Gwan-Chong Joo

Fabrication of semiconductor optical switch module using laser welding technique

The 4/spl times/4, 1/spl times/2, and 1/spl times/4 semiconductor optic-switch modules for 1550 nm optical communication systems were fabricated by using the laser welding technique based on the 30-pin butterfly package. For better coupling efficiency between a switch chip and an optical fiber, tapered fibers of 10-15 /spl mu/m lens radius were used to provide the coupling efficiency up to 60%. The lens to lens distance of the assembled tapered fiber array was controlled within /spl plusmn/1.0 /spl mu/m. A laser hammering technique was introduced to adjust the radial shift, which was critical to obtain comparable optical coupling efficiencies from all the channels at the same time. The fabricated optical switch modules showed good thermal stability, with less than 5% degradation after a 200 thermal cycling. The transmission characteristics of the 4/spl times/4 switch module showed good sensitivities, providing error free transmissions below -30 dBm for all the switching paths. The dynamic ranges for the 4/spl times/4 and 1/spl times/2 switch modules were about 8 dB for a 3 dB penalty and about 17 dB for a 2 dB penalty, respectively.

A novel bidirectional optical coupling module for subscribers

To overcome drawbacks and limitations of planar lightwave circuit based modules for bidirectional communications, such as the demand for several chips and in consequence more packaging efforts, we have recently developed a novel optical coupling technique using our unique 155 Mbps bidirectional laser chip. Since the chip is structured with a pin-photodiode monolithically integrated on a laser diodes waveguide, the optical coupling requires only the alignment of the chip with a fiber. To optically couple the laser diode and photodiode simultaneously with a single fiber, we have designed an unusual coupling structure using a fiber having a cleaved surface whose normal is 35/spl deg/ angled to the fiber core axis, and using an index-controlling medium with a refractive index of /spl sim/1.3. The bidirectional chip is flip-chip bonded and the fiber is passively aligned using a V-groove on the same substrate of 2.5/spl times/1.3 mm/sup 2/ in size. Even with this extremely small and simple scheme for bidirectional optical coupling, we could obtain an optical output power of -7/spl sim/-10 dBm and a responsivity of <-30 dBm, which are satisfactory to the STM-1 level telecommunications specifications.

Fabrication of optical Tx/Rx subscriber modules incorporating passive alignment technique

Compact optical transmitter/receiver modules for STM-1 transmission systems have been developed incorporating custom ASICs (application specific integrated circuit) and novel packaging technologies. Coupling of optical chips and fibers for both modules is accomplished utilizing passive alignment method to lessen package cost and size. A fully integrated module is as compact as 3 cc in volume.

Quantitative evaluation of passive-aligned laser diode-to-fiber coupling

Quantitative evaluation of passive-aligned laser diode-to-fiber coupling is presented. From the assembly of 250 transmitter optical subassemblies, flip-chip bonding of laser chips and fiber fixing yields are reported. The coupling characteristics of passive-aligned laser diode modules are evaluated in comparison with the active alignment data and the misalignment tolerances. The assembly and coupling results have showed about 80% overall yield and 1.79 dB/spl plusmn/1.55 dB excess coupling loss, respectively.

Pb/In solder bump formation for a flip-chip bonding technique at high speed optical communication devices

The increasing speed of advanced chip technologies has greatly challenged the interconnection methods and processes in order to achieve enhanced capability. We have successfully fabricated the solder bump and its reflowing process for flip-chip bonding interconnection technique instead of conventional wire bonding for high speed devices. The lead (Pb: 350/spl deg/C) and the Indium (In: 157/spl deg/C) were used for solder bump and deposited by using thermal evaporation. The thickness of the deposited metal for solder bump was in the range of 5/spl sim/6 /spl mu/m thickness. Specially, to increase the accuracy and the reliability of the flip-chip bonding Technique, 3 layer thick photoresist about 30 /spl mu/m was used to control the deposition area for solder bump. It was also used for the lift-off process of excess deposited metal for solder bump. The height of solder bump through the reflowing process was controlled in the range of 10/spl sim/40 /spl mu/m according to the deposited area and shape. Also, the deposited area and shape was one of the most important parameters for solder bump fabrication. In addition, it was found that an oxidized surface layer effects on the increased melting temperature of deposited metal for solder bump. In this process, the reflowing temperature of PB/In (60:40 wt%) solder bumps was 230/spl plusmn/5/spl deg/C.

Failure and yield analysis of fabrication process of 155 Mbps optical transmitter modules

The failure and yield on the preliminary result of our pioneer fabrication line of 155 Mbps OTMs adopting a modern Si V-groove and FCB techniques have been studied. The yields of LD purge, sub-module assembly, and final assembly were found to be 78%, 95%, and 77% respectively out of total 319 samples. The yield of whole fabrication process has been found to be 57%, where it can be improved to be 70% or higher by replacing the electrical component assembly process with more advanced IC process.

Optical coupling efficiency of bidirectional transceiver sub-module with refractive index control

Conventionally, optical communication modules for subscriber have been composed of transmitter and receiver as separated or combined requiring two lines of optical fibers to constitute a network. To realize the fiber-to-the-home (FTTH), it is necessary to make the cheaper and more compact module as well as to reduce the fiber installation cost. In this study, an accurate silicon optical bench (SiOB) has been designed for passive integration of bidirectional transceiver sub-module. Optical coupling between the transceiver chip and a single mode fiber is accomplished by aligning an acute angle-faceted fiber on the V-groove of SiOB to the front facet of the flip-chip bonded chip. Transmitted light from the laser diode of the transceiver chip is coupled into fiber core as in usual buff coupling, while receiving light from the fiber is refracted downward by Snells law and absorbed into pin-PDs photosensitive area after being reflected at the metal coated V-groove side-wall.

Relationship between initial thermal characteristics and lifetime projection of semiconductor laser diodes

A novel reliability projection model of semiconductor laser diodes (LD) is presented. By correlating initial thermal characteristics and long-term degradation, a relationship between LD degradation and ambient temperature has been investigated. The proposed model is found to be efficient for the reliability projection of LDs, which requires a thermal characterization only at t=0.

Structure-dependent reliability assessment of 1.3 /spl mu/m InGaAsP/InP uncooled laser diodes by accelerated aging test

The purpose of this paper is to demonstrate reliability analysis of 1.3 /spl mu/m InGaAsP/InP MQW-PHB laser diodes (LD) for high speed optical communication systems. We have accelerated aging tests and compared the assessment of 1.3 /spl mu/m InGaAsP/InP strain-compensated MQW PBH-LDs with different numbers of quantum well (N/sub QW/) and active width (W/sub A/). The experimental results show that /spl Delta/I/sub th/ is related with W/sub A/ rather than with N/sub QW/. For the same W/sub A/, we have observed that the variation of N/sub QW/ has less effect on /spl Delta/I/sub th/ which is primarily due to the limitation of the fabrication process in controlling the uniformity and homogeneity in the MQW layer.