Integrating Optics with Microfluidic

Glas microfluidic chip with integrated opticsGlas microfluidic chip with integrated opticsTranslume fabricates custom-design microfluidic fused silica glass platforms that integrate optics and microfluidic functionalities. We have fabricated a wide range of this type of device. Typically, the device incorporates some microfluidic channels, and an optical system comprising of one or more lenses, waveguides, and light guide, with input and output fiber ports. Optoelectronic components (diode lasers, photodetectors, etc.) can be connected to the glass platform using optical fibers, or bonded directly onto the glass chips.

 
 
 
 
 

An inverted layout (bottom-up design) is a simple way to address space limitation issuesAn inverted layout (bottom-up design) is a simple way to address space limitation issues

Glass Chip Size

2”x 1” is a common size, but we can work with larger or smaller glass chips if desired. There are a couple size considerations that you must keep in mind: If you are going to use optical fibers, the width of the chip needs to be at least 1” to allow for the integration of fiber insertion ports and associated integrated lenses. Regarding the minimum length of the glass chip, a common limiting factor is the size of the equipment that you may use in conjunction with your device. For example, if you want to observe the microfluidic channels with a large diameter microscope objective, you need to allow for sufficient space between the sample fluid ports (luers or Nanoports) for the insertion of your equipment. If this introduces too many design constraints, the sample ports can be easily moved onto the backside of the glass chip.

 

Microfluidic design

There are very few limitations associated with the fabrication of the microfluidic circuitry. You should, however, keep in mind that the microfluidic layout must accommodate any constraint dictated by the design of the optical system (see below).

 
 

 

 

Three fiber insertion ports with integrated lenses. A fiber is inserted in the central assembly. Three fiber insertion ports with integrated lenses. A fiber is inserted in the central assembly.

Integrated Lenses

We fabricate any lens called for by your design using our femtoEtch process. We can provide a variety of radius and lens types (cylindrical or spherical). There are three limiting factors associated with our lenses: (1) The lens must physically fit within the glass layer; (2) the lens surface roughness is approximately 200-nm, which introduces significant scattering in the UV and visibility; and consequently we cannot reach the optical diffraction limit in this wavelength range (our micro-fabricated lenses are much better in the near-infrared): and (3) optical aberrations, especially spherical aberrations, are quite severe with micro-optic (this is unrelated to our manufacturing, but it is a general result of physical optics).

 

 

Close-up view of a fiber port with a facing integrated lensClose-up view of a fiber port with a facing integrated lens

Fiber Type

We can attach various fibers to the glass microfluidic chip or the flow cell, as long as they have a 125-micron cladding diameter. (We sometimes work with other cladding diameters, but you should be aware that the associated NRE costs may be significant). The input fiber(s) can be single-mode (SM) or multimode (MM) fiber. Please note that we do not manufacture fibers; we purchase them from Thorlabs. We can also work with specialty fibers provided by you. The protective jacket is removed over the last inch of the fiber, and the fiber is pushed into a fiber attachment port until it reaches the designed position. Once the fiber position has been optimized, the fiber is frozen in position with UV curing glue. There is NO glue in the optical path. The fiber tip is located in a sealed cavity to protect it from dust. The output fiber (if required) is typically, a multimode fiber. Here again, we work with a variety of 125-micron cladding diameter fibers.

Fused Silica microfluidic chip equipped with three fiber portsFused Silica microfluidic chip equipped with three fiber ports

Location of the fiber/lens relative to the microfluidic

Typically, the fiber-lens assemblies lay in the main plane of the chip and are perpendicular to the channel. However, we have occasionally fabricated chips where the fiber-lens assemblies are not perpendicular to the channel.