High common mode rejection ratio InP 90° optical hybrid in ultra-broadband at 60 nm with deep-rigded waveguide based on × 4 MMI coupler*

Abstract

An InP optical 90° hybrid based on a × 4 MMI coupler with a deep ridged waveguide is designed and fabricated. The working principle of the 90° hybrid is systematically introduced. Three-dimensional beam ropagation method (3D BPM) is used to optimize the structure parameters of the 90° hybrid. The designed compact structure is demonatrated to have a low excess loss less than –0.15 dB, a high common mode rejection ratio better than 40 dB, and a low relative phase deviation less than ± 2.5°. The designed hybrid is manufactured on a sandwitched structure deposited on an InP substrate. The measured results show that the common mode rejection ratios are larger than 20 dB in a range from 1520 nm to 1580 nm. The phase deviations are less than ± 5 ° in a range from 1545 nm to 1560 nm and less than ± 7° across the C band. The designed 90° optical hybrid is suitable well for realizing miniaturization, high-properties, and high bandwidth of coherent receiver.

Subwavelength gratings engineered 90-degree optical hybrid for coherent detection

“…In this case, the MMI tapers gradually from a width of 11.79 µm to 12.81 µm, which offers a good balance between the four output arms of the device with good splitting ratios and reasonable phase relations. The ideal output phase relationships of a 90-degree optical hybrid are given in the table below [6]: As we can see when port 1 and port 3 are given with signal input and local oscillator input, the phase difference will be 90 degrees between the in-phase ports (1 and 4) and the quadrature ports (2 and 3). The 90degree phase difference occurs when both ports are given signals.…”

Miniaturization of 2 × 4 90-Degree Hybrid Optical Couplers

“…The structure of a typical 2x4 MMI hybrid coupler is shown in Fig 1 . It consists of two input ports on the left, and four output ports on the right, the first input port, symmetrical to the output Channel 1, is used for the received Signal (S), and the second, symmetrical to the output Channel 3, is used for the Local Oscillator (L.O.) [21], [22]. Because of this configuration, this structure is also referred to 4x4 hybrid in the literature [22], [23], with reference to the 2 unused virtual ports opposite to the output channels.…”

“…[21], [22]. Because of this configuration, this structure is also referred to 4x4 hybrid in the literature [22], [23], with reference to the 2 unused virtual ports opposite to the output channels. Other configurations of 90-degree couplers also exist, usually involving cascades of lower order MMIs [21], [24] or more exotic configurations [25].…”

Low-loss silica-based 90 deg optical hybrid in c band based on 4 × 4 multimode interference coupler for coherent receiver

“…As a key component of passive devices in the QPSK coherent detection system, the performance of the 90 deg optical hybrid detecting the optical signal divided into in-phase and quadrature-phase planes is critically significant 11 – 14 According to the self-imaging principle, the field distribution of any input in a 4×4 multimode interference (MMI) coupler is reproduced at the output plane of the coupler in the form of fourfold images that ideally have equal magnitudes and different phases, whose relative phase differences to output channel 1 of each output are 0 deg, 90 deg, 270 deg, 180 deg, 15 – 19 which means 4×4 MMI perfectly meets the needs of QPSK coherent detection system.…”