Milestone-Proposal:Vertical-Cavity Surface-Emitting Laser, 1977

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Docket #:2022-11

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To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

Year or range of years in which the achievement occurred:


Title of the proposed milestone:

Vertical-Cavity Surface-Emitting Laser, 1977

Plaque citation summarizing the achievement and its significance:

A vertical-cavity surface-emitting laser (VCSEL) was conceived at Tokyo Institute of Technology in 1977 and its leading research has been pursued. The laser-cavity is vertical to the surface and can be short near to wavelength. This enabled monolithic fabrication, single-frequency operation, and continuous-frequency tuning. The VCSEL has been used for communication and sensing as in datacoms, computer mice, printers, 3D face-recognition, and laser radars.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

March 22, 1977, Kenichi Iga of Tokyo Institute of Technology perceived a surface emitting laser whose light output comes vertically from the wafer surface, contrary to the conventional edge-emitting laser. The target of research motivation was the realization of current injection semiconductor laser that satisfies (i)monolithic fabrication, (ii)stable single frequency oscillation, and (iii)continuous-frequency tuning. The device was later named vertical-cavity surface-emitting laser (VCSEL). Iga and his group clearly showed the feasibility of VCSELs by proving a laser oscillation with this new structure in 1979.

Iga and his group’s innovative and persistent research have brought significant progress for VCSEL performance and productivity. Among excellent performance that they realized included very low threshold and driving currents, circular light beams, and so on. Along with the development the three problems that Iga pointed as the motivation was clarified; monolithic fabrication, stable single frequency oscillation, and continuous-frequency tuning. From device fabrication view point, the array formation allows us to check the chip characteristic in a wafer scale, not in a separated chip scale.

With devoting research, Kenichi tried to make VCSELs popular by having lectures frequently in world-wide. These efforts contributed to expand VCSEL applications from communications to consumer electronics.

VCSEL has grown to be a key component for supporting and further developing the information society of the 21st century. From the original invention to the technology development for higher performance and commercialization of VCSEL s, Iga’s contribution is quite significant and difficult to be replaced. (249words)

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

IEEE Photonics Society

In what IEEE section(s) does it reside?

IEEE Tokyo Section

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: IEEE Tokyo Section
Senior Officer Name: Dr. Kiyoharu Aizawa

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: IEEE Tokyo Section
Senior Officer Name: Dr. Kiyoharu Aizawa

IEEE section(s) monitoring the plaque(s):

IEEE Section: IEEE Tokyo Section
IEEE Section Chair name: Dr. Kiyoharu Aizawa

Milestone proposer(s):

Proposer name: Kohroh Kobayashi
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

Milestone plaque site:

       Tokyo Institute of Technology, Suzukake-dai Campus, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan
      GPS: 35.5154784, 139.4824420

Milestone replica plaque site:

      Tokyo Institute of Technology Museum 2-12-1, O-okayama, Meguro-ku, Tokyo, 152-8550 Japan
      GPS: 35.606876, 139.684802

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. C-6) Details of the plaque mounting: 1) Milestone plaque: The milestone plaque will reside in the Suzukake-dai campus of Tokyo Institute of Technology. The plaque will be installed on the grounds along the way from the campus entrance to the FIRST building where Professor Kenichi Iga’s laboratories existed. The plaque site is in proximity to the FIRST building and is supposed to be located next to the Milestone plaque of Koga’s temperature-insensitive quartz oscillation plate (Fig.13). Media: FIGPDF13.pdf Both milestone plaques will be fixed on each heavy stone monument. 2) Milestone replica plaque: The replica plaque will be displayed in the special showcase at the Exhibition Room of the Institute Museum of Tokyo Institute of Technology at O-okayama Campus (Fig. 14). Media: FIGPDF14.pdf

Fig. 13 Milestone plaque site: Stone monument installed on the ground floor in Suzukake-dai Campus, Tokyo Institute of Technology. 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503 Japan. The left is the place planned to be set. The right is the Milestone plaque of Koga's quartz oscillation plate.

Are the original buildings extant?

Yes, Professor Kenichi Iga’s laboratories existed in the main building of the FIRST (Future Interdisciplinary Research of Science and Technology) Laboratory (Building R2 in Fig. 12) at Suzukake-dai Campus of Tokyo Institute of Technology in 1975-2001. Media: FIGPDF12.pdf

Details of the plaque mounting:

1) Milestone plaque: The milestone plaque will reside in the Suzukake-dai campus of Tokyo Institute of Technology. The plaque will be installed on the grounds along the way from the campus entrance to the FIRST building where Professor Kenichi Iga’s laboratories existed. The plaque site is in proximity to the FIRST building and is supposed to be located next to the Milestone plaque of Koga’s temperature-insensitive quartz oscillation plate (Fig.13). Both milestone plaques will be fixed on each heavy stone monument. 2) Milestone replica plaque: The replica plaque will be displayed in the special showcase at the Exhibition Room of the Institute Museum at O-okayama Campus (Fig. 14).

How is the site protected/secured, and in what ways is it accessible to the public?

Visitors are subject to the entrance security protocol for both Milestone plaque site and Milestone plaque replica site. 1) Milestone plaque site: Ground floor in front of FIRST Laboratory The plaque is open to the public when the Suzukake-dai campus is open, i. e., open weekdays 8:30-17:15. The plaque is protected by a heavy stone monument. 2) Milestone replica site: Institute Museum The museum is open to the public on weekdays from 10:30 to 16:30. Closed nights and holidays.

Who is the present owner of the site(s)?

Tokyo Institute of Technology National University Corporation

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

Its technological, scientific, and social importance is described as follows:

  1. Technological: Invention and pioneering study of vertical-cavity surface-emitting laser (VCSEL)
  2. Scientific: Device realization including semiconductor crystal growth and nanofabrication or theoretical and experimental study on the physics of short-cavity lasers.
  3. Social: Room temperature continuous operation enabled industrialization.

(1) Perception of a Current-Injection and Short Cavity Surface Emitting Laser

   In 1977, Kenichi Iga of Tokyo Institute of Technology perceived a unique semiconductor laser, whose simple drawing is shown in Fig. 1[A1]. File:FIGPDF1.pdf Contrary to the conventional Fabry-Perot edge-emitting semiconductor lasers, his invention comprises a laser cavity vertical to a wafer surface on which many layers are epitaxially grown, including an active layer. It was later named VCSEL (Vertical-Cavity Surface-Emitting Laser).
   Kenichi Iga at Tokyo Institute of Technology was dissatisfied with the edge-emitting semiconductor lasers from the viewpoints of their fabrication and device characterization. The laser cavity of conventional semiconductor lasers used to be fabricated by manually cleaving the epitaxially grown wafers in a specific crystal plane .The cleaving process was conducted manually. Cavity formation by the cleaving was time consuming and not suited volume production.
   As far as the laser performance was concerned, spectral characteristics such as single frequency oscillation and its tunability were serious issues to be realized. Toward ideal semiconductor lasers, Kenichi Iga considered three requirements as follows [A2], [A3].

(i) The laser should be manufactured by a monolithic process.

(ii) The oscillation frequency should be single.

(iii) The oscillation frequency should be tunable.

   Before the VCSEL was conducted, Iga and Y. Takahashi (graduate student) had analyzed the single-frequency oscillation of a semiconductor laser at high-speed pulse modulation in 1978[A4].
    After careful consideration to solve these issueconfigurations, Iga had a conception of the laser cavity vertical to the wafer surface as shown in Fig. 1 [A1].  He also suggested some current injection scheme.
   By introducing a vertical cavity configuration, monolithic cavity fabrication became possible. Furthermore, a short cavity as short as a wavelength order was easy to realize. Such a short cavity led to  single frequency oscillation and to emission frequency tunability.
   Based on the idea of VCSEL, Kenichi Iga and his group promoted analytical and experimental research on this new device. The concept and the first experimental results on spontaneous vertical light emission from GaInAsP/InP diodes were presented by Iga at the Spring Meeting of Applied Physics Societies, Japan, March 1978 [A5]. Almost the same content was orally presented in November 1978 at the Fall Meeting of the Applied Physics Societies, Japan[A6]. 
   In 1979, H. Soda (Iga’s graduate student) successfully demonstrated lasing operation of a GaInAsP/InP VCSEL under pulsed injection current condition at 77 K [A7]. The cross-sectional structure and light output vs. current characteristics are shown in Fig. 2. Media:FIGPDF2.pdf This is the first demonstration of the current-injected VCSEL lasing oscillation, which clearly showed the possibility of a VCSEL as a practical vertical-cavity laser. Iga and his group concentrated on paving the way for this new and attractive semiconductor laser. 
   Following the world’s first lasing of a VCSEL, Iga, Y. Motegi and H. Soda (graduate students) made a breakthrough by fabricating a short cavity of about 10-micron long [A8]. They developed a fine chemical etching technology to realize such a short cavity length. The image of the cross section is shown in Fig. 3. Media: FIGPDF3.pdf A flat-enough surface was obtained for laser resonator formation. The emission spectra under pulsed current excitation at 77 K are shown in Fig. 4.  Media:FIGPDF4.pdf A single-longitudinal-mode oscillation was maintained up to at least 1.7 times the threshold. The longitudinal-mode spacing was large(175 Å), reflecting the short cavity length.
   As mentioned before, the theoretical simulation had pointed out that a short-cavity is effective in achieving single-frequency oscillation [A4]. Their theory was confirmed by this experiment with a short-cavity VCSEL [A8].
   In 1986, Iga’s graduate student, S. Kinoshita succeeded in reducing the threshold current of VCSELs to less than 10 mA for the first time in the world [A9], [A10]. The threshold current was 4.5 mA at 77 K under CW current and 6 mA at room temperature under pulsed injection, with a buried hetero-structure AlGaAs/GaAs VCSEL. This low-threshold current achievement was attracted attention from the community of semiconductor lasers.
   Since then, Iga and his group have been continuously conducting elaborate research and development on VCSELs and achieved many results, which have contributed to the growth of VCSEL devices and related applications. Theoretical and experimental studies for VCSELs done by Iga’s group were summarized as a paper in IEEE Journal of Quantum Electronics in 1988 [A11]. Based on the research results, dynamic single frequency operation, extremely low threshold current of <1 mA, and a possibility of room temperature CW operation of VCSELs were predicted in the paper. Fundamental results on a 5x5 two-dimensional array were also described.    

(2) Pioneering work for developing new technologies of VCSELs

(i) Conception of surface-emitting semiconductor laser and the first verification of its possibility

   In 1977, Iga conceived a semiconductor laser where a laser cavity was formed in a direction vertical to the semiconductor wafer surface and the light came out of the same direction[A1].

(ii) Single-frequency oscillation in VCSEL

   Iga had suggested through theoretical analysis that a single-frequency oscillation is possible by making cavity length being less than several ten’s of micron even at high-speed pulse modulation [A4]. In 1982, Iga,s graduate-student, Motegi and Soda successfully demonstrated a single-frequency operation for the first time in the world. They used a GaInAsP/InP double heterostructure with a cavity length of about 10 microns by etching a substrate off [A8].

(iii) Continuous-wave operation at room temperature

   Continuous-wave (CW) operation at room temperature is one of the criteria for the device to be acknowledged as applicable to equipment and systems. In the case of VCSELs, more than ten years have passed from the conception in 1977[A1] to obtain the CW oscillation at room temperature. It was achieved by Fumio Koyama of Iga’s group in 1988 [A12]. They used an AlGaAs/GaAs VCSEL structure with a micro-cavity made of dielectric multilayer mirrors at the wavelength of 0.8 microns as shown in Fig. 5(a). The threshold current was about 30 mA at room temperature as shown in Fig.5(b). Media:FIGPDF5.pdf
   The first room-temperature CW operation of long-wavelength VCSEL was also achieved by T. Baba of Iga’s group in 1993 with InGaAsP/InP system and a thermally conductive MgO/Si multilayered mirror [A13]. The emission wavelength was 1.2 microns.

(iv) Low-threshold-current laser operation

   Many researchers in the world have striven to further reduce the threshold current. In 1995, Iga’s group again achieved the record low threshold current of 70 μA in native oxide-confined index-guided VCSELs (Fig. 6) [A14]. Media:FIGPDF6.pdf Their effort and results have significantly accelerated the development and progress of VCSELs.

(v) Introduction of MQW active region into VCSEL

   As a higher gain medium for VCSELs, an AlGaAs/GaAs MQW structure was first introduced into VCSELs by Kenichi Iga, and H. Uenohara (graduate student) in 1987 [A15], [A16]. After this trial, a single-quantum well or an MQW has become a standard active medium in VCSELs.

(vi) Semiconductor multilayered Bragg reflector

   The semiconductor multilayered Bragg reflector was also first introduced by Kenichi Iga as one of the mirrors for a laser vertical cavity. The first VCSEL with this semiconductor mirror was successfully demonstrated by Iga’s group with an AlGaAs/AlAs multilayered Bragg reflector in 1988 [A17]. This enabled the fabrication of lasers with full monolithic semiconductor processing, which drastically improved the productivity of laser fabrication. This is really one of the advantages that Kenichi Iga desired to realize with the VCSEL configuration. 

(vii) Continuous-frequency tuning

   Owing to the short cavity length, a VCSEL emits single-frequency light defined by the cavity length. Continuous-frequency tuning was demonstrated by N. Yokouchi, graduate student of Iga’s group with an InGaAsP/InP VCSEL, one of the mirrors of which was replaced by a mechanically movable external mirror in 1992 as depicted in Fig. 7 [A18], [A19].  Media:FIGPDF7.pdf The wavelength was continuously changed over 40−86 Å at 77 K. This study was followed by a monolithic version, Micro- Electro-Mechanical System (MEMS) of frequency-tunable VCSEL in later time [B28].

(viii)Two-dimensional array

   The surface emitting laser enables a two-dimensional array formation. Iga’s group tried to realize two-dimensional VCSEL arrays and demonstrated a 2x2 array in 1985 [A20] and a 5x5 array in 1988 [A11]. The structure and emission pattern of a 5x5 array are shown in Fig. 8 [A11].  Media:FIGPDF8.pdf All the VCSEL devices are simultaneously driven by one electrical contact in this experiment. This feasibility trial for the array formation encouraged people toward high productivity by making possible chip characterization on a wafer scale. The two-dimensional VCSEL array configuration was industrialized later in high-density and high-speed laser printers in 2001.

(3) Social importance of the proposal and development of VCSELs

   Besides the room-temperature continuous-wave (CW) operation of VCSELs[A12], which is indispensable to the industrialization of devices,  many disruptive features of VCSELs such as high productivity, high efficiency, low power consumption, a circular beam, a single frequency, and a two-dimensional array, all of which were realized by Iga’s group, are becoming well-recognized worldwide, and their application areas have been expanding since the mid-90s. The VCSEL applications are shown in Fig. 9 [A2], [A3], [A22], [A23].  Media: FIGPDF9.pdf
   The application areas started with data communications, followed by sensors, printers, and computer mouse pointers until the mid-2010s. Since then, although the market size of data communication and sensing has steadily grown and is still expected to grow and occupy the main body of the VCSEL’s markets and related ones, VCSELs are exploring applications in new areas such as face recognition and LiDARs (Light Detection And Ranging) for automatic driving, infrared illumination, pumping, and industrial heating.   
   These applications will provide huge potential for VCSEL markets. VCSELs are the most suitable light sources for these applications because of their advantageous features such as low cost owing to high productivity, high reliability, low power consumption, small size, and ease of two-dimensional array integration. 
   As described here, VCSELs are becoming indispensable key components, which support the information society for today and the future from data-com to smart sensing. It is not easy to imagine societies without VCSELs. 
   VCSELs are becoming indispensable key components, which support the information society today and in the future from data-com to smart sensing. It is not easy to imagine societies without VCSELs.

What obstacles (technical, political, geographic) needed to be overcome?

B-2) What obstacles (technical, political, and geographic) need to be overcome?

   At the beginning of 1970s, semiconductor lasers were extensively studied worldwide as a light source for optical fiber communications. With such efforts, performances of semiconductor lasers were significantly improved, including reliability. Kenichi Iga thought these devices were quite attractive but had some serious disadvantages in their productivity, especially in the stage of future large-volume production. The lasers at that time frame were called edge-emitting laser diodes (EE-LDs). A pair of crystal facets formed the laser cavity in a direction parallel to that of the semiconductor substrate surface. The laser cavity of the semiconductor laser was fabricated by cleaving almost manually a thin semiconductor substrate, on which semiconductor laser structures were formed. This manual process was supposed to be a crucial obstacle to mass production of semiconductor lasers. 
   Kenichi Iga pointed out another drawback, which would emerge from the essential structure in EE-LDs. No practical wafer-scale inspection was possible in EE-LDs for the device characterization and/or the initial chip selection. Such inspection was only possible after the semiconductor wafer was cleaved and separated into laser bars/chips, because the light from the laser came out through the cleaved mirror facet in a direction parallel to that of the semiconductor substrate. This feature of inspection inevitably degrades the semiconductor laser productivity. 
   Kenichi Iga solved these problems by inventing a new laser structure in which the laser cavity was formed in a direction perpendicular to the semiconductor substrate surface [A1]. The VCSELs were considered, in principle, to be completely fabricated by efficient semiconductor processes, not only by time-consuming but also costly manual processes. An obstacle to preventing lasing oscillation in VCSELs came from the fact that the active region was limited to be quite thin because of the limitation in the crystal growth in the thickness direction and the limited carrier diffusion length. Kenichi Iga successfully achieved lasing in current-injecting VCSELs for the first time in the world by combining a thin active region with a highly reflective mirror [A4]. Since this breakthrough, he has devoted continuous effort to improve the laser performance of VCSELs. By combining a highly efficient quantum well gain medium with highly reflective semiconductor DBR mirrors, Kenichi Iga realized high performance and practical VCSELs. The VCSEL devices, fabricated by a fully mass-producible semiconductor monolithic process, were aligned in a two-dimensional array on a wafer and all devices were characterized and inspected one by one in the wafer-scale situation if necessary. Crucial issues of semiconductor laser productivity caused by the fabrication and characterization/inspection process were overcome by the invention of VCSELs. Kenichi Iga has overcome the obstacle and paved the way for a new laser source world of VCSELs with ample applications, which have been significantly contributing to the prosperity and welfare of the world.

What features set this work apart from similar achievements?

B-3) What features set this work apart from similar achievement?

(1) Similar works

(i) Early similar works

   In 1964, coherent light emission from an InSb bulk surface was reported by Melngailis et al. of Lincoln Laboratory, Massachusetts Institute of Technology[B4], followed by an additional report by the same author in 1965[B5]. The current injection was longitudinal to the coherent light emission, which was parallel to it. This laser operated at a very low temperature of 10 K with current confinement by an intense magnetic field. Even with such current confinement, the drive current was quite high, i.e., 20 A (=60 kA/cm2) under pulsed conditions. Because a crystal-cleaving technique was not developed at this time, the laser cavity was formed by polishing both surfaces of InSb bulky semiconductor wafers. Any short cavity was not supposed. The longitudinal cavity length was 220 microns. No further significant performance improvement has been realized compared with those of the edge-emitting lasers. 
   Several other reports have appeared on thin-film semiconductor lasers and related devices since the 1960s. Most of them are optically pumped or electron-beam-pumped and no practical relations are found with the present VCSELs. These include a thin-film CdSe laser by Stillman et al. of University of Illinois, Urbana, in 1966[B6]; a radiating mirror by Basov et al. of Levedev Physics Institute, Academy of Science, USSR, in 1966[B7]; electron-beam-pumped CdS laser by Packard et al. of 3M Company in 1969[B8]; thin dielectric-coated CdS laser by Smiley et al. of Naval Electronics Laboratory Center, San Diego, in 1971[B9]; optical bistability in thin GaAs film by Gibbs et al. of Bell Laboratories in 1979 [B10]; optically pumped ribbon whisker by Duguay et al. of Bell Laboratories, in 1980[B11]; and optically pumped GaAs thin-film laser under low temperature (<115 K) by Passner et al. of Bell Laboratories in 1980[B12].
   As described, prior to the proposal and invention by Kenichi Iga in 1977, there existed several fundamental research on semiconductor lasers emitting light vertically from the surface. Most of these studies, however, read optically pumped or electron-beam-pumped thin-film lasers, which turned out not to extend to the present VCSELs, which Kenichi Iga strove for more than 25 years to establish a new semiconductor laser direction with current injection scheme maintained. The VCSELs developed and commercialized at present are on the line where Iga and his group had paved the way.
(ii) Patent by Tokyo Institute of Technology and Xerox-PARC
   In the initial stage of VCSEL development, two inventions were applied. One was invented by Kenichi Iga et. al, all from Tokyo Institute of Technology, Japan, applied on January 9th, 1980. We call this Titech Patent (Fig.10) [A21].  Media: FIGPDF10A.pdf, Media: FIGPDF10B.pdf
   Independently from the Titech Patent, R. D. Burnham, D. R. Scifres, and W. Streifer, all from Xerox Corporation, United States of America, applied for a patent on September 13th, 1979. This is called Xerox Patent in this proposal. The title was "Transverse Light Emitting Electroluminescent Devices"[B13].  
   The said Titech Patent and Xerox Patent were granted as independent inventions. Thus, both parties were recognized as independent patent inventors. However, the Xerox patent had not been recognized by most VCSEL research communities until Burnham and Scifres received the 2002 Rank prize as co-recipients together with Iga. On the other hand, Iga received the Streifer Award in 1992 for the VCSEL initiator. This award was established by Xerox in memory of the late William Streifer, who was one of the inventors of the Xerox Patent. The Xerox group performed outstanding work on high-power lasers and edge-emitting DFB lasers, not VCSELs, as far as we know.

(2) Later similar work

(i) J. Jewell's microlaser

   A microlaser was reported by Jewell and his group of AT&T Bell Laboratories[B14]. The active region was a GaInAs 100-Å-thick single-quantum well. The laser cavity was formed by a pair of semiconductor DBR mirrors consisting of AlAs/GaAs multilayers. The threshold currents of 1.3 mA under pulsed condition were reported with a 5-micron square microlaser. The threshold current was reduced to 1.1 mA and 1.5 mA under pulsed and CW current conditions, respectively [B15]. The microlaser was considered as the component of optical computers, which was the mission of their department at AT&T Bell Labs at that time. 

(ii)Threshold current reduction and device performance progress

   With the hopeful results on VCSEL achieved in the initial feasibility study by Iga and his group many organizations worldwide attracted interest in VCSELs and started research in the 1990s. To show the progress of VCSELs, we track the threshold current reduction by Iga and his group of Tokyo Inst. Tech. and many others from other organizations. Major players and their results on the threshold current are listed in Table I Media: TABPDF1.pdf and depicted in Fig. 11. Media: FIGPDF11.pdf The data were limited to the threshold current under CW conditions at room temperature, except those with a specific remark in the figure. The results achieved by Iga and his group are shown as star marks in Fig. 11. The open stars show threshold current under pulsed current and closed ones show those under CW current.
   From the second half of the 1980s to the first half of the 1990s, the threshold current of VCSELs further reduced from a few milliamperes to sub-milliamperes. Jewell et al., of AT&T Bell Laboratories, achieved a low-threshold current of 1.3 mA (pulsed) with three GaInAs quantum wells in 1989[B14]. Soon after that, he announced a CW threshold current as low as 1.5 mA with GaInAs single-quantum well and 5-micron square micro-post structure, as described in (i) in this section[B15]. Geels and Coldren of U. C. Santa Barbara reported the threshold current of 0.7 mA in a VCSEL with a strained InGaAs single-quantum-well active region [B17]. This is the first report for threshold current less than 1 mA. A few years later, he claimed the threshold current of 290 µA[B25]. In 1993, Numai et al., of NEC, achieved a threshold current as low as 190 µA under pulsed condition at room temperature with an InGaAs/GaAs strained single-quantum well active region and an air post structure of 5-micron diameter[B18]. Huffaker et al., of the University of Texas, Austin, achieved a low-room-temperature CW threshold current of 225 µA in a VCSEL with an InGaAs single-quantum-well active region[B19]. The current was effectively confined by a native oxide aperture of 8-micron square. The threshold current went down to 91 µA by reducing the buried oxide aperture to 2-micron square, as reported by Huffaker of Texas at Austin[B20]. These excellent results were followed by the 70 µA threshold current achieved by Iga’s group in March 1995[A14]. This was again a world record at that time.
   A couple of months later, in May 1995, Yang in Dapkus’s group of University of Southern California, Los Angels, published a paper claiming a lower threshold current of a VCSEL, less than 10 µA[B21]. 
  Besides the organizations described here, many others have participated in the research on VCSELs and achieved low threshold current of sub-milliamperes, which include University of Ulm [B22], B23], and Sandia National Laboratories [B24]. In addition to the threshold current reduction of VCSELs described in TableⅠand Fig. 11, important and turning innovations led by Kenichi Iga and his group are listed in Table II Media: TABPDF2.pdf with significant related achievement by other groups. 

(iii) Wavelength-tunable VCSEL

   Wavelength/Frequency-tunable VCSELs are important light sources for spectroscopic sensing and datacom with wavelength division multiplexing. Very recently, a tunable VCSEL has been used for a ranging sensor in combination with a monolithically integrated light beam deflector where the emitting beam angle depends on the wavelength [B3]. Continuous-tuning of 18 Å was achieved by current injection through a newly added electrode into the n-DBR mirror, as reported by Chang-Hasnain et al., of Bellcore, in 1991 [B27]. The active junction can be cooled owing to the Peltier effect or heated by DBR resistance Ohmic contact heating. Another approach toward the continuous frequency-tuning was realized by providing a top DBR mesa and the third electrode into a VCSEL. Highly resistive heterointerfaces of the top DBR mesa cause extra heating of the cavity, resulting in a continuous wavelength change toward the longer wavelength. A wavelength shift of 2.2 nm was derived by the tuning current of 700 μA, as reported by Wipiejewski in Ebeling’s group, at University of Ulm [B22]. 
   To further expand the tunability, Iga’s group verified the wide frequency tuning in a VCSEL with a mechanical movable external mirror[A18], [A19]. Chang-Hasnain of Stanford University realized a monolithic MEMS version of the external mirror VCSEL and showed the record-high wavelength tuning range of 15 nm [B28]. The wavelength tunable VCSEL has opened various applications.

(3) Application Progress of VCSEL in the 21st century

   Application areas of VCSEL have been expanding since the mid-1990s. They started from short-reach data communications including local area networks (LANs) and optical interconnects inside high-performance computers, servers, and data centers, followed by laser printers, computer mice, displays, and ranging sensors, as shown in Fig. 9 [A2], [A3], [A22], [A23]. Media: FIGPDF9.pdf

(i) LANs and datacom

   In response to the rapid growth of internet traffic, strong requirements occurred to expand the network bandwidth in a data center and between data centers. Standardization was promoted in a family of 100 Gbps Ethernet (100 GbE), including 1 00GBASE-SR10, 100GBASE-LR4, and 100GBASE-ER4. SR10 is based on 10 parallel 850-nm multi-mode fiber transmissions with 10 Gbps per fiber. The SR10 supports reaches up to at least 100 m. LR4 and ER4 are based on dense wavelength division multiplexing (DWDM) technology. They support single-mode fiber transmission of at least 10 km and 40 km, respectively. Four wavelength light signals of around 1300 nm with a separation of 800 GHz are transmitted through a single-mode fiber. Each wavelength carries 25 Gb/s. SR10 is supposed to be used in a data center, while ER4 is suitable for connection between data centers. LR4 is applicable to both inside a data center and in-between them; 850-nm VCSELs are supposed to be applied to SR10. For LR4 and ER4, the optional usage of VCSELs and edge-emitting DFB lasers is supposed. For even higher capacity systems, standardization of 400 Gb/s Ethernet is in preparation[B29]. In parallel with the effort for the standardization of datacom, such as 100GbEs, research and development are being continuously conducted on optical communication to meet the strong demand for the higher bandwidth.

(ii) Optical interconnects

   The main market for VCSELs will be, besides the communications for intra- as well as inter-data centers, interconnections in high-performance computers (HPCs) and servers. High-density and highly parallel optical interconnects are extensively deployed for rack-to-rack connections in HPC and servers with multi-mode optical fibers. Requirements for the number of parallel channels and the transmitter/receiver bandwidth are gradually increasing. IBM developed VCSEL-based optical interconnects; 48-channel parallel optical transceivers were demonstrated to transmit and receive up to 20 Gb/s per channel by flip-chip bonding of two optoelectronic arrays with 2 x 12 850 nm VCSEL arrays and GaAs PD arrays on a holey CMOS IC [B30].   
   Tokyo Institute of Technology announced the start of the operation of a newly developed supercomputer Tsubame 3.0, a leading cloud-type green super computer with high performance and efficient power consumption, where high-capacity and high-speed optical networks connect many computing nodes. The total communication capacity counts 432 Tb/s in the bi-direction mode, whose main body is carried by optical interconnects. The detail is presented on the Web pages of Tokyo Institute of Technology Global Scientific Information and Computer Center [B31]. 
   Effort to increase the modulation bandwidth of VCSELs enabled 64 Gb/s-57m multi-mode optical fiber transmission, as presented by Kuchta of IBM-T. J. Watson Research Center and by Westbergh of Chalmers University of Technology [B32]. Besides such efforts to increase the bandwidth of a single-channel, parallel schemes, such as 1 x n or two-dimensional arrangement, m x n, will be indispensable to meet the required aggregate bandwidth. VCSELs are the only solution from the viewpoint of the two-dimensional array configuration and low power-consumption capability. In 2014, aggregated capacity as high as 1.34 Tb/s was realized for incorporation with 2D VCSEL arrays of 14 x 12, as reported by Grabherr and Ebeling of Philips Technologies GmbH U-L-M Photonics, Germany [B33]. A prediction indicated that billions of channels per year will be required soon, as pointed out by Grabherr of Philips GmbH, U-L-M Photonics, Germany [B34]. VCSEL has grown up to be a key component that supports networks and computers of the present and future days. 

(iii) Laser printers

   A laser printer is known as a high-quality and high-speed machine for digital printing markets. A conventional laser printer often uses a one-dimensional array of lasers, where scanning the laser beams by rotating a polygon mirror. Replacing the one-dimensional laser array with a two-dimensional array of VCSELs, a higher speed of printing is possible while maintaining high printing quality. For example, Fuji Xerox Co. Ltd. developed a high-performance laser raster output scanner using an 8 x 4 VCSEL array as the engine for the printing machine. High quality of 2,400 DPI was achieved with a printing speed of more than 100 sheets per minute by Fuji Xerox Corp. [B35]. The high quality and high-speed operation were realized by applying two-dimensional VCSEL arrays for the first time. Ricoh Co. Ltd. developed a high light-output-power 780 nm array of 40ch VCSELs. By designing and fabricating a low-thermal-resistance DBR mirror, they realized a single-mode light output power of >1.5 mW with reduced thermal interference between VCSELs in the arrays [B36]. With this high-power stable VCSEL array as a multibeam light source, Ricoh Co. Ltd. also produced a high-speed of 150 pages per minute and high precision of 4,800 DPI printing machines [B37]. 

(iv) Computer mice

   The first volume commercial application of VCSELs might be a light source for a computer mouse pointer. The laser mice emerged in 2004. Since then, the shipped quantities of VCSELs have dominated for use in laser mice. Because of the circular output light beam with a small diameter from a single-mode VCSEL, higher tracking precision, as well as a lower electric power consumption is possible in VCSEL mice over the conventional LED mice, as reported by Grabherr in 2013 [B38]. 

(v)Ranging and sensing

   Several companies such as Finisar Corp., II-VI, and Philips U-L-M Photonics shipped 100 to 200 million VCSELs per year in 2013 or 2014, as described by Grabherr in the SPIE Journal referred above[B33]. The total number of VCSELs shipped over the last 20 years is estimated to be nearly 1 billion by Tatum of Finisar Corp. [B39]. Although the past and the present markets, related to VCSEL applications, are still datacom, new and promising volume applications have recently emerged in consumer electronics. They are smart sensors in electronic devices, as described also by Grabherr in the same SPIE journal [B39]. Smartphones today are installed with many VCSELs for use in, for example, laser autofocusing and proximity sensing by time-of-flight range detection, 3D (three dimensional) face recognition for a new security system of smartphones by the use of structured light, low noise optical microphone, and some devices for gesture recognition. These applications will provide a huge potential for VCSEL markets. VCSELs are the most suitable light sources for these applications because of their advantageous features such as low cost owing to high productivity, high reliability, low power consumption, high signal bandwidth and small size. 
   Fumio Koyama of Tokyo Institute of Technology has succeeded to extend the ranging distance further by monolithic integration of a VCSEL and a VCSEL-based fully solid-state light beam steering device, resulting in a beam steering LiDAR (Light Detection And Ranging) with small size, high resolution, and long measurable distance [B3]. These features are attractive for various sensor applications such as automatic driving, automatic production lines, infrastructure inspection, and many others.

(vi) Iga and his group’s contributions

   In summary, Iga’s pioneering work in collaboration with his group revealed many disruptive natures of VCSELs and opened new application areas. VCSEL has developed to be a key component for supporting and further developing the information society of the 21st century. From the original invention to the technology development for higher performance and commercialization of VCSELs, Iga and his group’s contribution is quite significant and difficult to be replaced.

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

B-4) List of Selected References

A: References related directly to the work by Kenichi Iga and his group

[A1] K. Iga, Laboratory Notebook of Precision & Intelligence Laboratory, 1977 Issue, Tokyo Institute of Technology, Tokyo, Japan, Mar. 22, 1977. Refer to Fig. 1. Media: A1-InitialIDEA.pdf

[A2] K. Iga, “Forty years of vertical-cavity surface-emitting laser: Invention and innovation”, Jan. J. Appl. Phys., Vol. 57, No. 08PA-1, pp. 1-7, 2018. Media:A2-Forty Years.pdf

[A3] K. Iga, "VCSEL: born small and grown big, Proc. of SPIE, Vol. 11263, pp. 1126302-1-1126302-13, March 2020. Media:A3-grownbig.pdf

[A4] K. Iga, and Y. Takahashi, “An Analysis on Single Wavelength Oscillation of Semiconductor Laser at High Speed Pulse Modulation,” Trans. IECE Japan, Vol. E61, No. 9, pp. 68-72, Sept. 1978. Media: A4-Analisis.pdf

[A5] K. Iga, T. Kambayashi and C. Kitahara, “GaInAsP/InP Surface Emitting Laser(I),” The 25th Spring Meeting of Applied Physics Societies, 27p-C-11, p.63, Mar. 1978.  (In Japanese:Translated English text attached). Media: A5-27pC11.pdf

[A6] C. Kitahara, T. Kambayashi and K. Iga, "GaInAsP/InP Surface Emitting Laser (II)," The 39th Fall Meeting of Applied Phys. Societies, 5p-Z-1, p.497, Nov.,1978. (In Japanese:Translated English text attached). Media: A6-5pZ1.pdf

[A7] H. Soda, K. Iga, C. Kitahara and Y. Suematsu, “GaInAsP/InP Surface-Emitting Injection Lasers,” Jpn. J. Appl. Phys., vol. 18, no. 12, pp. 2329-2330, Dec. 1979. Media: A7-FirstLasing.pdf

[A8] Y. Motegi, H. Soda, and K. Iga, “Surface-Emitting GaInAsP/InP Injection Laser with Short Cavity Length,” Electron. Lett., Vol. 18, No. 11, pp. 461-463, May 1982. Media: A8-ShortCavity.pdf

[A9] K. Iga, S. Kinoshita, and F. Koyama, “Micro-cavity GaAlAs/GaAs Surface-Emitting laser with Ith=6 mA,” International Semiconductor Laser Conference, PD-4, Oct. 1986. Media: A9-6mALDConf.pdf

[A10] K. Iga, S. Kinoshita, and F. Koyama, “Micro-cavity GaAlAs/GaAs Surface-Emitting laser with Ith=6 mA,” Electron. Letters, Vol. 23, No. 3, pp. 134-136, 29th, Jan. 1987. Media: A10-6mAEL.pdf

[A11] K. Iga, F. Koyama, and S. Kinoshita, “Surface Emitting Semiconductor Lasers,” IEEE J. Quantum Electronics, Vol. 24, No. 9, pp. 1845-1855, Sept. 1988. Media: A11-JQEReview.pdf

[A12] F. Koyama, S. Kinoshita and K. Iga, “Room temperature CW Operation of GaAs Vertical Cavity Surface Emitting Laser,” Trans. IEICE, Vol. E71, No. 11, pp. 1089-1090, Nov. 1988. Media: A12-RTCW.pdf

[A13] T. Baba, Y. Yogo, K. Suzuki, F. Koyama and K. Iga, “First Room Temperature CW Operation of GaInAsP/InP Surface Emitting Laser,” IEICE Trans. Electron., Vol. E76-C, No. 9, pp. 1423-1424, Sept. 1993. Media: A13-RTCWLW.pdf

[A14] Y. Hayashi, T. Mukaihara, N. Hatori, N. Ohnoki, A. Matsutani, F. Koyama, and K. Iga, “Record low-threshold Index-guided InGaAs/GaAlAs vertical-cavity surface-emitting laser with a native oxide confinement structure,” Electron. Lett., Vol. 31, No. 7, pp. 560-562, Mar. 1995. Media: A14-70uA.pdf

[A15] H. Uenohara, F. Koyama, T. Sakaguchi, and K. Iga: “Multi quantum well structure for surface emitting lasers”, National Conference Record, Semiconductor Devices and Materials, IEICE, No. 279, Nov. 1987. (In Japanese: Translated English text attached) Media: A15-MQW-JETranslated.pdf

[A16] H. Uenohara, F. Koyama, and K. Iga: “Application of the multi-quantum well (MQW) to a surface emitting laser”, Jpn. J. Appl. Phys., Vol. 28, No. 4, pp. 740-741, April 1989. Media: A16-MQWJJAP.pdf

[A17] T. Sakaguchi, F. Koyama, and K. Iga, "Vertical Cavity Surface-Emitting Laser with an AlGaAs/AlAs Bragg Reflector," Electron. Lett., Vol. 24, No. 15, pp. 928-929, July 1988. Media: A17-DBR.pdf

[A18] N. Yokouchi, T. Miyamoto, T, Uchida, Y, Inaba, F. Koyama, and K. Iga, "40Å continuous tuning of a GaInAsP/InP vertical-cavity surface-emitting laser using an external mirror," IEEE Photon. Technol. Lett., Vol. 4, No. 7, pp. 701-703, July 1992. Media: A18-40A.pdf

[A19] N. Yokouchi, T. Miyamoto, T. Uchida, Y. Inaba, F. Koyama, and K. Iga, “GaInAsP/InP Surface Emitting Laser Grown by CBE and Wavelength tuning Employing External Reflector,” Int. Conf. on Solid State Devices and Materials, B-6-4, pp. 613-615, Tsukuba, Aug. 1992. Media: A19-TuningISDM.pdf

[A20] S. Uchiyama and K. Iga, “Two-Dimensional Array of GaInAsP/InP Surface-Emitting Lasers”, Electronics Letters, Vol. 21, No. 4, pp. 162-164, Feb. 1985. Media: A20-2DArray.pdf

[A21] K. Iga, Y. Suematsu, K. Kishino, and H. Soda, ”Surface-Emitting Semiconductor Lasers”, Japanese Patent, applied on January 9th, 1980, and granted as Heisei-1-56547 on November 30th, 1989. (In Japanese: A part of the first page of the patent was translated). Media: A21-Patent.pdf

[A22] K. Iga, “Surface emitting laser - Its birth and generation of new optoelectronics field”, IEEE J. Selected Topics in Quantum Electron., Vol.6, No.6, pp.1201-1215, Nov./Dec. 2000. Media: A22-ItsBirth.pdf

[A23] K. Iga, “Vertical-Cavity Surface-Emitting Laser(VCSEL)”, Proc. IEEE, Vol. 101, No. 10, pp. 2229-2233, Oct. 2013. Media: A23-ProcIEEE.pdf

[A24] T. Mukaihara, Y. Hayashi, N. Hatori, N. Ohnoki, A. Matsutani, F. Koyama, and K. Iga, “Low-threshold mesa-etched vertical-cavity InGaAs/GaAs surface emitting lasers grown by MOCVD,” Electron. Lett., Vol. 31, No. 8, pp. 647-648, April 1995. Media: A24-0.33mA.pdf

B: References related to work done by groups other than Kenichi Iga.

[B1] Y. Arakawa, and H. Sakaki, “Multidimensional quantum well laser and temperature dependence of its threshold current”, Appl. Phys. Lett., Vol. 40, pp. 939-941, 1982.

[B2] M. Asada, Y. Miyamoto, and Y. Suematsu, “Gain and the threshold of three-dimensional quantum-box lasers”, IEEE J. Quantum Electron., Vol. QE-22, pp. 1915-1921, 1986.

[B3] Z. Ho, K. Shimura, X. Gu, M. Nakahama, A. Matsutani, and F. Koyama, “High-resolution of Beam Steering of Slow Light VCSEL Amplifier”, The 12th Conference of Lasers and Electro-Optics Pacific Rim, 2-1G-5, Aug. 2017.

[B4] I. Melngailis, R. J. Phelan, and R. H. Rediker, “Luminescence and coherent emission in a large-volume injection plasma in InSb,” Appl. Phys. Lett., vol. 5, No. 5, pp. 99-100, Sept. 1964.

[B5] I. Melngailis, “Longitudinal injection-plasma laser of InSb,” Appl. Phys. Lett., Vol. 6, No. 3, pp. 59-60, Feb. 1965.

[B6] G. E. Stillman, M. D. Sirkis, J. A. Rossi, M. R. Johnson, and N. Holonyak Jr., “Volume Excitation of an Ultrathin Single-Mode CdSe Laser”, Appl. Phys. Letts., Vol. 9, pp. 268-269, Oct. 1966.

[B7] N. G. Basov, O. V. Bogdankevich, and A. Z. Grasyuk, “Semiconductor Lasers with Radiating Mirrors”, IEEE J. Quantum Electron., Vol. QE-2, pp. 594-597, September 1966.

[B8] J. R. Packard, W. C. Tait, D. A. Campbell, “Standing Waves and Single-Mode Room-Temperature Laser Emission from Electron-Beam-Pumped Cadmium Sulfide”, IEEE J. Quantum Electron., Vol. QE-5, pp. 44-47, Jan. 1969.

[B9] V. N. Smiley, H. F. Taylor, and A. L. Lewis, “Laser Emission in Thin Dielectric-Coated CdSe Lasers”, J. Appl. Phys., Vol. 42, No. 13, pp. 5859-5861, Dec. 1971.

[B10] H. M. Gibbs, S. L. McCall, T. N. C. Venkatesan, A. C. Gossard, A. Passner, and W. Wiegmann, “Optical Bistability in Semiconductors”, Appl. Phys. Letts., Vol. 35, pp. 451-453, Sept. 15, 1979.

[B11] M. A. Duguay, and T. C. Damen, “Picosecond Pulses from an Optically Pumped Ribbon Whisker Laser”, Appl. Phys. Letts., Vol. 37, p.369-370, Aug. 15, 1980.

[B12] A. Passner, H. M. Gibbs, A. C. Gossard, S. L. McCall, T. N. C. Venkatesan, and W. Wiegmann, “Ultrashort Laser: Lasing in MBE GaAs Layer with Perpendicular-to-Film Optical Excitation and Emission”, IEEE J. Quantum Electron., Vol. QE-16, pp. 1283-1285, Dec. 1980.

[B13] R. D. Burnham, D. R. Scifres, and W. Streifer, applied to US Patent on September 1979, and granted as a patent USP4,309,670, “Transverse Light Emitting Electroluminescent Devices, on January 5th ,1982.

[B14] J. L. Jewell, A. Scherer, S. L. McXll,Y. H. Lee, S. Walker, J. P. Harbison, and L. T. Florez, "Low-Threshold Electrically Pumped Vertical-Cavity Surface-Emitting Microlasers,” Electron. Letts., Vol. 25, pp. 1123-1124, Aug. 1989.

[B15] Y. H. Lee, J. L. Jewell, A. Scherer, S. L. McCall, J. P. Harbison, and L. T. Florex, “Room-Temperature Continuous-Wave Vertical-Cavity Single-Quantum-Well Microlaser Diodes,” Electron. Lett., Vol. 25, No. 25, pp.1377-1378, Sept. 1989.

[B16] D. I. Babic, K. Streubel, R. P. Mirin, J. Pirek, N. M. Margalit, J. E. Bowers, E. L. Hu, D. E. Mars, L. Yang, and K. Carey, “Room temperature performance of double-fused 1.54 micron vertical-cavity lasers,” in IPRM 96, ThA1-2, Apr.1996 

[B17] R. S. Geels and L. A. Coldren, “Narrow-Linewidth, Low Threshold Vertical-Cavity Surface-Emitting lasers,” 12th International Semiconductor Laser Conf., Vol. B-1, pp. 16-17, Davos, Switzerland, 9-14 Sept. 1990

[B18] T. Numai, T. Kawakami, T. Yoshikawa, M. Sugimoto, Y. Sugimoto, H. Yokoyama, K. Kasahara, and K. Asakawa, “Record Low Threshold Current in Microcavity Surface-Emitting Laser,” Jpn. J. Appl. Phys, Vol. 32, Part2, No. 10B, pp. L1533-L1534, Oct. 1993

[B19] D. L. Huffaker, D. G. Deppe, K. Kumar, and T. J. Rogers, “Native-oxide defined ring contact for low threshold vertical-cavity lasers,” Appl. Phys. Lett., Vol. 65, No. 1, pp. 97-99, July 1994

[B20] D. L. Huffaker, J. Shin, and D. G. Deppe, “Low threshold half-wave vertical-cavity lasers,” Electron. Lett., Vol. 30, No. 23, pp. 1946-1947, Nov. 1994.

[B21] G. M. Yang, M. H. MacDougal and P. D. Dapkus, “Ultralow threshold current vertical-cavity surface-emitting lasers obtained with selective oxidation,” Electron. Lett., Vol. 31, No. 11, pp. 886-888, May 1995.

[B22l T. Wipiejewski, K. Panzlaf, E. Zeeb, and K. J. Ebeling, “Submilliamp vertical cavity laser diode structure with 2.2-nm continuous tuning,” 18th European Conf. Opt. Comm., PDII-4, Sept.1992.

[B23] M. Grabherr, R. Michalzik, B. Weigl, G. Reiner, and K. J. Ebeling, "Efficient Single-Mode Oxide-Confined GaAs VCSEL's Emitting 850-nm Wavelength Regime," IEEE Photon. Tech. Lett., Vol. 9, No. 10, pp. 1304-1306, Oct. 1997.

[B24] K. L. Lear, K. D. Choquette, R. P. Schneider, Jr., S. P. Kilcoyne and K. M. Geib, “Selectively oxidized vertical cavity surface emitting lasers with 50% power conversion efficiency,” Electron. Lett., Vol. 31, No. 3, pp. 208-209, Feb. 1995.

[B25] J. Ko, R. Hegblom, Y. Akulova, B. J. Thibeault, and L. A. Coldren, “Low-Threshold 840-nm Laterally Oxidized Vertical-Cavity Lasers Using AlInGaAs-AlGaAs Strained Active Layers,” IEEE Photonics Tech. Lett., Vol.9, No. 7, pp. 863-865, July 1997

[B26] S. W. Corzine, R. S. Geels, R. H. Yan, J. W. Scott, and L. A. Coldren: “Efficient, narrow-linewidth distributed-Bragg reflector surface emitting laser with periodic gain,” Photo. Tech. Lett., vol. 1, no. 3, pp. 52-54, March 1989.

[B27] C. J. Chang-Hasnain, J. P. Harbison, C. E. Zah, L. T. Florez, N. C. Andreevas’: "Continuous wavelength tuning of two-electrode vertical cavity surface emitting lasers", Electron. Lett., vol. 27, pp.1002-1003, May 1991.

[B28] M. S. Wu, E. C. Vail, G. S. Li, W. Yuen and C. J. Chang-Hasnain, “Tunable Micromachined Vertical Cavity Surface emitting lasers,” Electron. Lett., Vol. 31, No. 19, pp. 1671-1672, Sept. 1995.

[B29] J. D’ambrosia, “100 Gbit Ethernet and Beyond,” IEEE Communication Magazine, Vol. 48, Issue 3, pp. S6-S13, Mar. 2010.

[B30] F. E. Doany, B. G. Lee, D. M. Kuchta, A. V. Rylakov, C. Baks, C. Jahnes, F. Libsch, and C. L. Schow, “Terabit/Sec VCSEL-Based 48-Channel Optical Module Based on Holey CMOS Transceiver IC”, J. Lightwave Tech., Vol. 31, No. 4, pp. 672-680, Feb. 2013.

[B31] Tsubame 2.5,3.0, please refer web pages.

[B32] D. M. Kuchta, A. V. Rylyakov, C. L. Schow, J. E. Proesel, C. Bals. P. Westbergh, J. S. Gustavsson, and A. Larsson, “64Gb/s Transmission over 57m MMF using an NRZ Modulated 850nm VCSEL,” OFC2014, Th3C.2, March 2014.

[B33] M. Grabherr, S. Intemann, R. King,”VCSEL arrays for high-aggregate bandwidth of up to 1.34 Tbps,” Proc. SPIE 9001, Vertical-Cavity Surface-Emitting Lasers XVIII, 900105, pp. 4-1 to 4-10, Feb. 2014.

[B34] M. Grabherr, “New applications boost VCSEL quantities: recent developments at Philips”, Vertical-Cavity Surface-Emitting Lasers XIX, edited by Chun Lei, and Kent D. Choquette, Proc. of SPIE, Vol. 9381, 938102-1-938102-13, 2015.

[B35] N. Ueki, J. Ichikawa, C. Ikeda, H. Tezuka and A. Ohta,”Light Exposure System Using a Vertical-Cavity Surface-Emitting Laser Diode Array”, Fuji Xerox Tech. Report, No. 16, pp. 11-19. 2006.(in Japanese).

[B36] K. Harasaka, H. Motomura, K. Hara, A. Ito, N. Jikutani, and S. Sato, “Low thermal resistance 780nm GaInPAs/GaInP 40ch VCSEL array for laser printers”, 17th Microoptics Conf.(MOC’11), Sendai, Japan, Paper L2,Oct.- Nov. 2011.

[B37] S. Sato, “Laser printer applications of VCSEL arrays and trends of VCSELs”, Optonews, Vol. 12, No. 1, pp.2-6, 2017. (in Japanese)

[B38] M. Grabherr, H. Moench, and A. Pruijmboon, “VCSELs for Optical Mice and Sensing”, Book of Springer Series in Optical Sciences, October 2013.

[B39] J. A. Tatum, “Evolution of VCSELs”, Proc. Vol. 9001, Vertical-Cavity Surface-Emitting Lasers XVIII, Feb. 2014.

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