CW DFB laser

A CW DFB laser is a continuous-wave distributed-feedback laser: a semiconductor chip that emits a steady, single-wavelength beam of light. In AI data centers, it supplies the "carrier" light for silicon-photonics optical transceivers and co-packaged optics, where external modulators imprint data onto that light to move terabits per second between chips and servers.

What a CW DFB laser is (in plain terms)

Break the name into three parts. **CW** means *continuous wave*: the laser is simply switched on and shines a constant, unblinking beam, rather than pulsing data itself. **DFB** means *distributed feedback*: the chip has a finely etched grating running along its length that reflects only one precise wavelength, so the output is a very pure, single-color (single-frequency) beam. **Laser** is the light-emitting semiconductor itself, almost always made from indium phosphide (InP), a material that emits efficiently at the infrared wavelengths fiber optics use (around 1310 nm). So a CW DFB laser is a tiny, clean, steady light source. On its own it carries no information. Its job is to provide reliable raw light that *something else* will turn into a data signal.

How it works, and how data gets onto the light

There are two ways to send data on light. An **EML** (electro-absorption modulated laser) integrates the laser and the modulator on one chip, so the laser itself flickers the data on and off. A **CW DFB** laser takes the opposite approach: it stays on continuously, and a *separate* external modulator (typically built into a silicon-photonics chip) chops and shapes that steady light into bits. Separating the light source from the modulation is the key idea. Modern modulators in silicon photonics can switch far faster and more cleanly than a laser can blink, especially at 200 Gbps per lane and beyond using PAM4 signaling. The DFB grating matters here because precise, narrow-linewidth light is what lets the modulator and receiver keep bits distinct at extreme speeds and over distance.

Why it matters for AI and data centers

Training and serving large AI models requires moving enormous amounts of data between thousands of GPUs. Electrical copper links run out of reach and burn too much power at these speeds, so interconnects are going optical, right up to the edge of the switch and accelerator package. This is where CW DFB lasers become foundational. Silicon-photonics transceivers and **co-packaged optics (CPO)** don't make their own light efficiently, so they need an external CW source feeding them. Because optical links are now measured in the millions, power efficiency per laser directly affects a data center's total electricity bill. Suppliers compete on exactly that: Coherent, for example, markets 1310 nm CW DFB lasers it says are roughly 15% more power-efficient than the prior industry standard.

Where it sits in the photonics supply chain

The CW DFB laser is an upstream *component*, not a finished product. The rough stack: (1) a laser maker grows and dices InP chips into CW DFB lasers or laser arrays; (2) those are packaged into an optical engine or transceiver, often paired with a silicon-photonics modulator chip; (3) the transceiver plugs into a switch or sits co-packaged next to it; (4) hyperscalers like Nvidia, Google, and Meta buy these by the millions. A growing variant is the **external laser source (ELS)** or external light source: a centralized, high-power CW laser module that lives outside the optical engine and feeds light to it through fiber. For co-packaged optics, vendors offer pluggable external laser modules (sometimes called ELSFP) so a hot, replaceable laser sits apart from the delicate switch silicon. Lumentum, for instance, sells ultra-high-power CW and ELS modules aimed squarely at CPO.

Who the key players are

Capacity is concentrated. According to TrendForce, in CW-DFB laser diodes Broadcom and Sumitomo Electric lead, followed by Coherent and LandMark/LuxNet, together about 74% of capacity. **Lumentum**, **Coherent**, and **MACOM** are prominent merchant suppliers of CW lasers and arrays for 800G and 1.6T optics; at OFC 2025 MACOM (Nasdaq: MTSI) showed a 16-channel, 75 mW CW laser array. Smaller specialists also play here. **Sivers Semiconductors** (Nasdaq: SIVE / OTC: SIVEF) supplies high-power InP CW DFB laser chips and arrays through its Sivers Photonics arm, and has announced collaborations with Jabil on a 1.6T module and with O-Net and Enablence on external light sources for AI data centers. Others active in the space include Casela Technologies and QD Laser.

What's changing now

Three shifts stand out. First, **volume is exploding**: TrendForce projects combined monthly capacity for EML and CW-DFB lasers reaching about 50.7 million units in 2026, as hyperscalers lock up supply. Second, the industry is racing past 1.6 Tbps per module, pushing to 200G+ per lane, which favors the CW-DFB-plus-external-modulator approach used in silicon photonics and CPO. Third, **architecture is moving the laser out of the module**: external and centralized laser sources let operators replace a failed laser without touching the switch, and concentrate cooling where it's easiest. Together these trends turn the humble, unglamorous CW DFB laser into one of the most strategically contested components in AI infrastructure.

Frequently asked

What is the difference between a CW DFB laser and an EML?

A CW DFB laser emits a constant, single-wavelength beam and relies on a separate external modulator to add data. An EML integrates the laser and an electro-absorption modulator on one chip, so the laser itself encodes the data. CW DFB lasers dominate silicon photonics and co-packaged optics; EMLs are common in directly modulated, medium-to-long-reach transceivers above 800G.

Why do silicon photonics chips need a separate CW laser?

Silicon is poor at efficiently generating light, so silicon-photonics modulators need light supplied from an external source. A CW DFB laser, usually made of indium phosphide, provides that steady carrier light, which the silicon chip then modulates with data.

What does CW stand for in CW laser?

CW stands for continuous wave, meaning the laser stays on and emits a constant, uninterrupted beam, as opposed to a pulsed or directly modulated laser that switches on and off to send data.

Which companies make CW DFB lasers?

Major suppliers include Broadcom, Sumitomo Electric, Lumentum, Coherent, and MACOM, with smaller specialists such as Sivers Semiconductors, Casela Technologies, and QD Laser. By capacity, a handful of players control the majority of the market.

Why are CW DFB lasers important for AI data centers?

AI clusters move massive data between GPUs, which is shifting interconnects from copper to optics. CW DFB lasers are the light source feeding the silicon-photonics transceivers and co-packaged optics that carry this traffic, and their power efficiency directly affects data center energy costs at the scale of millions of links.

Related companies