Iridian Whitepapers

The Application of WDM Channel Skip Filters

Channel skip filters are components added to wavelength division multiplexing (WDM) add/drop modules — in both coarse wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM) applications — to facilitate band splitting and to manage multiple ITU channels.

These filters feature narrow transitions from pass band to blocking band, minimizing lost channels while maintaining high spectral efficiency (i.e., limiting insertion loss) since the express channels undergo only one reflection.


Advantages of Multiple Band Pass Filters in Telecommunications Applications

In wavelength-division multiplexer (WDM) and passive optical network (PON) modular design, single band pass filters and multiple band pass filters are used for the same purpose: permitting narrow wavelength ranges to pass through while rejecting wavelengths outside that range (known as the filter’s upper and lower cutoff frequencies).

Multiple band pass filters are used to transmit two or more standard coarse wavelength division multiplexing (CWDM) channels, separating them from the other CWDM bands — replacing two or more single band pass filters with a single component.


Hybrid Gain Flattening Filters in Optical Fiber Amplifiers

Much like vehicle hand cranks in their day, the use of a gain flattening filter (GFF) paired with a wavelength- division multiplexer (WDM) in optical fiber amplifiers – such as erbium-doped fiber amplifiers (EDFA) — has been accepted not because it is ideal, but because a superior solution had yet to be created. Until now.

This article explains what a Hybrid GFF is and how it works. It also details the advantages of using Iridian Spectral Technologies’ Hybrid GFFs in lieu of a conventional two-filter setup in EDFA and other optical filter applications.


Effect of an optical coating on in-band and out-of-band transmitted and reflected wavefront error measurements

The wavefront error (WE) of a surface with an optical coating (“filter”) is ideally measured at the in-band wavelength of the filter. However, quite often this is not possible, requiring that the filter be measured at an out-of-band wavelength (typically 633 nm), assuming that the filter transmits (for transmitted WE, or TWE) or reflects (for reflected WE, or RWE) at this wavelength. This out-of-band TWE/RWE is generally assumed to provide a good estimation of the desired in-band TWE/RWE. It will be shown in this paper that this is not the case for a large class of filters (i.e., bandpass) where the group delay is significantly different at the in-band and out-of-band wavelengths and where the optical filter exhibits a thickness non-uniformity across the surface.


Messages From Above – Optical Satcom Lights the Way

We live in the “Communications Age” – rapid access to information and connectivity to each other, anytime, nearly everywhere. But despite the massive strides that have been made in the past half century – from hardline telephony to the current ubiquitous wireless “smart” device connectivity – there is still further evolution to come that will necessitate extending the communications reach even further. While we have laid down a large physical infrastructure of wireline fiber-optic networks and wireless cellular base stations, the next advances in communications, 5G and machine-to-machine communications, will require “help from above” to blanket literally every corner of our planet with high speed, ultra-low latency, secure networks – telecom meet satcom.


Remote Sensing With LiDAR Requires Optical Filter Trade-Offs

LiDAR, short for light detection and ranging, uses pulsed lasers to accurately calculate distances as well as correctly detect the size and shape of objects. The high resolution of the information — LiDAR can resolve to a few centimeters from more than 100 meters away — and the ability to create accurate model three-dimensional images have made the technology critical in many applications. Some uses include autonomous vehicles and automobile crash avoidance, surveying, environment, construction, agriculture, oil and gas exploration, and pollution modeling.


LiDAR and Optical Filters for Autonomous Vehicles

“What’s a ‘steering wheel’?” At the present time this would be a very strange question to hear asked from anyone who has driven, ridden in, or even seen a car but in a couple of decades this may not seem so unusual. The evolution of increasingly affordable and capable sensing and imaging systems combined with the desire to create safer, more efficient transportation systems is driving the development of autonomous vehicles (pun intended). LiDAR is a key technology that will eventually help carry this growth through to “Level 5” autonomy : no steering wheels, no brake pedals, no human intervention in driving.


The Right Filter for MWIR Equipment

Utilization of mid-wavelength, also called midwave, infrared (MWIR) light is critical in many areas, including thermal monitoring of equipment and homes; gas absorption; military enhanced-vision systems for imaging vehicles, people, and terrain; and environmental monitoring of gases. Even diagnosis of pregnancy in dairy cows, among other applications, can productively use infrared in the MWIR range.


Optical Filters for Sensors and Detectors

Clear the Air: New Optical Filters for Sensors and Detectors Environmental air quality; proximity control; crowd counting; climate change; the “Internet of Things”.  Our world has become an increasingly monitored place where the proliferation of sensors and detectors allows us, and our devices, to better understand and interact with our environments.  Photonics is one of […]


Large Format Narrow Bandpass Filters – A Uniformity Challenge

1       Introduction Large format (>100 mm diameter), narrow bandpass filters (NBPF) are required in many fields. Applications requiring a large field of view drive the need for large collection optics, however high wavelength selectivity provided by narrow, flat-top bandpass optical filtering is also required to facilitate specific and selective analysis of a phenomena or substance […]