From January 1985 to February 2001, Welch served in various executive roles, including Chief Technology Officer and Vice President of Corporate Development of SDL, an optical component company.^[6] JDS Uniphase acquired SDL in 2001.^[7][8]

From February 2001 to April 2001, Welch served as Chief Technology Officer of the Transmission Division of JDS Uniphase Corporation, an optical component company.^{[citation needed]}

Welch is a co-founder, President and a member of the Board of Directors of Infinera Corp, an optical transport networking company.^[9][10][11]

In 2016, Welch was elected to the National Academy of Engineering "For contributions to high-power semiconductor lasers and photonic integrated circuits."^{[citation needed]}

In November 2013, Welch was awarded the Institute of Engineering and Technology (IET) J J Thomson Medal for Electronics. IET Achievement Medals are awarded to individuals who have made major and distinguished contributions in the various sectors of science, engineering and technology.^[12] In February 2013, Welch was recognized as #5 of the "Top Ten: Optical Movers and Shakers" by telecommunications publication Light Reading^[13]

In 2011, the Optical Society of America (OSA) presented Welch the 2011 John Tyndall Award. The Tyndall Award is the highest recognition in the optical telecommunications community and is co-sponsored by OSA and the IEEE Photonics Society. The Tyndall Award recognizes an individual who has made pioneering, highly significant, or continuing technical or leadership contributions to fiber optics technology.^[14][15]

In 2010, Welch was recognized by the University of Delaware for his outstanding professional and public service achievements by being inducted into the University Alumni Association Wall of Fame.^[16][17]

In 1999, Welch received the Joseph Fraunhofer Award/Robert M. Burley Prize from the Optical Society of America. The award recognizes significant research accomplishments in the field of optical engineering.^[18]

In 1998, Welch was the recipient of the IEEE LEOS Engineering Achievement Award, presented to him "for the design, development and commercialization of high power diffraction limited semiconductor lasers."^[19]

In 1992, Welch received the Adolph Lomb Medal from the Optical Society of America. The Adolph Lomb Medal, established in 1940, is presented to a person who has made a noteworthy contribution to optics at an early age. The candidate cannot be older than the age of 35 in the calendar year of presentation.^[20]

Welch has made numerous contributions to the field of optical communication systems—including more than 250 published articles and 125 patents^[21][22]

In 2011, Welch founded Students Matter, a non-profit organization committed to ensuring access to quality education through impact litigation, communications and advocacy.^[23] Students Matter's nationally-watched case, Vergara v. California, challenged California's teacher employment laws around teacher tenure, dismissal and layoffs. Vergara plaintiffs, a group of 9 California public school students, received a favorable decision from the California Superior Court in 2014 in which the judge wrote, "The evidence is compelling. Indeed, it shocks the conscience.".^[24] In 2016, a three-judge state appellate court panel reversed the superior court's ruling ^[25] Students Matter indicated it would appeal that decision to the California Supreme Court,^[26] but the Supreme Court let the appellate court's ruling stand.^[27]