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d2:d2_250_heterodyne_module [2016/05/10 00:26] Michael Radunskyd2:d2_250_heterodyne_module [2021/08/26 15:26] (current) – external edit 127.0.0.1
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 <WRAP right round box 300px> <WRAP right round box 300px>
-<imgcaption image1|D2-250 Heterodyne Module>{{:d2:d2-160:hirose-connector.png?200 }}</imgcaption>+<imgcaption 250-side|D2-250 Heterodyne Module>{{ :d2:d2_250:d2-250-side_no_fiber_01.png?300 }}</imgcaption>
  
 </WRAP> </WRAP>
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 Please read [[:limited_warranty|Limited Warranty]] and [[:warnings_cautions|General Warnings and Cautions]] prior to operating the D2-250. Please read [[:limited_warranty|Limited Warranty]] and [[:warnings_cautions|General Warnings and Cautions]] prior to operating the D2-250.
  
 +=====Description=====
  
 +The D2-250 heterodyne module is designed to provide a fiber-coupled heterodyne optical beat note formed by picking-off a small proportion of light from each of two laser beams. Light is coupled into a multi-mode fiber. A second output port can be used to align the overlap the two picked-off beams.  The light entering the module should be linearly polarized in either vertical or horizontal direction for best results.
  
- +<imgcaption 250-system|D2-250 in phase lock system>{{ :d2:d2_250:d2-250_schematic.png?400 }}</imgcaption>
- +
-=====Description===== +
- +
-The heterodyne module is designed to provide a fiber coupled heterodyne beat note formed by picking-off a small proportion of light from each of two laser beams. Light is coupled into a multi-mode fiber. A second output port can be used to overlap the two picked-off beams.  The light entering the module should be horizontally polarized for best results.+
  
 =====Purchase Includes===== =====Purchase Includes=====
   * D2-250 Heterodyne Module   * D2-250 Heterodyne Module
 +  * VPN00460 Fiber Optic Cable (multimode)
 +  * F220FC-B Fiber Coupler
 +  * 5/64" Hex Key
  
 ===== Absolute Maximum Ratings ===== ===== Absolute Maximum Ratings =====
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 =====Specifications===== =====Specifications=====
-<WRAP center round box 400px>+<WRAP center round box 700px>
 ^    ^  Value  ^  Units  ^ ^    ^  Value  ^  Units  ^
-^Transmission|  96   %  | +^In-coupling|  Free-space   %  | 
-^Proportion of light picked-off|  1-2.5   %  | +^Wavelength Range|  700 - 1,000  |  nm  | 
-^Wavelength Range|  630-1000  |  nm  | +^Input Power Range|  0.1 - 200  |  mW  | 
-^Output Fiber Connector|  FC  |   |+^Pick-off Percentage|  1 - 98   %  | 
 +^Transmission|  up to 98  |  %  | 
 +^Input Polarization|  Linear  |  Horizontal or Vertical 
 +^Minimum Power in Beat Note|  >50 μW, optimally 200 μW  |  for use with D2-160  | 
 +^Maximum Power at Detector((In the optical beat note.  Since the beat note is delivered through a multi-mode fiber for ease of alignment, the power at the detector is not necessarily the same as the power in the beat note.  Damage may occur to the optical element if >1 mW of overall optical power is delivered to the detector.))|  <1  |  mW  | 
 +^Fiber Connector|  FC  |    | 
 +^Compatible Fiber Type|  MM, PM  |    |
 </WRAP> </WRAP>
  
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 =====Components===== =====Components=====
  
-The module consists of two beam cubes designed to pick-off 1-2.5% of the light from each laser beam, a 50/50 beam splitting cube, and a fiber coupler.  All 3 beam cubes are on a 2-axis adjustable plate that allows for horizontal adjustment by rotating a screw with a cone-shaped head that is next to the plate and vertical adjustment by rotating the screw in the plate  +The D2-250 Heterodyne Module utilizes the same three pickoff-cube architecture as the D2-150With this revision, each input beam passes through a rotatable zero-order half-waveplate prior to a polarizing beam splitter, enabling the user to adjust the amount of power from each source beam diverted to the optically mixed outputs. A 50:50 non-polarizing beam splitter overlaps the pickoff light into a fiber coupler. Each cube rests on a 2-axis kinematic mount adjustable from the module exterior, enabling horizontal and vertical beam pointing adjustment.
- +
  
 +<imgcaption 250-label|D2-250 Key Components>{{ :d2:d2_250:d2-250_labeled_schematic.png?400 }}</imgcaption>
  
 =====Alignment Procedure===== =====Alignment Procedure=====
  
-For easiest optical alignment the module should be positioned so that the two laser beams are well centered in the input and output apertures with the beam directions as shown below For clarity, the two laser beams are depicted in red and greenalthough real applications will use beams that have small differences in frequency.  Then, the lid of the module should be removed by removing the four screws on the top of the module so that the inside of the module is visible as shown below.+The D2-250 Heterodyne Module provides for any two lasers capable of being phase locked to be spatially overlapped and directed into a fiberThis procedure does not assume any specific incoming laserswith the only restrictions (average powerwavelength) as indicated in the specifications above.
  
 +===Required Equipment===
 +  * (2x) Input laser
 +  * (1x) D2-250 Heterodyne Module
 +  * (1x) VPN00460 Fiber Optic Cable with A/R Coating (included)
 +  * (1x) F220FC-B Fiber Coupler for Heterodyne Module (included)
 +  * (1x) Hex key, 5/64" (included)
 +  * (1x) Power Meter
  
 +===Procedure===
 +Mount both laser modules and the D2-250 Heterodyne Module to an optical breadboard or table. Leave sufficient space between the lasers and optical modules to allow for the adjustment of the hex screws and insertion of the F220FC-B Fiber Coupler and VPN00460 Fiber Optic Cable. Turn on both lasers. During mounting, align the first laser such that the beam enters "INPUT1" and exits "OUTPUT1" centered through each aperture. Repeat with the second laser through "INPUT2" and "OUTPUT2".
  
 +<imgcaption sys-top|D2-250 and Laser Mounting>{{ :d2:d2_250:LaserHeterodyneMount.jpg?300 }}</imgcaption>
  
 +Turn OFF both lasers, then screw the F220FC-B Fiber Coupler into the "FC Port" on the D2-250 and hand tighten. Screw in the FC/APC connector of the VPN00460 Fiber Optic Cable into the F220FC-B Fiber Coupler and hand tighten.
  
 +With the power meter, observe the output power through the VPN00460 Fiber Optic Cable. With the 5/64" hex key, adjust the first kinematic mount in the "INPUT1" beam path (Stage 1) to optimize the optical power observed (and thus the fiber coupling). Using a note card or IR card to observe the "MIXER" output very near to the D2-250, adjust the first kinematic mount in the "INPUT2" beam path (Stage 2) and overlap the observed beams. In the far field, adjust the "MIXER" kinematic mount (Stage 3) until both beams overlap. Some iteration may be required between the second beam and the final kinematic mount.
  
 +<imgcaption 250-top-photo|D2-250 Interior>{{ :d2:d2_250:LaserHeterodyneAlign.jpg?300 }}</imgcaption>
  
-Once the module has been placed such that high power beams are well centered on the input and output apertures, the pick-off beams can be aligned.  First, the upper right beam cube should be adjusted horizontally and vertically to maximize the coupling of the beam shown in green into the multi-mode fiber through the fiber coupler shown on the left of the module.  These adjustments can be made with a 0.050Allen wrench.  The horizontal adjustment is made by turning the black screw with a cone-shaped head to the right of the metal plate that the beam cube rests on.  The vertical adjustment can be made with the screw inserted into the same metal plate.  Note that it is important to use the screws provided with the module, as replacing the screws with longer ones can cause permanent distortion of the metal plate.+Fully optimize the coupling into the fiber by adjusting the "INPUT2" kinematic mount and the "MIXER" kinematic mount to optimize the power observed on the power meter.
  
-After the laser beam shown in green is adjusted, the picked-off light shown in red should be adjusted to overlap with the picked-off light shown in green This beam can be adjusted using horizontally and vertically using the beam cubes shown on the lower and upper left corners of the module The beams should appear to overlap both close to the module and far from it when the beams are seen through the large unused fiber coupling port.  Generally, the overlap of the beams in the near field should be achieved by adjusting the beam cube in the lower left of the picture and the overlap in the far field should be achieved with the beam cube in the upper left of the picture Iterating between adjusting the beams in the near field and far field will yield the best beam overlap.  Once the beams are well overlapped, the fiber output can be measured on a high-speed photodetector and the resulting beat note can be measured with a spectrum analyzer.  Additional small adjustments to the beams may be necessary to improve the strength of the beat note.+Block laser #1and rotate the "INPUT2" waveplate to reduce the observed power below 0.50mWBlock laser #2, and rotate the "INPUT1" waveplate to reduce the observed power below 0.50mW. To protect the D2-160 Beat Note module, the combined power should not exceed 1mWThe SC fiber end can now be connected to the D2-160 or other beat note detector.
  
-While it is possible to replace the multi-mode fiber with a single-mode fiber, it is not recommended.  It will be very difficult to couple light in the beam shown in green into the fiber since adjustments can only be made with two degrees of freedom.  Since multi-mode fiber has a wide acceptance range, it is possible to achieve good fiber coupling in multi-mode fiber with only 2 degrees of freedom.  Typically ~50% of the light directed at the fiber coupler is coupled into the multi-mode fiber. 
  
-The procedure outlined above should work to align the module, but if difficulties are encountered another alignment procedure is possible with a fiber coupled laser such as the laser pens that are used to check fiber continuity and align light into fibers.  In this procedure, light should travel the reverse direction through the fiber so that the light is output into the module.  The beams should then be adjusted such that this reverse-coupled light overlaps well with the two laser beams entering the module.   
d2/d2_250_heterodyne_module.1462839969.txt.gz · Last modified: 2021/08/26 14:26 (external edit)