I. Introduction
Low-cost tunable transceiver modules are key enablers for next-generation wavelength division multiplexing (WDM) based metro, access and data center networks. Currently tunable lasers are mostly deployed in long-haul optical transmission systems due to their high cost resulting from fabrication and testing complexity for structures such as sampled grating distributed Bragg reflector (SGDBR) [1], [2], superstructure grating (SSG) DBR laser [3], digital supermode DBR [4], modulated grating Y-branch [5], and MEMS based external cavity lasers [6]. For wide deployment of the WDM technology in metro, access networks and data center networks, the cost reduction of tunable transceivers has become a key issue. Recently, a simple and compact tunable V-cavity laser has been proposed and demonstrated [7], [8]. It does not require complex grating and epitaxial regrowth. Its fabrication process is similar to that of Fabry-Perot lasers with only an additional step of deep etching for cavity mirrors. By using a specially designed half-wave coupler, single-mode operation with high side-mode suppression ratio (SMSR) of 35-40 dB has been achieved. Discrete wavelength tuning up to 50 channels at 100 GHz spacing has been demonstrated experimentally with simple tuning algorithms [9]. Single-electrode controlled fast wavelength tuning in the order of ~10 ns has also been achieved by using a quantum well intermixed tuning section [10].