Fabrication of multimode interference waveguides in glass by use of a femtosecond laser

We report on the fabrication of multimode interference (MMI) waveguides that split single-mode light into multimode light in synthesized silica by use of femtosecond laser pulses. The number of modes at the output facet is dependent on both the width and the length of the MMI waveguides. The output spectral responses of the MMI waveguides in the visible region were examined. The fabricated MMI waveguides can be used as compact power splitters with large fan-outs.     

Study of selectively buried ion-exchange glass waveguides using backside masking

In this Letter, we study the characteristics of a selectively buried glass waveguide that is fabricated by the backside masking method. The results show that the surface region appears when the width of the backside mask is larger than 7 mm. Here, the glass substrate is 1.5 mm thick. It is also found that the buried depth evolution of the transition region remains almost unchanged and is independent of the width of the backside mask. The loss of the transition region is only 0.28 d B at the wavelength of 1.55 μm if the surface condition is good enough.     

Principal modes in multimode waveguides

We generalize the concept of principal states of polarization and prove the existence of principal modes in multimode waveguides. Principal modes do not suffer from modal dispersion to first order of frequency variation and form orthogonal bases at both the input and the output ends of the waveguide. We show that principal modes are generally different from eigenmodes, even in uniform waveguides, unlike the special case of a single-mode fiber with uniform birefringence. The difference is most pronounced when different eigenmodes possess similar group velocities and when their field patterns vary as a function of frequency. This work may provide a new basis for analysis and control of dispersion in multimode fiber systems.     

Assessment of ion exchanged channel waveguides in glass using interference microscopy

The use of an interference microscope in the assessment of channel waveguides formed by ion exchange in glass is presented. In the particular mode of operation discussed, light is passed through the guide parallel to the surface normal to yield the lateral index profile. It is shown that the surface expansion of the glass that occurs during the exchange has a significant effect on the interference data. A simple method of correcting for this effect is reported and justified. The application of the above technique to the characterisation of Cu ion exchanged channel guides is demonstrated. Some observations concerning the relationship between the index profile and surface expansion profile are made.     

Characterization of graded-index planar waveguides and analysis of modal coupling for the design of integrated optical components produced by ion-exchange in glass and induced by Kerr effect

An experimental analysis of graded-index (GRIN) planar waveguides produced by ion exchange in soda-lime glass is presented. This study is based on a recent model describing nonlinear diffusion. Likewise the modal coupling between planar waveguides, produced in the same substrate, is analyzed in order to design efficient integrated optical components. Finally, waveguiding structures induced by Kerr effect in glass are proposed and analyzed.     

Two-photon path-entangled states in multimode waveguides

We experimentally show that two-photon path-entangled states can be coherently manipulated by multimode interference in multimode waveguides. By measuring the output two-photon spatial correlation function versus the phase of the input state, we show that multimode waveguides perform as nearly ideal multiport beam splitters at the quantum level, creating a large variety of entangled and separable multipath two-photon states.     

Transmission characteristics in plasmonic multimode waveguides

In this article, we examine spectral transmission characteristics based on the self-imaging effect in plasmonic multimode waveguides. For the analysis, we calculate the correlation between an input field and the field in the self-imaging plane. We perform full vectorial computations using the Method of Lines as numerical method. The resulting transmission profile is discussed with regards to the attenuation, the even and odd mode sets and for several structural parameters of the plasmonic waveguide. The introduced transmission characteristic may offer the opportunity for the implementation of filtering operations in plasmonic waveguides.     

Beaming effect in multimode photonic crystal by using coupled waveguides

Beaming effect of a multimode photonic crystal (PC) covered by a waveguide array on the exit plane is investigated theoretically. The simulation results show that the multimode PC can make the incident light split into two beams, which can be regarded as secondary sources radiating light into the waveguide array. As a result, many light beams can be generated in the array by the coupling among the waveguides, and the interference of these light beams after passing the system leads to directional emission. Additionally, the directional emission is greatly affected by the beam distribution on the exit plane of the system. Once the main light beams are formed on the exit plane of the system by modulating the system size, steady beaming effect can be obtained in the horizontal direction.     

Guided-mode resonances in multimode planar periodic waveguides

<正>Using the effective medium theory and the waveguide eigenvalue equation,we design a multimode planar periodic waveguide.When a plane wave illuminates the grating at the designed angle and wavelength, more than one leaky modes are excited coincidentally.Then the reflection efficiency around this designed angle and wavelength is investigated using a rigorous coupled wave analysis formulation and a gap of reflection peaks is found.Electric field distributions reveal that this high reflectivity gap is due to the coupling between these two coincidentally excited leaky modes.     

Loss calculations in bent multimode optical waveguides

We present a straightforward geometric optics method to calculate the power attenuation induced by a circular bend in the axis of a multimode optical waveguide. The method involves tracing of rays and use of generalized power transmission coefficients. Both slab and fibre waveguides (with either step-index or parabolic core profiles) have been considered; the source has been assumed to be Lambertian.     

Field focusing control in multimode plane-layered waveguides

The possibility of controlling localized fields in multimode regular waveguides on the basis of the interference invariant principle is studied by numerical simulation. It is demonstrated that, by tuning the radiation frequency of an array without changing the initial field distribution at the aperture, it is possible to perform the scanning by a focal spot in a waveguide. Estimates of the efficiency of this method depending on the size of a vertical linear array are presented.     

Resolving power of gratings in planar multimode waveguides

A multimode planar grating spectrograph focuses, into the same point, all modes with equal propagation constants. Guided waves with equal propagation constants may have different free-space wavelengths within a bandwidth determined by the numerical aperture of this structure. The consequences for the spectral resolution of a multimode planar grating are quantitatively discussed.     

Optical limiting properties of nonlinear multimode waveguides

An experimental investigation of the transmission of multimode capillary waveguides with a nonlinear absorber in the core shows an enhanced nonlinear absorption relative to the same length of bulk material. The results are consistent with partial mode filling within the cores of the waveguides. This study confirms the promising optical limiting capabilities of multimode nonlinear waveguides and implies that the mode structure should be considered in the design and evaluation of capillary array optical limiters.     

An ultra-short double-wavelength optical power splitter for two waveguides operation based on photonic crystal multimode interference

In this paper, we design an ultra-short 1 × 2 1310/1550 nm double-waveguide optical power splitter based on photonic crystal multimode interference. The device can be used to divide the input beam equally for both 1310 nm and 1550 nm at the same time. The total multimode waveguide length of this device is only about 13 μm, which is one 210th of the conventional dielectric counterparts reported. On the basis of the guided-mode propagation analysis method, the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam in the multimode interference. The results show that the repetitive appearances of single image and twofold image of the input field occur alternatively in this device.