Archive for February, 2011

Back to the grind

Last week I was on vacation, relaxing by the beach and the pool at a resort in Mexico. Now I’m back home, and today is my first day back at work. I’m slowly easing myself back into it, checking emails, updating the blog, talking with friends. But eventually I will have to go talk shop with my boss and colleagues. I’m interested to see what progress has been made while I was gone; part of me hopes that they took copious amounts of data so I won’t have to do it, but we’ll see. Regardless of what measurements they did, I know I’ll have plenty more to do before I’m done.  But every bit helps!

Getting back from vacation is almost as tiring as the vacation itself. We got back on Saturday and had all of Sunday to recuperate, and we spent all afternoon and evening sitting on the couch streaming TV shows off Netflix. Despite all of that relaxing, I still feel worn out this morning, but the fog in my head is slowly dissipating as the day wears on. Most of the laundry is done, though, and I finally got motivated to go grocery shopping last night. Arriving home to a bare refrigerator is one of the worst parts about vacation, but going to the store was not high on my list of want-tos. I purposefully avoided the Sunday grocery rush, but it was late enough that shelves were sparse and there wasn’t a ripe banana to be had in the whole county. Still preferable to fighting the crowd, in my opinion.

So, now that I’m refreshed, it’s back to the routine. Gotta keep pushing toward the goal! The end is in sight!

A light at the end of the fiber?

At the beginning of February, our group welcomed a new guest researcher who will be with us for a few months. It just so happens that he has been involved with research similar to mine; thus, his first tasks were to work with me to reconstruct my old experiments and take them to the new laser.

Now, I’ve really just been sitting around a lot at the beginning of this new year, trying to drum up some motivation to get some of this research done so I can get closer to graduating. But motivation has definitely been lacking. However, this situation has presented if not motivation at least a severe kick in the pants to go do something in the lab. I know it’s exactly what I need, but boy does it ever go against the grain of my bum-sitting sensibilities. I have been unscrupulously thrown into the lab, trying to recall things from nine months ago while our guest probably assumes I just know it all. Stuff is supposed to come together immediately, but I am a graduate student and, thus, very slow. So it’s slightly embarrassing to have to tell him to wait a minute with his opinions and suggestions while I try to reorient myself in the universe amidst a whirlwind. It’s also strange for a meager grad student to be directing an older, more experienced researcher like he’s a small child…”don’t touch that!” “Please don’t pull out that connector!” “No, this is how we do it.”

Sometimes I am really frustrated almost beyond what I can bear, so I have to try really hard to remain calm and be kind; sometimes I fear that I don’t succeed. But after a couple of weeks, most of the measurements are set up again, and taking data is more methodical and somewhat calming. Plus, now that he’s more comfortable around the lab, I no longer feel the strong obligation to hold him by the hand and make sure he is “entertained” every minute of the day. While I am still working like crazy, I am gaining just a little more time on my own to breath each day. It’s still not the hours and hours of mindless web-surfing I got to do all of January, but I didn’t really need to be doing that anyway. At least I finally have a chance to post to the blog again!

Maybe the most excruciating part of this is that next week I will be on a sunny beach in the Caribbean, generating lots of Vitamin D and eating way too much. This is on top of the fact that the end of January and the beginning of February have been brutal weather-wise. Perhaps you were familiar with Snowmaggedon 2011, too? Below-zero temps and dreary skies do not help with motivation, either. So no wonder I have been in a funk. And the anticipation of being off makes me want to just sit at my computer and ride a wave of web-surfing all the way into Friday afternoon. However, I can’t exactly do that, and it’s better for me to not do that anyway.

So, while I have been incredibly frustrated at times, I know that this whole experience is good for me. In fact, the amount of progress I will have made in 2.5 weeks is almost ridiculous. And, to be honest, I have a huge chunk of data that I could write more about in, say, a thesis. My work with this new laser isn’t done by any means, but without getting too ahead of myself, I can see a whole lot of promise and maybe even some 1550 nm light at the end of the fiber. Which isn’t really true….1500 nm is invisible to the human eye. And if you were staring into the end of a lighted fiber, you’d burn your eye out. So please don’t do that. It’s just a metaphor.

Notice of Publication

Fluctuations of the optical power incident on a photodiode can be converted into phase fluctuations of the resulting electronic signal due to nonlinear saturation in the semiconductor. This impacts overall timing stability (phase noise) of microwave signals generated from a photodetected optical pulse train. In this paper, we describe and utilize techniques to characterize this conversion of amplitude noise to phase noise for several high-speed (>10 GHz) InGaAs P-I-N photodiodes operated at 900 nm. We focus on the impact of this effect on the photonic generation of low phase noise 10 GHz microwave signals and show that a combination of low laser amplitude noise, appropriate photodiode design, and optimum average photocurrent is required to achieve phase noise at or below -100 dBc/Hz at 1 Hz off a 10 GHz carrier. In some photodiodes we find specific photocurrents where the power-to-phase conversion factor is observed to go to zero.

As you can probably surmise, my paper has finally been published! It appears in the online IEEE Photonics Journal this February. We will also be publishing an open-source version on ArXiv (that’s “archive,” the X is pronounced as the Greek letter “chi”), an online site for researchers to publish their own material that’s free for all to view (most journals require a subscription for you to view their papers). One caveat for ArXiv is that it isn’t peer-reviewed, so it isn’t the same level of reputation as a journal. But for papers that have been accepted to a journal, it is a way of getting similar information out to a broader audience.

It is satisfying to see my work come to fruition after many months of hard, frustrating work. But sharing your results is what it’s all about.