Complex Optical Signal Research Articles

On-Chip, Single-Shot Characterization of GHz-Rate Complex Optical Signals

Phase reconstruction based on optical ultrafast differentiation is implemented using an integrated-waveguide Mach-Zehnder interferometer to demonstrate self-referenced phase characterization of gigahertz-rate complex modulated signals (e.g., quadrature phase shift keying and amplitude phase shift keying modulation formats), through a single-shot and real-time technique. This method is transparent to both modulation format and bit rate, limited only by the bandwidth capabilities of the temporal intensity measurement instrumentation.

Self-mixing vibration measurement using emission frequency sinusoidal modulation

In this paper, a simplified phase demodulation scheme is applied to recover vibration trail on a laser self-mixing interferometer for noncontact vibration measurement. The emission of semiconductor laser diode is modulated by injecting sinusoidal wave, and corresponding interference signal is a quasi-sinusoid wave. The vibration mathematical model for semiconductor laser diode is theoretically educed from basic self-mixing theory, the variation of target is converted into phase information. The simulation of demodulation algorithm and standard deviation are presented and the reconstructed waveform displays a desirable consistence with various moving trails. Following the principle, a minimum experimental system is established and position variation of the target mirror driven by voltage signal is translated into phase shifts, feedback is controlled at weak level during experiment, Fourier transform is implemented to analyze phase information. The comparisons of both amplitude and velocity with a Germany Doppler vibrometer are performed to testify vibration model, the error of proposed demodulation method is less than 30nm and achieve a high accuracy in vibration frequency. The experimental results indicate the traditional phase technology can be applied on complex optical power signal after adaption providing a feasible application prospects in industrial and scientific situation with an inexpensive semiconductor laser.

Synthetic optical holography with nonlinear-phase reference.

Synthetic optical holography (SOH) provides efficient encoding of the complex optical signal, both amplitude and phase, for scanning imaging methods. Prior demonstrations have synthesized reference fields with a plane-wave-like linear variation of the phase with position. To record large images without probe-mirror synchronization, a long-travel, closed-loop reference mirror stage has been required. Here we present SOH with a synthetic reference wave with sinusoidal spatial variation of the phase. This allows the use of open loop, limited mirror travel range in SOH, and leads to a novel holographic inversion algorithm. We validate the theory with scans of graphene grain boundaries from a scanning near-field optical microscope, for which SOH has been shown to drastically increase scan speeds [Nat. Commun. 5, 3499 (2014)].

Time-domain holograms for generation and processing of temporal complex information by intensity-only modulation processes

The time-domain counterpart of traditional spatial holography is formalized and experimentally demonstrated. This concept involves the recording, generation and/or processing of complex (amplitude and phase) optical time-domain signals using intensity-only temporal detection and/or modulation optical devices. The resulting procedures greatly simplify present approaches aimed to similar generation and processing tasks. As a proof-of-concept, we successfully demonstrate a time-domain computer holography scheme. This scheme is used for experimental generation of user-defined complex optical temporal signals, in particular, a sequence of arbitrarily chirped Gaussian-like optical pulses and complex-modulation (16-QAM) optical telecommunication data streams, by CW-light intensity-only modulation.

Highly complex optical signal generation using electro-optical systems with non-linear, non-invertible transmission functions

We present a scheme whereby a static non-linear, non-invertible transmission function performed by the electro-optic Mach-Zehnder modulator produces highly complex optical chaos. The scheme allows the deterministic transformation of low-dimensional band-limited chaotic signals into much higher-dimensional structures with broadband spectra and without using any delay elements or feedback. Standard benchmark tests show that all the considered complexity indices are highly increased due to this transformation in a controlled fashion. This mechanism allows the design of simple optoelectronic delayed oscillators with extremely complex chaotic output.

On the Use of Delay-Decorrelated I/Q Test Sequences for QPSK and QAM Signals

We report on limitations of the commonly used method to generate complex optical signal constellations from delay-decorrelated copies of a bit sequence to modulate in-phase (I) and quadrature (Q) components of a signal constellation. Using closed-form analytical solutions, numerical simulations, and an experimental verification, we show that I/Q delays shorter than the combined channel and adaptive equalizer length can result in artificial improvements of the measured bit-error ratio.

Single-shot real-time frequency chirp characterization of telecommunication optical signals based on balanced temporal optical differentiation

A simple single-shot frequency chirp characterization technique for telecommunication optical waveforms is introduced. The proposed technique is based on what we believe to be a novel balanced all-optical ultrafast differentiation scheme, and it enables a real-time conversion of the instantaneous frequency variation of an arbitrary complex (amplitude and phase) optical signal into a temporal intensity profile while simultaneously providing an efficient cancellation of the intensity noise. Single-shot real-time frequency chirp measurements of gigahertz-bandwidth phase-only and amplitude and phase temporal modulation waveforms are performed.

Analysis of short optical signals by the Gabor transformation

An expression is obtained for the reconstruction of a complex optical signal from the modulus of the Gabor transform of the signal spectrum. It is shown that the temporal resolution of systems with an image-converter streak camera can be improved by spectral expansion of the signal and by mathematical processing of the results obtained.

Addition of Complex Optical Signals in a Compacted Autoidolon

In the present work addition or/and subtraction of complex optical signals is obtained without the aid of any optical accesories such as lenses or spatial filters. In the self-addition process the properties of periodic optical objects are used. The principle of self-addition involves coherently illuminating a suitable periodic object. The object is composed of several various transmittances which represent the optical signals which are to be added. The transmittances are grouped and periodically spaced in sets of mutually shifted sublattices of the compound object. When the object is coherently transilluminated, then the images of the sum and difference of the transmittances appear in its diffraction light field. The effect of forming multiple images, called compacted autoidolons, in the diffraction light field of periodic transmittances is here described and demonstrated experimentally.

Addition of complex optical signals by matched spatial filtering

A new method of addition of 2-D complex optical signals is proposed. The addition is performed by suitably matched spatial filtering. For that purpose the effect of compacting of periodic objects images is employed.