through the straight waveguide with 4-m width are plotted in Figure 4. Similar single-mode outputs for TE and TM polarizations are observed. By using the cutback method, the propagation losses were measured, as listed in Table 1. The propagation loss of TM polarization is slightly larger than that of TE polarization. Moreover, waveguides with wider widths have smaller propagation losses.Waveguide bends are basic components of integrated optical devices. They are often used to change the lightwave-propagation direction in, for example, Mach-Zehnder modulators and directional couplers. For comparison, several waveguide bends with different bending angles were fabricated. Calculated and measured results are shown in Figure 5. The normalized transmission efficiency of the device was obtained by calculating the ratio of the total output power through the bent waveguide to that through the straight waveguide. Numerical simulations were performed using the 3D beam-propagation method. As can be seen, the measured values are quite consistent with the simulated ones. Moreover, the waveguide bends with wider widths exhibit higher transmission efficiencies.
CONCLUSIONWe have successfully fabricated single-mode BCB optical waveguides by using single-step electron-beam direct writing, which has the significant advantage of not requiring any photolithography, chemical wet etching, or dry etching. The refractive indices increased by about 0.27% and 0.26% for TE and TM polarizations, respectively, under an electron-beam irradiation dose of 800 C/cm 2 . The refractive index of the irradiated film remained unchanged after being stored at 120°C for 500 hr. With a width of 4 m, we have observed propagation losses of 0.82 and 0.9 dB/cm for TE and TM polarizations, respectively. In addition, given a width of 6 m, the propagation losses are 0.76 and 0.86 dB/cm for TE and TM polarizations, respectively. Waveguide bends with various bending angles were also demonstrated. They exhibit characteristics that agree with the simulation results. These preliminary results show that this single-step process provides a simple and flexible approach to the fabrication of polymer waveguide devices. Further application of electron-beam-irradiated BCB waveguides will be of interest in the future.
ACKNOWLEDGMENTThis work was supported by the National Science Council, Taipei, Taiwan, Republic of China, under contract no. NSC92-2215-E-002-009. Millimetre-wave operation is of growing importance to the distribution of broadband telecommunication services and to wireless, local-area networks [1, 2]. Millimetre-wave transceivers based on GaAs and Indium Phosphide (InP) MMICs are a key component of these wideband systems [3, 4]. However, wider use of MMICbased systems requires lower-cost chips and packaging solutions. 0.15-m GaAs pHEMT MMICs satisfy the first of these requirements, thus providing a cheaper, higher output power alternative for transmitter applications when compared to InP circuits. This paper describes an up-converting transmitter module, based...