Laser Design Engineer (Epi/Device)

About the role

CScale is building the interconnect for gigawatt-scale AI. As AI scale-up moves toward deployments spanning thousands of accelerators and dozens of racks, the network needs to deliver high bandwidth, predictable low latency, and continuous communication. CScale is building integrated optical interconnect designed for this new scale, enabling accelerators to work together like a single, much larger computer. But at this scale, performance is only part of the challenge. Optical failures are inevitable, and the system needs to keep running. CScale is designing the interconnect for continuity. Lasers will fail. Compute shouldn’t. The ambition is simple: Build AI interconnect you can take for granted. CScale came out of stealth in September 2026 with $145 million in Series C funding, bringing total funding to $188 million. At the core of our technology is a high-density III-V laser array — a critical integrated component in our broader optical system — designed for high-volume deployment in AI infrastructure. We are seeking a Senior Laser Design Engineer to own device design and simulation for this laser array, working in a small, cross-functional team where individual contributions are highly visible and directly shape product outcomes. This role spans the full vertical of laser device design — from active region and heterostructure engineering through waveguide, cavity, and grating simulation for single-frequency laser architectures, as well as electroabsorption modulator design for integrated photonic products. The designs produced in this role must be manufacturable, process-tolerant, and optimized for yield and consistency across production volumes — not just peak performance on a best-case die. In a fabless environment, simulation is the primary design tool and the foundry interface is the execution path; this engineer must be fluent in both. The right candidate brings deep device physics knowledge across multiple laser and modulator architectures and the practical judgment to make design decisions that survive contact with a real foundry process. Responsibilities - Design and optimize III-V heterostructures and multi-quantum well (MQW) active regions for laser, SOA, and electroabsorption modulator applications, with explicit consideration of growth tolerance, process variation, and production yield; develop and maintain active region simulation models using commercial tools (e.g., band structure solvers, 1-D optical confinement solvers, traveling wave laser models). - Simulate and optimize laser waveguide geometry, optical confinement factor, far-field profiles, and cavity design parameters for manufacturability; perform grating simulation for DFB and DBR structures including coupling coefficient, stopband, and SMSR — with design margins appropriate for high-volume foundry execution, not worst-case lab conditions. - Balance output power, threshold current, slope efficiency, SMSR, and linewidth across the full operating envelope — including temperature range and target wavelength window — for production laser devices (DFB, DBR, and related single-frequency architectures); design for specification compliance across all operating conditions, not only at nominal temperature and center wavelength. - Design and simulate electroabsorption modulator (EAM) structures — including quantum-confined Stark effect active regions, waveguide integration, and modulation bandwidth — for integrated and stand-alone modulator products; account for the interplay between absorber bias, extinction ratio, insertion loss, and chirp in the context of real driver circuit constraints. - Serve as the primary technical interface to epitaxy foundry partners: specify growth recipes, review and approve process travelers, evaluate growth run results, and drive resolution of material quality issues. - Define and execute epitaxial qualification protocols — photoluminescence (PL), X-ray diffraction (XRD), and surface scan (surfscan) metrology — and establish acceptance criteria for material qualification consistent with production requirements. - Collaborate with device layout, process engineering, FA, and systems teams to translate simulation results and device physics requirements into manufacturable designs; communicate findings through technical reports and design reviews. Required Qualifications - Deep understanding of III-V semiconductor laser device physics — heterostructure theory, MQW active region design, optical waveguiding, and cavity design — with hands-on experience applying this knowledge to devices that have been fabricated and characterized, not only simulated. - Demonstrated experience simulating and designing laser photonic structures for real foundry implementation: waveguide modes, optical confinement, and grating design for DFB or DBR architectures — including how design margins are set to accommodate process variation and maintain yield targets. - Working knowledge of DFB and DBR laser design principles and the practical trade-offs between output power, threshold, slope efficiency, SMSR, and linewidth as they must be balanced across thermal operating conditions in production devices. - Experience with electroabsorption modulator device design — QCSE active region engineering, EAM integration, and modulation bandwidth optimization — for integrated and stand-alone modulator products. - Proficiency with commercial device simulation software used to support design decisions with production intent — including one or more of: traveling wave laser model tools (e.g., VPI Photonics, Lumerical INTERCONNECT, Photon Design HAROLD), waveguide and mode solvers (e.g., Ansys Lumerical MODE, Photon Design FIMMWAVE), grating/EME solvers, and band structure or gain simulation tools (e.g., Crosslight, SiLENSe, or equivalent); scripting in MATLAB or Python for simulation automation and data analysis. - Experience working with external epitaxy foundries: specifying growth recipes, reviewing characterization results, managing qualification cycles, and interpreting run-to-run variation in the context of product specifications. - Working knowledge of epi qualification metrology — photoluminescence spectroscopy, high resolution XRD, and surface scan inspection — including interpretation of results and definition of acceptance criteria tied to device performance. Preferred Qualifications - Practical experience with laser device characterization: LIV measurements, optical spectral analysis, linewidth, relative intensity noise (RIN), optical backscatter reflectometry (OBR), and gain measurement methods including Hakki-Paoli. - Hands-on characterization experience with integrated laser-modulator devices or stand-alone EAMs (extinction ratio, insertion loss, chirp, frequency response). - Experience defining technical specifications for III-V optical products that account for production distributions, driver circuit interoperability, and packaging or integration constraints. - Familiarity with optical communications standards and key link budget parameters (AOP, OMA, TDECQ, BER, coupling loss). - Hands-on experience with GDS mask design and layout generation for laser and modulator devices. - Exposure to failure analysis or reliability qualification methods as applied to III-V optical devices. Education Ph.D. in Electrical Engineering, Applied Physics, Materials Science, or a closely related discipline with emphasis in semiconductor photonics, optoelectronics, or III-V laser devices. Candidates with an M.S. or M.Eng. and a minimum of 6 years of directly relevant industry experience — including demonstrated device design ownership on products that reached production — will be considered.