Visible Wavelength fiber coupled acousto-optic modulator for biomedical applications

G&H Hermetic Fiber-QThe Gooch & Housego Fiber-Q is a range of fiber coupled acousto-optic modulator products. Following receipt earlier this year of an inquiry from a large Japanese company for Fiber-Qs operating at 488nm (blue) and 532nm (green), G&H have decided to extend the Fiber-Q range with the introduction of a product operating in the visible wavelength region (approximately 400nm-700nm).

The Fiber-Q, or fiber coupled acousto-optic modulator, allows light travelling along an optical fiber to be injected into an acousto-optic modulator cell. After passing through the cell, the light can be either deflected into the output fiber or allowed to miss the fiber by application of a radio frequency modulating signal. In this way, light pulses can be produced. The product was jointly developed by the G&H engineering groups at the Ilminster, Torquay and Melbourne sites shortly after the Torquay fiber optics facility was acquired in 2007. The Fiber-Q range was developed for fiber laser materials processing applications at a wavelength of 1060nm and for fiber sensor applications at wavelengths around 1550nm. The product has been very successful with customers valuing the combination of small, robust packaging and high performance acousto-optics. Since its introduction there have been several additions to the Fiber-Q range. A low cost, non-hermetic package option is now produced to serve the commodity end of the fiber laser market. This year, the wavelength range of the Fiber-Q was extended to 2000nm for thulium doped fiber laser applications.

Now for the first time, Fiber-Qs will be available in the visible wavelength range. The majority of applications for 400nm-700nm Fiber-Qs are biomedical. These include laser microscopy and flow cytometry. Visible wavelength lasers are used to generate detailed microscope images of biological samples in 3-D. Clinicians use flow cytometry to analyse the biological cell content of liquids such as blood to diagnose, amongst other things, leukaemia.

There have been a number of technical challenges to overcome in the development of a visible wavelength device. The light in a visible wavelength fiber is confined to a core that is only 3mm in diameter. This small diameter means that the alignment of the optics that couple light in and out of fiber must be extremely precise. In addition, unlike free space, standard optical fibers do not maintain the polarisation state of the launch. Specialist polarisation maintaining (PM) fibers are available, however they are very sensitive to stress or pressure exerted during assembly and must be handled with great care. As well as these fiber related challenges, the UV curing adhesives used to hold the lenses can produce unwanted outgassing products when illuminated with blue light. Blue light is close to the UV curing wavelength.

The first Fiber-Q operating at 488nm was shipped in March following the extremely encouraging results of a three day soak test. The transmission efficiency was high (~65%) as was the polarisation extinction ratio of 23dB (200:1). The development of the product continues with refinement of alignment techniques to improve efficiency and polarization extinction ratio (PER). Qualification is planned for later this year. Products operating in the 450nm-700nm range are now available from G&H in sample quantities and can be ordered from the datasheet on G&H’s new website.

For further details on G&H Fiber-Qs, please visit the Fiber Coupled Device section on the G&H website, download the Visible Wavelength Fiber-Q datasheet,  or contact G&H Fiber Optic Product Director, Toby Reid at