With the development of optical phased array (OPA) chips, it is urgent to design an optical system for detecting OPA chips. We propose a near- and far-field common optical path detection system adapted to commercial cameras. By changing the focal length of the rear set of lenses, the optical system can be used to realize the near-field detection, far-field field of view (FOV) detection, and far-field resolution detection of OPA chips. The object spatial resolution of the near-field system is 1.11 μm, and the far-field system can achieve ±45 deg FOV detection and 0.0185 deg angular resolution. Simulation results show that it can be used to characterize the far-field spot with 0.1 deg resolution. The optical system is designed with spherical lenses, and its imaging performance approaches the diffraction limit.
Based on the ITO-HfO2-graphene stacked layers, a modulator that can achieve independent modulation of TE mode and TM mode within a single silicon waveguide is proposed. Graphene and ITO are employed as electrodes of graphene-HfO2-ITO capacitor. Under applied voltage, carriers accumulate within the 5 nm thick ITO film, leading to a modification of the optical dielectric constant. Using ITO’s epsilon-near-zero behavior and its sensitivity to optical polarization, a modulation depth (MD) of no <2.5 dB/μm and an insertion loss of less than 0.054 dB/μm are achieved at the 1.55 μm. Furthermore, when modulating TE and TM modes independently, the mode crosstalk between the two modes is <0.02 dB/μm, demonstrating the high performance of the polarization-multiplexing (PM) modulator. At near-infrared band of 1.35 to 1.6 μm, the broadband properties of ITO and graphene are used to achieve an MD of no <2.2 dB/μm while maintaining mode crosstalk and insertion loss of less than 0.06 dB/μm. This modulator has robustness to top Si waveguide sidewall angle and compatibility with complementary metal oxide semiconductor processes. It is expected to be used in highly integrated polarization de-multiplexing and polarization switching systems.
A self-calibrated electrical method to measure magnitude response of optical filters is proposed based on dual-frequency-shifted heterodyne. The combined response of optical modulation, filtering, and photodetection is determined from the first frequency-shifted heterodyne, while the reference response of optical modulation and detection is simultaneously obtained from the second frequency-shifted heterodyne, with which the magnitude response of optical filter under test is extracted and self-calibrated. Our method eliminates the extra separate calibration to correct the responsivity fluctuation in the optical modulation and detection. Moreover, it extends double frequency range due to both upper and lower frequency direction measurement at every swept frequency. Magnitude response of optical filter is experimentally measured with our method and compared to that with the conventional method to check its consistency.
An electrical method is proposed for the microwave characterization of dual-drive Mach–Zehnder modulators based on heterodyne mixing. The proposed method utilizes the heterodyne products between the two-tone modulated optical sidebands and frequency-shifted optical carrier, and achieves calibration-free and bias-drift-free microwave measurement of dual-drive Mach–Zehnder modulators with high resolution electrical-domain techniques. Our method avoids the extra calibration for the photodetector and reduces half the bandwidth requirement for the photodetector and the electrical spectrum analyzer through carefully choosing a half frequency relationship of the two-tone modulation. Moreover, our measurement avoids the bias drifting problem due to the insensitivity to the bias phase of the modulator under test. The frequency-dependent modulation depths and half-wave voltages are measured for a commercial dual-drive Mach–Zehnder modulator with our method, which agree well with the results obtained by the conventional optical spectrum analysis method.
The chirp properties of semiconductor optical amplifiers in all-optical switches are numerically investigated using a field propagation model. The chirp dynamics in the blue-shift and red-shift sideband are analyzed under the injection of random optical pump pulses. We also analyze the impact of the blue-detuned filtering scheme that is used to eliminate the pattern effect and enhance the operating speed of the optical switching. The reason for overshoots in eye diagrams in the blue-detuned filtering scheme is explained. We find that overshoots result from the ultrafast blue chirp induced by carrier heating and two-phonon absorption. These results are very useful for semiconductor optical amplifier-based ultrafast all-optical signal processing.
We present the investigation results on the nonlinear phase and chirp dynamics in semiconductor optical amplifiers (SOAs). Time-resolved gain and phase dynamics of a quantum well SOA are measured using 2 ps pump pulses into an integrated Mach-Zehnder interferometer switch under a co-propagation arrangement. Ultrafast component in the phase recovery is clearly observed. We explain the ultrafast phase dynamic by using a field propagation numerical model that includes the impact of sub-picosecond intra-band effects of the SOA. In addition, we investigate the chirp properties of the SOA in all-optical switches, and analyze the influences of chirp dynamics upon the detuned-filtering-based optical switches that extract the ultrafast chirp component to realize more than 160 Gbit/s optical switching. The results are very useful for SOA-based ultrafast optical signal processing in photonic networks.
We report on the experimental observation of sideband generation in a passively mode-locked erbium-doped fiber laser.
The fiber laser has a conventional ring-cavity configuration for passive mode locking based on nonlinear polarization
rotation. Self-starting and stable mode-locking operation is easily achieved in the laser. The output soliton pulses have a
duration of about 248 fs and a repetition rate of 13.7 MHz at 1565-nm wavelength. Detailed pulse dynamics of the laser
is measured under different operation conditions. Dip-type sidebands are observed on the soliton spectra of the laser,
which have clearly different characteristics to those of the conventional Kelly sidebands. The soliton operation of the
fiber laser is numerically simulated based on the coupled Ginzburg-Landau equations. The simulation results are
consistent with the experimental observations, which confirm that dip-type spectral sidebands can appear on the soliton
spectra of a uniform soliton-emission fiber laser.
Single mode propagation is an important requirement for optical waveguide devices for use with single-mode fiber, it
can reduce the coupling loss. In this paper, a technique is used for calculating the field distribution of the polymeric
Y-junction rib waveguide. The technique is based on the combination of the effective index method(EIM) and the
variational method(VM). It is mixed between the advantages of each method and avoided their disadvantages, where EIM
can make the calculations procedures simple but it has some difficult to find the field distribution, other wise, VM can be
used with very good accuracy to find the field distribution. An algorithm is implemented to study the effect of the
structure parameters on the field distribution of the polymeric Y-junction rib waveguide. In our simulation, the core layer
is PU-FTC (n=1.65@1.3μm),the cladding layers were NOA73 (n=1.54@1.3μm) and Epoxylite9653 (n=1.54@1.3μm).
The obtained single mode rid waveguide structure parameters are: the core thickness is 1.5μm, the rib height is 0.2μm,
the rib width is 5μm.
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