JP2000124529A - Wide band light amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a wide band light amplifier having uniform gain spectra. SOLUTION: A wise band amplifier 200 has at least two sections of a first (common) section 202 and a second (branch) section 204. After a light signal enters the common section 202, the light signal is branched into two (more than two) independent subbands. These independent subbands are respectively sent to the separate branches of the branch section 204 and after the subbands are amplified there, they are recombined to turn into an output signal. In concrete terms, the signal is branched into a short-wavelength (S) band, an intermediate-wavelength (M) band and a long-wavelength (L) band. These bands respectively correspond to each branch of the section 204. In am embodiment, the S band is in a range of 1510 to 1525 nm, the M band is in a range of 1525 to 1565 nm and the L band is in a range of 1565 to 1610 nm. It is also possible that one branch or a plurality of branches is or are further made to branch to realize a hybrid structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the field of optical communications, and more particularly, to a broadband optical amplifier.

[0002]

BACKGROUND OF THE INVENTION There is a great interest in using rare earth doped fiber optic amplifiers to amplify optical signals used in communication systems and networks. Such rare earth doped fiber amplifiers have been found to be cost effective, exhibit low noise, provide a relatively wide bandwidth that is not polarization dependent, have very low crosstalk, and have insertion at the relevant operating wavelength. Low loss. As a result of these favorable properties, rare earth doped fiber amplifiers (eg, erbium doped fiber amplifiers (EDFs)
A) is replacing the current optoelectronic regenerator in many lightwave communication systems, especially wavelength division multiplexing (WDM) optical communication systems and networks.

To increase the capacity of such WDM optical communication systems and networks, it has generally been shown that it is preferable to provide as many wavelength division multiplexing (WDM) optical channels as possible in a given WDM system. ing. As will be appreciated, such a "dense"
In order to realize a WDM (Dense WDM) optical system and network, a broadband optical amplifier is required.

As shown in FIG. 1, the total possible gain spectrum of an EDFA is very wide. However, unfortunately, ED
The only gain bandwidth available in FA is about 10 nm, which limits the use of this broad spectrum in DWDM systems.

[0005] Of course, as is known to those skilled in the art, the gain bandwidth of this EDFA can be reduced from about 1525 nm to 1 by using a gain equalizing filter (GEF).
It can be extended to about 40 nm up to 565 nm (for example, see the following literature).・ AK Srivistava, JB Judkins, Y. Sun, L. Garr
ett, JL Zyskind, JW Sulhoff, C. Wolf, RM D
erosier, AH Gnauck, RW Tkach, J. Zhou, RP
Espindola, AM Vengsarkar, and AR Chraplyvy,
"32 x 10 Gb / s WDM Transmission Over 640 km Using
Broad Band Gain-Flattened Erbium-Doped Silica Fibe
r Amplifiers ", Proc. OFC (Dallas, Texas, USA) p
p.PD18 (February 16-21, 1997) ・ Y. Sun, JB Judkins, AK Srivastava, L. Garr
ett, JL Zyskind, JW Sulhoff, C. Wolf, RM D
erosier, AH Gnauck, RW Tkach, J. Zhou, RP
Espindola, AM Vengsarkar, and AR Chraplyvy,
"Transmission of 32 WDM 10 Gb / s Channels Using Br
oad Band, Gain-Flattened Erbium-Doped Silica Fiber
Amplifiers ", IEEE Photon Tech. Lett., 1997 ・ PF Wysocky, JB Judkins, RP Espindola,
M. Andrejco, AM Vengsarkar, and K. Walker, "Erb
ium Doped Fiber Amplifier Flattened Beyond40 nm Us
ing Long-Period Grating ", Proc. OFC (Dallas, Texas, USA) pp. PD2 (February 16-21, 1997)

As can be seen with reference to FIG.
The DFA gain is in the region below 1525 nm and 156
It falls sharply in the region of 5 nm or more. As a result, EDFA
It is not practical to further increase the gain bandwidth of the GEF. Because such an approach requires an unacceptably large amount of pump power, and correspondingly a large number of GEFs to maintain an acceptable low noise figure.

According to the prior art, 1.57 to 1.60 μm
A large optical gain is obtained in the wavelength range of m (for example, see the following document).・ JF Massicott, JR Armitage, R. Wyatt, BJ
Ainslie, and SPCraig-Ryan, "High Gain, Broadba
nd 1.6 μm Er ³⁺ Doped Silica Fiber Amplifier ", Ele
c. Lett., Vol.26, No.14, pp.1038-1039, September 1
990 ・ JF Massicott, R. Wyatt, and BJ Ainslie, "L
ow Noise Operation of Er ³⁺ Doped Silica Fiber Ampl
ifier Around 1.6 μm ", Elec. Lett., Vol. 26, No. 20,
pp.1645-1646, September 1990

Further, new doping materials have been used to improve erbium-doped fibers in the wavelength range from 1.53 to 1.56 μm. In particular, fluoride ED
F has been shown to further increase the gain, and
There have been reports showing that telluride EDF is highly promising (eg, A. Mori, Y. Ohishi, M. Yamada, H. On
o, Y. Nishida, K. Oikawa and S. Sudo, "1.5 μm Broa
dband Amplificationby Tellurite-Based EDFA's ", Pro
c. OFC (Dallas, Texas, USA) pp.PD1 (February 1997)
16-21), see).

[0009]

However, despite this perspective, the gain spectrum of these EDFs is generally non-uniform, and other important properties such as mechanical stability are poorly understood. Not.

Therefore, as is apparent from the above background,
There is a need for an alternative approach to developing broadband optical amplifiers.

[0011]

According to the present invention, a broadband optical amplifier having a split (split) band structure is realized. The broadband amplifier has at least two sections, a first (common) section and a second (branch) section. In operation, the optical signal enters the common section and is then split into two (or more) independent subbands. Each of these independent subbands is sent to a separate branch of the second (branch) section, where it is for example amplified and then recombined into an output signal.

According to the invention, each branch of the branch section is optimized for the subbands passing through it. In addition, one or more branches can be further branched to achieve a hybrid structure exhibiting other properties.

[0013]

FIG. 2 shows the basic principle of a broadband optical fiber amplifier according to the present invention. The broadband amplifier 200 is basically divided into two sections, a first (common) section 202 and a second (branch) section 204. Briefly, the optical signal is transmitted to the broadband optical amplifier 2.
00 enters the common section 202. Then the signal
It is branched into two (or more) independent bands, each of which is sent to a separate branch of the second (branch) section 204. In parallel, after these independent bands have been amplified in these separate branches,
Recombination results in an output signal. Optionally, the recombined output signal can be further amplified or processed at output section 206.

On the basis of this principle, a broadband optical amplifier is realized. Still referring to FIG. 2, the optical signal enters the broadband optical amplifier 200 through the input port 208 and exits the output port 266. Output port 266 is “downstream” of input port 208. Elements 210-212 are optical isolators. Elements 220-230 are erbium-doped fiber amplifiers. Elements 240-243 are wavelength selective fiber optic couplers (WDMs) for combining pump radiations 244-247. Elements 231 to 238 are GEFs. Element 260 is an attenuator. Element 250 is a demultiplexer. Element 25
1 is a multiplexer. Optical isolators, attenuators,
GEFs, WDMs, multiplexers, and demultiplexers are commonly known and some are commercially available. As is known to those skilled in the art, optical isolators may optionally be provided upstream and downstream of the EDFA, respectively.

As can be seen from FIG. 2, all input optical signals pass through the common section 202. Here, the optical signal is
It is also possible to amplify before branching. In this exemplary configuration, the signal is split into three subbands under the action of demultiplexer 250. Specifically, the signal is:
It is divided into a short wavelength band (S (short) band), an intermediate wavelength band (M (middle) band; also called a normal band (C (conventional) band)) and a long wavelength band (L (long) band). These each correspond to a respective branch of the branch section 204. As is evident, splitting the optical signal into a plurality of bands in this manner allows these bands to be separately amplified in parallel.

Of course, as will be appreciated by those skilled in the art, the sub-bands into which the optical signal is split are not fixed but can be varied and can be described by their wavelength ranges. However, in this example, the S band is 15
10 nm to 1525 nm, and the M band is 15 nm.
25 nm to 1565 nm, and the L band is 15 nm.
It is assumed to be in the range of 65 nm to 1610 nm. Of course, these ranges can vary depending on the particular EDF, design and application.

In general, common section 202 is strongly inverted to achieve a low noise figure. Furthermore, S
The inversion level of the EDF in the band is to achieve high gain and high output power in this sub-band,
Kept high. Also, this produces strong gain variations across multiple signal channels, so using multiple GEFs with EDFs simultaneously achieves substantially flat gain and low noise figure.

Similarly, additional design is considered for the remaining subbands shown in the configuration of the present embodiment. Specifically, the M-band is designed to achieve high power, flat gain and low noise figure by using GEF and one or more stages. In the L band, the inversion level must be kept at a low level, and it is preferable to use GEF to improve the flatness of the gain. Similarly, multiple stages are used to increase the output power for this subband.

The multiplexing (MUX) and demultiplexing (DEMUX) of optical signals, represented by reference numerals 250 and 251 respectively in FIG.
Alternatively, it can be realized using various methods such as a combination of a fiber grating and a circulator. As will be appreciated, the width of the waveguide band between two adjacent sub-bands is mainly due to the MUX and DE used
It is determined by the sharpness of the MUX and the accuracy of the GEF.

Numerical simulations were performed using the broadband optical amplifier configuration of FIG. 2 where the entire optical spectrum was divided into three subbands. In this simulation, six GEFs 231 to 236 were used for the S band. All pump lasers 245 to 247 operate at 980 nm and S
The pump power in the band was 26 dBm and the pump power in the M and L bands was 20.8 dBm. In the S band, high pump power is generally required to generate a high population inversion in the EDF.

FIG. 2 obtained from this simulation
FIG. 3 shows the output power spectrum for the exemplary configuration of FIG. From this figure, it can be seen that high output power is a characteristic of an amplifier constructed according to the present invention.

FIG. 4 is a schematic diagram of an alternative embodiment of a wideband amplifier configuration in accordance with the principles of the present invention. The illustrated configuration has a common section 402 and a branch section 404 having two branches. Circulator (rotor) 46
Perform DEMUX and MUX before and after branch section 404 using 0-461 and broadband Bragg fiber gratings 450-451. This exemplary wideband amplifier configuration uses one-stage amplification in the M band and L
Perform two-stage amplification on the band. All pumps are 980
work in nm.

Two signals, a 1530 nm signal in the M band and a 1592n in the L band
The m signal was used as the saturation light source. Total input power is-
At 4.7 dBm, the total output power was 18.3 dBm, resulting in a gain of 23 dB. FIG. 5 shows the output spectrum of this broadband amplifier configuration.

From the foregoing, it will be readily appreciated by those skilled in the art that various modifications of the branch band arrangement of the present invention are possible. In particular, depending on the gain and loss spectrum of the EDF utilized, 2
It is possible to split one, three or more subbands. Further, although only two sections are used in the configuration of the embodiment of the present invention, more sections and a hybrid structure can be realized within the principle of the present invention.

FIG. 6 shows such a hybrid broadband amplifier configuration. Similar to the configuration described above, the hybrid broadband amplifier 600 schematically illustrated in FIG. 6 basically comprises two sections: a first (common) section 602 and a second (branch) section.
It is divided into sections 604. Branch section 604
Has several branches through which independent branch subbands of the optical signal pass. Further characterizing this hybrid broadband amplifier configuration is that branch section 604 is further branched (hybrid).
Section 606 is included. Hybrid section 6
At 06, one (or more) branches further diverge into several branches.

The optical signal enters the common section 602 of the broadband optical amplifier 600 and is split by the DEMUX 650 into two independent subbands. Each of these independent subbands is sent to a separate branch of the second (branch) section 604. The signal passing through the branch above branch section 604 is further split by DEMUX 651 into independent subbands. In parallel, all independent sub-bands are amplified as needed in these branches and then recombined by MUX 652 to the output signal.

Although several embodiments of the present invention have been described above, those skilled in the art can make various modifications based on the principle of the present invention. In particular,
Some or all of the optical signals can be reused. For example, it is possible to pump another subband using the power rejected from one subband. It is also possible to further hybridize the structure, as will be appreciated by those skilled in the art. Further, the subband can be amplified by a semiconductor amplifier instead of the EDF amplifier.

[0028]

As described above, according to the present invention, a broadband optical amplifier having a substantially uniform gain spectrum is realized.

[Brief description of the drawings]

FIG. 1 shows gain factor (dB / m) versus wavelength (n) of erbium-doped silica fiber at various inversion levels.
FIG. 7 is a diagram plotting m).

FIG. 2 is a schematic diagram of a broadband fiber amplifier according to the present invention.

FIG. 3 is a plot of output power (dB / m) versus wavelength (nm) obtained from a numerical simulation of a three-subband branch-band fiber amplifier according to the present invention.

FIG. 4 is a schematic diagram of an experimental apparatus for a branch band fiber amplifier according to the present invention having two subbands.

FIG. 5 is a plot of the output spectrum measured for the fiber amplifier of FIG. 4;

FIG. 6 is a schematic diagram of a hybrid branch-band optical amplifier according to the present invention.

DESCRIPTION OF SYMBOLS 200 Broadband amplifier 202 First (common) section 204 Second (branch) section 206 Output section 208 Input port 210 to 212 Optical isolator 220 to 230 Erbium-doped fiber amplifier 231 to 238 GEF 240 to 243 Wavelength selective light Fiber coupler (WDM) 244 to 247 Pump radiation (pump laser) 250 Demultiplexer 251 Multiplexer 260 Attenuator (Attenuator) 266 Output port 400 Broadband amplifier 402 Common section 404 Branch section 450 to 451 Broadband Bragg fiber grating 460 to 461 circulator ( Rotator) 600 hybrid broadband amplifier 602 common section 604 branch section 606 hybrid section 650 DEMUX 651 DEMUX 652 MUX

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 596077259 600 Mountain Avenue, Murray Hill, New Jersey 07974-0636 U.S.A. S. A. (72) Inventor Atul Kay. Srivastava United States, 07724 New Jersey, Eatontown, White Street 111 (72) James W. Inventor. Salhoff United States, 07712 New Jersey, Ocean, Deal Road 1147 (72) Inventor. Sun United States, 07748 New Jersey, Middletown, Norwood Drive 908 (72) Inventor John El. Giskind United States, 07702 New Jersey, Shrewsbury, Constitution Drive 16 F-term (reference) 5F072 AB09 AK06 JJ20 YY17

Claims (16)

[Claims] 1. A broadband optical amplifier having a branch band structure. 2. The broadband optical amplifier according to claim 1, further comprising a hybrid structure. 3. The split band structure has a common input section and a split section, and the optical signal entering the common input section is split into a plurality of independent sub-bands and then separated into separate sub-bands. 2. The broadband optical amplifier according to claim 1, wherein the signals are sent to a branch, amplified in parallel, and then recombined into an output signal. 4. In the hybrid structure, at least one of the subbands sent to the branch of the branch section.
One subband is further split into a plurality of independent subbands and then sent to separate branches of the split section;
4. The broadband optical amplifier according to claim 3, wherein after being amplified in parallel, it is recombined into an output signal. 5. The broadband optical amplifier according to claim 4, wherein said common input section is an amplification section for amplifying an optical signal before branching. 6. The broadband optical amplifier according to claim 5, further comprising a common output amplification section for amplifying the output signal before outputting the output signal. 7. The branch section may be 1510 nm
7. The broadband optical amplifier according to claim 6, having an S-band amplification branch in the range of 1525 nm. 8. The branch section may be 1525 nm
The broadband optical amplifier according to claim 7, having an M-band amplification branch in the range of 1565nm. 9. The branch section may be 1565 nm
9. The broadband optical amplifier according to claim 8, having an L-band amplification branch in the range of 1610 nm. 10. A method for splitting an optical signal into a plurality of sub-bands, amplifying the plurality of sub-bands independently in parallel, and re-combining the plurality of sub-bands into an output signal. An optical signal amplification method, comprising: 11. The method of claim 10, further comprising amplifying the optical signal before branching. 12. The method of claim 11, further comprising amplifying the output signal. 13. At least one of said subbands
The method of claim 12, further comprising the step of splitting one sub-band into further sub-bands. 14. The method of claim 14, wherein the plurality of subbands are 1510n
The method of claim 10, comprising an S band in the range of m to 1525 nm. 15. The method of claim 15, wherein the plurality of subbands are 1525n.
15. The method according to claim 14, comprising M bands in the range m to 1565 nm. 16. The method of claim 16, wherein the plurality of subbands are 1565n
The method of claim 15, comprising an L band in the range of m to 1610 nm.