C-band Wavelength Research Articles

Optimizing 20 Gbps of ground-to-satellite free-space optical communication in low earth orbit with hybrid wavelength-mode division multiplexing

High-speed free-space optical (FSO) communication has emerged as a promising technology for low earth orbit (LEO) region in the last decade. In this paper, we simulate 20 Gbps simplex ground-to-satellite with various wavelengths and transmitter beam pointing error of 0.1 to 2.5 urad. The C-band wavelength is chosen, and a non-return-zero (NRZ) pulse generator with 16 channels hybrid wavelength-mode division multiplexing (WDM-MDM) technique employing Hermite-Gaussian (HG) modes is used to vary the pointing error. The effect of beam pointing error and receiver aperture diameter was discussed in this paper. A transmitter beam pointing error of 2.5 urad can work appropriately at distances of 1000 km and 1500 km, with a BER value of 1.41 × 10−6 and 3.56 × 10−5, respectively. Based on the receiver aperture diameter of 100 cm, it successfully achieves a BER value of 2.4 × 10−8 at the LEO region and a clear eye diagram.

Investigation of Polymer-Based 1×2 All-Optical Switches at C-Band Wavelength

All-optical switches play a significant role in optical communication and signal processing using purely optical signals and offer efficient high-speed data transmission over conventional switches, which rely on optic–electronic conversions. This paper demonstrates 1 × 2 all-optical switches realized with the Mach–Zehnder interferometer (MZI) and directional couplers (DCs) for next-generation high-speed computing systems. We numerically design and simulate this optical switch by using the commercially available RSoft CAD BeamPROP solver. The proposed switches leverage the combined influence of DCs to achieve precise control over switching states by demonstrating remarkable phase-shifting properties with phase differences of 4π/3 and π/2 between the MZI and DC. The optical switch exhibits excess losses (ELs) from 1.27 dB to 1.40 dB and crosstalk ranging from −13.303 dB to −11.034 dB in a wavelength range of 1.53–1.56 μm, and minimal EL and crosstalk are 1.27 dB and −13.303 dB at 1.55 μm. The proposed polymer-based 1 × 2 all-optical switches could be novel devices in high-speed data transmission for optical circuitry.

Entangled photon pair generation in an integrated SiC platform

Entanglement plays a vital role in quantum information processing. Owing to its unique material properties, silicon carbide recently emerged as a promising candidate for the scalable implementation of advanced quantum information processing capabilities. To date, however, only entanglement of nuclear spins has been reported in silicon carbide, while an entangled photon source, whether it is based on bulk or chip-scale technologies, has remained elusive. Here, we report the demonstration of an entangled photon source in an integrated silicon carbide platform for the first time. Specifically, strongly correlated photon pairs are efficiently generated at the telecom C-band wavelength through implementing spontaneous four-wave mixing in a compact microring resonator in the 4H-silicon-carbide-on-insulator platform. The maximum coincidence-to-accidental ratio exceeds 600 at a pump power of 0.17 mW, corresponding to a pair generation rate of (9 ± 1) × 103 pairs/s. Energy-time entanglement is created and verified for such signal-idler photon pairs, with the two-photon interference fringes exhibiting a visibility larger than 99%. The heralded single-photon properties are also measured, with the heralded g(2)(0) on the order of 10−3, demonstrating the SiC platform as a prospective fully integrated, complementary metal-oxide-semiconductor compatible single-photon source for quantum applications.

C-band wavelength tunable mode locked noise-like pulse source using an asymmetrically reflecting Fabry-Perot filter

We report a widely wavelength tunable mode locked noise-like pulse (NLP) source from an erbium doped fiber ring laser. By making use of the reflection of an asymmetric Fabry- Perot interferometer (FPI), continuous tunability of the central wavelength over the entire C-band (1530 nm to 1565 nm), with an independent control over bandwidth (3.5 nm to 17 nm) is demonstrated. Using a single control parameter, i.e. the length of the FPI, it is thus possible to select from a range of output spectral bandwidths and desired central wavelengths. Using the same control on the length of the FPI and intracavity polarization settings, generation of dual wavelength NLPs, temporally shifted noise-like pulse pairs, harmonic mode locked NLPs and loosely bound NLP doublets and NLP triplets are reported. Owing to the simplicity of the tuning mechanism and the adaptable output spectrum, we believe, such a laser will be useful for various applications like sensing, spectroscopy and imaging. The novel combination of a reflecting FPI-based filter, and the complex nonlinear polarization rotation (NPR) based mode locking mechanism, also offers the opportunity to further explore the rich physics of NLPs.

High-throughput quantum photonic devices emitting indistinguishable photons in the telecom C-band.

Single indistinguishable photons at telecom C-band wavelengths are essential for quantum networks and the future quantum internet. However, high-throughput technology for single-photon generation at 1550 nm remained a missing building block to overcome present limitations in quantum communication and information technologies. Here, we demonstrate the high-throughput fabrication of quantum-photonic integrated devices operating at C-band wavelengths based on epitaxial semiconductor quantum dots. Our technique enables the deterministic integration of single pre-selected quantum emitters into microcavities based on circular Bragg gratings. Respective devices feature the triggered generation of single photons with ultra-high purity and record-high photon indistinguishability. Further improvements in yield and coherence properties will pave the way for implementing single-photon non-linear devices and advanced quantum networks at telecom wavelengths.

A Comprehensive Study on EDFA Gain Flattening for WDM Transmission using Cascaded Fiber Bragg Gratings

The gain flattening of optical amplifiers plays a crucial role in optical Wavelength Division Multiplexing (WDM) communication systems, ensuring uniform amplification across all channels. This study focuses on investigating the gain flattening characteristics of Erbium-Doped Fiber Amplifiers (EDFAs) using cascaded Fiber Bragg Gratings (FBGs) in the C-band wavelength range. A comparative analysis of various optical amplifiers revealed that EDFA exhibited the highest gain variation, making it an optimal choice for gain flattening. The key parameters to achieve optimal EDFA gain flattening include the wavelengths of the channels, EDFA length, noise figure (NF), and the number of cascaded FBGs. Simulation experiments are conducted using Optisystem software (ver. 14.2) and the obtained results reveal that EDFA gain flatness can be achieved within the wavelength range of 1531 to 1533 nm, utilizing an EDFA length of 6 m and 12 cascaded FBGs. These findings contribute to the advancement of gain flattening techniques in optical WDM systems, enhancing their performance and reliability.

Integration of large-extinction-ratio resonators with grating couplers and waveguides on GaN-on-sapphire at O-band.

Photonic integrated circuits (PICs) based on gallium nitride (GaN) platforms have been widely explored for various applications at C-band (1530 nm∼1565 nm) and visible light wavelength range. However, for O-band (1260 nm∼1360 nm) commonly used in short reach/cost sensitive markets, GaN-based PICs still have not been fully investigated. In this article, a microring resonator with an intrinsic Q-factor of ∼2.67 × 104 and an extinction ratio (ER) of 35.1 dB at 1319.9 nm and 1332.1 nm, is monolithically integrated with a transverse electric-polarized focusing grating coupler and a ridge waveguide on a GaN-on-sapphire platform. This shows a great potential to further exploit the optical properties of GaN materials and integrate GaN-based PICs with the mature GaN active electronic and optoelectronic devices to form a greater platform of optoelectronic-electronic integrated circuits (OEICs) for data-center and telecom applications.

Magic wavelengths for the 6S-7P transition of cesium atoms

For the trapped pre-cooled atoms in an optical dipole trap (ODT), the magic-wavelength ODT can eliminate the differential light shift of the transition between two atomic states, so that the transition frequency between the two states is the same as that of atoms in the free space, which is of great significance for improving the experimental repetition rate and reducing the atomic decoherence in the fields of cold atom physics, quantum optics, and precision measurement. Here we calculate the dynamic polarizabilities of cesium 6S ground state and 7P excited state by using the multi-level model for the ODT with laser wavelength from 1200 to 2000 nm. The magic wavelengths of ODT are obtained for the linearly and circularly polarized laser beams at the intersection of dynamic polarizabilities of two atomic states. Furthermore, we analyze the robustness of the magic trapping conditions and the feasibility of the experimental operation near the telecom C-band wavelength.

Hybrid integrated Si3N4 external cavity laser with high power and narrow linewidth.

We have designed and fabricated a hybrid integrated laser source with full C-band wavelength tunability and high-power output. The external cavity laser is composed of a gain chip and a dual micro-ring narrowband filter integrated on the silicon nitride photonic chip to achieve a wavelength tuning range of 55 nm and a SMSR higher than 50 dB. Through the integration of the semiconductor optical amplifier in the miniaturized package, the laser exhibits an output power of 220 mW and linewidth narrower than 8 kHz over the full C-band. Such a high-power, narrow-linewidth laser diode with a compact and low-cost design could be applied whenever coherence and interferometric resolutions are needed, such as silicon optical coherent transceiver module for space laser communication, light detection and ranging (LiDAR).

Design of Silicon Photonics Integrated Bulk Zigzag and Sinusoidal Structured Mode Conversion Devices Using Genetic Algorithm (GA) Optimization

To increase the optical interconnect transmission capacity, different multiplexing technologies, including wavelength division multiplexing (WDM), polarization division multiplexing (PolDM) and mode division multiplexing (MDM), can be utilized. Among them, MDM is a promising technique in silicon photonics (SiPh) integrated optical interconnects since higher order modes can be easily generated and preserved in SiPh waveguides. In this work, we propose and demonstrate the designs of SiPh-based bulk zigzag and sinusoidal structured MDM mode conversion devices using genetic algorithm (GA) optimization. A traditional periodic zigzag structured mode converter design has many sharp zigzag angles in the periodic structure, which are very sensitive to the fabrication error. Here, first of all, we propose and demonstrate a bulk zigzag structure to achieve MDM mode conversion. The proposed bulk zigzag structure can reduce the zigzag angle error as a large number of zigzag angles in the periodic structure are eliminated. Moreover, we further improve our device by proposing a bulk sinusoidal structure to further eliminate the zigzag angle. Results show that both the proposed bulk zigzag and sinusoidal MDM mode converters can still maintain high transmissions of >86%, while the mode conversion lengths of both devices can be significantly reduced by >60% in the C-band wavelength window. In addition, as there are many degrees of freedom (DOFs) during the design of the SiPh mode converter, including the waveguide width, length, period, zigzag angle, etch depth, duty cycle, etc., the GA optimization algorithm is employed. Here, detailed implementation of the GA optimization is discussed.

Plasmonic internal-photoemission-based Si photodetector design suitable for optical communication.

We propose a high-performance plasmonic photodetector based on the internal photoemission (IPE) process for the C-band communication wavelength. This photodetector takes advantage of an embedded nanohole array in Schottky metal. Owing to localized surface plasmon resonance, the absorption of the active metal layer increases, which results in the generation of more hot carriers and subsequently compensates for the low efficiency of IPE-based photodetectors. Simulations show that for the proposed photodetector with 2-nm-thick Au, Cu, and Ag Schottky contacts, the absorptance dramatically enhances to 95.1%, 93.2%, and 98.2%, respectively, at the wavelength of 1.55 µm. For the detector based on Au, the highest external quantum efficiency of 25.3% and responsivity of 0.32 A/W are achieved at a reverse bias voltage of 1 V. Furthermore, the 3 dB bandwidth can exceed 369 GHz owing to the low capacitance of the structure and the fast transit time of carriers from the thin p-Si layer. Finally, by studying the current-voltage characteristics of the photodetector, it is shown that under the reverse bias voltage of 1 V, the dark current is 665 nA at room temperature, and by reducing the temperature to 200 K, it improves three orders of magnitude and decreases to 810 pA.

Low-Loss Silicon Photonic 16 × 16 Cyclic AWGR Based on SOI Platform

We experimentally demonstrate a low-loss and low-crosstalk 16-channel 200 GHz-channel-spacing arrayed waveguide grating router (AWGR) with a size of 0.67 × 0.37 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , targeting for C-band wavelength division multiplexing (WDM) interconnect routing applications. As a result, the AWGR features a channel spacing of 200±10 GHz, a free spectral range of 25.62 nm and a 3 dB channel bandwidth of 0.9 nm. Based on comprehensive optimal design, the measured characterization revealed 5.55 dB maximum channel loss non-uniformity with 1.13 dB best-case channel insertion loss. Besides, the fabricated device exhibits good cyclic-frequency operation for all 16 × 16 port combinations with channel crosstalk of –15.11 dB.

CMOS-Compatible and Temperature Insensitive C-Band Wavelength (De-)multiplexer

The high thermal sensitivity of the Silicon Photonics (SiP) platform compromises the performance of variant devices and increases the power consumption to stabilize the temperature. To address this issue, we demonstrate a CMOS-compatible and temperature insensitive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> C-band wavelength division (de-)multiplexer on the 220-nm-thick silicon-on-insulator platform. The (de-)multiplexer design is based on cascading Mach-Zehnder interferometers (MZIs). The waveguide widths of the MZI delay lines are matched to decrease the overall thermo-optic coefficient (TOC). For comparison, an MZI-based (de-)multiplexer with uniform delay lines is also fabricated on the same chip. The transmission spectra of the proposed and reference devices are measured when the wavelength is swept from 1500 nm to 1600 nm and the temperature is varied from 293.15 K to 323.15 K. The measured results show that the TOCs of the proposed and reference device are 4.8 pm/K and 85 pm/K, respectively. This power-efficient multiplexer with high integration density is promising for data center applications.

Experimental demonstration of robust nanophotonic devices optimized by topological inverse design with energy constraint

In this paper, we present the experimental results for integrated photonic devices optimized with an energy-constrained inverse design method. When this constraint is applied, optimizations are directed to solutions that contain the optical field inside the waveguide core medium, leading to more robust designs with relatively larger minimum feature size. We optimize three components: a mode converter (MC), a 1310 nm/1550 nm wavelength duplexer, and a three-channel C-band wavelength demultiplexer for coarse wavelength division multiplexing (CWDM) application with 50 nm channel spacing. The energy constraint leads to nearly binarized structures without applying independent binarization stage. It also reduces the appearance of small features. In the MC, well-binarized design, improved insertion loss, and cross talk are obtained as a result. Furthermore, the proposed constraint improves the robustness to fabrication imperfections as shown in the duplexer design. With energy constraint optimization, the corresponding spectrum shifts for the duplexer under ± 10 nm dimensional variations are reduced from 105 nm to 55 nm and from 72 nm to 60 nm for the 1310 nm and 1550 nm channel, respectively. In the CWDM demultiplexer, robustness toward ± 10 nm fabrication error is improved by a factor of 2. The introduction of the energy constraint into topological optimization demonstrates computational gain with better-performing designs.

Wavelength-Tunable Optical Two-Tone Signals Generated Using Single Mach-Zehnder Optical Modulator in Single Polarization-Mode Sagnac Interferometer

We demonstrate 60 GHz separation optical two-tone signal generation at arbitrary C-band wavelengths without involving complicated optical wavelength filtering. By utilizing a polarizer, the selective suppression of undesired low-order optical sidebands has been proven and optimized based on model analysis. By utilizing this scheme in conjunction with the optimized parameters, more than 20 dB of suppression of undesired optical sidebands have been successfully achieved over a 40 nm wavelength range. This scheme allows us to generate optical two-tone signals at the desired wavelength.

Optical fiber sensor network integrating SAC-OCDMA and cladding modified optical fiber sensors coated with nanomaterial

Three modified single mode optical fiber ammonia sensors coated with nanocomposite of polyaniline/graphite nanofiber (PANI/GNF) are integrated with optical code division multiple access utilizing spectral amplitude coding (SAC-OCDMA) optical fiber sensors network. The sensors are modified using both etching and tapering processes. A thin layer of PANI/GNF is spared on the etched–tapered SMF sensors. The sensors based on the evanescent wave absorption are investigated by measuring the output optical power in the C-band wavelength range (1535–1560 nm) at room temperature. SAC-OCDMA using Khazani Syed (KS) code is deployed as it has the capability to remove multiple access interference (MAI) and it is cost effective. The performance of the developed optical fiber sensor network based on star topology is investigated remotely over 3 km using Erbium doped fiber amplifier for NH3 sensing in terms of received optical power, crosstalk, and optical signal-to-noise ratio (OSNR). OSNR is observed to vary with fiber diameter and NH3 concentration level. The smaller tapering diameter and higher NH3 concentrations generate lower OSNR at the output of the related decoder. The measured OSNR for the developed optical fiber sensor network was 22 and 18.45 dB when sensors implied in the network exposed to 0.125% and 1% NH3 concentrations, respectively.

Effect of Nonlinear Dispersion Fiber Length and Input Power on Raman Scattering

The increasing demand for information transmission makes the problem of establishing a laser system is operating in C-band (1530-1565nm) wavelength region is a significant task, which attracts a lot of researchers' attention lately. In this paper, the ability to produce signals of multi wavelengths using a single light source was adopted to employ the Raman scattering effect for establishing Raman shift configuration-based multi-wavelength fiber lasers, which is not currently addressed in available schemes. This is what prompted to simulate the performance of C-band multi-wavelength produced by Raman fiber laser that utilizing fiber Bragg grating (FBG) to amplify pumped power and also utilizing the single-mode fiber (SMF) as the nonlinear gain medium. The proposed laser system is designed by OptiSystem software. The resulted maximum output power was 22.07dB at Wavelength Division Multiplexing (WDM) of 23.01dB input power. The achieved multi-wavelength that generated by Bragg grating and SMF was containing six Stokes and anti-Stokes, they are: 1548.51nm, 1549, 31nm, 1550.116nm, 1550.91nm, 1551.72nm, and 1552.52nm, in which the resulted computed efficiency of the system was raised up to 80.23% at input power 20 dB and dispersion fiber length of 0.2 km.

Characterization of focusing grating couplers for telecom wavelengths in the first and second diffraction order

In this work we studied how focusing grating couplers, developed for telecommunication C-band wavelength range, can be applied in the near infrared range. In the paper we presented prospects of usage of both first and second diffraction maxima of theoretically computed diffraction grating couplers for photonic aims. The dependence of the central wavelength of the grating on the etching depth of the photonic layer, on the period and filling factor of the grating was studied. We have compared our experimental results with numerical study, performed using finite elements method of solving differential equations. The work is important for different photonic applications and introduces new prospects in application of the already fabricated devices, developed for telecommunication wavelengths.

Compact behavioral model and parametric extraction for optical phase shifters in carrier-depletion Mach–Zehnder silicon modulators

Testing of active photonic devices is totally different from testing of pure electronics; in particular, reduction of testing time in silicon photonics has been a significant issue. In this study, a compact behavioral model of optical phase shifters is constructed for carrier-depletion Mach–Zehnder (MZ) silicon modulators in the push–pull regime. The target characteristics, i.e., the dynamic extinction ratio (ER), absorption loss, and chirp parameter, are expressed in simple forms in terms of parameters representing the voltages-dependent modulation efficiency (ME) and the imaginary part of the effective index. The parameters reflecting manufacturing variability can be quickly extracted from fast DC measurements, which shortens the testing time. The theoretical concept relies on the proposal of a generalized form of the large-signal ME and an effective approximation for model construction that avoids the problem of the conventional small-signal definition being not applicable and large-signal definition leading to a cumbersome and non-intuitive formulation. It is shown that the constructed model suitably explains the physics and the reported experimental results for the slightly positive chirp characteristics of balanced phase shifters. Moreover, a parametric extraction applying the model is demonstrated in the C-band wavelength on a 300-mm SOI wafer.

Performance analysis of fiber Bragg grating sensor interrogators based on arrayed waveguide gratings

A planar lightwave circuit-based multi-channel arrayed waveguide grating (AWG) is used as a critical part of the fiber Bragg grating (FBG) interrogation unit and designed to be integrated into the fiber grating sensing system. We designed and fabricated a high-performance, 40 channels AWG in the device, enabling whole C-band wavelength demodulation while maintaining high-measurement resolution. The AWG was designed to have 100-GHz channel spacing; the channel crosstalk was measured to be −45 dB. An AWG-based FBG interrogation system was built to analyze the characteristics of our unit. The testing result shows that our system has the capability of demodulating wavelength from 1526.438 to 1563.863 nm with wavelength accuracy within ±10 pm; the wavelength resolution is measured to be 1 pm. Our testing result confirms that an AWG-based FBG interrogator is an excellent choice for FBG sensing systems.