Bentham Releases FAQs for Their Fiber-Coupled Optical Homogenizer
Bentham released a set of FAQs to answer queries regarding the newly released FCH Fiber-Coupled Optical Homogenizer.
Can the FCH be used with customer systems, or only with Bentham systems?
Yes, the FCH can be used with customer systems, provided the source is fibre-coupled. Standard interfaces are SMA-905 and FC-PC.
The current design is optimised for 0.22 NA multimode fibre. Smaller NA fibres may reduce uniformity; higher NA fibres may reduce throughput. Fibre diameter is more flexible. The system has been tested with a 600 µm core fibre, but fibres from around 200 µm should give comparable performance.
If you have a specific customer system in mind, please send us the fibre details and application requirements. We can then estimate the expected performance.
Can the FCH be used with non-fibre-coupled sources?
Not as standard. The current FCH design is fibre-coupled and requires a suitable fibre input.
A free-space input version could be considered as a future development, but this would require additional design work. We are keen to understand customer requirements in this area, so please pass on any enquiries where a non-fibre-coupled input would be useful.
Can we provide application notes for the FCH?
Not yet. We plan to prepare an application note towards the end of August, based on a current customer order using the 120 mm patch FCH for large CCD chip characterisation.
In the meantime, please send us any application-specific questions. We can provide supporting information or help prepare customer responses where needed.
Can we provide comparison data versus integrating-sphere solutions?
Yes. We have an indicative throughput comparison against a representative integrating-sphere uniform source.
The FCH provides uniform illumination without the high optical losses normally associated with integrating sphere based uniform sources. This is important where source power is limited, or where high irradiance is required at the measurement plane.
Using power delivered into the uniform patch divided by optical power entering the uniform-source optic as the comparison metric, the FCH achieves around 50% usable-patch throughput while maintaining U2 ≥ 98% spatial uniformity.
Integrating spheres involve a stronger trade-off between throughput, working distance, and uniformity. For example, a 300 mm diameter sphere with a 134 mm exit port (5% of sphere surface area) provides useful throughput only very close to the port. As working distance increases, the field initially becomes less uniform: by 7 mm working distance, throughput is around 15%, but the field is already below U2 ≥ 98%. The field only recovers to U2 ≥ 98% in the far field, at around 410 mm working distance, where throughput has fallen to approximately 0.5%.
A larger integrating sphere can extend the near-field region and reduce the working-distance constraint, but at the cost of much lower port throughput. For example, a 1 m diameter sphere with the same 5% exit-port area ratio has a maximum comparable throughput of only around 1.4%, even at 0 mm working distance.
The key advantage of the FCH is therefore not simply uniformity, but a large, practical, highly uniform projected field with far higher usable throughput across realistic measurement geometries.
Was the FCH developed for a specific customer or application?
Yes. The FCH was inspired by a customer requirement to characterise pixel uniformity in large CCD chips used for space-telescope imaging.
The same capability is useful in other applications that require a large, stable, uniform illumination field. These include detector characterisation, camera and image-sensor testing, solar-cell QE/EQE measurement, hyperspectral and multispectral imager calibration, and general sample-plane illumination.
The common requirement is high spatial uniformity over a practical working area, with much higher delivered irradiance than is typically possible from integrating-sphere based uniform sources.
Can the FCH compete with existing uniform-source products?
Yes. The main competing approach is the integrating-sphere uniform source, which is widely used for camera, detector, and imaging-system calibration. Integrating spheres are well established and can provide excellent spatial and angular uniformity, but usually with high optical attenuation.
The FCH takes a different approach. It uses a fibre-fed MLA optical design to project a large square uniform field with much higher usable-patch throughput. This is especially attractive where high irradiance is required, source power is limited, or the customer wants to use fibre-coupled monochromator, LDLS, laser, LED, or supercontinuum sources.
There are also laser beam homogenisers and MLA beam-shaping optics on the market, but these are usually optical components or laser-processing solutions rather than complete fibre-coupled scientific illumination modules.
Can the FCH be used with Bentham light sources?
Yes. As a fibre-input product, the FCH is best suited to fibre-coupled sources. Example Bentham source systems are presented in the datasheet.
These include the FTMC100-LDS with LDLS sources for high-power wavelength-tuneable illumination, the FTMC50-SCL with supercontinuum lasers, and the FTMC50V fibre-to-fibre monochromator for existing fibre coupled sources. The FCH can also be used directly with suitable fibre-coupled sources such as the Bentham WLS-3LED, TLS120Xe, lasers, LDLS sources, and other broadband or monochromatic fibre outputs.
Can we provide a demo unit or details of the marketing release plan?
The FCH is already in the field with a customer, as it was developed from a real customer requirement. Online marketing has begun with the launch of the product web pages and datasheet.
We plan to add further application material over time, including an application note based on the 120 mm patch FCH for large CCD chip characterisation.
We do not currently have a demo unit available, but plan to make one available in the coming months. In the meantime, please send us any customer enquiries. We can help with technical information, performance estimates, and application-specific responses.
Can we identify the strongest applications for the FCH?
Yes. The strongest applications are those where customers need a large, highly uniform illumination field, but cannot accept the high optical losses of an integrating sphere.
The most important examples are:
- Camera, CCD, and image-sensor characterisation: especially pixel-response uniformity, flat-field correction, vignetting, linearity, saturation, and spectral-response testing.
- Detector and photodiode-array characterisation: where a stable, uniform field is needed for responsivity, spatial-uniformity, and wavelength-dependent measurements.
- Hyperspectral, multispectral, and QE/EQE measurements: where uniform illumination is required across wavelength, and where high delivered irradiance helps improve measurement quality.
In simple terms, the FCH makes the biggest difference where the customer needs integrating-sphere-like uniformity, but with much higher throughput and delivered irradiance.
About Bentham’s FCH Fiber-Coupled Optical Homogenizer
The FCH Fiber-Coupled Optical Homogenizer from Bentham is a high-throughput optical system for generating large, square, spatially uniform illumination fields from fiber-coupled light sources.
The FCH uses a microlens-array-based optical design to convert broadband or monochromatic fiber input into a flat-top illumination field at the working plane. It is designed for applications requiring both high irradiance and high spatial uniformity, including detector characterization, camera and image-sensor testing, hyperspectral imager calibration, solar-cell QE/EQE measurement, and related sample-plane illumination tasks.
Key features include:
- 200 nm to 2.5 µm spectral range
- 60 mm × 60 mm or 120 mm × 120 mm square projected fields
- U2 ≥ 98% spatial uniformity across the projected field
- Large contiguous regions achieving U2 ≥ 99% uniformity
- Typical optical throughput of 50% at 550 nm
- Single-input or motorized dual-input configurations
- Compatibility with standard 0.22 NA multimode fiber
- SMA-905, FC-PC, and custom fiber interface options
Download the datasheet for a concise product introduction.
To request more information or a quotation for Bentham products, contact IL Photonics.