Hamamatsu Photonics' Small and Low-Cost Grating Spectrometer

Hamamatsu Photonics has recently developed their smallest grating spectrometer, the SMD series mini-spectrometer C14384MA, offering high near-infrared sensitivity, compact size, light weight and low cost. Compared to Hamamatsu’s existing range of MS series mini-spectrometers, the C14384MA is about 1/40th of the cubic size and 1/30th of the weight.  It also offers sensitivity in the same near-infrared range, but around 50 times higher. This makes the C14384MA ideal for applications where real-time on-site measurement is required, for example quality inspection of food or agricultural crops and environmental analysis from quadcopters to drones.

[Note] A grating is an optical element that separates light into its component wavelengths by utilizing the fact that the light refraction angle differs according to wavelength.

Overview of product

Hamamatsu Photonics already manufactures thumb-size mini-spectrometers, the MS series, with near-infrared sensitivity and micro-spectrometers even smaller than the MS series, which are sensitive in the visible light region.

Our new C14384MA is the world’s smallest grating spectrometer consisting of a light entrance slit, primary reflection mirror, secondary reflection mirror, diffraction grating and image sensor. Typically, light tends to travel while spreading outward. In the C14384MA, light coming in through the entrance slit is collimated by a primary reflection mirror and guided by the secondary reflection mirror onto the grating. The light is then separated by the grating into its component wavelengths and focused on each pixel of the image sensor while being reflected from the concave surface of the grating. The image sensor outputs electrical signals matching the light intensity at each wavelength.

Shrinking the spectrometer size required Hamamatsu to increase the curvature of the concave surface and to shorten the distance to the image sensor. However, fabricating a grating onto a concave surface with a large-curvature concave is extremely difficult. Therefore, Hamamatsu employed a return structure comprising of a primary reflection mirror and a secondary reflection mirror based on our unique optical design technology. This succeeded in making the distance to the image sensor shorter, while maintaining the desired curvature of the concave surface, resulting in the creation of the C14384MA, the world’s smallest grating spectrometer. As it incorporates the latest high sensitivity image sensor, the C14384MA also offers enhanced near-infrared sensitivity. By reducing the number of parts used in manufacturing, Hamamatsu achieved a substantial reduction in cost. Specifically, the grating is formed directly on the inner side of the package and the entrance slit, secondary reflection mirror and image sensor are integrated onto the same chip. This allows the C14384MA to be assembled into various types of equipment where there are limits to the size and weight of components to be mounted. For example, portable analytical instruments, quadcopters and drones. Therefore, the C14384MA is ideally suited to a diverse range of applications.

Hamamatsu also plans to make even further cost reductions by automating the manufacturing process.

Background of development

Spectrometers are devices for separating light into its component wavelengths and measuring the light intensity at each wavelength. They are used in spectrophotometry to measure the light at wavelengths emitted from or absorbed by substances to analyze the composition and properties of substances. Spectrophotometry is used for chemical and physical analysis in a wide range of fields such as industry, agriculture, environment, food, medicine and pharmaceuticals. In recent years, grating spectrometers have become widely used in spectrophotometric applications because of their high resolution for separating light into wavelengths.

Spectrophotometry normally takes place in a chemical laboratory, equipped with high-performance benchtop or floor-standing spectrophotometers that are usually large, bulky and expensive. Hamamatsu have been promoting the development of compact spectrometers for portable analytical instruments that can be used on-site without having to bring measurement samples into the chemical laboratory room. Recently, there has been increasing interest in sensing technology to ensure the safety and security of food and agricultural crops. This has increased demands for more compact, lightweight spectrometers that are low cost, yet have high sensitivity and can be mounted in portable analytical instruments, quadcopters and drones.

Features of the C14384MA

1. World’s smallest grating spectrometer

The return structure fabricated is based on our unique optical design technology and achieves a cubic size of 11.7mm×4.0mm×3.1mm (W×D×H), and weighs below 0.3 grams. These dimensions are respectively about 1/40th and 1/30th of our current range of MS series mini-spectrometers. This allows the C14384MA to be assembled into various types of equipment that limit the size and weight of components to be mounted, such as portable measuring and analytical instruments. In spectrophotometry, the complex information from light absorbed by various components must be accurately measured. The grating spectrometer measures changes in the light intensity at each wavelength as continuous data and is capable of applying advanced analysis techniques.

2. High sensitivity measurement using near-infrared light

By incorporating the latest high-sensitivity image sensor, the C14384MA offers enhanced near-infrared sensitivity of around 50 times higher than our currently available MS series mini-spectrometers. This allows high-sensitivity measurement of various components in food such as water, sugar and organic acids which absorb near-infrared light.

3. Low cost due to the reduced number of parts

Forming the grating directly on the inner side of the package and integrating the entrance slit, secondary reflection mirror and image sensor all onto the same chip, enabled Hamamatsu to reduce the number of parts resulting in reduced costs.

Main specifications

Note 1: At 800 nm or longer wavelengths

Note 2: At 1000 nm wavelength relative to the MS series mini-spectrometer sensitivity that is defined as 1.

Note 3: At 850 nm wavelength

Hamamatsu will start accepting sample product orders from domestic and overseas measurement and inspection equipment manufacturers from the 1^st November 2018.

This product will be on display from the 1^st to 3^rd November 2018 at the Hamamatsu Photonics exhibition “PHOTON FAIR”, an event held every 5 years at Act City Hamamatsu, Naka-ku, Hamamatsu City, Japan.