Photoresist imaging traditionally uses silver halide or diazo based phototools for contact exposure to an actinic UV light source. By contrast, laser direct imaging uses digital imaging data to control a laser beam scanner to write directly on to the photoresist, therefore eliminating the need for phototools. In the past, even though the benefit of a UV system was recognised, laser direct imaging was mainly limited to the use of a visible laser as early UV lasers were low in power, unreliable and expensive. So far, no visible systems have gained commercial recognition because of the inherent deficiencies of the visible system. Recent advantages in UV laser equipment and UV sensitive photoresist have now made UV laser direct imaging a viable alternative to traditional contact imaging. As new UV laser imaging systems start to emerge, interest and attention are also growing among printed circuit board manufacturers. This paper discusses various attributes of a UV laser direct imaging system and fundamental differences in photophysics between laser direct imaging and conventional UV imaging.
of the laser is about 0.4 nm, and the 3-dB bandwidth nearly maintains the constant when the pump power increases. The sidemode-suppression ratio of the laser increases with the increasing pump power and reaches about 45 dB at higher pump power. When the pump power is higher than 1 W, the laser spectrum becomes very stable, without any power jitter or wavelength shifting. Figure 5 presents a continuously repeated scan of the laser spectra under the pump power of 2.25 W, which indicates the good stability of the output laser. In addition, the light polarization has minor influence on both the output power and the laser spectra.It is necessary to note that no ytterbium-lasing occurs (around 1060.0 nm), even under the maximum pump power, mainly due to the high-energy-conversion efficiency from the ytterbium ions to the erbium ions in the EYDF and the pump power being not strong enough [5]. Thus, higher pump power can be launched in order to enhance the output power of the EYDFL. CONCLUSIONIn this paper, an all-fiber EYDFL has been presented and the influence of the BCM reflectivity on the output characteristics of the EYDFL has been analyzed. With a 4% reflecting-fiber facet replacing the FLM with the PC as the output port, the EYDFL realizes highly stable laser output with fine shape. Output power as high as 1.027 W at 1567.0 nm was obtained under the pump power of 3.16 W. The slope efficiency with respect to the launched pump power reaches 34.5%. ACKNOWLEDGMENT INTRODUCTIONWith the spread of fiber-to-the-home (FTTH) in optical communications, the low-cost optical transceiver is regarded as one of the most important devices for access networks. Promising packaging technologies such as the planar lightwave circuit (PLC) platform and passive alignment have already been introduced [1]. In the case of the bidirectional transceiver, one of most popular packaging methods [2][3][4] is the use of the thin-film filter (TFF) on the PLC platform with flip-chip bonding for passive alignment of active devices. However, the use of an additional component and the complexity of packaging when inserting the TFF after sawing on the PLC, as well as the sensitivity of filter to the angle of incident light, have been regarded as practical problems for realizing low-cost and mass production. In this paper, we demonstrate a hybrid bidirectional device based on passive alignment and the filter-integrated PLC platform. Especially, as the structure of the proposed PLC platform is designed to use V-groove and flip-chip bonding for passively making optical interconnection, we expect the proposed hybrid transceiver will be very suitable for low-cost packaging. Also, we discuss the configuration of the PLC platform, the assembly process, and the optical performance of the fabricated transceiver. CONFIGURATION OF PLC PLATFORMThe configuration of the 3.5 ϫ 15 mm PLC platform, including the flip-chip-bonding, integrated-filter, and V-groove sections, is shown in Figure 1. First, active devices are bonded in the flip-chip bonding section, where a 3...
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