Light Reading
What they are and how they can be used for: * Optical Amplification * Optical Switching * Wave Conversion

Semiconductor Optical Amplifiers

Light Reading
5/15/2002
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Several new products based on Semiconductor Optical Amplifiers (SOAs) made a splash at the recent OFC conference (see Vendors Unveil Amplifier Advances). The technology has been under significant development over the last 10 years, and it seems as if the day of the SOA may at last be arriving. In this report by Stephen Montgomery, the president of ElectroniCast Corp., we take a look at some of the reasons why SOAs are attracting so much attention – specifically focusing on three key applications of the technology. The first and most obvious application of SOAs is Optical Amplification. Although the prevalence of Erbium Doped-Fiber Amplifiers (EDFAs) over recent years has restricted growth in this area, there are now niche applications where SOAs are proving a useful alternative. For example, recent products have been aimed at power and pre-amplification (see Kamelian Launches First Products and Genoa Releases Two Amps) and metro applications (see Corning Intros Amplifiers). SOAs are by no means a one-trick pony – they can also be used as all-optical switching elements and wavelength converters (see Interest Grows in Wavelength Conversion). An inherent advantage with these applications is that, in general, the optical losses of the switching/conversion process are neatly compensated for by the inherent amplification capability of SOAs. The predicted market for these three applications of SOAs is certainly significant – expected to rise to a total world consumption of over $250 million in 2005, according to an ElectroniCast forecast (see Report Sees SOA Market Growth). Although wavelength converters take the smallest share of this total, they are expected to be the largest growth area, with a 75 percent annual increase in consumption anticipated for the first five years of this decade. Table 1 below has the full details. Table 1: SOA Global Consumption Value Forecast

SOA Function 2000 2001 2002 2003 2004 2005 2010 Growth 2000-2005 Growth 2005-2010
Optical Amplifier 25.9 35.8 49.9 65.1 86.8 118.1 405.4 35% 28%
Optical Switch Element 20.0 28.4 40.1 61.2 81.0 105.2 401.2 39% 31%
Wavelength Converter 2.1 5.9 10.3 19.0 25.8 34.0 141.8 75% 33%
Figures in $Millions


Read on to discover how all of this SOA technology actually works and what challenges still lie ahead. Here's a hyperlinked summary of the report: Technical Basics
An overview of what SOAs are, what they do, and how they do it Research History
A brief rundown of the background of research and development that has brought SOAs to their current situation Optical Amplification
The merits and drawbacks of SOAs against other optical amplifier technologies Optical Switching
The design of SOA-based optical switches Wavelength Conversion
The use of nonlinear effects to convert wavelengths — Introduction by Craig Williamson, Associate Editor, Light Reading
http://www.lightreading.com Next: Technical Basics

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netchinta
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netchinta,
User Rank: Light Beer
12/4/2012 | 10:23:41 PM
re: Semiconductor Optical Amplifiers
Stephen/Craig,

There is at least one other approach to getting linear performance from an SOA - it is to simply design the SOA well enough to boost saturation power well above signal level. There has been a lot of work done in this direction (for a while now) at Dagenais' group at the Univ. of Maryland and is likely being productized by Quantum Photonics Inc. in Jessup, MD (Dagenais was a founder, I believe).

On a different note - would it be possible for you folks to create a table comparing SOAs to EDWAs and low-cost EDFAs at similar gain levels with respect to NF, footprint, cost, stability, etc.? It would definitely help generate a good debate about the relative merits and demerits of these approaches for amplification.

Thanks!

-NetChinta
Ultrafast
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Ultrafast,
User Rank: Light Beer
12/4/2012 | 10:23:38 PM
re: Semiconductor Optical Amplifiers
Hi Netchinta,
As to my knowledge, there is already a company that has used this approach on their SOAs and is shipping samples.


Thanks!

-Ultrafast
scouser
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scouser,
User Rank: Light Beer
12/4/2012 | 10:23:33 PM
re: Semiconductor Optical Amplifiers

EDFA SOA LOA EDWA
Typical signal gain30dB 20dB 13dB10dB
Output Power+17dBm+6dBm+10dBm+6dBm
Noise Figure<5dB 9dB 8dB 6dB
PDG<0.2dB 1dB 1dB0.5dB
High Pump EfficiencyGood Average Poor Poor
Crosstalk None High LowNone
Package Size (mm) 90x70x12 30x15x10 30x13x81 33x27x13
Mature TechnologyYes No No No
Overall Performance Excellent Poor Average Poor
Present Cost (2001 Data)Low Medium Medium High

It's a bit out of date though
Petabit
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Petabit,
User Rank: Light Beer
12/4/2012 | 10:23:31 PM
re: Semiconductor Optical Amplifiers
The article is a little misleading in the way that it reports the SOA as an alternative to a rare earth based amplifier.

The biggest system limitation of SOAs is not FWM (four wave mixing) it is XGM (cross gain modulation) and XPM (cross phase modulation). XGM occurs because the very short lifetime of the carriers means that a modulated signal travelling through the SOA depletes the energy store that is used for amplification. This means that in amy WDM system, the SOA will cause amplitude and pahse information to be transferred between all of the channels. Typically this effect is not well understood by the SOA manufacturers, and has not been reported much in the literature. Also since the effect is so fast, optical gain clamping (e.g. LOAs) does not solve the problem.

Which is why you do not see any SOAs being using in WDM systems today. As an aside the Bell Labs technique is normally referred to as FSK, and has been known about for decades. It solves some non-linear problems, but at the expense of spectral efficiency.

Another disingenuous statement is that SOAs are smaller than EDWAs. You need to compare apples with apples - in general the SOAs are sold as a gain block. This corresponds to the erbium and the pump and the pump coupler in an EDFA/EDWA. There are EDWAs and EDFAs on the market already that are very similar sizes to a packaged SOA, and so it is incorrect to say that SOAs are small.

Normally the SOA manufacturer will compare an SOA to a fully featured EDFA - complete with isolators, taps, and electronics in the EDFA (but of course not in the SOA). EDWA manufacturers are often guilty of this trick as well. I think I am bitter from too many supplier presentations.

There is not much that will distinguish the cost of an EDWA from a SOA of similar performance. If you still beleive that SOAs are cheap, then you are not talking to the right EDWA manufacturers.

SOAs and LOAs make good single channel amps, and they make good non-linear elements, but they are very poor WDM amplifiers compared to erbium based solutions.

P.
Pauline Rigby
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Pauline Rigby,
User Rank: Light Beer
12/4/2012 | 10:22:58 PM
re: Semiconductor Optical Amplifiers
Alcatel sells a wavelength converter chip commercially. It contains more than just SOAs --the chip has a MZ interferometer with an SOA in each arm. The chip needs packaging with lasers and some kind of control system before it can be used in a real system.

Some companies do this packaging on the Alcatel chip. Optovation is one. There might be others. Maybe that is what's meant by "a variety of companies". I have not come across other wavelength converter companies with commercial SOA-based products yet, though there are probably some out there still in stealth mode.

rigby@lightreading.com

Snell
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Snell,
User Rank: Light Beer
12/4/2012 | 10:22:58 PM
re: Semiconductor Optical Amplifiers
"SOA-based wavelength converters are commercially available as qualified telecommunication products from a variety of companies" - this seems a little
surprising - I'm aware of all-optical research devices and samples, but not of anything qualified for this application. Is there any evidence for this which could be shared? I would imagine that straightforward SOAs qualified for amplification might also be touted for wavelength conversion - is this all that was meant? SOAs are not an easy subject despite apparent simplicity!
gea
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gea,
User Rank: Light Beer
12/4/2012 | 10:22:56 PM
re: Semiconductor Optical Amplifiers
Dude:
Are you sure you know what "disingenuous" means?
From your post it would seem that you meant "inaccurate", or "misleading". "Disingenuous" basically implies that a speaker or author was somehow deliberately nonforthcoming about some information, and that they basically sought to decieve their readers.
Petabit
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Petabit,
User Rank: Light Beer
12/4/2012 | 10:21:10 PM
re: Semiconductor Optical Amplifiers
Hi gea,

I do know what 'disingenuous' means. It was a little stronger than I probably really mean - but these boards need a little provocation at times. You try and start a decent techie debate, and no-one turns up.

P.
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