Sc450 2 Aotf Manual v1.1

Fianium

FemtoPower1060

Tunable Supercontinuum Source

SC450-AOTF

Fianium Ltd, Unit 20 Compass Point, Ensign Way, Hamble, Southampton, UK SO31 4RA 2 Tel - +44 (0)2380 458776, Fax – +44(0)2380 458734

e-mail – [email protected], website – www.fianium.com

Laser Safety

CAUTION:- Use of controls or adjustments or performance of procedures other than those specified here in may result in hazardous radiation exposure.

The laser beam is emitted from the optical collimator at the end of the flexible cable attached to the front of the laser enclosure where the laser aperture label is fixed. This is a collimated beam; there is a manual shutter on the AOTF head to block the beam if required. There is the facility for an external interlock to be connected into your existing interlocks if required, this is the wire loop in the signal D plug. If the interlock is opened, the laser must be reset. To do this, turn the key switch to the off position and press the push button interlock. This is a sealed laser unit. The removal of any panels will invalidate the warranty.



Labels Fixed to this Unit

Classification Label Manufactured Label Warning Triangle (A) (B) (C)

LASERAPERTURE

Laser Aperture Certification Label Product Information Label (D) (E) (F)

Input : DC 15 V

Serial Number :

5A max

06071

Compliance Label (G) Labels position Label A and B are fixed to the left hand side panel Label C is fixed to the back panel above the Laser emission indicator Label D is fixed on the top of the manual shutter Label E and F are fixed on the right hand side panel Label G is fixed on the rear Panel.



Important – Key Points to note before turning on your SC450-AOTF

i- Read Laser Safety Section, Pages 2-3, before operating the Laser -ii- When power is removed from the SC450 laser, internal software

interlocks delay turn-on of the oscillator for approximately 10-minutes when power is re-applied. As supplied, there will be a delay of approximately 10 minutes before the laser will modelock when power is applied to the system.

iii- Always ensure that the master source is mode locked (point 5, section

6.1) before turning on the high-power amplifier. -iv- Always try to turn the amplifier to a low level (preferably to zero drive)

before turning the laser off. -v- Always try to reduce the risk of back reflection into the laser.

-In bulk-optic systems, try to make sure that all reflective optics are bolted down and cannot move, creating spurious back reflected light into the laser.

-When setting up a new experiment for the first time, be careful not to cause back reflection into the amplifier. There is an automatic back reflection cut off. If the SC450 shuts down whilst aligning bulk optics, check optical train for alignment before turning power up again. - With the AOTF in-line, there is not risk of back reflection since the majority of IR light is filtered out within the AOTF head.

-vi- Never turn on the AOTF driver with the AOTF disconnected. The AOTF

driver unit includes a high power RF amplifier which requires load before being powered up.



Table of Contents

1 GETTING STARTED –..................................................................................................................... 6

2 INTRODUCTION .............................................................................................................................. 6

2. PRODUCT TECHNICAL SUMMARY ........................................................................................... 7

2.1 POWER SUPPLY UNIT......................................................................................................................... 8

3 FULL SYSTEM DESCRIPTION ...................................................................................................... 9

3.1 SC450-4 SUPERCONTINUUM FIBRE LASER ..................................................................................... 9

3.1.1 Master Source....................................................................... 10

3.1.2 Power Amplifier .................................................................... 10

3.1.3 Supercontinuum Generator ................................................... 11 3.2 MULTI-CHANNEL AOTF ................................................................................................................. 12

4. TEST DATA .......................................................................................................................................... 13

4.1 SC450-4 SUPERCONTINUUM LASER SOURCE ......................................................................... 13

4.1.1 Optical Spectrum.................................................................. 13

4.1.2 Typical Beam Profile ............................................................. 13

4.1.3 Pulse shape .......................................................................... 14 4.2 SC450-AOTF.......................................................................................................................... 15

5. CONTROL INTERFACES - LASER.............................................................................................. 16

5.1 7W2 PIN MALE MIXED D-SUB CONNECTOR .......................................................................... 16 5.3 SMA SOCKET ........................................................................................................................... 17 5.4 USB SOCKET............................................................................................................................. 17 5.5 INTERLOCKS ................................................................................................................................. 17

6. OPERATING INSTRUCTIONS..................................................................................................... 17

6.1 SC450 - MANUAL OPERATION -............................................................................................. 18 6.2 SC450 – PC OPERATION........................................................................................................ 22

6.2.1 USB Communications............................................................ 22

6.3 Control summary..................................................................... 31 6.4 ALARMS ............................................................................................................................................ 31 6.5 STATUS LEDS .................................................................................................................................. 32

7. SC450 AND AOTF INTEGRATION ........................................................................................... 33

7.1 SC450-AOTF MECHANICAL ASSEMBLY................................................................................ 33

7.1.1 RF Driver Connection ........................................................ 33

7.1.2 AOTF Head ....................................................................... 34 7.2 AOTF OPERATION................................................................................................................... 35

7.2.1 Driver Installation ............................................................. 35

7.2.2 GUI (Graphical User Interface) Installation.......................... 37

7.2.3 AOTF Calibration............................................................... 40 7.3 AOTF ALIGNMENT .................................................................................................................. 41

8. CUSTOMER SERVICE.................................................................................................................... 42



1 Getting Started – Section 3 of this manual describes the SC450 and AOTF system in greater detail. In order to get started using the SC450 or SC450-AOTF system, refer to sections 6 and 7 of this manual. Section 6.1 - Manual operation of the SC450 Section 6.2 - PC operation of the SC450 Section 7.1 - Physical connection of the AOTF system Section 7.2 - Operation of the AOTF

2 Introduction

The SC450-AOTF is a high power fibre continuum source with additional multi-channel AOTF (Acousto-Optic Tunable Filter) and RF driver unit. The system is designed to enable operation of the laser source in two separate configurations – -i- Stand alone SC450-4 supercontinuum fibre laser -ii- SC450-4 plus 8-channel AOTF providing free space collimated output

directly from the AOTF. Such a system design provides full flexibility as a research and development tool, enabling the user access to either the full supercontinuum spectrum from 450nm to beyond 1750nm, or providing means for high speed wavelength selection across the visible spectrum from 450nm to 700nm. When operated in configuration A, the supercontinuum laser delivers more than 2.5W optical power. This is a class4 laser and you should read the laser safety section of this manual before operating the laser. This also contains pump laser diodes which are Class4 lasers at 915nm.



2. Product technical summary Table 1 below describes the key technical specifications of the SC450-2 laser source. SC450-4 Parameter Value Unit Operating Wavelength 450 - 1750 nm Average output power Adjustable to 2.5 Watts Fundamental Pulse width ~ 6 ps

Repetition rate 20 MHz RMS amplitude noise <3 % Long term power stability <5 % Output beam quality 1.1 M² Power consumption ~120 Watts Dimensions (W x L x H) 250 x 300 x 120 mm Weight <10 kg

Table 1

Table 2 overleaf describes the key technical specifications of the laser source with integrated AOTF. SC450-4-AOTF Value Parameter Min Max Unit /

Notes Operating Wavelength (Tunable)

450 - 700 nm

Number of available channels

Up to 8

Channel spectral bandwidth

~3nm (at 450nm)

~7nm (at 700nm)

nm *1

Channel Output Power – free-space

~0.5 (at 450)

~ 6.0 (at 700nm)

mW *2

Polarisation Linear Output Beam Size 1.0

mm

Output beam quality 1.1 Uncharacterised

M² AOTF *3

Power consumption 120 max 30

W Laser W Driver

Dimensions (W x L x H)

250 x 300 x 120 250 x 300 x 50 75 x 200 x 30

mm Laser mm Driver mm AOTF

Weight ~10 ~4

~0.5

Kg Laser Kg Driver Kg AOTF



Table 2 Notes - *1 Channel bandwidth is a function of wavelength and RF power to the AOTF. At shorter wavelengths (into the blue region of the spectrum), the maximum bandwidth is in the region of 3nm. This increases with increasing wavelength, but the channel bandwidth at longer wavelengths can be reduced through varying RF power. *2 Output optical power through the AOTF is wavelength dependent and due to both the spectral power distribution of the SC450 as well as the efficiency of the AOTF as a function of wavelength. *3 At present, the output beam through the AOTF has not been fully characterised.

2.1 Power Supply Unit The laser module comes provided with two compact switch mode power supplies for the laser and AOTF driver which plug directly into the mains supply. Table 3 summarises the power specifications of the two power supply units. Parameter Minimum

Value Maximum Value

Unit

Input Voltage 100 240 Volts Frequency 50 60 Hertz Laser Supply Input current 2.0 Amps Output Voltage

- 15 Volts

Output Current

10 Amps

Driver Supply Input current 2.0 Amps Output Voltage

- 24 Volts

Output Current

5 Amps

Table 3



3 Full System Description The SC450-AOTF system is described schematically in figure 1 below. The system comprises two main sub systems; an SC450-4 supercontinuum fibre laser, 8-Channel RF driver plus AOTF. Both the SC450 and the AOTF RF driver have communication to a PC through RS232 or USB interface. Full details of these interfaces are described in section 7 (AOTF) and section 5 (SC450) of this manual.

Multi-Channel

AOTF RF Driver

A

O

T

F

Laser Enclosure

Flexible, protected

Single Mode Fibre

Output – ~1.5m in length

Removable optical head

Including collimating optic

(removable), IR Filter and

Broadband, multi-channel AOTF

Removable bulk-optic

Launch into PM SMF

Figure 1 – Full system configuration

3.1 SC450-4 Supercontinuum Fibre Laser The SC450 laser consists of three main sub-systems: a passively mode-locked low power fibre laser (master source), a high power cladding pumped fibre amplifier and a high nonlinearity supercontinuum generator.

Master Source

High Power Amplifier

High Nonlinearity Fibre PVF

Collimator



The broadband output channel of the SC450 is free-space delivered in a collimated beam with the collimator mounted externally at the end of a flexible armored optical cable.

3.1.1 Master Source

The master source is a passively mode locked fibre laser based on a core-pumped, Yb-doped fibre The laser operates at a repetition rate of approximately 20MHz, providing transform limited pulses of approximately 6.0 picoseconds. The pulse-to-pulse stability of the master source is excellent as shown in figure 3. The master source is self-starting at the touch of a button and operates maintenance free with high reliability since there are no bulk optic elements within the laser cavity.

Fig.3 Temporal stability of a soliton fibre laser in real time (no digitizing)

3.1.2 Power Amplifier

The high power fibre amplifier is based on a double-clad Yb-doped fibre, pumped by a high power, multi-emitter laser diode pump module (PUMA915-40). The pump module is air-cooled with inlet and outlet fans, mounted on the laser side-plates, forcing the air over the pump heat sink. Control of the amplifier drive current is achieved through three different operational modes – -i- Potentiometer open loop mode – where full control of the drive current to the power amplifier is provided manually by a 10-turn potentiometer on the rear panel of the laser.



-ii- USB open loop mode – where full control of the drive current to the power amplifier pump laser diode is provided through a computer interface. -iii- External voltage controlled open loop mode - In this mode, a voltage within the range 0V up to +5V DC is applied to pin 3 of the external control port. This control voltage is used to set the amplifier current and therefore the output power Further details of this operational procedure are described within section 6.

3.1.3 Supercontinuum Generator

The supercontinuum generator comprises a length of highly-nonlinear optical fibre, with dispersion and length tailored to the high power picosecond fibre source. Due to the high pulse-peak-powers and high nonlinearity within the fibre, the pulses experience large spectral broadening within the nonlinear fibre, covering the spectrum from approximately 450nm to greater than 1750nm. Since the supercontinuum generation process is driven by optical peak power, the spectral bandwidth of the supercontinuum is determined by the output of the high power fibre amplifier. When the amplifier is in the off-state, a few milliWatts of residual power from pre-amplifier stages will be emitted from the supercontinuum source. The spectral bandwidth of this output is narrow and centred at approximately 1064nm. Increasing the drive current to the amplifier increases both the optical output power as well as spectral bandwidth. The nonlinear process of supercontinuum generation causes firstly an increase in the spectral bandwidth to longer optical wavelengths (greater than 1064nm) which in turn leads to the generation of wavelengths shorter than 1064nm as the amplifier power increases further. When viewing the output beam on a surface with the eye, the laser output first shows the red wavelength which slowly becomes brighter and moves through orange to yellow and eventually to white as the amplifier output is increased to maximum. At full power the laser delivers greater than 2.5 Watts of optical power over the entire bandwidth spanning from approximately 450nm to beyond 1750nm.



3.2 Multi-Channel AOTF The AOTF element of the SC450-AOTF comprises a Crystal Technology Inc. broadband AOTF plus an amplified 8-Channel (OCTAL) AOTF RF driver system (Direct Digital Synthesizer – DDS) also from Crystal Technology. In an AOTF, a piezoelectric transducer is bonded to a birefringent crystal, (for example tellurium dioxide or lithium niobate) to generate ultrasonic waves that periodically modulate the material’s refractive index. This periodic modulation creates a phase grating whereby an incident beam traversing across the Bragg angle splits into its appropriate diffraction orders. In this interaction, the energy flow of the acoustic wave and optical beam are practically orthogonal to one another. By varying the acoustic wave frequency, the period of the phase grating is changed, as is the wavelength of the diffracted light, providing wavelength tunability of the diffracted beam through adjustment of the acoustic wave frequency. The DDS controller provides the ability to drive the AOTF with up to 8 separate channels at different RF frequencies and provide tunable wavelength and power at 1 to 8 separate wavelengths. Communication with the DDS is achieved through USB or RS232 communication, enabling fast selection of the wavelength and amplitude of each AOTF channel. Three graphical user interfaces (GUI’s) provided with the system enable

- either a simplified control, with adjustment of wavelength and RF power to each channel, or

- Full control of the AOTF with full functionality. The DDS controller and RF amplifier are mounted within an enclosure that can be positioned underneath the SC450-Laser, having a very similar footprint. The enclosure also contains fans to provide forced-air cooling of the RF amplifier. The AOTF is mounted within a remote optical head which can be removed from the optical output of the SC450 laser source. The optical head comprises, AOTF and visible mirrors to both filter out the IR from the supercontinuum output, as well as steer the optical beam through the AOTF and to the output.



4. Test Data

4.1 SC450 Supercontinuum laser source

4.1.1 Optical Spectrum

As the drive current is increased to the high power fibre amplifier, the output power of

the laser increases, as does the spectral bandwidth of the source. Plots of the spectra at various output power levels are shown in the plot below. At

maximum power, the laser delivers in excess of 2.5W average power, with an estimated 0.5W between 450nm and 800nm.

Wavelength, nm

400 600 800 1000 1200 1400 1600

Sp

ectra

l Inte

nsity

, a.u

.

-60

-55

-50

-45

-40

-35

Figure 4 – SC450 typical spectral evolution – Black – low power, increasing to the full power spectrum shown by the brown trace.

Figure 4 shows example spectra of SC450 systems with increasing output power, showing the typical evolution of the optical spectrum with increasing peak power from the Infra-Red pump source.

4.1.2 Typical Beam Profile

The output of the SC450 is through an optical fibre which is single mode over the entire spectral bandwidth of the source, delivering diffraction limited output at all wavelengths.



In the SC450 laser source supplied as part of the AOTF integrated system, the output of the SC450 is not supplied collimated, but instead is slightly wasted in order to optimize diffraction efficiency through the AOTF crystal. Collimation of the beam can be achieved by adjusting the collar mounted within the SC450 output optic. Figure 5 shows typical beam profiles of the SC450 output. The M2 value is <1.1 over the entire bandwidth.

Figure 5 – Beam profile of the SC450 laser output in both axes.

4.1.3 Pulse shape

The master oscillator produces transform limited optical pulses with approximately 6ps pulse duration – shown by the autocorrelation trace in figure 6. During amplification, the temporal quality of the pulse is maintained. However, due to the complex dispersion characteristics of the highly nonlinear optical fibre used to generate the supercontinuum, the SC450 output pulse duration will vary quite significantly over the spectral bandwidth, ranging from up to 100ps in the short visible wavelengths, down to a few hundred femtoseconds in the infra red.



Autocorrelation Trace of the Master Source from SC1060-1 SN050009

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-8 -6 -4 -2 0 2 4 6 8

Time Delay (ps)

SH INtensity (a.u)

Fig. 6 – Typical Autocorrelation of the master oscillator providing approximately 6ps pulses, close to transform limited.

4.2 SC450-AOTF Transmission of the SC450 optical beam through an AOTF, provides the ability to select required wavelength bands of the supercontinuum spectrum. The SC450 output has a random state of polarization, where the AOTF has high diffraction efficiency (80% to 90%) only for linear polarized incident light. The effective transmission of the AOTF is therefore only between 40% and 45% with respect to the SC450 laser output. Furthermore, the transmission and diffraction efficiency of an AOTF has wavelength dependence. The SC450 supercontinuum source also has a wavelength dependent output power spectral density. The combined output of the SC450 and AOTF has been characterised with the AOTF RF power level optimized – set to provide maximum output power for a given wavelength. In the attached Test Data Sheet is the test data used to characterize the wavelength vs. RF

frequency relationship of the AOTF.

It is worth noting that the power meter used to characterize the optical power, had only two wavelength calibration settings at 488nm and 633nm. The reliability of the power levels close to 488nm and 633nm can be guaranteed. At wavelengths far from these calibration wavelengths (for example 532nm), the measured values will have a degree of error.



In addition, the DAC setting of 2000 counts used to calibrate the AOTF, is not optimized. The DAC value can be increased to a maximum value of 16383 counts. Increasing the DAC drive level to the RF amplifier will produce distortion of the AOTF output and optimization will therefore be required.

5. Control Interfaces - Laser The following sections describe the Electrical connections on the rear panel of the SC450 supercontinuum fibre laser.

7W2 pin Male Mixed D-Sub Connector

Pin Signal Direction Description

A1 +15V +15V Supply

A2 0V 0V Supply

1, 2, 3, 4, 5

Not connected Do not connect

External Control Port Pin Signal Direction Description 1 Interlock + Output Remote interlock signal 2 Interlock Return Input Remote interlock return signal 3 Output required Input External control voltage in the

range 0V up to +5V. 8, 14 0V Ground reference for external

signals 9 nAlarm Output Laser Alarm signal. Active low 10 nLaser Emit Output Laser output emit signal. Active

low 4, 5, 6, 7, 11, 12, 13, 15

Not connected Do not connect



SMA Socket The rear panel SMA connector provides an analog output voltage from the master source oscillator. This is a low voltage pulse signal which can be monitored on an oscilloscope with 50Ω input impedance. The frequency of this signal is the fundamental frequency of the master source oscillator.

USB Socket The USB socket is known as a Type B Socket and can be connected to either a USB1.1 or USB2 PC Connection.

5.5 Interlocks

1. Remote interlock. This interlock, available on pins 1 and 2 of the 15 way control connector, can be connected to an external switch.

2. Push button interlock. The push button interlock enables the master source oscillator within the laser.

3. Key switch interlock. The key switch enables the high power section of the Laser. It can only be enabled if the other interlocks are enabled first.

Push button Remote Key switch Laser enabled Off Off Off Off On Off Off Off Turning on On Off Low power only On On Turning on Yes

Interlock operating sequence

6. Operating instructions



6.1 SC450 - Manual Operation -

Figure 7 – Photograph of the SC450 (A)

(B) (3)

(B1

A1

A2

A4

A5

A3

A6



The SC450 has three modes of operation – -i- Open loop Pot mode – in which the current to the high power amplifier

pump laser is controlled by a 10-turn potentiometer mounted on the laser rear panel

-ii- Open loop USD mode – in which the amplifier pump diode drive current is set via USB.

-iii- External voltage controlled open loop mode - In this mode, a voltage within the range 0V up to +5V DC is applied to pin 3 of the external control port. This control voltage is used to set the amplifier current and therefore the output power

The laser is supplied as default in mode –i- Open loop pot mode. This section describes the operating procedure when using the system in mode –i- open loop Pot mode. Selection between the two modes of operation is made via a PC through the USB port of the laser – section 6.2. Manual operation in open loop pot mode -

1. This is a Class 4 Laser device: Ensure the safety notices within these Instructions and the Hazard Labels on the product, are read, noted and adhered to before any operation is attempted. If in doubt consult your laser safety officer.

2. A 15V 10A power supply unit (PSU), enclosed in the package, is used to power the SC450 laser. This is connected via the Power D-plug on the rear panel of the laser (A1).

3. Connect the Signal D-Plug Connector to the signal port on the Laser A2. There is a remote interlock facility via the Signal D-plug (Loop Wire) (A2), which will shut down the entire source when interrupted. This enables integration with any existing interlock systems within the user’s laboratory set-up.

4. Connect SMA connector (A3) to an oscilloscope via a 50Ω coaxial cable to view the pulse train from the master source.

5. When power is removed from the SC450 laser, an in-built time delay of approximately 10 minutes is applied by onboard software which delays enabling of the oscillator. This delay is added as a precaution to allow for stabilization of the laser internal temperature. After powering up the laser, a 10-minute delay should be expected before continuing with this procedure..

6. The master source does not require any adjustments and self-starts mode-locking operation once enabled. The unit is enabled by pressing the green push button (A4), resulting in illumination of the push button



and self-starting of the master source. Correct operation of the master source is indicated by a pulse train on the scope which should be seen immediately on enabling of the instrument. In the absence of a scope, the master source mode lock indicator (A4) will illuminate to indicate the Master source is operating correctly.

Note – -i-The photodiode monitors a tap-output from the master source, through

a polariser. Pulses of equal amplitude, as shown in the figure above, demonstrate that all pulses have the same state of polarization. Since the output is monitored via a polariser, some variation in the amplitude of the pulses (pk-pk measurement on the scope trace above) may be observed with time and temperature. This should not affect the overall performance of the laser.

-ii- If the scope trace shows that all pulses are clearly not of equal

amplitude but instead show obvious signs of modulation, contact Fianium for advice.

-iii- When turning the unit on in a cold environment (<20C), the master source may not self-start first time, although this is unlikely. If the pulse train is not immediately visible, or the error indicator illuminates, on switching on the unit, wait for two to three minutes, with the power on, to allow the master source to start mode locking. If there is still no pulse train on the scope, check the scope set-up and triggering and then turn the laser off and on again. If mode locking is not achieved after several attempts, contact Fianium for advice.



7. ONLY once mode locking has been established, should the high-power amplifier be turned on at the laser key switch (A5). Turning the key switch activates the pump laser to the high-power amplifier module. The laser on LED (A6) will also become illuminated.

8. When installing the SC450 into an experimental set up or system without the AOTF in place, care must be taken to avoid reflecting light back into the laser. The SC450 does not have an output isolator and hence any additional back reflected signal could destroy the amplifier and possibly the master source. There is an automatic feed back cut off within this laser, during set up if the back reflected signal goes above a set level the laser will shut down. And is indicated by the Mode lock indicator led going out.

9. The laser is provided with the drive current to the amplifier at a minimum. The amplifier drive current is adjusted by turning the pot clockwise. It is advisable that the drive current to the laser is increased relatively slowly and always turned down to low power levels before turning off the unit. The potentiometer should be returned to zero at switch off to prevent the unit being turned on at full power.

Master Source Enable Button Mode lock indicator

Key Switch

Emission Indicator LED

Power D-Plug

Master Source Monitor

10 Turn Pot

Signal D-Plug



6.2 SC450 – PC Operation

6.2.1 USB Communications

The laser is controlled using the USB interface on the rear panel. A device driver must be installed onto the PC which is used to communicate with the laser.

6.2.1.1Driver Installation The driver for the USB interface installs a virtual communications port onto the PC and allows most popular serial port applications to communicate with the Laser. Connect the device to a spare USB port on your PC. The Windows Found New Hardware Wizard will launch. If there is no available Internet connection or Windows XP SP 2 is configured to ask before connecting to Windows Update, the screen below is shown. Select "No, not this time" from the options available and then click "Next" to proceed with the installation. If there is an available Internet connection, Windows XP will silently connect to the Windows Update website and install any suitable driver it finds for the device in preference to the driver manually selected.



Select "Install from a list or specific location (Advanced)" as shown below and then click "Next".

Select "Search for the best driver in these locations" and enter the file path in the combo-box ("E:\CDM 2.00.00" in the example below) or browse to it by clicking the browse button. Note that the file is provided on the CD provided with the SC450-AOTF. Once the file path has been entered in the box, click next to proceed.

If Windows XP is configured to warn when unsigned (non-WHQL certified) drivers are about to be installed, the following screen will be displayed unless installing a Microsoft WHQL certified driver. Click on "Continue Anyway" to continue with the installation. If Windows XP is configured to ignore file signature warnings, no message will appear.



The following screen will be displayed as Windows XP copies the required driver files.

Windows should then display a message indicating that the installation was successful. Click "Finish" to complete the installation for the first part of the device driver.

Next, the COM port emulation driver is loaded as indicated in the following steps.

The Found New Hardware Wizard will launch automatically to install the COM port emulation drivers. As above, select "No, not this time" From the options and click "Next" to proceed with the installation.



Select "Install from a list or specific location (Advanced)" as shown below and then click “Next".

Select "Search for the best driver in these locations" and enter the file path in the combo-box ("E:\CDM 2.00.00" in the example below) or browse to it by clicking the browse button. Once the file path has been entered in the box, click next to proceed.



If Windows XP is configured to warn when unsigned (non-WHQL certified) drivers are about to be installed, the following screen will be displayed unless installing a Microsoft WHQL certified driver. Click on "Continue Anyway" to continue with the installation. If Windows XP is configured to ignore file signature warnings, no message will appear.

The following screen will be displayed as Windows XP copies the required driver files.



Windows should then display a message indicating that the installation was successful. Click "Finish" to complete the installation for the device driver.

Open the Device Manager (located in "Control Panel\System" then select the "Hardware" tab and click "Device Manger") and select "View > Devices by Connection", the device appears as a "USB Serial Converter" with an additional COM port with the label "USB Serial Port". Note down the COM port number as this is used in the next section.

6.2.1.2 Communications software The laser can be operated using a PC software application called “HyperTerminal.” This application has been included with most versions of the Windows operating system. In Windows XP SP2, the program can be started by navigating to the Programs -> Accessories -> Communications menu folder and then selecting the HyperTerminal application.



When the program starts, the following window is displayed. A name should be created for the connection between the PC and the SC450 Source. An example could be “SC450.” This name is used as a filename for storing the configuration settings defined in this section. An icon can be chosen to be associated with the filename.

Once a name and icon have been chosen, the OK button should be selected to clear the window and display the interface configuration window.

The window above shows an example of the port used (COM3) on a particular PC. The correct COM port to be used was noted down at the end of the driver installation section.



The OK button should be selected to allow the port settings to be configured. As in the image below, the port should be configured to transfer 19200 bits per second, 8 data bits, No parity, 1 Stop bit and No Flow Control.

The window below shows the main communications window. The <Enter> key should be pressed to confirm that the laser is able to talk to the PC. The command “V?” can also be typed to display the version and release date of the control software within the laser.



6.2.1.3 Command List

The following commands are available on the USB interface.

Command Data Description

A? Get Alarms.

A= 0 Clear all alarms.

B? Get back reflection photodiode value

H? Display list of commands.

I? Get status display interval

I= 1 Set status display interval

M? Get laser control mode

M= 0 or 1 or 2 Set laser control mode

P? Get preamplifier photodiode value

Q? Get amplifier control DAC value

Q= Set amplifier current control DAC value in USB mode

V? Get control software version and release date.

W? Get laser operating time counter.

X? Get status display mode

X= 0 or 1 Set status display mode

In general, most of these commands will only be required for diagnostic purposes if the laser shows signs of poor performance. During operation in USB mode, the key commands required will be – - M? Reports on the current mode of control – see section 5.3 - M=* Where * is 0, 1 or 2 and refers to different modes of amplifier control (section 5.3)



- Q= **, where ** is a number from 0 to 3200, with zero corresponding to the amplifier in the off state and 3200 being full power, corresponding to 10 turns of the manual potentiometer in open loop Pot mode. - Q? Reports the current setting of Q - Fianium will supply details of any other commands upon request.

6.3 Control summary

The laser can be controlled using one of three methods. The control mode is defined using the M= command. In all three modes the laser will operate in open loop mode – the output power is not maintained and can be affected by ambient air temperature. The control mode selected is stored in long term flash memory. This means that when the laser is next switched on, the operating mode is remembered.

1. Pot controlled open loop mode (M=0). In this mode, the potentiometer on the front panel is used to set the amplifier current and therefore the output power.

2. USB controlled open loop mode (M=1). In this mode, the Q= command is

used on the USB interface to set the amplifier current and therefore the output power.

3. External voltage controlled open loop mode (M=2). In this mode, a

voltage within the range 0V up to +5V DC is applied to pin 3 of the external control port. This control voltage is used to set the amplifier current and therefore the output power

6.4 Alarms When an alarm occurs, the laser is disabled and the LEDs on the front panel will switch off. The alarm can be identified using the “A?” command and can be cleared by using the command A=0. In general, if an alarm is persistently raised, please consult Fianium for advice.

1. Output power failure alarm. Current is being applied to the laser diode drivers but no output power has been detected above a defined threshold. This error can be caused by one of two events:-

i. Fibre break in the optical path. This should be checked by re-enabling the laser. If the alarm is repeated, then the laser should be shutdown and the fault reported to Fianium Ltd.

ii. The key switch has been switched off while the laser is emitting power. This event can be cleared without any risk of damage. The laser should be closed down safely by first setting the required power to 0W using either the



potentiometer, the USB Q=0 command or setting the external control voltage to 0V and then by turning the key switch off.

2. Mode Lock alarm. The master source is no longer oscillating reliably. The response time between the failure and this alarm being asserted is 20us.

3. 25% Power drop alarm. An internal monitoring photodiode has measured a sudden drop in the preamplifier power. The laser has been shutdown automatically. 4. Back reflection alarm. A backwards facing photodiode, within the laser, has detected a light level above a predefined level. This can be caused by pointing the laser output at a reflective surface. The laser has been shutdown to prevent damage. 5. Laser driver failure alarm. One of the laser diode drivers has failed. The rest of the laser has been shutdown to prevent further damage.

6.5 Status LEDs

1. Push button LED. Green. This LED will glow when the seed and master source oscillator have been enabled. They are enabled by pressing the push button in. The LED will switch off if an alarm is generated.

2. Laser Emit LED. Green 3mm. When the high power laser output is

enabled, the LED will glow green. The high power laser output is enabled using the key switch.



7. SC450 and AOTF Integration The SC40-AOTF is supplied with the supercontinuum and AOTF systems separated. In order to use the SC450 integrated with the AOTF, the following mechanical assembly (section 7.1) and software installation (section 7.2) must be carried out.

7.1 SC450-AOTF Mechanical Assembly The AOTF system comprises two units, an RF driver and DDS unit and an AOTF and filter head.

** Note – The RF Driver assembly also has an on/off swith mounted on the rear panel. The RF driver should only be powered up when a load (the AOTF) is connected to the output –Always Connect the AOTF SMA to the front panel SMA of the RF driver before powering up the unit!

7.1.1 RF Driver Connection

Connect the front panel of the RF driver (SMA) to the AOTF SMA on the rear of the AOTF Head using the 1.5m long SMA to SMA co-axial cable provided. Connect the 24V DC power supply to the RF Driver unit at the 9-Way D-socket. The RF Driver unit is powered up when the rear-panel switch is on (1). Only with the RF driver unit on, can PC communication be established with the AOTF DDS driver.

RF Driver AOTF

Filter

USB

Connector

24V Power

connector

RS232

connection

SMA – to

AOTF



7.1.2 AOTF Head

The AOTF head comprises an adjustable mount for the SC450 collimator assembly, an AOTF with SMA and temp-compensation connector at the rear of the unit, four mirrors with high reflectivity in the visible region of the spectrum and high transmission to IR (wavelengths > 820nm) which steer the beam within the head and an AOTF positioned within the beam path. The SC450 output collimator fits directly into the socket at the rear of the AOTF head as shown below. A spring plunger mounted on the base of the AOTF head, below the collimator socket, should have been loosened to enable removal of the collimator. This spring plunger should be tightened again when the collimator is in place and aligned correctly.

The SC450 collimator has an alignment mark etched on its outer surface which, if aligned to the corresponding mark on the AOTF head, should help ensure good alignment of the SC450 beam through the AOTF. With the collimator is in place, further alignment requires that an output from the SC450 and correct functioning of the AOTF.

Collimator

Alignment

marks



7.2 AOTF Operation

7.2.1 Driver Installation

Install the CD provided with the SC450-AOTF and select Install.exe in folder - /8 Channel AOTF Drivers/Installer, resulting in the following window –

Close all running applications within Windows and select “Next>”, displaying the following window -



Select a preferred location for the program files or simply accept the default location and select “Next>”, displaying the following window –

Select “Next>” to begin installation, resulting in the following installation status window-



When the green bars reach the end of the row, installation is complete resulting in the following window –

Select “Finish” and the AOTF driver installation is complete.

7.2.2 GUI (Graphical User Interface) Installation

Three GUI’s are provided with the AOTF/DDS hardware, all provided on the CD supplied with the laser system, within a folder - /8 Channel AOTF Drivers/… The contents of this folder should be copied either to the PC desktop or another preferred position within the users PC. The folder contains the GUI’s but also contains libraries and calibration data required for operation of the software and communication between the AOTF and DDS. The three GUI’s have varying levels of complexity –

7.2.2.1Supercontinuum color- Supercontinuum colour is a very simple GUI, mainly used by Fianium as a form of demonstration. The figure below shows the general facilities provided by this GUI. The GUI provides access to the command line with which commands can be sent to the AOTF to set wavelengths, frequencies, RF amplitudes, calibration figures etc.



The GUI provides simple control of the wavelength and RF amplitude of each AOTF channel. A channel is selected by clicking on the On/Off pad for a given channel, producing a bright green button when the channel is in the ON state. Wavelength can be selected by either typing in the value in the wavelength box for each channel, OR using the PC mouse or mouse-pad, by clicking (and holding) on the slider for each channel, dragging it along the color slide and letting go when the correct wavelength is selected. On letting go of the mouse button, the command is sent to the AOTF and the channel wavelength should be selected. The RF drive power per channel can be set at any level between 0 and 16383. The RF drive power adjusts the efficiency of the AOTF for a given wavelength, providing a means of wavelength power control up to a certain level, when the RF signal saturates the AOTF and the resulting channel spectrum becomes distorted. Because of the AOTF dynamics and efficiency as a function of wavelength, the RF levels need to be calibrated to meet the application requirements. At any time, if the wavelength and power settings within the GUI should be saved, this can be achieved by clicking the “Save Spectrum” button on the GUI. If the GIU is closed and these settings should be restored, “Load Spectrum” should be selected.



Many additional features of the AOTF and DDS are accessible through the Command string and other GUI’s. Further details are available from Fianium or through Crystal Technology Inc.

7.2.2.2 Supercontinuum Controller A second GUI developed for the SC450 is the supercontinuum controller, which has all of the functions of the Supercontinuum Color GUI, but without the color slider bars. Otherwise all other features are very similar.

A screen print of the Supercontinuum Controller GUI panel is shown below.

7.2.2.3 AODS Controller The AODS controller overleaf is the standard GUI provided by Crystal Technology Inc. with their 8-Channel AOTF system. This GUI contains all of the currently available features of the DDS and AOTF system, but requires either the input of an RF frequency (rather than wavelength entry) for each channel. Alternatively, the Command String can be used to enter the wavelength once the tuning parameters for the AOTF have been entered. Additional features include the use of FSK (Frequency Shift Keying) which allows up to 4 pre-set frequencies for each of the 8-channels, whereby switching



between these frequencies can be made at very high speeds, either through PC or hardware control via the RS232 input on the RF amplifier housing - further details on request from Fianium and Crystal technologies Inc.

7.2.3 AOTF Calibration

Wavelength calibration of the AOTF is provided through a .txt file (tuning curve 95-02934-03.txt) with a set of polynomial coefficients used to fit the Wavelength Vs RF Frequency calibration data to a polynomial curve. This .txt file should be installed within the same folder as the GUI executable files and the polynomial calibration coefficients are automatically used when issuing wavelength commands to the AOTF. The absolute wavelength calibration of the AOTF does have some level of higher order dependence on temperature. It is possible to compensate for this temperature dependence via the DDS through a second RF cable attached between the DDS and the AOTF. This cable can be supplied separately, as can details of the operation of the system when using the temperature compensation facility.



7.3 AOTF Alignment Using the Supercontinuum color or Supercontinuum controller GUI, establish communication between PC and the AOTF RF driver and, with the SC450 on and with the potentiometer turned at least 2-turns to provide output power in the red part of the spectrum, select a single channel of the AOTF and choose a wavelength in the red – for example 633nm. In this condition, if the SC450 collimator is correctly positioned within its socket on the AOTF head, the diffracted 1st order 633nm beam through the AOTF should exit the AOTF head through the output hole within the 4-axis manipulator. To determine that the output beam is the required diffracted 1st order, increase the number of turns on the SC450 potentiometer and change the wavelength on the AOTF towards the yellow part of the spectrum (for example 570nm). The output beam colour should change from red to yellow when the new wavelength is selected. If the output beam does not respond to the AOTF, then it is likely that optical alignment has been lost and the zero or -1 order of the AOTF has become aligned to the output. In this case, or in the case where no light exits the optical head enclosure (ensuring that the mechanical shutter is open), the SC450 collimator optic must be re-positioned within the socket. Re-alignment of the collimator is achieved by – -1- Loosen the small grub screw mounted on the underside of the AOTF head and adjust the four collimator adjustment screws mounted on the rear and side of the head. Centre the diffracted output beam within the exit hole of the AOTF head, using the SC450 collimator adjustment screws mounted on the top and sides of the AOTF head. If using the AOTF output directly, a suitable pin-hole may be required at the output of the AOTF head.



8. Customer Service

In the unlikely event of a malfunction within the SC450, contact Fianium Ltd for onsite diagnosis or return. If the product is to be returned to Fianium, ensure that all relevant return documentation is included within the shipment. Details of the documentation required can be obtained from Fianium Ltd. The SC450 should be returned within the original packaging and include all accessories and documentation as originally delivered in order to prevent damage to the product during transport. If the original packaging is unavailable, please contact Fianium Ltd for a replacement.

End of document

Sc450 2 Aotf Manual v1.1

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Transcript of Sc450 2 Aotf Manual v1.1