A polarization beam splitter (PBS) with a high extinction ratio that is based on multimode interference (MMI) is proposed and experimentally demonstrated on a silicon-on-insulator platform. The PBS is designed using cascaded MMI to enhance the extinction ratio (ER) and minimize insertion loss (IL) compared to a conventional MMI structure. The proposed device has a high extinction ratio (22.3 dB for TE and 25.6 dB for TM) and a low insertion loss (0.7 dB for TE and 0.1 dB for TM) at a wavelength of 1550 nm while the device supports a broad bandwidth of 60 nm (
E
R
>
16
d
B
) for both polarizations over a wavelength between 1520–1580 nm. Moreover, the eigenmode expansion method shows that the device has a large fabrication tolerance of an MMI width
±
40
n
m
and a length
±
1500
n
m
. The proposed PBS can be used in on-chip silicon photonic integrated circuits for polarization division multiplexing.
In this paper, a compact and broadband mode converter and demultiplexer based on multimode interference (MMI) is designed and experimentally demonstrated on silicon-on-insulator. We have designed a mode converter using cascaded MMI to convert the fundamental mode into a higher-order (first-order mode) and vice versa. Subsequently, we have demonstrated an on-chip two-mode demultiplexer with a compact footprint and low loss. The proposed mode demultiplexer shows low insertion loss (0.22 dB for
T
E
0
and 0.36 dB for
T
E
1
mode) and crosstalk (
−
25.2
d
B
for
T
E
0
and
−
24.4
d
B
for
T
E
1
mode) at wavelength 1550 nm using the eigenmode expansion method. Moreover, the device supports a broad bandwidth having crosstalk
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