Table 1 Summary of optical memory technologies

Switching time (ps)		Freq. (GHz)	Energy efficiency (pJ/bit)				Footprint (μm²)/cell	Capacity (bits)	Technology/refs.
Switching time (ps)			Switching^a	Static^b		Total
On	Off		Switching^a	Electr.	Opt	Total
20	20	50^c	0.0055	2.16^d	–	2.16	720³⁰	1	Micro-ring lasers³⁰
<50	<50	5^e	~0.6	120	–	120.6	540 × 106⁶⁸	1	Silica on silicon coupled SOA-MZIs^22,68
50^f	50^f	40^e	0.00475	0.1^f	–	~0.105	36	4	1550-/980 nm PB VCSEL^40,41
60	~100	10^g	0.0018	0.6^f	–	0.6	56.25³⁵	1	Microdisk laser³⁵
58	65	~15^c	0.00031	–	0.0017	~0.002^h	<10	1	BH-InP PhC nanolaser³⁷
44	7 × 103	0.142ⁱ	0.0025	–	0.00021	~0.0027	<10	104/128	BH-PhC nanocavity^38,39
200	200	5^c	~0.6	~450	–	~450.6	40 × 10⁶	1	Monolithic SOA-MZI with feedback loop³⁶
10	60	10^e	~18	36	–	~54	0.03 × 10⁶	1	Semiconductor ring laser³³
70	70	10^e	3	~120		~123	12 × 10⁶	1	Monolithic coupled SOA-MZIs²⁵
25	75	10	0.5	~180		~180.3	12 × 10⁶	1	Monolithic coupled SOA-MZIs with differentially biased push-pull technique⁷⁰
50	50	10^e	0.0032	–	0.01	0.013^h	6.2	1	III–V on SOI PhC nanocavity laser⁴³
10 × 103	10 × 103	1^g	5.3	–	–	5.3	0.16–0.25	3	PCM⁵²

^aBased on the reported switching energy or calculated as the product of the switching power and the pulse duration
^bCalculated as the product of the electrical/optical power and frequency (pulse duration). Electrical static power is noted for electrically pumped memories, whereas optical static power refers to the bias power required in the case of optically pumped memories
^cFrequency estimated by the authors of the current work based on the reported response time
^dBased on the calculation provided in ref. ³⁵, we estimated the electrical consumption for both micro-ring lasers (2 × 30 mA assuming 1.8 V with 20 ps pulses) excluding wavelength tuning
^eFrequency demonstrated by the authors in their respective papers
^fBased on the performance table of ref. ³⁸. The total energy excludes the wavelength tuning energy consumption
^gFrequency reported by the authors in their respective papers
^hExcluding wavelength tuning energy consumption
ⁱFrequency estimated based on the switch-OFF time, which equals 7 ns according to refs. ^38,39
⁹Based on the performance table of ref. ³⁸ and including the wavelength tuning energy consumption. The overall power consumption according to ref. ⁵³ is estimated to be 6 mW (3.5 mA × 1.5 V + 0.8 mW for wavelength tuning)

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