Polarization Dependent Loss Research Articles

Dual Orthogonally Polarized Lasing Assisted by Imaginary Fermi Arcs in Organic Microcavities.

The polarization control of micro- and nanolasers is an important topic in nanophotonics. Up to now, the simultaneous generation of two distinguishable orthogonally polarized lasing modes from a single organic microlaser remains a critical challenge. Here, we demonstrate simultaneously orthogonally polarized dual lasing from a microcavity filled with an organic single crystal exhibiting selective strong coupling. We show that the non-Hermiticity due to polarization-dependent losses leads to the formation of real and imaginary Fermi arcs with exceptional points. Simultaneous orthogonally polarized lasing becomes possible thanks to the eigenstate mixing by the photonic spin-orbit coupling at the imaginary Fermi arcs. Our work provides a novel way to develop linearly polarized lasers and paves the way for the future fundamental research in topological photonics, non-Hermitian optics, and other fields.

Polarization-independent and high-efficiency 2D dielectric transmission grating under Littrow incidence

In this paper, a transmission two-dimensional (2D) all-dielectric grating with cuboid arrays is proposed, which has high diffraction efficiency and good polarization independence under Littrow mounting conditions at an incident wavelength of 780 nm. The optimization results indicate that when the incident wavelength is 780 nm, the diffraction efficiency of the (−1, 0) order of transverse electric (TE) and transverse magnetic (TM) polarizations can reach 98.62% and 98.23%, respectively, with the polarization-dependent loss (PDL) of 0.017 dB. To the best of our knowledge, high-efficiency polarization-independent 2D transmission grating with a simpler and more effective structure is proposed for the first time, which demonstrates significant enhancements in bandwidth and manufacturing tolerances while maintaining high diffraction efficiency. The results suggest that the grating has great potential for applications in high-precision displacement measurements such as grating interferometers.

In-fiber waveguide-based mode-locker for generating diverse ultrafast pulses

The pursuit of an optimal mode-locker in nonlinear photonics is crucial for advancing high-performance laser technologies. Addressing the market demands and technical complexities in creating highly integrated and robust saturable absorbers, we present a femtosecond laser-inscribed in-fiber straight waveguide, seamlessly integrating a few-mode fiber segment into a single-mode fiber. This design reduces costs, simplifies fabrication, and enhances system integration and stability. As a saturable absorber, it enables nonlinear polarization rotation and multimode interference, which are essential for ultrafast pulse generation. It exhibits slight polarization-dependent loss and significant modulation depth, effectively inducing mode-locking. Based on the waveguide, 1.36 ps soliton pulses with a 2.9 nm bandwidth at a central wavelength of 1573 nm are initially achieved in an anomalous dispersion regime. Transitioning to the normal dispersion regime, at 190 mW pump power, the system produces Q-switched mode-locked pulses at 1574 nm. Increasing the pump power to 295 mW results in 712 fs noise-like pulses at 1572 nm, featuring an 8 nm bandwidth and 4.57 MHz repetition rate. This advancement in fiber lasers, facilitated by hybrid nonlinear effects in the waveguide, represents a significant milestone, promising for nonlinear optics and photonics due to its simplicity, cost-effectiveness, compactness, robustness, and high damage threshold.

Asymmetric bi-level dual-core mode converter for high-efficiency and polarization-insensitive O-band fiber-chip edge coupling: breaking the critical size limitation

Abstract Efficient coupling between optical fibers and on-chip photonic waveguides has long been a crucial issue for photonic chips used in various applications. Edge couplers (ECs) based on an inverse taper have seen widespread utilization due to their intrinsic broadband operation. However, it still remains a big challenge to realize polarization-insensitive low-loss ECs working at the O-band (1,260–1,360 nm), mainly due to the strong polarization dependence of the mode coupling/conversion and the difficulty to fabricate the taper tip with an ultra-small feature size. In this paper, a high-efficiency and polarization-insensitive O-band EC is proposed and demonstrated with great advantages that is fully compatible with the current 130-nm-node fabrication processes. By introducing an asymmetric bi-level dual-core mode converter, the fundamental mode confined in the thick core is evanescently coupled to that in the thin core, which has an expanded mode size matched well with the fiber and works well for both TE/TM-polarizations. Particularly, no bi-level junction in the propagation direction is introduced between the thick and thin waveguide sections, thereby breaking the critical limitation of ultra-small feature sizes. The calculated coupling loss is 0.44–0.56/0.48–0.61 dB across the O-band, while achieving 1-dB bandwidths exceeding 340/230 nm for the TE/TM-polarization modes. For the fabricated ECs, the peak coupling loss is ∼0.82 dB with a polarization dependent loss of ∼0.31 dB at the O-band when coupled to a fiber with a mode field diameter of 4 μm. It is expected that this coupling scheme promisingly provides a general solution even for other material platforms, e.g., lithium niobate, silicon nitride and so on.

Rapid-calibration optical tunable delay line on 3-µm-thick SOI photonic platforms

Optical tunable delay lines (OTDLs) which can capture temporal optical signals, and overcome the challenge of halting light are crucial for optical communications and microwave photonics. Here, a rapid-calibration 8-bit OTDL on the 3-µm-thick silicon-on-insulator (SOI) platform consisting of waveguide spirals and integrated optical switches is proposed, achieving a maximum delay time of 3570 ps with a resolution of 14 ps/stage. The large delay is attributed to the spirals of a 3-µm-thick SOI platform featuring a delay efficiency of approximately 11.49 ps/mm, with wavelength-insensitivity transmission loss of 0.32 dB/cm, and the polarization-dependent loss is only 0.075 dB/cm within 140 nm bandwidth. In addition, the optical switches with extinction ratios up to 50 dB. Integrated variable optical attenuators can suppress crosstalk and facilitate rapid calibration for OTDLs. The advantages of OTDLs’ large delay time, high signal-to-noise, and rapid calibration make them suitable for optical programmers and microwave photonics radars.

Transceiver impairment robust and joint monitoring of PDL, DGD, and CD using frequency domain pilot tones for digital subcarrier multiplexing systems

Optical performance monitoring is vital for enabling dynamically reconfigurable optical networks. This paper introduces a monitoring scheme that is robust to transceiver impairments for coherent digital subcarrier multiplexing (DSCM) systems that simultaneously monitors polarization-dependent loss (PDL), differential group delay (DGD), and chromatic dispersion (CD). In the proposed scheme, a pair of frequency domain pilot tones (FPTs) are inserted into the X and Y polarizations of the transmitted dual-polarization signal. Both the signal and the FPTs endure identical channel impairments during fiber transmission. At the receiver side, the transmitted FPTs are extracted to monitor the channel impairments. We begin by establishing a simplified system model using a single frequency tone to analyze the effects of system impairments on the frequency domain pilots. Based on this model, CD, PDL, and DGD are jointly and accurately estimated. In addition, the influences of temporal, amplitude, and phase mismatches between in-phase (I) and quadrature (Q) components of transceivers on channel impairment monitoring are completely eliminated. This achieves a channel impairment monitoring scheme that is robust to transceiver impairments. Experimental verification shows that the proposed scheme can jointly and accurately estimate a wide range of CD, PDL, and DGD. Additionally, the proposed monitoring scheme demonstrates strong robustness against transceiver impairments, rapid polarization fluctuations, and amplified spontaneous emission (ASE) noise.

Design of high-efficiency InP/InGaAsP diluted waveguide for edge couplers

To transition integrated optical communication devices from laboratory settings to practical applications, efficient coupling between optical fibers and chip waveguides remains pivotal. This paper presents a systematic design of a diluted waveguide, a key component in the edge couplers of photonic integrated circuits. The primary purpose of the diluted waveguide lies in facilitating superior edge coupling with fiber waveguides, thereby seamlessly integrating external light sources into the waveguide structure. To commence, we employ the transfer matrix and effective refractive index techniques to simplify the 3-dimensional diluted waveguide into 2-dimensional multi-layer slab waveguides. By computing the field distribution of the fundamental mode within the diluted waveguide, the fiber-to-waveguide coupling efficiency can be derived using a simplified overlap equation and optimized diluted waveguide structure through particle swarm optimization algorithms. Consequently, we achieve a remarkable fiber-to-waveguide coupling efficiency exceeding 95% for TE-mode and 92% for TM-mode, with a polarization dependent loss (PDL) of merely 0.13 dB. Interestingly, the optimized diluted waveguide exhibits quasi-single mode behavior, as the fundamental mode containing 98% of the total energy propagates within it. Additionally, the diluted waveguide edge coupler demonstrates favorable alignment tolerance, with 1-dB excess losses of ±2.3 μm and (−2.5, +3) μm along the horizontal and vertical directions, respectively. Notably, our approach offers a versatile methodology for designing multi-layer waveguides across various materials. This method has the potential to be universally applied.

O-band and C-band dual-polarization SMF-28 edge coupler with SiON taper cladding based on silicon nitride platform.

Optical communication is progressing towards low power consumption and lightweight solutions, necessitating the integration of multispectral output capabilities within a single optical module. We demonstrate a SiN photonic platform-based edge coupler for a standard single mode fiber (SMF) that enables operation in both the O-band and C-band simultaneously. The device is composed of a multi-segment SiN inverse taper and SiON taper cladding with specific refractive index. The measured edge coupler exhibits a coupling loss of less than 1 dB/facet, 0.5 dB bandwidth exceeding 100 nm from 1260 nm to 1360 nm; and a coupling loss of less than 2 dB/facet, 1 dB bandwidth exceeding 100 nm from 1500 nm to 1600 nm. Furthermore, the polarization dependent loss (PDL) remained less than 0.3 dB throughout the measurement range.

Multimode interference coupler based on general interference for integrated optical and quantum optic devices: a review

Integrated optics play important role in the development for optical network devices, optical processing, instrumentation and quantum information device. Here, multimode interference (MMI) coupler is one of basic component preferred for these integrated optic devices in which MMI coupler based on general interference (GIMMI) has been focused for large scale integrated optic devices because of compact size in comparison to MMI coupler based restricted interference (RIMMI). In this paper, we have reviewed different GIMMI structures reported previously. Different waveguide materials are mentioned and compared for fabrication of GIMMI device. The coupling behaviors and modal analysis of GIMMI couplers and their different tapered structures are estimated by using simple model based on sinusoidal modes showing reduced coupling lengths in down tapered structures in comparison to other structures. The excess loss, polarization dependence loss and crosstalk versus fabrication tolerances are obtained to compare their performances revealing almost same losses and fabrication tolerance. The paper reports the use of the GIMMI coupler in wavelength multiplexing, power splitting, switching, optical processing. Finally, Quantum optic application of GIMMI coupler is shown indicating high quantum fidelity of 50:50 coupling ratio.

Free-standing microscale photonic lantern spatial mode (De-)multiplexer fabricated using 3D nanoprinting

Photonic lantern (PL) spatial multiplexers show great promise for a range of applications, such as future high-capacity mode division multiplexing (MDM) optical communication networks and free-space optical communication. They enable efficient conversion between multiple single-mode (SM) sources and a multimode (MM) waveguide of the same dimension. PL multiplexers operate by facilitating adiabatic transitions between the SM arrayed space and the single MM space. However, current fabrication methods are forcing the size of these devices to multi-millimeters, making integration with micro-scale photonic systems quite challenging. The advent of 3D micro and nano printing techniques enables the fabrication of freestanding photonic structures with a high refractive index contrast (photopolymer-air). In this work we present the design, fabrication, and characterization of a 6-mode mixing, 375 µm long PL that enables the conversion between six single-mode inputs and a single six-mode waveguide. The PL was designed using a genetic algorithm based inverse design approach and fabricated directly on a 7-core fiber using a commercial two-photon polymerization-based 3D printer and a photopolymer. Although the waveguides exhibit high index contrast, low insertion loss (−2.6 dB), polarization dependent (−0.2 dB) and mode dependent loss (−4.4 dB) were measured.

Polarization-insensitive and high-efficiency edge coupler for thin-film lithium niobate.

In this Letter, we propose and demonstrate a fiber-to-chip edge coupler (EC) on an x-cut thin film lithium niobate (TFLN) for polarization-insensitive (PI) coupling. The EC consists of three width-tapered full-etched waveguides with silica cladding and matches well with a single-mode fiber (SMF). The measured results show that the minimum coupling losses for TE0/TM0 modes remain to be 0.9 dB/1.1 dB per facet, and the polarization dependent loss (PDL) is <0.5 dB over the wavelength range from 1260 to 1340 nm. Moreover, the EC features large misalignment tolerance of ±2 µm in the Z direction and ±1.5 µm in the X direction for both polarizations for a 1 dB penalty. To the best of our knowledge, this is the first realized O-band edge coupler on TFLN with SMF. The proposed device shows promising potential for integration into TFLN polarization diversity devices.

Low-loss and polarization insensitive 32 × 4 optical switch for ROADM applications

Integrated switches play a crucial role in the development of reconfigurable optical add-drop multiplexers (ROADMs) that have greater flexibility and compactness, ultimately leading to robust single-chip solutions. Despite decades of research on switches with various structures and platforms, achieving a balance between dense integration, low insertion loss (IL), and polarization-dependent loss (PDL) remains a significant challenge. In this paper, we propose and demonstrate a 32 × 4 optical switch using high-index doped silica glass (HDSG) for ROADM applications. This switch is designed to route any of the 32 inputs to the express ports or drop any channels from 32 inputs to the target 4 drop ports or add any of the 4 ports to any of the 32 express channels. The switch comprises 188 Mach-Zehnder Interferometer (MZI) type switch elements, 88 optical vias for the 44 optical bridges, and 618 waveguide-waveguide crossings with three-dimensional (3D) structures. At 1550 nm, the fiber-to-fiber loss for each express channel is below 2 dB, and across the C and L bands, below 3 dB. For each input channel to all 4 drop/add channels at 1550 nm, the loss is less than 3.5 dB and less than 5 dB across the C and L bands. The PDLs for all express and input channels to the 4 drop/add channels are below 0.3 dB over the C band, and the crosstalk is under −50 dB for both the C and L bands.

Silicon-Nanowire-Based 100-GHz-Spaced 16λ DWDM, 800-GHz-Spaced 8λ LR-8, and 20-nm-Spaced 4λ CWDM Optical Demultiplexers for High-Density Interconnects in Datacenters

Several types of silicon-nanowire-based optical demultiplexers (DeMUXs) for use in short-reach targeted datacenter applications were proposed and their spectral responses were experimentally verified. First, a novel 100-GHz-spaced 16λ polarization-diversified optical DeMUX consisting of 2λ delayed interferometer (DI) type interleaver and 8λ arrayed waveguide gratings will be discussed in the spectral regimes of C-band, together with experimental characterizations showing static and dynamic spectral properties. Second, a novel 800-GHz-spaced 8λ optical DeMUX was targeted for use in LR (long reach) 400 Gbps Ethernet applications. Based on multiple cascade-connected DIs, by integrating the extra band elimination cutting area, discontinuous filtering response was analytically identified with a flat-topped spectral window and a low spectral noise of &lt;−20 dB within an entire LR-8 operating wavelength range. Finally, a 20-nm-spaced 4λ coarse wavelength division multiplexing (CWDM)-targeted optical DeMUX based on polarization diversity was experimentally verified. The measurement results showed a low excessive loss of 1.0 dB and a polarization-dependent loss of 1.0 dB, prominently reducing spectral noises from neighboring channels by less than −15 dB. Moreover, TM-mode elimination filters were theoretically analyzed and experimentally confirmed to minimize unwanted TM-mode-oriented polarization noises that were generated from the polarization-handling device. The TM-mode elimination filters functioned to reduce polarization noises to much lower than −20 dB across the entire CWDM operating window.

On the detection, modeling, and mitigation of anomalous QoT fluctuations in optical networks

Monitoring data from deployed backbone networks shows that many lightpaths present large fluctuations of their quality of transmission (QoT), beyond 1 dB in range. In this paper, we investigate the hypothesis that the evidenced fluctuations stem from anomalies in polarization-dependent loss (PDL), equivalent to one large PDL element. We eventually propose and experimentally test a closed-loop automation designed to stabilize the QoT at a maximal level for lightpaths impaired by such a PDL anomaly.

High Efficiency O‐band Preamplified Receiver Integrated with Semiconductor Optical Amplifier and Uni‐travelling Carrier Photodiode for Passive Optical Network

With the continuous increase in data traffic and enormous consumption of data in terms of video on demand services and cloud computing, there is an increasing demand for high speed and high sensitivity short reach receivers for passive optical networks (PON) access network which are point to multi‐point networks. Avalanche photodiodes (APD) are the standard receivers in PON networks due to their high sensitivity and low cost. However, it is currently not clear if they can provide high bandwidth above 40 GHz with good performance (gain, noise, etc.). Furthermore, standard PIN photodiodes do not provide sufficient sensitivity for PON networks. Therefore, in this article a SOA‐UTC receiver is proposed, which is a photonic integrated circuit (PIC) comprising a semiconductor optical amplifier (SOA) for optical preamplification and a high‐speed uni‐travelling‐carrier (UTC) photodiode for opto‐electronic conversion. A very high responsivity of 140 A W−1 is demonstrated, with a polarization dependent loss (PDL) around 1 dB and a 3 dB bandwidth of 48 GHz, which is very promising for future PON network with 50 Gbit s−1 capacity and above.

Multiwavelength erbium-doped fiber laser using the polarization-hole-burning effect for multichannel acoustic detection.

We propose and demonstrate a novel, to the best of our knowledge, fiber-optic multipoint acoustic detection system based on a multiwavelength erbium-doped fiber (EDF) laser (MWEDFL) using the polarization-hole-burning effect with Fabry-Perot interferometers as the acoustic cavity-loss modulator. A polarization-wavelength-related filter is designed to assign a distinct polarization state to each laser wavelength. By adjusting the polarization state, the polarization-dependent loss and gain of each laser line are tuned to be equal, effectively suppressing the mode competition of EDF and enabling a stable MWEDFL. Each laser line serves as a separate channel for acoustic detection. Theoretical and experimental analyses are conducted to study the transient-response-amplification effect on the acoustic perturbation of the MWEDFL. The results show that the proposed MWEDFL exhibits an amplification effect on the sound-induced cavity-loss modulation, effectively enhancing the sensitivity by 13 dB compared to that obtained using an external-light-source demodulation method. In addition, the MWEDFL based on the PHB effect avoids cross talk between laser channels and can achieve high sensitivity and simultaneous multichannel acoustic detection.

Near-infrared Y-branch polymer splitters realized with compact MMI structures for efficient power splitting

Optical splitters are promising photonic devices for next-generation photonic integrated circuits, which enable signal distribution and routing between the different components, facilitating complex optical functionalities on a single chip. This research introduces what we believe is a novel numerical technique for enhancing optical network efficiency by incorporating a taper-based step-index (SI) Y-branch multimode interference (MMI) splitter with organic-inorganic hybrid polymer materials. The proposed device comprises a core width of 5 µm for the input and output waveguides to satisfy the single-mode conditions. We designed and optimized the MMI splitter using the beam propagation method (BPM). The splitter demonstrates the power splitting property with an efficiency of 86%. The excess losses for the MMI splitter are 0.52 dB and 0.50 dB for TE and TM modes, respectively, at 1.55 µm. The polarization dependence loss (PDL) and propagation loss (PL) are 0.015 dB and 0.00019 dB/µm, respectively.

Polar Decomposition of Jones Matrix and Mueller Matrix of Coherent Rayleigh Backscattering in Single-Mode Fibers.

The Jones matrix and the Mueller matrix of the coherent Rayleigh backscattering (RB) in single-mode fibers (SMFs) have been derived recently. It has been shown that both matrices depict two polarization effects-birefringence and polarization-dependent loss (PDL)-although the SMF under investigation is purely birefringent, having no PDL. In this paper, we aim to perform a theoretical analysis of both matrices using polar decomposition. The derived sub-Jones/Mueller matrices, representing birefringence and PDL, respectively, can be used to investigate the polarization properties of the coherent RB. As an application of the theoretical results, we use the derived formulas to investigate the polarization properties of the optical signals in phase-sensitive optical time-domain reflectometry (φ-OTDR). For the first time, to our knowledge, by using the derived birefringence-Jones matrix, the common optical phase of the optical signal in φ-OTDR is obtained as the function of the forward phase and birefringence distributions. By using the derived PDL-Mueller matrix, the optical intensity of the optical signal in φ-OTDR is obtained as the function of the forward phase and birefringence distributions as well as the input state of polarization (SOP). Further theoretical predictions show that, in φ-OTDR, the common optical phase depends on only the local birefringence in the first half of the fiber section, which is occupied by the sensing pulse, irrelevant of the input SOP. However, the intensity of the φ-OTDR signal is not a local parameter, which depends on the input SOP and the birefringence distribution along the entire fiber section before the optical pulse. Moreover, the PDL measured in φ-OTDR is theoretically proven to be a local parameter, which is determined by the local birefringence and local optical phase distributions.

Simultaneous generation of wavelength multiplexing and polarization multiplexing from a wavelength-tunable ultrafast fiber laser

A wavelength-tunable mode-locked erbium-doped all-fiber laser delivering both wavelength multiplexing and polarization multiplexing asynchronous pulses is experimentally demonstrated, which is challenging in previous studies. The numerical simulations validate the experimental observations and reveal that the cavity birefringence and polarization dependent loss (PDL) induced by the wavelength division multiplexer play a significant role in the formation of different types of asynchronous pulses. Our results not only provide insights into the physical mechanism of the asynchronous pulses generation, but also offer a potential low-complexity light source for dual-comb applications.

Analytical Formulation of Fiber Nonlinear Noise Statistics in the Presence of Polarization Dependent Loss

Analytical Formulation of Fiber Nonlinear Noise Statistics in the Presence of Polarization Dependent Loss