speeds, which intensifies as the resonance is repeated, causing the pulse width to expand. When the color dispersion of the optical fiber has a positive value at the oscillation wavelength, the light having a long wavelength moves faster because the group speed is larger than that of the short light. Conversely, when chromatic dispersion has a negative value, light having a shorter wavelength is faster than long light. Common single mode fiber is 1.5 In the case of forming a fiber laser resonator with a single-mode fiber with negative chromatic dispersion, the long wavelength portion at the oscillation line width is located at the end of the pulse, and the short wavelength portion is located at the front of the pulse. This phenomenon is called chirping, and as the chirped light moves through the resonator, the speed difference between the long-wavelength light and the short-light light accumulates as it moves, which causes the pulse to expand. Even if the value of chromatic dispersion is positive, only the wavelength distribution located before and after the pulse is different and the result is the same. Therefore, in order to obtain a short pulse, the chromatic dispersion value in the resonator must be made near zero. There are roughly two ways to zero out the chromatic dispersion.

The first is to use optical fibers with group velocity dispersion of zero at the oscillation wavelength, and the second is to make color dispersion as zero using optical fibers with positive and negative optical dispersion. It is not practical to match all the chromatic dispersion wavelengths of the optical fiber elements in the fiber laser resonator to the laser output wavelength, so the first method is not effective. Therefore, the second method is used for most fiber laser mode locking. In the second method, a general single mode optical fiber is used for a positive chromatic dispersion, and a dispersion transition optical fiber is used for a negative optical dispersion. However, it is not easy for the negative chromatic dispersion value to have a large value at the oscillation wavelength. Therefore, the length of the dispersion transition optical fiber is inevitably long, and thus the length of the laser resonator is long. The repetition rate of the output pulse of the laser is inversely proportional to the resonator length, and the repetition rate of the laser inevitably decreases when the resonator length becomes longer. This is a disadvantage of the laser resonator using a dispersion transition optical fiber.

Accordingly, the present invention can more easily implement the difficulties of dispersion compensation when using the conventional dual mode optical fiber and two optical fiber mode converters, while compensating for the disadvantages of using the distributed transition optical fiber. In order to reduce the optical pulse of the most powerful mode-locked fiber laser to the conversion limit, the optical fiber rotator can compensate the color dispersion, which is the main factor of optical pulse expansion, by using the optical fiber rotator, dual mode optical fiber and one mode converter in the resonator. It is an object of the present invention to provide a method for compensating color dispersion of a ring-type fiber laser using a dual mode optical fiber.

The present invention for achieving the above object is an erbium-doped optical fiber which is a gain medium of the laser, a pumping laser for optically pumping the erbium-doped optical fiber, and a dichroic optical fiber combiner for injecting the pumping laser into the erbium-doped optical fiber And a single mode optical fiber used to obtain a nonlinear effect on light incident from the erbium-doped optical fiber, an optical fiber rotator for compensating for color dispersion of the single mode optical fiber, and to reflect light incident from the optical fiber rotator. And a dual mode optical fiber for compensating color dispersion for light incident from the optical fiber rotator and the mirror, and one mode converter for converting light incident from the optical fiber rotator and the mirror.

The method may further include converting the light incident to the optical fiber rotator from the LP01 mode, which is the basic mode of the optical fiber, to the LP11 mode in the mode converter, performing color dispersion compensation of the converted LP11 mode in the dual mode optical fiber, and the dual mode. Repeating the reflection of the light passing through the optical fiber in a mirror and performing color dispersion compensation through the dual mode optical fiber, reconverting the chromatic dispersion light into an LP11 mode to an LP01 mode in a mode converter, and performing the LP01 mode. The light is converted into the optical fiber rotator, characterized in that consisting of the step of color dispersion.

1 is a structural diagram of a mode locking fiber laser shown in order to explain a method for compensating color dispersion of a mode locking fiber laser using a distributed transition fiber.

2 is a structural diagram of a mode locking fiber laser shown to explain a method for compensating color dispersion of a mode locking fiber laser using a dual mode optical fiber.

3 is a structural diagram of a chromatic dispersion compensation ring optical fiber shown in order to explain the chromatic dispersion compensation method of the optical fiber laser using the optical rotator and the dual mode optical fiber according to the present invention.

* Explanation of symbols for main parts of the drawings

1, 11: erbium-doped optical fiber 2, 12: pumping laser

3, 13: dichroic optical fiber coupler 4: advertiser

5, 15: single mode optical fiber 6: dispersion transition optical fiber

7, 17: laser power 8, 18: optical fiber coupler

20: dual mode fiber 21: mode converter M1

22: mode converter M2 31: fiber optic rotator

32: mode converter M 33: dual mode fiber

34 mirror

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a structure of a mode-locked fiber laser shown to explain a color dispersion compensation method using a conventional dispersion transition optical fiber and a single mode optical fiber.

Dichroic optical fiber for injecting the erbium-containing optical fiber 1, the pumping laser 2 for optically pumping the erbium-containing optical fiber 1, which is a gain medium of the laser, and the pumping laser 2 to the erbium-containing optical fiber 1 Combiner 3, advertiser 4 for advancing light in one direction only, single mode optical fiber 5 used for obtaining nonlinear effects, and dispersion transition optical fiber for compensating for color dispersion of single mode optical fiber 5 6) and an optical fiber combiner 8 for extracting the laser output 7 from the resonator.

1.5 The chromatic dispersion value of the single mode optical fiber 5 at is about 20 psec / nm / km, and the chromatic dispersion value of the dispersion transition optical fiber 6 is about 0.1 to 1psec / nm / km. Therefore, in order to compensate for the color dispersion of the 10 m single mode optical fiber 5, a dispersion transition optical fiber 6 of about 20 to 200 m is required. Therefore, the repetition rate of the laser is bound to fall.

2 is a structure of a mode locked fiber laser with color dispersion compensation using a conventional dual mode optical fiber and two optical fiber mode converters. The other part is shown in FIG. 1, and is composed of a dual mode optical fiber 9 and optical fiber mode converters M1 and M2 (10 and 11) instead of the dispersion transition optical fiber used to compensate for color dispersion of the single mode optical fiber 5. have.

The optical fiber mode converter M1 10 converts the LP01 mode, which is the basic mode of the optical fiber, into the LP11 mode, and the mode converter M2 11 converts the LP11 mode back to the LP01 mode. 1.5 Since the color dispersion of TMF is about 100 ~ 1000 psec / nm / km, only 0.02 ~ 0.2m is needed to compensate for 1m of single mode fiber (5). Therefore, the resonator length becomes very short compared with the case of using the dispersion transition optical fiber, and thus the repetition rate can be increased. However, the disadvantage of this composition is that when using fiber mode mode converters M1 and M2, it is easy to convert LP01 mode, which is the basic mode of the fiber, to LP11 mode using the first mode converter M1, but the second mode converter M2 is LP11 mode. Must be converted back to LP01 mode, which is not easy.

FIG. 3 is a schematic diagram of a chromatic dispersion compensation ring type fiber laser comprising only the optical rotator, the dual mode optical fiber, and one optical fiber mode converter proposed in the present invention, which compensate for the disadvantages of the first and second embodiments.

Most structures are the same as in FIG. 2, where the difference from FIG. 2 is that instead of two mode and dual mode fiber optic fiber 31 and one mode converter 32, dual mode fiber 33 and mirror It consists of 34.

Here, the principle of the optical fiber rotator 31 will be described with reference to 1,2,3 shown in FIG.

When light enters 1, the light proceeds to 2, and when light enters 2, it proceeds to 3. On the other hand, the light incident to the third can not proceed in any direction. Thus, this case also serves as an optical isolator. The operating principle of the optical fiber rotator can be used to obtain the effect in FIG.

This part is explained in detail as follows. When the oscillated light enters No. 1 of the optical fiber rotator 31, the light proceeds to No. 2, and the mode converter 32 converts the LP01 mode, which is the basic mode of the optical fiber, to the LP11 mode. In the converted LP11 mode, color dispersion compensation is performed while passing through the dual mode optical fiber 33, and light is reflected from the mirror 34 to perform color dispersion compensation again via the dual mode optical fiber 33. The mode converter 32 converts the LP11 mode back to the LP01 mode. The light converted to the LP01 mode is incident to No. 2 of the optical fiber rotator 31 and proceeds to No. 3, and subsequent processes are the same as those of FIGS. 1 and 2.

The mode converter 32 used here converts the LP11 mode to the LP01 mode when the advancing direction converts the LP01 mode to the LP11 mode.

As described above, according to the present invention, by using an optical fiber rotator, a dual mode optical fiber and one mode converter in the resonator to reduce the optical pulses of the mode-locked optical fiber laser which is a strong light source to be used in ultra-fast optical transmission, to the conversion limit, There is an excellent effect to compensate for the main factor, color dispersion.

In addition, the optical fiber isolator used in FIGS. 1 and 2 is not required, and since the dual mode optical fiber is processed twice, a higher repetition rate can be obtained because the optical fiber is twice as short as in FIG.

Claims (6)

An erbium-doped optical fiber, which is a gain medium of a laser, a pumping laser for optically pumping the erbium-doped optical fiber, a dichroic optical fiber coupler for injecting the pumping laser into an erbium-doped optical fiber, and light incident from the erbium-doped optical fiber A single mode optical fiber used to obtain a nonlinear effect on the optical fiber, an optical fiber rotator for compensating for color dispersion of the single mode optical fiber, a mirror for reflecting light incident from the optical fiber rotator, and A ring-shaped fiber laser using an optical fiber rotator and a dual mode optical fiber, comprising a dual mode optical fiber for compensating color dispersion for incident light, and a mode converter for converting light incident from the optical fiber rotator and mirror. The optical fiber rotator of claim 1, wherein the optical fiber rotator proceeds to the second light when the light is incident on the first, and proceeds to the third light when the light is incident on the second, and the light incident on the third in any direction A ring-shaped fiber laser using an optical fiber rotator and a dual mode optical fiber, characterized in that it can not proceed. A method for compensating color dispersion of a ring-shaped laser beam using an optical fiber rotator and a dual mode optical fiber, the method comprising: converting light incident to the optical fiber rotator from a mode converter to a LP11 mode, which is a basic mode of an optical fiber, and converting the converted LP11 Performing color dispersion compensation on a dual mode optical fiber, reflecting light passing through the dual mode optical fiber from a mirror, and then performing color dispersion compensation on the dual mode optical fiber, and performing the color scattered light mode. Color conversion of an optical fiber rotator and a ring-shaped fiber laser using dual mode optical fibers, comprising converting the LP11 mode into the LP01 mode in the converter and injecting the light converted into the LP01 mode into an optical fiber rotator. Compensation method. The optical fiber rotator and the dual mode optical fiber according to claim 3, wherein when one of the advancing directions of the mode converter converts the LP01 mode to the LP11 mode, the LP11 mode is converted back to the LP01 mode when proceeding in the opposite direction. Color dispersion compensation method of ring type fiber laser using [4] The ring-type optical fiber using the optical fiber rotator and the dual-mode optical fiber according to claim 3, wherein the optical fiber rotator and the dual-mode optical fiber use a ring optical fiber laser to compensate for color dispersion in the optical fiber resonator to generate ultra-short optical pulses. Color dispersion compensation method of laser. The optical fiber rotator and the ring-shaped optical fiber using the dual mode optical fiber according to claim 3, wherein the optical fiber rotator and the optical fiber rotator do not use a separate optical fiber isolator for the color dispersion compensation method of the ring optical fiber laser using the optical fiber rotator and the dual mode optical fiber. Color dispersion compensation method of laser.