Model 77529 F/# Matcher, with Multi-Track Fiber, mounted to MS257 Monochromator.
Our Model 77529 Fiber Optic F/Number (F/#) Matcher increases the F/# of the beam from a fiber optic by a factor of 2. Use it to match fused silica fibers, which have an F/# of ~2, to the input of Oriel Monochromators and Spectrographs, most of which have an F/# of ~4. This gives you two significant advantages: Decreases stray light inside your instrument Increases throughputThe F/# Matcher uses reflective imaging optics and is usable over the wavelength range of 190 nm to 24 µm. The efficiency is over 75%.
The output of most fiber optics, characterized by the fiber F/#, is too divergent for efficient acceptance by a monochromator or spectrograph. This leads to potentially significant loss in efficiency and increased stray light due to the overspill of the beam inside the instrument.
Because of the various fiber types and because any conversion of the fiber output beam to match the monochromator cannot beat the fundamental concept of optical extent, there is no universal solution to the problem. However, depending on resolution requirements, the 77529 F/# Matcher offers, in many cases, efficiency improvements and reduction in stray light. Fig. 1 illustrates the problem and the solution. Note, when you use the F/# matcher, the fiber image is magnified by a factor of 2.
You can also use the F/# Matcher on the output of a monochromator for coupling monochromatic light into a fiber. The slit image is demagnified by a factor of 2.
Glass bundles have an F/# of ~1. Increasing the F/# by a factor of 2 is not enough to match it to the input of our monochromators and spectrographs, however, it is still useful to use the F/# Matcher with glass fiber optics because it decreases stray light and may increase throughput, depending on your slit size.
Most imaging spectral instruments have 1-1.5 magnification in the image direction. Additionally, F/# matchers have a 2X magnification. This magnification is inherent to any F/2 to F/4 F/# matcher. Altogether, you may have 3X magnification in the image direction. To fit your image into the 6 mm high InstaSpecTM CCD, the multi-track fiber can then be no more than 2 mm high. To image such a small object with a fine structure, the F/# matcher must have extremely good resolution. Oriels F/# matcher offers the required resolution. Fig. 2 shows five 200 µm fibers distanced at 400 µm from each other, and the image produced by our F/# matcher. For comparison, the image produced by a standard two lens F/# matcher is also shown. As you can see, the resolution of the typical lens F/# matcher is very poor. In addition, its efficiency is lowered due to significant chromatic aberrations. To ensure superior resolution, particularly with 5 and 9-track fiber bundles, we recommend using Multi-track Fiber Bundles with 100 µm core diameters .
When you send light from a fiber optic directly into a monochromator, you lose energy if the output angle of the fiber optic is larger than the input angle of the monochromator, and/or if the fiber size is larger than the slit size. Using an F/# Matcher significantly reduces the loss. Without the F/# matcher the loss factor (K) is:
Where:(F1 /#) = Output F/# of the fiber(F2 /#) = Input F/# of the monochromatorV = Vignetting factorV= 1 when the fiber diameter is smaller than both the width and height of the slit; V <1 for other cases. The smaller K is, the greater the energy loss. Since the F/# Matcher matches the output cone angle of fused silica fibers to the input acceptance angle of our monochromators, you collect all the energy from the fiber; the equation is now just:
The new vignetting factor (V*) is different from V, and usually smaller than V, due to image magnification (m) produced by the F/# Matcher:
The 77529 has precise X,Y and Z focus adjustment for optimal alignment of the fiber image with the monochromator slit. It has a 1.5 Inch Series female Quick Connect flange and an adapter to hold any Oriel Fiber with standard or Quick Connect 11 mm ferrule. The 77529 also has a 1/4-20 tapped hole for rod mounting. Even with flange mounting, you should rod mount the F/# Matcher for added stability. A 4.4 inch (112.5 mm) clearance between the F/# Matchers housing and its output focal point allows enough room to place Motorized Optical Filter Wheels. The fiber image is focused through the filters, into the monochromator. We supply an adjustable extension tube with the F/# Matcher, adjustable from 65 to 112.5 mm.