JP2001127363A - Ase light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of the parts of an ASE light source. SOLUTION: With one end of an Er-added optical fiber 30, a reflecting mirror 32 is connected, and with the other end of the fiber 30, an optical isolator 34 for preventing any incident light from the external is connected. Between the Er-added optical fiber 30 and the optical isolator 34, a WDM coupler 38 for introducing into the Er-added optical fiber 30 an excitation light outputted from an exciting semiconductor laser 36 is interposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
ASE with wide emission wavelength range over 1.62 μm band
(Amplified Spontaneous Emi
session) light source.

2. Description of the Related Art An ASE light source in the 1.52 to 1.62 μm band is disclosed in S.A. P. Parry, R .; DiMuro,
K. J. Cordena, A, Robbinso
n, S. J. Wilson and N.W. E. FIG. Jo
lley: 'High power, 80 nm opt
ical noise source usinga
single Erbium doped silic
a fiber ', Optical Amplifier
rs and Their Application
s, Techn. Dig. 128 / TuD3-
1, July 27-29, 1998, Colorado
It is described in. The configuration and operation will be briefly described with reference to FIG.

[0002] WDM couplers 12 and 14 are disposed on both sides of an Er-doped quartz fiber 10, and one WDM coupler 12 has a 0.98 μm band semiconductor laser 1 for excitation.
6, and the other WDM coupler 14 is connected to a 1.48 μm band semiconductor laser 18 for excitation. That is, E
The r-doped quartz fiber 12 is 0.98 μm from one side.
Excitation is performed with the laser light in the band, and the other side is excited with laser light in the 1.48 μm band. One end of the Er-doped quartz fiber 10 is open, and the other end is connected via an optical isolator 20 to an optical element or an optical fiber into which ASE light is to be introduced.

When an Er-doped fiber is excited by pump light, if the product of the Er concentration and the fiber length is small, ASE light in the 1.52 to 1.56 μm band called the C band is obtained. 1.57 called band
The phenomenon of obtaining ASE light in the 1.62 μm band is well known. This apparatus uses two excitation light sources so that ASE light in both the C band and the L band can be obtained with one fiber. Er doped in the quartz fiber 10 is an ordinary ED for optical amplification.
The concentration is higher than F (excitation light absorption is about 14 dB / m), and the length of the fiber 10 is as long as 51 m.

[0004] Such a long fiber 1 having a high Er concentration is used.
When 0 is excited from the front, 1.57 μm to 1.62 μm
An ASE light in a band (L band) is generated and can be extracted from the fiber 10. On the other hand, the 1.48 μm band semiconductor laser 18 excites the Er-doped fiber 10 behind the fiber 10, that is, in the direction traveling in the direction opposite to the target output light. In the backward pumping, even if the fiber 10 has a high Er concentration and is long, strong pumping light exists at the output end of the fiber 10, so that 1.52 .mu.m-1.
ASE light in the 56 μm band (C band) can be efficiently extracted. That is, ASE light in the 1.52 to 1.56 μm band (C band) can be obtained by backward excitation of 1.48 μm.

[0005] Thus, as a whole, 1.52 to 1.52
ASE light in a wide band of 1.62 μm band (C band and L band) can be obtained.

US Pat. No. 4,938,556 discloses a stronger ASE by using an optical coupler and a reflecting mirror.
A method for obtaining light is described. However, no means for expanding the wavelength band of the ASE light is described. U.S. Pat. No. 5,185,749 describes a method in which a three-level laser element is used as a light emitting material to obtain a quantum efficiency of 50% or more. However, there is no description of means for expanding the wavelength band of the ASE light.

[0007]

The conventional ASE light source is
In order to widen the emission wavelength range from 1.52 to 1.62 μm, two pumping semiconductor lasers 16 and 18 and two W
DM couplers 12 and 14 are required. Also, Er
The doped silica fiber 10 had to be as long as 51 m. Therefore, the conventional example has a disadvantage that it is expensive.

Therefore, an object of the present invention is to present a cheaper ASE light source.

Another object of the present invention is to provide an ASE light source capable of covering a wide wavelength range with a smaller number of components.

[0010] The present invention further provides a semiconductor laser for excitation and W
It is intended to present an ASE light source that requires only one DM coupler each.

Another object of the present invention is to provide an ASE light source that can shorten the optical amplification fiber.

[0012]

An ASE light source according to the present invention includes an optical transmission medium including a light emitting material that is a three-level laser element, and an excitation light source that generates excitation light that excites the light emitting material to emit light. And an optical coupler that introduces, from one side of the optical transmission medium, the excitation light output from the excitation light source into the optical transmission medium, and a light that is disposed on the other side of the optical transmission medium and outputs from the optical transmission medium. And a reflection mirror for returning the light to the optical transmission medium.

The ground state absorption (g) of the light that is excited by the excitation light to generate a luminescent material is included.
round state absorption (hereinafter abbreviated as GSA). ) Is reflected by the reflection mirror, re-enters the transmission medium, and becomes ASE light from one side of the optical transmission member together with the short-wavelength light traveling in the opposite direction to the excitation light. Output to the outside. By transmitting light in a long wavelength band twice through an optical transmission medium, ASE light in a long wavelength band can be generated even if the optical transmission medium is short.

An excitation light is introduced from one side of the optical transmission medium, and C-band ASE light having large amplification gain and GSA is provided.
Both the amplification gain and the GSA generate light in two wavelength bands of ASE light in the L band, which are small.

The length of the optical transmission medium, the amount of the light-emitting material added, and the intensity of the excitation light are adjusted so that at least a part of the optical transmission medium is attenuated for C-band light and amplified for L-band light. ASE of these two wavelength bands
Light can be output almost uniformly. This allows
ASE light in a wide wavelength band can be easily obtained.

By providing an optical isolator for preventing return light to the optical transmission medium, laser oscillation can be suppressed, and higher output ASE light can be obtained.

By providing a light intensity adjusting member for adjusting the intensity distribution with respect to the wavelength of light output from the optical transmission medium to the outside, the wavelength distribution of the ASE light can be made more uniform. In addition, it becomes possible to obtain a stable quality ASE light source by absorbing variations in optical components. The light intensity adjusting member is the same as the optical transmission medium or a gain equalizing filter using an optical multilayer film. In the former case, the number of components to be prepared is reduced, and in the latter case, good characteristics are easily obtained as the light intensity distribution with respect to the wavelength of the output light.

The optical transmission medium is made of, for example, an optical fiber to which a luminescent material is added. Fluoride fibers have the advantage that the fiber length can be significantly reduced. The fluoride fiber is an ASE 1.52 to 1.62 μm band doped with Er.
In the case of a light source, since the wavelength dependence of the amplification gain is small, laser oscillation can be further suppressed and an ASE having a higher output can be obtained.
You can get light.

The luminescent material produces GSA, for example, Er.
And rare earth elements such as Tm.

[0020]

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

FIG. 1 is a schematic block diagram of a first embodiment of the present invention. In the present embodiment, the reflection mirror 32 is connected to one end of the Er-doped optical fiber 30 having a predetermined length, and the other end of the Er-doped optical fiber 30 is used to prevent laser oscillation due to light returning to the Er-doped optical fiber 30. For this purpose, an optical isolator 34 is connected.

The length and Er concentration of the Er-doped optical fiber 30 need to be adjusted optimally. The optimal length is some E
1.5 emitted when forward-excitation of r-concentration fiber
The ASE light intensity of the L band of 7 to 1.62 μm is about の of the fiber length at which the ASE light intensity becomes maximum. The concentration of Er and the fiber length are in inverse proportion. For example, in the case of a single mode fluoride fiber, when the Er concentration is 2000 ppm, a fiber length of 9 to 12 m is a suitable range.

A WD for introducing the pumping light output from the pumping semiconductor laser 36 toward the Er-doped optical fiber 30 is provided between the Er-doped optical fiber 30 and the optical isolator 34.
An M coupler 38 is provided. The wavelength of the semiconductor laser 36 for excitation may be 0.98 μm or 1.48 μm.

The operation of this embodiment will be described. The pumping light output from the pumping semiconductor laser 36 is supplied to the WDM coupler 3.
4 is introduced into the Er-doped optical fiber 30. The pumping light is attenuated as it propagates through the Er-doped optical fiber 30 toward the reflection mirror 32, during which the Er ions of the Er-doped optical fiber 30 are excited to generate both C-band and L-band light.

There are two types of light generated in the Er-doped optical fiber 30, light traveling toward the reflection mirror 32 and light traveling toward the optical isolator 34 in the opposite direction. In the following description, the direction in which light generated by the Er-doped optical fiber 30 travels toward the optical isolator 34 is referred to as a + z direction or a plus direction, and the direction toward the reflection mirror 32 is referred to as a −z direction or a minus direction.

In any of the plus and minus directions,
When the generated light propagates through the Er-doped optical fiber 30, the pump light is amplified if it is strong, and is attenuated if it is weak. This is a phenomenon that occurs because Er is a three-level laser element. That is, if the excitation light is strong, stimulated emission occurs due to the formation of population inversion, and if the excitation light is weak, attenuation by GSA occurs. However, amplification gain and GSA
Has a wavelength dependence, and as the wavelength becomes longer, the amplification gain is smaller, but it is possible to amplify even weak pump light. In the present invention,
By utilizing the wavelength dependence of amplification gain and GSA, ASE
Broadband light source is realized.

Of the light generated in the Er-doped optical fiber 30 and propagating in the negative direction, the long wavelength component is amplified in the Er-doped optical fiber 30, reflected by the reflection mirror 32, and returned to the Er-doped optical fiber 30. Incident. The light re-entering the Er-doped optical fiber 30 is
Is further amplified while propagating in the plus direction, and becomes ASE light having a long wavelength component. Light emitted from the Er-doped optical fiber 30 passes through the optical isolator 34 and is emitted to the outside.

On the other hand, light generated in the Er-doped optical fiber 30 and propagated in the plus direction from the beginning is amplified in the Er-doped optical fiber 30 to become ASE light having a strong short wavelength component, and is incident on the optical isolator 34. .

The 1.52 to 1.62 μm band light generated by Er ions in the Er-doped optical fiber 30 has C band (1.52 to 1.56 μm band) and L band (1.57 to 1.57 μm band).
(1.62 μm band) It can be considered to be divided into two wavelength bands.

The short-wavelength C-band light is characterized in that it has a large gain but a large attenuation due to GSA. The light propagating in the minus direction becomes weaker as the excitation light becomes weaker as it travels through the Er-doped optical fiber 30, so that it is rapidly attenuated by GSA, and is hardly output. However, the light propagating in the plus direction travels in the direction in which the intensity of the excitation light is high, and is thus amplified and emitted as ASE light.

The long-wavelength L-band light has a characteristic that the gain is small but the attenuation by GSA is small. Er
By appropriately setting the concentration and the fiber length, a portion close to the reflection mirror 32 where the excitation light intensity is weak can be an attenuation region for C-band light but an amplification region for L-band light. That is, for the L band, the fiber 30
Becomes the amplification region, so that the light propagating in the minus direction is reflected by the reflection mirror 32, strongly amplified while reciprocating through the Er-doped optical fiber 30, and emitted as ASE light.

By adjusting the Er concentration and the fiber length, the ratio of the light intensity in the C band and the L band can be changed.
For example, if the product of the Er concentration and the fiber length is increased so that an attenuating region is formed even for the L-band light, the intensity of the L-band light decreases and the intensity of the C-band light relatively increases. Conversely, when the product of the Er concentration and the fiber length is reduced so as to reduce the C band attenuation region, the C band light sharply increases.

The fiber length of the fiber 30 that can make the light intensities of the C band and the L band most uniform is such that the L band ASE light intensity emitted from the other side when the fiber having the same Er concentration is excited from one side is emitted. It is about 1/2 of the maximum fiber length. Since the Er concentration and the fiber length are inversely proportional, the fiber length may be shorter if the Er concentration increases. In the case of a single mode fluoride fiber, when the weight ratio of ErF ₃ is expressed in ppm, Er concentration (ppm) × fiber length (m) = 18,000-
24000 (ppm · m) is an appropriate range.

As described above, in the light generated in the Er-doped optical fiber 30, the light initially propagating in the minus direction is dominant in the L band, and the light propagating in the positive direction from the beginning is dominant in the C band. . The wavelength characteristics of light incident on the optical isolator 34 from the Er-doped optical fiber 30 are a combination of these. Wavelength characteristics of light incident on the optical isolator 34 from the Er-doped optical fiber 30, ie, L band and C
The band intensity ratio can be adjusted by the length of the Er-doped optical fiber 30 (and the amount of Er added and the excitation intensity).

The optical isolator 34 serves to prevent the Er-doped optical fiber 30 from oscillating by laser. Thereby, ASE light with higher output power can be obtained. If a low output power is sufficient, the optical isolator 34 may be omitted.

If it is desired to equalize the intensity ratio between the L band component and the C band component of the ASE light obtained in this embodiment, as shown in FIG. What is necessary is just to arrange | position the light intensity equalizer 40 which has a rate. The same components as those in FIG. 1 are denoted by the same reference numerals. The light intensity equalizer 40 is, for example, a gain equalizing filter using an optical multilayer film for flattening the gain of an optical fiber amplifier used in WDM transmission, or an Er-doped optical fiber similar to the Er-doped optical fiber 30. It consists of an optical fiber. In the latter case, the length of the Er-doped optical fiber depends on the amount of Er doping, but is about 0 to 2 m in the case of a quartz fiber,
It is expected to be about 0 to 1 m for fluoride fiber.

The light intensity equalizer 40 may be arranged between the optical isolator 34 and the Er-doped optical fiber 30 under the condition that no reflection causing laser oscillation occurs.

Although the luminous material is exemplified by Er, this is an example, and any three-level laser element can be used.

The ASE light source according to the present invention comprises an optical coupler,
It can be used to measure loss wavelength characteristics, polarization mode dispersion and polarization dependent loss of optical components such as optical isolators and optical fiber gratings, and can also be used as a noise source in system experiments. That is, the ASE light source according to the present invention can be used for measurement of various optical components and experiments of an optical wavelength division multiplexing communication system, and can greatly contribute to the optoelectronics and communication fields.

[0040]

As can be easily understood from the above description, according to the present invention, ASE light in a wider wavelength range can be obtained with a smaller number of parts and a simple structure than before.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a first embodiment of the present invention.

FIG. 2 is a schematic block diagram of a modified embodiment of the present invention.

FIG. 3 is a schematic configuration block diagram of a conventional example.

[Explanation of symbols]

 10: Er-doped quartz fiber 12, 14: WDM coupler 16: 0.98 μm band semiconductor laser 18: 1.48 μm band semiconductor laser 20: Optical isolator 30: Er-doped optical fiber 32: Reflection mirror 34: Optical isolator 36: For excitation Semiconductor laser 38: WDM coupler 40: Light intensity equalizer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Nakai 2-1-1-15 Ohara, Kamifukuoka City, Saitama Prefecture Inside Kadeidi Laboratory Co., Ltd. (72) Toshio Tani 2-1-1 Ohara, Kamifukuoka City, Saitama Prefecture No. 5 F072 AB09 AK06 JJ01 JJ08 KK07 KK30 PP07 RR01 SS01 YY17

Claims (10)

[Claims] 1. An optical transmission medium including a three-level laser element light emitting material, an excitation light source that generates excitation light that excites the light emitting material and emits light, and an excitation light source from one side of the optical transmission medium. An optical coupler that introduces the excitation light output from the optical transmission medium into the optical transmission medium; and a reflection mirror that is disposed on the other side of the optical transmission medium and returns the light output from the optical transmission medium to the optical transmission medium. An ASE light source characterized in that: 2. The ASE light source according to claim 1, further comprising an optical isolator for preventing light from entering the optical transmission medium from outside. 3. The optical transmission medium according to claim 1, further comprising a light intensity adjusting member that adjusts an intensity distribution with respect to a wavelength of light output from the one side of the optical transmission medium to the outside of the optical transmission medium. ASE light source. 4. The ASE light source according to claim 3, wherein the light intensity adjusting member has the same composition as the optical transmission medium. 5. The AS according to claim 3, wherein the light intensity adjusting member comprises a gain equalizing filter using an optical multilayer film.
E light source. 6. The ASE light source according to claim 1, wherein the optical transmission medium comprises an optical fiber doped with the luminescent material. 7. The ASE light source according to claim 1, wherein said luminescent material is made of a rare earth element. 8. The optical transmission medium according to claim 1, wherein the length of the light transmission medium, the amount of the light emitting material added, and the intensity of the excitation light are attenuated with respect to the light of the short wavelength side and the light of the long wavelength side in at least part of the optical transmission medium. The ASE light source according to claim 1, wherein the ASE light source is adjusted to amplify the ASE. 9. The ASE light source according to claim 8, wherein the luminescent material is Er, and the optical transmission medium is a single mode fluoride fiber. The 10. The length of the concentration and the optical transmission medium of the light-emitting material, when viewing the weight ratio of ErF ₃ in ppm, Er concentration (ppm) × fiber length (m) = 18000~
The ASE light source according to claim 9, wherein the ASE light source is 24000 (ppm · m).