The word “laser” is an acronym for Light Amplification by Stimulated Emission of Radiation. Within an atom or a semiconductor, an electron in a stable state can be excited by optical energy. While the electron is excited, by applying light with a wavelength (energy) equivalent to the difference in energy between the excited and stable states, as it returns to the stable state the electron releases coherent light. That is, light of the same wavelength, in the same direction, and at the same phase. This phenomenon is called “stimulated emission.” The released light then hits the next excited electron, causing coherent light to be released again. Repeating this process for many electrons produces a stream of coherent light.
　To amplify the light, the electrons must be kept excited within a “resonator,” in which the light is repeatedly reflected between two mirrors facing each other. By repeating stimulated emissions within the resonator, the light amplification eventually offsets the inevitable light losses within the resonator caused by light leaks and attenuation, etc. At this point, a completely new state called “oscillation”*1 occurs. Within the resonator, energy is concentrated at the resonated wavelength and light of a single color and of unified wavelength and phase is obtained. This light can be condensed into a single point using lenses. This is a laser light. Today, lasers are widely used in telecommunications, optical disks, printers, various measurement systems, medical devices, industrial applications such as mechanical processing and welding, and entertainment.
　While a laser is generated by oscillation, Light Emitting Diodes (LEDs) have a completely different nature. LEDs produce dispersed light containing various wavelengths and directions, generated by spontaneous emission from a semiconductor device. They are used, for example, in lighting and computer displays.
　Amplification of electromagnetic waves by stimulated emission was researched by Dr. Arthur Schawlow and Dr. Charles Townes at Bell Laboratories in the late 1950s, when it was named Microwave Amplification by Stimulated Emission of Radiation or MASER. Research later shifted to visible light, and the world’s first working laser using a ruby crystal was demonstrated by Dr. Theodore Maiman in 1960*2 at the Hughes Research Laboratories, owned by Hughes Aircraft. In 1962, during his undergraduate studies at the then Tokyo Institute of Technology, Dr. Kenichi Iga researched this ruby laser under the guidance of Dr. Yasuharu Suematsu (then professor and later president). When Dr. Iga was appointed as an assistant professor, he chose “lasers” and “optical transmission,” —the subjects he studied for his PhD—as his research theme. His subsequent research in these two areas eventually led him to conceive his own surface emitting laser.

　Lasers comes in various types, for example, using solid materials like ruby, or liquids, gases, or semiconductors. Of these, the semiconductor lasers were perfectly suited for telecommunication purposes as it could be miniaturized to less than 1 millimeter and their extremely low power consumption—just 1/100 of watt. In 1970, Dr. Izuo Hayashi and others at Bell Laboratories successfully achieved continuous laser oscillation using a semiconductor laser at room temperature. Dr. Iga, who was inspired by Dr. Hayashi’s lectures, started his research into a semiconductor laser for optical communications in 1974.
　The semiconductor laser that only existed at that time was an Edge Emitting Laser (EEL). EEL’s amplification was carried out by optical resonation in strips within a cavity along the substrate surface, and a pair of cleaved silicon wafers set in parallel were used as resonating mirrors. However, the traveling distance within the resonator was 300 times greater than the wavelength of the light, and therefore it was difficult to unify the wavelength. Also, standardizing production proved challenging. Be around 1976, Dr. Iga recognized that all these issues need to be overcome.
　 Dr. Iga’s intention was “to create a semiconductor laser that could be produced through a standardized process and which provides single wavelength oscillation with excellent wavelength reproducibility.” —This was his “dream laser.” One night in 1977, Dr. Iga pursuing his idea was had a sudden flash of intuition—“What if I change the direction of the light from horizontal to vertical?”

　When Dr. Iga presented the initial concept of the VCSEL in 1978, the reception was not skeptical: “An interesting concept but one that could never be practically realized.” However, Dr. Iga continued his research in his laboratories with the help of his students and tirelessly promoted his ideas at academic meetings and international conferences in Japan and overseas.
In 1988, ten years after Dr. Iga’s first VCSEL presentation, Dr. Fumio Koyama—then a member of Dr Iga’s Lab and later became a professor —successfully demonstrated continuous wave operation at room temperature. By the late 1990s, more researchers had entered the field, and the VCSEL technology finally progressed to commercialization. As of 2025, the VCSEL market has grown into a $4 billion industry , with widespred applications in everyday devices such as computer mouses and laser printers. VCSELs are also a key component in optoelectronics, used in parallel optical technologies to enable high-speed, large-volume data transmission over LANs and in data centers, energy-efficient 3D facial recognition on smartphones, and LiDAR applications. In this way, VCSEL technology has dramatically transformed our lives. On October 28, 2025, this technology will be dedicated as one of the IEEE Milestones, recognizing key electrical and electronic achievements throughout history.

*1 Oscillation: Imagine a system where the waves emitted from an amplifier are fed back to an input device. Although the emitted waves usually attenuate (weaken) due to dispersion and absorption, amplification eventually exceeds attenuation. This is when oscillation occurs causing energy to be concentrated in a wave of a specific resonated wavelength, intensifying the wave.
For example, when a microphone picks up the output from a speaker, a powerful howling or screeching sound is generated. This “feedback” is a type of sonic oscillation.
*2 Note Light has existed since the beginning of the universe. The invention of the laser device and realization of laser light by Dr. Maiman was a truly historic and epoch-making event.