Detection & noise
Photodetectors and the noise floors beneath every measurement: responsivity, NEP, shot and thermal noise, receiver architectures.
10 articles · 97 glossary terms · 2 tools
Start here: Photodetectors and noise in 11 pages
From photons to photocurrent, the noise that sets the floor, and how to measure a detector.
- 1PhotodiodeGlossary
- 2Responsivity (R)Glossary
- 3Quantum efficiencyGlossary
- 4PIN photodiodeGlossary
- 5Avalanche photodiode (APD)Glossary
- 6Dark current (I_d)Glossary
- 7Shot noiseGlossary
- 8Thermal noiseGlossary
- 9Noise equivalent power (NEP)Glossary
- 10Photodiode Noise CalculatorTool
- 11Photodetector Characterization: Responsivity, NEP, and BandwidthArticle
Tools
Detectors and noise
Photodiode Noise Calculator
Which noise source limits a PIN or avalanche photodiode receiver, and what is the weakest signal it can see: signal shot, dark-current shot, thermal and amplifier noise summed over the bandwidth into SNR, noise-equivalent power, minimum detectable power, the shot-noise crossover power and the optimum APD gain, with the shot-noise limit, noise and SNR plots, guided experiments and a validation table.
Fiber and telecom
OSNR and Noise Figure Calculator
OSNR at the end of a chain of amplified spans from launch power, span loss, noise figure, span count and reference bandwidth, with per-amplifier ASE, margin over a required OSNR and the longest chain that meets it, plus the Friis gain and noise figure of up to five amplifiers and losses, with plots, presets, guided experiments and a validation table.
Articles
- How to Measure a Detector's NEP and D*Procedure for measuring the noise equivalent power (NEP) and specific detectivity (D*) of a photodetector: measuring the dark noise spectrum, removing the amplifier's contribution, measuring responsivity, normalizing to bandwidth and area, with a worked InGaAs example in which the feedback resistor, not the photodiode, sets the NEP.
- How to Calibrate and Cross-Check an Optical Power MeterProcedure for checking an optical power meter between calibrations: zeroing, comparison with a reference meter, the wavelength setting, linearity by the superposition method, fiber connector repeatability, and a simple uncertainty budget, with worked numbers in percent and dB.
- Choosing a Laser Power Meter: Photodiode, Thermal or Pyroelectric SensorHow to choose a laser power or energy meter: photodiode, thermopile and pyroelectric sensors compared, with power ranges, wavelength coverage, speed, aperture and damage limits, worked examples for wavelength-setting errors, overfilled apertures and pulsed beams, and a checklist.
- Types of Photodetectors: Photodiodes, APDs, Single-Photon and Thermal Detectors ComparedReference to the main photodetector types and how to choose between them: silicon, InGaAs and germanium photodiodes, PIN and UTC structures, avalanche photodiodes, SPADs, superconducting nanowire detectors, photomultipliers, thermal detectors and cameras, compared by wavelength range, sensitivity, speed and gain.
- Lidar: Time of Flight vs FMCWHow pulsed time-of-flight and FMCW coherent lidar measure distance, with the range, resolution and Doppler equations, worked numbers, the choice of 905 nm or 1550 nm, detectors, scanning methods, and the strengths of each approach.
- How to Measure Photodetector Bandwidth and Frequency ResponseProcedure for measuring the frequency response and 3 dB bandwidth of a photodiode or optical receiver: the calibrated-modulator network-analyzer method, the optical heterodyne method with its expected RF power, the impulse-response method, de-embedding the RF path, and the bias and photocurrent dependences that change the answer.
- Common-Mode Rejection in Balanced DetectorsWhere the common-mode rejection ratio of a balanced photodetector comes from (responsivity mismatch, path-delay mismatch, bandwidth mismatch), the formula that gives CMRR as a function of frequency with worked numbers, what a given CMRR buys against local-oscillator intensity noise, and a step-by-step measurement and trimming procedure.
- What the Coherent DSP Actually DoesA function-by-function account of the digital signal processing behind coherent optical links: chromatic dispersion compensation as a static filter, adaptive polarization demultiplexing, carrier frequency and phase recovery, timing, and FEC, and why shedding parts of this chain is what coherent-lite trades for power.
- Photodetector Characterization: Responsivity, NEP, and BandwidthProcedures for measuring the three primary parameters of photodetectors used in photonics (wavelength-dependent responsivity, noise-equivalent power, and 3-dB electrical bandwidth), with focus on the standard measurement configurations for InGaAs PIN photodiodes.
- Relative Intensity Noise (RIN): How to Measure ItMeasure a laser's relative intensity noise (RIN) in dB/Hz with a photodiode and spectrum analyzer: formula, shot-noise calibration, worked DFB example, errors.
Glossary
- Absorption coefficient
- Absorption edge
- Analog optical link (RF photonics, radio over fiber)
- Avalanche photodiode (APD)
- Balanced detection
- Blackbody radiation
- Bolometer
- Boxcar averager (gated integrator)
- Brightness and luminance
- Burst-mode receiver
- Carrier lifetime
- CCD vs CMOS image sensors
- Coherent detection
- Coherent DSP
- Dark count rate (DCR)
- Dark current (I_d)
- Depletion region
- Diffusion length
- Direct detection
- Dynamic range
- Electrical spectrum analyzer (ESA, RF spectrum analyzer)
- Electron-hole pair
- Excess noise factor (F)
- Fixed-pattern noise
- Flicker (1/f) noise
- FMCW lidar
- Full-well capacity
- Germanium-on-silicon photodetector
- Heterodyne detection
- HgCdTe detector (MCT)
- Ideality factor
- Impedance matching (50 Ω termination)
- Infrared bands (NIR, SWIR, MWIR, LWIR)
- InGaAs photodetector
- Integrating sphere
- Integration time (exposure time)
- Junction capacitance
- Lidar
- Local oscillator (LO)
- Microchannel plate (MCP)
- Modal noise
- Network analyzer
- Noise bandwidth (equivalent noise bandwidth)
- Noise equivalent power (NEP)
- Noise figure (NF)
- Noise floor
- Optical hybrid (90° hybrid)
- Optical power meter
- P-n junction
- Phase noise and frequency noise
- Photoconductive detector (photoconductive gain)
- Photodiode
- Photodiode array
- Photoelectric effect (work function)
- Photomultiplier tube (PMT)
- Photon
- Photon counting
- Photon flux
- Photon statistics
- Photon transfer curve
- Photon-number-resolving detector
- PIN photodiode
- Power spectral density (PSD)
- Pyroelectric detector
- Quantum efficiency
- Quantum key distribution (QKD)
- Quantum photonic integrated circuit (QPIC)
- Radiance
- RC time constant (RC-limited bandwidth)
- Read noise
- Receiver sensitivity
- Relative intensity noise (RIN)
- Resolution bandwidth
- Responsivity (R)
- Reverse bias
- Rise time (10–90%)
- Sampling oscilloscope
- Shot noise
- Shunt resistance
- Signal-to-noise ratio (SNR)
- Silicon photomultiplier (SiPM)
- Single-photon avalanche diode (SPAD)
- Solar cell
- Solid angle
- Specific detectivity (D*)
- Squeezed light
- Streak camera
- Superconducting nanowire single-photon detector (SNSPD)
- SWIR camera
- Thermal detector
- Thermal noise
- Thermopile
- Time-correlated single-photon counting (TCSPC)
- Timing jitter
- Transimpedance amplifier (TIA)
- Transit time
- Uni-traveling-carrier photodiode (UTC-PD)