We demonstrate a single chip silicon-based optical single sideband (OSSB) modulator which is composed of a branch line coupler (BLC) and a silicon dual-parallel Mach-Zehnder modulator (DP-MZM). Benefit from the powerful tool of optical domain compensation we propose, the constrains such as power imbalance and phase offset of BLC are eliminated. As a result, we realize a fully functional OSSB chip to implement full carrier OSSB (FC-OSSB) and suppressed carrier OSSB (SC-OSSB) modulations. The maximum sideband suppression ratio (SSR) of 35 dB is derived at 21 GHz.
We demonstrate a 32-element silicon OPA chip with on-chip phase calibration. The on-chip phase calibration structure consists of interferometric structures and germanium silicon photodetectors (GeSi PDs). This structure can control any angle deflection within the scanning range without detecting the far-field patterns. In the horizontal direction, the on-chip phase calibration structure is used to achieve beam steering within the 36° scanning range, and the side-lobe suppression ratio can be close to 7dB.
We demonstrate a hybrid solid-state beam scanner based on 32-channel silicon nitride optical switch with the assistance of transmission blazed grating. The optical switch exhibits rather low power consumption of 7.2 mW/π. Besides, end-fire antennas offer high optical efficiency with less reflection. Non-mechanical two-dimensional beam steering with range of 14.32° × 9.94° and beam divergence of <0.1° is achieved by wavelength tuning and onchip optical path switching. The proposed system eliminates complex control and time-consuming array phase calibration, providing a flexible, scalable and effective solution for all solid-state coaxial light detection and ranging (LiDAR) technology.
We demonstrate the 4-stage and 8-stage silicon traveling-wave photodetectors (TWPDs) with inductive gain peaking technique. Compared with un-peaked TWPDs, the bandwidths of 4-stage and 8-stage TWPDs integrated with inductors are improved from 32 GHz to 44 GHz, and from 16GHz to 24 GHz, respectively. It is experimentally validated that gain peaking is an effective technology to improve bandwidths for multiple-stage TWPDs.
We demonstrate 32-channel dispersive optical phased arrays on a Si3N4-on-SOI integration platform. The phase difference is introduced by the arrayed waveguide. Beam steering in phased-array direction with an aliasing-free range of 22.4° and free spectrum ranges of ∼ 60 nm and ∼ 6 nm is achieved. Meanwhile, the main lobe is deflected simultaneously by 19.67° in the other direction by tuning the wavelength from 1500 nm to 1630 nm. Measurement results show that the dispersive optical phased array provides a compact, low-power and massively parallel solution for LiDAR applications.
Multimode waveguide Bragg gratings filters with square shape amplitude responses and well-controlled dispersion characteristics are achieved by the Time-Domain Layer Peeling method for the first time, the Bragg grating structures can be mapped by the complementary lateral-misalignment modulation apodization. Three filters with different amplitude and phase responses are demonstrated. For the dispersion-less filter, the dispersion compensation filter and the three-channel dispersionless filter, the 3 dB bandwidth and the group delay of the realizable spectral responses are 4.0 nm, 4.7 nm, 2.1 nm and 0 ps/nm, 5.7 ps/nm, 0 ps/nm, the group delay ripples have a standard deviation of 1.7 ps, 1.5 ps, and 2.0 ps. The multimode relaxes the fabrication requirement in terms of both the lithography resolution and minimum feature size/spacing while maintaining the advantages of low insertion loss.
Based on cascaded Mach-Zehnder lattice filter, an eight-channel silicon photonic (de-)multiplexer with flat passband is demonstrated in the O-band. The insertion loss of the device is -0.55~-2.48dB and the channel crosstalk is below -7dB. The FSR and channel spacing are about 36nm and 4.4nm respectively.
ultra-compact silicon mode (de)multiplexers are demonstrated based on asymmetric directional couplers with subwavelength structure (ADCWSS), the subwavelength structure is a series of corrugation on the sidewalls of waveguides, and the two arrays of corrugation extend into the gap region between the waveguides and interlace with each other. The coupling length of ADCWSS are 5.6μm, 6.5μm, and 7.9μm for TE0-TE1, TE0-TE2, TE0-TE3 mode (de)multiplexers, respectively. The four-mode mode-division-multiplexing (MDM) link was fabricated and measured. The insertion losses of TE0-TE0-TE0, TE0-TE1-TE0, TE0-TE2-TE0, and TE0-TE3-TE0 are 0.2dB, 0.7dB, 0.7dB and 0.9dB (around 1.55μm). The maximum insertion losses and crosstalk are 2.4dB, 2.9dB, 3.0dB, 4.0dB and -18dB, -19dB, -16dB, -18dB for the TE0, TE1, TE2 and TE3-mode channels over a 50-nm bandwidth.
We present that the linearity of silicon ring modulators in microwave photonics links can be improved by manipulating the quality factor in the cavity. By reducing Q factors of silicon ring modulators from 11000 to 5880 and tuning the operation wavelength for modulation, the measured Spurious-Free Dynamic Ranges of the third-order intermodulation distortion are improved from 98.5 dB·Hz2/3 to 104.3 dB·Hz2/3 and from 90.6 dB·Hz2/3 to 94.7 dB·Hz2/3 at 1 GHz and 10 GHz, respectively.
A dual-microring resonator replaces one of the couplers of the Mach-Zehnder interferometer (MZI) to achieve a widely tunable twin-fano resonance, which originates from the interference and coupling of mode in a dual-microring resonator. The slope can be tuned in a wide range from -84.2 dB/nm to 91.0 dB/nm by metal heaters integrated on one arm of the MZI, and the resonant wavelength fixes when slope changes. The “X-type” spectrum is shown by self-alignment, which means manual alignment to form “X-type” line is unnecessary after tuning dual-microrings because the “X-type” line can be produced easily by the difference of two correlated spectrums rather than two independent spectra. Meanwhile, it shows high wavelength resolution of 1 pm with an ideal resolution of 0.4 pm in the region of the slope of 127.4 dB/nm, which can be applied to wavelength monitoring with ultra-high resolution.
KEYWORDS: Switches, Digital signal processing, Silicon, Control systems, Palladium, Optical fibers, Modulators, Signal attenuation, Photodetectors, Waveguides
We proposed a novel automatic approach for tuning automatically different delay in a 7-bit silicon-based optical delay line. The measured results of delay line by automatic tuning are also given and compared with the design values.
A tunable nonreciprocal device is presented based on PT symmetry. This device structure is composed of two pairs PT symmetry ring. Signal λ1 is only transmitted in the forward direction, while another signal λ2 is transmitted in the backward direction. The signal channel spacing can also be controlled.
The optical waveguide switch utilizing the principle of total internal reflection (TIR) is a promising structure since its
merits such as compact size, digital response characteristic, insensitivity to wavelength and polarization, and so on. In
this paper the TIR switch is studied both in theory and in experiment. At first, we give a comprehensive analysis about
reflection mechanism in the TIR switch from the following three issues: the grazing incidence of a narrow beam in the
free space, the beam reflection in a bounded space, and the beam expansion induced by the reflection in a two-dimensional
gradient field of the refractive index decrease. Then based on the analytical works, we successfully fabricate
practical TIR switches by utilizing the thermo-optical effect of polymer and the carrier injection effect of GaAs (both the
current injection and the photon injection manners are employed). The testing results show that: the extinction ratio of
the thermo-optical TIR switch exceeds 35 dB at an power consumption of 80 mW; for the carrier injection TIR switch
utilizing the current injection manner, its operation speed is faster than 20 ns and its operation current is about 70 mA.
The modal expansion method is utilized to study the reflection mechanism in the total-internal-reflection (TIR) switch. Due to the confinement of the waveguide, the beam reflection within the TIR switch is completely different from that in the free space. Its essence is the degeneracy between the even and odd modes in the waveguide of the reflection region.
We propose a compact variable optical attenuator (VOA) based on the W type five-layer symmetric slab waveguide. Simulation result shows that: for the attenuator based on GaAlAs/GaAs epitaxial layers, with a refractive index change of -0.01 in the current injection region of 1000 &mgr;m long (corresponding to injected current of about 80mA), an attenuation of more than 30dB is achieved. The attenuation range can be scaled to fit the requirements by varying the electrode length.
Generally, in the section of photonic crystal fiber, all air holes are arranged to a triangular regulation, when the size of air holes, the pitch of between neighboring air holes, and refractive index of background material are mapped optimally, one missing air hole in the central of section can localize optical field and form a single mode fiber. Here, each air hole is replaced by twin air holes with fixed distance and axis direction. Accordingly, we can think the central of
section where twin air holes missing is the core of fiber, and optical field is guided in here. In the novel photonic crystal
fiber, all twin air holes arranged according to identical axis direction in the cladding of PCF bring an asymmetry structure of section, and birefringence can come into being in this novel PCFs. After some parameters are selected optimally, the effective refractive index difference between two orthogonal directions Δneff can reach the magnitude of 10-4. From the result of numerical calculation, we also can see that the birefringence parameter Δneff can increase
slightly when the distance between twin air holes is shortened a little but keeping each air holes size and the pitch of
neighboring cell composed by twin air holes.
We propose an analytical reflection model for the waveguide switch with total-internal-reflection structure, which is the grazing reflection of beam with narrow beamwaist. For such incidence condition, the output optical field is the superposition of incident and reflected fields, we deduce the effective reflection coefficient together with angular spectrum of the output field.
An ultra compact, highly integrated photonic switch with 2×3 configuration was designed and fabricated using the thermo-optical effect of polymer materials. By exerting voltage to proper compartment of the electrode, the input light can be switched freely among three output ports. The experiment results show: for the "insufficient reflection" state, the extinction ratio is 16.64dB for the middle output port; for the "bar" state, the extinction ratio for the reflection port is 26.8 dB. The power consumption is on the scale of 100 mW, and varies with different function mode.
In this paper, the beam-propagation characteristics of the total internal reflection induced by the thermo-optic effect are investigated. Based on the Fourier heat transmission principle and variable separation method, we derive the analytical transient expression of thermal field for general thermo-optic (TO) devices. Based on the analytical expression, time response and steady-state temperature distribution of thermal-optic devices are presented. The expansion rule of total internal reflection (TIR) in the thermal field is developed mathematically, and quantitative calculation is given about specific expansion value. As an illustration and application of this rule, a X-junction 2×2 TIR switch is designed to accomplish the object of high reflection efficiency. The computer simulation results show the structure presents a high reflection coefficient indeed, the reflection loss is only -0.76dB. The computer simulation results agree with the calculation well.
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