JP2647590B2 - Multiwavelength oscillation erbium-doped fiber ring laser - 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 fiber ring laser, and more particularly to an erbium-doped optical fiber ring laser.

[0002]

2. Description of the Related Art With the development of frequency multiplexing optical communication in recent years, a light source having a stable frequency and a narrow spectral line width is required, and this light source is required simultaneously at many frequencies. Was. These oscillation wavelengths are desirably in the 1.5 μm band, which is a low loss region of the optical fiber.

[0003] The optical fiber ring laser has the advantage that it can oscillate with a narrow spectral line width because the optical resonator wavelength can be lengthened, and has the advantage that single mode oscillation becomes easy because of the traveling waveform type. Is thriving. Erbium-doped optical fiber (hereinafter referred to as EDF)
Some examples have been reported in which single mode oscillation was confirmed using a highly uniform gain medium as described above. However, there are no reports of simultaneous oscillation at multiple frequencies. Report of oscillation at three wavelengths (H. Schmuck et al., ECOC)
'91 TuB3-3 1991), but EDF
If the gain is not sufficiently flat with respect to wavelength, simultaneous oscillation is impossible as it is, and this report does not confirm simultaneous oscillation at three wavelengths. Although this report shows that the laser oscillates at a plurality of wavelengths using an optical spectrum analyzer, it has not been verified that the laser oscillates at the same time.

[0004]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an erbium-doped fiber ring laser which oscillates in a single longitudinal mode with a narrow spectral linewidth at a plurality of tunable oscillation wavelengths. .

[0005]

SUMMARY OF THE INVENTION The multi-wavelength oscillation erbium-doped optical fiber ring laser according to the present invention solves these problems, and comprises a common optical fiber path and a laser medium in the common optical fiber path. erbium doped optical fiber which is provided as the erbium-doped
An excitation light source for generating excitation light for exciting an optical fiber;
Injecting the excitation light into the erbium-doped optical fiber
An optical multiplexing unit, an optical fiber branch connected to the common optical fiber path, two or more individual optical fiber paths respectively connected in parallel to the common optical fiber path via the optical fiber branch, A narrow band-pass filter and an optical loss imparting unit respectively provided in a part or all of the optical fiber path, and each of the common optical fiber path and the two or more individual optical fibers is provided with an optical fiber ring resonator. It is characterized by having been formed.

[0006]

According to the multi-wavelength oscillation erbium-doped optical fiber ring laser of the present invention, laser oscillations of different wavelengths can be obtained from a plurality of optical fiber ring laser resonators using a single EDF as a common laser medium. . As a result, these multi-frequency oscillation outputs are integrated into one optical fiber and taken out. Since each resonator commonly uses one EDF as a laser medium, a simple configuration is efficient.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings, but the present invention is not limited to only the following embodiments.

In FIG. 1, a multi-wavelength erbium-doped optical fiber ring laser 1 according to the present invention includes an erbium-doped optical fiber (EDF) 2 and a dichroic mirror 4 receiving excitation light from an excitation light source 3 through a common optical fiber path 5. , And an isolator 6 is inserted into the common optical fiber path 5. The isolator 6 is connected to the EDF 2, and couplers 7 a are respectively provided at two portions of the common optical fiber path 5 not including the EDF 2. An optical fiber portion (a portion not including the EDF 2) between the couplers 7a is referred to as an individual optical fiber path 8a. On this individual optical fiber path 8a, a narrow band filter 9a and an attenuator 10a are inserted and connected.

The branch ends of these couplers 7a which are not connected to the individual optical fiber paths 8a are respectively connected to one of the branch ends of the second coupler 7b via optical fibers. A second individual optical fiber path 8b is formed. This individual optical fiber path 8
b, similarly, the narrow band filter 9b and the attenuator 1
0b is inserted and connected.

The branch ends of these couplers 7b which are not connected to the individual optical fiber paths 8b are respectively connected to one branch end of a third coupler 7c via an optical fiber. The fibers form a third individual optical fiber path 8c. Similarly, a narrow band filter 9c and an attenuator 10c are inserted and connected to the individual optical fiber path 8c.

Thus, the EDF 2, the dichroic mirror 4, the isolator 6, the coupler 7a,
The individual optical fiber paths 8b and 8c are connected in parallel as bypass paths to an optical system in which the narrow band filter 9a, the attenuator 10a, and the coupler 7a are connected by the common optical fiber path 5 (a part of which is the individual optical fiber path 8a). ing.
That is, three individual optical fiber paths 8a, 8b, and 8c are connected in parallel as portions of the optical fiber forming the optical fiber ring resonator that do not include the erbium-doped optical fiber.

The EDF 2 is excited by the excitation light from the excitation light source 3 via the dichroic mirror 4. The narrow-band filter 9a, 9b, 9c is Ri tunable filter der the pass wavelength is set differently from each other, these
In the transmission band of the optical filter laser oscillation. The attenuators 10a, 10b, 10c are adjustable, and by adjusting them to adjust the optical loss in each resonator,
The round optical loss is made to match the gain of the EDF with respect to the passing wavelength of each filter 9a, 9b, 9c, and as a result, the gain can be equivalently flattened with respect to the wavelength. As a result, simultaneous oscillation is enabled in each resonator, and the wavelength-multiplexed laser output is extracted as the optical output 11 from the branch end of one coupler 7a.

Since the gain spread is substantially uniform (homogeneous), the laser oscillation near each oscillation wavelength becomes a single mode. This optical spectrum line width is basically on the order of kilohertz like the line width conventionally obtained using a single erbium-doped optical fiber ring laser resonator.

With respect to such a basic configuration, frequency modulation or intensity modulation can be performed by using a phase modulator or an intensity modulator for the individual optical fiber paths 8a, 8b, 8c in each resonator. Due to the uniformity of gain, crosstalk occurs between each laser during low-speed intensity modulation,
There is no problem above 10 kHz. In addition, the modulation speed that can be applied to each of the oscillated lights is basically limited by the time required for circling the resonator. Therefore, in order to perform high-speed modulation, a laser resonator using an optical waveguide that can shorten the circumference of the resonator is suitable.

The case where two bypass paths are provided has been described above, but one bypass path (the number of resonators:
2) or three or more (the number of resonators: four or more). The number of effective individual optical fiber paths may be adjusted by intermittently turning on / off individual optical fiber paths connected in parallel by a switch (not shown).

FIG. 2 is a spectrum diagram of laser light oscillated by using the multi-wavelength oscillation erbium-doped optical fiber ring laser of the present invention. In this example, the number of resonators is set to 2 for theoretical confirmation, and the light loss of each resonator is controlled to obtain two oscillation spectra.

FIG. 3 shows laser outputs oscillating at different frequencies, respectively, extracted by a narrow band filter and displayed simultaneously on an oscilloscope. The maximum frequency of crosstalk of both oscillation intensities is about 1
It is determined to be 0 ms and is considered to be about 1 kHz or less. However, simultaneous oscillation was observed at a resolution of 1 ms / div which was higher than that, and it was confirmed that simultaneous oscillation was performed.
The simultaneous oscillation interval could be set in the range of 0.5 to 14 mm. As a result of observing the output during the simultaneous oscillation of two wavelengths with a swept optical spectrum analyzer (FSR 6 GHz, finesse> 6000, resolution <1 MHz), there is a mode jump near the oscillation wavelength of each optical fiber ring resonator, but at the same time a vertical mode Was not observed, and it was confirmed that a single mode was observed around each oscillation wavelength. It was also found that the line width was less than the resolution of the swept optical spectrum analyzer.

As described above, in the multi-wavelength oscillation erbium-doped optical fiber ring laser 1 according to the present embodiment, a single mode laser can be selected over a wide range in the vicinity of each oscillation wavelength and a plurality of lasers can be obtained simultaneously.

[0019]

As described above, the multiwavelength oscillation erbium-doped optical fiber ring laser of the present invention is a single mode laser that oscillates simultaneously at a plurality of frequencies that can be set over a wide range. The spectral line width of this light is considered to be extremely narrow, on the order of kilohertz. These can be individually modulated by a modulator placed inside the resonator, and the modulated light is frequency-multiplexed and output directly into one optical fiber. Therefore, there are many applications as a wavelength multiplexed light source having high coherence for communication and measurement. These oscillation wavelengths are highly effective because they are in the 15 μm band, which is a low loss region of the optical fiber.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic configuration of a multi-wavelength oscillation erbium-doped optical fiber ring laser of the present invention.

FIG. 2 is a spectrum diagram when two oscillation spectra are obtained by controlling the optical loss of each resonator.

FIG. 3 is a diagram illustrating two laser outputs oscillating at different frequencies, each extracted by a narrow-band filter, and drawn from images simultaneously displayed on an oscilloscope.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Multiwavelength oscillation erbium-doped optical fiber ring laser 2 Erbium-doped optical fiber 3 Excitation light source 4 Dichroic mirror 5 Common optical fiber path 6 Isolator 7a, 7b Coupler 8a, 8b, 8c Individual optical fiber path 9a, 9b, 9c Narrow band filter 10a , 10b, 10c Attenuator 11 Optical output

Claims (1)

(57) [Claims] 1. A common optical fiber path, an erbium-doped optical fiber provided as a laser medium in the common optical fiber path, and an excitation light for exciting the erbium-doped optical fiber.
A pump light source generated and injecting the pump light into the erbium-doped optical fiber.
Optical multiplexing means, an optical fiber branch connected to the common optical fiber path, two or more individual optical fiber paths each connected in parallel to the common optical fiber path via the optical fiber branch, A narrow band pass filter and an optical loss applying unit respectively provided in a part or all of the individual optical fiber paths, wherein an optical fiber ring resonator is formed by the common optical fiber path and each of the two or more individual optical fibers. A multi-wavelength oscillation erbium-doped optical fiber ring laser, each of which is formed.