Electronic – this? Identifying Proximity Sensor Chip (IR)

I am in a bit of a pickle. If anyone could help/has any ideas I will be very grateful – am aware this post is pretty long but thought if anyone was clever enough to know it would be you guys. If anyone needs more information/has ideas then I'm also listening! Thank you.

Have a specialist bit of kit which uses proximity sensors and would dearly like to be able to replace sensors on it with the same model. However, I am unable to ID the chip and manufacturer of product will not help. Therefore – does anyone know what chip this might be? The chip senses reflectance from a person from about 1cm to closer.

Visually inspecting the chip it consists of an LED and a sensor, separated by some dividing plastic. On the underside, it has 4 pads, with 4 microvias.

Initially it looks like the chip was mounted on a small PCB but I think this is an integral part of the chip – or at least I have been unable to separate it with hot air. No markings anywhere other than an arrow of copper to indicate direction, on underside, as well as a slightly larger pad on the top layer of the "pcb" to again indicate LED.

On PCB layout it is measured as shown.

Pad layout on the chip is pretty similar. I was unable to measure the microvias so haven't included dimensions.

Pin layout is (from pin1 marked on PCB layout moving clockwise):

Phototransistor/diode Anode
IR LED Anode
IR LED Cathode
Phototransistor/diode Cathode

The phototransistor/diode is operating in reverse bias. Vcc is connected to pins 2 + 4. Pin 3 connected via current limiting resistor (100 ohm) to digital ground. Pin 4 is run to analog ground via 1k resistor w cap in parallel for noise reduction (standard voltage divider). It (pin 4) also runs to an ADC where measurement is taken. Vcc is approx 3.6V.

I don't have a spectrometre so am unable to confirm what wavelength of light is but I assume it's IR as it is not visible.

I have sketched the dimensions here –