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7. Fibre coupling

The output beam profile of a

diode can be highly irregular and highly

astigmatic. Nevertheless it is still possible to achieve good coupling into a

singlemode fibre. Some examples of fibre coupling efficiency are provided

in the figure below. Fibre coupling efficiency varies from diode to diode

due to many factors, so as a guide net coupling efficiency from fibre coupler

(FC) input power to FC output power is generally 50% or better, and 60%

is not unusual, despite Fresnel losses at each facet of the fibre (8%).

50%

52%

54%

56%

58%

60%

62%

64%

66%

68%

ber

f s

tem

Fibre coupling e

ﬃ

ciency

Fibre coupling e

ﬃ

ciency

Figure 7.1:

Measured fibre coupling efficiency for 20 fibre coupled

systems

ranging from 670nm to 1080nm with input powers from 500mW to 3000mW. The

average result is 57% for this sample set.

The

output beam profile and astigmatism both vary with operating cur-

rent. It is thus advised to correct

beam astigmatism at high current

(or your desired operation current)

before

attempting fibre coupling (see

Chapter 6). Note that

operating powers typically exceed the damage

threshold tolerance at fibre facets and thus it is easy to damage fibre facets

if attempting to correct astigmatism at high currents

during

fibre coupling.

Содержание MOA

Страница 1: ...Amplified laser system Model MSA internal seed Model MOA MOA L MOA C external seed Revision 2 00 ...

Страница 2: ...quential damages in connections with or arising out of the performance or use of any of its products The foregoing limitation of liability shall be equally applicable to any service provided by MOGLabs Copyright Copyright MOG Laboratories Pty Ltd MOGLabs 2017 2021 No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechan...

Страница 3: ...nly MOA or with seed laser MSA Con figurations may include input and or output fibre coupling and input and output Faraday isolators The MOGLabs DLC and LDD drivers are ideally suited for operating the seed and amplifier components of the amplifier system We hope that the MOGLabs optical amplifier system can work well for your application We are proud of our products and continuously improving the...

Страница 4: ...ii ...

Страница 5: ...appropriate input seed Operation exceeding that condition can cause fatal structural degradation of the TA diode Refer to the Maximum current unseeded specified in the amplifier test report CAUTION USE OF CONTROLS OR ADJUSTMENTS OR PERFORMANCE OF PROCEDURES OTHER THAN THOSE SPECIFIED HEREIN MAY RESULT IN HAZARDOUS RADIATION EXPOSURE Laser output from the MSA and MOA can be dangerous Please ensure ...

Страница 6: ...ed amplifier TA diode so that most of the electrical input energy is converted to optical output rather than lost as heat which would damage the TA diode NOTE The MOGLabs MSA and MOA are designed for use in scientific re search laboratories They should not be used for consumer or medical applications Protection Features The MOGLabs MSA and MOA include a number of features to protect you and the de...

Страница 7: ...1 Manufactured JUNE 2017 Complies with 21 CFR 1040 10 and 1040 11 except for deviations pursuant to Laser Notice No 50 dated 24 June 2007 MOG Laboratories Pty Ltd 49 University St Carlton VIC 3053 AUSTRALIA AVOID EXPOSURE VISIBLE AND INVISIBLE LASER RADIATION IS EMITTED FROM THIS APERTURE Aperture label engraving US FDA compliance Warning and advisory label Class 4 IEC 60825 1 2007 AS NZS 2211 5 2...

Страница 8: ... June 2007 MOG Laboratories Pty Ltd 49 University St Carlton VIC 3053 AUSTRALIA Model number MSA003 Serial number A41706002 Manufactured JUNE 2017 Complies with 21 CFR 1040 10 and 1040 11 except for deviations pursuant to Laser Notice No 50 dated 24 June 2007 MOG Laboratories Pty Ltd 49 University St Carlton VIC 3053 AUSTRALIA FDA compliance and serial number Laser warning advisory Figure 2 Schema...

Страница 9: ...nment 9 4 2 Substantial adjustment to seed alignment 10 5 MOA external seed alignment 19 5 1 Seed alignment 19 5 2 Reverse propagating TA diode beam collimation 24 6 Output beam optimisation 27 6 1 Procedure for output beam optimisation 28 7 Fibre coupling 31 7 1 Fibre alignment touch up 33 7 2 Fibre alignment procedure 35 7 3 Fibre coupler collimation 38 7 4 Troubleshooting 39 8 Diode replacement...

Страница 10: ...viii Contents A 1 Amplifier headboard MOA MSA 45 A 2 Connector pinouts 48 B Chassis dimensions 51 ...

Страница 11: ...s in the MSA The MOA is an amplifier only configuration of the MSA without built in seed laser There are two smaller versions of the MOA the MOA L with one isolator on the TA output and the compact MOA C without isolators Fibre coupling options are available for the MSA MOA MOA L output and for MOA MOA L input with an external seed laser The TA diode is mounted in a block U chassis with aspheric i...

Страница 12: ...iode orientation with the small area ridge waveguide on the input side and large area tapered waveguide on the output side The input lens focuses the seed laser onto the input waveguide of the TA diode The output lens collimates the amplified TA laser beam emitted from the output waveguide In normal operation the seed laser should provide a collimated beam of 10 to 60 mW The minimum seed power req...

Страница 13: ...ong their paths and parallel linear polarisation The MOGLabs am plifiers have a zero order half wave plate installed for adjusting the seed polarisation to match the TA diode Usually the half wave plate is installed in the end cap of the input isolator in MSA systems or on the chassis for MOA systems see figs 4 1 4 3 and 5 1 The main TA output beam propagates through a high power Faraday iso lator...

Страница 14: ...4 Chapter 1 Introduction ...

Страница 15: ...rlock switch located along the top edge of the chassis is activated if the cover is removed while the TA injection current is above the Maximum current unseeded current see fig 1 1 The interlock can be defeated for alignment and test purposes by holding the switch actuator down for example with adhesive tape or by changing the interlock mode under the headboard settings in the LDD menu 2 2 Photodi...

Страница 16: ...separate mount with a dedicated fused silica beam sampling optic Please be aware that any changes in optical alignment that affect the output beam and or reflected signal from the cylindrical lens will require re calibration of the photodiode threshold as described in the LDD user manual ...

Страница 17: ...e provided for connection to 4 mm OD optionally 6 mm tubing but for most applications water cooling is not required dissipation to the air and or optical table is sufficient Proceed with the following steps for initial installation 1 The MOGLabs amplifier chassis should be firmly mounted to an opti cal table or other stable surface using the mounting through holes suitable for both metric and impe...

Страница 18: ...diode 6 For future reference record a power vs current PI curve for the main output beam of the unseeded TA diode NOTE Some power sensors e g Si photodiode have a highly reflective surface To avoid damage to the TA diode ensure the sensor is not close to normal incidence relative to the TA emission 7 For MSA systems power on the seed laser to a suitable current according to the system test report ...

Страница 19: ...re 4 1 optimise the seed alignment using the procedure outlined below 1 Ensure proper seed laser operation according to the instructions provided in the MOGLabs CEL cateye laser user manual 2 Take note of the Maximum current unseeded listed in the MSA test report and the maximum expected output power at this TA current 3 Terminate the TA output beam path with a power sensor rated to at least the p...

Страница 20: ...g procedure a Measure the TA output power while making small e g 1 16 turn adjustments to the horizontal axis of M1 until the output power is maximised b Adjust only the horizontal axis of M2 to further optimise PREF c Repeat above two steps until PREF is optimised d Repeat the above steps for the vertical axis of M1 and M2 until PREF is optimised 6 Compare the recorded power of the TA with the ap...

Страница 21: ...h a power sensor rated to at least the power noted in step 1 preferably after the isolator at location E in fig 4 1 NOTE Measuring the TA output power before isolator could damage the TA diode with a back reflection from the power sensor Take care to avoid normal incidence reflections NOTE If a sufficiently slim power sensor is not available insert a mirror in the beam path after preferably or bef...

Страница 22: ... required Adjust the reverse propagating beam divergence by rotation of the TA input lens mount using the supplied lens tube spanners see fig 1 2 and fig 4 2 There is an outer tube spanner for loosening the retaining lock ring and an inner tube spanner for adjusting the lens focus Make sure to tighten the retaining ring once the lens position has been adjusted The beam spot size should be as small...

Страница 23: ...ransmission efficiency of the Faraday isolator s If the amplifier configuration has two input isolators the isolator close to the seed laser should be installed first Compare the isolator efficiency with the efficiency value specified in the system test report If the value from the test report and the measured efficiency are different by more than 10 contact MOGLabs customer support 13 Remeasure t...

Страница 24: ...the output power by less than 25 as the alignment improves e g 10 or 5 g If the new measured power after step 15e is instead lower than PREF readjust the horizontal axis of M1 anti clockwise to return to the original angle as noted at step 15d then reoptimise the horizontal axis of M2 to return to PREF Now iterate steps 15d and 15e with an anticlockwise adjustment at step 15d h Once PREF is maximi...

Страница 25: ...d PREF with the value from the table Guide for seed coupling at low and high tapered amplifier current either Before isolator or After isolator column in the test report as appropriate 20 If PREF has been measured after the output isolator and it is not within 10 of the value given in the system test report instead mea sure and compare the TA power before the isolator for agreement If there is sti...

Страница 26: ...16 Chapter 4 MSA internal seed alignment A B E D C OUTPUT ISOLATOR CYL LENS TA DIODE INPUT ISOLATOR 1 M2 M MSA INTERNAL SEED LASER INPUT ISOLATOR 2 M1 λ 2 OPTIONAL λ 2 λ 2 ...

Страница 27: ...gure 4 2 Lens tube spanners for adjusting TA collimation lenses 0 035 or 0 9mm hex key λ 2 waveplate λ 2 waveplate Figure 4 3 Schematic diagram showing location of half wave plate in isolator endcaps Ensure set screw is loosened before rotating endcap ...

Страница 28: ...18 Chapter 4 MSA internal seed alignment ...

Страница 29: ...eed light into the TA diode polarisation and spa tial mode matching are required that is the seed beam and TA reverse propagating beam should have the same polarisation beam width and di vergence The TA input lens in the U chassis see chapter 1 is optimised by MOGLabs for a collimated seed laser Depending on the amplifier configuration the input seed laser could be fibre coupled or free space With...

Страница 30: ... of 100 mA less than the Maximum current unseeded The TA injection current should be chosen to match one of the values in the table Guide for seed coupling at low and high tapered amplifier current from column TA current mA on the test report but still be below Maximum current unseeded NOTE The TA diode injection current should not be more than Max imum current unseeded see test report NOTE Do not...

Страница 31: ...entre of the chassis input aperture and is both parallel to the long edge of the chassis 7 Adjust M1 to reflect the seed laser beam into the input isolator aper ture if installed Ensure that the seed laser beam goes through the centre of the input and output isolator apertures without clipping Measure the transmission efficiency of the Faraday isolator and if installed adjust the half waveplate in...

Страница 32: ...djustment was made e g 1 16 turn clockwise e Next adjust only the horizontal axis of M2 to maximise the out put power from the TA The adjustment range should be less than half a turn of the actuator at this step and this range should reduce upon iteration f If the new measured power is greater than PREF this higher power is the new reference power PREF Iterate steps 8d and 8e until PREF is maximis...

Страница 33: ...1 Verify optimum seed alignment by again walking the M1 M2 mirror pair according to step 8 with very small adjustments 12 Record the final TA output power PREF along with the seed power and injection current Temporarily block the seed beam and record the unseeded amplifier output power Compare the measured PREF with the value from the table Guide for seed coupling at low and high tapered amplifier...

Страница 34: ...assis For older MOA chassis this cannot be completed so skip this step 3 Allow the reverse propagating beam to propagate over 4 to 5 m in serting a mirror into the beam path to deflect the beam as required Adjust the reverse propagating beam divergence by rotation of the TA input lens mount using the supplied lens tube spanners see fig 1 2 and fig 4 2 There is an outer tube spanner for loosening t...

Страница 35: ...MOA re install the input Faraday isolator if installed Make sure the seed laser beam propagates through the centre of the iso lator input and output apertures without clipping 6 Repeat the walking procedure from section 5 1 step 8 through to the end of the section ...

Страница 36: ...26 Chapter 5 MOA external seed alignment ...

Страница 37: ...ved Typically the TA output will be fibre coupled to produce a high quality TEM00 Gaussian beam A simple measure of the beam quality is known as the M2 factor or beam quality factor M2 ω0θ π λ where ω0 is the waist radius and θ is the half angle of the beam divergence The beam quality factor provides an indication of how well the beam can be focused compared to an ideal diffraction limited Gaussia...

Страница 38: ...the TA output is incident exactly on the centre of the cylindrical lens and the TA beam passes through the centre of the output aperture on the amplifier chassis If a photodiode in installed in the TA output plate the reflection from the cylindrical lens should also be centred on this photodiode If the TA beam is not centred on the output aperture adjust the vertical and horizontal alignment of th...

Страница 39: ...n has been adjusted Use an M2 beam profiler or an external lens with an imaging sensor positioned at the lens focal distance to achieve the best collimation The major axis beam waist on the imag ing sensor should be minimised Note that the cylindrical lens will be acting on the minor slow axis which is typically the horizontal axis for almost all MOGLabs amplifiers 7 Once the beam is collimated al...

Страница 40: ...30 Chapter 6 Output beam optimisation ...

Страница 41: ...3 4 5 50 52 54 56 58 60 62 64 66 68 Number of systems Fibre coupling eﬃciency Fibre coupling eﬃciency Figure 7 1 Measured fibre coupling efficiency for 20 fibre coupled TA systems ranging from 670nm to 1080nm with input powers from 500mW to 3000mW The average result is 57 for this sample set The TA output beam profile and astigmatism both vary with operating cur rent It is thus advised to correct ...

Страница 42: ...ing silicon photodiodes can easily saturate below their maximum rated power and thus give false readings particularly when the entire sensor surface is not illuminated as for a small beam Sensors based on integrating spheres are preferred Polarisation control The polarisation of the TA output can be aligned to that of a polarisation maintaining PM singlemode fibre in two ways A half wave retarder ...

Страница 43: ...vertically and the astigmatism compen sation is optimised for the desired TA diode operating current The beam cross section should be approximately circular but achieving a symmetric aspect ratio may not be possible given the limited range of cylindrical lens focal lengths available and variations in TA diode astigmatism 1 The seed power into the TA should be set in the range of seed power recomme...

Страница 44: ...or the output power measurement where possible and if used make sure to allow for any losses due to the mirror Do not proceed unless the total net efficiency is at least 10 If this is not possible using the above procedure review the troubleshooting section 7 4 implement any changes and repeat steps 3 to 7 If the net efficiency is still not sufficient skip the remaining steps here and proceed to t...

Страница 45: ...ection 7 2 7 2 Fibre alignment procedure The following procedure can be used when substantial fibre coupling align ment optimisation is required 1 Ensure the seed power into the TA is set in the range of seed power recommended in the test report The TA injection current should be chosen to provide 10 mW before the fibre coupler 2 Adjust M3 see figs 4 1 and 5 1 so the TA output is incident at the v...

Страница 46: ...ord output to a power sensor There should be some nanowatts or more power detected when you block unblock the TA beam in front of the fibre coupler If not check your fibre patch cord end facets see section 7 4 or contact MOGLabs support for how to proceed 7 Walk the mirror pair to optimise output power as follows a For the horizontal axis first adjust M4 to achieve maximum output power from the fi...

Страница 47: ...osition with the appropriate fibre coupler focus tool provided as part of the system toolkit see fig 7 3 Make note of the direc tion of adjustment Repeat a single iteration of the horizontal and vertical walking procedure from step 7 and compare the efficiency to PREF If the efficiency is greater than the original PREF make an other tiny adjustment to the fibre coupler lens position in the same di...

Страница 48: ...ler to accom modate the changes Initially when focus is very far from optimised the fibre coupler lens collimation can be approximately set using the VFL see fig 7 2 as a light source 1 Connect the fibre patch cord to the MSA MOA fibre output connector 2 Connect the exit of the fibre to the VFL laser source 3 Examine the red beam emitted back towards the TA diode from the output fibre coupler 4 Us...

Страница 49: ...h cord Note for 780 795 nm we generally find that PM630 fibres achieve better efficiency and polarisation preservation Another frequent problem is the variation in astigmatism and thus beam collimation with injection current Changing the operating current to vary the output power of the TA diode will affect the beam collimation and thus fibre coupling efficiency At the MOGLabs factory astigmatism ...

Страница 50: ...40 Chapter 7 Fibre coupling ...

Страница 51: ...d head cables discon nected then follow these steps 1 Open the PCB cover plate underneath the chassis and disconnect the diode anode and cathode wires at the PCB The diode connectors are labelled on the PCB If the diode connectors are laying flat on the PCB Hirose lever the connectors up gently from the wire entry end of the connector If the diode connectors are standing upright from the PCB JST g...

Страница 52: ...serted in the connector 3 Remove the lens tube locking rings using the focus tool s pro vided see fig 1 2 Rotate the TA input and output lenses counter clockwise to pull the lenses away from the diode taking note of approximately how many rotations you make Four full rotations should be sufficient for the lenses to be well clear of the copper mount 4 Referring to fig 8 4 remove the 4x screws secur...

Страница 53: ...lock as you tighten the M2 screw When soldering the cathode ribbon to the turret pin use low temperature silver solder Do not resolder until the TA diode is firmly attached to the copper to act as a heatsink 6 Install the new TA diode mounted on the MGM 068 mount by fol lowing the steps in reverse taking care to replace the dowel pins and threading the diode wires which have crimp terminals but no...

Страница 54: ... tempera ture approaching the set point followed by powering on the current controller at 100 mA Referring to the test report table Guide for seed coupling at low and high tapered amplifier current set the TA diode injection current to a value where you expect a few mW of Unseeded light and verify that some output light is visible on an IR viewing card 9 Restore the lens collimation see Chapter 6 ...

Страница 55: ...ier headboard MOA MSA The amplifier is connected to a controller via a B1048 B1055 or B1056 headboard figs A 1 A 2 which provides connections to the TA diode TEC and a passive NTC thermistor temperature sensor Connections from the B1048 B1055 boards to the components use Hirose DF59 swing lock wire to board connectors B1056 uses JST EH series connectors There is also a photodiode amplifier which c...

Страница 56: ... U 1 R2 R13 C14 R12 R 8 C3 C4 C11 C13 R 10 C 15 R 14 R 16 S W 1 U2 R 15 U 3 R 11 U 5 C 12 R1 R4 LE D1 C16 C17 D2 R L1 U4 P1 Temp P7 Current Interlock LED Las_A Las_A Las_K Las_K Pelt2 Therm PD Pelt1 R8 U7 R3 R1 C9 R7 C3 C12 R10 C8 C6 R5 R12 R13 FB1 C20 D1 R19 R18 C5 C1 R2 R15 C7 C4 Q1 R20 R9 R17 C19 U1 C2 R6 C10 LED1 U2 C17 C15 R14 R16 C14 C13 D2 C18 SW1 R11 U5 R21 R4 C16 RL1 C11 U3 U6 L1 P1 Temp ...

Страница 57: ...onnection 1 Pelt2 TEC connection 2 Las A Laser anode Las K Laser cathode Figure A 3 B1048 and B1055 B1056 headboard connector legend The two TEC connections each have polarities and should be connected in parallel to provide greater current carrying capacity Each of the laser anode and cathode connectors have two pins connected in parallel ...

Страница 58: ...ode anode 3 Photodiode status 11 5 V 4 Laser diode cathode 12 I2C SCL 5 Laser diode anode 13 Laser diode cathode 6 0 V ground 14 Laser diode cathode 7 0 V ground 15 Laser diode anode 8 0 V ground Figure A 4 DE15 female current supply connector P6 P7 pinout Relay should be grounded to open the protection relay and enable operation ...

Страница 59: ...mperature Pin Signal Pin Signal 1 Thermistor NTC 10 kΩ 6 Thermistor NTC 10 kΩ 2 0 V ground 7 Peltier TEC 3 Peltier TEC 8 Peltier TEC 4 Peltier TEC 9 Peltier TEC 5 Peltier TEC Figure A 5 DE9 female temperature supply connector P1 pinout ...

Страница 60: ...50 Appendix A Electrical connections ...

Страница 61: ...B Chassis dimensions MSA MOA amplified laser BOTTOM VIEW 155 OA 300 OA 62 60 36 35 92 60 58 C L 58 40 35 225 228 60 9 127 5 125 51 ...

Страница 62: ...52 Appendix B Chassis dimensions MOA L standard amplifier 290 58 36 5 95 92 6 100 101 6 75 76 2 61 4 ...

Страница 63: ...53 MOA C compact amplifier 92 6 95 0 160 50 8 50 0 75 0 76 2 58 ...

Страница 64: ......

Страница 65: ...r amplifier based on a semiconduc tor tapered amplifier Appl Opt 37 4871 1998 3 2 JCB Kangara AJ Hachtel MC Gillette JT Barkeloo ER Clements et al Design and construction of cost effective tapered amplifier systems for laser cooling and trapping experiments Am J Phys 82 805 2014 http doi org 10 1119 1 4867376 3 55 ...

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