Sensors

[Juliana Carvalho]

Dears,

I want to know if you have a contact email technical support about the Optifiber. I need to simulate a fiber as a gas sensor, by light absorption.

Thanks,

Best regards,

Juliana.

[Steve Dods]

Please describe the physical process your fibre uses to sense the gas. I’m not sure by what means gas will lead to light absorption. If we know the physics we can tell you if OptiFiber or another one of our products could help with simulation and design.

[Juliana Carvalho]

Mr. Steve,

Our first idea is to simulate a optical fiber with transmition by evanescent field. I want to do the core with refractive index of 1.452, for example, and the cladding as air (n = 1). I want to evaluate and compare with a fiber the wave propagation in both case.

[Luis Acevedo]

I do not know if you can simulate this with OptiFiber

I know that Dr, Suzanne Costello was working in Hermeticity for MEMS, She was using mass spectrometer to sense the gas or leakage of the chip.

Hermeticity is a measure of how well a package can maintain its intended ambient cavity environment over the device lifetime. Since many Micro-Electro-Mechanical Systems (MEMS) sensors, actuators and microelectronic devices require a known cavity environment for optimum operational performance, it is important to know the leak rate of the package for lifetime prediction purposes. In this field, limitations in the traditional leak detection methods and standards used originally for integrated circuits and semiconductors have been blindly and often incorrectly applied to MEMS and microelectronic packages. The aim of this project is to define accurately the limitations of the existing hermeticity test methods and standards when applied to low cavity volume MEMS and microelectronic packages and to demonstrate novel test methods, which are applicable to such packages. For the first time, the use of the Lambert-W function has been demonstrated to provide a closed form expression of the maximum true leak rate achievable for the most commonly used existing hermeticity test method, the helium fine leak test. This expression along with the minimum detectable leak rate expression is shown to provide practical guidelines for the accurate testing of hermeticity for ultra-low volume packages. The three leak types which MEMS and microelectronic packages are subject to: molecular leaks, permeation and outgassing, are explained in detail and it is found that the helium leak test is capable of quantifying only molecular leak in packages with cavity volumes exceeding 2.6 mm3. With many MEMS and microelectronic package containing cavities with lower volumes, new hermeticity test methods are required to fill this gap and to measure the increasingly lower leak rates which adversely affect such packages. Fourier Transform Infra-Red (FTIR) spectroscopy and Raman spectroscopy are investigated as methods of detecting gas pressure within MEMS and microelectronics packages. Measured over time, FTIR can be used to determine the molecular and permeation leak rates of packages containing infra-red transparent cap materials. Future work is required to achieve an adequate signal to noise ratio to enable Raman spectroscopy to be a quantitative method to determine molecular leaks, permeation leaks and potentially outgassing. The design, fabrication and calibration procedure for three in-situ test structures intended to monitor the hermeticity of packages electrically are also presented. The calibration results of a piezoresistive cap deflection test structure show the structure can be used to detect leak ii rates of any type down to 6.94×10-12 atm.cm3.s-1. A portfolio of hermeticity test methods is also presented outlining the limitations and advantages of each method. This portfolio is intended to be a living document and should be updated as new research is undertaken and new test methods developed.

http://www.ros.hw.ac.uk/handle/10399/2611

[Steve Dods]

Thanks for the update on packaging technology. If the proposed system will require detailed design and simulation of optical fibres or other waveguides, then Optiwave probably has something useful to offer. We can also simulate certain non-linear optical effects by the FDTD method (Chi^2, Chi^3, Kerr, Raman). If you have requirements in these domains, please contact us.

[Steve Dods]

Juliana, I’m not sure what you mean by transmission by evanescent field. Can you send us a drawing of the structure? (You can put a diagram in an attachment).

[Juliana Carvalho]

Dear,
I tried to do now a drawing about my work. I so sorry if it was not good, but I can try to explain better. It is attached.

Thanks!

Attachments:

1. 

   evanescent-wave-in-optic-fiber.jpg
   

2. 

   evanescent-wave-in-optic-fiber1.jpg
   

[Steve Dods]

OptiFiber can find the modes for the fibre core with no cladding, the place of interest in your picture. That will include the evanescent field in the air. There is a high index contrast from the core to air, so you will probably need to use vector modes to find the modes accurately. If you need to use vector modes, it is better to use OptiMode, since it has better capacity to display vector mode fields. Try to find LP modes as well, and compare. If LP is appropriate, the vector mode effective indeces will be grouped near the LP mode indeces (There are more vector ones, so a few vector modes found close to each LP mode). If there are vector modes far from any LP one, you know that LP is not adequate. The core without cladding will have more modes than the fibre with cladding. It could be too many. Too many to make modal analysis practical, and you will need to use another method… FDTD?

[Juliana Carvalho]

Thanks for the informations! I am starting to use the software, I have a lot of doubts and few time to finish the simulations. Do you have any example about it? If yes, could you send me?

Today I installed the FDTD and BPM. I am trying to use them.

Thanks again!

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