ABSTRACT
In this paper, we present an efficient polymer two-mode (de)multiplexer with two cascaded horizontal waveguide asymmetric directional couplers (ADCs). Through extensive simulations, the optimized waveguide core dimensions were determined, and the distance L from the starting position of the first ADC to the cascaded position was 35300 µm. With the cascaded ADCs, the E21x mode of the wider waveguide was coupled into the E11x mode of the narrower waveguide with a coupling ratio of 96.73% at 1550 nm when the separation between the waveguide cores was 5 µm. The coupling ratio and extinction ratio of the fabricated (de)multiplexer reached a maximum of 96.12% and 14.21 dB at 1540 nm, respectively. The coupling ratios were greater than 90% in the wavelength range 1533-1565 nm with a minimum insertion loss of 9.75 dB. The influence of different cascaded positions on the mode coupling ratio, mainly caused by the large phase difference between the modes owing to the slowly varying envelope approximation, is analyzed theoretically and verified experimentally. The proposed cascaded two-mode (de)multiplexer can reduce the preparation process requirements and increase the channel capacity of optical communication systems.
ABSTRACT
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 E11x mode of the two narrower waveguides are highly coupled into the E21x and E31x 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.
ABSTRACT
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.
ABSTRACT
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.
