Research Facilities | Centre for Programmable Photonic Integrated Circuits and Systems

Photonic IC (PIC) packaging requires both electrical as well as optical interfacing. Current packaging strategies include monolithic co-integration, flip-chip bonding, and hybrid integrations. However, no standard packaging rules have been recognized so far for universal usages. Recently, there have been demands for multifunctional Field Programmable Photonic Gate Array (FPPGA) alongside presently available Application Specific PIC (ASPIC) design modules. CoE-CPPICS has committed to developing indigenous PIC design rules and hardware infrastructure for precision packaging in in-house system-level applications and field trials. In this mission, CoE-CPPICS IIT Madras has signed an MoU with Si2 Microsystems, Bangalore (https://www.si2microsystems.com/) for joint development of packaging rules, transfer of technology and futuristic start-up business.

Lumerical is a high-performance photonic simulation software. It houses various physical solvers for electromagnetics, heat transfer, charge distribution etc. adopting different numerical methods like Finite Difference, Finite Element, Finite Difference Time Domain and so on. We use it to design and simulate various passive and active photonic devices like waveguides, directional couplers, MMIs, DBR, phase shifters etc. and also photonic circuits.

COMSOL is a general-purpose simulation environment housing multiple scientific models including acoustics, electromagnetics, chemical reactions, fluid dynamics, heat transfer and much more. Our interest in the software is focused on heat transfer physics and electromagnetics, and is used for modeling thermo-optic phase shifters and photonic waveguides.

A photonic integrated circuit needs electronic driver circuits to control the flow of light in the chip actively. The monolithic integration of electronic and photonic circuits offers a cost-effective scheme for a PIC. Cadence offers the Electronic and Photonic Design Automation (EPDA) environment for parallel electronics and photonics circuits simulations. We use the software to design the driver circuits for photonic integrated circuits.

Inductively Coupled Plasma Reactive Ion Etching (ICPRIE)

This process is used to etch the required area and thickness of the substrate to get desired devices.Oxford Plasmalab System 100 is the equipment available for this process with Cl2 + Br2.

Photolithography

It’s the process of transferring the desired device patterns onto the substrate/sample (Silicon and Silicon Nitride in our case) using light. The Mask Aligner tool MA6/BA6 from Suss Microtec, Germany is capable of giving a minimum feature size down to 1 µm along with user-friendly interface,Also, the DUV lithography tool, similar to above model is available and capable of minimum feature size of 700nm.

Mask Writing

Photo masks contain the patterns that get transferred to substrate during photolithography. DWL 66 from Heidelberg Instruments GmbH, Germany is the tool used for direct laser writing of photo masks which has capability to write feature size down to 1 µm.

E-Beam Lithography

This is also used to transfer patterns unto a substrate, but with the use of electron beams instead of light. Raith 150 Two Direct Write is the tool used which gives minimum feature size down to 50 nm.

Oxidation & Diffusion & Thin film Deposition

It’s the process of growing thin oxide layer over the surface of the substrate (in our case, Silicon Dioxide over Silicon). This process is usually carried out at around 1100˚-1200˚C. SVCS (4 Stack Furnace) is the equipment available to carry out this process.the process of doping the Silicon wafer with Boron or Phosphorus atoms to get p and n-type doping respectively. It’s also a high temperature process carried out around 900˚-1100˚C. SVCS (4 Stack Furnace) is the equipment available to carry out this process.

Metallization

It’s the process of depositing thin layer of metals on top of sample for getting contact pads and microheaters. Three types of equipment are available mainly for Thermal Evaporation (HPVT 305G Hydro Pneo Vac Technologies, India), E-beam Evaporation (BOC Edwards Auto 306 and Hind Hi Vac BC 300T), DC and RF Sputtering (Hind High Vac).

Dicing

It’s the method of separating individual die from each other on the wafer. The equipment used is Advanced Dicing Technology 7100-Provectvs.

Polishing

This process helps in removing the surface roughness and getting rid of contaminants or subsurface damages. The equipment used is Ultra Pol Ultra Tech Manufacturing Inc., USA.

Wire Bonding

It’s the process of making interconnects between the IC and the PCB or between multiple ICs. The equipment used is TPT HB10.

Chemical Mechanical Polishing

CMP (Logitech, UK) is used for nanometer scale planarization for semiconductors and metals.

Upcoming Facilities

E-Beam Deposition System : Fully automatic stand alone Electron Beam evaporator system.

* Mentioned Process Facilities are Available as Part of CPPICS and CNNP (Centre for NEMS and Nanophotonics) ,IIT Madras. *

Ellipsometer

An ellipsometer is helpful for the characterization of thin films (in the order of nm) deposited/grown on top of a substrate. The Woollam Spectroscopic M-2000VI Ellipsometer provides the measurement spectrum over the range of 370-1690 nm (ultra-violet, visible and infra-red). The device can measure the characteristics for 580 wavelengths in the span of 2-5 seconds. The device can also characterize the deposited film for different incident angles, thus improving the measurement accuracy.

Confocal Microscope

The Olympus laser microscope OLS4000 is helpful in the nanometer level imaging and estimate the surface roughness. The non-contact surface profile measurement (using a low spot size laser source) is non-destructive and allows the accuracy to go to the sub-micron range.

Optical Spectrum Analyzer

APEX 2043B optical spectrum analyzer offers a wavelength resolution bandwidth of up to 0.04 pm to characterize optical devices. The resolution provided by the device is very beneficial, especially in the case of high Q (narrow bandwidth) micro-ring resonators, for Microwave and Quantum Photonics applications. The device also offers a tunable laser source over the wavelength range of 1520-1630 nm, with the capability to sweep the entire range in few seconds.

Grating Coupler Setup

The grating coupler setup helps to characterize the fabricated silicon photonic devices. It enables the launch and detection of the laser through the optical fibre with a 6 dB/facet coupling loss. The setup was designed and tested by our group of alumni here at IIT Madras. The launch angle into the on-chip device is 10 degree. The fibre alignment is done manually with the help of a microscope. The setup is isolated from any ambience disturbances through the vibration isolation system of the table.

Wave Shaper

Programmable Optical Wave Shaper (II-VI 1000A) provides a range of programmable optical filtering and switching options for photonics experiments. It has a Operating Wavelength Range of 1530 nm to 1565 nm. Two units are available in the lab.

Mode Lock Laser

Mode Lock Laser (Pritel FFL Series) produces pulses of light of extremely short duration, on the order of picoseconds. It has a Wavelength range of 1530 - 1565 nm and equiped with Pulse Repetition Rate (PRR) of 31.25 MHz, 62.5 MHz, 125 MHz, 250 MHz, 500 MHz, 1 GHz, 5 GHz, and 10 GHz with Internal RF Synthesizer.

Lightwave Component Analyzer

The Lightwave Component Analyzer (Keysight) is used to measure the linear electro-optic transmission and electrical reflection characteristics of a component as a function of modulation frequency. It is the instrument of choice to test all relevant opto-electronic S-parameters, like S21, S11 and, S22 for electro Optical components in 26.5Gb/s

Erbium Doped Fiber Amplifier

High Power Erbium Doped Fiber Amplifier amplifies (EDFA) the low input optical signal and gives high optical output power. We have high power EDFA (Pritel) and polarization maintaining EDFA (Pritel) with a wavelength range of 1535 nm to 1565 nm and saturated output power greater than 37 dBm.

Highly Coherent Laser Source

Highly Coherent Tunable Laser Source (Santec TSL-550) has equiped with a wavelength tuning range of 1480 nm to 1630 nm and max output power of +13 dBm.

Tunable Laser Source

A Tunable Laser Source (Apex AP3350A ) has equiped with a Two different module types are available: AP3350A and AP3352A, which covers C-band and L-band respectively. These tunable laser source modules can cover a wavelength range of 82 nm from 1526 nm to 1608 nm.

Probe Station

High Precision Silicon Photonics Probe Station is used for Wafer level passive and active characterization of optical devices.

Superconducting Nanowire Single Photon Detector

A near-infrared superconducting nanowire single-photon detector (SNSPD) system (Single Quantum Eos CS-8 channel and efficiency>80%) is being used for quantum photonics experimental studies.

RF Phase Noise Analyzer

A USB based Phase Noise Analyzer with controller.

Upcoming Facilities
High Resolution Source Optical Analyzer: Tunable Laser Source output for both Static and Sweep Modes Control.

High Speed Photodetector: A ultra high speed photodetector with high responsivity.

40 GHz Intensity Modulator & Phase Modulators: An intensity modulator with wavelength tunibility.

* Mentioned Characterization Tools are Available as Part of CPPICS and IO Lab (Integrated Optoelectronics Lab) ,IIT Madras. *

Photonic IC packaging is a complex, multi-disciplinary design process which requires sub-micron precision alignment and bonding. Our research objective for packaging of silicon photonic devices is to understand the various available coupling schemes for optical assembly and required dimensions of contact pads and pitch size for electrical assembly for efficient packaging of our in-house fabricated devices. In this mission, CoE-CPPICS IIT Madras has signed a MoU with Si2 Microsystem Bangalore (https://www.si2microsystems.com/) for a joint development of packaging rules, transfer of technology and futuristic start-up business, etc.