diff --git a/src/hardware_implementations/lcc1620_attenuator/lcc1620_device_notes.md b/src/hardware_implementations/lcc1620_attenuator/lcc1620_device_notes.md index ca3cf82..065dfec 100644 --- a/src/hardware_implementations/lcc1620_attenuator/lcc1620_device_notes.md +++ b/src/hardware_implementations/lcc1620_attenuator/lcc1620_device_notes.md @@ -1,211 +1,28 @@ -# Thorlabs LCC1620(/M) Liquid Crystal Shutter — Manual Reference +# Thorlabs LCC1620(/M) liquid crystal attenuator — driver notes -Complete technical content of the official Thorlabs user guide -(**CTN002190-D02, Rev D, January 8, 2020**), restated chapter by chapter for -this repo, with a rig/driver appendix at the end. Original PDF (graphs and -mechanical drawings in full fidelity): - +Official user guide (specifications, figures, timing tables, mechanical +drawing): Thorlabs CTN002190-D02, +. +Refer to it for anything not covered here; the earlier restatement of the +manual was removed from this repo. ---- +Facts the driver depends on (from the manual): -## Ch. 1 — Warning symbols +- The EXT. INPUT (SMC) takes 0–5 V. In ATTENUATOR mode it is summed with the + front potentiometer, so the pot must be fully clockwise for the external + voltage to span the full range. +- 0 V is maximum transmission; transmission falls monotonically with voltage + and is saturated dark by about 3 V, so the useful calibration range is + 0–2.5 V. Transmission is wavelength dependent. +- Switching is step-and-settle: opening takes about 5 ms, closing under + 1 ms, and contrast degrades when modulated above a few tens of Hz. -Standard IEC symbol legend used on the device and in the manual: DC, AC, -DC+AC, earth ground, protective conductor, frame/chassis terminal, -equipotentiality, supply on/off, bi-stable push control in/out positions, and -caution triangles for electric shock, hot surface, general danger, laser -radiation, and spinning blades. - -## Ch. 2 — Safety - -- **Do not open the housing.** No user-serviceable parts; service only by - trained personnel. -- Safety statements and technical data apply only when the unit is operated - correctly. -- FCC Part 15 compliance: may not cause harmful interference and must accept - any interference received. -- **Laser radiation warning — avoid exposure to the beam.** - -## Ch. 3 — Product overview - -The LCC1620 is a precision, high-speed shutter intended as a laser switch. It -consists of three parts in one housing: a **liquid crystal (LC) cell**, an -**electronic control unit**, and the mechanical housing. - -The LC cell sits between two protective glass plates and **two polarizers -whose transmission axes are crossed**. A line on the front of the housing -marks the shutter's transmission axis; linearly polarized input light must be -aligned to this mark. When powered, the drive voltage controls the LC cell: -at full drive the cell rotates the input polarization by **90°**, aligning it -with the output polarizer so the light passes with little attenuation. At -intermediate drive the rotation is partial, so the device also works as a -**variable attenuator**, not just an on/off shutter. The drive level is set -by the top potentiometer (shutter mode: on/off; attenuator mode: output power -level). - -## Ch. 4 — Setup - -**4.1 Mounting and alignment.** Input must be linearly polarized and aligned -to the front-face line; a polarizer or wave plate upstream can set this. Two -8-32 (M4 on the /M version) post-mounting holes, typical thread depth 4.5 mm, -are offset by 90° so the housing can be posted with either a vertical or -horizontal polarization axis. Four 4-40 holes on the front make it compatible -with Thorlabs 30 mm cage systems, in either orientation. - -**4.2 Power supply.** Operates from **12 VDC**; the supply is included. - -**4.3 Powering on.** The unit powers on as soon as the supply is connected — -**there is no power switch**. - -**4.4 Beam centering.** For best performance, center the beam in the input -aperture (face is marked "MAX BEAM 20mm"). - -## Ch. 5 — Operation - -- Ensure the beam is linearly polarized, aligned to the front marking, at - normal incidence, and centered through the LC cell. -- Connect the power supply. -- A top slide switch selects one of two modes: - - **SHUTTER mode** — the potentiometer simply blocks or transmits the beam. - Fully counterclockwise = shutter off (**red LED**); turning the knob - eventually switches it on (**green LED**). - - **ATTENUATOR mode** — the potentiometer is a variable attenuator: - clockwise = more transmitted power. The **green LED is always lit** in - this mode. -- **External control** ("EXT. INPUT" SMC connector, 0–5 V DC signal): - - In SHUTTER mode the potentiometer must be **fully clockwise** for the - external signal to control the shutter. - - In ATTENUATOR mode the external input **adds an offset to the - potentiometer setting**: pot fully counterclockwise → no effect; the - effect grows as the pot is turned clockwise and is **full only with the - pot fully clockwise**. - - Manual's explicit note: in ATTENUATOR mode with the pot not fully - clockwise, the external voltage **cannot reach full transmission** — it - only spans from off up to the attenuation level the pot allows. - -## Ch. 6 — Specifications and graphs - -| Item | LCC1620(/M) | -|---|---| -| Operating wavelength range | 420 – 700 nm | -| Transmission (avg) | > 60 % | -| Contrast ratio (CR; avg)¹ | > 8000:1 | -| Laser damage threshold — CW | 1 W/cm² (532 nm, Ø0.471 mm) | -| Laser damage threshold — pulsed | 0.4 J/cm² (532 nm, 10 ns, 10 Hz, Ø0.750 mm) | -| Clear aperture | Ø20 mm | -| Surface quality | 40-20 scratch-dig | -| Max incidence angle | ±5° | -| Switching speed (shutter mode, typ.)² | opening 5 ms / closing 1 ms | -| Wavefront distortion | ≤ λ/4 @ 633 nm | -| External input | SMC connector, 0 – 5 V, 25 kΩ input impedance | -| Power adapter | 12 VDC / 1.25 A, with power cord | -| AC power requirements | 110 – 240 VAC, 47 – 63 Hz, 0.4 A | -| Mounting | two 8-32 (M4) post holes · 30 mm cage compatible · Ø1" lens tube compatible | -| Operating temperature | 15 °C to 60 °C | -| Dimensions | 60 mm × 60 mm × 27 mm | - -¹ Average CR is specified over the operating wavelength range. -² Shutter mode with a 0–5 V TTL input on the EXT port. Opening time: input -falls to 10 % → transmission rises to 90 % of total. Closing time: input -rises to 90 % → transmission falls to 10 %. - -### Figure 5 — Transmission and contrast ratio vs wavelength - -Transmission (linear scale) and CR (log scale) from 400–800 nm. Transmission -climbs steeply from ~5 % at 400 nm to ~80 % near 500 nm, then declines gently -to ~65 % at 700 nm and ~52–57 % at 750–800 nm. CR exceeds 10⁴ across roughly -450–650 nm, stays near 10⁴ to ~680 nm, then collapses above 700 nm to about -5:1 at 800 nm. - -### Figure 6 — Transmission spectra at fixed external voltages - -Curves at 0, 0.5, 1, 1.5, 2, 2.5, 3, and 5 V over 350–800 nm. All curves cut -on near 400 nm. Peak transmission (~450–520 nm): ≈78 % at 0 V, ≈70 % at -0.5 V, ≈53 % at 1 V, ≈33 % at 1.5 V, ≈18 % at 2 V, ≈8 % at 2.5 V, and ≈0 % -at 3 V and 5 V (the two overlap). All curves rise again above ~750 nm where -the polarizers lose contrast. - -### Figure 7 — Transmission vs external voltage ("attenuator mode") - -Transmission vs 0–5 V attenuation voltage at 500, 550, 600, 650, 700, and -750 nm. Monotonic S-shaped decrease: at 0 V transmission is ≈80 % (500 nm) -down to ≈53 % (750 nm); the steepest slope is around 0.5–1.5 V; all -wavelengths converge below ~5 % by 2.5–3 V and stay essentially flat (0–3 %) -to 5 V. Note: all curves taken with linearly polarized light aligned to the -front-surface transmission axis; CR plots use a log₁₀ scale. - -### Figure 8 — Normalized contrast ratio vs frequency - -Modulating the shutter degrades contrast with frequency: normalized CR ≈ 1.0 -up to ~40 Hz, ~0.8 at 100 Hz, ~0.5 at ~140 Hz, falling to ~0.28 at 200 Hz. - -### Figure 9 — Switching-time stability - -Over six weeks of monitoring, rise (opening) switching time stays ~5.2–6.0 ms -and fall (closing) time stays ~0.3–0.4 ms — both essentially flat over time. - -### Shutter timing specifications (typ., vs temperature) - -Points A–F refer to the manual's timing diagram: the external 0→5 V -modulation pulse (10 %/90 % levels) and the shutter's optical response. - -| Key | Description | 25 °C | 40 °C | 60 °C | -|---|---|---|---|---| -| A→B | input rising edge @90 % → shutter starts closing (down to 90 %) | 0.065 ms | 0.061 ms | 0.052 ms | -| B→C | falling edge, 90 % → 10 % | 0.346 ms | 0.344 ms | 0.342 ms | -| A→C | input rising edge @90 % → shutter down to 10 % (**total close**) | 0.416 ms | 0.404 ms | 0.392 ms | -| D→E | input falling edge @10 % → shutter starts opening (up to 10 %) | 2.23 ms | 1.89 ms | 1.73 ms | -| E→F | rising edge, 10 % → 90 % | 3.24 ms | 2.71 ms | 2.61 ms | -| D→F | input falling edge @10 % → shutter up to 90 % (**total open**) | 5.47 ms | 4.60 ms | 4.34 ms | - -(Voltage applied = shutter **closes**; voltage removed = shutter **opens** — -opening is the slow LC-relaxation direction, ~10× slower than closing, and -both speed up slightly with temperature.) - -## Ch. 7 — Mechanical drawing - -All shutter models share the same housing; the /M version has M4 tapped holes -instead of 8-32. Key dimensions: - -- Housing: 2.36" (60.0 mm) square × 1.06" (27.0 mm) deep; 3.14" (79.7 mm) - overall height including the knob. -- Clear aperture: Ø0.79" (20.0 mm), centered 1.18" (30.0 mm) from the edges. -- Internal **SM1 (1.035"-40) threads, 0.16" deep**, on both faces. -- Four **4-40 tapped holes** (30 mm cage system) on both front and back faces. -- **8-32 (M4) post-mounting holes** on the bottom and side, 0.53" (13.5 mm) - from the face, 1.18" (30.0 mm) from the edge — the 90° offset pair. -- Side panel carries the 12 VDC power jack. - -## Ch. 8 — Maintenance and troubleshooting - -No maintenance required under normal operation; no serviceable parts — do not -open the unit; contact Thorlabs technical support for problems. - -| Problem | Solution | -|---|---| -| No output power | Remove the caps. SHUTTER mode: adjust the knob until the LED is green. ATTENUATOR mode: turn the knob clockwise until the LED is green. | -| Output power can't be attenuated | Ensure the device is powered on; switch to ATTENUATOR mode; adjust the knob until the LED is green. | -| Output is unstable | When using EXT INPUT to control the output, ensure the control voltage itself is stable. | - -## Ch. 9–11 — Certification, regulatory, contacts - -- **CE certified** (EMC 2004/108/EC & LVD 2006/95/EC; EN 61326-1:2013, - EN 61010-1:2010) — covers LCC1620, LCC1620/M, LCC1621, LCC1621/M. -- **WEEE**: EU end-of-life units can be returned to Thorlabs for disposal at - no charge; do not discard in general waste. -- Contacts: (offices worldwide; - techsupport@thorlabs.com). - ---- - -# Appendix — this rig & the `LCC1620` driver - -Everything below is ours, not Thorlabs'. +# This rig & the `LCC1620` driver ## Rig settings - Mode switch: **ATTENUATOR**. Potentiometer: **fully clockwise** — the EXT - INPUT is summed with the pot (Ch. 5), so anything less silently compresses + INPUT is summed with the pot (see the manual, Ch. 5), so anything less silently compresses the achievable range. If the range looks wrong, check the pot before suspecting the DAQ. - The **12 V supply must be connected** (auto-powers, no switch) — EXT INPUT @@ -236,7 +53,7 @@ DAC 2 (SMA) ── coax ───────────────► LCA 2 ## Driver implications -- **0 V = maximum transmission, rising voltage = darker** (Fig. 7). So +- **0 V = maximum transmission, rising voltage = darker** (manual Fig. 7). So `shutdown`, which drives to `min_voltage` (0 V), leaves the attenuator **fully transmitting**, not blocked. A beam-blocked shutdown would mean driving to 5 V instead — a deliberate change, not the default. `shutdown` @@ -248,13 +65,13 @@ DAC 2 (SMA) ── coax ───────────────► LCA 2 default ⇒ ~0.2 s per set). Fine for step-and-settle attenuation; not a modulation path — for hardware-timed sequences use the Triggerscope's PROG_DAC/ARM sequence mode instead. -- The curve is **saturated dark by ~3 V** (Fig. 6/7: the 3 V and 5 V curves +- The curve is **saturated dark by ~3 V** (manual Fig. 6/7: the 3 V and 5 V curves overlap at ≈0 %). Concentrate `set_calibration!` sweep points in **0–2.5 V**; the upper half of the range carries no information. The curve is monotonic, so `settransmission`'s LUT-inversion requirement is naturally satisfied. - Transmission is wavelength dependent — calibrate at the working wavelength. - **Step-and-settle, not modulation**: total open ≈ 5.5 ms vs close ≈ 0.4 ms - at 25 °C (timing table), and contrast degrades above ~40–60 Hz (Fig. 8). + at 25 °C (manual timing table), and contrast degrades above ~40–60 Hz (manual Fig. 8). Allow **≥ 5–10 ms** after a voltage step before trusting a photodiode reading; the bench `run_test!` script's 0.1 s holds are comfortably safe.