Moti Fridman

Demonstration of temporal cloaking

Recent research has uncovered a remarkable ability to manipulate and control electromagnetic fields to produce effects such as perfect imaging and spatial cloaking. To achieve spatial cloaking, the index of refraction is manipulated to flow light from a probe around an object in such a way that a ‘hole’ in space is created, and the object remains hidden. Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking has been proposed in which the dispersion of the material is manipulated in time, producing a ‘time hole’ in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap—inside which an event occurs—such that the probe beam is not modified in any way by the event. The probe beam is then restored to its original form by the reverse manipulation of the dispersion. Here we present an experimental demonstration of temporal cloaking in an optical fibre-based system by applying concepts from the space–time duality between diffraction and dispersive broadening. We characterize the performance of our temporal cloak by detecting the spectral modification of a probe beam due to an optical interaction and show that the amplitude of the event (at the picosecond timescale) is reduced by more than an order of magnitude when the cloak is turned on. These results are a significant step towards the development of full spatio-temporal cloaking.

Fiber lasers generating radially and azimuthally polarized light

A simple, robust, and efficient method to produce either radially or azimuthally polarized output beam from a fiber laser is presented. Experimental results reveal that polarization purity of 90% or better can be obtained.

Demonstration of Temporal Cloaking

We present the first experimental demonstration of cloaking an event in the time domain. Our temporal cloaking scheme is based on the time-space duality and novel split time-lenses.

Efficient coherent addition of fiber lasers in free space

An efficient technique in which fiber lasers are coherently added in free space is presented. Since the high power of the combined output light propagates in free space rather than inside, fiber optical damage and deleterious nonlinear effects are substantially reduced. Two different configurations are investigated. One involves conventional intracavity coupling between the lasers. The other is a novel configuration where the coupling is done out of the combined cavities. The latter configuration requires much less coupling for obtaining the same output power, so the damage to the fiber is further reduced.

Controlling synchronization in large laser networks.

Synchronization in large laser networks with both homogeneous and heterogeneous coupling delay times is examined. The number of synchronized clusters of lasers is established to equal the greatest common divisor of network loops. We experimentally demonstrate up to 16 multicluster phase synchronization scenarios within unidirectional coupled laser networks, whereby synchronization in heterogeneous networks is deduced by mapping to an equivalent homogeneous network. The synchronization in large laser networks is controlled by means of tunable coupling and self-coupling.

Passive phase locking of 25 fiber lasers.

Our experiments on passively phase locking two-dimensional arrays of coupled fiber lasers reveal that the average phase locking level of 25 lasers is low (20%-30%) but can exceed 90% in rare brief events. The average phase locking level was found to decrease for a larger number of lasers in the array and to increase with the connectivity of the array.

Fiber amplification of radially and azimuthally polarized laser light

The results of amplifying either radially or azimuthally polarized light with a fiber amplifier are presented. Experimental results reveal that more than 85% polarization purity can be retained at the output even with 40 dB amplification and that efficient conversion of the amplified light to linear polarization can be obtained.

Phase locking of two coupled lasers with many longitudinal modes.

Detailed experimental and theoretical investigations of two coupled fiber lasers, each with many longitudinal modes, reveal that the behavior of the longitudinal modes depends on both the coupling strength and the detuning between them. For low to moderate coupling strength only longitudinal modes that are common for both lasers phase lock, while those that are not common gradually disappear. For larger coupling strengths, the longitudinal modes that are not common reappear and phase lock. When the coupling strength approaches unity the coupled lasers behave as a single long cavity with correspondingly denser longitudinal modes. Finally, we show that the gradual increase in phase locking as a function of the coupling strength results from competition between phase-locked and non-phase-locked longitudinal modes.

Real-time measurement of space-variant polarizations

A configuration for real-time measurement of unique, space-variant, polarizations is presented. The experimental results reveal that the full state of polarization at each location within the beam can be accurately obtained every 10 msec, limited only by the camera frame rate. We also present a more compact configuration which can be modified to determine the real-time wavelength variant polarization measurements.

Phase locking of two fiber lasers with time-delayed coupling

Two coupled fiber laser arrangements demonstrating isochronal and achronal phase locking with long-time-delayed coupling are presented. Experimental results show that stable phase locking with coupling delay lines as long as 4 km can be obtained and that phase locking can be invariant to the time delay.