Characterization Of Phase Modulators Research Articles

Efficient characterization of phase modulator based on Lyot-Sagnac interferometer

An effective method for evaluating the performance of an electro-optic phase modulator (EOPM) based on the Lyot-Sagnac interferometer is presented and experimentally demonstrated. The Sagnac loop is made up of an EOPM with polarization-maintaining fiber (PMF) pigtails and a length of PMF, which serves as the reference segment. The reference PMF contributes to catalyzing the Vernier effect and magnifying the measurement sensitivity. In order to obtain a better spectrum, numerical investigations are carried out to optimize the parameters in the structure. The experimental results validate the theoretical simulation and display that the envelope of the output spectrum will shift significantly with increasing the modulation voltage. The measurement sensitivity is estimated to be −5.2271 nm/V with linear fit index R2 up to 0.9965 which is amplified by about 87.25 times compared to that of the single Sagnac interferometer. And the measured half-wave voltage and modulation index of the EOPM are around 3.61 V and 0.87 rad/V, respectively. The entire structure is constructed with optical fiber, which is extremely compact and can be extended to plug-and-play scheme for more practical applications.

Photonic methods of millimeter-wave generation based on Brillouin fiber laser

In optical communication link, generation and delivering millimeter-wave (mm-waves) in radio over fiber (RoF) systems has limitation due to fiber non-linearity effects. To solve this problem, photonic methods of mm-wave generation based on characterizations of Brillouin fiber laser are proposed in this work for the first time. Three novel photonic approaches for mm-wave generation methods based on Brillouin fiber laser and phase modulator are proposed and demonstrated by simulation. According to our theoretical analysis and simulation, mm-waves with frequency up to 80GHz and good signal to noise ratio (SNR) up to 90dB are generated by new and cost effective methods of generation that make them suitable for applications of the fifth generation (5G) networks. The proposed configurations increase the stability and the quality of the mm-wave generation system by using a single laser source as a pump wave and the fiber non-linearity effects are reduced. A key advantage of this research is that proposed a number of very simple generation methods and cost effective which only use standard components of optical telecommunications. Stimulated Brillouin Scattering (SBS) effect that exists in the optical fiber is studied with the characterization of phase modulator. An all optically stable mm-wave carriers are achieved successfully in the three different methods with different frequencies from 20GHz up to 80GHz. Simulation results show that all these carriers have low phase noise, good SNR ranging between 60 and 90dB and tuning capability in comparison with previous methods reported. This makes them suitable for mm-wave transmission in RoF systems to transmit data in the next generation networks.

Study of oblique incidence characterization of parallel aligned liquid crystal on silicon

The phase-only liquid crystal on silicon (LCOS) spatial light modulator has been used as a wavefront generator and reconstruction device for display applications due to its phase-only modulating property of incident light. In order to achieve the best reconstructed phase modulated wavefront, the properties of LCOS have to be fully known. The intensity of reflected light from LCOS decreases under normal incidence by going through a beam splitter. In order to improve the intensity of the reflected light beam, the oblique incidence is preferred during many applications. The oblique incidence characterization of a parallel aligned LCOS is investigated at a working wavelength of 532 nm on the basis of double-hole interferometric method. Through experiments, the phase modulation characterization of LCOS under the oblique incidence is obtained. In addition, an image postprocessing method is proposed to overcome the effect of flicker and coherent noise by simplifying the computation and increasing the measurement accuracy. The comparison of experimental results for different incident angles indicates that it plays an important role in the performance of phase modulation of LCOS, where the phase modulation decreases with the increasing angle of incidence.

Mueller–Stokes polarimetric characterization of transmissive liquid crystal spatial light modulator

In the twisted nematic liquid crystal spatial light modulators (TN-LCSLM), distortion of uniform twist and decrease in tilt angle of liquid crystal molecules on application of an electric field lead to amplitude and phase modulations of the transmitted or reflected wavefront, respectively. The amplitude and phase modulation characterization of TN-LCSLM using Jones calculi is simple and extensively used but does not give any information about important polarimetric parameters such as diattenuation and depolarizance. On the other hand, the characterization using Mueller calculi provides all information in terms of polarimetric properties such as diattenuation, retardance (birefringence) and depolarization. In this paper, polarimetric properties of the transmissive TN-LCSLM (HOLOEYE LC2002) are characterized measuring 17 different Mueller matrices at different addressed gray scale through Mueller Matrix Imaging Polarimeter (MMIP) at 530 nm wavelength. Lu–Chipman polar decomposition for Mueller matrix is utilized to separate out three independent Mueller matrices for diattenuation, depolarization and retardance as a function of addressed gray scale. Further, Mueller–Stokes combined formulation is used to examine the effect of depolarization present in the TN-LCSLM on six different states of polarization and evaluation of eigenpolarization states for the TN-LCSLM has been presented.

Full-field phase modulation characterization of liquid-crystal spatial light modulator using digital holography

A direct quantitative phase measurement method to characterize intrinsic phase modulation from an entire active area of transmissive twisted-nematic liquid-crystal spatial light modulator (TN-LCSLM) is presented using digital holography (DH). The change in birefringence of liquid crystal material with respect to addressed gray scale produces phase modulation of wavefront transmitted through TN-LCSLM. Existing methods for phase modulation characterization of LCSLM mainly provides point measurement on its total active region. In this paper, the DH method is evolved to extract quantitative phase information of an entire active area from a single digital hologram formed using the complex wavefront transmitted through TN-LCSLM.

Dynamic calibration for improving the speed of a parallel-aligned liquid-crystal-on-silicon display

The speed of most parallel-aligned liquid-crystal-on-silicon (LCoS) spatial light modulators (SLMs) is limited to the video rate of their drivers, which is a limitation for high-speed applications. However, the LCoS SLM presented here has a driver allowing a frequency range of up to 1011 Hz. Using the static phase modulation characterization and the static lookup table (LUT), the phase modulation characterization versus frequency shows that the SLM can operate at around 130 Hz or even higher for small phase changes and at 32 Hz for extreme phase changes. A dynamic calibration is carried out, and we propose a method allowing an increase of the frame rate while maintaining a maximum phase modulation of 2pi. Experimental results of dynamic diffractive optical elements displayed on the SLM at a frame rate of 205 Hz show that the dynamic LUT improves the reconstruction quality.