R****a
发帖数: 199 | 1 What happens if you inject current to all three contacts?
Also, you made the laser or you buy/get it from somewhere else?
A schematic drawing of your laser might also be helpful (including the
waveguide structure and material).
1574nm)
this
bigger |
|
c******k
发帖数: 1140 | 2 Thank you for your interest.
1.To keep the same current density on the waveguide, the bias current for
the middle contact is always 1.8 times larger than that of the contact 1 and
contact 3. If I inject current for all three contacts, the center lasing
wavelength would be around 1546nm. See the attached picture.
2.We made this FP laser on our own with a pretty standard procedure, and the
commercial available substrate is InP with 6 AlGaInAs quantum wells (Well:
6nm Al0.27GaIn0.71As Barrier: 10n |
|
R****a
发帖数: 199 | 3 QW material does (should) have different behavior in terms of the lasing
frequency comparing to bulk material. I am not quite familiar with that.
On the other hand, if you have some kind of absorbers (like un-driven
sections) in your laser, it might get too messy to understand its behavior
easily.
and
the
3um.
contact |
|
M***a
发帖数: 175 | 4 三个sections公用同一个光学腔。所以中心波长不仅仅受偏置section的gain spectra
peak决定。另两个sections的吸收谱会同时影响中心波长。 |
|
g**h
发帖数: 15 | 5 Don't know if the issue solved or not. But here are my 2 cents.
You also need to consider the heating effect. I noticed that the driving
current is so different: injection with all regions 20mA, region2 80mA, and
region3 120mA. 20mA is the pretty standard for this type of laser.
When you only inject current into certain region of your laser waveguide,
the other region becomes absorber, and force you to inject more current into
it to get enough gain. If no temperature effect, the more current you |
|
c******k
发帖数: 1140 | 6 When I am injecting current to the InP lasers, I am always using a thermal-
electric cooler (TEC) control, and the setting point of temperature is 20C.
So you are saying the 14nm wavelength shift corresponds 30-40C temperature
change. But because of the TEC, I don't think so the laser device could have
so high temperature change.
I talked to my boss, and he is thinking the larger wavelength shift could be
due to the refractive index change with the increasing of injection current
.There is a pap |
|
g**h
发帖数: 15 | 7 What I mean 30-40C temperature change is the QW local temperature, but not
LD substrate temperature. Most of current injected will recombine in QWs and
generate heat there, so the QW local temerature is quite different from
where you put thermocouple for your TEC. You should examine carefully on
where the thermocouple is located, because that's where you get 20C
temperature reading.
For most efficient cooling, LD should be bonded upside down, did you use TEC
in that way? Btw, If my speculation i |
|
c******k
发帖数: 1140 | 8 Let's focus on the middle contact only with bias. Here at T=20C we have had
a lasing center wavelength with 1560nm. If I increase T=40C using TEC for
the whole laser substrate, what lasing wavelength would you expect? I think
you will say the lasing wavelength at T=40C will be a red shift (lower
energy of light), right?
I will do this test later to see the lasing wavelength is having a blue
shift or red shift when I have a higher T.
and
into
generally |
|
g**h
发帖数: 15 | 9 If you increase temperature of TEC from 20C to 40C and meanwhile only add
bias on middle contact, I would expect the following:
1. Higher threshold current.
2. Lasing wavelength red shift 5~10nm.
3. The relative change of lasing wavelength from different bias schemes won'
t change much.
had
think |
|
c******k
发帖数: 1140 | 10 I just did the test. You are right. The lasing wavelength is shifted to be
around 1581nm when I am driving a current (125mA) only with the middle
contact meanwhile the TEC temperature is set to be 40C. The threshold
current at T=40C is up to 110mA compared to 70mA at T=20C.
For the case of TEC location, our device is attached on the surface of a
piece of bulk AlN.The bulk AlN is on the top of a copper stage. There is a
thermistor inside the stage,and the stage is on the TEC. In this case, I
beli |
|
g**h
发帖数: 15 | 11 Quote: "If the band gap is not shrinked, those electrons in the valence band
maybe occupy those lower energy states of the conduction band of QW when
the temperature is high. So the lasing wavelength is red-shifted." |
|
c******k
发帖数: 1140 | 12 Sorry, 我的意思是说：
你讨论的高温度下QW band-gap shrinkage是解释激射波长红移是唯一的一个原因呢？
还是只是可能的一个原因。或者说你这个说法已经是一个不容置疑的事实呢？还是只是
你的一个猜测。
当然我自己也要查查这方面的文献，
我自己想到的一个原因是 （只是猜想或者是空想）：如果高的温度下QW band-gap 宽
度维持不变，但是价带的电子在高温下只能占据导带的较低的那些能级，如果这样，激
射波长也是红移。
Thank you!
band |
|
g**h
发帖数: 15 | 13 If no other major effect, the higher the temperature, the lower the bandgap
and longer lasing wavelength. This is a fact.
What I proposed is just my speculation based on my understanding. I don't
have first experience to obserse such type of laser before. But I can
predict that if you enhance TEC cooling efficiency (for example, by putting
laser upside down), you will find it's more difficult to get lasing if my
guess is right.
About your speculation, I don't know what you mean "electrons in the |
|
c******k
发帖数: 1140 | 14 It is very had to put the laser upside down to increase the TEC cooling
efficiency, since there are three gold wires sticking out from the three
contact pads.Some papers say they are using pulse current injection to avoid
to increase the temperature resulting from the bias itself.
Anyway, you help me a lot. Many thanks!
bandgap
putting
valence
describe
electrons |
|
g**h
发帖数: 15 | 15 Cityhawk, my bad. Since I was not doing any laser stuff for years, forgot a
lot of things. Yes, if you have a pulsed laser current source and companion
equips, you can test my speculation quickly.
Hope my 2 cents useful and you're very welcome. |
|
T*****e
发帖数: 361 | 16 I worked for PSGS (Perot Systems Government Services) before and they
sponsored my cap-exempt H1B visa. Now I am with TBG (The Baldwin Group)
with a visa transfer (yet to be approved). Another contractor at my working
place is IMSG. All have no problem with H1B visa/green card applications.
The last two are much smaller than the first, though. Good luck. |
|
n********y
发帖数: 187 | 17 看看美国超级科学家是怎样内斗的
第六部:迫害
MAIMAN在他的”激光历险(LASER ODYSSEY)”一书中详细控诉了激光爷爷TOWNES和他的
妹夫,光谱老爹SCHALOW,对他的迫害.
1. 首先HUGHES的新闻发布会后TOWNES无法接受这个脉冲激光的怪物,他当时是白宫
直属机构的IDA(INSTITUTE FOR DEFENSE ANALYSIS) 的副总(VP),在他的主持下,IDA要
MAIMAN到DC去详细报告进展, DARPA的官员也列席会议.MAIMAN讲完RUBY脉冲激光的几大
证据后,TOWNES一时无法接受. DARPA当时主管GOULD的TRG激光项目的DARPA官员听
TOWNES说这些MAIMAN的证据可能是ARTIFACTS的时候,问到说:那我们(TRG)的项目应该继
续? TOWNES明显是持肯定态度的. 当然当时MAIMAN去IDA的时候可能是7月20日之前,而
由于第一批RUBY晶体的质量问题, MAIMAN还没有得到一个特别好的激光输出光束. 因此
当TOWNES没有看见高质量的光学输出的时候,加上这是一个脉冲怪物,他自然有理由怀疑
... 阅读全帖 |
|
n********y
发帖数: 187 | 18 看看美国超级科学家是怎样内斗的
第六部:迫害
MAIMAN在他的”激光历险(LASER ODYSSEY)”一书中详细控诉了激光爷爷TOWNES和他的
妹夫,光谱老爹SCHALOW,对他的迫害.
1. 首先HUGHES的新闻发布会后TOWNES无法接受这个脉冲激光的怪物,他当时是白宫
直属机构的IDA(INSTITUTE FOR DEFENSE ANALYSIS) 的副总(VP),在他的主持下,IDA要
MAIMAN到DC去详细报告进展, DARPA的官员也列席会议.MAIMAN讲完RUBY脉冲激光的几大
证据后,TOWNES一时无法接受. DARPA当时主管GOULD的TRG激光项目的DARPA官员听
TOWNES说这些MAIMAN的证据可能是ARTIFACTS的时候,问到说:那我们(TRG)的项目应该继
续? TOWNES明显是持肯定态度的. 当然当时MAIMAN去IDA的时候可能是7月20日之前,而
由于第一批RUBY晶体的质量问题, MAIMAN还没有得到一个特别好的激光输出光束. 因此
当TOWNES没有看见高质量的光学输出的时候,加上这是一个脉冲怪物,他自然有理由怀疑
... 阅读全帖 |
|
m*******e
发帖数: 119 | 19 你在测两片和三片合在一起时， reference 也是两片和三片slides合在一起吗？
如果不是，你的光谱会有一些周期性震荡。slides其实是一个很弱的Febry-Perot 光学
腔。如果你的参考光路和测量光路的slides厚度一样，可以抵消光干涉的影响。 |
|
n********y
发帖数: 187 | 20 第六部:迫害
MAIMAN在他的”激光历险(LASER ODYSSEY)”一书中详细控诉了激光爷爷TOWNES和他的
妹夫,光谱老爹SCHALOW,对他的迫害.
1. 首先HUGHES的新闻发布会后TOWNES无法接受这个脉冲激光的怪物,他当时是白宫
直属机构的IDA(INSTITUTE FOR DEFENSE ANALYSIS) 的副总(VP),在他的主持下,IDA要
MAIMAN到DC去详细报告进展, DARPA的官员也列席会议.MAIMAN讲完RUBY脉冲激光的几大
证据后,TOWNES一时无法接受. DARPA当时主管GOULD的TRG激光项目的DARPA官员听
TOWNES说这些MAIMAN的证据可能是ARTIFACTS的时候,问到说:那我们(TRG)的项目应该继
续? TOWNES明显是持肯定态度的. 当然当时MAIMAN去IDA的时候可能是7月20日之前,而
由于第一批RUBY晶体的质量问题, MAIMAN还没有得到一个特别好的激光输出光束. 因此
当TOWNES没有看见高质量的光学输出的时候,加上这是一个脉冲怪物,他自然有理由怀疑
. 但是, 当MAIMAN得到高... 阅读全帖 |
|
b*****n
发帖数: 50 | 21 没有一定要争个输赢的意思，但是我的确是觉得你将single-peaked理解成为“strong
ordering”是不对的。而且black theorem当中的single－peaked condition绝对不是
“
strong ordering”。
如果按你说的我刚才列举的关于Clinton，Perot 和Bush的三个preferences都是single
－peaked的话，那么按照black theorem, median voter就是majority winner。但是你
用Cordorcet procedure做一下就知道，在一个三人group（BPC, PCB和CBP）中，是没
有
majority winner的。你得到的只是一个group choice的cycle， P>C>B>P，也就是medi
an voter无法脱颖而出。
更简单的方法，你把C，P,B三个alternative按照其ideology从左到右排列起来，CBP这
样的preference的图形是有两个peak的。而BPC和PCB是只有一个peak的。直观来看，CB
P就不是single－pea |
|
b*****n
发帖数: 50 | 22 Single-peakedness condition is more than "strict ordering" and should
include the meanning of geometric distance between different alterantives,
even which are strictly ordered. This is the reason I related this condition
with Eucilidean Preferences as Unameme has explained.
For example, assume Clinton, Perot and Bush are three alternatives who are
on an ideological line from left to right. The preference of C>P>B is single
-peaked, the preference of P>B>C is also single-peaked, but the prefere |
|
b*****n
发帖数: 50 | 23 没有一定要争个输赢的意思，但是我的确是觉得你将single-peaked理解成为“strong
ordering”是不对的。而且black theorem当中的single－peaked condition绝对不是
“
strong ordering”。
如果按你说的我刚才列举的关于Clinton，Perot 和Bush的三个preferences都是single
－peaked的话，那么按照black theorem, median voter就是majority winner。但是你
用Cordorcet procedure做一下就知道，在一个三人group（BPC, PCB和CBP）中，是没
有
majority winner的。你得到的只是一个group choice的cycle， P>C>B>P，也就是medi
an voter无法脱颖而出。
更简单的方法，你把C，P,B三个alternative按照其ideology从左到右排列起来，CBP这
样的preference的图形是有两个peak的。而BPC和PCB是只有一个peak的。直观来看，CB
P就不是single－pea |
|
w****k
发帖数: 6244 | 24 好笑就笑
笑口常开有利于身心健康
刚才读Ross Perot的传记，这老头是个大牛人
当初如果扳倒克林顿，也许这个国家和这个世界
都是另一个景象。历史真是充满偶然性。 |
|
