A base transceiver station (BTS) is the radio access node that bridges mobile devices to the core network. Every call, data session, and IoT packet moves through it. In 4G LTE, the BTS was largely self-contained. In 5G and the emerging 6G architecture, it has been disaggregated into radio units (RU), distributed units (DU), and centralized units (CU), each connected by high-speed optical links.
That disaggregation is what puts optical modules at the center of BTS infrastructure in 2026. A 4G site might have needed a single 1G or 10G fiber uplink. A 5G Massive MIMO deployment can require multiple 25G fronthaul links per radio unit, plus 100G midhaul and 400G backhaul capacity at the aggregation layer. The optics are no longer a footnote in the BTS bill of materials — they are a primary cost and planning variable.
The O-RAN Alliance's split architecture divides the base station stack into three segments, each with distinct optical requirements.
Fronthaul carries raw or lightly processed radio data between the RU and the DU. eCPRI reduced bandwidth requirements significantly compared to the older CPRI standard, but a single 64T64R Massive MIMO radio unit still demands 25G per fiber pair at minimum. Dense urban deployments with multiple RUs per site can push fronthaul aggregate bandwidth to 100G or higher.
Latency is the harder constraint. Fronthaul must stay under 100 microseconds one-way, which limits fiber reach to roughly 10KM to 20KM in most deployments. That makes 25G SFP28 SR and LR modules the dominant fronthaul transceiver in 2026, with 10G SFP+ covering legacy or lower-density sites.
Midhaul (DU to CU) and backhaul (CU to core) operate at longer distances and higher aggregated bandwidths. A single DU aggregating traffic from four to eight RUs needs 100G or more on its uplink. Regional aggregation rings often run at 400G.
Distance requirements in midhaul and backhaul regularly exceed 40KM, and metro ring deployments can stretch to 80KM or 120KM. That is where DWDM optics become the practical choice. A single fiber pair carrying 40 or 80 DWDM channels multiplies capacity without new fiber builds — which matters enormously in dense urban markets where dark fiber is expensive or simply unavailable.
1.25G SFP modules still appear in older BTS backhaul links, particularly in rural or developing-market deployments running 4G or early 5G NSA. 10G SFP+ covers mid-tier backhaul and remains the standard uplink for small cell and micro-cell installations.
For long-haul backhaul at 10G, DWDM SFP+ modules at 80KM and 100KM are the practical choice when fiber distance exceeds what standard LR or ER optics can handle.
25G SFP28 is the fronthaul workhorse of 5G in 2026. The form factor fits existing SFP+ cage slots on most O-RAN-compliant hardware, and the 25G data rate aligns directly with eCPRI Option 7-2x requirements for mid-band Massive MIMO.
SR variants cover in-building and campus fronthaul under 100 meters. LR variants handle the 10KM reach typical of urban macro deployments.
100G QSFP28 dominates the DU uplink and aggregation switch layer. LR4 is the most common variant for distances up to 10KM. For longer midhaul runs, ER4 and DWDM-based 100G modules extend reach to 40KM and beyond.
At the aggregation layer, 100G QSFP28 also connects the transport routers feeding multiple DU sites into a regional hub.
6G standardization is still in progress, but transport network planning for 6G is already shaping 400G and 800G procurement decisions today. The expected 6G radio architecture will require fronthaul bandwidths that make today's 25G links look modest. Network operators building or refreshing transport infrastructure in 2026 are specifying 400G QSFP-DD and 800G OSFP at the aggregation and core layers to avoid another full hardware refresh cycle in three to four years.
Both WDM technologies appear in BTS transport, but they serve different scenarios.
CWDM uses wider channel spacing (20nm) and uncooled lasers, which keeps module cost lower. It supports up to 18 channels on a single fiber pair, making it well-suited for metro aggregation rings where capacity needs are moderate and fiber runs stay under 80KM. CWDM SFP+ modules at 40KM and 80KM are a common choice for mid-tier backhaul in suburban deployments.
DWDM uses tight channel spacing (0.8nm or less) and temperature-controlled lasers to pack 40 to 96 channels onto a single fiber pair. The higher per-module cost is offset by the capacity density — which makes DWDM the only practical option for high-density urban backhaul and long-haul transport exceeding 80KM. DWDM SFP+ at 100KM and 120KM covers the longest BTS backhaul segments without optical amplification in many deployments.
The decision usually comes down to channel count and distance. More than 18 channels, or distances beyond 80KM with amplification, and DWDM is the answer.
OTN framing is increasingly used in 5G transport to provide deterministic latency, forward error correction, and OAM capabilities across midhaul and backhaul segments. OTN wraps the eCPRI or Ethernet payload and carries it across the DWDM layer with guaranteed performance characteristics.
When specifying optics for OTN-based transport, the module requirements are the same as for standard DWDM — but the system must be validated against the OTN framer's compatibility list. HYTOPTODEVICE's OTN Systems solution page covers this use case in detail.
CPRI and eCPRI operate at Layer 1 and Layer 2 respectively. eCPRI's Ethernet-based framing is what allows standard 25G SFP28 Ethernet optics to carry fronthaul traffic, rather than requiring proprietary CPRI-specific modules. That convergence on standard Ethernet optics is one reason third-party compatible modules have become a viable option in fronthaul applications.
A 10G DWDM SFP+ from a Tier 1 OEM like Cisco typically runs $200 to $500 per unit. A 100G QSFP28 LR4 from the same source can exceed $500. Multiply those figures across a 5G transport deployment with hundreds of sites, each requiring multiple modules, and the optics line item becomes a serious budget constraint.
Third-party compatible modules deliver the same electrical and optical specifications at 70 to 90 percent lower cost. The compatibility concerns that once gave procurement managers pause have been addressed by published test results and video validation. For BTS transport specifically — where modules are installed in standard transport routers and switches rather than proprietary radio hardware — third-party compatibility rates are high.
The approach most network engineers use in 2026: validate one or two modules per platform against the compatibility list or test video, then standardize procurement on the validated third-party SKU.
A few criteria separate a reliable supplier from a risky one when you are sourcing optics for BTS infrastructure:
Reach and wavelength coverage. BTS transport spans 10KM fronthaul to 120KM long-haul backhaul. You need a supplier stocking CWDM and DWDM variants at every distance — not just the common SR and LR SKUs.
Protocol support. Confirm the module supports OTN framing if your transport layer uses it. Fibre Channel and SONET/SDH compatibility matters for carriers running legacy protocol overlays.
Compatibility validation. Published compatibility test videos against specific switch and router platforms are the fastest way to de-risk a third-party purchase. Datasheets and product downloads should be available before you commit.
OEM/ODM capability. If you are deploying at scale or building a white-label product, custom-programmed modules reduce integration time. A supplier with a real OEM/ODM program can pre-program modules to your platform's vendor ID and configuration requirements.
HYTOPTODEVICE covers all of these: CWDM and DWDM from 10KM to 120KM, OTN and Fibre Channel protocol support, published compatibility test videos, and an OEM/ODM program for custom-programmed and white-label modules.
Q1:What optical modules are used in 5G fronthaul?
A1:25G SFP28 is the dominant fronthaul module in 2026, covering the eCPRI bandwidth requirements of Massive MIMO radio units at distances up to 10KM. 10G SFP+ covers lower-density or legacy fronthaul links.
Q2:What is the difference between fronthaul, midhaul, and backhaul in a 5G BTS?
A2:Fronthaul connects the RU to the DU, midhaul connects the DU to the CU, and backhaul connects the CU to the mobile core. Each segment has different bandwidth, latency, and reach requirements, which drive different optical module choices.
Q3:Why is DWDM used in BTS backhaul?
A3:DWDM multiplies fiber capacity by carrying 40 to 96 wavelength channels on a single fiber pair. In dense urban markets where dark fiber is scarce or expensive, it is the practical way to scale backhaul bandwidth without new fiber builds.
Q4:Are third-party compatible transceivers suitable for BTS transport equipment?
A4:Yes, in most cases. BTS transport routers and switches from vendors like Cisco, Juniper, and Huawei accept third-party modules when the module is correctly programmed to the platform's vendor ID. Compatibility test validation before deployment is standard practice.
Q5:What reach distances do BTS optical modules need to cover?
A5:Fronthaul typically requires 10KM to 20KM. Midhaul can extend to 40KM. Backhaul and long-haul transport segments range from 40KM to 120KM, with DWDM modules at 80KM, 100KM, and 120KM covering the longest spans.
Q6:What is OTN and how does it relate to BTS optics?
A6:OTN is a framing standard used in 5G midhaul and backhaul to provide deterministic latency, forward error correction, and OAM capabilities. The optical modules themselves are standard DWDM transceivers; OTN framing is handled by the transport equipment they plug into.
Q7:What is the cost difference between OEM and third-party BTS optical modules?
A7:Third-party compatible modules typically cost 70 to 90 percent less than OEM equivalents. A 10G DWDM SFP+ from Cisco can run $200 to $500 per unit; a third-party compatible equivalent covers the same spec at a fraction of that price.
The base transceiver station has become an optical-intensive infrastructure node. 5G's disaggregated architecture and 6G's anticipated bandwidth demands mean the modules you specify today will shape your network's capacity and cost structure for years. Matching the right module to each segment — 25G at fronthaul, 100G at midhaul, 400G with DWDM where distance demands it — is the core engineering decision.
Sourcing from a supplier with full-spectrum coverage, verified compatibility, and real OEM/ODM capability removes the two biggest risks: paying OEM prices and discovering a compatibility problem after deployment.
Explore the full catalog and wireless and 6G optical networking solutions at hytoptodevice.com.
