JP3218693B2 - Fiber optic 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 using a rare earth doped optical fiber.

[0002]

2. Description of the Related Art Some rare earth-doped optical fibers are excited by light of a specific wavelength and have gain. It is known that oscillation occurs when feedback is applied to a gain medium, and an optical fiber laser can also oscillate based on this principle. For example, it is described in the 1991 IEICE Spring National Convention C-316 and JP-A-2-43782.

Next, the configuration of a conventional optical fiber ring laser will be described with reference to FIG. In FIG. 2, reference numeral 21 denotes an excitation light source, 22 denotes a wavelength division multiplexed optical fiber coupler (hereinafter, simply referred to as an optical coupler), and 24 denotes a rare earth-doped optical fiber (hereinafter, referred to as an optical coupler).
It is simply called an optical fiber. ) And 26 are fiber type optical isolators and 28 is an output plug.

The light of wavelength λa emitted from the excitation light source 21 passes through the optical coupler 22 and then enters the optical fiber 24,
The optical fiber 24 is excited. Pumped optical fiber 24
Emits spontaneous emission light in the gain wavelength band Δλ. The emitted light in the wavelength band Δλ is converted into a fiber type optical isolator 26 → an optical coupler 22 → an optical fiber 24 for limiting the traveling direction of the light.
The optical fiber 24 which is a gain medium is optically fed back and oscillates. A part of the laser-oscillated light is output through an optical coupler 22 to an output plug 28
Taken out of

[0005]

In FIG. 2, a polarization-independent fiber-type optical isolator 26 is used to limit the traveling direction of light in a wavelength band Δλ around an optical loop. The fiber type optical isolator 26 has a large transmission loss of about 1.5 dB, and increases the loss of the optical loop. The loss of the optical loop according to FIG.
5 dB, about 0.5 dB in crosstalk of optical coupler 22, 3
It is 0.3 dB at each of the optical fiber fusion parts, which is about 3 dB in total. Optical coupler 2 for extracting output light
Excluding about 0.5 dB due to the crosstalk of 2, the loss of the optical loop without taking the extraction efficiency into account is about 2.5 dB. In addition, the fiber-type optical isolator 26 has a large shape, and the optical fiber ring laser cannot be downsized.

In FIG. 2, since the crosstalk of the optical coupler 22 is used, light in the wavelength band Δλ leaking from the optical coupler 22 is extracted as an output. The optical coupler 22 includes the excitation light source 21.
From the optical fiber 24. The role of efficiently guiding the light of the wavelength λa incident from the optical fiber 24 to the optical fiber 24, and returning the light of the wavelength band Δλ incident from the fiber type optical isolator 26 into the optical loop.
Also serves to provide optical feedback to the About 10% of the light in the wavelength band Δλ that goes around the optical loop leaks to the output plug 28 side, and this becomes output light. Due to the nature of the optical coupler 22, the output light extracted from the output plug 28 has a wavelength band Δ
about 10% of the light at λ.

According to the present invention, the output light of the excitation light source 1 is put into an optical loop composed of an optical filter, an optical fiber, a polarizing beam splitter, an optical isolator and a quarter-wave plate, and the light separated by the polarizing beam splitter is output. The objective is to provide a compact, low-cost, high-output optical fiber ring laser using light.

[0008]

According to the present invention, there is provided an excitation light source for emitting light having a wavelength of λa.
Excited by the incident light of the excitation light source 1
Rare earth additive that emits spontaneously emitted light in the gain wavelength band Δλ
Additive fiber 4, the excitation light source 1 and the optical fiber 4
Outgoing light from the
A plurality of lenses 2a, 2b, 2c incident on the optical fiber 4 are provided.
The optical fiber ring laser obtained, wherein the lenses 2a, 2
b, 2c, the wave from the excitation light source 1
Output light having a length λa, and a wavelength band Δλ from the optical fiber 4.
And the light having the wavelength λa and the wavelength band Δ
one of the light of λ is reflected and the other
To combine the light having the wavelength λa and the light having the wavelength band Δλ.
An optical filter 3, an output light of the optical fiber 4 as an input, a polarization beam splitter 5 for splitting a first parallel light and a second parallel light of linear polarization, and an optical isolator having the first parallel light as an input 6 and a quarter-wave plate that receives the output light of the optical isolator 6 as input and converts the first parallel light into circularly polarized parallel light.
7 and is provided, placed the output light of the quarter-wave plate 7 in the optical filter 3, the output light of the light and the quarter-wave plate 7 of the pumping light source 1 and combined by the optical filter 3 Through the lens 2b
While being incident on the optical fiber, the second parallel light is extracted as output light.

[0009]

Next, the configuration of an optical fiber ring laser according to the present invention will be described with reference to FIG. 1 is an excitation light source, 2
a to 2d are lenses, 3 is an optical filter, 4 is an optical fiber, 5 is a polarizing beam splitter, 6 is an optical isolator,
7 is a 1/4 wavelength plate, 8 is an output plug, and 11 to 15 are parallel lights.

In FIG. 1, light emitted from an excitation light source 1 having an oscillation wavelength λa is converted into a parallel light 11 by a lens 2 a and is incident on an optical filter 3. The optical filter 3 transmits light having a wavelength λa and reflects light having a wavelength band Δλ. The parallel light 11 that has passed through the optical filter 3 is condensed by the lens 2b, is incident on the optical fiber 4, and excites the optical fiber 4. The pumped optical fiber 4 emits spontaneous emission light in the gain wavelength band Δλ.
The emitted light in the wavelength band Δλ is converted into parallel light 12 by the lens 2 c and is incident on the polarization beam splitter 5. The parallel light 12 is split into parallel light 13 and parallel light 15 by the polarization beam splitter 5. The parallel light 13 and the parallel light 15 are each linearly polarized light.

The parallel light 13 is input to the optical isolator 6, and the output of the optical isolator 6 is incident on the quarter-wave plate 7. The quarter-wave plate 7 converts the parallel light 13 into a parallel light 14 of circular polarization. The parallel light 14 is reflected by the optical filter 3, is multiplexed on the same optical axis as the parallel light 11 from the excitation light source 1, is condensed by the lens 2b, and is incident on the optical fiber 4 again.

As described above, the light in the wavelength band Δλ emitted from the optical fiber 4 enters the optical isolator 6 from the polarization beam splitter 5, and enters the 光 wavelength plate 7 from the optical isolator 6.
And enters the optical filter 3 from the quarter-wave plate 7 and again goes around the optical loop entering the optical fiber 4.
Is subjected to optical feedback and oscillates.

The optical filter 3 reflects the light of the wavelength λa and transmits the light of the wavelength band Δλ. The optical filter 3 multiplexes the excitation light of the wavelength λa and the light of the wavelength band Δλ that goes around the optical loop. You may. Further, the positions of the polarization beam splitter 5 and the quarter-wave plate 7 may be interchanged, the direction of the optical isolator 6 may be reversed, and the traveling direction of the light in the wavelength band Δλ around the optical loop may be reversed.

The quarter-wave plate 7 converts the light in the wavelength band Δλ for applying optical feedback to the optical fiber 4 into circularly polarized light. by this,
When circularly polarized light propagates inside the optical fiber 4 and the emitted parallel light 12 is split into the parallel light 13 and the parallel light 15 by the polarizing beam splitter 5, the ratio can be made approximately 1: 1. That is, the output light that can be extracted to the output plug 8 is about 50% of the light in the wavelength band Δλ propagating through the optical loop.

The parallel light 13 of the parallel light 13 and the parallel light 15 separated by the polarization beam splitter 5 is
Return to. The parallel light 13 is linearly polarized light and passes through a normal polarization-dependent optical isolator 6 with a low loss of 0.5 dB or less. Parallel light 13 passing through optical isolator 6
Is converted into a circularly-polarized parallel light 14 by the quarter-wave plate 7, and then enters the optical fiber 4 to perform optical feedback.

At this time, the loss of the optical loop is such that the output light is reduced by 50
%, About 3 dB by the polarizing beam splitter 5, about 0.5 dB by the optical isolator 6, and the coupling loss between the optical fibers, the transmission loss of the quarter-wave plate 7, and the reflection loss of the optical filter 3. About 1dB, Total about 4.5d
B. Here, excluding about 3 dB by the polarization beam splitter 5 for extracting the output light, the loss of the optical loop in which the extraction efficiency is not taken into account is about 1.5 dB, which is an improvement of about 1 dB as compared with the prior art. Book as above
In the present invention, the pump light source 1 and the optical fiber 4
The outgoing light is converted into parallel light by the lenses 2a and 2c.
In the optical system, an optical filter 3, a polarizing beam splitter 5,
An optical isolator 6 and a quarter-wave plate 7 are arranged. You
That is, optical systems other than the optical fiber 4 are arranged on the spatial light.
Optical coupler and optical fiber type
No element is required, and loss in these parts
Can be reduced. For example, an optical isolator
From the fiber type optical isolator with large insertion loss
The loss is reduced by replacing the optical isolator 6
Can be reduced. In addition, the polarization beam splitter 5
Is used, the spatial light from the optical fiber 4
The emitted light can be divided into feedback light and output light.
At this time, the parallel light beams
Since it becomes linearly polarized light, it is a polarization-dependent spatial optical isolator.
Data 6 can be used. That is, the polarized beam
By using splitter 5, output and feedback on spatial light
Can separate light into light and use polarizing plates, etc.
At least use a polarization-dependent spatial optical isolator 6
can do. Conventionally, rare earth doped optical fiber
The oscillation light in 4 is linearly polarized light,
Linear polarization fluctuates due to external factors
Although it was difficult to obtain the power, using the 1/4 wavelength plate 7
By using circularly polarized light, a polarizing beam splitter 5 can be used.
To obtain a stable output when extracting output light.
Wear.

[0017]

Next, an embodiment of FIG. 1 will be described. Excitation light source 1
A semiconductor laser module with an oscillation wavelength of 1.48 μm and an optical output of 10 mW to 100 mW is used for the optical filter 3.
An interference filter that transmits light in the 1.48 μm band and reflects light in the 1.55 μm band is used. An erbium-doped optical fiber is used for the optical fiber 4, and 1.55 μm is used for the optical isolator 6.
Use the polarization dependent type of the band.

The light in the 1.48 μm band from the excitation light source 1 is converted into parallel light 11 by the lens 2a, passes through the optical filter 3, and is coupled to the erbium-doped optical fiber by the lens 2b. 1.
Erbium-doped optical fiber pumped by 48μm light
It emits light in the 1.55 μm band. The outgoing light in the 1.55 μm band from the erbium-doped optical fiber is converted into parallel light 12 by the lens 2c, and the polarization beam splitter 5 is placed in front thereof. The output from the polarization beam splitter 5 is a parallel light 13 and a parallel light 15
The parallel light 15 is condensed by the lens 2 d and guided to the output plug 8.

The parallel light 13 passes through the optical isolator 6 whose polarization plane is adjusted so as to minimize the transmission loss, and is incident on the quarter-wave plate 7. The quarter-wave plate 7 converts the parallel light 13 into a circularly polarized parallel light 14 by adjusting the optical axis of the crystal. The parallel light 14 is reflected by the optical filter 3, is coupled again to the erbium-doped optical fiber, and performs optical feedback, and oscillates in the 1.55 μm band.

[0020]

According to the present invention, the output light of the excitation light source is put into an optical loop composed of an optical filter, an optical fiber, a polarizing beam splitter, an optical isolator, and a quarter-wave plate.
Since the light separated by the polarization beam splitter is used as the output light, a polarization-dependent optical isolator that is smaller and less expensive than a fiber-type optical isolator can be used as the optical isolator, and the loss of the optical loop is improved by 1 dB. can do. Also, about 50% of the light in the wavelength band Δλ propagating through the optical loop can be extracted as output light from the split output of the polarizing beam splitter. As described above, in the present invention,
Is a lens for emitting light from the excitation light source 1 and the optical fiber 4
2a and 2c make parallel light, and this parallel light system
Filter 3, polarization beam splitter 5, optical isolator
A 6, 1/4 wavelength plate 7 is provided. That is, the optical fiber
Optical systems other than Iva 4 are arranged on the spatial light,
Optical couplers and optical fiber type optical elements
And reduce losses in these areas.
Can be. For example, if an optical isolator is
Spatial light type optical eye from high fiber type optical isolator
The loss can be reduced by replacing the
it can. Also, the use of the polarizing beam splitter 5
Return light from the optical fiber 4 in the spatial light for feedback
And output.
The row lights are linearly polarized light orthogonal to each other.
In this case, a polarization-dependent spatial optical isolator 6 is used.
Can be That is, the polarization beam splitter 5 is
By using it, the light is separated for output and return on the spatial light.
Polarization without using a polarizing plate, etc.
Dependent spatial type optical isolator 6 can be used
You. Conventionally, the oscillation light in the rare earth-doped optical fiber 4 is
Although it is linearly polarized light, external factors added to the optical fiber 4
The linearly polarized light fluctuates to obtain a stable output.
Difficult, using a quarter-wave plate 7 to make circularly polarized light
Output light is extracted using the polarization beam splitter 5.
In this case, a stable output can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical fiber ring laser according to the present invention.

FIG. 2 is a configuration diagram of a conventional optical fiber ring laser.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 excitation light source 3 optical filter 4 optical fiber (rare-earth doped optical fiber) 5 polarization beam splitter 6 optical isolator 7 1/4 wavelength plate

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01S 3/00-3/30

Claims (1)

(57) [Claims] An excitation light source for emitting light having a wavelength of λa;
Excitation light is emitted by the excitation light source (1).
Rare earths that emit and emit spontaneous emission in the gain wavelength band Δλ
The doped optical fiber (4), the excitation light source (1) and the optical fiber
The light emitted from the laser (4) is made parallel light, and these parallel lights are collected.
A plurality of lenses (2a,
2b, 2c), and in the system of parallel light by the lens (2a, 2b, 2c) , the output light of the wavelength λa from the excitation light source (1), Light
The output light of the wavelength band Δλ from the fiber (4) is incident, and
One of the light of the wavelength λa and the light of the wavelength band Δλ
The light of wavelength λa is reflected and transmitted through the other light.
And an optical filter (3) for multiplexing light in the wavelength band Δλ, and an output light of the optical fiber (4) as an input, and a first linearly polarized light.
Polarizing beam splitter for splitting parallel light and second parallel light
(5), an optical isolator (6) having the first parallel light as an input, and an output light of the optical isolator (6) as an input and converting the first parallel light into a circularly polarized parallel light. 4 wavelength plate (7) and is provided with al
Is, the quarter-wave plate outputs light (7) placed above the optical filter (3), the light and the quarter-wave plate of the excitation light source 1 output light (7)
The light is combined by the optical filter (3) and passes through the lens (2b).
An optical fiber ring laser , wherein the second parallel light is extracted as output light while being incident on the optical fiber.