A compact and efficient polymer three-mode (de)multiplexer with two cascaded waveguide directional couplers fabricated on the same substrate along the horizontal direction is proposed. Three waveguides formed two couplers, where two narrower waveguides were placed on either side of the central waveguide. By optimizing the core height and width, the two couplers can ensure that the E 11 x mode of the two narrower waveguides are highly coupled into the E 21 x and E 31 x modes of the central waveguide at a wavelength of 1310 nm. The structural size of the fabricated three-mode (de)multiplexer using ultraviolet (UV) lithography technology is in agreement with the designed value. The fabricated device, which is 35 mm long, exhibits coupling ratios of 98.07% and 95.43% for the two couplers, respectively. The insertion losses of the three waveguides are 5.23 dB, 8.58 dB, and 14.39 dB, respectively. The device can achieve the multiplexing of three modes in two dimensions, which can increase the channel capacity of optical communication.

Based on gray-tone optical lithography technology combined with the overlay alignment method, a spherical concave micro-mirror is fabricated at the end of a rectangular optical waveguide (ROW) for low vertical coupling loss. The optimal structures of the spherical concave micro-mirrors were designed through ray-tracing simulation. The results indicate that the minimal vertical coupling loss is only 1.02 dB for the ROW core size of 20 μm × 20 μm. The surface roughness of the micro-mirror is considered, and it should be less than 106 nm to ensure that the vertical coupling loss is less than 1.5 dB. The radius of the fabricated spherical concave micro-mirror was measured as 263.3 μm and the surface roughness of the micro-mirror is 29.19 nm. The vertical coupling loss induced by the micro-mirror was measured as 1.39 dB. 1-dB tolerances in the direction of x-, y-, and z-axes are calculated to be ± 6.9 μm, ± 6.3 μm, and 46.2 μm, respectively.

In this report, we present a stepped laser-ablation method for the fabrication of concave micromirrors in rectangular optical waveguides. The numerically simulated vertical coupling loss of the reflection of the concave micromirror can be reduced to 1.53 dB. The processing parameters of the utilized excimer laser, such as the step number, width, and depth, were optimized to fabricate the concave micromirrors. After the thermal reflow process, the measured curve of the circular concave micromirrors obtained using a 3D optical profiler agreed well with a standard circle with a surface roughness of 39.56 nm. Furthermore, vertical coupling for 62.5 µm MMF revealed that the loss of the circular concave micromirror coated with a 50 nm thick Au film is as low as 1.83 dB, corresponding to a high coupling efficiency of 65.61%. This new, convenient, and efficient fabrication technology for the fabrication of concave micromirrors can be applied to vertical coupling for optical printed circuit board (OPCB) interconnection technology.

We propose a novel fabrication of total internal reflection spherical concave with polymer material by gray-tone optical lithography on printed circuit boards for vertical optical coupling between waveguides and optoelectronic devices.

The aspheric and spherical concave micro-mirrors are designed by ray-tracing simulation at the end of a rectangular polymer waveguide for vertical coupling. The results indicate that the loss of hyperboloidal micro-mirror is 0.8 dB.