arXiv subjects

Md Ghulam Saber

Publications and source records attributed to Md Ghulam Saber.

6 recordsLinked to original sources

arXiv2026

Per-Channel Launch-Power Optimization in Hollow-Core Fiber Systems

In single-mode fiber (SMF) the Kerr effect ties every channel's quality of transmission to its neighbors' launch powers through cross-phase modulation (XPM), four-wave mixing (FWM) and inter-channel stimulated Raman scattering (ISRS), forcing a jointly planned launch profile. Hollow-core fiber (HCF), with a Kerr coefficient three to four orders of magnitude below silica, turns the per-channel powers into nearly independent knobs limited only by the shared amplifier budget. We build a per-channel generalized signal-to-noise ratio (GSNR) budget for amplified HCF links, including amplified spontaneous emission (ASE) with a wavelength- and output-power-dependent erbium-doped fiber amplifier (EDFA) noise figure (NF), inter-modal interference (IMI), nonlinearity in amplifier pigtails, CO2 gas-line loss and a flat transceiver (TRx) noise ceiling, and derive a sensitivity law that predicts when power shaping pays: its gain is bounded by the ASE noise share, canceled by self-phase modulation (SPM) at the SMF single-channel optimum, and positive in HCF. Across 80x64-GBaud C-band links over 400-3200 km, per-channel optimization buys up to 1.0 dB of worst-channel GSNR over a flat launch as the EDFA NF spread grows to 4 dB, cuts cross-channel power sensitivity by more than two orders of magnitude relative to SMF, and reaches a given GSNR at about 3 dB lower aggregate amplifier output. At a fixed amplifier budget this becomes a 1.26 to 1.41 times worst-channel reach extension, against at most 15% on the nonlinearity-capped SMF link.

physics.optics↗

arXiv2026

System-Level Limits of Higher-Order QAM in Hollow-Core Fiber Systems

Hollow-core fiber (HCF) is widely expected to enable higher-order quadrature amplitude modulation (QAM) because of its near-vacuum Kerr nonlinearity and higher launch power. We develop a per-channel effective signal-to-noise ratio (SNR) budget that combines, in reciprocal form, optical-link impairments including amplified spontaneous emission, Kerr nonlinear interference (NLI), inter-modal interference (IMI), pigtail NLI, and CO2 gas absorption; a parameterized, symbol-rate-dependent transceiver back-to-back SNR ceiling determined by effective-number-of-bits at rate, analog bandwidth, and Tx/Rx nonlinearity; and the remaining transceiver and line impairments, including laser phase noise, equalization-enhanced phase noise, timing jitter, polarization-dependent loss, and amplifier gain ripple with filter narrowing, each expressed as an equivalent SNR floor. The central result, at a representative 64GBaud system with 75GHz channel spacing over 6THz, is that once HCF removes the fiber limits, the transceiver ceiling rather than the fiber sets the achievable modulation order: a roughly 25dB ceiling at 64GBaud makes 1024-QAM and above infeasible on either fiber, confining ultra-high-order QAM to low baud rates. HCF therefore provides its main advantage in reach and achievable baud rate at a given modulation order: at an IMI coefficient of kappa=-55dB/km, 256-QAM reach increases from about 45km to about 170km and 64-QAM reach from about 415km to about 2275km when moving from single-mode fiber to HCF. In the C-band, CO2 absorption lines are weak and sparse, so channels placed away from the lines follow the gas-free baseline, while only worst-case placements lose reach at long distances. In the L-band, the stronger absorption bands are denser than the channel bandwidth, making line avoidance spectrally costly, and a channel placed on a line loses one to two QAM orders.

physics.optics↗

arXiv2026

Transition-Aware Routing in Hybrid Hollow-Core/Single-Mode Fiber Networks: A Cost--Throughput Investigation

Incremental deployment of hollow-core fiber (HCF) in single-mode-fiber (SMF) networks introduces a routing tradeoff: reducing HCF-SMF transitions can improve physical-layer feasibility, but overly transition-averse routing incurs harmful path detours. We study this tradeoff using a common event-driven simulator that compares six protected routing schemes spanning fiber-blind, generalized signal-to-noise ratio (GSNR)-aware, and explicitly transition-aware designs on hybrid HCF/SMF topologies. The model includes a per-transition GSNR penalty and an exploratory splice-failure availability term. Across six reference topologies, five HCF deployment fractions, and dynamic loads at 300 Erlang, the strongest transition minimizers, transition-penalty-aware routing (TPAR) and the GSNR/fiber-transition joint scheme (GFJ), halve the mean transition count at a 20-25% carried-traffic penalty. Among the intermediate designs, GSNR- maximal routing with transition-aware reranking (GMR-T) cuts transitions by approximately 22% relative to distance-adaptive routing and spectrum assignment (DA-RSA) at a 3% throughput cost, while bounded-detour TPAR (BD-TPAR) cuts transitions by approximately 11% at only a 1% cost. Deployment pattern also matters: contiguous HCF rollout lowers transitions by approximately 40% on average while improving carried traffic, reducing the benefit of aggressive transition-aware routing. These results support BD-TPAR as a practical default under fragmented deployment, GMR-T as a lower-complexity alternative, and TPAR or GFJ only where the external cost of transitions is high.

cs.NI↗

arXiv2026

Beyond Silica Assumptions: Optical Network Design in the Hollow-Core Era

Hollow-core fiber (HCF) is often presented as a modestly improved transmission medium that can be inserted into networks originally designed for solid-core silica. We argue instead that recent progress -- most notably the reported attenuation below 0.1 dBkm$^{-1}$, together with a broad low-loss window, reduced propagation delay, and extremely low optical nonlinearity -- makes it timely to reconsider which long-standing design conventions are fundamental to optical communication and which are specific to silica fiber. By reviewing implications at the physical-layer, transceiver, and network-architecture levels, we suggest that the most durable benefits of HCF may arise not from its use as a drop-in replacement, but from cross-layer co-design. We also outline the studies and experimental demonstrations needed to determine where such advantages are genuinely achievable.

physics.optics↗

arXiv2026

Protection Switching in Hybrid Hollow-Core and Single-Mode Fiber Networks: Challenges, Analysis, and Mitigation Strategies

Hollow-core fibers (HCF) are transitioning from laboratory curiosities to production-deployed infrastructure, with cloud providers operating thousands of kilometers of hollow-core links. As operators upgrade their networks, working and protection paths will inevitably traverse different fiber types, creating a class of protection switching challenges absent in homogeneous single-mode fiber networks. This article provides a comprehensive overview of these challenges and presents a comparative analysis of protection switching under two architectures - 1+1 dedicated and shared backup path protection (SBPP) - in hybrid hollow-core and single-mode fiber networks. Using Monte Carlo simulation with random per-link fiber assignment across six reference topologies (1,602 node pairs), we quantify chromatic dispersion (CD) steps, generalized signal-to-noise ratio (GSNR) penalties, and modulation-format degradation for both architectures. At 50% HCF deployment mean CD steps range from 4,000 to 22,000 ps/nm, with GSNR penalties of 1.6-3.1 dB and 38-59% of node pairs requiring modulation downgrade under 1+1 protection. A complementary cross-fiber extreme analysis reveals that the two switching directions are fundamentally asymmetric: HCF-to-SMF switching doubles the CD step and inflicts about a 10 dB GSNR penalty while SMF-to-HCF switching delivers a negative GSNR penalty (the protection path is higher quality than the working path). SBPP shows up to 7% higher CD steps and 4 percentage points more downgrade in sparsely connected topologies due to its greedy shortest-first path selection. Capacity retention improves with HCF penetration for both architectures, reaching 85-99% at full HCF deployment. We present mitigation strategies including DSP pre-loading, spectral pre-equalization, and network planning guidelines, concluding that 1+1 dedicated protection is preferable to SBPP for hybrid deployments.

cs.NI↗

arXiv2026

Hollow-Core Fiber in Direct-Detection Optical Networks: Technology Readiness, Deployment Drivers, and Adoption Outlook

This paper presents a comprehensive analysis of hollow-core fiber (HCF) for intensity-modulation and direct-detection (IMDD) optical networks, covering fiber-level physics, system-level performance, and deployment economics. We quantify the three principal advantages of anti-resonant HCF over standard single-mode fiber (SMF) for IMDD: (i) chromatic dispersion of 2-4 ps/(nm km) versus 17 ps/(nm km), which shifts the first dispersion-induced power-fading null from about 10 GHz to 20-28 GHz at 40 km, extending the dispersion-limited reach by 4-8x; (ii) a nonlinear coefficient approximately 1,000x lower than silica, permitting launch powers of +10 to +20 dBm and yielding 7-17 dB of additional link budget; and (iii) a group index near unity (ng about 1.003), reducing propagation latency by 31%. We further analyze inter-modal interference (IMI) as the dominant impairment for HCF-based IMDD. We show that differential modal attenuation (DMA) exceeding 12 dB/km suppresses IMI-induced crosstalk below the -30 dB multipath interference threshold required for PAM4. The reduced dispersion also lowers the required feed-forward equalizer (FFE) tap count by 3-6x, directly decreasing noise enhancement penalty and DSP complexity. A deployment cost model across five application scenarios - intra-data center, campus DCI, metro DCI, 5G fronthaul, and PON - reveals that fiber cable constitutes only 5-10% of outside-plant deployment cost, and that coherent transceiver avoidance savings of $1000 to $2000 per transceiver can offset the current HCF premium at metro distances. We provide a technology adoption roadmap indicating that HCF is economically justified now for intra-DC and campus DCI, with metro DCI following in 2027-2030 as manufacturing costs continue to decline.

physics.optics↗