Abstract

There has been growing interest in the use of optical fiber for the efficient transport of millimeter-wave (>30 GHz) signals. The low-loss, immunity to electromagnetic interference, and high bandwidth make fiber ideal for applications such as phased-array antennas. The broadband direct modulation bandwidth of semiconductor lasers has been demonstrated up to 30 GHz. Most millimeter-wave applications, however, require only a narrow bandwidth centered at a high frequency. Applying active modelocking techniques, a semiconductor laser coupled to an external cavity can create a "resonantly enhanced" transmission window at the cavity round-trip frequency.¹-² At millimeter-wave frequencies, the cavity length is compatible with that of a monolithic device.³ The resonant reseponse can be further enhanced by incorporation of a passive mode-locking structure involving a saturable absorber section. We demonstrate such a device at 45 GHz with modulation efficiency 10 dB higher than that of a standard device at dc. A carrier-to-noise ratio (CNR) of 88 dB (1 Hz) was attained at an input RF power of 10 dBm, and the bandwidth of the transmission was between —0.1 to 1% of the center frequency depending on bias conditions.

© 1994 Optical Society of America