InP EML — process and capacity

The electro-absorption modulated laser (EML) is the dominant transmitter source inside fiber-optic transceivers operating at 100 Gbps per lane and above. An EML is a monolithic photonic integrated circuit on indium phosphide (InP) that combines a distributed-feedback (DFB) laser cavity with an integrated electro-absorption modulator (EAM) on the same chip — enabling the laser to be left in a continuous-wave state while the EAM imprints data on the optical output through field-induced absorption. The integration shrinks packaging complexity, reduces parasitics, and improves thermal behavior versus discrete laser-plus-modulator alternatives Lumentum EML blog 2025-2026 ✓.

Lumentum is one of two merchant InP EML suppliers globally — the other being Coherent Corp (post-II-VI/Finisar consolidation). NTT Innovative Devices and Sumitomo also fabricate EMLs, but largely for telecom-internal or partnership use. The Lumentum / Coherent duopoly controls the merchant supply that feeds module-builders such as Innolight, Eoptolink, and Lumentum’s own Cloud Light division. (See 01_company / Cloud Light acquisition and 03_ecosystem / competitors.)

Generations and timing

The progression of EML modulation rates per optical lane follows a roughly two-year doubling cadence — Lumentum’s own framing at OFC 2025 was “optical link speeds in AI back-end networks are doubling about every two years” Lumentum OFC 2025 ✓.

Lane rate	Status (2026-Q1)	Transceiver applications	Source
50 Gbps PAM4 (50G/lane)	Mature; fully shipped — legacy	200G FR4 (4×50G), early 400G builds	Industry-baseline ✓
100 Gbps PAM4 (100G/lane)	Mass production	400G FR4/DR4, 800G DR8/2×FR4	Lumentum EML blog ✓
200 Gbps PAM4 (200G/lane)	Volume ramp — shipping at scale to multiple customers since FY2025-Q2	800G 2×DR4, 1.6T DR8	Lumentum OFC 2025; Lumentum FY25 10-K ✓
400 Gbps PAM4 (400G/lane)	Research demonstrations — 224 GBaud PAM4 EML, 448 Gbps single-lane	3.2T transceivers, future CPO modules	Lumentum + Keysight + NTT Innovative Devices OFC 2025 ✓
450 Gbps PAM4 DFB-MZI	Live demo at OFC 2025 — distributed-feedback laser with integrated Mach-Zehnder modulator	Future 3.6T+ research path	Lumentum OFC 2025 ✓

200G/lane — load-bearing AI-photonics node

The 200G/lane EML is what feeds 800G 2×DR4 and 1.6T DR8 transceiver builds — the optical interconnect Lumentum’s own Cloud Light division uses, and the same EML chip Coherent and Innolight rely on for their hyperscaler module shipments.

Lumentum’s public technical framing of its 200G/lane EML node:

The 200G/lane device is a differential-drive electro-absorption modulated laser (DD EML) that “operate[s] at a lower drive voltage, reducing power dissipation while offering excellent signal integrity and cross-talk immunity” Lumentum OFC 2025 release ✓.
Lumentum “started to deliver 200G lane-speed EMLs to multiple customers” during fiscal Q2 2025 (the October-December 2024 quarter) Lumentum OFC 2025 ✓.
Capacity guidance: ~40% growth in 200G EML capacity from June 2024 to June 2025, with a further ~40% by end of calendar 2025 Lumentum FY25 disclosures ✓.
Lumentum’s own statement: “Lumentum is currently shipping 200 Gbps per lane EMLs at scale, the foundational component enabling the latest 800G & 1.6T transceivers” Lumentum EML blog ✓.
A complementary 200G receiver-side device, the Lens Integrated Photodiode (LIPD), was unveiled at OFC 2025 — “high responsivity and wide bandwidth … integrates seamlessly with flip-chip bonding techniques” Lumentum OFC 2025 ✓.

400G/lane — research stage

Lumentum demonstrated single-lane 224 GBaud PAM4 transmission at 448 Gbps at OFC 2025, jointly with Keysight Technologies and NTT Innovative Devices. The 224 GBaud symbol rate is the foundation for the next-generation 400G/lane PAM4 standard that will feed 3.2T pluggables and CPO modules. A separate 450 Gbps PAM4 demonstration used a distributed-feedback laser with an integrated Mach-Zehnder interferometer (DFB-MZI) — “providing superior chirp control, power efficiency and reduced signal distortion” Lumentum OFC 2025 ✓.

Both 400G/lane approaches remain research-stage as of 2026-Q1; mass production is not expected before the 2027-2028 timeframe.

⚠ Inferred / estimate: 400G/lane volume timing is not formally guided by Lumentum. Industry consensus places 400G/lane in early-volume around 2027-2028, aligned with the next Nvidia GPU generation cadence. Confirm against the next Lumentum OFC release.

Fab footprint

Lumentum’s InP wafer-fab footprint is multi-site, with new US capacity coming online to absorb the NVIDIA-funded expansion. The seed brief listed the UK fab as “Towcester” — the actual fab is at Caswell, Northamptonshire (Towcester is the postal town).

Site	Wafer size	Function	Source
San Jose, CA (Rose Orchard Way)	InP + GaAs	HQ + InP fab; 1310 nm CW & UHP laser fab; co-design with Cloud Light transceiver assembly	Lumentum EML blog; Semiconductor Today 2025-08-08 ✓
Caswell, Northamptonshire UK (postal: Towcester)	3-inch InP	Heritage Marconi → Bookham → Oclaro fab; InP modulator chips; cleanroom expanded ~25% by spring 2024; Lumentum bought the land outright in September 2023	PIC Magazine 2023 ✓
Sagamihara, Japan	InP	Wafer-fab capacity acquired through prior NeoPhotonics integration	Lumentum EML blog ✓
Takao, Japan	InP	Companion fab for telecom-grade InP devices	Lumentum EML blog ✓
Greensboro, NC (announced March 26, 2026)	6-inch InP	New US-domestic fab for CW and ultra-high-power (UHP) 1310 nm DFB lasers; acquired from Qorvo; >400 jobs preserved/created; production ramp mid-2028; NVDA is anchor customer	Lumentum 2026-03-26 release; Semiconductor Today 2026-03-26 ✓
Thailand (Chonburi)	n/a	Backend transceiver assembly; flagship Cloud Light heritage facility	Lumentum EML blog ✓

The Caswell facility focus on indium-phosphide modulator chips is structurally important: the Mach-Zehnder modulator demonstrations at OFC 2025 leverage UK fab capability that traces back to the Marconi III-V semiconductor lineage. The gallium arsenide field-effect transistor and monolithic microwave integrated circuit (MMIC) were originally invented at Caswell — that legacy expertise is part of what made the Oclaro acquisition strategically rational PIC Magazine 2023 ✓.

NVIDIA $2B strategic investment — capacity-expansion mechanics

On March 2, 2026, Lumentum announced it had issued and sold 2,876,415 shares of new Series A Convertible Preferred Stock to NVIDIA at $695.31 per share, raising $2,000,000,000 in cash through a private placement under Section 4(a)(2) Lumentum 8-K via StockTitan ✓.

Series A terms (per the 8-K disclosure):

One-for-one conversion into common stock; conversion requires expiration of Hart-Scott-Rodino waiting period or occurs automatically before a qualified sale.
Dividends pari-passu with common stock.
Voting rights with common stock on as-converted basis except for director elections (preferred has no director-election vote).
Majority consent required for adverse changes to preferred-stock rights.
No preemptive rights; no redemption rights.

The cash proceeds, plus a multibillion-dollar purchase commitment and a multi-year supply agreement granting NVIDIA future capacity access rights for advanced laser components, dedicate the resulting capacity expansion primarily to the 200G/lane EML node and the UHP 1310 nm DFB lasers used as external laser sources (ELS) for NVIDIA’s CPO switches NVIDIA press release 2026-03-02 ✓.

The structural significance: the $2B investment is what funded the Greensboro, NC fab acquisition (announced 24 days later on March 26, 2026) and the parallel San Jose UHP-laser capacity expansion announced August 2025 Lumentum 2026-03-26 release ✓.

Per Lumentum CEO Michael Hurlston: “Our customers are building the infrastructure that will define the next era of computing. Adding this new InP manufacturing facility significantly expands our capacity.” Lumentum 2026-03-26 release ✓.

Per NVIDIA EVP Operations Debora Shoquist: “Lumentum’s investment in expanded U.S. manufacturing capacity strengthens supply continuity and positions us to meet growing infrastructure demands.” Lumentum 2026-03-26 release ✓.

The Greensboro fab is a 240,000-square-foot facility acquired from Qorvo Inc. (an RF and power-device manufacturer based in Greensboro). The site is currently operational and being retrofitted for InP wafer manufacturing on 6-inch InP substrates, with a workforce transfer from Qorvo. Lumentum plans to invest “hundreds of millions of dollars over the next several years” — production ramp expected mid-2028 Semiconductor Today 2026-03-26 ✓.

The 6-inch wafer scale at Greensboro is a generational step up from the 3-inch InP wafers historically used in legacy InP fabs (including parts of the Caswell footprint). 6-inch InP enables higher die-per-wafer counts and lower per-chip cost — fundamental to making 200G/lane EML capacity meet hyperscaler-scale volumes.

Process — what Lumentum does in-house

Lumentum is vertically integrated end-to-end in the InP EML supply chain:

InP wafer epitaxy (in-house) — including upstream IQE epitaxy supply via a multi-year extended agreement IQE press release 2025 ✓
EML chip fabrication on InP substrates (San Jose, Caswell, Sagamihara, Takao; future Greensboro)
Chip-on-carrier assembly
Optical sub-assembly (OSA) integration
Pluggable transceiver module assembly (Cloud Light heritage in Thailand)

This contrasts with module-only competitors (Innolight, Eoptolink) that depend on Lumentum or Coherent for the merchant EML chip supply.

Cross-thesis links

LWLG (Lightwave Logic) — electro-optic polymer modulators are a structurally different modulation technology; LWLG modulators integrate onto silicon photonics platforms, while Lumentum’s EML is monolithic InP. The two could in principle complement (polymer modulator on SiPh paired with InP source laser) or compete on the modulation path. As of 2026-Q1, Lumentum has not publicly engaged with polymer-modulator integration; the Mach-Zehnder demonstrations Lumentum showed at OFC 2025 used InP-MZI, not polymer.
MRVL (Marvell) — Marvell’s DSPs feed pluggable transceiver modules including Cloud Light builds. Lumentum’s 200G/lane EML and Marvell’s PAM4 DSP are a paired stack inside many 800G/1.6T pluggables.
TSEM PH18 / GFS Fotonix — silicon photonics foundries that fabricate SiPh modulators do not replace InP source lasers; SiPh and InP-EML are complementary. Lumentum’s 800G 2×DR4 OSFP product (see datacom transceivers) actually uses SiPh modulators with separately-coupled InP CW laser sources, illustrating the complementarity.