By Bengt O. Hallberg
In 1983, I worked full-time on my WDM project at BOH Optical AB. Previously, I had worked part time setting up fiber optics laboratories for doctoral and final-year engineering physics students. I also lectured on fiber optics at KTH as I continued with for some time.
The TX
The most important module in the project was the fiber optic transmitter, which would later be labeled BOH Optical TX B 201 in the finished system. First, however, I needed to pursue a lot of additional photonics research and development.
At that time, the few scientific articles published internationally about WDM mainly dealt with the MUX and DEMUX components. Although these components were high-tech, I considered them uncomplicated in this context. As I mentioned in a previous blog post, such components were available for purchase from NEC in Japan as early as 1981. At that time, the French company Jobin Yvon was also manufacturing such components. Therefore, the problem for us was not manufacturing them in the future, given that they were available for purchase with the required quality.
Extreme stability requirements
The TX units were required to deliver extremely stable wavelengths in order to pack many wavelengths tightly onto each fiber in a cable. This process is now known as dense wavelength division multiplexing (DWDM). Based on my research, I knew that the wavelength of coherent photons from laser diodes could fluctuate over time. However, this is unacceptable in a WDM system that must operate flawlessly around the clock because the reception "windows" for the different wavelengths in the DMUX devices are fixed. Due to limited resources, I chose to patent only the transmitter's unique design and forfeited other possible patents.
The condensation problem
One such patent was titled "Condensation Moisture Elimination in Cooled Components." When cooling electronic components, such as laser diodes and detectors, condensation can form as precipitated water or ice. Droplets in connection with that can damage other electronics. This patent had eliminated that problem.
The success on March 3, 1985
During my time as a scientist at IOF, I developed a rudimentary method for stabilizing the wavelength in the laboratory. However, it was not good enough for a functional system. After years of research, development, and design, the first BOH TX B 201 transmitters were ready. On March 3, 1985, we conducted a successfull benchmark test and celebrated with champagne!
Patents
For those of you who are interested in the design, here are the patents in English in three important Anglo-Saxon countries
- United States Patent #4,829,533 – May 9, 1989 (foreign application priority March 30, 1984).
- United Kingdom Patent #2168838 – December 23, 1987 (filed March 29, 1985).
- Canadian Patent #1 232 326 – February 2, 1988 (priority date March 30, 1984).
According to the patent engineers, the US patent was a broad-claim patent, which is why it was difficult to obtain.
Broadcasted interview on October 3, 1979
In my previous blog post, I mentioned the interview with Swedish Radio's science desk that aired on October 3, 1979, forty-seven years ago. The topic was the state of photon transmission science in optical fibers in the context of telecommunications. At that time, few people were even aware of this development. This may have been the first serious, comprehensive public report on the subject in Sweden.
I would like to include a clip from that interview in my audio file, but I need permission from Swedish Radio to do so. I am holding off on publishing the file on the website while waiting for it.
Next blog
My next blog post, scheduled for publication on Tuesday, March 17, 2026, will discuss what happened next with the system.
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