Complex sentence: He then worked for France Télécom (1980-1986) before founding his first company Chorus systems (1987-1997), purchased by Sun Microsystems, where he was director of telecom software engineering for 5 years.
Split into simpler sentences: He then worked for France Télécom (1980-1986). He founded Chorus systems in 1987, purchased by Sun Microsystems in 1997, where he was director of telecom software engineering for 5 years.