---
# System prepended metadata

title: Photonic Readout Sheme
tags: [' Readout', MQI]

---

---
tags: MQI, Readout
---

# Photonic Readout Sheme



| Pro                             | Con                              |
| ------------------------------- | -------------------------------- |
| Low Heat Dissipation            | Crosstalk with detector possible |
| No amplification required       | Count Rate might be limited      |
| No RF cable connection required | ...                              |
| ...                             | ...                              |


![](https://i.imgur.com/FCr6urj.png)


## Working Principle

### Microring modulators Basics

- Based on  silicon microring resonator with with p–n junctions interleaved along the azimuthal dimension (see image below)
- The ring exhibits a sharp, notch-flter optical transmission with a stop-band at the desired resonant wavelength of the ring 
- Applying a voltage across the junctions modulates the free carrier concentration (electrons and holes)
- Change in the free carrier concentration then changes the resonance frequency
- Depending on applied voltage/current the resonance frequency then can be controlled quite precicesly
    - Modulation can be achieved with the output voltages of the sspd, also the low input impendace makes direct connection possible 

### Forward and Backward biasing operation

- Forward Bias:
    - $V > V_{ON}$
    -  The change in carrier density is due to carrier injection
    -  Exponential dependence of charge carrier density on voltage
    - Modulation Efficiency: Up to 10.000 pm/V (@40µA)


- Reverse Bias:
    - $V<0$
    - The carrier density change comes from modifying the depletion region 
    - Weaker voltage dependence ($\sqrt{V}$)
    - Increased sensitivity to doping density
    - Modulation Efficiency: 16-250 pm/V

|                                      |
| ------------------------------------ |
| ![](https://i.imgur.com/gAa5XY3.png) |
| Text                                 |


### Dependence on Temperature

At RT foroward bias has several drawbacks such as high electrical power consumption and low modulation speed



|  |                             |
| -------- | ------------------------------------ |
|          | ![](https://i.imgur.com/b2Tt1tU.png) |
|          | ![](https://i.imgur.com/rn1Xayb.png) |
|          | Text                                 |


## SSPD Readout



| Step by Step                         |
| ------------------------------------ |
| ![](https://i.imgur.com/WOb23S1.png) |
| ![](https://i.imgur.com/mNym3ES.png) |
| ![](https://i.imgur.com/OdZofaP.png) |

## Critical Operation Parameters

### Biasing Current

### Modulation



## Fabrication

fabricated using a commercial high-performance 45 nm CMOS silicon-on-insulator (SOI) process

### CMOS with photonic modulator 
- Fabrication of CMOS optical resonator and optical gratings necessary
![](https://i.imgur.com/Ej4zkPb.png =400x400)

- Dimensions of the ring:
    - Example for 1550nm microring resonator
    - Outer Radius: 10µm
    - Width: 1.7µm
    - Thickness: 100nm
    - Material of microring: crystalline-silicon
    - Different doping regions required, easy integration in CMOS process possible

- The chip can be fabricated using a commercial high-performance 45 nm complementary metal–oxide semiconductor (CMOS) silicon-on-insulator (SOI) process, without any modifcation to the process flow, in what is known as zero-change CMOS.

### Cyogenic Fiber attachement

### PCB / Interfacing Chip Design 

- A PCB can be designed for interfacing the SSPD with the optical modulator CMOW chip. 
- The PCB can be gold-plated on the bottom to ensure thermalization.
- Appropriate components on the PCB for cryogenic operation can be used 


|                                               |                                               |
| --------------------------------------------- | --------------------------------------------- |
| ![](https://i.imgur.com/xC00xA3.png =300x250) | ![](https://i.imgur.com/xG1f9MW.png =300x250) |


For a more advanced technology inegrated in a product it is possible to integrate all the passive components in the CMOS chip to allow for direct interfacing between the modulator and SNSPD chips.


## Scalability

### Heat Dissipation

- Thermal load of the photonic modulator can be on the order of the biasing current, which is ~50µA, depending on the modulation strength one wants to achieve


### Optical Input for Readout

- Optical power for the modulator can be as low as ~10µW, when proper coupling efficiencies are achieved
- WDM Design


# Conclusion

# Sources

https://www.nature.com/articles/s41598-020-65971-5.pdf

https://static-content.springer.com/esm/art%3A10.1038%2Fs41598-020-65971-5/MediaObjects/41598_2020_65971_MOESM1_ESM.pdf

https://www.sciencedirect.com/science/article/pii/S0924424701007452

https://www.laserfocusworld.com/optics/article/14187644/100-gbits-optical-modulator-has-both-photonics-and-electronics-on-cmos-silicon


