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131 changes: 51 additions & 80 deletions arxiv/main.tex
Original file line number Diff line number Diff line change
Expand Up @@ -827,19 +827,22 @@ \subsection{Training with verifier-derived signals}
B(c) &= \frac{\max\{0,T(c)-T(c_{\mathrm{rect}})\}}
{\max\{1-T(c_{\mathrm{rect}}),0.3\}}.
\end{align*}
\begin{subequations}\label{eq:rlreward}
\begin{samepage}
For $x_0=1$, $N(x;x_0)$ is defined as zero. When
$J_{\mathrm{rect}}<0.95$, the training reward is
\begin{align}
R ={}& 0.05 + 0.40N(J;J_{\mathrm{rect}}) \nonumber\\
&+ 0.15N(D;D_{\mathrm{rect}}) + 0.40B(c).
\label{eq:rlreward}
\label{eq:rlreward-general}
\end{align}
\end{samepage}
For rectangle-like targets with $J_{\mathrm{rect}}\geq0.95$, the reward is
\[
\begin{equation}
R = 0.05 + 0.40J + 0.15D + 0.40T(c).
\]
\label{eq:rlreward-rectangle}
\end{equation}
\end{subequations}
The rectangle baseline removes geometric credit for filling the target
bounding box. The boundary term provides a signal for count and boundary
changes that may not yet improve overlap.
Expand Down Expand Up @@ -887,83 +890,51 @@ \subsection{Training with verifier-derived signals}
representation curriculum while leaving substantial room between the trained
policy and the coding agents of Sec.~\ref{sec:results}.

\section{Research contracts}\label{sec:conclusion}

The same separation between open-ended search and deterministic measurement
also structures follow-on work. A research contract freezes five elements
before execution: a question, acceptance tests, required evidence, a verdict
procedure, and a claim boundary. Researchers or agents choose how to pursue
the objective; an independent gate settles it by recomputing the declared
measurements from retained artifacts. Four contracts are currently open:
RC-01, shape-aware visual verification; RC-02, process-faithful 2D-to-3D
retargeting; RC-03, a representation and scale dataset; and RC-04, the
smallest qualifying open model. Complete gates, evidence manifests, failure
taxonomies, claim boundaries, and bounty terms are versioned under
\texttt{research-contracts/}. Through the
\href{https://pixcell.qpaig.com/\#research-contracts}{PixCell project page},
a researcher or agent can inspect the frozen terms, claim a funded contract,
work against the released PixCell environment and versioned fixtures, and
submit the required evidence bundle. The marketplace maintains live claim
state and funding; issuer-side recomputation determines settlement.

PixCell formulates visual photonic component authoring as executable program
synthesis under deterministic verification. Across 26 coding-agent
configurations and eight blind targets, the system produces 208 programs,
of which 193 satisfy the source contract. The strongest configurations
reach mean IoU values of $0.974$ and $0.955$. The iterative API record
explains why verification matters beyond final scoring: only $12.7\%$ of
first seeds are best, and best-of-five revision improves $18.3\%$ over the
first turn. A cheap verifier turns additional inference into a controlled
choice among executable artifacts.

The principal value of the output is its representation. A reconstructed
program records how geometry is assembled and exposes coordinates that can
be changed after visual matching. Both MZI reconstructions use this freedom
to fold the delay path and meet the $8.0$\,nm FSR and footprint gates on
three stack models. Fixed polygons fail every off-diagonal transfer. The
broader fixed-interface experiment is deliberately balanced: reconstructed
programs pass 21 of 30 cases and library PCells pass 22, with 23 paired
agreements. Neither representation class dominates. Retargetability follows
from the reachable geometries exposed by a particular program.

Physical evaluation determines what can be claimed about those geometries.
The analytic evaluator predicts the tested MZI fringe spacing within
$2.9\%$ of broadband FDTD, yet overestimates the SiN directional-coupler
ratio by $5.5\times$. Sidewall tilt then changes the coupler response by
nearly its full range while a mirror-symmetric splitter remains balanced
within $0.0072$. These results define a hierarchy of evidence: calibrated
IoU verifies reconstruction, local solvers support inexpensive
retargeting, and full-wave models test optical behavior and fabrication
variables that the two-dimensional layout does not contain.

The same executable verifier supplies a training reward. Run B adapts
Qwen3.6-35B-A3B from its raw base checkpoint through 150 GRPO steps without
supervised demonstrations or critic feedback. A direct draw on the
training-excluded paper figures reaches mean IoU $0.228$ and mean
best-of-eight IoU $0.467$. In the attempt-measure-revise loop, mean champion
IoU rises from $0.422$ after the initial attempts to $0.491$ after three
revision rounds. This establishes that deterministic geometric rewards can
produce cross-figure transfer in an open-weight model. The record contains
one training lineage and does not estimate variation across independent
training runs.

The current evidence covers eight components, one retained
coding-agent run per matrix cell, simplified stack models, and selected
full-wave fixtures. F8 also lacks a recovered bibliographic source. The next
experiments should add replicated agent runs, broader and fully sourced
component families, typed port and connectivity checks, enforced foundry
rules, anisotropic material models, and untouched training evaluations.
These extensions preserve and strengthen the central mechanism: agents
search over executable component programs, while deterministic tools measure
the resulting artifacts.

PixCell therefore establishes a visual interface to photonic component
creation that remains compatible with programmatic circuit design. The
agent recovers an editable construction from pixels, the conductor verifies
it at absolute physical scale, and the resulting variables connect visual
reconstruction to stack-specific evaluation and learning. This combination
provides a practical foundation for multimodal agents that author, test, and
retarget photonic components through code.
\section{Conclusion and research contracts}\label{sec:conclusion}

PixCell establishes a visual-to-executable interface for photonic component
creation. Multimodal coding agents recover parametric programs from calibrated
silhouettes, deterministic verification makes those programs measurable, and
their live variables connect reconstruction to cross-stack evaluation. The
same executable relationship enables synthetic dataset creation and
verifier-derived training. These results connect representation, verification,
retargeting, simulation, and training through one program interface.

The results leave four research directions that matter directly to what
PixCell can establish. We release them as research contracts. The paper records
their purpose, while the versioned contract files define the current tests,
evidence requirements, and claim boundaries:
\begin{enumerate}
\item \textbf{RC-01, shape-aware visual verification,} extends geometric scoring so
structurally correct reconstructions can be separated from visually similar
shortcuts. This matters because verification guides reconstruction, selection,
and training throughout PixCell.
\item \textbf{RC-02, process-faithful 2D-to-3D retargeting,} carries editable programs
into fuller stack and fabrication models. This connects the parametric freedom
demonstrated in Sec.~\ref{sec:pdk} to physical conclusions beyond
simplified two-dimensional geometry.
\item \textbf{RC-03, representation and scale dataset,} expands the data linking
topology, physical-scale evidence, and executable construction. This supports
controlled study of what a model learns from pixels, calibration, and program
structure.
\item \textbf{RC-04, smallest qualifying open model,} maps how model scale
affects reconstruction across the representation curriculum. This extends the
single open-weight training lineage studied here towards smaller,
reproducible systems.
\end{enumerate}

The current versioned terms, evidence requirements, and executable verdict
logic for these directions are released under
\href{https://github.com/QPG-MIT/PixCell/tree/main/research-contracts}
{\texttt{research-contracts/}}. The
\href{https://pixcell.qpaig.com/\#research-contracts}{PixCell project page}
shows live funding and claim state, links each specification, and provides the
claim controls. A claimant signs in through GitHub and selects an available
contract, or opens a claim-request issue in the repository. Issuer-side
recomputation of the required evidence determines settlement. The contracts
therefore extend PixCell's central separation to follow-on work: researchers
and agents choose how to search, while frozen evidence and independent
recomputation determine what can be claimed.

\paragraph*{Data and code availability.} The PixCell implementation,
benchmark fixtures, 208 reconstruction programs, conductor measurements,
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