Focus Tunable Lens

  • Update:Jul 05, 2020
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Our focus tunable lenses was inspired by the working principle of the human eye. Within milliseconds, the focal length of our electrical lenses is tuned by applying a control current. The unique principle enables the design of faster and more compact

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Within milliseconds, the focal length of our electrical lenses is tuned by applying a control current. The unique principle enables the design of faster and more compact optical systems without complex mechanics. We are a leading supplier of focus tunable lenses for perse applications. Whether electrically or mechanically actuated, the advantages of tunable lenses over traditional optics are striking. Our lenses can be tailored to your specific demands in terms of size, tuning range, transmission range or speed. Tell us your requirements and we will be happy to assess the feasibility.

Our electrical lenses are current controlled. There are several options for current drivers ranging from regular lab power supplies to tiny VCM driver ICs.  We offers a high-precision USB driver with a resolution of 0.1mA, which includes read-out of integrated temperature sensors over I2C.

The following table summarizes the main specifications of our most popular focus tunable lenses:

 

STOT-EL-3-10

 STOT-EL-10-30
Series

STOT-EL-10-30-C
Series

STOT-STOT-EL-10-42-OF

STOT-STOT-EL-16-40-TC
Series

STOT-ML-20-37
Series

Specs

tunable lens

Product description

Fast electrically tunable lens

Fast electrically tunable lens

Fast electrically tunable lens

Fast electrically tunable lens

Fast electrically tunable lens

Manually
tunable lens

Size (ØxH)

10x4.0mm

 30mm x 9.7mm

 30mm x 20.7mm

42mm x 36mm

 40mm x 11.9mm

 37mm x 8mm

Clear aperture

3m

 10mm

 10mm

10mm

 16mm

 20mm

Lens Type

Plano convex to plano concave

 Plano convex

 Plano convex
(offset lens optional)

Plano convex + plano concave offset lens

Plano convex to plano concave

 Plano convex to plano concave

Focal length range

+50 to +120mm

 +20 to +140mm

-600 to +170 mm 

-500 to +500 mm

-500 to +333 mm

-40 to +40mm

Refractive Index

1.300

 1.300 or 1.559

 1.300

1.300

  1.300

   1.300 or 1.559

Fast Electrically Tunable Lens STOT-EL-3-10

The compact STOT-EL-3-10 lens was designed for OEM integration into optical systems for various applications. The working principle is based on the well-established shape-changing lens technology. The curvature of the lens is adjusted by applying an electrical current. Thereby, the focal length is tuned to a desired value within very few milliseconds. The lens architecture is “push pull” which means that the lens curvature is deflected from concave to convex. With actuators based on proven voice-coil technology, the EL-3-10 focus tunable lens is extremely reliable and robust, well suited even for applications in harsh environments over large temperature ranges.

Applications

tunable lensSTOT-EL-3-10 is the ideal choice for:

 Mechanical specifications

Electrical specifications

Optical specifications STOT-EL-3-10-XXX-26D

Overview of standard products

Standard products

Tuning range

Flex cable

Cover glass

Container- and/or cover glass coating

Wavefront error

EL-3-10-VIS-26D-FPC

-13 to +13 dpt

Yes

Yes

420 – 900 nm

<0.2/<0.2 λ

EL-3-10-NIR-26D-FPC

-13 to +13 dpt

Yes

Yes

850 – 1600 nm

<0.2/<0.2 λ

EL-3-10-VIS-26D-OEM

-13 to +13 dpt

No

No

420 – 900 nm

<0.2/<0.2 λ

EL-3-10-NIR-26D-OEM

-13 to +13 dpt

No

No

850 – 1600 nm

<0.2/<0.2 λ

EL-3-10-VIS-26D-OEM-CG

-13 to +13 dpt

No

Yes

420 – 900 nm

<0.2/<0.2 λ

Remark: (1) 420-900 nm T>94%; (2) 850-1600 nm T>94%

Driver

The compact STOT-EL-3-10 lens can be driven with our STOT-EL-E-4 lens driver by simply connecting the flex cable of the lens to the Molex connector on the lens driver. In our software interface, the current to the lens can be adjusted to drive the lens. It’s important to note that +/-120 mA are required to tune across the whole optical power range. As the lens driver can output more current, it has to be connected to the PC without the lens connected first. Then, in the “Hardware Configurations” tab, the software limit has to be set to +/-120mA. Afterwards the lens driver can be disconnected, the lens connected to the lens driver and the lens driver connected back to the PC. The current will now only be adjustable from +/-120mA, hence an overdriving of the lens can be prevented.

Working principle

The working principle of the STOT-EL-3-10 is based on ours well-established technology of shape-changing polymer lenses. The core that forms the lens contains an optical fluid, which is sealed off with an elastic polymer membrane. An electromagnetic actuator is used to exert pressure on the container and therefore changes the curvature of the lens. By changing the electrical current flowing through the coil of the actuator, the optical power of the lens is controlled.

tunable lens tunable lens

Response time

The rise time when applying a current step is <1 ms and it takes only about 4 ms until the lens has fully settled. The graphs of the step response measurements below show the optical response of the STOT-EL-3-10 lens. Low pass filtering of the drive signal to the lens allows to damp the oscillations seen in the step response graphs below and as a result drive a controlled 80% step in <2ms.

Optical power versus current

The optical power of the STOT-EL-3-10 increases with positive current and decreases with negative current as shown as follows. The specified optical power range is from +13 to -13 diopters.

tunable lens

Fast Electrically Tunable Lens STOT-EL-10-30 Series

The curvature of this shape changing polymer lens is adjusted by applying current. The focal length is accordingly tuned to a desired value within milliseconds. We offer three different types of housings of the STOT-EL-10-30. The compact 30x10.7 mm housing, a 30x20 mm housing with C-mount threads and the Industrial C-mount housing (Ci) with Hirose connector. For each housing there are different options to adapt the lens to your needs:

The table below summarizes the possible options for the three different housings.

Option

STOT-EL-10-30-TC

STOT-EL-10-30-C

STOT-EL-10-30-Ci

Cover glass coating

VIS(1), NIR(2)

VIS, NIR, 1064nm(3)

VIS, NIR, 1064nm

Optional offset lens

No

Yes

Yes

(1) 400-700 nm broad band; (2) 700-1100 nm infra-red broad band; (3) narrow band 1064 nm

The following table outlines the specifications of our standard electrically tunable lens STOT-EL-10-30. Cover glass coatings and tuning range can be adapted on demand.

Mechanical Specifications

Part number

STOT-EL-10-30-TC

STOT-EL-10-30-C

STOT-EL-10-30-Ci

Clear aperture

10mm

10mm

10mm

External diameter

30mm

30mm

Oval shape 48x30.5mm

Thickness

10.7mm

24.6mm

24.6mm

Weight

22.9g

34.0g

46.0g

Connector length

100

100

10001mm

Lifecycles (10-90% sinusoidal)

>1‘000‘000’000

>1‘000‘000’000

>1‘000‘000’000

Electrical specifications

Part number

STOT-EL-10-30-TC

STOT-EL-10-30-C

STOT-EL-10-30-Ci

Absolute maximum voltage (coil)

5V

5V

Absolute maximum voltage (temp. sensor)

4.3V

4.3V

I2C supply voltage

3.3 (nominal),

3.6 (maximum)

3.3 (nominal),

3.6 (maximum)

Nominal control current with Lens Driver 4

0 to 250mA

0 to 250mA

Absolute max. control current

0 to 400mA

0 to 400mA

Power consumption

0 to 0.9 (nominal), 0 to 2.0 (absolute max.)

0 to 0.9 (nominal), 0 to 2.0 (absolute max.)

Temperature sensor & memory

Yes ( STTS2004)

Yes ( SE97B or equivalent STTS2004)

Response time (10%-90% step)

<2.5

 

Settling time (typical at 30°C)

15 (rectangular step),

6 (controlled step)

 15 (rectangular step),

6 (controlled step)

Optical Specifications

Focal tuning range @ 30°C2

+50 to +120mm

+100 to +200 mm

Dispersion (at 20°C) 486 nm

1.302

1.302

 589 nm

1.300

1.300

 656 nm

1.299

1.299

 800 nm

1.298

1.298

 1065 nm

1.297

1.297

 1550 nm

1.296

1.296

Abbe number V

100

 

Wavefront error (@530 nm, 0 mA) Optical axis vertical / horizontal

<0.25 / <0.6λ RMS

<0.15 / <0.25λ RMS

Lens type

plano-convex

plano-convex

Optical retardance @590nm

 6.4 nm

 6.4 nm

Optical damage threshold @ 1064 nm

 10 kW/cm2

 10 kW/cm2

Polarisation

Perserving

Perserving

Overview of available standard products

 

Turning range

Refractive index

Cover glass coating

RMS wavefront error

Integrated offset lens

Temp. sensor

STOT-EL-10-30-TC-VIR-12D

+8.3 to +20dpt

1.30

400 – 1100nm

<0.25/<0.60 

No

Yes

STOT-EL-10-30-TC-NIR-12D

+8.3 to +20dpt

1.30

700 – 1100nm

<0.25/<0.60 

No

Yes

STOT-EL-10-30-C-VIS-LD

+5 to +10dpt

1.30

400 – 700nm

<0.15/<0.25 

No

Yes

STOT-EL-10-30-C-NIR-LD

+5 to +10dpt

1.30

700 – 1100nm

<0.15/<0.25 

No

Yes

STOT-EL-10-30-C-VIS-LD-MV

-1.5 to +3.5dpt

1.30

400 – 700nm

<0.15/<0.25 

Yes (-150 mm)

Yes

STOT-EL-10-30-C-NIR-LD-MV

-1.5 to +3.5dpt

1.30

700 – 1100nm

<0.15/<0.25 

Yes (-150 mm)

Yes

STOT-EL-10-30-Ci-VIS-LD

+5 to +10dpt

1.30

400 – 700nm

<0.15/<0.25 

No

Yes

STOT-EL-10-30-Ci-NIR-LD

+5 to +10dpt

1.30

700 – 1100nm

<0.15/<0.25 

No

Yes

STOT-EL-10-30-Ci-VIS-LD-MV

-1.5 to +3.5dpt

1.30

400 – 700nm

<0.15/<0.25 

Yes (-150 mm)

Yes

STOT-EL-10-30-Ci-NIR-LD-MV

-1.5 to +3.5dpt

1.30

700 – 1100nm

<0.15/<0.25 

Yes (-150 mm)

Yes

Housings

The STOT-EL-10-30-TC is preferably mounted in a 30 mm ring holder. The relevant mechanical drawings are depicted below in Figure 1. Figure 2 shows the drawings of the C-mount housing. This housing has threads on either side and exhibits an M4 threaded hole in the housing for mounting on optical posts. Figure 3 shows the drawings of the industrial C-mount STOT-EL-10-30-Ci. This housing has an oval shape and no M4 threaded hole, however C-mount threads on either side like the C-mount housing. Apart from the housing and connector, the performance of the STOT-EL-10-30-C and STOT-EL-10-30-Ci are identical.

tunable lens

tunable lens tunable lens

Electrical connection

The industrial design STOT-EL-10-30-Ci comes with a 6-pin Hirose connector. A 1m long cable to connect the STOT-EL-10-30-Ci to the STOT-EL-E-4i driver is available (P/N CAB-6-100). The STOT-EL-10-30-TC and STOT-EL-10-30-C has a 10 cm long FPC connection, which is compatible with Molex 0.5mm pitch 6 way FPC backflip connector (P/N 503480-0600). All STOT-EL-10-30 lenses feature an SE97B temperature sensor with 256 bytes of memory. The I2C addresses of the temperature sensor and the EEPROM are 0x18 and 0x50, respectively.

Optical layout

Figure 4 contains the information needed to model the STOT-EL-10-30 lenses for simulation.

tunable lens

Using offset lenses

In the STOT-EL-10-30-C and -Ci the protective cover glass can be replaced by an offset lens of 12 or 12.7-mm diameter. This allows shifting the focal length range to any desired value. For example, adding an offset lens with f = -150 mm to the STOT-EL-10-30-C-VIS-LD will yield a focal length range of about -666 mm to infinity to +286 mm (1/fres= 1/fEL-10-30 + 1/foffset). The design of the STOT-EL-10-30-C is optimized for good alignment of the tunable lens and the offset lens. The maximal thickness of the offset lens may be 4.7 mm.

Working principle

The STOT-EL-10-30 is a shape-changing lens, as illustrated in Figure 5. It consists of a container, which is filled with an optical fluid and sealed off with an elastic polymer membrane. The deflection of the lens is proportional to the pressure in the fluid. The STOT-EL-10-30 has an electromagnetic actuator that is used to exert pressure on the container. Hence, the focal distance of the lens is controlled by the current flowing through the coil of the actuator.

tunable lens

Focal length versus current

The optical power of the STOT-EL-10-30 increases with current, shown in Figure 6. The starting point at zero current is set during production and can be varied from lens to lens, whereas the maximal value is 500 mm. The slope of the optical power is influenced by the mechanical properties of the membrane, which can also be varied on request to achieve different ranges. In open loop systems, a calibration of the lens with look-up tables is recommended. The focal length also depends on temperature, see paragraph temperature effects.

tunle lens

Transmission range

Both the optical fluid and the membrane material are highly transparent in the range of 400 to 2500 nm. As the membrane is elastic it cannot be coated using standard processes, hence a reflection of 3 – 4% is to be expected. Cover glasses can be coated as desired. Figure 7 and Figure 8 show the transmission spectrum for our two standard broad-band coatings (visible and near infrared) as well as a custom narrow-band coatings:

tunable lens tunable lens

tunable lens

Laser damage measurements

The CW damage threshold of the lens material is 10 kW/cm2 for a wavelength of 1064 nm. Further damage measurements with pulsed lasers have been performed with the following results:

For 1064 nm, long term measurements over 2000h show no degradation or change in the optical characteristic of the lens. The parameters of this measurement were: 100 ns-pulsed at 100 kHz and 40mJ/cm2 fluence. For 532 nm, measurements over 60h show no degradation or change in the optical characteristic of the lens. The parameters of this measurement were: 10 ns-pulsed at 30 kHz and 1.4mJ/cm2 fluence. While no heating up of the lens is observed with the pulsed lasers, a 200 W CW laser does heat up the lens, resulting in a focus drift, which stabilizes after about 10 seconds. To avoid heating of the lens due to reflections hitting absorbing surfaces, it is advised to calculate such reflections and preferably not use more than 8 mm of the clear lens aperture.

Temperature effects

tunable lensHeating up of the lens has two consequences: First, the refractive index of the optical fluid decreases. Second, the fluid expands in volume. While the first effect would decrease the optical power, the second effect increases it. With the STOT-EL-10-30 design, the second effect prevails. The optical power increases by approximately 0.7 diopters per 10°C temperature increase.

This temperature effect is systematic and reproducible. This means the focal length can be controlled if the  temperature is known. All STOT-EL-10-30 lenses have a built-in temperature sensor (SE97B). Heating up of the lens occurs at room temperature if driven at high currents or due to absorption of high power laser light. In such cases the lens is preferably mounted using heat-conducting metal clamps. For custom designs it is possible to balance the two temperature effects such that the focus shift becomes minimal at a certain focal length.

Resolution and reproducibility

The step size of the focal power is limited by the resolution of the DAC of the current driver. For high precision applications a driver with 12 bits is recommended. As the relation between current and focal power is linear, the smallest step of e.g. the STOT-EL-10-30-C-VIS-LD about 0.0018 Dpt.

Unlike piezo systems, the STOT-EL-10-30 exhibits no hysteresis. The current through the coil induces a force, which is directly transferred onto the elastic membrane. There is no friction in the system. This means that at a constant temperature jumping between alternate current levels will always yield the same focal length. The effect of changes in temperature are described above. Our Lens Driver 4 offers a focal power mode, which makes use of calibration data stored in the lens (EEPROM of the SE97B). The absolute reproducibility achieved over an operating temperature range of 10 to 50°C amounts to typically 0.1 diopters. More details on the focal power mode are provided in the Lens Driver manual.

Resistance and Inductance of the driving coil

In principle, the STOT-EL-10-30 can be driven using a DC voltage (e.g. even a simple battery) or a current source. However, the focal length of the lens depends on the current flowing through the coil and the resistance of the coil changes with temperature (12.5 Ohm at 25°C) with a linear rate of 3.93%/°C. That is why, for highest stability, it is recommended to use a current source. Note that this temperature effect is visible within seconds and has nothing to do with the expansion of the optical fluid described above, which is on the order of minutes. For AC operation, the inductance of the coil, which depends on frequency, is an important parameter.

Frequency(Hz)

Coil Inductance (mH)

10000

0.76

1000

1.1

100

1.14

10

1.15

Recommended drivers and power supplies

We provide its own high-precision USB drivers with a resolution of 0.1 mA. It includes the I2C readout of the temperature sensor, which can be used for temperature compensation.

The lens can also be driven using pulse width modulation (PWM) with a frequency between 20 kHz and 50 kHz. Another very useful component is the ADN8810 programmable precision current source of Analog Devices, which features 12 bits of resolution and can be controlled with an SPI interface.

Exchanging the offset lens of the STOT-EL-10-30-C Series

tunable lensThe STOT-EL-10-30-C is shipped with a planar cover glass or with an integrated offset lens (MV version), which is held in place by a retainer ring. The cover glass or offset lens can easily be exchanged by hand following the procedure outlined below. Please note that this is preferably done in a clean room or under a flow hood to avoid dust entering the tunable lens.

  1. Loosen the retainer ring carefully with a small screw driver
  2. After about 5 rotations turn the lens with the ring pointing down so no dust can get into the lens
  3. Take out the cover glass / offset lens with the retainer ring. Prepare the new cover glass or lens.
  4. Turn the lens again, but be careful, that no dust gets inside. Carefully drop the new cover glass or lens (planar side should usually look down towards the lens) inside using tweezers.
  5. Put the retainer ring in by hand
  6. Tighten the retainer ring with a screw driver. Be careful not to scratch the glass.

IMPORTANT: At the end, do not exert much torque (<1 Nm) as this might damage the tunable lens.

Ordering information for custom versions of the STOT-EL-10-30

For custom versions, please use the following concept for part numbers: STOT-EL-10-30-H-AR-MAT-RANGE

Example: STOT-EL-10-30-C-NOC-LD refers to a custom electrical tunable lens of 10 mm aperture and 30 mm outer diameter (C-mount housing) with uncoated cover glasses, low dispersion lens material and a focal tuning range from +5 to +10 dpt.

Safety and compliance

The product fulfills the RoHS and REACH compliance standards. The customer is solely responsible to comply with all relevant safety regulations for integration and operation.

1. Fast Electrically Tunable Lens STOT-EL-10-30-TC

Design faster and more compact optical systems without complex mechanics using the electrically focus tunable lens STOT-EL-10-30-TC. By applying a current, the focal length of the 10 mm aperture lens can be tuned to a specific value in milliseconds. Thanks to an integrated temperature sensor and characterization data, the lens can be driven to precise focal powers using our lens driver 4. The STOT-EL-10-30-TC is available with two broadband coating options, VIS for 400-700nm and NIR for 700-1100nm.

The following table summarizes the main specifications of the compact STOT-EL-10-30-TC:

Standard products

Tuning range

Refractive index

Cover glass coating

Wavefront error* 

STOT-EL-10-30-TC-VIS-12D

+120 to +50 mm
+8.3 to +20 dpt

1.30

400 - 700nm

<0.25 / <0.60 λ

STOT-EL-10-30-TC-NIR-12D

+120 to +50 mm
+8.3 to +20 dpt

1.30

700 - 1100nm

<0.25 / <0.60 λ

* Wavefront error provided in λ RMS @525nm with optical axis vertical / horizontal

Applications

2. Fast Electrically Tunable Lens STOT-EL-10-30-C

Design faster and more compact optical systems without complex mechanics using the electrically focus tunable lens STOT-EL-10-30-C. By applying a current of 0 to 300mA, the focal length of the 10 mm aperture lens can be tuned to a specific value within milliseconds. The STOT-EL-10-30-C also features threads on either side for easy mounting as well as the possibility to replace the cover glass with a fixed focus offset lens, allowing for free adjustment of the focal length range according to the requirements of your application.

STOT-EL-10-30-C
(OEM version)

STOT-EL-10-30-Ci
(industrial version)

The STOT-EL-10-30-C has two main optical configurations:

1.  The basic configuration has planar cover glasses and a focal tuning range of 200mm down to 100mm, making this the best choice for macro imaging.

2.  The "MV" configuration is optimized for the machine vision market. It contains a negative offset lens so that the overall focal tuning range goes from slightly negative down to 286mm, making this the ideal choice for combinations with infinity corrected fixed-focus lenses.

The following table summarizes the main specifications of the STOT-EL-10-30-C series:

Standard products*

Tuning range with Lens Driver 4
(0 - 250mA)

Integrated offset lens

Cover glass coating

Wavefront error**

STOT-EL-10-30-C-VIS-LD

200 to 100 mm
5 to 10 dpt

No

400 - 700nm

<0.15 / <0.25 λ

STOT-EL-10-30-C-NIR-LD

200 to 100 mm
5 to 10 dpt

No

700 - 1100nm

<0.15 / <0.25 λ

STOT-EL-10-30-C-VIS-LD-MV

-667 to +286mm
-1.5 to +3.5 dpt

Yes (-150mm)

400 - 700nm

<0.15 / <0.25 λ

STOT-EL-10-30-C-NIR-LD-MV

-667 to +286 mm
-1.5 to +3.5 dpt

Yes (-150mm)

700 - 1100nm

<0.15 / <0.25 λ

* All the above models are available with a 6-pin FPC connector (OEM version) or with a 6-pin Hirose connector (industrial version)
** Wavefront error provided in λ RMS @525nm with optical axis vertical / horizontal

Since 2014 all lenses offer "Focal Power Mode", which makes use of calibration data saved directly on the lens, allowing for open loop control including temperature compensation at a repeatability of typically +/-0.1 diopters.

Applications

Fast Electrically Tunable Lens STOT-EL-10-42-OF

The electrically focus-tunable lens STOT-EL-10-42-OF is dedicated to 3D laser processing applications and sets the highest standards in terms of spot quality, speed and repeatability. With a focus tuning range of -2.0 to +2.0 diopters the spot can be controlled over a large range along the z-axis (working distance change of up to 180mm). Our proprietary built-in optical feedback mechanism allows for a long term repeatability of <0.02 diopters. The STOT-EL-10-42-OF is optimized for the use at 1064nm and 532nm. 

The working principle of STOT-EL-10-42-OF lens with integrated optical feedback is based on the well-established shape-changing flexible lens. The curvature of the lens is adjusted by applying an electrical current. The focal length is accordingly tuned to a desired value within milliseconds. The STOT-EL-10-42-OF has an integrated optical feedback, measuring the optical power of the lens in real-time. Optimal control is guaranteed using the STOT-EL-E-OF-A analog driver board or STOT-DSD digital driver board developed. This makes STOT-EL-10-42-OF suitable for laser marking and engraving applications.

Applications

Main specifications

Product

STOT-EL-10-42-OF-1064

STOT-EL-10-42-OF-1064-S (SCAPS)

Clear aperture

10mm

10mm

Focal length

-500 to ∞  to +500 mm

-555 to ∞  to +555 mm

Optical power: tuning range

-2.0 to 0 to +2.0 dpt

-1.8 to 0 to +1.8 dpt

Optical power: pointing stability (+/- STD)

< +/- 0.002 dpt

< +/- 0.002 dpt

Optical power: repeatability (+/- STD)

< +/- 0.010 dpt

< +/- 0.010 dpt

Optical power: long term stab. 8h (+/- STD)

< +/- 0.0201  dpt

< +/- 0.0201  dpt

Lateral spot shift over full tuning range

< 45μRadλμRad

< 45μRadλμRad

Lateral long term drift at fixed focal length

< 5μRadμRad

< 5μRadμRad

Wavefront error

< 0.25 @ 525 nm RMS

< 0.25 @ 525 nm RMS

Transmission

> 95% @ 1064 nm

> 95% @ 1064 nm

Long term radiation damage @ 1064 nm:

40 mJ/cm2 at 20 kHz

No effect after 2000 h

No effect after 2000 h

Damage threshold2 @ 1064 nm:

125 ns-pulsed at 50 kHz

10 ps-pulsed at 50 kHz

 

2.6 J/cm2

2.05 J/cm2

 

2.6 J/cm2

2.05 J/cm2

Response time

Controlled with EL-E-OF-A analog board

80% step: 12 20% step: 6ms

80% step: 12 20% step: 6ms

Response time

Controlled with STOT-DSD digital board

 

80% step: 8ms

 20% step: 4.5 ms

Tracking delay  Controlled with STOT-DSD digital board

 

< 2 ms

Focal length resolution

Continuous (depends on control electronics)

Continuous (depends on control electronics)

Lifecycles (10%-90% sinusoidal)

> 1‘000‘000’000

> 1‘000‘000’000

Weight

90 g

90 g

Heater set temperature

47 °C

47 °C

Operating temperature

10 to 40 °C

10 to 40 °C

Storage Temperature

-20 to 80 °C

-20 to 80 °C

Parameters in combination with f = 160 mm f-theta lens3

Max z-tuning range in a marking system

100mm

90mm

Repeatability (10%-90% step)

< 250 μm

 

Long term drift over 8h

< 500 μm

 

Electrical specifications

Max lens power consumption

1.5 W

Max lens current

385 mA

Max heater power consumption

12 W

Heater resistance @ 25°C

25 +/- 10% Ohm

Voltage Vcc

3.3 V

LED forward voltage

1.5 V

  1. Mainly due to residual temperature effects
  2. Characterization done by Inspire AG and IWF/ETH Zurich
  3. See laser processing application note for details

Housing

The STOT-EL-10-42-OF comes with a black metallic housing. The rectangular shaped part of the housing at the side includes the electrical connections. Four M3 thread holes located at the front surface of the housing are designated for mounting. A typical assembly is shown in section Alignment and mounting. The Ø40.0 mm and Ø25.5 mm diameter flank is tightly tolerated (ISO tolerance g6) and suitable as an alignment feature. The included Teflon washer provides thermal isolation and has to be placed between the STOT-EL-10-42-OF and an external holder.

Please click here for mechanical drawing of the STOT-EL-10-42-OF (unit: mm). Four M3 thread holes are available four mounting. The Teflon washer has a thickness of 2mm and its flatness is tolerated within +- 0.05 mm.

Electrical connection

The electrical connection of the STOT-EL-10-42-OF consists of two female 1.5 mm AMP Mini CT connectors with 6 and 8 pins (see e.g. www.te.com, No. 292207-6 and 292207-8). The detailed pin-out is summarized in the table below.

focus tunable lens

Position

Function

Value

Position

Function

Value

1

GND

-

8

Control current -

-

2

Heater in

Max. 12W

9

GND

-

3

Heater out

-

10

LED + Anode

30mA @1.5V

4

I²C SDA

Digital signal

11

LED – Cathode

-

5

I²C SCL

Digital signal

12

Photodiode Common Cathode GND

-

6

Vcc

3.3V

13

Photodiode Anode back

Typ. 100 μA

Optical power (focal length) versus current

The optical power of the STOT-EL-10-42-OF increases with increased current, shown in Figure 3. The working principle is based on our well-established technology of electrically tunable lenses. The core that forms the lens contains an optical fluid, which is sealed off with an elastic polymer membrane. An electromagnetic actuator is used to exert pressure on the container and therefore changes the curvature of the membrane such that the focal length is adjusted. By applying the electrical current to the coil of the actuator, the optical power of the lens is controlled.

focus tunable lens focus tunable lens

Optical feedback signal

Optical feedback is used to stabilize the focus of the lens in real time. The way to establish optical feedback is to detect light passing through the lens, emitted from a built-in LED. There are two photodiodes installed inside the lens which are used to measure the LED light. The typical photodiode signals are as shown in Figure 4. The slopes of the two curves are different, and both photo currents strongly depend on the optical power of the lens. With subsequent electronics these currents are converted into voltages through transimpedance amplifiers. The normalized signal (V1-V2)/(V1+V2) of the two voltages V1 and V2 is then calculated in order to perform the optical feedback control for the lens. Note that the normalized signal is independent of intensity fluctuations of the LED.

Alignment and mounting

An important aspect when mounting the STOT-EL-10-42-OF is to ensure proper alignment with respect to the optical axis. The figure below shows an implementation of a holder plate. For detailed dimensions in your design, we can provide a CAD file of the holder. We propose a scheme that utilizes the part of the smaller diameter of the lens which is specified with low tolerance (ISO g6). The through hole of the holder plate has the corresponding DIN tolerance H8. The lens is screwed from the front onto the holder plate. This guarantees best alignment with respect to the optical axis. The elongated holes give the rotational freedom to align the connectors, since the relative position of the connectors and the screw holes vary from lens to lens. For best thermal isolation, a Teflon washer (included in the package) has to be placed between the lens and the holder. Also, it is recommended to use plastic screws to fix the lens. In the case shown, the lens is rotated such that the connectors point to the side.

focus tunable lens

Bode diagram

In order to characterize the dynamics of the STOT-EL-10-42-OF itself, which behaves similar to a mass-spring system, it is common to measure the Bode diagram. It contains both the magnitude of the frequency response and the phase shift. The result is shown in Figure 5 which is applicable as a generic model for the STOT-EL-10-42-OF. Lens to lens variations are negligible. The first resonance peak is at 200 Hz and in the same region the phase shift reaches -90° and continues to lower values. The diagram gives an indication of the physical limit of the lens’ maximum control speed, which will be around 100 Hz (half of the resonance frequency).

focus tunable lens focus tunable lens

Temperature stabilization

In order to have the highest focus stability, STOT-EL-10-42-OF lens is operated at a fixed temperature of 47 °C. This can be achieved using the controller boards we provide. The set temperature is controlled using a PI controller for the heater element. When the lens is initialized, it requires a certain amount of time until the set temperature is reached. In Figure 6, two extreme conditions (environmental temperature of 10°C and 40°C) are demonstrated. It can be seen that the system takes approximately 4 and 6 minutes respectively to get the temperature stable. After a short time, indicated by the red and blue arrows, the lens is set to maximum current (300 mA) in order to see the effect of additional heat input. Even for the 40°C environmental temperature only a small increase of about 2°C is visible, which is the desirable result.

Please click here for application note for 2.5D laser processing using STOT-EL-10-42-OF tunable lens and STOT-EL-E-OF-A controller board

Fast Electrically Tunable Lens STOT-EL-16-40-TC

With a clear aperture of 16 mm we presents the world’s largest electrically focus tunable lens. Its design has been optimized in many ways:

The STOT-EL-16-40-TC is available in its compact form for OEM integration but also with multiple thread adapters and a robust Hirose connector for industrial use, where the tunable lens can be easily combined with off-the-shelf imaging lenses.

STOT-EL-16-40-TC

(OEM version)

STOT-EL-16-40-TC

with thread adapters (industrial version)

The STOT-EL-10-30-C has two main optical configurations:

  1. The basic configuration has planar cover glasses and a focal tuning range of 200mm down to 100mm, making this the best choice for macro imaging.
  2. The "MV" configuration is optimized for the machine vision market. It contains a negative offset lens so that the overall focal tuning range goes from slightly negative down to 286mm, making this the ideal choice for combinations with infinity corrected fixed-focus lenses.

The following table summarizes the main specifications of the STOT-EL-16-40-TC series:

Standard products*

Tuning
range

Wavefront error**

Top
thread

Bottom
thread

STOT-EL-16-40-TC-VIS-5D

-500 to 333 mm
-2 to 3 dpt

<0.25 / <0.5 λ

None

None

STOT-EL-16-40-TC-VIS-20D

-100 to 100 mm
-10 to 10 dpt

<0.50 / <2.5 λ

None

None

STOT-EL-16-40-TC-VIS-5D-M25.5

-500 to 333 mm
-2 to 3 dpt

<0.25 / <0.5 λ

M25.5x0.5
male

M40.5x0.5
female

STOT-EL-16-40-TC-VIS-5D-M27

-500 to 333 mm
-2 to 3 dpt

<0.25 / <0.5 λ

M27x0.5
male

M40.5x0.5
female

STOT-EL-16-40-TC-VIS-5D-M30.5

-500 to 333 mm
-2 to 3 dpt

<0.25 / <0.5 λ

M30.5x0.5
male

M40.5x0.5
female

STOT-EL-16-40-TC-VIS-5D-C

-500 to 333 mm
-2 to 3 dpt

<0.25 / <0.5 λ

C-mount
male

C-mount
female

STOT-EL-16-40-TC-VIS-5D-M42

-500 to 333 mm
-2 to 3 dpt

<0.25 / <0.5 λ

M42x1
male

M42x1
female

* All models are available with a 6-pin FPC connector. The models with thread adapters come with a 6-pin Hirose connector
** Wavefront error provided in λ RMS @525nm with optical axis vertical / horizontal

Applications

Manually Tunable Lens STOT-ML-20-37

The STOT-ML-20-37 adapts itself to your specific requirements. By manually rotating an adjustment ring, the lens changes its shape from convex to flat or to concave. This unique feature allows you to choose and finely tune the focal length of the lens within -40 to +40 mm range.focus tunable lens

Applications:

Mechanical specifications

Optical specifications

Environmental specifications

Standard product number

Turning range

AR coating

C-mount adapter

STOT-ML-20-37-VIS-36D

-18 to +18dpt

400-700nm

no

STOT-ML-20-37-VIS-36D-C

-18 to +18dpt

400-700nm

yes

Mechanical mounting

Figure 1 shows the dimensions of the STOT-ML-20-37 lens. The back-focal range is measured from the mating surface of the housing of the OEM lens. This surface lies 5.4 mm behind the outermost surface of the C-mount adapter. The ring is used to set the focal range to the desired value.

tunable lens

Motorization

The STOT-ML-20-37 can be motorized using either a direct drive or a worm gear. The magnet can be used for calibration purposes.

Transmission

Both the optical fluid and the membrane material are highly transparent in the range of 400 to 2500 nm. As the membrane is elastic it cannot be coated using standard processes, hence a reflection of 3 – 4 % is to be expected. Cover glasses can be coated as desired. Figure 2 shows the transmission spectrum for the standard broad-band VIS coating.

tramsmission tunable lens

Optical layout

Figure 3 contains the information needed to model the STOT-ML-20-37 lens for simulation. A precise ZEMAX model can be given upon request. As the cover glass is moved up and down, the membrane deflection changes continuously.

Mounting possibilities

tunable lens

 As depicted there exists different mechanical mounting possibilities of the C-mount version. For mounting recommendations of the version without C-mount adapter, please contact us.

Figure 4:shows mounting possibilities for the STOT-ML-20-37-C.

Safety and compliance

The product fulfills the RoHS and REACH compliance standards. The customer is solely responsible to comply with all relevant safety regulations for integration and operation.

Electrical Lens Driver 4

The Lens Driver 4 offers a simple yet precise way to control our electrically tunable lenses, in particular the EL-6-18 and STOT-EL-10-30 series. Communication with the driver follows an open simple serial protocol, which can be implemented in any programming language on Windows or Linux (C#, Labview and Python source code available). The driver comes with free software and can be used as a standalone solution or integrated into OEM designs. As a compact USB-powered current source, it also serves for driving LEDs or laser diodes.

Main features:

This constant current source is suitable for:

Industrial Lens Controller STOT-TR-CL180 by Gardasoft

Designed for industrial use, this Lens Controller by Gardasoft is the ideal solution for machine vision customers. GigE Vision, RS232 and analog interfaces as well as numerous SDKs allow for easy integration. The trigger input and fast response time of the controller make it also interesting for Z-stacking in microscopy and life science applications.

Main features:

STOT-EL-E-OF-A Lens Driver for STOT-EL-10-42-OF with Analog Interface (0-5V)

The STOT-EL-E-OF-A enables the control of the STOT-EL-10-42-OF lens module via an analog voltage signal. Several digital signals are available for status verification. The electronics essentially provides an analog-to-digital stage to read the control and set voltage signal, digital processing with an implemented PID-loop and current sources to drive the lens and the heater unit. The board is optimized for OEM-integration in laser marking systems and therefore comes without housing.

Main features:

SCAPS DSD Lens Driver for STOT-EL-10-42-OF with Digital Interface (XY2-100)

Optotune-DSD is an FPGA-based digital controller which is used for the control of the STOT-EL-10-42-OF lens module. The board is composed of two layers for which the top one is Digital Servo Interface (DSI-1-O16) and the bottom one is Digital Servo Controller (DSC-1). The board is particularly designed and optimized for OEM-integration in 3D laser marking systems.

Main features:

Applications Notes:

Focus Tunable Lenses (Moire Lenses)   Dynamic Focusing   3D Marking Heads

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