Temperature desensitised uncooled multi-quantum well lasers

Start date May 2012

Client University of Surrey
Investigator

Dr David Nugent
david.nugent@elucidare.co.uk

Abstract

Researchers from the University of Surrey have developed a novel design of multi-quantum well (MQW) laser that possesses a reduced thermal sensitivity over a wide temperature range. Bandgap engineering alone is used to improve the thermal stability of threshold current and slope efficiency compared to traditional techniques. The patent-pending approach is fully compatible with standard MQW materials and growth methods, and hence is readily adoptable by existing MQW fabricators. Interested parties should contact Dr David Nugent to discuss development and licensing opportunities.

Background

The lasing characteristics of MQW lasers, especially the threshold current and therefore the output power at a given current, are very sensitive to temperature variations. Because of this temperature sensitivity, thermoelectric coolers (TECs) are required in order to maintain and control the ambient temperature of these lasers when used in applications such as optical communications system and medical instruments. However, TECs are an added cost in the packaging of these devices and their reliability is also of some concern. Therefore, it is desirable to design lasers that are less sensitive to temperature variations, and which are capable of lasing at elevated operating temperatures (>100°C) without the need for cooling.

Technology

Customised band gap modifications dramatically alter the temperature characteristics of the MQW laser. As illustrated below, the engineered structure exhibits a significantly higher characteristic temperature and therefore a weaker temperature sensitivity. At lower temperatures the device exhibits a seemingly anomalous phenomenon where the threshold current increases at lowered temperatures. Via related mechanisms the slope efficiency is also stabilised.

The net effect is a MQW laser whose optical output power is essentially temperature independent over a wide temperature range.

 

Applications

Uncooled 13xx-nm datacom

The design can be applied to almost any quaternary material system operating at any optical wavelength. This includes both datacoms (13xx-nm) and long-distance carrier (15xx-nm) networks. Elimination of the TEC may prove particularly attractive for applications such as high-density 100-GbE switches, and remotely powered systems such as GPON networks.

 

Uncooled 14xx-nm Raman pumps

Conventional 14xx-nm Raman pumps require thermoelectric coolers to maintain stable operation at elevated ambient temperatures. Simulations indicate the band gap engineered designs can operate up to 350°K with minimal change to the threshold current and thereby optical power. As illustrated below, the threshold current remains with 10 percent of its ambient temperature (300°K) value from 270°K to 330°K, and within 20 percent from 260°K to 350°K.

Elimination of the thermoelectric cooler reduces the pump module power consumption from c.7W to 1.7W for comparable output optical power (mW) at 75°C.

Parameter
Symbol
Vendor 1
Vendor 2
Vendor 3
Uni Surrey
Optical power
mW
150
>140
180
160
Operating current (nominal)
mA
800
600
870
700
Operating voltage (max)
V
2.5
2.5
2.4
2.5
TEC current (max)
A
1.5
1.5
2.2
Uncooled
TEC voltage (max)
V
3.8
3.5
3.0
Uncooled
Module power consumption at Tc=75°C (max)
W
5.4
6.7
8.7
1.7