This photo exhibition is an extraordinary tribute to missing Bangladeshi activist Kalpana Chakma

You could call Kalpana Chakma Bangladesh's Irom Sharmila, the political activist from Manipur who has become the symbol of resistance against state-sponsored repression. With one important difference — unlike Irom, who's been forcibly kept alive by India, Kalpana has probably not lived to tell her tale. At any rate, no one knows what happened to her since June 12, 1996, the day this young political activist from the Chittagong Hill Tracts in the southeast reaches of Bangladesh bordering Myanmar was picked up from her home by Bangladeshi military and police personnel. Eighteen years on, she remains missing.

Kalpana Chakma's is not an unfamiliar tale — the modern histories of many countries are full of instances of human rights abuse by the military. Abductions or forced disappearances, torture and rape, summary killings, wanton destruction of property are regular occurrences where armed forces have been given a free reign to put down insurgencies or separatists — think Kashmir, Naxal-affected or several parts of northeast India. In the case of Kalpana, she was leader of the Hill Women's Federation, an organisation of the indigenous communities (the Chakmas being the largest of them) of Chittagong who've been fighting for political autonomy from Bangladesh.

The Chakmas' struggle is a long-standing one that reached a head post the 1970s, after the construction of a dam and reservoir on the Karnafuli river submerged 254 square miles, including the palace of the Chakma king.

Most such abuses go unreported, but even those that do come out to the outside world, are forgotten soon after they have created a splash of anger and condemnation.

Kalpana's Warriors, an exhibition of photographs by the acclaimed Bangladeshi lensman Shahidul Alam showing at Gallery Art and Aesthetic, is a caution against such forgetting. The way the show has been mounted, you could even call it a shrine - a shrine to the memory of a brave woman whose mysterious, tragic fate has been all but forgotten to the majority of her countrymen. As with a temple, the gallery is a mostly dark space, lit by candles placed in terracotta plates hanging in front of large blow-ups of the faces of unknown, unnamed men and women printed on straw mats - the madurs that are so much a part of the daily lives of the Chakmas. These are Kalpana's "warriors", the activists who've carried forward her fight and are standing up for their rights and against state repression.

Kalpana's Warriors is part of a public awareness campaign initiated in 2010 by Alam, who is a human rights activist as much as he is Bangladesh's best known contemporary photographer, called "No More", which focuses on issues and events – the floods and cyclones that hit Bangladesh regularly or extra-judicial killings and garment factory deaths – that the government would like to sweep under the carpet.

Kalpana's disappearance, of course, has been a longer term engagement with Alam. Kalpana's Warriors is his third show on the subject, all of them inaugurated on June 12, the anniversary of her abduction.

The first of these, Searching for Kalpana Chakma - A Photo Forensic Study, in 2013 was a moving installation comprising images of various things associated with Kalpana – a segment of the bark of the tree where she was standing blindfolded before being separated from her brothers, a fragment of a new kameez she had stitched for her trip to attend the fourth women's conference in Beijing; her ribbon found in the bamboo slat next to her bed; a segment of her shoe; the palm of her brother Kalindi, who remembers how the torch light reflected from his hand lit up the abductors' faces. These are magnified images, the kind you see through a microscope in a forensic laboratory, beautifully coloured and printed – so that a sham reprisal of the methods used by modern police forces to uncover long-standing mysteries – except that the investigation never happened in Kalpana's case.

What's noticeable in Searching for Kalpana Chakma as well as with the current Kalpana's Warriors show is how material and process come together with political and aesthetic purpose. And it's not just the use of the straw mat as photographic medium. The physical process itself incorporated the politics. "The fire that had been used to raze pahari homes, also needed to be represented, so a laser beam was used to burn the straw, etching with flames, the images of rebellion," explains Alam.

It's an extraordinary tribute to an extraordinary woman.