Numerical analysis of a 3D optical sensor based on single mode fiber to multimode interference graphene design

This paper shows mainly the performance study on tapered section of Multimode Interference (MMI) coupler having either parabolic or exponential taper section. The comparative study of the 1 × 2 MMI coupler with proposed structure, such as the normalized width variation, and variation of MMI length are investigated by the 2D finite difference beam propagation method (BPM). We have found that exponential tapered MMI coupler has advantageous compared to parabolic tapered MMI coupler. The relation between numbers of allowed modes with power transmission has been predicted along with pulse propagation through MMI coupler. At the output of proposed structure, S-bend waveguides used to provide sufficient separation between the two output waveguides. At the end of paper, compared the excess loss of proposed structure. Our results are unique, because, we have analyzed relatively a new structure compared to existing structure found in literature. Keywords: Linear waveguide, Parabolically tapered waveguide, Exponentially tapered waveguide, S-bend Arc waveguide

Power splitting ratio couplers based on MMI structures with high bandwidth and large tolerance using silicon waveguides

Fiber laser sensor based on multimode interference (MMI) effect can achieve high sensitivity with lower temperaturestrain cross sensitivity by designing optimally the MMI structure. An erbium-doped fiber laser for temperature, stress and refractive sensing based on single mode fiber spliced a short section of no-core fiber was proposed in this paper. The optical field characteristics of this MMI structure have been analyzed, indicating the spectral filtering effect existed. An erbium-doped fiber laser with the MMI structure inserted as the sensor element, the enhanced sensing sensitivity is achieved on the sensing experiments of ambient temperature, mechanical stress and liquid refractive index. The sensitivity of this MMI-based fiber laser sensor is up to 13.24 pm/°C with the measured range from 30 °C to 220 °C, 1.29pm/μe from 0 to 7776.05μe, 180.21nm/RIU from 1.34 to 1.42, respectively.

The passive components in the integrated optic chip applied by fiber optic gyroscope are analyzed and designed on silicon-on-insulator (SOI) wafers. These components include a polarizer and a multimode interference (MMI) coupler. The MMI coupler acts as the traditional Y-branch power splitter. The polarizer consists of two 3dB MMI couplers and two straight single mode waveguides between these two MMI couplers. These two straight waveguides have equal length but have different rib width. The mode propagation constants of TE or TM light are not same and the appropriate selection of the length of the straight waveguide will result in the splitting of TE and TM light. The scalar or semivectorial finite difference beam propagation method (FD-BPM) is used to design these photonic components. The mode parameters of straight waveguide with different rib width are analyzed by semivectorial FD-BPM and the reasonable length of straight waveguide was selected. The MMI coupler is designed by scalar FD-BPM and the length of multimode waveguide and the positions of the input or output ports are determined accurately. The curving waveguide is avoided completely, therefore the design is more reliable and the fabrication of the device is much easy.

Optimal design of a multimode interference (MMI) coupler for broadening the spectral response of an arrayed-waveguide grating (AWG) demultiplexer is considered. By using a Gaussian beam approximation, an analytical expression for the spectral response of an AWG demultiplexer (with an MMI section) is obtained. A simple analytical formula is derived to relate the optimal MMI length to the separation between the peaks of the twofold images in the MMI region. This peak separation is related to the width of the MMI section. In the proposed design method, a required 1-dB passband width determines the peak separation, which then determines the optimal value for the length of the MMI section according to the analytical formula. The designed flat-top AWG demultiplexer is verified by the beam propagation method.

All-optical logic gates have attracted considerable attention over the past decade. They have found application as adders, subtractors, header recognizers, parity checkers and in encryption systems. In this paper, we present a new structure based on cascaded 4×4 and 2×2 multimode interference (MMI) couplers for implementing optical XOR, XNOR, NAND and OR logic gates. The emphasis of the design is on optimising bandwidth and fabrication tolerance. Such a design would be useful for optical label swapping and recognition in optical packet switching networks. We use silicon on insulator (SOI) waveguides that are compatible with the CMOS technology, for designing the whole device. The Beam Propagation Method (BPM) and the Eigenmode Expansion Method (EEM) are used for numerical simulations. We show that the contrast ratios for logic 1 and logic 0 for XOR, XNOR, NAND, and OR gates are from 18 dB to 28 dB for a bandwidth of 30nm, respectively. A large fabrication tolerance of ±500 nm can be achieved by using this structure.

In this letter, a novel method to realize all-optical discrete sine transform (DST) and discrete cosine transform (DCT) is proposed. The approach requires only one multimode interference (MMI) coupler and several phase shifters at the input and output ports. By properly arranging the length of the MMI coupler and adjusting the phase shifters, the DST can be directly realized all-optically. Meanwhile, the DCT is related to the DST with a simple formula. By changing the input phase and relabeling the output ports, it can also be realized on the MMI structure. The proposed methodology has no limit on the number of the inputs.

We present a new design of wavelength division demultiplexer based on self-imaging principle in the multimode interference (MMI) structure. To the best of our knowledge, this work presented for the first time in MMI structure with almost 5nm channel spacing and 2451 average quality factor in the telecommunication range. The beam propagation method is used for simulation of this device.

Unbalanced multimode interference (MMI) couplers are optical integrated components widely used in photonic integrated circuits. Couplers with two fixed coupling ratios: 85/15 and 15/85 are studied in this paper. Low-loss MMI couplers are designed and fabricated. Excitation of the first-order mode in access waveguides of MMI couplers can influence the excess losses and the coupling ratio of these components. The effect of the first-order mode excitation was simulated and confirmed by the experimental results, which are presented in this paper.

We report about a design of a bi-directional planar optical multiplex/demultiplex filter (triplexer) for the optical part of planar hybrid WDM bi-directional transceiver in fiber-to-the-home (FTTH) PON applications. The triplex lightwave circuit is based on the Epoxy Novolak Resin SU-8 waveguides on the silica-on-silicon substrate with Polymethylmethacrylate cladding layer. The triplexer is comprised of a linear butterfly concept of multimode interference (MMI) coupler separating downstream optical signals of 1490 nm and 1550 nm. For the upstream channel of 1310 nm, an additional directional coupler (DC) is used to add optical signal of 1310 nm propagating in opposite direction. The optical triplexer was designed and optimized using beam propagation method. The insertion losses, crosstalk attenuation, and extinction ratio for all three inputs/outputs were investigated. The intended triplexer was designed using the parameters of the separated DC and MMI filter to approximate the idealized direct connection of both devices.

A temperature sensor based upon a single mode - multimode-single mode – multimode - single mode (SMSMS) fiber structure is experimentally demonstrated. The SMSMS structure is covered by ethanol-glycerol solution, and changing the ratio of ethanol to glycerol changes the temperature sensitivity. A theoretical calculation was developed to characterize the influence of the ethanol-glycerol content upon the sensor performance,. Multimode interference (MMI) occurs between single mode fibers (SMF) and multimode fibers (MMF), and temperature measurements were achieved by monitoring the movement of the interference profile in the transmission spectrum. The results show that covering the SMSMS structure with an ethanol-glycerol solution improves the temperature sensitivity of the sensor. The temperature sensitivity was is 0.700 nm/°C from 30 °C to 80 °C.

In this paper, a balanced optical fanout using 1/spl times/4 thin film metal-semiconductor-metal (MSM) photodetector array embedded in a photoimageable polymer multi-mode interference (MMI) coupler is fabricated, demonstrated, and compared to theoretical estimates. This is the first MMI coupler reported with an integrated photodetector array, and the first MMI coupler reported that has been fabricated with a photoimageable polymer. For optical signal distribution (e.g. optical clock distribution), balanced signal routing is an important optical function, and MMI couplers provide compact design, low splitting loss, and balanced output.

This work reports the design of a 1x2 photonic digital switch controlled by an electrically induced metasurface, configurated by a rectangular array of points where the refractive index is locally changed through the application of an external bias. The device is simulated using the Beam Propagation Method (BPM) and Finite Difference Time Domain (FDTD) algorithms and the structure under evaluation is an amorphous silicon 1x2 multimode interference (MMI), joined to an arrayed Metal Oxide Semiconductor (MOS) structure Al/SiNx/a-Si:H/ITO to be used in active-matrix pixel fashion to control the output of the switch. MMI couplers, based on self-imaging multimode waveguides, are very compact integrated optical components that can perform many different splitting and recombining functions. The input–output model has been defined using a machine learning approach; a high number of images have been generated through simulations, based on the beam propagation algorithm, obtaining a large dataset for an MMI structure under different activation maps of the MOS pixels. This dataset has been used for training and testing of a machine learning algorithm for the classification of the MMI configuration in terms of binary digital output for a 1x2 switch. Also, a statistical analysis has been produced, targeting the definition of the most incident-activated pixel for each switch operation. An optimal configuration is proposed and applied to demonstrate the operation of a digital cascaded switch. This proof of concept paves the way to a more complex device class, supporting the recent advances in programmable photonic integrated circuits.

We propose and demonstrate a hybrid fiber-based sensor combining a multimode interference (MMI) structure and a surface plasmon resonance (SPR) structure for simultaneous measurement of temperature and refractive index (RI) of a liquid sample. We configure the MMI structure by connecting a single-mode fiber, a no-core fiber, and a single-mode fiber sequentially. We set up the SPR structure by coating a gold film with a thickness of 50 nm on the surface of the no-core fiber. We measure the sensitivity of RI and the temperature of the MMI and SPR structure, respectively. Then we obtain the coefficient matrix to simultaneously measure the temperature and RI of a liquid sample and obtain the highest RI sensitivity of 2061.6 nm/RIU and temperature sensitivity of 37.9 pm/°C. We verify the feasibility of the sensor in liquid alcohol. The testing results indicate that the proposed sensor and testing method are feasible, accurate, and convenient.

A novel design of a bi-directional triplexer based on Bragg grating assisted multi-mode interference (MMI) coupler is proposed in this letter. The MMI coupler de/multiplexes the upload 1310nm channel and the download 1490nm channel, while the grating reflects the download 1550nm channel to the other download port. The bandwidths for 1310nm, 1490nm and 1550nm are about 110nm, 50nm, and 15nm, respectively.