\input{preamble.tex}
\graphicspath{{images}, {images/1550}}

\title{1550 Laser Diode Driver Kirdy}
\author{M-Labs Limited}
\date{April 2025}
\revision{Revision 1}
\companylogo{\includegraphics[height=0.73in]{artiq_sinara.pdf}}

\begin{document}
\maketitle

\section{Features}

    \begin{itemize}
        \item{307.2 mA max output current, 20-bit resolution}
        \item{Low noise current source, 300 pA/rtHz @ 1 kHz}
        \item{Modulation input with DC-18 MHz bandwidth}
        \item{Monitor photodiode and LD protection}
        \item{Temperature controller with sub-mK stability}
        \item{Full digital control over Ethernet}
        \item{Bias-tee for RF modulation input}
    \end{itemize}

\section{Applications}

    \begin{itemize}
        \item{Spectroscopy}
        \item{Laser cooling}
        \item{Atomic clocks}
        \item{Suitable for use with adapter and preinstalled laser assembly or with external laser heads}
    \end{itemize}

\section{General Description}

    The 1550 Laser Diode Driver Kirdy is an 8hp EEM module, part of the Sinara open hardware family. It serves as a precision laser diode driver, featuring a low-noise current source, low- and high-frequency modulation inputs, and full digital control over Ethernet. Soft start, laser power monitoring with a user-defined trip point, overtemperature protection, and a protection relay minimize the risk of damage to the laser diode.

    1550 Kirdy supports both low-frequency modulation, suitable for laser locks and linewidth reduction, as well as RF modulation injected directly into the diode, typically to add sidebands to the optical output and implement stabilization schemes such as Pound-Drever-Hall and modulation transfer spectroscopy.

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%    \caption{Simplified Block Diagram}
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\begin{figure}[hbt!]
    \centering
    \includegraphics[height=2.5in]{photo1550.jpg}
    \caption{Kirdy card photo}
    \includegraphics[height=3in, angle=90]{fp1550.pdf}
    \caption{Kirdy front panel}
\end{figure}

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\onecolumn

\sourcesection{1550 Laser Diode Driver Kirdy}{https://git.m-labs.hk/sinara-hw/kirdy} The associated adapter can be found at the repository \url{https://git.m-labs.hk/sinara-hw/kirdyAdapter/src/branch/master}.

\section{Electrical Specifications}

    These specifications are based upon various information from the Sinara hardware repository\footnote{\label{repo}\url{https://git.m-labs.hk/sinara-hw/kirdy/}}.

    \begin{table}[hbt!]
        \centering
        \begin{threeparttable}
        \caption{Recommended Operating Conditions}
        \begin{tabularx}{0.8\textwidth}{l | c c c | c | X}
            \thickhline
            \textbf{Parameter} & \textbf{Min.} & \textbf{Typ.} & \textbf{Max.} &
            \textbf{Unit} & \textbf{Conditions} \\
            \hline
            Input power & & & & & \\
            \hspace{3mm} Voltage & & 12 & & V \\
            \hspace{3mm} Current & & & 2.0 & A & \\
            \hline
            LF modulation input\textdagger & & & & & \\
            \hspace{3mm} Voltage & -1 & & 1 & V \\
            \hspace{3mm} Bandwidth (-3 dB) & & 18 & & MHz & \\
            \hspace{3mm} Impedance & & 50 / 43.3k & & $\Omega$ & Termination switch on/off \\
            \thickhline
        \end{tabularx}
        \end{threeparttable}
    \end{table}

    1550 Kirdy supports Power-over-Ethernet, PoE+ (802.3at) and PoE (802.3af) standards. Alternatively, power can be provided via input in front panel. When using PoE, TEC output current should be limited to ±2A.

    \begin{table}[hbt!]
        \centering
        \begin{threeparttable}
        \caption{Electrical Specifications}
        \begin{tabularx}{\textwidth}{l | c c c | c | X}
            \thickhline
            \textbf{Parameter} & \textbf{Min.} & \textbf{Typ.} & \textbf{Max.} &
            \textbf{Unit} & \textbf{Conditions} \\
            \hline
            Photodiode\textdagger & & & & & \\
            \hspace{3mm} Photocurrent range & 0 & & 3.0 & mA & \\
            \hspace{3mm} Photocurrent resolution & & 0.8 & & μA & \\
            \hspace{3mm} Bandwidth (-3 dB) & & 500 & & Hz & \\
            \hline
            Laser diode current driver & & & & & \\
            \hspace{3mm} Resolution & & 0.292 & & μA & \\
            \hspace{3mm} Control range & & & 307.2 & mA & \\
            \hspace{3mm} Current limit & & 319 & & mA & \\
            \hspace{3mm} Compliance & 4.928 & & & V & \\
            \hspace{3mm} Current noise @ 1 kHz & & & 300 & pA/rtHz & 300 mA DC bias, 10 $\Omega$ load \\
            \hspace{3mm} RMS noise @ 10 Hz-1 MHz & & & 300 & nA & 300 mA DC bias, 10 $\Omega$ load \\
            \hspace{3mm} Temp. coefficient & -1 & & +1 & ppm/°C & 50 mA DC bias, tested 43-56 °C \\
            \thickhline
        \end{tabularx}
        \end{threeparttable}
    \end{table}

    \textdagger Circuit may be damaged if photodiode input current exceeds 3.0 mA. It is possible to modify the circuit and reprogram the photodiode current monitor range in the Kirdy driver.

\newpage

    \begin{table}[hbt!]
        \centering
        \begin{threeparttable}
        \caption{Electrical Specifications, cont.}
        \begin{tabularx}{\textwidth}{l | c c c | c | X}
            \thickhline
            \textbf{Parameter} & \textbf{Min.} & \textbf{Typ.} & \textbf{Max.} &
            \textbf{Unit} & \textbf{Conditions} \\
            \thickhline
            PID temperature controller & & & & & \\
            \hspace{3mm} Stability & & 1 & & mK & with Kirdy adapter, copper plate; \mbox{subject} to operating conditions \\
            \hline
            TEC output & & & & & \\
            \hspace{3mm} Resolution & & 22.9 & & μA & \\
            \hspace{3mm} Control range & -3.0 & & 3.0 & A & 12 V power, active cooling \\
                & -2.0 & & 2.0 & A & with PoE (802.3af) \\
            \hspace{3mm} Compliance & & 4.3 & & V & \\
            \hspace{3mm} Voltage reading resolution & & 3.22 & & mV & \\
            \hspace{3mm} Current reading resolution & & 2.9 & & mA & \\
            \hline
            TEC limits & & & & \\
            \hspace{3mm} Voltage limit range & 0 & & 4.3 & V & \\
            \hspace{3mm} Voltage limit resolution & & 3.14 & & mV & \\
            \hspace{3mm} Current limit range & -3.0 & & 3.0 & A & \\
            \hspace{3mm} Current limit resolution & & 1.57 & & mA & \\
            \hline
            NTC thermistor sensor & & & & \\
            \hspace{3mm} Resolution & & 0.01 & & mK & 10 k$\Omega$, B-constant 3950K, $T_{0}$ 25°C \\
            \hspace{3mm} Sampling rate & & 16.67 & $>$1000 & Hz & Subject to operating conditions \\
            \thickhline
        \end{tabularx}
        \end{threeparttable}
    \end{table}

\section{Modulation inputs}

    1550 Kirdy supports two additional modulation inputs via SMA in the front panel, respectively \texttt{HF MOD} for high-frequency and \texttt{LF MOD} for low-frequency. LF modulation input can accept DC input to impose a DC offset on the output current. HF modulation input is AC-coupled and acts as a bias-tee.

    The relationship of modulation input to output current is governed by the following equation:

    \[I_{L} = max(I_{D} + U_{in} \cdot G_{mod}, 0)\]

    where $I_{L}$ is the laser diode current, $I_{D}$ is the laser diode driver output current, $U_{in}$ is the input voltage, and $G_{mod}$ is the modulation gain. Care should be taken that $I_{L}$ always remains under the current limit. Otherwise, overcurrent protection may be triggered.

\newpage

    Modulation gain is adjustable by DIP switch in top right of board. \textit{Exactly one} DIP switch should be enabled at all times. Enabling zero DIP switches may cause serious damage to the laser diode. Other configurations (multiple switches enabled) are invalid, but will not cause damage.

    \begin{multicols}{2}

        \centering
        \vspace*{10pt}
        \begin{tabular}{|l|c|}
            \hline
            \textbf{Switch} & \textbf{Setting} \\
            \thickhline
            1 & 25 mA/V \\
            2 & 2.5 mA/V \\
            3 & 0.25 mA/V \\
            \thickhline
        \end{tabular}
        \captionof{table}{DIP switch settings}

    \columnbreak

        \centering
        \includegraphics[height=1.5in]{kirdy_mod_switch.jpg}
        \captionof{figure}{Position of DIP switch}

    \end{multicols}

    \begin{multicols}{2}

\section{Configuring termination}

    LF modulation input termination must be configured by setting a physical switch on the board. The termination DIP switch is found at the upper left part of the board, behind the front panel. Turning this switch on adds a 50 $\Omega$ termination to the LF modulation input. Without the switch, the input impedance is approximately 43.4k $\Omega$.

    \vspace*{20pt}

    \columnbreak

        \centering
        \includegraphics[height=1.5in]{kirdy_imp_switch.jpg}
        \captionof{figure}{Position of DIP switch}

    \end{multicols}


\section{Adapter and Laser Options}

    An optional adapter allows compact lasers in butterfly packages to be mounted directly onto 1550 Kirdy, with a fibre-optic output in the front panel. Multiple single-frequency narrow-linewidth lasers are currently available as preinstalled options for order.

    Alternatively, Kirdy accepts laser signals broken out to the front panel and is suitable for use in driving external laser heads, including commercial or custom ECDLs (with additional piezo driver not included with Kirdy) or injection-locked Fabry-Perot diodes.

\section{Firmware and driver}

    1550 Kirdy features front panel Ethernet and USB-C. Either DFU or OpenOCD can be used to flash firmware; OpenOCD however requires a JTAG adapter.

    Using M-Labs firmware, communication with a host system is performed over Ethernet/TCP in the form of predefined JSON objects. A Python driver implementing these can be found in the Kirdy firmware repo, hosted at \url{https://git.m-labs.hk/M-Labs/kirdy/}, under \texttt{pykirdy}. See inline documentation for descriptions of particular functions and implemented capabilities.

    This driver may be used directly or through the Kirdy GUI, hosted in the same repo. To start the GUI, run the file \texttt{pykirdy/pykirdy/kirdy\_qt.py}, or install it using \texttt{pykirdy/pyproject.toml}. Users familiar with the Nix package manager through ARTIQ or for other reasons may note that the root of the repository includes a \texttt{flake.nix} with an appropriate development shell (e.g. \texttt{nix develop}) including all dependencies.

    Examples in the \texttt{pykirdy} folder further demonstrate the use of the Kirdy driver, as well as the PID autotune temperature regulation feature.

\newpage

    \begin{figure}[hbt!]
        \centering
        \includegraphics[width=\textwidth]{kirdy_gui.jpg}
        \caption{Kirdy driver GUI}
    \end{figure}

    To first connect to Kirdy, use the "Connect" button in the lower right corner and the IP address and port number assigned to Kirdy. By default, these are \texttt{192.168.1.128} and \texttt{1550} respectively. They can also be changed using commands supplied by the Python driver.


\ordersection{1550 Laser Diode Driver Kirdy}

    Kirdy can ship with a single-frequency narrow-linewidth laser pre-mounted and configured. Current wavelength options include 1270-1610 nm and 633-1064 nm. See the M-Labs hardware selection tool or contact M-Labs for prices and details.

\finalfootnote

\end{document}
