Tracking a light pulse through a waveguide in space and time

We present first direct observation of the propagation of a femtosecond laser pulse in space and time through a waveguide structure. With an interferometric photon scanning tunneling microscope (PSTM), the local amplitude and phase of the pulse were retrieved with high spatial, spectral and time resolution. The relative field profiles, the wave vectors and the spectra of the pulses in the TE00 and TE01 modes in the waveguide have been experimentally determined

Phase mapping of optical fields in integrated optical waveguide structures

The phase evolution of optical waves in a waveguide structure has been studied with a heterodyne interferometric photon scanning tunneling microscope. Both phase and amplitude of the local optical field are measured with subwavelength resolution. Topographical maps of the waveguide surface are obtained simultaneously with the optical information. Unexpected phase patterns, with phase jumps and phase singularities, have been observed. The phase patterns can be fully understood by taking into account the total field that is the sum of the optical fields of the various modes. We show that with the unique spatial phase information, the relative field profiles and wave vectors of all the excited modes in a multimodal waveguide structure can be determined independently

Nanoscale coherent imaging of photonic structures by PSTM

We present an alternative instrument to map local optical field distributions: a photon scanning tunneling microscope (PSTM). In a PSTM a near-field optical fiber probe is used to frustrate the evanescent field above an integrated optical device. The evanescent wave is converted into a propagating wave that is coupled into the fiber, guided through it and subsequently detected by a photomultiplier tub

Local phase measurements of light in a one-dimensional photonic crystal

For the first time the local optical phase evolution in and around a small, o­ne-dimensional photonic crystal has been visualized with a heterodyne interferometric photon scanning tunnelling microscope. The measurements show an exponential decay of the optical intensity inside the crystal, which consists of a periodic array of subwavelength air rods fabricated in a conventional ridge waveguide. In addition it is found that the introduction of the air rods has a counter- intuitive effect o­n the phase development inside the structure. The heterodyne detection scheme allows the detection of low- intensity scattered wanes. In the vicinity of the scattering air rods phase singularities are found with a topological charge of plus or minus o­n

Spectral mode-beat phenomena in a cylindrical microcavity

Detailed spectral analysis of photon scanning tunneling microscope images has been carried out. The analysis of spectral mode-beat phenomena leads to an accurate determination of mode profiles and gives evidence of counterpropagating mode

High-resolution photon-scanning tunneling microscope measurements of the whispering gallery modes in a cylindrical microresonator

A detailed analysis of spatio-spectral photon scanning tunneling microscope scans of the light intensity inside a cylindrical microresonator has been carried out. By comparing the experimental results with theory, it is shown that the inclusion of spectral mode-beat phenomena is crucial for an accurate analysis of the modes present in the microresonator

Detailed analysis of the intracavity phenomena inside a cylindrical microresonator

Based o­n a rigorous analysis of the intensity distribution inside a cylindrical microresonator (MR), a detailed description of the wavelength and spatial dependence of the intracavity intensity is given. The theory is in accordance with photon scanning tunneling microscopy (PSTM) of an integrated optics MR. Good agreement between the theory and the PSTM measurements is found

Pulse tracking in complex photonic structures

Time-resolved near-field microscopy allows the propagation of ultrafast pulses to be visualized en route while they travel through complex photonic structures. These measurements enable the unambiguous determination of both local phase and group velocities. We illustrate this powerful technique by tracking an ultrashort wavepacket as it completes several round trips in a ring resonator

Pulse tracked through waveguide

Conventionally, researchers study pulse propagation by coupling pulses into a medium and deducing what goes on inside from the radiation that is transmitted or reflected. Now a team from the University of Twente in Enchede, the Netherlands, has found a way to track the group and phase velocities of a femtosecond laser pulse inside a photonic structure using a heterodyne-detection, phase-sensitive photon scanning tunneling microscope.\ud \ud The researchers used a frequency-doubled, Ti:sapphire-pumped optical parametric oscillator to produce a 300-fs-long pulse inside a silicon nitride planar-channel waveguide. They captured snapshots of the pulse's position while moving the microscope's reference point along the medium with it. They then compiled the snapshots to form a full picture of what was happening to the pulse in the waveguide.\ud \ud The team expects this methodology to lend more insight into the dynamic behaviors of photonic crystals and integrated optical circuits