Questions tagged [photonics]

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Why are low band gap semiconductors (like silicon) not ideal for most solar cells? Are their atoms ionized by higher-energy photons?

Most sources on the web say that 1.3 eV or 1.4 eV is 'ideal' for most solar cells... What happens to lower-gap, gapless or overlap materials (conductors)? Are they ionized, rather than sending their ...
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What are the ramifications of the existence of this "modulation rate" for the use of these lasers for interferometry?

I'm looking for a specific type of laser for interferometry experiments. There seem to be a lot of 1550nm fiber-coupled DFB laser diodes on websites like Alibaba. This seems to be because they are ...
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Finding the PPF and PPFD using a LED data sheet

I would like to design my own grow lights to grow indoor plants like strawberries, herbs, etc. But I have a problem that I need some help to work out: How many LEDs do I need to light up an area of 0....
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Why is it that the maximum fringe contrast is observed when the signal mean is half the amplitude?

I am currently reading the Fringe Contrast section of this document. This section says the following: Why is it that the maximum fringe contrast is observed when the signal mean is half the amplitude?...
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What does the term "boresight", and what do the phrases "boresight adjustment" or "boresight calibration", mean in the context of laser scanning?

I have been studying the laser scanning literature. In doing so, I often come across the term "boresight", and the phrases "boresight adjustment" or "boresight calibration&...
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How does using a high-pass filter and an amplifier maximize the signal amplitude for analog-to-digital conversion?

I am currently reading the Fringe Contrast section of this document. This section says the following: Use a high-pass filter (HPF) and an amplifier (G) to maximize the signal amplitude for analog-to-...
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1 answer
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Setup for fringe contrast measurement

I am currently reading the Fringe Contrast section of this document. This section says the following: Be sure to use a DC-coupled detector when measuring fringe contrast. Adjust the interferometer ...
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Can I simply adjust the output power of these laser diodes to meet my specifications? If so, then what are the consequences of doing such a thing?

I need a CW laser diode, with an integrated photodiode, with wavelength around 800nm and power 1-1.5mW. Although I didn't find anything that exactly matching my specifications, I did find this from ...
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Are the parameters of pulsed laser diodes adjustable? Does making such adjustments negatively impact the laser diode in any way?

I am currently reviewing pulsed laser diodes from suppliers. The specifications are somewhat unique, so there doesn't seem to be many suppliers that offer what I'm looking for. I require an IR ...
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Understanding how laser pulsing is characterised

I'm trying to understand how laser pulsing is characterised. My understanding is that we can characterise pulsed lasers as pulsing a certain amount per second (pulses per second). Furthermore, my ...
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How is the measurement light frequency shifted with respect to the reference light frequency by some carrier frequency in practice?

I've been studying heterodyning in interferometry. My understanding is that heterodyning is achieved by shifting the measurement light frequency with respect to the reference light frequency by some ...
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Building laser doppler vibrometer

I'm interested in building my own laser doppler vibrometer using laser diodes. The reason I mention laser diodes is because (1) I want it to be cheap and (2) I want to incorporate it into robotics ...
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8 votes
1 answer
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Why is the light emitted by the LED not of a single wavelength but consists of a narrow range of wavelength instead? Spectral linewidth change?

I do understand that the wavelength of the lights depends on the energy gap of the semiconductor, but why does it consist of a narrow range instead of a fixed value? is it because during recombination ...
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Tuning current limitation for VCSEL laserdiode

Recently, we have bought a VCSEL laser diode, in which we can vary the wavelength by tuning the voltage and/or tuning current. Also, we got an application note in which it states as follows: "Set ...
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Difference between \$\epsilon\$ and \$\epsilon_0\$?

I have been given the following equation for the speed of light: \$V = \Large {1 \over {\sqrt {\mathstrut \epsilon \cdot \mu}}} = {1 \over \sqrt{\mathstrut \epsilon_0 \cdot \epsilon_r \cdot \mu_0 \...
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Photon lifetime in an optical cavity

Hi I have the following problem and data for an optical cavity. Length \$ L=100 \mu m\$ Reflectivity \$R=0.33\$ Refraction index \$n=3.6\$ Inner losses \$p_i=20 cm^{-1}\$ Now I have to determine the ...
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4 answers
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Geometric information within 1D streams of electrons/photons

How is light—or actually any frequency in the EM spectrum—self-encoding and self-modulating 3D info in its 1D self, so that it “knows,” once it strikes a surface, to discharge all the data perfectly ...
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4 answers
218 views

Laser scanning: why are things like deflection and mirrors used instead of just a mount and servo?

In the Wikipedia article for laser scanning, it is said that laser scanning is the controlled deflection of laser beams, visible or invisible. It then lists some of the technologies used, such as ...
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2 votes
2 answers
58 views

Biasing network for phototubes and photomultipliers

I have some doubts about typical biasing network for vacuum phototubes and photomultipliers. Precisely, let's start by a simple photocathode. I have seen some biasing network like this one: In this ...
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4 votes
1 answer
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Charge transfer in CCD

I have a basic doubt about charge transfer between pixels of a CCD. Let's consider this animation (picture taken from wikipedia): A precise time sequence of applied voltages between gates and bulk ...
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Q-value in APD photodetector

I try to calculate the Q value of APD photodetector with these parameters: $$R \hspace{0.1in} (response) = 1$$ $$M \hspace{0.1in} (magnification) = 10$$ $$k \hspace{0.1in} (ionization \hspace{0.1in} ...
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1 vote
1 answer
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Further Understanding Optical Parameter of Image Sensors for Use In Spectroscopy

I’m attempting to build a spectrometer and I’m having difficulty assessing the performance of a particular sensor. I am a novice and other posts on this forum have helped me greatly but I still haven’...
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2 votes
2 answers
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Can linearity of photoreceptor be improved by calibration?

I am trying to determine if equipment I already have can be used to take a reading in mcd/m2, for a quality control test. I have a sensor which meets all the requirements listed in the standard test ...
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1 answer
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Control of large number of analog devices

For research that I work on we have photonic chips that have 100-200 analog devices on board. I wish to control these devices at a rate of ~-1 MHz from an fpga. Some require a current source and ...
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9 votes
1 answer
346 views

Photon count with ADC, am I doing it right?

I have this LED and I want to characterize this photodiode. The LED should produce light of 370 nm, but I measured it and it is around 358 nm, and at that wavelength the quantum efficiency (\$\eta\$) ...
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1 vote
2 answers
839 views

Influence of active area of photo diode on sensitivity

I am using a photodiode for detecting the laser. I have a question regarding the active area of the photodiode. Is smaller active area photodiode less sensitive? Or it totally depends on the laser ...
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1 answer
288 views

Importance of laser numerical aperture in selecting photo diode

I want to design a circuit in which the laser light will be detected by a photodiode. I just wanted to know how the laser numerical aperture will affect the photodiode selection. Am I have to ...
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26 votes
3 answers
8k views

How is 255 Tbit/s processed in optical fiber communication?

I have never understood how the new record breaking data transfer speeds are achieved in terms of converting from/to electrical and optical signals. Suppose we have 255 Tbits of data and we want to ...
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11 votes
6 answers
5k views

LED as power generator

As many of you probably know, a normal light emitting diode, while very handy as a cheap and ubiquitous indicator, can double as a power generator. The mechanism is the same that is exploited in ...
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-1 votes
1 answer
227 views

What are the advantages of a photonic crystal versus a liquid crystal or piezoelectric grating tunable optic filter?

I want to design a tunable optical filter that can quickly change from being a red light filter to being a blue light filter. For this purpose, I am wondering about photonic crystal tunable optical ...
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2 votes
2 answers
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Can we send multiple signals in same core at the same time in the fiber optics? If yes, how? [duplicate]

I am curious to know how exactly does the fiber optics works. I understand the basic concepts of the fiber optics communications but am curious to know if there is a way to send multiple signals in ...
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