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APPENDIX B - Mode hops

Mode hops are discrete jumps in wavelength when the laser, due to some reasons,
finds it more favourable to abandon the present longitudinal mode and start lasing at
a neighbouring longitudinal mode. The size of the discrete jump in wavelength is set
by the actual design of the laser cavity. Adjusting the temperature of the laser cavity
moves the absolute wavelength at which a mode hop occurs. The mode hop, if pre-
sent, will be visible as a discontinuity in

e.g.

wavelength

vs

control voltage plots.

Figure 6-1 (below) shows the mode hop free areas for the PICO D laser. Note that
the wavelength range for areas b and c are 50 nm as a target specification. Note
also that area b and c are totally independent of each other concerning the wave-
length limits.

Figure 6-1 Mode hop free region. Areas a, b, and c indicate mode hop free region
in swept wavelength mode.

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Summary of Contents for PICO D

Page 1: ...PICO D USERS MANUAL ...

Page 2: ...2 This page is intentionally left blank Thorlabs Sweden AB Göteborg Sweden Document info 740 OSL 103 XXX PA1 PICO D Maual doc LS 2 10 2005 7 41 ...

Page 3: ...n temperature The PICO D is not designed for outdoor use Protect the equipment from rain and snow Make sure that the equipment is not exposed to dust dusty air con densing humidity or equivalent Always store and use the PICO D in a vertical position as further described in the manual Handle with care when unpacking the PICO D The original transport case supplied by Thorlabs Sweden AB should always...

Page 4: ...ason for failure of electronic equipment The total operating time can be reduced if precautions against ESD damage are not taken See Figure 0 1 WARNING Always wear an ESD wrist strap connected to the ESD terminal whenever han dling boards and units Figure 0 1 The ESD wrist strap The wrist strap is connected to ground to ensure that no electrostatic field is built up ...

Page 5: ...DITIONS 15 2 5 ELECTRICAL INTERFACES 16 2 5 1 GROUNDING ISSUES 19 2 5 2 POWER SUPPLIES 20 2 5 3 DIGITAL CONTROL AND STATUS SIGNALS 21 2 5 4 ANALOG CONTROL SIGNALS 25 2 5 5 ELECTRICAL POWER AND SIGNAL CONNECTORS 28 2 6 OPTICAL INTERFACE 31 2 6 1 FIBER OPTICAL CONNECTOR 31 3 OPERATION 32 3 1 SWITCHING ON THE PICO D 32 3 2 SWITCHING OFF THE PICO D 33 3 3 CALIBRATION OF PICO D 33 3 3 1 CALIBRATION MET...

Page 6: ...6 APPENDIX B MODE HOPS 41 APPENDIX C DEFINITIONS ACRONYMS AND ABBREVIATIONS 43 APPENDIX D CHECK LIST FOR FAILURE REPORT 44 ...

Page 7: ...r inte referenskälla Some of the highlighted features are described below High absolute accuracy means no need for frequent calibrations Good repeatability results in consistent measurements Truly continuous smooth tuning i e small tuning speed variations no back ward movements or mode hops are important for many applications such as in terferometry and fiber sensing Narrow linewidth is prerequisi...

Page 8: ...ident may occur if the safety precautions or the instruc tions are neglected This type of accident may be fatal or cause serious injury It may also damage the product IMPORTANT This is an example of an IMPORTANT message WARNING This is an example of a warning message ...

Page 9: ...in measure versus wavelength is performed Each application requires de tailed knowledge on some or all parameters characterizing a TLS e g wavelength range side mode levels spontaneous noise levels line width sweep characteris tics 2 2 Brief system overview PICO D see Figure 2 1 is a Tunable Laser Source TLS based on a semiconduc tor laser mounted in a Littrow external cavity laser geometry This t...

Page 10: ...e 2 1 The output beam is collimated and sent through an optical isolator before the beam is launched into the optical fiber Due to the analog interface PICO D is easy to integrate in the user s system configu ration The user supplies an analog signal to tune sweep the laser between the minimum and maximum wavelengths defining the tuning range The tuning of PICO D is truly continuous The output wav...

Page 11: ...sensor mechanics The outer casing is made of metal and a layer of thermal isolating material Furthermore there is a mag netic shield made of a high permeability material for preventing external magnetic fields to interfere with the motor coils All lasers and especially lasers having a resonator cavities defined by mechanical tolerances are delicate precision instruments and they must be handled ac...

Page 12: ...12 Warm air outlet Warm air outlet Cold air inlet Cold air inlet Figure 2 2 The PICO D case bulk head version All measures in millime ters ...

Page 13: ...CO D front panels Both bulkhead fiberoptical connector and pigtail options are available All measures in millimeters Com pare Figure 2 2 Figure 2 4 Mechanical dimensions om PICO E side view All measures in milliters Compare Figure 2 2 ...

Page 14: ...is specified in Figure 2 6 the hole patterns on either long side of the unit are identical The weight of a PICO D unit is 1 8 kg Figure 2 5 PICO D physical layout PICO D should always be mounted and stored in vertical position as indicated by the leftmost arrow in the figure above Optical bulkhead connecter is available at the front to the left Electrical connectors for power and interface are ava...

Page 15: ...r mounting PICO E The holes are threaded M3 all measures in millimeters Compare Figure 2 2 2 4 2 Environmental Conditions WARNING Sudden changes in temperature should be avoided as this may cause conden sation on the optical equipment that could have a negative influence on the performance of the device ...

Page 16: ... 61000 4 2 4 3 4 4 4 5 4 6 and 4 8 Imunity against radiation according to ENV 50204 2 4 2 1 3 Safety standards EN 61010 1 UL 3101 1 According to IEC 60825 1 edition 1 2 2001 08 laser safety the PICO D is classified as 1M IEC 825 laser safety 2 4 2 1 4 Exceptions and Extensions to Standards Compliance Operating temperature range 10 to 40 C Dew point 26 C non condensing environment RH 85 30 C Extern...

Page 17: ...aph 2 5 4 1 DC voltage low noise 1 V 10 V for setting the optical output power level see paragraph 2 5 4 2 Setting appropriate digital control signals 0 V 5 V logical levels see para graph 2 5 3 1 Reading the status of appropriate digital status signals 0 V 5 V logical levels paragraph see 2 5 3 3 The electrical signals are accessible via the two connectors located on the rear side of PICO D see F...

Page 18: ...ING Analog Control 10 V to 10 V _MODE_HOP_ADJUST Analog Control 10 V to 10 V _OPTICAL_POWER Analog Control 1 V to 10 V _MODE _HOP _ADJUST _ENABLE Digital Control On 0 V Off 5 V _OPTICAL_POWER_ENABLE Digital Control On 0 V Off 5 V _WAVELENGTH_TUNING ENABLE Digital Control On 0 V Off 5 V _COHERENCE _CONTROL ENABLE Digital Control On 0 V Off 5 V _CONSTANT _CURRENT _ENABLE Digital Control On 0 V Off 5...

Page 19: ...one connector for the control and status signals Both connectors have pins connected to ground ALL pins see Table 2 10 and Table 2 11 labeled GND are physically joined inside PICO D We recommend that PICO D is connected to the signal ground via the electrical power connector in Table 2 10 all Row B pins are 0 V and physically joined This connection scheme ensures that the 5 V 15 V and 15 V supplie...

Page 20: ... required voltages and Table 2 3 list the requirements set on the power supplies and finally Table 2 10 lists the pin configuration of the DC power connector The full pin configuration of the PICO D power and signal connectors are shown in Figure 2 15 Table 2 2 DC power supply Voltage Comments 5 V 5 volts supply GND 5 V Return for 5V connected to the circuit board ground 15V 15 volts supply ...

Page 21: ... Overall power consumption 20 W The electrical power is connected to the top 6 pin connector located at the rear side of PICO D see Figure 2 8 2 5 3 Digital control and status signals 2 5 3 1 Definition of the logical states The digital control signals are defined with 0V LOW as ON TRUE active able and with 5 V HIGH as OFF FALSE inactive disable IMPORTANT If the input signal is not connected its d...

Page 22: ...ABLE When enabled the cavity temperature can be adjusted to compensate for mode hops Figure 2 10 Digital input circuitry 2 5 3 2 2 Digital control _WAVELENGTH_TUNING_ENABLE When digital control signal _WAVELENGTH_TUNING_ENABLE is set to LOW 0 V the unit is ready to accept and respond to wavelength tuning using analog control WAVELENGTH_TUNING see 2 5 4 1 When _WAVELENGTH_TUNING_ENABLE is set to HI...

Page 23: ...re 2 5 3 3 Digital status signals The digital status signals are defined having 0V LOW as ON TRUE ERROR and 5 V HIGH as OFF FALSE Safe The digital status signals can be read form the in terface Carefully read paragraph 2 5 3 1 Definition of the logical states before con necting PICO E The digital output circuitry is shown in Figure 2 11 Table 2 5 The digital status signals Name Short description _...

Page 24: ... control signal see 2 5 4 2 When digital status signal _OPTICAL_POWER_ERROR is FALSE HIGH 5 V the difference between output optical power and set wavelength is within specifications If the OPTICAL_POWER see 2 5 4 2 is increased beyond the voltage corresponding to a maximum recommended laser diode drive current the _OPTI CAL_POWER_ERROR will change its logical state to TRUE LOW 0 V A further increa...

Page 25: ...ons of this order are easily disturbed by stray ground return potentials that typically can be tenths of volts In or der to ease customer requirements we have incorporated a differential input ampli fier see Figure 2 12 with very high CMRR Common Mode Reaction Ration Note that this is a differential input stage and that e g both voltages labeled and must be connected Table 2 6 The analog control s...

Page 26: ...st be of high quality and noise free The fol lowing example illustrates this critical issue Assume that 110 nm tuning range i e 110 000 pm is achieved by a 20 V control voltage peak to peak This means that the voltage step is 20 V 110 000 pm 180 µV pm Alternatively a D A converter resolution better than 2 log 110 000 16 7 bits Hence a D A converter with minimum 18 bit capacity is recommended 2 5 4...

Page 27: ... state to TRUE LOW 0 V A further increase of OPTICAL_POWER will for some laser units further increase the optical output power The increase will vary from individual to individual The PICO D control elec tronics will protect the laser diode however it is not recommended to operate the la ser if the _OPTICAL_POWER_ERROR is TRUE LOW 0 V Minimum optical power is difficult to define this state is clos...

Page 28: ... located on the rear side of PICO D see Figure 2 8 The top connector 6 pin is the power connector whereas the 40 pin connector carries all digital and analog signals Figure 2 15 show the pin configuration of the two connectors The electrical power connector carries all the required DC power lines Note in Table 2 10 the increased recommended cable area for the 5 V supply Table 2 11 lists the signal...

Page 29: ...lu sively for internal use Compare Figure 2 8 The full pin configura tion of the PICO D power and signal connectors are shown in Figure 2 15 Pin number Signal name Description 1 Service 0 DO NOT CONNECT 2 Service 0 DO NOT CONNECT 3 _SYSTEM_ERROR Status Signal 4 _WAVELENGTH_TUNING_ENABLE Control Signal 5 _WAVELENGTH_ERROR Status Signal 6 _COHERENCE_CONTROL_ENABLE Control Signal 7 _OPTICAL_POWER_ERR...

Page 30: ...e 33 Service 9 internal use only Service 34 Service 10 internal use only Service 35 Service 11 internal use only Service 36 Service 12 internal use only Service 37 Service 13 internal use only Service 38 Service 14 internal use only Service 39 Service 0 DO NOT CONNECT 40 Service 0 DO NOT CONNECT 2 5 5 1 Power connector The connector for the power to PICO E Figure 2 8 comes from FCI Connectros it h...

Page 31: ...1 Fiber Optical Connector Standard Bulkhead Option Fiber pigtail FC APC narrow key standard FC PC and FC APC versions are available For the Fujikura Panda Polarization Maintaining fiber the polarization power is parallel to the slow axis For Fujikura Panda Polarization Maintaining fiber the slow axel is parallel to the key See Figure 2 16 The PICO D product number defines the type of connector ava...

Page 32: ...in the tuning range However PICO D can also be fixed tuned to a specific wavelength or jump ing between any fixed wavelengths in a random sequence 3 1 Switching ON the PICO D Wavelength and optical output power are controlled with connector located on the rear side of PICO D see Figure 2 15 Step by step instruction 1 Connect the 5 V 2 Next connect 15 V and 15 V supplies 3 When the system is starte...

Page 33: ...ferent power values The optical output power level is controlled through measurement of light split off from the optical fiber Due to the non linearity at the onset of lasing or equivalently at the threshold current the output power can only be controlled above this mini mum level up to the maximum output power above which saturation occurs Using linear interpolation and a sufficiently dense grid ...

Page 34: ...lines are PICO should be calibrated in the same way that it will be used Never use the digital control signal _POWER_ENABLE to turn on the optical power Radians recommend the general purpose start up and calibration procedure 3 3 1 1 Start up The purpose of the start up procedure is to find a stable mode to ensure that the calibration procedure will be successful Set WAVELENGTH _TUNING to 0 V Set ...

Page 35: ...form the start up procedure Set OPTICAL_POWER to the desired value Measure the actual optical power using a power meter Increase WAVELENGTH_TUNING monotonically between the calibration points Measure the actual wavelength using a wavemeter Perform the start up procedure see paragraph 3 3 1 1 Set OPTICAL_POWER to the desired value Decrase WAVELENGTH_TUNING monotonically between the calibraton point...

Page 36: ...1 1 1 Storage in partially temperature controlled locations within tem perature 10 C 14 F to 50 C 122 F ETS 300 019 1 2 1 Very careful transport Transportation of PICO D shall always be in the original packaging which is special designed for PICO D The PICO D unit shall always be stored in vertical position see Figure 2 5 Detailed description on how to un package package and transport PICO D are f...

Page 37: ...LE is TRUE Paragraph 2 5 3 1 defines the logical states 2 Check that the digital status signal _TUNING_ENABLE is TRUE Para graph 2 5 3 1 defines the logical states The output power is lower than expected 3 Check that the optical connector is clean 4 Check that the connection to the optical cable is in order The PICO D does not respond as quick as expected 5 Check that the PICO D is warm enough 6 C...

Page 38: ...ny trouble with the PICO D that cannot be solved please contact our support at Address Support Thorlabs Sweden AB Box 141 94 S 400 20 Göteborg Sweden Telephone 46 31 733 30 00 Fax 46 31 733 40 45 e mail Scandinavia thorlabs com ...

Page 39: ... specifications No Parameter Min Typical Max Comment 1 Tuning Range nm CL Band 1519 1630 The wavelength range given by 10 and 10 V wavelength tuning input voltage See comment in section 4 1 1 2 Mode hops 0 At 0 dBm 0 2 dB output power applying a sweep mode See figure in section 4 1 2 3 Tuning speed continuus nm s 0 100 0 130 4 Tuning speed 1 nm 10 nm 100 nm step 30ms 100ms 800ms 50 ms 150 ms 1 000...

Page 40: ...Signal to Total Source Spontaneous Emission Ratio STSSER dB 60 65 19 Optical isolation dB 1560 nm 60 20 RIN dB Hz 140 21 Temperature range C 10 to 40 C 22 Fiber Type Standard SM fiber SMF28 See section 4 1 4 Option PM Fujikura Panda fiber Polarization extinction ratio 15 dB 23 Connector FC APC bulkhead connector standard See section 4 1 5 24 Physical size Max 49 x 93 x 273 mm See section 4 2 1 25 ...

Page 41: ...re of the laser cavity moves the absolute wavelength at which a mode hop occurs The mode hop if pre sent will be visible as a discontinuity in e g wavelength vs control voltage plots Figure 6 1 below shows the mode hop free areas for the PICO D laser Note that the wavelength range for areas b and c are 50 nm as a target specification Note also that area b and c are totally independent of each othe...

Page 42: ...an 10 ms This enables the de termination of the position of the modehop with an accuracy better than 1 nm Mode Hop Enable The digital control signal mode_hop_enabla enables the use of of the Mode Hop Adjust signal When this signal is FALSE PICO D runs with factory settings on the Mode Hop Adjust Mode Hop Adjust The analog control signal MODE_HOP_ADJUST is used for fine tuning the laser wavelength ...

Page 43: ... Definitions Acronyms and Abbreviations APC Automatic Power Control ECL External Cavity Laser ESD Electrostatic Discharge GND Ground MLH Modular Laser Head NC Not Connected TBD To Be Defined TLS Tunable Laser Source ...

Page 44: ...__ ___ ______ After demo Date ___ ___ ______ Other _________________________ Date ___ ___ ______ Short description of error Check list Status signals ON OFF Temp overload Laser current limit System overload Output power at 1V power signal _______ dBm Maximum output power _______ dBm E mail or fax this list to Thorlabs Sweden AB E mail scandinavia thorlabs com Fax 46 31 703 40 45 ...

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