We have demonstrated active mode hopping suppression in external-cavity semiconductor lasers including a diffraction grating as a wavelength-selecting device. The feedback control nullifies the difference between the oscillation wavelength and selected wavelength based on observed changes in diffraction angle. The control has suppressed mode hopping over a 7.5 times wider span than without control. And when combined with conventional mode hopping suppression techniques, mode-hop-free oscillation is achieved over 130 nm. Our approach can be used for most Littman-type external-cavity semiconductor lasers with simple attachments; it will be useful for continuous wavelength sweeping and for long-term wavelength stabilization.

We propose a novel method for measuring the matched total radiated power (TRP) and matched total radiated sensitivity (TRS) of small radio terminals, called over-the-air (OTA) measurement, using a spheroidal coupler (SC). To measure these parameters accurately in a multiple-reflection environment, such as in an SC, we developed two key techniques, i.e. displacement method and reflection compensation method, and verified their effectiveness by several simulations and fundamental experiments on a test transmitter. We also describe an absolute method for measuring antenna radiation efficiency using the displacement method. Furthermore, we describe TRP and TRS measurements for actual UMTS (Universal Mobile Telecommunications System) terminals, and verify that the proposed method achieves quick measurements with good accuracy. The SC provides a compact, low-cost OTA measurement system with high sensitivity and high speed.