Exploring LIDAR, Part II

In last week’s blog, we discussed the performance constraints that telecom-grade lasers present to light detection and ranging (LIDAR) developers due to their limited coherence length and high frequency noise.  Luna’s RIO Lasers developed proprietary PLANEX technology specifically to address the needs of optical sensing and meteorology where high coherence length and low noise are critical enabling specifications.  It’s an external cavity laser (ECL) and based on silica-on-silicon planar lightwave circuit (PLC) waveguide with Bragg gratings.  The cavity is formed by coupling a semiconductor gain chip (GC) with waveguide Bragg grating on a PLC.

This design provides a unique combination of performance comparable to long cavity fiber lasers, with the cost effectiveness, simplicity, small size, stability, and reliability of semiconductor lasers. 

Lasers are available as PLANEX, in the typical 14 pin butterfly package, and as an ORION module, where the PLANEX laser is integrated with drivers in a user-friendly self-contained module with a processor to enable GUI and easy controls. 

Performance parameters match practically all requirements of CDL.

  • Narrow linewidth, corresponding to very long coherence length. Lasers are available in various grades of performance, from linewidth < 15 kHz, corresponding to coherence length ~ 6 km down to < 1 kHz with coherent length ~ 90 km. Those options enable customers to optimize the price/performance ratio. Ultra narrow linewidth may not seem necessary for the short reach  LIDARs, however additional margin on linewidth increases signal to noise ratio (SNR) and enables the customer to reduce requirements and related costs of other components of LIDAR, with overall cost reduction realized by using premium performance lasers. 

  • PLANEX lasers offer very low relative intensity noise (RIN), enabling simplified receiver and data processing.

  • PLANEX and ORION lasers are very reliable and suitable for deployment in very demanding environmental conditions. Reliability is proven by many years of high-volume field deployment for various applications, including LIDARs. Both laser modules are also available and qualified for various space applications, including Navigation Doppler LIDAR (NDL), developed by NASA for lunar landing. RIO Lasers’ NDL capabilities was featured in a 2021 Photonics Spectra article, Photonics Scores a Touchdown for Space Exploration.

  • Some application of FMCW LIDARs require high linearity and large bandwidth of frequency modulation (FM). For these applications, customers utilize RIO lasers with an external modulator, taking full advantage of narrow linewidth/ long coherence length. Also, PLANEX and ORION modules offer a built-in frequency modulation feature utilizing high speed direct current modulation and removing the need for expensive external modulators in some cases.  The PLANEX technology platform is flexible, and RIO has demonstrated and patented new laser designs with enhanced linear FM, potentially enabling further reduction of cost for FMCW LIDARS by removing the external modulator or the need for alternative FM linearization.