Optical interleaver is a 1x2/2x2 ports device that separates one set of densely multiplexed narrowband channels with equal channel spacing of ∆λ into two sets with 2∆λ channel spacing. This device is usually employed in Dense Wavelength Division Multiplexing (DWDM) systems for dividing densely multiplexed signals to reduce the stringent specification required for filters in the DWDM systems. Lots of researches about optical waveguide interleavers have been reported in last decade. Mach-Zehnder Interferometer (MZI) structure is always a component among them. These devices can offer high extinction ratio of 30dB, low insertion loss of 0.9dB, large operating range with 100nm and so on. Moreover, optical interleavers are compact and compatible with optical integrated circuit because of in-optical waveguide platform. However, the interleaver realized by Mach-Zehnder Interferometer (MZI) structure has a high potential for use in other applications that also worth to be studied. Higher optical carrier is needed to overcome the rapid growth of IP traffic. Thus, two data transfer rates; for example, 40 Gbit/s (OC-768) and 10 Gbit/s (OC-192), may be introduced in optical communication before the entire system is upgraded to adapt the faster optical carrier. In this case, the traditional interleaver will not be able to separate the data; hence, a MZI based asymmetric optical interleaver has been proposed to handle such problem. Compared with bulk or optic fiber-based asymmetric optical interleavers, our design can be imprinted on planar waveguide to offer rigid structure. The proposed device is less sensitive to environmental stimulation, compact, and compatible with optical integrated circuit. The additional features of the passband width and center wavelength tuning also increase the accuracy in fitting the ITU grid and obtaining the desired passband width. The proposed device is demonstrated as an asymmetric optical interleaver by close form simulation. This device offers 40/100 GHz of passband widths to separate the DWDM signals with two transfer bit rates. The feasibility of heat tuning the center wavelength and passband widths is also shown. Given that the capacity expansion provided by the DWDM systems with existing modulation methods will certainly meet a bottleneck in the near future, finding methods for handling the rapid growth of IP traffic caused by the demand for higher data rates in transmitting multimedia signals has always been a big interest in optics communication. One of the latest solutions is increasing the bandwidth capacity by mode division multiplexing scheme. Exploring a device with multiplexing and de-multiplexing modes is therefore worthwhile for supporting the scheme. The MZI structure has high potential and can be easily developed as a two-mode multiplexer/demultiplexer (mux/demux). This study aims to design a two-mode mux/demux based on MZI. Multiplexing and demultiplexing functions are demonstrated after the fabrication of the device. Furthermore, the device can be reconfigurable as two-mode division mux/demux, such that de-multiplexed signals from two output ports can be swapped. Aside from application in optical communication, my study also explores the feasibility of applying the MZI with two-mode interferometer in sensing application. Wavelength interrogated sensors have high sensing sensitivities, yet it need an expensive and bulky optical spectrum analyzer for visualizing the change of targeted physical property. In compare of wavelength interrogated sensors, intensity interrogated sensors are cost effective and have good mobility. The measurement can be simply visualized by cost effective portable power detector. However, extra referencing part must be included to compensate the launching power fluctuation. Therefore, we focus on developing a self-referencing intensity interrogated sensors by using MZI together with two-mode interferometer. Such design can offer high sensitivity and huge immunity to input power fluctuation. For demonstration, the design was fabricate to sense temperature changes. It had a sensing range of 100 °C and was immune to launching power fluctuation, which agreed well with the theoretical prediction.