Optics & Photonics News

Then we got ambitious with our trials: In February 1980 at the Winter Olympics at Lake Placid, the television feed was carried over an experimental optical fiber system and broadcast around the world. Many of us had our fingers crossed! In the end, it was fabulous to see the “Miracle on Ice” performance of the U.S. men’s ice hockey team via the superior television picture made possible by our fiber system. These first-generation lasers were subsequently used in the fiber systems for the Northeast Corridor and many other terrestrial trunk applications. Technology “proof of principle” had become “ technology of choice!”

The U.S. men’s hockey team defeat- ed the Soviets at the 1980 Olympics in Lake Placid. The television feed was carried on an optical fiber sys- tem developed at Bell Labs.

Semiconductor lasers—the second generation

Our second-generation lasers were designed for use in the

1. 3 µm window of the improved, single-mode, 5-µm-diameter fibers. Their buried-heterostructure design made use of two epitaxial growth sequences with an etching step in between.

The first (planar) growth sequence of this improved device was made using metal-organic chemical-vapor deposition (MOCVD) and incorporated a highly resistive Fe-doped layer adjacent to the substrate; this greatly reduced current leakage and improved the high temperature performance of the device. This layer had the desirable high resistance of a proton-bombarded layer, but without the proton bombardment!

Most important, the layer reduced the capacitance, making the device suitable for high-speed modulation. Following an etching step to produce the “V” groove, the final growth sequence was done using LPE. This growth made use of the fact that LPE, when used to grow in a groove, could produce the crescent-shaped active layer shown in the figure on the facing page.

This seemingly contorted fabrication process ultimately produced very high-yield, high-performance, high-reliability lasers that stayed in volume production for more than 10 years (from about 1984 to 1997). These multimode lasers could be used at data rates up to about 2 Gb/s. They were, for example, the mainstay of the Bell System’s 417 Mb/s applications, and, later, its FT-series-G 1. 7 Gb/s applications. For example, the lasers were used to provide the first high-speed 1.7-Gb interconnects among some 200 major U.S. cities.

One of the reasons that these and subsequent lasers came to possess such high reliability and could be applied in terrestrial trunk and undersea applications, was that we became increasingly able to screen out lasers that had non-fundamental modes of degradation. This process came to be called “purging.” It used short-duration high-stress regimes, specific to the individual laser design, in the laser certification process. An example would be the application of 250-m A dc current for 10 hours in

Wikimedia Commons

a 150 °C ambient followed by a before-and-after comparison of the laser’s room temperature characteristics.

We subsequently designed, developed and manufactured more
sophisticated InP-based lasers, including designs with distrib-
uted feedback gratings to produce a single,
stabilized wavelength. Zilko et al. described
an example in 1989 (J. Quantum Electron
25, 2091). An electro-absorption modula-
tor was later incorporated, on the same
chip, into this design. Descendants of these
devices—operating at data rates as high as
40 Gb/s, but more typically at 10 Gb/s—
are useful for wavelength-division-multi-
plexing applications and remain in volume
production in the United States, Japan
and other parts of the world. They make
use of the “ultimate” low loss 1. 5-1. 6 µm
region in modern single-mode fibers. My
understanding is that MOCVD technol-
ogy has now substantially replaced LPE in
laser manufacture.

In February 1980 at the Winter Olympics at Lake Placid, the television feed was carried over an experimental optical fiber system and broadcast around the world. Many of us had our fingers crossed!

Device Research Conferences

I went to a good many meetings during these years, but I always found the Device Research Conferences to be special. They were small and somewhat informal gatherings held in late June at a university after summer recess had begun (and where the room and board was cheap). Early on, it was decided that the conference location would alternate between East and West. After awhile, “West” came to mean the University of California at Santa Barbara and “East” to mean the University of Colorado in Boulder.

We had some fun too, and we got to know one another well. For example, I remember near the end of the conference I chaired, Herb Kroemer asked me at dinner in his strong voice to come over to the table where he was sitting with several other previous conference chairs and join “The Old Farts’ Club.” This was before Herb became famous.