2430 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 16, NO. 11, NOVEMBER 2004 Thermally Controlled Wavelength Locker Integrated in Widely Tunable SGDBR-LD Module Jongdeog Kim, Member, IEEE, Byung Seok Choi, Hogyeong Yun, Su Hwan Oh, Jong-Hyun Lee, Hyunsung Ko, Kwang-Seong Choi, Sahnggi Park, Jong Tae Moon, and Moon-Ho Park Abstract—A sampled-grating distributed Bragg reflector laser module having an integrated multiwavelength locker has been developed and evaluated. The uniquely designed wavelength locker made of thermally controlled etalon has provided uniform wavelength monitoring and very stable wavelength locking in the 188-ITU grid channels (37 nm) with 25-GHz spacing. Over the case temperature from 5 C to 65 C, the laser wavelength was locked within 0.5 GHz, and the total power consumption of the module was less than 4 W. Index Terms—Dense wavelength-division multiplexing (DWDM), etalon, tunable laser, wavelength monitor. I. INTRODUCTION W ITH THE demand for the increased channel number and narrower channel spacing in the dense wave- length-division-multiplexing (DWDM) transmission system, an internal wavelength locker to be integrated in a laser module is a good solution for the low cost, compact, and reliable system design. From the enhanced research results in widely tunable laser [1]–[3] and wide-band wavelength-selectable light source [4], multichannel capability over the wide-band wavelength range has been an inevitable requirement and the wavelength locker based on the etalon is the most attractive one among the various wavelength monitoring techniques by its capabilities of wide-band coverage, low-cost, and compactness. Recently, remarkable research activities have been reported on the precision wavelength monitoring and the locking capa- bility over a large temperature range. The reported schemes are a second thermoelectric cooler (TEC) for etalon [3]–[5], firmware compensation for etalon with temperature sensing [6], and a temperature-insensitive etalon with a novel material [7]. As another considerable factor in the etalon-based tech- nologies, a sensitive angle dependence of the etalon affects the manufacturing feasibility as well as the performance of the locker because the wavelength discrimination for the ITU grid is initially decided by the initial angle of the etalon and the divergence angle of the collimated laser beam in the module as- sembly. As a useful approach, an additional TEC for etalon [3], [5] has been introduced to make easy not only the packaging process but also the wavelength discrimination by a thermal adjustment of the etalon wavelength. This approach, however, Manuscript received May 4, 2004; revised June 18, 2004. The authors are with Telecommunication Basic Research Laboratory, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-350, Korea (e-mail: jd03@etri.re.kr; chbs@etri.re.kr; yunhg@etri.re.kr; osh@etri.re.kr; ljh63292@etri.re.kr; hsko85@etri.re.kr; kschoi@etri.re.kr; sahnggi@etri.re.kr; jtmoon@etri.re.kr; mhpark@etri.re.kr). Digital Object Identifier 10.1109/LPT.2004.835202 Fig. 1. Schematic side view of the laser module. may be improved by minimizing the cost, the space, and the power consumption brought in by using the second TEC. In this research, instead of the additional second TEC, a thin-film resister has been introduced in the uniquely designed multiwavelength locker (MWL) to achieve not only the im- proved manufacturing process but also the high performance of the locker over the wide-band range. This novel MWL has been integrated with a widely tunable sampled-grating distributed Bragg reflector (SGDBR) laser diode (LD) within a 20-pin standard-size butterfly package. We report the wavelength monitoring capability of the locker in 188-ITU grid channels (37 nm) with 25-GHz spacing. We also present the power consumption of the laser module and the wavelength stability with the case temperature change. II. DESIGN AND STRUCTURE A schematic structure of the SGDBR-LD module with a uniquely designed wavelength locker is shown in Fig. 1. The SGDBR-LD with the planar buried heterostructure has four sections: active, phase control, front SGDBR, and rear SGDBR with a chip size of 400 1450 m, as reported in [1] that describes the chip fabrication and the performance. A pair of lens has been used in the front and rear of the laser chip to inject the collimated laser beams into a wavelength locker and a polarization-maintaining fiber pigtail. The MWL designed for high thermal resistance, low cost, and compact size is preassembled, as shown in the dashed-line circle of Fig. 1, and it is finally aligned with the SGDBR-LD which is mounted on a TEC in a 20-pin standard-size butterfly package. The first pho- todiode (PD1), having a rectangular shape of active area (500 400 m), is mounted on an alumina substrate which has a hole of 1-mm diameter in the center. The collimated laser beam has a diameter of 600 m at the intensity of . The first 1041-1135/04$20.00 © 2004 IEEE