The device is fabricated as a 1 X 8 star coupler and their basic properties have been measured. The insertion loss is 10.44 dB on the average at a wavelength of 1.3 1 pni with index-matching material. Figure 2(a) shows the histogram of the excess losses of 50 devices. The excess loss is 0.54 dB on the average, which can be nearly identified with the sum of two connection losses at both ends of the device. The value is sufficiently good, suggesting that the compatilsility of the device with MT connectors has been verified. Repeatability 3f loss values has been also checked. Figure 2(b) shows the histogram of the maximum loss changes during three repetitions of connection and disconnection. The change is 0.12 dB on the average. Additionally, return losses are >40 dB for all devices. As for reliability, several kinds of ctnvironmental tests have been done. Details of the tests are summarized in Table 1. Loss deviation was monitored under the heat cycle and i emperature-humidity cycle tests. The maximum loss deviation from 25°C is less than k0.3 dB and 20.4 dB for each test respectively. Accordingly the device should be of practical use.In conclusion, we have developed a 1 X 8 star coupler waveguide device with MT-compatible connections, which is easy to fabricate because the assembling process autl2matically involves adjusting the position of waveguides. In addition to this convenience, the device has low connection losses and good relialiility. The device structure is favorable to mass production and can be applied to various waveguide circuits with low cost.

1 5 5 5 Z M b l r . N R Z 1-1 3 u m ........ P N 4 3 -4 4 -4 3 -4 2 -4 1 -4 0 -3 9 -38 Averaged optical power [dBm] ThD4 Fig. 3. Bit-error-rate characteristic.pm 155.52 Mb/s NRZ signal is shown in Fig. 3. This performance was little dependent on the type of the input bit sequences. The sensitivity was -39.7 dBm measured at a BER of lo-" using the input signal of PN = 23. A maximum optical power before incurring BER degradation was 0 dBm. The dynamic range thus exceeded 39 dB. We consider that these BER performances of the preamplifier satisfies a requirement in most of 156 Mb/s application. Moreover, the power consumption was as small as 108 mW operated at a power supply voltage of 3.3 V. We have developed a preamplifier IC with a high sensitivity and wide dynamic range which operates at the power supply voltage of 3.3 V. We believe that the preamplifier IC is widely applicable for 156 Mb/s optical fiber communication systems. 1. R. Bayruns, et al., IEEE International symposium on circuits and systems, L. E. Larson, et al., Electron. Lett. 22, Surface-hybrid integration techniques using planar lightwave circuits (PLC) or Sioptical benches are useful for low-cost optical modules.1,2 A p-i-n photodiode (PD) incorporating a waveguide (WG) s t r~c t u r e~'~ has been proposed for the hybrid integration. This device is attractive not only for signal detectors but also for laser diode (LD) power monitors from the point of view of direct optical coupling (see Fig. 1). However, there is very scant knowledge of the use of a WG-PD as a monitor diode. In this paper, we investigate the optical coupling properties between the LD and the WG-PD. For low-cost nonhermetic packages, we also investigate the case where the gaps be-tween WG-PD and LD are filled with transparent resin.' Figure 1 shows a schematic structure of a subassembly using the surface-hybrid integration. The PD and LD are diebonded on a Si optical bench with a Vgroove by detecting the alignment marks on the PD (LD) and Si substrate. An optical fiber is mounted on the V-groove. This optical coupling system is molded with transparent resin to obtain high-reliability in nonhermetic environment.First, we investigated the coupling properties of the WG-PD to the LD at a wavelength of 1.3 pm along the optical axis in the higher refractive index resin and in air. The experimental results are shown in Fig. 2. The far-field angle of the LD is 25" in air. A coupling loss as low as 4 d B (the responsibility is as high as 0.4 A/W at an operating voltage of 2.0 V) in the resin was obtained at a gap of 30 pm between the WG-PD and the LD. The coupling loss in the resin is 1 dB better ~Iypype elecl!ode WG-PD polyimide absorption layer ThD5 Fig. 1. Schematic structure of a subassembly using the surface-hybrid integration 0 10 20 30 40 50 Optical axis displacement ( U m) ThD5 Fig. 2. Coupling properties of WG-PD to the LD at a wavelength of 1.3 pm along the optical axis in the higher refractive index resin and in air. Displacement ( u m ) ThD5 Fig. 3. Horizontal and vertical opti...