Oral-History:Izuo Hayashi
About Izuo Hayashi
Izuo Hayashi received his education from Tokyo University’s physics department, graduating in 1945. He played a key role in the development of the laser by discovering high luminescence in the aluminum gallium arsenide laser, and worked on achieving continuous-wave operation of this laser at different temperatures. Hayashi was interested early in life by physics and the movement of stones on flat ice; after working during World War II on microwaves and the detection of the US B-29 bomber, he became interested in light waves, which led him to work on laser technology. The tiny lasers Hayashi helped to develop are now used in long-distance communication in trans-continental telephone cables.
Hayashi begins the interview by describing his work on the aluminum gallium arsenide laser, and discusses testing its performance at certain temperature thresholds. He goes on to describe various applications of lasers in general in medicine and communications. Finally, Hayashi describes his intellectual development in Japan and how he came to work on lasers. The interview concludes with his thoughts on some of the surprising developments in the use of laser technology and a brief mention of the time he spent living in Murray Hill, NJ.
About the Interview
IZUO HAYASHI: An Interview Conducted by Robert Colburn, IEEE History Center, 20 May 2004
Interview # 441 for the IEEE History Center, The Institute of Electrical and Electronics Engineers, Inc.
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It is recommended that this oral history be cited as follows:
Hayashi, Izuo, an oral history conducted in 2004 by Robert Colburn, IEEE History Center, Piscataway, NJ, USA.
Interview
Interview: Dr. Izuo Hayashi
Interviewer: Robert Colburn
Date: 20 May 2004
Place: via telephone to Hayashi's home in Tokyo, Japan
Discovery of high luminescence in the aluminum gallium arsenide laser
Hayashi:
A typhoon was expected to come to Tokyo this morning but it passed and it is very good weather now.
Colburn:
I am glad to hear that. I hope that typhoon did not do any damage.
Hayashi:
No, only from the amount of rain. That's all.
Colburn:
I received the very helpful diagrams that you drew for me and I appreciate them very much. I was wondering if I could ask you some questions about how you discovered the luminescence.
Hayashi:
How I discovered the high luminescence?
Colburn:
Yes, in the aluminum gallium arsenide laser.
Hayashi:
At the beginning I was working with gallium arsenide only. Morton Panish was my collaborator, and Mort grew the crystals and I was looking at the luminescence. One day we found that if we had a small amount of aluminum gallium material on top of the gallium arsenide it is much brighter than luminescence from gallium arsenide alone. That was the beginning.
Colburn:
Was that an accidental discovery?
Hayashi:
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Yes. At the very first it was accidental. Up to that point Mort Panish tried to grow gallium arsenide crystals only, but he became interested in growing aluminum gallium arsenide. Therefore one day he put some aluminum gallium arsenide on the top of the gallium arsenide. At that time, I found that some of the crystals had a much brighter luminescence than with gallium arsenide alone. That was a discovery. I soon realized that this must indicate a very clean interface between aluminum gallium arsenide and gallium arsenide. With gallium arsenide alone the surface is covered by a lot of defects - a non-absorbing layer - and aluminum gallium arsenide removes the defective layer, making a very clean defect-free interface and the luminescence intensity increased by orders of magnitude.
Aluminum gallium arsenide laser construction
Hayashi:
The purpose of our study was to find out how we could make a very efficient gallium arsenide laser and I thought that this clean interface must be useful for this purpose. Therefore we started to make such structure. The first structure for an aluminum gallium arsenide laser would hopefully operate at a much higher temperature – hopefully at room temperature. That was our goal.
Colburn:
How cold were the first ones?
Hayashi:
The first one we made was a single heterostructure laser, but the single heterostructure laser did not have a high enough temperature for continuous operation. Continuous operation was not obtained because it was still somewhat lower than room temperature. Therefore we tried another structure by making an aluminum gallium arsenide layer on the back of gallium arsenide so that both the front and back were covered by aluminum gallium arsenide. That was a better structure. Morton Panish put a lot of effort into making such a structure.
Colburn:
At what temperature did the single heterostructure laser operate?
Hayashi:
I don't know. Rather than temperature I talk in threshold current.
Colburn:
Good.
Hayashi:
The temperature at which we could obtain CW operation. We increased the temperature starting from somewhere around 100° Kelvin and gradually raised the temperature gradually to ascertain at how high of a temperature we could still achieve continuous-wave (CW) operation. The threshold current decreased by something like 20 amperes per square centimeter in the single heterostructure. In double heterostructures of course we can get about 1,000 or 2,000 amperes per square centimeter. We obtained that number with a double heterostructure after several months.
Colburn:
How large were these lasers when you had reduced the threshold current to that stage?
Hayashi:
The final complete laser itself was a few hundred microns by 100 millimeters width and length. That was the size we were testing.
Colburn:
Was it already very small and able to be used for communications?
Hayashi:
In principle, yes, but a lot of improvements needed to be made. A piece of crystal called a wafer, the crystal size itself of the single or double heterostructure, its height is about 1 cm by 1 cm. We cut these into hundreds of small pieces and tested the individual pieces for lasing. Initially only small fractions of these small pieces could be lased. Many were not lased because there were still a lot of defects in the individual lasers. The important thing was to make even a small fraction into good low-threshold lasers. That first stage was still far from commercial use. Many improvements still had to be made after that.
Colburn:
What were some of those improvements?
Hayashi:
For commercial usage a good laser must be almost a 100 percent fraction of the main crystal. That took many years to achieve from the first success. The first CW operation in which I obtained data from the laboratory was in 1970. Then I came back to Japan, and the use for commercial applications was not until several years after that.
Commercial applications of the aluminum gallium arsenide laser
Colburn:
Where was the first commercial application?
Hayashi:
It was long distance use between some cities, say from Tokyo to Osaka. I don't know which cities were first. The first venture application was must have been somewhere in the States, perhaps New York. It covered several hundred kilometers.
Colburn:
There was one from New York to Boston and Washington in 1973 or 1974, I think.
Hayashi:
Yes. I don't know what year. It took several years. Later they were used across the ocean using undersea cables. Today there are lots of lines all over the world.
Colburn:
I believe our telephone call is probably using them right now.
Hayashi:
Oh yes. I believe this telephone line crosses the Pacific Ocean.
Colburn:
That must be very satisfying for you to know. You must be very happy that people are using them every day.
Hayashi:
Yes, exactly. We make calls so easily today and it is very, very inexpensive today. We can call our friends anyplace in the world almost anytime.
Colburn:
It is very good. My brother lives in Paris, France, and it doesn't cost any more for me to call him than to make a call a few hundred miles away.
Hayashi:
Right. Yes, it is wonderful.
Attaining room temperature for reliable continuous wave operations
Colburn:
Do you remember when you first reached room temperature for reliable continuous wave operations? Was that in 1970?
Hayashi:
The very first laser I obtained was at the Murray Hill laboratory. I think that lasted somewhere between a few minutes or maybe a few tens of minutes. It stopped lasing within a short period of time. It took several years to achieve a longer life. We were able to keep some lasers lasing 2,000 hours at one point. I must have the number.
Colburn:
I have a copy of the article that mentions that 2,000 hours.
Hayashi:
Yes. I couldn't find what year the 2,000 hours was obtained.
Colburn:
Looking in that article now, it does not give the date. It sounds like perhaps 1973.
Hayashi:
Yes, I think so. One thing I remember clearly was that there was a conference in communications around that time. I think the conference was somewhere in the States. I wrote about the longest time for CW operation obtained in the laboratory in NEC (Nippon Electric Corporation). I was invited to that conference. People from Bell Telephone wrote about the longest life they had achieved, and the lengths of time were almost equal to our results. Both were about 2,000 hours, but our (NEC) results were slightly longer.
Colburn:
Do they last for years now?
Hayashi:
Yes, of course. It is years, some million hours today. That required a lot of effort by many, many people, including the process of production. For instance the wafer size was increased and then the oven temperature becomes more uniform. Also the material infused must be increased. Many things had to be tried by many people.
Colburn:
Yes.
Hayashi:
I don't know. I did not do what many engineers have done.
Diverse applications of high-power lasers
Colburn:
Have those lasers been used for purposes other than long-distance communications?
Hayashi:
Other applications?
Colburn:
Yes.
Hayashi:
The lasers we are discussing have very little power. Each laser emits lasing light less than tens of microns. That's the kind of laser used for communications. There are lots of applications that use a high-power laser like lasers for medical applications or making holes through hard materials, etc. Some of these semiconductor lasers can be used for preventing collisions between cars for instance. I don't know how frequently this kind of application is used. Such laser light can monitor the distance between cars. Microwave can be used for that application. I don't know which is better; I don't know in detail.
Colburn:
Those answers are very helpful to me.
Origin of interest in science
Hayashi:
You asked me earlier about how I came to be interested in physical science or natural science. I think I was just born with the desire to have active physical images of thing in my mind. I believe some of these stories were published in the Kyoto Conference papers.
Colburn:
Yes. You talked about the plants and the insects.
Hayashi:
My interest was more in physics than plants or insects. I was playing with [unintelligible word] something.
Colburn:
Yes. And the slab of stone.
Hayashi:
Yes, that's right. Those were the kinds of things that interested me. I am more interested in such things. That is one example. [The image of the slab of stone sliding across ice was one of the ways Hayashi visualized physical concepts such as the laws of motion.]
Colburn:
In what other physical things were you interested?
Hayashi:
The first thing I was interested in was movement through materials. Somewhere I have a picture. Do you have the picture of some movement of stones on flat ice?
Colburn:
Yes.
Hayashi:
It shows how these stones move on the ice surface. The direction of motion is only changed by external force so that it is an image for mechanical motion. That's one of the first things that interested me.
Shift in focus from microwaves to light waves
Hayashi:
During wartime I was working on microwaves and how to detect microwaves from the U.S. B-29 bomber that flew on Tokyo. At that time I was trying to get my image of microwaves. The image of microwaves changed to light waves. Microwaves and light waves are both electromagnetically created. The only difference was the wavelength; the wavelength being shorter in light waves. That way, for me, it was rather easy to get an image of light waves. That was useful helping me to see the way the CW laser operated. This was a kind of change in my interest.
Colburn:
When did your interest change from microwaves to light waves?
Hayashi:
When World War II stopped in 1945, I graduated from the physics department of Tokyo University at that time. I was doing some experiments using microwave tubes. Are you familiar with some of the areas in Tokyo?
Colburn:
Yes.
Hayashi:
Kanda?
Colburn:
Yes.
Hayashi:
Fairly inexpensively we could get microwave tubes used for the U.S. bomber, and I was playing around with microwaves using that tube. One can make many various experiments using a microwave wavelength of about 1 cm or so. Metal wires can reflect microwaves. It depends on the polarization of the microwaves. That was when I could make the comparison or connection from microwave to optical light.
By changing the frequency from radio to microwave and microwave to optical light, it relatively easy for me to make the images of electromagnetic behavior of optical light. This is a kind of insight I had.
Unexpected applications of lasers
Hayashi:
In your first letter to me at the very end of your sentence you asked in what ways lasers have been used that I would not have expected.
Colburn:
Yes.
Hayashi:
I think that the use of lasers through very thin things, glass wire where the thickness is about the same as the human hair.
Colburn:
Yes.
Hayashi:
I think no one expected to use such fine optical light through transparent fiber for communications. That is something I think people had never expected beforehand. Marconi started to use electromagnetic spark for communication. That was the first. Then that became wireless communications.
Actual microwave communications through air. These things have a different use for long distance communications. Through many technologies, finally today even very long-distance communications have become most economical and high capacity. Now we use optical waves through transparent glass wire.
Colburn:
Yes.
Hayashi:
It this is something we never expected.
Colburn:
Yes, that is true.
Hayashi:
I think there is another paper I didn't show you about the heterostructure laser. It was in the IEEE Transactions on Electron Devices. Do you know that?
Colburn:
I have not read that.
Hayashi:
I didn't give you that. That paper was in the November 1984 IEEE Transactions on Electron Devices, volume 31, no. 11, pages 1630 to 1642. That is a paper I wrote which covers various things we have talked about.
Colburn:
I can find it back at the IEEE and will read it.
Hayashi:
It is right in your area.
Colburn:
Yes. I do not wish to take too much of your time and I thank you very much.
Recollection of residence in New Jersey
Hayashi:
You are very welcome. I am sorry that my English is so rusty. I lived in New Jersey. I was living about one hour from New York across from the Bell Telephone laboratory at Murray Hill.
Colburn:
Yes, Murray Hill.
Hayashi:
I was there from 1963 to 1971. How often have you been to Japan?
Colburn:
I have been to Japan once. The IEEE sent me there on business.
Hayashi:
You stayed in Tokyo area?
Colburn:
In Tokyo and Nagoya and Kyoto and Nara.
Hayashi:
Some good things there.
Colburn:
Yes. Kyoto was beautiful and Nara was also beautiful.
Hayashi:
Very interesting.
Hayashi:
If you have another question don't hesitate to give me a call or write.
Colburn:
Yes. I will email with questions if I have them. Thank you very, very much.
Hayashi:
I enjoyed it very much.
Colburn:
I too. Goodnight.
Hayashi:
Goodnight. I enjoyed it very much.
