Digital wavelength switching by thermal and carrier injection ef fects in V-coupled cavity semiconductor laser

Abstract

Consecutive wavelength switching characteristics of a simple, compact, and digitally wavelength-switchable laser based on V-coupled cavities are reported. Wavelength switching through thermal and carrier injection effects is examined. Without using band gap engineering for the tuning section, 26-and 9-channel wavelength switching schemes are achieved via thermal and carrier injection effects, respectively. The performances of these two tuning schemes are then compared.OCIS A wide wavelength tuning range is an important parameter for semiconductor lasers in advanced wavelengthdivision multiplexing (WDM) systems. As the WDM technology extends towards metro and access networks, cost reduction and operational simplicity become increasingly important. Unlike tunable lasers based on Bragg gratings [1,2] or microelectromechanical system switches [3] , a recently proposed discrete wavelengthswitchable V-coupled cavity laser does not require complex gratings, multiple epitaxial growths, or complex tuning algorithms [4] while providing a wide wavelength tuning range and an excellent side-mode-suppression ratio (SMSR) near 40 dB [5] . In this letter, the experimental results of the wavelength switching characteristics of the V-coupled cavity laser under thermal tuning are reported under a carrier injection scheme. We show that a maximum discrete 26-channel wavelength switching scheme with 100-GHz channel spacing and a SMSR of approximately 37 dB can be achieved using thermal effects via single-electrode control. Meanwhile, through carrier injection tuning, a nine-channel switching scheme with the same 100-GHz spacing and SMSR of approximately 32 dB was achieved without using any band gap engineering for the tuning section. With the potentially higher switching speed provided by the carrier injection, the V-coupled cavity laser can be used in advanced optical networks where the wavelength switching speed is crucial.The V-coupled cavity laser was composed of a reflective 2 × 2 half-wave coupler and two waveguides with slightly different lengths. The etched facet version of the device is shown in Fig. 1(a). Three deep-etched facets define the reflecting mirror of the coupler and the other ends of the two resonant cavities. The fixed gain cavity (also referred to as short cavity) was designed to be 466-µm long so that its resonance frequency interval matches the 100-GHz spacing of the International Telecommunication Union operating frequency grid. As shown in Fig. 1(b), the channel selector cavity (long cavity) has a slightly different lengths (5%-10% length difference with respect to the fixed gain cavity) so that the Vernier effect can be used to increase the wavelength switching range. The half-wave coupler where the crosscoupling coefficient has a relative phase of π with respect to the bar-coupling coefficient is essential for achieving high SMSRs [6] . As shown in Ref.[4], the V-coupler has optimal coupling coefficients in amplitude and phase at the same time. Thus, its performance is superior to that of the previously r...