Hello, and thank you for your question! The Vector path control is a feature only implemented in the brushless DC servo controllers and stages (like the BBD3XX and MLS203 seen in this video). Since the LTS is an integrated stepper, it doesn't have this control option in the software. If you would like more information about Thorlabs products or about your setup, please contact [email protected].

Yes, the typical goal of collimating light is to provide an output beam with all the rays traveling parallel to one another. In an ideally collimated beam, the image of the light source would only be visible infinitely far away from the lens. In between the lens and infinity no image would be visible, because in the ideally collimated beam, rays from all points on the light source would overlap one another. However, in real world applications, it is typically not possible to move the image infinitely far away. This is because divergence separates the collimated ray bundles originating from different points on the light source. Due to this, one approach to collimating light from a relatively large source is to adjust the lens until the image is as far away as possible. When the viewable distance is too short to confirm that the image has been moved to the maximum possible distance, adjusting the lens to move the image past the farthest viewable distance is one way to push the expected image closer to its maximum possible distance.

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@ParTaban The collimated beam with the higher 0.76 NA lens collected more power and provided a larger irradiance at the measurement plane in the video compared to the collimated beam provided by the lower 0.24 NA lens, as you pointed out in the measurements. However, the collimated beam output from the higher NA lens also has a larger divergence, so the irradiance will reduce at a quicker rate as the measurement plane moves away from the collimating lens. This means that while the lower NA lens has a lower overall irradiance near the collimating lens, the lower divergence provides a more consistent irradiance as the collimated beam travels away from the lens.

@rachelanderson1232 We are glad you liked the video! While this video includes alignment techniques generally useful for spherical and off-axis parabolic mirrors, there would be challenges to using the complete demonstrated approach to align spherical mirrors. One challenge is that the focal region of spherical mirrors is directly in front of the mirror (i.e. these mirrors have obstructed focal regions). Since a spherical mirror’s collimated beam passes over its focal region, a fiber end face placed within the focal region would create a shadow in the collimated beam, which may not be desirable for the application. (This is the geometry of Newton telescopes.) If an off-axis approach is used with the spherical mirror, the collimated beam will be aberrated (primarily due to astigmatism, which is caused by the spherical mirror shape). Additional optics would likely be needed to improve the beam quality.

@EXYZ3 We are glad to have been able to help! Yes, this technique and these lenses are routinely used to collimate white-light LEDS. The resulting beam quality will be similar to the beam quality obtained when collimating light from narrower-spectrum LEDs. However, the collimated light from a white-light LED often includes a rainbow effect around the edges of the beam due to the lens’ chromatic aberrations. The color separation around the collimated beam’s edge can be reduced by using an achromatic lens in place of the aspheric condenser lens, although achromatic lenses typically have lower NAs than aspheric condensers.

@USAsuperstore Response 1: The temperature-controlled breadboard we used has a temperature range between 15 °C and 45 °C. We used the range from about 25 °C to 45 °C, which suited this demonstration well, but other applications and fibers may be better served by a different temperature range. The temperature needs to change in order to make the measurement. Temperature cycles can occur periodically to confirm alignment at discrete times or the temperature could be cycled continuous to visualize dynamics. But it is important to remember that temperature change will induce continuous polarization change at the fiber output during the assessment. Yes! The points on the Poincaré sphere will plot in opposite directions, depending on whether the temperature is increasing or decreasing. Response 2: This analysis technique assumes that the fiber’s birefringence changes, but that light does not couple between the fiber’s fast and slow axes. As you’ve noted, physically straining the fiber also changes the fiber’s birefringence. However, physically straining the fiber can also cause microbends and other effects that enable light to more easily couple between the slow and fast axes. When this occurs, even when the input light is perfectly aligned to one fiber axis, some light can couple into the orthogonal axis due to the stress. Since there will then be light in both axis, and the amount depends on the stress applied to the fiber, the center polarization state of the output light can drift.

@@thorlabs Excellent and super clear answers. Much appreciated.

@The Rojecas Yes, indeed! The red light you see is typically called leakage. Light leakage is not only common, it can also be a handy alignment tool when observed near the fiber connector. Leakage is common since it is almost impossible to perfectly couple all of the light from a light source into a single-mode fiber core. This is because perfect coupling into the core would require perfectly matching the size, shape, and alignment of the light’s beam waist to the optical fiber’s mode field diameter and geometry. Inevitably, the match will be slightly imperfect, and some light will be coupled into the fiber’s cladding. Because light coupled into the fiber’s cladding is not guided well, this light propagates out of the cladding and into the fiber’s surroundings. This is what makes the fiber’s yellow jacket glow red in the video. This phenomenon can be a useful alignment tool when working with visible light sources. When you start to see the fiber jacket glow near the connector, you know your light source is overlapping the fiber’s end face. As the alignment improves, more light couples into the fiber core and less light will leak into the jacket. Some people look for the leakage near the connector to dim to confirm their alignment.

@user-xt5ff3xb8v The fiber optic, three-paddle, polarization controller models you are working with allow people to take an arbitrary input polarization state and convert it into a different output polarization state. Setup includes coiling the fiber into each of the controller’s paddles. The bending strain in a fiber coil induces birefringence in standard (i.e. non-polarization controlling) optical fiber. The phase shift provided by each paddle depends on the fiber’s material properties, the wavelength of the light, and the length of the fiber coiled in the paddle. Essentially, the coiled fiber in a paddle acts as a wave plate. Rotating the paddle rotates the fiber-based wave plate, similar to rotating a conventional wave plate. In the case of a three-paddle controller configuration, the number of fiber loops in each paddle are typically customized so that the two paddles on either end act as quarter-wave plates and the paddle in the middle acts as a half-wave plate. However, the paddles generally do not provide exactly quarter- and half-wave retardances. In addition, the exact input polarization state is usually unknown. Because of this, each paddle’s rotation angle (i.e. the polarization change provided by the paddle) is typically optimized based on system feedback. We have a resource on our website that demonstrates one approach for obtaining the desired output polarization state. The web page is here: www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=343&tabname=Lab%20Facts and the PDF of the related summary slides is here: www.thorlabs.com/images/TabImages/Fiber_Polarization_Controller_Lab_Facts.pdf .

@user-gz3sf7gy6z We are sorry that you had trouble understanding. Are there one or more topics that you would like us to explain in more detail in an upcoming video?

@@thorlabs I thank your efforts but I understood the subject.

Thanks for your question! Volume Bragg Gratings are synonymous with Volume Phase Holographic gratings. An optical Bragg grating is a transparent optic with a periodic variation of the refractive index.

@giammi56 Thank you, twice! You are correct, we typo-ed at 7:55. The equation at the top of the diagram should have tan(phi) in the denominator, but the calculated value (~29 cm) is correct.

@JyotiArya-bw1lg The FiberPort includes a fiber collimating lens, so both collimate light from a fiber. However, the FiberPort is also a mount that includes a 5-axis micro-positioner and can be integrated into a FiberBench. A FiberPort’s additional functionality and stability can be useful when assembling and aligning setups.

@szu-yulee390 In general when optimizing alignment, it is often necessary to look for small changes in output power when making adjustments. These small changes can be very difficult to detect when they are being added to, or subtracted from, a high-power baseline. Because of this, it can be very difficult to know when the power is truly maximized. Instead, it is often helpful to look for the minimum power, since small changes compared with a low-power baseline can be a lot easier to see. However, both of these approaches assume that the system can provide a constant maximum or minimum value. The PM fiber and linear polarizer system will typically not provide a stable maximum or minimum power output, since some light will always be coupled into the fiber’s orthogonal axis. Rather than try to take this effect into account, we find it easier to optimize alignment by setting the linear polarizer’s axis between the fiber’s axes and minimizing the amplitude of the oscillations.

@@thorlabsthank you very much for the details! I am still one step behind the logic. So the linear polarizer right before the power meter is set to between PM fiber's axes. Then, why minimizing the amplitude of the power oscillations by rotating the HWP means the linearly polarized input is aligned to one of the PM axis? Is it because otherwise the PM fiber output is in general elliptically polarized and we will see power oscillation?

@szu-yulee390 That is correct! Light output by PM fibers almost always includes a small fraction of elliptically polarized light. This is caused by a variety of reasons including: imperfect linear polarizers transmitting a small amount of light polarized in the orthogonal direction, obtaining perfect alignment is difficult, and light aligned to one fiber axis scattering into being aligned to the other fiber axis at perturbations like bends and irregularities in the glass material. This is why, in the demonstration, we could reduce - but not eliminate - the power oscillations.

@@thorlabsthis is again very clear and insightful explanations to me. Thank you very much. Keep the high quality videos coming!

@szu-yulee390 You are welcome, thanks for asking :) And, if you have a topic suggestion for us, please let us know!

@JulianJXhori Thanks Julian! Good luck in your upcoming physics courses!

@lotharmayring6063 Our camera SDK is currently available for the Windows and Linux Operating Systems. These allow the user to retrieve the raw data from the camera and create their own processing on those platforms. Please let us know if you need a different platform supported.

@@thorlabs sorry, but what i see in this video is not better than the camera app od windows. How many pixels has the camera and what size of sensor. Why is it not in color..

@lotharmayring6063 You are correct, this Video Insight was intended to help someone start writing their own program to control a camera we had in the lab. Are there specific functions you would like to see another camera programming video address? The camera we used in the video is the CS165MU1, which has 1440 x 1080 pixels, each 3.45 µm x 3.45 µm in size. A link for the product is provided in the description.

@mukulsharma3447 Thanks for the suggestion! There are different approaches to minimizing the error. One approach is to adjust the wave plate’s alignment, until the wave plate provides as close to optimal retardance as possible. For example, input linearly polarized light to the wave plate, while simultaneously adjusting the wave plate’s alignment and using a polarimeter to analyze the output light. Another approach, which can be used alone or in addition to the previous approach, is to mathematically correct the results provided by the system after making a measurement. This requires measuring the wave plate’s actual retardance. When this is known, the actual retardance can be used when analyzing the results provided by the optical setup. The approach is described in Section 3.A.3 of Paul A. William’s paper (Applied Optics, Vol. 38, No. 31 (1999) 6508).

Thank you for your comment! Sunglasses with polarizers aligned horizontally will work best for blocking the strongly polarized reflections off of vertically aligned surfaces. As a result, they may be more effective for reducing the glare from reflections off buildings or windows when the sun is lower in the sky. As you suggested, horizontally aligned polarizers would not be as effective for blocking the strongly polarized reflections off the horizon like bodies of water. I hope this helps!

@adityaasopa4031 There are many different kinds of mirrors, and they all have different reflectivities. Some metallic mirrors, like silver and gold mirrors, have reflectivities above 90% for a wide range of wavelengths and angles of incidence. There are also some dielectric (non-metallic) mirrors that have special coatings that provide >98% reflectivity over specific wavelengths and a wide range of incident angles. This video shows that a piece of uncoated glass can also be used like a mirror, although its reflectivity varies a lot with angle of incidence. When the light’s path is nearly perpendicular to the glass surface, about 4% of the light is reflected. The poor reflectivity at this angle is why people typically use glass windows to see through. But, when the light hits the glass at a glancing angle, so that the light’s path is nearly parallel to the surface, the reflectivity approaches 100%. Reflectivities for these scenarios and other interesting angles of incidence can be predicted using the Fresnel equations.

It is tempting to think so, but the ‘s’ in s-polarized light actually stands for ‘Senkrecht,’ which means 'perpendicular' in German. This is because s-polarized light is perpendicular to the plane of incidence, where the plane includes the incident, reflected, and transmitted light vectors.

@user-cf5sm9cn6v The bi-convex lens shape can collimate light from an LED but the collimated beam will include more aberrations (particularly spherical) compared to other lens shapes. Whether this collimated beam is suitable depends on your particular application. Typically bi-convex lenses are used for imaging applications where both surfaces are used to focus the light to a point in the image plane.

@ahmedmostafa-tf2vo Yes, lenses like the aspheric condensers used in this demonstration are regularly used to collimate light from a variety of different light sources, including filament lamps. Achromatic lenses are another option, since they can provide better results for broad-spectrum sources, but it can be difficult to find high-NA achromatic lenses. However, in all cases, the divergence of the collimated beam will increase as the size of the emitter increases.

That's great! The motorized stage assembly used the PRMTZ8 rotating stages. The telescope used the CS165MU monochrome camera. For the full components list, please refer to the video description or github link of the Design Files for this project below: github.com/Thorlabs/Insights_and_Applications/tree/main/Tracking%20Solar%20Telescope/Design%20Files Most of our apochromatic lens designs are objective lenses. Something to consider for this application is that you could use a narrow bandpass filter to reduce the chromatic aberration if you plan to use a monochrome camera. If you have a specific application or design requirement, please feel free to contact Tech Support.

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@@thorlabs will do!